GABOREAU Stéphane

Titre : Les sulfates phosphates d’aluminium hydratés (APS) dans l’environnement des gisements d’uranium associés à une discordance protérozoïque : caractérisation cristallochimique et signification pétrogénétique

Laboratoire : HYDRASA UMR 6532

Directeurs de thèse : D. BEAUFORT et P. VIEILLARD

Date de soutenance : 16/11/05 Table des matières

TABLE DES MATIERES

INTRODUCTION 13

PRÉSENTATION DU MÉMOIRE DE THÈSE 15

LES SULFATES PHOSPHATES D’ALUMINIUM 17

GÉNÉRALITÉS 17

FORMATION ET STABILITÉ 18

CLASSIFICATION 18

PROPRIÉTÉS CRISTALLOGRAPHIQUES 20

LES GISEMENTS D’URANIUM ASSOCIÉS À UNE DISCORDANCE PROTÉROZOÏQUE 25

GÉNÉRALITÉS 25

LES MODÈLES DE GENÈSE 27

PARTIE I 33

LES SULFATES PHOSPHATES D’ALUMINIUM DANS L’ENVIRONNEMENT DES GISEMENTS D’URANIUM ASSOCIÉS À DISCORDANCE PROTÉROZOÏQUE 33

INTRODUCTION 33

1 Table des matières

CHAPITRE 1 37

ABSTRACT 38

INTRODUCTION 39

REGIONAL GEOLOGICAL SETTING 40

SAMPLING 41

METHODS 42

RESULTS 43

PETROGRAPHIC RESULTS 43 Petrographic relationships between APS and hydrothermal clay phases 43 Petrographic relationships between APS and other phosphate minerals 46 CHEMICAL RESULTS 50

INTERPRETATION 51

CRYSTAL CHEMISTRY OF APS MINERALS 51

SOURCE MATERIAL FOR APS MINERALS IN THE EARUF 54

APS MINERALS: MARKERS OF THERMODYNAMIC CONDITIONS 57 CONCLUDING REMARKS 59

REFERENCES 60

CHAPITRE 2 65

ABSTRACT 66

INTRODUCTION 67

REGIONAL GEOLOGICAL SETTING 69

SAMPLING 71

METHODS 72

PETROGRAPHIC RESULTS 73

RELATIONSHIPS BETWEEN APS MINERALS AND CLAY ALTERATION 74

RELATIONSHIPS BETWEEN APS MINERALS AND OTHER ACCESSORY MINERALS 81 CHEMICAL RESULTS 82

DISCUSSION 85

CRYSTAL CHEMICAL VARIATIONS OF APS MINERALS 85

SOURCE MATERIAL FOR APS MINERALS 88 CONCLUDING REMARKS 90

REFERENCES 93

2 Table des matières

PARTIE II 99

MODÉLISATIONS THERMODYNAMIQUES DES PARAGENÈSES MINÉRALES APS- ARGILES AUTOUR DES GISEMENTS D’URANIUM ASSOCIÉS À UNE DISCORDANCE PROTÉROZOÏQUE 99

INTRODUCTION 99

CHAPITRE 3 103

ABSTRACT 104

INTRODUCTION 105

METHODOLOGY 106

= Z+ DEFINITIONS OF PARAMETERS ∆GO M (AQ) AND ∆G°F,OX 106

INVENTORY AND SELECTION OF ∆G°F OF MINERALS BELONGING TO THE ALUNITE SUPERGROUP.108

= Z+ RELATIONSHIPS BETWEEN ∆G°F,OX AND ∆GO M (AQ)110 = RELATIONSHIPS BETWEEN ∆G°F,OX AND ∆GO MZ+(C)114 RESULTS 118

MINIMIZATION 118 DISCUSSION 119

ACCURACY OF THE MODEL.119

PREDICTION OF GIBBS FREE ENERGIES OF UNCOMMON MINERALS OF THE ALUNITE SUPERGROUP.120 CONCLUSIONS 123

REFERENCES 125

CHAPITRE 4 129

ABSTRACT 130

INTRODUCTION 131

ALTERATION PATTERNS IN UNCONFORMITY-TYPE DEPOSITS 133

CONCEPTUAL APPROACH AND COMPUTER PROGRAM 139

CONSTRAINTS ON THE INTENSIVE VARIABLES OF THE ALTERATION SYSTEM 140

THERMODYNAMIC DATA 142

AQUEOUS AND MINERALS DATA 142 RESULTS 145

3 Table des matières

EARLY ALTERATION PROCESS 145

SYNORE ALTERATION PROCESS 146 Quartz mica-schist 148 Felsic gneiss 150 DISCUSSION 152

CONCLUDING REMARKS 156

REFERENCES 157

CONCLUSIONS GÉNÉRALES 163

FORMATION DES SULFATES PHOSPHATES D’ALUMINIUM 163

TRANSITION SVANBERGITE-FLORENCITE 164

LES PRINCIPAUX FACTEURS QUI CONTRÔLENT LA TRANSITION SVANBERGITE-FLORENCITE AUTOUR

DES GISEMENTS ASSOCIÉS À UNE DISCORDANCE PROTÉROZOÏQUE 165

PEUT ON UTILISER LA TRANSITION SVANBERGITE-FLORENCITE COMME MARQUEUR DE

PALÉOCONDITIONS DANS LES GISEMENTS 166

PERSPECTIVES 166

BIBLIOGRAPHIE 169

ANNEXES ANALYTIQUES 175

4 Liste des tableaux

LISTE DES TABLEAUX

Tableau 1. Classification des minéraux du groupe de l’alunite (Jambor, 1999). ______19 Tableau 2. Classification des minéraux du groupe de la beudantite (Jambor, 1999).______20 Tableau 3. Classification des minéraux du groupe de la crandallite (modifiée à partir de Jambor, 1999) ______21 Tableau 4. Etude de diffraction de rayons X sur monocristaux des APS du supergroupe de l’alunite – jarosite (Jambor, 1999) ______22 Tableau 5. Principaux gisements d'uranium associés à une discordance protérozoïque (Canada) ______28 Tableau 6. Principaux gisements d'uranium associés à une discordance protérozoïque (Australie)______29 Tableau 7. Petrologic observations of the different samples associated to unconformity-type uranium deposits in the East Alligator River Uranium Field. ______42 Tableau 8. Microprobe analysis and structural formulae of representative APS minerals associated with unconformity-type uranium deposits in the East Alligator River Uranium Field.______49 Tableau 9. Thermodynamic values at 25°C of some minerals of the alunite supergroup____ 58 Tableau 10. Solubility products of dissolution reactions at 25, 200°C and 500 bars of the APS minerals ______58 Tableau 11. Petrologic observations of the different samples associated to unconformity- type uranium deposits in the Athabasca Basin. ______71 Tableau 12. Results of electron microprobe analyses and structural formulas of APS minerals associated with unconformity-type uranium deposits in the Athabasca basin, Canada ______83

5 Liste des tableaux

Tableau 13. Gibbs free energies of formation of oxides and ions, and calculated parameters = Z+ ∆GO M (aq) of selected cations. ______107 Tableau 14. Values of solubility products and Gibbs free energy of formation of minerals + + + + + 2+ 2+ (K , Na , NH4 , Ag , H3O , Pb , Sr ) analog to jarosite. ______108 Tableau 15. Values of solubility products and Gibbs free energy of formation of phosphates and arsenates minerals.______110 Tableau 16. Chemical composition and selected, calculated and predicted Gibbs free energies of formation at 298K of some minerals of the alunite supergroup. ______112 Tableau 17. General equation of Gibbs free energy of formation from the oxides of alunite

KAl3(SO4)2(OH)6.______118 Tableau 18. General equation of Gibbs free energy of formation from the oxides of

crandallite CaAl3(PO4)2(OH)5H2O. ______118 = Z+ Tableau 19. Values of parameter ∆GO M (c) obtained by minimization. ______120 Tableau 20. Selected and predicted Gibbs free energies of formation of some minerals of the alunite supergroup. ______122 Tableau 21. Predicted Gibbs free energies of formation of some minerals of the alunite supergroup. ______123

Tableau 22. Detailed computation of ∆G°f,ox of hinsdalite. ______124

Tableau 23. Detailed computation of ∆G°f,ox of hydronium jarosite. ______124 Tableau 24. Average structural formulae of the three main populations of APS used in this work.______138 Tableau 25. Chemical composition of the initial fluid (200°C, 600 bars). ______141 Tableau 26. Molar composition of a quartz mica schist in the synore alteration process___ 142 Tableau 27. Molar composition of a felsic gneiss in the synore alteration process ______142 Tableau 28. Ce, Sr, P aqueous species, equations of dissociation and dissociation constants used in KINDISP.______143 Tableau 29. Thermodynamic data for phosphate minerals ______144 Tableau 30. Molar composition of a sandstone in the early diagenetic process. ______145 Tableau 31. Chemical composition of the sandstone derived fluid. ______148 Tableau 32. Analyses chimiques et formules structurales des APS des zones qualifiées de ‘distales’ de la région de Pine Creek (EARUF, Australie). ______175 Tableau 33. Analyses chimiques et formules structurales des APS des zones qualifiées ‘d’intermediate’ de la région de Pine Creek (EARUF, Australie). ______176

6 Liste des tableaux

Tableau 34. Analyses chimiques et formules structurales des APS des zones qualifiées ‘de proximal’ de la région de Pine Creek (EARUF, Australie).______177 Tableau 35. Analyses chimiques et formules structurales des APS des zones qualifiées ‘de proximal’ de la région de Pine Creek (EARUF, Australie).______178 Tableau 36. Analyses chimiques et formules structurales des APS des zones qualifiées de ‘distal’ du bassin d’Athabasca (Canada). ______179 Tableau 37. Analyses chimiques et formules structurales des APS des zones qualifiées de ‘distal’ du bassin d’Athabasca (Canada). ______180 Tableau 38. Analyses chimiques et formules structurales des APS des zones qualifiées ‘d’intermediate’ du bassin d’Athabasca (Canada). ______181 Tableau 39. Analyses chimiques et formules structurales des APS des zones qualifiées de ‘proximale’ du bassin d’Athabasca (Canada). ______182 Tableau 40. Analyses chimiques et formules structurales des APS des zones qualifiées de ‘proximale’ du bassin d’Athabasca (Canada). ______183

7

Liste des figures

LISTE DES FIGURES

Figure 1. La structure de l’alunite, vu parallèle à l’axe a.______23 Figure 2. Assemblage des continents à environ 900 Ma montrant la position des principaux gisements d'uranium des bassins du Thélon, de l'Athabasca et de Mc Arthur. Les ronds et les carrés noirs indiquent respectivement les bassins et la position des principaux gisements d'uranium dits de discordance et des principaux gisements sédimentaires à sulfures de Zn-Pb-Ag (modifié d'après Kyser et al., 2000).______30 Figure 3. Modèle conceptuel (Ruzicka, 1996) de la formation des gisements d’uranium de type discordance. Coupe verticale simplifiée. Les flèches indiquent les trajets d’écoulement des fluides oxydants et réduits entraînés par convection. Les numéros encerclés indiquent les emplacements des divers styles de minéralisation. 1) minéralisation monométallique à teneur moyenne au-dessous de la discordance, 2) minéralisation polymétallique à forte teneur au niveau de la discordance, 3) minéralisation monométallique à faible teneur dans les roches sédimentaires au dessus de la discordance. ______32 Figure 4. Location of the study area on a geological map of the East Alligator River Uranium Field (EARUF), Northern Territory, Australia (modified from Needham, 1988).44 Figure 5. SEM images of APS minerals from EARUF. a) aggregate of small euhedral APS minerals located in the intergranular porosity of the clay matrix in a distal alteration area. b) Features of growth zoning of APS crystal in the basement rocks. c) Disseminated euhedral crystals of LREE-Sr Al-phosphates (white spots) in a matrix of hydrothermal illite-sudoite close to the major discontinuities. d) Monazite replaced by APS minerals in a sample of metamorphic basement almost totally chloritized (trioctahedral chlorite) close to the uranium ore body of Ranger 3. e) Monazite relics in a clay matrix illite-clinochlore below the unconformity in an intermediate alteration area. f) alteration sites of monazite

9 Liste des figures

and pyrite around which occured secondary apatite and APS associated with trioctahedral chlorite + illite below the unconformty in intermediate alteration area. ______47 Figure 6. Cross plot diagram P+LREE versus S+Sr of the wide range of chemical compositions recorded in APS. ______52 Figure 7. Cross plot diagrams between the major elements from the A and X sites of the different APS minerals encountered in all the different geological units surrounding the EARUF deposits or prospects. ______53 Figure 8. Projection in Ce-La-Nd+Pr coordinates of the microprobe analyses of the different monazite and APS minerals for a same sample encountered in all the different geological units surrounding the EARUF deposits or prospects. Open symbols refer to APS analyses. Solid symbols refer to monaziteanalyses.______55 Figure 9. Projection in S-Sr-LREE coordinates of the microprobe analyses of the different APS minerals encountered in all the different geological units surrounding the EARUF deposits or prospects. ______56 Figure 10. Activity-activity diagrams Log [Sr2+/Ce3+] vs pH representing the stability

domains of svanbergite, goyazite, florencite for two different values of log aO2.______59 Figure 11. Crustal and lithostructural domains of the sub-Athabasca basement, studied areas and main unconformity-type deposits in the Athabasca basin (modified from Ruzicka, 1986). ______72 Figure 12. SEM images of APS minerals from the Athabasca basin. a) Pseudocubic habit of APS grain in illite matrix in a distal alteration area. b) Aggregate of small euhedral grain of APS minerals in the intergranular pore space in sandstone. c) Cluster of APS minerals lining altered micas surface. d) LREE-end member APS crystals along the surface of detrital monazite grain. e) Disseminated crystals of LREE-Sr Al-phosphate (white spots) in a matrix of hydrothermal illite-sudoite close to a discontinuity. f) Larger euhedral grain of APS minerals in the paleoweathered basement.______75 Figure 13. a) Zoning APS crystals associated with relict monazite grain in the basement rocks. b) APS minerals in contact with pyrite and apatite in the basement rocks ______79 Figure 14. Projection in terms of Ca-Sr-LREE (electron microprobe data) of the various APS minerals encountered in all geological units surrounding the Athabsca basin. _____ 84 Figure 15. Cross-plot diagram of P + LREE versus S + Sr showing the wide range of chemical compositions recorded in APS.______85 Figure 16. Projection in terms of Sr-S-LREE (electron microprobe data) of the various APS minerals encountered in all the geological units surrounding the Athabasca deposits or

10 Liste des figures

prospects. Open symbols refer to APS analyses in sandstone. Solid symbols refer to APS analyses in the basement rocks. ______87 Figure 17. Projection in terms of Ce-La-(Pr+Nd) (electron microprobe data) of some monazite and the various APS minerals encountered in all the geological units surrounding the Athabasca basin.______89 Figure 18. Projection in terms of Sr-S-LREE (electron microprobe data) of the various APS minerals encountered in all the geological units surrounding the australian and canadian deposits or prospects. Open symbols refer to APS analyses from the Kombolgie basin. Solid symbols refer to APS analyses from the Athabasca basin. ______91 = z+ Figure 19. Relationship between ∆G°f,ox versus ∆GO M (aq) for minerals from different groups of the alunite supergroup. ______113 Figure 20. Crystal structure of the minerals belonging to the alunite supergroup viewed perpendicular to the c axis.______117 = z+ = z+ Figure 21. Relationship between ∆GO M (c) and ∆GO M (aq) for cations from different sites in the alunite supergroup. ______121 Figure 22. Schematic spatial distribution of the different alteration assemblages in unconformity-type uranium deposits ______134 Figure 23. Vertical distribution of alteration assemblages in U unconformity deposits. ___ 135 Figure 24. Projection in S-Sr-LREE coordinates of the microprobe analyses of APS minerals from the Kombolgie and Athabasca basins.______136 Figure 25. Saturation index (Log Q/K) of selected minerals versus the reaction progress variable ξ during the reaction of the initial fluid with a sandstone. ______147 Figure 26. Saturation index (Log Q/K) of selected minerals versus the reaction progress variable ξ during the reaction of the sandstone derived fluid with a quartz mica-schist. 149 Figure 27. Saturation index (Log Q/K) of selected minerals versus the reaction progress variable ξ during the reaction of the sandstone derived fluid with a felsic gneiss. _____ 151 Figure 28. Paleoconditions of formation of APS minerals according to the parental host rocks (modified from Iida, 1993) ______155

11

Introduction

Introduction

L’histoire des dépôts de minéralisation est généralement liée à celle des minéraux d’altération hydrothermale qui y sont associés. Certains de ces minéraux, argiles, carbonates, phosphates, marqueurs des interactions fluide/roche, sont parfois utilisés pour retracer l’évolution des conditions de formation (Eh, pH, P, T) à l’origine des dépôts métalliques. Ces paragenèses minérales, du fait de leur caractère ubiquiste et de leur grande réactivité aux changements de conditions physico-chimiques sont souvent utilisés dans de nombreux domaines d’applications géologiques liés à la recherche de nouvelles ressources minérales et notamment dans l’environnement des gisements d’uranium de type discordance.

Les concentrations d’uranium liées spatialement aux discordances, sont celles qui sont situées entre un socle métamorphique et/ou granitique d’âge Archéen à Paléo-Protérozoïque et une couverture sédimentaire intracratonique non métarmophisée d’âge Méso-Protérozoïque. Ces concentrations minérales peuvent être situées dans le socle, dans la couverture ou à la fois dans le socle et la couverture. Dans le socle, elles peuvent s’étendre à des profondeurs importantes, jusqu’à plus de 300 mètres, alors que dans la couverture, elles ne sont éloignées de la discordance que de quelques dizaines de mètres. La morphologie des corps minéralisés est très variée. On rencontre des minéralisations en amas, en filons, en remplissage de brèches ou en disséminations. Lorsque la couverture a été érodée, certains gisements de socle sont classés dans le groupe des gisements liés aux discordances sur des critères pétrographiques, minéralogiques et géochimiques (zones d’altération).

13 Introduction

Les gisements d’uranium liés spatialement aux discordances protérozoïques sont d’une importance économique considérable, en particulier ceux du bassin d’Athabasca (Saskatchewan, Canada) et ceux du géosynclinal de Pine Creek (Territoires du Nord, Australie).

De nombreux travaux ont été réalisés sur les paragenèses minérales des gisements d'uranium sous discordance, autour des altérations argileuses (halo d'altération) caractéristiques des dépôts uranifères en Australie et au Canada (Hoeve and Quirt, 1984, Patrier et al., 2003, Laverret et al., 2005, Beaufort et al., 2005, Kister et al., 2005, Polito et al., 2004). De nombreux auteurs ont également mentionné la présence de sulfates phosphates d'aluminium hydratés (APS) associés avec les minéraux argileux identifiés (illite, kaolinite, chlorites…) dans le halo d'interaction fluide/roche entourant les corps minéralisés. A titre d'exemple, ces minéraux ont été mentionnés dans les gisements des bassins d'Athabasca et de Kombolgie (Hoeve and Sibbald, 1978; Hoeve and Quirt, 1984; Drits et al., 1993; Pacquet and Webber, 1993; Kotzer and Kyser, 1995; Thomas et al., 2000; Quirt, 2003; Beaufort et al., 2005; Laverret et al., 2005) ou encore dans le bassin de Franceville autour des réacteurs d'Oklo (Mathieu et al., 2001; Janeczek and Ewing, 1995).

Les sulfates phosphates d'aluminium (APS) sont des minéraux complexes qui sont disséminés dans la plupart des formations géologiques de la partie superficielle de la terre. Malgré leur faible abondance, les APS jouent un rôle majeur sur le comportement géochimique de nombreux éléments majeurs ou traces à fort impact environnemental tel que le phosphore, le strontium, les éléments traces métalliques ou encore les lanthanides. A ce jour, aucune étude systématique n'a été entreprise sur ces minéraux dont la structure complexe intègre de très larges gammes de solution solide avec de nombreux pôles parmi lesquels les termes riches en calcium (crandallite CaAl3[PO3(O0.5(OH)0.5)]2(OH)6), woodhouseite CaAl3(PO4,SO4)(OH)6), en strontium (goyazite SrAl3[PO3(O0.5(OH)0.5)]2(OH)6, svanbergite SrAl3(PO4,SO4)(OH)6) et en terres rares légères (florencite LREEAl3(PO4)2(OH)6). Il n'existe pas pour l'instant de travaux permettant de situer de manière rigoureuse les relations spatiales et temporelles entre ces APS et les divers phénomènes de concentration ou de dispersion des éléments métalliques dans les formations géologiques superficielles.

Les objectifs du travail de thèse qui est présenté dans les chapitres suivants sont de deux ordres.

14 Introduction

Sur le plan cognitif, il s'agit de réaliser une étude extensive des APS dans le contexte régional des gisements d’uranium sous discordance en focalisant les travaux sur (1) l'origine de ces minéraux et leur relation avec les argiles, (2) sur la détermination de leurs propriétés cristallochimiques et l'étendue de leur variabilité chimique à l'échelle des gisements et (3) sur les conditions physico-chimiques qui régnaient dans le système géologique au moment de leur cristallisation (T, P, pH, Eh, activité des éléments en solution…). Sur le plan appliqué, il s'agit de préciser l'utilisation de ces minéraux comme outil de prospection de corps minéralisés cachés en définissant des critères pertinents (texturaux ou cristallochimiques) qui sont accessibles par des méthodes routinières d'analyses minéralogiques. Il s'agit notamment de préciser les relations entre ces minéraux et les anomalies géochimiques qui caractérisent l'environnement des gisements d’uranium sous discordance, et surtout de développer des outils de modélisation numérique thermodynamique permettant de prédire le comportement géochimique des divers éléments traces en fonction des domaines de stabilité des divers APS.

Ces travaux de recherche ont été réalisés de manière comparative sur des gisements d'uranium sous discordance situés sur les deux bassins sédimentaires d’âge Protérozoïque moyen qui contiennent les gisements d'uranium les plus importants au monde en terme de ressources économiques, le bassin de Kombolgie (Australie) et la bassin d’Athabasca (Canada).

Présentation du mémoire de thèse Les résultats s’organisent en deux parties autour de 4 articles:

Au préalable, quelques rappels bibliographiques sur les propriétés minéralogiques des sulfates phosphates d’aluminium hydratés et les principales caractéristiques géologiques des gisements d’uranium associés à une discordance protérozoïque seront présentés.

La première partie est consacrée à la caractérisation des APS dans le contexte des deux bassins de Kombolgie et d'Athabasca. Les résultats sont présentés sous la forme de deux articles scientifiques complémentaires qui combinent des données de pétrographie des altérations, les relations de phase entre APS et minéraux argileux et les variations spatiales des propriétés cristallochimiques et texturales des APS pour définir un modèle général de variation des propriétés de ces minéraux autour des corps minéralisés.

15 Introduction

Dans la deuxième partie du mémoire, le modèle de variations cristallochimiques servira de support à l’étude thermodynamique des conditions de stabilité des APS dans les gisements d’uranium associés à une discordance protérozoïque et à la modélisation géochimique des zones d’altération dans lesquelles les minéraux argileux et les APS coexistent. Comme pour la partie précédente, les résultats sont présentés suivant deux articles. Dans un premier temps l'approche a été focalisée sur la détermination des grandeurs thermodynamiques qui n'existent pas dans la littérature pour des espèces déjà identifiées dans les environnements géologiques superficiels (e.g. la svanbergite, article 3). Une modélisation des interactions fluide-roche a ensuite été entreprise pour simuler les conditions de formation des différents assemblages minéralogiques d’altération (argiles, phosphates) associés autour des gisements d’uranium sous discordance (article 4).

16 Les sulfates phosphates d’aluminium

Les sulfates phosphates d’aluminium

Généralités

Les Sulfates Phosphates d’Aluminium (APS) sont des minéraux ubiquistes disséminés dans un grand nombre d’environnements géologiques: sédimentaires, diagénétiques, hydrothermales, métamorphiques, magmatiques ou dans les profils d’altération des sols. Ces minéraux ont très longtemps été négligés par les géologues et les géochimistes du fait de leurs très petites tailles (< 1-10 µm) et de leur faible concentration dans les roches (< 0.05 %), ce qui empêchait le plus souvent leur identification par des techniques d’observations classiques alors que leur insolubilité à faible température les rendait inertes aux séquences d’extraction géochimique.

Des études récentes durant ces dix dernières années ont néanmoins montré l’intérêt de ces minéraux pour les sciences de la terre sur des problèmes liés aux paléoconditions de formation dans les systèmes naturels et les problèmes environnementaux: 1) les APS sont sensibles aux changements de conditions physico-chimiques du milieu, se traduisant par des variations de compositions chimiques dont la structure complexe intègre de très larges gammes de solution solide (Mordberg et al., 2000; Stoffregen, 1993; Stoffregen et al., 1994) et qui, après cristallisation, sont omniprésents dans les systèmes géologiques supergènes. 2) Les APS jouent un rôle majeur sur le comportement géochimique de nombreux éléments majeurs ou traces à fort impact environnemental tel que le phosphore et les éléments traces

17 Les sulfates phosphates d’aluminium métalliques incorporées dans leur structure qui ont été négligés dans les bilans géochimiques à la surface de la Terre (Rasmussen, 1996).

Formation et stabilité

Les sulfates phosphates d’aluminium (APS) sont des minéraux ubiquistes souvent observés en association avec des paragenèses argileuses dans de nombreux environnements géologiques (Dill, 2001; Rasmussen, 1996; Spötl, 1990). Ces minéraux sont dépendants de la disponibilité des éléments Al, P, S et donc des minéraux accessoires présents dans les roches (monazite, apatite, pyrite, silicates d’aluminium). Ces minéraux ne sont pas uniquement tributaires de l’activité des éléments en solution, mais également des conditions de pH et d’Eh dans lesquelles ils cristallisent (Dill, 2001; Kolitsch et Pring, 2001). De nombreux auteurs (e.g. Schwab et al., 1989, Nriagu, 1976; Vieillard et al., 1979; Stoffregen et Alpers, 1987) s’accordent pour dire que les APS sont stables pour des concentrations en phosphore dissous faible (a <10-5) dans des conditions aussi bien oxydantes que réductrices. De plus ils H3PO4 peuvent se former dans des gammes de pH variables, dans des conditions acides (pH<4) jusqu’à des pH proche de la neutralité. Les APS sont également stables à des températures allant jusqu’à 400°C et pour des pressions de fluides allant jusqu’à 1kbar (Dill, 2001).

Classification

Les sulfates phosphates d’aluminium symbolisés par les lettres “APS” appartiennent au supergroupe de l’alunite. Ce supergroupe comprend différents sous-groupes minéralogiques, qui, combinés, représentent plus de 40 espèces minéralogiques dont la formule générale est

AB3(XO4)2OH6.

A, B et X correspondent à trois sites cristallographiques. Le site A, en coordinence 12, peut

être occupé par des ions monovalents (H3O, K, Na, Rb, NH4, Ag, Tl etc.), divalents (Ca, Sr, Ba and Pb etc.), trivalents (Bi, et Terres Rares) et parfois tétravalents (Th, U). Le site B, en coordinence 6 peut être occupé par Al3+, Fe3+, Ga3+ ou V3+ et le site X, en coordinence 4, est occupé par, S6+, P5+, As5+ et plus rarement par Cr6+, Sb5+ et Si4+ (Jambor, 1999; Scott, 2000; Scott, 1987; Stoffregen, 1987). Beaucoup de ces minéraux sont exotiques, ayant été décrits dans de nombreuses régions à la surface de la Terre, le plus souvent associés à des dépôts métallifères. Rares également sont les occurrences naturelles qui présentent des compositions

18 Les sulfates phosphates d’aluminium

proches de pôles pures, le plus souvent les APS observés forment de très larges gammes de solutions solides entre les différents sites A, B, X.

En raison du potentiel d’une très large possibilité de substitutions complexes dans le supergroupe et pour éviter la prolifération de nouveaux noms de minéraux Scott (2000), en accord avec Jambor (1999) a proposé une nouvelle classification dont les limites seraient fixées par des groupes déjà définis que sont l’alunite, la beudantite et la crandallite. Dans les 6+ 5+ 5+ trois groupes, S , As et P sont les principaux cations X observés dans le site (XO4)2. Le

groupe de l’alunite est composé essentiellement de minéraux à dominante (SO4)2 (Tab. 1),

alors que dans le groupe de la beudantite un SO4 est remplacé par PO4 ou AsO4 (Tab. 2). Le

groupe de la crandallite caractérise les minéraux dont le site (XO4)2 est occupé soit par P soit par As ou les deux (Tab 3). Ces changements du groupe de l’alunite jusqu’au groupe de la crandallite caractérise une progression d’un pôle sulfate vers un pôle phosphate ou arsénate en

passant par des compositions mixtes (SO4)(PO4) ou (SO4)(AsO4) du groupe de la beudantite.

Tableau 1. Classification des minéraux du groupe de l’alunite (Jambor, 1999). Al > Fe Fe > Al

Alunite KAl3(SO4)2(OH)6 Jarosite KFe3(SO4)2(OH)6

Natroalunite NaAl3(SO4)2(OH)6 Natrojarosite NaFe3(SO4)2(OH)6

Ammonioalunite (NH4)Al3(SO4)2(OH)6 Ammoniojarosite (NH4)Fe3(SO4)2(OH)6

Schlossmacherite (H3O,Ca)Al3(SO4)2(OH)6 Hydronium jarosite (H3O)Fe3(SO4)2(OH)6

― Argentojarosite AgFe3(SO4)2(OH)6

― Dorallcharite TlFe3(SO4)2(OH)6

Osarizawaite Pb(Al,Cu)3(SO4)2(OH)6 Beaverite Pb(Fe,Cu)3(SO4)2(OH)6

― Plumbojarosite PbFe6(SO4)4(OH)12

Minamiite (Na,Ca,K)2Al6(SO4)4(OH)12 ―

Huangite CaAl6(SO4)4(OH)12 ―

Walthierite BaAl6(SO4)4(OH)12 ―

A cette classification parfois complexe des APS, Stoffregen et al. (2000) subdivisent ces minéraux en deux sous-groupes sur la base Fe > Al (groupe de la jarosite) par rapport à Al > Fe (groupe de l’alunite). Plusieurs subdivisions sont ensuite généralement faites en fonction de l’occupation du site X.

19 Les sulfates phosphates d’aluminium

Tableau 2. Classification des minéraux du groupe de la beudantite (Jambor, 1999). S, As S, P

Beudantite PbFe3[(As,S)O4]2(OH)6 Corkite PbFe3[(P,S)O4]2(OH)6

Hidalgoite PbAl3[(As,S)O4]2(OH)6 Hinsdalite PbAl3[(P,S)O4]2(OH)6

Kemmlitzite (Sr,Ce)Al3[(As,S)O4]2(OH)6 Svanbergite SrAl3[(P,S)O4]2(OH)6

― Woodhouseite CaAl3[(P,S)O4]2(OH)6

Gallobeudantite PbGa3[(As,S)O4]2(OH)6 ―

Propriétés cristallographiques

De nombreuses études de diffraction de rayons X sur monocristaux des minéraux du supergroupe ont été réalisées et ont été synthétisées par Jambor (1999, Tab. 4). La cristallographie des minéraux du supergroupe de l’alunite a été déterminée en premier par Hendricks (1937), qui a présenté des données sur l’alunite, la jarosite et la plumbojarosite. Des nombreuses études réalisées sur la structure des minéraux du supergroupe de l’alunite, bien qu’il existe des exceptions, ont montré que la majorité de ces minéraux ont un système de symétrie rhomboédrique, avec a ≈ 7, c ≈ 17 Å, et un groupe d’espace R3 m, avec un nombre de molécules par maille élémentaire (Z) de 3.

Le motif élémentaire des minéraux du supergroupe comprend des tétraèdres XO4 et des

octaèdres B(O, OH6) déformés aléatoirement. Les octaèdres sont reliés entre eux par les ions hydroxyles et sont reliés aux tétraèdres par les deux oxygènes apicaux des octaèdres, pour former des feuillets parallèles au plan (001), de cette façon formant une séquence perpendiculaire à l’axe c (Fig. 1).

Les tétraèdres XO4, qui sont alignés suivant l’axe [001], sont disposés suivant deux orientations cristallographiques dans un même feuillet; une position où les tétraèdres s’orientent vers le haut le long de l’axe c et une seconde position où les tétraèdres s’orientent vers le bas. Les oxygènes et les hydroxyles forment un polyèdre au milieu duquel se situe les cations du site A.

20 Les sulfates phosphates d’aluminium

Tableau 3. Classification des minéraux du groupe de la crandallite (modifiée à partir de Jambor, 1999) Al > Fe Fe > Al Gorceixite Arsenogorceixite Dussertite BaAl3[(PO3(O0.5(OH)0.5)]2 (OH)6 BaAl3[(AsO3(O0.5(OH)0.5)]2 (OH)6 BaFe3[(AsO3(O0.5(OH)0.5)]2 (OH)6 Crandallite Arsenocrandallite Segnitite CaAl3[(PO3(O0.5(OH)0.5)]2(OH)6 CaAl3[(AsO3(O0.5(OH)0.5)]2(OH)6 PbFe3[(AsO3(O0.5(OH)0.5)]2 (OH)6 Goyazite Arsenogoyazite Benauite SrAl3[(PO3(O0.5(OH)0.5)]2(OH)6 SrAl3[(PO3(O0.5(OH)0.5)]2(OH)6 SrFe3[(PO3(O0.5(OH)0.5)]2(OH)6 Plumbogummite Philipsbornite Kintoreite PbAl3[(PO3(O0.5(OH)0.5)]2(OH)6 PbAl3[(AsO3(O0.5(OH)0.5)]2 (OH)6 PbFe3[(PO3(O0.5(OH)0.5)]2(OH)6 Florencite-Ce Arsenoflorencite-Ce ― CeAl3(PO4)2(OH)6 CeAl3(AsO4)2(OH)6 Florencite-La Arsenoflorencite-La ― LaAl3(PO4)2(OH)6 LaAl3(AsO4)2(OH)6 Florencite-Nd Arsenoflorencite-Nd ― NdAl3(PO4)2(OH)6 NdAl3(AsO4)2(OH)6 Waylandite Arsenowaylandite Zairite (Bi,Ca)Al3(PO4, SiO4)2(OH)6 (Bi,Ca)Al3(AsO4)2(OH)6 BiFe3(PO4)2(OH)6 Eylettersite ―― (Th,Pb)Al3(PO4,SiO4)2(OH)6 ―― Springcreekite BaV3[(PO3(O0.5(OH)0.5)]2(OH)6

Plusieurs changements de symétrie des minéraux du supergroupe de l’alunite ont été identifiés. Ainsi, pour des compositions avec le même cation dans le site XO4, la taille du paramètre c est principalement influencée par la taille du cation A et la substitution de l’aluminium par le fer dans le site B. La symétrie change également à cause de la distribution aléatoire des tétraèdres XO4 ou à cause de l’ordre – désordre et/ou de la distorsion provoquée par les cations A sur la structure. Pour maintenir le groupe d’espace R3 m, les tétraèdres SO4

– PO4 – AsO4 doivent être désordonnés; l’état ordonné, comme dans les structures de la corkite ou de la gallobeudantite, réduisent la symétrie à un groupe d’espace R3m. Un deuxième changement est aussi causé par la présence de cations divalents dans le site A. + 3+ Dans un tel cas, la formule type de la jarosite A B 3(SO4)2(OH)6 devient soit 2+ 3+ 2+ 3+ A [B 3(SO4)2(OH)6]2 (ordonné) ou A 0.5B 3(SO4)2(OH)6 (désordonné). Ainsi pour la plumbojarosite, par exemple, où le cation du site A est Pb2+, pour maintenir l’électronégativité, la moitié des sites A sont vacants. La distribution aléatoire des atomes de plomb et les sites vacants produisent ainsi un surdimensionnement qui se manifeste par un dédoublement de l’axe c à 33-34 Å.

21 Les sulfates phosphates d’aluminium

Tableau 4. Etude de diffraction de rayons X sur monocristaux des APS du supergroupe de l’alunite – jarosite (Jambor, 1999) Groupe Nom Composition a, Å c, Å d’espace Alunite Composition non donnée 6.970 17.270 R3 m

Natroalunite (Na0.58K0.42)Al3(SO4)2(OH)6 6.990 16.095 R3 m

Minamiite (Na0.36K0.1Ca0.27□0.27)Al3(SO4)2(OH)6 6.981 33.490 R3 m Jarosite Synthétique, non donnée 7.305 17.190 R3 m Naturel, non donnée 7.304 17.268 R3 m

Gorceixite BaAl3(PO4)(PO3 OH)(OH)6 Monoclinique Cm

Crandallite CaAl3[PO3(O0.5(OH)0.5]2(OH)6 7.005 16.192 R3 m

Woodhouseite Non donnée ;CaAl3(PO4)(SO4)(OH)6 6.993 16.386 R3 m

Goyazite Non donnée ;SrAl3[PO3(O0.5(OH)0.5)]2(OH)6 7.015 16.558 R3 m

Svanbergite Non donnée ;SrAl3(PO4)(SO4)(OH)6 6.992 16.567 R3 m

Osarizawaite Pb(Al1.62Cu0.98Fe0.19Zn0.02)(SO4)2(OH)6 7.075 17.248 R3 m

Plumbojarosite Non donnée ;Pb[Fe3(SO4)2(OH)6]2 7.200 33.600 R3 m

Beudantite Pb0.99(Fe2.98Cu0.02Zn0.01)(SO4)0.99(AsO4)0.99(OH)6.07 7.339 17.034 R3 m

Corkite Pb0.98(Fe2.99Cu0.05[(PO4)(SO4)0.97(OH,H2O)6 7.280 16.821 R3m

Hinsdalite PbAl3[(PO4)1.38(SO4)0.62](OH,H2O)6 7.029 16.789 R3 m

Gallobeudantite Pb1.04(Ga1.53Al1.14Fe0.33Zn0.18Ge0.05)(AsO4)1.04(SO4)0.96(OH)6.50 7.225 17.030 R3 m

Plumbogummite PbAl3[(PO4)1.90(AsO4)0.10](OH,H2O)6 7.039 16.761 R3 m

Kintoreite PbFe3(PO4)1.3(AsO4)0.4(SO4)0.3(OH,H2O)6 7.331 16.885 R3 m 3+ 5+ Dussertite Ba(Fe 0.84Sb 0.16)3(AsO4)2(OH,H2O)6 7.410 17.484 R3 m

Florencite-(Ce) (Ce0.54La0.27Nd0.11Sm0.04Ca0.04)Al3(PO4)2(OH)6 6.972 16.261 R3 m

Pour les minéraux du groupe de la crandallite, dont le site A est occupé par un cation divalent

un troisième effet est causé par la charge du site XO4. Quand Le site XO4 est occupé par PO4

ou AsO4 au lieu de SO4, un proton est requis pour compenser le déficit de charge. En effet pour la crandallite, Blount (1974) a conclu que la formule prenait la forme

CaAl3[PO3O0.5(OH)0.5]2(OH)6, ainsi la compensation de charge s’effectue par la substitution

partielle d’oxygène par un hydroxyl autour des tétraèdres PO4. Radoslovich (1982), par contre, a déterminé qu’une telle configuration n’était pas possible pour la gorceixite à cause de la trop grande taille du baryum. Il conclue que la formule de la gorceixite était mieux

représentée par BaAl3(PO4)(PO3·OH)(OH)6.

22 Les sulfates phosphates d’aluminium

Figure 1. La structure de l’alunite, vu parallèle à l’axe a.

23

Les gisements d’uranium associés à une discordance protérozoïque

Les gisements d’uranium associés à une discordance protérozoïque

Généralités

En 1993, environ le tiers des ressources mondiales en uranium (si l’on exclut l’ex-Union Soviétique et la Chine) assurées extractibles à des prix ne dépassant pas 130 $US/kg se trouvait dans des gisements d’uranium associés à des discordances protérozoïques. Cette proportion augmente actuellement par suite de nouvelles découvertes et de la viabilité décroissante des autres types de ressources en minerai d’uranium à moindres teneurs (Ruzicka, 1996).

Actuellement, les gisements d’uranium associés à une discordance protérozoïque sont d’une importance économique considérable, représentant les ressources à forte teneur/fort tonnage et à faibles coûts les plus importantes exploitées dans le monde. Les dépôts d’uranium sont généralement situés à proximité de l’interface entre un socle métamorphique et/ou granitique d’âge Archéen à Paléo-Protérozoïque (2500 – 1800 Ma) et une couverture sédimentaire gréseuse intracratonique d’âge Méso-Protérozoïque (1700 – 1500 Ma), non métamorphisée.

Méconnu il y a encore une trentaine d’années, plus d’une quinzaine de gisements d’uranium associés à une discordance protérozoïque ont été découverts dans le bassin d’Athabasca (Canada) depuis 1968, date à laquelle le premier gisement a été découvert (Rabbit Lake). Des

25 Les gisements d’uranium associés à une discordance protérozoïque gisements importants, tels que Ranger 1 et 3, Nabarlek, Jabiluka, Koongara ont également été découverts dans le géosynclinal de Pine Creek, dans le Territoire du Nord (Australie), ainsi que dans les Territoires du Nord, Canada (Kiggavik), et en Russie (Karku). Les gisements les plus importants sont situés dans le bassin d’Athabasca (Saskatchewan, Canada), avec les gisements de McArthur, Cigar Lake, Key Lake et Rabbit Lake et Eagle Point dans la partie est du bassin, et les gisements de Cluff Lake et Shea Creek dans la partie ouest.

Les gisements du bassin d’Athabasca sont caractérisés par leurs fortes teneurs avec par exemple 225 000 tonnes à 15.34% d’U à McArthur et 142 000 tonnes à 15% d’U à Cigar Lake (Tab. 5). Le Canada est aujourd’hui le plus gros producteur mondial. En 2004, il a produit 11,676 tonnes d’U représentant 30% de la production mondiale (≈ 39 000 t), pour un coût total de 800 millions de $C. Les gisements australiens sont caractérisés par des minerais à plus faibles teneurs que celles des gisements de l’Athabasca (Tab. 6).

Au Canada, les parties du bassin actuellement préservées sont essentiellement constituées de sédiments clastiques d’origine continentale, qui ont été déposés dans des systèmes fluviatiles ou marins de faible profondeur dans une atmosphère oxygénée (Ramaekers, 1991, Ramaekers et al., 2001). Les sédiments sont généralement composés de séquences de couches rouges (“red-bed”) formées de grès arénitiques riches en quartz, et dans une moindre mesure de conglomérats, de shales et de dolomie. Ces sédiments reposent en discordance sur un socle cristallin constitué de roches métasédimentaires aphébiennes (Protérozoïque inférieur) riches en graphite et pyrite et de granitoïdes gneissiques archéens. Au contact avec les grès, le socle est fortement altéré sur une zone épaisse de 10 à 20 mètres. Ce régolithe, correspondrait à un profil d’altération latéritique qui se serait développé avant le dépôt des sédiments (Hoeve et Quirt, 1984, Quirt, 2002). Les gisements d’uranium associés à une discordance protérozoïque australiens sont localisés dans le socle alors que les gisements canadiens se retrouvent aussi bien dans le socle qu’à l’interface grès-socle et/ou dans la couverture gréseuse. Dans les deux derniers cas ils se situent le plus souvent à l’intersection d’un ou plusieurs systèmes de failles riches en graphite avec la discordance.

