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TitleGeology, geochemistry, and trace elements in sulfides and gold distribution at the polymetallic Nico (au-co-bi±cu-w) Deposit, Northwest Territories, Canada
AuthorAcosta-Gongora, P; Gleeson, S A; Samson, I M; Ootes, L; Corriveau, L; Taylor, B E
Source40th Annual Yellowknife Geoscience Forum, abstracts of talks and posters; by Watson, D M (ed.); Northwest Territories Geoscience Office, Yellowknife Geoscience Forum Abstracts Volume 2012, 2012 p. 1 (Open Access)
LinksOnline - En Ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20130430
Meeting40th annual Yellowknife Geoscience Forum; Yellowknife; CA; November 13-15, 2012
Mediapaper; on-line; digital
File formatpdf
ProvinceNorthwest Territories
NTS85N; 86C; 86D; 86E; 86F; 86K; 86L
AreaGreat Bear Lake; Lac la Martre; Hottah Lake
Lat/Long WENS-119.0000 -116.0000 67.0000 63.0000
Subjectseconomic geology; structural geology; magnetite; glacial deposits; iron oxides; copper; gold; mineralization; fluid flow; paleomagnetic interpretations; paleomagnetism; structural analyses; structural interpretations; Great Bear magmatic zone
ProgramGEM: Geo-mapping for Energy and Minerals, Iron-oxide Copper-gold (IOCG) / Multiple Metals - Great Bear Lake (NWT)
AbstractThe Great Bear Magmatic zone (GBmz) in the Northwest Territories is host to the NICO (Au-Bi-Co±Cu-W) deposit and other smaller iron-oxide dominated polymetallic systems. Many of these systems have analogous alteration and mineralization styles and tectonic environments to the Iron-Oxide Copper Gold (IOCG) deposits in Chile and Australia (e.g. Olympic Dam, La Candelaria, Raúl-Condestable). The NICO deposit is located is located in the southern GBmz. This deposit hosts economic Au-Co-Bi (+Cu-W) mainly in magnetite-amphibole rich rocks of the Treasure Lake group, with some late-stage mineralized veins in the strongly potassic-altered felsic volcanics of the Faber group. The polymetallic mineralization is concentrated in the Bowl Zone, with 43-101 compliant reserves of 33 Mt @ 1.02 g/t Au, 0.112% Co, 0.14% Bi, 0.04 % Cu (Fortune Minerals Ltd. press release, July 5th, 2012). The early ore stage (M1) is represented by the precipitation of arsenopyrite, cobaltite, loellingite, scheelite and pyrrhotite, with gangue minerals such as magnetite and pyrite and variable amounts of amphibole, biotite, quartz, potassic feldspar and fluorite. The Co-As-Fe sulphides are recognized to occur in four principal styles: i) veins (1mm to 20cm thick); ii) disseminated along the bedding planes; iii) randomly disseminated within wallrock; and iv) as massive mineral aggregates. The late ore assemblage (M2) consists of native Bi, bismuthinite, emplectite, whittichenite, and chalcopyrite, with minor amounts of molybdenite. Associated with the ore minerals are chloro-potassichastingsite, hematite, quartz and variable amounts of amphibole, magnetite, fluorite, and potassic feldspar. Locally, M2 mineral assemblages are variable and three have been identified: i) magnetite-native Bi-bismuthinite (±quartz-chloro-potassichastingsite); ii) chloro-potassichastingsite-bismuthinite-chalcopyrite-emplectite-whittichenite-hematite-native Au- tellurides (±chlorite,fluorite); and iii) actinolite-chalcopyrite-molybdenite-(±bismuthinite). These late ore fluids likely resulted in partial arsenopyrite re-crystallization and during this process multiple inclusions of native Bi, Bi-Cu sulphides and silicates could have been incorporated to the arsenopyrite crystals. LA-ICP-MS raster analysis was carried out on arsenopyrite-rich samples pyrite, cobaltite and loellingite. No major geochemical differences were identified with a specific arsenopyrite mineralization style, but some slight differences in Ni, Se, Sb, and Pb concentrations between the sulphide phases were found. In addition, it was confirmed that native gold (Au) is present mainly as inclusions. The richest Au inclusions (4752 ppm) are also associated with high Te and Bi (as defined by spectral peaks). Only one analysis showed the presence of Au evenly distributed in the crystal lattice of an arsenopyrite grain; however, its overall concentration is very low (3 ppm). Petrographic and trace element studies indicate the occurrence of Au as inclusions in arsenopyrite is closely related to the emplacement of the late Bi- and Bi-Cu sulphides and hematite, indicating that Au is post-dating the Co-As-Fe sulphides.