THÈSE

Pour l'obtention du grade de DOCTEUR DE L'UNIVERSITÉ DE POITIERS UFR des sciences fondamentales et appliquées Institut de chimie des milieux et matériaux de Poitiers - IC2MP (Diplôme National - Arrêté du 7 août 2006)

École doctorale : Sciences pour l'environnement - Gay Lussac (La Rochelle) Secteur de recherche : Terre solide et enveloppes superficielles

Présentée par : Thomas Riegler

Système d'altération et minéralisation en uranium le long du faisceau structural Kiggavik-Andrew Lake (Nunavut, Canada) : modèle génétique et guides d'exploration

Directeur(s) de Thèse : Daniel Beaufort

Soutenue le 10 décembre 2013 devant le jury

Jury :

Président Alain Meunier Professeur des Universités, Université de Poitiers

Rapporteur Michel Cuney Directeur de recherche CNRS, Université de Nancy 1

Rapporteur Michel Jébrak Professeur, Université du Québec à Montréal

Membre Daniel Beaufort Professeur des Universités, Université de Poitiers

Membre Maurice Pagel Professeur des Universités, Université Paris Sud 11, Orsay

Membre David Quirt Senior Geoscientist, AREVA Resources Canada

Membre Thierry Allard Directeur de recherche CNRS, Université Paris 6, Jussieu

Membre Charlie Jefferson GEM uranium Project leader, Geological Survey of Canada

Pour citer cette thèse : Thomas Riegler. Système d'altération et minéralisation en uranium le long du faisceau structural Kiggavik-Andrew Lake (Nunavut, Canada) : modèle génétique et guides d'exploration [En ligne]. Thèse Terre solide et enveloppes superficielles. Poitiers : Université de Poitiers, 2013. Disponible sur Internet

THESE

Pour l’obtention du Grade de

DOCTEUR DE L’UNIVERSITE DE POITIERS

(Diplôme National - Arrêté du 7 août 2006) UFR Sciences Fondamentales et Appliquées Ecole Doctorale : Gay-Lussac

Secteur de Recherche : Terre solide et enveloppes superficielles.

Présentée par :

Thomas Riegler

************************

Système d’altération et minéralisation en uranium le long du faisceau structural Kiggavik - Andrew Lake (Nunavut, Canada) : modèle génétique et guides d’exploration

************************ Directeur de Thèse : M. Daniel Beaufort ************************

Soutenue le 10 décembre 2013

devant la Commission d’Examen

************************

JURY

Rapporteurs: MM. M. Cuney Directeur de recherche CNRS, Nancy I M. Jébrak Professeur, Université du Québec à Montréal

Examinateurs: MM. M. Pagel Professeur, Université Paris Sud XI Orsay D. Quirt Senior Geoscientist, AREVA Resources Canada C. Jefferson GEM uranium Project Leader, Geological Survey of Canada T. Allard Directeur de recherche CNRS, Paris VI Jussieu A. Meunier Professeur, Université de Poitiers D. Beaufort Professeur, Université de Poitiers

Remerciements

Ce travail est le fruit d’une longue aventure commencée dans les prairies de la Saskatchewan, il y a de cela trois années. Je remercie donc les initiateurs de se projet : Joseph Roux, Dave Quirt, Jean-Pierre Milesi et Jean-Luc Lescuyer de m’avoir fait confiance pour mener à bien cette étude. Merci à AREVA Resources Canada, AREVA NC et ERM pour le support financier et admnistratif de cette thèse, enfin bien sur au laboratoire HydrASA pour son acceuil.

Je tiens également remercier Daniel Beaufort, pour sa patience, ses conseils, et le partage de ses connaissances. Ce fût un plaisir depuis notre première rencontre à Shea Creek, et j’espère que cette relation scientifique et amicale durera après le strict cadre de cette thèse.

Bien évidement je suis reconnaissant à Michel Cuney et Michel Jébrak de bien vouloir être les rapporteurs de ce travail. A Maurice Pagel, Dave Quirt, Charlie Jefferson, Thierry Allard et Alain Meunier de me faire eux aussi l’honneur de faire partie de mon jury.

De manière plus particulière je voudrais remercier Thierry Allard, Mostafa Fayek et Maurice Pagel pour leur accueil dans leurs laboratoires respectifs et de leur aide au cours de ce travail.

Une pensée chaleureuse pour Peter Wollenberg donc la contribution a été essentielle de par son experience et sa connaissance de la zone de Kiggavik. J’attends avec impatience le livre du récit de tes aventures arctiques !

J’aurai aussi une pensée pour mes collègues et amis, présents ou passés. De l’Université de Poitiers ou d’HydrASA ; merci Alain pour tes conseils toujours judicieux, ta disponibilité et ton humour, à mes voisins de palier Paul et Laurent, Thierry toujours là quand il faut, Abder bien sûr, et pardon pour tous les autres. Je garderai un excellent souvenir de mon passage ici. Merci également à Marion, Freddy, Mélissa, Emilie, Antoine et Jo pour votre accueil lors de mon arrivé à Poitiers. Plus récement à Fabien, Jean-Christophe, Sophie et Valentin pour leur amitié, avec une mention spéciale pour les pros de la belote et de l’ultracentrifugeuse. Un pensée aussi pour les amis de l’ESIP, Anne-Laure et Benoit ; du 504 à Orsay, Tony et Morgane ; ou ceux Dysart Road à U of M, thanks Ryan. Enfin, de Saskatoon, Dwayne, Mario, et tout particulièrement Nancy, Drew, et Rebecca.

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Ces trois années à Poitiers ont été riches de nouvelles rencontres. La liste est trop longue, mais je ne peux pas oublier Lindsay, Mariana, Juan-Pablo, Jamal, Solweig, Camila, Chi-Wei, Blandine, Emilie, et Gabriel.

Une pensée aux Gaúchos : Amanda, et sa famille ; Edson, Victória.

À Christophe mon camarade depuis maintenant 10 ans. Pour le soutien dans les moments difficiles et les discussions sur la métallogénie toujours passionnante.

Enfin merci à ma famille ; à Mathias, Maud, et Mathieu pour leur générosité lors de mes nombreux passages à Paris ; à ma sœur Chloé bien sûr, et tout particulièrement à mes parents pour leur soutien indéfectible depuis toujours.

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Aussi audacieux soit-il d’explorer

l’inconnu, il l’est plus encore de remettre

le connu en question.

Kaspar

C’était un ancien basset qui, à force de

travail, d’énergie, d’ambition, de

volonté, de sens civique, avait réussi à

devenir un saint-bernard fort correct.

Pierre Dac

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Table des matières

1. INTRODUCTION ...... 9

1.1. Introduction générale ...... 9

1.2. Enjeux ...... 10

2. PRÉSENTATION DU MÉMOIRE DE THÈSE ...... 11

3. RAPPELS BIBLIOGRAPHIQUES ...... 14

3.1. Le oulie Caadie et les assis d’âge Palopotozoiue ...... 14

3.2. Les minéralisations de type discordance ...... 19

3.3. Gitologie des ialisatios uaifes assoies au disodaes d’âge palopotozoïue 21

3.4. Contrôle structural régional et local des minéralisations ...... 25

3.5. Typologie des altérations ...... 26

3.6. Quelques repères chronologiques : âges des minéralisations, événements thermiques (diagenèse

& intrusions) et otete godaiue e lie ave les ialisatios d’uaiu de l’Athaasa et du

Thelon 30

3.7. Gologie des giseets d’uaiu du distit de Kiggavik ...... 32

4. RÉFÉRENCES ...... 41

5. ECHANTILLONNAGE ...... 47

A. LE SYSTEME D’ALTERATION DU FAISCEAU DE KIGGAVIK-ANDREW LAKE ET SES RELATIONS AVEC LES

MINERALISATIONS EN URANIUM ...... 48

1. ALTERATION RELATED TO URANIUM DEPOSITS IN THE KIGGAVIK-ANDREW LAKE STRUCTURAL TREND, NUNAVUT, CANADA;

NEW INSIGHTS FROM PETROGRAPHY AND CLAY MINERALOGY ...... 49

1.1. Abstract ...... 49

1.2. Introduction ...... 50

1.3. Geological setting ...... 53

1.4. Sampling and analytical procedure ...... 54

1.5. Petrography and mineralogy...... 57

1.6. Textural properties and crystal structure of phyllosilicates ...... 63

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1.7. Phyllosilicate crystal chemistry ...... 66

1.8. Discussion ...... 69

1.9. Concluding remarks ...... 77

1.10. References ...... 79

2. ETUDE MICROTHERMOMETRIQUE DES INCLUSIONS FLUIDES DANS LES QUARTZ ET DOLOMITE ASSOCIEES AUX

MINERALISATIONS URANIFERES DU FAISCEAU STRUCTURAL KIGGAVIK-ANDREW LAKE ...... 83

2.1. Introduction ...... 83

2.2. Bong ...... 83

2.3. End Grid ...... 85

2.4. Interprétations et perspectives...... 91

3. ILLITE & URANINITE GEOCHRONOLOGY ...... 96

3.1. Introduction ...... 96

3.2. Ar/Ar principle and method ...... 96

3.3. Samples ...... 98

3.4. Results ...... 99

3.5. Discussion ...... 103

3.6. References ...... 107

4. THE BASAL THELON FORMATION AT KIGGAVIK ...... 108

4.1. Methods ...... 108

4.2. Sandstones regional setting ...... 109

4.3. Bulk-rock chemistry of the Basal Thelon sandstones ...... 112

4.4. Petrography and mineralogy...... 114

4.5. Crystallochemical properties of kaolin minerals...... 120

4.6. Microcrystalline quartz cement chemistry and in situ composition of oxygen isotopes ...... 126

4.7. Discussion ...... 128

4.8. Conclusion ...... 133

4.9. References ...... 135

5. CARBONACEOUS MATERIAL OCCURRENCE IN THE KIGGAVIK URANIUM DEPOSITS (THELON, NUNAVUT, CANADA)...... 139

5.1. Introduction ...... 139

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5.2. Geological setting and petrography ...... 141

5.3. Samples & Methods ...... 144

5.4. Results ...... 144

5.5. Discussion ...... 151

5.6. Conclusion ...... 157

5.7. References ...... 157

B. LES MARQUEURS MINÉRALOGIQUES ...... 163

1. SPATIAL DISTRIBUTION AND COMPOSITIONAL VARIATION OF APS MINERALS RELATED TO URANIUM DEPOSITS IN THE

KIGGAVIK ANDREW LAKE STRUCTURAL TREND, NUNAVUT, CANADA...... 164

1.1. Abstract ...... 164

1.2. Introduction ...... 165

1.3. Regional geological setting ...... 166

1.4. Sampling and methods ...... 169

1.5. APS minerals and alteration petrography ...... 172

1.6. Electron microprobe data ...... 179

1.7. Whole rock chemistry and REE distribution...... 188

1.8. Discussion ...... 193

1.9. Conclusion ...... 200

1.10. References ...... 202

2. NATURE AND STABILITY OF RADIATION INDUCED DEFECTS IN NATURAL ILLITE NEW RESULTS AND IMPLICATIONS FOR ANCIENT

RADIOELEMENT MOBILITY ...... 205

2.1. Introduction ...... 205

2.2. Sampling ...... 206

2.3. Methods ...... 207

2.4. Annealing Experiments protocol ...... 208

2.5. Results ...... 209

2.6. Preliminary discussion and concluding remarks ...... 214

2.7. References ...... 216

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C. DISCUSSION GÉNÉRALE, CONCLUSIONS ET PERSPECTIVES ...... 217

1. DISCUSSION GENERALE ...... 218

1.1. Histoie des veets d’altatio ...... 219

1.2. Evénements précoces Hudsoniens ...... 219

1.3. Mise e plae du pofil d’altatio P-Thélon ...... 223

1.4. Diagenèse et évolution du bassin du Thelon ...... 224

1.5. Altération hydrothermale et mise en place de la minéralisation ...... 225

2. CONCLUSION GENERALES ET PERSPECTIVES ...... 228

3. RÉFÉRENCES ...... 229

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Introduction

1. Introduction

1.1. Introduction générale

La région de Kiggavik dans le Territoire du Nunavut est un district majeur pour l’exploration de l’uranium dans le bouclier Canadien, et l’un des plus actifs au Canada en dehors de l’Athabasca dans la province de la Saskatchewan. Les premiers travaux d’exploration menés dans la zone du bassin du Thelon, il y a une trentaine d’années ont fait suite aux découvertes de minéralisations uranifères à hautes teneurs dans le bassin Paléoprotérozoïque de l’Athabasca. Dans les deux cas, les reconnaissances radiométriques au sol et aéroportées ont permis la découverte des minéralisations encaissées dans le socle et dans les formations gréseuses sus-jacentes. Par la suite, lorsque le modèle de minéralisation de type discordance a

été établi, l’exploration s’est poursuivie plus en profondeur, sur des cibles cachées sous la couverture sédimentaire et parfois même sous des épaisseurs conséquentes de roches de socle.

Ainsi la géophysique a permis d’identifier les grandes structures régionales tandis que la pétrographie, la minéralogie, et la géochimie ont fourni les outils pour tracer les systèmes hydrothermaux potentiellement favorables à la formation de gites uranifères. A Kiggavik les minéralisations ne sont pour le moment que rattachées par extrapolation à un modèle de type discordance, de par leur localisation à deux kilomètres des grès de la Formation du Thelon. Il est alors fondamental de le confirmer par une approche gîtologique, et pétrographique géochimique, minéralogique afin de mieux cerner le fonctionnement du système d’altération et de minéralisation et si possible de définir des métallotectes pertinents. Enfin la position des minéralisations reconnues à plusieurs centaines de mètres sous la surface d’érosion actuelle à

Kiggavik, pose la question de l’extension potentielle en profondeur des minéralisations encaissées dans le socle dans l’Athabasca. Il y a alors une problématique aux multiples implications ne se limitant pas aux seules minéralisations du Thelon et qui peuvent s’étendre à

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Introduction d’autre district uranifère associées aux discordances, dans le bouclier Canadien ou en

Australie.

1.2. Enjeux

Les enjeux de ce travail sont multiples et recouvrent à la fois la minéralogie, pétrologie, la géochimie et la gîtologie des minéralisations uranifère de Kiggavik pour tenter de comprendre les relations entre l’altération et les concentrations en uranium dans une vue prospective. Pour cela une approche globale, de l’échelle du district à celle du minéral, a été nécessaire afin de cerner les objets minéralisés dans leur contexte. Il s’est agi de prendre en compte l’ensemble des éléments favorables à la formation des concentrations en uranium tels que les discontinuités, les lithologies, les minéraux ou bien encore les paramètres contrôlant l’oxydo- réduction pour n’en citer que quelques uns. C’est donc par une approche multidisciplinaire, intégrée, et en ayant recourt à un grand nombre de méthodes chacune pertinente pour la compréhension d’un élément clef du système géologique si particulier qu’est un gîte métallique que nous tenterons de répondre aux thématiques ou questions suivantes :

- Quelles sont les paragenèses d’altération associées aux minéralisations uranifère de

Kiggavik ?

- Quelles sont leurs implications pour l’interprétation géologique et quel potentiel

représentent les minéraux argileux produits par ces altérations pour l’exploration.

- Comment s’organisent ces altérations à l’échelle régionale ?

- Quelle est leur contribution au modèle génétique de la minéralisation ?

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Présentation du mémoire de thèse

2. Présentation du mémoire de thèse

Les résultats présentés dans ce mémoire s’organisent autour de β grandes parties, elles-mêmes subdivisées en chapitres, principalement sous forme d’articles. De manière préliminaire le cadre géologique régional, local concernant les minéralisations en uranium, sera présenté de même que l’échantillonnage de la zone d’étude.

Le premier volet de ce travail (partie A) s’attardera sur la caractérisation du système d’altération et ses relations avec les minéralisations en uranium, tandis que le second (partie

B) sera axé sur les marqueurs minéralogiques s.l. de ce système. Enfin les éléments présentés dans ces deux grands axes feront l’objet d’une synthèse et seront discutés dans la partie C.

Dans le premier chapitre (article 1), il s’agit de caractériser l’altération en relation avec les minéralisations uranifère de Kiggavik et pour cela d’identifier la minéralogie et les paragenèses minérales résultant des différents épisodes d’interactions fluide roches qui se sont succédés au cours du temps. La minéralogie permet alors de proposer des clefs d’interprétation des systèmes hydrothermaux de Kiggavik par comparaison avec les signatures d’altération déjà identifiées autour des gisements de type associés aux discordances au Canada et en Australie et de proposer des pistes pour les transferts élémentaires lors de l’altération. Enfin la cristallographie détaillée des minéraux argileux, permet, en plus des aspects comparatifs, de proposer un nouvel outil cartographique de l’altération. De plus cet article sera complété d'un deuxième chapitre traitant des aspects paléofluides afin de mieux cerner les fluides en relations avec les phénomènes d’altération et de minéralisation. Enfin, un troisième chapitre présentera des éléments de géochronologie, à la fois sur les minéraux argileux et sur la minéralisation.

Dans un quatrième chapitre (article 2), on s’interessera aux relations entre le socle et la couverture gréseuse, principalement par l’étude des formations basales du bassin du Thelon. Il

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Présentation du mémoire de thèse s’agira alors de retracer la nature et l’origine des apports sédimentaires puis de suivre l’évolution diagénétique du bassin grâce entre autres aux minéraux du groupe kaolin.

Enfin en prélude à la conclusion de cette première partie, le cinquième chapitre (article 3) concernera les matières carbonées, autre composante fréquemment associée aux gîtes de type discordance. Elles feront l’objet d’une caractérisation poussée afin de proposer leur intégration comme une composante de la paragenèse d’altération.

La deuxième partie (B) du manuscrit sera consacrée à l’identification de marqueurs minéralogiques connus pour leur réponse cristallochimique aux variations du pH et des conditions d’oxydoréduction du milieu ou leur potentiel pour la dosimétrie de la radioactivité naturelle. Le premier chapitre (article 4), consiste en la compréhension spatiale et temporelle des phosphates et sulfates d’aluminium formés lors des événements diagénétiques et hydrothermaux. Il s’agit également de comprendre, à travers le prisme des terres rares, les transferts et la mobilité des éléments, dont l’uranium, au cours de l’histoire géologique ayant conduit à la formation des zones minéralisées à Kiggavik. Une approche « bilan de masse » sera mise en œuvre pour compléter la pétrographie et la cristallochimie. Le deuxième chapitre aura pour objet la compréhension de l’expression des défauts d’irradiation dans l’illite. Il s’agit de raffiner la compréhension de la manifestation des différentes composantes constitutives du signal RPE dans l’illite pour dégager ses caractéristiques fondamentales et ainsi contribuer à une meilleure interprétation des circulations des radioéléments (pre, syn ou post minéralisation) dans un système géologique ou les remobilisations de l’uranium sont un phénomène fréquent (article 5).

Enfin, la troisième dernière partie (C) sera consacrée à une discussion globale de l’ensemble des résultats des travaux de la thèse dans laquelle l‘accent sera mis sur la proposition d’un

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Présentation du mémoire de thèse modèle métallogénique pour les minéralisations uranifère du faisceau structural de Kiggavik –

Andrew Lake et sur les perspectives scientifiques.

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Rappels bibliographiques

3. Rappels bibliographiques

La présentation du contexte géologique multi-échelle qui suit a pour objectif de replacer la zone de Kiggavik dans un cadre lithologique et structural en accordant une attention particulière à la métallogénie de l’uranium et aux processus d’altération associés. Bien

évidemment compte tenu de la proximité des contextes géologiques, de nombreux éléments de la littérature qui font référence aux bassins d’âge Méso-Paléoproterozoique de l’Athabasca

(Canada) et de Kombolgie (Australie) seront également mentionnés.

3.1. Le bouclier Canadien et les bassins d’âge Paléoprotérozoique

Figure 3-1 : Carte géologique simplifiée du bouclier canadien, (Corrigan et al. 2007)

Le bouclier canadien, figure 3-1, est un ensemble géologique complexe dont l’organisation actuelle est liée à l’accrétion de cratons archéens soudés par des ceintures orogéniques lors des phases Talson - Thelon (2.0 -1.9 Ga) et Trans-Hudsonienne (1.9 - 1.8 Ga) (Hoffman

14

Rappels bibliographiques

1988; Hoffman 1990). Le supercontinent de la Laurentia était alors composé de blocs constitués des provinces du Supérieur-Nain, de Churchill-Wyoming et de l’Esclave respectivement à l’est et l’ouest de la baie d’Hudson. De grandes zone mylonitiques à l’échelle lithosphérique telle que la Snowbird Tectonic Zone (STZ) séparant les sous provinces de Rae et de Hearne constituent l’une des discontinuités majeures de la partie ouest de la province de Chuchill. Elles marquent un événement majeur de dislocation puis de suture du bloc Churchill-Wyoming avec le bloc de Queen Maude (Hanmer et al. 1995; Hoffman

1988). Au final, la configuration du bouclier résulte à la fois des phases multiples de structuration des cratons à l’Archéen, et des phases d’extension (rifting) avec mise en place de séries volcano-sédimentaires archéennes au niveau des marges passives de ces cratons qui sont à l’origine des ceintures de roches vertes avec les groupes de Murmac Bay, Woodburn,

Prince Albert et Mary River pour la province de Churchill (Hartlaub et al. 2004; Ashton

1988).

L’orogène Trans- Hudsonien est d’une importance majeure du point de vue métallogénique.

On retrouve toutes les étapes de son évolution sur une période allant de 2.45 à 1.95 Ga, incluant la phase de rifting lors de l’ouverture de l’océan Manikewan (Stauffer 1984) suivie du dépôt de sédiments sur les marges des cratons archéens ou des bassins intra-cratoniques

(e.g Groupe de Wollaston, Hurwitz, Amer) (Aspler et al. 2001), puis la formation de croûte océanique, d’arc volcaniques océaniques et continentaux et de bassins d’arrière arc. Cet enregistrement complet de l’orogène et la variété des environnements géologiques qui le composent expliquent sa renommée mondiale pour les amas sulfurés volcanogéniques (e.g

Flin-Flon), magmatiques à Ni-Cu-EGP (e.g Thompson, Raglan) et dans une moindre mesure pour l’or orogénique (e.g Seabee), ainsi que pour les formations de fer rubanées (Corrigan et al. 2007; Kerrich et al. 2005). A cela s’ajoute des événements tectono-metamorphiques exprimés dans une tectonique ductile le long de zones de cisaillement, d’écaillage et de

15

Rappels bibliographiques plissement ainsi que la recristallisation des roches dans les conditions des faciès schiste vert à amphibolite supérieur du métamorphisme régional (Aspler et al. 2002).

Vers la transition Paléo -Méso-protérozoique, de grands bassins intra-continentaux de composition silicoclastique se sont mis en place lors des phases de démantèlement des grands orogènes Paléoproterozoiques. On en identifie plusieurs au Canada: Il s’agit des bassins d’Athabasca, du Thelon, d’Hurwitz, ou d’Hornby Bay (Figures 3-1 et 3-3). Parmi ces bassins, certains possèdent des gisements d’uranium associés à des discordances en cours d’exploitation et/ou de prospection (Athabasca, Thelon) et les autres présentent de forte potentialité pour l’exploration (Jefferson et al. 2007a). Enfin les études géodynamiques et les reconstructions paléogéographiques suggèrent un lien génétique entre le fonctionnement des grandes orogénèses du Protérozoïque et la formation de grands bassins intra-continentaux via des phénomènes de tectonique d’échappement et de contraintes à distance, ou de flexuration thermique d’une croûte épaissie et structurée (Karlstrom et al. 2001; Molnar et al. 1998;

Eriksson et al. 2001; Ramaekers and Catuneanu 2004). Il existe des similitudes entre les caractéristiques des bassins silicoclasitiques du bouclier Canadien et celles du bouclier nord- australien, en terme de facies sédimentaires, d’âge, de position paléogéographique et de métallogénie de l’uranium. Ceci est à rapprocher des reconstitutions paléogéographiques

(Figure 3-2) qui indiquent la proximité des bassins de la Laurentia avec ceux du craton nord australien vers la fin du Paléoprotérozoique (Betts et al. 2008; Kerrich et al. 2005; Zhao et al.

2004).

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Rappels bibliographiques

Figure 3-2 : Reconstitution de l’évolution de l’ensemble Australia-East Antartica et Laurentia entre 1780-1650

Ma. In (Betts et al. 2008) d’après (Bagas 2004; Duebendorfer and Houston 1987; Duebendorfer et al. 2001;

Karlstrom and Bowring 1988)

Les minéralisations d’uranium sont associées à ces bassins intracontinetaux formés d’une séquence sédimentaire quasi horizontale, dominée par des environnements fluviatiles, continentaux dans lesquelles des grés très riches en quartz constituent la lithologie dominante.

On retrouve néanmoins des red beds et des siltites que l’on peut rapprocher de facies de plaine d’inondation ainsi que des facies conglomératiques fluviatiles, comme par exemple ceux qui

17

Rappels bibliographiques sont mentionnés à la base de la formation du Thelon (Rainbird et al. 2003; Rainbird and Davis

2007). Ces bassins sont décrits comme de grands lacs intracontinentaux remplis de sables et de graviers avec un début de sédimentation estimé entre 1730-1740 Ma pour le bassin d’Athabasca et 17β0-1750 Ma pour le Thelon, soit quelques dizaines de millions d’années après les derniers événements du métamorphisme enregistrées dans les sphènes des roches de la ceinture de plis de Wollaston et daté à 1750Ma (Rainbird et al. 2006; Miller et al. 1989;

Orrell et al. 1999).

Les roches du socle situées au niveau de la discordance sont affectées par une intense hématitisation dont l’épaisseur varie de quelques centimètres à plusieurs centaines de mètres.

L’hématitisation est particulièrement développée à l’aplomb de grandes structures. Elle est généralement interprétée comme un paléo-profil d’altération liée à la mise en place d’un régolithe antérieurement à la formation du bassin sur la base d’arguments texturaux ou minéralogiques (présence de diaspore) ou bien encore de par la nature graduelle du contact entre les zones à hématite et à chlorite, ou bien par un comportement géochimique des

éléments traces analogue à celui décrit dans d’autres profils d’altération continentale d’âge précambrien (Macdonald 1980; Hoeve and Quirt 1984). Toutefois des éléments probants de paléosol (tel que des pisolithes par exemple) reste encore à trouver (Hoeve and Quirt 1984).

Selon une autre hypothèse, l’hématitisation pourrait être la conséquence de l’interaction des saumures oxydantes issues du bassin avec la partie superficielle des roches réduites du socle au cours de la diagenèse (Cuney et al. 2003).

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Figure 3-3 : Localisation actuelle des bassins intracontinentaux MesoProterozoic de la partie West du bouclier

Canadien, d’après Jefferson et al, 2007 et Thomas, 2000.

3.2. Les minéralisations de type discordance

Les gîtes et gisements d’uranium associés aux discordances sont des objets géologiques uniques formant une classe à part parmi les autres types de minéralisation uranifère de part les teneurs (avec en moyenne ≈ β % U pour l’Athabasca, et ≈ 0.4 % pour le Thelon et la

Kombolgie) et les tonnages exceptionnels (Gandhi 1995; Ruzicka 1996; Jefferson et al.

2007a). La production issue des mines canadiennes représentait 17 % de l’uranium produit dans le monde en 2011.

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La découverte et l‘interprétation des gisements uranifères canadiens est une longue et riche histoire qui commence par les découvertes de minéralisation de type filoniennes à proximité du Grand lac de l'Ours (Port Radium) aux alentours de 1930, puis en 1952 avec la mine

Gunnar à Uranium City, exploitée par Eldorado, une compagnie minière qui deviendra

Cameco Corporation dans les années 80. Elle s’est poursuivie par la découverte d’Elliot Lake, un modèle de minéralisation que l’on pourrait rapprocher de ce qui est connu dans le

Witwatersrand en Afrique du Sud (Hills 1987).

Par la suite, le tournant majeur pour l’exploration de l’uranium au Canada s’est produit à la fin des années 60, avec la découverte de minéralisations à l’affleurement dans le bassin de l’Athabasca. Le gisement de Rabbit Lake a été découvert conjointement par Gulf Minerals

Ltd & Uranerz Exploration and Mining limited dans l’Est du bassin d’Athabasca en 1968.

Celui de Cluff Lake a été découvert dans l’ouest du bassin en 1969 par Amok Limited

(Gandhi 2006), Figure 3-4. On peut d’ailleurs noter que les découvertes de Nabarlek et

Ranger en (Territoire du Nord, Australie) ont été faites à la même époque.

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Figure 3-4 : Panneau d’indication de l’ancien camp d’Amok limited (prédécesseur de COGEMA devenu

AREVA Resources Canada) situé entre rive Sud du lac de Carswell et le site minier de Cluff Lake

(Saskatchewan, Canada).

3.3. Gitologie des minéralisations uranifères associées aux discordances d’âge

paléoprotérozoïque

Les minéralisations sont formées de lentilles massives à semi massives mais aussi de veines à remplissage quasi exclusif d’uraninite (UO2) et situées au voisinage de la discordance basale des bassins, entre les grès conglomératiques d’âge Paléo à Mésoproterozoiques et leur socle métamorphique d’âge Archéen à Paléoproterozoique.Les minéralisations forment des objets de dimensions relativement limitées mais pour lesquelles les teneurs peuvent atteindre 15 à 20

% U comme dans les mines de Cigar Lake ou de McArthur River Figure 3-5. On peut

également noter que les volumes de minéralisation reconnus pour le bassin du Thelon représentent le dixième de celle de l’Athabasca et que les teneurs moyennes enregistrées

(environ 0.5 %) sont beaucoup plus faibles que celles mesurées dans l’Athabasca et proches de celles rencontrées dans les gisements Australiens de l’Alligator River (Battey et al. 1987;

Ruzicka 1993). Ainsi on peut légitiment questionner le potentiel de découverte pour cette zone encore sous explorée que constitue le Thelon et dans lequel s’inscrit la présente étude.

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Figure 3-5 : Relation entre teneur et tonnage des différents gisements d'uranium associés à des discordances en

Australie et au Canada (d'après Gandhi 1995; Ruzicka 1996; Jefferson et al. 2007a; Gandhi 2006). Les différents gisements et prospects de Kiggavik sont représentés en bleu alors que les deux gisements géants de l’Athabasca que sont McArthur et Cigar sont en rouge. L’encadré donne les teneurs moyennes les ressources et les réserves ainsi que la production passée pour chacun des bassins Paléoprotérozoiques dans lesquels des minéralisations de type discordances ont été reconnues. Bien qu’il soit distinct du point de vue génétique, le gisement d’Olympic

Dam est donné pour comparaison, car il constitue le plus gros gisement connu dans lemonde.

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On peut alors distinguer trois sous-types de minéralisation en fonction de la localisation des corps minéralisés (Jefferson et al. 2007b): (1) les minéralisations encaissées dans le socle

(gisement de Collins Bay par exemple), (2) les minéralisations distribuées dans des failles ou des corridors de fractures la long de la discordance basale (gisement de Cigar Lake par exemple) et (3) les minéralisations situées au dessus de la discordance (minéralisation dite perchée), Figure 3-6. Les différents sous-types de minéralisation ne sont pas exclusifs. Ils peuvent être associés dans un même gisement comme c’est le cas à Key Lake ou à Shea

Creek (Andrade 2002; Thomas et al. 2000). Les profondeurs sous la discordance à laquelle se font les nouvelles découvertes de minéralisation dans le socle sont de plus en plus importantes. Elles atteignent plus de 300m dans le bassin d’Athabasca (Shea Creek) et plus de

200m dans le gisement de Jabiluka (Australie).

Il est également possible de déterminer deux sous ensembles de minéralisation sur une base de critères géochimiques : (1) la minéralisation monométallique est essentiellement constituée de’uraninite. Elle est surtout encaissée dans le socle et est globalement pauvre en terres rares légères (2) La minéralisation polymétallique est généralement encaissée dans le grès ou localisée à la discordance. Elle se caractérise par un minerai riche en Ni, Co, Cu, Mo et en terres rares légères, Figure 3-7.

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Figure 3-6 : Exemples de gisements illustrant les trois styles de minéralisation dans des gisements d’uranium associées aux discordances d’après (Andrade 2002; Thomas et al. 2000; Jefferson et al. 2007b).

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Figure 3-7 : Schéma simplifié des environnements géologiques associées aux gîtes mono- et polymétalliques dans les systèmes de type discordance d’après (Jefferson et al. 2007b; Sibbald et al. 1976; Hoeve and Sibbald

1978; Hoeve and Quirt 1984; Ruzicka 1996; Thomas et al. 2000; Tourigny et al. 2007).

3.4. Contrôle structural régional et local des minéralisations

Quelles que soient les typologies de minéralisation rencontrées, il existe un fort contrôle structural de leur mise en place. A l’échelle régionale, ce contrôle s’exerce par de grandes structures souvent héritées des phases de structuration Archéennes et Paléoprotérozoiques qui sont exprimées sous la forme de zones mylonitiques graphiteuses (Athabasca, bordure Sud ouest du Thelon) ou non (Nord Est du Thelon, Kombolgie) (Wilde and Wall 1987). C’est le cas par exemple de la structure P2 le long de laquelle se distribuent les gisements de Cigare

Lake et McArthur River ou bien celle du « Saskatoon Lake Conductor » qui contrôle les minéralisations du district de Shea Creek dans les parties est et ouest du bassin de l’Athabasca respectivement.

Ces zones de déformation majeure du socle ont ensuite été réactivées lors de l’histoire tectonique post-dépôt sédimentaire. A cela s’ajoute l’ensemble des réseaux de failles subsidiaires qui forment des zones favorables pour la circulation des fluides et dont le rôle

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(Hoeve and Sibbald 1978; Hoeve et al. 1980), à Cigare lake (McGill et al. 1993), à Cluff Lake

(Beaudemont and Fedorowich 1996) ou bien encore à Shea Creek par le biais de « couloirs brèchiques » (Lorilleux 2001) pour ne citer que quelques exemples.

3.5. Typologie des altérations

La manifestation des interactions fluides roches guidées par les structures et responsables de la formation des minéralisations, est le témoin d’échanges et de circulations entre le bassin et les roches de socle sous jacentes. Les conditions nécessaires sont celles décrites par les auteurs du modèle de type diagénétique-hydrothermal dans lequel les saumures de bassins sont à la fois les vecteurs de l’altération et de la minéralisation (Hoeve and Sibbald 1978;

Hoeve and Quirt 1984). Ces processus sont mis en œuvre lors des phases de réactivation permettant la mise en circulation de ces fluides, alors que le bassin est soumis à une diagenèse poussée (Pagel 1975).

La minéralogie et la géochimie des altérations des roches encaissantes des gisements d’uranium associées aux discordances ont fait l’objet d’études au Canada, principalement dans l’Athabasca et dans une moindre mesure dans le Thelon, et en Australie dans l’Alligator

River afin de décrire et comprendre les zonalités des gisements et de les comparer (Hoeve and

Quirt 1984; Miller and LeCheminant 1985; Kotzer and Kyser 1995; Kyser et al. 2000;

Beaufort et al. 2005; Renac et al. 2002; Cuney et al. 2003; Percival and Kodama 1989),

Figure 3-8.

On remarque alors une minéralogie des halos d’altération associés aux minéralisations uranifères très semblable pour les trois bassins Paléoproterozoiques avec un assemblage à illite ( interstratifié illite-smectite) sudoite (chlorite Al-Mg) clinochlore (chlorite Mg)

chlorite Fe-Mg phosphate sulfate d’alumium hydratés apatite en différentes

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également la présence de la dravite parfois en abondance ( tourmaline magnésienne).

Figure 3-8 : Paragenèse minérales associées aux minéralisations de types discordances dans les Bassins de la

Kombolgie, du Thelon et de l’Athabasca in (Jefferson et al. 2007b) d’après (Kyser et al. 2000; Polito et al. 2004;

Polito et al. 2005; Creaser and Stasiuk 2007)

Cette minéralogie des phases d’altération est fortement dominée par l’illite dont les halos peuvent s’étendre à plusieurs centaines de mètres des minéralisations aussi bien dans le socle que dans la couverture sédimentaire. Cette altération se manifeste par une forte desilicification et une déstabilisation des minéraux initialement présents, principalement les aluminosilicates, et aussi les minéraux accessoires (zircon, monazite, tourmaline, etc). Ces processus induisent une déstabilisation des minéraux ferromagnésien du socle tels la biotite ou l’amphibole et se manifeste sous la forme d’un blanchiment des roches ainsi altérées (Hoeve and Quirt 1984).

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Enfin, le potassium libéré par la dissolution des aluminosilicates du socle peut alors alimenter l’illitisation des kaolinites présentes dans la couverture gréseuse.

De plus une zonalité apparaît, dans la répartition des polytypes de l’illite autour des corps minéralisés (Laverret 2002) et la distribution spatiale des différentes chlorites Fe-Mg ou Al-

Mg (sudoite) (Hoeve and Quirt 1984). Cette zonation minéralogique est contrôlée par plusieurs facteurs tels que l’évolution de la composition du fluide hydrothermal, la durée des phénomènes d’interaction fluide-roche ou bien encore l’hydrodynamisme du système.

Enfin la distribution spatiale des altérations argileuses s’exprime schématiquement sous la forme de deux typologies selon que l’expression de l’altération est prédominante dans le socle ou dans la couverture, Figure 3-9. Ces distributions donnent lieu à une interprétation selon les modes « egress » ou « ingress » (Quirt 2003). Le mode « egress » se distingue par une large enveloppe à illite sudoite largement exprimée dans la couverture gréseuse entourant une zone plus riche en sudoite et un cœur riche en chlorite ferromagnésienne, biotite et sudoite qui semble s’enraciner sur la structure guidant l’altération. Le mode « ingress » affecte essentiellement le socle. Il montre une zonalité inverse des altérations avec au cœur un assemblage à illite sudoite entouré d’un halo à sudoite illite puis d’une zone à chlorite

Fe-Mg, biotite et sudoite. On peut éventuellement considérer que ce dernier assemblage, dominé par les minéraux métamorphiques du socle est l’expression plus distale de l’altération.

Chacune de ces altérations est considérée comme un marqueur du passage des fluides soit du socle vers la couverture (egress) soit de la couverture vers le socle (ingress).

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Figure 3-9 : Schéma des types de minéralisations "egress" et "ingress" in (Jefferson et al. 2007b) d’après (Hoeve and Quirt 1984; Sibbald 1985; Fayek and Kyser 1997)

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3.6. Quelques repères chronologiques : âges des minéralisations, événements

thermiques (diagenèse & intrusions) et contexte géodynamique en lien avec les

minéralisations d’uranium de l’Athabasca et du Thelon

Figure 3-10 : Mise en relation des grands événements tectoniques à l’échelle du bouclier avec les âges des

minéralisations uranifère dans le bassin de l’Athabasca, (Alexandre et al. 2009)

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Les travaux de datation des minéralisations sont toujours complexes de part la forte réactivité chimique de l’uraninite et sa propension à recristalliser au cours des temps géologiques. Les différentes études géochronologiques permettent néanmoins de caler l’âge des minéralisations avec un certain nombre de moments clefs de la géodynamique du craton canadien

(orogenèses, magmatisme, ritfing, diagenèse), Figure 3-10.

Les principaux âges de mise en place des minéralisations uranifères du le bouclier canadien s’étalent entre 1800 et 900 Ma. Pour les minéralisations de l’Athabasca, ils peuvent être résumés comme suit: (1) 1780 20 Ma pour les veines de Beaverlodge (Koeppel 1967), (2)

1586 15 (Alexandre et al. 2009) 1519 22 et 1486 9 Ma U/Pb à McArthur River et

1467 47 à Cigare Lake parmi les plus anciennes mesurées a la sonde ionique dans l’Athabasca (Fayek et al. 2002), (3) 1329 17 Ma à Key lake (Cumming and Krstic 1992), (4)

1275 22 à Shea Creek, ou bien encore 900 Ma (Fayek et al. 2002). Ces datations n’excluent pas la possibilité de remobilisations plus tardives d’une partie de la minéralisation sous la formes de fronts d’oxydo-réduction datés jusqu’à moins de 400 Ma (Mercadier et al.

2010).

A Shea Creek, il existe une bonne concordance entre les âges obtenus sur les illites du halo d’altération (1453 2, 1330 20 et 1235 Ma ) et ceux obtenus sur les uraninites du gisement

(Laverret et al. 2010).

Comme ces auteurs l’on proposé il est possible de relier ces différents âges d’une part à l’événement diagénétique ayant affecté l’ensemble du bassin au alentour de 1500 Ma

(contemporain de la fin de l’orogène Mazatzal et des minéralisations les plus anciennes) et d’autre part aux remobilisations qui ont pu être contemporaines d’autres phases tectoniques tels que les orogènes Bertoud et Grenville respectivement vers 1400 et 1100 Ma et les dykes de Mackenzie à 1267 2 Ma (LeCheminant and Heaman 1989), la formation et dislocation de

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Les données de datations de la littérature sont bien moins abondantes pour les gisements du bassin du Thelon. On peut toutefois mentionner des âges à 1403 10 Ma U/Pb (Farkas

1984) sur roche totale pour Kiggavik ainsi que des âges K/Ar sur illite à 1386 24 Ma, 1362

21 Ma (Miller and LeCheminant 1985) ou 1073 Ma (Miller 1981). Des âges plus récents à environ 1200 Ma ont été obtenu sur la minéralisation massive d’End, échantillonné en 2010 et confiée à M. Brouand pour analyse à la microsonde ionique. On retrouve des gammes d’âges concordantes entre évènements de minéralisation et d’altération. On peut noter des âges pafois proches pour les minéralisations en uranium associées à l’Athabasca et au Thelon.

Enfin l’âge de la sédimentation ou du début de la diagenèse à été contraint à 1730-1750 Ma pour le bassin d’Athabasca par la datation des derniers épisodes métamorphiques (Orrell et al.

1999) et à 1720 6 Ma et 1667 5 Ma par datation Pb/Pb sur apatite diagénétique en ciment à la base du Thelon (Miller et al. 1989) et datation in situ U/Pb sur fluorapatite (Davis et al.

2011) respectivement pour le bassin du Thelon .

3.7. Géologie des gisements d’uranium du district de Kiggavik

3.7.1. Localisation et bref historique des travaux d’exploration

Le projet Kiggavik anciennement dénommé Lone Gull est situé à 80 km à l’ouest du hameau

Inuit de Baker Lake, au Nunavut. Les premiers travaux d’exploration de ce gisement qui est activement prospecté depuis quelques années, remontent à 1974 lors de la découverte de minéralisations uranifères sub-affleurantes à Kiggavik s.s lors d’une campagne de radiométrie aéroportée menée par Urangesellschaft Canada (UG). Ceci conduira à la découverte de la lentille de Main Zone en 1977 avec un premier sondage intersectant 35m de roches altérées contenant 1% U3O8 (Fuchs et al. 1986). L’actuel camp d’exploration des équipes d’AREVA

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Resources Canada (ARC) se situe à quelques centaines de mètres à l’Est de cette zone, à l’emplacement de l’ancien camp Schutlz-Sissons South d’UG, Figure 3-11.

Figure 3-11 : Camp d’exploration de Kiggavik, crédit photo aérienne : AREVA Resources Canada

Le district comprend plusieurs zones minéralisées d’importance économique ainsi que de nombreux prospects ou zones à fort potentiel en cours de développement ou de test. Ainsi du

Nord Est au Sud Ouest des propriétés formant le projet on retrouve Kiggavik ss., la découverte initiale (1974), Bong (1986) , End (1987), et enfin Andrew (SW Grid, 1988) puis

Jane (1993), l’ensemble de ces zones minéralisées totalise un contenu de ressources historiques d’approximativement 58000t d’uranium. Le projet comprend deux grandes zones non contigües de permis d’exploration composées de St Tropez au Nord et de Kiggavik au

Sud, Figure 3-12 et 3-15.