Deux types principaux d’association métallique sont observés dans les gîtes d’uranium associés à des discordances. Certains gîtes se composent d’une minéralisation polymétallique (Ni-Co-Cu-Fe-Mo-Au-Bi-S-Te-As-S) et se situent immédiatement au niveau de la discordance ou dans les grès (Key Lake, Cigar Lake, Shea Creek).

26 Les gisements d’uranium associés à une discordance protérozoïque

D’autres sont constitués par une minéralisation monométallique (U), pauvres en éléments métalliques associés, et se rencontrent généralement soit en dessous (McArthur River pod 2, Rabbit Lake, Eagle Point), soit (rarement) au dessus de la discordance (McArthur pods 1, 3 et 4).

Les minéralisations, le plus souvent de la pechblende ou de la coffinite, se trouvent dans des veines, des brèches ou des lentilles associés à des zones de failles inverses ou normales. Ces gisements sont toujours associés à un halo d’altération argileuse plus ou moins étendu dans les grès jusqu’à 400 mètres en largeur, 500 mètres en hauteur et plusieurs milliers de mètres en longueur (Thomas et al., 2000), faisant état de plusieurs phases d’altération. La première due au métamorphisme rétrograde des roches du socle, est suivi du lessivage et de l’érosion de ce socle, à l’origine d’un régolithe (MacDonald, 1985) et par la suite une altération diagénétique et hydrothermale des différentes lithologies du socle et des grès, contemporaines des processus de minéralisations. La minéralogie de ces halos d’altération est dominée par la kaolinite et l’illite, associés à des quantités variables de chlorite (sudoïte, chlorite trioctaédrique), de tourmaline magnésienne pauvre en alcalins (dravite), de quartz automorphe et plus accessoirement à des alumino-sulphates-phosphates.

Des différences significatives existent entre les dépôts uranifères du bassin d’Athabasca et ceux de la région de Pine Creek. Pour exemple, tous les gisements de la région de Pine Creek, sans exceptions, sont encaissés dans les roches du socle, soit dans des métapélites bréchifiées du socle d’âge Protérozoïque inférieur, soit dans des roches carbonatées. L’évidence d’un développement régolithique est également moins prononcé et l’extension du halo d’altération est plus limitée au niveau des grès.

Les modèles de genèse

Les bassins sédimentaires canadiens et australiens semblent s’être formés dans des environnements similaires et à des âges comparables (1700 – 1690 Ma, Kyser et al., 2000). La figure 2 représente le supercontinent Rodinia pendant le Néoprotérozoïque, à environ 900 Ma, avec la localisation des principaux bassins et gisements d’uranium. Les cratons, au sein desquels se sont formés les bassins, se sont séparés dans l’intervalle 900 – 700 Ma, à la suite du démantèlement tectonique du supercontinent Rodinia en plusieurs fragments.

27 Les gisements d’uranium associés à une discordance protérozoïque

Tableau 5. Principaux gisements d'uranium associés à une discordance protérozoïque (Canada) I – BASSIN DE L'ATHABASCA 1 - Est Athabasca t U Teneur (%U) Statut

Rabbit Lake 16 250 0.27 Epuisé Eagle Point Nord 22 300 1.76 En cours d'exploitation Eagle Point Sud 28 600 1.10 En cours d'exploitation Collins Bay A 3 040 6.30 Epuisé Collins Bay B 14 700 0.38 Epuisé Collins Bay D 2 150 1.85 Epuisé Raven 3 900 0.13 Stand-by Horse Shoe 3 100 0.13 Stand-b Dawn Lake 5 000 1.44 Stand-by Midwest Lake 4 060 4.72 Stand-by McClean Lake 10 060 1.09 Stand-by JEB 2 070 1.41 Epuisé Sue (5 lentilles A,B,C,D,E°) 16 050 0.51-2.85 En cours d'exploitation Key Lake 68.000 2.30 Epuisé Cigar Lake 142 000 15.00 En cours de développement McArthur River 225.100 15.34 En cours d'exploitation Millenium 27 000 2.20 En cours d'exploration La Rocque 3000–4000 En cours d'exploration P. Patch 6 550 0.70 En cours d'exploration 2 - Ouest Athabasca Cluff D 4 450 2.93 Epuisé Claude 2 350 0.33 Epuisé Dominique – Jeanine 7 865 0.60 Epuisé Dominique – Peter 9 310 0.80 Epuisé Shea Creek 15 000 2.00 En cours d'exploration II – BASSIN DU THELON Kikgavik-Sissons 11 150 0.49 Stand-by Andrew Lake 20 400 0.57 Stand-by End Grid 10 500 0.38 Stand-by

28 Les gisements d’uranium associés à une discordance protérozoïque

Tableau 6. Principaux gisements d'uranium associés à une discordance protérozoïque (Australie) I - PINE CREEK GEOSYNCLINE (NT) t U Teneur (%U) Statut "East Alligator River Uranium field" JABILUKA 1 2 800 0.25 En cours d'exploration JABILUKA 2 90 400 0.46 Stand-by KOONGARRA 1 14 500 0.79 Stand-by KOONGARRA 2 2 000 ? En cours d'exploration RANGER 1 54 000 0.35 Epuisé RANGER 3 56 500 0.31 En cours d'exploitation NABARLEK 11 500 1.86 Epuisé RANGER 68 4 500 0.30 En cours d'exploration "South Alligator River Uranium field" PALETTE Epuisé ROCK HOLE 750 ? Epuisé EL SHERANA Epuisé "Rum Jungle district" DYSON'S RUM JUNGLE CREEK WHITE'S 3 850 ? Epuisé KYLIE-KYLIE South MT FITCH II - PATERSON PROVINCE (WA) KINTYRE 30 500 0.30 Stand-by TUREE CREEK 800 0.124 En cours d'exploration III – WESTMORELAND AREA (QLD) REDTREE 8 720 0.12 Stand-by JUNNAGUNNA 3 300 0.11 Stand-by HUARRABAGOO 1 100 0.18 Stand-by OUTCAMP 580 0.16 Stand-by SUE 810 0.16 Stand-by BLACK HILLS ? ? En cours d'exploration

Plusieurs modèles conceptuels ont été proposés pour expliquer la formation des ces gisements d’uranium de type discordance: le modèle supergène, le modèle magmatique hydrothermal et le modèle diagénétique-hydrothermal. Le modèle supergène, proposé initialement par

29 Les gisements d’uranium associés à une discordance protérozoïque

Knipping (1974), provient du lessivage de l’uranium et des autres constituants métalliques des roches du socle par des eaux de surface, puis d’une reprécipitation à la rencontre de zones réductrices du socle, avant le dépôt du bassin sédimentaire. Cependant les datations des minéralisations uranifères ont montré que les gisements se sont formés postérieurement aux dépôts des sédiments dans des conditions de diagenèse profonde. De plus, ce modèle ne fait pas intervenir la tectonique alors que les gisements canadiens sont clairement associés à des mouvements tectoniques post-Athabasca (Strnad, 1980). Une origine magmatique hydrothermale des gisements a été proposée par Binns et al. (1980), où des fluides minéralisateurs ascendants chauds, d’origine profonde se bloqueraient au niveau du piège de la discordance.

Figure 2. Assemblage des continents à environ 900 Ma montrant la position des principaux gisements d'uranium des bassins du Thélon, de l'Athabasca et de Mc Arthur. Les ronds et les carrés noirs indiquent respectivement les bassins et la position des principaux gisements d'uranium dits de discordance et des principaux gisements sédimentaires à sulfures de Zn-Pb- Ag (modifié d'après Kyser et al., 2000).

30 Les gisements d’uranium associés à une discordance protérozoïque

Le modèle diagénétique-hydrothermal proposé par Hoeve et al. (1980) est celui qui explique actuellement le mieux la formation de ces gisements. Dans ce modèle, la minéralisation uranifère est associée à des processus diagénétiques qui ont agi à des températures élevées (180 ± 20°C) dans les sédiments après leur dépôt (Ruzicka, 1996). Les minéralisations uranifères résulteraient de l’interaction, à la discordance, entre des fluides réducteurs riches en méthane circulant le long des failles enracinées dans le socle avec des fluides oxydants de bassin transportant l’uranium (Fig. 3).

Cependant la nature et l’origine des fluides de socle sont encore méconnues. De récentes études d’inclusions fluides (Derome et al., 2000a,b), en partie sur les gisements australiens, ont toutefois mis en évidence un fluide de socle plus chaud diluant. Fayek et Kyser (1997) ont distingué une variante à ce modèle, dans laquelle les fluides acides et oxydants de bassin interagiraient directement avec la lithologie du socle et se réduiraient par interaction eau- roche avec les roches réductrices du socle (riches en Fe2+, Komninou et Sverjensky, 1995). D’après Hoeve et Quirt (1984) et Raffensperger et Garven (1995a), les fluides de bassin ont circulé de manière convective pendant la formation des minéralisations. Le mélange de fluides aurait eu lieu lors d’injections périodiques de fluides de socle dans les grès provoquées par des réactivations tectoniques.

31 Les gisements d’uranium associés à une discordance protérozoïque

Figure 3. Modèle conceptuel (Ruzicka, 1996) de la formation des gisements d’uranium de type discordance. Coupe verticale simplifiée. Les flèches indiquent les trajets d’écoulement des fluides oxydants et réduits entraînés par convection. Les numéros encerclés indiquent les emplacements des divers styles de minéralisation. 1) minéralisation monométallique à teneur moyenne au-dessous de la discordance, 2) minéralisation polymétallique à forte teneur au niveau de la discordance, 3) minéralisation monométallique à faible teneur dans les roches sédimentaires au dessus de la discordance.

32 Partie I – Les sulfates phosphates d’aluminum associés aux gisements de type discordance

PARTIE I

Les sulfates phosphates d’aluminium dans l’environnement des gisements d’uranium associés à discordance protérozoïque

Introduction

De nombreuses études sur les gisements d’uranium associés à une discordance protérozoïque ont été publiées durant les vingt dernières années sur l’origine et l’évolution des minéraux secondaires en relation avec les processus d’interaction fluide/roche à l’origine des dépôts d’uranium. Les minéraux argileux apparaissent de loin comme les constituants majeurs des halos d’altération (Beaufort et al., 2005; Patrier et al., 2003; Polito et al., 2004a et b; Hoeve et Sibbald, 1978; Hoeve et Quirt, 1984; Drits et al., 1993; Quirt, 2003; Kotzer et Kyser, 1995; Laverret et al., 2005; Kister et al., 2005).

33 Partie I – Les sulfates phosphates d’aluminum associés aux gisements de type discordance

Ces études ont permis de mettre en évidence une distribution spatiale des altérations hydrothermales, tant à l’échelle locale (forage) que régionale, autour des gisements d’uranium. La minéralogie de ces argiles est dominée par l’illite qui se retrouvent dans toutes les zones d’altération du socle et de la couverture gréseuse. Des quantités variables de chlorite (di-tri ou tri) et de dravite (tourmaline magnésienne) sont également associées à l’illite au niveau des zones de failles, à la discordance et dans le socle.

Les argiles ne sont pas les seules phases d’altération observées autour de ces gisements associés à une discordance protérozoïque. Certains auteurs (Miller, 1983; Hoeve et Quirt, 1984; Wilson, 1985; Quirt et al., 1991; Fayek et Kyser, 1997; Lorilleux, 2001; Beaufort et al., 2005; Kister et al., 2005; Laverret et al., 2005) ont en effet mentionné la présence d’alumino- phosphates associés aux halos d’altération, qui sont considérés comme contemporains des phases d’altération à l’origine de la formation des argiles et des dépôts d’uranium (Beaufort et al., 2005).

Beaufort et al. (2005) ont également mis en évidence que ces minéraux avaient des compositions intermédiaires entre la florencite, la goyazite et la crandallite et que les proportions relatives de ces différents termes de solution solide variaient de manière significative en fonction de leur distance aux corps minéralisés. Cette étude a été axée sur l'étude comparative des phosphates d'aluminium hydratés (APS) dans deux environnements géologiques distincts contenant des gisements d'uranium associés à une discordance protérozoïque: -La discordance à la base du bassin de Kombolgie (Territoire du Nord, Australie) -La discordance à la base du bassin d'Athabasca (Canada)

Ces travaux, focalisés sur les différents gisements de Jabiluka, Ranger3 en Australie, Shea Creek, Cigar Lake et McArthur au Canada ont consisté à identifier les APS au niveau de chaque zone d’altération, caractériser leur variabilité cristallochimique à l’échelle des gisements et ainsi établir une étude comparative entre les différentes séquences minéralogiques liées au processus d’altération, à l’origine des dépôts d’uranium associés à une discordance Protérozoïque.

Cette partie s’organise autour de 2 articles et présentent les résultats obtenus sur 1) les APS associés aux gisements de type discordance dans la région de Pine Creek (Alligator River,

34 Partie I – Les sulfates phosphates d’aluminum associés aux gisements de type discordance

Australie). 2) les APS associés aux gisements de type discordance du bassin d’Athabasca (Canada).

35

Partie I – Ch. 1. APS in the East Alligator River Uranium Field

Chapitre 1

Aluminum phosphate sulfate minerals associated with proterozoic

unconformity-type uranium deposits in the East Alligator River

Uranium Field, Northern Territories, Australia.

Stephane GABOREAU1,2, Daniel. BEAUFORT1, Philippe. VIEILLARD1, Patricia. PATRIER1 and Patrice. BRUNETON3

Article publié dans ‘The Canadian Mineralogist’ (2005), 43, pp. 813-827

1 HydrASA, Université de Poitiers, CNRS-UMR 6532, 40 avenue du Recteur Pineau, F 86022 Poitiers Cedex, France 2 ERM SARL, Laboratoire-Bureaux, Université de Poitiers, bât de Géologie, 40 Av. du Recteur Pineau. 86022 POITIERS-Cedex, France 3 COGEMA-BUM-DEX, 2 rue Paul Dautier, BP 4, F 78141 Vélizy Cedex, France

37 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

Abstract

Aluminium Phosphate Sulfate minerals (APS minerals) occur as disseminated crystals in a wide range of geological environments near the Earth surface, including weathering, sedimentary, diagenetic, hydrothermal, metamorphic and also post magmatic systems. Their general formula is AB3(XO4)2(OH)6 in which A, B and X represent three different crystallographic sites. These minerals are known to incorporate a great number of chemical elements in their lattice and to form complex solid solution series which are controlled by the physico-chemical conditions of their formation (Eh, pH, activities of constituent metals, P and T). These minerals are particularly widespread and spatially related to hydrothermal clay parageneses in the East Alligator River Uranium Field (EARUF) environment associated with the uranium orebodies in the Proterozoic basin of Kombolgie (Northern Territories, Australia). This field contains several high grade unconformity related uranium deposits including Jabiluka and Ranger. Both petrography and chemical data obtained in this study are used to discuss the significance of APS minerals in the alteration processes from the EARUF. The wide range of chemical compositions recorded in APS is essentially due to coupled substitutions of Sr to LREE and S to P in the A and X sites respectively. The major variations of the APS solid solution series (s.s.s.) mainly consist in the relative proportions of svanbergite, goyazite and florencite end members. The APS minerals result from the interaction of oxidising and relatively acidic fluids with aluminous host rocks enriched in monazite. The spatial distribution of these minerals and their compositional variation around the uranium orebodies allow us to consider them as good tracer of redox and pH paleo- conditions responsible for the development of fronts during the alteration processes, and hence as potential tools for mineral exploration.

Key-words: APS minerals, florencite, goyazite, svanbergite, unconformity-type uranium deposits, EARUF, Kombolgie basin, clay minerals, paleo-conditions.

38 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

Introduction

Aluminum Phosphate Sulfate minerals (APS minerals) occur as disseminated grains in a wide range of geological environments near the Earth surface, including weathering, sedimentary, diagenetic, hydrothermal, metamorphic and postmagmatic systems (Dill, 2001). APS minerals belong to the alunite supergroup (Scott 1987, Jambor 1999) and crystallise most commonly as authigenic rhombohedral crystals. Their general formula is AB3(XO4)2(OH)6 in which A, B and X represent three different crystallographic sites: 12-fold coordinated sites (A), occupied by monovalent (H3O, K, Na, Rb, NH4, Ag, Tl, etc.) divalent (Ca, Sr, Ba and Pb, etc.), trivalent (Bi and rare-earth elements) and more rarely tetravalent (Th4+) cations; 6-fold coordinated sites (B), occupied by Al3+, Fe3+ and, more rarely, Ga3+ or V3+; 4-fold coordinated sites (X), occupied by S6+, P5+, As5+, and more rarely Cr6+, Sb5+ and minor Si4+.

For a long time, APS minerals have been neglected by geologists and geochemists because of minute size of crystals (<0.1-10 µm) and their low concentration (generally less than 0.05 wt%), which hindered their identification by conventional microscopic techniques. At the same time, their marked insolubility at low temperature also rendered them inert to sequential extraction in solvents. However, several studies in the last ten years pointed out the interest of APS minerals for the Earth scientists who deal with paleo-conditions in natural systems or environmental problems: (1) APS minerals are highly sensitive to their physicochemical conditions of formation through a wide range of compositional variations, due to complex solid-solutions among more than 20 end-members (Stoffregen 1993, Stoffregen et al. 1994, Jambor 1999, Mordberg et al. 2000). After crystallisation, these minerals become very resistant of weathering and dissolution, and are ubiquitous minerals in near-surface environments. (2) APS minerals represent a powerful sink for reactive P and the huge amount of trace elements incorporated in their structure, which has been neglected in the global budget of chemical elements at the Earth’s surface (Rasmussen 1996).

APS minerals are particularly abundant in the clay assemblages associated with some uranium fields in the middle Proterozoic basins. These fields contain several high-grade unconformity- type uranium deposits and several unexplored important prospects in Canada and Australia (Miller 1983, Wilson 1984, Quirt et al. 1991, Fayek and Kyser 1997, Lorilleux 2001, Beaufort et al. 2004). Up to now, no systematic investigations have been performed on the

39 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

APS minerals in these deposits and no data are available on their compositional variations in relation to the uranium deposits, though it is well known that their emplacement was controlled by physico-chemical conditions (Eh, pH, activities of constituent metals, P and T) to which APS are particularly sensitive (Dill 2001, Kolitsch and Pring 2001).

The aim of this study are to clarify the nature and the origin of the APS minerals on both sides of the middle Proterozoic unconformity between the overlying Kombolgie sandstones and the underlying metamorphic basement rocks that host the uranium orebodies of the East Alligator River Uranium Field (EARUF). Spatial variations of both crystal chemistry and phase relationships with clay minerals, on a regional scale, have been investigated in order to improve our knowledge on the suitability of these minerals to indicate the paleo-conditions at which the alteration processes relative to the uranium deposition operated.

Regional geological setting

The study area is located on the Arnhem Land Plateau area and is the northern part of the larger McArthur Basin in the Northern Territory of Australia. The EARUF is located to the east of the Pine Creek Geosyncline, close to the kakadu Group, which is a part of the North Australian Craton. The oldest rocks of the EARUF correspond to Archean granitic gneisses of the Nanambu Complex that form the basement to the west (Jabiru area). The complex is overlain by a thick early Proterozoic metamorphic sequence, composed of arkosic metasediment in turn overlain by the Cahill Formation, which includes calcareous rocks, carbonaceous schists and amphibolites, and host the major uranium deposits (Ranger 1, Ranger 3, Jabiluka and Koongarra) known in the Jabiru area (Needham 1988). East of the East Alligator River, in west Arnhem Land, the Cahill Formation grades into metamorphically differentiated schists, gneisses and amphibolites of the Myra Falls Metamorphic which contain the Nabarlek deposit. These rocks partly surround the granitic and migmatitic Nimbuwah Complex.

This Paleo- to Mesoproterozoic basement is unconformably overlain by a thick (5-15 km) middle Proterozoic cover forming the large intracratonic McArthur Basin. This sequence of nearly flat-lying sedimentary rocks, interpreted to have formed in terrestrial and marine environments (Kyser et al. 2000), corresponds to the Kombolgie Subgroup, part of the Katherine River Group (Sweet et al. 1999). The Kombolgie Subgroup, which is about 1500 m

40 Partie I – Ch. 1. APS in the East Alligator River Uranium Field thick, was deposited in a mainly braided stream environment punctuated by brief intervals of marine deposition (Ojakangas 1986). The Kombolgie Subgroup consists of at least three units of sandstones and conglomerates separated by volcanic units. More details on the stratigraphy, lithology, and structure of the Kombolgie sandstones may be found in Gustafson & Curtis (1983). The age of the Kombolgie Subgroup has been constrained between 1822 and 1720 Ma (Sweet et al. 1999).

The main characteristics of the EARUF unconformity-type uranium deposits are summarised in Wilde et al. (1989) and Maas (1989). There is a close spatial relationship between the mineralized zones and the middle Proterozoic unconformity. The genetic models proposed for these uranium deposits are based on the interaction of hypersaline, oxidizing and acidic basinal fluids from the Kombolgie sandstones with the underlying metamorphic basement rocks, and in turn, a progressive reduction and neutralization of the hydrothermal solutions with increasing overall progress of the time (Komninou & Sverjensky 1996). Most of the primary uranium mineralisation (dominantly uraninite) is located within and adjacent to reverse fault zones and their associated breccias, which are post-Kombolgie in age. Mineralization is invariably accompanied by an intense alteration in which clay minerals constitute most of the newly formed minerals (Gustafson and Curtis 1983, Wilde et al. 1989, Nutt 1989). Hydrothermal alteration occurred in halos surrounding the mineralized zones up to several hundreds of meters from the ore (Gustafson and Curtis 1983, Wilde et al. 1989) and extended along the structural discontinuities that represent the permeable zones (faults, fractures, breccias, etc) on both sides of the middle Proterozoic unconformity (Beaufort et al. 2004). In both the basement rocks and the overlying sandstones, alteration resulted in illite and chlorite formation with accompanying dissolution of quartz. Minute crystals of APS were observed in association with most of the clay minerals formed during the various stages of alteration that constitute the alteration halo associated with U-mineralisation in the EARUF area (Beaufort et al. 2004).

Sampling

Eleven representative core samples were selected within a set of 220 core samples from 25 diamond drill-holes covering seven distinctive areas (Fig. 4). These samples have been previously studied in detail for alteration petrology and crystal-chemistry of clay minerals (Beaufort et al. 2004). These samples (Tab. 7) were chosen on the basis of the following

41 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

criteria: (1) host-rock petrography, (2) lateral distance to the orebodies or to identified uranium anomalies, (3) vertical distance to the unconformity, and (4) lateral distance to faults or brecciated zones. The samples collection are from the surroundings of major uranium deposits (Jabiluka, Nabarlek and Ranger) or mineralized prospects (Caramal, South Horn, SML Boundary) and from exploration drill-holes in West Arnhem Land. This sampling included a drill hole (U65-3) that is considered representative of the regional background of the Kombolgie sandstones. This drill hole intersects the lowermost Kombolgie units overlying the unconformity far from any known uranium anomaly and presents only minor traces of alteration close to the unconformity (Patrier et al. 2003).

Tableau 7. Petrologic observations of the different samples associated to unconformity-type uranium deposits in the East Alligator River Uranium Field.

Samples Location Identified non APS minerals Host rocks

Jabiluka, Ranger 3, Trioctahedral chlorite, Altered metamorphic rocks, below 1-3 Nabarlek deposits monazite, pyrite the unconformity Illite, sudoite, ± trioctahedral Altered metamorphic rocks, close 4-6 chlorite, monazite, apatite, to the unconformity and SML Boundary pyrite discontinuities fault prospect Altered sandstone above and close 7-8 Illite, sudoite to the unconformity Regional Unaltered Kombolgie sandstone, 9 Illite, hematite background above the unconformity

Methods

Samples were examined in polished thin section using an Olympus BH2 polarizing microscope. Freshly fractured rock fragments and polished thin sections were studied with a JEOL JSM6400 scanning electron microscope (SEM) equipped with an energy-dispersion spectrometer (EDS) for chemical analysis. SEM observations were made in secondary electron mode for morphological investigations on gold-coated slabs and in back-scattered electron mode for identification of APS on the basis of chemical contrasts in carbon-coated polished thin sections. The conditions of observation were as follows: current intensity, 0.6 nA and accelerating voltage, 15 kV.

42 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

Electron microprobe analyses were obtained with a CAMECA SX 50 using wavelength- dispersion spectrometer (WDS). We sought Al, Sr, P, Ca, La, Ce, Nd, Pr, Fe, S, Th and U.

The microprobe was calibrated using the following synthetic and natural standards: SrSiO3, apatite, monazite, pyrite, NdCu, glass doped in rare-earth elements, UO2 and La3ReO8. Corrections were made with a ZAF program. The analytical conditions were as follows: current intensity, 20 nA ; accelerating voltage, 15 kV ; spot size 2-4 µm ; counting time 30 to 40s per element. The relative error on the elements sought is below 1.5%. The structural formulas of APS minerals were calculated on the basis of 1 mol A, 2 mol (XO4) and 3 mol B site per formula unit (Scott 1987).

Results

Petrographic results

Petrographic relationships between APS and hydrothermal clay phases

Several APS-bearing clay assemblages have been distinguished as a function of the distance from the uranium orebodies or from the structural discontinuities that focussed the hydrothermal solutions during mineralization events. At a regional scale, three main types of alteration zones can be distinguished on the basis of both the overall intensity of the alteration and the nature of the clay paragenesis:

(1) zones of proximal alteration in which intense and zoned alteration induced features occur as far as several hundred of meters around the economic uranium orebodies, located in the basement rocks below the unconformity, (2) zones of intermediate alteration in which more or less intense and zoned alteration induced features occur as far as several tens of meters around the unconformity and the regional faults, in areas where anomalous but sub-economic amounts of uranium have been detected, and (3) zones of distal alteration in which weak alteration induced features occur only close to the unconformity between the Kombolgie sandstone cover and the underlying metamorphic basement rocks, farther than 10 km from any known uranium deposit or prospect.

43 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

Figure 4. Location of the study area on a geological map of the East Alligator River Uranium Field (EARUF), Northern Territory, Australia (modified from Needham, 1988).

44 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

In both the proximal and the intermediate zones, the alteration halo is centered on the unconformity and the major faults that cross-cut the overlying sedimentary formations and the underlying basement rocks. The main difference between these two zones consists in the width of the alteration halo and the occurrence of massive chlorite near the uranium orebodies in the proximal areas. In both the proximal and the intermediate zones, alteration consists in intense dissolution of all the earlier silicates (including quartz) and strong transformation of both the sedimentary and the metamorphic rocks above and below the unconformity to clay- mineral assemblages (Gustafson & Curtis 1983, Wilde et al. 1989). Minute crystals of APS were observed in the clay matrix by SEM because of their brightness in BSE mode, due to their high content in heavy elements such as Sr and LREE. Crystals of APS occur as very small euhedral rhombs (2–10 µm in average width, exceptionally up to 50 µm) located in the intergranular pore space of the clay matrix, which constitutes most of the alteration products (Fig. 5a). Locally in the basement rocks, coarser-grained APS crystals display features of growth zoning characterized by alternation of thin concentric bright and light grey zones, less than 1 µm wide (Fig. 5b), reflecting chemical variations.

Globally, the mineralogical composition of the APS-bearing assemblages displays a zonal pattern as a function of the distance to the structures that focussed the hydrothermal solutions and probably controlled the uranium deposition in these areas. The following assemblages have been identified:

1- illite + APS ± hematite, in the sandstones farther than several tens of meters above the unconformity (Fig. 5a). 2- illite + sudoite + APS ± hematite, on both sides close to the unconformity and close to the regional faults that reworked both sandstones and the basement rocks above and below the unconformity (Fig. 5c). 3- illite ± sudoite ± trioctahedral chlorite ± APS ± apatite, in the basement rocks at greater depth below the unconformity. 4- massive trioctahedral chlorite ± APS ± apatite ± uraninite, close to the uranium ore-bodies (Fig. 5d).

In the distal zones, the alteration assemblage is composed of assemblage 1. APS minerals are disseminated in the clay matrix whose illite crystals differ from the diagenetic illite (in the sandstones) or the phengitic micas (in the metamorphic rocks) by their texture and their

45 Partie I – Ch. 1. APS in the East Alligator River Uranium Field structure. Such illite is very fine-grained (less than 1 µm) particles with capillary habit and

1MTrans dominant polytype (Beaufort et al. 2004). Close to the unconformity, this illite matrix is superimposed upon the coarse-grained diagenetic illite of the altered sandstones, whereas it tends to replace the primary silicates in the underlying basement rocks.

Petrographic relationships between APS and other phosphate minerals

Several assemblages of alteration have been observed within the basement rocks from both the proximal and the intermediate zones of alteration. The APS ± secondary apatite are closely associated with the alteration of monazite. Residue of strongly etched crystals of monazite have been observed inside the APS crystals from the zones of massive chlorite formation that surround the ore deposits at Jabiluka and Ranger (Fig. 5d). Numerous indications of alteration and replacement of monazite by secondary phosphate minerals have been observed along the regional faults, along metabasic rocks from the basement at more than one hundred meters below the unconformity were reworked. In these samples, ragged and frayed residue of coarse-grained monazite still persist in the illite + trioctahedral chlorite clay matrix, which replaces all the earlier silicate minerals (Fig. 5e). Grains of secondary subhedral to euhedral apatite are only observed close to the residue of monazite (Fig. 5f) whereas euhedral APS crystals are disseminated in the clay matrix slightly farther from the site of alteration of the monazite (Fig. 5e). Observation at higher magnification of the clay matrix surrounding the APS crystals reveals the presence of tiny residual grains of monazite and pyrite. The relationships between APS and apatite are complex. Detrital apatite was not observed in the altered sandstones, whereas coarse-grained, pore-sealing, diagenetic apatite was locally observed in sandstone samples containing APS disseminated in the illite matrix near the bottom of the sedimentary basin. These coarse-grained apatite show many dissolution features, but no evidence of a direct replacement by APS. At least two distinct generations of apatite were encountered in the basement rocks below the unconformity: partially dissolved, coarse-grained and globular crystal of primary apatite and fine-grained subhedral to euhedral crystals of apatite that surround the residue of altered monazite. These observations suggest that the dissolution of primary apatite was complete in the altered sandstones but only partial in the basement rocks. No direct replacement induced feature of apatite involving the APS have been observed.

46 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

Figure 5. SEM images of APS minerals from EARUF. a) aggregate of small euhedral APS minerals located in the intergranular porosity of the clay matrix in a distal alteration area. b) Features of growth zoning of APS crystal in the basement rocks. c) Disseminated euhedral crystals of LREE-Sr Al-phosphates (white spots) in a matrix of hydrothermal illite-sudoite close to the major discontinuities. d) Monazite replaced by APS minerals in a sample of metamorphic basement almost totally chloritized (trioctahedral chlorite) close to the uranium ore body of Ranger 3. e) Monazite relics in a clay matrix illite-clinochlore below the unconformity in an intermediate alteration area. f) alteration sites of monazite and pyrite around which occured secondary apatite and APS associated with trioctahedral chlorite + illite below the unconformty in intermediate alteration area.

47

deposits in ) Mean* dv. Std apfu apfu ), 3 (Al, Fe) 4 , PO ) Mean* Std dv. ( 4 apfu teration areasteration alteration areas Distal associated with unconformity-type uranium associated with unconformity-type ) Mean* dv. Std ( apfu microprobe analyses per samplemicroprobe the East Alligator River Uranium Field. Uranium River the East Alligator al formulae of representative APS minerals of representative APS minerals al formulae ) Mean* dv. Std ( apfu Structural formula were calculated on the basis of 1 mol A, 2 (SO were calculated on the basis of 1 mol Structural formula Proximal alteration areasProximal al Intermediate *Mean calculated on the basis of 10 ) Mean* dv. Std ( 5.3 6.25 10.02 10.36 6.33 6.78 4.09 5.07 0.73 1.36 1.444.04 1.170.77 3.48 0.750.94 1.270.51 0.98 0.48 1.06 0.84 1.61 1.29 0.83 2.45 3.03 0.89 0.79 0.79 2.34 0.43 0.85 1.88 0.72 0.42 1.52 1.20 0.69 1.84 2.78 0.98 0.77 2.29 1.80 1.21 1.80 1.81 0.11 1.11 0.56 0.36 0.27 0.91 0.48 4.06 1.82 6.62 6.52 D.L. 11.98 12.0428.17 28.4025.46 8.19 23.33 8.29 27.01 26.52 19.45 17.81 9.86 10.10 29.78 31.22 22.15 22.43 8.47 29.39 9.06 27.21 22.13 20.36 1.74 28.62 3.11 29.97 16.45 21.43 apfu Wt% Mean* Wt% Mean* Wt% Mean* Wt% Mean* Wt% Mean* ( < 3 O 2 3 3 3 3 3 3 2 5 O O O O O 3 2 O 2 2 2 2 2 O 2 Sample 1 2 5 6 9 SrOCaOLa 2.24Ce 1.33Pr 1.68Nd 1.28ThO Al Fe P 2.06SO 1.57Sum 1.66 1.12 82.18 80.15 4.03 1.80 4.32 75.29 1.71 71.55 3.90 2.10 79.75 3.13 2.07 82.75 12.02 78.13 12.28 2.06 74.09 2.27 73.24 80.54 CaLaCePr 0.13Nd 0.17 0.13Th 0.39 0.21 0.05 0.05 0.40Fe 0.13 0.03 0.02 0.04 0.16 0.05 0.11S 0.35 0.02 0.01 0.06 0.13 0.28 0.02 0.39 0.01 0.03 0.08 0.02 0.29 0.04 0.04 0.04 0.03 0.03 0.05 0.01 0.05 0.17 0.04 0.02 0.20 0.01 0.16 0.01 0.01 0.32 0.16 0.01 0.20 0.03 0.22 0.08 0.07 0.32 0.01 0.04 0.01 0.08 0.01 0.03 0.06 0.21 0.01 0.05 0.02 0.01 0.14 0.00 0.21 0.29 0.01 0.17 0.07 0.11 0.00 0.02 0.02 0.31 0.09 0.03 0.02 0.03 0.03 0.21 0.14 0.02 0.08 0.03 0.03 0.00 0.11 0.21 0.06 0.01 0.02 0.04 0.01 0.00 0.12 0.02 0.09 0.02 0.13 0.01 0.01 0.01 0.04 0.02 0.03 0.09 0.01 0.25 - 0.01 0.02 0.11 - 0.53 0.06 0.43 0.06 Tableau 8. Microprobe analysis and structur Note: U A Sr 0.12 0.09B 0.02 AlX 0.11 P 2.94 0.10 2.92 0.01 1.96 0.05 1.96 0.20 2.84 0.01 0.22 2.80 1.92 0.02 0.04 1.92 0.21 2.95 0.02 0.17 1.89 2.93 0.03 0.03 1.86 0.67 2.89 0.61 0.02 2.88 0.05 1.87 0.04 1.91 2.75 0.02 2.89 1.47 0.06 1.57 0.06

49 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

Chemical results

Representative and mean results of electron microprobe analyses of APS minerals from the three alteration areas distinguished in the above section are presented in table 8. The chemical elements sought in individual crystals have been selected on the basis of preliminary qualitative EDS investigations. The low analytical total (between 60 and 85 wt %) obtained in some of the analyses is essentially due to the size of some APS grains (often <2 µm), which was commonly smaller than the volume of sample emitting the secondary X-ray radiation. Consequently there is a partial integration of the surrounding minerals and micropores in the volume analyzed by the electron beam. It should be noted that the chemical by variable zones observed in some APS crystals (Fig. 5b) are too thin to be analyzed individually with an electron microprobe.

All the analytical results agree with the general formula of APS minerals (AB3(XO4)2(OH)6). They indicate a complex chemical composition corresponding to intimate mixtures or solid solutions between different compositional end-members, which combine essentially the following cations: Sr, LREE, Ca and Th at the A site; Al and Fe at the B site; P and S at the X site. Globally, the analytical results of APS crystals display a rather slight compositional variation in each given type of alteration zones, and a wide range of compositional variation from one type of alteration zone to another (Tab. 8). The major chemical variations measured in the APS from the different domains of alteration in the EARUF involve P, S, Sr and LREE (for comparison of these effects, the results analyses were normalised to 85 wt%, the total in well-crystallized APS). The highest amounts of SrO and SO3 (respectively, 13.33 and 7.82 wt%) and the lowest amounts of LREE2O3 and P2O5 (respectively, 6.33 and 22.49 wt%) have been found in APS minerals from the distal alteration zones, whereas the lowest amount of

SrO and SO3 (respectively 2.32 and 0.53 wt%) and the highest amounts of LREE2O3 and P2O5 (respectively 23.54 and 26.33 wt%) have been found in APS minerals close to or from the Jabiluka, Ranger or Nabarlek orebodies. According to these results, Ce is the predominant LREE element encountered in the APS minerals close to the Jabiluka and Nabarlek deposits, whereas La predominates in the APS minerals close to the Ranger deposit. APS minerals from the intermediate alteration zones show amounts of P2O5, SO3, SrO and LREE2O3 (respectively 24.07, 1.96, 4.24 and 17.43 wt%) intermediate but distinct than that from the other alteration zones. The APS minerals from all the alteration zones identified in the EARUF contain minor but significant amounts of Ca and Th at their A site. Ca is roughly constant (CaO ranges from

50 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

1 to 2.3 wt%) whereas Th seems more variable, with lower amounts in APS from the zones of distal alteration and a slight enrichment in the APS surrounding the uranium deposits (ThO2 ranges from 0.12 to more than 2 wt%). Aluminum is by far the dominant cation, in association with minor but variable amounts of Fe, in the B site of all the APS minerals. It should be noted that the uranium content of all the APS minerals analysed is below the detection limit of the microprobe.

Interpretation

Both the alteration petrography and the chemical data obtained in this study are used to discuss the significance of APS minerals in the alteration processes associated with uranium deposition in the EARUF. We will discuss these APS minerals successively in terms of crystal chemistry, element sources and signature of thermodynamic conditions of the alteration processes, which operated at a regional scale in the EARUF.

Crystal chemistry of APS minerals

The APS minerals from the EARUF have complex compositions that are seldom close to the pure end members of the alunite supergroup described in the literature (Scott 1987, Dill 2001, Jambor 1999). Dill (2001) indicated that such a chemical feature is typical of APS from natural environments which generally belong to several complex solid-solution series. The wide range of chemical compositions recorded in the APS throughout the EARUF altered zones (Fig. 6), is essentially due to coupled substitutions of Sr to LREE and S to P at the A and X sites, respectively. These substitutions change the relative proportion of end members of the beudantite group (namely svanbergite (SrAl3(PO4,SO4)(OH)6) and woodhouseite

(CaAl3(PO4,SO4)(OH)6)), and of the crandallite group, (namely goyazite

(SrAl3[PO3·(O0.5(OH)0.5)]2(OH)6, crandallite (CaAl3[PO3·(O0.5(OH)0.5)]2(OH)6), and florencite

(LREEAl3(PO4)2(OH)6).

At every scale of observation, the major variation of the APS series. consists essentially in the relative proportion of svanbergite and florencite end members. APS from the zones of distal alteration have a very distinctive compositional field, which differs from those from the intermediate and proximal zones of alteration by predominance of svanbergite in the APS. Florencite predominates in the APS from both the intermediate and proximal zones of

51 Partie I – Ch. 1. APS in the East Alligator River Uranium Field alteration which form a compositional continuum. The proportion of florencite significantly increases in the APS series from intermediate to proximal zones of alteration.

Figure 6. Cross plot diagram P+LREE versus S+Sr of the wide range of chemical compositions recorded in APS.

Cross-plot diagrams between the major elements at the A and X sites of the APS (Fig. 7) indicate that the chemical variations are not exclusively due to a svanbergite-to-florencite transition. The linear regression curves between all the points of analyse does not fit with the ideal LREE-for-Sr and P-for-S substitutions involved in a svanbergite-to-florencite transition. Slight excess of Sr (5 to 10%) at very low S content and depletion of S (40 to 50%) at high Sr content should be noted. The cross-plot data of both S versus Sr and P versus Sr suggest that goyazite is associated with svanbergite and florencite in proportions that tend to decrease with decreasing distance from the orebodies. The Ca content of the APS does not significantly vary throughout the EARUF alteration areas and seems to be mostly attributed to the crandallite end-member.

52 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

Figure 7. Cross plot diagrams between the major elements from the A and X sites of the different APS minerals encountered in all the different geological units surrounding the EARUF deposits or prospects.

On the basis of the aforementioned chemical data, the mean composition of APS from each EARUF alteration areas can be characterized as follows:

53 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

3+ 1-(Sr0.61Ca0.21LREE0.17Th0.01)(Al2.89Fe 0.11)[PO3·(O0.76(OH)0.24)]1.57(SO4)0.43](OH)6 corresponding to a s.s.s. svanbergite 0,43, goyazite 0,18, crandallite 0,21, Th Al phosphates 0,01, florencite 0,17 in the zones of distal alteration.

3+ 2-(Sr0.22Ca0.16LREE0.61Th0.01)(Al2.93Fe 0.07)[PO3·(O0.88(OH)0.12)]1.86(SO4)0.14](OH)6 corresponding to a s.s.s. svanbergite 0,14, goyazite 0,08, crandallite 0,16, Th Al phosphates 0,01, florencite 0,61, in the zones of intermediate alteration.

3+ 3-(Sr0.09Ca0.13LREE0.76Th0.02)(Al2.92Fe 0.08)[PO3·(O0.92(OH)0.08)]1.96(SO4)0.04](OH)6 corresponding to a s.s.s. svanbergite 0,04, goyazite 0.05, crandallite 0,13, Th Al phosphates 0,02, florencite 0,76, in the zones of proximal alteration.

The overall variation of APS compositions determined above indicate global depletion in sulfates and conversely a general enrichment in phosphate of the aqueous solutions with increasing proximity to the uranium ore deposits. The concomitant enrichments of the APS in P and LREE toward the ore deposits suggests a common source and an extensive mobility of both these elements in the EARUF altered zones.

Source material for APS minerals in the EARUF

According to the wide range of environments documented for APS formation near the Earth’s surface, the source material for these minerals can be multiple. We have searched in the products of alteration (weathering, hydrothermal or diagenetic alteration) of primary minerals, including phosphates and REE bearing minerals (Dill 2001) and in the precipitation of reactive P and REE released from inorganic compounds during early diagenesis of clastic sediments (Rasmussen 1996). The source of the major elements incorporated in the APS minerals associated with the unconformity-type uranium deposits has never been investigated specifically. Several sources of elements have been proposed for the APS minerals formed in the Athabasca Basin, Canada. Diagenetic and hydrothermal alteration of detrital or early diagenetic clay and phosphate minerals of the siliciclastic formations during the basin evolution and the intense alteration of the metamorphic or magmatic monazite in the basement rocks are considered as the two best candidates for the release of the major elements incorporated in the APS on both sides of the unconformity (Wilson 1984, Fayek & Kyser 1997, Quirt et al. 1991, Hecht & Cuney 2000).

