GEOCHEMICAL, STRUCTURAL AND ECONOMIC MINERAL CHARACTERIZATION OF A SEQUENCE OF PALEOZOIC VOLCANIC ROCKS NEAR TERRACE, BRITISH COLUMBIA

Recent regional geologic mapping in the Terrace area, British Columbia has identified a deformed and metamorphosed sequence of Paleozoic volcanogenic and marine sedimentary strata that have potentially significant economic mineralization (Nelson et al., 2008). These newly discovered Paleozoic strata host, and have potential for new, volcanic hosted massive sulphide (VHMS) deposits. The primary component of the Paleozoic section, called the Mt. Attree volcanics, are interpreted to have originated in a submarine setting in an extensional tectonic environment which is favorable for VHMS deposit formation. Geologic mapping and sampling from both Paleozoic and other regionally important units characterized lithologic variations, geometries and structures in the Mt. Attree volcanics and other associated units. A 200m pseudo-stratigraphic section was completed to carefully examine the petrologic, geochemical and structural variations in the sequence. Field and geochemical data show that volcanic units within the section range from basaltic through rhyolite with andesitic and rhyolitic compositions most common. Intercalated within the package are several biotite schist layers, interpreted to have a sedimentary origin. Mapping revealed unique characteristics in the section, including large (0.2-0.8 mm), anhedral, lavender quartz phenocrysts/clasts typically within more felsic volcanics. However, these distinctive lavender quartz eyes were observed locally within more mafic units. Sulphide mineralization, in the form of disseminated pyrite and chalcopyrite was also observed and trace element geochemistry shows elevated Cu concentrations, locally. The sequence is tilted steeply to the north and is variably deformed. Volcanic flows and volcaniclastics have a weakly developed foliation parallel to steep lithologic layering (bedding) while schist lenses have a well developed, steep foliation defined by coarse crystalline biotite. Steep brittle faults cut the entire package which are interpreted to be significantly younger than ductile deformation and which dissect the section. Mapping, geochemistry and mineralization of the pseudo-section suggest that the Mt. Attree volcanics may be related to extension within an island arc setting.