Preliminary Geology of the Nimpkish Map Area (NTS 092L/07), Northern Vancouver Island, British Columbia By G.T. Nixon, M.C. Kelman, D. Stevenson 1 , L.A. Stokes 2 , and K.A. Johnston KEYWORDS: Vancouver Group, Karmutsen Formation, Quatsino Formation, Parson Bay Formation, Bonanza Group, Bonanza volcanics, Island Plutonic Suite, Triassic, Jurassic, Vancouver Island, Nimpkish, Bonanza Lake, re- gional geology, stratigraphy, structure, skarn, mineral oc- currences, mineral potential, mineralization INTRODUCTION Northern Vancouver Island is richly endowed in a vari- ety of base and precious-metal deposits. For example, the Cu-Mo-Au porphyry deposit at the former Island Copper mine (1971–1994) produced approximately 345 million tonnes of ore with average head grades of 0.41 wt% Cu, 0.017% Mo, 0.19 g/t Au and 1.4 g/t Ag (Perello et al., 1995). Other porphyry deposits are known to exist in the re- gion (e.g., Hushamu [MINFILE occurrence 92L 240] and Red Dog [92L 200]; MINFILE, 2005) and, thanks to a re- cent surge in metal prices, the potential for bringing these and future discoveries into production is currently high. In order to improve understanding of the geological setting of mineral occurrences and the exploration potential of northern Vancouver Island, a regional mapping project (1:50 000 scale) was initiated this past summer in the Nimpkish map area (Fig. 1). The project encompasses the region between Nimpkish and Bonanza lakes, and extends northeast to Robson Bight and south to the Nimpkish River. The area is contiguous with regional mapping at the same scale completed more than a decade ago in the Quatsino Sound region (discussed below). This paper presents the preliminary results of the 2005 field season. Further details on the mapping and geological setting of the mineral occur- rences are presented by Nixon et al. (in press). The Nimpkish sheet covers an area of more than 1000 km 2 with moderate to rugged relief and heavy forest cover except for the higher ridges. Access is provided by an extensive system of active and decommissioned logging roads; however, road coverage is poor in the northeastern part of the project area. Outcrop is generally sparse. Thick deposits of glacial till and outwash typically occupy the main valley bottoms and form veneers on valley slopes. The best exposures are found in roadcuts, along ridge crests and forming bluffs on valley sides, and where streams have incised narrow canyons. PREVIOUS WORK The earliest recorded geological investigations of northern Vancouver Island were made by G.M. Dawson during his pioneering voyage (Dawson, 1887). Early min- eral deposit studies were conducted by Dolmage (1919) and Gunning (1930), who carried out the first systematic mapping of the Nimpkish area (Gunning, 1930, 1932, 1938a, b). Hoadley (1953) incorporated much of Gun- ning’s earlier work in his study of the geology and mineral deposits of the Zeballos-Nimpkish area. The most compre- hensive reports dealing specifically with the geology and mineral deposits of northern Vancouver Island are those of Muller et al . (1974), Jeletsky (1976) and Muller and Roddick (1983). More recently, the results of 1:50 000- scale map ping combined with geo chron ologi cal and biostratigraphic studies in the Quatsino Sound region have been published in a series of preliminary reports by Nixon and coworkers (Nixon et al., 1993a, b, 1994a, b, 1995a, b; Friedman and Nixon, 1995; Archibald and Nixon, 1995). The lithostratigraphic no men clature ap plied to the Nimpkish area (discussed below) draws upon this existing knowledge base. TECTONIC SETTING AND REGIONAL GEOLOGY The geology of Vancouver Island is characterized prin- cipally by Upper Paleozoic to Lower Mesozoic rocks of the Wrangell tectonostratigraphic terrane, which extends north through the Queen Charlotte Islands into southern Alaska (Fig. 1; Wheeler and McFeely, 1991). Wrangellia was amalgamated with the Alexander Terrane in the Alaska panhandle to form the Insular Superterrane as early as the Late Carboniferous time (Gardner et al., 1988), and was accreted to inboard terranes of the Coast and Intermontane belts as late as the mid-Cretaceous (Monger et al., 1982) or as early as the Middle Jurassic (van der Heyden, 1991). At the latitude of the project area, Wrangellia is in- truded to the east by granitoid rocks of the Coast Plutonic Complex and fault bounded to the west by the Westcoast Crystalline Complex, part of the basement to Wrangellia, and Pacific Rim Terrane (Wheeler and McFeely, 1991). The relatively low relief and high heat flow of northern- most Vancouver Island reflect tectonism associated with the development of the Queen Charlotte Basin, a Tertiary transtensional province related to oblique convergence of the Pacific and Juan de Fuca plates with the North Ameri- can plate (Riddihough and Hyndman, 1991; Lewis et al., Geological Fieldwork 2005, Paper 2006-1 135 1 Department of Earth and Ocean Sciences, University of British Columbia, Vancouver BC 2 Department of Earth Sciences, Memorial University of Newfoundland, St. John’s, NL This publication is also available, free of charge, as colour digital files in Adobe Acrobat PDF format from the BC Ministry of Energy, Mines and Petroleum Resources internet website at http://www.em.gov.bc.ca/Mining/Geolsurv/Publications/catalog/ catfldwk.htm