CHARACTERIZATION OF HYDROTHERMAL ALTERATION RELATED TO MAGMATIC NI-CU-PGE MINERALIZATION AT THE NICKEL RIM SOUTH DEPOSIT, SUDBURY, ONTARIO

The Sudbury area hosts one of the world's premier magmatic Ni-Cu-PGE mining districts with the recent (2010) Nickel Rim South (NRS) operation (9.1 Mts of 1.57% Ni, 2.85% Cu, 2.55 g/t Pt+Pd) being one such high grade deposit. The NRS deposit is composite in nature with contact-style magmatic ores at the base of the Sudbury Igneous Complex, a layered crystallized melt sheet consisting of norite and granophyre, and magmatic-hydrothermal style ores in its underlying footwall environment. The footwall rocks include granite, granodiorite, mafic and felsic gneisses, gabbro, and impact-related breccia bodies. Alteration associated with the footwall ore system extends into the distal parts of the footwall and this study aims at characterizing the nature and extent of this ore-related alteration. To date, the study has identified various textures and styles of alteration that relate to mineralization. Alteration assemblages consist of varying proportions of epidote, chlorite, actinolite and quartz with lesser amounts of sericite, hematite, biotite and carbonate. Near the contact ore, wall rocks exhibit chlorite and epidote alteration with aggregates of recrystallized quartz. In the upper portion of the footwall zones, mineralization is associated with heavily brecciated and altered rocks containing actinolite, chlorite, and epidote, the latter occurring either in or adjacent to sulfide veins. The actinolite has an increase in fe (Fe/(Fe+Mg)) in the footwall setting from distal (fe=0.53) to proximal mineralization (fe=0.75). In the most distal footwall setting there occurs low-sulfide, PGM-rich zones with intense epidote and chlorite alteration; similar alteration can, however, occur in barren rock. Fluid inclusion types present in quartz from both the contact and footwall zones include L+V+H types that have Th values that group at ≈180°C and ≈300°C and L+V type with Th ≈140°C. The alteration types identified here extend into the distal area of the footwall and are interpreted to be associated with fluids somehow related to the footwall style mineralization. The characterization of the mineralogy, mineral chemistry and fluid chemistry of these assemblages will be used to better understand the origin of these deposits and also as vectors for the discovery of further ore deposits.