Metallogenesis in the Bay d'Espoir area, Southern Newfoundland

CIM Bulletin, Vol. 75, No. 839, 1982

H. SCOTT SWINDEN, Mineral Development Division, Newfoundland Department of Mines and Energy, St. John's, Nfld.

Bay d'Espoir is in the approximate center of the south coast of Newfoundland. The geology of the area can most conveniently be considered in terms of three units: (1) an Ordovician or older polydeformed terrain termed the Little Passage Gneisses; (2) a Lower-Middle Ordovician volcano-sedimentary sequence assigned to the Bate d'Espoir Group; and (3) granitoid intrusive rocks of mid-Paleozoic age. Mineralizing events accompanied the formation of the latter two units.The Bate d'Espoir Group comprises a dominantly sedimentary sequence of pre-Middle Ordovician shelf and distal tur-bidite sediments deposited on the eastern margin of lapetus. A significant volcanic component is, however, present in the Isle Galet Formation, consisting of up to 30% felsic volcanic rocks interbedded with sedimentary and epiclastic rocks. The Isle Galet Formation hosts several disseminated to thinly bedded Pb-Zn-Ag occurrences associated with altered felsic tuff and graphitic shale. They occasionally grade laterally into pyrite iron formation and appear to have been deposited in a very distal volcanic environment. The Isle Galet Formation is a time equivalent of the mineralized pre-Caradocian island-arc sequences of central Newfoundland, but differs from them both in style of volcanism and in the nature of the associated mineral deposits. It is, however, comparable in many respects to mineralized volcanic sequences in the La Poile Bay area of southwestern Newfoundland.Mineralization associated with granitoid rocks in Bay d'Espoir is best developed around the southeast margin of the North Bay Granite, where two-mica leucogranite forms a marginal phase. Numerous minor base metal showings occupy quartz, quartz-carbonate and barite veins in the adjacent sedimentary rocks. Collectively, the showings exhibit a well-developed, zonal pattern around the granite margin; molybdenite (±py, cpy) predominates near the contact, giving way outward to galena (±sph, py, asp, cpy) and eventually to stibnite (±asp, py) at the periphery. Mineralization associated with granites in similar settings elsewhere in southern Newfoundland includes tungsten in the Grey River and Granite Lake areas and molybdenite in the Rencontre Lake area.
Keywords: Geology, Metallogenesis, Bay d'Espoir area, Newfoundland, Mineralization, Ordovician rocks, Granitoids, Lithology.