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TitreRegional potassic alteration corridors spatially related to the 1750 Ma Nueltin Suite in the northeast Thelon Basin region, Nunavut - guides to uranium, gold and silver?
AuteurPeterson, T D; Scott, J M J; Jefferson, C W; Tschirhart, V
SourceAssociation géologique du Canada-Association minéralogique du Canada, Réunion annuelle, Programme et résumés vol. 35, 2012 p. 1
LiensOnline - En ligne
Séries alt.Secteur des sciences de la Terre, Contribution externe 20110354
RéunionGeological Association of Canada, Mineralogical Association of Canada, Joint Annual Meeting; St. John's; CA; mai 27-29, 2012
Documentpublication en série
Sujetsaltération; altération hydrothermale; roches ignées; roches intrusives; granites; Bassin de Thelon ; Suite de Nueltin ; pétrologie ignée et métamorphique; Précambrien; Protérozoïque
ProgrammeUranium, GEM : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
Shallow granitic intrusions commonly generate mineralized, hydrothermally altered zones in porous roof rocks. Typically the alteration involves potassic metasomatism, which can be revealed as enhanced K/Th and K/U ratios in airborne gamma ray maps. 1.75 Ga Nueltin granite plutons in the Dubawnt-Baker-Aberdeen lakes area are subvolcanic, intruding co-magmatic rhyolitic carapaces of the Pitz Formation. A north-opening triangle of enhanced K/Th extends from the Pamiutuq intrusion at Tulemalu Lake (65O) toward Mallery Lake, and a corridor of enhanced K/Th extends north from Dubawnt Lake (65N). These domains coalesce south of Abderdeen Lake (66B,C) at an east-west high-K domain. Although large exposures of Pitz Formation and Nueltin granite constitute portions of these domains, broad tracts with high K/Th have no obvious relation to silicic intrusions.
The Geomapping for Energy and Minerals Program has demonstrated that the 65O triangle contains previously known basaltic intrusions (McRae Lake Dyke and an unnamed intrusion east of it) and newly recognized hi-Ti basalt flows within the Pitz Formation (SE of Tebesjuak Lake, in 650, on Thelon River south of Beverly Lake, and at Mallery Lake), all correlated with the mafic trigger that generated silicic Nueltin/Pitz magmas. Two sets of dykes correlated with the Pitz basalts (~015° parallel to the McRae Lake dyke, and ~075° parallel to the Thelon Fault) are prominent in the high K/Th domain in 66B. We postulate that regional potassic metasomatism is a result of alteration driven by the basaltic phase of the Nueltin event, which is unusually prominent in these domains, with local enhancement by Nueltin granites.
Geochronological tests of this hypothesis are in progress at the University of Manitoba. Fluorite from the Au-Ag deposit at Mallery Lake, located above the roof of a Nueltin pluton near its contact with Pitz Formation basalt, has been dated by Nd-Sm isochron at 1434 ± 60 Ma. Uraninite at Kiggavik, which has a close spatial association with hypabyssal Nueltin bodies, has been dated by a U-Pb method at 1.4 Ga; this age is also represented in Athabasca Basin uranium deposits. The driver for the 1.4 Ga event is uncertain, but it must reflect a crustal scale disturbance which has no known relation to igneous activity in these areas. We speculate that at Kiggavik, this age represents low T resetting of an original higher-grade metasomatic event in wall rocks of the Nueltin Suite which is proposed as an exploration guide to U-Au-Ag deposits.