A l’échelle régionale, les guides de prospection suivis ont été tout d’abord, la géophysique avec la combinaison de données de résistivité et de gravimétrie permettant de localiser les structures et les zones altérées (Hasegawa et al. 1990). Par la suite de proche en proche, l’exploration a été menée en suivant le contact entre les bancs de quarztites massifs (archéen

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Ce contact étant lui-même souligné par de puissantes zones de brèches à remplissage de quartz, souvent associées à une forte hématitisation. Ces brèches sont par ailleurs recoupées en sondages dans l’ensemble des zones minéralisées de Kiggavik ou elles délimitent souvent deux zones de minéralisations de part et d’autre du couloir de brèche à remplissage de quartz.

Figure 3-12 : Carte des droits miniers pour les projets ARC de la bordure Sud Ouest du bassin du Thelon

(Kiggavik et St Tropez) et localisation du camp d’exploration de Kiggavik (Morisson et al. 2012)

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3.7.2. Séquence lithostratigraphique de la bordure Sud Est du bassin du

Thelon et position des minéralisations

L’encaissant des minéralisations et principalement formé par des métagraywackes Archéens

(2711 3 Ma) appartenant au groupe de Woodburn, et dans une moindre mesure dans des métagranodiorites (assignées au méso-Archéen) mis eu contact avec les métagraywackes par le biais d’une structure mylonitique plate, parallèle à la foliation, Figure 3-13. Les granites et syénites Hudsonienne ou Nuetlin peuvent être minéralisés plus rarement. Un lien génétique entre la minéralisation en uranium et les roches intrusives été évoqué dans les travaux historiques sur le gisement de Kiggavik (Weyer et al. 1987). Cette proximité spatiale entre roches intrusives et minéralisations uranifères est exprimée à Kiggavik ss, à End Grid et à

Andrew Lake. Les roches intrusives sont majoritairement représentées par des granites et des syénites hudsoniennes souvent riches en fluorine (1840-1830 Ma) sous la forme de dykes sécants sur la foliation horizontale ou de sills entourés d’un fin halo de cornéennes (Jeffrey et al. 2010; Peterson et al. 2002). Les intrusions de l’épisode Nuetlin et leur équivalent volcanique (Pitz rhyolite) datés à à 1750 Ma sont présents à l’affleurement à Andrew lake et sont fréquemment recoupées en sondage sous la forme de dykes de granite porphyrique à texture rapakivi.

Les minéralisations semblent s’enraciner plus en profondeur vers le SW du faisceau minéralisé. De Kiggavik jusqu’à Andew, la minéralisation est trouvée à l’affleurement, dans les métagraywackes altérés. A Jane, elle est encaissée dans des orthogneisses sous la forme de veines à remplissage de pechblende. Les quartzites qui séparent les lentilles supérieures et inférieures du gisement de Kiggavik sont également rencontrés au dessus de la zone minéralisée à Bong, Figure 3-14.

On peut enfin noter que les contacts entre les unités lithologiques ou les structures brêchiques forment souvent des zones favorables au dépôt des lentilles minéralisées. C’est tout

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Figure 3-13 : Coupe géologique dans une section du gisement d’Andrew Lake (données UG/AREVA Resources

Canada Inc.)

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Figure 3-14 : Coupe du gisement de Center Zone à Kiggavik montrant la position des minéralisations par rapport aux bancs massifs de quartzite (Weyer 1992)

3.7.3. Structuration ductile et déformation fragile

Comme il a été présenté précédement, un lien fort est établi entre les structures et les minéralisations dans les gisements de type discordance. A Kiggavik l’histoire tectono- métamorphique polyphasée et complexe a contribué au développement des discontinuités qui sont les drains préférentiels des fluides minéralisateurs. On reprendra rapidement ici les résultats établis par les travaux de terrains et les analyses structurales de Jean-Louis Feybesse et Nicolas Flotté réalisés en 2009, 2010 autour de Kiggavik (Flotté 2009; Feybesse 2010).

- La déformation ductile

On peut identifier deux grandes phases tectoniques tardi-archéennes avec (1) la mise en place de plis à vergence NW et NNW dans le socle méso-Archeén puis (2) la mise en place de nappes de chevauchement exprimée par une zone mylonitique faiblement pentée à la base des

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1995).

Une troisième phase de déformation est caractérisée par le developpement d’une zone de cisaillement Nβ70 à linéation d’étirement E-W. Elle est principalement observée à la base des quartzites et elle constitue une des discontinuités majeures de la zone de Kiggavik avec pour conséquence l’entrainement des quartzites massifs dont la position dans la pile lithologique

(elles reposent sur les roches du Woodburn Group par le jeu d’une zone mylonitiques faiblement pentée vers le Nord) fait toujours l’objet de débat. Cette phase de déformation est attribuée à la phase hudsonienne (Paléoproterozoique)

- Déformation fragile

Plusieurs familles de failles sont identifiées avec à l’échelle régionale. Il s’agit de la faille du Thelon, Judge Sisson lake ou leur parallèles dont l’expression est visible aussi bien à l’affleurement qu’en sondage autour des zones End Grid et Bong. On a alors, pour structure de premier ordre, la faille d’Andrew lake, d’orientation NE-SW et de cinématique interprétée dextre par la suite réactivée en senestre. Les minéraliations d’Andrew et Jane se trouvent distribuées le long de cette structure. Le second ordre de faille est d’orientation globale

WNW-ESE (N70 à N100) avec une cinématique dextre. Ces dernières structures sont soulignées par une forte cataclase et de puissantes zones de brèches à remplissage de quartz.

Elles présentent également une hématitisation intense qui affecte le socle métamorphique, les intrusifs (hudsonien et Nuetlin) ainsi que les sédiments du Thelon.

A ces failles (et les brêches tectoniques associées) sont reliés un ensemble de structures dextres redressées d’orientation N1β0-N130, formant parfois des zones de relais avec les

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Nord.

Enfin une série de failles tardives sont venues modifier la géométrie des éléments structuraux précédents et affecter les sédiments des bassins de Baker lake et de Wharton. Il s’agit, soit de failles Nord-Sud, à N30 senestres, soit de failles N160 dextre (Rainbird and Hadlari 2000).

Ces structures tardives ne se limitent pas à la zone de Kiggavik. Elles s’expriment dans l’ensemble de la province de Rae. Elles ont été observées dans le gisement de Sue C dans la partie est du bassin d’Athabasca (Flotté et Feybesse, 2008).

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Figure 3-15 : Carte géologique révisée de la bordure Sud Ouest du Thelon et synthèse stratigraphique des formations Archéennes d’après (Jefferson et al. 2011)

40

Références

4. Références

Alexandre P, Kyser K, Thomas D, Polito P, Marlat J (2009) Geochronology of unconformity- related uranium deposits in the Athabasca Basin, Saskatchewan, Canada and their integration in the evolution of the basin. Miner Deposita 44:41-59. doi: 10.1007/s00126-007-0153-3. Andrade N (ed) (2002) Geology of the Cigar Lake uranium deposit. Geological Association of Canada - Mineralogical association of Canada, Saskatoon, SK. Ashton KE (1988) Precambrian Geology of the Southeastern Amer Lake Area (66H/1), Near Baker Lake, N.W.T. Queens University. Aspler LB, Wisotzek IE, Chiarenzelli JR, Losonczy MF, Cousens BL, McNicoll VJ, Davis WJ (2001) Paleoproterozoic intracratonic basin processes, from breakup of Kenorland to assembly of Laurentia: Hurwitz Basin, Nunavut, Canada. Sedimentary Geology 141–142:287-318. doi: http://dx.doi.org/10.1016/S0037-0738(01)00080-X. Aspler LB, Chiarenzelli JR, McNicoll VJ (2002) Paleoproterozoic basement-cover infolding and thick-skinned thrusting in Hearne domain, Nunavut, Canada: intracratonic response to Trans-Hudson orogen. Precambrian Research 116:331-354. doi: http://dx.doi.org/10.1016/S0301-9268(02)00029-3. Bagas L (2004) Proterozoic evolution and tectonic setting of the Northwest Paterson Orogen, Western Australia. Precambrian Research 128:475-496. Battey GC, Miezitis Y, McKay AD (1987) Australian uranium resources. Bureau of Mineral Resources, Geology and Geophysics, pp 69. Beaudemont D (1995) Sisson Project, regional tectonics and structural control of mineralization, report on summer 1995 inverstigation. Cogemac Inc, pp 41. Beaudemont D, Fedorowich J (1996) Structural control of uranium mineralization at the Dominique-Peter deposit, Saskatchewan, Canada. Economic Geology 91:855-874. Beaufort D, Patrier P, Laverret E, Bruneton P, Mondy J (2005) Clay Alteration Associated with Proterozoic Unconformity-Type Uranium Deposits in the East Alligator Rivers Uranium Field, Northern Territory, Australia. Economic Geology v. 100:pp. 515–536. Betts PG, Giles D, Schaefer BF (2008) Comparing 1800 – 1600 Ma accretionary and basin processes in Australia and Laurentia: Possible geographic connections in Columbia. Precambrian Research 166:81-92. doi: http://dx.doi.org/10.1016/j.precamres. 2007.03.007. Corrigan D, Galley AG, Pehrsson S (2007) Tectonic evolution and metallogeny of the southwestern Trans-Husdon Orogen In: Goodfellow WD (ed) Mineral Deposits of Canada: A synthesis of Major Deposit-Types, District Metallogeny, the Evolution of Geological Provinces, and Exploration Methodes. Geological Association of Canada, Mineral Deposits Division, pp 881-902. Creaser RA, Stasiuk LD (2007) Depositional age of the Douglas Formation, northern Saskatchewan, determined by Re-Os geochronology In: Jefferson CW (ed) EXTECH IV: Geologyand Uranium EXploration TECHnology of the Proterozoic AthabascaBasin, Saskatchewan and Alberta. Geological Survey of Canada, pp 341- 346.

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Cumming GL, Krstic D (1992) The age of unconformity related uranium mineralization in the Athabasca Basin, northern Saskatchewan. Canadian Journal of Earth Sciences 29:1623-1639. Cuney M, Brouand M, Cathelineau M, Derome D, Freiberger R, Hecht R, Kister P, Lobaev V, Lorilleux G, Peiffert C, Bastoul AM (2003) What parameters control the high grade- large tonnage of the Proterozoic unconformity related uranium deposits? In: Cuney M (ed) International conference on uranium geochemistry. Université Henri Poincaré, Nancy, pp 123-126. Davis WJ, Gall Q, Jefferson CW, Rainbird RH (2011) Fluorapatite in the Paleoproterozoic Thelon Basin: Structural-stratigraphic context, in situ ion microprobe U-Pb ages, and fluid-flow history. Geological Society of America Bulletin 123:1056-1073. doi: 10.1130/b30163.1. Duebendorfer EM, Houston RS (1987) Proterozoic accretionary tectonics at the southern margin of the Archean Wyoming craton. Geological Society of America Bulletin 98:554-568. Duebendorfer EM, Chamberlain KR, Jones CS (2001) Paleoproterozoic tectonic history of the Cerbat Northwestern Arizona:Implications for crustal Southwestern United States. Geological Society of America Bulletin 113:575-590. Eriksson PG, Martins-Neto MA, Nelson DR, Aspler LB, Chiarenzelli JR, Catuneanu O, Sarkar S, Altermann W, Rautenbach CJdW (2001) An introduction to Precambrian basins: their characteristics and genesis. Sedimentary Geology 141–142:1-35. doi: http://dx.doi.org/10.1016/S0037-0738(01)00066-5. Farkas A (1984) Mineralogy and host rock alteration of the Lone Gull deposit Internal report. Urangesellschaft, Frankfurt am Main, pp 45. Fayek M, Kyser K (1997) Characterization of multiple fluid events and rare-earth-element mobility associated with formation of unconformity-type uranium deposits in the Athabasca Basin, Saskatchewan. The Canadian Mineralogist 35:627-658. Fayek M, Kyser K, Riciputi LR (2002) U and Pb isotope analysis of uranium minerals by ion microprobe and the geochronology of the McArthur River and Sue zone uranium deposits, Saskatchewan, Canada. Canadian Mineralogist 40:1553-1569. Feybesse J-L (2010) Sequence of structural events in the Kiggavik district ( Nunavut, Canada): The uranium mineralization in its geological and tectonic setting and structural control on the ore bodies geometry. AREVA BGM/DGS. Flotté N (2009) End Grid geological and structural study. AREVA Resources Canada, Saskatoon. Fuchs HD, Hilger W, Prosser E (eds) (1986) Geology and exploration history of the Lone Gull property. CIM. Gandhi SS (1995) An overview of the exploration history and genesis of Proterozoic uranium deposits in the Canadian Shield. Exploration and Research for Atomic Minerals 8:1- 47. Gandhi SS (2006) Significant unconformity-associated uranium deposits of the Athabasca Basin, Saskatchewan and Alberta and selected related deposits of Canada and the world In: GSC (ed) Open File 5005. pp (CD-ROM). Hanmer S, Williams ML, Kopf C (1995) Striding-Athabasca mylonite zone: implications for the Archean and Early Proterozoic tectonics of the Western Canadian shield. Canadian Journal of Earth Sciences 32:178-196. Hartlaub RP, Heaman LM, Ashton KE, Chacko T (2004) The Archean Murmac Bay Group: evidence for a giant Archean rift in the Rae Province, Canada. Precambrian Research 131:345-372.

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Hasegawa K, Davidson GI, Wollenberg P, Yoshimasa I (1990) Geophysical exploration for unconformity-related uranium deposits in the northeastern part of the Thelon Basin, Northwest Territories, Canada. Mining Geology 40:83-95. Hills FA (1987) Tectonic environment of Precambrian quartz-pebble conglomerate uranium deposits formed along the southern margin of the Archean shield in North America In: Agency IAE (ed) Report of the working group on uranium geology organized by the International Atomic Energy Agency. Vienna, pp 453. Hoeve J, Sibbald TII (1978) On the genesis of the Rabbit Lake and other unconformity-type uranium deposits in Northern Saskatchewan, Canada. Economic Geology 73. Hoeve J, Sibbald TII, Ramaekers P, Lewry JF (1980) Athabasca basin unconformity-type uranium deposits : a special class of sandstone-type deposits? In: Ferguson J, Goleby AB (eds) Uranium in the Pine Creek Geosyncline. International Atomic Energy Agency, Vienna, pp pp. 575-594. 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 Concil Technical report. Saskatchewan Reasearch Council, pp 197. Hoffman PF (1988) United Plates of America, The Birth of a Craton: Early Proterozoic Assembly and Growth of Laurentia. Annual Review of Earth and Planetary Sciences 16:543-603. doi: doi:10.1146/annurev.ea.16.050188.002551. Hoffman PF (1990) Subdivision of the Churchill Province and extent of the Trans-Hudson orogen In: Lewry JF, Stauffer MR (eds) The Early Proterozoic Trans-Hudson Orogen of North Amercia. Geological Survey of Canada Special Paper, pp 15-39. Jefferson CW, Thomas DJ, Gandhi SS, Ramaekers P, Delaney G, Brisbin D, Cutts C, Portella P, Olson RA (2007a) Unconformity-associeted uranium deposits of the Athabasca Basin, Saskatchewan and Alberta EXTECH IV. pp 23-67. Jefferson CW, Thomas DJ, Gandhi SS, Ramaekers P, Delaney G, Brisbin D, Cutts C, Quirt D, Portella P, Olson RA (2007b) Unconformity-associated uranium deposits of the Athabasca Basin, Saskatchewan and Alberta In: Goodfellow WD (ed) Mineral Deposits of Canada: A synthesis of Major Deposit-types, District Metallogeny, the Evolution of Geological Provinces, and Exploration Methods. Geological Association of Canada, Mineral deposits division, pp 273-305. Jefferson CW, Pehrsson S, Peterson T, Chorlton L, Davis DW, Keating P, Gandhi SS, Fortin R, Buckle JL, Miles W, Rainbird RH, LeCheminant AN, Tschirhart V, Tschirhart P, Morris W, Scott J, Cousens B, McEwan B, Bethune K, Riemer W, Calhoun L, White J, MacIssac D, Leblon B, Lentz D, laRocque A, Shelat Y, Patterson J, Enright A, Stieber C, Riegler T (2011) Northeast Thelon region geoscience framwork-new maps and data for uranium in Nunavut In: Canada NR (ed). Geological Survey of Canada. Jeffrey S, Peterson T, Jefferson CW, Cousens B (2010) Proterozoic (1.85-1.7 Gaà granitoid rocks and uranium in the Baker Lake -Thelon Basin region, Nunavut GeoCanada2010. Calgary. Karlstrom KE, Bowring SA (1988) Early Proterozoic assembly of tectonostratigraphic terranes in Southwestern North America. J Geol 96:561-576. Karlstrom KE, Åhäll K-I, Harlan SS, Williams ML, McLelland J, Geissman JW (2001) Long lived (1.8-1.0 Ga) convergent orogen in southern Laurentia, its extensions to Australia and Baltica, and implications for refining Rodinia. Precambrian Research 111:5-30. Kerrich R, Goldfarb RJ, Richards JP (2005) Metallogenic Provinces in an Evolving Geodynamic Framework. Economic Geology 100th Anniversary Volume:1097-1136. Koeppel V (1967) Age and history of uranium mineralization of the Beaverlodge area, Saskatchewan. Geological Survey of Canada, pp 111.

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Kotzer TG, Kyser TK (1995) Petrogenesis of the Proterozoic Athabasca Basin, northern Saskatchewan, Canada, and its relation to diagenesis, hydrothermal uranium mineralization and paleohydrogeology. Chemical Geology 120:45-89. doi: http://dx.doi.org/10.1016/0009-2541(94)00114-N. Kyser K, Hiatt EE, 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: Kyser K (ed) Fluids and Basin Evolution. Mineralogical Association of Canada, pp 225-258. Laverret E (2002) Evolution temporelles et spatiales des altérations argileuses des gisements d'uranium sous discordance, secteur de Shea Creek (basin d'Athabasca, Canada). Université de Poitiers, pp 192. Laverret E, Clauer N, Fallick A, Mercadier J, Patrier P, Beaufort D, Bruneton P (2010) K–Ar dating and δ18O–δD tracing of illitization within and outside the Shea Creek uranium prospect, Athabasca Basin, Canada. Applied Geochemistry 25:856-871. doi: http://dx.doi.org/10.1016/j.apgeochem.2010.03.004. LeCheminant AN, Heaman LM (1989) Mackenzie igneous events, Canada: Middle Proterozoic hotspot magmatism associated with ocean opening. Earth and Planetary Science Letters 96:38-48. doi: http://dx.doi.org/10.1016/0012-821X(89)90122-2. Lorilleux G (2001) Les brèches associées aux gisements d'uranium de type discordance du bassin d'Athabasca, Saskatchewan, Canada Institut National Polytechnique de Lorraine. Université Henri Poincaré, Vandoeuvre les Nancy. Macdonald R (1980) Mineralogy and geochemistry of a Precambrian regolith in the Athabasca Basin. University of Saskatchewan, Saskatoon, pp 151. McGill B, Marlat J, Matthews RB, Sopuck V, Homenuik L, Hubergtse J (1993) The P2 North uranium deposit, Saskatchewan, Canada. Exploration Mining Geology 2:321-331. Mercadier J, Cuney M, Cathelineau M, Lacorde M (2010) U redox and kaolinisation in basement-hosted unconformity-related U ores of the Athabasca Basin (Canada): late U remobilisation by meteoric fluids. Miner Deposita 46:105-135. Miller AR (1981) Lone Gull deposit district of Keewatin, N.W.T. Geological Survey of Canada. Miller AR, LeCheminant AN (1985) Geology and uranium metallogeny of Proterozoic supracrustal successions, central District of Keewatin, N.W.T with comparisons to northern Saskatchewan Geology of uranium deposits. Canadian Institute of Mining and Metalurgy, pp 167-185. Miller AR, Cumming GL, Krstic D (1989) U-Pb, Pb-Pb, and K-Ar isotopic study and petrography of uraniferous phosphate-bearing rocks in the Thelon Formation, Dubawnt Group, Northwest Territories, Canada. Canadian Journal of Earth Sciences 26:867-880. Molnar P, Houseman GA, Conrad CP (1998) Rayleigh-Taylor instability and convective thinning of mecanically thickened lithosphere:effects of non-linear viscosity decreasing exponentially with depth and horizontal shortening of the layer. Geophys J Int 133:568-584. Morisson D, McCallum B, Zunti D, Jackson K, Carter C, Calayan N, Richard Y (2012) Kiggavik Project Field Program 2012 Annual Report In: Stumborg N (ed). AREVA Resources Canada Inc., Saskatoon. Orrell SE, Bickford ME, Lewry JF (1999) Crustal evolution and age of thermotectonic reworking in the western hinterland of the Trans-Hudson Orogen, northern Saskatchewan. Precambrian Research 95:187-223.

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Pagel M (1975) Détermination des conditions physico-chimique de la silicification diagénétique des grès Athabasca (Canada) au moyen des inclusions fluides. Comptes Rendus de l'académie des Sciences Paris 280:2301-2304. Percival JB, Kodama H (1989) Sudoite from Cigar Lake, Saskatchewan. Canadian Mineralogist 27:633-641. Peterson TD, Van Breemen O, Sandeman H, Cousens B (2002) Proterozoic (1.85-1.75 Ga) igneous suites of the Western Churchill Province: granitoid and ultrapotassic magmatism in a reworked Archean hinterland. Precambrian Research 119:73-100. Polito P, Kyser K, Thomas DJ, Marlat J, Dreaver G (2005) Re-evaluation of the Petrogenesis of the Proterozoic Jabiluka unconformity-related uranium deposit, Northern Territory, Australia. Miner Deposita 40:257-288. Polito PA, KYSER TK, Marlatt J, Alexandre P, Bajwah Z, Drever G (2004) Significance of Alteration Assemblages for the Origin andEvolution of the Proterozoic Nabarlek Unconformity-Related Uranium Deposit,Northern Territory, Australia. Economic Geology 99:113-139. doi: 10.2113/gsecongeo.99.1.113. Quirt D (2003) Athabasca unconformity type uranium deposits: one deposit type with many variations. In: Cuney M (ed) Uranium Geochemistry International Conference. Nancy, France, pp 309-312. Rainbird RH, Hadlari T (2000) Revised stratigraphy and sedimentology of the Paleoproterozoic Dubawnt Supergroup and the Northern Margin of Baker Lake Basin, Nuanvut Current Research. Geological Survey of Canada, pp 9. Rainbird RH, Hadlari T, Aspler LB, Donaldson JA, LeCheminant AN, Peterson TD (2003) Sequence stratigraphy and evolution of the Paleoproterozoic intracontinental Baker Lake and Thelon basins, western Churchill Province, Nunavut, Canada. Precambrian Research 125:21-53. Rainbird RH, Stern RA, Rayner N, Jefferson CW (2006) Ar-Ar and U-Pb geochronology of a late Paleoproterozoic rift basin: support for a genetic link with Hudsonian orogenesis, western Chruchill Province, Nunavut, Canada. The Journal of Geology 114:1-17. Rainbird RH, Davis WJ (2007) U-Pb detrital zircon geochronology and provenance of the late Paleoproterozoic Dubawnt Supergroup: Linking sedimentation with tectonic reworking of the western Churchill Province, Canada. Geological Society of America Bulletin 119:314-328. doi: 10.1130/b25989.1. Ramaekers P, Catuneanu O (2004) Develoment and sequences of the Athabasca Basin, Early Proterozoic, Saskatchewan and Alberta, Canada In: Eriksson PG, Altermann W, Nelson DR, Mueller WU, Catuneanu O (eds) The Precambrian Earth: Tempos and Events. Elsivier, Amsterdam, Netherlands, pp 705-723. Renac C, Kyser K, Durocher K, Dreaver G, O'Connor T (2002) Comparison of diagenetic fluids in the Proterozoic Thelon and Athabsca Basins, Canada: implications for protracted fluid histories in stable intracratonic basins. Can J Earth Sci 39:113-132. Ruzicka VR (1993) Unconformity type uranium deposits In: Kirkham RV, Sinclair WD, Thorpe RI, Duke JM (eds) Mineral Deposit Modeling. Geological Survey of Canada, Ottawa, pp 125-149. Ruzicka VR (1996) Unconformity-associated uranium In: Eckstrand OR, Sinclair WD, Thorpe RI (eds) Geology of Canadian Mineral Deposits. Geological Survey Of Canada, pp 197-210. Sibbald TII, Munday RJC, Lewry JF (1976) The geolgical setting of uranium mineralization in northern Saskachtewan In: Dunn CE (ed) Uranium in Saskatchewan. Saskatchewan Geological Society, pp 51-98. Sibbald TII (1985) Geology and genesis of the Athabasca Basin uranium deposits In: Macdonald R, Sibbald TII, Paterson DF (eds) Summary of Inversitgations 1985.

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Saskatchewan Geological Survey: Saskatchewan Energy and Mines Miscellaneous Report, pp 133-156. Stauffer MR (1984) Manikewan and early proterozoic ocean in central Canada, its igneous history and orogenic closure. Precambrian Research 25:257-281. Thomas DJ, Matthews RB, Sopuck V (2000) Athabasca Basin (Canada) unconformity-type uranium deposits: exploration model, current mine developpments and exploration directions In: Cluer JK, Price JG, Struhsacker EM, Hardyman RF, Morris CL (eds) Geology and Ore Deposits 2000:The Great Basin and Beyond, Geological Society of Nevada symposium proceedings. Reno, NV, pp 103-126. Tourigny G, Quirt D, Wilson N, Wilson S, Breton G, Portella P (2007) Basement geology of the Sue C uranium deposit, McClean Lake area, Saskatchewan In: Jefferson CW, Delaney G (eds) EXTECH IV:Geology and uranium EXploration TECHnology of the Proterozoic Athabsca Basin, Saskatchewan and Alberta. Geological Survey of Canada, Mineral Deposits division, pp 229-248. Weyer H-J, Friedrich G, Bechtel A, Ballhorn RK (1987) The Lone Gull uranium deposit-New geochemical and petrological data as evidence for the nature of the ore bearing solutions Metallogenesis of uranium deposits. IAEA, Vienna. Weyer H-J (1992) Die uraniagnerstätte Kiggavik, Nordwesterritorien, Kanada Fakultät für Bergbau, Hüttenwesen und Geowissenschaften. Rheinisch-Westfälischen Technischen Hochschule, Aachen, pp 223. Wilde AR, Wall VJ (1987) Geology of the Nabarlek uranium deposit, Northern Territory, Australia. Economic Geology 82:1152-1168. Zhao G, Wilde SA, Li S (2004) A Paleo-Mesoproterozoic supercontinent: assembly, growth and breakup. Earth-Science Reviews 36:678-686.

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Echantillonnage

5. Echantillonnage

Tableau 5-1 : Description générale de l’échantillonnage de la zone de Kiggavik – St Tropez.

Depth DrillHole (m) Samples Purpose W97-4 191.1 18 Regional Alteration background B1-94-1 224.3 9 " BSE1 154.5 5 " W-2 94.2 4 "

Bong51 300.6 4 carbonaceous material Bong50 386.7 28 Reference in Bong prospect Bong45 405.0 40 Reference in Bong prospect Bong42 459.0 43 Reference in Bong prospect Bong43 495.0 36 Reference in Bong prospect Bong33 223.4 11 Reference in Bong prospect Bong39 486.2 29 Reference in Bong prospect Bong26 225.6 8 Reference in Bong prospect Bong24 312.4 17 Reference in Bong prospect Bong8 232.6 16 Reference in Bong prospect Bong6 204.9 4 Reference in Bong prospect BongExt2 177.1 9 Alteration without mineralisation

SW8 191.1 17 Reference in Andrew deposit And10-01 387.0 38 "

End09- 11 378.8 15 Reference in End deposit End09-10 377.6 17 Reference in End deposit End09-09 393.0 20 Reference in End deposit End09-08A 347.4 18 Reference in End deposit End09-07 348.6 10 Reference in End deposit End09-05 272.0 16 Reference in End deposit End09-04 420.0 35 Reference in End deposit/Mineralization End09-03 436.2 18 Reference in End deposit End09-02 465.0 13 Reference in End deposit End13 230.7 9 alteration without mineralization

SL9 335.9 5 Sleek Area alteration without Umin

Th18 123.6 7 regional sandstones NE of Kiggavik

Outcrops Granite Grid 7 basal Thelon Fm conglomeratic sandstones St Tropez 7 basal Thelon Fm conglomeratic sandstones Uno 1 Fluorite bearing granite Andrew&End 10 quartz breccia & porphyitic rhyolite Unconformity Lake 8 basal Thelon & Woodburn

47

Echantillonnage

A. LE SYSTEME D’ALTERATION DU FAISCEAU DE KIGGAVIK-

ANDREW LAKE ET SES RELATIONS AVEC LES

MINERALISATIONS EN URANIUM

48

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy 1. Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy

Thomas Riegler*, Jean-Luc Lescuyer***, Peter Wollenberg***

Dave Quirt*** and Daniel Beaufort**

Accepted in Canadian Mineralogist

*IC2MP, HydrASA / ERM, Université de Poitiers, CNRS UMR 7285, Bâtiment

B08, Rue Albert Turpin, 86022 Poitiers cedex, [email protected]

** IC2MP, HydrASA, Université de Poitiers, CNRS UMR 7285, Bâtiment B35,

Rue Michel Brunet, 86022 Poitiers cedex, [email protected]

***AREVA Mines & AREVA Ressources Canada, Tour AREVA, 1 place Jean

Millier 92084 Paris la Défense Cedex

1.1. Abstract

The Kiggavik project, located 70km west of Baker Lake (Nunavut) is a major uranium exploration project in the Canadian arctic, with three significant basement hosted uranium deposits (Kiggavik, End and Andrew) which spread along a NE-SW trend a few kilometers to the south-eastern border of the Thelon Basin. These deposits are closely associated with alteration zones in which clay minerals are abundant. At the scale of the whole structural trend, the alteration paragenesis is composed of illite ± sudoite ± hematite ± aluminum phosphates sulfates minerals (APS). Alteration petrography and mineral paragenesis are similar to those identified in basement hosted uranium deposits related to Paleoproterozoic unconformities in the Athabasca Basin (Canada) or the Alligator River (Australia). The

49

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy alteration haloes are characterized by two similar types of phyllosilicate assemblages

(dioctahedral micas or illite and chlorites) corresponding to a regional retrograde metamorphic stage that was overprinted by hydrothermal alteration during the mineralization event. These two assemblages can be distinguished on the basis of crystallographic and chemical properties and mapping of structural parameters such as the variation of crystallinity along the c-axis or the polytypes of phyllosilicates can been used as a vector to mineralization. The crystal-chemistry of the hydrothermal phyllosilicates replacing the previous metamorphic minerals indicates a release of iron. This last point is fundamental regarding the occurrence of hematite in alteration zones and points out the potential effects of iron redox state in the control of uranium precipitation during the hydrothermal event.

1.2. Introduction

The Kiggavik project (previously named Lone Gull), located 70km west of Baker Lake,

Nunavut hosts several significant uranium deposits and very prospective areas, with an overall uranium content of approximately 50,000t U of historical resources (Jefferson et al. 2007).

The deposits and prospects are structurally controlled along a NE-SW trend and are exclusively basement hosted in Late Archean metasediments. This rock package consists of dominant meta-arkose (wacke) and minor quartzite and rhyolites (Miller and LeCheminant

1985) later intruded by a suite of igneous bodies including Hudsonian fluorite-bearing granites, syenites and lamprophyres (Peterson et al. 2002). The northern end of the trend, where the Kiggavik deposit is located lies two kilometers south of the unconformity between the Archean basement the late Paleoproterozoic Thelon Formation sandstones (Miller et al.

1989). Sub-outcropping mineralization was first discovered in 1974 following an airborne radiometric survey by Urangesellschaft Canada, then followed with ground resistivity and gravity surveys in further exploration work to detect alteration zones (Fuchs et al. 1986,

Hasegawa et al. 1990). This target identification method has been successfully used and lead

50

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy to several additional discoveries along the trend indicating that alteration features where in most cases spatially related to mineralized zones.

Following the trend toward the southwest are found the Bong prospect, the End and

Andrew deposits (Fig. 1-1). The last known mineralization southward of this 18 kilometer long mineralized trend is the Jane prospect. The main structural feature and regional pathfinder are kilometer long ENE-WSW faults showing an intense hydrothermal activity with both hematization and quartz veining. The nature and origin of the hydrothermal processes responsible for uranium mineralization and its associated alteration haloes are still unclear at Kiggavik.

Initially, exploration was carried out to find high-grade uranium in a geological context similar to the basement rocks underlying the late Paleoproterozoic Athabasca Basin in

Northern Saskatchewan. Alternative models favored hydrothermal systems partly related to heat sources generated by the numerous intrusive bodies identified in the area (Weyer et al.

1987) but geochronology of pitchblende (bulk U/Pb) and illite (whole rock K/Ar) from altered and mineralized metasediments showed younger but discordant with possible lead loss or late remobilization ages respectively around 1403 10 Ma, (Farkas 1984) and 1386±24 Ma K/Ar

(Miller and LeCheminant 1985). Salinity of the basinal brines, stable isotopes on diagenetic clays and geochronology in the Thelon and Athabasca Basins had highlighted similar diagenetic histories (Hiatt et al. 2010, Renac et al. 2002). However, uranium deposits within the Kiggavik-Andrew Lake trend significantly differ from the unconformity-related uranium deposits in the Athabasca basin by (1) the absence of graphite along the regional faults as well as in the mineralized structures and (2) a lower average ore grade (around 0.5%).

51

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy

Figure 1-1 : Kiggavik-Andrew Lake simplified geological map, showing deposit & prospects. Black dots for sampled drillhole locations, simplified geology based on GSC Open file 1839, Schultz Lake GIS map.

52

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy The aim of the present study is to determine the sequence of mineral crystallization that occurred in the alteration halo associated with uranium mineralization along the

Kiggavik-Andrew Lake trend. Alteration petrology has been used to refine the spatial distribution of the mineral assemblages and the chronological relationships between the secondary mineral phases related to uranium mineralization. The mineralogical characteristics of the alteration halo have been compared with those of the unconformity-related uranium deposits of the Athabasca Basin in order to provide new insight on the genesis of uranium mineralization at Kiggavik. Finally, crystal structure and crystal chemistry of clay minerals and associated mineral phases have been investigated to identify new vectors to mineralization at the prospect scale.

1.3. Geological setting

A simplified geological map of the Kiggavik-Andrew lake area is presented in Figure 1-1

(Hadlari et al. 2004). At a regional scale, the litho-structural pile consists of Mesoarchean granitic, granodioritic and augen gneisses (2866±6 Ma; (Zaleski et al. 2001) tectonically overlain by a Neoarchean metavolcano-sedimentary package retromorphosed to greenschist facies. The latter consists in quartzo-feldspatic wackes and minor quartzite with thin interbedded banded iron formation layers, rare black shales, and locally komatiite and rhyolite. Geochronology on interbedded volcanics in the wacke give a U-Pb zircon age of

2710±2.1 Ma (Davis and Zaleski 1998). This Archean supracustal package, known as the

Woodburn Lake Group (WLG), belongs to a set of several greenstone belts due to continental rifting of the Rae Province, which extends over 2000 km from northern Saskatchewan to the

North of Baffin Island (Hartlaub et al. 2004). Both Archean and the unconformably overlying

Early Paleoproterozoic Amer and Ketyet River Groups, underwent tectono-metamorphic events during Middle Paleoproterozoic times (Hoffman 1990), due to the polyphased tectonic accretion of the Laurentian Craton during Trans-Hudson (2.0-1.8 Ga) and Taltson-Thelon

53

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy orogens (2.0-1.9 Ga). Both the Woodburn and Amer-Ketyet Groups were intruded by Hudson granite and syenite around 1.85-1.79 Ga and by Nueltin granite and associated Pitz rhyolite at

1.75 Ga (Peterson et al. 2002, Van Breemen et al. 2005). Following late Hudsonian metamorphic events, dated at 1750 Ma in the northern Saskatchewan (Orrell et al. 1999), post orogenic uplift and erosion generated large volumes of detrital material while regional thermal and tectonic subsidence accommodated space for deposition of thick flat lying siliciclastic sequences, forming the Dubwant Supergroup (Rainbird et al. 2003). This Late

Paleoproterozoic non metamorphic rock package comprises the Wharton and Baker Lake

Groups and the uncomformably overlying Barrensland Group which includes the Thelon

Formation sandstones (Rainbird et al. 2003). The siliciclastic sequences accumulated in widespread intercontinental sag and fault controlled basins. Late thermal events of

Mesoproterozoic age are evidenced by the Kuungmi Formation basalts, of limited extent in the central part of the Thelon basin, and by the McKenzie dyke swarms (Fahrig 1987).

At the regional and deposit scale uranium mineralization is typically hosted in the Woodburn

Group metagraywackes, in the vicinity of a N080 fault trend, preferably where second order structures are present. Ore is located within a clay alteration halo centered on faults, itself surrounded by a hematite pervasive alteration extending over tens of meters. Disseminated mineralization can also be found in relatively weakly argillized or hematized rocks (e.g. End deposit).

1.4. Sampling and analytical procedure

Sampling has been carried out extensively along the Kiggavik-Andrew Lake trend in various basement lithologies to determine the regional alteration background and the specific clay signature related to uranium ore deposits. A total of 217 samples (selected from 17 diamond

54

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy drillholes) were collected for detailed petrology and crystal-chemistry. Sampling has been both focused on altered rocks in mineralized zones (i.e., Bong prospect, End deposit and

Andrew Lake deposit) and on poorly altered to fresh rocks from barren drill holes at various distances laterally to the main structures controlling the mineralization. Such sampling allows the lateral variation of mineral paragenesis from fresh rocks to strongly altered fault cores with or without mineralization. The Bong prospect was chosen for its rock package of homogeneous metasediments to minimize the influence of the protolith chemistry on the mineral paragenesis.

Rock samples were gently crushed and put in deionized water to get mineral suspensions afterwards dispersed ultrasonically during 2 minutes. Clay size fractions < 4µm were extracted by sedimentation for oriented and randomly oriented powder mounts. No cation exchange was performed. Chemical composition, morphology and texture of clay mineral assemblage were studied using a JEOL® 5600 electron microscope equipped with a Bruker energy dispersive X-ray spectroscopy detector (EDS). Analytical conditions were as follows: accelerating voltage 15 kV, probe current 1 nA, working distance 17 mm, counting time of

100 s. The analyzed elements were Na, Mg, Al, Si, Mn, Fe, Ti, K, and Ca. The microanalysis system was calibrated using synthetic and natural oxides and silicates (MnTiO3, hematite, albite, orthoclase, and diopside) and corrections were made using a ZAF program. The relative errors on the analyzed values are <1.5% (except Na which is >3%). Total Fe has been arbitrarily considered as FeO or Fe2O3 according to the nature of the analysed mineral.

All clay preparations were analyzed on a Bruker D8 Advance diffractometer. Diffracted beam

CuKα1+2 radiation was used (40kV, 40mA) and collected by a linxeye detector. Relative humidity was not controlled during data acquisition. Experimental conditions used for X-ray diffraction (XRD) data collection are given in Table 1-1.

55

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy Table 1-1 : Conditions used for X-ray diffraction data collection

Angular range Scanned range Step size Counting time Type of preparation °βƟ (Å) °βƟCuKα (s)

Oriented slides 2-30 44.0-2.98 0.01 1 Clay separation: AD and EG1

Randomly oriented preparations 19-34 4.67-2.64 0.01 5 (polytypes determination)

Randomly oriented preparations 58-65 1.59-1.43 0.01 5 determination of the 060 reflection

1AD: Air dried, EG ethylene glycol solvated 2060 reflection is used to determine the b parameter and hence to distinguish the dioctahedral, di- trioctahedral and triocataedral phyllosilicates

The crystallinity of illite along the c axis was estimated by measuring the full width at half maximum intensity (FWHM) of the typical d001 reflection on oriented preparations.

Although more advanced methods have been developed recently (Drits et al., 1997, among others), this broad method still remains suitable for illite (Guggenheim et al., 2002). Illite polytypes were identified by XRD on clay separates that were randomly oriented using a back-loading method as described and recommended by Moore and Reynolds (1989). The diffraction patterns were recorded using the step-scanning mode from 19 to 34 °2(4.67-2.64

Å) with a step size of 0.01 °2 and a counting time of 5s per step. Illite polytype identification was based on comparisons with reference data given in Bailey (1980) and (Brindley and

Brown 1980) for 1M and 2M1 polytypes and (Drits et al. 1993) for pure tv-1M (1M polytype with trans-vacant octahedral cation occupancy) and cv-1M (1M polytype with cis-vacant octahedral cation occupancy) polytypes. Note that earlier references used the terms “1M” and

“3T” for illite polytypes that are now considered to be tv-1M and cv-1M respectively (Drits et al. 1993, Reynolds 1993), Table 1-2.

56

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy Table 1-2 : X-ray diffraction lines characteristic of illite polytypes: tv-1M (octahedral trans vacant), cv-1M

(octahedral cis vacant) and 2M1 polytypes.

tv-1M cv-1M 2M1 Pos Å hkl Pos Å hkl Pos Å hkl Properties Diagnostic peaks of of tv-1M and 3.655 1 12 3.591 112 cv-1M polytypes Diagnostic peaks of tv-1M and cv- 3.073 112 3.126 112 1M polytypes Common to 2M1 and 1Mc 3.885 3.889 polytypes Common to 2M1 and 1Mc 2.875 2.870 115 polytypes 3.735 023 Specific to 2M1 polytype 3.500 114 Specific to 2M1 polytype 3.208 114 Specific to 2M1 polytype 2.999 025 Specific to 2M1 polytype

ArcGIS® and the Geosoft Target® module were used for Kriging interpolation and mapping of the crystal properties of clay mineral in 2D & 3D with a 12*12*12 meters cell size.

1.5. Petrography and mineralogy

The lithology of fresh rocks and their altered and mineralized equivalents encompasses the

Woodburn Group metasediments, the underlying augen gneiss and highly silicified feldspar bearing aphanitic rocks thought to be porphyritic rhyolite or mylonitized (micro)granite.

Locally, these rocks have been intruded by late mafic rich gabbro or biotite rich lamprophyre to more differentiated, coarse to fine grained syenite, and quartz- K feldspar granite and feldspar porphyry. The dominant ore bearing lithology are the Woodburn Group metasediments in which alteration is the most widely developed. Macroscopically, fresh rocks of the metasedimentary package are dark green and dominated by fine to medium grain meta- arkose to wacke with rare lithic fragments. Pyrite rich pelitic horizons as well as thin layers of banded iron formation (up to 10 cm thick) are interbedded. The metasediments consists of

57

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy feldspar (55 %), with dominant K-feldspar and quartz (40 %); accompanied by biotite, white mica, minor garnet in places and accessory minerals such as tourmaline, zircon, rutile, pyrite and magnetite. These metasediments were affected by a retrograde metamorphism

(greenschist facies) which consists of pervasive chloritization of biotite, sericitization of feldspars and occurrence of minor veinlets filled by epidote, alkali feldspars and late carbonates.

1.5.1. Alteration features

Macroscopically, hydrothermal alteration of the metamorphic basement resulted in color change of the rocks in response to mineralogical transformation as well as transfer of chemical elements, especially iron. Several contrasting features have been noted (Figure 1-2): bleaching related to strong argillization (illitization and chloritization) and desilicification, reddish coloration related to crystallization of iron oxide (mostly hematite), and late silicification (secondary quartz). All these features are spatially related to faults from millimeter to several meters wide fault zones, highlighting the strong structural control of the alteration. Both fractures and alteration decrease in intensity from the fault core (Figure 1-

2a), to the damage zone and then to the distal surrounding rocks in which only diffuse alteration is present (Figure 1-2b). The regional N070 fault trends, such as the Thelon and

Judge Sisson North Faults, are characterized by extensive hematization and silicification.

Protracted tectonic and hydrothermal activity is expressed by numerous phases of brecciation and alteration that led to complex textures of hydraulic quartz breccia (Figure 1-2c) frequently overprinted by late pervasive silicification, resulting in alternating bands of hematized and silicified breccia. Strong argillization (bleaching) associated with various degrees of desilicification occurs along the fault core and within the main mineralized zones.

