THE OPAQUE MINERALOGY OF METASEDIMENTARY ROCKS OF THE MEGUMA GROUP, BEAVERBANK-RAWDON AREA, NOVA-SCOTIA

Opaque mineralogy of a representative cross-section of deformed and me tamorphosed turbiditic slate and metasandstone of the Meguma Group has been investigated optically and by electron microprobe. A strong stra tigraphic control over the presence and abundance of certain opaque mi nerals is recognized, which may prove useful for environmental evaluat ion such as acid drainage potential. Abundant pyrite and pyrrhotite in the lower Halifax Formation reflect concentration of early diagenetic pyrite resulting from the reduction of seawater sulphate under anoxic conditions. Magnetite is restricted to the Goldenville Formation. Ilm enite and rutile occur throughout the succession, and minor chalcopyri te, arsenopyrite, covellite, hematite and glaucodot were also noted. P yrrhotite and ilmenite, as well as spessartine, chlorite and chloritoi d porphyroblasts, developed during prograde metamorphism before and/or during cleavage formation, which also resulted in removal of early di agenetic pyrite. Later pyrite formed by replacement or remobilization of pyrrhotite during retrograde metamorphism. Colloform pyrite, arseno pyrite and chalcopyrite are the youngest mineral phases.