54 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

Monazite replacement by APS seems common, whereas no example of apatite replacement by APS has been observed. The parental links between monazite and APS, pointed out petrographic relationships, are supported by geochemical considerations on LREE and Th. Indeed, the relative proportions of cerium, lanthanum and neodymium measured in the APS minerals are close to those measured in the monazite residue (Fig. 8), which persist in the same altered samples of basement rocks or at a much lesser degree in sandstones (as mineral inclusions in detrital quartz exclusively). In the same way, the increasing amount of LREE in APS minerals from distal to proximal alteration areas is correlated with a slight increase of the average amount of Th both suggesting a monazite source. No correlative Ca enrichment accompanies the P enrichment of APS noted from distal to proximal zones of alteration, suggesting apatite is not a major source of P and Ca.

Figure 8. Projection in Ce-La-Nd+Pr coordinates of the microprobe analyses of the different monazite and APS minerals for a same sample encountered in all the different geological units surrounding the EARUF deposits or prospects. Open symbols refer to APS analyses. Solid symbols refer to monaziteanalyses.

All the above arguments indicate that the alteration of monazite represents the major source for the chemical elements involved in the compositional variations of APS between the distal

55 Partie I – Ch. 1. APS in the East Alligator River Uranium Field and the proximal areas of alteration in the EARUF (P, LREE and Th). Such inference is an important clue to understand the geochemical links existing between the LREE-rich APS and the uranium deposits around where they are currently encountered. The monazite contains significant amounts of uranium, which was not incorporated in the products of alteration observed. The U content is below the detection limit of the electron microprobe in the APS, while uranium-bearing minerals have been detected near the alteration sites of monazite only close to the uranium orebodies. At least a part of the uranium contained in the orebodies and most of P, LREE and Th incorporated in APS minerals thus are genetically related. They are issued from the same process of alteration of monazite.

Figure 9. Projection in S-Sr-LREE coordinates of the microprobe analyses of the different APS minerals encountered in all the different geological units surrounding the EARUF deposits or prospects.

56 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

The source material of the svanbergite-rich APS, which characterizes the distal zones of alteration is not clearly identified. However, it probably originated during the burial diagenesis of the Kombolgie sandstones and could represent the APS phase stable with the subbasinal solutions of the diagenetic aquifers. Indeed, APS minerals with high Sr and S contents have frequently been reported in literature on sandstones world-wide (Rasmussen 1996, Spötl 1990, Dill 2001).

All the above considerations indicate that the crystal-chemical nature of APS in the Kombolgie sandstones could be indicative of the alteration rate of the monazite. The chemical trend of the APS (Fig. 9) leads us to interpret this as a signature of the degree of interaction between the diagenetic fluids from the Kombolgie sandstones (producing APS near the svanbergite end-member) with solutions enriched in P, LREE and Th (nearly the florencite end-member). In agreement with the genetic model and the alteration patterns proposed for the EARUF unconformity-type uranium deposits (Komninou and Sverjensky 1996, Beaufort et al. 2004), this origin could be relate to the alteration of monazite within the underlying basement rocks.

APS minerals: markers of thermodynamic conditions

The chemical trend exhibited by the APS from the EARUF suggests their compositional variation is controlled by large scale changes in their physicochemical conditions of formation. Thermodynamic calculations on the respective stability of svanbergite, goyazite, and florencite end-members have been made to better interpret such chemical variations. The thermodynamic calculations have been performed for the following conditions:

1- constant temperature and pressure fixed at T=200°C and P=500 bars, in agreement with the data already used for geochemical modeling (Komninou and Sverjensky 1996, Iida 1993) or obtained from fluid-inclusion studies (Derome et al. 2003) on the EARUF unconformity-type uranium deposits. 2- tetravalent cerium (Ce4+) has been neglected because this ion is stable only in extremely oxidizing conditions. 3- a constant aluminum content was assumed between all the APS relations. 4- the effect of pressure on equilibrium between any two phases has been neglected.

57 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

Gibbs free energies of formation of these APS end members are given in table 9. Entropy and heat capacities of APS minerals were estimated from experimental values for alunite-jarosite by the method proposed by Helgeson et al. (1978). Enthalpies of formation were calculated from Gibbs free energies of formation and entropy given in table 9. Equilibrium constants for the dissolution reactions of the APS minerals were calculated with the SUPCRT program (Johnson et al. 1992) and are given in table 10.

Tableau 9. Thermodynamic values at 25°C of some minerals of the alunite supergroup

° ° 3 -5 Mineral ∆G f ∆Hf S° V a b (10 ) c (10 ) -1 -1 -1 -2 -1 -1 (kJ⋅mol-1) (kJ⋅mol-1) (J.K-1.mol-1) (cc.mol ) (J.K .mol ) (J.K .mol ) (J.K.mol ) Florencite -5737.521 -6256.173 330.284 137.517 366.396 352.846 -64.896 Goyazite -5625.391 -6159.273 321.874 142.126 363.336 369.036 -60.156 Svanbergite -5286.612 -5752.503 508.844 142.270 408.696 264.326 -73.626

(1) Schwab et al. (1993) (2) Gaboreau & Vieillard (2004) (3) Calculated from S° (4) Estimation from S° of alunite by the algorithm method of Helgeson et al. (1978) (5) Stoffregen et al. (2000) (6) Estimation from Cp of alunite by the algorithm of Helgeson et al. (1978).

Tableau 10. Solubility products of dissolution reactions at 25, 200°C and 500 bars of the APS minerals LogK LogK Mineral Dissolution reaction (25°C) (200°C) + 3+ 3+ Florencite CeAl3(PO4)2(OH)6+12H →Ce +3Al +2H3PO4+6H2O 19.544 -5.491

+ 2+ 3+ Goyazite SrAl3[PO3·(O0.5(OH)0.5)]2(OH)6+11H →Sr +3Al +2H3PO4+6H2O 19.628 -1.429

+ 2+ 3+ 2- Svanbergite SrAl3(PO4,SO4)(OH)6+9H →Sr +3Al +H3PO4+SO4 +6H2O 9.991 -11.257

The stability domains of svanbergite, goyazite, and florencite have been plotted in a 2+ 3+ Log[Sr /Ce ] vs pH for two different values of pO2 and for total phosphorus (PT) and total sulfur (ST) maintained constant. It can be seen that the stability of these minerals is highly sensitive to pH. Svanbergite is the stable APS end-member at low pH and relatively oxidizing -30 conditions, i.e., at pO2 equal 10 atm (Fig. 10a). More reducing conditions in the system, i.e., -38 at pO2 equal 10 atm, (Fig. 10b), will strongly narrow the stability domain of svanbergite toward still more acidic conditions and hence promote the stability of goyazite at high Sr2+:Ce3+ ratio, or florencite at lower Sr2+:Ce3+ ratio. In other words, the transition svanbergite to florencite exhibited by APS minerals around the EARUF unconformity-type deposits can

58 Partie I – Ch. 1. APS in the East Alligator River Uranium Field be explained by concomitant increase of pH and reducing conditions and decrease of the Sr2+:Ce3+ ratio in the hydrothermal solutions. No data exist on the Sr2+:Ce3+ ratio of the fluids associated with the uranium deposition in the EARUF unconformity-type deposits. However, on the basis of petrography, it seems reasonable to consider that the Sr2+:Ce3+ ratio is strongly dependent on the degree of interaction between the acidic diagenetic solutions and monazite from the basement rocks.

Figure 10. Activity-activity diagrams Log [Sr2+/Ce3+] vs pH representing the stability domains of svanbergite, goyazite, florencite for two different values of log aO2.

Concluding remarks

The results of this study indicate that the APS minerals are genetically related to the alteration features associated with uranium deposition in the East Alligator River Uranium Field unconformity-type deposits. The APS minerals are mostly alteration products of monazite and present significant compositional variations. These depend on chemical factors that are consistent with those proposed in the genetic models for unconformity-type uranium deposits. These models infer the interaction of hypersaline, oxidizing and relatively acidic fluids (i.e. subbasinal brines derived from the overlying sandstones) with the underlying basement-rocks (Plant et al. 1999) and development of redox and pH fronts during the overall process of

59 Partie I – Ch. 1. APS in the East Alligator River Uranium Field alteration (Hoeve & Quirt 1984). Once these fluids moved into the basement, they were progressively reduced by interaction with reducing agents such as graphite or ferrous-iron- bearing minerals, and the fluid pH was increased during the alteration. The major proportion of the uranium in these deposits was deposited in zones of the basement where high degrees of reduction and neutralization of the hydrothermal fluids were attained. We suggest here that the transition from svanbergite to florencite in the APS series is a good marker to investigate the distribution of the pH front that results from the interaction of the diagenetic solutions with the basement rocks below the unconformity. Svanbergite-rich APS minerals were formed only from diagenetic reactions in the Kombolgie sandstones, whereas the florencite content of APS increases with increasing degree of alteration of monazite bearing rocks (mostly basement rocks). The transition from florencite-rich APS to apatite, which was observed at various scales (i.e., alteration assemblages about individual monazite grains or regional zoning in basement rocks) is also consistent with a higher degree of neutralization of acidic diagenetic fluids by interaction with basement rocks. Indeed, APS minerals are known to be more stable in a lower pH environments (in which LREE are relatively mobile) than apatite (Spötl 1990 , Stoffregen and Alpers1987, Vieillard et al. 1979). Further investigations are needed to determine the extent of the various solid solutions in APS minerals from unconformity-type uranium deposits, before one we can proceed to use them as appropriate indicators of paleoconditions and hence as potential mineral exploration tools. We would like to see a comparative study of the composition of APS minerals from the Proterozoic basins in Canada, containing high-grade uranium orebodies (Athabasca, Thelon), the use of thermodynamic models integrating solid-solutions for both the APS and the associated clay minerals, and isotope studies on purified mineral fractions (stable and unstable). These additional investigations are required to approve the present study and will contribute to improve our knowledge on the conditions of formation (P, Eh, pH) of such uranium type deposits.

References

Beaufort, D., Patrier, P., Laverret, E., Bruneton, P., Mondy, J. (2004). Clay alteration associated with Proterozoic unconformity-type uranium deposits in the East Alligator River Uranium Field (Northern Territory, Australia). Economic Geology, Accepted. Derome, D., Cuney, M., Cathelineau, M., Dubessy, J. & Bruneton, P. (2003). A detailed fluid inclusion study in silicified breccias from the Kombolgie sandstones (Northern territory,

60 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

Australia): application to the genesis of middle Proterozoïc unconformity-type uranium deposits. Journal of Geochemical Exploration, 80, 259-275. Dill, H.G. (2001). The geology of aluminium phosphates and sulphates of the alunite group minerals: a review. Earth-Science Reviews, 53, 35-93. Fayek, M. & Kyser, T.K. (1997). Characterization of multiple fluid flow events and Rare Earth element mobility associated with formation of unconformity-type uranium deposits in the Athabasca Basin, Saskatchewan. Can. Mineral., 35, 627-658. Gaboreau, S. & Vieillard, P. (2004). Prediction of Gibbs free energies of formation of minerals of the alunite supergroup. Geochemica and Cosmochimica Acta, 68, 3307-3316. Gustafson, L.B. & Curtis, L.W. (1983). Post Kombolgie metasomatism at Jabiluka, Northern Territory, Australia, and its significance in the formation of high grade uranium mineralization in lower Proterozoic rocks. Economic Geology, 35, 26-56. Hecht, L., & Cuney, M. (2000). Hydrothermal alteration of monazite in the Precambrian crystalline basement of the Athabasca basin (Saskatchewan, Canada): implications for the formation of unconformity-related uranium deposits. Mineralium Deposita, 35, 791-795. Helgeson, H.C., Delany, J.M., Nesbitt, H.W. & Bird, D.K. (1978). Summary and critique of the thermodynamic properties of the rock-forming minerals. American Journal of Science., 278-A, 229. Hoeve, J. & Quirt, D. (1984). Mineralization and host rock alteration in relation to clay mineral diagenesis and evolution of the middle-Proterozoic Athabasca Basin, Northern Saskatchewan, Canada: Saskatchewan Research Council Technical Report 187, 187p. Iida, Y. (1993). Alteration and Ore Forming Processes of Unconformity Related Uranium Deposits. Resource Geology Special Issue, 15, 299-308. Jambor, J.L. (1999). Nomenclature of the Alunite Supergroup. Can. Mineral., 37, 1323-1341. Johnson, J.W., Oelkers, E.H. & Helgeson, H.C. (1992). Supcrt 92: a software package for calculating the standard molal thermodynamic properties of minerals, gases, aqueous species and reactions from 1 to 5000 bars and 0°C to 1000°C. Computers and Geosciences, 18, 899-947. Kolitsch, U. & Pring, A. (2001). Crystal chemistry of the crandallite, beudantite and alunite groups: a review and evaluation of the suitability as storage materials for toxic metals. Journal of Mineralogical and Petrological Sciences, 96, 67-78. Komninou, A. & Sverjensky, D.A. (1996). Geochemical modeling of the formation of an Unconformity-type Uranium deposit. Economic Geology, 91 (Mining Annual Review, 2001), 590-606.

61 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

Kyser, K., Hiatt, E., Renac, C., Durocher, K., Holk, G. & Deckart, K. (2000). Diagenetic fluids in paleo- and meso-Proterozoic sedimentary basins and their implications for long protracted fluid histories. In K. Kyser, Ed. Fluids and Basin Evolution, 28, 225-262. Mineralogical Association of Canada, Calgary. Lorilleux, G. (2001). Les brèches associées aux gisements d'uranium de type discordance du bassin d'Athabasca, Saskatchewan, Canada. Thèse Univ. Nancy, 319 p. Maas, R. (1989). Nd-Sr isotope constraints on the age and origin of unconformity-type uranium deposits in the Alligator River Uranium Field, Northern Territory, Australia. Economic Geology, 84, 64-90. Miller, A. R. (1983). A progress report: uranium-phosphorous association in the Helikian Thelon Formation and sub-Thelon saprolite, central District of Keewatin [Canada]. Paper - Geological Survey of Canada, 83-1A, 449-456. Mordberg, L.E., Stanley, C.J. & Germann, K. (2000). Rare earth element anomalies in crandallite group minerals from the Schugorsk bauxite deposit, Timan, Russia. European Journal of Mineralogy, 12, 1229-1243. Needham, R.S. (1988). Geology of the Alligator River Uranium Field, Northern Territory. BMR Bulletin, 96, 224. Nutt, C.J. (1989). Chloritization and associated alteration at the Jabiluka unconformity-type uranium deposit, Northern Territory, Australia. Canadian Mineralogist, 27, 41-58. Ojakangas, R.W. (1986). Sedimentology of the basal Kombolgie Formation, Northern Territory, Australia: A Proterozoïc fluvial quartzose sequence (abs): Internat. In S.-B.M.R. Australia, Ed. Sediments down under, p. 30, Canberra Australia.

Patrier, P., Beaufort, D. & Bruneton, P. (2003). Dickite and 2M1 illite in deeply buried sandstones from the middle Proterozoic Kombolgie Formation (Northern Territory, Australia). Clays and Clay Minerals, 51, 102-116. Plant, J.A., Simpson, P.R., Smith, B. & Windley, B.F. (1999). Uranium deposits-products of the radioactive earth. In Burn, P.C., and Finch, R. editors, Uranium: Mineralogy, Geochemistry and the Environments. Mineralogical Society of America Reviews in Mineralogy, 38, 255-319. Quirt, D., Kotzer, T. & Kyser, T.K. (1991). Tourmaline, phosphate minerals, zircon and pitchblende in the Athabasca group: Maw Zone and McArthur River Areas, Saskatchewan., p. 181-191. Saskatchewan Geological Survey.

62 Partie I – Ch. 1. APS in the East Alligator River Uranium Field

Rasmussen, B. (1996). Early diagenetic REE-phosphate minerals (florencite, gorceixite, crandallite, and xenotime) in marine sandstones: a major sink for oceanic phosphorus. American Journal of Science, 296, 601-632. Schwab, R.G., Gotz, C., Herold, H. & Oliveira, N.P. (1993). Compounds of the crandallite type - thermodynamic properties of Ca-phosphates, Sr-phosphates, Ba-phosphates, Pb- phosphates, La-phosphates, Ce-phosphates to Gd-phosphates and Ca-arsenates, Sr- arsenates, Ba-arsenates, Pb-arsenates, La-arsenates, Ce-arsenate. Neues Jahrb Miner. Monatsh, 12, 551-568. Scott, K.M. (1987). Solid solution in, and classification of, gossan-derived members of the alunite-jarosite family, northwest Queensland, Australia. American Mineralogist, 72, 178- 187. Spötl, C. (1990). Authigenic aluminium phosphate-sulphates in sandstones of the Mitterberg formation, Northern Calcareous Alps, Austria. Sedimentology, 37, 837-845. Stoffregen, R.E. (1993). Stability relations of jarosite and natrojarosite at 150–250°C. Geochimica et Cosmochimica Acta, 57, 2417-2429. Stoffregen, R.E., & Alpers, C.N. (1987). Woodhouseite and svanbergite in hydrothermal ore deposits: products of apatite destruction during advanced argillic alteration. The Canadian Mineralogist, 25, 201-211. Stoffregen, R.E., Rye, R.O. & Wasserman, M.D. (1994). Experimental studies of alunite: I. 18O-16O and D-H fractionation factors between alunite and water at 250–450°C. Geochimica et Cosmochimica Acta, 58, 903-916. Stoffregen, R.E., & Alpers, C.N. & Jambor, J.L. (2000). Alunite-Jarosite Crystallography, Thermodynamics, and Geochronology. Reviews in mineralogy & geochemistry, 40 (sulfate minerals), 453-479. Sweet, I.P., Brakel, A.T. & Carson, L. (1999). The Kombolgie Subgroup, a new look at an old "formation". AGSO Research letter, 30, 26-28. Vieillard, P., Tardy, Y., Nahon, D. (1979). Stability fields of clays and aluminium phosphates: parageneses in lateritic weathering of argillaceous phosphatic sediments. American Mineralogist, 64, 626-634. Wilde, A.R., Mernagh, T.P., Bloom, M.S. & Hoffmann, C.F. (1989). Fluid inclusion evidence of the origin of some Australian unconformity-related uranium deposits. Economic Geology, 84, 1627-1642. Wilson, J.A. (1984). Crandallite group minerals in the Helikian Athabasca group in Alberta, Canada. Canadian Journal of Earth Sciences, 22, 637-641.

63

Partie I – Ch. 2. APS in the Athabasca basin

Chapitre 2

Aluminium Phosphate Sulfate minerals associated with Proterozoic

unconformity-type deposits in the Athabasca basin, Canada

Stéphane GABOREAU1,2, Dave QUIRT3, Daniel BEAUFORT1, Patricia PATRIER1 and Régis MATHIEU4

Aticle destiné à ‘The Canadian Minearlogist’

1 HydrASA, Université de Poitiers, CNRS-UMR 6532, 40 avenue du Recteur Pineau, F 86022 POITIERS Cedex, France 2 ERM SARL, Laboratoire-Bureaux, Université de Poitiers, bât de Géologie, 40 Av. du Recteur Pineau. 86022 POITIERS-Cedex, France 3 Saskatchewan Research Council, 125 – 15 Innovation Blvd., Saskatoon, SK, S7N 2X8, Canada 4 COGEMA-BUM-DEX, 2 rue Paul Dautier, BP 4, F 78141 Vélizy Cedex, France

65 Partie I – Ch. 2. APS in the Athabasca basin

Abstract

APS minerals have been described from a variety of middle Proterozoic sandstone basins, including the Athabasca and Thelon Basins in Canada and the Kombolgie Formation of the McArthur Basin in Australia. In particular, APS minerals are abundant in the clay mineral host-rock alteration assemblages associated with some uranium fields in these middle Proterozoic basins. Few systematic investigations have been performed on the APS minerals in these deposits and little data are available on their compositional variations in relation to the uranium deposits. However, it is well known that their formation was controlled by physicochemical conditions (Eh, pH, constituent element activities, P, T), to which the APS minerals are particularly sensitive. The chemical data obtained on the APS minerals formed in the surroundings of the unconformity-type deposits of the Athabasca region and those obtained in their Australian counterpart are very similar (e. g. Gaboreau et al., 2005). The crystal-chemical nature of the APS minerals appears to be associated with the hydrothermal processes controlling the alteration rate of monazite within the basement rocks. Both the content of florencite (i. e. the relative proportion of LREE) incorporated in the APS minerals of the sandstone can be used to determine the extent and the intensity of the hydrothermal processes and the potential rate of uranium mobilisation within the basement rocks underlying the unconformity. Phase relationships between APS and clay minerals need to be addressed because taking into account the compositional data of coexisting APS minerals and clay mineral phases will significantly improve the geochemical modelling of the formation of the alteration zoning observed around the uranium ore-bodies

Key-words: APS minerals, florencite, goyazite, svanbergite, unconformity-type uranium deposits, Athabasca basin, clay minerals.

66 Partie I – Ch. 2. APS in the Athabasca basin

Introduction

Aluminum phosphate-sulphate (APS) minerals are found in a wide range of geological environments, ranging from surficial weathering through sedimentary, diagenetic, hydrothermal, and metamorphic environments, to post-magmatic systems (Dill, 2001). These minerals belong to the alunite supergroup (Scott 1987, Jambor 1999) and crystallize most commonly as authigenic pseudocubic (rhombohedral) crystals. Their general formula is ideally AB3(XO4)2(OH)6, in which A, B, and X represent three different crystallographic sites:

12-fold coordinated A sites, occupied by monovalent (H3O, K, Na, Rb, NH4, Ag, Tl, etc.), divalent (Ca, Sr, Ba, Pb, etc.), trivalent (Bi, REE) and, more rarely, tetravalent (Th) cations; 6-fold coordinated B sites, commonly occupied by Al3+and Fe3+; and 4-fold coordinated X sites, commonly occupied by S6+, P5+, and As5+.

APS minerals have been described from a variety of middle Proterozoic sandstone basins, including the Athabasca (Hoeve and Quirt, 1984; Wilson, 1985; Quirt et al., 1991, Mwenifumbo et al., 2002) and Thelon (Miller, 1983) Basins in Canada and the Kombolgie Formation of the McArthur Basin in Australia (Beaufort et al., 2005; Gaboreau et al., 2005), as well as from Cretaceous sandstone in Nova Scotia, Canada (Pe-Piper and Dolansky, 2005). However, APS minerals have generally been neglected by geologists and geochemists because of the minute size of the crystals (<0.1–10 µm) and their low concentration (generally less than 0.05 wt%) which have hindered their identification by conventional microscopic techniques. As well, their very low solubility at low temperatures renders them inert to sequential extraction in solvents.

In particular, APS minerals are abundant in the clay mineral host-rock alteration assemblages associated with some uranium fields in these middle Proterozoic basins (Miller, 1983; Hoeve and Quirt, 1984; Wilson, 1985; Quirt et al., 1991; Fayek and Kyser, 1997; Lorilleux, 2001; Beaufort et al., 2005; Gaboreau et al., 2005). The uranium fields in Canada and Australia contain high-grade unconformity-type uranium deposits and a number of important prospects (Sibbald et al., 1990; Andrade et al., 2002). Few systematic investigations have been performed on the APS minerals in these deposits (e.g. Gaboreau et al., 2005) and little data are available on their compositional variations in relation to the uranium deposits (e.g. Quirt et al., 1991; Gaboreau et al., 2005). However, it is well known that their formation was

67 Partie I – Ch. 2. APS in the Athabasca basin controlled by physicochemical conditions (Eh, pH, constituent element activities, P, T), to which the APS minerals are particularly sensitive (Dill, 2001, Kolitsch and Pring, 2001).

The Athabasca Basin is a moderately-sized (approximately 100,000 sq. km) sandstone basin which occupies nearly one-third of the surface area of the exposed Canadian Shield of northern Saskatchewan and extends to the west into northern Alberta. It contains the preserved portion of the unmetamorphosed, generally undeformed, PaleoHelikian Athabasca Group which is dominantly composed of variably hematitic, coarse fluvial quartz sandstones and conglomerates and it hosts numerous high-grade unconformity-type uranium deposits. The world-class, high-grade, unconformity-type uranium deposits associated with the Athabasca Basin represent the most significant high-grade, low-cost uranium resource currently being exploited on a world-wide basis. This region is the premier host for unconformity-type uranium deposits and has an estimated resource in excess of 375,000 t U

(969 M lbs U3O8). These epigenetic deposits formed through the circulation of diagenetic brines in the middle Proterozoic Athabasca sedimentary basin and the redox interaction of these oxidized basinal brines with reduced basement fluids (Hoeve and Sibbald, 1978; Hoeve and Quirt, 1984; Kotzer and Kyser, 1995). The uranium ore occurs close to the unconformity separating the Athabasca Group sediments and the underlying Archean-Paleoproterozoic crystalline basement rocks. The ore zones are spatially controlled by faults crosscutting this unconformity. The redox-related uranium deposition occurred at sites of basement-sandstone fluid interaction along these structures, wherever a suitable stable redox front was present (Hoeve and Quirt, 1987). The formation of clay-rich host-rock alteration halos was associated with this fluid interaction and these halos envelop the main ore-controlling structures (Hoeve and Sibbald, 1978; Hoeve and Quirt, 1984; Pacquet and Weber, 1993; Percival et al., 1993; McGill et al., 1993; Kotzer and Kyser, 1995; Thomas et al. 2000; Lorilleux et al., 2002, 2003; Kister et al, 2005). These alteration halos overprinted the original sandstone and basement mineral parageneses and thus the alteration minerals record the ancient mineralizing fluid flow pathways and form a major exploration guide to the location of uranium mineralization (Hoeve and Quirt, 1984; Kister et al., 2005). Due to their very high grade and reserve potential, unconformity-type uranium deposits became the most sought-after targets over the last 20 years and will continue to be the model of choice in the near future (Thomas et al., 2002).

68 Partie I – Ch. 2. APS in the Athabasca basin

Numerous investigations have been performed on this type of deposit over the last several decades in order to improve our knowledge concerning their formation, including Hoeve and Quirt (1984), Ruzicka (1993), Kotzer and Kyser (1995), Fayek and Kyser (1997), Quirt (1997b, 2001, 2003), Hecht and Cuney (2000), Lorilleux et al. (2002, 2003), Gaboreau et al. (2003), Ramaekers et al. (2005), Kister et al. (2005), Laverret et al. (2005). However, investigations on the APS minerals present in the regional sandstone and in the alteration halos have been few and of varying detail (Quirt et al., 1991; Gaboreau et al., 2005).

The aim of this study is to clarify the nature and the origin of the APS minerals present in the middle Proterozoic Athabasca sandstone and in the host-rock alteration halos that host the Athabasca unconformity-type uranium orebodies. Spatial variations of both crystal chemistry and phase relationships with clay minerals, on a regional scale, have been investigated in order to improve our knowledge on the suitability of these minerals to indicate the paleoconditions at which the alteration processes relative to the uranium deposition operated. These results will be compared with those already obtained in the alteration halos associated with the unconformity-type uranium deposits of the Australian counterpart (Gaboreau et al., 2005) in order to confirm the utility of these minerals as a mineralogical tool for worldwide exploration of unconformity related high-grade uranium orebodies.

Regional geological setting

The Mesoproterozoic Athabasca Basin covers approximately 100 000 km2 in northern Saskatchewan and northeastern Alberta, Canada (Fig. 11). It contains the preserved portion of the unmetamorphosed Athabasca Group which is presently composed of up to 2300 m of two major fining-upward orthoquartzitic clastic successions composed of variably hematitic, coarse fluvial quartz sandstones and conglomerates to silty marine to lacustrine clastic sediments capped by dolomite, deposited during the PaleoHelikian circa 1750 - 1700 Ma (Rainbird et al., 2005). The sediments are interpreted to have been deposited in major river systems and near shore to shallow-shelf environments in a tectonically active sedimentary basin (Ramaekers et al., 2005).

The basin is an intracratonic successor (‘second generation’) basin developed in response to continued uplifts and plate movement after the initial Trans-Hudson Orogeny (THO). Its age relationship to the 1860 – 1775 Ma THO (Annesley et al., 2005) shows that it is not the

69 Partie I – Ch. 2. APS in the Athabasca basin primary foreland sequence. While the sedimentary fill in the Athabasca basin is presently 1 to 2 kilometres thick, temperature estimates derived from fluid inclusions, however, indicate that the sedimentary sequence may have reached a thickness of 5 km during peak diagenesis (Pagel et al., 1980).

The Athabasca Group can be subdivided into several fining-upward sequences that are separated by unconformities or by coarse-grained units that abruptly overlie finer-grained units of the previous sequence. The overall fine-grained, gritty sediments unconformably overly a crystalline basement and consist of conglomerate, red-bed sandstones, and minor siltstones of the Fair Point, Manitou Falls, Lazenby Lake, Wolverine Point, Locker Lake, and Otherside Formations (Ramaekers, 1981, 1990; Ramaekers et al., 2005). The lithostratigraphic subdivisions are based upon changes in the size and/or abundance of granules, pebbles, clay intraclasts, conglomerates, and mudstones. The sequence is generally flat-lying and undeformed except within the Carswell structure, where bedding is steeply dipping and locally overturned. The sandstone is unmetamorphosed but was extensively clay- altered during prolonged diagenesis at temperatures of 150-200 °C (Hoeve and Quirt, 1984; Kotzer and Kyser, 1995). There is a well-developed paleoweathering profile on the crystalline basement rocks underlying the Athabasca group that extends to a depth of several meters (Macdonald, 1980, 1985).

The lower Proterozoic and Archean sub-Athabasca basement lithologies have been affected by Thelon-Taltson (~2000-1900 Ma) and Hudsonian orogenesis (1860-1775 Ma) in the western and eastern Athabasca, respectively. The Archean basement lithologies are generally composed of orthognessic crystalline rocks overlain by variably graphitic metasediments, including metapelites, amphibolites, arkosic metasediments, quartz conglomerate and metaquartzite, and pelitic muscovite and biotite schists. In the Eastern Athabasca, the Aphebian metasedimentary rocks and Archean gneisses that comprise the basement are members of the Wollaston Domain of the THO (Lewry and Sibbald, 1979, 1980; Macdonald, 1985; Annesley et al., 2005). The Aphebian metasedimentary rocks unconformably overlie the Archean granitoid gneisses and consist typically of quartz, plagioclase, biotite, cordierite, garnet, and tourmaline pelitic to psammitic gneisses, with anatectic and graphitic intervals (Ey et al., 1991; Marlatt et al., 1992; Annesley et al., 2005). Individual metaquartzite units occur locally and are generally separated by intervals of garnet-cordierite pelitic gneiss (Marlatt et al., 1992). In the western part of the Athabasca region, the Lloyd Domain includes a package

70 Partie I – Ch. 2. APS in the Athabasca basin

of graphitic metasedimentary lithologies, including garnetite, intercalated between two felsic orthogneiss units (Card, 2001, 2002). In Saskatchewan, the Lloyd domain is overprinted by the north-trending aeromagnetic Clearwater Domain that subdivides the Lloyd Domain into eastern and western parts (Card et al., 2003).

Sampling

All of the rock samples were taken from drill core and standard polished thin sections were prepared from them. Over 300 samples, representing 15 drill holes, covering the eastern and western parts of the Athabasca Basin, were studied, including the Rumple Lake stratigraphic drill hole situated in the middle of the basin.

Samples taken for the study, summarized in table 11, include representative material taken from throughout the sandstone column and the basement lithologies. The samples were selected according to distance from ore deposits, discontinuities (fault, brecciated zones, unconformity), and types of clay alteration. From these criteria, we have considered three major groups of samples: (1) barren samples from regional drill holes, such as Erica1 and Rumple Lake; (2) “anomalous” samples, that are near an uranium anomaly on both sides of the unconformity; and (3) samples from the vicinity of the major uranium deposits in the Athabasca basin, including Cigar Lake, McArthur River, and Shea Creek (Anne Area).

Tableau 11. Petrologic observations of the different samples associated to unconformity-type uranium deposits in the Athabasca Basin.

Samples Location Identified non APS minerals Host rocks Shea Creek Sudoite, illite ± trioctahedral Altered metamorphic rocks, below 1-2 (Anne deposit) and chlorite, monazite, pyrite, the unconformity and altered McArthur deposits apatite sandstones close the unconformity Cigar Lake and Altered sanstones above 3-4 Sudoite, illite McArthur deposits unconformity Illite, sudoite ± trioctahedral Altered metamorphic rocks, close 5-6 chlorite, monazite, apatite, to the unconformity and Anomalous pyrite discontinuities prospects Altered sandstone above and close 7-8 Illite, sudoite to the unconformity Unaltered basement rocks below 9 Trioctahedral chlorite Regional the unconformity background Unaltered Athabasca sandstone, 10-11 Illite, hematite above the unconformity

71 Partie I – Ch. 2. APS in the Athabasca basin

Figure 11. Crustal and lithostructural domains of the sub-Athabasca basement, studied areas and main unconformity-type deposits in the Athabasca basin (modified from Ruzicka, 1986).

Methods

Samples were examined in polished thin section using an Olympus BH2 polarizing microscope and a Nikon LABOPHOT2-POL polarizing and reflected light microscope. Freshly-fractured rock fragments and polished thin sections were studied using a scanning electron microscope (SEM); a JEOL JSM6400 SEM at the University of Poitiers and a

72 Partie I – Ch. 2. APS in the Athabasca basin

Hitachi S-3000 variable-pressure SEM at the Saskatchewan Research Council, both equipped with energy-dispersive spectrometers (EDS) for chemical analysis. SEM observations were made in secondary electron mode for morphological investigations on gold-coated slabs and in back-scattered electron mode for identification of APS on the basis of chemical contrasts in carbon-coated (JEOL SEM) and uncoated (Hitachi SEM) polished thin sections. The conditions of observation were as follows: current intensity - 0.6 nA and accelerating voltage - 15 kV. Electron microprobe analyses were obtained with a CAMECA SX 50 (University of Poitiers) and a JEOL JXA8600 Superprobe (University of Saskatchewan) using wavelength-dispersion spectrometery (WDS). Analytical data for Al, Sr, P, Ca, Ba, La, Ce, Nd, Pr, Fe, S, Th, and U were obtained. The microprobes were calibrated using the following synthetic and natural standards: SrSiO3, apatite, monazite, pyrite, NdCu, glass doped in rare-earth elements, UO2, and La3ReO8. Matrix corrections were made using a ZAF program. The analytical conditions were as follows: current intensity - 20 nA ; accelerating voltage - 15 kV ; spot size - 2-4 µm ; counting time 30 to 40s per element. The relative error on the elements sought is below 1.5%. The structural formulae of the APS minerals were calculated on the basis of 1 mol A-site, 2 mol (XO4)-group, and 3 mol B-site per formula unit (Scott 1987), as in the formula

AB3(XO4)2(OH)6.

Petrographic results

APS crystals are commonly rhombohedral and have a pseudocubic habit (Fig. 12a), and are closely associated with the clay matrix throughout the sandstone and clay-altered material in the basement lithologies. In the manner described by Rasmussen (1996), the APS minerals occur in the sandstone as clusters of minute euhedral crystals (Fig. 12b), 1-20 µm in size, within pockets of clay matrix lining detrital quartz surfaces and within early diagenetic quartz overgrowth material. They occur less commonly within altered mica (Fig. 12c) or as thin rims lining cavities left by quartz grain dissolution in the sandstone. Rare florencite [LREE-end- member APS mineral] crystals form along the surface of monazite grains locally present within, and armoured by, detrital quartz grains (Fig. 12d). In the basement rocks and in the sandstone within a few meters above the unconformity, APS minerals are observed associated with weak clay alteration commonly encountered at the base of the basin, below the unconformity, and along the fault zones (Fig. 12e). Close to the unconformity, APS minerals also locally appear as clusters of minute crystals or as larger individual euhedral grains up to

73 Partie I – Ch. 2. APS in the Athabasca basin

50 µm in the paleoweathered basement (Fig. 12f) and become rarer with depth. APS minerals are best observed with SEM under BSE mode, due to their high average atomic weight relative to quartz and the clay matrix minerals. They have a pseudocubic crystal habit in thin section that is essentially unique in the sandstone. Some crystals display a compositional zonation on a scale of less than 2 µm (Fig. 13a) which probably reflects the changing concentrations of cations and anions in the fluid during their precipitation (Rasmussen, (1996).

Relationships between APS minerals and clay alteration

As Gaboreau et al. (2005) have shown for the Kombolgie basin (Australia), APS minerals appear as disseminated minerals associated with clay alteration in the environment of unconformity-related uranium deposits (URUD). In the Australian URUD, the distribution and the nature of clay minerals are related to their position relative to the ore deposits and to the distance from the intensive flow of water-rock interaction which took place at the sub- Kombolgie unconformity. But in the Athabasca basin, different associations have also been distinguished.

In the Athabasca Basin, diagenetic illite and kaolin are the most abundant clay minerals and are observed in the intergranular porosity (Hoeve and Quirt, 1984; Quirt, 2001, 2003; among others). At the base of the sandstone, in the basal Manitou Falls formation, illite is commonly associated with variable amounts of di,trioctahedral chlorite (sudoite) and occasionally dravite, and forms a weak halo of alteration mostly on the sandstone side of the unconformity. Near unconformity-type uranium deposits and in barren alteration halos, illite and sudoite occur in hydrothermally-altered sandstone and metasedimentary rocks of the basement near the unconformity and in fault zones that intersect the unconformity (Hoeve and Quirt, 1984; Quirt, 1986; Wilson and Kyser, 1987; Kotzer and Kyser, 1995; Quirt, 2003). Diagenetic- hydrothermal alteration illite has also been identified in relatively distal drill holes, as well as in proximal and mineralized drill holes (Laverret et al., 2005). The presence of illite has resulted from several (re)crystallization processes operating during diagenesis or related to the syn-ore alteration event.

74 Partie I – Ch. 2. APS in the Athabasca basin

Figure 12. SEM images of APS minerals from the Athabasca basin. a) Pseudocubic habit of APS grain in illite matrix in a distal alteration area. b) Aggregate of small euhedral grain of APS minerals in the intergranular pore space in sandstone. c) Cluster of APS minerals lining altered micas surface. d) LREE-end member APS crystals along the surface of detrital monazite grain. e) Disseminated crystals of LREE-Sr Al-phosphate (white spots) in a matrix of hydrothermal illite-sudoite close to a discontinuity. f) Larger euhedral grain of APS minerals in the paleoweathered basement.

75

Partie I – Ch. 2. APS in the Athabasca basin

Sudoite and dravite also occur locally in fault zones up to 300 m above the basal unconformity, suggesting that these faults allowed fluids associated with basement interactions access to much higher stratigraphic levels (Kotzer and Kyser, 1995). Trioctahedral chlorite is found deeper in the basement rocks in zones of strong alteration of the Mg-rich metasediments and in the core of the diagenetic-hydrothermal alteration halos (Hoeve and Quirt, 1984; Quirt, 1986, 2003; Kotzer and Kyser, 1995).

In barren sandstone, away from the unconformity, APS minerals are associated with diagenetic illite in the intergranular quartz porosity. They are also found with Fe-Mg trioctahedral chlorite formed during retrograde metamorphic alteration (eg. Quirt, 1997a) deeper in the basement rocks. In the weakly-altered zone at the base of the sandstone and in the upper paleoweathered zone below the unconformity, they are associated with a finely- mixed clay mineral assemblage composed of illite and sudoite with some relict kaolin. This association is also noted in the sandstone up to few hundred meters along faults. In the diagenetic-hydrothermal clay mineral alteration halos in the sandstone above the unconformity near the mineralized zones (e.g. Cigar Lake, McArthur River, Yalowega Lake), APS minerals are associated with massive clay mineral alteration composed of illite and sudoite, and more rarely trioctahedral chlorite in the core of the alteration halo. In mineralized zones in the basement, APS minerals are associated with illite, trioctahedral chlorite, and sudoite (eg. McArthur River, Shea Creek). In the Athabasca basin, U deposits are encountered in the sandstone (eg. Cigar Lake, McArthur River, Key Lake, Midwest, Collins Bay, Shea Creek, Cluff Lake) and in the basement rocks (eg. McArthur River, Key Lake, Rabbit Lake, Eagle Point, Shea Creek, Cluff Lake). In Australia, the U deposits have only been found deeper in the basement rocks. This difference means that there are somewhat different clay mineral parageneses associated with the U deposits in the two basins. In the sandstone and adjacent to the unconformity, on both sides, the clay mineral parageneses are quite similar. The main difference is found in the clay mineral alterations associated with the U deposits. Gustafson and Curtis (1983) and Beaufort et al. (2005) have shown that in the Kombolgie Basin, the basement ore deposits were associated with a massive trioctahedral chlorite host-rock alteration. In the Athabasca basin, this component is only noted as patches deeper in the basement rocks, and the major clay mineral alteration associated with the Athabasca basement deposits consists of illite and di,trioctahedral chlorite (sudoite) (Sopuck et al., 1983; Hoeve and Quirt, 1984; Quirt, 1997a, 2003).

77

Partie I – Ch. 2. APS in the Athabasca basin

Figure 13. a) Zoning APS crystals associated with relict monazite grain in the basement rocks. b) APS minerals in contact with pyrite and apatite in the basement rocks

79

Partie I – Ch. 2. APS in the Athabasca basin

So we have considered three main associations of clay minerals and APS minerals:

1- Illite ± kaolin, hematite, APS minerals: in unaltered sandstone away from the unconformity and any mineralization.

2- Illite, sudoite, hematite, APS minerals (± dravite, pyrite): in the different zones of weak clay alteration associated with faults and adjacent to both sides of the unconformity away from zones of anomalous mineralization.

3- Illite, sudoite, APS minerals, dravite (± trioctahedral chlorite, hematite, pyrite, apatite): in the different zones of strong clay alteration associated with the diagenetic-hydrothermal mineralization process on both sides of the unconformity.

Relationships between APS minerals and other accessory minerals

The dominant potential source of aluminium for the precipitation of APS minerals in the Athabasca region is the intergranular clay mineral matrix (eg. Gaboreau et al., 2005; Pe-Piper and Dolansky, 2005). Similarly, detrital monazite and apatite are the dominant potential sources of REE, Ca, Sr, and P for the APS minerals (eg. Fayek and Kyser, 1997), while pyrite is the dominant potential source for S (Quirt, 2000). Close associations of these accessory minerals have been observed in the different samples used in this study, throughout the sandstone and the basement rocks.