Although the original foliation is still visible in most of the intensely altered rocks, the lithology and structure of the protolith is difficult to identify. The thickness of the fault gouge

58

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy is generally limited to 10s of centimeters whilst the width of the whole mineralized structure

(gouge + damage zone and associated alteration halo) may reach several tens of meters. Fault gouges are often superimposed on inherited structures such as quartz-carbonate veined corridors resulting in mixed fragments of sub-angular argilized basement, quartz and carbonates embedded in an illitic matrix. At greater lateral distance from the uranium deposits and their associated altered zones, minor faults are expressed as tectonic brecciation corridors in which the mechanical grinding (attrition) led to a chlorite-rich greenish fault gouge.

Usually, hematization is observed at the transition between the fault damage zone and surrounding weakly altered basement rocks. These transition zones outlined by redox fronts are frequently mineralized.

A B

C D

Foliation plan

Figure 1-2 A : Totally argilized fault gouge at the footwall of mineralized zone, Bong-043 drillhole; B, Fresh metagraywacke bleached over 50 cm by diffusive illitization around a centimeter microfault, Bong-045 drillhole.

C, Outcrop along the Sisson North Fault showing intense N080 quartz veining in a strongly hematized

59

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy metagraywacke; D, Mineralized rock sample with pitchblende impregnation along the foliation plans Bong-042 drillhole around 400 m below erosion surface.

At the thin section scale, alteration is related to dissolution of preexisting metamorphic silicates and to crystallization of an abundant clay matrix composed of illite associated with variable amounts of sudoite (di-trioctahedral Al-Mg chlorite). Illitization occurs both as pseudomorphic replacement of K-bearing metamorphic minerals (Figure 1-3a) and chlorite, and as neoformation of fine grained (less than 10m) laths or whiskers in the secondary porosity of the altered rocks. In altered intrusive rocks, the feldspars phenocrysts are totally replaced by illite and specular hematite. Sudoite is intimately associated with illite, forming millimetre size pockets of extremely fine grained flaky or lathy particles aggregates (Figure 1-

3b) or as partial replacement of exfoliated metamorphic phyllosilicates.

In addition iron remobilization from metamorphic phases (phyllosilicates and sulfides) is shown by textural relashionships. The corrosion of iron bearing minerals is followed the release of iron and precipitation of hematite in the secondary porosity (Figure 1-3c). Hematite as well as barite grows after titanium oxides (Figure 1-3d).

Minor amounts of phosphate minerals are closely associated with illite and sudoite. They consist of aluminum phosphate-sulfate minerals (APS) and apatite. APS minerals occur as tiny euhedral crystals ranging in size from less than to 10 µm up to 50 µm, and frequently display features of chemical zoning. Sr and S rich APS (svanbergite) dominate in the external alteration halo, up to hundreds of meters away from the mineralized zones. With decreasing distance from orebodies the general trend is a transition from svanbergite to LREE-rich phosphate (florencite). Locally, The APS minerals can be fractured and partly dissolved with smoothed edges. Secondary apatite occurs close to and within the mineralized zones. It is textural association with pitchblende displays features of cogenetic growth, with inclusions of

60

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy pitchblende inside apatite or coatings of colloform pitchblende around apatite and titanium oxides.

A B Ms Ill

Ill Sud

Qtz Qtz Brt C D Ill Hem

TiO2 Qtz Hem ChlFeMg ChlFeMg

Figure 1-3 A : Hanging wall of the main mineralized structure with strong alteration and replacement of metamophic 2M1 micas by laths of tv-1Millite (identified by XRD) showing an exfoliation texture; Bong-042;

B, Sudoite (S) pocket occurring in illitized phengite laths, Bong-008; C Metamorphic chlorite partially altered to illite with associated crystallization of hematite, End09-11 ; D Illitization of metamorphic Fe-Mg phyllosilictates leading to precipitation of titanium oxides, hematite spherules and minute crystals of barite in the secondary porosity, End09-11.

Abbreviations; Brt: barite, Cal: calcite, Chl: chlorite, Coff: coffinite, Gn: galena, Hem: hematite, Ill: illite, Qtz: quartz, TiO2: titanium oxide, Sud: sudoite, Uran: uraninite

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Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy 1.5.2. Ore paragenesis

Uranium mineralization is spatially related to the faults and their alteration haloes. At least two generations of uranium mineralization have been found. The first consists of pitchblende coatings on foliation planes and along fracture walls in weakly to strongly bleached host rock

(Figure 1-2d & 1-4a). In this type of primary ore, metamorphic chlorite is normally partially altered to illite and sudoite and disseminated patches of pitchblende occur in the fault gouge.

Uraninite is epigenetic on iron magnesium chlorite as well as pyrite with boxwork textures

(Figures 1-4b, 1-4c & 1-4d). Uraninite is altered and replaced by coffinite in corrosion pits latter filled with barite and galena. Pitchblende is also present as fracture filling and smearing along microfaults planes with or without iron oxides as well as along redox fronts in the fault damage zone. This last mineralization setting could be interpreted as secondary remobilization of primary mineralization. Pitchblende does not appear to be associated with iron oxides, and hematite staining frequently overprints argillized zones that are not necessarily mineralized.

The primary ore paragenesis observed in thin section is uraninite later replaced by coffinite.

Metallic sulfides are rare, mainly as chalcopyrite and Cu, Co & Ni sulfides. They occur as minute crystals and colloform products which are cogenetic to pitchblende and clay alteration minerals. Subhedral to euhedral titanium oxides, apatite and APS disseminated in the clay matrix often show partial dissolution features, and are frequently rimed by pitchblende overgrowths. Apatite is particularly abundant within the mineralized zone.

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Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy

A B Qtz

Uran Uran S

C D Pyrite Gn Cal boxwork Uran Cal Brt Uran

Coff Coff

Figure 1-4 : A Mineralized rock sample of metasediments showing the pitchblende (colloform uraninite) precipitation along the foliation plans in which the metamorphic phyllosilicates have been transformed to illite.

The intergranular voids are cemented by pitchblende, Bong-042 drillhole; B Metamorphic phyllosilicate pseudomorphs and uraninite overgrowths, End09-04 drillhole; C Metamorphic phyllosilicate pseudomorphs and uraninite overgrowths, postdated coffinite crystallization and calcite cementation, End09-04; D Pyrite and uraninite (boxwork texture) subsequently altered in coffinite and cemented by late calcite, End09-04.

1.6. Textural properties and crystal structure of phyllosilicates

Two distinctive types of phyllosilicates have been identified on the basis of textural characteristics. Metamorphic phyllosilicates in large subhexagonal plates ranging from 15 to

50 µm are oriented along foliation planes, whereas hydrothermal phyllosilicates replace all the minerals of the basement rocks (including the micas) in zones of intense alteration and consist of fine grained laths to flakey particles of < 5 µm.

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Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy

The XRD data of oriented and randomly oriented powders of the <4 m size fraction of all samples investigated along the Kiggavik-Andrew Lake trend are dominated by dioctahedral potassic phyllosilicates (micas and illite) associated with variable but generally small amounts of chlorite (Figure 1-5). The crystal structure of phyllosilicates was investigated through the full width at half maximum (FWHM) of the peaks corresponding to the d001 reflections

(close to 10 Å and 14 Å for illite and chlorite respectively) and through the relative amounts of different polytypes identified from the randomly oriented powders mounts.

chl/sud chl/sud chl/sud chl/sud

Ill

Ill Ill

C

B

Qtz A

3 8 13 18 23 28 °2θ, Cu Kα

Figure 1-5 : X-ray diffraction patterns of oriented preparations of clay separates (< 4m) of representative samples from the alteration halo surrounding the Bong deposit. (A) sample from the damaged zone, (B) sample

64

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy from the fault core hosting the mineralization; (C) sample from a sudoite-rich level. Ill: Illite, Sud/Chl: Sudoite

& Chlorite, Qtz : quartz diffraction peaks.

In fresh to very poorly altered basement rocks, the phyllosilicate assemblage of metamorphic origin is made of dioctahedral micas (muscovite or phengite) and trioctahedral Fe-chlorite with weak intensities of odd basal reflections compared to the even ones and d060 ranging between 1.54 and 1.55Å). The d001 reflections of K-mica and chlorite are characterized by very low FWHM (less than 0.1° 2) and the XRD patterns of mica has all the index hk reflections of the 2M1 polytype (Figures 1-6 and Table 2).

2 2M1 2M1

2 1 1 1 1 1 2

C

1Mc 2M1/1Mc 1Mc 2M1/1Mc 1Mt 1Mt B

A

19 24 29 34 °2θ, CuKα

Figure 1-6 : XRD diffraction patterns of randomly oriented mount of clay separates illustrating the change in polytype of the dioctaedral phyllosilicates as a function of their distance from a mineralized structure in the altered metagraywacke. The index XRD reflections of 2M1 (dotted lines), cv-1M (solid lines) and tv-1M (dashed line) are from Drits and Tchoubar, (1990). A fault gouge hosting most of the mineralization, B fault damage zone, C fresh metagraywacke. Note the presence of significant amounts of unaltered feldspar and quartz in the less than 4 µm size fraction of the fresh metagraywacke. 1 hk reflections of K feldspar, 2 hk reflections of albite.

65

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy In basement rocks affected by hydrothermal alteration, the phyllosilicate assemblage is largely dominated by illite associated with small amounts of chlorite. Compared to those of the metamorphic phyllosilicates, the d00l reflections of both hydrothermal illite and chlorite have distinctive peak profiles and intensity ratios (Figure 1-5). The d00l reflections of illite and chlorite are broad (0.30.15° 2, respectively). XRD patterns of hydrothermal illite indicate a mixture of tv-1M and cv-1M polytype with a trend to predominance of tv-1M polytype in the fault gouge that is totally illitized (Figure 1-6). In addition, the XRD patterns of the hydrothermal chlorite are characteristic of the sudoite. They differs from that of the trioctahedral chlorite by an intense d003 reflection compared to the d001 reflection (Figure 1-5) and by a d060 spacing close to 1.51 Å (instead of 1.54 Å or more for a trioctahedral chlorite) . Comparing the XRD patterns of all rocks samples, it appears that the FWHM values of the dioctahedral K-phyllosilicates strongly increase and the amount of 2M1 polytype decreases and then disappears with increasing hydrothermal alteration (Figure 1-6). As 2M1 polytype and the lowest FWHM values are representative of the metamorphic micas, such a trend can be a consequence of the alteration of metamorphic micas and their replacement by illite as observed by SEM investigations (Figure 1-3a).

However, the FWHM values of the hydrothermal illite continue to increase with increasing alteration, such that in the highly altered zones, no 2M1 micas persist. Increase in FWHM values of the d00l reflection of illite is correlated with the increasing amount of tv-1M polytype close to the uranium mineralization.

1.7. Phyllosilicate crystal chemistry

Microprobe analyses of metamorphic micas by EDS and the calculated structural formulas on the basis of 11 oxygens per half formula unit are fairly homogeneous and are comparable to muscovite with phengitic substitutions (Si+R2+ = AlIV+AlVI ). This is illustrated by (1) Si

66

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy contents higher than 3 atoms coupled with amounts of divalent atoms ranging from 3.04 to

3.29 (2) interlayer charges totally satisfied by K and ranging between 0.9 and 1 atom, and (3) octahedral occupancies close to 2 atoms (Table 3a). The Fe/Fe+Mg ratios (XFe) of these micas range between 0.6 and 0.8. The structural formula of hydrothermal illite (Table 3b) differs from those of metamorphic micas by a higher Si content from 3.3 to 3.4 atoms coupled with a lower interlayer charge ranging from 0.75 to 0.85 atom. Compared to metamorphic micas (Figure 1-6), the composition of illite is very poor in Fe (<0.04 atom) and richer in Mg

(>0.20 atom). As a consequence, they can be easily distinguished by their very low Fe/Fe+Mg ratios of < 0.1.

Chemical analyses and structural formulae of metamorphic chlorite indicate an iron-rich species of trioctahedral chlorite (Table 1-3). Their octahedral occupancy is close to 6 atoms when the structural formulae were calculated with total Fe in the ferrous state and their XFe is generally higher than 0.5. The structural formulas of the hydrothermal chlorites are more heterogeneous than those of the metamorphic chlorites. Most of them are comparable to those of the sudoite (Table 1-3), which is the di-trioctahedral chlorite species identified by XRD investigations. The structural formula of sudoite is characterized by an Al-Mg rich composition and an octahedral occupancy close to 5 atoms. The fact that many analyses of what was initially thought to be sudoite are in fact mixture of variable amounts of sudoite with illite is indicative of the very small size of the crystals and their close association with illite even at a few micrometers scale. Chemical analysis of hydrothermal chlorites has also permit to identify Mg-rich trioctahedral chlorites in a few altered samples (Table 1-3). These chlorites sealed late microfractures in some hydrothermally altered samples. The chemical composition of this Mg-rich chlorite is typical of the clinochlore species. It is characterized by low iron content (XFe<0.10) and a trioctahedral structure with the presence of a small amount of octahedral vacancy (octahedral occupancy averaging 5.75 atoms).

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Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy Table 1-3 : EDS analysis and structural formulas of representative phyllosilicates in the Kiggavik- Andrew Lake trend

1 2 3 4 5 6 7 8

SiO2 24.01 31.59 33.86 43.96 45.45 42.33 43.00 48.38 TiO2 0.05 0.01 0.06 0.56 0.36 0.34 0.00 0.04 Al2O3 19.32 15.58 28.78 31.44 33.38 29.35 27.61 27.78 FeO 27.17 4.39 0.20 2.11 2.31 4.28 Fe2O3 0.04 0.45 MnO 0.22 0.00 0.00 0.00 0.10 0.06 0.00 0.03 MgO 11.90 28.33 17.26 1.46 1.32 1.48 1.80 2.63 CaO 0.03 0.19 0.07 0.00 0.03 0.00 0.06 0.14 Na2O 0.26 0.36 0.32 0.39 0.49 0.44 0.21 0.27 K2O 0.03 0.00 0.22 10.23 10.37 10.03 8.60 8.14 Total 83.00 80.45 80.77 90.15 93.83 88.32 81.33 87.85

Si 2.73 3.22 3.27 3.12 3.09 3.11 3.30 3.42 AlIV 1.27 0.78 0.73 0.88 0.91 0.89 0.7 0.58

AlVI 1.32 1.09 2.54 1.74 1.77 1.65 1.80 1.73 Ti 0.00 0.00 0.00 0.03 0.02 0.02 0.00 0.00 Fe 2.58 0.37 0.02 0.12 0.13 0.26 0.00 0.02 Mn 0.02 0.00 0.00 0.00 0.01 0.00 0.00 0.00 Mg 2.02 4.31 2.48 0.15 0.13 0.16 0.21 0.28

Occ 5.94 5.78 5.04 2.05 2.06 2.10 2.01 2.03 XFe 0.56 0.08 0.01 0.45 0.50 0.62 0.01 0.08

Ca 0.00 0.02 0.01 0.00 0.00 0.00 0.00 0.01 Na 0.06 0.07 0.06 0.05 0.06 0.06 0.03 0.04 K 0.00 0.00 0.03 0.93 0.90 0.94 0.84 0.73 Int. Ch. 0.07 0.11 0.10 0.98 0.97 1.00 0.88 0.79

1 Metamorphic chlorites; 2 Hydrothermal clinochlore associated with a dolomite veinlet; 3 Sudoite filling veinlet; 4-5 Metamorphic micas; 6 Relics of metamorphic micas persisting in a mineralized zone; 7 illite pocket in a fault gouge; 8 illite in a mineralized zone. Xfe:(Fe/Fe+Mg), Int. Ch : Interlayer Charge, Total: sum of the oxide Wt%. The fact that the total oxide Wt% of hydrothermal illite and chlorite are slightly lower than expected for theoretical ones (>90% and 86% respectively) can be explained by the microporosity of the clay material.

Such a deviation did not affect the calculation of the structural formulas.

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Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy 1.8. Discussion

1.8.1. Comparing the alteration pattern of the Kiggavik-Andrew Lake trend

to those of unconformity-related uranium deposits in the Athabasca

or the Kombolgie Basins.

The alteration pattern associated with the uranium deposits of the Kiggavik-Andrew Lake trend shows a great number of similarities with those of basement hosted unconformity- related uranium deposits described in both the Athabasca Basin (Cloutier et al. 2009,

Jefferson et al. 2007) and references therein) or the Kombolgie Basin (Beaufort et al. 2005,

Gustafson and Curtis 1983) and references therein). Such similarities include the geometric shape of the alteration halo as well as the sequence of mineral crystallization and the mineralogical characteristics of the secondary minerals. They can be summarized as follows:

(1) Similar alteration halos in fracture controlled uranium mineralization in clay-rich rocks associated with dissolution of silicates and quartz in retro-metamorphosed basement rocks.

(2) Similar crystal chemistry of the secondary mineral phases dominated by illite and both di- trioctahedral (sudoite) and trioctahedral chlorites with minor amounts of phosphate minerals

(APS, apatite) and hematite.

(3) Similar time-space alteration sequence expressed by zoned alteration around the fracture network which hosts the uranium mineralization: i.e. illite ± sudoite followed by late clinochlore in veinlets and lateral transition from APS to apatite toward the mineralized zone.

The occurrences of unconformity-related uranium deposits in Canada and Australia are usually interpreted on the basis of the widely accepted diagenetic-hydrothermal genetic model originally proposed by (Hoeve and Quirt 1984, Hoeve et al. 1980). According to this model and all the refinements proposed thereafter, the uranium ores formed close to the

69

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy unconformity are the result of a long period of tectonically controlled interaction between diagenetic oxidizing basinal brines at the base of deep continental basins and hydrothermal reducing fluids circulating in basement faults (Jefferson et al. 2007, Kyser and Cuney 2008).

The spatial distribution of the alteration haloes associated with unconformity uranium mineralization in the Athabasca Basin show contrasting patterns interpreted as representative of discharge (“egress” style) and recharge (“ingress” style) zones (Quirt 1989, 2003). Egress style is characterized by extensive and zoned alteration pattern in the sub-basinal sandstones in response to upward fluid flow from basement-rooted faults. Ingress style shows more limited inverted alteration haloes, mainly within the faulted basement, in response to downward infiltration of basinal fluids in probable extensional local settings.

From the aforementioned considerations, the alteration pattern associated with the uranium deposits along the Kiggavik-Andrew Lake area have many of the characteristics associated with basement hosted unconformity-related uranium deposits. This suggests a close relationship between the genesis of these ore deposits and both the burial history and tectonic evolution of the Thelon Basin which has a potential for hidden uranium deposits (Beyer et al.

2011, Miller and LeCheminant 1985, Rainbird et al. 2003). However, compared to the basement-hosted uranium deposits of the Athabasca Basin such as Shea Creek (Laverret et al.

2006) or Millenium (Cloutier et al. 2009), the alteration pattern associated with the uranium deposits of the Kiggavik-Andrew Lake differs by the absence of significant amounts of graphite in the fault system and the absence of dravite in the paragenetic sequence.

1.8.2. Crystal structure of clay minerals as a vector to mineralization in the

Bong prospect

70

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy Several authors have shown that the crystal structure of phyllosilicates can be used as a vector to mineralization in the unconformity-related uranium deposits of Australia and Canada

(Beaufort et al. 2005, Laverret et al. 2006). As the full width at half maximum (FWHM) of phyllosilicates depends on the degree of order-disorder in the layer staking sequence, the d001

XRD reflections of illite or chlorite are broad indicators of P-T conditions in geological environments (see reviews and critical comments in (Guggenheim et al. 2002). The FWHM of the d001 reflection of metamorphic white micas (FWHM< 0.10 °βθ) is lower than those of the hydrothermal illite (0.15 °βθ

The FWHM values of the d001 reflection of illite have been systematically measured to map their variation around the Bong deposit.

I

D

C

B

A

8 8.5 °2θ, CuKα 9

Figure 1-7 : Change in peak profile of the d001 reflection of the K-bearing dioctahedral phyllosilicates according to their distance to the uranium mineralization. The FWHM of the peak gradually increases from less than 0.10

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Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy

°2θ to more than 0.70 °2θ from the unaltered metagraywakes until the mineralized fault core. A, fresh metagraywacke, B fault damaged zone, C barren fault core, D mineralized fault core.

1.8.2.1. MAPPING THE FWMH OF THE ILLITE/MICA D001 REFLECTION

The extensive dataset of FWHM values obtained from samples from the Bong prospect are distributed in four categories arbitrarily based on the crystallographic data and the intensity of clay alteration (Figure 1-8). These ranges corresponds to (1) fresh rocks containing only metamorphic micas (FWHM< 0.10 βθ), (2) very weakly illitized rocks (FWHM< 0.15 βθ) that are “fresh” macroscopically; (3) moderately to strongly illitized rocks (FWHM< 0.30 βθ) which are sill cohesive with a weak to moderate desilicification and that show a typical mixture of 2M1 and 1M polytypes in the damage and distal alteration zones around the structure; and (4) totally illitized rocks (FWHM > 0.30 βθ) in which illite is the only potassic phyllosilicate in the strongly desilicified metasediments and the fault gouges.

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Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy

Figure 1-8 : Interpolation of FWHM values of the d001 XRD reflection of illite/micas using Kreiging method permits to ouline a zoned distribution of the average crystallinity along the c axis of these minerals around the uranium orebodies of the Bong prospect. The edge of the mineralized halo in the section is indicated by the black dotted line.

The spatial populations of samples (in average a point every 10 m in the Z direction and every

20 m on the XY plan) allow to use interpolation tools, in this case Kriging method, to map the intensity of the alteration related to the mineralization process on the basis of the d001

FWHM of the potassic phyllosilicates. The result of such interpolation methods allows to map the intensity of the alteration process and to outline the geometry of the hydrothermal haloes at larger scale (Figure 1-8). Knowing the position of the main structure in the Bong prospect, this alteration map confirms the location of the uranium orebodies inside the more strongly illitized part of the alteration halo. Such maps could be also very useful for further assessment of the altered rock volume around the structures. As a general statement, illite with the highest FWHM values are closely related to the fault gouge and more specifically to

73

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy the mineralized zones. Micas with low FWHM values have been found in fresh rocks as well as in the damage zone where the dioctaedral micas have been only partially transformed during the alteration processes.

1.8.2.2. MAPPING THE DISTRIBUTION OF SUDOITE

Sudoite occurs proximal to the uranium orebodies in most unconformity-related uranium deposits (Quirt 1989, 2003). The spatial distribution of this mineral has been mapped in the alteration halo of the Bong prospect (Figure 1-9).

Figure 1-9: Interpolation of the chlorite-sudoite relative proportions estimated from the diffraction peakratio (

Kcs factor) with a Kreiging method permitting to map the spatial distribution of sudoite in the alteration halo of the Bong prospect. The edge of the mineralized halo in the section is indicated by the black dotted line.

The relative amount of sudoite in the bulk chlorite material has been estimated based on the intensity ratio between the d003 and d001 reflections of the chlorite minerals (corresponding

74

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy to d spacing close to 14Å and 4.75Å respectively) measured after background stripping in the

XRD pattern of oriented clay preparations (referred to Kcs factor hereafter). Trioctahedral chlorite largely predominates if the Kcs factor is <1, both trioctahedral chlorite and sudoite are mixed in equal proportions if the Kcs factor is close to 1, and sudoite largely predominates over trioctahedral chlorite if the Kcs factor >1. It should be mentioned that this method is only a broad approximation of the amount of sudoite in the altered rocks. A more accurate quantification could be done using quantitative XRD methods such as decomposition of X-ray diffraction profile or Rietveld method. However such methods are time consuming and not really appropriate to the analysis of a great number of heterogeneous samples. The good correlation that is noted between the obtained Kcs factor and the petrographic observations give confidence that this parameter highlights the major contrasts in alteration mineralogy.

Nevertheless, the confidence in this factor for mapping hydrothermal alteration has been also checked on the basis of other structural parameters such as the b parameter of the chlorite lattice cell (expected from the d 060 reflection of chlorite minerals) and the estimation of mineral proportions from chemical analysis on clay separates.

Mapping the spatial distribution of sudoite in the Bong prospect shows that this mineral is present throughout the alteration zone around the main structure where iron rich chlorite tends to disappear. Thus, sudoite-rich zones are not strictly associated with the mineralization. At a larger scale it seems distributed along two distinctive structures. The first one, relatively poor in sudoite, is associated with the mineralization while the other one which occurs above is richer in sudoite but contains only trace to weak amounts of uranium mineralization.

1.8.3. Relationships between clay alteration and hematization.

The crystal chemistry of phyllosilicates and the chemiographic representation of both the metamorphic and hydrothermal assemblages in a MR3-2R3-3R2 diagram (Velde 1977, 1985) outline a close relationship between clay alteration and hematization within the alteration

75

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy halos (figure 1-10). Dissolution of iron-rich phyllosilicates such as Fe-Mg trioctahedral chlorite (XFe<0.5) and phengitic micas (0.6

(XFe<0.1) and sudoite (XFe<0.02) is a geochemical evidence for a leaching of iron from the silicate minerals during the hydrothermal process. Such a leaching can be explained by the oxidation of ferrous iron during the dissolution of metamorphic minerals (silicates, Fe-Ti oxides and sulfides) by the oxidizing and acidic basinal brines infiltrated along the fracture network in the basement rocks. As incorporation of ferric iron in phyllosilicates such as chlorite, di-tri or trioctahedral, is very limited (Billault et al. 2002, Nelson and Guggenheim

1993), most of the ferric iron precipited as cogenetic hematite. Moreover, as ferric iron mobility is generally very limited due to its very low solubility in hydrothermal solutions, the iron redistribution is centered on the structures where alteration took place.

Observations on the hydrothermal clay assemblage chemistry as well as the textural evidences of hematite precipitation in the secondary porosity developed with alteration lead to the conclusion that hydrothermal hematization was effective along the Kiggavik-Andrew lake fault trend. Even if this does not mean that all the hematite observed at regional scale is a by- product of the hydrothermal alteration process, we suggest that the hematite haloes observed at the field scale are probably good indicators of proximal hydrothermal alteration zones.

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Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy

Figure 1-10 : Chemiographic representation of the phyllosilicate assemblages formed during both retrograde metamorphic (■) and hydrothermal (◊) stages which successively affected the metasediments hosting uranium mineralization. Structural formulas of phyllosilicates have been plotted in a MR3-2R3-3R2 diagram (Velde 1977) in which MR3 represent feldspar compositions (Na+, K+, 2Ca2+ + Al3+) in atomic proportions, 2R3 represents the dioctahedral pole [1/2 (Fe3+ + Al3+ + Ti4+)-MR3] and 3R2 represents the trioctahedral pole [1/2 (Fe2+ + Mg2+ +

Mn2+)]. The microprobe analyses which fall between the compositional fields of the phyllosilicates phases labeled in the triangle correspond to two-phases (and more rarely three phases) admixtures.

1.9. Concluding remarks

This study indicates that most of the secondary minerals found within the alteration haloes associated with uranium mineralization along the Kiggavik-Andrew Lake fault trend are similar to those produced by diagenetic-hydrothermal alteration in basement hosted

77

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy unconformity-related uranium deposits (Figure 1-11). Only minor occurrences of propylitic alteration expressed as epidote and feldspar veinlets give credit to the possible link invoked between intrusive granitic bodies and a possible early stage of uranium mineralization in the

Kiggavik deposit (Weyer et al. 1987). Nevertheless the extent of such alteration is too limited to be considered as representative of a major mineralizing event at regional scale.

Figure 1-11: Paragenetic sequence in the Kiggavik-Andrew Lake trend.

Diagenetic-hydrothermal alteration associated with uranium mineralization in the Kiggavik

Andrew Lake trend involves fluids originating from the Late Paleoproterozoic Thelon Basin.

Due to the present level of erosion, only basement hosted mineralization can be found in the study area and the thickness of basement rocks which has been eroded since the formation of the ore deposits is unknown. However both alteration and mineralization studied along the

78

Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy Kiggavik Andrew Lake trend are related to steep structures and can be compared to the basement hosted uranium deposits like Jabiluka in Australia or Shea Creek in the Western

Athabasca Basin of Canada in which mineralization and alteration follow corridors down to several hundred meters below the unconformity. Nevertheless, contrarily to the Athabasca basement, basement uranium mineralization in the Thelon Basin area is dominantly hosted by coarse Late Archean metasediments along faults without graphite. The source of uranium within the Kiggavik Andrew Lake trend is still conjectural but the very low uranium content in unaltered metasediments and the evidence of interaction between diagenetic fluids and basement rocks argue for a potential contribution of uranium from the Thelon Basin or for mobilization of uranium from fertile basement rock at distance from the structural trend.

A few implications for uranium exploration can be deduced from the findings of this study.

The Kiggavik Andrew Lake trend is interpreted as the deep roots of an unconformity related uranium deposit system, so the possibility of discovering uranium deposits closer to the unconformity below the Thelon Basin at appropriate structural locations cannot be discarded.

Perhaps the findings on the mineralogical indicators developed in this study of would permit to delineate new prospective uranium bearing alteration systems.

Acknowledgment

The authors would like to thank AREVA Mines for financial and technical support of this study. The authors would like to thanks the reviewers, Pr Kyser and Pr Pagel for their detailed comments which greatly helped to improve the manuscript.

1.10. References

BEAUFORT, D., PATRIER, P., LAVERRET, E., BRUNETON, P. and MONDY, J. (2005): Clay Alteration Associated with Proterozoic Unconformity-Type Uranium Deposits in the East Alligator Rivers Uranium Field, Northern Territory, Australia. Economic Geology. v. 100, pp. 515–536.

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Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy BEYER, S.R., HIATT, E.E., KYSER, K., DALRYMPLE, R.W. and PETTMAN, C. (2011): Hydrogeology, sequence stratigraphy and diagenesis in the Paleoproterozoic western Thelon Basin: Influences on unconformity-related uranium mineralization. Precambrian Research. 187, 293-312. BILLAULT, V., BEAUFORT, D., PATRIER, P. and PETIT, S. (2002): Crystal chemistry of Fe-sudoites rom uranium deposits in the Athabasca basin ( Saskatchewan, Canada). Clays and Clay Minerals. 50, 69-80. BRINDLEY, G.W. and BROWN, G. (1980): Crystal structures of clay minerals and their X- ray identification, Mineralogical Society, London, UK CLOUTIER, J., KYSER, K., OLIVO, G.R., ALEXANDRE, P. and HALABURDA, J. (2009): The Millennium Uranium Deposit, Athabasca Basin, Saskatchewan, Canada: An Atypical Basement-Hosted Unconformity-Related Uranium Deposit. Economic Geology. 104, 815-840. DAVIS, W.J. and ZALESKI, E. (1998): Geochronological investigations of the Woodburn Lake group, western Churchill Province: preliminary results. Current Research 1998-F, Geological Survey Of Canada DRITS, V.A., WEBER, F., SALYN, A.L. and TSIPURKY, S.I. (1993): X-ray identification of one-layer illite varieties: application to the study of illites around uranium deposits of Canda. Clays and Clay Minerals. 41, 389-398. FAHRIG, W.F. (1987): The tectonic settings of continental mafic dyke swarms: Failed arm and early passive margin In Mafic dyke swarms. 34, Geological Association of Canada Special Paper FARKAS, A. (1984): Mineralogy and host rock alteration of the Lone Gull deposit. Internal report, Urangesellschaft FUCHS, H.D., HILGER, W. and PROSSER, E. (1986): Geology and exploration history of the Lone Gull property. Uranium Deposits of Canada, CIM Special Volume 33 GUGGENHEIM, S., BAIN, D.C., BERGAYA, F., BRIGATTI, M.F., DRITS, V.A., EBERL, D.D., FORMOSO, M.L.L., GALAN, E., MERRIMAN, R.J., PEACOR, D.R., STANJEK, H. and TAKASHI, W. (2002): Report of the association internationale pour l'étude des argiles(AIPEA) nomenclature committee for 2011: Order, disorder and crystallinity in phyllosilicates and the use of the "crystallinity index". Clays and Clay Minerals. 50, 406-409. GUSTAFSON, L.B. and CURTIS, L.W. (1983): Post-Kombolgie metasomatism at Jabiluka, Northern Territory, Australia, and it's significance in the formation of high grade uranium mineralization in Lowar Proterozoic rocks. Economic Geology. 78, 26-56. HADLARI, T., RAINBIRD, R.H. and PEHRSSON, S.:(2004) Geology Schultz Lake, Nunavut, open file 1839, scale 1: 250 000. Geological Survey Of Canada. HARTLAUB, R.P., HEAMAN, L.M., ASHTON, K.E. and CHACKO, T. (2004): The Archean Murmac Bay Group: evidence for a giant Archean rift in the Rae Province, Canada. Precambrian Research. 131, 345-372. HASEGAWA, K., DAVIDSON, G.I., WOLLENBERG, P. and YOSHIMASA, I. (1990): Geophysical exploration for unconformity-related uranium deposits in the northeastern part of the Thelon Basin, Northwest Territories, Canada. Mining Geology. 40, 83-95. HIATT, E.E., PALMER, S., E., KYSER, K. and O'CONNOR, T. (2010): Basin evolution, diagenesis and uranium mineralization in the Paleoproterozoic Thelon Basin, Nunavut, Canada. Basin Research. 22, 302-323. 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. Saskatchewan Research Concil Technical report, Saskatchewan Reasearch Council

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Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy HOEVE, J., SIBBALD, T.I.I., RAMAEKERS, P. and LEWRY, J.F. (1980): Athabasca basin unconformity-type uranium deposits : a special class of sandstone-type deposits? In Uranium in the Pine Creek Geosyncline. International Atomic Energy Agency HOFFMAN, P.F. (1990): Subdivision of the Churchill Province and extent of the Trans- Hudson orogen In The Early Proterozoic Trans-Hudson Orogen of North Amercia. 37, Geological Survey of Canada Special Paper JEFFERSON, C.W., THOMAS, D.J., GANDHI, S.S., RAMAEKERS, P., DELANEY, G., BRISBIN, D., CUTTS, C., PORTELLA, P. and OLSON, R.A. (2007): Unconformity- associeted uranium deposits of the Athabasca Basin, Saskatchewan and Alberta In EXTECH IV. Geology and Unranium EXploration TECHnology of the Proterozoic Athabasca Basin, Saskatchewan and Alberta, Geological Survey of Canada, Bulletin 588, KYSER, K. and CUNEY, M. (2008): Unconformity-related uranium deposits In Recent and not so recent developments in uranium deposits and implications for exploration. Short Course 39, Mineralogical Association of Canada LAVERRET, E., PATRIER, P., BEAUFORT, D., KISTER, P., QUIRT, D., BRUNETON, P. and CLAUER, N. (2006): Mineralogy and geochemistry of the host-rock alterations associated with the Shea Creek unconformity-type uranium deposits (Athabasca basin, Saskatchewan, Canada) Part1. Spatial variation of illite properties. Clays and Clay Minerals. 54, 275-294. MILLER, A.R., CUMMING, G.L. and KRSTIC, D. (1989): U-Pb, Pb-Pb, and K-Ar isotopic study and petrography of uraniferous phosphate-bearing rocks in the Thelon Formation, Dubawnt Group, Northwest Territories, Canada. Canadian Journal of Earth Sciences. 26, 867-880. MILLER, A.R. and LECHEMINANT, A.N. (1985): Geology and uranium metallogeny of Proterozoic supracrustal successions, central District of Keewatin, N.W.T with comparisons to northern Saskatchewan. NELSON, D.O. and GUGGENHEIM, S. (1993): Inferred limitations to the oxidation of Fe in chlorite : a high-temperature single-crystal X-ray study. American Mineralogist. 78, pp. 1197- 1207. ORRELL, S.E., BICKFORD, M.E. and LEWRY, J.F. (1999): Crustal evolution and age of thermotectonic reworking in the western hinterland of the Trans-Hudson Orogen, northern Saskatchewan. Precambrian Research. 95, 187-223. PETERSON, T.D., VAN BREEMEN, O., SANDEMAN, H. and COUSENS, B. (2002): Proterozoic (1.85-1.75 Ga) igneous suites of the Western Churchill Province: granitoid and ultrapotassic magmatism in a reworked Archean hinterland. Precambrian Research. 119, 73- 100. QUIRT, D. (1989): Host rock alteration at Eagle Point South. R-855-1E-89, Saskatchewan Research Council QUIRT, D. (2003): Athabasca unconformity type uranium deposits: one deposit type with many variations. . Uranium Geochemistry International Conference, Nancy, France RAINBIRD, R.H., HADLARI, T., ASPLER, L.B., DONALDSON, J.A., LECHEMINANT, A.N. and PETERSON, T.D. (2003): Sequence stratigraphy and evolution of the Paleoproterozoic intracontinental Baker Lake and Thelon basins, western Churchill Province, Nunavut, Canada. Precambrian Research. 125, 21-53. RENAC, C., KYSER, K., DUROCHER, K., DREAVER, G. and O'CONNOR, T. (2002): Comparison of diagenetic fluids in the Proterozoic Thelon and Athabsca Basins, Canada: implications for protracted fluid histories in stable intracratonic basins. Can. J. Earth Sci. 39, 113-132. REYNOLDS, R.C. (1993): Three-dimentional X-ray powder diffraction form disordered illite: Simulation and interprétation of the diffraction patterns. LECTURES

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Alteration related to uranium deposits in the Kiggavik-Andrew lake structural trend, Nunavut, Canada; new insights from petrography and clay mineralogy VAN BREEMEN, O., PETERSON, T.D. and SANDEMAN, H. (2005): U-Pb zircon geochronology and Nd isotops geochemistry of Proterozoic granitoids in the western Churchill Province: intrusive age pattern and Archean source domains. Canadian Journal of Earth Sciences. 42, 339-377. VELDE, B. (1977): Proposed Phase-Diagram For Illite, Expending Chlorite, Corrensite and Illite-Montmorillonite Mixed Layered Minerals. Clays and Clay Minerals. 25, 264.270. VELDE, B. (1985): Clay minerals: A physico-chemical explanation of their occurence. Developments in Sedimentology, Elsevier WEYER, H.-J., FRIEDRICH, G., BECHTEL, A. and BALLHORN, R.K. (1987): The Lone Gull uranium deposit-New geochemical and petrological data as evidence for the nature of the ore bearing solutions. Metallogenesis of uranium deposits, 542/19, Proceedings of a technical committee meeting, Vienna ZALESKI, E., DAVIS, W.J. and SANDEMAN, H. (2001): Continental rifting, mantle magmas and basement/cover relashionships. 4th International Archean Symposium, Perth, Australia

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Etude microthermométrique des inclusions fluides dans les quartz et dolomite associées aux minéralisations uranifères du faisceau structural Kiggavik-Andrew Lake

2. Etude microthermométrique des inclusions fluides dans les quartz et dolomite associées aux minéralisations uranifères du faisceau structural Kiggavik-Andrew Lake

2.1. Introduction

Les nombreuses études d’inclusions fluides menées sur les gisements de type discordance associés au basin de l’Athabasca sont venues étayer les modèles de minéralisations de type diagénétique-hydrothermal dans lesquels des saumures oxydantes de bassin viennent interagir avec des fluides et/ou des lithologies réductrices du socle (Pagel 1975, Pagel et Jaffrezic,

1977, Kotzer & Kyser, 1995, Derome et al, 2005, Hoeve & Quirt, 1984).

Une seule étude, limitée à des échantillons d’Andrew Lake a été réalisée sur les cristaux de quartz associés aux gisements du faisceau de Kiggavik (Pagel et Ahamdach, 1995). Elle a mis en évidence à la fois la circulation de fluides du bassin dans les roches du socle ainsi qu’une histoire hydrothermale complexe plus précoce associée à des fluides de plus haute température.

La présente étude vient donc compléter ces observations en étendant les investigations au inclusions fluides présentes dans les cristaux de quartz et de dolomites associées au gisement d’End Grid et Andrew Lake, et aussi au prospect de Bong. Deux échantillons provenant du gisement d’End Grid seront étudiés. End09-05_13 à 254.9 m dans une veine de dolomite massive et End09-07_06 à 210.0m dans une brèche hydraulique à remplissage de quartz laiteux.

2.2. Bong

83

Etude microthermométrique des inclusions fluides dans les quartz et dolomite associées aux minéralisations uranifères du faisceau structural Kiggavik-Andrew Lake Les brèches hydrauliques à quartz et/ou carbonates sont relativement peu abondantes à l’échelle de la zone de Bong. Elles sont sont cependant bien représentée dans le sondage

Bong33 situé au NE de la zone explorée. La structure portant la minéralisation a un pendage vers le WSW. L’échantillon Bong39_04 64.8m est constitué par une veine à quartz et carbonate de couleur miel clair à rosâtre montrant un jeu normal apparent reactivant partiellement une microfracture cimentée par de la chlorite, dans un metagraywack très faiblement altéré, Figure 2-1.

Figure 2-1 : Echantilllon BG39_04 présentant une microfaille à remplissage de quartz et carbonates avec mouvement normal apparent et traces d’illitisation le long des épontes de la veinule, carotte diamètre NQ. Le haut de l’image est dirigé vers le haut du sondage

84

Etude microthermométrique des inclusions fluides dans les quartz et dolomite associées aux minéralisations uranifères du faisceau structural Kiggavik-Andrew Lake 2.3. End Grid

2.3.1. Echantillon : End09-05_13 @ 254.9m

Cet échantillon représente une veine de dolomite massive de 60 cm de puissance apparente et encaissée dans un metagraywacke fortement argilisé au mur d’une zone de faille plurimétrique.

Les 4 types d’inclusions identifiés dans les échantillons sont :

(1) Des inclusions triphasées constituées d’un liquide, d’une bulle de vapeur (estimée à environ 1% du volume de l’inclusion) et d’un cube de sel (L+V+H). Certaines de ces inclusions présentent également des inclusions solides sous forme de lamelles de nature indéterminée (illite ?). (2) Des inclusions L+V (1 à10%) dans lesquelles ont observe parfois le mouvement de la bulle de gaz à température ambiante (3) Des inclusions L+V (80%) (4) Des inclusions monophasées L

Les inclusions triphasées sont de loin les plus nombreuses. Elles sont de grande taille de 20 jusqu'à 50x150 µm et suivent généralement les plans de clivage du cristal de dolomite, figure

2-2.

Les inclusions biphasées présentent une grande hétérogénéité de taille et de morphologie, certaines sont semblables au type (1) et tandis que d’autres en général de dimension micrométriques et oblongues se répartissent sous forme d’alignements typiques de fractures cicatrisées.

Les inclusions de types 3 et 4 sont elles aussi fréquement associées à des fractures secondaires cicatrisées. Le necking down des inclusions n’étant pas un phénomène isolé il est fort probable que de nombreuses inclusions des types β, 3, 4 résultent de la striction d’inclusions triphasées de plus grande taille.

85

Etude microthermométrique des inclusions fluides dans les quartz et dolomite associées aux minéralisations uranifères du faisceau structural Kiggavik-Andrew Lake Seules les inclusions triphasées L+ V + H et les L + V à petites bulle de vapeur ont été mesurées.

100 µm

Figure 2-2 : Microphotographie des inclusions triphasées (L+ V + H) de grande taille dans la dolomite. De l'échantillon End09-05_13

Les données microthermométriques montrent des températures d’homogénéisation figure 2-3 ainsi que des températures de fusion de la halite (TfNaCl) figure 2-4 très homogènes quelles que soient la taille et la morphologie des inclusions considérées.

86

Etude microthermométrique des inclusions fluides dans les quartz et dolomite associées aux minéralisations uranifères du faisceau structural Kiggavik-Andrew Lake

Th Dolomite 8 7 6 5 4 3 fréquence 2 1 0 152 154 156 158 160 162 164 166 168 170 172 174 176 178 180 182 184 186 188 190 Th en °C

Figure 2-3 : Histogramme de fréquence des températures d'homogénéisation (en °C) dans l'échantillon End09-

05_13

190.00

170.00

150.00

Th 130.00 carbonates quartz 110.00

90.00

70.00 70.00 90.00 110.00 130.00 150.00 170.00 190.00 210.00 230.00 Tfglace °C

Figure 2-4 : Temperature de fusion de la glace en fonction des temperatures d'homogénisation, séparation des inclusions triphasées des carbonates et de quartz

87

Etude microthermométrique des inclusions fluides dans les quartz et dolomite associées aux minéralisations uranifères du faisceau structural Kiggavik-Andrew Lake

Les températures de fusion de la glace sont plus homogènes parmis les inclusions triphasées des cristaux de dolomite tandis que celles mesurées dans les quartz sont relativement dispersées. De ce fait, il apparaît que certaines inclusions triphasées dans les quartz sont situées sur des plans de fractures cicatrisées ce qui implique de possible réovertures ou des piégeages à des instants différents. Au contraire dans les carbonates, les inclusions apparaissent toutes primaires ou pseudo-primaires. Ainsi soit les carbonates ont piégé un seul

événement ce qui paraît peu probable ou bien les inclusions sont toutes secondaires et marquent un seul et même événement de réactivation qui a conduit au remplissage des cavités néoformées avec les saumures de fond de bassin. Cette réactivation est d’autant plus aisée que les carbonates sont facilement clivables.

