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Origins and geochemical characterization of the Iron-Oxide-Copper-Gold deposits in the Great Bear Magmatic Zone, NWT, Canada Open Access


Other title
IOCG deposits
Type of item
Degree grantor
University of Alberta
Author or creator
Acosta, P
Supervisor and department
Gleeson, Sarah (Department of Earth and Atmospheric Sciences)
Examining committee member and department
Currie, Claire (Department of Physics)
Gleeson, Sarah (Department of Earth and Atmospheric Sciences)
Richards, Jeremy (Department of Earth and Atmospheric Sciences)
Chacko, Thomas (Department of Earth and Atmospheric Sciences)
Marshall, Dan (Simon Fraser University, BC)
Department of Earth and Atmospheric Sciences

Date accepted
Graduation date
Doctor of Philosophy
Degree level
The Great Bear magmatic zone (GBMZ) in the Northwest Territories, Canada, contains the NICO (Au-Co-Bi±Cu-W) and Sue Dianne (Cu-Ag-Au-±U-Co) deposits, and the DAMP and FAB prospects, all of which represent iron-oxide dominated polymetallic systems with comparable alteration and mineralization styles similar to iron-oxide copper gold (IOCG) deposits in Chile and Australia. Also in the study area, is the vein hosted Nori/RA (Mo-U±Cu-REE), which has less affinity to the IOCG class of deposits. In this work, trace and major element analyses, along with stable (C, H, S, O and Cu), radiogenic isotopes (Re-Os), and fluid inclusion studies were used to constrain the origin of the IOCG systems, and the Nori/RA showing, and to suggest the potential of magnetite as a mineral indicator in till sampling exploration surveys. Regionally, the Cr/Co ratio is higher in barren and pre-ore magnetite compared to that of magnetite co-precipitated with ore minerals and/or present in ore-rich veins and breccias. At DAMP and Sue Dianne the Co/Ni ratio is extremely high and clearly different from those of other GBMZ magnetite samples. Collectively, the analytical data supports a magmatic-hydrothermal origin for all these systems that are temporally associated with the emplacement of the Great Bear volcanic arc between 1875 and 1865 Ma. However, some sulfur, copper and arsenic could have been recycled from carbonate-rich metasedimentary and rocks and incorporated in the ore-bearing fluids as is suggested for the NICO deposit. Some copper might have also been leached from felsic volcanic rocks and metasedimentary rocks and incorporated into the GBMZ mineralized systems. In NICO deposit, Ca-Na-Bi(Au?)-bearing, and saline (~20 wt.% NaCl equiv + CaCl2 equiv) to hyper-saline aqueous fluids (>42 wt. % NaCl equiv.) formed at 4 to 8 km depth. The Au mineralization in this system occurred via: (i) remobilization of refractory gold and Bi(?) from Fe-S-As-S mineral phases during re-crystallization of the latter, and (ii) scavenging of Au by Bi melts from co-existing hydrothermal fluids. Despite the stable isotopes signature, and the geochronological constraints, mass balance calculations shows that felsic volcanic and metasedimentary rocks hosting these deposits are feasible sources of metals (e.g., Au, Co and Cu) for the GBMZ IOCG systems. However, for this to be true, it would require high permeabilities and efficient fluids capable of leaching, concentrating and re-precipitating metals at a single site, and a suitable hydraulic regime.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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