In the sandstone, monazite is locally present within, and armoured by, detrital quartz. In this case, further sites of mineral growth, as clusters of minute euhedral APS crystals onto monazite grains, have occasionally been observed (Fig 12d). In the basement rocks, alteration of monazite grains is apparent locally throughout the basement lithologies (Hecht and Cuney, 2000). Associated with the ghosts of monazite grains, APS minerals sometimes display compositional zoning with alternation of light elements (dark zones by SEM) and heavy elements (bright zones by SEM) which have been described as alternations of Ca-Sr-rich and LREE-rich zones (Gaboreau et al., 2005). APS minerals associated with these monazite alteration sites, also show some inclusions of monazite (Fig. 13a). In basement rocks where apatite still persists, APS minerals are often observed to be in contact with subhedral grains of

81 Partie I – Ch. 2. APS in the Athabasca basin apatite (Fig. 13b). Stoffregen and Alpers (1987) have shown that dissolution of apatite by acidic fluids at high temperatures can induce the precipitation of APS minerals. Contacts between pyrite and APS minerals are also often observed in the basement rocks (Fig. 13b).

Chemical results

Representative results of electron microprobe analyses of APS minerals from the three types of alteration areas distinguished above are presented in table 12. The chemical elements were selected for analysis on the basis of preliminary qualitative EDS investigations. The low analytical totals (between 75 and 85 wt %) obtained in some of the analyses is essentially due to the presence of hydroxyl ions in their structure (up to 15%) and to the small size of many APS grains, which was commonly smaller than the volume of sample emitting the secondary X-ray radiation. Consequently there is a partial integration of the surrounding minerals and micropores in the volume analyzed by the electron beam. The low analytical total could also be induced by a deficiency of cations in the X-sites which can be explained by either the presence of carbons, undetectable by microprobe in the crystal lattice or a lack of X-site cations due to the radiation damage induced by Th (Mordberg, 2004). It should be noted that the chemical zonations observed by SEM in some APS crystals are too thin to be analyzed individually with an electron microprobe.

For a better comparison of their compositional variation, the results of the microprobe analyses of APS were normalized to 85%, (the total weight% of anhydrous APS). The highest amount of Sr and S (19.36 wt% SrO and 10.15 wt% SO3, respectively) and the lowest amounts of LREE and P (0.15 wt% LREE2O3 and 6.10 wt% P2O5, respectively) were found in APS minerals from the distal zones of alteration, whereas the lowest amount of Sr and S (1.69 wt% SrO and 0.89 wt% SO3), and the highest amount of LREE and P (24.85 wt% LREE2O3 and 28.88 wt% P2O5) were found in APS minerals close to U deposits encountered in the basement rocks. APS minerals from the intermediate alteration zones present chemical compositions intermediate to, but distinct from, those of the other two zones of alteration. The APS minerals from all the alterations zones studied in the Athabasca basin contain also small amounts of CaO, ThO2, and Fe2O3. CaO and Fe2O3 do not vary significantly throughout the different alteration zones, whereas ThO2 strongly increases from the distal to the proximal alteration zones (from 0.01 to 2.44 wt%).

82 ranium Mean* Std dv. apfu Mean* Std dv. t% Mean* Std dv. Wt% Mean* Std dv. apfu rals associated with unconformity-type u rals associated with unconformity-type Structural formula were calculated on the basis of one Structural formula Mean* Std dv. apfu Intermediate alterationIntermediate areas Distal alteration areas Mean* Std dv. oprobe analyses per sample. oprobe analyses per sample. t% Mean* Std dv. Wt% Mean* Std dv. W apfu (atom per formula unit). per formula (atom deposits in the Athabasca basin, Canada yses and structural formulas of APS mine yses and structural formulas apfu Mean* Std dv. apfu ) groups, and 3 (Al, Fe) 4 Proximal alteration areas Proximal , PO 4 *Mean calculated on the basis of 10 micr Mean* Std dv. D.L. 6.34 6.111.26 0.283.21 1.330.35 4.56 3.72 0.15 4.68 0.36 0.550.21 0.73 0.15 1.08 3.37 0.24 0.840.89 1.48 2.44 0.16 4.02 0.23 1.24 1.36 4.51 0.67 1.48 0.26 0.52 0.43 0.79 1.08 2.05 0.64 2.18 2.91 0.09 1.95 0.57 0.10 2.21 2.98 0.19 0.27 0.55 1.21 0.53 0.12 0.30 1.44 1.69 0.56 0.56 2.18 2.33 1.26 0.26 0.14 2.47 1.20 2.15 0.16 0.48 1.37 0.29 0.53 0.80 0.22 0.98 0.33 0.20 3.77 0.76 1.10 0.43 0.16 3.33 0.16 1.42 0.24 0.01 1.28 0.06 0.60 0.59 0.22 0.08 2.61 0.03 4.53 0.21 0.13 1.57 0.02 0.07 4.27 0.27 0.02 0.62 0.34 8.09 0.10 7.79 0.58 apfu < Wt% Mean* Std dv. Wt% Mean* Std dv. W 12.34 12.19 0.24 8.02 8.05 0.87 6.48 7.08 0.35 5.35 5.17 0.42 4.12 3.43 0.86 0.74 0.49 0.24 3 29.58 28.9427.76 0.38 27.83 30.07 0.91 28.98 20.73 1.38 24.74 33.05 2.84 32.42 22.24 0.78 21.49 33.50 1.00 33.12 18.47 0.62 18.62 30.74 1.68 29.91 24.61 0.85 22.90 32.03 1.11 28.77 23.29 3.11 21.84 1.79 O 2 3 3 3 3 3 3 2 5 O O O O O 3 2 0 2 2 2 2 2 O Tableau 12. Results of electron microprobe anal Tableau 12. Results of electron microprobe 2 ape357911 Sample13 SrOCaOLa 1.98 1.01Ce 2.12Pr 1.25 0.23Nd 0.36Th0 5.73Al 3.25 5.28Fe 3.17P 0.61SO 0.61 6.58Total 2.78 6.49 84.93 2.47 85.34 0.50Ca 0.27 8.94La 2.24Ce 8.19 0.10Pr 81.60 2.55 0.22 1.02Nd 0.12 82.83 0.24 0.42Th 0.20 0.03 9.42 0.04 0.40 3.18 0.01 0.11 10.02 0.26Fe 0.04 0.02 0.01 3.69 1.70 0.12 0.13 0.27 0.00 16.66 81.68 0.41 0.01 0.22 0.02S 0.14 81.76 0.01 16.55 0.04 0.02 0.00 2.83 0.23 0.09 0.80 0.03 0.02 0.02 0.25 2.34 0.03 0.07 0.06 0.03 0.01 0.13 0.22 0.42 0.02 78.35 0.01 0.08 0.20 0.02 0.14 0.09 0.02 87.93 0.02 0.02 0.01 0.22 0.01 0.07 0.06 0.21 0.02 0.01 0.17 0.00 0.09 0.06 0.24 0.04 0.00 0.17 0.15 0.00 0.01 0.10 82.54 0.02 0.07 0.02 0.00 81.83 0.16 0.04 0.01 0.03 0.10 0.28 0.02 0.01 0.01 0.04 0.07 0.16 0.01 0.31 0.00 0.02 0.13 0.00 0.06 0.19 0.03 84.36 0.03 0.01 0.01 0.10 0.07 78.59 0.02 0.04 0.23 0.06 0.01 0.03 0.01 0.01 0.03 0.31 0.20 0.02 0.01 0.02 0.03 0.01 0.00 0.02 0.27 0.00 0.08 0.01 0.01 0.00 0.00 0.04 0.16 0.01 0.00 0.00 0.01 0.09 0.28 0.00 0.00 0.00 0.02 0.28 0.00 0.04 0.02 0.01 0.47 0.48 0.01 Note: U A-site cation, 2 (SO A Sr 0.11 0.11 0.01B 0.25 Al 0.24X P 2.99 0.02 2.98 0.32 1.94 0.01 0.32 1.92 2.91 0.02 0.02 2.93 0.45 1.83 0.04 0.41 1.85 0.03 2.93 0.03 2.90 0.46 1.84 0.01 0.46 1.81 2.97 0.06 0.02 0.74 2.94 1.69 0.02 0.77 1.73 0.03 2.92 0.04 2.84 1.72 0.09 1.72 2.98 0.04 2.98 1.53 0.01 1.52 0.01

83 Partie I – Ch. 2. APS in the Athabasca basin

Thorium enrichment is also responsible for local occurrences of increased radioactivity in conglomeratic sandstone of the lower Manitou Falls Formation (Mwenifumbo et al., 2002). The high thorium content observed in these conglomeratic sandstones is due to the presence of very fine-grained thorium-rich APS minerals within the intergranular pores, ranging in composition from Th-bearing ‘crandallite’ to eylettersite (ThAl3(PO4)2(OH)6). The thorium- rich material occurs as rounded cores within the pseudocubic APS crystals, and is overgrown by Sr-rich APS similar to that found elsewhere in the Athabasca Basin.

Figure 14. Projection in terms of Ca-Sr-LREE (electron microprobe data) of the various APS minerals encountered in all geological units surrounding the Athabsca basin.

All of the analytical results agree with the general formula for APS minerals

(AB3(XO4)2(OH)6). The data indicate the presence of complex chemical cation substitutions that form solid solutions between different compositional end-members: Sr, LREE, Ca, and Th in the A-site; Al and Fe in the B-site; P and S in the X-site. The principal variations encountered in the different varieties of the APS minerals are found in the A- and X-sites. Most of the variations found in the A-site concerns the respective amounts of Sr and LREE (Fig. 14) and those found in the B site concern essentially P and S. The APS minerals are LREE- and P-rich near the different zones of U mineralization (Cigar Lake in the eastern

84 Partie I – Ch. 2. APS in the Athabasca basin

Athabasca; Shea Creek in the western Athabasca) with compositions closer to that of florencite (LREEAl3(PO4)2(OH)6). Conversely, APS observed in unaltered, barren sandstone, far from the unconformity (Erica 1 in the western Athabasca; Rumple Lake in the middle of the Basin), are Sr-rich and are relatively S-rich with compositions closer to those of goyazite

(SrAl3[PO3(O0.5(OH)0.5)]2(OH)6) and svanbergite (SrAl3(PO4,SO4)(OH)6). Zones of clay alteration in the sandstone and the basement close to the principal discontinuities (unconformity, fractures, fault) contain REE- and P-enriched APS minerals with compositions intermediate to those observed from the two previous areas. It should be noted that small amounts of Fe replace Al in the B site and that the uranium content is always below the detection limits in the APS minerals of all the alteration zones identified in the Athabasca Basin.

Discussion

Crystal chemical variations of APS minerals

Figure 15. Cross-plot diagram of P + LREE versus S + Sr showing the wide range of chemical compositions recorded in APS.

85 Partie I – Ch. 2. APS in the Athabasca basin

Alteration petrography and the chemical data presented in this study demonstrate that the APS minerals coexisting with the different clay parageneses of the altered zones related to the unconformity-type uranium deposits of the Athabasca basin exhibit a wide range of chemical variation. These variations mostly consist of coupled substitutions of Sr for LREE and S for P in the A and X sites, respectively (Fig. 15), which change the relative proportions of the end– member solid-solution components of the APS minerals. These solid-solution components

(Dill, 2001) are from the woodhouseite-series (svanbergite SrAl3(PO4,SO4)(OH)6 and woodhouseite CaAl3(PO4,SO4)(OH)6) and the crandallite-series (goyazite

Sr[PO3(O0.5(OH)0.5)]2(OH)6, florencite LREEAl3(PO4)2(OH)6, and eylettersite

ThAl3(PO4)2(OH)6). The actual solid-solution compositions of the Athabasca APS minerals can be denoted using the proportions of these end-member components; svanbergite (sv), goyazite (gy), crandallite (cr), florencite (fl), and eylettersite (ey) (eg. sv25gy20cr20fl30ey5). According to the mean chemical compositions obtained from APS minerals of each alteration zone determined in both the sandstone and the metamorphic basement rocks, the crystal- chemical variations of the APS minerals are listed as follows:

1-Distal alteration areas, unaltered (barren) areas -Unaltered sandstone 3+ Sr0.77Ca0.20LREE0.02(Al2.98Fe 0.02)[(PO3(O0.66(OH)0.34)]1.52(SO4)0.48(OH)6 corresponding to the solid solution: sv48gy29cr20fl2ey0 , coexisting with illite and hematite -Underlying metamorphic basement rocks 3+ Sr0.46Ca0.31LREE0.20Th0.03(Al2.84Fe 0.16)[(PO3(O0.73(OH)0.27)]1.72(SO4)0.28(OH)6 corresponding to the solid solution: sv28go18cr31fl20ey3, coexisting with illite ± sudoite and hematite.

2-Intermediate alteration areas in both sandstones and basement rocks 3+ Sr0.41Ca0.24LREE0.32Th0.02(Al2.97Fe 0.03)[(PO3(O0.77(OH)0.23)]1.73(SO4)0.27(OH)6 corresponding to the solid solution: sv27go14cr24fl32ey2 , coexisting with illite , sudoite and dravite.

3-Proximal alteration areas (U deposits) -U deposits hosted in sandstones 3+ Sr0.24Ca0.27LREE0.46Th0.02(Al2.93Fe 0.07)[(PO3(O0.8(OH)0.2)]1.85(SO4)0.15(OH)6 corresponding to the solid solution: sv15go9cr27fl46ey2 , coexisting with sudoite, illite , and dravite ( ± trioctahedral chlorite, hematite, pyrite, apatite).

86 Partie I – Ch. 2. APS in the Athabasca basin

-U deposits hosted in crystalline rocks of the basement 3+ Sr0.11Ca0.12LREE0.76Th0.01(Al2.98Fe 0.02)[(PO3(O0.93(OH)0.07)]1.92(SO4)0.08(OH)6 corresponding to the solid solution: sv8go3cr12fl76ey1 , coexisting with sudoite, illite , and dravite ( ± trioctahedral chlorite, hematite, pyrite, apatite).

From the above data it appears that an increasing proportion of florencite in the APS solid solutions coincides with a decreasing distance from the uranium ore bodies and also with change in the nature of the cogenetic clay mineral assemblages.

Figure 16. Projection in terms of Sr-S-LREE (electron microprobe data) of the various APS minerals encountered in all the geological units surrounding the Athabasca deposits or prospects. Open symbols refer to APS analyses in sandstone. Solid symbols refer to APS analyses in the basement rocks.

The overall compositional variation can be illustrated by the projection in terms of Sr-S- LREE of all the compositions of APS measured in the alteration zones surrounding the

87 Partie I – Ch. 2. APS in the Athabasca basin uranium orebodies of Athabasca (Fig. 16). This projection outlines a chemical trend very similar to that reported and discussed by Gaboreau et al. (2005) for unconformity-type uranium deposits of the East Alligator River Uranium Field in Australia. It consists of a linear trend extending between the composition of the svanbergite- and goyazite-rich APS minerals identified in the unaltered barren areas and the altered sandstones of the distal alteration zone, and a for the APS minerals from very close to the uranium orebodies. However, the data collected in this study gives more details on the variations observed between the two aforementioned compositional poles. They show particularly that, beyond of the distance from the uranium ore bodies and the change in the nature of the cogenetic clay mineral assemblages, the chemical variation of APS minerals is also influenced by the host-rock lithology. Indeed for an equivalent alteration zone, the APS minerals formed in basement rocks are systematically enriched in P and LREE when compared to those formed in sandstones (Fig. 16).

Source material for APS minerals

The above noted variations in chemical data give rise to the problem of the source material for the APS minerals encountered at different distances from the uranium orebodies in the unconformity-type deposits of both the Athabasca and East Alligator River Uranium Fields. The source material of the Sr-rich APS which characterizes the barren sandstones of the distal alteration areas is not clearly identified, but it is related to the burial diagenesis in which this mineral represents the APS phase stable with the basinal solutions during peak diagenesis. Indeed, APS minerals with high Sr and S contents have been frequently reported in literature on sandstones worldwide (Rassmussen, 1996; Spötl, 1990; Dill, 2001). The facts that the composition of Sr-rich APS is very similar in both the Athabasca and Kombolgie sedimentary basins (similar S/Sr ratio particularly) and the commonly-observed position of these crystals beneath and within early-diagenetic quartz overgrowth material support the hypothesis of a similar origin which is likely diagenetic.

According to the chemical variation existing between the APS minerals of the alteration zones associated with the unconformity-type uranium of the East Alligator River Uranium Field, Gaboreau et al. (2005) suggested that the aqueous solutions, from which the Sr-rich APS in the distal sandstones were previously crystallized, were progressively subjected to phosphatization and LREE enrichment with increasing proximity to the uranium ore deposits.

88 Partie I – Ch. 2. APS in the Athabasca basin

Such concomitant enrichments in P and LREE toward the ore deposits indicate a common source, which consisted of dissolution of monazite in basement rocks, and an extensive mobility of both sets of elements in the altered zones. In this study, the parental links between basement monazite and APS minerals are supported by several facts: (1) the petrographic observations of neoformed APS in the alteration sites of monazite within the altered basement rocks; (2) the absence of LREE fractionation between the monazite crystals analysed in the basement rocks and the APS minerals analysed at large scale and in both the sandstone and the basement rocks of the proximal and the intermediate alteration zones (Fig. 17); and (3) the systematic enrichment in the florencite solid solution component of APS minerals in altered basement rocks in which primary monazite has been strongly to totally dissolved.

Figure 17. Projection in terms of Ce-La-(Pr+Nd) (electron microprobe data) of some monazite and the various APS minerals encountered in all the geological units surrounding the Athabasca basin.

89 Partie I – Ch. 2. APS in the Athabasca basin

Conversly, the fact that LREE fractionation exists between monazite and the APS of the distal sandstones (which contain less than 2% florencite component) and the LREE show a strong depletion in La and a variable Ce/Pr+Nd ratio (Fig. 17) confirms that the svanbergite rich APS minerals of the distal sandstones are chemically distinct. This argues for a different origin which could be diagenetic as already suggested by different authors (Hoeve and Quirt, 1984; Wilson, 1985; Quirt et al., 1991, Gaboreau et al., 2005). In such conditions, the source of sulphur was likely from oxidation of early diagenetic pyrite (Quirt, 2000), while the source of the phosphorus was likely from dissolution of detrital or diagenetic phosphates. (Fayek and Kyser, 1997).

In summary, the chemical data obtained on the APS minerals formed in the surroundings of the unconformity-type deposits of the Athabasca region and those obtained in their Australian counterpart are very similar. Both APS series show the same chemical continuum between the diagenetic Sr-rich APS minerals of the barren sandstones and the LREE-rich composition of the APS minerals in the altered sandstone (Fig. 18) which is controlled chemically by the transport and the redistribution of P and LREE elements released from the dissolution of monazite in the basement rocks during the syn-ore alteration processes. The fact that the S/Sr ratio measured in the APS minerals of the unaltered sandstone away from the unconformity and any mineralization is preserved during the syn-ore alteration processes indicate that the fluids involved in both deep burial diagenetic processes and syn-ore alteration system were essentially derived from a very similar diagenetic reservoir in both the Athabasca and Alligator River regions.

Concluding remarks

All the above considerations confirm that APS are key minerals which need to be investigated much more systematically in all the unconformity-type uranium deposits. In all the studied cases, it is found that APS minerals are closely linked to the alteration processes which controlled the ore deposition and, through their variation of crystal-chemical properties and their phase relation with coexisting clay parageneses, these minerals can provide relevant information relative to the time space evolution of the fluid involved in the different water- rock interaction processes with which they were associated (i.e., diagenesis in sandstones away from the unconformity and hydrothermal alteration closer to the mineralized areas). From the present study and the previous one (Gaboreau et al., 2005), which considered

90 Partie I – Ch. 2. APS in the Athabasca basin specifically APS minerals in the unconformity-type uranium deposits of the East Alligator River Uranium Field, it seems possible to generalize our findings and to list below some critical information on the genesis of the uranium ore-bodies in the unconformity-type uranium deposits that could be addressed from APS minerals.

Figure 18. Projection in terms of Sr-S-LREE (electron microprobe data) of the various APS minerals encountered in all the geological units surrounding the australian and canadian deposits or prospects. Open symbols refer to APS analyses from the Kombolgie basin. Solid symbols refer to APS analyses from the Athabasca basin.

The crystal-chemical nature of the APS minerals appears to be associated with the hydrothermal processes controlling the alteration rate of monazite within the basement rocks. Both the content of florencite (i. e. the relative proportion of LREE) incorporated in the APS minerals of the sandstone can be used to determine the extent and the intensity of the

91 Partie I – Ch. 2. APS in the Athabasca basin hydrothermal processes and the potential rate of uranium mobilisation within the basement rocks underlying the unconformity. More specifically, this would allow determination of the extent of the upward vertical transfer of LREE obtained from the altered and depleted basement (Cuney et al., 2000).

Thermodynamic calculations have already demonstrated that the transition from svanbergite to florencite in the APS series does not only depend on the REE activity in the fluids but also on the pH and Eh conditions at which they crystallized (Dill, 2001, Kolitsch and Pring, 2001, Gaboreau et al., 2005). The transition from svanbergite to florencite in the APS series is a good candidate for investigation of the distribution of the pH and redox fronts in the hydrothermal fluids that are considered to result from the interaction of the diagenetic solutions with the basement rocks below the unconformity (Hoeve and Quirt, 1984). Sr-rich APS is stable at rather acidic conditions compatible with the composition of basinal fluids involved in the diagenetic reactions (Komininou and Sverjensky, 1996) whereas the florencite content of APS increases with increasing pH and more reducing conditions. In other words, the compositional variation of APS toward florencite could depend on both the redox and pH fronts which are well known to have controlled the deposition of the uranium ore bodies. The transition between LREE-rich APS and apatite which was observed at several scales (i.e., alteration sites of individual monazite and regional zoning in basement rocks) is also consistent with a higher neutralisation of acidic diagenetic fluids by interaction with basement rocks. Indeed, APS minerals are known to be more stable in lower pH environment (in which LREE are rather mobile) than apatite (Spötl, 1990; Stoffregen and Alpers,1987; Vieillard et al., 1979).

Phase relationships between APS and clay minerals need to be addressed because taking into account the compositional data of coexisting APS minerals and clay mineral phases will significantly improve the geochemical modelling of the formation of the alteration zoning observed around the uranium ore-bodies. Such a thermodynamic approach would be particularly relevant to better understanding the causes of the main difference found in the clay mineral alterations associated with the U deposits in the two basins hosting URUD (Athabasca and Kombolgie). Indeed, the fact that the basement ore deposits were associated with a massive trioctahedral chlorite host-rock alteration in the Kombolgie Basin, whereas the major clay mineral alteration associated with the Athabasca basement deposits consists of illite and sudoite, suggests that pH and oxygen fugacity of the syn-ore fluids probably differ

92 Partie I – Ch. 2. APS in the Athabasca basin in the alteration systems of the two basins at the moment of the deposition of the uranium orebodies.

References

Andrade, N., Breton, G., Jefferson, C.W., Thomas, D., Tourigny, G., Wilson, S., and Yeo, G. (2002). Field Trip A1: The eastern Athabasca Basin and its uranium deposits. Field trip guidebook, Geological Association of Canada-Mineralogical Association of Canada joint annual meeting, Saskatoon, SK, May 2002, 102 p.. Annesley, I.R., Madore, C., and Portella, P. (2005). Geology and thermotectonic evolution of the western margin of the Trans-Hudson Orogen: evidence from the eastern sub-Athabasca basement, Saskatchewan. Canadian Journal of Earth Science, v. 42, pp. 573-597. Beaufort, D., Patrier, P., Laverret E., Bruneton, P. & Mondy, J. (2005). Clay alteration associated with Proterozoic unconformity-type deposits in the East Alligator Rivers Uranium Field, Northern Territory, Australia. Economic Geology, 100, pp. 515-536. Card, C.D. (2001). Basement rocks in the western Athabasca basin in Saskatchewan. Summary of investigations 2001. Saskatchewan Geological Survey, Saskatchewan Energy and Mines, 321-333. Card, C.D. (2002). New investigations of basement to the western Athabasca basin. Summary of investigations 2002. Saskatchewan Geological Survey, Saskatchewan Energy and Mines, 17. Card, C.D., Campbell, J.E., and Slimmon, W.L. (2003). Basement lithologic framework and structural features of the western Athabasca Basin; In: Summary of Investigations 2003, Volume 2, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2003- 4.2, CD-ROM, Paper D-3, 17p. Cuney, M., Brouand, M., Hecht, L. & Bruneton, P. (2000). Contrasted Rare Earth mobility during hydrothermal alteration in the Jabiluka uranium deposit (Alligator Rivers District, Northern Territory, Australia). Geocanada 2000, Geological Association of Canada- Mineralogical Association of Canada anniversary meeting, Calgary. Dill, H.G. (2001). The geology of aluminium phosphates and sulphates of the alunite group minerals: a review. Earth Science Review, 53, pp. 35-93. Ey, F., Piquard, J.P. and Zimmerman, J. (1991). The Sue uranium deposits, Saskatchewan, Canada: Geological Society of CIM, 35-36.

93 Partie I – Ch. 2. APS in the Athabasca basin

Fayek, M. & Kyser, T. (1997). Characterization of multiple fluid-flow events and Rare-Earth- Element mobility associated with formation of unconformity-type uranium deposits in the Athabasca basin, Saskatchewan. The Canadian Mineralogist, 35, pp. 627-658. Gaboreau, S., Vieillard, Ph., Patrier, P., Bruneton, P.& Beaufort, D. (2003). Aluminium phosphate sulphate minerals associated with unconformity uranium deposits of the Kombolgie basin (Northern Territory, Australia). In: M. Cuney (Editor), Uranium Geochemistry, International Conference Proceeding, Nancy, pp. 157-160. Gaboreau, S., Beaufort, D., Vieillard, Ph., Patrier, P. and Bruneton, P. (2005). Aluminium phosphate sulfate minerals associated with Proterozoic unconformity type uranium deposits in the East Alligator River Uranium Field, Northern Territories, Australia. The Canadian Mineralogist, 43, pp. 813-827. Gustafson, L.B. and Curtis, L.W. (1983). Post-Kombolgie metasomatism at Jabiluka, Northern Territory, Australia, and its significance in the formation of high-grade Uranium mineralization in Lower Proterozoic rocks. Economic Geology, v.78, p. 26-56. Hecht, L. and Cuney, M. (2000). Hydrothermal alteration of monazite in the Precambrian crystalline basement of the Athabasca basin (Saskatchewan, Canada): implications for the formation of unconformity-related uranium deposits. Mineralium Deposita, 35, pp. 791- 795. Hoeve, J. and Quirt, D. (1984). Mineralization and host rock alteration in relation to clay mineral diagenesis and evolution of the middle-Proterozoic Athabasca basin, northern Saskatchewan, Canada: Research Council Tech. Rep. 187, 187p. Hoeve, J. and Quirt, D. (1987). A stationary redox front as a critical factor in the formation of high-grade, unconformity-type uranium ores in the Athabasca Basin, Saskatchewan, Canada. Bulletin Minéralogique, v. 110, p. 157-171. Hoeve, J. & Sibbald, T.I.I. (1978). On the genesis of Rabbit Lake and other unconformity- type uranium deposits in northern Saskatchewan, Canada. Economic Geology, 73, pp. 1450-1473. Jambor, J.L. (1999). Nomenclature of the alunite supergroup. Canadian Mineralogist, 37, pp. 1323-1341. Kister, Ph., Vieillard, Ph., Cuney, M., Quirt, D. & Laverret, E. (2005). Thermodynamic constraints on the mineralogical and fluid composition evolution in a clastic sedimentary basin: the Athabasca basin (Saskatchewan, Canada). European Journal of Mineralogy, 17, pp. 325-342.

94 Partie I – Ch. 2. APS in the Athabasca basin

Kolitsch, U. & Pring, A. (2001). Crystal chemistry of the crandallite, beudantite and alunite groups: a review and evaluation of the suitability as storage materials for toxic metals. J. Mineral. Petrol. Sci., 96, pp. 67-78. Kotzer, T.G. and Kyser, T.K. (1995). Petrogenesis of the Proterozoic Athabasca Basin, northern Saskatchewan, Canada, and its relation to diagenesis, hydrothermal uranium mineralization and paleohydrology. Chemical Geology, 120, 45-89. Laverret, E., Patrier, P., Beaufort, D., Kister, Ph., Quirt, D., Bruneton, P., and Clauer, N. (2005). Mineralogy and geochemistry of host-rock alterations associated with the Shea Creek unconformity-type uranium deposits (Saskatchewan, Canada). Part 1: spatial variation of illite properties. Clays and Clay minerals, submitted. Lewry, J.F. and Sibbald, T.I.I. (1979). A review of pre-Athabasca basement geology in northern Sasktchewan, 91-99, in: Parslow, G.R. (ed.), Uranium Exploration Techniques, Proceedings of a Symposium in Regina, 1978: Saskatchewan Geological Society, Spec. Pub. 4. Lewry, J.F. and Sibbald, T.I.I. (1980). Thermotectonic evolution of the Churchill Province in northern Saskatchewan: Tectono-physics, 68, 45-82. Lorilleux, G. (2001). Les brèches associées aux gisements d’uranium de type discordance du bassin d’Athabasca (Saskatchewan, Canada). Unpublished Ph. D. thesis, Université Henri Poincaré, Nancy, 319 p. Lorilleux, G., Jebrak, M., Cuney, M. & Baudemont, D. (2002). Polyphase hydrothermal breccias associated with unconformity-type uranium mineralization (Canada): from fractal analysis to structural significance. Journal of Structural Geology, 24(2), pp. 323-338. Lorilleux, G., Cuney, M., Jebrak, M., Rippert, J.C. & Portella, Ph. (2003). Chemical brecciation processes in the Sue unconformity-type uranium deposits, eastern Athabasca basin (Canada). Journal of Geochemical Exploration, 80, pp. 241-258. Macdonald, C. (1980). Mineralogy and geochemistry of a Precambrian regolith in the Athabasca Basin. Unpublished M.Sc. thesis, University of Saskatchewan, Saskatoon, Saskatchewan, 151 p. Macdonald, C. (1985). Mineralogy and Geochemistry of the sub-Athabasca regolith near Wollaston Lake, 155-158, in: Sibbald, T.I.I. and Petruk, W. (eds.), Geology of uranium Deposits: The Canadian institute of Mining and Metallurgy, Spec. Vol. 32. Marlatt, J., McGill, B., Matthews, R., Sopucks, V. And Pollock, G. (1992). The discovery of the McArthur uranium deposit, Saskatchewan, Canada, 118-127, in: New Developments in Uranium Exploration, Resources, I.A.E.A. and the Nuclear Energy Agency of the

95 Partie I – Ch. 2. APS in the Athabasca basin

Organization for Economic cooperation Development, Vienna, 26-29 August, 1991: IAEA-TECDOC-650. McGill, B.D., Marlatt, J.L., Matthews, R.B., Sopuck, V.J. & Homeniuk, L.A. (1993). The P2 North uranium deposit, Saskatchewan, Canada. Exploration and Mining Geology, 2(4), pp. 321-331. Miller, A.R. (1983). A progress report: uranium phosphorus association in the Helikian Thelon Formation and sub-Thelon saprolite, central district of Keewatin. Geological Survey of Canada, Paper 83-1A, p. 449-456. Mordberg, L.E. (2004). Thorium in crandallite-group minerals: An example from a devonian bauxite deposit, Timan, Russia. Russian Research Geological institute (VSEGEI), St Petersburg, Russia. Mineralogical Magazine, 68(3), 489-497. Mwenifumbo, C.J., Elliott, B.E., Drever, G., and Wood, G. (2002). Borehole geophysical logging of two deep surface boreholes and one underground borehole at McArthur River. In: Summary of Investigations 2002, Volume 2, Saskatchewan Geological Survey, Saskatchewan Industry and Resources, Miscellaneous Report 2002-4.2, CD-ROM, Paper D-5, 5p. Pacquet, A. & Weber, F. (1993). Pétrographie et minéralogie des halos d’altération autour du gisement de Cigar Lake et leurs relations avec les minéralisations. Can. J. Earth Sci., 30, pp. 674-688. Pagel, M., Poty, B. And Sheppard, S.M.F. (1980). Contributions to some Saskatchewan uranium deposits mainly from fluid inclusion and isotopic data, 639-654, in: Ferguson, S. and Goleby, A. (eds.), Uranium in the Pine Creek Geosyncline: IAEA, Vienna. Pe-Piper, G. and Dolansky, L.M. (2005). Early diagenetic origin of Al phosphate-sulfate minerals (woodhouseite and crandallite-series) in terrestrial sandstones, Nova Scotia, Canada. American Mineralogist, v. 90, p. 1434-1441. Percival, J. B., Bell, K., & Torrance, J.K. (1993). Clay mineralogy and isotope geochemistry of the alteration halo of the Cigar Lake uranium deposit. Can. J. Earth Sci., 30, pp. 689- 704. Quirt, D.H., 1986. Host-rock alteration in the Spring Point area, northern Saskatchewan. Saskatchewan Research Council, R-855-8-E-86. Quirt, D.H. (1997a). Chloritization below the Dawn Lake uranium deposit (11A Zone), northern Saskatchewan. Geological Association of Canada-Mineralogical Association of Canada joint annual meeting, Abstract volume 22, p. A-122.

96 Partie I – Ch. 2. APS in the Athabasca basin

Quirt, D.H. (1997b). Geochemistry, host-rock alteration, mineralization, and uranium metallogenesis of the Wollaston Eagle project area; In: Thermotectonic and uranium metallogenetic evolution of the Wollaston Eagle project area, Saskatchewan Research Council, Publication Number R-1240-2-C-97, 98 p. Quirt, D.H. (2000). Sub-Athabasca group fanlomerate in the McArthur River-Read Lake area, Saskatchewan, in Proceedings, GeoCanada2000, The Millenium Geoscience Summit, Calgary: Geological Association of Canada-Mineralogical Association of Canada joint annual meeting, abstract 251. Quirt, D.H. (2001). Kaolinite and Dickite in the Athabasca sandstone, Northern Saskatchewan, Canada, Saskatchewan Research Council, 10400-16D01. Quirt, D.H. (2003). Athabasca unconformity-type uranium deposits: one deposit type with many variations. In: M. Cuney (Editor), Uranium Geochemistry, International Conference Proceeding, Nancy, pp. 309-312. Quirt, D., Kotzer, T. & Kyser, T.K. (1991). Tourmaline, phosphate minerals, zircon and pitchblende in the Athabasca group: Maw zone and McArhtur River Areas, Saskatchewan. Saskatchewan Geological Survey, Technical Report, 91-4, pp. 181-191. Rainbird, R., Stern, R.A., Rayner, N., and Jefferson, C.W. (2005). Age, provenance, and regional correlation of the Athabasca Group, Saskatchewan and Alberta constrained by igneous and detrital zircon geochronology. In: EXTECH IV: Geology and EXploration TECHnology of the Proterozoic Athabasca Basin, Saskatchewan and Alberta (Jefferson, C.W. and Delaney, G., eds.), Geological Survey of Canada, Bulletin 588. Ramaekers, P. (1981). Hudsonian and Helikian Basins of the Athabasca Region, Northern Saskatchewan. Edited by F.H.A. Campbell. Proterozoic Basins of Canada. Geological Survey of Canada. Paper 81-10, pp. 219-233. Ramaekers, P. (1990). Geology of the Athabasca Group (Helikian) in Northern Saskatchewan. Saskatchewan Energy and Mines, Report 195, pp.49. Ramaekers, P., Jefferson, C.W., Yeo. G.M., Collier, B., Long, D.G., Catuneanu, O., Bernier, S., Kupsch, B., Post, R., Drever, G., McHardy, S., Jircka, D., Cutts, C., and Wheatley, K. (2005). Revised geological map and stratigraphy of the Athabasca Group, Saskatchewan and Alberta. In: EXTECH IV: Geology and EXploration TECHnology of the Proterozoic Athabasca Basin, Saskatchewan and Alberta (Jefferson, C.W. and Delaney, G., eds.), Geological Survey of Canada, Bulletin 588.

97 Partie I – Ch. 2. APS in the Athabasca basin

Rasmussen, B. (1996). Early-diagenetic REE-phosphate minerals (florencite, gorceixite, crandallite, and xenotime) in marine sandstones: a major sink for oceanic phosphorus. American Journal of Science, 296, 601-632. Ruzicka, V. (1993). Unconformity-type uranium deposits; in Mineral Deposit Modeling, (ed.) R.V. Kirkham, W.D. Sinclair, R.I. Thorpe, and J.M. Duke; Geological Association of Canada, special paper 40, pp. 531-540. Scott, K.M. (1987). Solid solution in, and classification of, gossan-derived members of the alunite-jarosite family, northwest Queensland, Australia. American Mineralogist, 72, pp. 178-187. Sibbald, T.I.I., Quirt, D.H. & Gracie, A.J. (1990). Uranium deposits of the Athabasca basin, Saskatchewan. In “Field Trip 11 Guidebook”, 8th IAGOD Symposium, Ottawa, Ontario, Geological Survey of Canada, Open File 2166, 72p. Sopuck, V., de Carle, A., Wray, E.M., and Cooper, B. (1983). Application of lithogeochemistry to the search for unconformity-type uranium deposits in the Athabasca Basin. In: Uranium exploration in Athabasca Basin, Saskatchewan, Canada (Cameron, E.M., ed.), Geological Survey of Canada, Paper 82-11, p. 191-206. Spötl, C. (1990). Authigenic aluminium phosphate-sulphates in sandstones of the Mitterberg Formation, Northern Calcareous Alps, Austria. Sedimentology, 37, pp. 837-845. Stoffregen, R.E. and Alpers, Ch. N. (1987). Woodhouseite and svanbergite in hydrothermal ore deposits: products of apatite destruction during advanced argilic alteration. Canadian Mineralogist, 25(2), 201-211. Thomas, D.J., Jefferson, C.W., Yeo, G.M., Card, C. and Sopuck, V.J. (2002). The Eastern Athabasca Basin and its uranium deposits. Field Trip Guid, GAC MAC 2002, Saskatoon. Thomas, D.J., Matthews, R.B. & Sopuck, V. (2000). Athabasca basin (Canada) unconformity- type uranium deposits: exploration model, current mine developments and exploration directions. geology and ore deposits: The great basin and beyond, Geological Association of Canada-Mineralogical Association of Canada, pp. 1-23. Vieillard, Ph., Tardy, Y. & Nahon, D. (1979). Stability fields of clays and aluminum phosphates: parageneses in lateritic weathering of argillaceous phosphatic sediments. American mineralogist, 64, pp. 626-634. Wilson, J.A. (1985). Crandallite group minerals in the Helikian Athabasca group in Alberta, Canada. Can. J. Earth Sci., 22, pp. 637-641. Wilson, M.R. and Kyser, T.K. (1987). Stable isotope geochemistry of alteration associated with the Key Lake uranium deposit. Economic Geology, 82, 1450-1557.

98 Partie II – Modélisation thermodynamique ds paragenèses minérales

PARTIE II

Modélisations thermodynamiques des paragenèses minérales APS-argiles autour des gisements d’uranium associés à une discordance protérozoïque

Introduction

Les sulfates phosphates d’aluminium (APS) associés aux paragénèses argileuses dans l’environnement des gisements de type discordance sont étroitement liés aux circulations hydrothermales à l’origine des dépôts d’uranium. Ces minéraux semblent s’être formés lors de l’altération des lithologies riches en P et S (pyrite et monazite) par des fluides acides et oxydants. Leur distribution spatiale et leurs variations de compositions chimiques autour des

99 Partie II – Modélisation thermodynamique ds paragenèses minérales gisements d’uranium nous permettent de les considérer comme des marqueurs potentiels de paléoconditions et des indicateurs de gîtes uranifères. L’approche thermodynamique réalisée pour ce travail de thèse a été entreprise pour tenter d’expliquer ces variations de compositions chimiques des APS associés aux paragenèses argileuses autour des gisements d’uranium de type discordance. Cette partie nous permet d’aborder la discussion autour des problèmes et des questions rattachés à ces gisements d’uranium associés à une discordance protérozoïque: 1) comprendre l’évolution des solutions solides, riches en strontium, phosphate, sulfate vers des solutions solides riches en terres rares et phosphate, en tenant compte du rapport constant S/Sr de cette distribution, qui a été mesuré dans les gisements d’Athabasca et de Kombolgie. 2) Quels sont les paléo-conditions de formation qui ont contrôlé la distribution de ces minéraux secondaires d’altération (argile- APS) contemporains de la formation des dépôts uranifères ?. 3) Comprendre par une approche simple la genèse de ces formations.

La réalisation des modèles thermodynamiques suivants, qui réunissent les données de stabilité des APS, des argiles et des différents minéraux accessoires qui ont réagi, a nécesité l’acquisition d’une base de données sur les grandeurs thermodynamiques (Enthalpies libre de ° ° formation ∆Gf enthalpie de formation ∆Hf , entropie S°, Chaleur spécifique Cp, paramètres de maille a, b, c de ces différents minéraux). Pour la plupart, ces données étaient accessibles via la littérature. Les données sur l’illite (1Mt), la sudoïte et la dravite sont issues des travaux de Kister (2003). Les valeurs thermodynamiques du pôle chlorite-trioctahédrique ont été calculées en utilisant la méthode d’estimation de Vieillard (2002) à partir des compositions chimiques analysées au niveau du bassin de Kombolgie (Beaufort et al., 2005). Concernant les minéraux accessoires de la roche (pyrite, hématite, monazite, feldspath et apatite strontique, …) introduits dans la simulation, ainsi que les minéraux réactant de la roche mère (Quartz, micas, plagioclases, kaolinite…), leurs valeurs étaient déjà incluses dans les base de données des programme de calcul SUPCRT92 (Johnson et al., 1992) et KINDISP (Fritz, 1975; Madé et al.,1994). Tous les minéraux accessoires utilisés sont ceux de la roche qui participent à la formation des APS ou des argiles. Pour exemple l’apatite strontique a été introduite dans la simulation car elle représente une source possible de strontium nécessaire à la formation de la solution solide comprise entre la goyazite et la svanbergite. La pyrite, la monazite sont respectivement les sources en sulfates, phosphates et terres rares.

100 Partie II – Modélisation thermodynamique ds paragenèses minérales

Seules certaines valeurs des alumino-phosphates comme la svanbergite

(SrAl3[PO3O0.5(OH0.5)]2(OH)6 n’étaient pas disponibles dans la littérature. Ce manque de ° données nous a contraint à estimer les valeurs d’enthalpies libre de formation ∆Gf pour les solutions solides d’APS analysées dans l’environnement des gisements d’uranium de type discordance du bassin de Kombolgie et d’Athabasca. Ce calcul s’appuie sur les méthodes de calcul utilisées par Vieillard (2000) sur les minéraux argileux et Vieillard (2002) sur les micas et chlorites. Ce travail a fait l’objet d’une publication (Gaboreau et Vieillard, 2004). Les valeurs d’entropie (S°) et de chaleur spécifique (Cp) ont ensuite été estimées à partir de la méthode de Helgeson et Holland qui s’appuie sur la somme des oxydes qui compose un minéral. Ces valeurs inédites nous ont ainsi permis de compléter la base de données déjà existante sur les alumino-phosphates. Leur application déborde largement du cadre de cette étude sur les gisements d’uranium associés aux discordances protérozoïque.

