Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Large mafic and ultramafic layered intrusions contain layers enriched in Platinum-Group Element (PGE) in many cases associated with sulphides. Several models of formation have been proposed for this kind of deposits. In this work, we proposed to test the model where PGE were collected by sulphides droplets (Campbell et al. 1983) and the sulphide liquid filtered into dilatancy structures. These structures formed during compaction (Barnes and Maier 2002). Two oriented samples of Merensky Reef and JM Reef, respectively, were scanned and the microstructure was examined. The study is based on: (i) the determination distribution of sulphide in 3-D (by X-Ray Computed Tomography, X-Ray CT); (ii) the microstructural analysis of oriented (parallel to the paleovertical) polished thin sections made of each samples. The two results were compared. For the two samples, sulphides are connected in 3-D and located along the paleovertical. The petrographic study shows that sulphides are interstitial to the silicates and oxides minerals. Furthermore, for Merensky Reef evidences of crystal deformation formed during compaction of the crystal pile have been observed. Low temperature alteration has obscured the microstructures in the JM Reef sample and thus the relationship between compaction and sulphide distribution is not proven.