The Nechako NATMAP Project of the central Canadian Cordillera
Geological Survey of Canada - Vancouver,
101-605 Robson Street, Vancouver, BC V6B 5J3, Canada
c/o British Columbia Geological Survey Branch,
PO Box 9320 Stn Prov Gov’t, Victoria, BC V8W 9N3, Canada.
(email: BC Geological Survey)
The Canadian Cordillera in central British Columbia has seen the Mesozoic subduction of an oceanic terrane, the amalgamation of volcanic-arc terranes, continued intermittent Mesozoic compression and magmatism, and Tertiary wrenching, extension and magmatism. Except in its northernmost mountain ranges, the area is extensively covered in glacial drift and thin veneers of Tertiary volcanic rocks. In 1994, a group of scientists and technologists believed they could understand that cover, see through it and discover the components of that collision and extensional orogen. They would apply modern techniques of isotopic and paleontological geochronology; lake-sediment, till, and plant geochemistry; detailed gravity, magnetic, radiometric, paleomagnetic and electromagnetic surveys; and isotopic and trace element lithochemistry as they conducted extensive bedrock and surficial mapping. This compilation summarizes a cross-section of the scientific contributions derived from that mapping conducted under the auspices of the Nechako NATMAP Project. It demonstrates the absolute necessity of applying modern isotopic and paleontologic geochronology to understand the Phanerozoic geology of the Cordillera. It emphasizes the necessity of detailed aeromagnetic surveys (500 m or less line spacing) in looking through covered terranes at anything more than 1:250 000 scale. And it shows the immense utility of applying various geochemical techniques to solve geological problems and establish baselines for future research and economic development. Bedrock and surficial mapping in the central Cordillera, using these and other techniques, have established the nature and timing of Mesozoic crustal growth, Tertiary crustal thinning, and the associated formation of mineral deposits.
Earth scientists from several government agencies, eleven universities and four companies joined forces, formally and informally, from 1995 to 2000 to study Eocene tectonics in the central Canadian Cordillera in British Columbia (Fig. 1). They conducted their research under the auspices of the Geological Survey of Canada’s National Mapping Program (NATMAP) as the Nechako Project.
The project was jointly coordinated and principally funded by the Geological Survey of Canada (GSC) and British Columbia Geological Survey (BCGS). It gained immensely from the large contributions of university researchers and from various companies.
The scientific contributions on this disk come from research directed at key geological issues, whose resolution relied on regional and detailed mapping. Results of bedrock and surficial mapping were integrated with site- and area-specific studies of metallic and industrial mineral deposits, biostatigraphy, geochronology, lake bottom sediment, till and tree geochemistry, airborne and ground geophysics, paleomagnetism, and Geographic Information System (GIS) interpretations. New regional and detailed geological and geophysical maps were published for the Nechako River (93F), Fort Fraser (93K) and parts of Prince George (93G/12,13), Smithers (93L/16), Hazelton (93M/1,8), and Manson River (93N/4,5,12) map areas (Fig. 2). In addition to hardcopy maps and reports, all data are in computer-accessible, GIS-compatible format and are being made available on disk and through the BCGS MapPlace and GSC CORDLink internet web sites.
As originally envisaged, Nechako Project set out to test 5 hypotheses and in doing so to make more detailed geological maps (Struik and McMillan 1996). Those hypotheses were that in central British Columbia:
- the Eocene volcanic complex represents the tectonic-magmatic expression of a regional north-northwest directed extensional event whose rocks and structural environments have potential for precious metal epithermal and intrusion-related copper-gold and molybdenum deposits,
- the Triassic-Jurassic volcanic arc sequence of the east-west Skeena Arch through the Nechako area has further potential for copper-gold mineralization,
- the boundary between Stikine and Cache Creek Terranes is a regional east-dipping thrust fault,
- the Permo-Triassic Sitlika Assemblage is equivalent to the Kutcho Formation of northern British Columbia and has the potential to host volcanogenic massive sulphide deposits, and
- the regional Pleistocene glacial ice flowed in various easterly directions throughout its history and those flow directions can be used for drift prospecting,
The project addressed and contributed to each of these hypotheses and, as expected, came up with several surprises outside the realm of these hypotheses. The papers published in The Nechako NATMAP Project Special Issue (Struik and MacIntyre 2001) provide information and evaluation of several of these hypotheses and the context for the rock suites involved. Some key ideas have been published elsewhere (e.g. Selby and Creaser 2001; Villeneuve et al. 2001). References to these publications can be found on this disk.
