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

Résumé

Previously characterised as a sulphide-poor Pd ore deposit, massive sulphides have recently been discovered in Lac-des-Iles. The massive sulphides occur across the different lithological units and show variable degrees of alteration. The least altered samples comprise a typical magmatic assemblage of pyrrhotite, pentlandite and chalcopyrite. Chalcopyrite-rich samples are found at the edges of the pyrrhotite/pentlandite-rich pods. Base metal and platinum-group element (PGE) compositions indicate that as a whole they represent a frozen sulphide liquid, different from the one that formed the sulphide-poor samples, that was injected along structural features. The altered samples are rich in pyrite and magnetite. Molecular proportions of base metals and S/Se ratios are the same for the altered and unaltered samples indicating that neither S nor Fe has been remobilized from the system. We propose instead that oxidation was responsible for the observed changes in mineralogy. This alteration event appears not to have affected the PGE content.