101

Partie II – Ch. 3. Prediction of Gibbs free energies of formation

Chapitre 3

Prediction of Gibbs free energies of formation of minerals of the

alunite supergroup.

Stéphane GABOREAU1,2 and Philippe VIEILLARD1

Article publié dans ‘Geochimica and Cosmochimica Acta’ (2004), 68-16, 3307-3316

1 HydrASA, Université de Poitiers, CNRS-UMR 6532, 40 avenue du Recteur Pineau, F 86022 Poitiers Cedex, France 2 ERM SARL, Laboratoire-Bureaux, Université de Poitiers, bât de Géologie, 40 Av. du Recteur Pineau. 86022 POITIERS-Cedex, France

103 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

Abstract

A method for the prediction of Gibbs free energies of formation for minerals belonging to the = z+ alunite family is proposed, based on an empirical parameter ∆GO M (c) characterizing the oxygen affinity of the cation Mz+. The Gibbs free energy of formation from constituent oxides is considered as the sum of the products of the molar fraction of an oxygen atom bound to any = z+ two cations, multiplied by the difference of oxygen affinity ∆GO M (c) between any two = z+ consecutive cations. The ∆GO M (c) value, using a weighing scheme involving the electronegativity of a cation in a specific site (12-fold coordination site, octahedral and tetrahedral) is assumed to be constant. It can be calculated by minimizing the difference between experimental Gibbs free energies (determined from solubility measurements) and calculated Gibbs free energies of formation from constituent oxides. Results indicate that this prediction method gives values within 0.5 % of the experimentally measured values. The = z+ relationships between ∆GO M (alunite) corresponding to the electronegativity of a cation in = z+ either dodecahedral sites, octahedral sites or tetrahedral sites and known as ∆GO M (aq) were determined, thereby allowing the prediction of the electronegativity of rare earth metal ions and trivalent ions in dodecahedral sites and highly charged ions in tetrahedral sites. This allows the prediction of Gibbs free energies of formation of any minerals of the alunite supergroup (bearing various ions located in the dodecahedral and tetrahedral sites). Examples are given for hydronium jarosite and hindsalite, and the results appear excellent when compared to experimental values.

Key-words: Gibbs free energies of formation, Svanbergite, Alunite, Chromate analog jarosite, Florencite, Hindsalite, Jarosite, Alunite-like minerals

104 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

Introduction

Experimental methods to determine Gibbs free energies of formation of minerals belonging to the alunite supergroup by calorimetry or solubility measurements are both complex and time consuming.

Minerals of the alunite supergroup (more than 40 species), having variable compositions (Scott, 1987; Jambor, 1999), present even greater difficulties since the Gibbs free energy of formation must be determined for each individual composition. The difficulties in the experimental processes, therefore, limits the availability of free energy data to a few selected minerals species such as jarosite and alunite minerals sensu stricto (Stoffregen et al., 2000), thereby reducing the general applicability of thermodynamics to a relatively small number of alunite supergroup mineral systems.

There are numerous empirical methods to evaluate Gibbs free energies of formation for minerals in general but their presentation would exceed the scope of this introduction. However, at present, there is no empirical method to predict thermodynamic data of minerals belonging to the alunite supergroup. That is why this paper describes an empirical method to predict the Gibbs free energies of these minerals. This method is based on the difference of electronegativity of cations located in two sites having a common oxygen.

This method has been already tested for hydrated clay minerals (Vieillard, 2000) and for micas and chlorites (Vieillard, 2002) and gave acceptable errors of prediction. It has two advantages: first, the technique is simple to implement because the chemical formula and the nature of cations in different sites are known; and secondly, this method allows to predict Gibbs free energies of thallium, bismuth, vanadium and chromium bearing minerals of the alunite supergroup thanks to some linear relationships between calculated and theoretical electronegativities of cations in the involved sites.

105 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

Methodology

The details concerning the prediction method of Gibbs free energies of formation of minerals = z+ have been explained by Vieillard (2000) and are based on parameters ∆GO M (aq) and

Gibbs free energies of formation from constituent oxides, ∆G°f,ox.

= z+ Definitions of parameters ∆GO M (aq) and ∆G°f,ox

= z+ z+ The parameter ∆GO M (aq) characterizes a given cation M and is defined as the difference between the Gibbs free energy of formation of the corresponding oxides [∆G°f MOx(c)] and z+ the Gibbs free energy of formation of the corresponding aqueous cation [∆G°f M (aq)]:

= z+ z+ -1 ∆GO M (aq) = (1/x) [ ∆G°f MOx(c) − ∆G°f M (aq)] (kJ⋅mol )(1) where, z is the charge of the cation Mz+ and x is the number of oxygen atoms combined with one atom of M in the oxide (x = z/2), so the difference in Eq. (1) refers to one oxygen atom. A = z+ set of values of ∆GO M (aq) is proposed here (Tab. 13) and comes mostly from Robie and Hemingway (1995) for oxides and from Shock and Helgeson (1988) for aqueous cations. Vieillard (2000) showed the dependence of a cation with the oxygen affinity by a = z+ relationships between the parameter ∆GO M (aq) with the difference of electronegativity between cation and oxygen.

The second parameter ∆G°f,ox, designating Gibbs free energy of formation of a mineral from constituent oxides, is the difference between the Gibbs free energy of formation of a mineral of the alunite supergroup, ∆G°f (mineral), and the sum of the Gibbs free energies of formation of the different constituent oxides in the alunite-like minerals. It is given by:

i=n s ∆G° = ∆G° (Mineral) − n ∆G° M O (2) f ,ox f ∑()i f ()i x i i=1 where ni is the number of moles of oxides. The Gibbs free energies of formation of oxides are given in Tab. 13.

106 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

Tableau 13. Gibbs free energies of formation of oxides and ions, and calculated parameters = Z+ ∆GO M (aq) of selected cations.

= z+ Oxides ∆G°f Ions ∆G°f ∆GO M (aq) (kJ⋅mol-1) (kJ⋅mol-1) (kJ⋅mol-1) 1 + 1 Ag2O -11.20 Ag 77.11 -165.41 2 + 7 Na2O -376.00 Na -261.88 147.76 2 + 7 K2O -322.10 K -282.46 242.82 3 + 2 (NH4)2O -234.30 NH4 -79.41 -75.47 1 + 1 Tl2O -147.30 Tl -32.40 -82.50 PbO (red) -188.902 Pb2+ -24.202 -164.70 BaO -520.402 Ba2+ -563.807 43.40 SrO -560.702 Sr2+ -555.407 -5.30 CaO -603.102 Ca2+ -552.797 -50.31 2 3+ 7 Fe2O3 -744.40 Fe -16.28 -237.28 2 3+ 7 Al2O3 -1582.30 Al -487.62 -202.36 1 3+ 1 Ga2O3 -998.30 Ga -159.00 -226.77 4 3+ 4 V2O3 -1138.87 V -241.71 -218.48 5 3+ 1 La2O3 -1705.98 La -683.70 -112.86 1 3+ 1 Ce2O3 -1706.20 Ce -672.00 -120.73 5 3+ 1 Pr2O3(hex) -1720.24 Pr -679.10 -120.68 5 3+ 1 Nd2O3(hex) -1721.05 Nd -671.60 -125.95 5 3+ 1 Sm2O3(cub) -1737.38 Sm -666.60 -134.73 5 3+ 1 Eu2O3(cub) -1566.36 Eu -574.10 -139.39 5 3+ 1 Gd2O3(cub) -1739.55 Gd -661.00 -139.18 1 3+ 1 Bi2O3 -493.70 Bi 82.80 -219.77 1 5+ 8 P2O5 -1348.85 P -325.72 3- 1 PO4 -1018.70 1 6+ 9 SO3 -374.21 S -385.58 2- 1 SO4 -744.53 1 5+ 10 As2O5 -782.30 As -228.98 3- 1 AsO4 -648.41 6 6+ 10 CrO3 -504.50 Cr -264.39 2- 1 CrO4 -727.75 2 H2O liq. -237.18

1 Wagman et al. (1982); 2 Robie and Hemingway (1995); 3 Wilcox and Bromley (1963); 4 Naumov et al. (1971); 5 Barin (1985); 6 Ball and Nordstrom (1998); 7 Shock and Helgeson (1988); 8 Tardy and Vieillard (1977); 9 Tardy and Gartner (1977); 10 Gartner (1979)

107 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

Tableau 14. Values of solubility products and Gibbs free energy of formation of minerals (K+, + + + + 2+ 2+ Na , NH4 , Ag , H3O , Pb , Sr ) analog to jarosite. Log K* Log K** ∆G° Mineral f (298K) (298K) (kJ⋅mol-1) Jarosite -29.51 -12.50 -3313.73 Natrojarosite -25.57 -8.56 -3270.66 Ammoniojarosite -26.77 -9.76 -3095.01 Argentojarosite -28.55 -11.55 -2948.71 Hydroniumjarosite -25.68 -8.67 -3246.59 Plumbojarosite -28.43 -11.42 -3037.19 Strontiumjarosite -27.46 -10.45 -3297.24

+ *Mineral solubility product including Fe(OH)2 terms (Kashkai et al., 1975).**Mineral solubility product calculated according to the following reaction:

+ + 3+ 2- AFe3(SO4)2(OH)6 + 6 H → A (aq) + 3 Fe (aq) + 2 SO4 (aq) + 6 H2O(l)

Inventory and selection of ∆G°f of minerals belonging to the alunite supergroup.

The ∆G°f of alunite-like minerals (alunite and natroalunite) recommended by Stoffregen et al.

(2000) are used here. A detailed compilation of ∆G°f of jarosite has been performed by Baron and Palmer (1996a) and the recommended solubility product is logK = −11 giving a ∆G°f = -1 −3309.8 kJ⋅mol . This value is retained because of good concordance of ∆G°f of ions given by Baron and Palmer (1996a) and those given in Tab. 13. Baron and Palmer (1996b) measured the solubility product of a chromate analog to jarosite giving a ∆G°f = −3305.5 kJ⋅mol-1, this value is selected in this study.

Kashkai et al. (1975) provided solubility measurements of different cations bearing jarosites + + + + + 2+ 2+ (K , Na , NH4 , Ag , H3O , Pb and Sr ) that are given in table 14. The Gibbs free energies of formation of minerals analog to jarosite given by Kashkai et al. (1975) are not used here because of differences of Gibbs free energies of formation for ions from Kashkai et al. (1975) and those given in table 13. Thus, the solublility products of the minerals analog to jarosite are calculated according to the following reaction:

108 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

+ + 3+ 2- AFe3(SO4)2(OH)6 + 6 H (aq) → A (aq) + 3 Fe (aq) + 2 SO4 (aq) + 6 H2O(l) using the following equation:

+ + 3+ Fe(OH)2 (aq) + 2H (aq) → Fe (aq) + 2H2O(l); log K = −5.67 (Baes and Mesmer, 1976)

From the calculated solubility products, the free energies of formation of different minerals analog to jarosite are computed using the Gibbs free energies of formation for the ions (Tab. 13) and are given in table 14.

The ∆G°f values of minerals of the crandallite group were reported by Schwab et al. (1989) who determined the equilibrium constants for dissolution reactions at 298K in aqueous solution after equilibration for at least one year. These measurements were reconducted at 333K for the determination of equilibrium constants of REE bearing florencite and minerals of the arseno-crandallite and arseno-florencite series (Schwab et al., 1993). Only ∆G°f of crandallite, goyazite, and plumbogummite are given at 298K, the ∆G°f values for all other minerals are given at 333K. The ∆G°f at 298K and 333K for ions given by Schwab et al. (1993) allow the calculation of equilibrium constants for minerals of the crandallite – arseno- crandallite group (Tab. 15). It appears that the crandallite-like minerals are more stable at 333K than at 298K. Thus solubility products at 298K of minerals of florencite, arseno- crandallite and arseno-florencite series are assumed to be equal to the product of dissociation constants at 333K by a correction factor which is the average of the ratio logK(298K)/logK(333K) = 0.852 for crandallite, goyazite and plumbogummite. From these calculated equilibrium constants, the ∆G°f of minerals of the crandallite are calculated with

∆G°f of ions from table 13 and are given in table 15.

All these selected values are gathered in table 16. Their Gibbs free energies of formation from oxides were calculated from the ∆G°f of oxides (Tab. 13).

109 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

Tableau 15. Values of solubility products and Gibbs free energy of formation of phosphates and arsenates minerals. ∆G° ∆G° ∆G° calc.+ Mineral f LogK* f LogK** LogK*** f (kJ⋅mol-1) (kJ⋅mol-1) (kJ⋅mol-1) T=298K T=298K T=333K T=333K T=298K T=298K Phosphates Crandallite -5604.891 -23.57 -5608.651 -27.53 -23.57 -5610.69 Goyazite -5625.391 -26.13 -5629.151 -29.71 -26.13 -5627.90 Plumbogummite -5122.891 -31.83 -5153.432 -38.79 -31.83 -5129.25 Gorceixite -5632.501 -29.80 -25.40 -5632.11 -5646.312 -31.97 -27.24 -5642.65 Florencite Ce -5737.522 -27.56 -23.49 -5741.10 Florencite La -5737.522 -30.05 -25.61 -5742.53 Arsenates Arseno-crandallite -4851.772 -31.13 -26.53 -4887.01 Arseno-gorceixite -4879.802 -34.07 -29.03 -4912.29 Arseno-goyazite -4871.012 -33.12 -28.23 -4899.29 Phillipsbornite -4333.792 -32.55 -27.74 -4365.31 Arseno-florencite Ce -4976.452 -30.51 -26.00 -5014.88 Arseno-florencite La -4985.652 -34.45 -29.36 -5023.34

1 2 Schwab et al. (1989); Schwab et al. (1993); * Calculated from ∆G°f,298 ions given in Schwab et al. (1993); ** Calculated from ∆G°f,333 ions given in Schwab et al. (1993); *** + Calculated from Log K at 333K with a correction factor (0.852); ∆G°f calculated from Log Kcalc. at 298K and ∆G°f ions given in table 13.

= z+ Relationships between ∆G°f,ox and ∆GO M (aq)

= By plotting calculated Gibbs free energies of formation from oxides, ∆G°f,ox versus ∆GO Mz+(aq) of the cations located in the A site (Fig. 19), several relationships are observed for six different groups of minerals: the jarosite group for which seven different cations occupy the 12 fold coordination A site. In the alunite group, there are three different linear relations depending on the nature of the ions in the tetrahedral site: the alunite series (K and Na), the crandallite, and florencite series (six data), the arseno-crandallite and arseno-florencite series (six data) corresponding to divalent and trivalent cations of the A site. The REE bearing florencite and arseno-florencite significantly depart from the linear relationships with divalent

110 Partie II – Ch. 3. Prediction of Gibbs free energies of formation ions. This is due to the absence of H in the charge compensation between the florencite and crandallite series on the one hand, and between the arseno-florencite and the arseno- crandallite series on the other hand. It appears that within a same family, the greater the = z+ parameter ∆GO M (aq) (more electropositive), the lower the Gibbs free energy of formation from oxides. The electronegativity scale for these cations is K+ > Na+ > Ba2+ > Sr2+ > Ca2+ > + 3+ 3+ 2+ + NH4 > La > Ce > Pb , where K is the most electropositive. This relationships is also true for compounds having the same cations in 12 fold coordination and 4 fold sites (alunite = 3+ = and jarosite series); thus, ∆GO Al (aq) appears to be more electropositive than ∆GO Fe3+(aq).

There is a strong analogy with previous works on phosphates (Tardy and Vieillard, 1977; Vieillard, 1978), sulfates (Tardy and Gartner, 1977; Gartner, 1979), and arsenates (Gartner, 1979). By considering phosphates, sulfates, and arsenates as double oxide compounds, , these previous authors showed an empirical relationships between ∆G° ()Mi n (M j ) O N f,ox i n j

= z+ and ∆GO M (aq) by the following equation:

° = zi + = z j+ ∆G f,ox ()Mi n (M j ) O N = − α N (XiXj)[ ∆GO M(aq)i − ∆GO M j (aq)] (3) i n j where:

- N is the total number of oxygen atoms in the compound and is equal to the sum of the

number of oxygens ni and nj, respectively related to the cations Mi and Mj in each oxide ( M O and M)O i.e.: i xi j x j

N = nixi + njxj (4)

zi + - Xi and Xj are the molar fractions of oxygen atoms respectively related to cations Mi and

zj+ in the individual oxides M O and M O ; Mj i xi j x j

= zi + = z j + = - ∆GO Mi (aq) and ∆GO M j (aq) are, respectively, the ∆GO parameter as calculated

zi + z j + for cations Mi and M j in their aqueous states according to Eq. (1).

- α is an empirical coefficient characterizing a given family of compounds.

111 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

Tableau 16. Chemical composition and selected, calculated and predicted Gibbs free energies of formation at 298K of some minerals of the alunite supergroup.

∆G°f select. ∆G°f,ox calc. ∆G°f pred. Residuals % Mineral Formula (kJ⋅mol-1) (kJ⋅mol-1) (kJ⋅mol-1) (kJ⋅mol-1) Residual Alunite group Alunite1 K Al3 (SO4)2 (OH)6 -4659.30 -664.84 -4659.32 0.02 0.00 1 Natroalunite Na Al3 (SO4)2 (OH)6 -4622.40 -600.99 -4622.17 -0.23 0.00 Plumbogummite group

2 Crandallite Ca Al3 (PO4)2 (OH)5 H2O -5610.69 -455.16 -5612.55 1.86 0.03 2 Gorceixite Ba Al3 (PO4)2 (OH)5 H2O -5642.65 -569.82 -5642.18 -0.47 0.00 2 Goyazite Sr Al3 (PO4)2 (OH)5 H2O -5627.90 -514.77 -5627.84 -0.06 0.00 2 Plumbogummite Pb Al3 (PO4)2 (OH)5 H2O -5129.25 -387.92 -5118.69 -10.56 0.21 3 Philipsbornite Pb Al3 (AsO4)2 (OH)5 H2O -4365.31 -190.53 -4390.30 24.99 0.57 3 Arseno-crandallite Ca Al3 (AsO4)2 (OH)5 H2O -4887.01 -298.03 -4884.16 -2.85 0.06 3 Arseno-gorceixite Ba Al3 (AsO4)2 (OH)5 H2O -4912.29 -406.01 -4913.79 1.50 0.03 3 Arseno-goyazite Sr Al3 (AsO4)2 (OH)5 H2O -4899.29 -352.71 -4899.45 0.16 0.00 Florencite group

3 Florencite La La Al3 (PO4)2 (OH)6 -5742.53 -455.70 -5749.94 7.41 0.13 3 Florencite Ce Ce Al3 (PO4)2 (OH)6 -5741.10 -454.16 -5741.68 0.58 0.01 3 Arseno-florencite La La Al3 (AsO4)2 (OH)6 -5023.34 -303.06 -5021.56 -1.78 0.03 3 Arseno-florencite Ce Ce Al3 (AsO4)2 (OH)6 -5014.88 -294.49 -5013.29 -1.59 0.03 Jarosite group

4 Jarosite K Fe3 (SO4)2 (OH)6 -3309.80 -572.19 -3307.94 -1.86 0.06 5 Natrojarosite Na Fe3 (SO4)2 (OH)6 -3270.66 -506.10 -3270.79 0.13 0.00 5 Ammoniojarosite NH4 Fe3 (SO4)2 (OH)6 -3095.01 -401.30 -3095.01 0.00 0.00 5 Argentojarosite Ag Fe3 (SO4)2 (OH)6 -2948.71 -377.75 -2948.71 0.00 0.00 5 Plumbojarosite Pb0.5 Fe3 (SO4)2 (OH)6 -3037.19 -366.18 -3037.17 -0.02 0.00 5 Strontiumjarosite Sr0.5 Fe3 (SO4)2 (OH)6 -3297.24 -440.33 -3297.24 0.00 0.00 5 Hydroniumjarosite (H3O) Fe3 (SO4)2 (OH)6 -3246.59 -314.26 -3246.59 0.00 0.00 6 Chromate analog jarosite K Fe3 (CrO4)2 (OH)6 -3305.50 -307.31 -3305.50 0.00 0.00 Average = 0.06

1 Stoffregen et al. (2000); 2 Schwab et al. (1989); 3 Schwab et al. (1993); 4 Baron and Palmer (1996a); 5 Kashkai et al. (1975); 6 Baron and Palmer (1996b)

= z j + Thus, for families such as sulfates, phosphates and arsenates, ∆GO M j (aq) and α are

= 6+ -1 respectively evaluated to ∆GO S (aq) = −385.68 kJ⋅mol and αsulfate = 1.332 (Tardy and = 5+ -1 Gartner, 1977; Gartner, 1979); ∆GO P (aq) = −325.72 kJ⋅mol and αphosphate = 1.37 (Tardy

112 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

= 5+ -1 and Vieillard, 1977; Vieillard, 1978); ∆GO As (aq) = -228.984 kJ⋅mol and αarsenate = 1.474 (Gartner, 1979). The Gibbs free energy of formation of minerals, derived from their constituent oxides, appears to be proportional to three parameters: (1) coefficient α, which relates to the nature of the family, (2) the stoichiometric coefficient N (Xi Xj), and (3) the

= zi + = z j+ difference [∆GO M(aq)i - ∆GO M j (aq)]. When two cations have the same oxygen affinity, the Gibbs free energy of formation of a compound from the two oxides must be equal or close to zero. The lowest Gibbs free energies of formation from oxides are obtained for

= zi + = z j + electropositive cations, which show a ∆GO Mi (aq) value very different from ∆GO M j

(aq). Compared to their constituent oxides, the corresponding compounds are the most stable. In minerals of the alunite supergroup, cations are uniformly surrounded by oxygens, whereas oxygens have several different cations as nearest neighbors. In developing empirical models of thermodynamic predictions, it is logical to concentrate on those aspects of bonds between oxygens and different cations and protons in order to explain these different linear relationships in figure 19.

= z+ Figure 19. Relationship between ∆G°f,ox versus ∆GO M (aq) for minerals from different groups of the alunite supergroup.

113 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

= z+ To generalize the technique and to increase its accuracy, a new set of parameters ∆GO M (c) of different cations in the three different sites A (12 fold coordination), B octahedral, and T tetrahedral is proposed and can be obtained from the knowledge of the crystal structure. The = z+ concept of the parameter ∆GO M (c) has been initially proposed to predict enthalpies of formation of different compounds (Vieillard, 1982; Vieillard and Tardy, 1988a). It has been tested on numerous silicates (Vieillard, 1994a and b). Vieillard (2000) proposed a method to predict Gibbs free energies of formation of hydrated clay minerals based on a new electronegativity scale for different ions located in interlayer, octahedral and tetrahedral sites. This method has been successfully applied to micas and chlorites (Vieillard, 2002).

= Relationships between ∆G°f,ox and ∆GO Mz+(c)

The Gibbs free energy of formation from the oxides, ∆G°f,ox defined in Eq.(2), is calculated by the following equation, which is analogous to that for the enthalpy of formation (Vieillard, 1994a):

i=n −1 j=n  s s z +  °   = zi + = j  ∆Gf ,ox = −14 ∑∑XiX j∆G O M (c) − ∆ G O M (c) (5)   i j   i=1 j=i+1 

zi + z j + where Xi and Xj are the molar fractions of oxygen bound to the cations Mi and M j in the individual oxides M O and MO , respectively, in the mineral formula: i xi j x j

X i = ()()1/14 ni xi (6)

X j = ()1/14 (n j x j ) (7)

The total number of oxygen atoms of the compound must be equal to 14: i=ns ∑ni xi =14 (8) i=1

= = z + zi + j The parameters ∆GO Mi (c) and ∆GO M j (c) characterize the electronegativity of

zi + z j + cations Mi and M j , respectively, in a specific site. These terms depend on structural parameters such as shortest bond length, average bond length, and polarizability (Vieillard, 1982, 1994a) and they are assumed to be constant here.

114 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

zi + z j + In Eq. (5), the interaction energy between two cations Mi and M j is defined by the

= zi + = z j + difference ∆GO M(c)i – ∆GO M j (c). This term characterizes short-range and long-range interactions between the different sites. Vieillard and Tardy (1988b, 1989) showed that the = difference between the two ∆GO parameters is positive and can be assumed to be equal:

= zi + = z j + 2 [∆GO M(c) − ∆GO M (c)] = 96.483 (χ − χ ) (9) i j Mi M j

Z+ in which χM designates the Pauling’s electronegativity of the cation M (Pauling, 1960) in the considered crystal structure. When two cations sharing the same oxygen are identical, i.e. the same oxygen affinity, the interaction energy is equal to zero. The greater the difference of oxygen affinity between two cations is, the stronger is the interaction energy.

The development of Eq. (5) can be illustrated by a short description of the crystal structure of minerals belonging to the alunite supergroup. The crystal structures of alunite, jarosite and plumbojarosite were first determined by Hendricks (1937). The crystal structures of numerous minerals in this supergroup have been determined and condensed by Jambor (1999). Most of these studies showed that the minerals have trigonal symmetry, space group R3 m. Even among the exceptions where a monoclinic or triclinic system was established, the basic topology of the structure remains strongly pseudotrigonal regardless of the chemical composition (Jambor, 1999). The basic structure is built from sheets of distorted B octahedra.

Each of these octahedra shares four corners (labelled O3 or OH) with other octahedra (Fig. 20). Thus, large hexagonal and small trigonal rings perpendicular to the c axis are formed.

Each tetrahedron shares three corners (labelled O2) with three B octahedra of a trigonal ring.

The remaining unshared oxygens (labelled O1) point towards one another through a hexagonal hole built by an overlying sheet and in case of divalent cation in A site, they are linked by a hydrogen bond which disappears if the divalent cation is substituted by a trivalent cation.

Taking the example of KAl3(SO4)2(OH)6, four types of sites can be defined as follows: K in the 12-fold coordinated A site, Al in the octahedral B site, S in the tetrahedral T site and a hydrogen in the hydroxyl site (O3 or OH). If we consider this compound as a sum of oxides:

115 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

KAl3(SO4)2(OH)6 → 0.5 K2O + 1.5 Al2O3 + 2 SO3 + 3 H2O

with the molar fraction of oxygen bound to the following oxides K2O, Al2O3, SO3 and H2O being respectively, 0.5/14, 4.5/14, 6/14, and 3/14. The equation for ∆G°f,ox is given in table 17. The equation for the Gibbs free energies of formation from constituent oxides of alunite contains five interaction terms between any two different cations located within and between + 3+ + 6+ + consecutive different sites: K and Al (oxygens O3 and O2), K and S (oxygens O2), K + 3+ 6+ 3+ + and H O3 (oxygens O3), Al and S (oxygens O2), and Al and H O3 (oxygens O2). The + 6+ missing interaction term H O3 and S is justified because there is no common oxygen between these two sites. The principles of Pauling (1960) regarding the predominance of nearest-neighbor interactions (short-range interactions) observed in a crystal structure were applied here and had been successfully applied in silicates (Vieillard 1994a and b), hydrated clay minerals (Vieillard, 2000), and phyllosilicates (Vieillard, 2002). Thus, the presence of a non-bridging oxygen between any two adjacent sites in any mineral implies that long-range interaction energy terms between two sites are not required, and consequently:

= zi + = z j + [ ∆GO M i (c) − ∆GO M j (c)] = 0 (10)

=+ =+6 In this case, [ ∆∆OH (c)− OS (c)] = 0 (11) GO3 GT

In crandallite, whose chemical formula can be expressed as CaAl3(PO4)2(OH)6H or

CaAl3(PO4)2(OH)5H2O or CaAl3[PO3(O1/2(OH)1/2)]2(OH)6 in which Blount (1974) + considered the hydroxyl H O1 bound to the tetrahedra, five sites are defined as follows: Ca in + 12-fold coordinated A site, Al in octahedral B site, P in tetrahedral T site, a hydrogen H O3 of + the hydroxyl site, and another hydrogen H O1 bound to the oxygen of the tetrahedra. If we consider this compound as a sum of oxides:

CaAl3(PO4)2(OH)5H2O → CaO + 1.5 Al2O3 + P2O5 + 3.5 H2O

with the molar fraction of oxygen bound to the following oxides CaO, Al2O3, P2O5, H2O(O3) and H2O(O1) being respectively, 1/14, 4.5/14, 5/14, 3/14 and 0.5/14. The calculated equation of

∆G°f,ox is given in table 18.

116 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

Figure 20. Crystal structure of the minerals belonging to the alunite supergroup viewed perpendicular to the c axis.

The equation for the Gibbs free energies of formation from constituent oxides of crandallite contains six interaction terms between any two different sites. The four missing interaction + 5+ + + +3 + +2 + terms between H O3 and P , H O3 and H O1, Al and H O1, Ca and H O1 do not appear in the general equation of Gibbs free energies of formation from constituent oxides because they are considered as long-range interactions energies due to the absence of common oxygens between each of these two sites. For crandallite, the following four interaction terms are given by:

= + = 5+ = + = + [ ∆GO H (c) − ∆GO PT (c) ] = [ ∆GO H (c) − ∆GO H (c)] = O3 O3 O1

= 3+ = + = 2+ = + [ ∆GO Al (c) − ∆GO H (c) ] = [ ∆GO Ca (c) − ∆GO H (c) ] = 0 (12) O1 O1

117 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

Tableau 17. General equation of Gibbs free energy of formation from the oxides of alunite KAl3(SO4)2(OH)6.

0.5 4.5 0.5 6  ×∆O=+ K (c) −∆ O = Al36 + (c) +×∆ O =+ K (c) −∆ O =+ S (c) +  14 14GG 14 14 GG   0.5 3 4.5 6  ∆=−×∆G° 14 O =+=+ K (c) −∆ O H (c) +×∆ O =+=+ Al36 (c) −∆ O S (c) + f,ox  G G O3 G G   14 14 14 14    4.5 3 =+3 =+  ×∆GGO3OAl(c) −∆ OH (c)   14 14  

Tableau 18. General equation of Gibbs free energy of formation from the oxides of crandallite CaAl3(PO4)2(OH)5H2O.

 14.5 1 5  ×∆O=+ Ca23 (c) −∆ O =+ Al (c) +×∆ O =+ Ca 25 (c) −∆ O =+ P (c) + 14 14GG 14 14 GG    13 4.55  ∆=−×∆G° 14 OCa(c) =+=+235 −∆ OH (c) +×∆ OAl(c) =+=+ −∆ OP (c) + f,ox  G G O3 G G  14 14 14 14    4.5 3=+3 =+ 5 0.5 =+5 =+  ×∆GGO3OAl(c) −∆ OH (c) +×∆GGO1OP (c)−∆ OH (c)   14 14 14 14 

Results

Minimization

+ + + + 2+ 2+ 2+ 2+ 3+ 3+ We considered the following cations Ag , NH4 , Na , K , Pb , Ba , Ca , Sr , La , Ce in the 12 fold coordination, Al3+ and Fe3+ in octahedral sites, S6+, P5+, As5+ and Cr6+ in + = + = + tetrahedral sites. By assuming that ∆G°f H (c) = 0, the parameters ∆GO H O3 , ∆GO H O1 and = + -1 ∆GO H3O are all together equal to -237.18 kJ⋅mol , which represents the reference value for the setting of an electronegativity scale for different cations located in different sites of a = z+ alunite mineral. Using a short-range approach, the parameters ∆GO M (c) of 16 cations characterizing the electronegativity of ions located in different sites were determined by minimizing the difference between calculated Gibbs free energies of formation from oxides and those computed by Eqs.(5) and (9).

118 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

These values obtained by minimization are given in table 19 and contribute to the determination of Gibbs free energy of formation from constituent oxides. Consequently, the determined Gibbs free energies of formation of the alunite minerals may be compared with experimental (or calculated) values (Tab. 16). The average difference between the predicted and the measured values is 0.1% with a maximum value (0.57%) for philipsbornite. This mineral has an abnormal ∆G°f that has already been pointed out by Schwab et al. (1993) which are unable to explain the strange behavior of lead in comparison with the solubility products of Ba, Sr, Ca and Pb bearing crandallite and arseno-crandallite series (Tab. 15).

Discussion

Accuracy of the model.

= z+ = z+ Values ∆GO M (c), obtained from minimization (Tab. 19) are different from ∆GO M (aq) = z+ given in table 13. Among the values for ∆GO M (c) corresponding to different sites in the mineral of the alunite supergroup, three sets of values are observed, corresponding to the interlayer, octahedral, and tetrahedral sites (Fig. 21).

- 12-fold coordination site (11 data) = z+ = z+ ∆GO M (c) = 26.848 + 1.051 [∆GO M (aq)] (13) with a regression coefficient r = 0.9919 and a standard deviation σ = 13.65 kJ⋅mol-1

- Octahedral sites ( 2 data) = z+ = z+ ∆GO M (c) = − 1.9888 + 0.9913 [∆GO M (aq)] (14)

- Tetrahedral sites (4 data) = z+ = z+ ∆GO M (c) = − 46.447 + 0.8698 [∆GO M (aq)] (15) with a regression coefficient r = 0.9674 and a standard deviation σ = 11.02 kJ⋅mol-1

The accuracy of the model was tested by predicting the thermodynamic properties of minerals not used to develop the model. Experimental measurements of equilibrium constants of Pr3+, Nd3+, Gd3+, Sm3+ and Eu3+ bearing florencite and arseno-florencite are available only at 333K (Schwab et al., 1993). By using the same correction factor (logK(298K)/logK(333K) = 0.852) as for crandallite minerals, solubility products are predicted at 298K and Gibbs free energies

119 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

= Z+ Tableau 19. Values of parameter ∆GO M (c) obtained by minimization. = z+ = z+ Ions ∆GO M (c) Ions ∆GO M (c) (kJ⋅mol-1) (kJ⋅mol-1) 12 fold coordination A site 12 fold coordination A site Ag+ -128.71+ Ca2+ -40.29+ Tl+ -59.89* Bi3+ -204.22* Na+ -161.00+ La3+ -97.22+ K+ 293.94+ Ce3+ -103.47+ + + 3+ NH4 -56.63 Pr -100.03* + + 3+ H3O -237.18 Nd -105.58* Pb2+ -129.51+ Sm3+ -114.81* Ba2+ 85.81+ Eu3+ -119.71* Sr2+ 24.32+ Gd3+ -119.49* Tetrahedral T site Octahedral B site P5+ -332.10+ Fe3+ -237.20+ S6+ -383.84+ Al3+ -202.59+ As5+ -256.57+ V3+ -218.57** Cr6+ -261.10+ Ga3+ -226.79**

+ Obtained by minimization. ∗ A site value calculated from Eq.(12). ∗∗ B site values calculated from Eq.(13). of formation for Pr3+, Nd3+, Gd3+, Sm3+ and Eu3+ bearing florencite and arseno-florencite are = z+ calculated with ∆G°f for ions (Tab. 13). The evaluations of ∆GO M (c) for rare earth ions (Pr3+, Nd3+, Gd3+, Sm3+ and Eu3+) given in table 19 contribute to the prediction of Gibbs free energies of formation of some REE bearing florencite and arseno-florencite. Table 20 compares the results of the model with experimental data for 11 different minerals and gives associated differences. Average residuals for these minerals are 0.25% for 11 data.

Prediction of Gibbs free energies of uncommon minerals of the alunite supergroup.

Equations (13), (14), and (15) are useful relationships in order to predict the affinity of = z+ + 3+ 3+ 3+ oxygen, ∆GO M (c) of cations such as Tl and Bi located in the A sites, V and Ga located in octahedral sites. Table 21 introduces the predicted Gibbs free energies of different minerals in their ideal formula of the alunite supergroup for which thermodynamic data are unknown.

120 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

= z+ = z+ Figure 21. Relationship between ∆GO M (c) and ∆GO M (aq) for cations from different sites in the alunite supergroup.

Two minerals hindsalite and hydronium jarosite were chosen in order to describe the protocol for estimating their Gibbs free energy of formation, using the model described above. 5+ 6+ Hindsalite, [PbAl3(PO4, SO4)(OH)6] has two different ions P and S in tetrahedral site. The detail of the expression of the Gibbs free energy of formation from constituent oxides is given in table 22. ∆G°f,ox contains 7 interaction terms corresponding to the difference between oxygen affinity of different ions around a common oxygen. The calculated Gibbs free energy of formation from oxides is -449.44 kJ⋅mol-1. The predicted Gibbs free energy of formation from elements is -4774.9 ± 11.9 kJ⋅mol-1. Our predicted value is not in good agreement with -1 the value ∆G°f = -4672.69 kJ⋅mol reported by Baker (1964). This disparity can be explained by the fact that Baker (1964) did not consider the formation of ion-pairs in his calculation. This precision of calculation, can be improved by considering the formation of ion-pairs in the measurement of solubility data of pyromorphite, Pb5(PO4)3Cl (Nriagu, 1973), which lead to a more negative value than this of Baker (1964). Other data for hindsalite from Nriagu (1974) -1 are ∆G°f = -4759.0 kJ⋅mol , but the origin and nature of this measurement are unknown.

121 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

Tableau 20. Selected and predicted Gibbs free energies of formation of some minerals of the alunite supergroup.

Mineral Formula ∆G°f select. ∆G°f pred. Residuals % (kJ⋅mol-1) (kJ⋅mol-1) (kJ⋅mol-1) Residual 1 Arseno-florencite Pr PrAl3(AsO4)2(OH)6 -5010.92 -5024.91 -13.99 0.28 1 Arseno-florencite Nd NdAl3(AsO4)2(OH)6 -5009.17 -5017.88 -8.71 0.18 1 Arseno-florencite Sm SmAl3(AsO4)2(OH)6 -4994.91 -5013.69 -18.78 0.38

Arseno-florencite Eu EuAl3(AsO4)2(OH)6 -4907.52 -4921.61 -14.09 0.29 1 Florencite Pr PrAl3(PO4)2(OH)6 -5740.01 -5753.31 -13.30 0.23 1 Florencite Nd NdAl3(PO4)2(OH)6 -5744.96 -5734.86 10.10 0.18 1 Florencite Sm SmAl3(PO4)2(OH)6 -5748.90 -5742.09 6.81 0.12 1 Florencite Eu EuAl3(PO4)2(OH)6 -5633.73 -5650.01 -16.28 0.29 1 Florencite Gd GdAl3(PO4)2(OH)6 -5715.84 -5736.90 -21.06 0.37

K0.77Na0.03 Hydronium jarosite -3293.502 -3289.90 3.60 0.11 (H3O)0.20Fe3(SO4)2(OH)6 3 Corkite PbFe3(PO4,SO4)(OH)6 -3421.13 -3431.72 -10.59 0.31 Average = 0.25

1 Schwab et al. (1993); 2 Alpers et al. (1989); 3 Nriagu (1974)

A solid solution of composition K0.77Na0.03(H3O)0.20Fe3(SO4)2(OH)6 was analyzed by Alpers + + + et al. (1989). This mineral exhibits three different ions K , Na and H3O in the alkali site (site A). The Gibbs free energy of formation from constituent oxides contains 11 effective interaction terms and is developped in table 23. The calculated Gibbs free energy of formation from constituent oxides is -512.50 kJ⋅mol-1. By considering the following reaction:

K0.77Na0.03(H3O)0.20Fe3(SO4)2(OH)6 →

0.375 K2O + 0.015 Na2O + 0.1 [(H3O)2O] + 1.5 Fe2O3 +2 SO3 + 3 H2O + ∆G°f,ox

-1 The Gibbs free energies of formation from elements is ∆G°f = -3289.9 ± 8.22 kJ⋅mol . This value is very close to the experimental value of –3293.50 ± 2.1 kJ⋅mol-1 calculated from the experimental solubility product (Alpers et al., 1989).

122 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

Tableau 21. Predicted Gibbs free energies of formation of some minerals of the alunite supergroup.

Mineral Formula ∆G°f pred. (kJ⋅mol-1) Hinsdalite PbAl3(PO4,SO4)(OH)6 -4771.9

Svanbergite SrAl3(PO4,SO4)(OH)6 -5286.6

Beudantite PbFe3(AsO4)2(OH)5H2O -3055.6

Hidalgoite PbAl3(AsO4,SO4)(OH)6 -4414.5

Woodhouseite CaAl3(PO4,SO4)(OH)6 -5269.0

Gallobeudantite PbGa3(AsO4,SO4)(OH)6 -5853.6

Waylandite BiAl3(PO4)2(OH)6 -5002.0

Arseno-waylandite BiAl3(AsO4)2(OH)6 -4273.6

Springcreekite BaV3(PO4)2(OH)5H2O -4941.3

Zairite BiFe3(PO4)2(OH)6 -3671.3

Dorallcharite TlFe3(SO4)2(OH)6 -3049.9

Walthierite Ba0.5Al3(SO4)2(OH)6 -4658.1

Huangite Ca0.5Al3(SO4)2(OH)6 -4638.6

Kintoreite PbFe3(PO4)2(OH)5H2O -3784.0

Benauite SrFe3(PO4)2(OH)5H2O -4293.1

Dussertite BaFe3(AsO4)2(OH)5H2O -3579.3

Segnitite PbFe3(AsO4)2(OH)5H2O -3576.0

Conclusions

= Z+ The model of prediction of Gibbs free energies of formation based on ∆GO M (c), a parameter assumed to be constant within three sites of an alunite mineral, give very good results if the formalism of the Gibbs free energies of formation from constituent oxides uses an approach from short-range interactions. The only data needed for the estimation technique is the chemical composition. The advantages of this model are its simplicity, its widespread application to all minerals of the alunite supergroup thanks to the large diversity of ions and its suitability to any solid solutions.

123 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

Tableau 22. Detailed computation of ∆G°f,ox of hinsdalite. Interaction Nature of interactions [∆ O=M Z+(c) − ∆ O=M Z+(c)] -14 X X G i G j energy2 terms1 i j (kJ⋅mol-1) (kJ⋅mol-1) 2+ 3+ Pb (A) − Al (B) -0.321 73.08 -23.49 2+ 5+ Pb (A) − P (T) -0.179 202.59 -36.18 2+ 6+ Pb (A) − S (T) -0.214 254.33 -54.50 2+ + Pb (A) − H (O3) -0.214 107.67 -23.07 3+ 5+ Al (B) − P (T) -0.804 129.51 -104.07 3+ 6+ Al (B) – S (T) -0.964 181.25 -174.78 3+ + Al (B) – H (O3) -0.964 34.59 -33.35 -1 ∆G°f,ox (kJ.mol ) = -449.44

1 A, B, T denote 12-fold coordination, octahedral and tetraedral sites, respectively. 2 Product = Z+ = Z+ of the two first columns, i.e., equal to –14XiXj[∆GO Mi (c) − ∆GO Mj (c) ].

