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

Résumé

Precious, semi-, and base metals have been shown to be mobilised from metasedimentary rocks during prograde metamorphism. These form an important source of metals for orogenic gold systems. Similar metal enrichments are observed in reduced intrusion-related gold systems (RIRGS) hosted in the Selwyn basin area. However, no assessment has previously been attempted to determine whether prograde metamorphism of the surrounding metasediments could represent an important metals source for RIRGS. In this study, we focus on the availability and mobilisation of semi- and base metals through mineral reactions occurring in the contact aureole around the Dublin Gulch RIRGS. Pyrite and chlorite are observed in the regionally metamorphosed rocks dominating the semi- and base metals budget. During contact metamorphism, these recrystallise to pyrrhotite and chalcopyrite, and biotite, respectively. These mineral phases contain significantly lower concentrations of metals, compared to their precursor minerals (except Cu and Zn in chalcopyrite). Whole rock geochemistry shows that relative to the contact metamorphosed rocks, the regionally metamorphosed rocks are enriched in As, Sb, Te, Bi, Pb, Zn, and H2O. This suggests, mobilisation of these elements has occurred, possibly as a metal-rich fluid that could provide an alternative or additional metal source for RIRGS.