La seule température de fusion de la glace mesurée est extrêmement basse à -35.0°C, figure

2-5 et donne des salinités calculées de 14.7 wt% NaCl et 18.9 wt% CaCl2 en utilisant l’équation de Steele-MacInnis, M., Bodnar, R.J. and Naden, J. (2010). A cette exception près aucune prise de glace n’a été observée dans les inclusions triphasées malgré un refroidissement jusqu’à -196°C.

88

Etude microthermométrique des inclusions fluides dans les quartz et dolomite associées aux minéralisations uranifères du faisceau structural Kiggavik-Andrew Lake

12

10

8

6 TfgQuartz fréquence 4 TfgDolomite 2

0 0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20 -22 -24 -26 -28 -30 -32 -34 -36 -38 -40 Tfglace en °C

Figure 2-5 : Température de fusion de la glace des inclusions triphasées dans la dolomite et biphasées le quartz

2.3.2. Echantillon : End09-07_06 @ 210.0m

Cet échantillon provient d’une brèche hydraulique à remplissage de quartz mise en place dans un métagraywacke frais. Il se caractérise par une très forte densité d’inclusions fluides qui rend difficile l’identification des différentes générations d’inclusions.

Les inclusions sont de petites taille avec des diamètres <20 microns. Elles se répartissent dans la masse de quartz (sans organisation spatiale particulière) et le long de plans entre deux phases de croissance de quartz ou des fractures cicatrisées.

4 types d’inclusions ont été identifés :

(1) L+V (1-5 %) prédominantes (2) L+V (> 80%) fréquentes (3) L rares (4) L+V+H rares

On note que le long de plans de fractures les inclusions de type (3) à une seule phase liquide

(généralement micrométriques) sont associées à des inclusions biphasées.

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Etude microthermométrique des inclusions fluides dans les quartz et dolomite associées aux minéralisations uranifères du faisceau structural Kiggavik-Andrew Lake L’ensemble de ces inclusions a une morphologie ovoïde plus ou moins lobée ou de cristal négatif de quartz.

Les mesures microthermométriques ont été effectuées sur les inclusions biphasées à bulle de gaz de petite taille ainsi que sur les inclusions à cube de sel et bulle de gaz, figure 2-4 et 2-5.

Les températures de fusion de la glace mesurées permettent de calculer des salinités comprises entre 2.8 et 11.2 wt% NaCl. Il est possible de mettre en évidence deux populations avec une salinitée moyenne de 3.0 wt% NaCl pour l’une et de 9.3 wt% NaCl pour l’autre, figure2-6. Ces deux familles d’inclusions sont pétrographiquement semblables. On remarque de plus des températures d’homogénéisation moyenne de 305.5°C pour la population d’inclusions présentant les salinités les plus élevées ainsi qu’une plus forte dispersion de température d’homogénéisation, figure 2-7.

500.0 450.0 400.0 350.0 300.0 250.0 200.0 150.0 100.0 50.0 Température d'homgénéisationTempérature en °C 0.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 Salinité calculé en wt% NaCl

Figure 2-6 : Températures d'homogénéisation en fonction de la salinité dans les inclusions biphasées de l'échantillon End09-07_06

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Etude microthermométrique des inclusions fluides dans les quartz et dolomite associées aux minéralisations uranifères du faisceau structural Kiggavik-Andrew Lake

Th Quartz Fréquence 5

4

3

fréquence 2

1

0 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 Th en °C

Figure 2-7 : Histogramme de fréquence des températures d’homogénéisation des inclusions fluides dans les quartz de l’échantillon End09-07_06

2.4. Interprétations et perspectives

L’ensemble des données microthermométriques acquises a permis de calculer les isochores figure 2-8.

En prenant l’hypothèse d’une couverture sédimentaire de 5km avec une densité de 2600 kg/m3 et d’un gradient géothermique de 40°C/km (cas idéal purement diffusif) on remarque que les températures de piégeage données par les isochores sont légèrement plus élevées mais proches des températures d’homogénéisation mesurées sur les inclusions triphasées à cube de sel dans la dolomlite, aux environs de 210°C. Dans le cas des inclusions biphasées les températures sont beaucoup plus variable mais dans l’ensemble plus élevées que celles calculées sur les inclusions triphasées. Elles pourraient signifier un apport de chaleur local plus important ou une mise en place à plus grande profondeur.

91

Etude microthermométrique des inclusions fluides dans les quartz et dolomite associées aux minéralisations uranifères du faisceau structural Kiggavik-Andrew Lake Ces observations sont en accord avec les résultats précédemment acquis sur le gisement d’Andrew lake (1) avec la mise en évidence de circulation de saumures de bassin à plusieurs centaines de mètres dans le socle et (2) une histoire des fluides polyphasée avec des saumures de moyenne température et des fluides peu salés de plus haute temperature, figure 2-9. Il convient maintenant d’étudier les inclusions des cristaux de quartz et carbonates des autres gisements du faisceau afin de confirmer ces tendances. Ces mesures pourrant être

éventuellement complétées par de la spectroscopie RAMAN, du LIBS ou encore de l’ablation laser pour determiner la composition chimique des saumures.

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Etude microthermométrique des inclusions fluides dans les quartz et dolomite associées aux minéralisations uranifères du faisceau structural Kiggavik-Andrew Lake

3500 TmodelConductif(30°C/km) TmodelConductif(40°C/km)

END090513_1.1

3000 END090513_1.8

END090513_1.9

END090513_2.1 2500 END090513_2.2

END090513_2.4

END090513_2.15 2000 END090513_4.3

END090513_4.4

END090513_5.1 1500 END090513_5.2

END090513_5.3 P lihto 1000 END090513_5.4 END090513_6.1

END090513_7.1 500 END090513_7.2 Phydro(Bar)

Phydro(Bar)

0 END090706_1.1 50 150 250 350 450 550 650 750 END090706_2.2

END090706_2.3 -500

Figure 2-8 : Isochores calculées à l’aide de Flincor en utilisant l’équation de Brown & Lamb, 1989

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Etude microthermométrique des inclusions fluides dans les quartz et dolomite associées aux minéralisations uranifères du faisceau structural Kiggavik-Andrew Lake

40

35

30

25

20 HistoFReq_Th_Carbonates Fréquence HistoFReq_Th_Quartz Fréquence 15

10

5

0

0 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 Temperature °C

Figure 2-9 : Histogramme de fréquence des températures d’homogénéisation de l’ensemble des inclusions étudiées le long du faisceau structural de Kiggavik Andrew Lake

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Etude microthermométrique des inclusions fluides dans les quartz et dolomite associées aux minéralisations uranifères du faisceau structural Kiggavik-Andrew Lake Réferences

Derome D, Cathelineau M, Cuney M, Fabre C, Lhomme T, Banks DA (2005) Mixing of Sodic and Calcic Brines and Uranium Deposition at McArthur River, Saskatchewan, Canada: A Raman and Laser-Induced Breakdown Spectroscopic Study of Fluid Inclusions. Economic Geology 100:1529-1545. doi: 10.2113/gsecongeo.100.8.1529. 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 Concil Technical report. Saskatchewan Reasearch Council, pp 197. Kotzer TG, Kyser TK (1995) Petrogenesis of the Proterozoic Athabasca Basin, northern Saskatchewan, Canada, and its relation to diagenesis, hydrothermal uranium mineralization and paleohydrogeology. Chemical Geology 120:45-89. doi: http://dx.doi.org/10.1016/0009-2541(94)00114-N. Pagel M (1975) Détermination des conditions physico-chimique de la silicification diagénétique des grès Athabasca (Canada) au moyen des inclusions fluides. Comptes Rendus de l'académie des Sciences Paris 280:2301-2304. Pagel M, Jaffrezic H (1977) Analyses chimiques des saumures des inclusionsdu quartz et de la dolomite du gisement d’uranium de Rabbit Lake(Canada). Aspect méthodologique et importance génétique. Comptes Rendus de l'Académie des Sciences 284:113-116. Pagel M, Ahamdach N (1995) Etude des inclusions fluides dans les quartz des gisements d'uranium de l'Athabasca et du Thelon (Canada). Centre de Recherche sur la Geologie des matières premieres minerales et énérgétiques - CREGU, Vandoeuvre les Nancy, pp 1-10.

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3. Illite & Uraninite geochronology

3.1. Introduction

Temporal constrains on alteration and mineralization events are of main importance for geologists who deal with metallogenic interpretation of uranium deposition and more particularly with the timing of deposition of the present uranium ore deposits. From the previous study on petrography and mineralogy of both uranium ore bodies and alteration haloes along the Kiggavik-Andrew Lake structural trend, uraninite and illite seems to be the best mineral candidates for gaining the radio-chronological data necessary to refine the age and the temporal relationships between mineralization and uranium alteration processes.

Uranium ore-forming minerals like uraninite are very likely to be remobilized in oxidizing conditions, (via the oxidation of the U4+ to U6+ which is highly soluble in aqueous solutions).

Then, losses of radiogenic lead or gain of common lead can occur and mislead the interpretation of the original crystallisation age. However, this could be seen as a great advantage because uraninite resets may help to record the various remobilisation events since the primary uranium deposition, either controlled by regional events (e.g. intrusion emplacements, meteoric water circulation in faults and fractures) either controlled by far field effects of the continental crust geodynamics (e.g. rifting, diagenesis, collision, uplift, isostatic rebound).

3.2. Ar/Ar principle and method

The principle of the 40Ar/39Ar geochronology is a variant of the K / Ar method, based on the fact that potassium rich mineral present elevated 40Ar/36Ar ratios due to the 40K decay

(Aldrich and Nier 1948). Then the amount of radiogenic 40Ar* is proportional to the initial potassium content in the mineral and time.

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In nature both stable isotopes (36Ar, 38Ar and 40Ar*) and radioactive ones (37Ar & 39Ar) are presents. Then artificial irradiation allows the precise quantification of the initial 40K from the relative abundance between argon isotopes and the argon produced via neutron irradiation

39 ( Ark), with the relations:

40 39 40 K = 0.0000125 * K, and 39Ark = K * J’ with J’, the irradiation parameter.

Then the isotopic ratios and the combination of the different yields can give access to the

40Ar/39Ar age using the equation:

with λ the decay constant and J the irradiation parameter.

The J’ and J parameter constrains the abundance of potassium isotopes, the decay constant, the neutron fluence, the effective cross section of the K (n, p) reaction, as well as the duration of irradiation. These parameters are obtained from the co-irradiation of standard of known age with the samples (Mitchell 1968).

One of the advantages of the Ar/Ar method over the conventional K/Ar is the step heating degassing (Merrihue and Turner 1966). This is providing information about potential Ar unrelated to the radioactive decay of potassium, and can possibly be plotted as an isochron diagram comprising a plot of 40Ar/36Ar vs 39Ar/36Ar. Then one sample can give many ages, and the presence or absence of plateau is critical for interpretation. The lack of plateau forces to a more carful interpretation. Then ages resulting from the interpretation of Ar realised must be taken more carefully. Such assessment and control over the data in not possible with the

K/Ar were the age is representative of the mean value of all the released radiogenic argon.

Then two types of ages can be calculated: (1) an average age comprising several steps that define a plateau, and (2) a total fusion age, were all the measured steps are used, and then is

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Illite & Uraninite geochronology equivalent to a K/Ar age. Since the several decades the definition of the plateau varied according to the analytical progress and the authors. As a general guideline, a plateau can be defined a segment of the age spectrum which consist of 3 steps with overlapping age within the analytical error ( 2σ) in which more than 50 % of the argon is released. All samples were run as conventional furnace step heating analyses on bulk illite mineral separates. All data are reported at the 1σ uncertainty level, unless noted otherwise. Furnace step heating analyses produce what is referred to as an apparent age spectrum. The "apparent age" derives from the fact that ages on an age spectrum plot are calculated assuming that the non- radiogenic argon (often referred to as trapped, or initial argon) is atmospheric in isotopic composition (40Ar/36Ar = 295.5).

3.3. Samples

The dataset of our geochronological study consists in 6 mineral Table 3-1 (1) Four of them consist in illite and sudoite separates which were dated by the Ar/Ar method. Sudoite persists in the illite concentrate because it was not possible to efficiently separate these two clay minerals. They constitute a clay assemblage impossible to sort by any existing method of mineral separation. However, it can be expected that sudoite which does not contain potassium (or other alkali element) in its crystal structure has not significant influence on the measured ages. Each clay sample was encapsulated prior to irradiation to avoid Ar losses

(Hess and Lippolt 1986; Foland et al. 1992) and processed in the Nevada Isotope

Geochronology Laboratory at the University of Nevada, Las Vegas, USA. A sudoite-rich, sample (Bong42_25) was selected in order to test the timing of alteration comparatively with zones where illite is dominant. The work hypothesis was a possible reset of the illite geochronometer during the sudoite precipitation. (2) Two semi-massive uraninite samples from the End Grid deposit were analysed via SIMS using the U/Pb geochronometer at the

CRPG-CNRS facility on a CAMECA IMS 1270 ion-probe. The analytical protocol is given in

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Illite & Uraninite geochronology

(Alexandrov et al. 2000) and the ISOPLOT software was used for the isochron calculations

(Ludwig 1993).

Table 3-1 : Main characteristics of minerals samples selected for geochronology

Sample Depth Macroscopic description Illite Sudoite Method

End09_04_32/ 345.1 uraninite in fracture in a redox front zone, no data U/Pb

9568-38 bleaching SIMS

End09_04_33/ 355.6 semi-massive pitchblend in a fracture parallel to xxx x “

9568-39 the foliation

Bong42_21 309.3 microfault gouge parallel to the foliation xx xx Ar/Ar

Bong42_25 347.7 pervasively altered metagraywacke x xxx “

Bong42_32 388.2 pervasively altered metagraywacke xx x “

Bong42_40 441.0 microfault gouge parallel to the foliation xxx x “

3.4. Results

3.4.1. Ar-Ar datation of illite

All the samples produced discordant age spectrum, while the K/Ca ratios were low and consistent with illite separate. In addition the high radiogenic yields in agreement indicates that the samples were not affected by recent alteration. The total gas ages obtained were 1248,

1072, 1033 and 952 Ma (Figure 3-1 and table 3-1). However most of the samples showed a relatively complex age spectrum, and only one plateau age at 1124 9 Ma can be calculated from the Bong42_40 sample (figure 3-1d). Nevertheless, some significant steps of the age spectrum diagrams showing overlaps can cautiously be interpreted, as “pseudo-plateau”. This age which doesn’t fully agree with the requirements for a plateau definition (in term of age

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Illite & Uraninite geochronology overlap and Ar released) may provide more knowledge on the alteration and mineralization relationships. From these data, several groups of ages can be identified, near 1300 Ma in the

Bong4221 & 4225 samples and near 1100 Ma in the Bong4232 and Bong4240 samples. A last an age around 1200 Ma can be also suspected with less confidence.

Figure 3-1 : Age spectrum of illites of the Bong prospect obtained from Ar/Ar datation method. a: Bong42_21; b: Bong42_25; c: Bong42_32; d: Bong42_40.

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Table 3-2 Ar/Ar geochronology data

T t step (°C) (min.) 36Ar 37Ar 38Ar 39Ar 40Ar %40Ar* % 39Ar rlsd Ca/K 40Ar*/39ArK Age (Ma) 1s.d. Bong42_21, Illite, 0.19 mg, J = 0.00543 ± 0.50% 1 450 12 0.118 0.023 0.192 8.963 1347.69 98.3 9.1 0.08033758 148.094449 1064.6 7.6 2 500 12 0.047 0.022 0.115 6.233 977.83 99.7 6.3 0.110502883 156.763618 1111.0 7.7 3 550 12 0.045 0.017 0.151 9.552 1608.99 99.8 9.7 0.055718043 169.307208 1176.2 8.1 4 600 12 0.050 0.022 0.194 13.161 2222.12 99.8 13.3 0.052332878 169.979488 1179.7 8.0 5 650 12 0.055 0.025 0.269 17.968 3362.74 99.8 18.2 0.043559211 188.752426 1272.8 9.1 6 700 12 0.049 0.028 0.345 22.443 4385.28 99.9 22.7 0.039058566 197.360166 1314.0 8.6 7 750 12 0.031 0.020 0.226 14.783 2902.95 100.0 15.0 0.042355226 197.627568 1315.3 8.9 8 800 12 0.029 0.015 0.062 3.602 814.771 100.0 3.7 0.130376126 223.734354 1434.6 9.3 9 850 12 0.027 0.016 0.021 1.242 323.665 100.0 1.3 0.403350707 248.229084 1539.8 9.8 10 910 12 0.036 0.014 0.016 0.541 153.107 100.0 0.5 0.810337177 250.430085 1549.0 10.2 11 970 12 0.042 0.016 0.014 0.187 58.036 99.9 0.2 2.680684089 167.943639 1169.3 9.5 Cumulative %39Ar rlsd = 100.0 Total gas age = 1248.2 7.3 Bong42_25, Illite, 0.39 mg, J = 0.00472 ± 1.55% 1 450 12 0.596 0.049 2.155 20.042 1901.65 91.0 20.3 0.077876847 87.679309 624.78 9.29 2 500 12 0.161 0.061 1.302 24.770 2048.34 98.3 25.1 0.078443549 81.899919 589.63 8.75 3 540 12 0.073 0.045 0.531 14.914 2595.82 99.6 15.1 0.096111195 174.883789 1085.74 14.15 4 570 12 0.044 0.028 0.323 9.758 2128.38 99.9 9.9 0.091401271 219.612617 1283.18 15.96 5 600 12 0.043 0.029 0.237 8.190 1882.00 99.9 8.3 0.112790305 231.224893 1331.09 16.47 6 640 12 0.222 0.033 0.278 9.022 2122.05 97.5 9.2 0.116511623 231.250191 1331.20 16.40 7 690 12 2.220 0.046 0.711 7.371 2242.50 72.7 7.5 0.198792401 223.065351 1297.56 16.93 8 740 12 0.050 0.014 0.036 1.443 298.336 99.3 1.5 0.309060685 410.064354 1942.77 20.67 9 840 12 0.153 0.023 0.089 2.286 448.787 94.6 2.3 0.320505207 179.954762 1109.24 14.65 10 1000 12 0.189 0.032 0.064 0.706 75.517 42.5 0.7 1.44433639 29.580690 235.79 5.23 Cumulative %39Ar rlsd = 100.0 Total gas age = 952.49 14.92 Bong42_32, Illite, 0.10 mg, J = 0.00474 ± 1.37% 1 400 12 0.069 0.014 0.118 2.727 294.022 96.7 5.3 0.164422178 101.868836 710.76 9.55 2 450 12 0.043 0.013 0.117 3.132 398.964 99.5 6.1 0.132933729 124.984666 839.36 10.62 3 480 12 0.031 0.009 0.103 3.076 429.522 99.9 6.0 0.093705459 137.874793 907.29 11.32 4 510 12 0.035 0.014 0.110 4.048 619.357 100.0 7.9 0.110763932 152.413632 980.95 11.96 5 540 12 0.042 0.021 0.126 5.367 852.669 99.8 10.5 0.125314216 158.622804 1011.52 12.25 6 570 12 0.032 0.016 0.128 6.002 995.231 100.0 11.7 0.085375188 166.133281 1047.81 12.65 7 600 12 0.036 0.016 0.135 6.078 1059.91 100.0 11.8 0.084307621 174.877712 1089.17 12.89 8 640 12 0.505 0.014 0.277 8.625 1632.74 91.9 16.8 0.051984331 175.153282 1090.46 13.08 9 690 12 4.233 0.029 1.037 7.700 2565.11 54.2 15.0 0.120620002 182.139769 1122.81 15.47 10 740 12 0.103 0.016 0.091 3.226 613.706 98.4 6.3 0.15884459 183.675258 1129.84 13.29 11 840 12 0.114 0.016 0.067 1.096 254.611 94.8 2.1 0.46758933 205.979005 1229.02 14.66 12 1000 12 0.179 0.016 0.043 0.242 102.156 66.6 0.5 2.118677458 209.431054 1243.90 17.20 Cumulative %39Ar rlsd = 100.0 Total gas age = 1032.96 13.94 Bong42_40, Illite, 0.26 mg, J = 0.00484 ± 1.38% 1 400 12 0.118 0.015 0.175 4.771 634.887 86.3 3.8 0.102158706 127.854730 869.02 11.06 2 450 12 0.063 0.022 0.195 5.649 780.443 99.0 4.5 0.126545782 136.870450 917.00 11.42 3 480 12 0.038 0.012 0.158 5.432 755.730 99.9 4.3 0.071781289 139.021735 928.27 11.56 4 510 12 0.039 0.013 0.183 7.532 1144.59 99.9 5.9 0.056081659 152.582126 997.69 12.33 5 540 12 0.042 0.012 0.216 10.217 1599.84 99.9 8.1 0.038163082 158.598822 1027.66 12.37 6 570 12 0.042 0.020 0.248 12.560 2017.40 99.9 9.9 0.051740144 161.907354 1043.93 12.58 7 600 12 0.043 0.024 0.248 13.829 2355.68 99.9 10.9 0.056390808 171.838464 1091.91 13.03 8 640 12 0.162 0.029 0.394 20.673 3642.17 99.9 16.3 0.045580701 176.431866 1113.67 13.20 9 690 12 2.722 0.038 1.105 27.837 5656.73 86.7 22.0 0.044355505 178.419659 1123.01 13.60 10 760 12 0.142 0.020 0.297 15.464 2798.37 98.9 12.2 0.042023694 180.891527 1134.55 13.36 11 1000 12 0.334 0.016 0.148 2.685 644.618 88.9 2.1 0.193633545 207.465883 1254.22 14.65 Cumulative %39Ar rlsd = 100.0 Total gas age = 1072.18 6.29 Plateau age = 1123.60 8.98 note: isotope beams in mV, rlsd = released, error in age includes J error, all errors 1 sigma 4 amu discrimination = 1.0598 ± 0.62%, 40/39K = 0.0086 ± 27.68%, 36/37Ca = 0.000256 ± 2.01%, 39/37Ca = 0.000658 ± 1.01% isotope beams in mV, rlsd = released, error in age includes J error, all errors 1 sigma (36Ar through 40Ar are measured beam intensities, corrected for decay for the age calculations)

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3.4.2. SIMS U/Pb datation of uraninite

Uranium and lead isotopic ratios (206Pb/238U and 207Pb/235U) measured in samples End0904-32 and End0904-33 were plotted on Concordia diagrams, figure 3-2 & 3-3.

0.34

Intercepts at 0.30 124±25 & 1293.1 ±6.2 [±8.4] Ma MSWD = 27 1600

0.26

206Pb/238U 1400

0.22 1200

0.18 1000

0.14 800 KIGGAVIK (End Grid) - 9568-38

0.10 600 207Pb/235U 0.06 0.5 1.5 2.5 3.5

Figure 3-2 : U/Pb concordia diagram for End Grid veinlet mineralization

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0.28 Intercepts at

U 46 ± 57 & 1187 ± 19 [±20] Ma 1400 238 0.24 MSWD = 8.3 Pb/ 1200 0.20 206

1000 0.16 800 0.12 600 KIGGAVIK (End Grid) - 9568-39 0.08 400

0.04 200 207Pb/235U 0.000 0 1 2 3

Figure 3-3 : U/Pb Concordia diagrams for End Grid semi-massive mineralization

Veinlet type mineralization data gave an upper intercept at 1293 6 Ma and a Mean Square

Weighted Deviation (MSWD) of 27, figure 3-2. The data for the semi-massive mineralization gave an upper intercept of 1187 19 Ma and a MSWD of 8.3, Figure 3-3. In both case the high MSWD indicates relatively scattered values.

3.5. Discussion

Until know most of the available literature on the Kiggavik area were TIMS U/Pb ages on the mineralization or K/Ar geochronology on illite (c.f introduction). The gathered geochronological data can be integrated with the literature data especially the recent work done with in-situ techniques, more suitable to discriminate distinct events of mineralization and alteration.

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The Ar/Ar data obtained on illite from the Bong deposits can be compared with U/Pb in-situ data ages on Bong uraninite (Sharpe 2013), as well as the age obtained on End mineralization,

Figure 3-4. Both the identified plateau and pseudo-plateau are within the errors range of the

U/Pb ages on uraninite. In addition, ages around 1300 Ma seems recurrent in all the analysed samples. This age is in the same time frame as the MacKenzie dykes, so this event could be a control of the mineralization via the far field tectonics related to Poseidon ocean opening.

They could be indicative of the first mineralization stage, but older ages cannot be totally excluded. Nevertheless, the step heating doesn’t indicate that this age could be related to a major reset due to the absence of ages older than 1300 Ma. The only possibility as showed in the Bong4225 would be the presence of trace of unaltered metamorphic micas, giving a non significant step of Hudsonian age. These ages are slightly younger than the 1403 Ma U/Pb

TIMS age on uraninite or the K/Ar ages on illite 1386 24 Ma and 1362 21 Ma at Kiggavik

(Farkas 1984; Miller and LeCheminant 1985). However, the comparison between the bulk ages and in situ or Ar/Ar via step heating degassing may be not relevant as heterogeneities and numerous remobilizations affected uraninite. In fact, remoblization could result in contamination by common lead and apparently older ages. The younger ages around 1100

Ma are possibly connected to a later event of uranium remobilization. They could also be related to the Grenville orogen.

Finally, it can be noted that similar ages have been obtained for both the uranium mineralization and the illite crystallization in the associated alteration halo in the Bong and the End uranium mineralizations. This confirms a close temporal relationship between the two process, highlighting so the interest of alteration minerals as marker of the paleoconditions of uranium deposition. The fact that similar ages have been obtained in the two studied areas confirms also the regional extension of the alteration and mineralization processes. This also indicates that reactivation of both local and regional faults allowed the fluid circulation.

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Finally, the ages obtained in the uranium deposits along the Kiggavik-Andrew-lake structural trend indicate that alteration and mineralization processes were active over a large span of time ( ⋍ 200MA) which is not so different of the span of time reported for alteration mieralization processes in the Athabasca basin (Jefferson et al., 2007).

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Figure 3-4 : Summary of new geochronological data on alteration and mineralization at Kiggavik with comparison to tectonic or thermal events affecting the Canadian shield during the Paleoproterozoic, data from (Fahrig 1987; Rainbird et al. 2003; Davis et al. 2011; Peterson et al. 2002; Turner et al. 2001; Sharpe 2013)

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Illite & Uraninite geochronology

3.6. References

Aldrich LT, Nier AO (1948) Argon 40 in Potassium minerals. Phys Rev 74. Alexandrov P, Cheilletz A, Deloule É, Cuney M (2000) 319 ± 7 Ma crystallization age for the Blond granite (northwest Limousin, French Massif Central) obtained by U/Pb ion-probe dating of zircons. Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science 330:617-622. doi: http://dx.doi.org/10.1016/S1251-8050(00)00201-9. Davis WJ, Gall Q, Jefferson CW, Rainbird RH (2011) Fluorapatite in the Paleoproterozoic Thelon Basin: Structural-stratigraphic context, in situ ion microprobe U-Pb ages, and fluid-flow history. Geological Society of America Bulletin 123:1056-1073. doi: 10.1130/b30163.1. Fahrig WF (1987) The tectonic settings of continental mafic dyke swarms: Failed arm and early passive margin In: Halls HC, Fahrig WF (eds) Mafic dyke swarms. Geological Association of Canada Special Paper, St John's, Nfld, pp 331-348. Farkas A (1984) Mineralogy and host rock alteration of the Lone Gull deposit Internal report. Urangesellschaft, Frankfurt am Main, pp 45. Foland KA, Hubacher FA, Arehart GB (1992) 40Ar39Ar dating of very fine-grained samples: An encapsulated-vial procedure to overcome the problem of 39Ar recoil loss. Chemical Geology 102:269-276. doi: http://dx.doi.org/10.1016/0009-2541(92)90161-W. Hess JC, Lippolt HJ (1986) 40Ar/39Ar ages of tonstein and tuff sanidines: New calibration points for the improvement of the Upper Carboniferous time scale. Chemical Geology: Isotope Geoscience section 59:143-154. doi: http://dx.doi.org/10.1016/0168-9622(86)90066-7. Ludwig KR (1993) Isoplot:excel based program for plotting radiogenic isotopes. U.S. Geological Survey, pp 1-42. Merrihue C, Turner G (1966) Potassium-argon dating by activation with fast neutrons. Journal of Geophysical Research 71:2852-2857. doi: 10.1029/JZ071i011p02852. Miller AR, LeCheminant AN (1985) Geology and uranium metallogeny of Proterozoic supracrustal successions, central District of Keewatin, N.W.T with comparisons to northern Saskatchewan Geology of uranium deposits. Canadian Institute of Mining and Metalurgy, pp 167-185. Mitchell JG (1968) The argon-40argon-39 method for potassium-argon age determination. Geochimica et Cosmochimica Acta 32:781-790. doi: http://dx.doi.org/10.1016/0016- 7037(68)90012-4. Peterson TD, Van Breemen O, Sandeman H, Cousens B (2002) Proterozoic (1.85-1.75 Ga) igneous suites of the Western Churchill Province: granitoid and ultrapotassic magmatism in a reworked Archean hinterland. Precambrian Research 119:73-100. Rainbird RH, Hadlari T, Aspler LB, Donaldson JA, LeCheminant AN, Peterson TD (2003) Sequence stratigraphy and evolution of the Paleoproterozoic intracontinental Baker Lake and Thelon basins, western Churchill Province, Nunavut, Canada. Precambrian Research 125:21-53. Sharpe R (2013) The geochermistry and geochronolgy of the Bong uranium deposit, Thelon Basin, Nunavut, Canada Department of Geological Sciences. University of Manitoba, Winnipeg, Manitoba. Turner W, Richards J, Nesbitt B, Muehlenbachs K, Biczok J (2001) Proterozoic low-sulfidation epithermal Au-Ag mineralization in the Mallery Lake area, Nunavut, Canada. Miner Deposita 36:442-457. doi: 10.1007/s001260100181.

107

The basal Thelon Formation at Kiggavik

4. The basal Thelon Formation at Kiggavik

At Kiggavik, Thelon Formation is not widely encountered on actual land ARC land holdings, and mostly represented by a strip of sandstones outcrops located at the North of the Granite

Grid prospect, close to the Thelon fault escarpment and basal conglomerates outcrops, at the

WNW of Kiggavik camp and in the St Tropez area, south of Schultz Lake. All studied samples presented here where taken from outcrops in the Granite (labeled as GGx) & St

Tropez areas as well as in the historical Th18 BP drillhole, located 10 kilometers NNW of

Kiggavik.

Nevertheless, as the connection between the Thelon Basin and the mineralization system at

Kiggavik appears more and more preeminent, an overview of local petrographic and mineralogical properties of these sandstones would provide additional informations for the metallogenic interpretation of the Kiggavik area.

4.1. Methods

XRD diffraction were performed using a Bruker D8 diffractometer, on the 2- 65° 2θ range using a 0.02 °2θ step ad seod outig tie. Cu aode X-ray tube set up with a 40kV acceleration tension and 40mA current, 1° fixed divergence slit.

Transmission Fourier Infrared (FT-IR) spectra were recorded with a Nicolet 760 FT-IR spectrometer equipped with a Potassium Bromide (KBr) beamsplitter and a DTGS-KBr detector. Acquisitions were performed in the 400 – 4000 cm-1 (mid infrared range) with a

4cm-1 resolution. Pellets suitable for analysis were made using 1 mg of clay separates, used for XRD measurement, and grounded in an agate mortar with 150 mg of KBr. The mixture was therefore pressed in a vacuum die with 10 tons per cm2 of compression. Pellets were dried

24 hours at 120°C prior to measurements to avoid hygroscopic water in KBr. For each spectrum 100 scans were cumulated after a background acquisition.

108

The basal Thelon Formation at Kiggavik

Electron microprobe measurements on clay minerals were done on a Cameca SX100 using natural and synthetic standards for calibration. Albite, anortite and orthose, diopside, garnet and MnTiO3 respectively for Na, Ca, K, Si, Fe, Mn, and Ti, with a column setting with a

15kV acceleration tension and a 10nA beam current.

Quartz oxygen isotopes compositions measurements were performed in situ by secondary ion mass spectrometry (SIMS) on a CAMECA IMF 7f ion microprobe, at the University of

Manitoba. A ~2 nA primary beam of Cs+ was accelerated at 10kV and focused to a 10 x 15

m spot using a 100 m aperture in the primary column. An offset of 200-volts was used to eliminate molecular ion interferences (Fayek et al. 2002; Riciputi and Greenwood 1998). Ions were detected with a Balzers SEV 1217 electron multiplier coupled with an ion-counting system using an overall deadtime of 52 ns. Two isotopes of oxygen, 16O- and 18O-, were detected by switching the magnetic field. Analyses comprised 70 cycles and lasted ~10 minutes (Sharpe 2013). All stable-isotope data are presented in the δ-notation relative to the appropriate standard. Oxygen is reported relative to Vienna Standard Mean Ocean Water (V-

SMOW) in units of per mil (‰) and are calculated using the following equation: δ18O (‰) =

3 (Rsample / RV-SMOW -1) * 10 . Additional informations on SIMS are provided in appendix.

Chemical bulk rock analysis ICP-MS on major and traces elements were performed by the

Service d’Analyses des Roches et Minéraux (SARM) in CRPG, Nancy, France

4.2. Sandstones regional setting

The unconformity is mostly visible along the Thelon fault through the tectonic contact, the sandstones being generally found on the Northern side of the fault, Figure 4-1a. A significant vertical displacement, up to 200 meters, has been recognized from drillholes along this fault

109

The basal Thelon Formation at Kiggavik exhibiting a horst and graben structure (P.Wollenberg, pers. Comm.). Then in one compartment, both basement rocks at the topographic surface and the unconformity are eroded while in the other compartment tens or hundreds of meters of sandstones are still present above the unconformity. This feature reveals that the actual position of the Kiggavik trend deposits known form to surface up to several hundred meters into the basement rocks may have been formed deeply and thus are possibly the expression of deep seated unconformity type uranium deposits. The normal movements with a dextral component interpreted from the kinematic markers on fault surface, Figure 4-1b, are consistent with the regional ones and are observed on the both Thelon and judge Sisson faults and are also marked by significant alteration associated with hydraulic and tectonic breccias. Alteration is expressed with a zone of intense hematization centered on the fault core which intensity decrease rapidly in the damage zones in both foot and hanging walls. Into the fault core hematization zones are forming alternating corridors of silicified / desilificied / hematized rocks dominantly expressed in the Woodburn metasediments but also in the Archean or

Proterozoic quartzites. Hydraulic and tectonic brecciation is also present in the sandstones above the unconformity along the Thelon fault zone Figure 4-1f. The lateral change form strongly altered to fresh rocks is relatively sharp (over less than tens of meters) with hematization being more disseminated and patchier in a dominantly chloritic metasediments.

Moreover at the vicinity of these regional tectonic structures, the general trend of flat flying foliation is reworked and vertically reoriented, Figure 4-1c.

110

The basal Thelon Formation at Kiggavik

111

The basal Thelon Formation at Kiggavik

Figure 4-1a : Thelon fault escarpment where the Thelon Formation sandstones are tectonically in contact with the underlying Woodburn Group metasediments, view looking toward the NNW, outcrop located at the north of the Granite Grid area on CAMECO corp. ground (checked jointly with R. Hunter, CAMECO & C. Jefferson,

GSC); b, Detail of the previously indicated fault, looking at the handing wall the surface is showing quartzite fragments dragged into the fault and indicating a normal with a dextral component displacement; c Angular unconformity between the Thelon sandstones and the locally steep foliation of Woodburn Group metasediments, strong red-brick hematization, at Unconformity lake (Forum’s ground); d, symmetrical ripple marks develloped on the Thelon sandstones at Unconformity lake; e, red siltstone facies of the basal Thelon formation; f, hydraulic fracturation breccias with sub angular sandstones fragments cemented by hydrothermal quartz at 110.9 meter, with unconformity at 126.4m , BP historic drillcores; g, Polymictic conglomerate at the base of the Thelon

Formation in the St Tropez area, gravel to pebble boulder size elements of red siltite, gneisses and abundant quartzite in a siliceous and hematitic matrix.

The sedimentary cover overlying the unconformity is formed of gritty to conglomeratic, moderately to weakly sorted, and locally cross bedded, matrix supported sandstones containing abundant lithic fragments of basement rocks (various gneisses, quartzite).

Lenticular to isopachous, metric intercalation of red siltstone beds are present within the sandstones. Finally conglomerates seems to fill paleovalleys Figure 4-1e, d, g. in which sediments may have been deposited in a relatively high energy, continental environment, at shallow depth as are indicating from the observed symmetrical ripple marks, characteristic of the oscillating waves effects Figure 4-1d.

4.3. Bulk-rock chemistry of the Basal Thelon sandstones

Bulk rock chemical analysis from the basal Thelon Formation are representative of quartz arenite sandstones totally depleted in Na, Mg and Ca elements with only Al as major element in addition to the strongly predominant Si (table 4-1). In the sandstones samples, the

112

The basal Thelon Formation at Kiggavik

aluminum content ranges from 2 to 8 % and can be essentially assigned to the presence of

kaolinite (in absence of significant amount of K), while iron (less than 1%) is principally

assigned to hematite. The very low potassium amount of sandstones can be related to detrital

micas and locally to traces of illite related to later incipient hydrothermal alteration. The

higher potassium content measured in the siltite sample (GG3a) is representative of the high

content of detrital micas in the sample. All these data are indicative of the absence of

significant amount of feldspar in the sandstones of the basal Thelon formation investigated in

the Kiggavik area.

Table 4-1 Major and traces elements concentration of basal Thelon sandstones (sst) from the NE St Tropez

(NESTP4) and Granite Grid (GG) areas. Red siltites from Granite Grid are represented by the GG3a sample

SiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O TiO2 P2O5 PF Zr Th U NESTP4 sst 91.50 4.57 0.96 0.01 0.03 < L.D. 0.01 0.41 0.11 0.04 1.51 52.42 5.35 0.70 GG3b sst 93.25 4.36 0.22 0.00 0.02 < L.D. 0.02 0.28 0.13 0.07 1.46 83.88 8.58 0.40 GG3c sst 91.70 4.93 0.24 0.00 0.02 < L.D. 0.01 0.25 0.08 0.04 1.81 51.12 6.07 0.39 GG4 sst 91.46 4.94 0.15 0.00 < L.D. < L.D. 0.01 0.22 0.07 0.03 1.88 50.05 5.47 0.34 GG5 sst 95.01 2.50 0.16 0.00 0.04 < L.D. 0.01 0.61 0.07 0.03 0.58 66.38 5.29 0.34 GG7 sst 87.19 8.06 0.61 0.00 0.02 < L.D. < L.D. 0.33 0.07 0.05 2.79 64.70 5.30 0.44 GG3a siltite 82.74 8.98 1.94 0.00 0.16 0.77 0.02 2.33 0.34 0.28 2.08 68.89 23.40 0.92

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu ΣREE 21.08 32.63 3.46 10.60 1.31 0.23 0.77 0.11 0.52 0.09 0.26 0.04 0.32 0.05 71.19 29.04 50.28 5.18 15.88 2.08 0.40 1.28 0.15 0.56 0.07 0.20 0.03 0.24 0.04 105.23 19.57 33.48 3.46 11.10 1.50 0.31 0.85 0.10 0.38 0.06 0.18 0.03 0.24 0.04 71.11 18.49 18.61 3.18 9.76 1.15 0.23 0.52 0.06 0.27 0.04 0.13 0.02 0.18 0.03 52.54 11.96 21.40 2.18 7.09 1.02 0.22 0.64 0.07 0.32 0.05 0.15 0.03 0.20 0.03 45.20 18.72 35.23 3.47 11.30 1.65 0.35 1.16 0.14 0.67 0.11 0.32 0.05 0.37 0.06 73.28 92.91 133.00 19.44 72.43 12.31 2.30 7.17 0.74 2.08 0.21 0.60 0.09 0.73 0.12 343.52

Considering the trace elements, the basal sandstones can be characterized by very low

uranium concentrations (0.3 to 0.9 ppm) and U/Th ratios which range between 7.6 and 21.7.

In addition, sandstones are also characterized by light REE (La to Eu) > to heavy REE (Gd to

Lu) in the chondrite normalized patterns, Figure 4-2. Moreover the (La/Yb)ch ratios are

ranging from 34 to 82. Such fractionation is very common in weathering processes where

113

The basal Thelon Formation at Kiggavik residual products are enriched in LREE and depleted in HREE (Duddy 1980; Nesbitt 1979,

(Braun et al. 1990).

1000 NESTP4 GG3b GG3c 100 Siltite GG4 GG5 GG7 10 Sandstones GG3a

1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

0.1

Figure 4-2: chondrite normalized (Evensen et al. 1978) REE patterns for sandstones and siltites at the base of the

Thelon Formation

4.4. Petrography and mineralogy

According to the available sampling, petrographic and mineralogical study of sandstones samples is not representative of the whole diagenetic phenomenon throughout the Thelon basin. Its main goal is to describe in more details the basin / basement relationships at the vicinity of the N70 trend Thelon fault which is non graphitic and non mineralized, but need to be accounted for a fault of regional interest for the prospection of uranium mineralization in the Kiggavik area.

All hand samples present a well developed cementation of the intergranular porosity by very fine grained “cherty quartz”. Such silica cement trapped diagenetic APS minerals (see the

114

The basal Thelon Formation at Kiggavik paragenetic sequence in chapter 2) as well as large kaolinite vermicules or fragments of aggregated quartz / kaolinite material of detrital origin.

Three different generations of quartz can be identified in these cemented sandstones: (1) detrital, angular to sub rounded grains, (2) syntaxial quartz overgrowth forming 10 to 20 micrometer rims around detrital quartz grains, and (3) very fine grained microcrystalline quartz (Folk and Weaver 1952) sealing all the remaining porosity of the sandstone, figure 4-

3a. The quartz overgrowths display evidence of stopping at the contact with the kaolinite vermicules, Figure 4-3b, while the microcrystalline quartz cement not only heal the porosity but show evidences of jigsaw texture suggesting a fluid assisted brecciation. Such hydraulic fracture together with a matrix formed of a mosaic of tiny quartz crystals, is indicative of a brutal event of fluid-rock interaction (strong oversaturation of the solution versus quartz) during which nucleation is favored rather crystal growth.

According to their textural characteristics, three different types of kaolinite minerals have been distinguished: (1) smalls euhedral crystals (3 * 3m) disseminated in the cemented porosity (possibly neoformed or fragments of larger size kaolinite), Figure 4-3a, 4-3b; (2) large vermicular kaolinite up to 0.5 x 0.2 mm which occurred either as individual crystal either as aggregates, Figure 4-3c; and (3) composite aggregates of detrital quartz grains and kaolinite, Figure 4-3d.

115

The basal Thelon Formation at Kiggavik

Figure 4-3 : a, epitaxial diagenetic quartz overgrowths (Q2) and (Q3) microcrystalline quartz cement; b, large kaolinite booklets floating in the cemented porosity with evidence of stopping of the epitaxial growth of diagenetic quartz overgrowth (Q2), c, aggregate of large, (up to 0.5mm length) kaolinite booklets in the sandstone porosity, d, composite quartz and kaolinite lithic grain (red dotted circle); e, kaolinite & quartz lithic grain showing evidence of later illitization; f, detrital quartz grain cross cut by a fracture filled by microcrystalline quartz.