Tableau 23. Detailed computation of ∆G°f,ox of hydronium jarosite. Interaction [∆ O=M Z+(c) − ∆ O=M Z+(c)] Nature of interactions -14 X X G i G j energy2 i j (kJ⋅mol-1) terms1 (kJ⋅mol-1) + 3+ K (A) − Fe (B) -0.124 531.14 -65.72 + 3+ Na (A) − Fe (B) -0.005 76.20 -0.36 + 3+ H3O (A) − Fe (B) -0.032 0.02 -0.00 + 6+ K (A) − S (T) -0.165 677.78 -111.82 + 6+ Na (A) − S (T) -0.006 222.84 -1.42 + 6+ H3O (A) − S (T) -0.043 146.66 -6.28 3+ 6+ Fe (B) − S (T) -1.928 146.64 -282.81 3+ + Fe (B) − H (O3) -0.964 0.02 -0.02 + + K (A) − H (O3) -0.082 531.12 -43.82 + + Na (A) − H (O3) -0.003 76.18 -0.24 + + H3O (A) − H (O3) -0.021 0.00 -0.00 -1 ∆G°f,ox (kJ⋅mol ) = -512.50

1 A, B, T denote 12-fold coordination, octahedral and tetraedral sites, respectively.2 Product of = Z+ = Z+ the two first columns, i.e., equal to –14XiXj[∆GO Mi (c) − ∆GO Mj (c) ].

124 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

The success of this model based on the difference of oxygen affinity of two cations around a common oxygen has already been demonstrated for smectites (Vieillard, 2000) and in well crystallized phyllosilicates (Vieillard, 2002), and is fully justified in the alunite supergroup. This supports the concept that the properties of minerals belonging to a “cristallographic” family are more determined by nearest-neighbor interactions than by the long-range interactions. In addition, it is likely that this technique could successfully model the thermodynamic properties of some families of minerals such as amphiboles, pyroxenes, garnets, and pyrochlores.

References

Alpers, C. N., Nordstrom, D. K. and Ball, J. W. (1989). Solubility of jarosite solid solutions precipitated from acid mine waters, Iron Mountain, California, U.S.A. Sci.Géol.Bull., 42, 281-298. Baes, C. F. and Mesmer, R. E. (1976). The Hydrolysis of Cations. Wiley-Interscience, New York, N. Y. Baker, W. E. (1964). Mineral equilibrium studies of the pseudomorphism of pyromorphile by hinsdalite. American mineralogist, 49, 607-613. Ball, J. W. and Nordstrom, D. K. (1998). Critical evaluation and selection of standard state thermodynamic properties for chromium metal and its aqueous ions, hydrolysis species, oxides, and hydroxides. J. Chem. Eng. Data, 43, 895-918. Barin, I. (1985). Thermochemical data of pure substances part 1 and 2. Verlagsgesellschaft mbH V.C.H., 1600p. Baron, D. and Palmer, C. D. (1996a). Solubility of jarosite at 4-35°C. Geochimica et Cosmochimica Acta, 60, 185-195.

Baron, D. and Palmer, C. D. (1996b). Solubility of KFe3(CrO4)2(OH)6 at 4 to 35°C. Geochimica et Cosmochimica Acta, 60, 3815-3824. Blount, A. M. (1974). Crystal structure of crandallite. American Mineralogist, 59, 41-47. Gartner, L. (1979). Thesis. Relations entre enthalpies ou enthalpies libres de formation des ions, des oxydes et des composés de formule MmNnOz. Utilisation des fréquences de vibration dans l'infra-rouge, Strasbourg, France. 193 pp. Hendricks, S. B. (1937). The crystal structure of alunite and the jarosites. Am. Mineral., 22, 773-784.

125 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

Jambor, J. L. (1999). Nomenclature of the Alunite Supergroup. The Canadian Mineralogist, 37(6), 1323-1341.

Kashkai, C. M., Borovskaya, Y. B. and Badazade, M. A. (1975). Determination of ∆G°f,298 of synthetic jarosite and its sulfate analogues. Geokhimiya, 7, 771-783(In Russian). Naumov, G. B., Ryzhenko, B. N. and Khodakovsky, I. L. (1971). Handbook of thermodynamic Data. (In Russian) Moscou Atomizdat. , 239. Nriagu, J. O. (1973). Lead Orthophosphates II. Stability of Chloropyromorphite at 25°C. Geochimica and Cosmochimica Acta, 37, 367-377. Nriagu, J. O. (1974). Supergene formation of base metal phosphates. Proceed. Int. Symp. Water-Rock Interaction, Prague, 1974 , Cadek J. & Paces T. Ed., Ustredni Ustav Geologicky, 436-443. Pauling, L. (1960). The Nature of the chemical Bond, 3rd edition. Cornell University Press, New York, 430pp. Robie, R. A. and Hemingway, B. S. (1995). Thermodynamic Properties of Minerals and Related Substances at 298.15 K and 1bar (105 Pascals) Pressure and Higher Temperature. U.S. Geological Survey Bulletin 2131, Washington, D.C., 461 pp, 445-447. Schwab, R. G., Gotz, C., Herold, H. and Oliveira, N. P. (1993). Compounds of the Crandallite Type - Thermodynamic Properties of Ca-Phosphates, Sr-Phosphates, Ba-Phosphates, Pb- Phosphates, La-Phosphates, Ce-Phosphates to Gd-Phosphates and Ca-Arsenates, Sr- Arsenates, Ba-Arsenates, Pb-Arsenates, La-Arsenates, Ce-Arsenate. Neues Jahrb Miner Monatsh, 12, 551-568. Schwab, R. G., Herold H., Costa, M. L. D. and Oliveira, N. P. (1989). The Formation of Aluminous Phosphates through Lateritic Weathering of rocks. Weathering, Vol. 2, 369- 386. Scott, K. M. (1987). Solid solution in, and classification of, gossan-derived members of the alunite-jarosite family, northwest Queensland, Australia. American Mineralogist, 72, 178- 187. Shock, E. L. and Helgeson, H. C. (1988). Calculation of the thermodynamic properties and transport properties of aqueous species and equation of state predictions to 5kb and 1000°C. Geochim. Cosmochim., Acta 52, 2009-2036. Stoffregen, R. E., Alpers, C. N. and Jambor, J. L. (2000). Alunite-jarosite Crystallography, Thermodynamics, and Geochronology. Reviews in mineralogy & geochemistry 40 (sulfate minerals), 453-479.

126 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

Tardy, Y. and Gartner, L. (1977). Relationships among Gibbs energies of formation of sulfates, nitrates, carbonates, oxides and aqueous ions. Contributions to Mineralogy and Petrology, 63, 89-102. Tardy, Y. and Vieillard, P. (1977). Relationships among Gibbs free energies and enthalpies of formation of phosphates, oxides and aqueous ions. Contributions to Mineralogy and Petrology, 63, 75-88. Vieillard, P. (1978). Géochimie des phosphates. Etude thermodynamique, application à la genèse et à l'altération des apatites. Sciences Géologiques, Mémoire 51, 181pp. Vieillard, P. (1982). Modèle de calcul des énergies de formation des minéraux bâti sur la connaissance affinée des structures cristallines. Sciences Géologiques, Mémoire 69, 206pp. Vieillard, P. (1994a). Prediction of enthalpy of formation based on refined crystal structures of multisite compounds. 1. theories and examples. Geochimica et Cosmochimica Acta, 58, 4049-4063. Vieillard, P. (1994b). Prediction of enthalpy of formation based on refined crystal structures

of multisite compounds. 2. Application to minerals belonging to the system Li2O-Na2O-

K2O-BeO-MgO-CaO-MnO-FeO-Fe2O3-Al2O3-SiO2-H2O. Results and discussion. Geochimica et Cosmochimica Acta, 58, 4064-4107. Vieillard, P. (2000). A new method for the prediction of Gibbs free energies of formation of hydrated clay minerals based on the electronegativity scale. Clays Clay Miner., 48 , N°.4, 459-473. Vieillard, P. (2002). A new method for the prediction of Gibbs free energies of formation of phyllosilicates based on the electronegativity scale. Clays and Clay Minerals, 50, 352-363. Vieillard, P. and Tardy, Y. (1988a). Estimation of enthalpies of formation of minerals based on their refined crystal structures. American Journal of Science, 288, 997-1040. Vieillard, P. and Tardy, Y. (1988b). Une nouvelle échelle d'électronégativité des ions dans les cristaux. Comptes Rendus de l'Académie des Sciences. Principe et méthode de calcul. 306, 423-428. Vieillard, P. and Tardy, Y. (1989). A new scale of the electronegativity of ions in oxides and hydroxides. Comptes Rendus de l'Academie des Sciences, Serie II : Mecanique, Physique, Chimie, Sciences de la Terre et de l'Univers, 308, 1539-45. Wagman, D. D., Evans, W. H., Parker, V. B., Schumm, R. H., Halow, I., Bailey, S. M., Churney, K. L., and Nuttall, R. L. (1982). The NBS tables of chemical thermodynamic

127 Partie II – Ch. 3. Prediction of Gibbs free energies of formation

properties:selected values for inorganic and C1 and C2 organic substances in SI units. J. Phys. Chem., 11, Supplement N°2, 392. Wilcox, D. E. and Bromley, L. A. (1963). Computer estimation of heat and free energy of formation for simple inorganic compounds. Ind. Eng. Chem., 55, 7, 32-39.

128 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Chapitre 4

Geochemical modeling of the formation of the alteration zoning

associated with the unconformity-type uranium deposits.

Stéphane GABOREAU1,2, Philippe VIEILLARD1, daniel BEAUFORT1, Patricia PATRIER1 and Philippe KISTER3

Article destiné à ‘Geochimica and Cosmochimica Acta’

1 HydrASA, Université de Poitiers, CNRS-UMR 6532, 40 avenue du Recteur Pineau, F 86022 Poitiers Cedex, France 2 ERM SARL, Laboratoire-Bureaux, Université de Poitiers, bât de Géologie, 40 Av. du Recteur Pineau. 86022 POITIERS-Cedex, France 3 COGEMA-BUM-DEX, 2 rue Paul Dautier, BP 4, F 78141 Vélizy Cedex, France

129 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Abstract

In the last twenty years, several theories have been proposed for the formation of unconformity-type deposits but both the origin and the genesis of these ore formations is still debated in literature. Several attempts were made to model quantitatively the formation of unconformity-type uranium deposits in order to improve our knowledge of these geochemical systems and to better evaluate their conditions of formation. Recently, several petrologic studies of alteration associated with unconformity-type uranium deposits of Northern Territory, Australia and Saskatchewan, Canada and the crystal-chemical investigation on secondary mineral phases revisited paragenetic sequences of alteration and provided new data on the nature, the spatial distribution and the interpretation of the different mineral assemblages involved in the alteration zoning. Beyond of a better understanding of the phase relationships between the clay minerals in each alteration zone, several of these studies demonstrated that aluminum phosphate sulfates (APS) belong to almost all the paragenetic sequences of alteration and hence it was suggested that these minerals can be used to better constrain the conditions of formation of unconformity-type uranium deposits. Thermodynamic calculations on the stability of these APS minerals were used to interpret their chemical variations as a change in redox and pH conditions of the hydrothermal fluids with increasing distance from the ore. Undependantly of the nature of the host litholgies, alteration zoning presents the same type of spatial organization around the redox fronts (materialized by the uranium orebodies) and each type of alteration paragenesis distinguished in this study have been reported in both regions. The thermodynamic calculations developped in this study led us to interpret the aforementioned paragenetic differences as a result of distinct fO2 and pH conditions within the alteration systems and hence to invoke differences of composition between the ore bearing fluids in both regions. Precipitation of lower grade uranium deposits of the Alligator River region took place at higher pH and more reducing conditions than those at which were deposited the high-grade uranium deposits of the Athabasca region.

Key-words: thermodynamic modeling, APS minerals, florencite, svanbergite, clay minerals, redox, pH, EARUF, Athabasca basin, uranium.

130 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Introduction

Unconformity-type uranium deposits have been a major exploration target in the last three decades. Unknown before 1968, these deposits satisfy presently more than 40% of the uranium world production and, according to the Atomic Energy Association, they constitut high-grade uranium world reserves estimated to about 470000t in 2003. These deposits are spatially related to an unconformity between the Early Proterozoic basement and the overlying Middle Proterozoic sandstone and their disposition is controlled by a network of faults and fractures which affected both the basement and the overlying Middle Proterozoic sandstone. Ore is located within the basement rocks and/or the overlying sandstone close to the unconformity (Hoeve and Quirt, 1984; Ruzika, 1993; Kotzer and Kyser, 1995; Fayek and Kyser, 1997; Lorilleux, 2001; Derome, 2002; Quirt, 2003). In the last twenty years, several theories have been proposed for the formation of unconformity-type deposits but both the origin and the genesis of these ore formations is still debated in literature. The most commonly accepted genetic model, termed diagenetic-hydrothermal, requires structurally controlled hydrothermal processes which consist in mixing of fluids with different physico- chemical conditions: very saline and oxidizing diagenetic brines from Middle Proterozoic sedimentary basins and basement-derived reduced fluids (Fayek and Kyser,1993; Hoeve and Sibbald, 1978; Kotzer and Kyser, 1990). Some authors considered diagenetic brines as the single fluid involved in the hydrothermal processes which controlled the formation of ore and its associated spatial zonation pattern of alteration (Komninou and Sverjensky, 1996; Derome et al. 2003a and 2003c; Beaufort et al., 2005). According to these authors, the expulsed reducing fluids involved in the hydrothermal process could be derived from a long period of interaction between the infiltrated diagenetic fluids and the primary minerals of the basement rocks.

Several attempts were made to model quantitatively the formation of unconformity-type uranium deposits in order to improve our knowledge of these geochemical systems and to better evaluate their conditions of formation. Several geochemical models have been proposed in the last ten years. Some of them considered mostly ground water flow and heat transport within the sandstone cover (Raffensperger & Garven, 1995a and b) whereas others addressed the chemical aspects of hydrothermal alteration (Iida, 1993; Komninou & Sverjensky 1996). Komninou & Sverjensky (1996) have combined the paragenetic sequence of alteration

131 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning associated with uranium mineralization in unconformity-type uranium deposits with data of fluid inclusion studies to develop a model which permit to satisfactorily reconstruct the mineralogical reactions associated with the formation of these deposits. Their chemical mass transfer calculations suggest that Fe present in the aluminosilicates of the host rocks is the principal reductant agent of oxidized uranium present in the ore forming fluids and indicate that the observed paragenesis is a function of the fluid chemistry and the host-rock lithologies. Recently, several petrologic studies of alteration associated with unconformity-type uranium deposits of Northern Territory, Australia and Saskatchewan, Canada and the crystal-chemical investigation on secondary mineral phases revisited paragenetic sequences of alteration and provided new data on the nature, the spatial distribution and the interpretation of the different mineral assemblages involved in the alteration zoning (Patrier et al., 2003; Laverret et al, 2005, Beaufort et al. 2005; Polito et al., 2004; Gaboreau et al., 2005 and in prep.) Beyond of a better understanding of the phase relationships between the clay minerals in each alteration zone, several of these studies demonstrated that aluminum phosphate sulfates (APS) belong to almost all the paragenetic sequences of alteration and hence it was suggested that these minerals can be used to better constrain the conditions of formation of unconformity-type uranium deposits (Laverret, 2002, Beaufort et al, 2005, Gaboreau, 2005 and in prep.). Indeed APS minerals are well known to incorporate a great number of chemical elements in their crystal lattice and to form complex solid solution series which are controlled by the physico- chemical conditions of their formation (Eh, pH, elements activities). APS minerals have been reported in most of the prospected unconformity-type uranium deposits in both the Northern Territory, Australia and Saskatchewan, Canada (Beaufort et al., 2005; Kister et al., 2005; Laverret et al., 2005; Hecht and Cuney, 2000; Quirt et al., 1991). Gaboreau et al., 2005, and in prep. demonstrated that in several unconformity-type uranium deposits, the chemical compositions of APS minerals form solid solution between florencite (REEAl3(PO4)2OH6), and svanbergite (SrAl3[PO4,SO4]OH6) end members whose relative proportions change with the distance from the U ore-bodies: APS minerals from distal zone of alteration are rich in svanbergite solid solution and the general trend of chemical composition is an increase of the florencite end member at the expense of the svanbergite end member with decreasing distance between APS crystals and U ore-bodies.

Thermodynamic calculations on the stability of these APS minerals were used to interpret their chemical variations as a change in redox and pH conditions of the hydrothermal fluids with increasing distance from the ore.

132 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

The aim of the present study is to revisit the geochemical modeling of the formation of the unconformity-type uranium deposits proposed ten years ago (Komninou and Sverjensky, 1996) at the light of the paragenetic detail of the alteration processes collected in the last decade. This will enable us to improve our knowledge on the paleoconditions (pH, Eh, Log fO2) which prevailed during the formation of coexisting APS and clay minerals within each zone of the alteration pattern related to ore deposition and hence will permit a more comprehensive understanding of the geochemical controls on the alteration processes in both the sandstone and basement rocks included in the alteration system.

In the first part of the paper, we define the investigated geochemical system and examine the constraints imposed by the paragenetic sequences of mineral assemblages including both phyllosilicates and APS minerals. In a second part, reaction path modeling has been undertaken in order to simulate the alteration zones identified in the aforementioned previous papers as a result of two evolutionary stages in the history of the host-rock alteration. In all runs we simulate the mineralogical detail of the alteration assemblages and the crystal- chemistry of the APS minerals and chlorite included in the different alteration assemblages.

Alteration patterns in unconformity-type deposits

A huge amount of data is available on Proterozoic unconformity-type uranium deposits of both the Athabasca (Saskatchewan, Canada) and Alligator River (Northern Territory, Australia) regions. Most of them indicate that, despite of major differences concerning both the position relative to the unconformity and the shape of the U orebodies, the nature of the basement rocks (graphitic or non graphitic metasediments) and the average ore grade, the unconformity-type deposits have common characteristics of alteration. This suggests that ore- forming fluids had common chemical compositions and alteration processes (Iida, 1993; Plant et al., 1999 among others). This finally consists in alteration zoning dominated by clay minerals paragenetic sequence progressively formed as very saline fluid migrating through sandstones invaded into the metasedimentary or igneous rocks of the underlying basement and reacted with the rock-forming minerals of the host-rocks (Iida, 1993; Komninou and Sverjensky, 1996; Beaufort et al., 2005). In such an alteration process, it is considered that the zone boundaries of the alteration pattern slowly shifted toward down-flow side as reactions progressed (Fig. 22).

133 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Figure 22. Schematic spatial distribution of the different alteration assemblages in unconformity-type uranium deposits

During the last decade, several studies improved our knowledge of the nature and the distribution of paragenetic sequences of alteration related to the unconformity-type uranium deposits. They confirm the common alteration zoning and provide more details on the time- space development of the alteration features and phase relations in the different mineral assemblages.

Figure 23 summarizes the mineralogical and crystal-chemical data that have been compiled from the numerous studies related to alteration associated with unconformity-type deposits in both the Athabasca and Alligator River regions (Beaufort et al., 2005; Patrier et al., 2003; Polito et al., 2004a and b; Hoeve and Sibbald, 1978; Hoeve and Quirt, 1984; Drits et al., 1993; Quirt, 2003; Kotzer and Kyser, 1995; Laverret et al., 2005; Kister et al., 2005; Gaboreau et al., 2005; among others) and more specifically from the recent studies performed in the western part of the Athabasca basin in the Shea Creek exploration district (Kister et al.,

134 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

2005; Gaboreau et al., 2005 and in prep.) and in most of the deposits and explored prospects of the Alligator River regions (Patrier et al, 2003; Polito et al, 2004 a and b; Wilde, 2004; Gaboreau 2005; Beaufort et al., 2005).

Figure 23. Vertical distribution of alteration assemblages in U unconformity deposits.

In the unconformity-type uranium deposits, the ore-related alteration developed on both sides of the Proterozoic unconformity. In the overlying basin, it affected sandstone having previously suffered prograde diagenetic re-equilibration (Patrier et al., 2003). They are characterized by a more or less intense illitization of earlier minerals of the kaolin groups (dickite and kaolinite). Diagenetic illites are characterized by coarse grained textures and 1Mc or 2M1 polytypes (Laverret, 2002; Patrier et al., 2003; Beaufort et al., 2005; Kister et al., 2005). In the underlying basement crystalline rocks alteration developed in host-rocks previously affected by a retrograd metamorphism characterized by biotite and garnet chloritisation and feldspar sericitization (Pagel and Swab 1985, Laverret, 2002; Card, 2002, Beaufort et al., 2005).

135 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Figure 24. Projection in S-Sr-LREE coordinates of the microprobe analyses of APS minerals from the Kombolgie and Athabasca basins.

136 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Recent studies indicate that aluminum phosphate sulfate minerals which have been reported in many unconformity-type U deposits are cogenetic with the clay paragenesis and belong to the mineralogical assemblage which composes the alteration zones (Gaboreau et al., 2005, and in prep., Beaufort et al., 2005). The time space alteration sequence established in unconformity- type U deposits of both the Athabasca (Laverret, 2002; Kister et al., 2005; Laverret et al., 2005) and Alligator River regions (Beaufort et al., 2005) are quite similar (Fig. 23). The time- space alteration sequence established in this study can be summarized as follows: (1) early crystallization of illite ± illite-smectite (I-S) mixed layer minerals + LREE-Sr-bearing aluminum phosphate-sulfates (APS) in sandstones above the unconformity, illite ± I-S mixed layer minerals + sudoite + APS on both sides of the unconformity and in fault gouges, and illite ± I-S mixed layer minerals + trioctahedral chlorite ± sudoite ± apatite ± APS deeper in the basement; (2) late precipitation of chlorite in the open fracture network intersecting basement and sandstone host-rocks.

In all these mineral assemblages, the hydrothermal illite can be distinguished from the diagenetic and metamorphic illite-phengite by its poor crystallinity along the c-axis, interstratification with minor amounts of smectite layers, and a 1M polytype in which trans- vacant octahedral sites predominate (1Mt).

Detailed recent studies (Gaboreau et al., 2005 and Gaboreau et al., in prep.) report the presence aluminium phosphate sulfate (APS) minerals associated in all the different sequences of alteration and demonstrated on the basis of petrographic and geochemical data that these very fine grained minerals which can be often overlook in the petrographic studies are strongly linked to the alteration of monazite (a common accessory mineral in this type of deposits) by the solutions derived from the very saline acidic diagenetic fluids.

The chemistry of APS analyzed in both the altered sandstone and basement rocks of the unconformity-type U deposits of both the Athabasca and Alligator River regions can be interpreted as a solid solution series between the goyazite (SrAl3·[PO3(O0.5(OH)0.5)]2(OH)6), florencite (LREEAl3(PO4)2(OH)6), svanbergite (SrAl3(PO4,SO4)(OH)6) and woodhouseite

(CaAl3(PO4,SO4)(OH)6) end members. APS exhibit a wide range of compositional variation which mostly consists in a change of the relative proportion of svanbergite and florencite proportion in solid solutions (Fig. 24). In all the studied U-deposits, increasing amount of

137 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning florencite in the solid solutions coincides with decreasing distance from the uranium ore bodies and also with change in the nature of the cogenetic clay mineral assemblages.

Tableau 24. Average structural formulae of the three main populations of APS used in this work. Phase Structural formulae

APS1 Sr0.74Ca0.26[(PO3⋅(O0.71(OH)0.29))1.41(SO4)0.59](OH)6

APS2 Sr0.20Ca0.17Ce0.63[(PO3⋅(O0.86(OH)0.14))1.89(SO4)0.11](OH)6

APS3 Sr0.12Ca0.13Ce0.75[(PO3⋅(O0.89(OH)0.11))1.96(SO4)0.04](OH)6

On the basis of the above petrologic considerations, three main population of APS crystals were distinguished in the unconformity-type U deposits of both the Athabasca and Alligator River regions. Their respective average chemical compositions are given in table 24. The APS associated with illite in the sandstones of the distal alteration zones have a composition mostly dominated by the svanbergite end-member (APS1) whereas those which occurred in the basement rocks close to the ore-bodies in association with trioctahedral chlorite and apatite (proximal alteration zone) are dominated by the florencite endmember (APS3).

Intermediate composition between APS1 and APS3 were measured in the APS minerals associated with mixture of illite and sudoite in altered sandstone and basement rocks at intermediate distance of the U ore-bodies (APS2) and in APS minerals associated with sudoite ± trioctahedral chlorite close to the U ore-bodies trapped in the sandstone (only observed in the unconformity-type U deposits of Athabasca).

From the compilation of the alteration data, it results that the major difference concerning the alteration assemblages associated with the unconformity-type uranium deposits of both the Athabasca and Alligator River regions consists in a coupled variation of (1) the relative proportion of the different types of chlorite involved in the alteration assemblages and (2) the chemical composition of the cogenetic APS minerals crystallized near the U ore-bodies. Indeed, in the alteration zone proximal to the basement hosted U ore-bodies of the East Alligator River Uranium Field, trioctahedral chlorite largely predominates over sudoite and coexists with secondary apatite and APS with composition close to the florencite end member. In the alteration zone proximal to the U ore-bodies of Athabasca, hosted close to the unconformity or within the overlying sandstone, sudoite largely predominates over

138 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning trioctahedral chlorite and coexists with illite and APS minerals ± secondary apatite with composition in which the florencite end-member is significantly lower than in the previous case.

From a general point of view, compared to those obtained in Athabasca, the chemical composition of the APS minerals involved in the alteration zoning around the U ore-bodies in East Alligator River Uranium Field are significantly shifted toward the florencite end member (Fig. 24).

Conceptual approach and computer program

The thermodynamic models proposed in this study work in the way that alteration zoning took place in response to the structurally-controlled infiltration of basement rocks by very saline oxidizing and acidic fluids (Komninou and Sverjensky, 1996; Beaufort et al., 2005).

To simulate the spatial distribution of the different clay minerals-APS assemblages and to evaluate their conditions of formation in term of pH and oxygen fugacity, two sets of calculations have been performed. In the first one, hereafter named early alteration processes, the formation of the illite-APS1 assemblage by interaction of Na-Ca-Cl diagenetic brines with the rock forming minerals of the deeply buried sandstones has been modeled. The composition of the fluid APS1 has been calculated at saturation with coexisting illite and. In the second set of calculation hereafter named synore alteration process, we have simulated the interaction of the basin derived fluid at saturation with the illite-APS1 assemblage with the rocks forming minerals of the two major host-rocks lithologies of the metamorphic basement in order to determine the conditions at which occured successively the illite + sudoite + APS2 and the trioctahedral chlorite + apatite + APS3 assemblages observed close to the U-orebodies in the unconformity-type deposits of both the Athabasca and Alligator River regions.

The thermodynamic study on the stability domains of the APS minerals solid solution series and the associated clay minerals has been performed with the kinetic and thermodynamic geochemical model KINDISP software (Fritz, 1975; Fritz, 1981; Made et al., 1994) which describes the interactions between minerals and aqueous solutions, taking into account the irreversible dissolution of the reactants and the reversible precipitation of secondary products.

139 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Kinetic processes, which may be important in defining the molar fraction of reactant minerals, are not taken into account in the KINDISP software.

Such models provide a quantitative understanding of complex, multicomponent speciation in the aqueous phase, as well as precipitation dissolution equilibria for a wide variety of solid phases involved in the formation of ore deposits (Brimhall, 1979; Brimhall and Ghiorso, 1983; Reed, 1983; Sverjensky,1984, 1987). The large thermodynamic databases incorporated in the computer codes can lead to the most realistic reconstruction of the reactions taking place during rock alteration and ore formation. The use of solid solutions permits the direct comparison of the predicted mineral compositions with the analyzed compositions of these minerals and to test hypotheses for several important characteristic features of the unconformity-type uranium deposits (Komninou and Sverjensky, 1996).

Constraints on the intensive variables of the alteration system

The chemical composition of the initial Na-Ca-Cl diagenetic brines involved in the early alteration process is given table 25. The composition of these very saline fluids interacting with the sandstone has been assigned in agreement with the fluid inclusions data of Derome et al. (2002; 2003a, b and c) and the values already estimated by Komninou and Sverjensky (1996) for the geochemical modeling of the formation of an unconformity-type uranium deposit. All these data agree with the saline brines dominated by Na analyzed in the diagenetic quartz overgrowth in both the Kombolgie and Athabasca basins. In absence of any values for concentrations of Sr, Ce an B the literature, we have fixed default values of 10-9 mol/kgw have been introduced in the model for all of them. The choice of such low values is assumed by the fact that these three elements have been only detected near the lower level of detection in the fluid inclusions (Kister et al., 2005; McCready et al., 2005).

In all deposits, in the high-grade ore zones, intense alteration of the host rocks has commonly destroyed the original mineralogy and thus made the identification of the original host rock problematic (Komninou and Sverjensky, 1996).

140 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Tableau 25. Chemical composition of the initial fluid (200°C, 600 bars). Initial fluid mol/kgw Al 1.2·10-07a K2.0·10-04a Na 3.7·10-02b Sr 1.0·10-09c Fe 3.0·10-06 (hematite saturation) Ca 0.5·10-02b Mg 1.8·10-03a Si 4.0·10-04a P1.9·10-08a C7.9·10-04a S2.0·10-05 (pyrite saturation) Cl 4.7·10-02b Ce 1.0·10-09c B1.0·10-09c Log f c O2 -35 pH 3c Sources :

a Komninou & Sverjensky (1996); b Fluid inclusions studies from Derome et al. (2003a and b); c value by default

Two major host-rock lithologies have been observed in each Archean to Paleo-Proterozoic metamorphic basement rocks: quartz-mica schist and felsic gneiss. Both are very common in the basements lithologies of the Athabasca and Alligator River regions. The modal composition of aforementioned lithologies (Tab. 26 and 27) have been used in our simulation. The P-T conditions of formation of unconformity-type uranium deposits have been addressed in many papers. Most of them seem to agree on the fact that ore deposition took place in nearly constant thermal conditions approximated to about 200°C in both the Athabasca and the Alligator River regions by many authors (Hoeve and Sibbald, 1978; Pagel et al., 1980; Kotzer and Kyser, 1990; Fayek and Kyser, 1993; Kotzer and Kyser, 1995; Komninou and Sverjensky, 1996; Derome et al., 2003a). The pressure conditions are more difficult to determine and their values are still debated in the literature. Some authors considered lithostatic pressure (Pagel, 1975), whereas others suggested hydrostatic pressure in the vicinity of fault zone (Kotzer & Kyser, 1995). More recently Derome et al. (2003a and b) suggested that pressure regime fall down from lithostatic to infralithostatic conditions during the alteration and ore deposition processes. In the present study, the conditions of pressure have been arbitrarily fixed at 600 bars.

141 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Tableau 26. Molar composition of a quartz mica schist in the synore alteration process Mineral Structural formulae Amounts (%)

Quartz SiO2 54.000

Muscovite KSi3Al3O10(OH)2 11.000

Biotite KSi3AlFe3O10(OH)2 8.000

Anorthite CaAl2Si2O8 15.000

Albite NaAlSi3O8 10.000

Pyrite FeS2 1.000

Hematite Fe2O3 1.000

Monazite CePO4 0.100

Dravite (Mg2Al)Al6(BO3)3Si6O18(OH)4 0.100

Tableau 27. Molar composition of a felsic gneiss in the synore alteration process Mineral Structural formulae Amounts (%)

Quartz SiO2 31.000

K-feldspar KAlSi3O8 10.000

Biotite KSi3AlFe3O10(OH)2 34.000

Anorthite CaAl2Si2O8 10.000

Albite NaAlSi3O8 7.000

Pyrite FeS2 1.000

Hematite Fe2O3 1.000

Monazite CePO4 0.100

Dravite (Mg2Al)Al6(BO3)3Si6O18(OH)4 0.100

Thermodynamic data

Aqueous and minerals data

− + + 2+ 2+ 2+ Standard thermodynamic data of the aqueous species ( Al(OH)4 , K , Na , Ca , Mg , Fe ,

3+ 3− 2− Fe , B(OH)3, PO4 , H4SiO4, SO4 ), quartz, biotite, muscovite, K-feldspar, kaolinite, albite, anorthite and the different accessories minerals, used in the models, were taken from the database included within the SUPCRT92 computer code package (Johnson et al., 1992), except for the aqueous species of Ce, Sr and P which were taken from from Haas et al. (1995), Wagman et al. (1982) and Vieillard and Tardy (1984) (Tab. 28). The database has

142 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning been completed with Sr-feldspar and Sr-apatite whose data were taken in Chernyshova et al. (1991) and Khattech and Jemal (1997), respectively.

Tableau 28. Ce, Sr, P aqueous species, equations of dissociation and dissociation constants used in KINDISP. Log K Log K Aq. species Reactions 25°C 200°C 1 bar 600 bars 2+ a 2+ + 3+ Ce(OH) Ce(OH) + H ⇄ Ce + H2O 3.134 3.357 + a + 3+ - Ce(OH)2 Ce(OH)2 ⇄ Ce + 2(OH) 7.456 7.738 a + 3+ Ce(OH)3 Ce(OH)3 + 3 H ⇄ Ce + 3H2O 13.339 13.623 − a − 3+ - Ce(OH)4 Ce(OH)4 ⇄ Ce + 4(OH) 21.853 22.056 2+ b 2+ 3+ - CeCl CeCl ⇄ Ce + Cl 12.644 12.759 + a + 3+ - CeCl2 CeCl2 ⇄ Ce + 2Cl -2.972 -2.652 CeCl b 3+ - -2.117 -1.617 3 CeCl3 ⇄ Ce + 3Cl − a − 3+ - CeCl4 CeCl4 ⇄ Ce + 4Cl 0.275 0.842 + a + 3+ 2− CeCO3 CeCO3 ⇄ Ce + CO3 -7.227 -6.836 2+ a 2+ 3+ + 2− CeHCO3 CeHCO3 ⇄ Ce + H + CO3 -14.264 -13.799 + b + 3+ 2− CeSO4 CeSO4 ⇄ Ce + SO4 -5.746 -5.377 2+ c 2+ 3+ + 3− CeH2PO4 CeH2PO4 ⇄ Ce + 2 H + PO4 -23.274 -22.481 +b + 2+ - Sr(OH) Sr(OH) ⇄ Sr + (OH) -1.050 0.210 b 2+ 2− SrCO3 SrCO3 ⇄ Sr + CO3 -6.020 -4.806 b 2+ 2− SrSO4 SrSO4 ⇄ Sr + SO4 -2.770 -1.005 + a + 2+ + 2− SrHCO3 SrHCO3 ⇄ Sr + H + CO3 -16.880 -15.443 b + 3− H3PO4 H3PO4 ⇄ 3H + PO4 -23.574 -22.716 − b − + 3− H2PO4 H2PO4 ⇄ 2H + PO4 -20.298 -19.641 2− b 2− + 3− HPO4 HPO4 ⇄ H + PO4 -12.431 -12.063 ° c ° 2+ + 3− CaHPO4 CaHPO4 ⇄ Ca + H + PO4 2.611 2.324 + c + 2+ + 3− CaH2PO4 CaH2PO4 ⇄ Ca + 2H + PO4 -4.269 -4.002 ° c ° 2+ + 3− MgHPO4 MgHPO4 ⇄ Mg + H + PO4 2.111 0.563 + c + 2+ + 3− MgH 2 PO 4 MgH 2 PO 4 ⇄ Mg + 2H + PO4 -4.269 -2.478

(a) ∆fG° from Haas et al. (1995); (b) ∆fG° from Wagman et al. (1982); (c) ∆fG° from Vieillard & Tardy (1984)

143 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Thermodynamic data of these minerals are necessary to calculate their solubility products at 600 bars and 200°C. The Gibbs free energies of formation of illite 1Mt, dravite and sudoite were taken in Kister et al. (2005) and those of trioctahedral chlorite has been estimated from the structural formulae given in Beaufort et al. (2005) using the method of difference of electronegativities (Vieillard, 2002). The Gibbs free energies of formation of monazite and apatite were taken in Vieillard and Tardy (1984). Thermodynamic data of all APS minerals being not yet available in the literature, the Gibbs free energies of formation of these minerals were estimated using the prediction of formation of minerals of the alunite supergroup (Gaboreau and Vieillard, 2004). The Holland’s algorithm was used for the estimation of entropy (Holland, 1989) and the heat capacities were estimated from alunite data by the Helgeson’s algorithm (Helgeson et al., 1978, Tab. 29).

Tableau 29. Thermodynamic data for phosphate minerals ° ° ° ∆G ∆H S Vm -2 Phases f.,298 f,298 298 Cp = a + bT + cT (KJ.mol-1) (KJ.mol-1) (J.K-1.mol-1) (cm3.mol-1) a b⋅103 c⋅10-5 (J⋅K-1⋅mol-1) (J⋅K-2⋅mol-1) (J⋅K⋅mol-1) (1) (3) (2) (5) (5) (5) APS1 -5420.12 -5930.19 357.52 141.70 143.37 27.57 -51.71 (1) (3) (2) (5) (5) (5) APS2 -5659.49 -6167.13 371.83 138.56 141.96 35.93 -51.21 (1) (3) (2) (5) (5) (5) APS3 -5697.64 -6205.29 371.75 138.15 141.78 37.13 -51.16 Monazite -1817.70 (4) -464.29 (4) 104.47 (4) 120.00 120.24 (5) 34.86 (5) -25.08 (5) Apatite-(OH) -6266.67 (4) -6665.48 (4) 390.36 (4) 159.60 112.38 (5) 21.95 (5) -23.90 (5)

Structural formulae: Monazite CePO4 Apatite-(OH) Ca5(PO4)3(OH)

Sources: (1) Gaboreau & Vieillard (2004) (2) Estimated by the method of Holland (1989) (3) ° ° Calculated from ∆G f.298 and S 298 (4) Vieillard & Tardy (1984) (5) See text

144 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Results

Early alteration process

Theoretical calculations has been done to simulate the farthest alteration zone observed in the sandstone and to determine the characteristics of the fluids after they react with these sedimentary rocks. These calculations addressed the interaction of Na-Ca-Cl diagenetic brines with the rock forming minerals of sandstones which have previously suffered deep burial diagenesis, in order to calculated the composition of the fluid consistent with saturation with coexisting illite and APS1. The modal composition of the reactant rock has been chosen in agreement with the mineralogy of a sandstone only affected by burial diagenesis (Tab. 30).

Tableau 30. Molar composition of a sandstone in the early diagenetic process. Mineral Structural formulae Amounts (%)

Quartz SiO2 95.000

Kaolinite Si2Al2O5(OH)4 2.000

K-feldspar KAlSi3O8 2.000

Pyrite FeS2 0.100

Hematite Fe2O3 0.100

Apatite Ca5(PO4)3(OH) 0.100

Monazite CePO4 0.100

Sr-feldspar SrAl2Si2O8 0.100

Sr-apatite Sr5(PO4)3(OH) 0.001

Small amounts of hypothetical minerals (i.e., Sr-carbonates, Sr-phosphates, aluminous minerals with trace of Sr in their structure) have been tested in order to provide the elements required to the formation of (Sr, S)-rich APS. It was found that the formation of APS1 occured only in presence of reactant minerals such as Ca, Sr-apatite and Sr-feldspar. Figure 25 displays the evolution of the saturation index (Log Q/K) for the reactant minerals (Fig 25a), the product minerals (Fig. 25b) as a function of the reaction progress of the fluid rock interaction and provides the calculated values of pH and oxygen fugacity at each step of the reaction (Fig. 25c). The diagram, reactant minerals versus the reaction progress, illustrates the dissolution of the reactant minerals of the sandstone up to they reach equilibrium with the

145 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning fluid. The diagram, product minerals versus the reaction progress, illustrates the calculated precipitation of the secondary minerals.

The solution initially becomes saturated with pyrite (log of reaction progress, ξ =-6) and with quartz (log ξ =-5). The saturation of the solution with the hematite (log ξ =-3) is marked by a drop of the oxygen fugacity.

It can be seen in figures 25a and 25b that the combined dissolution of kaolinite and K-feldspar induces in an increase of precipitation of illite, which is the unique clay mineral formed in this simulation. This occurrence is marked by both a drop of pH and an increase of the oxygen fugacity. In absence of Mg-bearing reactant minerals, no sudoite and/or Mg chlorite appear to be stable in this alteration system.

Only pure apatite reaches the equilibrium and strontium bearing minerals like Sr-feldspar, Sr- apatite go on to dissolve. The strontium ion leached by the dissolution of apatite and feldspar in the one hand, and the sulfate anion, coming from the oxidation of sulfide from the dissolution of pyrite, are the main sources for the precipitation of APS1 in acid and oxidized conditions (Log fO2 = -35.5 and pH = 4.5). Table 31 gives the chemical composition of the fluid saturated with illite + APS1 mineral assemblage of the distal alteration zone.

Synore alteration process

In order to determine the conditions of formation of the two others types of APS minerals

(APS2 and APS3) observed in the intermediate and the proximal alteration zones close to the unconformity and/or in the basement rocks, a second set of simulation has been performed. In this part, we will present the theoretical calculations of the interaction of two possible metamorphic host-rocks of the basement, a quartz mica-schist and a felsic gneiss, with the sandstone derived fluid whose chemical composition results from the simulation of the earlier alteration process in the above section (Tab. 31). In such a model, the infiltrating fluid is supposed to react with the minerals of each metamorphic rocks as far as it reaches the saturation with APS minerals (APS2 or APS3) and the coexisting clay phases which belong to the intermediate and proximal alteration zones.

146 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Figure 25. Saturation index (Log Q/K) of selected minerals versus the reaction progress variable ξ during the reaction of the initial fluid with a sandstone.

147 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Tableau 31. Chemical composition of the sandstone derived fluid. Sandstone derived fluid mol/kgw Al 1.2·10-04 K2.7·10-02 Na 8.0·10-03 Sr 6.9·10-03 Fe 1.2·10-05 Ca 2.8·10-03 Mg 1.8·10-03 Si 4.1·10-03 P2.8·10-03 C1.1·10-03 S2.1·10-05 Cl 5.4·10-02 Ce 1.6·10-11 B1.0·10-09 Log f O2 -35.5 pH 4.47

Quartz mica-schist

The consequences of the reaction of the sandstone derived fluid (Tab. 31) with a quartz mica- schist are illustrated in figure 26. The dissolution of the reactant minerals and the precipitation of product minerals as a function of reaction progress are depicted in figure 26a and 26b. Figure 26c illustrates the change in pH and oxygen fugacity during fluid–rock interaction. Initially, the solution is saturated with pyrite, quartz, and monazite (log ξ =-7.09). Reaction of the sandstone derived fluid with the quartz mica-schist leads first to the precipitation of apatite. This mineral is found at all metamorphic grades from transitional diagenetic environments and low-temperature alteration to migmatites, and in ultra high pressure samples (Spear and Pyle, 2002). Close to log ξ =-6.5, fluid reaches saturation with illite whereas the solution appears in equilibrium with primary muscovite. The formation of illite consumes Al and involves a modification of the behavior of Log (Q/K) versus time of sudoite. At log of reaction progress close to –5, the saturation of hematite is attained. Then the solution experiences a combined drop of the oxygen fugacity and increase of pH. The reaction continues by the precipitation of di,trioctahedral chlorite (sudoite), in response to the destruction of biotite, dravite, albite and anorthite. Precipitation of sudoite involves also the destabilization of illite (log ξ = -4.5).

