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ARTICLE Petrology and geochronology of Paleoproterozoic intrusive rocks, Kiggavik uranium camp, Nunavut Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by Natural Resources Canada on 06/05/15 For personal use only.
J.M.J. Scott, T.D. Peterson, W.J. Davis, C.W. Jefferson, and B.L. Cousens
Abstract: We investigated the age and petrology of Paleoproterozoic granitic intrusions in the area of the Kiggavik uranium exploration camp, near the southeast margin of the Aberdeen subbasin of the Thelon Basin. A subset of these intrusions (e.g., the Lone Gull stock) is spatially associated with and mineralized by basement hosted, unconformity-related uranium deposits. Surface (outcrop) samples have field relations, textures, and compositions consistent with Hudson Suite granitoids and mixtures of monzogranite with minette. We obtained U–Pb (zircon) ages ranging from ca. 1818 to 1840 Ma, within the known range of the Hudson Suite and cogenetic minettes of the Baker Lake Group (1.80–1.84 Ga). Core samples of granitic rocks adjacent to mineralized zones are more complex and indicate an influence from the younger Nueltin Granite (Kivalliq Igneous Suite, ca. 1.77–1.73 Ga). One sample from the Lone Gull stock contains two zircon populations in texturally distinctive domains, one at 1806 ± 41 Ma and the other at 1748 ± 9.4 Ma. A porphyritic hypabyssal syenite below the Bong deposit yielded a U–Pb zircon age of 1837.8 ± 7.7 Ma and a U–Pb titanite age of 1758.5 ± 44 Ma. We recognize a Kivalliq-age overprint in the form of metasomatism and partial remelting or melt infiltration in the drill core samples, which is not evident at the surface and is consistent with the presence of a Nueltin Granite intrusive complex at depth. The geochemistry and primary igneous textures of the Bong syenite, including its euhedral zircons, resemble those of lava flows near the base of the Baker Lake Group, and we recognize a mixed magma (i.e., Martell Syenite) continuum between intrusive Hudson granitoids and minette with extrusive equivalents in the lower felsic minette member of the Christopher Island Formation. Résumé : Nous avons étudié l’âge et la pétrologie d’intrusions granitiques (Paléozoïque) dans le secteur du camp d’exploration pour l’uranium Kiggavik, près de la bordure sud-est du sous-bassin Aberdeen du bassin Thelon. Un sous-ensemble de ces intrusions (p. ex. le stock de Lone Gull) est associé dans l’espace a` des gisements d’uranium situés dans le socle et qui sont en relation de discordance ; le sous-ensemble est aussi minéralisé en uranium. Des échantillons prélevés en surface (affleurements) ont des relations de terrain, des textures et des compositions qui concordent avec les granitoïdes de la suite d’Hudson et des mélanges de monzogranites avec des minettes. Nous avons obtenu des âges U–Pb (sur zircons) variant de ~1818 a` 1840 Ma, ce qui est dans la plage connue de la suite d’Hudson et des minettes cogénétiques du Groupe de Baker Lake (1,80–1,84 Ga). Des échantillons de carottes prélevées dans les roches granitiques adjacentes aux zones minéralisées sont plus complexes et montrent une influence du granite Neultin, plus jeune, (de la suite ignée Kivalliq, ~1,77–1,73 Ga). Un échantillon du stock de Lone Gull contient deux populations de zircons situés dans des domaines a` textures distinctes, un domaine a` 1806 ± 41 Ma et l’autre a` 1748 ± 9,4 Ma. Une syénite porphyrique hypabyssale sous le gisement Bong a donné un âge U–Pb (zircon) de 1837,8 ± 7,7 Ma et un âge U–Pb (titanite) de 1758 ± 44 Ma. Dans les carottes échantillonnées, nous reconnaissons une surimpression d’âge Kivalliq sous la forme de métasomatisme et de refusion partielle ou d’infiltration de produits en fusion, ce qui n’est pas évident a` la surface; cela concorde cependant avec la présence d’un complexe intrusif de granite Nueltin en profondeur. La géochimie et les textures ignées primaires de la syénite de Bong, incluant ses zircons idiomorphes, ressemblent a` celles des écoulements de lave a` proximité de la base du Groupe de Baker Lake et nous reconnaissons un continuum de magma mixte (c.-a`-d. la syénite de Martelle) entre les granitoïdes intrusifs de Hudson et la minette avec des équivalents extrusifs dans le membre inférieur de minette felsique de la Formation de Christopher Island. [Traduit par la Rédaction]