The Canadian Cordillera is interpreted to be a collage of oceanic and island arc crustal fragments or terranes accreted to ancestral North America (Monger et al. 1972; Monger and Nokelberg 1996) sometime in the early Mesozoic. The ancestral North American rocks occur mainly in two geomorphological belts – the Foreland fold and thrust Belt and the Omineca crystalline Belt (Fig. 1); accreted rocks comprise the Intermontane, Coast, and Insular belts.
The study area is within the Intermontane Belt (Fig. 1) and includes the Stikine (Stikinia) and Quesnel (Quesnellia) volcanic arc terranes separated by the oceanic Cache Creek Terrane (Fig. 1). Stikine Terrane is comprised of Carboniferous to Middle Jurassic island arc volcanic and sedimentary rocks of the Asitka, Takla and Hazelton groups and the related Topley, Stern Creek, and Spike Peak plutonic suites (Schiarizza and MacIntyre 1999). Cache Creek Terrane consists of Carboniferous to Lower Jurassic ultramafic, metavolcanic, and metasedimentary rocks of the Sitlika Assemblage, Tezzeron succession, and Cache Creek Complex, where Cache Creek Complex is interpreted as part of an oceanic accretionary complex (Struik et al. 2001b; Tardy et al. 2001). Quesnel Terrane is made up of Carboniferous to Middle Jurassic extensional to volcanic-arc volcanic, sedimentary and plutonic rocks (Struik 1987; Monger and Nokelberg 1996).
Stikine Terrane is overlain by post-accretion Upper Jurassic to Upper Cretaceous marine and non-marine sedimentary rocks of the Bowser Lake, Skeena and Sustut groups (Fig. 3). Both Stikine and Cache Creek terranes are cut by post accretion plutons of the Middle Jurassic Stag Lake and Late Jurassic-Early Cretaceous François Lake plutonic suites (Whalen et al. 2001). Cache Creek Terrane is also cut by, Early Cretaceous Mitchell Range intrusive suite (Schiarizza and MacIntyre 1999). Both terranes were overlapped by Upper Cretaceous and Paleocene continental volcanic arc and related sedimentary rocks of the Kasalka and Sustut groups, and by Eocene volcanic-arc influenced, extension-generated volcanic and minor sedimentary rocks of the Ootsa Lake and Endako formations (Fig. 3).
Quesnel Terrane lies east of Cache Creek Terrane and they are separated primarily by the steeply dipping Pinchi Fault. Quesnellia at the latitude of Nechako Project consists mainly of Middle Triassic to Lower Jurassic volcanic-arc rocks, interpreted to have formed above subducting Cache Creek Terrane oceanic rocks and to the northeast contains upper Paleozoic arc-like volcaniclastic rocks (Ferri and Melville 1994).
Nechako NATMAP Project area spans the zone of westward-directed thrust faulting that marks the boundary between the Stikine and Cache Creek terranes. This structural imbrication occurred prior to 165 Ma (Schiarizza and MacIntyre 1999) as indicated by isotopic ages for plutons that cut the bounding fault between the terranes (Fig. 3). Folds and thrust faults related to this imbrication are offset by a complex pattern of high angle faults. The timing of this faulting and its relationship to regional Late Cretaceous to Eocene transpressional and transtensional tectonics is discussed more fully in MacIntyre and Villeneuve (2001) and Lowe et al. (2001).
