The Geochemical Behavior of Metalloids and Their Effect on the Highly Siderophile Elements During the Crystallization of a Magmatic Sulfide Liquid in Relation to the Formation of Ni-Cu- PGE Magmatic Sulfide Deposits by Fabio Cafagna A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Ph.D.) in Mineral Deposits and Precambrian Geology The Faculty of Graduate Studies Laurentian University Sudbury, Ontario, Canada © Fabio Cafagna, 2015 THESIS DEFENCE COMMITTEE/COMITÉ DE SOUTENANCE DE THÈSE Laurentian Université/Université Laurentienne Faculty of Graduate Studies/Faculté des études supérieures Title of Thesis Titre de la thèse The Geochemical Behavior of Metalloids and Their Effect on the Highly Siderophile Elements During the Crystallization of a Magmatic Sulfide Liquid in Relation to the Formation of Ni- Cu-PGE Magmatic Sulfide Deposits Name of Candidate Nom du candidat Cafagna, Fabio Degree Diplôme Doctor of Philosophy Department/Program Date of Defence Département/Programme Mineral Deposits and Precambrian Geology Date de la soutenance April 9, 2015 APPROVED/APPROUVÉ Thesis Examiners/Examinateurs de thèse: Dr. Pedro Jugo (Co-supervisor/Co-directeur de thèse) Dr. Andrew McDonald (Co-supervisor/Co-directeur de thèse) Dr. Doug Tinkham (Committee member/Membre du comité) Approved for the Faculty of Graduate Studies Approuvé pour la Faculté des études supérieures Dr. David Lesbarrères M. David Lesbarrères Dr. James Brenan Acting Dean, Faculty of Graduate Studies (External Examiner/Examinateur externe) Doyen intérimaire, Faculté des études supérieures Dr. Nelson Belzile (Internal Examiner/Examinateur interne) ACCESSIBILITY CLAUSE AND PERMISSION TO USE I, Fabio Cafagna, hereby grant to Laurentian University and/or its agents the non-exclusive license to archive and make accessible my thesis, dissertation, or project report in whole or in part in all forms of media, now or for the duration of my copyright ownership. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also reserve the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. I further agree that permission for copying of this thesis in any manner, in whole or in part, for scholarly purposes may be granted by the professor or professors who supervised my thesis work or, in their absence, by the Head of the Department in which my thesis work was done. It is understood that any copying or publication or use of this thesis or parts thereof for financial gain shall not be allowed without my written permission. It is also understood that this copy is being made available in this form by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner. Ai miei Genitori To my Parents Abstract The highly siderophile elements (HSE), which include Re, Au and the platinum-group elements (PGE: Ru, Rh, Pd, Os, Ir, Pt) are of scientific and economic interest because they are tracers of geological processes (e.g., planetary differentiation) or have industrial or investment value. In most ore deposits, HSE are usually mined as by-products of Ni-Cu mineralization, such as those of the Sudbury district (Canada). Although at high temperature HSE are expected to be in lattice of sulfides they are usually found as discrete phases or platinum-group minerals (PGM). Many of PGM have metalloids (As, Se, Sb, Te and Bi) as essential constituents but, despite this relationship, the role of metalloids on HSE mineralization is still unclear. This dissertation documents the results of three experimental studies undertaken to investigate the effect of metalloids on the geochemistry of HSE. The first study examined whether the metalloids can mobilize HSE in an anhydrous environment. The results show that metalloids do not transport the HSE but also that Au, Pd and Pt can be efficiently fractionated from the other HSE and transported away from a sulfide assemblage through a relatively low-porosity, low-permeability medium in absence of hydrothermal fluids. The second study investigated the solubility of metalloids in monosulfide solid solution (mss) and intermediate solid solution (iss), to asses the conditions required for the formation of immiscible metalloid liquids and their effect on HSE partitioning. The results show that the metalloids form two separate phases, one that is As- rich and strongly sequestered Pt from the sulfides and another that is Bi-Te rich and affected mostly Pd and Au. The results also show that the other HSE (Ru, Rh, Re, Os, Ir) are largely unaffected by the presence of metalloids. In addition the results show that mss can dissolve significant amounts of metalloids (hundreds of ppm) before metalloid IV saturation can occur. The third study constrained the geochemical behavior of metalloids and HSE in a pyrite-bearing sulfide system. The results show that Co-Ni-rich and HSE bearing pyrite can form during cooling of a sulfide melt and also that the HSE partition roughly equally between mss and pyrite, whereas Pd that partitions preferentially into mss and Au partitions preferentially into iss. Moreover, pyrite showed compositional zonation of many elements similar to that documented in natural pyrite samples that are also Co- rich and HSE-bearing. Thus, identification of such pyrite in natural assemblages is consistent with a magmatic origin. Keywords Platinum-group elements, PGE, highly siderophile elements, HSE, metalloids, As, Se, Sb, Te, Bi, platinum-group minerals, PGM, magmatic sulfides, ore deposits, Sudbury Igneous Complex, footwall, experimental study, transport of PGE, HSE fractionation, solubility of metalloids, partitioning of HSE, partitioning of PGE, monosulfide solid solution, mss, intermediate solid solution, iss, pyrite. V Statement of co-authorship The initial design of the first study was done when the project was conceived by Dr. Pedro Jugo. However, the execution of the experiments, the analyses of the results and the conclusions reached are entirely my work, executed under the supervision of Dr. Jugo. The second and third studies were conceived and carried out by me, after discussing and confronting ideas with Dr. Jugo, who constantly offered advice and supervised all the steps of the work. VI Acknowledgements This thesis was a long and complex work. Several problems and obstacles slowed down the work. I would not have been able to complete the project without the help and support of several people along the way. It is difficult, if not impossible, to thank everybody. If someone is forgotten from this list, I sincerely apologize. A special thank to my supervisor, Dr. Pedro Jugo. He always believed in me and in the project, even when I did not. He kept me on the project even when I had to interrupt for a long period of time. Not many other people would have had his patience. Furthermore, I would like to thank my advisory committee, composed by my co-supervisor Dr. Andy McDonald and by Dr. Doug Tinkham, for their advices and inputs. This thesis would not have been completed without the help of some outstanding technicians who helped me through analytical techniques. Therefore, thanks to Willard Desjardins for teaching me how to make epoxy “pucks” and how to polish samples; to Sandra Clarke for teaching me how to use an SEM and to Dave Crabtree for the help with the microprobe; finally, thanks to Joe Petrus, for the hours spent on the LA-ICP-MS and for guiding me through Iolite. I would like to thank my mother, Luisanna, who always encouraged me to look beyond the horizon, supported me and never had a doubt I would have made it. Together with her, I would like to thank the rest of my family, in Italy; it was hard for them to know me so far away. I will never thank enough my love, Zsuzsanna, whom I met here in Canada. She is always by my side, no matter what. She taught me that working hard is rewarding, that I can reach any goal if I want. We made it, together, Szerelmem. VII I also want to thank all my friends, in Canada and in Italy. In my years here in Canada, I had the chance to meet people from literally all around the world. They made a better person of me and I had the chance to learn the beauty of multiculturalism and diversity. This is something that few lucky people have the luxury to experience. VIII Table of contents Abstract ........................................................................................................................................ IV Keywords ............................................................................................................................................ V Statement of co-authorship .................................................................................................................. VI Acknowledgements ............................................................................................................................. VII Table of contents ......................................................................................................................... IX Index of tables ................................................................................................................................... XIII Index of figures ..................................................................................................................................