GEOLOGY OF THE BABINE LAKE - TAKLA LAKE AREA, CENTRAL BRITISH COLUMBIA (93K/11, 12, 13, 14; 93N/3, 4, 5, 6) By Paul Schiarizza and Don MacIntyre (British Columbia Geological Survey Branch contribution to the Nechako NATMAP Project) KEYWORDS: Bedrock mapping, Nechako Natmap, Stikine Terrane, Asitka Group, Takla Group, Hazelton Group, Cache Creek Complex, Sitlika assemblage, Trembleur ultramafic unit, North Arm succession, ophiolite, sheeted dikes, M Area of enlargement N Fort showing. Smithers K O L P Fort St. James Vanderhoof J INTRODUCTION E Prince I F George G This paper summarizes the results of D QuesnelH bedrock mapping in the area between Babine C B Lake and Takla Lake in central British Columbia A (Figure 1). This work was done as part of the Nechako Natmap project (see MacIntyre and Struik, 1999, this volume). The 1998 bedrock mapping crew was comprised of Don MacIntyre Vancouver and Paul Schiarizza as co-leaders and geology students Angelique Justason (Camosun Victoria College), Sheldon Modeland (University of Victoria), Stephen Munzar (University of British 93N13 Columbia) and Deanne Tackaberry (University 0204060 of Victoria). The primary objective in 1998 was Kilometres to complete mapping in the northwest quadrant 1996 of the Fort Fraser (93K) map sheet. This work 93N12 Area of Figure 2 was started in 1997 with preliminary mapping of Takla Landing the Tochcha Lake (93K/13) map sheet 93M7 93M8 93N5 (MacIntyre et al., 1998). It also builds on map- Fort BabIne ping by Ash and Macdonald (1993) and Ash et Tak la L 1996 ake al. (1993) around Stuart Lake, and incorporates 93M2 Takla Narrows 93M1 93N4 data gathered by the GSC Natmap crew in the 93N3 1997 vicinity of Trembleur Lake (Hrudey and Struik, 1995 1998). Within most of the area, however, the Granisle 1998 93L16 93K13 MAC 93K14 Ba ke b r La in leu only previous regional mapping dates back to e mb L re Topley Landing a T k e Armstrong (1949). Te l kw a From early June until the end of August, the 93L9 k. L art 93K12 93K11 Stu bedrock geology of NTS map sheets 93K/11, 12, FORT Cunningham Lk. 14 and 93N/3 (Figure 1) were mapped at 1:100 ake Babine L 000 scale. In addition, fill-in mapping was done in map sheets 93K/13, 93N/4 and 93N/5, which Figure 1. Location of bedrock mapping completed had been largely completed in 1997 (MacIntyre in 1998. Inset shows location relative to the et al., 1998; Schiarizza et al., 1998). This work Nechako Natmap Project (light grey shading), cen- tral British Columbia. Also shown is the area cov- provides continuity between Natmap programs ered by Figure 2. concentrated on the Sitlika assemblage in west- Geological Fieldwork 1998, Paper 1999-1 33 Figure 2a. General geology of the Babine-Takla lake area. See Figure 2b for legend. 34 British Columbia Geological Survey Branch Figure 2b. Legend to accompany Figure 2a (facing page). Geological Fieldwork 1998, Paper 1999-1 35 ern 93N map sheet (Schiarizza and Payie, 1997; Complex. Eastern elements of the Cache Creek Schiarizza et al., 1998), the Babine porphyry Complex include a Permian to Lower Jurassic belt of Stikine Terrane in eastern 93L and 93M succession of predominantly pelagic metasedi- map sheets (MacIntyre et al., 1996, 1997; mentary rocks and thick Pennsylvanian - MacIntyre, 1998), and the Cache Creek Terrane Permian carbonate sequences associated with in the eastern 93K map sheet (Struik and ocean island basalts. Structural imbrication of Orchard, 1998, and references therein). Cache Creek Terrane, across predominantly The information contained in this report is west-directed thrust faults, occurred in Early to preliminary; the results from samples submitted Middle Jurassic time, and was approximately for radiometric dating and microfossil extraction coincident with its amalgamation with the adja- have not yet been received. This forthcoming cent Stikine Terrane. data may change or refine some of the interpre- Intrusive rocks are common in the region and tations presented here. belong to several distinct suites. In the current study area Late Triassic-Early Jurassic and Middle Jurassic plutons assigned to the Topley REGIONAL GEOLOGIC SETTING and Spike Peak intrusive suites cut rocks of the The northwest quadrant of the Fort Fraser Stikine Terrane; whereas the adjacent Cache map sheet (93K) and southwest quadrant of the Creek Terrane is host to at least three distinct plu- Manson River map sheet (93N) straddle the tonic suites of late Middle Jurassic, Late Jurassic- boundary between Stikine and Cache Creek ter- Early Cretaceous and Early Cretaceous age. ranes. The oldest rocks exposed along the east- ern margin of the Stikine Terrane are upper LITHOLOGIC UNITS Paleozoic carbonates and island-arc volcanic and volcaniclastic rocks of the Asitka Group. Overlying the Asitka Group are basaltic calc- Stikine Terrane alkaline to alkaline island arc volcanic and sedi- mentary rocks of the Middle to Upper Triassic In the current study area the Stikine Terrane Takla Group and mafic to intermediate calc- is represented