Introduction Geological and geochronological context of the Kiggavik camp We report the petrography, geochemistry, and uranium–lead geochronology of zircon and titanite in undeformed granitoid intrusions associated with and surrounding drilled uranium deposits in the area of the Kiggavik uranium camp. The Kiggavik camp, located approximately 80 km west of Baker Lake and 27 km south of Schultz Lake (Fig. 1), is located within the Rae domain of the western Churchill Province, south of the Thelon Fault. This region has recently generated renewed exploration interest due to its endowment of basement-hosted uranium deposits suitable for open-pit mining,
and the continued addition of drill-indicated resources as well as several local discoveries (AREVA Resources 2012). Uraninite at the Kiggavik deposit is disseminated across the contact zone between Neoarchean feldspathic metagreywacke and the undeformed but faulted Paleoproterozoic Lone Gull granite stock. This spatial association has raised questions regarding the role Paleoproterozoic intrusive bodies may have played in ground preparation for later mineralization. Paleoproterozoic granitoid rocks in the region comprise two groups. The Hudson Suite (ca. 1.79–1.84 Ga) and Nueltin Granites (part of the Kivalliq Suite, ca. 1.73–1.76 Ga) have contrasting origins (late syn-orogenic and anorogenic, respectively; Fig. 2) with some overlap in geochemical and petrographic features (Scott 2012). Resolving the
Received 4 September 2014. Accepted 17 March 2015. J.M.J. Scott and B.L. Cousens. Department of Earth Sciences, 1125 Carleton University, Colonel By Drive, Ottawa, ON K1S 5B6, Canada. T.D. Peterson, W.J. Davis, and C.W. Jefferson. Geological Survey of Canada, 601 Booth Street, Ottawa, ON K1A 0E9, Canada. Corresponding author: T.D. Peterson (e-mail:
[email protected]). Can. J. Earth Sci. 52: 1–24 (2015) dx.doi.org/10.1139/cjes-2014-0153
Published at www.nrcresearchpress.com/cjes on 16 April 2015.
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Can. J. Earth Sci. Vol. 52, 2015
Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by Natural Resources Canada on 06/05/15 For personal use only.
Fig. 1. Regional geological setting, after Peterson et al. (2010) and Jefferson et al. (2013). Abbreviations: AbL, Aberdeen Lake; AMZ, Amer mylonite zone; BFZ, Bathurst fault zone; Blsz, Big Lake shear zone; CFZ, Chesterfield Fault Zone; DRSZ, Dubawnt River shear zone; MFZ, Macdonald fault zone; MLF, Marjorie Lake Fault; PB, Pike Break; S-CMZ, South Chantry mylonite zone; STZ, Snowbird tectonic zone; TF, Tulemalu Fault; TL, Tebesjuak Lake; TSZ, Tulemalu Shear Zone; TqF, Turqavik Fault; WBSZ, Wager Bay shear zone. Inset map: TO, Thelon Orogen; WO, Wopmay Orogen; AB, Alberta; SK, Saskatchewan; Nu, Nunavut; MB, Manitoba.
relationship of local Paleoproterozoic granitoid rocks to uranium mineralization by investigating their setting, composition, textures, and timing of emplacement may help to identify favourable sites for the discovery of new resources within the Kiggavik camp and in the wider Thelon Basin region, and this is the purpose of this study. Regional geology The Kiggavik camp comprises multiple deposits and prospects, hosted mainly by highly deformed Neoarchean supracrustal rocks of the ca. 2.73–2.68 Ga Woodburn Lake Group, the