116

The basal Thelon Formation at Kiggavik

In addition it can be noted that micrometer grained size hematite grains are observed between the booklets of kaolinite vermicules, as well as disseminated in the porosity in absence of any trace of associated illitization. These iron oxides, likely hematite, are quite abundant in the sandstone porosity, as lath and detrital, sub rounded grains, both cemented by the APS minerals and the microcrystalline quartz, Figure 4-4a & b. It can be noted that a later generation of hematite is also present in association with illite and APS minerals fillings of fractures which cross cutt the microcrystalline quartz cement (see part B, chapter 1, on APS minerals).

Lastly, one centimeter clay filled fracture cross cutting the basal Thelon Formation sandstone in one of the historical BP drillcore site (located around 10 kilometers at the NW of the

Kiggavik camp, collar coordinates unknown), showed a white clay mineral with a blocky habit characteristic of diagenetic dickite, figure 4-4c & d &e.

A detailed SEM observation and a chemical mapping of the pore filling material of the cemented sandstones close to the unconformity (figure 4-5a to d) permitted to identify fragments of detrital material mostly composed of aluminum-rich minerals associated with disseminated micrograins of quartz and tiny crystals of cerium oxide. The chemical composition of the aluminum-rich minerals agree with that of aluminum oxi-hydroxide such as diaspore or boehmite ( 35.5 % Al, 60.1 % O, 2.8 % Si), Figure 4-4f which contain significant amount of cerium (Figure 4-4g & h and table 4-2). In addition, some disseminated cerium oxide (cerianite) are frequently associated with aluminum oxi- hydroxides minerals, Figure, 4-4f & g.

117

The basal Thelon Formation at Kiggavik

118

The basal Thelon Formation at Kiggavik

Figure 4-4 : a hematite lath cemented by microcrystalline quartz, b hematite grain cemented by APS minerals and microcrystalline quartz, c kaolinite booklet cemented by microcrystalline quartz (Q3) cementing the sandstone porosity; d & e blocky dickite (+detail view on the picture) filling a fracture cross cutting the quartz cemented Thelon sandstones; f, aluminum oxy - hydroxide minerals coating associated with cerium rich grains on detrital quartz grain later cemented (by Q3), g aluminum hydroxide and kaolinite/dicktite blocky crystals and associated with cerium oxides (cerianite), h, Ce-rich (over 4%) aluminum hydroxide matrix EDS spectra.

Figure 4-5 : SEM EDS chemical element maps (Si, Al, Ce) of aluminum rich compounds, identified as oxy hydroxide, a SEM secondary electron image, b, Silicon image, c, Aluminum and silicon composite images, and d, silicon and cerium composite image.

119

The basal Thelon Formation at Kiggavik

Table 4-2 : Chemical composition of the Al-rich mineral phase identified in the detrital material filling the pore space of sandstone overlying the basal unconformity between the Thelon sedimentary formation and the basement rocks (sample GG7).

Al2O3 SiO2 K2O CaO Fe2O3 Ce2O3 total 71,34 6,45 0,53 0,32 0,05 5,12 83,80 65,04 6,91 0,12 0,23 0,07 4,42 76,78 69,75 12,60 0,32 0,26 0,33 2,75 86,00

4.5. Crystallochemical properties of kaolin minerals

The crystal-chemistry of the kaolin group minerals occurring at the base of the Thelon basin has been done using XRD, mid infra-red spectroscopy and EMPA.

As showed on XRD diffraction patterns, figure 4-6a, kaolin group minerals are well represented in the basal Thelon sandstones were they have been preserved from subsequent hydrothermal alteration. In both oriented as well as randomly oriented powder all the kaolin group minerals are identified by their strong d00l and d002 diffraction peaks at 7.16 Å & 3.57

Å respectively. According to the obtained XRD patterns, both kaolinite and dickite have been identified in the basal Thelon samples. Kaolinite and dickite polytype has been identified within all the samples which contain kaolin minerals disseminated within the quartz cemented porosity (fig 4a). Evidences of a kaolinite/dickite mixing is given by (1) the broadening of the

020 diffraction line resulting from the contribution of both kaolinite (4.47 Å) and dickite (4.44

Å) 020 diffraction lines and (2) specific dickite diffraction peaks in the 35-40 2 theta range,

Figure 4a. Moreover, using the peak intensity ratio between the 132,204 reflections of the dickite polytype and the 20-2 ,1-31 reflections of the kaolinite polytype (Beaufort 2014) the proportion of dickite in the bulk kaolin material can be estimated to 35%. In addition to these estimations, pure dickite polytype has been identified in the late fractures which crosscut the cemented sandstone (Th18_3), Figure 4-6b.

120

The basal Thelon Formation at Kiggavik

Figure 4-6 : X-ray diffraction patterns for Thelon Formation kaolin group minerals, showing, a a kaolinite/dickite mixture, and b, a pure dickite fracture. Both diffractograms of kaolinite and dickite display the diffraction peaks attributed to highly ordered minerals.

121

The basal Thelon Formation at Kiggavik

These results are confirmed by the mid IR technique which appears to be the most effective to discriminate kaolinite and dickite using the differences in position and relative intensity of

OH stretching bands, figure 4-7. In the GG3 and GG7 samples (disseminated kaolin minerals) the four bands observed at 3696, 3669, 3653 and 3620 cm-1 are in agreement with data given in literature for the hydroxyl-stetching bands region of kaolinite (Farmer 1974). In addition the good distinction between the bands at 3669 and 3653 cm-1, as well as the narrow and symmetrical shapes of the other bands are characteristic of a rather well ordered kaolinite microcrystals. It can be noticed that the inflexion at 3598 cm-1 observed on the GG3 spectra is characteristic of the Al- Fe3+ OH vibration and thus indicate the presence of structural ferric iron in the kaolinite of certain samples (Petit and Decarreau 1990; Petit et al. 1999).

The 3706, 3654 and 3621 cm-1 bands observed in the FTIR spectrum of the kaolin minerals from the late fracture which crosscut the cemented sandstone (Th18_3 sample) are typical of a pure dickite polymorph, figure 4-7.

2.2

2.0

1.8

1.6 1.4 GG3b (kaolinite) 1.2

1.0 GG7 (kaolinite) Absorbance abitrary units Absorbance units abitrary 0.8

0.6 Th18_3 Fracture (dickite) 0.4

3800 3750 3700 3650 3600 3550 Figure 4-7 : Mid Infra-red spectra of Thelon formationWavenumbers Kaolin Group (cm- minerals1) in the OH-stretching domain.

122

The basal Thelon Formation at Kiggavik

4.5.1. Crystallographic properties of kaolin group minerals: order /disorder

The structural order of the kaolin group minerals could be investigated using classical

Hinckley index of crystallinity calculation method on XRD diffraction patterns and IR spectroscopy spectra (Hinckley 1963; Crowley and Vergo 1988). However, this approach requires the absence of quartz in the analysed kaolin material and the study of samples series, a major difficulty in our area where most of the sandstones are eroded and in which quartz microcrystals cannot be separted from kaolin minerals. Nevertheless, the crystallographic properties giving the level of structural order of kaolinite and dickite can be assessed using both XRD and IR (Brindley and Brown 1980).

Then the basal Thelon formation kaolinite, are matching with the order criteria of prominent basal reflections 001 and 002 together with well defined 02l and 11l reflection in the 19-33°

(2θ range (Hayes 1963; Keller et al. 1966). In addition, in the range, 35-40° (2θ), the 13l, 20l reflections occurs with the 003 basal reflection. These reflections forming two groups of triplets in the well ordered kaolinites (Brindley and Brown 1980), Figure 4-6a. Lastly, the tiny shoulder observed on the right sides of diffraction peaks and due to the Kαβ reflection indicates the presence of highly ordered crystals. Such a high order is moreover coherent with the presence of dickite diffraction lines.

As in kaolinite, dickite diffraction lines can be used to characterize the level of structural order. Then even if dickite is generally seen as an highly ordered polymorph of the kaolin mineral group, some differences in crystallinity have been described in dickite series

(Brindley and Porter 1978). Then, the better ordered samples as the Th18_3 dickite, show all the X-ray powder diffraction lines (Newnham and Brindley 1956; Newnham 1961), Figure 4-

6b.

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The basal Thelon Formation at Kiggavik

4.5.2. Chemistry of kaolinite minerals

The electron microprobe data acquired on the kaolinite vermicules confirmed their relatively high iron content (up to 0.73 % Fe2O3), with a moderate compositional variability in each single crystal, Table4-3 4-9 & figure4-9. Two distinct populations of kaolinite can be identified on the basis of their morphology & chemistry. The first one being iron poor with virtually no iron while the second is iron rich with an average content around 0.5 % wt Fe2O3.

However they are both represented by large booklets and minute crystals in the microcrystalline quartz matrix.

Table 4-3 : Representative microanalysis of the two kaolinite morphologies present in the basal Thelon

Formation sandstones

Na2O MgO Al2O3 SiO2 K2O CaO TiO2 MnO Fe2O3 H2O total Large kaolinite Fe 0.01 0.05 38.00 46.99 0.07 0.05 0.00 0.01 0.67 14.00 99.85 Large kaolinite 0.00 0.05 38.30 47.47 0.02 0.07 0.00 0.00 0.06 14.00 99.96 Minute kaolinite 0.01 0.01 38.77 47.16 0.08 0.04 0.00 0.06 0.35 14.00 100.47

Basal Thelon Fm sandstones kaolinites 40.0

39.0

38.0 Al2O3 Al2O3 % 37.0 y = -0.19x + 38.31

36.0 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 Fe2O3 %

Figure 4-8 : plot of the chemical microanalyses of kaolin minerals from the basal Thelon Formation sandstones in the Al2O3-Fe2O3 cross plot diagram.

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The basal Thelon Formation at Kiggavik

0.80 0.70 GG4_kaol_Trsct2 0.60 GG4_kaol_Trsct3 0.50 GG4_kaol_Trsct4 0.40 GG4_kaol_Trsct6 0.30

Fe2O3 wt Fe2O3 % GG3b_KaoITrsct4 0.20 0.10 GG3b_KaolTrsct2 0.00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 number of analysis points in the transect

Figure 4-9 : Electron microprobe chemical transects in the aggregates of kaolin of the basal Thelon sandstones of the Kiggavik area. Average distance between the punctual analyses ranges from 10 to 20 micrometers according to the size of the kaolin grains.

In addition, the kaolinite crystals tends to be chemically homogeneous throughout the grain with no significant compositional variation near the edges or along the crystallographic c or ab axis, as shown by the microchemical transects, Figure 4-10 & 4-11.

Figure 4-10 : Location of some of the electron microprobe transects in kaolinite (GG4 sample)

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The basal Thelon Formation at Kiggavik

4.6. Microcrystalline quartz cement chemistry and in situ composition of

oxygen isotopes

2.00 1.80 1.60 1.40 1.20 3 3 O

2 1.00 Al 0.80 0.60 Detrital Quartz 0.40

0.20 Microcrystalline quartz 0.00 96.00 97.00 98.00 99.00 100.00

SiO2

Figure 4-11 : Silica and alumina content measured in detrital and microcrystalline quartz. Note that the measurements were performed on a SEM-EDS

In addition to their petrographic characteristics, the microcrystalline quartz reveals a peculiar chemical signature with an increase in aluminum content relatively to the detrital quartz, figure 4-12. Such variation in Al content has been described in burial diagenesis in successive quartz overgrowths generations (Tournier 2010). In addition the aluminum content of quartz, as hydrous Al species, seems to be correlated to the amount of defects and the rate of crystal growth (Ihinger and Zink 2000). Then, the oxygen isotopes composition has been investigated to better constrain the paleoconditions at which they crystallized.

126

The basal Thelon Formation at Kiggavik

4

3

2

1

0 16 18 20 22 24 26 28 30 32 34 36 38 40 42 18 δ OV-SMOW (‰)

18 Figure 4-12 : Histogram of  O values measured in microcrystalline (Qtz3) and detrital quartz from the basal

Thelon Formation sandstones.

Table 4-4 : SIMS oxygen isotopic data and detrital quartz grain and the microcrystalline quartz (Qtz3).

18 16 18 Mineral O/ O FF 1σ  OV-SMOW (‰) T (°C) GG4_Qtz3-1 Quartz 1.848399 0.9241131 1.2 32.5 54 GG4_Qtz3-2 Quartz 1.850852 0.92533948 1.3 33.9 48 GG4_Qtz3-3 Quartz 1.857398 0.92861217 1.2 37.5 35 GG4_Qtz3-4 Quartz 1.862655 0.93124043 1.2 40.4 25 GG4_Qtz3-5 Quartz 1.84891 0.92436857 1.2 32.8 53 GG4_Qtz3-6 Quartz 1.847598 0.92371263 1.3 32.0 56 GG4_Qtz3-7 Quartz 1.860585 0.93020553 1.2 39.3 29 GG4_Qtz3-8 Quartz 1.854224 0.92702532 1.3 35.7 41 GG4_Qtz3-9 Quartz 1.857503 0.92866467 1.2 37.6 35 GG4_Qtz3-10 Quartz 1.86143 0.93062799 1.3 39.8 27 GG3_Qtz3-1 Quartz 1.861797 0.93081147 1.2 40.0 27 GG3_Qtz3-2 Quartz 1.860428 0.93012703 1.2 39.2 29 GG3_Qtz3-3 Quartz 1.864177 0.93200136 1.2 41.3 22 GG3_Qtz3-4 Quartz 1.856241 0.92803373 1.2 36.9 37 GG3_Qtz3-5 Quartz 1.855203 0.92751478 1.2 36.3 39 GG4_Detrital-Gr-1 Quartz 1.826909 0.9133691 1.2 20.5 102 GG4_Detrital-Gr-2 Quartz 1.831189 0.9155089 1.2 22.9 85 GG4_Detrital-Gr-3 Quartz 1.826232 0.91303063 1.2 20.1 106 GG4_Detrital-Gr-4 Quartz 1.820232 0.91003091 1.2 16.8 135

127

The basal Thelon Formation at Kiggavik

The δ18O values obtained from in situ measurements in the microcrystalline quartz which cement the porosity of the sandstones range between 31.9 and 41.3 per mil with an error of

1.2 (1σ). The data presents two modes centered on 33 ‰ and 40 ‰, Figure 4-13 & table 4-4.

For comparison the detrital grain were ranging from 16.8 to 22.9 per mil, in a similar range than other Thelon sandstones detrital quartz grains (Hiatt et al. 2007). Then using the extrapolation of classical quartz-water fractionation (Clayton et al. 1972) and AlphaDelta program (Beaudoin and Therrien 2004; Beaudoin and Therrien 2009), the calculated temperature range from from 1°C up to 35°C and are rather questionable. However, the use of most recent fractionation equation for low temperature quartz - kaolinite-water system, between 0 and 130°C (Méheut et al. 2007), provides more realistic temperatures. A water composition in equilibrium with sea water was chosen for temperature calculation as a more saline water composition can be assumed in an intracratonic, possibly warm environement, with shallow water depht. The obtained temperatures show a bimodal distribution, each mode being centered on 27 °C and 52°C respectively.

4.7. Discussion

Petrographic studies carried on the basal Thelon Formation sandstones around Kiggavik, showed peculiar mineralogy and textures with (1) the large kaolinite crystals embedded in the sandstone matrix and (2) the quartz-kaolinite composite grains, (3) the local presence of Al oxides or oxide-hydroxides associated with cerium oxides, (4) evidences of dickite as fracture filling material and (5) a sandstone porosity sealed by microcrystalline quartz, figure 4-14.

Another very interesting point is the preservation of most of the basal Thelon formation of the

128

The basal Thelon Formation at Kiggavik postdating hydrothermal alteration which is strongly developed along the major faults of the underlying basement rocks. Then, the petrography and the mineralogy of this compartment of basal Thelon sandstone formation, makes possible an attempt to reconstruct the early history of the bottom part of the Thelon basin (from sedimentation to the end of diagenetic evolution).

Figure 4-13 : Paragenetic sequence of minerals determined in the basal Thelon formation. See Part B chapter 2 on APS minerals for more details on the crystal-chemistry of the different aluminium phosphate minerals.

The detrital mineralogy raises questions about the origin of the material leading to such assemblage as well as the genetic processes involved in there formation prior to erosion transport and sedimentation. Diagenetic processes and paleoburial conditions have to be considered at the view of the kaolinite/ dickite transition evidenced from crystallographic properties in this study, with respect to previous works on kaolin diagenesis in siliciclastic basins (Beaufort et al. 1998; Shutov et al. 1970; Eckhardt and Von Gaertner 1962; Eckhardt

1965).

129

The basal Thelon Formation at Kiggavik

4.7.1. On the origin of detrital and diagenetic Al bearing minerals in the

basal Thelon Formation

The presence of detrital aluminum minerals with kaolinite, hematite aluminum phosphate sulfate and local cerium oxide raise the question of the source of the detrital material. Similar minerals assemblages have been described in various actual or recent lateritic profiles or bauxites (Valeton 1972; McFarlane 1976; Loughnan and Bayliss 1961; Braun et al. 1990;

Curtis and Spears 1971). In addition the crystallochemical properties of kaolinite with

3+ frequent and relatively high (from 0.3 up to 2% Fe2O3) structural Fe observed in the Thelon

Formation kaolinite is also common in kaolinites formed in laterite under intense weathering

(Herbillon et al. 1976; Malden and Meads 1967; Tardy and Nahon 1985; Cantinolle et al.

1984). Moreover it has been showed that the amount of structural iron is of great influence on the kaolinite crystallinity, with an increase of disorder positively correlated to the iron content

(Mestdagh et al. 1980; Brindley et al. 1986).

On the contrary in the kaolinite and quartz composite grains, the morphology of kaolinite is by far more irregular and indicate that the lithic fragments was originally of analogous composition, and possibly formed by a mechanical mixing of the two minerals. In addition, the sub rounded shape for such a fragile assemblage also indicates a likely moderate distance of transport.

As described in many studies, three type of kaolin are widely recognized depending on their textural properties: (1) as micas replacement, where authigenic kaolinite crystallization takes place in between expended detrital micas flackes (Nedkvitne and Bjorlykke 1992; Ehrenberg et al. 1993; Macaulay et al. 1993), (2) as vermicules and (3) as blocky kaolinite (Lanson et al.

2002). The last two types raise numerous questions on the processes responsible for their crystallization including temperature, pH, H+/K+ ratio and reaction kinetics.

130

The basal Thelon Formation at Kiggavik

Then, the well developed crystals and the pristine shape of kaolinite booklets observed at the base of the Thelon Formation sandstone is thus in agreement with an in-situ formation in the sandstone porosity. Moreover petrography showed that the diagenetic quartz overgrowths

(Qtz2) are stopped by the presence of the kaolinite vermicule present in the porosity.

Then it could seem in contradiction with the relatively high crystallographic order of the kaolinite present in the basal Thelon Formation. However, the evidence of neoformation of hematite between kaolinite stackes or in place the fine grain hematization observed in the sealed porosity surrounding the grain might be directly linked to the high iron initially present in the kaolinite. Such feature, could be explained by diagenetic dissolution recrystallization processes in which iron is partially taken out from the kaolinite to precipitate as hematite.

Then, it could also indicate that the detrital kaolinites could have been iron richer and that the vermicules of kaolinite are pro parte recrystallized sedimentary kaolinites or generated through aluminum oxy-hydroxides silicification processes or neoformation (Trolard and

Tardy 1989).

Nevertheless, our interpretation of such mineral assemblages at the view of present geological is limited by the two following points:

(1) the atmosphere redox and pH conditions during the Paleoproterozoic paleoweathering events are not clearly defined but probably developed in a more reducing environment than today (Partin et al. 2013). Then the condition would have been less oxidizing with consequences of an higher iron mobility, and a preferential integration of iron in phyllosilicates rather than in iron oxides or sulfide that would also suggest that sulfur wasn’t available in the system (2) the persistence of aluminum hydroxides, minerals common in laterite or bauxite is very rarely found in the sediments and even more in the sandstone affected by deep burial diagenesis.

131

The basal Thelon Formation at Kiggavik

4.7.2. Sandstone quartz cementation, some contradictory observations

The Churchill province of the Canadian Shield presents several occurrences of silicified weathering profiles or silicified sediments which were described as silcretes, as in the Thelon or Hornby Bay Basins (Gall 1994; Ross and Chiarenzelli 1985; Ross 1983). Oxygen isotopes on the quartz cements are then a critical tool to assess the crystallization conditions but the comparison with modern cherts and careful use of the actualism principle is necessary. Indeed some differences in formation environments and forming processes have been established between Precambrian and Phanerozoic cherts (Maliva et al. 2005). In addition several isotopic composition of the quartz is then dependent of the crystallization temperature, as well as the salinity and the isotopic composition of the fluid in equilibrium with the quartz.

Relatively high oxygen isotopes values on quartz are the expression of very low temperature processes not uncommon in surface environments (Kolodny et al. 2005). In addition such high silica rich rocks as cherts or silcretes had been studies for a long time and used as indicators of surface temperature or weathering conditions through geological times (Knauth and

Epstein 1976; Sayin and Jackson 1973).

In addition, the present results are partially in agreement with the petrography and oxygen isotopes of the quartz cements at the base of the Thelon Formation (Hiatt et al. 2007). These authors described isopachous microcrystalline quartz rims fringing the detrital quartz grains, in both eolian facies of Thelon sandstones and the Pitz formations, without any prior diagenetic overgrowth. In fact, at Kiggavik the microcrystalline is not present as comb structure and seems to be developed after a first stage of diagenetic overgrowth. However, the oxygen isotopic composition is quite similar with values between the microcrystalline quartz at Kiggavik and the quartz cements or even some of the latter quartz generation filling the porosity described by the same authors. Then two opposite trends are presents, which may indicate different porosity evolutions throughout the Thelon formation sandstones. In one case

132

The basal Thelon Formation at Kiggavik the earlier cements have the highest δ18O values up to 33 ‰ with a 26 ‰ mean (Hiatt et al.

2007), while the present study the microcrystalline quartz have a maximum δ18O values value of 41.3 ‰ with a 37 ‰ mean. These significantly higher values are in agreement with very low temperatures but contradictory with the petrographic evidence of a rapid precipitation associated with hydraulic fracturation.

Finally, the sedimentary features as the ripples marks observed at the base of the Thelon indicates relatively shallow environment. In addition, in similar Paleoproterozoic Basins as the Athabasca Basin Boron, and Chlorine isotopes studies have proposed an evaporated sea water as sources for the ore related brines (Richard et al. 2011; Richard et al. 2013). Then, the position over the Tropics during the Paleoproterozoic (Betts et al. 2008) of these huge intracratonic basins could be considered as relatively close environment favourable for water evaporation. This raise numerous question about the water isotopic composition, and might

18 suggest that the δ O (H2O) would have been higher. If so, the calculated temperature from the microcrystalline quartz cement would be necessarily shifter toward higher temperatures.

Then, the temperature would be even more compliant with an hydrothermal origin for the microcrystalline quartz cement, possibly in relaton with a brutal pressure change.

4.8. Conclusion

Petrography and cystal-chemistry gave a series of arguments to relate the composition of the clay minerals of the basal Thelon Formation sandstones to a product of paleo weathering profile dismantling, possibly lateritic or bauxitic, developed during the regolithisation of the

Archean and Paleoproterozoic basement rocks which preceeded the sandstone deposition.

This is also supported by the very specific location of the studies sandstones in the vicinity of

133

The basal Thelon Formation at Kiggavik an ancient fault system that may have been reactivated with a tectonic control of the sedimentation, with very little transport of the basin filling material studied. Such settings are then highly favorable to preserve the fragile clay / quartz composite of the dismantled weathering profile, or the large kaolinite later recrystallized as massive vermicules in the porosity during burial diagenesis, as well as the aluminum oxi-hydroxides such as diaspore or boehmite.

The diagenesis also includes the precipitation of the quartz overgrowths as well as the recrystallisation of the coarse grained vermicules of ordered kaolinite in the porosity. This reasonably indicates that significant burial depth may have been reach to generate such a degree of order in the kaolinite, prior to the microcrystalline quartz cementation. Finally, this might also be supported by even later fracture controlled precipitation under even higher pressure condition with the presence of the cross cutting dickite fracture.

Then the basis of the Thelon sandstones, at this particular location are recording the early basin filling history and the weathering processes active before the Thelon deposition. The structural control of the sedimentation is giving a good indication on the source material due to the expected short distance of transport. Finally this preservation of kaolin group mineral from both the sedimentary and diagenetic histories highlight the fact the sandstone had been chemically isolated in the Kiggavik area. This could appear contradictory with the occurrence of authigenic K-feldspar and illite diagenetic cements described in the Thelon basin (Renac et al. 2002). Such a fact probably indicates that the Thelon Basin was compartmented during its evolution history as did many others younger basins worldwide.

134

The basal Thelon Formation at Kiggavik

4.9. References

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Fayek M, Kyser K, Riciputi LR (2002) U and Pb isotope analysis of uranium minerals by ion microprobe and the geochronology of the McArthur River and Sue zone uranium deposits, Saskatchewan, Canada. Canadian Mineralogist 40:1553-1569. Folk RL, Weaver CE (1952) A study of the texture and composition of chert. American Journal of Science 250:498-510. doi: 10.2475/ajs.250.7.498. Gall Q (1994) The Proterozoic Thelon paleosol, Northwest Territories, Canada. Precambrian Research 68:115-137. doi: http://dx.doi.org/10.1016/0301-9268(94)90068-X. Hayes JB (1963) Kaolinite from Warsaw geodes, Keokuk region, Iowa. Proceedings of the Iowa Academy of Sciences 70:261-272. Herbillon AJ, Mestdagh MM, Vielvoye L, de Rouane EG (1976) Iron in kaolinite with special reference from tropical soils. Clay Minerals 2:201-220. Hiatt EE, Kyser TK, Fayek M, Polito P, Holk GJ, Riciputi LR (2007) Early quartz cements and evolution of paleohydraulic properties of basal sandstones in three Paleoproterozoic continental basis: Evidee fo i situ δO aalysis of uatz eets. Cheial Geology 238:19-37. doi: http://dx.doi.org/10.1016/j.chemgeo.2006.10.012. Hinckley DN (1963) Variability in "crystallinity" values among the kaolin deposits of the coastal plain of Georgia and South Carolina In: Swineford A (ed) Clays and Clay Minerals, Proc 11th Natl Conf. Pergamon Press, New York, Ottawa, Ontario, pp 229- 235. Ihinger PD, Zink SI (2000) Determination of relative growth rates of natural quartz crystals. Nature 404:865-869. Keller WD, Pickett EE, Reesman AL (1966) Elevated dehydroxylation temperature of the Keokuk geode kaolinite Proc Int Clay Conf. Jerusalem, pp 75-85. Knauth LP, Epstein S (1976) Hydrogen and oxygen isotope ratios in nodular and bedded cherts. Geochimica et Cosmochimica Acta 40:1095-1108. doi: http://dx.doi.org/10.1016/0016-7037(76)90051-X. Kolodny Y, Chaussidon M, Katz A (2005) Geochemistry of a chert breccia. Geochimica et Cosmochimica Acta 69:427-439. Lanson B, BEAUFORT D, Berger G, Bauer A, Cassagnabère A, Meunier A (2002) Authigenic kaolin and illitic minerals during burial diagenesis of sandstones: a review. Clay Minerals 37:1-22. Loughnan FC, Bayliss P (1961) The mineralogy of bauxite deposits. American Mineralogist 46:207-217. Macaulay CI, Fallick A, Hasezeldine RS (1993) Textural and isotopic variations in diagenetic kaolinite form the Magnus oilfield sandstones. Clay Minerals 28:625-639. Malden PJ, Meads RE (1967) Substitution by Iron in Kaolinite. Nature 215:844-846. Maliva RG, Knoll AH, Simonson BM (2005) Secular change in the Precambrian silica cycle: Insights from chert petrology. Geological Society of America Bulletin 117:835-845. doi: 10.1130/b25555.1. McFarlane MJ (1976) Laterite and landscape. Academic Press, London. Méheut M, Lazzeri M, Balan E, Mauri F (2007) Equilibrium isotopic fractionation in the kaolinite, quartz, water system: Prediction from first-principles density-functional theory. Geochimica et Cosmochimica Acta 71:3170-3181. doi: http://dx.doi.org/10.1016/j.gca.2007.04.012. Mestdagh MM, Vielvoye L, Herbillon AJ (1980) Iron in kaolinite. II. The relashionship between kaolinite and iron content. Clay Minerals 15:1-13.

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Nedkvitne T, Bjorlykke K (1992) Secondary porosity in the Brent Group (Middle Jurassic), Huldra Field, North Sea; implication for predicting lateral continuity of sandstones? Journal of Sedimentary Research 62:23-34. doi: 10.1306/d426787a-2b26-11d7- 8648000102c1865d. Nesbitt HW (1979) Mobility and fractionation of rare earth elements during weathering of a granodiorite. Nature 279:206-210. Newnham RE, Brindley GW (1956) The structure of dickite. Acta crystallographica 9:759-764. Newnham RE (1961) Refinement of the dickite structure and some remarks on polymorphism in kaolin minerals. Mineralogical Magazine 32:231-243. Partin CA, Bekker A, Planavsky NJ, Scott CT, Gill BC, Li C, Podkovyrov V, Maslov A, Konhauser KO, Lalonde SV, Love GD, Poulton SW, Lyons TW (2013) Large-scale fluctuations in Precambrian atmospheric and oceanic oxygen levels from the record of U in shales. Earth and Planetary Science Letters 369–370:284-293. doi: http://dx.doi.org/10.1016/j.epsl.2013.03.031. Petit S, Decarreau A (1990) Hydrothermal (200°C) synthesis and crystal chemistry of iron-rich kaolinites. Clay Minerals 25:191-196. Petit S, Madejova J, Decarreau A, Martin F (1999) Charcterization of octaedral substitutions in kaolinites using near infrared spectroscopy. Clays and Clay Minerals 47:103-108. Renac C, Kyser K, Durocher K, Dreaver G, O'Connor T (2002) Comparison of diagenetic fluids in the Proterozoic Thelon and Athabsca Basins, Canada: implications for protracted fluid histories in stable intracratonic basins. Can J Earth Sci 39:113-132. Richard A, Banks DA, Mercadier J, Boiron M-C, Cuney M, Cathelineau M (2011) An evaporated seawater origin for the ore-forming brines in unconformity-related uaiu deposits Athaasa Basi, Caada: Cl/B ad δCl aalysis of fluid inclusions. Geochimica et Cosmochimica Acta 75:2792-2810. doi: http://dx.doi.org/10.1016/j.gca.2011.02.026. Richard A, Boulvais P, Mercadier J, Boiron M-C, Cathelineau M, Cuney M, France-Lanord C (2013) From evaporated seawater to uranium-mineralizing brines: Isotopic and trace element study of quartz–dolomite veins in the Athabasca system. Geochimica et Cosmochimica Acta 113:38-59. doi: http://dx.doi.org/10.1016/j.gca.2013.03.009. Riciputi LR, Greenwood JP (1998) Analysis of sulfur and carbon isotope ratios in mixed matrices by secondary ion mass spectrometry: implications for mass bias corrections. International Journal of Mass Spectrometry 178:65-71. doi: http://dx.doi.org/10.1016/S1387-3806(98)14086-1. Ross GM (1983) BigBear erg: a Proterozoic intermontane eolian sand sea in the Hornby Bay group, Northwest Territories, Canada In: Brookfield ME, Ahlbrandt TA (eds) Eolian Sediments and Processes. Elsevier, Amsterdam, pp 483-519. Ross GM, Chiarenzelli JR (1985) Paleoclimatic significance of widespread Proterozoic silcretes in the Bear and Churchill provinces of the northwestern Canadian Shield. Journal of Sedimentary Research 55:196-204. doi: 10.1306/212f8666-2b24-11d7- 8648000102c1865d. Sayin M, Jackson ML (1973) Scanning electron microscopy of cherts in relation to the oxygen isotopic variation of soil quartz. Clays and Clay Minerals 23:365-368. Sharpe R (2013) The geochermistry and geochronolgy of the Bong uranium deposit, Thelon Basin, Nunavut, Canada Department of Geological Sciences. University of Manitoba, Winnipeg, Manitoba.

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The basal Thelon Formation at Kiggavik

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138

Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada). 5. Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada).

Riegler Thomas & Beaufort Daniel.

Paper in preparation

5.1. Introduction

Carbonaceous materials (CM) in the early earth history are always controversial with two possible origin, one involving life where bitumen are deriving from classical kerogen thermal evolution, while the second is the expression of abiotic synthesis of organic compounds in hydrothermal or magmatic systems e.g. via Fischer-Tropsch type synthesis (FTT) (Shock

1990; Gize 1999; Foustoukos and Seyfried 2004; McCollom and Seewald 2006; Horita 2005;

Ueno et al. 2004; Curiale 1986; McCollom 2013). Both processes are being tracked by specific geochemical signatures such as molecular markers, carbon and sulfur stable isotopes, together with petrographic evidences. Such carbonaceous materials, referred as bitumens, have been frequently identified within the alteration halos surrounding the Mid-Proterozoic unconformity type uranium deposits (Hoeve and Sibbald 1978; Hoeve et al. 1980; Hoeve and

Quirt 1984; Pagel et al. 1980; Sangély et al. 2007). The reducing potential, the source and the distribution in brecciated and altered Archean to Paleoproterozoic metamorphic basement or in the Meso-Proterozoic sedimentary cover of such material have been discussed for uranium metallogenesis (Leventhal et al. 1987; Kyser et al. 1989; Landais and Dereppe 1985; Yeo and

Potter 2010; Sangély et al. 2007) without strong evidence for ore control, while it was invoked as ore controlling parameter in gold bearing veins (Mastalerz et al. 1995). On the contrary in the Paleoproterozoic Oklo mineralization the paragenesis indicates a more obvious

139

Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada). link between bitumen and oil occurrences with uranium precipitation, in a petroleum-like system were faults creates trap and path for oil migration as well as favorable contact between marine black shale and the bitumen hosting deltaic sandstones (Gauthier-Lafaye and Weber

1989; Nagy et al. 1991).

In previous works in the Athabasca Basins, bitumen is considered to post-date the main uranium mineralization stage (Wilson et al. 2002; Leventhal et al. 1987) or is sometimes seen to be contemporaneous to it (Alexandre and Kyser 2006). However the host rock is composed of a various package of metasediments or meta-igneous rocks devoid of any carbon other than graphite on faults. Although several lithologies are known as potential sources of oil with including the Phaneroic blackshales of the Exshaw Formation (Sangély et al. 2007), who might have migrated downwards trough 1500 meters of Athabasca Group sandstones and several hundred meters below the unconformity, along the fault and fracture network controlling the uranium mineralization. The main debate being the in situ formation versus the migration of the organic compounds.

The aim of this work is to identify and to characterize the chemistry and structure of the carbonaceous materials associated with the uranium mineralizations at the Southeastern margin of the Meso-Proterozoic Thelon Basin. Then geochemical, isotopic, petrographic and crystallographic evidences with comparison with (1) similar type of mineralization in the

Athabasca Basins and (2) laboratory synthesis of organic compounds will gives the basis of discussion for the genesis and emplacement of such material several hundred meters below the eroded unconformity at Kiggavik in alteration envelopes surrounding one of the major uranium ore zones in Canada outside the Athabasca basin. Lastly the new knowledge on the crystal structure of carbonaceous material in unconformity type uranium mineralization will give a new perception for metallogenesis and approach in ore deposits studies.

140

Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada). 5.2. Geological setting and petrography

Uranium mineralization (mainly uraninite and coffinite) at Kiggavik is composed of several ore bodies but one at Bong is particularly rich in carbonaceous material very often easy to distinguish with the strong cabbage / garlic smells associated with its presence. All the ore shoots are surrounded by tens of meters large clay alteration envelopes developed in Achean metagraywackes belonging to the Woodburn Lake Group (Farkas 1984; Miller and

LeCheminant 1985) and controlled by fault and fracturation corridors and slip opening along the foliation plan. Then all the primary metamorphic silicates (feldspars, muscovite, biotite, chlorite) are replaced by an alteration paragensis dominated by illite and sudoite (Al-Mg chlorite) in various proportions displaying similar feature as many other unconformity associated uranium mineralization in Canada and Australia (Beaufort et al. 2005; Laverret et al. 2006; Hoeve and Quirt 1984; Polito et al. 2004), as in the present work. Accessory minerals in the non altered are largely represented by zircon, monazite, titanium oxides, magnetite and pyrite, that latter being quite abundant in places where the medium to fine grain graywacke tends to be more pelitic.

Carbonaceous materials are exclusively found within clay alteration zones as fracture filling up to 1 centimeter thick of massive carbonaceous material, a dark black, stainy, relatively hard and brittle material showing concoïdal fractures. Dots of similar material are presents scattered in the argilized host rock. The other expression of carbonaceous material are black to dark gray fractures and coating (no visible CM aggregate under the SEM) on foliation plan with a typical cabbage / garlic smell, Figure 5-1a, b. There distribution doesn’t seems to follow any spatial organization other than alteration but rich zones but most of it is found at the hanging wall of the alteration envelop in Bong where sudoite is slightly dominant over illite. In addition there are frequently intersected with several drillholes in the same area

141

Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada). roughly over several a tens of meters radius. The CM nodule are ranging from millimetric to micrometric in diameter and are developed in an illite and sudoite clay matrix showing in places thin coatings of uraninite are presents as fracture fillings of the CM nodules Figure 5-

1c, d. Uraninite is found dissemintated in the carbonaceous matrix as mint euhedral crystals, often partially altered to coffinite and organized in pseudo concentric rings forming alternating bands with the massive carbon carbon in which elevated U and Cu level are noticeable Figure 5-1e. Finally dissolution pits have been identified at the surface of the carbonaceous material forming circular to oblate holes of a few micrometers in diameter

Figure 5-1f.

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Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada).

Figure 5-1 : Carbonaceous materials occurrences at Kiggavik. 1a: carbonaceous material along the foliation plan and filling millimetric fractures in altered metagraywacke, S : schistosity, BG5101. 1b: detail of fracture filling material under binocular lense, button of carbonaceous material in the intergrain porosity BG5101. 1c: carbonaceous nodule in argilized metagrawacke BG4326. 1d: Carbonaceous material nodule in an illite and sudoite matrix, some microfrature plans are coated with uraninite BG4238. 1e Disseminated uraninite partially altered to coffinite and chalcopyrite in massive carbonaceous material. 1f Hollow point in massive carbonaceous material

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Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada). 5.3. Samples & Methods

Representative samples of each type of carbonaceous material had been chosen. In addition a particular care had been taken in the sampling itself in taking the samples just after drilling to avoid contamination as much as possible, as well as alteration of the carbonaceous material by bacteria.

All the 3 samples from the Bong prospect are representative of the two types of carbonaceous material found in the alteration halos in association with uranium mineralization. One is composed of massive carbonaceous material (MCM) (BG4238), at the hanging wall of fault zone, while the second is set as diffuse impregnations of carbonaceous material (DiffuseCM) as staining and coating on fractures and foliation plans in a highly argilized rock with the

BG4326 and 5101 samples. Samples were collected respectively at 428, 316 and 286 meters below the actual erosion surface.

5.4. Results

The both type of material have been analyzed with the most suitable method in order to extract all the possible information from (1) volatile organic compound disseminations and

(2) the massive carbonaceous material, and tie the two concurrencies in the alteration history.

The two expression of carbon bearing compounds are very distinct in term of petrographic expression but also in term of carbon content from tenth of per mil to tens from tens of percent in the massive CM.

5.4.1. GC-MS pyrolysis

Several organic sulfur compounds have been identified in GC-MS flash pyrolysis using both

600 / 400°C as well as low temperature extraction of volatiles at 300°C in dichloromethane with a HMDS & TMAH treatment. Both methods yield similar results with the identification of low molecular weight and volatile compounds: carbon disulfide, dimethyldisulfide

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Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada). (DMDS) and dimethyltrisulfide in the black to grayish disseminations in the argilized metagraywacke. Such compounds haven’t been detected in the massive carbonaceous sample and the identified alcanes or aromatic are possible contaminations. Sulfur dioxide is also present in all studied samples and is very likely the expression of sulfides roasting, chalcopyrite in that case. All these molecules are responsible for the characteristic smell associated with some areas in the alteration zone, even if in traces. The trace characters of these compounds make their identification.

5.4.2. X-Ray Diffraction

The massive carbonaceous material 66 % C doesn’t exhibit any reflection of the graphite diffraction pattern in a whole rock randomly oriented powder mount of the <50 μm size fraction. This surprising feature raises the question of the type of bonds between the Carbon atoms and the structure of this material, Figure 5-2. The only minerals identified are uraninite, coffinite, chalcopyrite, johannite [Cu(UO2)(SO4)2(OH)2.8H2O)] and studtite

[UO4.4H2O] according to XRD data from (Walenta 1974). In addition an oriented slide of the infra 0.1 μm size fraction extracted by ultracentrifugation haven’t shown any diffraction peak for graphite either, only a broad baseline indicating either an amorphous material or a structure without enough layers stacked to induce the X-ray diffraction. Such characteristic possibly reflect a graphene structure or amorphous graphitic material.

Then in order to probe the structure of C-C bonds and possible spatial organization the Raman spectroscopy and transmission electron microscopy appears to be the most suitable techniques.

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Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada).

Ccp graphite main 1 diffraction line Coff 2

2

2 Uran 1 Joh Stu 3 2 2 4 2 1 1 4 5 3 2 5 2 3 2 1 4 5 5 5 5 3 2 2

5 15 25 2θ 35 45 55 65

Figure 5-2 : Randomly oriented powder XRD diffractogram of massive carbonaceous material, (5-65° 2theta scan, 0.02 stepsize and 4 seconds counting time). Abbreviations, Ccp (1): Chalcopyrite; Coff (2): coffinite; Uran

(3) uraninite; Joh (4): johannite and Stu (5): studtite.

5.4.3. Raman spectroscopy

Raman spectra obtained on massive CM show two pronounced bands at about 1340 (D) and

1600 (G) cm-1 as well as a relatively marked fluorescence responsible for the moderate baseline but also hiding the second order Raman bands (overtone) in the 2000 – 4000 cm-1 range, Figure 5-3. Of these two bands the first one, broad and relatively intense, is attributed to disordered carbons and edges effects (D band) while the second is the graphite band (G) linked to the sp2 C-C configuration of the graphene planes (Chu and Li 2006; Jehlička et al.

2003; Tuinstra and Koenig 1970b). The shift toward higher wavelength values of the G band seems to be indicative of extremely small crystallites (Tuinstra and Koenig 1970a). In addition, the spectrum decomposition using pseudo Voigt function leads to the identification of 4 different bands respectively at 1188, 1334, 1510 & 1601 cm-1, and a final fitted profile

(cross) with a reasonable match with the original spectrum Figure 5-3. The graphite G & D

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Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada). bands at 1334 & 1601 cm-1 are also well identified in the decomposition, while in addition the 1188 cm-1 band assigned to disorder in the graphitic lattice and the 1510 cm-1 band revealing an amorphous component in the signal (Sadezky et al. 2005; Al-Jishi and

Dresselhaus 1982; Dippel and Heintzenberg 1999).

Finally the band intensity ratio ID/IG (0.54) gave an in-plane crystallite size (La), ranging from 2 to 30 nm using two empirical formula given in literature (Knight and White 1989;

Cancado et al. 2006).

1601 Spectrum decomposition

1334 1188

1510

1000 1200 1400 1600 1800

G 1601 D 1338

1000 1200 1400 1600 1800 Raman shift (cm-1)

Figure 5-3 : Raman spectra of massive carbonaceous material, a raw signal & b decomposed Raman spectrum showing 4 components (dotted lines) and fit (cross) after linear background correction.

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Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada).

5.4.4. Transmission electron microscope study of the carbonaceous

material

In addition to RAMAN spectroscopy and XRD, TEM observed were performed in order to obtain microstructural information. The general view in Figure 5-4a indicates that the massive carbonaceous materials are in fact formed of carbon veil, best described as graphen layers. In close association to it, nanometric crystals of size ranging from 5 to 50 nm are disseminated in the carbonaceous material between the graphen layers. In addition, HRTEM images (Figure 5-4b) confirm that the structure of the carbonaceous matrix is fully disordered along the C axis.

