The Mineralogy of NYF Pegmatites from the Coldwell Alkaline Complex, Northwestern Ontario Malcolm Alexander Lakehead University Thunder Bay, Ontario Library and Bibliotheque et 1*1 Archives Canada Archives Canada Published Heritage Direction du Branch Patrimoine de I'edition 395 Wellington Street 395, rue Wellington Ottawa ON K1A0N4 Ottawa ON K1A0N4 Canada Canada Your file Votre reference ISBN: 978-0-494-49953-5 Our file Notre reference ISBN: 978-0-494-49953-5 NOTICE: AVIS: The author has granted a non­ L'auteur a accorde une licence non exclusive exclusive license allowing Library permettant a la Bibliotheque et Archives and Archives Canada to reproduce, Canada de reproduire, publier, archiver, publish, archive, preserve, conserve, sauvegarder, conserver, transmettre au public communicate to the public by par telecommunication ou par Plntemet, prefer, telecommunication or on the Internet, distribuer et vendre des theses partout dans loan, distribute and sell theses le monde, a des fins commerciales ou autres, worldwide, for commercial or non­ sur support microforme, papier, electronique commercial purposes, in microform, et/ou autres formats. paper, electronic and/or any other formats. The author retains copyright L'auteur conserve la propriete du droit d'auteur ownership and moral rights in et des droits moraux qui protege cette these. this thesis. Neither the thesis Ni la these ni des extraits substantiels de nor substantial extracts from it celle-ci ne doivent etre imprimes ou autrement may be printed or otherwise reproduits sans son autorisation. reproduced without the author's permission. In compliance with the Canadian Conformement a la loi canadienne Privacy Act some supporting sur la protection de la vie privee, forms may have been removed quelques formulaires secondaires from this thesis. ont ete enleves de cette these. While these forms may be included Bien que ces formulaires in the document page count, aient inclus dans la pagination, their removal does not represent il n'y aura aucun contenu manquant. any loss of content from the thesis. Canada ACKNOWLEDGEMENTS I am very grateful to the several people who have supported me throughout this project. Special thanks to my supervisor Dr. Roger Mitchell for his dedication, commentary and willingness to clarify any difficulties 1 encountered. Many thanks to Anne Hammond for her assistance while making polished rock sections. 1 am sincerely grateful to Allan MacKenzie for his help troubleshooting SEM-EDS. I would also like to acknowledge Roisin Kyne and my parents, Elizabeth and Steve Alexander, for their input while drafting my revisions. ABSTRACT The Coldwell Complex, northwestern Ontario, is a multiphase alkaline intrusion that is host to rare earth element, actinide and other high field strength element mineralization. Preliminary studies have shown that these minerals are concentrated in pegmatites associated with Center One ferrorichterite-ferroaugite syenites and Center Three syenites. The Center One syenites differentiate to pegmatitic residua and are characterized by cumulus perthitic-to-cryptoperthitic alkali feldspar, hedenbergite-aegirine pyroxenes, and intercumulous quartz, calcite, and calcic- to-sodic-calcic-to-sodic amphiboles. Center Three residua are similar, except that amphiboles are limited to calcic varieties (hastingsite) and precipitate before feldspar (as opposed to after). All pegmatitic residua are of the niobium-yttrium-fluorine (NYF) type. Back-scattered electron petrography has been used to characterize the mineral paragenesis. Pegmatitic syenitic residua emplaced in, but not derived from the border gabbro (Border Gabbro pegmatite), and residua within ferroaugite syenite units (Railway pegmatites) contain a wide range of rare element minerals which include britholite, chevkinite, fergusonite, monazite, allanite, kainosite, xenotime, REE fluorocarbonates bastnaesite, synchysite and parisite. Other rare element enriched minerals include apatite, thorite, zircon, zirconolite, niobium rutile and U-Th-Si- pyrochlore. Early-formed rare element minerals such as allanite, britholite, chevkinite, kainosite, and pyrochlore are commonly replaced by complex aggregates of later-forming phases such as REE-fluorocarbonates. Other riebeckite-quartz (Upper Marathon Shore pegmatites), richterite- quartz (Black pegmatites) and hastingsite-quartz (Center Three pegmatites) bearing pegmatitic residua contain a more restricted range of rare element minerals, which include zircon, xenotime, monazite and fluorocarbonates together with REE-bearing apatite, thorite and pyrochlore. The differences in rock forming and accessory mineralization suggest that most, if not all, residua are derived from different batches of ferroaugite syenite and syenite