Geochemistry of the alteration pipe at the Amulet Upper A deposit, Noranda, Quebec
The Amulet Upper A orebody is a stratiform pyritiferous copper–zinc deposit situated within a sequence of andesitic pillow lavas. Underlying the massive sulphides is a cylindrical alteration pipe containing sulphides plus cordierite–anthophyllite-bearing rock. Hydrothermal alteration considered coincident with the formation of the overlying massive sulphides resulted in the development of a chlorite–quartz assemblage occupying the center of the alteration pipe, with a sericite–epidote–quartz assemblage at the fringes. Contact metamorphism resulting from the intrusion of the Lac Dufault granodiorite isochemically transformed the chlorite–quartz assemblage to cordierite–anthophyllite, and the sericite–epidote–quartz assemblage to biotite–epidote–quartz. This caused the development of four mineralogical zones within the alteration pipe: (1) anthophyllite zone, (2) cordierite zone, (3) biotite zone, and (4) stockwork zone.Pillows within the alteration pipe and exterior to it were studied using whole-rock anal...