Summary of project contributions
These project contributions are organized by geological entity and from oldest to youngest. They encompass Stikine and Cache Creek Terranes and their structural imbrication, and their intrusive and depositional overlap assemblages and associated mineral deposits, Mesozoic through Tertiary orogenic features. In addition we include contributions to understanding the Quaternary evolution of glacial deposits, geomorphology, the distribution of toxic metals in the environment, hydrogeology of the Vanderhoof area, and the dissemination of information.
In Nechako Project area, Stikine Terrane ranges in age from Lower Carboniferous to Middle Jurassic. Its Mesozoic arc was built over east dipping subduction and eastern exposures of the terrane contain scattered ultramafic rocks. Project mapping has increased details of the stratigraphy, plutonism and distribution of Stikine Terrane rocks. For example, MacIntyre and Villeneuve (2001) now describe the Saddle Hill formation of the Hazelton Group as a thick volcanic succession of subaerial to submarine, porphyritic andesite flows, volcanic breccias and rhyolitic ash flow tuffs that have isotopic ages between 185 and 174 Ma.
Metamorphic rocks of Stikine Terrane, mainly south of Babine Lake, have been identified separately as the Taltapin Complex and consist of amphibolite, marble, calc-silicate, and lesser amounts of meta-rhyolite and muscovite schist (Hrudey et al. 1999). One of the meta-rhyolite tuff exposures yielded U/Pb isotopic ages on zircon ranging from 325-345Ma (M. Villeneuve, pers. comm. 1998). Taltapin Complex is interpreted to range in age throughout the upper Paleozoic and to include equivalents to the Permian Asitka Group.
The younger components of the Upper Triassic to Middle Jurassic volcanic-arc succession of Stikine Terrane encompass the redefined Topley intrusive suite constrained by new U/Pb and Ar40/Ar39 ages to be between 218 to 193 Ma, and the newly identified Spike Peak intrusive suite ranging in age from 179 to 166 Ma. Volcanic rocks of similar ages to these intrusions occur throughout the Babine porphyry copper district in western Nechako Project area (within 93L/16 and 93M/1, Fig. 2). The most economically important of these is the rhyolite-andesite assemblage of the Lower to Middle Jurassic Saddle Hill formation which is the same age as Jurassic sequences in northwestern British Columbia that host the Eskay Creek deposit. This confirms the hypothesis that rocks exposed along the Skeena Arch uplift are also prospective for this type of volcanogenic massive sulphide deposit.
Two localities of pyroxenitic ultramafic rocks referred to as the Butterfield complex (Schiarizza and MacIntyre 1999; Hrudey et al. 1999) occur in Stikine Terrane, immediately west of the Cache Creek Terrane. In the south the meta-pyroxenite is intruded by 219 Ma Stern Creek plutonic suite (Whalen et al. 2001). Post-accretionary Jura-Cretaceous sedimentary and volcanic rocks such as the Bowser Lake, Skeena, and Kasalka groups (Anderson et al. 1999; Schiarizza and MacIntyre 1999) are involved in Jura-Cretaceous contraction like the Skeena fold belt to the north (MacIntyre 1998).
Cache Creek Terrane
Nechako Project recognized, from west to east three principal units in the Cache Creek Terrane of central British Columbia: Sitlika Assemblage, Cache Creek Complex and Tezzeron succession. They form an oceanic accretionary complex. It was confirmed that Sitlika Assemblage, first defined by Monger and Paterson (1974), is equivalent to Kutcho assemblage of northern British Columbia, and that Sitlika Assemblage and Cache Creek Complex are likely thrust westward over Stikine Terrane. In addition we recognized within Cache Creek Complex a complex of thrust sheets composed of distinct depositional environments, and that the suture zone between the Cache Creek oceanic plate and the Quesnel volcanic-arc terrane to the east is primarily obscured by the Tertiary Pinchi Fault. Large tracts formerly mapped as western Cache Creek Complex have been recognized to be part of Stikine Terrane and Sitlika Assemblage (Struik et al. 2001b).