Moreover, figure 5-4c & d reported an example of HRTEM image from nanoparticle and the corresponding Fast Fourier Transform (FFT). The digital diffractogram from the particle shows spots with fringe spacing of 3.1A and an angle of 70° between the two sets of fringes.

This experimental result agrees with the d{111} planes of the uraninite cubic structure. The two other spots correspond to fringe spacing of 1.9A and 2.73 of the d{022} and d{002} respectively showing that the zone axis of the particle is <110>. Lastly, the diffraction pattern taken over a large area, Figure 5-4e& 5-4f suggests a preferential orientation of the {111} plans of uraninite.

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Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada).

Figure 5-4 : Transmission electron microscope image of MCM and associated nanocrystals; a, disseminated nano crystals in the carbonaceous material, b, HRTEM images of nano crystals and amorphous carbonaceous

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Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada). material matrix, c, lattice parameter of a euhedral crystal of uraninite, and d, corresponding FFT image, e & f uraninite crystal in the carbon matrix and electron diffraction over the same area.

5.4.5. Isotopy & geochemistry

Bulk geochemistry gathered on massive and disseminated carbonaceous materiel is given in the table 5-1. The massive material is almost entirely formed of carbon with more 66% C.

The Very little Si, Al, K, and Mg amounts are coherent with the absence of clay minerals within the massive material. Nevetheless the material is particularly rich only in Cu and U while other trace elements, especially those which are sensitive to redox condition like Mo,

Co, and V are negligible.

Table 5-1 : Chemistry and isotope composition of the two types of carbonaceous materials

Sample Massive CM Diffuse CM

SiO2 % 1.94 44.49

Al2O3 % 0.51 27.17

Fe2O3 % 3.44 0.66

K2O % 0.08 8.24

MgO % 0.06 2.06

TiO2 % 0.13 1.53

As (ppm) 139 36.67

Co (ppm) 142.1 31.18

Cu (ppm) 10020 167.9

Mo (ppm) 9.52 15970

Pb (ppm) 2192.82 234.52

U (ppm) 71910 403.6

V (ppm) 31.96 750.7

%C 66.3 0.04

%H 3.9 0.7

%S 4.68 0.5

δC °/00 -39.1 < detection limits

δS °/00 No data + 12.2

13 34  C relative to PDB and  S to CDT standards

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Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada). 5.5. Discussion

Considering the carbonaceous materials present at Kiggavik it appears that the petrographic and textural relationships with alteration minerals lead us to integrate these materials to the paragenesis formed during the hydrothermal alteration of the Archean basement and the associated the transport and deposition of uranium. In Kiggavik as well as in the Athabasca

Basin (Sangély et al. 2007; Landais and Dereppe 1985; Leventhal et al. 1987; Alexandre and

Kyser 2006), the carbonaceous materials are considered to belong to succession of hydrothermal events responsible for the main uranium deposition. Then, on the basis of this multi-method characterization we propose to refine the interpretation of the Kiggavik carbonaceous material in terms of genesis and potential role on uranium precipitation.

5.5.1. Forms of carbon and hydrothermal signatures

To sum-up the two main expressions of carbonaceous materials identified in alteration zone associated with uranium ore depositions at Kiggavik are: (1) dissemination of short chain carbon & sulfur compounds, the most common, and (2) more locally as massive, hard and brittle aggregates or spherules of carbonaceous material. In both cases these carbonaceous materials were compared with similar products formed by synthesis in laboratory. Then the comparison of data from literature on experimental synthesis with those collected in natural system may help to highlight the processes responsible for the genesis of carbonaceous material and give complementary information to constrain the hydrothermal conditions in unconformity related uranium deposits.

151

Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada). 5.5.2. Carbon sulfides a comparison between natural and laboratory created

hydrothermal systems

The first expression of carbonaceous material in the alteration system are the organic sulfur compounds as short chain carbon sulfides which can be compared to the artificial synthesis of the same chemical compounds, CS2 as well as thiols, from a FeS/HCl/CO2 or FeS/H2S/CO2 system at 75°C (Heinen and Lauwers 1996) via the 2 following reactions :

7FeS+ 8HCl +CO2 → 4FeCl2+3FeS2+CH3SH+2H2O and 2CH3SH +2H2O → CS2 +CO2+6H2

It also appears in the same study that DMDS and carbon disulfide are indicators of suboptimal conditions for CO2 reduction, as consequence of a limitation of H2 resulting from an unfavorable FeS/HCl (H2S) ratio or a low temperature. The formation of DMDS via the 2 methanthiol condensation in addition to short thiols may be significant of H2 limitation. It also needs to be noted that such reaction produces pyrite. In all these reaction oxidation conditions are controlled by mineral buffers, which are all present in the unaltered rock (pyrite & magnetite) prior to alteration and given in (Shock 1990), while a part of H2 may be generated from water radiolysis:

2 Fe3O4 + H2O = 3 Fe2O3 + H2 and 2 FeS + 4/3 H20 = FeS2 + 1/3 Fe304 + 4/3 H2

Finally thermodynamic studies on similar short chain carbon sulfides with the example of dimethlysulfide gives another temperature constrain to the hydrothermal condition necessary to the synthesis of such compounds, Figure 5-5 (Schulte 2010). Then when using the measured or calculated fluid temperature for the brines involved in the alteration processes

(fluid inclusion and stable isotopes on illite) and ranging from 150 to 220°C at Kiggavik, but similar to the one in the Athabasca Basins (Pagel and Ahamdach 1995; Kotzer and Kyser

1995; Pagel 1975; Renac et al. 2002), allows us to determine that the reaction is displaced in the sens of synthesis of carbon sulfide compounds with a LogK just above 0 at 220°C but

152

Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada). around 8 at 150°C . Then the hydrothermal conditions related to alteration processes were favorable for the in situ genesis of carbon sulfide compounds. It may also indicate that these products were synthesized when temperature started to decrease possibly at the end of an hydrothermal pulse.

Figure 5-5 : Stability of carbon sulfide coumpounds as a function of Log K and T °C, from

Schulte, 2010

Unfortunaly, the carbon content is too low in the disseminated material to get a carbon isotope footprint of such compounds.

Then after look at the more volatile compounds the massive carbonaceous materials

5.5.3. Massive carbonaceous materials: solid properties & genesis

The massive carbonaceous materials found at Kiggavik presents similarities in term of texture, petrographic relashionship with clays within alteration surrounding mineralization

13 zones as well as low  C to the one identified as solid bitumen in the Paleoproetrozoic

Athabasca Basins in unconformity related uranium deposits (Leventhal et al. 1987; Sangély et al. 2007). However the isotopic fractionation alone have been questioned as the efficient tool

153

Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada). to identified C fractionation from organic or inorganic processes, while only few literature refers to the massive carbonaceous material (also named condensed CM) isotopic fractionation experiments (Horita 2005). Nevertheless, the limited data avaliable quasi

13 systematic C depletion up to -60°/00 and ranging from -5 to – 50 °/00 have been measured on

MCM relatively to CO2 and CH4 between 200°C and 600°C in presence of metallic catalyst such as Ni produced via FT type reaction (Lancet and Anders 1970; Horita 2001; Kerridge et al. 1989; Sackett 1995).

As the with the carbon stable isotope fractionation, the solid properties and his structural characterization have been poorly considered while been of great importance because of the implications of the types of organic matter precursors, if there is any, in the formation of the massive carbonaceous materials in hydrothermal environments, or the alteration or chemical processes responsible for the transformation or neogenesis of such materials (Durand 1980).

5.5.4. Degree of tridimensional organization of massive carbonaceous

material

According to the XRD and RAMAN spectroscopy data the studied massive carbonaceous materials cannot be called graphite. The lack of diffraction of X-ray indicates no sufficient coherent carbon layer stacking along the c-axis (or a predominantly amorphous material). In addition the RAMAN signal (ID/IG band intensity ratio, positions and shapes) share some similarities with amorphous carbon, activated charcoal, graphite nano-particules or altered graphite from uranium deposits (Tuinstra and Koenig 1970a; Chu and Li 2006; Wang et al.

1989; Calderon Moreno et al. 2000). The in plane crystallite size ranging between 2 to 30nm and the images in TEM both indicate that the material is predominantly formed of sp2 bonded

(graphene) carbon mono layers or at best a few layer of graphene with a low degree of spatial organization. This is also marked by the broad D and G bands in the RAMAN spectra, with an amorphous component in the signal around 1500cm-1, while the D band at 1350cm-1 signs the

154

Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada). graphen layer edges of a disordered graphitic lattice as the interpreted band positions from spectrum decomposition (Sadezky et al. 2005).

Then if it is not graphite, the origin of such material and the formation processes can be questioned. In fact graphite resulting for the thermal maturation of organic matter is known to keep the acquired crystalline order (Luque et al. 1993). Then the low level of order of the massive carbonaceous material relatively to the regional greenschist to amphibolites metamorphic facies together with his only presence in the alteration halos seems in favor of a thermal event and formation processes unrelated with the prograde metamorphism (Pasteris and Wopenka 1991; Wopenka and Pasteris 1993; Lewry and Sibbald 1980). The hypothesis of fluid deposited during ore related hydrothermal activity might be given by crystallochemical properties via the RAMAN signature. From this perspective the massive carbonaceous from Kiggavik share more similarities with the Neoproterozoic, vein hosted, brittle solid bitumens or graphitoids described in hydrothermal environments related to

Klecany intrusive complex in Bohemia (Jehlička et al. β003) and also quite similar to shungite found in Karelia (La of 40 nm; disorder) (Jehlička et al. β005; Wopenka and Pasteris 1993) or to laboratory produced, fluid deposited graphite (Luque et al. 1998), rather than graphitized carbonaceous material under greenschist facies or even more to graphite host in higher metamorphic grade facies (Wopenka and Pasteris 1993). Then all low temperature (< 250°C) hydrothermally deposited carbonaceous or graphitic material appears to share a small in-plan crystallite size as well as a high level of disorder.

In addition during experimental precipitation of graphite in a C-H-O system, parameters as such as lower temperature, and higher fH2 lead to the formation of a poorly organize material

(Pasteris and Chou 1998; Ziegenbein and Johannes 1990; Mastalerz et al. 1995). Moreover, both nucleation and crystal growth must occur to produce graphite. Finally in unconformity related uranium deposits system such as Kiggavik the presence of CO2 and H2 have been

155

Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada). demonstrated and thought to be produce by water radiolysis (Derome 2002; Dubessy et al.

1988).

5.5.5. Nanoscale graphite and possible implications for uranium

precipitation

Graphite is known as chemically inert and though is role as been debated as a potential control for uranium mineralization in the Eastern and Western Athabasca Basins and in the

SW Thelon at Boomerang where major deposits are spatially related with regional scale graphitic fault systems (Davidson and Gandhi 1989; Thomas and Wood 2007; Laverret et al.

2006; Thomas et al. 2000). By contrast with the massive carbonaceous materials studied here, in these structures, graphite doesn’t show a low level of organization and belong to the metamorphic history of a metasedimentary rock package which underwent at least a green schist metamorphic grade (Lewry and Sibbald 1980). In contrast no such graphitic bearing fault is present at Kiggavik, and the only potential sources of organic compounds are to be related to black shales recognize at minima 10 km to the East.

In addition a nano-scale association has been identified with the MCM and mint crystals of uraninite and pyrite. Moreover Cu and U are both elevated in the carbonaceous matrix even if no mineral phase can be identified with the SEM. But nano crystal of uranium phases seems to coexist within the carbonaceous material. Such close association between the carbonaceous material and uraninite could be related to orientation-controlled growth on the graphene layer. In fact, the epitaxial growth of uraninite would be due to the match between uraninite lattice, on the {111} plan, and the (0001) hexagonal lattice of graphen.

Then the deposition of the carbonaceous material may be contemporanous to the uraninite deposition during the ore forming processes (both needing reducing condition to precipitate).

In such a process, the enhanced surface area of the carbonaceous material can act as a

156

Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada). potential site for nucleation or uraninite and chalcopyrite. Such process would be adequate to explain the disseminated low grade mineralization found widely in alteration zones where carbonaceous materials are present.

5.6. Conclusion

Then regarding the petrography, the isotopic measurement and the crystallographic properties, we propose that the carbonaceous material in Kiggavik could be the expression of abiotic, hydrothermal synthesis of carbonaceous compounds, with small chains of carbon sulfide and also massive carbon. This is supported by laboratory experiments of hydrocarbon synthesis via the CO2 or CH4 reduction on mineral catalyzes like magnetite or pyrite (Heinen and

Lauwers 1996). In addition the range of temperature used for the synthesis of short chains of carbon sulfides are similar to the one estimated via fluid inclusion work in unconformity type uranium deposits around 200°C, (see chapter 3) (Pagel 1975; Derome et al. 2005).

We also suggest that the solid properties may provide a favorable environment for uranium minerals, and metallic sulfide precipitation.

Acknowledgments:

Authors would like to express their gratitude to Marie-France Beaufort for the HRTEM charaterisation and to AREVA NC & ERM sponsors of this study.

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Carbonaceous material occurrence in the Kiggavik uranium deposits (Thelon, Nunavut, Canada).

B. LES MARQUEURS MINÉRALOGIQUES

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Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. 1. Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada.

Riegler, Thomas; Quirt, Dave & Daniel Beaufort

In preparation for submission in Mineralium Deposita

1.1. Abstract

The Kiggavik Andrew lake structural trend consists in four mineralized zones, partially outcropping, lying two kilometers south of the erosional contact with the unmetamorphosed sandstone and basal conglomerates of the Paleoproterozoic Thelon Formation. The mineralization is controlled by a major East-West fault system associated with illite and sudoite alteration halos developed in the Archean metagraywackes of the Woodburn Lake

Group. Aluminum phosphate sulfate minerals (APS) from the alunite group crystallized in association with the clay minerals in the basement alteration halo as well as in the overlying sandstones which suffered mostly diagenesis. APS minerals are Sr and S-rich (svanbergite end-member) in the sedimentary cover overlying the unconformity while they are LREE-rich

(florencite end member) in the altered basement rocks below the unconformity. The geochemical signature of each group of APS mineral together with the petrography indicates two distinct generations of APS minerals:(1) a first one related to sedimentation-diagenesis processes at the bottom of the Thelon sandstones and (2) a second one related to hydrothermal alteration processes which accompanied the uranium deposition in the basement and partially overlap the sedimentary-diagenetic mineral parageneses . The primary REE bearing minerals of the hosts rock were characterized in order to identify the potential sources of REE. The obtained chemical composition of REE highlights a local re-incorporation of the REE released from the alteration processes in the APS minerals. The distinctive geochemical signatures between diagenetic (or sedimentary) and hydrothermal APS minerals suggest a

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Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. different source material in the Thelon basin than the Athabasca basin. Lastly as some of the primary REE-bearing minerals are potential uranium sources, the potential fertility and the sources of the uranium can be questioned.

1.2. Introduction

Since several decades hydrated aluminum phosphate and sulfate (APS) minerals of the alunite supergroup have been found and studied in a broad range of geological environments; form soils to sedimentary basins, or hydrothermal and volcanic system (Dill, 2001; Stoffregen and

Alpers, 1987). They occur as minute, euhedral crystal with rhombohedral or pseudocubic habits. Their general structural formula is AB3 (XO4)(OH)6, where A, B, X are the 12, 6 and

4-fold coordinated crystallographic sites. The A site can be occupied by monovalent (H3O+,

K+, Na+, Rb+, NH4+, Ag+, Tl+, etc), divalent (Ca2+, Sr2+, Ba2+, Pb2+) or trivalent (Bi3+,

LREE3+) cations. More rarely tetravalent cation like Th4+ can integrate the APS crystal structure in this site. The B: 6-fold coordinence site is occupied by Al3+ and Fe3+, and lastly the X site is commonly occupied by S6+, P5+, and As5+. As the three sites are subject to numerous substitutions, and thus to complex solid solutions, these crystal-chemical properties give rise to tens of end-members within the alunite supergroup.

Despite their relative very low abundance as well as their very small size making them somehow difficult to identify in thin sections, recent studies have highlighted the potential of

APS mineral as geochemical markers of the proximity of orebodies in unconformity related uranium deposits (Gaboreau et al., 2005; Gaboreau et al., 2007). In fact, two major characteristics can be pointed out: (1) once formed, they resist to most of the chemical reactions involved during surface or subsurface alteration processes and (2) their sensitivity to physic-chemical condition of formation (such as Eh and pH) is recorded in their broad range of chemical composition, with the ability to trap and concentrate trace elements and particularly the light rare earth elements (LREE), (Herold, 1987; Stoffregen, 1993).

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Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. Worldwide in the paleoproterozoic unconformity related uranium deposits, APS minerals seem to be systematically associated with the clay alteration assemblages. They have been studied in the Kombolgie basin in Australia (Beaufort et al., 2005; Gaboreau et al., 2005) as well as in the Athabasca and Kombolgie Basins (Gaboreau et al., 2007; (Cloutier et al. 2010) and both the Thelon and Horny Bay Basins in Canada (Gall and Donaldson, 2006) as well as in the underlying saprolites (Miller 1983).

The spatial distribution and the compositional variation of these minerals around the uranium orebodies led some authors to consider them as good indicator of both the redox and pH paleo-conditions responsible for the development of fronts during the alteration process, and hence as potential tools for mineral exploration (Gaboreau et al., 2005, 2007).

The aim of this study is to determine the nature and the origin of the APS minerals present near the bottom of the middle Proterozoic Thelon sandstone formation and in the underlying archean basement rocks which host the alteration halos of the uranium ore bodies distributed along the Kiggavik Andrew lake structural trend, Nunavut, Canada . The main goals are (1) to determine the paragenetic association and the crystal chemistry of APS mineral in the basement and the overlying Thelon sandstones, (2) to determine the source material for APS minerals and (3) assign and replace each paragenesis in the basin and the uranium mineralization history. These results are compared and discussed with respect to those already obtained from APS in alteration halos associated with the unconformity-type uranium deposits of the both Australian and Canadian counterparts.

1.3. Regional geological setting

The Kiggavik exploration project is composed of two groups of claims, St Tropez to the

North and Kiggavik down South, going roughly from the Southern Shore of Schultz Lake to the East of Judge Sisson Lake, about 80km West of the Inuit hamlet of Baker Lake, NU. All

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Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. the deposits, Kiggavik, End and Andrew, and most of the prospects Bong, Granite, Sleek, are exclusively located in the Kiggavik part of the project, figure 1-1. The overall historical metal content is estimated to about 50 000t U, with an average 0.5% grade (Jefferson et al., 2007).

4

1

3

2

Figure 1-1 : Bedrock geology of the NE Thelon Basin margin, modified form Jefferson et al., 2013. Sampling area are indicated by the following number: 1 Granite Grid area; 2 W94-4 drillhole south of the Judge Sisson

Fault, W2 drillhole; 4 Uno Granite

The study area encompasses the St Tropez and the Kiggavik areas in order to have a more regional, vision of the geological factors that could be involved to generate a favorable environment for uranium mineral deposition (basement rocks lithology, structural control of the fluid flow paths, degree of fluid rock interaction in any place etc.).

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Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. The host of the mineralization is the Woodburn Lake Group (WLG), a 2.6-2.7 Ga, neoarchean supracrustal rock package formed mainly by a sequence of metagraywackes and metavolcanics, with minor quartzite and iron formation. This sedimentary pile retromorphosed in a greenschite facies overlies older granitic gneiss of uncertain age and is part of a series of greenstone belt known from Northern Saskatchewan to Northern Baffin

Island, set during the Rae craton continental riflting (Hartlaub et al., 2004). The archean rock package had his own tectonometamorphic history. During the paleoproterozoic the archean and the overlying paleoproterozoic cover where imbricated and structured together in several stages of deformation related to the Thelon-Taltson (2.0-1.9 Ga) and the Trans-Hudson (2.0-

1.8 Ga) orogens, respectively at the NW and SE during the Laurentia accretion (Hoffman,

1990). These events formed the main structural frame with main foliations and major shield scale ductile mylonite zones and led to a complex stratigraphic stack not yet completely understood (Pehrsson et al., 2010). Following the Thelon-Taltson orogeny collapse two major suites of igneous bodies took place. The older intrusive (1.82-1.85 Ga) belongs to the Hudson

Suite; composed of granite; Martell syenite and the Dubawnt minettes. It was followed

100Ma later by the Nueltin rapakivi granite and its volcanic equivalent, the Pitz rhyolites which belongs to the Wharton Group which constitute the intermediate and second sequence of the Dubawnt supergroup (Miller and LeCheminant, 1985; Peterson et al., 2002; Rainbird et al., 2003). The last sequence is the Barrensland Group which hold the Thelon Formation, a siliciclastic sedimentary sequence similar the Athabasca Group in term of age and lithology.

As already mentioned in the Athasbasca basin, the upper part the Thelon sandstone have been locally cemented by apatite during an early diagenesis stage dated between 1720 and 1647

Ma (Miller et al., 1989). Morever in addition to the fluor-apatite cement observed in the

Thelon and the Hornby bay basins, APS cements have been also described in the Thelon

Formation, (Gall and Donaldson, 2006).

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Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. In addition to those already observed in the sandstones, APS minerals where commonly observed in close association with illite and sudoite (Al-Mg chlorite) within the clay alteration halos which envelop the uranium deposits along the Kiggavik - Andrew lake structural trend

(Riegler et al. 2013).

1.4. Sampling and methods

A set of several tens of fresh and altered rocks samples from drillcores and outcrops coming from various locations in the Kiggavik and St Tropez area were selected for a preliminary petrographic analysis. Such a sampling encompasses the basement rocks with the metagraywackes and the later intrusive (Hudson Granite and aplite, Martell Syenite, Nueltin porphyritic rhylolite) as well as the overlying basal sedimentary beds of the Thelon Basin - conglomerates and conglomeratic sandstones) figure 1-1, Table 1-1. 13 samples were then selected within the previous extensive set of samples for a detailed analysis of APS minerals in altered rocks and their parental minerals in the fresh ones. In addition the chemical compositions of 189 core samples and 50 centimeter long composite samples of altered and fresh metagraywackes were acquired to investigate the elements transfers, Table 1-1. These samples are representative of the varying degree of alteration in the alteration halos developed around the major structures which controlled the deposition of uranium orebodies.

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Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. Table 1-1: Kiggavik-St Tropez APS, REE minerals bearing rocks sampling table

Geochemistry ICP- ICP- Sample name Area Drillhole/Outcrop rock type alteration Umin OES MS Thelon Formation: Sedimentary Cover GG3a Granite Grid outcrop mudstone no no 1 GG3b,c, GG4, 5, 7, StTropez " outcrop sandstone no " 6 Basment GGG Granite Grid outcrop Hudson granite no no W2-2 Sleek Lake drillhole " no " W2-03 " " metagraywacke no " 1 SL9_1 to 5 " " Hudson granite yes " 5 UnoGranite St Tropez outcrop " no " Judge W97-4_10 & 17 Sisson lake drillhole " no " 1 W97-4_3 " " metagraywacke no " B1-94-1_08 " " " no " 1 Andrew porphyritic ALCS Lake outcrop ryholite no " 1 BSE_05 Bong drillhole metagraywacke no " 1 BG45_13 " " " no " 1 BG42-23 " " metagraywacke yes yes BG42-21a, b; 25; 30; 40 " " " yes no 5 BG45_28 " " " yes yes 1 BG43_028 " " " yes " 1 BG42 composite set " " " yes " 133 BG49 composite set " " " no no 34

Then, for the Sedimentary cover (Thelon Formation): Unaltered mudstones: GG3a as well as unaltered sandstones GG3b, c; GG4 & GG7 samples have been taken on outcrop along the

Thelon fault North of the Granite Grid prospect, point #1 on the figure 1-2. The GG4 & 7 sampled were taken a few kilometers away to the East. In the basement rocks the main sample location were:

- Altered and/or mineralized metagraywacke form the Bong prospect with the BG42

and BG49 drillholes (DDH)

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Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. - Unaltered Intrusives: A prophyritic ryholite dyke belonging to the Nueltin Suite

located at the Andrew Lake core storage (ALCS). Hudson granite, part of the Schultz

lake intrusive complex with the W97-4_10 & W2-2 drillholes as well as an outcrop

sample form the Granite Grid and the NE St Tropez areas, respectively the point #2, 3

and 4 on the figure 1-1.

- Altered Hudson granite form the Sleek Lake area SL9_01 distal to mineralization &

SL9_05 in the vicinity of very local and weak mineralization intercepts. Such samples

are representative of barren alteration zones.

1.4.1. Methods

Petrographic study and mineralogical identification were made in thin sections using observation with a polarizing optical microscope and a scanning electron microscope (SEM,

JEOL 5600LV) equipped with a Brucker Energy Dispersive Spectrometer (EDS) X-ray analyser at the University of Poitiers (15kV acceleration voltage, 1 nA beam current).

Quantitative chemical analyses were performed using a Cameca SX100 electron microprobe with wavelength dispersion spectrometers (WDS) at the CAMPARIS micro-analysis facility,

UPMC Jussieu Paris. Chemical microanalysis of Si, Al, Fe, F, P, S, Ca, Ba, Sr, La, Ce, Pr,

Nd, Th and U were obtained at the following analytical conditions: 15kV accelerating voltage, 4 nA beam current, 2 micrometer spotsize and a counting time ranging from 5 to 20 seconds according to the specific element. The microprobe was calibrated using both natural and synthetic standards: anorthite, apatite, pyrite, diopside, barite, uraninite, thorite, monazite,

SrSiO3, NdCu and a glass doped in rare earth elements (REE). The relative error on the elements is below 1 %. The structural formulas of APS minerals were calculated using a 6 cations normalization as in the theoretical mineral formula AB3 (XO4)2(OH)6.

Bulk rock chemistry (including major and 54 traces elements) of representative samples selected in our study were done using ICP-MS at the Service d'Analyse des Roches et des

171

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. Mineraux - CNRS – CRPG, in Nancy France. These chemical data have been completed by an exploration chemical data set provided by AREVA Resources Canada (major and traces elements) analysed at the Saskatchewan Research Council Laboratory in Saskatoon, Canada using ICP-OES. Due to the lower detection limits and better accuracy provided by ICP-MS, only the samples analyzed at the SARM will be used to compare the trace elements.

In order to decipher and interpret the geochemical data gathered on the REE bearing phases we carried a petrographic study to highlight the textural and chronological relationships of these minerals. Thus the primary, magmatic or sedimentary/diagenetic paragenesis have to be identified and compared with secondary mineral assemblage linked to the hydrothermal events in relation with the mineralization processes.

1.5. APS minerals and alteration petrography

In thin sections APS were observed by SEM because of their brightness in backscattered electron (BSE) mode, due to their high content in heavy elements such as Sr and LREE.

Generally, APS crystals occur as very small euhedral rhombs (2–10 mm in average width, exceptionally up to 50mm) located in the intergranular porosity of the clay matrix which constitutes most of the alteration products of both sedimentary and basement rocks or are associated with secondary quartz and hematite as fracture controlled cement. Locally coarser grained APS crystals display features of growth zoning characterized by alternation of concentric bright and light grey thin zones.

Their identification is quite arduous in optical microscopy due to their small size and the possible confusion with apatite and their relatively scattered distribution in the rock even if they can form massive aggregate in places (figure 1-2a).

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Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada.

Figure 1-2 : Aluminum phosphate sulfate minerals (APS) of the Kiggavik area in Thelon Formation ( pictures A to D) and in the altered basement (E& F). A APS minerals in the sandstone in equilibrium with kaolinite, remanante porosity filled by microcrystalline quartz (QTZ3) GG7 sample; B Massive APS cement; C

Microcrystalline (QTZ3) and APS minerals fracture cross cutting unaltered red mudstone at the base of the

Thelon Fm, later re-opened and filled with illite and hematite, GG3a sample; D Local ililtization pocket developed in a large kaolinite booklet with co precipitation of APS, GG4 sample; E Altered granite with Illite

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Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. replacement of feldspar and devellopement of APS minerals, SL9 drillhole, Sleek lake area; F Illitic pocked with euhedral APS, Andrew Lake, And10-01 drillhole

Abbreviations, Ill: illite; Hm: Hematite; Kao: kaolinite; Qtz: quartz

1.5.1. APS of the basal Thelon Formation

In the sandstones APS (hereafter named and labeled by the number of each generation) minerals are relatively abundant in the following petrographic settings: (1) as pore filling aggregates of very fine crystals with a typical pseudocubic habits or as cements (Figure 1-2a

& 2b); (2) as disseminated euhedral crystals coeval of post diagenetic quartz overgrowths figure 2c and (3) locally associated with illite flakes in the late illitization pockets developed at the expense of the pore-filling kaolinite, figure 1-2d.

Late reopening the post diagenetic quartz hydraulic breccia is associated with co-precipitation of illite and anatase followed by specular hematite. The paragenetic sequence determined in the sandstone is presented figure 1-3.

Figure 1-3 : Mineral paragenesis of APS minerals in the basal Thelon Formation

174

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. According to the petrographic study, the first generation (APS1) is related to a sedimentary- diagenetic stage which emcompasses the deposition of large sedimentary kaolinite booklets and then their diagenetic recystallization into dickite ± hematite with increasing burial depth, contemporaneously of the formation of diagenetic quartz overgrowths (QTZ2). In addition, these APS1 are associated with a AlO(OH), cerianite, Ce-La oxides, thorianite and hematite paragenesis in the GG7 sample, figure 1-4. The second generation (APS2) is trapped in a very fine grained, microcrystalline, quartz filling the remaining porosity. This quartz cementation heals microbreccia and fractures which affected lithic fragements. The last generation (APS3) is associated with late illite which replace the previous diagenetic kaolinite during a postdating hydrothermal event which is well known to be related with the deposition of the uranium orebodies in the underlying basement rocks (Riegler et al., 2013).

In the sandstone, the crystals of diagenetic APS tend to be relatively homogenous in composition with no more than one generation of visible overgrowth showing a slightly brighter core in BSE mode, indicating the incorporation of more heavy elements during the first crystallization stage. Unfortunately the crystal size is often smaller than the electron spot size, permitting not to have EMP measurement of the chemical composition on both core and overgrowth for these crystals.

175

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada.

Figure 1-4 : a, Oxy-hydroxy aluminium minerals associeted with cerianite grains and exhibiting high Ce levels up to several percent; b, same AlOOH minerals associated with cerianite, La-Ce oxide and thorianite and related

EDS spectra for these phases:c, c, & e.

176

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. 1.5.2. Basement Alteration petrography and mineralogy

Figure 1-5 : Primary REE & Uranium bearing minerals in the Kiggavik & St Tropez area, A Non metamict unaltered monzite grain, Woodburn Group metagraywacke, W97-4; B Parisite (Ca,Ce, La)CO3 euhedral crystal with local partial dissolution associated with illite formation, granitoid at the bottom of the W97-4 drillhole; C

Altered allanite, Uno granite, D Uranothorite altered to thorogummite, Andrew lake syenite dyke.

Abbreviations, Aln: allanite, Cal: calcite, Par: Parisite, Py: Pyrite, Ttn:titanite

In the basement rocks, APS minerals are closely associated with the hydrothermal alteration processes which controlled the uranium ore genesis, Figure1-2e. The alteration of basement rocks is spatially related to faults at every scale. It results in a strong color change of the rocks. Two contrasting macroscopic alteration features have been noted: (1) bleaching related to strong argilization and (2) reddish coloration related to crystallization of iron oxide (mostly hematite) and local silicification of open fractures (quartz veins). Strong argilization

177

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. (bleaching) associated with various degrees of desilicification is the most common alteration feature observed in both the fault core and the major mineralized zones. At small scale, alteration is related to the dissolution of the preexisting metamorphic silicates and the crystallization of an abundant clay matrix composed of illite associated to variable but generally small amounts of sudoite (Al-Mg chlorite). In altered intrusive rocks, the feldspars phenocrysts are totally replaced by illite and specular hematite. Sudoite is always intimatly associated with illite.

Minor amounts of phosphate minerals are closely associated with illite and sudoite. They essentially consists in aluminum phosphate-sulfate minerals (APS) and secondary apatite and they display a marked zoning pattern around the mineralized bodies. APS minerals occur as tiny pseudocubic crystals which size range from less than to 10 µm up to 50 µm. APS minerals display frequently features of chemical zoning but the ones observed were quite homogeneous with only one generation of overgrowth and very little compositional change

(Figure1-2f). Secondary apatite occurs close to and within the mineralized zones.

APS minerals are totally absent in the fresh basement rocks. However, several accessory minerals of these rocks can be considered as the potential source for the chemical elements incorporated in the APS minerals observed in the altered zones. According to the nature of the host rock, they can consist in monazite (Figure 1-5a), mostly in the metagraywackes; bastnaesite/parasite (Figure1-5b), allanite or REE oxides (Figure1-5c) as accessory phases in granites, ryholites and syenites. In addition uranothorite altered to thorogummite can be found in place in ryholite (Figure 1-5d). This last mineral being a potential source for both U and REE.

To sum up the petrographic observations in both the sedimentary and basement rocks, it appears that two main generations of APS minerals can be identified with respect to their

178

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. relationships with clay minerals. In the Thelon sandstones APS1 & 2 coexist with kaolin minerals and are related to the basin evolution from sedimentation to deep diagenesis as indicated by the kaolinite to dickite transition (voir chapitre 4). The second generation of APS is clearly related to the hydrothermal alteration event associated with uranium mineralization within the underlying basement rocks. The APS3 observed locally with illite near the bottom of the Thelon sandstone is considered as a signature of the hydrothermal alteration event which is extensively developed below the unconformity.

Then, the crystal-chemical properties of APS minerals needs to be investigated in more details to determine if the textural observation can also be linked to a chemical evolution of the system and how this would fit in the general mineralization model for the uranium mineralization found along the Kiggavik Andrew lake structural trend. In addition, complementary EMP measurements have been done on the REE bearing mineral identified in the fresh rock (monazite, bastnaesite/parasite, allanite, REE oxides). Complementary data on accessory uranium-bearing mineral is also presented.

1.6. Electron microprobe data

1.6.1. Overall chemistry of APS minerals

Average representative electron microprobe data of each geological environment have been sum up in the table 1-2. The low and relatively variable sum of oxide weight percent of the analyses is a result of the water content of the APS minerals as well as a significant microporosity between the micrograins aggregates of the X-Ray emitting volume. However, even if the very small size of the APS minerals increases the possibility of contamination of the microprobe analysis by chemical elements of surrounding clay minerals or quartz, it has no significant influence on the relative proportions of the APS forming chemical elements (at the exception of aluminum).

179

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. Table 1-2 : Representative electron microprobe analyses of APS minerals, B: basement, C, sedimentary cover

B C

Distal Alteration; Intermediate Proximal Alteration GG7_APSCemen GG7_Mt GG4 GG3 SL9_01 Alteration; SL9_05 Zone, BG42_23 t x n = 32 n = 17 n = 17 n = 18 n = 31 n = 9 n = 20 Mean Wt% Std Dv. Mean Std Mean Wt% Std Mean Std Mean Std Mean Std Mean Std Wt% Dv. Dv. Wt% Dv. Wt% Dv. Wt% Dv. Wt% Dv. SrO 5.95 1.31 4.61 1.22 3.26 0.76 10.09 0.70 11.31 1.22 7.31 0.95 13.49 1.12 CaO 2.52 0.40 2.31 0.61 1.15 0.28 1.72 0.15 2.18 0.39 3.48 1.04 2.25 0.30 BaO 0.33 0.37 0.31 0.31 0.02 0.03 0.67 0.13 0.72 0.34 0.43 0.31 1.31 0.50 La2O3 6.11 1.63 5.99 1.43 7.71 1.08 5.54 1.04 2.37 1.57 3.00 1.32 1.15 0.28 Ce2O 6.97 2.06 9.55 1.98 11.60 0.90 2.23 0.72 3.01 0.78 3.69 0.94 1.49 0.42 3 Pr2O3 0.74 0.21 0.76 0.20 0.97 0.17 0.84 0.13 0.38 0.21 0.67 0.15 0.20 0.07 Nd2O 2.01 0.76 1.93 0.54 2.27 0.50 2.92 0.48 1.33 0.75 2.92 0.56 0.72 0.28 3 ThO2 0.36 0.30 0.37 0.43 0.02 0.03 0.30 0.12 0.38 0.13 0.25 0.33 0.36 0.24 Al2O3 29.48 1.42 28.94 1.42 32.78 1.21 31.50 0.55 31.61 1.72 32.70 1.71 31.76 1.00 FeO 0.72 0.66 0.80 0.82 0.08 0.05 1.17 0.50 1.18 0.64 0.54 0.58 1.59 2.28 P2O5 23.65 1.28 24.42 1.56 26.78 2.12 25.75 0.60 23.98 1.84 27.56 2.67 23.31 1.18 SO2 2.35 0.85 1.85 0.87 1.78 1.02 2.10 0.38 3.02 0.74 2.64 0.42 4.73 0.48 Total 81.18 81.83 88.41 84.81 81.48 85.19 82.35 Mean apfu Stdt Mean apfu Stdt Mean apfu Stdt Dv. Mean Stdt Mean Stdt Mean Stdt Mean Stdt Dv. Dv. apfu Dv. apfu Dv. apfu Dv. apfu Dv. A Sr 0.30 0.06 0.23 0.06 0.15 0.03 0.47 0.03 0.54 0.05 0.33 0.05 0.62 0.04 Ca 0.23 0.03 0.21 0.06 0.10 0.02 0.15 0.01 0.19 0.03 0.29 0.09 0.19 0.02 Ba 0.01 0.01 0.01 0.01 0.00 0.00 0.02 0.00 0.02 0.01 0.01 0.01 0.04 0.02 La 0.20 0.06 0.19 0.05 0.23 0.03 0.17 0.03 0.07 0.05 0.09 0.04 0.03 0.01 Ce 0.22 0.07 0.30 0.06 0.34 0.03 0.07 0.02 0.09 0.02 0.11 0.02 0.04 0.01 Pr 0.02 0.01 0.02 0.01 0.03 0.00 0.02 0.00 0.01 0.01 0.02 0.00 0.01 0.00 Nd 0.06 0.02 0.06 0.02 0.07 0.01 0.08 0.01 0.04 0.02 0.08 0.02 0.02 0.01 Th 0.01 0.01 0.01 0.01 0.00 0.00 0.01 0.00 0.01 0.00 0.00 0.01 0.01 0.00 B Al 2.99 0.05 2.96 0.06 3.11 0.09 3.01 0.05 3.05 0.09 3.01 0.10 2.99 0.10 Fe 0.05 0.05 0.06 0.06 0.01 0.00 0.08 0.03 0.08 0.04 0.04 0.04 0.10 0.15 X P 1.72 0.04 1.79 0.08 1.83 0.11 1.77 0.04 1.66 0.09 1.82 0.11 1.58 0.07 S 0.19 0.06 0.15 0.07 0.14 0.09 0.16 0.03 0.23 0.06 0.19 0.04 0.35 0.03

180

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. Table 1-3 : Electron microprobe analyes of primary REE and U bearing minerals in the Kiggavik-St Tropez area, n number of analyses; the low total elements for monazite could be explained by the fact that Pb, Y, Sm, Ga haven’t been analysed.

Hudson Granite Metagraywackes Bastnaesite/Parisite Allanite Monazite Thorogummite Thorogummite Monazite W97-4_10 & 17; W2 Uno W97-4; W2; Uno; W97-4_17 W97-4_10 W97-4_3 Granite Grid n= 26 n= 5 n= 8 n= 4 n= 3 n= 14 wt% Mean Std Dv. wt% Mean Std Dv. wt% Mean Std Dv. wt% Mean Std Dv. wt% Mean Std Dv. wt% Std Mean Dv. F 3.26 0.40 0.20 0.02 0.37 0.04 0.68 0.09 0.34 0.05 0.40 0.06 Al2O3 0.13 0.36 11.76 0.60 0.10 0.11 0.22 0.11 0.39 0.09 0.07 0.04 P2O5 0.00 0.01 0.31 0.26 24.88 2.14 0.25 0.25 1.81 0.39 26.19 1.46 SO2 0.00 0.00 0.00 0.00 0.00 0.01 1.06 1.01 0.46 0.44 0.29 0.25 CaO 17.07 0.70 8.90 0.36 0.55 0.35 1.57 0.14 2.84 0.36 1.16 0.43 FeO 0.36 0.94 12.31 0.98 0.85 1.26 1.95 1.04 2.04 1.46 0.15 0.14 SrO 0.02 0.03 0.28 0.04 0.11 0.13 0.08 0.06 0.05 0.03 0.20 0.11 La2O3 13.63 0.76 4.45 0.73 16.11 2.11 0.21 0.05 0.07 0.05 16.92 1.05 BaO 0.02 0.04 0.56 0.11 0.06 0.08 0.06 0.05 0.36 0.38 0.03 0.05 Pr2O3 2.43 0.21 0.82 0.28 3.22 0.21 0.15 0.09 0.25 0.06 3.32 0.13 Nd2O3 8.70 1.10 2.57 1.32 9.68 1.19 1.41 0.39 0.95 0.29 11.41 0.90 UO2 0.06 0.07 0.11 0.08 0.15 0.15 4.20 2.12 0.90 0.47 0.09 0.08 ThO2 0.23 0.63 1.02 0.22 4.29 2.71 53.32 3.19 56.10 2.63 0.49 0.65 Ce2O3 25.30 1.37 9.33 1.22 30.79 1.53 0.86 0.19 0.84 0.22 31.82 1.20 SiO2 0.15 0.43 28.55 0.84 1.88 1.22 13.45 0.88 13.22 0.20 0.18 0.07 Total 71.36 1.00 81.18 4.07 93.04 2.82 79.47 4.47 80.64 2.32 92.73 1.83

181

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. Nevertheless it appears that a clear chemical distinction can be made between APS minerals from the siliciclastic sedimentary cover, (C) and those from the basement (B), table 1-2. APS minerals from the siliciclastic sedimentary cover are Sr ,Fe and SO2 rich while APS minerals of the hydrothermal alteration zones are enriched in LREE with a concentration 2 to 3 times higher than in the APS form the sandstones, and correlatively lower Sr and SO2. These global consideration leads to the identification of two chemical fields of APS minerals easily differentiated in a Sr/LREE/S ternary diagram, figure 1-6. The first chemical field which is next to that of svanbergite, is representative of the sedimentary and diagenetic APS (GG3,

GG7) samples. The second compositional field which is next to the one of florencite is representative of the hydrothermal APS of the altered basement (SL1&SL5 and BG42).

Figure 1-6 : Ternary plot using Sr, LREE & S composition of APS minerals obtained from electron microprobe analysis. mineralized metagraywackes ◊ Mineralized zone graywacke BG4β, □ proximal to mineralization in granite SL9, ■ distal to mineralization SL9, ▲ sandstone GG7, ▽ sandstone GG3, △ sandstone GG4

182

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada.

In both chemical fields, the compositional variation of Sr and LREE follows the same direction with a distribution of analyses between a Sr (svanbergite, goyazite) and a LREE rich

(florencite) end members. Lastly, the GG4 sample represents a group of APS minerals with intermediate chemical composition between the APS of unaltered sandstones and those of the illitized basement especially for the Sr and LREE contents.

Figure 1-7 : Ternary plot using La, Pr+Nd & Ce of electron microprobe data on APS minerals form Thelon

formation conglomeratic sandstones and altered as well as mineralized metagraywackes. Mineralized zone

graywacke BG42, □proximal to mineralization in granite SL9, distal to mineralization SL9, ▲ sandstone

GG7, ▽ sandstone GG3, △ sandstone GG4

183

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. The relative proportion of the LREE incorporated in the APS minerals (La,Ce,Pr,Nd) can be illustrated using a La/Pr+Nd/Ce ternary diagram, figure 1-7. Over all the APS minerals analyzed, the greatest variability in LREE relative proportions correspond to the cerium in the

APS minerals from the sandstone and more particularly for the GG7 sample (solid triangle pointing up) with a broad range LREE proportion, from high Ce in the matrix APS to low in the massive APS cement. Such a feature of strong variation of cerium content in the APS minerals while La/Pr+Nd ratio is constant needs to be look at jointly with the presence of cerianite. Then, cerium might had been fractionated between Ce-oxide and APS minerals during the crystallization stage of early APS1. In the altered basement the relative proportions of APS seems broadly constant with a predominance of cerium over the other

LREE elements (figure 1-6).