magma. Intensive parameters have been estimated using the habit of perthites, the coexistence of zircon and baddeleyite, Fe-Ti-oxide compositions, amphibole mineralogy, and fluorocarbonate stability. These parameters indicate all pegmatitic units are similar, with initial silica activities of 10"075, alkali-feldspar precipitation at approximately 750 °C, magnetite-ilmenite subsolidus equilibration temperatures of 531 to 633 °C and oxygen fugacities of 10"165 to 10"22'9 bars, subsolidus quenching of magnetite occurs at approximately 450 °C, and subsequent 200 °C hydro- and carbothermal induced recrystallization of rare earth mineral and REE-bearing minerals. l CONTENTS Chapter One: Introduction and General Geology 1 1.1 Introduction 1 1.2 Midcontinental Rift 1 1.3 Age of the Coldwell Complex 4 1.4 Structure 6 1.5 Center One 7 1.6 Center Two 8 1.7 Center Three 8 1.8 Minor Intrusions 10 1.9 Pegmatites 11 1.10 Border Gabbro Pegmatite 12 1.11 Railway Pegmatite 14 1.12 Upper Marathon Shore Pegmatite 14 1.13 Black Pegmatite 15 1.14 Center Three Pegmatite 16 1.15 Chapter One Summary 16 Chapter Two: Analytical Techniques 22 2.1 Introduction 22 2.2 Back Scattered Electron Petrography and Energy Dispersive X-Ray Analysis 22 Chapter Three: Rock-Forming and Minor Minerals 24 3.1 Introduction 24 3.2 Feldspar Group 24 3.3 Pyroxene Group 29 3.4 Amphibole Group 33 3.5 Chlorite 40 3.6 Olivine 43 3.7 Calcite 45 3.8 Quartz 47 3.9 Fluorite 47 3.10 Biotite 48 3.11 Muscovite 50 Chapter Four: Accessory Minerals 53 4.1 Introduction 53 4.2 Allanite 53 4.3 Apatite and Britholite 58 4.4 Arsenopyrite 63 4.5 Astrophyllite 63 4.6 Baddeleyite 70 4.7 Barite 72 4.8 Chalcopyrite 74 4.9 Chevkinite 74 ii 4.10 Fergusonite 80 4.11 Fluorocarbonate Group 86 4.12 Galena 94 4.13 Kainosite 94 4.14 Ilmenite 96 4.15 Lollingite 98 4.16 Magnetite 99 4.17 Molybdenite 101 4.18 Monazite and Rhabdophane 101 4.19 Pyrite 106 4.20 Pyrochlore 108 4.21 Rutile 117 4.22 Sphalerite 122 4.23 Thorite 122 4.24 Titanite 127 4.25 Xenotime 129 4.26 Zircon 134 4.27 Zirconolite 138 Chapter Five: Petrogenesis 145 5.1 Introduction 145 5.2 Melt/Fluid Evolution 146 5.3 Conclusion 152 References 154 Appendix I: Symbols for Selected Minerals 170 Appendix II: Compositions of Rock Forming, Minor and Alteration Minerals.... 172 II.I Feldspar Group 172 II.II Pyroxene Group 176 II.III Amphibole Group 181 II.IV Chlorite 185 II.V Olivine 189 II.VI Biotite 190 II.VII Muscovite 193 Appendix III: Compositions of Accessory Minerals 194 III.I Allanite 195 III.II Apatite and Britholite 197 III.III Astrophyllite 205 III.IV Baddeleyite 207 III.V Barite 208 III.VI Chevkinite 209 III.VII Fergusonite 214 III.VIII Fluorocarbonates 218 III.IX Kainosite 228 III.X Magnetite and Ilmenite 229 III.XI Monazite and Rhabdophane 233 in III.XII Pyrochlore 237 III.XIII Rutile 257 III.XIV Thorite 260 HI.XV Titanite 266 III.XV Xenotime 267 III.XVII Zircon 271 III.XVIII Zirconolite 281 iv LIST OF FIGURES Chapter One: Introduction and General Geology. 1.1 NAMRS positive Bouger anomaly 2 2 Geological map of the Coldwell complex 4 3 Location of known diatremes near the Coldwell complex 5 4 Gravity anomaly profile of the Coldwell complex 7 5 Photomicrographs of the four crystallization stages 13 1.6 Border Gabbro paragenetic scheme 17 1.7 Railway paragenetic scheme 18 8 Upper Marathon shore paragenetic scheme 19 9 Black paragenetic scheme 20 10 Center Three paragenetic scheme 21 Chapter Two: Analytical Techniques 22 Chapter Three: Rock-Forming and Minor Minerals 24 3.1 BSE-images of feldspar 25 3.2 Feldspar Or - Ab - An ternary plot (Or and An reduced to 20 %) 28 3.3 Feldspar Or - Ab - An ternary plot (Ab and Ab reduced to 20 %) 28 3.4 Photomicrographs of pyroxene 30 3.5 BSE-images of pyroxenes 30 3.6 Pyroxene Ae - Di - Hd ternary plot 32 3.7 Pyroxene M2+ / (M++M3+) binary plot 34 3.8 Photomicrographs of amphiboles 35 3.9 BSE-images of amphiboles 36 3.10 Sodic-calcic amphibole plots 37 3.11 Calcic and sodic amphibole plots 37 3.12 BSE-images of chlorite 40 3.13 Photomicrographs of chlorite 41 3.14 Chlorite Mg-FeO*-AI ternary plot 42 3.15 Chlorite M2+ / (M++M3++M4+) binary plot 43 3.16 BSE-images of fayalite 44 3.17 Photomicrographs of fayalite 45 3.18 Photomicrographs of calcite 45 3.19 BSE-images of calcite 46 3.20 BSE-images of quartz 46 3.21 BSE-images of secondary quartz 47 3.22 Photomicrographs of fluorite 48 3.23 BSE-images of fluorite 48 3.24 Photomicrographs of biotite 49 3.25 Biotite 1-site substitution 49 3.26 Photomicrographs of muscovite 51 3.27 BSE-images of muscovite 51 v Chapter Four: Accessory Minerals 53 4.1 Photomicrographs of allanite 54 4.2 BSE-images of allanite 55 4.3 A-site substitution in allanite 57 4.4 M-site substitution in allanite 58 4.5 BSE-images of apatite 59 4.6 BSE-image of dissolved apatite