| Zusammenfassung: |
The Lac Soisson intrusive suite consists of a swarm of small plutons and pl...
The Lac Soisson intrusive suite consists of a swarm of small plutons and plugs of olivine-gabbro, gabbronorite and troctolite composition that were emplaced into Archean to Paleoproterozoic crust of the western Core Zone, west of the de Pas Batholith. These intrusions are essentially non-metamorphosed, with unaltered olivine visible in hand specimen and thin section. They were mapped in detail by the Ministère de l'Énergie et des Ressources naturelles (MERN) in 2013 as part of the Lac Saffray mapping project in the Core Zone, and revisited this past summer where a B.Sc. Honours thesis was initiated (Fleury, 2016), supported by the MERN. In 2000-2002, these intrusions had been targeted by the Western Mining Corporation (WMC) as part of their 'Quebec-7' Ni-Cu-PGE exploration program along the western margin of the SE Churchill Province. Some of the values reported by WMC range up to 2% chalcopyrite, < 2% pentlandite and 108 ppb PGEs over meter-length sections in drillcore. During our targeted mapping in 2014 we sampled one of the main gabbroic phases of the intrusion for U-Pb dating. The sample yielded abundant, large baddeleyite and zircon crystals, which were analyzed at the Geological Survey of Canada laboratory in Ottawa. Preliminary TIMS results stemming from the baddeleyite ages suggest that the magma was emplaced at 1312 ±1 Ma, slightly younger than the ca. 1333 ± 1 Ma Ni-bearing intrusions of the Voisey's Bay complex in Nain. Zircon from the same Lac Soisson sample, however, yields a younger SHRIMP concordia age of 1295 ±11 Ma. Interestingly, some of the Voisey's Bay zircons yield ages that are compatible with baddeleyite ages (1333 Ma), whereas others yield ages that are significantly younger, at ca. 1305 Ma. During the summer 2014, east-west oriented olivine gabbro dykes were also mapped and sampled as part of the regional mapping program. These E-W dykes are parallel to a set of crustal-scale faults and lineaments that appear to be associated to crustal extension related to emplacement of the Nain Plutonic Suite. Some may in turn be feeders to the Lac Soisson intrusions. However, preliminary TIMS results suggest an age of ca. 1270 Ma for one of these dykes. The age correlation shown herein suggests that Ni-Cu mineralized, olivine-bearing mafic intrusions of the Soisson Suite may very likely be related to the Voisey's Bay intrusions but were emplaced more than 300 km to the W-NW of the latter, in the western margin of the Core Zone.
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