1.6.2. Element distribution in crystallographic sites

As already demonstrated, (Dill, 2001; Gaboreau et al., 2005; Gaboreau et al., 2007), APS minerals are subject to numerous and various substitutions in the A, B and X sites forming solid solution between ten’s of end members of the alunite supergroup. Moreover, the chemo- sensitive behavior of APS mineral have been identified in the selective incorporation of REE depending mainly on Eh and to a less extent on pH of the forming environment.

The global composition of the different types of APS minerals identified in various locations along the Kiggavik Andrew lake structural trend preferentially varies in response to coupled substitutions of Sr and LREE in their A site and P and S in their X site. In the altered basement rocks both intra- and inter-sample chemical variations of APS range along a binary solid solution between Svanbergite [Sr(Al3)(PO4,SO4)(OH)6] (which belongs to the beudantite group) and Florencite [LREE( Al3)(PO4)2(OH)6] (which belong to the the crandallite group).

Sr-rich APS minerals (closer to the Svanbergite end member) are associated with non-altered to distal alteration zone while APS minerals with the highest LREE content were analysed

184

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. within the mineralized zones, and more particularly in the ore grade mineralization zone in which LREE-rich APS can coexist with secondary apatite.

In the overlying sandstones, the compositional variation of APS cannot be explained only by a change in svanbergite to florencite solid solution. Indeed, the fact that all the punctual analyses are anomalously enriched in of Sr versus S (figure 8) is indicative of a significant contribution the Goyazite end-member [SrAl3(PO3[(O0.5(OH)0.5]2(OH)6] to the crystal- chemistry of these minerals.

0.60

SL9_01 SL9_05 BG42_23

0.40 GG3 GG4 GG7 S (apfu) (apfu) S

0.20

0.00 0.00 0.20 0.40 0.60 0.80 Sr (apfu)

Figure 1-8 : Cross plot diagram S versus Sr of APS minerals

1.6.3. Chemistry of primary REE bearing minerals

Representative electron microprobe analyses given in % oxydes of primary REE and U, Th bearing mineral are presented in the table 1-3.

185

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. As described in the previous petrographic study, several primary REE-bearing minerals are found in the unaltered basement rocks in which they belong to magmatic or metamorphic paragenesis.

Rare earth carbonates are widely encountered in the Hudson granite but their concentration is to low to permit their characterization by classical X-ray diffraction methods, even after heavy minerals concentration using sodium polytungstate at a density of 2.9. Nevertheless the punctual EMP analysis provides valuable information to identify REE carbonates on the basis of the low sum of oxide weight % (near 70%) and the qualitative analysis of carbon on the

EDS spectra and the overall chemistry. The most common REE carbonates of igneous rock are: bastnaesite (Ce,La)CO3F, parisite Ca(Ce,La,Nd)(CO3)2F2, and synchysite

Ca(Ce,La)(CO3)2F. The ternary Thorium, calcium and total rare earth plot for the assumed carbonates, figure 1-9 shows that the REE carbonates are closer to the parisite end member with relatively high calcium content. More interesting, when plotted in a La/Pr+Nd/Ce ternary diagram (figure 9), all these minerals have a composition which is superimposed on the composition field determined for most of the APS minerals of the basement rocks (figure 6).

The second groups of REE bearing minerals are the monazites with higher thorium content in the Hudson granite monazite than in the metagraywacke ones table 1-3, 1-4. The low sum of oxide Wt% of the monazite analyses are explained by the fact that HREE have not been analyzed.

The following simplified structural formulas (without HREE) can be calculated for the monazite, Table 1-4.

186

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada.

Figure 1-9 : Ternary plot using La, Pr+Nd & Ce, of electon microprobe chemical composition on REE bearing minerals in unaltered Woodbun metagraywackes & Hudson granitoids in the Kiggavik & St Tropez area: ▲ monazite, allanite, REE oxides ? , REE carbonates. The field of composition and the phase identification for REE carbonates is given in the Ca, Th, REE ternary diagram.

Table 1-4 : Mean simplified structural formulas of monazite analysed in both the metagraywacke and Hudson granite. n: number of microprobe analysis

Metagraywacke Hudson Granite

n= 14 n= 8

(Ce0.50,La0.27,Pr0.05,Nd0.17,Th0.00)P0.95O4 (Ce0.51,La0.27,Pr0.05,Nd0.16,Th0.05)P0.93O4

Finally, allanite, zircon and uranothoriferous minerals occurs in the Hudson granite.

Uranothorite is frequently altered and replaced by thorogummite with up to 8% UO2, table 1-

187

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. 3. Moreover the Ce, and Nd concentration of the thorogummite (up to 1%) make this mineral a minor REE source released during the alteration processes.

This result highlights the potential role of the Hudson granite as a regional source of uranium, and REE while monazite is globally uranium poor but nevertheless a very good candidate as

LREE primary source.

Monazite has not been identified in the sandstone cover probably because of its total dissolution during the diagenetic processes.

1.7. Whole rock chemistry and REE distribution

The crystal-chemical study of REE and U bearing minerals has been completed by a bulk- rock chemical analysis of major and trace elements in order to identified the geochemical behavior of these elements and to to evaluate the elements transfers during the alteration- mineralization processes.

As the evaluation of a mass transfer requires the assumption of immobile elements, Ti, Al and

Th (or Zr which is not represented in figure 9) have been tested by a comparative study of their relative proportions in both unaltered and altered rocks of a same metagraywake protolith. A plot of the relative proportions of these elements from all the unaltered to highly altered samples of metagraywakes in a ternary diagram (figure 1-10) indicates that the Al and

Ti relative percentages remain constant while elements such as Th or Zr (not represented in figure 9) slightly vary. Such a geochemical behavior which is enhanced by the factor 1000 used in the ternary plot can be easily explained by bedding heterogeneities in the metasediments. A similar behavior is observed when Th or Zr have been replaced by the sum of LREE in the ternary plot. This indicates that Ti and Al can be considered as immobile elements in the system while minor changes in Th, Zr and LREE, can be reasonably assigned to the sedimentary control on the amount of detrital heavy minerals (zircon, monazite…).

188

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. However, the inter-sample variation in Th concentration which is quite low and has probably no significant impact on the use of Th, Ti or Al for mass balance calculation.

Figure 1-10 : Plot of the chemical composition of all the unaltered to highly altered samples of metagraywakes in a Ti, Th*1000, Al/10 ternary diagram. (□) altered metagraywacke and

(■) unaltered metagraywacke.

1.7.1. Pearce analysis & Mass balance calculation

Petrography and crystal chemistry lead to the identification of the REE ratio and content on both fresh and altered rocks. Pearce Element ratio analysis (PER) and mass balance calculation have been used to approach the chemical transfer during alteration.

At first, local redistribution needs to be assess comparing the samples of the altered zone. In the figure 1-11a, the Ce/Th and Al/Th molar ratio behavior gives a representation of the

189

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. redistribution of cerium in APS minerals during the alteration of monazite. It appears that some samples are depleted in LREE while other are enriched, this being concordant with the heterogeneities in APS content inside the illite & sudoite alteration halos. In addition the

Ce/Th vs La/Th reveals that very little fractionation between the various REE occurs figure

11b. This is in agreement with the La/Pr+Nd/Ce ternary diagrams where the LREE proportion between the sources minerals and APS is fairly constant. Then alteration and crystallization of

REE phases seems to be a topochemical processes leading to a redistribution of REE at small scale inside the alteration halos.

14 a 14 b y = 1.46x + 0.06 12 12 R² = 0.99 10 10

8 8 y = 1.99x - 0.42 R² = 0.98 6

Ce /Th Ce 6 unaltered unaltered Ce / Th / Ce 4 altered 4 altered 2 2

0 0 0 500 1000 0 5 10 Al / Th La / Th

Figure 1-11 : Pearce element ratio diagrams for unaltered and altered metagraywackes representing. a, the monazite and the florencite, and b evolution of REE ratios relatively to Th

The low mobility of REE can also be noticed in the mass balance calculation, figure 12. That method gives an estimate of the elemental transfers during alteration processes. The calculations have been done using both thorium and titanium as reference for immobile elements. The error on elements loss or gain is given by the relative loss or gain on the element chosen as immobile. In addition the concentration in the altered rock was corrected as a function of the rock density using d = 2.7 0.02 for the unaltered rock and d = 1.7 0.2 in

190

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. the altered equivalent on the basis of the determination of the density of 4 and 5 representative samples in laboratory. These values are in agreement with the density estimated from geophysical methods in the literature (respectively 2.7 and 2.3) (Hasegawa et al. 1990). The alteration is marked by a relative but moderately significant increase in Al, K, Mg concordant with the dissolution of the primary minerals (quartz, feldspars, biotite, chlorite and pyrite) and followed by the crystallization of illite and sudoite.

It can be noted that iron is globally leached out of the system, especially when Th is used as the immobile element in agreement with the pervasive hematization observed around the main alteration zones.

The enrichment in phosphorus in altered zone is not only related to formation of APS minerals because secondary apatite is the most frequent P-bearing mineral of the alteration halo close to the uranium orebodies.

Considering the trace elements, an important result of the mass balance calculation is the strong enrichment in U, V and Mo and the substantial gain in Bi, Co, Cr, Ni, W elements with increasing alteration (expressed by an increase of loss on ignition).

191

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada.

Relative Loss/Gain % corrected to densities

4500

4000

3500 Ti as immobile element 3000

2500

2000 Th as immobile element

1500

1000

500

0

V V Y U In Bi Ni Zr W Er Pr Sr Hf Cr La Lu As Sc Zn Ta Tb Th Dy Ba Be Eu Pb Sb Sn Yb Cs Cd Ce Co Cu Ho Nb Nd Rb Ga Gd Ge Mo Tm Sm K2O K2O CaO MnO MgO TiO2 SiO2 SiO2 P2O5 -500 Na2O Al2O3 Al2O3 Fe2O3

Figure 1-12 : Mass balance analysis for metagraywacke Ti & Th as stable elements. Corrected for density change using (average measured densities 2.7 for fresh and 1.7 for altered metagraywacke)

192

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada.

1.8. Discussion

Evidences from petrography and mineral crystal-chemistry support the successive occurrence of three types of APS minerals in the sedimentary and basement rocks encountered on both sides of the paleoproterozoic unconformity at which the uranium deposits in the Kiggavik

Andrew lake structural trend are related (Riegler et al., 2013). APS minerals have been already described in the paleoproterozoic Thelon and Hornby Bay basins (Gall and

Donaldson, 2006). They have been also extensively investigated in both altered basement rocks and sedimentary cover which constitute the alteration halos of the unconformity related uranium deposits of the Athabasca and Kombolgie basins (Beaufort et al., 2005; Gaboreau et al., 2005; Gaboreau et al., 2007).

The paragenetic sequence established from the petrographic study permitted to distinguish three different populations of APS minerals which can be related respectively to sedimentary

(APS1) and diagenetic (APS2) processes in the sandstones of the basal Thelon formation and to hydrothermal alteration (APS3) strongly developed in the basement rocks next to the regional faults and much weakly developed in the overlying Thelon sandstone (Figure 1-3).

The three distinctive generation of APS can be also distinguished on the basis of their crystal- chemical properties. When plotted in a diagram Ce2O3/La2O3 versus the total amount of the most abundant light rare earth elements (La2O3 + Ce2O3+ Nd2O3), three distinct compositional fields can be distinguished (figure 13):

1.8.1. Crystal-chemical signature of sedimentary and diagenetic APS of the

Kiggavik area

The APS related to the sedimentary and the diagenetic history (APS1 and APS2) differ from the hydrothermal ones (APS3) by their lower content in LREE and a great scattering of their

193

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada.

Ce2O3/La2O3 ratio. However this apparent scattering of the APS crystal chemistry within the basal sandstones can be interpreted in more details on the basis of the petrographic observations.

The sedimentary APS which are associated with detrital aluminum oxi-hydroxides and cerium oxides are characterized by a relatively high LREE oxide content (8 to 13%) and a strong depletion in cerium (Ce2O3/La2O3 ratio less than 0,5) whereas the compositional field of the diagenetic APS (APS2) characterized by a lower total amount of LREE oxide (from 2 to 7%) and a variable but quite much higher Ce2O3/La2O3 ratio (from 1 up to 7) which spread over the composition of APS analysed in upper sandstones elsewhere in the Thelon basin (Gall and

Donaldson, 2006). The variation of the Ce/La and total amount of LREE measured in the APS formed in sandstones could be related to change in the nature of the sedimentary material. For instance, the Wharton Group is known to host volcano-sedimentary sequences with rhyolitic tuffs (Miller and LeCheminant, 1985; Rainbird and Davis, 2007; Rainbird et al., 2003), and given the highly instable nature of such material and the large volumes possibly involved the contribution of these lithologies to the LREE budget can be assumed. However we cannot easily interpreted the APS compositional variations as the result of a chemical change in the source material because bulk-rock chemical analyses of the sandstone samples do not indicate any significant variation in total amount of rare earth or in Ce/La ratio.

A better explanation can be found in the possibility of partitioning of rare earth elements between coexisting mineral phases. Such a phenomenon can be invoked for the chemistry of the Ce-depleted APS1 minerals which coexist with cerianite and Al-oxi-hydroxides. Indeed,

All these aforementioned minerals as well as kaolinite and iron hematite are well known to be the typical mineral assemblage of the continental alterites in tropical climatic conditions.

APS can be found in modern laterites (Seghal 1998; Sehnke 1993), and the presence of persevered Al oxy-hydroxide and CeO2 are also indicative of lateritic environments. In such

194

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. alterites, cerium, preferentially present in the Ce4+ oxidizing state (Braun et al. 1990), is rather incorporated in cerianite (CeO2) than in other minerals such as APS in which Ce is preferentially incorporated in the Ce3+ state. The above considerations lead us to interpret the specific crystal chemistry of the APS1 as an inheritage of their condition of formation during the paleoweathering (regolith) of the continental crust prior the formation of the Thelon basin.

In other words, such a geochemical signature confirms that dismantled regolith was involved in the source material of the sedimentation at the first filling stage of the basin.

The presence of coexisting REE-bearing phases has not been clearly identified in the case of the diagenetic APS2 which are characterized by low REE content and high Ce/La. Diagenetic fluorapatite has been identified elsewhere in the Thelon basin (Gall and Donaldson, 2006) but its REE content remains very low and no information on their Ce/La ratio is available.

However APS related to early diagenetic processes have been already documented in other siliciclasic basins in which other REE-bearing minerals can be present (Rasmussen, 1996, Pe-

Piper and Dolansky, 2005).

1.8.2. Crystal-chemical signature of the hydrothermal APS of the Kiggavik

area

The hydrothermal APS which coexist with illite and minor sudoite in the altered basement are characterized by a high LREE oxide content (13 to 26%) and a nearly constant Ce2O3/La2O3 ratio (between 1 and 2) which fits fairly well with the Ce2O3/La2O3 ratio of the parental

REE-bearing minerals which still persist in the unaltered basement rocks (Figure1-13, Table

1-3). This is indicative of the absence of rare earth elements fractioning during the hydrothermal alteration process and agree with the rather immobile behavior of these chemical elements which are essentially incorporated in the APS3 minerals which crystallize close to the site of primary LREE-bearing minerals dissolution (monazite, bastnaesite,

195

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. parasite …). The first consequence of this phenomenon is the preservation of the relative ratio of LREE, figure 1-14.

14

12 APS from altered basement

10 APS from sandstone cover APS from Thelon Fm (Gall 8 and Donaldson., 2006)

6 Ce2O3/La2O3 Ce2O3/La2O3 4

2

0 0 5 10 15 20 25 30 LREE (oxide wt%)

Figure 1-13 : Ce/La oxides ratio verus the sum of REE in APS minerals from the cover and the basement. Data from Gall & Donaldson, 2006 as a comparison for sandstone APS minerals

196

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada.

Figure 1-14 : Synthetic plot of composition field REE ratio for all APS minerals in the

Kiggavik area and the primary REE minerals

However, the major compositional variation of APS3 consists in their large range of total

LREE content which variation seems well correlated with the distance to the uranium mineralization. Such a variation has been already demonstrated in other unconformity related uranium deposits (Gaboreau et al., 2005, 2007) and is interpreted as a result of Eh-pH variations in the alteration system. Regarding the previous works made on the Eh/Ph control,

(Dill, 2001; Kolitsch and Ping, 2001), the evolution between the Svanbergite Sr-end member to the Florencite REE end of APS minerals can be interpreted as an evolution from low pH oxidizing to more reduced and higher pH conditions (Gaboreau et al., 2005). Then the fact that LREE-rich APS coexisting with secondary apatite crystallized close to the uranium orebodies whereas APS with lower LREE content were crystallized outer in the alteration halo is interpreted as the result of a time-space chemical evolution of the infiltrating fluid

197

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. which Eh and pH progressively change towards more reducing and more neutral conditions with increasing interaction with the minerals of the basement rock. Such a geochemical process could be the cause of the synchronous deposition of uranium mineralization and

LREE-rich APS in both the Athabasca and Kombolgie unconformity type uranium deposits

(Gaboreau et al., 2007, Beaufort et al., 2005 among others).

Finally the mass-balance calculation related to the hydrothermal alteration of basement rocks lead to a geochemical signature similar to the one found in unconformity type uranium deposits in the Athabasca Basin (Hoeve and Sibbald 1978; Quirt 1997; Ruzicka 1993) but also in the Amer Group uranium occurrences, (Miller and LeCheminant 1985) with among others an increase in Bi, Co, Mo, V, W & U. All these elements been described in the

Athabasca basins either associated to red bed or in lateritic profile to ferric iron hydroxides and thought to be a possible sources for these metals (Macdonald 1980; Mosser et al. 1985;

Wedepohl 1978).

All the above considerations lead us to interpret the crystal-chemical variations of the hydrothermal APS related to the uranium deposits in the Kiggavik Andrew lake structural trend as the consequence of the same geochemical processes than those already identified in basement-hosted unconformity-related uranium deposits worldwide.

1.8.3. Comparing the overall APS compositional field at Kiggavik with that

of unconformity-related uranium deposits worldwide

First of all one of the striking chemical feature observed previously in both Athabasca and

Kombolgie basin is a fairly continuous range of composition of APS mineral from zone proximal to mineralization to barren altered and finally the unaltered sedimentary rocks in the basins (Gaboreau et al, 2005, 2007). The compositional field is then going roughly from the

198

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. florencite end-member to the svanbergite end-member, disseminated along a steady slope given by the constant S/Sr ratio, in a Sr-LREE-S ternary diagram figure 1-15.

Figure 1-15 : Comparison of the compositional field of the APS mineral from the Kiggavik area (dotted lines) with those of APS minerals determined by Gaboreau et al. (2005, 2007) in both the Athabasca & Kombolgie basins .

On the opposite the in-situ chemical data gathered on APS mineral from the Kiggavik area shows two groups of minerals with different S/Sr ratio according to the fact that APS mineral are found in the altered basement or in the un-altered sedimentary cover. The first group of

APS in the altered basement, defines a composition envelop chemically very similar to that established in the Athabasca and Kombolgie basins. Then, as the conclusions of the first studies on alteration lead to relate the Kiggavik Andrew lake trend uranium deposits to an unconformity related type of mineralization, APS minerals had a similar forming history in these three basins when basement alteration is considered. The second group in the sandstones defines an envelope of composition which slightly overlaps the Athabasca trend nevertheless

199

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. with a steeper slope of the composition envelop. This highlights the predominant role of the

S/Sr ratio in the Thelon APS when the Sr/LREE explains more the composition variability in the Athabasca sandstones. Such chemical differences illustrates the chemical specificity of the

APS minerals of the basal sandstones of the Thelon formation which have been mostly preserved of the hydrothermal alteration related to the basement hosted uranium mineralization and highlight their interest as markers of the basin evolution prior the occurrence of the U-mineralizing hydrothermal event. Contrary to other unconformity-related uranium deposits, the APS minerals of the sandstones which locally overly the basement hosted uranium deposits of the Kiggavik area cannot be considered as reliable indicators of the deep seated mineralizing process because they are inherited minerals from the earlier basin history which have been preserved from hydrothermal alteration in an unaltered compartment.

Finally the geochemistry lead to the identification of geochemical signature of alteration similar to the one found in unconformity type uranium deposits in the Athabasca Basin

(Hoeve and Sibbald 1978; Quirt 1997; Ruzicka 1993) but also in the Amer Group uranium occurrences, (Miller and LeCheminant 1985) with among others an increase in Bi, Co, Mo, V,

W & U. All these elements been described in the Athabasca basins either associated to red bed or in lateritic profile to ferric iron hydroxides and thought to be a possible sources for these metals (Macdonald 1980; Mosser et al. 1985; Wedepohl 1978).

1.9. Conclusion

The concluding remarks of this study are :

(1) The similar trend of composition for hydrothermally related APS minerals in the basement and locally in the sandstone cover where illitization takes place. The chemical zonation

200

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. expressed in the LREE enrichment is the same as in the Athabasca and the Kombolgie unconformity type uranium mineralization occurrences.

(2) To confirm and implement the knowledge of the relationship between the hydrothermal

APS and the ones related to an early diagenetic stage during the basin evolution, similar to the

APS cementation observed in Paleozoic siliciclastic basins, (Pe-Piper and Dolansky 2005).

Moreover the chemical composition of sedimentary cover APS is pro parte in a similar trend than APS minerals observed in other location within the Thelon. However, new evidence leads to the identification of pre diagenesis APS minerals. This features, enhanced here by the pristine conservation of the most early sedimentation stages would be very likely the same in the Athabasca Basin, in place with no later alteration overprint.

These two facts lead to the conclusions that APS should be observed as markers of a long lived evolution of the basin some being related to the mineralization and alteration events in a range of temperature in the range of hydrothermalism, somehow link to thermal peak during the diagenesis when the others are the relicts of laterites related to the paleoweathering, as well as witness of the early cementation during diagenesis.

Finally, APS minerals unique mineralogical markers able to record equally the early processes related to the sedimentation and diagenesis of these Meso-Proterozoic basins. Nevertheless their complex history doesn’t allow the use of the APS minerals as direct mineralogical pathfinders to alteration and then mineralization.

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Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada.

1.10. References

Braun J-J, Pagel M, Muller J-P, Bilong P, Michard A, Guillet B (1990) Cerium anomalies in lateritic profiles. Geochimica et Cosmochimica Acta 54:781-795. doi: http://dx.doi.org/10.1016/0016- 7037(90)90373-S. Beaufort, D., Patrier, P., Laverret, E., Bruneton, P., and Mondy, J., 2005, Clay Alteration Associated with Proterozoic Unconformity-Type Uranium Depositsin the East Alligator Rivers Uranium Field, Northern Territory, Australia: Economic Geology, v. v. 100, p. pp. 515–536. Cloutier J, Kyser K, Olivo GR, Alexandre P (2010) Contrasting Patterns of Alteration at the Wheeler River Area, Athabasca Basin, Saskatchewan, Canada: Insights into the Apparently Uranium- Barren Zone K Alteration System. Economic Geology 105:303-324. doi: 10.2113/gsecongeo.105.2.303. Dill, H.G., 2001, The geology of aluminium phosphates and sulphates of the alunite group minerals: a review: Earth-Science Reviews, v. 53, p. 35-93. Gaboreau, S., Beaufort, D., Vieillard, P., Patrier, P., and Bruneton, P., 2005, Aluminum phosphate- sulfate minerals associated with Proterozoic unconformity-type uranium deposits in the East Alligator River Uranium Field, Northern Territory, Australia: Canadian Mineralogist, v. 43, p. 813-827. Gaboreau, S., Cuney, M., Quirt, D., BEAUFORT, D., PATRIER, P., and Mathieu, R., 2007, Significance of alumium phosphate-sulfate minerals associeted with U unconformity-type deposits: The Athabasca basin, Canada: American Mineralogist, v. 92, p. 267-280. Gall, Q., and Donaldson, J.A., 2006, Diagenetic fluorapatite and aluminum phosphate-sulphate in the pPelaoproterozoic Thelon Formation and Hornby Bay Groupe, northwestern Canadian Shield: Canadian Journal of Earth Sciences, v. 43, p. 617-629. Hartlaub, R.P., Heaman, L.M., Ashton, K.E., and Chacko, T., 2004, The Archean Murmac Bay Group: evidence for a giant Archean rift in the Rae Province, Canada: Precambrian Research, v. 131, p. 345-372. Hasegawa K, Davidson GI, Wollenberg P, Yoshimasa I (1990) Geophysical exploration for unconformity-related uranium deposits in the northeastern part of the Thelon Basin, Northwest Territories, Canada. Mining Geology 40:83-95. Herold, H., 1987, Zur Kristallchemie und Thermodynamik der Phosphate und Arsenate vom Crandallit-Typ., Erlangen University.

Hoeve J, Sibbald TII (1978) On the genesis of the Rabbit Lake and other unconformity-type uranium deposits in Northern Saskatchewan, Canada. Economic Geology 73. 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, Saskatchewan Research Concil Technical report, Volume 197, Saskatchewan Reasearch Council, p. 197. Hoffman, P.F., 1990, Subdivision of the Churchill Province and extent of the Trans-Hudson orogen, in Lewry, J.F., and Stauffer, M.R., eds., The Early Proterozoic Trans-Hudson Orogen of North Amercia, Volume 37: Special paper, Geological Survey of Canada Special Paper, p. 15-39.

202

Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. Jefferson, C.W., Thomas, D.J., Gandhi, S.S., Ramaekers, P., Delaney, G., Brisbin, D., Cutts, C., Portella, P., and Olson, R.A., 2007, Unconformity-associeted uranium deposits of the Athabasca Basin, Saskatchewan and Alberta, EXTECH IV, Volume Geology and Unranium EXploration TECHnology of the Proterozoic Athabasca Basin, Saskatchewan and Alberta, p. 23-67. Kolitsch, U., and Ping, 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, p. 67-78. Macdonald R (1980) Mineralogy and geochemistry of a Precambrian regolith in the Athabasca Basin. University of Saskatchewan, Saskatoon, pp 151. Miller AR (1983) A progress report: uranium phosphorus association in the Helikian Thelon Formation and Sub-Thelon saprolite, central district of Keewatin, NWT. Current Research GSC 83- 1A:449-456 Miller, A.R., and LeCheminant, A.N., 1985, Geology and uranium metallogeny of Proterozoic supracrustal successions, central District of Keewatin, N.W.T with comparisons to northern Saskatchewan, Geology of uranium deposits, Volume Special Vol. 32, Canadian Institute of Mining and Metalurgy, p. 167-185. Mosser C, Leprun JC, Blot A (1985) Les éléments traces des fractions < 2 m à kaolinite et smectite formées par altération de roches silicatées acides en Afrique de l'Ouest (Sénégal et Haute- Volta). Chemical Geology 48:165-181. doi: http://dx.doi.org/10.1016/0009-2541(85)90044-0. 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. Pehrsson, S., Jefferson, C.W., Peterson, T.D., Scott, J., Chorlton, L., Hillary, B., Patterson, J., Lentz, D., Shelat, Y., and Bethune, K., 2010, Basement to the Thelon Basin, Nunavut- Revisited, GeoCanada2010: Calgary. Peterson, T.D., Van Breemen, O., Sandeman, H., and Cousens, B., 2002, Proterozoic (1.85-1.75 Ga) igneous suites of the Western Churchill Province: granitoid and ultrapotassic magmatism in a reworked Archean hinterland: Precambrian Research, v. 119, p. 73-100. Quirt D (1997) Athabasca Basin Uranium metallogenic model Thermotectonic and uranium metallogenic evolution of the Wollaston EAGLE project Area. Saskatchewan Research Council, Saskatoon, pp 1-41. Rainbird, R.H., and Davis, W.J., 2007, U-Pb detrital zircon geochronology and provenance of the late Paleoproterozoic Dubawnt Supergroup: Linking sedimentation with tectonic reworking of the western Churchill Province, Canada: Geological Society of America Bulletin, v. 119, p. 314- 328. Rainbird, R.H., Hadlari, T., Aspler, L.B., Donaldson, J.A., LeCheminant, A.N., and Peterson, T.D., 2003, Sequence stratigraphy and evolution of the Paleoproterozoic intracontinental Baker Lake and Thelon basins, western Churchill Province, Nunavut, Canada: Precambrian Research, v. 125, p. 21-53. 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 VR (1993) Unconformity type uranium deposits In: Kirkham RV, Sinclair WD, Thorpe RI, Duke JM (eds) Mineral Deposit Modeling. Geological Survey of Canada, Ottawa, pp 125-149. Stoffregen, R.E., 1993, Stability relations of jarosite and natroalunite at 100–250°C: Geochimica et Cosmochimica Acta, v. 58, p. 903–916. Stoffregen, R.E., and Alpers, C.N., 1987, Woodhouseite and svanbergite in hydrothermal ore deposits: products of apatite destruction during advanced argilic alteration: Canadian Mineralogist, v. 25, p. 201-211. Seghal J (1998) Red and lateritic soils. Rotterdam.

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Spatial distribution and compositional variation of APS minerals related to uranium deposits in the Kiggavik Andrew lake structural trend, Nunavut, Canada. Sehnke E (1993) REFRACTORY-GRADE BAUXITE: AN OVERVIEW- 1993 Unitecr'93 Congress Refractories for the New World Economy Proc Conf Sao Paulo, 31 October-3 November 1993. pp 658-670. Wedepohl KH (1978) Handbook of Geochemistry I, II. Springer Verlag, Berlin, New York.

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Nature and stability of radiation induced defects in natural illite new results and implications for ancient radioelement mobility 2. Nature and stability of radiation induced defects in natural illite new results and implications for ancient radioelement mobility

Riegler, Thomas; Allard, Thierry; Beaufort, Daniel. in preparation for submission to Physics and Chemistry of Minerals

2.1. Introduction

Illite is a common clay mineral, widespread in various geological contexts from soils, to sedimentary basins or hydrothermal systems. It is formed of a tetrahedral-octaedral-tetraedral layered structure, with a closed interlayer space occupied by potassium ions. Radiation induced defects (RIDs) spectrum, relatively similar to kaolinite has been identified in illite subject to artificial or natural irradiation. For the latter similar EPR signal were recorded in naturally irradiated illite coming from alteration halos associated with Paleo-Proterozoic uranium deposits in the Athabasca Basin in Canada (Allard et al. 2003; Morichon et al. 2008).

In both cases, in comparison with the extensive data available on kaolinite, the defects in these illites tend to present a smaller thermal stability. In addition the EPR spectrum showed very often a different look compared to kaolinite with a broader signal and very unclear expression of the A, A’ and B centers corresponding to defects in the signal (Allard et al.

2012; Morichon 2008). Then it is critical to have a better understanding of the expression and properties of radiation induced defects in illite, especially when old and long-lived open geological systems are considered. In such systems numerous events ( e.g. thermal, multiple radionuclide migrations) are superimposed over very long and short term periods from billons years to the actual and illite can be considered as a natural dosimeter. So refinements in the contribution of the short half life defects such as the A’ & B center in addition to the permanent A center defects in the total RIDs content would be critical to decipher the radio- elements migrations over time.

205

Nature and stability of radiation induced defects in natural illite new results and implications for ancient radioelement mobility The newly acquired data tends to make illite properties more similar to kaolinite than previously thought, in term of spectra and stability properties. Then, addition to previous authors work, we propose to revise and implement the knowledge of radiation induced defects in illite. In this work a naturally irradiated illite formed in an unconformity related deposit was studied with X & Q-bands hyperfrequencies on natural and annealed samples in order to :

(1) get a better estimation on the thermal stability of RIDs, (2) assess this stability throughout geological times and (3) refine the spectrum signature, and assign to it the contribution of the different defects centers. All these properties are critical to refine interpretations of the radioelement’s mobility and its signature in clay minerals, as around uranium deposits for both exploration and environmental considerations.

2.2. Sampling

Sample selection have been made in a larger data set of about 60 samples samples from illite

& sudoite rich alteration zones developed in the Woodburn lake Group, Archean volcano- sedimentary sequence hosting unconformity related uranium mineralization, in the Kiggavik area, Nunavut, Canada. The age of alteration related to the ore formation is yet relatively poorly constrained within 1.2-1.4 Ga on historical illite K/Ar geochronological data (Miller et al. 1989).

The majors’ constraints were to obtain a pure illite sample with a high concentration of radiation defects in which the distinct components of the Electron Paramagnetic Resonance spectrum are presents. This data screening (XRD followed by X-band EPR) lead to the selection of the BG814 sample for further characterization of the Electron Paramagnetique

Resonance (EPR) signature of radiation induced defects in illite. The interest of this peculiar sample is its strong and well defined defect spectra.

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Nature and stability of radiation induced defects in natural illite new results and implications for ancient radioelement mobility 2.3. Methods

All altered bulk rock samples were dispersed in deionzide water and the clay minerals extracted by sedimentation in order to obtain the infra 4 micrometer size fraction. Clay minerals identification and crystallographic properties were determined using X-ray diffraction (XRD) on oriented slides and randomly oriented powders, following the preparation methods given in (Brindley and Brown 1980). A D8 Advance Bucker diffractometer equipped with a Cu anode was used for X-ray diffraction and analytical conditions were set with a 40kV acceleration tension and 40mA current, and 1° fixed divergence slit. Data collection scan parameters were 2-30 (oriented slides) or 19-30 (random mounts) degrees 2theta both with a 0.01° 2theta step and 1 or 5 second counting time. In addition to XRD, chemical analysis major elements using SEM-EDS on on clay pellets separates were carried in order to recalculate the mineral proportion during sample selection phase.

Electron paramagnetic resonance spectra of RID were observed at X- (≈ 9.βGHz) and Q- bands (≈ 35GHz) and room temperature (20°C) using a Brucker EMXplusTM spectrometer on both natural and annealed illite. The use of an higher frequency as in the Q-band allows lower detection limits, and gives better resolved spectra by increasing the gap between spin levels

(Calas and Hawthorne 1988). The acquisition parameters were 1 G amplitude and a 327 ms time constant and microwave power of 40mW in X-bands.

All spectrums were normalized to sample mass, volume occupied in resonance cavity and acquisition gain. In addition EPR spectrums were labelled by their effective spectroscopic factor g values defined by the follow formula: h * = g * β * Ho. The different parameters being: h the Plack constant; the resonance frequency; g the Landé factor, a tensor with the eigenvalues: gxx, gyy, gzz calibrated by comparison with a 2,2 diphenyl-1picrylhydrazyl

207

Nature and stability of radiation induced defects in natural illite new results and implications for ancient radioelement mobility standard of known g value (gDPPH = 2.0036); β the Bohr magneton and Ho the external magnetic field. The accuracy on magnetic field and g-values measurements were respectively

Ho = 1G, and g 0.001. It must be noted that only the g values can be compared due to the frequency dependence of the magnitude and magnetic field positions of the resonances.

Concentrations are expressed in arbitrary units’ proportion to the number of spins per gram of clay.

2.4. Annealing Experiments protocol

With a similar approach to the work carried on kaolinite step annealing was used in order to differentiate RIDs in illite (Clozel et al. 1994). The isochronal annealing was carried out for 2 hours at 100°C intervals form 100 to 600°C, in order to define the thermal conditions for the individualization of the different defects center spectra. In addition the lifetime of some of the most stable defect centers were investigated with isothermal annealing experiments and were performed at 400°C and 450°C from 30 minutes up to 134 hours. Regarding data on kaolinite these center are thought to be stable over geological times under the Earth’s surface thermal regime and then of great interest to trace ancient irradiations. Then illite could be considered as a natural dosimeter.

A particular attention was given to the samples preparation for experiments in order to get accurate and reproducible annealing temperatures. Each sample consists in a few 10s of milligrams of illite, sieved at 50 micrometer and wrapped in aluminum foil and placed in a regulated furnace equipped with a PID controller. Sampled were sieved a second time in order to get randomly oriented powder in the Suprasil high purity silica glass capillaries used as sample holder in the resonance cavity.

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Nature and stability of radiation induced defects in natural illite new results and implications for ancient radioelement mobility 2.5. Results

2.5.1. EPR parameters of defects in illite

As a first approach natural and annealed illites were studied in X-band in order to identify the spectroscopic factors characteristic (g values) of the radiation induced defects in illite (A, A’ and B centers), figure 2-1a. Then, spectrums were obtained on natural illite and their annealed equivalent to be able to identify the characteristic of the A center defects. In the natural sample, 5 spectroscopic factors were identified respectively at 2.063, 2.050, 2.037,

2.013 and 2.002; while only 4 were present in the annealed illite at 2.063, 2.051, 2.011 and

2.002. It can already be noted that very little shift is present in the g-values positions between the natural and annealed samples. In addition the intensity ratio of the bands doesn’t seems affected by heating and the band at 2.063 could be very similar to the N1 defect described in montmorillonite in term of g-value and annealing temperature around 500°C, figure 2-1b

(Sorieul et al. 2005). Finally the EPR signal for naturally irradiated illite from the Kiggavik area shows similar spectroscopic parameters with a well expressed A center defect as well as the presence of less stable ones in the 2.037 region possibly resulting from the superimposed signal of the A’ and B centers.

Then, in addition to the illite EPR signal characterization, the stability and temperature dependant kinetics of decay were experimentally tested by both isochronal and isothermal annealing the latter being used to estimate the half life (t1/2) and the activation energy of Ea

(eV) of the A center defect in illite.

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Nature and stability of radiation induced defects in natural illite new results and implications for ancient radioelement mobility

Figure 2-1 : EPR spectra of defects in natural (a) and annealed illite (b) at X-Band (9.4GHz). DPPH (2,2

diphenyl-1picrylhydrazyl) is a standard compound with known g factor

2.5.2. Stability of the radiation induced defects in illite

First the stability of the radiation induced defects contents can be assessed using the overall defect content via double integration of the EPR signal in complement to the defect spectra evolution across the temperature range selected for annealing, Figure 2a & 2b. The annealing curve, indicate a sharp decrease in both the defects content as well as a clear diminution of the

2.037 spectroscopic factor at low temperature below 100 °C. From then to around 350°C the

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Nature and stability of radiation induced defects in natural illite new results and implications for ancient radioelement mobility defects concentration is increasing by about 30% and is marked by a continuous decrease of the 2.037 component and an increase of the 2.050, 2.011 and 2.002 g- values. Such behaviour is similar to the one observed in kaolinite and various materials and due to electron transfers during the annealing experiments (Griscom 1984; Hennig and Grün 1983). With increasing annealing temperature the total defects concentration decreases sharply for temperature higher than 450°C. Finally the total concentration evolution is a balance between at first below 400

°C the healing of the less stable with electron transfers phenomenon’s as a result of thermal activation and in a second time the healing of the most thermally stable defects, which present the g values characteristic of the center A type defects. Finally the A center appears to be stable at until temperatures reaches field of clay mineral deshydoxylation temperature in which the crystalline structure is affected. Then we propose to investigate the intrinsic properties of these centers in illite via isothermal annealing experiments.

Figure 2-2 : Isochronal annealing experiments, 2hours from 100 to 600°C

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Nature and stability of radiation induced defects in natural illite new results and implications for ancient radioelement mobility

Decay processes are generally described using first (Arrhenius) or second order equations

-Kt (Furetta 1988). The first order formula can be written: [A] = [A0]e , where the different parameters are: [A] is the instantaneous defect concentration (a.u.), [A0] the intial concentration , t the time of decay and K the probability of decay per second. This probability

-1 -Ea/kT parameters itself is expressed by the following relation K = (t1/2) Ln2 = so.e , where s0 is the frequency factor, usually in the range 108 - 1010 s-1 (Marfunin 1979), k the Boltzman constant (k =8.6 10-5 eV.K-1) and T the temperature (K). Then it appears that the half life of the defect in only temperature dependant and two isotherms would be required to determine the activation energy. The second order decay law is more suitable for more complexes mechanisms (transit stage or retrapping) that may occur during the decay processes, and can

-1 -1 -1 -Ea/kT be written as : [A] = K.t+[A0] with K = tgθ = (t1/2 . [A0]) = s0.e or lnK= Ln s0-

(Ea/k)T-1 with θ is the slope of the linear curve. In this case the half life temperature and time dependant.

Both first and second order equations were used to describe the isothermal annealing of the A- center in illite. Curves were plotted for the BG814 sample in the figure 2-3, in which the defect and the A center are particularly abundant. The decay curves, present two distinct tends with at first a rapid decrease of the defects concentration within the first 8 hours of annealing followed by a steady decreasing phases over the all annealing time span. Then, this behaviour might be related to the healing of the least stable components of the defects signal, as the A’ and B centers. Thereafter this rapid decay stage it can be assumed that the total defect concentration represent the A center concentration. In both cases at 400 and 450°C annealing temperatures, the second order law gives the best description of the data, figure 2-

3a. In addition the annealing curves, figures 2-3b, allowed the graphic determination of the center-A properties with a maximal range of 1.9 to 49 109 years for the half life and activation

212

Nature and stability of radiation induced defects in natural illite new results and implications for ancient radioelement mobility energies between 1.0 and 1.4 eV when estimation were made using both first and second order decay laws, Table 2-1. Moreover, as the second order law tends to give the best data description, the activation energy and half life at 15°C are a little bit lower than the ones obtained on kaolinite but within similar orders of magnitude (Clozel et al. 1994).

b

a

Figure 2-3 : Isothermal annealing experiments at 400 and 450 isotherms. The decay law is described by a second order kinetics. The fitting of the isotherms in the 1/[A] plot and the slope of the curves provides values of the temperature dependant decay constant K(h-1). The activation energy and the half life are estimated and deduced from decay equations.

213

Nature and stability of radiation induced defects in natural illite new results and implications for ancient radioelement mobility Table 2-1 : A center properties, half life (years) and activation energy (eV) estimated at 15°C for both first and second orders decay laws.

1st order 2nd order

-1 s0(s ) t1/2 @ 15°C t1/2 @ 15°C

108 3.9E+09 1.9E+09

1010 4.9E+10 2.9E+10

Ea (eV) 1.0 - 1.2 1.3 - 1.4

2.6. Preliminary discussion and concluding remarks

Additional electron paramagnetic resonance spectroscopy results in Q band couldn’t be added to this final version of the manuscript. These new data will potentially allow a more accurate identification of the radiation induced defects acciociated with illite and implement the current results.

To date, the two major contributions form the present work are (1) the identification of a singular EPR signal in naturally irradiated illite possibly linked to a type of radiation induced defect specific to illite, and (2) the determination of the physical properties of such defect.

Thus, the radiation induce defects in illite seem similar to the A center defect, both in term of

EPR spectra and physical properties (e.g. stability), to the ones in kaolinite or montmorillonite. This similarities could be explained by the nature of the defect and linked to an electronic vacancy on a Si-O bond. Therefore, the type of sheet assemblage between the tetrahedral and octaedral layers in the different clay minerals could have no influence on the defect itself as the control for the decfect is a the atomic bond scale.

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Nature and stability of radiation induced defects in natural illite new results and implications for ancient radioelement mobility Finally, the identification of defect stable at the scale of geological times (like center A defect) as well as others less stable (A’, B centers) is critical to attempt to discriminate recent and ancient radioelement circulations.

