The Geology, Petrography and Geochemistry of Gabbroic Rocks of the Pants Lake Intrusive Suite on the Donner/Teck South Voisey's Bay Property, North-Central Labrador, Canada Heather E. MacDonald A thesis submitted in conformity with the requirements for the degree of Mastet's of Science Graduate Department of the Department of Geology University of Toronto O Copyright by Heather E. MacDonald, 1999 National Library Bibliothèque nationale 1*1 of Canada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellingtori Street 395. rue Wellington OttawaON K1A ON4 OnawaON KlAONQ Canada Canada The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or seii reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la forme de rnicrofiche/film, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur consewe la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantiai extracts fiom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. The Geology, Petrography and Ceochernistry of Gabbroic Rocks of the Pants Lake Intrusive Suite on the Donner/Teck South Voisey's Bay Property, North-Central Labrador, Canada Heather E. MacDonald Master's of Science, 1999 Department of Geology University of Toronto Abstract The South Voisey's Bay property held by Donner Minerals Limited in North-Central Labrador hosts Ni-Cu-Co mineralization within gabbroic rocks of the Pants Lake Intrusive Suite (PLIS). Three drill holes from across the property were seiected for study. Samples were analyzed for major, trace, rare earth elements and examined by petrographic microscope. The data suggests that two distinct intrusions make up the PLIS denoted as the North and South Intrusions. Geochemical cornparisons to the Voisey's Bay troctolites indicates similar major element contents reflecting plagioclase- rich mineralogy, and trace element contents of Voisey's Bay are similar to the South gabbro units. Contamination sources are not obvious corn data collected. Al1 gabbros are chalcophile-element depleted when plotted on CdZr and Cu/Hf diagrams. Sulphides would have settled out of a silicate melt, due to a contrast in density, perhaps in a previous charnber or feeder conduit. Acknowledgments First and foremost, 1 would like to give thanks to Dr. A.J. Naldrett for his supervision, instruction and insight. Without his invaluable support this project would not have been possible. Also indispensable was the help of one cornmittee member, Dr. M.P. Gorton, for his assistance and instruction of neutron activation analysis, interpretation of geochemical data, and reviews of my thesis. Dr. Chusi Li also provided guidance and information regarding the Voisey's Bay deposit. Several other members of the department were a great source of information and advice: Dr. Steve Scott, another cornmittee member who added sorne important ideas; Dr. James Brenan, who added his critical reviews of this thesis; and Dr. Claudio Cermignani completed the microprobe analysis of my samples as a contract to Teck. Thanks to Jim for aiding (and sometimes rescuing files) in computer technical difficulties! Karen Gorra took some great photos of several of rny sarnples. Dr. James Scoates from the Universite Libre de Bruxelles was open to discussion and helpful hints. 1 also gratefully acknowledge the financial assistance of a University of Toronto Open Scholarship. Instrumental to this project was the generous support of Teck Exploration Limited and Donner Minerals Limited. They provided two summers of employment and limitless, extremely valuable help from a great crew that 1 had the privilege to work with: Paul Moore, Harvey Keats, Kerry Sparkes, Tom Lane, Denis, Guy, Kellie, Steve, Floyd, Trevor, Mike, Bing, and the rest of the Pants Lake Crews of 1997 and 1998! Andy Kerr, Bruce Ryan and Dick Bailey of the Newfoundland Department of Mines and Energy were al1 extremely approachable and enthusiastic, and greatly assisted in my understanding of regional and local geology. My good fnend and room-mate, Michelle Joyette crushed my samples and helped maintain my sanity by providing recreational breaks. Troy Small deserves a reaIly big thank-you for bolstering my confidence and managing to put up with me during the final stages of this project! My oflice-mate Andrew, and fnends, including the many graduate students of yesterday and today, GSU-goers, and Sleeman Breweries Honey Brown Lager were also much needed stress relievers. Ed and Harry of the GSU should also recognized for providing al1 us grad snidents with a place to blow off steam. My grandmother (December 8, 1908-July 22, 1999) was always very supportive even though she didn't quite understand why her pndaughter was interested in rocks! Unfortunately, she didn't get to see the final product, but 1 would like to thank her anyway. Finally, 1 would like also to extend my gratitude to my family for their unconditional support, and, who encouraged the completion of my tirne at U. of T. with such loving inquiries as: "Are you done yet?" Table of Contents Page Title Page 1 .