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TitreGenesis of the Paleoproterozoic NICO Iron-Oxide-Cobalt-Gold-Bismuth deposit, Northwest Territories, Canada: evidence from isotope geochemistry and fluid inclusions
AuteurAcosta-Gongora, P; Gleeson, S A; Samson, I M; Corriveau, L; Ootes, L; Taylor, B E; Creaser, R A; Muehlenbachs, K
SourcePrecambrian Research vol. 268, 2015 p. 168-193,
Séries alt.Secteur des sciences de la Terre, Contribution externe 20150047
Documentpublication en série
Mediapapier; en ligne; numérique
ProvinceTerritoires du Nord-Ouest
Lat/Long OENS-119.0000 -116.0000 67.0000 63.0000
Sujetsgisements minéraux; oxydes de fer; cuivre; or; bismuth; géochimie isotopique; minéralisation; rétrométamorphisme; chalcopyrite; chlorite; hématite; roches sédimentaires métamorphosées
Illustrationslocation maps; geological sketch maps; cross-sections; photographs; tables; plots; schematic diagrams
ProgrammeÉtude des gîtes d'uranium, Initiative géoscientifique ciblée (IGC-4)
Résumé(disponible en anglais seulement)
The NICO deposit is located in the southern portion of the Paleoproterozoic Great Bear magmatic zone,Northwest Territories, Canada. The majority of the mineralization lies within the Bowl Zone, hosted bythe Treasure Lake Group (TLG), where heavily altered precursor rocks are interpreted to be carbonate-richwackes and siltstones. These rocks are crosscut by a set of pre-ore quartz ± calcite + amphibole + K-feldspar veins (S1). The Co-Au-Bi (±W-Cu-Mo) mineralization at NICO is contained in stratabound orelenses within the Bowl Zone, and comprises a prograde assemblage of Co-rich arsenopyrite (arsenopyriteI) and loellingite, cobaltite, pyrite, actinolite, ferrohornblende, biotite and rare scheelite (±molybdenite)along with minor magnetite and amphibole. Retrograde assemblages resulted from re-crystallizationof the Co-bearing phases to form arsenopyrite II and III, along with precipitation of marcasite, pyrite,hastingsite, native Bi-Au (±Te) and minor bismuthinite and magnetite. The latest stage of retrogrademineralization comprises chalcopyrite, hastingsite, chlorite, and hematite (±emplectite). Two sets ofbarren quartz ± dolomite + amphibole + K-feldspar + chalcopyrite veins (S2 and S3) post-date the miner-alization. The Southern Breccia zone hosts minor U-Cu-Mo mineralization and is interpreted to be thedeepest portion of the NICO system. Two molybdenite samples from the Bowl Zone and the SouthernBreccia yielded Re-Os ages of 1865 ± 9 and 1877 ± 8 Ma, respectively, consistent with the interpreted ca.1870 Ma age of the NICO deposit. This age is also synchronous with the onset of magmatism in the GreatBear magmatic arc (ca. 1875-1850 Ma).Ore mineral \'0234S values (3.3-6.7 permil, sulfides) indicate that crustal sulfur was assimilated by upwellingfelsic magmatic melts. The \'0218O values of the fluids precipitating magnetite and Co-rich arsenopyrite(6 and 8 permil), and from pre- and syn-mineralization magnetite (-0.8 to 1.5 permil) support a magmatic-hydrothermal origin of the fluids. Two out of three calcite samples from pre-(S1) and post-ore (S3) veinshave also \'0213C values consistent with a magmatic origin (-5.5 to -3.6 permil). However, one calcite samplefrom the S3 veins has a value that indicates a reduced sulfur source (-15.6 permil). This value is similar tothose of the much younger (<1843 Ma) giant quartz veins cutting the GBMZ rocks. The quartz \'0218O values suggest that S1 (12.7 permil) formed at higher temperatures than S2 (13.2-19.14 permil) and S3 (9.4-17.1 permil), orthat in the latter two generations of veins,18O was enriched during fluid/rock equilibration.Secondary trails of native Bi in S1 vein quartz are associated with liquid-vapor (LV) andliquid-vapor-halite (LVS) inclusions, which indicates that Bi, and possibly Au, were transported in salineto hyper-saline brines (LV-Bi, 2-16 wt.% NaCl equiv., 8-22 wt.% CaCl2equiv.; LVS-Bi, >37 wt.% NaCl equiv.),with homogenization temperatures of 137-216 C and 192 to >350 C or LV-Bi (ThL+V?L) and LVS-Bi(ThL+ V - L), respectively. The presence of calcium-rich fluids might indicate extensive equilibration of those solutions with the host TLG rocks. If a pressure correction is applied to the LV inclusions using a minimumentrapment temperature of 271.4 C (the Bi melting point), a minimum crystallization depth of betweenapproximately 5 and 8 km is indicated.Trace element analyses carried out in this study and compiled from Acosta-Góngora et al. (2014) showthat the least altered metasedimentary TLG rocks contain up to six times more As (Carbonate unit,30.5 ppm) than the average upper continental crust. Conversely, concentrations of Au (<2 ppb), Co(10 ppm) and Cu (12 ppm) are lower than the crustal values. As such, it is possible that the TLG wasa source of As, but is a less likely source of Au, Co and Cu for the NICO deposit; this further supports amagmatic-hydrothermal origin for the metals. Nonetheless, the plurikilometer alteration halo of the NICOsystem indicates that large amounts of elements could have been leached from the TLG, and potentiallysome were incorporated to the system. However, detailed studies on structural geology, geochemicalmodeling, and mass balance calculations need to be carried out to consider if such a scenario is feasible.
Résumé(Résumé en langage clair et simple, non publié)
L'Initiative géoscientifique ciblée (IGC-4) est un programme géoscientifique fédéral de collaboration qui fournit à l'industrie les connaissances géoscientifiques et les techniques novatrices de prochaine génération dont elle a besoin pour mieux détecter les gîtes minéraux enfouis, réduisant ainsi certains risques liés à l'exploration. Ce document présent de nombreuses sources de données qui permettent de cibler la formation du gisement NICO dans les Territoires du Nord-Ouest, ce qui offre un modèle pour orienter l'exploration minérale dans la zone magmatique du Grand lac de l'Ours et d'autres terranes prometteuses pour des gisements d'oxydes de fer-cuivre-or (OFCO).