Geochronological sampling confirmed and increased the size of unique conodont, radiolaria and fusulinid fossil collections made in previous years in the Sitlika Assemblage, Cache Creek Complex, and Tezzeron succession. These collections contain Permian and Early Triassic faunal assemblages rare or previously unknown in western North America and that are restricted to these rock assemblages (Orchard et al. 2001).
Sitlika Assemblage consists of Permian volcanic rocks and Triassic and Lower Jurassic sedimentary rocks, which underlie the westernmost belt of Cache Creek Terrane in central British Columbia. Bellefontaine et al. (1995) postulated that Sitlika Assemblage was equivalent to the Kutcho Formation of northern British Columbia, because they both had Permian rhyolite and andesite, and lay along the west side of Cache Creek Terrane. This correlation has been confirmed within this project, based on isotopic age dating (Childe and Schiarizza 1997), fossil ages (Orchard et al. 2001) and lithological and chemical correlations (Childe and Schiarizza 1997).
Nechako NATMAP Project extended the distribution of the Sitlika Assemblage and thus the area prospective for Kutcho Creek type volcanogenic massive sulphide deposits southward from Takla Lake through Fort Fraser map area (Schiarizza and MacIntyre 1999; Hrudey et al. 1999). Rocks of the assemblage in this southern area had been mapped mainly as undifferentiated Cache Creek Complex. Chemical affinities of the Sitlika basalt and rhyolite are indicative of ocean floor to arc generation (P. Schiarizza, pers. comm. 2000).
Cache Creek Complex
Paleontology played a critical role in understanding the geology of the Cache Creek Complex and other sedimentary units of the Nechako Project area (Struik et al. 2001b; Orchard et al. 2001; Sano and Rui 2001). For example, the total age range of the Cache Creek Complex in central British Columbia has been extended to lowest-most Upper Carboniferous (Bashkirian) to upper Lower Jurassic (Toarcian) based on new identifications of conodonts, radiolaria, fusulinids and various macrofossils (mainly corals and pelecypods). The same fossil determinations were instrumental in determining older-over-younger thrusting in parts of Cache Creek Complex.
Cache Creek Complex could be divided into tectono-stratigraphic units that define thrust sheets within an accretionary complex (Fig. 3; Struik et al. 2001b). The thrust sheets cover large areas forming a semi-coherent thrust belt rather than a subduction generated mélange.
Limestone of the Cache Creek Complex has been constrained to four time intervals: earliest Upper Carboniferous to Lower Permian, Upper Permian, Lower Triassic, and Middle to Upper Triassic. Upper Carboniferous to Lower Permian Cache Creek Complex limestone is most voluminous and is generally clastic, shallow- to moderately shallow-water facies and thought to have developed on basaltic ocean islands (Sano and Rui 2001). Early and possible Middle Triassic crustal upheaval are recognized through identification of limestone conglomerate and breccia that contain mixed conodont fauna as young as Triassic (Sano and Rui 2001; Orchard et al. 2001).
From new lithogeochemistry, basalts of Cache Creek Complex represent a suite of various oceanic magmatic environments and near Fort St. James, are mainly of ocean-island and ocean plateau type (Tardy et al. 2001). Ophiolitic successions have been recognized in several places and the majority of the group appears to be composed of dismembered ophiolite, ocean plateaus, islands and atolls, and accretionary sedimentary assemblages. Thrust faults verge both easterly (eastern part of terrane) and westerly (western part of terrane) (Fig. 3).
Blueschist and eclogite of the Cache Creek Complex have been dated at 221 Ma by Ghent et al. (1995), and they form a narrow zone through Pinchi Lake along the eastern part of the Cache Creek Complex. They are interpreted to form part of a lower thrust sheet of Cache Creek Complex exposed by displacement along the Tertiary Pinchi Fault.
