The Isle aux Morts Prospect: the first significant base metal discovery in the Port aux Basques Complex of southwest Newfoundland

CIM Bulletin, Vol. 81, No. 910, 1988

P.P. O'NEILL, Department of Mines and Energy St. John's, Newfoundland, and D.F. STRONG, Memorial University, St. John's, Newfoundland

The Isle aux Morts Prospect is the first polymetallic, sulphide mineralization reported from the Port aux Basques Complex of southwest Newfoundland. Zn-Pb-Cu-Ba-Ag mineralization hosted by quartz-muscovite semipelite, occurs at the contact between a quartzofeldspathic unit and pelitic unit with intercalated amphibolite. Ore minerals comprise sphalerite-galena-chalcopyrite, in order of decreasing abundance. The principal gangue minerals are quartz, muscovite, feldspar and barite. Three morphologic types of mineralization are present: massive with more than 50% sulphide, flanked on one or both sides by disseminated and/or banded types. The massive type of mineralization exhibits a "durchbewegung" fabric of rounded silicate fragments in a sulphide matrix, characteristic of intensely deformed and metamorphosed sulphide bodies. Sulphide minerals have been mobilized and recrystallized and share the same metamorphic and deformational history as the host rocks. Quartz muscovite schist which hosts disseminated mineralization, displays a K2O enrichment and Na2O depletion, that is typical of alteration associated with sulphide bodies in volcano-sedimentary sequences. Isotopic ratios of sulphur are comparable to those of volcanogenic massive sulphide deposits. Despite penetrative deformation and metamorphic recrystallization, features of the local geology and the mineralization suggest that the Isle aux Morts Prospect is volcanogenic in origin.

Keywords: Mineral exploration, Sulphide mineralization, Isle aux Morts Prospect, Geochemistry, Ore mineralogy, Mineralogy, Petrology, Ore discoveries.