Carbonate-hosted Zn-Pb mineralization in the Lower Cambrian Sekwi Formation, Mackenzie Mountains, NWT: Stratigraphic, structural, and lithologic controls, and constraints on ore fluid characteristics by Beth J. Fischer Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science (M.Sc.) in Geology School of Graduate Studies Laurentian University Sudbury, Ontario © Beth Fischer, 2012 Library and Archives Bibliotheque et Canada Archives Canada Published Heritage Direction du 1+1 Branch Patrimoine de I'edition 395 Wellington Street 395, rue Wellington Ottawa ON K1A0N4 Ottawa ON K1A 0N4 Canada Canada Your file Votre reference ISBN: 978-0-494-87713-5 Our file Notre reference ISBN: 978-0-494-87713-5 NOTICE: AVIS: The author has granted a non­ L'auteur a accorde une licence non exclusive exclusive license allowing Library and permettant a la Bibliotheque et Archives 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 I'lnternet, preter, telecommunication or on the Internet, distribuer et vendre des theses partout dans le loan, distrbute and sell theses monde, a des fins commerciales ou autres, sur worldwide, for commercial or non­ support microforme, papier, electronique et/ou commercial purposes, in microform, autres formats. paper, electronic and/or any other formats. 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Canada Abstract The Sekwi Formation, a Lower Cambrian carbonate unit, is a preferred base metal sulfide host in the Mackenzie Mountains zinc district (Northwest Territories, Canada), but controls on the mineralization are poorly understood. Stratigraphic work in three mineralized areas together with petrographic, fluid inclusion and isotopic studies, demonstrate a first-order structural control (proximity to Cretaceous-Tertiary faults), a second-order lithological control (dolograinstone/rudstone and dark, mottled dolostone), and a local stratigraphic control on the distribution of mineralization. Structural relationships indicate a Late Cretaceous or Tertiary age for much of the mineralization, but some evidence implies that that there was also an earlier (Late Devonian or Early Carboniferous) mineralizing event. At least two fluids mixed to form the showings. Fluid 1 originated as Cretaceous seawater, or formation water containing dissolved Neoproterozoic evaporite rock, and had thermally equilibrated with the Sekwi Formation at 4-6 km depth by the time of mineralization. Fluid 2 originated in felsic crystalline basement, and carried the most radiogenic Sr yet recorded from the northern Canadian Cordillera. Fluid 2 scavenged metals from the sedimentary pile as it moved upward through a network of faults under pressure caused by Cretaceous-Tertiary compress ional orogeny. Fluid 2 was 250-350°C and hydrothermal when it penetrated susceptible strata of the Sekwi Formation by hydraulic fracturing and dissolution, and catalyzed thermochemical reduction of the sulfate in fluid 1. This reaction consumed local organic matter. The reduced-sulfur species then reacted with the metals brought by fluid 2, precipitating metal sulfides in the lowest susceptible units. Preferred sites of mineralization were in the hangingwall and immediate footwall of regional thrusts where steep faults intersected each other and susceptible units. This model will be a useful tool in exploration for new deposits or deposit extensions, but further work is needed to refine it. iii Acknowledgements My primary source of support for this thesis project was my employer, the Northwest Territories Geoscience Office, who was willing for me to take on the role of a student every summer for three years and who granted me nine months of unpaid leave in 2006-07. The NTGO is a partnership between the federal Department of Indian Affairs and Northern Development and the territorial Department of Industry, Tourism and Investment. The territorial side of the partnership funded the Sekwi Mountain project, which is the umbrella NTGO project that supported my field and analytical work, through the Strategic Investments in Northern Economic Development program. The federal manager of NTGO at the time, Carolyn Relf, and directors on the federal side granted permission for me to transform my function from that of Geoscience Information Manager to Project Geologist, despite the capacity gaps they were left to deal with The federal side of the partnership also provided funds for analyses, as well as personal financial support through the Career Development Program and the Northern Scientific Training Program. Carolyn Relf