Upper Triassic to Lower Jurassic sedimentary and volcaniclastic rocks, formerly mapped as Takla Group along the eastern boundary of Cache Creek Complex, have been renamed Tezzeron succession. They are interpreted to have been deposited onto the accretionary oceanic assemblages of Cache Creek Complex from the Quesnel Terrane arc to the east (Struik et al. 2001b). These rocks are overthrust by ultramafic rocks that locally form klippe and the highest structural levels of Cache Creek Terrane.
Isotopic dating complemented the mapping of the Endako Batholith in the Nechako NATMAP project to show that the composite intrusion spans more than 75 million years (Whalen et al. 2001; Villeneuve et al. 2001). Lithologically and chemically distinct pulses of magmatism are recognized at 220-215 Ma (Stern Creek Plutonic Suite), 181-165 Ma (Stag Lake Plutonic Suite), 159-145 Ma (François Lake Plutonic Suite), and the 112 Ma (Fraser suite) and 51-49 Ma (Sam Ross Creek phase) (Whalen et al. 2001). The batholith is noted for its association with molybdenite mineralization confined to a short time at the end of the Jurassic (Selby and Creaser 2001). From correlation of fluid inclusions in the Endako molybdenite mine with Eocene resetting of radiogenic argon systematics, it could be shown that molybdenite mineralization was remobilized during the Eocene (Selby and Creaser 2001; Villeneuve et al. 2001). The main mass of the batholith consists of Middle through Late Jurassic diorite, granodiorite and lesser monzogranite, and intruded Stikine and Cache Creek terranes. Near the Endako molybdenite mine, Stikine Terrane country rock has been completely displaced by Middle Jurassic to Eocene plutons. Based on Nd isotopes and other chemistry, the batholith was initiated during subduction-generated magmatism in Early Jurassic time and ended in intra-plate plutonism in the Eocene. These results build on and refine the geological understanding of the plutonic rocks by Kimura et al. (1976) and Carter (1982).
Radiometric surveys over the high-K plutons, which are mostly covered with glacial deposits, were ineffective in differentiating most of the plutonic suites, although it picked up areas of high concentrations of K associated with alteration. The form of K-alteration zones in the Endako Mine were found to correspond to the distribution of fault blocks as determined by paleomagnetic tilt studies (Lowe et al. 2001). Associated aeromagnetic surveys were useful in locating buried faults within the batholith and extending known faults such as the northwest trending dextral Casey Fault that truncates the eastern margin of the Endako ore body (Lowe et al. 2001). Biogeochemical surveys over the batholith have recognized the world's largest known biogeochemical anomaly for molybdenum, centred on the Endako Mine (C. Dunn, pers. comm. 1999; Dunn and Hastings 1998; 1999).
Eocene rocks and structures of the Nechako area were generated during north-northwest directed crustal extension. Detailed isotope geochronology has constrained the extensional event primarily to the time from 55 to 45 Ma (Struik et al. 2000). U/Pb and 40Ar/39Ar methods were used to date volcanic, metamorphic and plutonic rocks of this time interval, and the work for this and other isotopic dating for Nechako Project was done at laboratories at GSC Ottawa (M. Villeneuve), University of Alberta (R. Creaser, N. Grainger, L. Heaman, M. Hrudey, and D. Selby) and University of British Columbia (R. Friedman).