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Nature and stability of radiation induced defects in natural illite new results and implications for ancient radioelement mobility 2.7. References

Allard T, Ildefonse P, Del Villar LPr, Sorieul Sp, Pelayo M, Boizot B, Balan E, Calas G (2003) Radiation-induced defects in dickites from the El Berrocal granitic system (Spain): relation with past occurrence of natural radioelements. European Journal of Mineralogy 15:629-640. Allard T, Balan E, Calas G, Fourdrin C, Morichon E, Sorieul S (2012) Radiation-induced defects in clay minerals: A review. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 277:112-120. doi: http://dx.doi.org/10.1016/j.nimb.2011.12.044. Brindley GW, Brown G (1980) Crystal structures of clay minerals and their X-ray identification. Mineralogical Society, London, UK. Calas G, Hawthorne FC (1988) Introduction to spectroscopic methods. Reviews in Mineralogy and Geochemistry 18:1-9. Clozel B, Allard T, Muller J-P (1994) Nature and stability of radiation-induced defects in natural kaolinites: new resulats and a reappraisal of published works. Clays and Clay Minerals 42:657-666. Furetta C (1988) New calculations concerning the fading of thermoluminscent materials. Nucl Tracks Radiat Meas 14:413-414. Griscom DL (1984) Characterization of three E'-center variants in X- and γ-irradiated high purity a-SiO2. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 1:481-488. doi: http://dx.doi.org/10.1016/0168-583X(84)90113-7. Hennig GJ, Grün R (1983) ESR dating in quaternary geology. Quaternary Science Reviews 2:157-238. doi: http://dx.doi.org/10.1016/0277-3791(83)90006-9. Marfunin AS (1979) Spectroscopy, Luminescence and Radiation Centers in Minerals. Springer Verlag, Berlin, Heidelberg, New York. Miller AR, Cumming GL, Krstic D (1989) U-Pb, Pb-Pb, and K-Ar isotopic study and petrography of uraniferous phosphate-bearing rocks in the Thelon Formation, Dubawnt Group, Northwest Territories, Canada. Canadian Journal of Earth Sciences 26:867-880. Morichon E (2008) Les défauts d'irradiation dans les minéraux argileux: des marqueurs de la mobilité de l'uranium dans le contexte des gisements d'uranium associés à une discordance. Thèse Université de Poitiers, pp 297. Morichon E, Allard T, Beaufort D, Patrier P (2008) Evidence of native radiation-induced paramagnetic defects in natural illites from unconformity-type uranium deposits. Phys Chem Minerals 35:339-346. doi: 10.1007/s00269-008-0227-5. Sorieul S, Allard T, Morin G, Boizot B, Calas G (2005) Native and artificial radiation- induced defects in montmorillonite. An EPR study. Phys Chem Minerals 32:1-7. doi: 10.1007/s00269-004-0427-6.

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Nature and stability of radiation induced defects in natural illite new results and implications for ancient radioelement mobility

C. DISCUSSION GÉNÉRALE, CONCLUSIONS ET PERSPECTIVES

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Discussion générale

1. Discussion générale

La genèse d’un gîte métallique implique la succession d’une série d’étapes de pré- concentration, libération, transport, dépôt et enfin de préservation des minéraux formant le minerai d’intérêt économique. Les gisements d’uranium associés aux discordances du

Protérozoïque s’inscrivent eux aussi dans ce schéma, depuis les processus de différenciation magmatique à l’origine des sources primaires de l’uranium, aux divers processus superficiels qu’ils soient sédimentaires, diagénétiques ou hydrothermaux à l’origine des concentrations

économiques d’uranium (Cuney 2010). L’ensemble des données acquises à l’échelle du faisceau structural de Kiggavik-Andrew Lake dans ce travail permet d’identifier certaines de ces étapes et processus.

On peut replacer la formation des minéralisations en uranium de la bordure Sud-Est du bassin

Protérozoïque moyen du Thelon dans un cadre métallogénique plus large à l’échelle du bouclier Canadien. Il s’agira tout d’abord de retracer l’histoire des altérations ayant successivement affecté le district de Kiggavik afin de comprendre comment elles ont pu contribuer, par incrément, à la formation des minéralisations en uranium. Cela amènera à considérer les conditions physico-chimiques à l’origine des signatures minéralogiques propres

à chaque environnement, en considérant ses implications en termes de source, transport ou de piège de l’uranium. Enfin l’ensemble sera replacé dans le contexte géodynamique global ayant conduit à la formation des bassins intracontinentaux hôtes des minéralisations et contraint du point de vue temporel à l’aide d’éléments de géochronologie.

Au vu des données présentées dans ce mémoire, il est possible de proposer un schéma retraçant l’évolution géologique de la zone de Kiggavik au cours de la vaste période (1800-

1100Ma) qui couvre l’histoire de cette région, de l’initiation du processus sédimentaire lié à la mise en place du bassin du Thelon à la fin des épisodes d’altération argileuse associés à la

218

Discussion générale mise en place ou au remaniement de la minéralisation uranifère Figure 1-2. Enfin, chacune des étapes sera mise en parallèle avec les connaissances actuelles des gisements du bassin

Meso Proterozoique de l’Athabasca qui constitue une référence en termes de gisement d’uranium associé à une discordance Paléoprotérozoique.

1.1. Histoire des événements d’altération

On peut tout d’abord noter que la mise en place des minéralisations s’inscrit principalement dans le cycle orogénique Hudsonien. On peut alors mettre en parallèle les différents

événements d’altération et les grands événements géologiques ayant affecté la zone de

Kiggavik, depuis les événements tardi-orogéniques Hudsonien jusqu’à la mise en place des minéralisations uranifères.

1.2. Evénements précoces Hudsoniens

Ils regroupent à la fois les réactivations des grandes structures crustales Archéennes lors de l’orogenèse Husdonienne ainsi que tous les stades post-orogéniques. Il s’agit à la fois de la rétromorphose dans le faciès schiste vert des roches du socle métamorphique de la zone de

Kiggavik et de la mise en place d’un système de veines de quartz de haute température soulignant les failles régionales Est-Ouest. Elles sont identifiées dans la zone d’End Grid dans cette étude, mais aussi dans le gisement d’Andrew Lake (Pagel and Ahamdach 1995). On peut aussi rattacher à ces épisodes tardi- métamorphiques les évidences d’altération propylitique exprimée sous la forme de veinules d’épidotes et/ou d’adulaire localement. Cette structuration, permet de mettre en place les grandes discontinuités qui pourront par la suite

être réactivées et former les principaux drains empruntés par les fluides minéralisateurs qui contrôlent la localisation des minéralisations (Annesley et al. 1995; Annesley et al. 1996;

Beaudemont and Fedorowich 1996). De plus la mise en place des corridors brêchiques à remplissage de quartz, contribue à créer des zones de contraste rhéologiques, qui seront importantes pour contrôler l’ouverture des discontinuités (zone mylonitique, foliation) ou des

219

Discussion générale fractures. Dans le bassin de l’Athabasca de nombreux gisements d’importance économique sont eux aussi situés aux interfaces entre deux lithologies aux propriétés mécaniques contrastées. Parmi ceux-ci, on peut citer les dômes de gneiss au contact des roches supra- crustales de la ceinture de Wollaston (Yeo and Delaney 2007), de même que le contraste existant entre les quartzites et les autres métasediments, parfois graphitiques, de cette ceinture de plis et chevauchements.

A cette structuration s’ajoutent les phénomènes propres à l’effondrement de l’orogène

Hudsonien tel que la genèse de granites peralumineux par le biais de la fusion crustale lors de la phase d’extension post orogénique, puis la mise en place des syénites et des granites anorogéniques de la suite Nueltin (Van Breemen et al. 2005; Peterson et al. 2002).

Figure 1-4 : Rapport Th/ U des intrusions Hudsoniennes et Nueltin, d’après Van Breemen, β005

Les phases de fusion crustale de roches alumineuses permettent par ailleurs d’aboutir à des roches plus différenciées et ainsi enrichir la croûte en uranium, comme c’est le cas dans l’Est du bassin de l’Athabasca (Annesley and Madore 1999). Toutefois il semble que tous les

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Discussion générale granites Hudsonien ne soient pas tous aussi fertiles en uranium (Van Breemen et al. 2005),

Figure 1-1. Le granite de Kiggavik entre dans cette catégorie de granite faiblement fértile

(Weyer et al. 1987). Toutefois, et à contrario de ce qui est observé dans l’Est du bassin de l’Athabasca, on ne retrouve pas d’évidence de pegmatites à uraninite à Kiggavik. Cette fertilité moindre peut s’expliquer par une différence de nature des protolithes, les métasédiments pélitiques du Wollaston étant plus riches en uranium que les séries de l’Amer ou du Ketyet River Group, principalement constituées de quartzites et d’arkoses. Par ailleurs, les métagraywackes de la ceinture de roche verte du Woodburn lake Group sont particulièrement pauvres en U (<3 ppm U).

Dès le stade Hudsonien, il apparaît donc, des différences marquées entre le bassin d’Athabasca et la bordure Sud Est du bassin du Thelon en ce qui concerne le potentiel métallogénique des protores pour alimenter des gisements liés à la discordance bassin-socle.

Dans la région de Kiggavik, les sources de l’uranium pourraient être reliées aux tuffs ryholitiques du groupe de Wharton déposés lors de la mise en place du bassin de Baker Lake.

Ceux-ci pourraient avoir formé alors une source régionale associée ponctuellement à des sources « plutoniques » plus locales tels que les granitoïdes et les syénites du socle.

221

Discussion générale

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Discussion générale

Figure 1-5 : Reconstitution schématique de l’évolution des processus géologiques dans les roches situées au voisinage de la discordance paleoprotérozoïque dans la zone de Kiggavik.

1.3. Mise en place du profil d’altération Pré-Thélon

L’existence d’un régolithe ayant transformé la partie superficielle des roches du socle avant la mise en place des premiers sédiments silcoclastiques des bassins de l’Athabasca et du

Thelon a été évoquée par de nombreux auteurs sur la base d’évidence minéralogiques

(kaolinite, diaspore, hematite, phosphate sulfates d’aluminium hydratés) et pétrographiques

(Macdonald 1980; Pagel 1975; Cecile 1973). Les études pétrographiques et minéralogiques présentées dans ce mémoire démontrent que tous les minéraux index des altérites continentales de type latérite ou bauxite sont présents dans la matrice sédimentaire des premiers remplissages de conglomérats et de grès grossiers qui subsistent dans la région de

Kiggavik (kaolinite riches en fer, hématite, oxy-hydroxydes d’aluminium, oxydes de cérium et de thorium, ainsi que des phosphate-sulfate d’aluminium). Ces observations nous conduisent à interpréter ces premières formations sédimentaires comme des produits issus de l’érosion et démantèlement de la surface régolithisée des roches métamorphiques et magmatiques environnantes. La très faible concentration en uranium des premiers dépôts sédimentaires qui ont été préservés de l’altération hydrothermale (0,3 à 0,7 ppm) suggère une mobilité précoce du stock potentiel d’uranium issu des processus de régolithisation des roches du socle. Dans l’état d’avancement de nos connaissances sur les transferts géochimiques effectifs pendant la phase de sédimentation précoce du bassin du Thelon à Kiggavik, il semble prématuré d’établir un lien entre l’uranium mobilisé pendant ce phénomène précoce et les corps minéralisés actuels. On peut cependant mentionner des résultats préliminaires de travaux de spectroscopie de résonance paramagnétique électronique sur la kaolinite des formations sédimentaires basales du bassin du Thelon qui indiquent des concentrations de défauts d’irradiation élevées dans la région de Kiggavik qui ne sont pas en accord avec les

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Discussion générale concentrations actuelles en radio-éléments. De tels défauts pouvant être la conséquence du passage de fluides riches en radioélements comme cela a déjà été démontré dans le bassin d’Athabasca (Morichon 2008; Morichon et al. 2008; Morichon et al. 2010). Des travaux complémentaires seront nécessaires pour évaluer l’importance de ces migrations qui ont dû se produire a un stade très précoce de l’histoire du bassin du Thelon, avant la cimentation des grès et le confinement de l’ensemble des minéraux détritiques par le quartz microcristallin.

1.4. Diagenèse et évolution du bassin du Thelon

Dans le continuum d’évolution des bassins intracratoniques Protérozoïques, l’histoire diagénétique apparait prolongée pour aboutir à des conditions de diagenèse poussée (Patrier et al. 2003; Beaufort et al. 2005; Jefferson et al. 2007). La profondeur maximale d’enfouissement est alors estimée à environ 5km sur la base de données d’inclusions fluides

(Pagel 1975) ou du stade de transformation en dickite des minéraux du groupe kaolin

(Beaufort et al. 1998; Lanson et al. 2002). Cette évolution permet aux saumures de bassins oxydantes de remobiliser et transporter l’uranium en solution. Les données nouvellement acquises sur l’ordre/désordre, des kaolinites recristallisées de la base du bassin ainsi que les fractures à dickite indiquent également que dans la zone de Kiggavik les formations basales du bassin du Thelon ont subi un enfouissement similaire à ce qui a été évoqué dans le bassin d’Athabasca ou bien même dans les grès de Kombolgie en Australie (environ 5km ). De plus, on peut noter que les inclusions fluides triphasées à cube de halite observées dans les veines de quartz et surtout les dolomites du socle indiquent des paléotempératures aux alentours de

200 °C qui sont en accord avec la transition complète de la kaolinite en dickite dans les roches gréseuses comme cela a été observée dans les grès de Kombolgie (Patrier et al., 2003) et des salinités semblables à celles des saumures minéralisatrices connuesdans le bassin de l’Athabasca (Derome 2002; Pagel and Jaffrezic 1977).

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Discussion générale

Certaines caractéristiques des grès telles que les ciments phosphatés (Gall and Donaldson

2006), ainsi que les surcroissances de quartz (Hiatt et al. 2003; Hiatt et al. 2010) ou la présence de feldspaths potassiques néoformés (Renac et al. 2002) n’ont pas été retrouvées dans cette étude. On doit néanmoins prendre en compte le fait que ces travaux ne concernent que les roches sédimentaires de la base des grès du Thelon. Les ciments phosphatés ou les illites qui ont été mentionnés plus haut dans la série sédiementaire du bassin du Thélon par ailleurs peuvent avoir été érodés. La préservation de kaolinite détritique non illitisée dans les grès situés à la base du bassin n’est pas limitée à Kiggavik. En effet, celle-ci a déjà été mise en évidence à la base du bassin de l’Athabasca, dans la région de Shea Creek (Uri 2012).

Enfin, les températures calculées à partir de la composition isotopique de l’oxygène des illites néoformées des grès du Thelon par ces mêmes auteurs sont cohérentes avec celles obtenues à

Kiggavik dans le halo d’altération associé à la minéralisation de Bong (Sharpe 2013). Elles se situent aux alentours de 200°C, en cohérence avec les données microthermométriques de notre étude. Il est alors envisageable que la partie basale du bassin du Thelon étudiée dans la zone de Kiggavik appartienne à un compartiment du bassin qui a été préservé de l’altération hydrothermale à illite et sudoite. Ce type de compartiment se révèle très intéressant pour recueillir des informations originales sur l’histoire précoce (sédimentaire puis diagénétique) qui a précédé l’évènement d’altération hydrothermale régionale auquel sont associés les gisements d’uranium qui sont présents dans les roches de socle.

1.5. Altération hydrothermale et mise en place de la minéralisation

La prise en compte des saumures et de leur température amène naturellement à considérer leur interaction avec les roches du socle sous la discordance du Thelon, là où sont encaissées les minéralisations en uranium. De manière générale, ces interactions fluides/roche sont marquées par la déstabilisation des aluminosilicates et des sulfures du socle avec une précipitation concomitante de l’illite et de l’uraninite. On comprend alors que les lithologies

225

Discussion générale plus riches en phyllosilicates sensibles au redox (donneurs d’électrons comme l’oxydation du fer des phyllosilicates (chlorite-Fe ou de la biotite) et des sulfures (pyrite) puissent agir en tant que piège de la minéralisation au cours de leur altération, comme c’est le cas dans les méta- sédiments du Woodburn Lake Group. Le contrôle de la minéralisation apparaît alors local guidée par la richesse de l’encaissant en phyllosilicates ferreux ou en pyrite. De plus, les matières carbonées en relation avec les phénomènes d’altération peuvent localement consittuer des pièges supplémentaires efficaces. Les teneurs mesurées de plusieurs pour cent métal dépassant largement la moyenne de celle des gisements de la zone de Kiggavik.

L’étude de l’altération sur l’ensemble des gisements du faisceau structural de Kiggavik-

Andrew Lake a permis de mettre en évidence une séquence paragenétique d’altération commune à l’ensemble de zones minéralisées. Elle s’exprime de manière analogue à celle des gisements de type discordance de l’Athabasca ou de la Kombolgie par un mélange d’illite et de sudoite et la présence de phases accessoires comme les APS ou les matières carbonées. On notera l’absence de la dravite qui est souvent un minéral index abondant dans de nombreux gisements associés aux discordances du bassin d’Athabasca et plus accessoire dans les gisements de Kombolgie. Ces volumes de roches hydrothermalisées forment des halos d’altération qui sont contrôlés par les discontinuités structurales à toute échelle : les réseaux de failles et leurs zones d’endommagement, les fractures, mais aussi les plans de foliation des métasédiments à plus petite échelle. Il apparaît alors un double contrôle à la fois litholologique et structural pour la précipitation de la minéralisation. On peut aussi remarquer que la minéralisation peut être également présente dans des secteurs situés en périphérie des grands drains là où l’altération de la roche encaissante est modérée et où persistent une partie des minéraux porteurs de fer ferreux (progression des fronts rédox lors des phases de minéralisations primaire mais aussi des remobilisations). Ainsi, et compte tenu de la position des minéralisations rencontrées dans le socle à jusqu'à plusieurs centaines de mètres en

226

Discussion générale dessous de la surface d’érosion actuelle qui se situe à une profondeur indéterminée sous la discordance paleoprotérozïque, il semble très probable que les minéralisations du faisceau de

Kiggavik représentent l’extension en profondeur (voir les racines ?) d’un système de minéralisation en uranium de type discordance tel que ceux déjà connus par ailleurs dans le monde (Athabasca, Kombolgie…).

Un tel contexte géologique pourrait expliquer à la fois les plus faibles teneurs en uranium, ainsi que le caractère disséminé de la minéralisation, comparativement à celle connue au voisinage de la discordance dans le bassin de l’Athabasca et des caractéristiques plus proches de celles rencontrées dans les gisements australiens plus profonds de Kombolgie tels que celui de Jabiluka notamment (Jefferson et al. 2007). On ne peut de ce fait pas exclure que des minéralisations aient été ou soient présentes au niveau de la discordance par ailleurs dans le bassin du Thelon. Dans un tel schéma, la précipitation de l’uranium en solution est conditionné par la neutralisation et la reduction progressive du fluide minéralisateur du fait de son interaction avec les minéraux des roches de socle (Komninou and Sverjensky 1996).

Les derniers progrès réalisés sur l’interprétation des défauts d’irradiation de l’illite sont primordiaux pour tenter de reconstruire les paléo-circulations des radioéléments au travers des drains empruntés par les saumures oxydantes. La meilleure connaissance des signaux associés aux différents types de défauts électroniques devrait permettre de différencier les irradiations les plus anciennes, de celle plus récentes liées à des remobilisations des minéralisations actuelles.

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Conclusion générales et perspectives

2. Conclusion générales et perspectives

L’ensemble des travaux menés dans cette thèse ont permis d’affiner la compréhension du système d’altération associé aux minéralisations en uranium du faisceau structural de

Kiggavik en le reliant à l’expression profonde d’un système de type discordance tel que ceux déjà connus dans le bassin d’Athabasca au Canada et ceux de Kombolgie en Australie. Par certains aspects, les minéralisations de socles reconnues à Shea Creek dans le bassin d’Athabasca plus au sud pourraient constituer un contexte de dépôt proche de celui caractérisé vers la marge Sud Est du bassin du Thelon. Compte tenu du type de minéralisation la perspective de découvertes de minéralisations, dans les grès ou à la discordance basale de la formation du Thelon ne peut pas être exclue. On peut par ailleurs mentionner que l’altération dans les grès peut apparaître localement, la transition entre les roches altérées ou non pouvant

être réalisée en quelques centaines de mètres. Ainsi l’absence d’altération dans les grès au dessus de la discordance n’interdit pas que des zones altérées, et donc indicatices d’un potentiel pour l’exploration soit présente dans le socle sous jacent.

Les relations entre la circulation des fluides minéralisateurs et les structures fertiles sont en cours d’étude par le biais de l’étude des défauts d’irradiations de l’illite qui est un minéral ubiquiste dans les roches du socle. Un complément de travail de géologie structurale associée

à de la radiogéochronologie sur les minéraux argileux devraient permettre de mieux contraindre la succession des événements d’altération et minéralisations.

Par ailleurs, des études de la chimie des inclusions fluides par ablation laser couplée à la spectrométrie de masse pourraient permettre de donner des indications supplémentaires sur la composition des saumures et sur leur signature géochimiques.

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Références

3. Références

Annesley I, Madore C, SHi R (1995) Revision mapping/integrated geology Wollaston EAGLE project: Segment 1. Saskatchewan Research Council, Saskatoon, pp 132. Annesley I, Madore C, SHi R (1996) Wollastion EAGLE project, Revision mapping/integrated geology Wollaston EAGLE project:Segment 2. Saskatchewan Research Council, Saskatoon, pp 184. Annesley I, Madore C (1999) Leucogranites and pegmatites of the sub-Athabasca basement, Saskatchewan: U protore? In: Stanley CJ (ed) Mineral Deposits:Processes to Processing. Balkema, pp 297-30 Beaudemont D, Fedorowich J (1996) Structural control of uranium mineralization at the Dominique- Peter deposit, Saskatchewan, Canada. Economic Geology 91:855-874. Beaufort D, Cassagnabère A, Petit S, Lanson B, Berger G, Lacharpagne JC, Johansen H (1998) Kaolinite-to-dickite reaction in sandstone reservoirs. Clays minerals 33:297-316. Beaufort D, Patrier P, Laverret E, Bruneton P, Mondy J (2005) Clay Alteration Associated with Proterozoic Unconformity-Type Uranium Deposits in the East Alligator Rivers Uranium Field, Northern Territory, Australia. Economic Geology v. 100:pp. 515–536. Cecile MP (1973) Lithofacies analysis of the Proterozoic Thelon Formation, Northwest Territories. Carlton University, pp 119. Cuney M (2010) Evolution of Uranium Fractionation Processes through Time: Driving the Secular Variation of Uranium Deposit Types. Economic Geology 105:553-569. doi: 10.2113/gsecongeo.105.3.553. Derome D (2002) Evolution et origines des saumures dans les bassins protérozoiques au voisinage de la discordance socle/couverture. L'exemple de l'environnement des gisements d'uranium associés aux bassins Kombogie (Australie) et Athabasca (Canada). Université Henri Poincaré, Nancy. Gall Q, Donaldson JA (2006) Diagenetic fluorapatite and aluminum phosphate-sulphate in the Paleoproterozoic Thelon Formation and Hornby Bay Groupe, northwestern Canadian Shield. Canadian Journal of Earth Sciences 43:617-629. Hiatt EE, Kyser K, Dalrymple RW (2003) Relationships among sedimentology, stratigraphy, and diagenesis in the Proterozoic Thelon Basin, Nunavut, Canada: implications for paleoaquifers and sedimentary-hosted mineral deposits. Journal of Geochemical Exploration 80:221-240. doi: http://dx.doi.org/10.1016/S0375-6742(03)00192-4. Hiatt EE, Palmer S, E., Kyser K, O'Connor T (2010) Basin evolution, diagenesis and uranium mineralization in the Paleoproterozoic Thelon Basin, Nunavut, Canada. Basin Research 22:302-323. Jefferson CW, Thomas DJ, Gandhi SS, Ramaekers P, Delaney G, Brisbin D, Cutts C, Portella P, Olson RA (2007) Unconformity-associeted uranium deposits of the Athabasca Basin, Saskatchewan and Alberta EXTECH IV. pp 23-67. Komninou A, Sverjensky DA (1996) Geochemical modeling of the formation of an unconformity-type uranium deposit. Economic Geology 91:590-606. doi: 10.2113/gsecongeo.91.3.590. Lanson B, BEAUFORT D, Berger G, Bauer A, Cassagnabère A, Meunier A (2002) Authigenic kaolin and illitic minerals during burial diagenesis of sandstones: a review. Clay Minerals 37:1-22. Macdonald R (1980) Mineralogy and geochemistry of a Precambrian regolith in the Athabasca Basin. University of Saskatchewan, Saskatoon, pp 151. Morichon E (2008) Les défauts d'irradiation dans les minéraux argileux: des marqueurs de la mobilité de l'uranium dans le contexte des gisements d'uranium associés à une discordance. Thèse Université de Poitiers, pp 297.

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Morichon E, Allard T, Beaufort D, Patrier P (2008) Evidence of native radiation-induced paramagnetic defects in natural illites from unconformity-type uranium deposits. Phys Chem Minerals 35:339-346. doi: 10.1007/s00269-008-0227-5. Morichon E, Beaufort D, Allard T, Quirt D (2010) Tracing past migrations of uranium in Paleoproterozoic basins: New insights from radiation-induced defects in clay minerals. Geology 38:983-986. doi: 10.1130/g31453.1. Pagel M (1975) Détermination des conditions physico-chimique de la silicification diagénétique des grès Athabasca (Canada) au moyen des inclusions fluides. Comptes Rendus de l'académie des Sciences Paris 280:2301-2304. Pagel M, Jaffrezic H (1977) Analyses chimiques des saumures des inclusionsdu quartz et de la doloite du giseet d’uaiu de Rait LakeCaada. Aspet éthodologiue et importance génétique. Comptes Rendus de l'Académie des Sciences 284:113-116. Pagel M, Ahamdach N (1995) Etude des inclusions fluides dans les quartz des gisements d'uranium de l'Athabasca et du Thelon (Canada). Centre de Recherche sur la Geologie des matières premieres minerales et énérgétiques - CREGU, Vandoeuvre les Nancy, pp 1-10. Patrier P, Beaufort D, Laverret E, Bruneton P (2003) High diageentic dickite and 2M1 illite from the middle Proterozoic Kombolgie formtion (Northern Territory, Australia). Clays and Clay Minerals 51:102-116. doi: 10.1346/ccmn.2003.510112. Peterson TD, Van Breemen O, Sandeman H, Cousens B (2002) Proterozoic (1.85-1.75 Ga) igneous suites of the Western Churchill Province: granitoid and ultrapotassic magmatism in a reworked Archean hinterland. Precambrian Research 119:73-100. Renac C, Kyser K, Durocher K, Dreaver G, O'Connor T (2002) Comparison of diagenetic fluids in the Proterozoic Thelon and Athabsca Basins, Canada: implications for protracted fluid histories in stable intracratonic basins. Can J Earth Sci 39:113-132. Sharpe R (2013) The geochermistry and geochronolgy of the Bong uranium deposit, Thelon Basin, Nunavut, Canada Department of Geological Sciences. University of Manitoba, Winnipeg, Manitoba. Uri F (2012) Altération et minéralisation d'uranium à Shea Creek (Ouest Athabasca, Saskatchewan, Canada) : vers un nouveau modèle génétique de gisement. Université de Poitiers pp 338. Van Breemen O, Peterson TD, Sandeman H (2005) U-Pb zircon geochronology and Nd isotops geochemistry of Proterozoic granitoids in the western Churchill Province: intrusive age pattern and Archean source domains. Canadian Journal of Earth Sciences 42:339-377. Weyer H-J, Friedrich G, Bechtel A, Ballhorn RK (1987) The Lone Gull uranium deposit-New geochemical and petrological data as evidence for the nature of the ore bearing solutions Metallogenesis of uranium deposits. IAEA, Vienna. Yeo G, Delaney G (eds) (2007) The Wollaston supergroup stratigraphy and metallogeny of a Paleoproterozoic Wilson cycle in the Trans-Hudson orogen, Saskatchewan. Geological Survey of Canada.

230

Annexe

Méthodologie

Comme précédemment évoquées, de nombreuses méthodes ont pu être mises en œuvre afin de répondre aux objectifs de ce travail. Afin de rendre la lecture de ce manuscrit plus claire, et pour donner le supplément de détail qui fait parfois défaut par souci de concision dans les articles, une rapide revue des méthodes utilisées sera donnée. Il s’agira de présenter pour la spectroscopie en résonance paramagnétique électronique ou la sonde ionique, l’objet de sa mise en œuvre en rappelant son grand principe de fonctionnement en faisant un éventuel rappel à la théorie, et insistant pour certaines d’entre elles sur la méthodologie de traitement des données acquises.

La caractérisation des milieux géologiques passe par un ensemble de sauts d’ échelles d’observations et de mesures, de l’affleurement à la roche, agrégat de minéraux, puis aux minéraux eux-mêmes et enfin leur organisation spatiale ou leur composition isotopique. Ainsi

à la fois chimie et cristallographie sont mobilisées pour identifier, comprendre et interpréter leur relation texturales et in fine tenter de proposer une interprétation de l’histoire géologique.

A cela s’ajoute la contrainte temporelle afin d’ancrer les successions relatives des événements dans un l’échelle absolue des temps géologiques. Spectroscopie de résonance paramagnétique électronique

Généralités

La spectroscopie RPE (Résonance Paramagnétique Electronique) s’apparente à la RMN mais il s’agit alors de s’intéresser au comportement des électrons non appariés présent dans le média à analyser, en utilisant les transitions énergétiques entre différents niveaux d’énergie de spin électronique. Cette méthode de caractérisation d’une grande sensibilité, de l’ordre de la partie par million (ppm) en concentration s’apparente à de la dosimétrie. Ainsi les défauts induits par l’irradiation, principalement du aux particules alpha, permettent alors de tracer les circulations des radioéléments en solution au cours de l’histoire géologique du système considéré.

Deux appareils ont été utilisés, un spectromètre ESP 300E Bruker mais surtout son équivalent plus moderne, l’EMXplusTM, offrant à la fois une interface souple sous windows 7 ainsi qu’une plus grande sensibilité de la cavité de résonance, Figure 1. Le principe de fonctionnement étant quoi qu’il en soit le même. Les éléments constitutifs sont :

- L’électroaimant pour imposer le champ Ho

- La cavité de résonnance dans laquelle on introduit l’échantillon

- Le pont hyperfréquence (diode de type Gunn) qui génère une onde électromagnétique

de fréquence fixe à 9.4 GHz en bande X

- Un détecteur pour mesure les ondes électromagnétiques

- Ordinateur de contrôle pour paramétrer les conditions analytiques et d’exporter les

spectres acquis

- Système d’échange de chaleur pour le refroidissement du pont et de l’électroaimant. image: www.bruker.com

1

4

2 3

Figure 1 , Spéctromètre RPE, source de microonde (1) & électroaimant (2) et son alimentation (3), cavité de résonance (4)

Théorie

Les conditions de résonance

Sous l’influence d’un champ magnétique Ho l’électron de moment magnétique µ s’aligne sur l’axe du champ. Son moment angulaire propre, aussi appelé spin, est lui caractérisé par son nombre quantique S=1/β. L’énergie d’interaction entre le champ appliqué et le moment magnétique de l’électron s’écrit alors :

E = g * * Ms * Ho

Avec :

- le magnéton de Bohr, égal à eh/βmc - g le facteur spectroscopique de l’électron libre - Ms la projection du spin sur l’axe Ho L’effet Zeeman, à pour effet de produire des transitions électroniques de niveau d’énergie déterminées par les deux orientations possible du spin, donnant un état de basse et de haute

énergie (E= 1/2*g* *Ho), selon que le spin est parallèle ou antiparallèle au champ magnétique externe.

Les conditions de résonances sont alors obtenues en utilisant une source de micro-ondes constante (de fréquence =9.4 GHz pour la bande X) dans un champ magnétique variable. Il est alors possible de mesurer l’absorption induite du quantum d’énergie résultant de la transition de niveaux d’énergie à la condition de résonnance.

On peut l’exprimer par l’expression suivant :

h * = g * * Ho

Avec :

- h la constante de Planck - la fréquence des microondes - g le facteur de Landé, spécifique du type de défaut dont les valeurs dépendent des directions cristallographiques - le magnéton de Bohr - Ho le champ magnétique externe

Les types de défauts d’irradiation et leur genèse

Dès lors que les bases physiques théoriques sont posées, il faut maintenant considérer les différents types de défauts et les conditions de leur formation et plus important encore leur persistance dans le temps au sein du minéral.

Type de défaut Nature Stabilité T1/2 années T de (recuit °C) Kaolinite/Illite/Sudoite Centre A Si-O□ 1012 450 / 600 / 500 Centre A' Si-O□ 103 300 Centre B Al-O□-Al 10-100 200 D’après (Calas et al. 2003; Allard et al. 2012)

Figure 2, type de défaut d'irradiation (Allard et al. 2012)

Les défauts de centre A, les plus stables à l’échelle des temps géologiques, sont ceux responsables de la majeure partie du signal d’irradiation que l’on peut mesurer en RPE. La création du défaut peut être induite par tous types de radiation α, , et γ, mais elle nécessite toutefois la présence d’une substitution (d’un cation trivalent par un cation divalent) créant un déséquilibre local de charge qui sera par la suite compensé par l’éjection d’un électron lors de l’interaction matière particule (Jones et al. 1974).

Mise en œuvre et calcul des concentrations en défaut

L’acquisition des données est réalisée sur des extraits argileux purs pour (1) réduire les pertes de signal par effet de dilution, si par exemple du quartz est présent dans l’échantillon la quantité de défaut mesurée sera normalisée à 100% d’argile et (2) éviter la présence de minéraux porteurs de Fe2+/3+ qui peuvent perturber le signal RPE. Les échantillons sont tamisés (maille 50 microns) afin d’obtenir une orientation aléatoire des feuillets dans le tube en silice ultra pure qui contient l’échantillon.

Les spectres de défauts sont réalisés sur une gamme de champs magnétiques comprise entre

3100 et 3600 Gauss (soit 310 et 360 mT, 1Tesla = 10 000 Gauss) pour une puissance du pont hyperfréquence de 40mW. Une phase de post traitement et de correction du signal tenant compte de la quantité de matière présente dans le tube (en masse, et en hauteur par rapport à la longueur utile de la cavité) et du gain utilisé pour l’acquisition est alors nécessaire.

Le calcul de la concentration en défaut de l’échantillon passe par le traitement du signal avec le logiciel Kaleidagraph , il s’agit de corriger le signal de la ligne de base et de procéder à deux intégrations successives. L’aire sous la courbe de la seconde intégrale donne alors la quantité de défauts pour un échantillon en unités arbitraires, figure 2. Le passage en unités absolues est alors aisé après étalonnage de la cavité avec un standard xxx en utilisant la formule donnée par (Wertz and Bolton 1986) :

Avec :

- (Std) concentration en défaut dans l’étalon

- Sx surface sous la courbe (2nd intégration) pour l’échantillon

- Sstd surface sous la courbe (2nd intégration) pour l’étalon

- Pasx / Passtd pas du spectre de l’échantillon / de étalon

- Gx gain de l’échantillon ; Gstd gain de l’étalon

- gx facteur spectroscopique caractéristique du type de défaut

- gstd facteur spectroscopique du standard - Px /Pstd puissance de l’échantillon / du standard

Figure 2, séquence schématique du traitement des spectres RPE pou la uantification des défauts d’iadiations

SIMS (Secondary Ion Mass Spectrometry)

Généralités

La spectrométrie de masse à ionisation secondaire permet entre autre l’analyse ponctuelle, in situ, des rapports isotopiques. Initialement développée à l’Université d’Orsay par G. Slodzian dans les années 1960 pour l’étude des matériaux, elle s’avère d’une grande utilisé pour les géosciences ou son utilisation à pris un véritable essor aussi bien pour la datation (U/Pb) que pour la détermination des rapports isotopiques d’éléments stables (O, H, S). Elle permet de s’affranchir des problèmes de séparations ou de purifications des différentes phases (parfois techniquement impossible). Ainsi comme pour la microsonde électronique et la chimie des minéraux, on accède alors à des données isotopiques que l’on peut mettre en regard d’information pétrographiques à une échelle plus petites que celle des minéraux (Reed 1990;

Reed 1989). On peut évoquer pour l’exemple l’évolution de la composition isotopique de l’oxygène des fluides entre plusieurs phases de surcroissances, la mise en évidence d’âges distincts entre différentes plages de grains de zircons, de monazite ou d’uraninite permettant ainsi de mieux caler dans le temps l’histoire des cristallisations.

Un photographie ainsi qu’un schéma de l’appareil correspondant est présenté sur la figure 3a et 3b.

A

B Sources archives CAMECA

Figure 3, A SIMS CAMECA IMS7f, Université du Manitoba SIMS Facility, B schéma de fonctionnement (CAMECA IMS 6f)

Théorie

La spectrométrie de masse à ionisation secondaire dans le cas de son utilisation en mode dynamique repose sur le bombardement de la surface de l’échantillon par en faisceau d’ions primaires focalisés, de haute énergie (16O ou 133Cs) avec une incidence de 20 - 45° pour optimiser l’émission des ions secondaires. Les collisions atomiques génèrent l’ablation de la matière minérale en surface et l’éjection de particules neutres ou chargées dont une partie est ionisée spontanément. Ces ions sont ensuite transférés par un champ électrostatique, de la surface de l’échantillon vers le spectromètre de masse où ils sont séparés selon leur masse et charge (m/Q) avant leur introduction dans le détecteur (Ireland 2004). La mesure des isotopes stables de l’oxygène est la plus problématique du fait de l’usage d’ion primaire Cs+ qui tendent à s’accumuler à la surface du fait d’une évacuation incomplète par la couche conductrice déposée en surface (Au). Un canon à électron rentre alors en action pour compenser l’excès de charge positive sur la surface de l’échantillon et ainsi permettre une bonne extraction des ions secondaire (Lyon et al. 1994; Ireland 2004; Slodzian et al. 1987).

Un des éléments propres à la technique est le biais induit par le fractionnement des masses lié

à l’ionisation préférentielle des isotopes les plus légers. De ce fait l’enrichissement relatif en

éléments légers du faisceau d’ions secondaire doit être ajusté par rapport aux rapports isotopiques du standard pour prendre en compte ce phénomène. De plus pour garantir, la précision et la reproductibilité des mesures et éviter les effets de fractionnement du à la composition chimique ou la structure du minéral (effets de matrice), le minéral choisi comme standard doit être le plus proche que possible du minéral à analyser (Ireland 1986).

Mise en œuvre et présentation des données

Les échantillons sont montés sur section polie de diamètre 1ˮ (2.54 cm) puis recouverts d’un film d’or par évaporation sous vide.

Les résultats sont présentés sous la forme classique :

Réch et Rstd correspondent respectivement aux rapports isotopiques absolus de l’échantillon analysé et du standard.

Diffractométrie de rayon-X

La diffraction des rayons X gouvernée par la loi de Bragg est la seule technique rendant possible la connaissance de la position relative de tous les atomes au sein d’un cristal. Il est alors possible de connaitre la nature et la position des atomes, la présence de symétries, l’organisation périodique tridimensionnelle (polytypisme, ordre/désordre, cristallinité, ect.) mais encore de déterminer la taille des domaines cohérents ou les paramètres de maille cristalline. Elle résulte de l’interaction des rayons X avec les nuages électroniques des atomes constitutifs du cristal considéré, la nature des atomes (Z) considérés influant sur l’intensité diffractée (facteur de diffusion atomique).

La loi de Bragg peut alors s’écrire

Avec :

- dhkl, la distance réticulaire caractéristique des plans hkl

- θ l’angle d’incidence des rayons X sur les plans réticulaires

- n l’ordre d’interférence (nombre entier)

- λ la longueur d’onde du rayonnement

La préparation des échantillons s’effectuant selon un protocole tel que donné par (Brindley and Brown 1980) pour les poudres désorientées lorsque l’identification de toutes les directions cristallographiques sont nécessaire ou en lames orientées (dépôt filtre ou goutte) principalement pour les minéraux présentant une forte anisotropie, tel que l’habitus lamellaire des minéraux argileux.

Réferences

Allard T, Balan E, Calas G, Fourdrin C, Morichon E, Sorieul S (2012) Radiation-induced defects in clay minerals: A review. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 277:112-120. doi: http://dx.doi.org/10.1016/j.nimb.2011.12.044. Brindley GW, Brown G (1980) Crystal structures of clay minerals and their X-ray identification. Mineralogical Society, London, UK. Calas G, Allard T, Balan E, Morin G, Sorieul S (2003) Radiation-induced Defects in Nonradioactive Natural Minerals: Mineralogical and Environmental Significance. MRS Online Proceedings Library 792:null-null. doi: doi:10.1557/PROC-792-R2.6. Ireland TR (1986) Isotope systematics of refractory inclusions from carbonaceous chondrites. The Australian National University. Ireland TR (2004) Chapter 30 - SIMS Measurement of Stable Isotopes In: Pier AdG (ed) Handbook of Stable Isotope Analytical Techniques. Elsevier, Amsterdam, pp 652-691. Jones JPE, Angel BR, Hall PL (1974) Electron spin resonance studies of doped synthetic kaolinite II. Clay Minerals 10:257-270. Lyon IC, Saxton JM, Turner G, Hinton R (1994) Isotopic fractionation in secondary ionization mass spectrometry. Rapid Communications in Mass Spectrometry 8:837-843. doi: 10.1002/rcm.1290081009. Reed SJB (1989) Ion microprobe analysis-a review of geological applications. Mineralogical Magazine 53:3-24. Reed SJB (1990) Recent developments in geochemical microanalysis. Chemical Geology 83:1-9. doi: http://dx.doi.org/10.1016/0009-2541(90)90135-T. Slodzian G, Chainteau MP, Dennebouy RC (1987) SIMS: self-regulated potential at insulating surfaces in presence of strong electrostatic field. CAMECA news. Wertz J, Bolton J (1986) Electron paramagnetic resonance. Chapman and Hall.

Système d’altération et minéralisation en uranium le long du faisceau structural Kiggavik Andrew Lake (Nunavut, Canada) : modèle génétique et guides d’exploration

Ce travail présente une étude multi-échelle des relations entre altération et minéralisation en uranium le long de la bordure Sud Est du bassin Meso-Proterozoïque du Thelon, au Nunavut, Canada. Les altérations associées aux minéralisations sont développées dans une série volcano-sédimentaire Archéenne appartenant à la ceinture de roche verte du Woodburn Lake Group (WLG). Elles s’expriment majoritairement par un assemblage à illite (polytypes 1Mcis & 1Mtrans) sudoite hématite et phosphates sulfates d'aluminium hydratés (APS). De plus des composés carbonés, cogénétiques des minéralisations, ont été identifiés comme des produits des réactions hydrothermales. La signature de l'altération, fortement guidées par les structures Est-Ouest du corridor de Kiggavik-Andrew Lake, apparaît alors très similaire à celle rencontrée dans les roches de socles des parties profondes des autres gisements d'uranium de type discordance du bassin d’Athabasca (Canada) ou de la Kombolgie (Australie). L'étude des marqueurs minéralogiques tels que les APS ont permis de mettre en évidence les transferts élémentaires au cours des processus métallogéniques et de distinguer les caractéristiques pétrographique et chimiques des processus diagénétiques et hydrothermaux. Enfin la compréhension fine de l’expression de marqueurs cristallographiques issus de l’irradiation naturelle des minéraux argileux donne de nouvelles pistes pour le traçage et la compréhension des circulations des radios-éléments à l’échelle géologique.

Mots cléfs : Bassin Méso-Protérozoique du Thelon, altération, minéraux argileux, petrographie, cristallochimie et métallogenie de l’uranium.

Alteration system and uranium mineralization along the Kiggavik-Andrew Lake structural trend (Nunavut, Canada): genetic model and exploration guides

This work presents a multi-scale study of the relationships between alteration and uranium mineralization along the South Eastern margin of the Meso-Proterozoic Thelon Basin, Nunavut, Canada. The ore associated alterations are hosted in an Archean volcano-sedimentary sequence belonging to the Woodburn Lake Group (WLG). Their main expression is a mineral assemblage composed of dominant illite (1Mcis & 1Mtrans polytypes) together with sudoite hematite and aluminum phosphate sulfate minerals. Moreover carbonaceous materials cogenetic with the uranium mineralization have been identified as potential indicators of the hydrothermal conditions. At a regional scale, alteration is strongly controlled via East-West faults forming the main frame of the Kiggavik-Andrew Lake structural trend. Then from the regional to the mineral scale, alterations signatures at Kiggavik are similar to the ones described in deep basement rocks of unconformity type uranium deposits in both Athabasca (Canada) and Kombolgie (Australia) Paleoproterozoic basins. In addition mineralogical markers studies (APS minerals) lead to the distinction between hydrothermal and diagenetic processes as well as elemental transfers during fluid rock interaction. Finally, detailed studies on radiation induced defects on illite revealed new ways to tracing and better understanding the radio elements mobility in such deep seated natural systems.

Keywords : Meso-Proterozoic Thelon Basin, alteration, clay minerals, petrography, crystallochemistry and uranium metallogeny.