Geology of the Central Quesnel Belt, Swift River, South-central British Columbia

In 1988 regional mapping of the central Quesnel belt (the Quesnel Project; Panteleyev, 1987, 1988; Bailey, 1988; Bloodgood, 1988) continued in the Horsefly area (Panteleyev and Hancock, 1989, this volume) and in the Swift River area, north of the Quesnel River (Figure I-l 9I). In the latter area the Mesozoic stratigraphy was mapped to north of the Quesnel-Barkerville Highway (Figure I-19-2) where the volcanic element of the stratigraphy lenses wt. Upper Triassic pelitic and psammitic sedimentary rocks, equivalent to Bloodgood’s (1988) Units 5 to 7 which underlie the Mesozoic volcanic rocks, continue to the north. The area described in this report includes most of map sheet 938116, the northern part of 93Ai12 and the southeastern part of 93Gil and extends northward from the Hydraulic area mapped in 1987 (Bailey, 1988). The westcentral part of the map area is partly compiled from detailed mapping in the Cantin Creek area by Lu (1989, this volume). In the Swift River area Mesozoic outcrop is extremely sparse and geological interpretation relies to a large extent on the stratigraphic relationships determined in the Hydraulic area to the south and the aeromagnetic patterns of the various rock units. Nevertheless, the pattern of outcrop distribution is consistent with the geology of both the Hydraulic (Bailey, 1988) and Horsefly (Panteleyev, 1988) areas; volcanic rocks exhibit a regional synformal structure with local modifications. Intermediate to felsic volcanic rocks occupy the central part of the synform and matic rocks are exposed on the limbs. The basal sedimentary rocks are more asymmetrically distributed with finer grained varieties more common to the east (“phyllites” of Stmik, 1983, and Bloodgood, 1988) than in the west where psammite rather than pelite predominates. No attempt has been made to subdivide the basal sedimentary rocks (Unit 1) in the Swift River map area. Mapping was carried out by pace-and-compass traversing, at intervals determined by the nature of the terrain and the relative abundance of outcrop interpreted from aerial photographs. Several all-weather roads and numerous logging roads and trails provide good access to most parts of the area.