GEOLOGY AND U-Pb GEOCHRONOLOGY OF INTRUSIVE ROCKS ASSOCIATED WITH MINERALIZATION IN THE NORTHERN TAHTSA LAKE DISTRICT, WEST-CENTRAL BRITISH COLUMBIA

The Bulkley Suite of intrusions are spatially associated with numerous important mineral occurrences in westcentral British Columbia. Previous K-Ar dating studies indicated that the Bulkley Suite ranges in age from 70 to 84 Ma (Carter, 1981). The purpose of this study is to better constrain the timing of Bulkley Suite magmatism and associated mineralization in the northern Tahtsa Lake District. The mineral deposits in the study area that are suggested to be related to Bulkley Suite intrusions include Huckleberry, Whiting Creek, Emerald Glacier and Bergette. There are six closely related intrusive phases in the Whiting Creek area, several of which have associated mineralization. In order to resolve the timing of emplacement of the different intrusive phases in the Whiting Creek area, as well as any regional trends in magmatism, precise age constraints arc needed. Uraniumlead geochronological studies were undertaken in order to obtain the necessary precision. The project area is located near the western margin of the Intermontane Belt within the Stikine tectonostratigraphic terrane (Figure 32-l). Stikinia is composed of volcanic and sedimentary strata of Lower Devonian to Middle Jurassic age (Monger et al., 1991), and supracrustal sequences of Middle Jurassic to Early Tertiary age, which are intruded by several suites of intrusive rocks. Monger et al. (1991) suggested that all of the components of Stikinia are interrelated components of a complex island arc terra”e. Stikinia is in fault contact with the Cache Creek Terrane to the east, whereas the nature of the contact with the terranes to the west has been largely obscured by Cretaceous and Tertiary intrusions. Stikinia is thought to have been accreted to the North American continent by late Middle Jurassic time or possibly earlier (Monger et al., 1991).