Geology, Mineralization and Lithogeochemistry of the Stuart Lake Area, Central British Columbia

Economic mineral deposits found in oceanic terranes include: mesothermal gold-quartz veins, Cyprus-type massive sulphide, podiform chromite. platinum or cobalt associated with nickel sulphides, as well as asbestos and jade deposits. These are rither hosted by, or otherwise closely associated with oceanic crustal or mantle lithologies. Mesothermal gold-quartz veins and related placers are historically the most economically significant in British Columbia. Ophiolitic crustal and upper mantle rocks are significant in that they delineate deep crustal faults, a first order control for the development of mesothermal veins. Recognition of these lithologies is therefore an important criterion in identifying areas of high mineral potential. Due to their tectonic formation these oceanic terranes are lithologically heterogeneous in detail and they remain undifferentiated on many current geological maps as a result of the small scale of previous mapping. This is particularly true for rocks of the Cache Creek Terrane (CC) in central British Columbia (Stuart Lake belt) where the existing geological database was compiled at I :380 I60 scale (I inch to 6 miles) almost half a century ago (Armstrong. 1949; Rice, 1949). During the 1992 field season three weeks were spent geological mapping at I:50 000 scale in the Stuart Lake area, northeast of Fort St. James in central British Columbia (Figure 1-6-l). The area mapped occupies a northwesttrending belt to the southwest and northeast of Stuart Lake and includes parts of the NTS 93K/7 (Shass Mountain), 93K/X (Fort St. James), 93WlO (Stuart Lake) and 93Kll I (Cunningham Lake) map sheets. It was selected for mapping in order to provide a revised and more detailed geological database needed to evaluate its mineral potential. Stuart Lake itself, and an extensive network of logging roads with a high percentage of forest clear-cut to the west of the lake, provided easy access to a large area. Mapping has been compiled at I: 100 OO@scale and combined with the geology of Paterson (1973) for the Pinchi Lake area east of Stuart Lake (Ash ef al., 1993). Previous investigations by the authors in this area focused on characterizing the tectonic setting and timing of goldquartz vein mineralization and associated felsic intrusive rocks at the Snowbird antimony-gold mewthermal vein deposit (Ash er al., in preparation). This report describes the geology and discusses the mineral potential of the area mapped. Whole-rock major, trace and rare-earth elemental data obtained for metabasalts from