* Abstract Il *-a Acknowledments 111 vi i List of Tables .-. List of Plates Vlll List of Firmres- lx List of Appendices xi Map: Regional Geoloav Survev of the South Voisev's Bav Proiect 1 :50 000 back pocket Chapter 1. Introduction 1.1 General Statement 1.2 Obiectives 1.3 Methods 1.4 Location and Access Cha~ter2. Regional Geolow 2.1 Regional Settinp; 2.1.1 Makkovik Province 2.1.2 Grenville Province 2.1 -3 Superior Province 2.1 -4 Southeastern Churchill Province 2.1.5 Nain Province 2.1.6 Nain Plutonic Suite 2.1.7 Ham Lake Intrusive Suite 2.1.8 Flowers River Imeous Suite 2-2 Nain-Churchill Boundarv 2.3 Sequence of Intrusive Events 2-4 The Voisey's Bay Deposit Chapter 3. Local Geolorry 3.1 Pants Lake Property Description 3.2 Local Unit Descriptions 3.3 Field Relationshi~s 3.4 Sample Collection Chapter 4. Petroera~hv 4.1 Upper seauence gabbro 4.2 Coarse-mained gabbro 4.3 Black gabbro 4.4 Fine-mained olivine gabbro 4.5 Peridotite 4.6 Discussion Page Chapter 5. Rock Geochemistrv 5.1 Analytical Techniques 5.2 Ma-ior Element Anal-ytical Results 5.2. t Upper sequence gabbro 5.2.2 Coarse-mined gabbro 5.2.3 Black gabbro 5.2.4 Fine-grained olivine gabbro 5.2.4.1 North Intrusion (VBS-97-77) 5.2.4.2 South Intrusion (VBS-97-79] 5.2.5 Peridotite 5.3 Rare Earth and Trace Eiement Analvtical Results 5.3.1 Pants Lake Gabbros-S~idermarns 5.3.2 Pants Lake Gabbros. Tasiuvak and Nain Gneiss and Lower Crust-Soidermams:- Com~arison 5 -3-3 Pants Lake-Voisev's Bay S~idermams: Cornparison 5.3.4 Ratio Profiles 5.3.5 Modeling of Estimated Parental Liciuid of North and South Gabbros with Possible Contaminant: Diamms 5.3.6 Sul~hideDevletion: Histograms 5.4 Discussion Chapter 6. Mineral Chemistrv 6.1 Plagioclase 6.2 Olivine 6.2.1 Black Gabbro and Coarse-mained Gabbro 6.2.2 Fine-grained olivine Gabbro 6.2.3 Peridotite 6.3 Discussion Cha~ter7. Discussion and Conclusions Geological Mode1 and Ex~iorationRecomrnendations North Gabbro South Gabbro References Appendices List of Tables Page Chapter 2: 2.1 Sequence of intrusive events in North-Central Labrador 13 (Arnelin et al., 1999; Fitzpatrick et al., 1998; Wardle, 1993; Wardle et al., 1997). Chapter 3: 3.1 Summary of significant mineralization intersections (Donner Minerals, press release, November 18, 1998) Chapter 4: 4.1 Petrographic summaries of al1 units. Chapter 5: 5.1 a Whole rock major elements. 5.1 b Recalculated whole rock major elements with standard deviations. 5.2 Statistical analysis of identicality between units 40-42 and 41-42. 5.3 Whole rock trace and rare earth elements. 5.4 Original melt composition for the North and South Intrusions. Cha~ter6 6.1 Microprobe olivine compositions. vii List of Plates (Unless otherwise specified, al1 photos by H.MacDonald) Page Chapter 3 3.1 Scenic Pants Lake, taken fiom the helicopter. 3.2 Rapakivi-texture granite (photo by K-Gorra, University of Toronto). 3.3 Contaminated core. 3.4 Breccia unit with magnet/scriber for scale. 3.5 Minera1 Hill with K-Emon for scale. 3.6 "Oatmeal" texture, sample from Mineral Hill (photo by K-Gorra, University of Toronto). 3.7 Coarse-grained xenolith or dyke in fine-grained olivine gabbro fiom NDT area (photo by K-Gorra, University of Toronto). Close up of Plate 3.12. 3.8a Small scale layering in the NDT area. 3.8b Small scale Iayering in the NDT area. 3.9 Black gabbro vs. coarse-grained gabbro drill core (photo by K-Goma, University of Toronto). 3.10a Coarse-grained, fine-grained olivine gabbro contact with hammer for scale. 3.10b Coarse-grained, fine-grained olivine gabbro contact with hand for scale. 85 3.1 1 Chill zone of fine-grained olivine gabbro against coarse-grained gabbro 86 from isolated gabbro outcrop, south of Sarah Lake with pen for scale. 3-12 Coarse-grained xenolith/dyke in fine-grained olivine gabbro in NDT area 86 with C-Fitzgerald for scale. 3.13 Intrusive contact between rapakivi granite and fine-grained olivine 87 gabbro in the South Intrusion. Chapter 4 4.1 Thin section of coarse-grained gabbro with interstitial olivine grains.