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Bernard Charlier Faculté des Sciences Département de Géologie U.R. Pétrologie et Géochimie Endogènes PETROGENESIS OF MAGMATIC IRON-TITANIUM DEPOSITS ASSOCIATED WITH PROTEROZOIC MASSIF-TYPE ANORTHOSITES Thèse présentée pour l’obtention du grade académique de DOCTEUR EN SCIENCES par Bernard Charlier Diplômé d’Etudes Approfondies en Sciences Licencié en Sciences Géologiques Soutenue publiquement le 8 juin 2007, devant le jury de thèse composé de : A.-M. Fransolet Président Professeur, Université de Liège P. Barbey Professeur, Université Poincaré, Nancy O. Bolle Chercheur qualifié FNRS, Université de Liège J.-C. Duchesne Professeur Honoraire, Université de Liège J.-P. Liégeois Chef de Section, Musée royal d’Afrique central J. Vander Auwera Promotrice Chargé de cours, Université de Liège Faculté des Sciences Département de Géologie U.R. Pétrologie et Géochimie Endogènes PETROGENESIS OF MAGMATIC IRON-TITANIUM DEPOSITS ASSOCIATED WITH PROTEROZOIC MASSIF-TYPE ANORTHOSITES Thèse présentée pour l’obtention du grade académique de DOCTEUR EN SCIENCES par Bernard Charlier Diplômé d’Etudes Approfondies en Sciences Licencié en Sciences Géologiques Soutenue publiquement le 8 juin 2007, devant le jury de thèse composé de : A.-M. Fransolet Président Professeur, Université de Liège P. Barbey Professeur, Université Poincaré, Nancy O. Bolle Chercheur qualifié FNRS, Université de Liège J.-C. Duchesne Professeur Honoraire, Université de Liège J.-P. Liégeois Chef de Section, Musée royal d’Afrique central J. Vander Auwera Promotrice Chargé de cours, Université de Liège Acknowledgements Acknowledgements My acknowledgements are first dedicated to Pr. Jean-Clair Duchesne, who built the base of this project, for always keeping his door open in front of my office. His passion for geology has overflowed onto my work. Jacqueline Vander Auwera succeeded him brilliantly and continued developing a dynamic and pleasant working atmosphere. Her supervision of this project receive all my recognitions. The chapters of this Thesis and parallel researches have been reviewed before publications in scientific journals. Comments by Sarah-Jane Barnes, Richard Wilson, Brian Robins, Grant Cawthorn, Mike Toplis, Bernard Bingen and Jean Bédard have greatly contributed to my apprenticeship of redaction. This work was also stimulated by collaborations, many discussions and sometimes simple remarks or questions. Judy Hannah, Gurli Meyer, Caroline-Emmanuelle Morisset, Holly Stein, Janina Wiszniewska, Olivier Bolle, Iain Henderson, Are Korneliussen, Kåre Kullerud, Rais Latypov, Chusi Li, John Longhi, Ed Ripley, Leonid Shumlyanskyy, Øyvind Skår and Christian Tegner are all acknowledged for having expressed interest in the petrogenesis of Fe-Ti deposits. M.Sc. thesis by Olivier Namur, Isabelle Bonniver, Anne Bouton, Jean-Yves Storme, Emilie Navette, Simon Malpas have substantially contributed to this research project. Kari Berge, Ragnar Hagen and Brian Ballou from Titania A/S and Martin Sauvé, Emmanuel Sakoma and Kery Stanaway from Rio Tinto Quebec Iron and Titanium are thanked for their continuous interest and encouragement. This work has greatly benefited from their economic point of view. I would like to express my gratitude to Guy Bologne for assistance with chemical analysis. Heinz-Jürgen Bernhardt, Stuart Kearns, Jon Fong, Henrik Schiellerup have supervised many hours of chemical analysis. Jean-Paul Cullus and Guy Delhaze have contributed to sample preparation. I also thank Viviane and Mariella who cheerfully settled administrative matter. Members of the Jury Pierre Barbey, Olivier Bolle, André-Mathier Fransolet and Jean-Paul Liégeois are thanked for having accepted to evaluate this work. 4 Acknowledgements Finally Titania A/S is gratefully acknowledged for providing access to chemical data on the Tellnes deposit and for supporting the cost of new analyses. This work has also benefited from the financial supports by the “Fonds pour la formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA)”, the University of Liège, the “Fonds National de la Recherche Scientifique (FNRS)”, the “Commission Générale pour les Relations Internationales de la Communauté française de Belgique (CGRI)”, the “European Community Access to Research Infrastructure action of the Improving Human Potential Programme”, the Geological Survey of Norway, the Society for Economic Geologists Student research grants Programme, the “Patrimoine de l’Université de Liège”, the Geological Survey of Poland, the “Académie royale de Belgique, Classe des Sciences, Fondation A. De Potter”, the “Fondation Docquier” and the “Fondation Fourmarier”. 