148 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Figure 26. Saturation index (Log Q/K) of selected minerals versus the reaction progress variable ξ during the reaction of the sandstone derived fluid with a quartz mica-schist.

149 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

The formation of aluminium phosphate sulfate is certainly bound to the availability of Al in the system and consequently to the precipitation and the dissolution of Al-phases (illite, sudoite, feldspars, micas). This can be seen in figure 26b, with the modification of the behavior of Log (Q/K) versus time of APS2 and APS3, at log ξ close to –5.5 and –4.5. APS2 appears when the oxygen fugacity and pH are respectively closed to –44.5 and 4.79, in response to the destruction of the remaining primary Al-phases. At a log of reaction progress close to -4.09, APS3 reaches saturation with the fluid in more reduced conditions than APS2, (-45.7) and causes to the destabilization of this last one, by affecting the amount of Al, P, LREE of the fluid.

Felsic gneiss

The reactions of the sandstone derived fluid (Tab. 31) with a felsic gneiss are shown in figure 27. Incipient reactions of the sandstone derived fluid with a felsic gneiss generates the same alteration products that observed in the quartz-mica-schist system and leads to significant changes in the pH and the oxygen fugacity (Fig. 27c). The sequence of dissolution- precipitation events illustrated in figure 27a and 27b is the result of this drastic changes. Initially, the solution is saturated with pyrite, quartz and monazite (log ξ = -8) and leads first to the precipitation of apatite, like for the theoretical calculations performed above. The decrease of the oxygen fugacity starts when hematite reaches the equilibrium with the solution (log ξ = -6). The early formation of sudoite is due to the dissolution of tourmaline and biotite, which increase the availability of Mg in the system. Soon after, when the pH keeps decreasing, the precipitation of illite leads to the modification of the behavior of Log (Q/K) versus time for APS2 and APS3. Sudoite becomes unstable when the primary biotite attains the equilibrium with solution (log ξ = -5), in response to the drop of the oxygen fugacity. In the manner described by Komninou and Sverjensky (1996), the most drastic change in fluid chemistry observed during the synore alteration is the drop of oxygen fugacity. Reaction of the oxidized, sandstone derived fluid with a host rock containing significant amounts of Fe- rich biotite causes the oxygen fugacity to drop by 4 log units (Fig. 27c). The pH starts increasing at a log of reaction progress –5 (Fig. 27c). The destabilization of sudoite and the combined dissolution of anorthite and albite favour the occurrence of successively APS2 (log

ξ = -4) in reduced conditions (LogfO2 = -39.9, pH = 4.61) and the formation of high REE bearing alumino-phosphate (APS3) at log ξ = -3.21, i.e. in more reduced conditions than those obtained for APS2 (LogfO2 = -41.7, pH = 4.85). Soon after, sudoite appears saturated again,

150 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Figure 27. Saturation index (Log Q/K) of selected minerals versus the reaction progress variable ξ during the reaction of the sandstone derived fluid with a felsic gneiss.

151 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

whereas APS2 becomes unstable, in response to the precipitation of APS3. The pH and the oxygen fugacity start increasing at log of reaction progress –3, according to the saturation of anorthite and the destruction of dravite, and lead to the destabilization of APS3. The pH becomes progressively constant when albite reaches the equilibrium with the solution (Log ξ = -2). Trioctahedral chlorite appears saturated (alkaline conditions), in response to the destruction of biotite whereas sudoite and illite are unstable when the reacting fluid reaches equilibrium with the primary K-feldspar and the pH starts decreasing again (Log ξ = -1.5), which is maintained until the end of the reaction.

Discussion

One of the main results of this study is that the index mineral assemblages used in the recent literature to describe the three alteration zones around the uranium ore bodies of both the

Athabasca and Alligator River regions (i.e., illite + APS1 , illite + sudoite + APS2 and trioctahedral chlorite + apatite ± APS3) can be theoretically predicted by a set of thermodynamic calculations which simulate different steps of fluid-rock interaction processes related to a downward penetrating of hypersaline, oxidizing and acidic diagenetic fluids through the lower sandstone units of the basins and then into the metamorphic basement rocks. Geochemical modeling confirms that the time-space alteration sequence which is marked by increasing Mg content of hydrothermal clay minerals (illite → sudoite → clinochlore) coupled with the increase of the florencite end-member in coexisting APS minerals and finally the formation of secondary apatite (Beaufort et al., 2005, Gaboreau et al., 2005 and in prep) is consistent with the following processes: (1) the progressive neutralization and reduction of the reacting fluids with the host-rocks as generally invoked in most of the genetic model proposed for unconformity-type uranium deposits (Fayek and Kyser,1993; Hoeve and Sibbald, 1978; Kotzer and Kyser, 1990); (2) the increasing contribution of chemical elements released from the dissolution processes of rock forming minerals of the basement (Fe-Mg silicates and monazite) to the newly formed clay and APS mineral phases as reacting time progress. As regards to Al mobility, Kister et al. (2005) have considered Al conservation to determine the clay minerals stability relationships in such deposits, supposing that Al is entirely retained in solid phases. From this modeling approach, we have shown that Al is an important factor in the formation of APS and associated clay minerals and from its availability in the fluids depends the precipitation of APS.

152 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Beyond of the nature of the alteration zones and the index paragenesis used in the calculations, this geochemical model differs from that previously proposed by Komninou and Sverjensky (1996) on the following points: (1) the alteration system involves lithologies on both part of the unconformity and (2) the alteration processes did not consist in two stages of infiltration of distinct fluids through the same host-rock but rather in a spatially controlled sequence of fluid-rock interaction processes generated by the progressive infiltration of only one initial diagenetic fluid through the basal sandstone units and the basements rocks. Both the composition and origin of the ore-forming fluids of the unconformity-type uranium deposits have been discussed by Komninou and Sverjensky (1996). Even if it is admitted that the formation of U-orebodies is related to mixing of fluids with different redox conditions (Fayek and Kyser,1993; Hoeve and Sibbald, 1978; Kotzer and Kyser, 1990), the debate still persists on the origin of these fluids (Hoeve and Quirt, 1984; Kister et al., 2005; McCready et al., 2005; Fayek and Kyser, 1997; Iida, 1993; among others). Do they originate respectively from the sedimentary and metamorphic systems on both side of the unconformity (Fayek and Kyser,1993; Hoeve and Sibbald, 1978; Kotzer and Kyser, 1990) or do they all derived from only one initial diagenetic fluid (Iida, 1993; Komninou and Sverjensky, 1996; Derome et al., 2003a and 2003c; Beaufort et al., 2005).

Even if the origin of the fluids is beyond of the scope of this paper, the results of this study confirms the opinion that the alteration zoning pattern results of a sequence of water-rock interactions processes initiated by the infiltration of basin derived fluid which origin can be unique. This hypothesis is supported by the chemical data collected on the APS minerals from the three alteration zones. Indeed, it is particularly interesting to note that in both the unconformity-type uranium deposits of both the Athabasca and Alligator River regions, APS minerals exhibit a constant S/Sr ratio, whatever their location with respect to the alteration zoning pattern and the host-rock lithology (Fig. 24). In other words, the chemical variations of APS minerals from distal to proximal alteration zones seems to be essentially due to the incorporation in their structure of chemical elements (P, LREE, Th) whose origin has to be researched in the dissolution of monazite crystals of the altered basement rocks, as already demonstrated by several authors (Wilson, 1984; Fayeck and Kyser, 1997; Quirt et al., 1991; Hecht and Cuney, 2000, Gaboreau et al., 2005 and in prep.). In absence of other sulfates or Sr bearing phases in the sandstone, it seems reasonable to consider that the S/Sr ratio of APS was fixed by the chemistry of the hypersaline, oxidizing and acidic initial fluids. The persistence of such S/Sr ratio in all the APS minerals crystallized over the whole span of time concerned

153 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning by the formation of alteration zoning argues for a unique origin of the fluids involved in the alteration processes related to unconformity-type uranium deposits.

All the above arguments indicate that the alteration of monazite represents the major source material for the chemical elements involved in the compositional variations of APS determined between the distal and the proximal alteration areas (P, LREE and Th). Such inference is an important clue to understand the geochemical links existing between the LREE-rich APS and the uranium deposits around where they are currently encountered. Monazite containes significant amount of uranium which was not incorporated in its alteration products. U content is below the detection limit of the microprobe in the APS and uranium bearing minerals have been detected near the alteration sites of monazite only close to the uranium orebodies. This suggests that, at least a part of the uranium contained in the ore bodies and most of P, LREE and Th incorporated in APS minerals are genetically related. They are issued from the same alteration process of monazite.

The above considerations and the fact that APS with different crystal-chemical composition crystallised in a range of fO2 and pH at which uranium can either be transported in solution

(APS1) or precipited as uraninite (APS2 and APS3) in the host-rocks (Fig. 28) make these minerals not only good markers of the degree of alteration of the basement rocks (Beaufort et al., 2005) but also very good indicator of the fO2 and pH paleoconditions at which the formation of the U-ore bodies took place.

Even if the formation of the alteration paragenesis of each zone has been satisfactorily simulated by two steps of a sequential interaction of a fluid which progessively infiltrates the different lithologies on both sides of the unconformity, it is clear that this geochemical model represents only a rather static approach and that the hypothesis of a single path of the fluid through the host-rocks is not realistic. It would be necessary to improve it by addressing the possibility of recycling of the fluids in the alteration system and test the influence of kinetic constraints on the effective dissolution and crystallization processes in order to explain the following points that have been frequently reported in the literature: (1) mixing of fluids with different redox and pH necessary for the structurally controlled massive deposition of uranium mineralization, (2) superimposition of alteration features and the chemical zoning of phyllosilicates and/or APS minerals observed at more local scale. (Iida, 1993, Beaufort et al., 2005). (3) Upward migration of the near-neutral and more reducing fluids and transfer of

154 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning chemical elements (Mg, K, LREE) released from the alteration of rock-forming minerals of the basement rocks towards the sandstones overlying the unconformity (Kister et al., 2005). ka mu ° mu Ksp UO2CO3 h F h m F m e e

C C

l l + U O + + l 4 8 - 30 + 1 1 C l

0 0 2 C

- - O 2 4 5 U O U

-8 + -9 UO Cl 0 0 2 1 1

UO2 - 35 hm APS1 (URANINITE) py

py+bn - 40 cp APS2

APS3

APS - 45 2 1 2 345678

APS3

Figure 28. Paleoconditions of formation of APS minerals according to the parental host rocks (modified from Iida, 1993)

155 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Concluding remarks

Even if the geochemical modelling of the formation of alteration zoning associated with the unconformity-type uranium deposits presented in this study does not account for the dynamic aspects of the alteration processes, it contributes to a better understanding of the significant differences which exist between the alteration features related to the unconformity-type uranium deposits of both the Athabasca and Alligator River regions. Undependantly of the nature of the host litholgies, alteration zoning presents the same type of spatial organization around the redox fronts (materialized by the uranium orebodies) and each type of alteration paragenesis distinguished in this study have been reported in both regions. However, some differences exist between the deposits of these two regions (Plant and Alia, 1999); some of them concerning more specifically alteration and mineralization features:

(1) Redox fronts and most of the alteration zoning are located in basement rocks beneath the unconformity in the Pine Creek region , whereas some deposits in the Athabasca are also centered on unconformity or slighly shifted along structures intersecting the overlying sandstones in the Athabasca region.

(2) The upward extension of alteration zones in the sandstones is wider in most of the unconformity-type uranium deposits of Athabsca.

(3) the alteration assemblage which occured close to the uranium ore bodies consists of trioctaedral chlorite + apatite ± florencite rich APS minerals in the Pine Creek region whereas it consists rather of sudoite ± illite + APS minerals slighltly poorer in florencite in the Athabasca region.

(4) the deposits of the Athabasca region have higher grade than those of the Pine Creek region.

The thermodynamic calculations developped in this study led us to interpret the aforementioned paragenetic differences as a result of distinct fO2 and pH conditions within the alteration systems and hence to invoke differences of composition between the ore bearing fluids in both regions. Precipitation of lower grade uranium deposits of the Alligator River region took place at higher pH and more reducing conditions than those at which were

156 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning deposited the high-grade uranium deposits of the Athabasca region. If we assumed that the fluids involved in the alteration systems are only derived from initial diagenetic brines, the differences of paragenesis can be a consequence of the total amount of initial fluids involved in the alteration system.

According to the present geochemical model, trioctahedral chlorite and florencite crystallized close to the U-orebodies in the Alligator River region are indicative of an advanced reequilibration of the initial very saline oxidizing and acidic fluids with the crystalline rocks of the basement (which released most of the Mg, P and LREE necessary to the mineral reactions). In the Athabasca region, the formation of Al rich phases close to the U-orebodies (sudoite, illite, APS) is indicative of a major chemical contribution of the initial fluid phase to the mineral reaction. In other words our simulations of the alteration zoning suggest that the total amount of fluids which reacted with the host-rocks and that their recycling at large scale which permitted to get high-grade U-orebodies were much higher in the Athabasca region than in the Pine Creek Region.

References

Beaufort, D., Patrier, P., Laverret E., Bruneton, P. & Mondy, J. (2005). Clay alteration associated with Proterozoic unconformity-type deposits in the East Alligator River Uranium Field, Northern Territory, Australia. Economic Geology, 100, pp. 515-536. Brimhall, G.H., Ghiorso, M.S. (1983). Origin and ore-forming consequences of the advanced argilic alteration process in hypogene environments by magmatic gas contamination of meteoritic fluids. Economic Geology, 78, pp. 73-90. Brimhall, G.H. (1979). Lithologic determination of mass transfer mechanism of multiple- stage porphyry copper mineralization a butte, Montana: vein formation by hypogene leaching and enricment of potassium-silicate protore. Economic Geology, 74, pp. 556-589. Card, C.D. (2002). New investigations of basement to the western Athabasca basin. In summary of investigations, Saskatchewan Geological Survey, Saskatchewan Energy and Mines, 4-2, 17 p. Chernyshova, I.V., Semenov, Y.V. & Agoshov, V.M. (1991). Thermodynamic properties of strontium and barium feldspars. Thermochimica Acta, 175, pp. 119-127. Derome, D., Cathelineau, M., Cuney, M. & Fabre, C. (2003a). Reconstruction of the P, T, X characteristics of paleofluids in the Mc Arthur River unconformity-type uranium deposit

157 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

(Saskatchewan, Canada). In “international Conference Uranium Geochemistry”, M. Cuney ed., Nancy, pp. 141-144. Derome, D. Cathelineau, M., Cuney, M. & Lhomme, T. (2003b). Fluid inclusion evidence of the differential migration of H2 and O2 in the McArthur River unconformity-type uranium deposit (Saskatchewan, Canada). Possible role on the host rock alteration. Journal of Geochemical Exploration, 80, pp. 259-275. Derome, D., Cuney, C., Cathelineau, M., Fabre, C., Dubessy, J., Bruneton, P. & Hubert, A. (2003c). A detailed fluid inclusion study in silicified breccias from the Kombolgie sandstone (Northern Territory, Australia): application to the genesis of middle Proterozoic unconformity-type uranium deposits. Journal of Geochemical Exploration, 80, pp. 259- 275. Derome, D. (2002). Les circulations fluides à l’interface socle discordance dans l’environnement des gisements d’uranium de type discordance. Unpublished Ph. D. thesis, Université Henri Poincaré, Nancy, 232 p. Drits, V., Weber, F., Salyn, A.L. & Tsipursky, S.I. (1993). X-ray identification of one-layer illite varieties: Application to the study of uranium deposits of Canada. Clays and Clay minerals, 41, pp. 389-398. Fayek, M. & Kyser, T. (1997). Characterization of multiple fluid-flow events and Rare-Earth- Element mobility associated with formation of unconformity-type uranium deposits in the Athabasca basin, Saskatchewan. The Canadian Mineralogist, 35, pp. 627-658. Fayek, M. & Kyser, T. (1993). Petrography, chemical ages, stable isotopic compositions, and REE content of three stages of uranium mineralization from the Athabasca basin, in summary of investigations. Saskatchewan Geological Survey, Saskatchewan Energy and Mines, Misc. Report, 93-4, pp. 166-173. Fritz, B. (1981). Etude thermodynamique et modélisation des réactions hydrothermales et diagénétiques. Sci. Géol. Mém., 65, 197 p. Fritz, B. (1975). Etude thermodynamique et simulation des réactions entre minéraux et solutions. Application à la géochimie des altérations et des eaux continentales. Sci. Géol. Mém., 41, 152p. Gaboreau, S., Quirt, D., Beaufort, D., Patrier, P. & Kister, Ph. (2005). Aluminium Phosphate Sulfate minerals aasociated with Proterozoic unconformity-type uranium deposits in the Athabasca basin, Canada. The Canadian Mineralogist, submitted. Gaboreau, S., Beaufort, D., Vieillard, P., Patrier, P.& Bruneton, P. (2005). Aluminum Phosphate Sulfate minerals associated with Proterozoic unconformity-type uranium

158 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

deposits in the East Alligator Uranium Field Northern Territories, Australia. The Canadian Mineralogist, 43, pp. 813-827. Gaboreau, S. & Vieillard, P. (2004). Prediction of Gibbs free energies of formation of minerals of the alunite supergroup. Geochimica and Cosmochimica Acta, 68, pp. 3307- 3316. Haas, J.R., Shock, E.L., Sassani, D.C. (1995). Rare earth elements in hydrothermal systems: Estimates of standard partial molal thermodynamic properties of aqueous complexes of the rare earth elements at high pressures and temperatures. Geochimica and Cosmochimica Acta, 59, pp. 4329-4350. Hecht, L. and Cuney, M. (2000). Hydrothermal alteration of monazite in the Precambrian crystalline basement of the Athabasca basin (Saskatchewan, Canada): implications for the formation of unconformity-related uranium deposits. Mineralium Deposita, 35, pp. 791- 795. Helgeson, H.C., Delany, J.M., Nesbitt, H.W. & Bird, D.K. (1978). Summary and critique of the thermodynamic properties of the rock forming minerals. Am. J. Sci., 278. Hoeve, J. & Quirt, D. (1984). Mineralization and host rocks alteration in relation to clay mineral diagenesis and evolution of the middle-Proterozoic Athabasca basin, Northern Saskatchewan, Canada. Saskatchewan Research Council, Technical Report, 187, 187 p. Hoeve, J. & Sibbald, T. (1978). On the genesis of Rabbit of Rabbit Lake and other unconformity-type uranium in Northern saskatchewan, Canada. Economic Geology, 73, pp. 1451-1473. Holland, T.J.B. (1989). Dependance of entropy on volume for silicate and oxide minerals. A review and a predicture model. American Mineralogist, 74, pp. 5-13. Iida, Y. (1993). Alteration and ore-forming processes of unconformity related uranium deposits. Resource Geology, 15, pp. 299-308. Jonhson, J. W., Oelkers, E. H., Helgeson, H.C. (1992). SUPCRT92: a software package for calculating the standard molal thermodynamic properties of minerals, gases, aqueous species, and reactions from 1 to 5000 bars and 0 to 1000°C. Computers and Geosciences, 18, 899-947. Khattech, I. & Jemal, M. (1997). Thermochemistry of phosphate products. Part I: Standard enthalpy of formation of tristrontium phosphate and strontium chlorapatite. Thermochimica Acta, 298, pp. 17-21. Kister, Ph., Vieillard, Ph., Cuney, M., Quirt, D. & Laverret, E. (2005). Thermodynamic constraints on the mineralogical and fluid composition evolution in a clastic sedimentary

159 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

basin: the Atahbasca basin (Saskatchewan, Canada). European Journal of Mineralogy, 17, pp. 325-342. Komninou, A. & Sverjensky, D.A. (1996). Geochemical modeling of the formation of an unconformity-type uranium deposit. Economic Geology, 91, pp. 590-606. Kotzer, T. & Kyser, T. (1995). Petrogenesis of the Proterozoic Athabasca basin, Northern Saskatchewan, CCanada and its relation to diagenesis, hydrothermal uranium mineralization and paleohydrogeology. Chemical Geology, 120, pp. 45-89. Kotzer, T. & Kyser, T. (1990). Fluid history of the Athabasca basin and its relation to uranium deposits, in summary of investigations. Saskatchewan Geological Survey, Saskatchewan Energy and Mines, Misc. Report, 90-4, pp.153-157. Laverret, E., Patrier, P., Beaufort, D., Kister, Ph., Quirt, D., Bruneton, P. & Clauer, N. (2005). Mineralogy and geochemistry of host-rock alterations associated with the Shea Creek unconformity-type uranium deposits (Saskatchewan, Canada). Part 1: spatial variation of illite properties. Clays and Clay minerals, submitted. Laverret, E. (2002). Evolutions temporelles et spatiales des alterations argileuses des gisements d’uranium sous discordance, secteur de Shea Creek (Bassin d’Athabasca, Canada). Unpublished Ph. D. thesis, Université de Poitiers, 200 p. Lorilleux, G. (2001). Les brèches associées aux gisements d’uranium de type discordance du bassin d’Athabasca (Saskatchewan, Canada). Unpublished Ph. D. thesis, Université Henri Poincaré, Nancy, 319 p. Madé, B., Clément, A., Fritz, B. (1994). Modeling mineral/solution interactions: The thermodynamic and kinetic code KINDISP. Computers & Geosciences, 20, pp. 1347-1363. McCready, A.J., Derome, D., Annesley, I.R., Cuney, M., Cavell, R.G., Rickers, K., Bakker, R.J. & Webb, M.A. (2005). Synchrotron X-Ray fluorescence (SXRF) analysis of paleofluid chemistry from the McArthur River Uranium deposit, Athabasca basin, Canada: Results and implications. International symposium, IAEA, Uranium Production & Raw Materials for the Nuclear Fuel Cycle. Pagel, M., Poty, B. & Sheppard, S.M.F. (1980). Contribution to some saskatchewan uranium deposits mainly from fluid inclusion and isotopic data. In “Uranium in the Pine Creek geosyncline”, J. Ferguson, A. Goleby, eds., IAEA, Vienna, pp. 639-654. Pagel, M. & Svab, M. (1985). Petrographic and geochemical variations within the Carswell structure metamorphic core and their implications with respect to uranium mineralization. In “The Carswell Structure Uranium Deposits, Saskatchewan”, R. Lainé, D. Alonso, M. Svab, eds. Geological Association of Canada, Special paper, 29, pp. 55-70.

160 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Pagel, M. (1975). Détermination des conditions physico-chimiques de la silicification diagénétiquedes grès Athabasca (Canada) au moyen des inclusions fluides. Comptes rendus de l’Académie des Sciences, Paris, 280, pp. 2301-2304. Patrier, P., Beaufort, D., Laverret, E., Bruneton, P. (2003). Dickite and illite-2M1 in sandstones from the middle Proterozoic Kombolgie formation (Northern Territory, Australia). Clays and Clay minerals, 51, pp. 102-116. Plant, J.A., Peter, R., Simpson, P.R., Smith, B. & Windley, B.F. (1999). Uranium ore deposits-Products of the Radioactive Earth. Reviews in mineralogy, Uranium, Burns, P.C. & Finch, R. eds., 38-6, pp.255-319. Polito, P.A., Kyser, K., Marlatt, J., Alexandre, P., Bajwah, Z. & Drever, G. (2004a). Significance of the alteration assemblages for the origin and evolution of the Proterozoic Nabarlek unconformity-related uranium deposit, Northern Territory, Australia. Economic Geology, 99, pp. 113-139. Polito, P.A., Kyser, K., Marlatt, J., Alexandre, P., Bajwah, Z. & Drever, G. (2004b). Significance of the alteration assemblages for the origin and evolution of the Proterozoic Nabarlek unconformity-related uranium deposit, Northern Territory, Australia-a reply. Economic Geology, 99, pp. 1045-1048. Quirt, D. (2003). Athabasca unconformity-type uranium deposits: one deposit type with many variations. In Uranium Geochemistry, International conference Proceeding, M. Cuney, ed., Nancy, pp. 309-312. Quirt, D., Kotzer, T., Kyser, T.K. (1991). Tourmaline, phosphate minerals, zircon and pitchblende in the Athabasca group: Maw Zone and McArthur Rivers areas, Saskatchewan. In summary of investigations, Saskatchewan Geological Survey, Saskatchewan Energy and Mines, 4, pp. 181-191. Raffensperger, J.F. & Garven, G. (1995a). The formation of unconformity-type uranium ore deposits. 1. Coupled groundwater flow and heat transport modeling. American Journal of Science, 295, pp. 581-636. Raffensperger, J.F. & Garven, G. (1995b). The formation of unconformity-type uranium ore deposits. 2. Coupled hydrochemical modeling. American Journal of Science, 295, pp. 639- 696. Reed, M.H. (1983). Seawater-basalt reaction and the origin of greenstones and related ore deposits. Economic Geology, 78, pp. 446-485.

161 Partie II – Ch. 4. Geochemical modeling of the formation of the alteration zoning

Ruzicka, V. (1993). Unconformity-type uranium deposits; in Mineral Deposit Modeling, (ed.) R.V. Kirkham, W.D. Sinclair, R.I. Thorpe, and J.M. Duke; Geological Association of Canada, special paper 40, pp. 531-540. Spear, F.S. & Pyle, J.M. (2002). Apatite, Monazite, and xenotime in metamorphic rocks. Reviews in Mineralogy and Geochemistry, Phosphates, Kohn, M. J., Rakovan, J. & Hugues, J. M. eds., 48-7, pp.293-335. Sverjensky, D.A. (1987). The role of migration oil-field brines in the formation of sediment- hosted Cu-rich deposits. Econonmic Geology, 82, pp. 1130-1141. Sverjensky, D.A. (1984). Oil-field brines as ore forming solutions. Economic Geology, 79, pp. 23-37. Vieillard, Ph. (2002). A new method for the prediction of Gibbs free energies of formation of phyllosilicates based on the electronegativity scale. Clays and Clay Minerals, 50, pp. 352- 363. Vieillard, Ph. & Tardy, Y. (1984). Thermochemical properties of phosphates. Phosphate Minerals, Nriagu, J.O. & Moore, P.B. eds, pp.171-198. Wagman, D.D., Evans, W.H., Parker V.B., Schumm, R.H., Halow, I., Bailey, S.M., Churney, K.L. & Nutall, R.L. (1982). The NBS tables of chemical thermodynamic properties: selected values for inorganic and C1 and C2 organic substances in SI units. J. Phys. Chem., 11 (suppl. 2), 392. Wilson, J.A. (1984). Crandallite group minerals in the Helikian Athabasca group in Alberta, Canada. Canadian Journal of Earth Science, 22, pp. 637-641.

162 Conclusions générales

Conclusions générales

La caractérisation des sulfates phosphates d’aluminium (APS) du supergroupe de l’alunite a été réalisée dans le contexte des gisements d’uranium associés à une discordance protérozoïque. Cette étude a été effectuée dans deux environnements géologiques distincts : 1) l’East Alligator Uranium Field (EARUF) dans la région de Pine Creek, autour des gisements de Jabiluka, Ranger et Koongara (Territoire du Nord, Australie), 2) le bassin d’Athabasca autour des gisements de Shea Creek, Cigar Lake et Mc Arthur (Saskatchewan, Canada). Ces travaux représentent la première étude systématique entreprise sur la caractérisation de ces minéraux autour des phénomènes d’interaction fluide/roche qui sont mis en jeu dans les processus de mobilisation, transport et dépôt de l’uranium. Ils ont reposé essentiellement sur une double approche pétrographique et chimique, couplée à de la modélisation moléculaire et thermodynamique, qui sont des outils bien adaptés à la caractérisation des APS. Par ailleurs, cette étude a largement bénéficié de l’ensemble des travaux de reconnaissances géologiques, minéralogiques et géochimiques réalisé par la société COGEMA et plusieurs centres de recherche canadiens et français, afin de mieux comprendre et interpréter la formation de ces gisements exceptionnels.

Formation des sulfates phosphates d’aluminium

Les sulfates phosphates d’aluminium sont des minéraux ubiquistes dans l’environnement des gisements d’uranium associés à une discordance protérozoïque. Ils sont généralement observés en association avec les phases argileuses 1) dans les matrices illitiques, marqueurs

163 Conclusions générales des processus d’altération des bassins gréseux australiens et canadiens, 2) dans les halos d’altération autour des structures majeures, associés à l’illite et aux différentes populations de chlorite qui caractérisent les altérations du socle que ce soit au Canada (sudoïte) ou en Australie (chlorite trioctahédrique). Ces minéraux se rencontrant dans les grès et dans le socle altérés près de la discordance, ainsi que dans les couloirs de failles recoupant les roches sédimentaires et/ou le socle à des distances parfois assez importantes de la discordance (> 200m) montrent qu’ils sont en étroite relation avec les circulations hydrothermales auxquelles sont attribuées le transport et le dépôt de l’uranium.

Il existe également des évidences pétrographiques et chimiques d'une filiation entre les APS, les monazites du socle métamorphique et les monazites des grès situés au dessus de la discordance (microsystème). Au moins une partie des APS a été formée lors de l'altération de ces monazites que ce soit à l’échelle locale ou régionale. Cette filiation est marquée par la distribution quasi similaire des terres rares légères entre ces minéraux phosphatés primaires, considérés comme source potentielle d’uranium, et secondaires dans les zones d’altération hydrothermale autour de la discordance et des zones de faille. La cristallochimie des APS est ainsi liée au processus d’altération hydrothermale et au taux d’interaction des fluides avec les monazites du socle. Les APS montrent également des variations de compositions chimiques, relatives à la distance des dépôts d’uranium (variations des conditions de pH et redox ?).

Transition svanbergite-florencite

Les variations cristallochimiques majeures des APS consistent essentiellement dans la proportion relative de svanbergite (SrAl3[PO4,SO4]OH6) et de florencite

(LREEAl3(PO4)2OH6) donc entre un pôle riche en Sr, S et P et un pôle riche LREE et P. Cette transition qui s’effectue pour un rapport constant S/Sr s’observe aussi bien dans les zones d’altération de l’EARUF que dans celles du bassin d’Athabasca.

Ce rapport constant S/Sr s’accorde avec l’hypothèse de la signature d’un fluide unique à l’origine de la formation de ces gisements d’uranium. Ces modèles font intervenir des saumures de bassin, acides et oxydantes, à l’origine de la mobilisation et du transport de l’uranium, qui interagissent par infiltration avec les lithologies du socle et se réduisent progressivement par interaction avec les composants réducteurs (graphite et minéraux riches

164 Conclusions générales en fer ferreux). Cette évolution s’effectue avec une augmentation progressive du pH et la majorité de l’uranium s’est déposée dans des conditions réductrices à des pH proches de la neutralité.

Spatialement, les variations de compositions chimiques enregistrées par les APS marquent une phosphatisation couplée à un enrichissement en terres rares légères depuis les zones éloignées vers celles les plus proches des dépôts. Si cette évolution d’ordre cristallochimique est identique entre les APS analysés en Australie et au Canada, l’enrichissement en terres rares légères est moins important pour les APS associés aux dépôts uranifères du bassin d’Athabasca. De même, les différentes compositions minéralogiques argileuses associées à ces APS riches en terres rares légères entre les deux environnements (Australie et Canada) suggèrent des valeurs de conditions physico-chimiques distinctes dans les deux bassins.

Les principaux facteurs qui contrôlent la transition svanbergite-florencite autour des gisements associés à une discordance Protérozoïque

La très grande variation cristallochimique des sulfates phosphates d’aluminium qui a été mesurée autour des gisements de l’EARUF et du bassin d’Athabasca, avec un rapport constant S/Sr, est une des conséquences majeures du contrôle liées aux changement des conditions physico-chimiques de formation. La transition svanbergite-florencite témoignent des changements de pH et de potentiel redox à l’origine du transport et du dépôt de l’uranium. Le pôle Sr-S des APS représente ainsi les conditions acides et oxydantes du fluide qui a lessivé et transporté l’uranium tandis que le pôle riche LREE-P des APS représente les conditions réductrices et plus ou moins neutres à l’origine du dépôt de l’uranium.

Le taux d’interaction fluide/roche est également l’un des facteurs à l’origine des variations minéralogiques et cristallochimiques des associations APS-argiles. Ces variations témoignent des quantités de fluide différentes entre les bassins ou marquent des problèmes de porosité du système, qui conditionne le volume de fluide potentiellement réactif avec la roche.

165 Conclusions générales

Peut on utiliser la transition Svanbergite-florencite comme marqueur de paléoconditions dans les gisements

La transition svanbergite-florencite est gouvernée par des facteurs thermodynamiques (redox, pH), il est ainsi possible d’utiliser ces minéraux comme marqueurs de paléoconditions dans l’environnement des gisements associés à une discordance protérozoïque. Cependant il est difficile de donner des valeurs fiables de pH et de potentiel redox sans tenir compte de paramètres comme la cinétique et en considérant des modèles statiques sur des processus d’altération liés à la migration de fluides. Il faut également prendre en considération les influences du rapport fluide/roche, puisque l’étude comparative entre les deux formations géologiques nous a permis de mettre en évidence des variations d’ordre minéralogiques et cristallochimiques qui peuvent s’expliquer par des taux d’interaction fluide/roche et un degré d’avancement de réaction différent.

Perspectives

Dans le but d’affiner la caractérisation des APS, plusieurs travaux pourraient être envisagés. Une étude cristallographique sur monocristaux pourrait nous permettre 1) d’acquérir des données sur les paramètres de maille afin d’affiner les valeurs thermodynamiques, 2) d’évaluer la déformation des paramètres cristallins suivant l’intégration progressive des terres rares légères par substitution du strontium dans les sites A des APS. L’âge de ces minéraux pourrait également être mesuré par différentes méthodes Sm/Nd ou Rb/Sr ( ?). En effet, comme ils intègrent un très grand nombre d’éléments géochimiques, les APS pourraient représenter de bons chronomètres des temps géologiques, car plusieurs techniques de datation pourraient être employées sur une même population d’APS.

Cependant, pour effectuer ces analyses, il est nécessaire d’extraire les APS des autres phases secondaires associées (e. g. argiles). Des essais en laboratoire ont donc été réalisés par une méthode de séparation densimétrique au polytungstate de sodium, facilitée de par la densité élevée de ces minéraux (e. g. d ≈ 2.9) et nous ont permis d’obtenir des échantillons purifiés, dépourvus des autres phases secondaires d’altération (argiles). Il est donc d’ores et déjà possible d’appliquer ces méthodes, la diffraction sur monocristaux étant déjà en cours.

166 Conclusions générales

L’association APS-argile comme outil de prospection ?

Actuellement les outils de prospection utilisés pour la recherche de nouveaux gisements d’uranium sont basés sur des méthodes géophysiques, à la recherche d’anomalie magnétique graphitique, et des forages à l’aplomb de ces conducteurs. L’apport de cette étude montre que par des méthodes d’observation et d’analyse simples et routinières, il est possible de caractériser les taux d’interaction fluide/roche à l’origine des dépôts. De même, la minéralogie des argiles couplée à la cristallochimie des APS permettraient de définir la proximité d’un sondage à un corps minéralisé avec une meilleure résolution spatiale que par la simple caractérisation des minéraux argileux (illite, sudoïte, chlorite).

Le dernier point repose sur la capacité des APS à intégrer un très grand nombre d’éléments chimiques dans leur structure (e.g. des radionucléïdes; Janeczek et Ewing, 1995; Dymkov et al., 1997). De plus, nous avons vu qu’ils sont stables dans des domaines aussi bien réducteurs qu’oxydant et qu’ils précipitent dans un très large domaine de pH. Dans ces conditions, les APS pourraient être utilisés pour le piégeage des radionucléïdes dans les sites de stockage de déchets radioactifs à la place des verres ou encore afin de séquestrer des éléments traces métalliques dans tous les environnements géologiques pollués.

167

Bibliographie

Bibliographie

Beaufort, D., Patrier, P., Laverret E., Bruneton, P. et Mondy, J. (2005). Clay alteration associated with Proterozoic unconformity-type deposits in the East Alligator River Uranium Field, Northern Territory, Australia. Economic Geology, 100, pp. 515-536. Binns, R. A., McAndrew, J. et Sun, S. S. (1980). Origin of uranium mineralization at Jabiluka. Uranium Pine Creek Geosyncline, Proc. Int. Uranium Symp. Pine Creek Geosyncline, pp. 543-62. Blount, A.M. (1974). The crystal structure of crandallite. American Mineralogist, 59, pp. 41- 47. Derome, D., Cuney, M., Cathelineau, M., Fabre, C. et Brisset, F. (2000a). Fluid regime in the Kombolgie sandstones in the vicinity of unconformity type uranium deposits (Northern Territory, Australia), in Proceedings, GeoCanada2000, The Millenium Geoscience Summit, Calgary. GAC-MAC joint annual meeting, abstract 178. Derome, D., Cathelineau, M., Cuney, M., Fabre, C., Dubessy, J. et Lhomme, T. (2000b). Reconstitution of the composition of individual fluid inclusion using microthermometry, Raman microspectroscopy and laser induced breakdown spectroscopy. Application to the genesis of Australian and Canadian world-class unconformity-type uranium deposits, in Proccedings Symposium Metallogeny2000, Nanacy, France. Dill, H.G. (2001). The geology of aluminium phosphates and sulphates of the alunite group minerals: a review. Earth-Science Reviews, 53, 35-93.

169 Bibliographie

Drits, V., Weber, F., Salyn, A.L. et Tsipursky, S.I. (1993). X-ray identification of one-layer illite varieties: Application to the study of uranium deposits of Canada. Clays and Clay minerals, 41, pp. 389-398. Dymkov, Y., Holliger, P., Pagel, M., Gorskhov, A. et Artyukhina, A. (1997). Characterization of La-Ce-Sr-Ca aluminous hydroxy phosphate in nuclear zone 13 in the Oklo uranium deposit (Gabon). Mineralium Deposita, 32, pp. 617-620. Fayek, M. et Kyser, T. (1997). Characterization of multiple fluid-flow events and Rare-Earth- Element mobility associated with formation of unconformity-type uranium deposits in the Athabasca basin, Saskatchewan. The Canadian Mineralogist, 35, pp. 627-658. Fritz, B. (1975). Thermodynamic study and simulation of reactions between minerals and solutions. Applications to the geochemistry of alteration and to continental waters. Sciences Geologiques, Memoire 41, pp. 1-152. Gaboreau, S. et Vieillard, P. (2004). Prediction of Gibbs free energies of formation of minerals of the alunite supergroup. Geochimica and Cosmochimica Acta, 68, pp. 3307- 3316. Hendricks, S.B. (1937). The crystal structure of alunite and the jarosites. American Mineralogist, 22, pp.773-784. Hoeve, J. et Quirt, D. (1984). Mineralization and host rocks alteration in relation to clay mineral diagenesis and evolution of the middle-Proterozoic Athabasca basin, Northern Saskatchewan, Canada. Saskatchewan Research Council, Technical Report, 187, 187 p. Hoeve, J. et Sibbald, T. (1978). On the genesis of Rabbit of Rabbit Lake and other unconformity-type uranium in Northern saskatchewan, Canada. Economic Geology, 73, pp. 1451-1473. Hoeve, J., Sibbald, T.I.I., Ramaekers, P. et Lewry, J.F. (1980). Athabasca basin unconformity type uranium deposits: a special class of sandstone type deposits ? in Ferguson, S., and Goleby, A., eds., Uranium in the Pine Creek Geosyncline. International atomic Energy Agency, Vienna, pp. 575-594. Jambor, J.L. (1999). Nomenclature of the Alunite Supergroup. Can. Mineral., 37, 1323-1341. Janeczek, J. et Ewing, R.C. (1995). Mechanisms of lead release from uraninite in the natural fission reactors in Gabon. Geochimica et Cosmochimica Acta, 59 (10), pp.1917-1931. Jonhson, J. W., Oelkers, E. H., Helgeson, H.C. (1992). SUPCRT92: a software package for calculating the standard molal thermodynamic properties of minerals, gases, aqueous species, and reactions from 1 to 5000 bars and 0 to 1000°C. Computers and Geosciences, 18, 899-947.

170 Bibliographie

Kister, Ph., Vieillard, Ph., Cuney, M., Quirt, D. et Laverret, E. (2005). Thermodynamic constraints on the mineralogical and fluid composition evolution in a clastic sedimentary basin: the Atahbasca basin (Saskatchewan, Canada). European Journal of Mineralogy, 17, pp. 325-342. Kister, Ph. (2003). Mobilité des éléments géochimiques dans un bassin sédimentaire clastique, du Protérozoïque à nos jours: le bassin Athabasca (Saskatchewan, Canada). Thèse de doctorat, Université Henri Poincaré, Nancy, p.329. Knipping, H.D. (1974). The concepts of supergene versus hypogene emplacement of uranium at Rabbit Lake, Saskatchewan, Canada, Formation of uranium ore deposits. Proccedings of Symposium Athens, IAEA, pp. 531-549. Kolitsch, U. et Pring, A. (2001). Crystal chemistry of the crandallite, beudantite and alunite groups: a review and evaluation of the suitability as storage materials for toxic metals. J. Mineral. Petrol. Sci., 96, pp. 67-78. Komninou, A. et Sverjensky, D.A. (1996). Geochemical modeling of the formation of an unconformity-type uranium deposit. Economic Geology, 91, pp. 590-606. Kotzer, T. et Kyser, T. (1995). Petrogenesis of the Proterozoic Athabasca basin, Northern Saskatchewan, CCanada and its relation to diagenesis, hydrothermal uranium mineralization and paleohydrogeology. Chemical Geology, 120, pp. 45-89. Kyser, K., Hiatt, E., Renac, C., Durocher, K., Holk, G. et Deckart, K. (2000). Diagenetic fluids in Paleo- and Mesoproterozoic sedimentary basins and their implications for long protracted fluid histories. In: K. Kyser (Editor), Fluids and Basin Evolution. Short Course Series. Mineralogical association of Canada, Calgary, pp. 225-258. Laverret, E., Patrier, P., Beaufort, D., Kister, Ph., Quirt, D., Bruneton, P. et Clauer, N. (2005). Mineralogy and geochemistry of host-rock alterations associated with the Shea Creek unconformity-type uranium deposits (Saskatchewan, Canada). Part 1: spatial variation of illite properties. Clays and Clay minerals, submitted. Lorilleux, G. (2001). Les brèches associées aux gisements d’uranium de type discordance du bassin d’Athabasca (Saskatchewan, Canada). Unpublished Ph. D. thesis, Université Henri Poincaré, Nancy, 319 p. Macdonald, C. (1985). Mineralogy and Geochemistry of the sub-Athabasca regolith near Wollaston Lake, 155-158, in: Sibbald, T.I.I. and Petruk, W. (eds.), Geology of uranium Deposits: The Canadian institute of Mining and Metallurgy, Spec. Vol. 32.