The extension is widespread and expressed by the juxtaposition of fault blocks containing rocks with different stratigraphy, deformation, and metamorphism, and from different crustal levels. These blocks are separated by north-northwest and northeasterly trending faults mostly of unknown amounts and senses of displacement. Where displacement can be determined, the north-northwesterly trending faults are typically steeply dipping and have dextral strike-slip motions, whereas the northeasterly trending faults are moderately to shallowly dipping and have extensional down-dip motions. Lowe et al. (2001) describe the distribution and nature of the Tertiary fault pattern as derived from geophysical and outcrop observations. In general, local highlands are composed of pre-Eocene rocks, and expansive valleys are underlain by Eocene and Miocene volcanic and sedimentary rocks. Such features are well defined in the Babine porphyry copper district of map areas 93L/16 and 93M/1 (Fig. 2; MacIntyre and Villeneuve, 2001), along the Nechako River, and south of Tetachuk and Eutsuk lakes (Diakow et al. 1995). A single, well-defined metamorphic complex (Vanderhoof Complex) formed and was uplifted during less than 8 million years of the early Eocene (Wetherup 1997; Struik et al. 2000). The Vanderhoof Complex gneisses were found to be in shallow fault contact with overlying ultramafic rocks of the Cache Creek Complex (Wetherup and Struik 1996).
The Eocene volcanic complex was generated during the same time as the extension and uplift as recorded in the Vanderhoof Complex. Grainger et al. (2001) describe the rhyolite and andesite complex, and, with Villeneuve and MacIntyre (1997) and MacIntyre and Villeneuve (2001), establish its 9 million year time span. Anderson et al. (1998) outlined some of the preliminary chemical signatures of this suite as defined by the volcanics and the few plutons. The environments of deposition and intrusion they describe range from within-plate to arc, as derived from classical variation diagrams.
Faulting and hydrothermal alteration affected the Eocene volcanic rocks. The age of these events is constrained as post-45 Ma and pre-15 Ma. The faulting is mostly steep to moderately dipping, follows the trends of other early Eocene faults and does not appear to offset Miocene rocks. A description of the hydrothermal fluid system, with its low pH and temperature, and high water flow volumes, has been made by Barnes and Anderson (1999).
Eocene magmatism and tectonics formed the Babine porphyry copper district, and was superimposed onto a Jurassic copper-gold porphyry environment and a mid-Cretaceous magmatic event with potential for volcanogenic massive sulphide mineralization (MacIntyre and Villeneuve 2001). The extent and nature of the mid-Cretaceous magmatism was one of the project’s surprises.
Babine Porphyry Copper District
The northerly-trending Babine porphyry copper district lies west of the north-south trending Takla Fault in western Nechako Project area and includes several major prospects and two past producing mines - Bell and Granisle (Fig. 2). Copper-gold mineralization is associated with small porphyritic intrusions known to be Eocene in age. Our contribution to understanding the nature of the mineralization has been to clearly define the restrictive age range of the Babine intrusions and coeval Newman volcanic rocks (54-50 Ma) using 40Ar/39Ar isotopic dating (MacIntyre and Villeneuve 2001) and lithological correlations. Block faulting has displaced Eocene plutonic and volcanic rocks and associated mineral deposits during post-mineralization extension related to strike-slip faulting. The most prospective areas for mineral exploration are within grabens formed by this faulting. The better exposed, uplifted blocks expose deeper, less fertile, crustal levels.
Mid-Cretaceous bi-modal volcanism
U/Pb and 40Ar/39Ar isotopic dating in the Babine district defines a distinct magmatic event at 107-104 Ma (MacIntyre and Villeneuve 2001). This event involved emplacement of rhyolite domes into submarine volcanic rocks of the Rocky Ridge Formation of the Skeena Group. The rhyolite, which was previously mapped as Eocene, are re-interpreted to be part of a previously unrecognized mid-Cretaceous submarine caldera that could host important shallow water volcanogenic massive sulphide deposits of the Eskay Creek type. As a follow-up to the Nechako project, other areas in central British Columbia are currently being reassessed as potential target areas for the occurrence of similar bi-modal submarine volcanic centers of mid-Cretaceous age.