5 Abstract Abstract The petrogenesis of magmatic Fe-Ti oxide ores associated with massif-type andesine anorthosites is investigated through detailed studies of the world-class Tellnes ilmenite deposit (SW Norway), the Grader layered intrusion (Quebec, Canada) and Fe-Ti ores from the Suwalki anorthosite (NE Poland). Extensive sampling in the field and in drill-cores reveals significant petrographical and compositional variations within a single ore body and between deposits from different anorthosite complexes. The composition of phases from bulk XRF analyses on mineral separates and from in situ LA-ICP-MS, Sr isotopic composition of plagioclase, bulk rocks major and trace element contents and the spatial variation of these data are used to understand controlling factors on ore composition. Phase diagrams and experimental data on ferrobasalts as well as comparisons with the well-documented Bjerkreim- Sokndal layered intrusion (SW Norway) are systematically used to further refine our understanding on the genesis of Fe-Ti ores. More than 100 samples from drill-cores in the Tellnes ilmenite deposit, part of the late- Proterozoic (930-920 Ma) Rogaland Anorthosite Province (SW Norway), reveal significant petrographical and compositional variations within the ore body. Four zones are defined, based on variations in modal proportions and cumulus mineral assemblages: the Lower and Upper Central Zones and the Lower and Upper Marginal Zones. Plagioclase and whole-rock compositions discriminate the zones and display patterns interpreted as a result of mixing of either plagioclase- ilmenite or plagioclase-ilmenite-orthopyroxene-olivine cumulates with a melt of ferrodioritic (jotunitic) composition. Its content decreases from 80 to 20 % from the margins to the central part of the ore body. Phase diagrams for a jotunitic parental magma reproduce the crystallization sequence at 5 kbar. Uniform Sr isotope ratios do not support magma mixing. The cryptic layering of the ore body precludes injection as a crystal mush but favours in situ crystallization from an evolving magma in a sill-like magma chamber. The present trough-shape and mineral orientations result from deformation during gravity-induced subsidence and by up-doming of the anorthosite. Major and trace element XRF and in situ LA-ICP-MS analyses of ilmenite in the Tellnes ilmenite deposit further constrain the two-stage fractional crystallization model of a ferrodioritic Fe- Ti-P rich melt. Stage 1 is characterized by ilmenite-plagioclase cumulates, and stage 2 by ilmenite- 6 Abstract plagioclase-orthopyroxene-olivine cumulates. The concentration of V and Cr in ilmenite, corrected for the trapped liquid effect, (1) defines the cotectic proportion of ilmenite to be 17.5 wt.% during stage 1, Ilm and (2) implies an increase of DV during stage 2, most likely related to a shift in fO2. The proportion of 17.5 wt.% is lower than the modal proportion of ilmenite (ca. 50 wt.%) in the ore body, implying accumulation of ilmenite and flotation of plagioclase. The fraction of residual liquid left after crystallization of Tellnes cumulates is estimated at 0.6 and the flotation of plagioclase at 26 wt.% of the initial melt mass. The MgO content of ilmenite (1.4-4.4 wt.%) is much lower than the expected cumulus composition. It shows extensive postcumulus re-equilibration with trapped liquid and ferromagnesian silicates, correlated with distance to the host anorthosite. The Zr content of ilmenite, provided by in situ analyses, is low and uncorrelated with stratigraphy or Cr content. The data demonstrate that zircon coronas observed around ilmenite formed by subsolidus exsolution of ZrO 2 from ilmenite. The U-Pb zircon age of 920 ± 3 Ma probably records this exsolution process. The Grader layered intrusion belongs to the Havre-Saint-Pierre anorthosite in the Grenville Province (Quebec, Canada). This intrusion has a basin-like morphology and contains significant resources of Fe-Ti-P in ilmenite and apatite. Outcropping lithologies are massive oxide alternating with anorthosite layers, banded ilmenite-apatite-plagioclase rocks and layered oxide apatite (gabbro-) norites. Several drill cores provide evidence for stratigraphic variations of mineral and bulk cumulate compositions controlled by fractional crystallization and importantly the successive appearance of liquidus phases: plagioclase and ilmenite followed by apatite, then orthopyroxene together with magnetite, and finally clinopyroxene. This atypical sequence of crystallization results in the formation of plagioclase-ilmenite-apatite cumulates or “nelsonites” in plagioclase-free layers. Fine-grained ferrodiorites which cross-cut the coarse cumulates are shown to be in equilibrium with the noritic rocks. The high TiO 2 and P 2O5 contents of these liquids explain the early saturation of ilmenite and apatite before Fe-Mg silicates, which implies that nelsonites actually represent cumulates rather than Fe-Ti-P-rich
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