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TitreDeformation, metamorphism and mobilization of Ni-Cu-PGE sulfide ores at Garson Mine, Sudbury
AuteurMukwakwami, J; Lafrance, B; Lesher, C M; Tinkham, D K; Rayner, N M; Ames, D E
SourceMineralium Deposita vol. 49, (2014), issue 2, 2013 p. 175-198,
Séries alt.Secteur des sciences de la Terre, Contribution externe 20140501
Mediapapier; en ligne; numérique
Lat/Long OENS -81.5000 -80.5000 46.7500 46.2500
Sujetsdépôts de brèches; gisements minéraux hydrothermaux; gîtes magmatiques; gisements métasomatiques; gisements minéraux; gîtes sulfureux; déformation; zones de cisaillement; métamorphisme; roches ignées; roches métamorphiques; pentlandite; pyrrhotite; chlorite; roches ultramafiques; faciès à amphibolite; géologie économique; géochimie; pétrologie ignée et métamorphique; minéraux métalliques
Illustrationsgeologic sketch maps; structural maps; graphs; photomicrographs; equations; tables; photographs; ternary diagrams; phase diargrams
ProgrammeÉtude des gîtes magmatiques de Ni-Cu-EPG, Initiative géoscientifique ciblée (IGC-4)
Résumé(disponible en anglais seulement)
The Garson Ni–Cu–platinum group element deposit is a deformed, overturned, low Ni tenor contact-type deposit along the contact between the Sudbury Igneous Complex (SIC) and stratigraphically underlying rocks of the Huronian Supergroup in the South Range of the 1.85-Ga Sudbury structure. The ore bodies are coincident with steeply south-dipping, north-over-south D1 shear zones, which imbricated the SIC, its ore zones, and underlying Huronian rocks during mid-amphibolite facies metamorphism. The shear zones were reactivated as south-over-north, reverse shear zones during D2 at mid-greenschist facies metamorphism. Syn-D2 metamorphic titanite yields an age of 1,849?±?6 Ma, suggesting that D1 and D2 occurred immediately after crystallization of the SIC during the Penokean Orogeny. The ore bodies plunge steeply to the south parallel to colinear L1 and L2 mineral lineations, indicating that the geometry of the ore bodies are strongly controlled by D1 and D2. Sulfide mineralization consists of breccia ores, with minor disseminated sulfides hosted in norite, and syn-D2 quartz–calcite–sulfide veins. Mobilization by ductile plastic flow was the dominant mechanism of sulfide/metal mobilization during D1 and D2, with additional minor hydrothermal mobilization of Cu, Fe, and Ni by hydrothermal fluids during D2. Metamorphic pentlandite overgrows a S1 ferrotschermakite foliation in D1 deformed ore zones. Pentlandite was exsolved from recrystallized polygonal pyrrhotite grains after cessation of D1, which resulted in randomly distributed large pentlandite grains and randomly oriented pentlandite loops along the grain boundaries of polygonal pyrrhotite within the breccia ore. It also overgrows a S2 chlorite foliation in D2 shear zones. Pyrrhotite recrystallized and was flattened during D2 deformation of breccia ore along narrow shear zones. Exsolution of pentlandite loops along the grain boundaries of these flattened grains produced a pyrrhotite–pentlandite layering that is not observed in D1 deformed ore zones. The overprinting of the two foliations by pentlandite and exsolution of pentlandite along the grain boundaries of flattened pyrrhotite grains suggest that the Garson ores reverted to a metamorphic monosulfide solid solution at temperatures ranging between 550 and 600 °C during D1 and continued to deform as a monosulfide solid solution during D2.