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Serpentiniztaion of Dumont Dunite

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Serpentiniztaion of Dumont Dunite Generation of high-Ni sulfide and alloy phases during serpentinization of the Dumont Dunite, Quebec By MICHELLE SCIORTINO A Thesis submitted in conformity with the requirements for the degree of MASc Graduate Department of Geology, University of Toronto © Copyright Michelle Sciortino 2014 Generation of high-Ni sulfide and alloy phases during serpentinization of the Dumont Dunite, Quebec MASc Graduate Department of Geology, 2014 Michelle Sciortino Department of Geology University of Toronto Abstract The Dumont Sill in the Abitibi, Quebec, is broadly zoned from gabbroic chilled margins through peridotite to a principally dunitic core. The dunite contains several layers enriched in primary sulfide minerals. Serpentinization occurred isochemically with respect to major components apart from the addition of H2O. An extensive database which includes 1420 mineralogical samples and 4400 microprobe analyses has been used to understand alteration and nickel deportment in primary and secondary minerals. In layers containing primary accumulations of magmatic sulfide serpentinization has resulted in the remobilization of nickel from olivine to enrich cumulus sulfides. In layers lacking primary sulfide accumulations, serpentinization was accompanied by the formation of awaruite. Assemblages which are completely serpentinized contain lesser nickel in silicates, higher nickel tenor sulfides, and more modal awaruite compared to those which are weakly and partially serpentinized, which are characterized by higher nickel in silicates and lower Ni tenor sulfides. Key Words: Ultramafic Nickel, Serpentinization, Nickel Remobilization, Komatiites ii Acknowledgements The author would like the thank Royal Nickel Corporation for their support in this project, specifically, Johnna Muinonen, John Korczak and Alger St-Jean for their contributions to the various aspect of this research. Also special thank-you to Stephanie Downing and Kathryn Sheridan (SGS Lakefield) for their dedication and mineralogical expertise in executing Royal Nickel Corporation’s ExplominTM program. iii Contents Abstract ......................................................................................................................................................... ii Acknowledgements ...................................................................................................................................... iii Table of Abbreviations ................................................................................................................................. vi List of Figures .............................................................................................................................................. vii List of Tables .............................................................................................................................................. viii Introduction .................................................................................................................................................. 1 Geological Setting ......................................................................................................................................... 3 Methods ........................................................................................................................................................ 4 Assays ........................................................................................................................................................ 4 X-Ray Diffraction ....................................................................................................................................... 5 Electron Microprobe ................................................................................................................................. 5 Modal analysis .......................................................................................................................................... 5 Block Model Calculations .......................................................................................................................... 7 Observations: The Dunite Subzone at Dumont ........................................................................................... 7 Local geology ............................................................................................................................................. 7 Mineral Assemblages ................................................................................................................................ 11 Facies divisions .................................................................................................................................... 11 Ni-bearing phases in sulfide-bearing zones ........................................................................................ 12 Ni-bearing phases in low-grade low-sulfide zones ............................................................................. 12 Partial serpentinization ....................................................................................................................... 14 Completely serpentinized dunites: Fe-serpentine facies.................................................................... 15 Completely serpentinized dunite: Mg-serpentine facies ................................................................... 15 Paragenesis ......................................................................................................................................... 17 Mineral Compositions ............................................................................................................................. 20 Ni-rich phases ...................................................................................................................................... 20 Spinel ................................................................................................................................................... 23 Silicate and hydroxide phases ............................................................................................................. 24 Lithogeochemistry .................................................................................................................................. 28 CIPW norms......................................................................................................................................... 28 Distribution of Ni ................................................................................................................................. 28 Discussion.................................................................................................................................................... 29 iv Intensive parameters during sill emplacement ...................................................................................... 29 Primary redox state ............................................................................................................................. 29 Ni Content of Primary Sulfide Blebs .................................................................................................... 31 Metamorphism ........................................................................................................................................ 33 Modal variation ................................................................................................................................... 33 Metasomatism and volume change ..................................................................................................... 36 Serpentine composition and the redox state of Fe ............................................................................ 39 Nickel remobilization .......................................................................................................................... 41 Fluid Chemistry and Thermodynamics ................................................................................................... 44 Phase relations .................................................................................................................................... 44 Stability of Ni-Fe Alloys ....................................................................................................................... 49 Serpentinization of the Dumont Sill ........................................................................................................ 50 Mass Transfer to Intercumulus Sulfide Blebs and Nickel Remobilization .............................................. 56 Nickel Distribution and Controls ............................................................................................................ 57 Implications............................................................................................................................................. 59 Conclusions and Exploration Implications .............................................................................................. 60 References .................................................................................................................................................. 62 Appendix A: Methods Additional Information ............................................................................................ 70 A-1: Electron Micro Probe Measurement Conditions by Lab ................................................................. 70 Appendix A: Figures ...............................................................................................................................
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