s personal support and encouragement were key to beginning the project, and when Scott Cairns took over her job while I was away at school in 2007, he continued the support seamlessly. I am particularly grateful for his patience and understanding when I developed a devastating neurological disease, and over the three years it took to obtain a diagnosis and semi-effective medication. During that time, for the most part I could not function, at either my job or my thesis project. His support has meant more to me than he probably realizes. Many other staff at NTGO have provided support, inspiration, and encouragement. In particular, Edith Martel, who took on management of the Sekwi Mountain project, has provided a wonderful variety of assistance. It had been a quarter- century since I had used a Brunton compass; as soon as she realized how little I knew, she began to teach me, and has continued to provide advice whenever I asked, and encouragement when I didn't. Hendrik Falck reviewed an early draft, answered endless questions about how to approach things, kept reminding me of my priorities in life, and listened with compassion throughout the horrible times when the disease was ruining me. He helped my outlook more than anyone else and I cannot thank him enough for that. iv Eagle Plains Resources Ltd. and Terralogic Exploration Inc. were a major source of support, providing helicopter time and field accommodations for parts of the 2006, 2007, and 2008 field seasons. Thanks especially to Aaron Higgs, Glen Hendrikson, and the crew at the Border Lake camp in 2008, and to Brent VanSickle for flying me around that year. I was assisted in the field in 2007 by Ryan Pippy and Danielle Thomson, who put up with my idiosyncrasies with good humor, and in 2008 by John Law, an extraordinary source of cheer. Ryan Pippy found the TIC Ryan zone while taking a break from the pogo. Thank-you to Justin MacDonald and Chris Leslie, my fellow students on the Sekwi Mountain project in 2006, for being awesome, and to Rob MacNaughton for listening and teaching. Mike Pope led me on a tour of the Sekwi Formation, and has since been a source of knowledge and help. Stan and Helen Stevens and their family Glen, Dan, and Jessica (Mackenzie Mountains Outfitters) run the hunting lodge where we stayed in 2007; they are warm and genuine people and took exceptional care of the Sekwi Mountain project crew. A special thanks to Stan Stevens for flying me back to the Wells when I twisted my knee, and to Frank Pope for driving me around me when I got there. Harold Grinde and family at Shale Lake (Gana River Outfitters) were kind and welcoming hosts of our crew in 2007 and 2008, and the Simpson family (Ramhead Outfitters) at Godlin Lakes were likewise in 2006. The services provided by Canadian Helicopters, Sahtu Helicopters, and Fireweed Helicopters were dependable, skilled, and safe. Jane and her staff at the Mackenzie Valley Hotel in Norman Wells regularly went out of their way to make us comfortable; they are a model for exceptional service standards. My primary supervisor, Elizabeth Turner, opened up the fascinating world of carbonate rocks for me, sharing her knowledge and enthusiasm for three years. She showed me how to measure a stratigraphic section, how to look at a carbonate rock, and by her example, how to see the relationships between rock units and structures in the field. Elizabeth supported my work financially as well, through her NSERC Discovery Grant in 2006 and 2007. Daniel Kontak, my second supervisor, taught me how to think about fluid inclusions as well as use the equipment, guided my initial thoughts on the v analytical work, took it upon himself to walk me through use of the SEM on fluid inclusion evaporates, spent a memorable afternoon with me on the petrographic microscope discussing mineral textures, and provided a critical and detailed review of the analytical part of the first draft of this thesis, which improved the end product significantly. I thank both of my supervisors for teaching me these things, and for the time they spent with me. Also at Laurentian University, Mike Lesher and Darrel Long were unfailingly supportive and encouraging; thank you. A large number of people, including some I barely knew, took the time to advise and encourage me in various ways. At the forefront of these are Bob Sharp of Trans Polar Geological Consultants Inc. and Sarah Gleeson of the University of Alberta; others include Jeff Packard, Glen Prior, Michel Malo, Hamish Sandeman, Brian Cousens, and Dan Marshall.