by the upper Paleozoic Asitka alkaline volcanic and sedimentary rocks of the Group, Middle to Upper Triassic Takla Group Lower to Middle Jurassic Hazelton Group. and Lower Jurassic Hazelton Group. These arc successions are overlain by predomi- nantly marine clastic sedimentary rocks of the Asitka Group upper Middle Jurassic to Lower Cretaceous Bowser Lake and Skeena groups, which in turn The Asitka Group, as defined by Lord are overlapped by Upper Cretaceous to (1948), includes aphanitic basalts, rhyolites, Paleocene nonmarine clastic sedimentary rocks breccia, feldspar porphyry, chert, limestone and of the Sustut Group or Upper Cretaceous conti- argillites of mid-Pennsylvanian to Early nental arc volcanic rocks of the Kasalka Group. Permian age. The type area is located between Younger rocks, which overlie both the Stikine the Asitka and Niven rivers in the northeast Terrane and adjacent Cache Creek Terrane, McConnell Creek map area. Diakow and include Eocene volcanic rocks of the Ootsa Lake Rogers (1998) describe a two fold subdivision and Endako groups, as well as Miocene- in the McConnell Range. There, the Asitka Pliocene plateau basalts of the Chilcotin Group. Group is comprised of a lower volcanic unit of The Cache Creek Terrane includes the mainly aphanitic basalt and basaltic andesite Sitlika assemblage in the west and the Cache with minor interbeds of fragmental and felsic Creek Complex to the east. The Sitlika assem- volcanic rocks and marine sediments. The upper blage consists of Permo-Triassic bimodal vol- part of the Asitka Group is sedimentary and is canic rocks overlain by Upper Triassic to Lower characterized by a lower member of massive Jurassic clastic sedimentary rocks. This assem- grey limestone overlain by thinly bedded chert, blage is structurally overlain by a poorly dated, tuffaceous siltstone and sandstone, siliceous but partially age-equivalent ophiolitic sequence mudstone and carbonaceous chert. The contact that forms the western part of the Cache Creek with overlying Takla sediments is believed to be 36 British Columbia Geological Survey Branch a disconformity with a depositional hiatus rang- metamorphic rocks, which dips moderately to ing from Early Permian to Late Triassic. the northeast, is bounded to the west by an area However, west of the current study area at the underlain by massive grey limestone and to the Fulton river dam site, a bedded chert that over- east by pyroxene phyric flows of the Takla lies Early Permian limestone of the Asitka Group. The limestone is lithologically identical Group contains Middle Triassic radiolarians to one in the Fulton Lake area west of Babine (Fabrice Cordey, personal communication, Lake that contains Early Permian (Sakmarian 1996). This suggests that some of the sedimen- and Artinskian) conodonts (Orchard, 1996; tary rocks included in the upper sedimentary MacIntyre et al., 1996). A similar age is implied unit of the Asitka Group may actually be for the limestone in the northwest corner of the Triassic in age and should, therefore, be includ- 93K/12 map sheet. These limestone members are ed with the Takla Group. assigned to the Pennsylvanian-Permian Asitka Within the current study area, rocks Group which typically has limestone beds near assigned to the Pennsylvanian to Permian Asitka its upper contact with the Upper Triassic Takla Group underlie the northwest corner of the Group (Diakow and Rogers, 1998). 93K/12 map sheet, southeast of Wright Bay on The metavolcanic rocks east of the lime- Babine Lake (Figure 2). Here, a belt of green- stone in the 93K/12 map sheet are predominant- schist facies metasedimentary and metavolcanic ly chlorite schists and phyllites which locally rocks crop out as a series of northwest trending have layers containing flattened felsic clasts. A ridges with the best exposures occurring in areas sample for U-Pb isotopic dating was collected that have been logged and burned. This belt of from a lens of feldspar phyric, banded rhyolite within the chlorite schist succession (Photo 1). The protoliths for these metamorphic rocks are interpreted to be aphanitic mafic volcanics with lesser associated felsic pyroclastic rocks, a litho- logical mix that is typical of the lower part of the Asitka succession in the McConnell Creek map area (Diakow and Rogers, 1998). If these corre- lations are correct it implies the presence of a northeast dipping, overturned antiform cored by metavolcanic rocks of the Asitka Group. The western overturned limb of this antiform is mainly massive limestone; the eastern upright limb near the contact with Takla Group rocks is medium to thin bedded, metachert and metasilt- stone (Photo 2). These metasedimentary rocks may comprise an upper member of the Asitka Group; alternatively they are a lower deformed sedimentary member of the Takla Group, possi- bly the Dewar Peak Formation. These metasedi- ments are similar to those overlying the Early Permian limestone at the Fulton River dam site in the Fulton Lake map sheet (MacIntyre et al., 1996).