171 Bibliographie

Made, B., Clement, A. et Fritz, B. (1994). Modeling mineral/solution interactions: the thermodynamic and kinetic code KINDISP. Computers & Geosciences, 20 (9), pp. 1347- 63. Mathieu, R., Zetteerström, L., Cuney, M., Gauthier-Lafaye, F. et Hidaka, H. (2001). Alteration of monazite and zircon and lead migration as geochemical tracers of fluid paleocirculations around the Oklo-Okélobondo and Bagombé natural nuclear reaction zones (Franceville basin, Gabon). Chemical Geology, 171, pp. 147-171. Miller, A.R. (1983). A progress report: uranium phosphorus association in the Helikian Thelon Formation and sub-Thelon saprolite, central district of Keewatin. Geological Survey of Canada, Paper 83-1A, p. 449-456. Mordberg, L.E., Stanley, C.J., et Germann, K. (2000). Rare earth element anomalies in crandallite group minerals from the Schugorsk bauxite deposit, Timan, Russia. European Journal of Mineralogy, 12, 1229-1243. Nriagu, J.O. (1976). Supergene formation of base metal phosphates. Proc. Int. Symp. Water- Rock Interact., Meeting Date 1974, 436-43. Pacquet, A. et Weber, F. (1993). Pétrographie et minéralogie des halos d’altération autour du gisement de Cigar Lake et leurs relations avec les minéralisations. Can. J. Earth Sci., 30, pp. 674-688. Patrier, P., Beaufort, D., Laverret, E., Bruneton, P. (2003). Dickite and illite-2M1 in sandstones from the middle Proterozoic Kombolgie formation (Northern Territory, Australia). Clays and Clay minerals, 51, pp. 102-116. Polito, P.A., Kyser, K., Marlatt, J., Alexandre, P., Bajwah, Z. et Drever, G. (2004a). Significance of the alteration assemblages for the origin and evolution of the Proterozoic Nabarlek unconformity-related uranium deposit, Northern Territory, Australia. Economic Geology, 99, pp. 113-139. Quirt, D.H. (2003). Athabasca unconformity-type uranium deposits: one deposit type with many variations. In: M. Cuney (Editor), Uranium Geochemistry, International Conference Proceeding, Nancy, pp. 309-312. Quirt, D. (2002). Clay minerals: host-rock alteration related to uranium mineralization in the Athabasca Group. GAC-MAC, abstract volume 27, Saskatoon, p.94. Quirt, D., Kotzer, T. et Kyser, T.K. (1991). Tourmaline, phosphate minerals, zircon and pitchblende in the Athabasca group: Maw zone and McArhtur River Areas, Saskatchewan. Saskatchewan Geological Survey, Technical Report, 91-4, pp. 181-191.

172 Bibliographie

Radoslovich, E.W. (1982). Refinement of gorceixite structure in Cm. Neues Jahrb. Mineral., Monatsh., pp. 446-464. Ramaekers, P. (1991). Geology of the Athabasca Group (Helikian) in Northern Saskatchewan. Saskatchewan Energy and Mines, Saskatchewan Geological Survey, Technical Report 195. Ramaekers, P., Yeo, G. et Jefferson, G. (2001). Preliminary overview of regional stratigraphy in the late Paleoproterozoic Athabasca basin, Saskatchewan and Alberta. Summary of Investigations, Saskatchewan Geological Survey, Saskatchewan Energy and Mines, pp. 240-251. Rasmussen, B. (1996). Early diagenetic REE-phosphate minerals (florencite, gorceixite, crandallite, and xenotime) in marine sandstones: a major sink for oceanic phosphorus. American Journal of Science, 296, 601-632. Ruzicka, V. (1996). Gites d’uranium associés à des discordances. The Geology of North America, vol. P-1, Geological Society of America. Schwab R. G., Herold H., Costa M. L. D. et Oliveira N. P. (1989). The Formation of Aluminous Phosphates through Lateritic Weathering of rocks. Weathering Vol. 2, 369-386. Scott, K.M. (1987). Solid solution in, and classification of, gossan-derived members of the alunite-jarosite family, northwest Queensland, Australia. American Mineralogist, 72, 178- 187. Scott, K.M. (2000). Nomenclature of the alunite supergroup: Discussion. The Canadian Mineralogist, 38, pp. 1295-1297. Spötl, C. (1990). Authigenic aluminium phosphate-sulphates in sandstones of the Mitterberg formation, Northern Calcareous Alps, Austria. Sedimentology, 37, 837-845. Strnad, J.G. (1980). Genetic models and their impact on uranium exploration in the Athabasca sandstone basin, Saskatchewan, Canada, in Ferguson, S., et Goleby, A., eds., Uranium in the Pine Creek Geosyncline. International Atomic Energy Agency, Vienna, pp. 631-638. Stoffregen, R.E. (1993). Stability relations of jarosite and natrojarosite at 150–250°C. Geochimica et Cosmochimica Acta, 57, 2417-2429. Stoffregen, R.E. (1987). Genesis of acid-sulfate alteration and Au-Cu-Ag mineralization at Summitville, Colorado. Economic Geology, 82, pp. 1575-1591. Stoffregen, R.E., ALPERS, C.N. et JAMBOR, J.L. (2000). Alunite-Jarosite Crystallography, Thermodynamics, and Geochronology. Reviews in mineralogy & geochemistry, 40 (sulfate minerals), 453-479.

173 Bibliographie

Stoffregen, R.E., RYE, R.O. et WASSERMAN, M.D. (1994). Experimental studies of alunite: I. 18O-16O and D-H fractionation factors between alunite and water at 250–450°C. Geochimica et Cosmochimica Acta, 58, 903-916. Stoffregen, R.E., et ALPERS, C.N. (1987). Woodhouseite and svanbergite in hydrothermal ore deposits: products of apatite destruction during advanced argillic alteration. The Canadian Mineralogist, 25, 201-211. Thomas, D.J., Matthews, R.B. et Sopuck, V. (2000). Athabasca basin (Canada) unconformity- type uranium deposits: exploration model, current mine developments and exploration directions. geology and ore deposits: The great basin and beyond, Geological Association of Canada-Mineralogical Association of Canada, pp. 1-23. Vieillard, Ph. (2002). A new method for the prediction of Gibbs free energies of formation of phyllosilicates based on the electronegativity scale. Clays and Clay Minerals, 50, pp. 352- 363. Vieillard, P. (2000). A new method for the prediction of Gibbs free energies of formation of hydrated clay minerals based on the electronegativity scale. Clays Clay Miner. 48 , N°.4, 459-473. Vieillard, Ph., Tardy, Y. et Nahon, D. (1979). Stability fields of clays and aluminum phosphates: parageneses in lateritic weathering of argillaceous phosphatic sediments. American Mineralogist, 64 (5-6), pp. 626-34. Wilson, J.A. (1985). Crandallite group minerals in the Helikian Athabasca group in Alberta, Canada. Can. J. Earth Sci., 22, pp. 637-641.

174 Annexes analytiques

Annexes analytiques

Tableau 32. Analyses chimiques et formules structurales des APS des zones qualifiées de ‘distales’ de la région de Pine Creek (EARUF, Australie).

Kombolgie basin

Zones of distal alteration

SrO Al2O3 P2O5 SO3 CaO ThO2 BaO Nd2O3 Pr2O3 Fe2O3 U2O3 La2O3 Ce2O3

Ox % 13,38 30,26 22,00 6,79 2,44 0,42 0,00 0,80 0,32 2,59 0,00 1,33 3,25 F.S. 0,62 2,84 1,57 0,43 0,21 0,01 0,00 0,02 0,01 0,16 0,00 0,04 0,09 Ox % 12,02 28,63 16,45 6,62 2,06 0,27 0,00 0,57 0,12 4,06 0,00 0,73 1,74 F.S. 0,67 2,75 1,47 0,53 0,21 0,01 0,00 0,02 0,00 0,25 0,00 0,03 0,06 Ox % 12,52 28,56 18,10 6,51 1,96 0,19 0,00 0,67 0,18 0,69 0,00 0,76 1,91 F.S. 0,68 2,95 1,52 0,48 0,20 0,00 0,00 0,02 0,01 0,05 0,00 0,03 0,07 Ox % 12,72 31,82 23,78 6,72 2,32 0,57 0,00 1,06 0,33 1,48 0,00 1,76 4,10 F.S. 0,58 2,91 1,60 0,40 0,20 0,01 0,00 0,03 0,01 0,09 0,00 0,05 0,12 Ox % 12,06 32,38 24,46 6,54 2,55 0,64 0,00 1,25 0,48 2,04 0,00 1,73 3,94 F.S. 0,56 2,88 1,62 0,38 0,22 0,01 0,00 0,04 0,01 0,12 0,00 0,05 0,11 Ox % 12,25 28,63 20,67 7,19 1,80 0,47 0,00 1,02 0,34 1,28 0,00 1,34 3,13 F.S. 0,63 2,92 1,53 0,47 0,17 0,01 0,00 0,03 0,01 0,08 0,00 0,04 0,10 Ox % 11,46 29,86 22,59 6,25 2,53 0,51 0,00 0,91 0,50 1,60 0,00 1,56 3,65 F.S. 0,56 2,90 1,61 0,39 0,23 0,01 0,00 0,03 0,02 0,10 0,00 0,05 0,11 Ox % 13,32 30,86 21,71 7,33 2,31 0,53 0,00 0,81 0,39 0,95 0,00 1,14 2,54 F.S. 0,64 2,94 1,54 0,46 0,20 0,01 0,00 0,02 0,01 0,06 0,00 0,03 0,08 Ox % 10,80 27,96 21,75 5,33 2,26 0,73 0,00 0,95 0,59 2,00 0,00 1,71 3,46 F.S. 0,55 2,87 1,64 0,36 0,21 0,01 0,00 0,03 0,02 0,13 0,00 0,06 0,11 Ox % 12,31 30,81 22,77 5,93 2,55 0,47 0,00 1,10 0,37 1,60 0,00 1,51 3,42 F.S. 0,58 2,90 1,62 0,38 0,22 0,01 0,00 0,03 0,01 0,10 0,00 0,05 0,10

175 Annexes analytiques

Tableau 33. Analyses chimiques et formules structurales des APS des zones qualifiées ‘d’intermediate’ de la région de Pine Creek (EARUF, Australie).

Kombolgie basin

Zones of intermediate alteration

SrO Al2O3 P2O5 SO3 CaO ThO2 BaO Nd2O3 Pr2O3 Fe2O3 U2O3 La2O3 Ce2O3

Ox % 2,05 27,21 16,91 0,88 2,07 1,34 0,00 1,84 0,82 1,56 0,00 4,34 8,00 F.S. 0,13 2,89 1,91 0,09 0,24 0,03 0,00 0,07 0,03 0,11 0,00 0,17 0,32 Ox % 2,94 26,02 20,31 0,74 2,21 1,53 0,00 2,66 0,51 2,36 0,00 4,68 9,31 F.S. 0,16 2,84 1,94 0,06 0,22 0,03 0,00 0,09 0,02 0,16 0,00 0,16 0,32 Ox % 3,06 26,87 14,86 1,00 1,60 1,31 0,00 2,00 0,57 2,59 0,00 3,21 6,39 F.S. 0,22 2,83 1,89 0,11 0,21 0,04 0,00 0,09 0,03 0,17 0,00 0,14 0,28 Ox % 3,34 26,74 22,49 1,17 2,06 0,61 0,00 1,97 0,84 1,23 0,00 6,61 10,17 F.S. 0,17 2,91 1,91 0,09 0,19 0,01 0,00 0,06 0,03 0,09 0,00 0,21 0,32 Ox % 3,44 28,78 23,68 1,30 2,14 0,88 0,00 1,91 0,95 1,18 0,00 7,02 10,64 F.S. 0,17 2,92 1,91 0,09 0,19 0,02 0,00 0,06 0,03 0,08 0,00 0,22 0,32 Ox % 3,90 29,39 22,13 1,80 2,10 0,99 0,00 2,78 0,69 1,80 0,00 4,09 8,47 F.S. 0,21 2,89 1,87 0,13 0,21 0,02 0,00 0,09 0,02 0,11 0,00 0,14 0,29 Ox % 1,71 31,45 18,21 1,09 0,83 0,11 0,00 3,13 0,93 0,55 0,00 3,40 7,39 F.S. 0,14 2,97 1,90 0,10 0,12 0,00 0,00 0,15 0,05 0,03 0,00 0,17 0,37 Ox % 2,82 27,89 24,56 1,40 1,39 0,29 0,00 3,54 1,21 0,77 0,00 4,67 10,93 F.S. 0,15 2,95 1,90 0,10 0,14 0,01 0,00 0,12 0,04 0,05 0,00 0,16 0,38 Ox % 2,70 28,42 24,51 1,64 1,35 0,19 0,00 3,95 1,46 0,75 0,00 4,66 10,55 F.S. 0,15 2,95 1,89 0,11 0,14 0,00 0,00 0,13 0,05 0,05 0,00 0,16 0,37 Ox % 2,10 28,40 19,66 1,35 1,05 0,06 0,00 3,24 1,17 0,81 0,00 3,73 8,74 F.S. 0,14 2,95 1,89 0,11 0,13 0,00 0,00 0,14 0,05 0,05 0,00 0,16 0,38 Ox % 2,29 27,48 21,27 1,38 1,10 0,16 0,00 3,36 0,77 1,29 0,00 3,98 9,10 F.S. 0,15 2,91 1,89 0,11 0,13 0,00 0,00 0,14 0,03 0,09 0,00 0,17 0,38 Ox % 4,03 29,79 22,15 1,52 1,80 0,43 0,00 2,34 0,79 0,72 0,00 6,33 9,86 F.S. 0,20 2,95 1,89 0,11 0,17 0,01 0,00 0,07 0,03 0,05 0,00 0,20 0,32 Ox % 4,17 33,25 19,92 1,83 1,71 0,63 0,00 1,80 0,79 2,13 0,00 5,81 9,45 F.S. 0,22 2,88 1,85 0,15 0,17 0,01 0,00 0,06 0,03 0,12 0,00 0,20 0,32 Ox % 5,09 32,56 23,86 1,94 1,87 0,41 0,00 2,07 0,94 1,12 0,00 6,74 10,62 F.S. 0,24 2,94 1,87 0,13 0,16 0,01 0,00 0,06 0,03 0,06 0,00 0,20 0,31 Ox % 3,96 30,76 23,41 2,12 1,50 0,26 0,00 1,73 0,75 0,70 0,00 6,69 9,21 F.S. 0,21 2,96 1,85 0,15 0,15 0,01 0,00 0,06 0,03 0,04 0,00 0,23 0,32 Ox % 4,56 30,87 23,52 2,04 1,77 0,48 0,00 1,44 0,76 1,54 0,00 6,55 9,89 F.S. 0,23 2,91 1,86 0,14 0,17 0,01 0,00 0,04 0,02 0,09 0,00 0,21 0,32 Ox % 5,30 31,42 23,25 1,96 1,82 0,51 0,00 1,46 0,85 1,03 0,00 7,72 11,13 F.S. 0,24 2,94 1,86 0,14 0,15 0,01 0,00 0,04 0,02 0,06 0,00 0,22 0,32 Ox % 4,14 29,86 22,54 2,35 1,69 0,40 0,00 1,62 0,86 0,77 0,00 6,72 10,85 F.S. 0,21 2,95 1,83 0,17 0,16 0,01 0,00 0,05 0,03 0,05 0,00 0,21 0,34

176 Annexes analytiques

Tableau 34. Analyses chimiques et formules structurales des APS des zones qualifiées ‘de proximal’ de la région de Pine Creek (EARUF, Australie).

Kombolgie basin

Zones of proximal alteration

SrO Al2O3 P2O5 SO3 CaO ThO2 BaO Nd2O3 Pr2O3 Fe2O3 U2O3 La2O3 Ce2O3

Ox % 2,23 27,98 21,02 0,48 1,64 0,89 0,00 2,96 0,86 1,00 0,00 5,70 11,21 F.S. 0,12 2,93 1,96 0,04 0,16 0,02 0,00 0,10 0,03 0,07 0,00 0,19 0,38 Ox % 1,97 28,34 22,36 0,45 1,35 1,01 0,00 3,34 1,24 0,81 0,00 5,93 11,43 F.S. 0,11 2,95 1,97 0,03 0,13 0,02 0,00 0,11 0,04 0,05 0,00 0,20 0,39 Ox % 1,55 29,68 25,35 0,60 1,07 0,48 0,00 3,71 0,93 0,54 0,00 6,66 13,38 F.S. 0,08 2,97 1,96 0,04 0,10 0,01 0,00 0,12 0,03 0,03 0,00 0,22 0,44 Ox % 2,24 28,17 25,47 0,51 1,33 0,77 0,00 4,04 1,45 0,95 0,00 5,30 11,99 F.S. 0,12 2,94 1,96 0,04 0,13 0,02 0,00 0,13 0,05 0,06 0,00 0,17 0,39 Ox % 1,76 30,32 22,97 0,60 1,84 1,32 0,00 3,08 1,48 1,53 0,00 6,04 11,53 F.S. 0,09 2,91 1,95 0,05 0,17 0,03 0,00 0,10 0,05 0,09 0,00 0,20 0,37 Ox % 1,97 27,10 22,26 0,54 1,64 1,04 0,00 3,26 1,37 1,20 0,00 6,28 11,87 F.S. 0,10 2,92 1,96 0,04 0,15 0,02 0,00 0,10 0,04 0,08 0,00 0,20 0,38 Ox % 1,21 29,72 25,34 0,18 0,69 0,34 0,00 5,02 1,24 0,58 0,00 6,50 12,58 F.S. 0,07 2,96 1,99 0,01 0,07 0,01 0,00 0,17 0,04 0,04 0,00 0,22 0,43 Ox % 1,83 30,22 19,71 0,58 1,88 1,09 0,00 3,00 0,83 1,72 0,00 5,86 9,18 F.S. 0,10 2,89 1,95 0,05 0,20 0,02 0,00 0,10 0,03 0,11 0,00 0,21 0,33 Ox % 1,19 23,62 23,28 0,45 0,83 0,26 0,00 3,66 1,04 2,75 0,00 6,46 12,79 F.S. 0,07 2,79 1,97 0,03 0,09 0,01 0,00 0,13 0,04 0,21 0,00 0,23 0,45 Ox % 0,90 28,85 25,56 0,46 0,58 0,41 0,00 2,67 1,29 1,65 0,00 7,83 14,41 F.S. 0,05 2,89 1,97 0,03 0,06 0,01 0,00 0,09 0,04 0,11 0,00 0,27 0,49 Ox % 1,44 24,23 16,87 0,38 1,73 0,98 0,00 2,35 0,61 2,67 0,00 5,09 10,32 F.S. 0,09 2,80 1,96 0,04 0,19 0,02 0,00 0,09 0,02 0,20 0,00 0,19 0,39 Ox % 1,54 25,03 18,89 0,41 1,78 1,33 0,00 2,53 1,23 2,58 0,00 6,03 11,63 F.S. 0,08 2,81 1,96 0,04 0,17 0,03 0,00 0,08 0,04 0,19 0,00 0,20 0,39 Ox % 1,79 26,60 20,29 0,45 1,92 1,38 0,00 3,22 1,04 2,33 0,00 6,21 12,40 F.S. 0,09 2,84 1,96 0,04 0,17 0,03 0,00 0,10 0,03 0,16 0,00 0,19 0,39 Ox % 1,50 24,88 17,10 0,45 1,50 1,00 0,00 1,85 0,91 3,09 0,00 4,34 9,25 F.S. 0,10 2,78 1,95 0,05 0,18 0,03 0,00 0,08 0,04 0,22 0,00 0,18 0,39 Ox % 2,02 24,48 18,83 0,48 1,71 1,30 0,00 2,67 0,70 2,95 0,00 4,68 9,84 F.S. 0,12 2,79 1,96 0,04 0,19 0,03 0,00 0,10 0,03 0,21 0,00 0,18 0,37 Ox % 2,20 28,62 19,06 0,78 1,78 0,90 0,00 3,96 1,00 3,27 0,00 5,67 7,80 F.S. 0,13 2,80 1,93 0,07 0,19 0,02 0,00 0,14 0,04 0,20 0,00 0,21 0,28 Ox % 1,16 21,83 16,38 0,59 1,46 0,56 0,00 4,22 0,96 5,22 0,00 3,94 8,53 F.S. 0,08 2,60 1,94 0,06 0,18 0,01 0,00 0,17 0,04 0,40 0,00 0,17 0,36 Ox % 2,66 29,26 20,66 0,72 1,71 0,63 0,00 3,80 1,33 1,48 0,00 6,07 10,62 F.S. 0,13 2,91 1,94 0,06 0,16 0,01 0,00 0,12 0,04 0,09 0,00 0,20 0,34

177 Annexes analytiques

Tableau 35. Analyses chimiques et formules structurales des APS des zones qualifiées ‘de proximal’ de la région de Pine Creek (EARUF, Australie).

Kombolgie basin

Zones of proximal alteration (suite)

SrO Al2O3 P2O5 SO3 CaO ThO2 BaO Nd2O3 Pr2O3 Fe2O3 U2O3 La2O3 Ce2O3

Ox % 2,17 28,66 18,90 0,56 1,59 0,75 0,00 3,03 1,07 1,75 0,00 5,89 10,40 F.S. 0,12 2,89 1,95 0,05 0,16 0,02 0,00 0,10 0,04 0,11 0,00 0,21 0,36 Ox % 2,15 28,31 19,04 0,72 1,93 0,90 0,00 3,96 1,19 1,50 0,00 5,70 8,63 F.S. 0,12 2,90 1,93 0,06 0,19 0,02 0,00 0,13 0,04 0,10 0,00 0,20 0,30 Ox % 2,06 27,01 19,45 0,89 1,57 1,61 0,00 1,06 0,98 2,45 0,00 10,02 8,19 F.S. 0,11 2,84 1,92 0,08 0,16 0,03 0,00 0,04 0,03 0,16 0,00 0,35 0,28 Ox % 1,98 26,75 18,89 1,09 1,49 1,56 0,00 1,53 0,82 2,45 0,00 10,67 8,28 F.S. 0,11 2,83 1,90 0,10 0,15 0,03 0,00 0,05 0,03 0,17 0,00 0,35 0,29 Ox % 1,33 26,20 14,08 0,77 0,82 0,31 0,00 1,19 0,67 3,62 0,00 7,10 5,77 F.S. 0,11 2,76 1,91 0,09 0,12 0,01 0,00 0,06 0,03 0,24 0,00 0,37 0,30 Ox % 1,37 26,28 18,83 0,62 0,90 0,31 0,00 1,46 1,11 2,59 0,00 11,32 7,45 F.S. 0,09 2,82 1,94 0,06 0,10 0,01 0,00 0,06 0,04 0,18 0,00 0,43 0,29 Ox % 1,31 26,53 18,43 0,58 0,89 0,56 0,00 1,06 0,53 3,18 0,00 11,37 7,09 F.S. 0,09 2,79 1,95 0,05 0,11 0,01 0,00 0,04 0,02 0,21 0,00 0,43 0,29 Ox % 1,90 26,36 17,20 0,82 1,06 0,65 0,00 1,41 0,95 3,90 0,00 11,69 6,98 F.S. 0,12 2,74 1,92 0,08 0,13 0,02 0,00 0,06 0,04 0,26 0,00 0,41 0,28 Ox % 2,62 28,46 19,99 0,76 1,75 0,70 0,00 3,90 1,27 1,50 0,00 5,79 8,96 F.S. 0,14 2,90 1,93 0,07 0,17 0,01 0,00 0,13 0,04 0,10 0,00 0,20 0,30

178 Annexes analytiques

Tableau 36. Analyses chimiques et formules structurales des APS des zones qualifiées de ‘distal’ du bassin d’Athabasca (Canada). Athabasca basin

Zones of distal alteration (sandstone)

SrO Al2O3 P2O5 SO3 CaO ThO2 BaO Nd2O3 Pr2O3 Fe2O3 U2O3 La2O3 Ce2O3

Ox % 16,71 32,59 24,13 7,10 3,59 0,00 0,00 0,09 0,05 0,16 0,00 0,00 0,04 F.S. 0,71 2,99 1,59 0,41 0,28 0,00 0,00 0,00 0,00 0,01 0,00 0,00 0,00 Ox % 17,35 33,20 21,59 10,27 3,34 0,00 0,00 0,00 0,00 0,14 0,00 0,00 0,15 F.S. 0,73 2,99 1,41 0,59 0,26 0,00 0,00 0,00 0,00 0,01 0,00 0,00 0,00 Ox % 14,55 30,65 24,01 5,66 3,55 0,00 0,00 0,02 0,00 0,29 0,00 0,00 0,12 F.S. 0,69 2,98 1,65 0,35 0,31 0,00 0,00 0,00 0,00 0,02 0,00 0,00 0,00 Ox % 17,13 32,36 23,22 6,77 2,70 0,05 0,00 0,24 0,00 0,20 0,00 0,09 0,38 F.S. 0,76 2,99 1,59 0,41 0,22 0,00 0,00 0,01 0,00 0,01 0,00 0,00 0,01 Ox % 17,57 32,54 24,68 7,01 2,75 0,06 0,00 0,22 0,09 0,26 0,00 0,37 0,75 F.S. 0,75 2,98 1,60 0,40 0,22 0,00 0,00 0,01 0,00 0,01 0,00 0,01 0,02 Ox % 14,13 30,88 19,98 6,72 2,56 0,07 0,00 0,06 0,19 0,21 0,00 0,03 0,36 F.S. 0,73 2,99 1,54 0,46 0,25 0,00 0,00 0,00 0,01 0,01 0,00 0,00 0,01 Ox % 15,55 31,15 22,44 6,80 2,60 0,00 0,00 0,23 0,05 0,39 0,00 0,43 0,98 F.S. 0,73 2,98 1,58 0,42 0,22 0,00 0,00 0,01 0,00 0,02 0,00 0,01 0,03 Ox % 16,80 31,10 23,75 6,66 2,53 0,08 0,00 0,23 0,20 0,55 0,00 0,45 0,87 F.S. 0,74 2,97 1,60 0,40 0,21 0,00 0,00 0,01 0,01 0,03 0,00 0,01 0,02 Ox % 15,52 32,39 24,88 7,21 4,39 0,02 0,00 0,05 0,07 0,14 0,00 0,02 0,02 F.S. 0,65 2,99 1,59 0,41 0,34 0,00 0,00 0,00 0,00 0,01 0,00 0,00 0,00 Ox % 15,85 32,95 24,38 6,40 3,36 0,00 0,00 0,00 0,03 0,29 0,00 0,09 0,24 F.S. 0,71 2,98 1,62 0,38 0,28 0,00 0,00 0,00 0,00 0,02 0,00 0,00 0,01 Ox % 17,10 31,61 22,80 8,21 2,51 0,02 0,00 0,26 0,13 0,37 0,00 0,21 0,74 F.S. 0,76 2,98 1,52 0,48 0,21 0,00 0,00 0,01 0,00 0,02 0,00 0,01 0,02 Ox % 16,66 32,03 23,29 8,09 2,83 0,03 0,00 0,22 0,01 0,27 0,00 0,20 0,74 F.S. 0,74 2,98 1,53 0,47 0,23 0,00 0,00 0,01 0,00 0,02 0,00 0,01 0,02 Ox % 16,75 31,12 22,71 8,01 2,52 0,01 0,00 0,33 0,35 0,31 0,00 0,22 0,68 F.S. 0,75 2,98 1,52 0,48 0,21 0,00 0,00 0,01 0,01 0,02 0,00 0,01 0,02 Ox % 16,56 30,08 21,98 7,94 2,41 0,00 0,00 0,21 0,00 0,38 0,00 0,18 0,51 F.S. 0,77 2,98 1,51 0,48 0,21 0,00 0,00 0,01 0,00 0,02 0,00 0,01 0,01 Ox % 15,55 25,75 19,47 6,97 1,85 0,01 0,00 0,16 0,02 0,41 0,00 0,17 0,24 F.S. 0,80 2,97 1,52 0,48 0,18 0,00 0,00 0,01 0,00 0,03 0,00 0,01 0,01 Ox % 15,51 25,60 19,15 6,94 1,68 0,05 0,00 0,15 0,08 0,46 0,00 0,10 0,34 F.S. 0,81 2,97 1,51 0,49 0,16 0,00 0,00 0,00 0,00 0,03 0,00 0,00 0,01 Ox % 17,75 25,17 23,47 8,34 2,60 0,00 0,00 0,16 0,00 0,17 0,00 0,06 0,19 F.S. 0,78 2,99 1,52 0,48 0,21 0,00 0,00 0,00 0,00 0,01 0,00 0,00 0,01

179 Annexes analytiques

Tableau 37. Analyses chimiques et formules structurales des APS des zones qualifiées de ‘distal’ du bassin d’Athabasca (Canada).

Athabasca basin

Zones of distal alteration (basement)

SrO Al2O3 P2O5 SO3 CaO ThO2 BaO Nd2O3 Pr2O3 Fe2O3 U2O3 La2O3 Ce2O3

Ox % 9,61 30,57 23,34 3,95 3,73 1,69 0,00 1,36 0,17 2,69 0,00 2,17 3,31 F.S. 0,45 2,84 1,74 0,26 0,32 0,03 0,00 0,04 0,01 0,16 0,00 0,06 0,10 Ox % 12,27 28,88 22,52 4,30 3,48 1,38 0,00 0,91 0,27 2,38 0,00 1,60 2,74 F.S. 0,54 2,85 1,71 0,29 0,28 0,02 0,00 0,02 0,01 0,14 0,00 0,04 0,08 Ox % 9,90 28,98 21,88 4,70 4,38 2,17 0,00 1,07 0,46 5,61 0,00 1,36 2,58 F.S. 0,44 2,67 1,68 0,32 0,36 0,04 0,00 0,03 0,01 0,33 0,00 0,04 0,07 Ox % 11,49 30,61 21,63 4,94 3,85 1,82 0,00 0,75 0,24 1,42 0,00 1,83 3,06 F.S. 0,50 2,91 1,66 0,34 0,31 0,03 0,00 0,02 0,01 0,08 0,00 0,05 0,08 Ox % 7,44 29,67 23,44 3,21 3,53 0,71 0,00 1,12 0,60 2,29 0,00 3,61 4,79 F.S. 0,36 2,86 1,78 0,22 0,32 0,01 0,00 0,03 0,02 0,14 0,00 0,11 0,15 Ox % 9,42 30,74 24,61 4,53 3,18 0,76 0,00 1,37 0,22 1,28 0,00 2,33 4,12 F.S. 0,46 2,92 1,72 0,28 0,28 0,01 0,00 0,04 0,01 0,08 0,00 0,07 0,13 Ox % 10,40 32,26 24,33 4,51 3,95 1,45 0,00 1,12 0,33 2,75 0,00 2,20 3,51 F.S. 0,46 2,84 1,72 0,28 0,31 0,03 0,00 0,03 0,01 0,15 0,00 0,06 0,10 Ox % 11,22 29,49 22,01 4,65 3,90 1,79 0,00 0,91 0,32 3,14 0,00 1,60 2,79 F.S. 0,49 2,81 1,68 0,32 0,32 0,03 0,00 0,02 0,01 0,18 0,00 0,04 0,08 Ox % 11,12 30,02 22,50 4,39 3,69 1,63 0,00 1,01 0,23 2,16 0,00 1,87 3,04 F.S. 0,49 2,87 1,70 0,30 0,30 0,03 0,00 0,03 0,01 0,13 0,00 0,05 0,09 Ox % 10,73 32,66 24,44 4,61 4,02 1,51 0,00 1,10 0,32 2,78 0,00 2,12 3,41 F.S. 0,47 2,84 1,71 0,29 0,31 0,03 0,00 0,03 0,01 0,15 0,00 0,06 0,10

180 Annexes analytiques

Tableau 38. Analyses chimiques et formules structurales des APS des zones qualifiées ‘d’intermediate’ du bassin d’Athabasca (Canada).

Athabasca basin

Zones of intermediate alteration

SrO Al2O3 P2O5 SO3 CaO ThO2 BaO Nd2O3 Pr2O3 Fe2O3 U2O3 La2O3 Ce2O3

Ox % 9,44 32,51 21,21 3,99 2,50 1,29 0,24 1,45 0,74 0,69 0,00 3,27 5,69 F.S. 0,38 2,85 1,62 0,38 0,14 0,04 0,02 0,06 0,03 0,03 0,00 0,13 0,20 Ox % 8,14 32,71 19,10 3,02 2,57 1,22 0,42 1,08 0,59 0,71 0,00 3,26 5,31 F.S. 0,35 2,84 1,67 0,33 0,16 0,04 0,03 0,05 0,03 0,03 0,00 0,14 0,20 Ox % 6,28 34,05 17,76 2,10 2,57 0,78 0,32 1,15 0,36 1,11 0,00 3,08 5,04 F.S. 0,31 2,77 1,74 0,26 0,18 0,03 0,03 0,06 0,02 0,06 0,00 0,15 0,22 Ox % 9,15 33,30 20,61 3,75 2,93 1,11 0,08 1,21 0,40 1,03 0,00 3,12 5,47 F.S. 0,38 2,78 1,63 0,37 0,18 0,04 0,01 0,05 0,02 0,05 0,00 0,13 0,20 Ox % 7,41 33,38 17,45 3,33 2,58 2,37 0,01 1,41 0,74 0,99 0,00 3,11 5,38 F.S. 0,32 2,79 1,62 0,38 0,16 0,08 0,00 0,06 0,03 0,05 0,00 0,13 0,21 Ox % 8,01 32,14 18,29 3,14 2,76 1,17 0,37 1,32 0,58 1,90 0,00 2,44 4,62 F.S. 0,36 2,61 1,65 0,35 0,18 0,04 0,03 0,06 0,03 0,09 0,00 0,11 0,19 Ox % 8,17 33,40 16,06 3,51 2,23 1,11 0,08 1,04 0,49 0,90 0,00 2,66 4,48 F.S. 0,40 2,81 1,57 0,43 0,16 0,04 0,01 0,05 0,03 0,05 0,00 0,13 0,19 Ox % 8,94 33,50 18,47 3,77 2,24 0,56 0,14 1,44 0,55 0,48 0,00 2,91 5,35 F.S. 0,40 2,89 1,60 0,40 0,14 0,02 0,01 0,07 0,03 0,02 0,00 0,13 0,21 Ox % 6,65 31,25 20,80 2,96 2,10 0,25 0,20 1,93 0,59 1,63 0,00 4,75 6,99 F.S. 0,34 2,90 1,78 0,22 0,20 0,00 0,01 0,06 0,02 0,11 0,00 0,15 0,22 Ox % 6,58 33,05 22,24 2,18 2,78 0,09 0,48 2,05 0,52 1,21 0,00 4,02 6,48 F.S. 0,32 2,93 1,84 0,16 0,25 0,00 0,02 0,06 0,02 0,08 0,00 0,13 0,20 Ox % 6,06 32,65 19,69 2,50 2,46 0,26 0,33 2,01 0,73 1,67 0,00 4,42 7,50 F.S. 0,30 2,91 1,80 0,20 0,23 0,01 0,01 0,06 0,02 0,11 0,00 0,14 0,23 Ox % 6,53 33,75 22,10 2,91 2,06 0,05 0,42 1,99 0,77 2,04 0,00 5,47 7,46 F.S. 0,23 2,89 1,79 0,21 0,19 0,00 0,01 0,06 0,02 0,13 0,00 0,17 0,23 Ox % 7,08 32,40 22,27 2,26 2,55 0,26 0,34 1,69 0,60 1,55 0,00 4,29 7,05 F.S. 0,34 2,91 1,83 0,16 0,23 0,01 0,01 0,05 0,02 0,10 0,00 0,13 0,21 Ox % 6,94 32,37 20,33 2,47 2,50 0,41 0,39 1,76 0,50 1,57 0,00 4,48 6,95 F.S. 0,34 2,91 1,81 0,19 0,22 0,01 0,01 0,05 0,02 0,10 0,00 0,14 0,21 Ox % 6,95 31,91 21,36 2,35 2,30 0,15 0,55 1,56 0,64 1,91 0,00 4,19 6,73 F.S. 0,35 2,89 1,82 0,18 0,21 0,00 0,02 0,05 0,02 0,12 0,00 0,13 0,21 Ox % 6,00 31,56 22,30 2,43 2,73 0,17 0,29 2,51 0,78 1,65 0,00 4,28 7,48 F.S. 0,29 2,90 1,82 0,18 0,24 0,00 0,01 0,07 0,02 0,10 0,00 0,13 0,23 Ox % 5,63 32,86 22,35 2,15 2,76 0,06 0,12 2,08 0,66 1,98 0,00 4,68 7,09 F.S. 0,28 2,89 1,84 0,16 0,25 0,00 0,00 0,06 0,02 0,13 0,00 0,15 0,22

181 Annexes analytiques

Tableau 39. Analyses chimiques et formules structurales des APS des zones qualifiées de ‘proximale’ du bassin d’Athabasca (Canada).

Athabasca basin

Zones of proximal alteration (sandstone)

SrO Al2O3 P2O5 SO3 CaO ThO2 BaO Nd2O3 Pr2O3 Fe2O3 U2O3 La2O3 Ce2O3

Ox % 6,03 28,94 24,58 1,98 4,12 2,40 0,00 2,24 0,58 1,48 0,00 3,92 7,26 F.S. 0,26 2,90 1,87 0,13 0,33 0,04 0,00 0,06 0,02 0,08 0,00 0,11 0,20 Ox % 5,68 28,77 25,23 1,56 3,92 2,24 0,00 2,02 0,59 1,80 0,00 3,22 6,71 F.S. 0,26 2,88 1,90 0,10 0,33 0,04 0,00 0,06 0,02 0,11 0,00 0,09 0,20 Ox % 5,73 30,07 20,73 2,18 3,25 1,48 0,00 3,37 0,73 1,48 0,00 4,56 8,02 F.S. 0,25 2,91 1,83 0,17 0,26 0,03 0,00 0,09 0,02 0,08 0,00 0,13 0,22 Ox % 5,12 29,65 29,09 3,09 2,65 0,49 0,00 1,81 0,80 0,77 0,00 6,63 8,92 F.S. 0,24 2,95 1,83 0,17 0,23 0,01 0,00 0,05 0,02 0,05 0,00 0,19 0,26 Ox % 5,21 26,22 21,59 2,73 2,79 0,31 0,00 1,84 1,00 0,16 0,00 5,34 7,81 F.S. 0,25 2,99 1,80 0,20 0,25 0,01 0,00 0,06 0,03 0,01 0,00 0,16 0,24 Ox % 4,18 28,80 26,15 1,84 2,71 1,19 0,00 3,37 0,98 0,70 0,00 4,68 8,64 F.S. 0,20 2,95 1,88 0,12 0,24 0,02 0,00 0,10 0,03 0,04 0,00 0,14 0,26 Ox % 5,03 30,41 25,80 2,11 2,76 1,39 0,00 2,47 1,18 1,14 0,00 4,43 9,01 F.S. 0,23 2,93 1,86 0,14 0,24 0,03 0,00 0,07 0,03 0,07 0,00 0,13 0,27 Ox % 5,49 31,49 26,32 2,34 3,41 1,38 0,00 2,50 0,86 1,13 0,00 4,80 8,25 F.S. 0,24 2,93 1,85 0,15 0,27 0,02 0,00 0,07 0,02 0,06 0,00 0,14 0,23 Ox % 4,99 29,07 26,82 2,16 3,09 1,31 0,00 2,40 0,79 1,09 0,00 4,84 8,09 F.S. 0,23 2,93 1,87 0,13 0,27 0,02 0,00 0,07 0,02 0,07 0,00 0,14 0,24 Ox % 5,62 27,58 23,09 2,36 3,46 1,35 0,00 2,04 0,79 0,82 0,00 4,63 7,54 F.S. 0,26 2,95 1,83 0,17 0,29 0,02 0,00 0,06 0,02 0,05 0,00 0,14 0,22

182 Annexes analytiques

Tableau 40. Analyses chimiques et formules structurales des APS des zones qualifiées de ‘proximale’ du bassin d’Athabasca (Canada). Athabasca basin

Zones of proximal alteration (basement)

SrO Al2O3 P2O5 SO3 CaO ThO2 BaO Nd2O3 Pr2O3 Fe2O3 U2O3 La2O3 Ce2O3

Ox % 2,37 28,89 26,98 1,51 1,79 0,54 0,00 3,87 1,28 0,58 0,00 5,72 11,87 F.S. 0,12 2,96 1,91 0,09 0,16 0,01 0,00 0,12 0,04 0,04 0,00 0,18 0,37 Ox % 1,75 29,24 29,12 1,03 0,73 0,06 0,00 4,56 1,69 0,15 0,00 6,66 12,73 F.S. 0,09 2,99 1,94 0,06 0,07 0,00 0,00 0,15 0,06 0,01 0,00 0,22 0,42 Ox % 2,02 29,12 27,13 1,25 1,05 0,47 0,00 4,32 1,33 0,28 0,00 6,35 12,31 F.S. 0,10 2,98 1,92 0,08 0,10 0,01 0,00 0,14 0,04 0,02 0,00 0,21 0,40 Ox % 2,40 28,95 28,65 1,42 1,24 0,35 0,00 3,83 1,25 0,45 0,00 5,89 12,08 F.S. 0,12 2,97 1,92 0,08 0,12 0,01 0,00 0,12 0,04 0,03 0,00 0,19 0,39 Ox % 1,80 29,15 29,21 1,00 0,89 0,23 0,00 3,90 1,32 0,21 0,00 6,12 12,15 F.S. 0,10 2,99 1,94 0,06 0,09 0,00 0,00 0,13 0,05 0,01 0,00 0,21 0,42 Ox % 2,25 28,33 27,02 1,45 1,43 0,43 0,00 2,98 1,23 0,13 0,00 5,95 12,11 F.S. 0,12 2,99 1,91 0,09 0,14 0,01 0,00 0,10 0,04 0,01 0,00 0,20 0,40 Ox % 1,98 29,58 27,76 0,89 1,01 0,35 0,00 3,21 1,26 0,21 0,00 6,34 12,34 F.S. 0,11 2,99 1,94 0,06 0,10 0,01 0,00 0,11 0,04 0,01 0,00 0,22 0,42 Ox % 2,22 28,69 28,30 1,42 1,56 0,23 0,00 2,89 1,16 0,14 0,00 6,04 12,04 F.S. 0,12 2,99 1,91 0,09 0,15 0,00 0,00 0,09 0,04 0,01 0,00 0,20 0,40 Ox % 2,05 29,10 27,21 0,93 1,09 0,50 0,00 3,61 1,31 0,18 0,00 6,17 12,28 F.S. 0,11 2,99 1,94 0,06 0,11 0,01 0,00 0,12 0,04 0,01 0,00 0,21 0,41 Ox % 2,34 28,40 26,96 1,54 1,71 0,46 0,00 4,03 1,45 0,09 0,00 5,89 11,95 F.S. 0,11 2,99 1,90 0,10 0,16 0,01 0,00 0,12 0,04 0,01 0,00 0,18 0,37

183