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TitreThermomechanical erosion at the Alexo Mine, Abitibi Greenstone Belt, Ontario: implications for the genesis of komatiite-associated Ni-Cu-(PGE) mineralization
AuteurHoulé, M G; Lesher, C M; Davis, P C
SourceMineralium Deposita 2011.,
Séries alt.Secteur des sciences de la Terre, Contribution externe 20100537
Documentpublication en série
Mediapapier; en ligne; numérique
SNRC42A/10; 42A/11; 42A/14; 42A/15
Lat/Long OENS-81.5000 -80.5000 49.0000 48.5000
Sujetsgisements minéraux; gîtes minéralogiques; nickel; cuivre; platine; minéralisation; roches ignées; komatiites; érosion; genèse des minerais; genèse des gîtes minéraux; Archéen; Mine Alexo ; Ceinture d'Abitibi Greenstone ; Formation de Dundonald ; géologie économique
Illustrationslocation maps; photographs; plots; cross-sections
ProgrammeÉtude des gîtes magmatiques de Ni-Cu-EPG, Initiative géoscientifique ciblée (IGC-4)
Résumé(disponible en anglais seulement)
The archetypical komatiite-hosted Alexo Ni-Cu-(PGE) deposit occurs in the 2,720-2,710-Ma Kidd-Munro Assemblage of the western Abitibi greenstone belt in Dundonald Township, Ontario. Detailed mapping of a 200-m long glacially polished outcrop provides nequivocal evidence that the host komatiite flow thermomechanically eroded footwall andesites: (1) the contact between komatiite and andesite is very sharp but delicately scalloped, marked by a <1-cm-thick selvedge of black aphanitic komatiite and clearly transgresses pillow structures and interpillow breccias in the andesite without any evidence of a regolith, shearing, or folding, producing multiple nested
embayments on scales from hundreds of meters to a few centimeters; (2) the andesites have been contact metamorphosed and altered along the entire length of the outcrop and the degree of metamorphism/alteration is thicker and more intense around embayments; (3) xenoliths of andesite in komatiite are more common within embayments; (4) komatiitic dikes penetrate downward into underlying andesites, primarily along the lateral margins of embayments; and (5) many of the dikes and marginal rocks exhibit geochemical evidence of contamination. This physical and geochemical evidence for thermomechanical erosion, combined with S isotopic evidence for a major component of non-magmatic country-rock S in the ores, provides additional support for the roles of thermomechanical erosion and incorporation of country-rock S in the genesis of komatiite-associated Ni-Cu-(PGE) deposits. The detailed mapping also reveals that the stratigraphy of the ore zone is considerably more complex than previously reported, indicating that the sulfides were emplaced in several stages, confirming the dynamic nature of the ore emplacement process in komatiite-associated Ni-Cu-(PGE) deposits.