Miocene magmatic event
Miocene basalt in central British Columbia occurs as scattered volcanic centres and some extensive flows, mainly in the southern part of the Nechako Project area (Anderson et al. 2001). Xenoliths and xenocrysts appear to be derived from both mantle and crustal sources. As part of Nechako Project the basalt centres and flows were dated using 40Ar/39Ar and found to range in age from 13-11 Ma (Anderson et al. 2001). K/Ar ages from equivalent rocks to the east in Prince George and Mcleod Lake map areas range in age from 13-9 Ma (Mathews 1989). The rocks, which differ in age and composition from typical Chilcotin Group basalt in southern British Columbia, contain mantle xenolith and isotopic compositions, which distinguish mantle on either side of the Pinchi Fault (Resnick 1998; Grainger 2000).
During the course of the Nechako NATMAP Project, it was discovered that the ice divide of the Late Wisconsinan glaciation (Fraser Glaciation) migrated easterly from the Coast Mountains to an area centered about a north-northwesterly line from northern Babine Lake to west of Cheslaslie Arm of Tetachuck Lake in Nechako River (NTS 93F) map area (Levson et al. 1998; Levson 2001; Plouffe and Levson 2001; Stumpf et al. 2000). From this ice divide, ice flowed westerly and overrode the Coast Mountains. To the east of the ice divide, such as in the Fawnie Range, ice flow indicators including glacial striations, roches moutonnées and erratics indicate a general eastward ice movement. The use of till geochemistry for drift prospecting requires clear knowledge of the evolution of ice-flow directions and migration of the ice divide.
Drift prospecting programs can take advantage of the much more detailed maps of the distribution of glacial lake sediment (Plouffe and Williams 2001). Glacial lake sediments locally overlie and mask till deposits, which are the best material for drift prospecting, because till is transported along the direction of paleo-ice flow (Plouffe and Levson 2001). The maximum elevation of continuous glacial lake sediment cover decreases to the west (Plouffe 2000).
Till geochemical sampling programs throughout the project area have, as reconnaissance and detailed coverage, given base lines for regional economic development and environmental assessment (Cook et al. 1999; Levson 2001; Plouffe and Williams 2001; Plouffe et al. 2001). Detailed till, lake sediment and water geochemical surveys in the Babine district have defined numerous precious and base metal geochemical anomalies, some in underexplored parts of the district. Those data have been released in various reports (Cook et al. 1999; Plouffe and Williams 1998; Plouffe et al. 2001; Levson 2001).
Additional information about Quaternary geology within the project area.
Metals in the environment
Nechako Project was able to capitalize on its unique geographic location to conduct limited studies on the distribution of mercury and molybdenum. The Pinchi Fault has long been known to have yielded mercury, precipitated mainly as hydrothermal cinnabar. The Endako area was known for its regional distribution of molybdenum (Hastings et al. 1999). In addition to these sites C. Dunn (pers. comm. 1998) discovered a large area with high backgrounds of mercury in lodgepole pine north of Ootsa Lake and south of François Lake. The potential for such an anomaly was brought to our attention by C.A. McDevitt of British Columbia Research Inc. who had done chemical analyses for mercury in various aquatic fauna of a few of the area’s lakes.
A. Plouffe, under the auspices of the GSC Metals in the Environment (MITE) program, undertook a study along the Pinchi Fault to 1) determine if there was any anthropogenic mercury in the humus horizon of soil profile; 2) identify the different phases of mercury in soil profiles developed on till, glacial lake, and glaciofluvial sediments; 3) establish the mobility of these phases; 4) develop criteria to distinguish between natural and anthropogenic mercury; and 5) provide a framework to measure mercury flux to the atmosphere (Plouffe 1998). Selective leach analyses showed that mercury derived from anthropogenic sources is confined to humus portion of soil near inactive Pinchi and Takla-Bralorne Mines. Samples of non-vascular plants (moss and lichen) were collected along the Pinchi fault zone as part of a nation-wide survey of natural mercury emissions to the atmosphere (P. Rasmussen, pers. comm. 1997).
As a trial study we looked at the immediate subsurface of the Vanderhoof area using water well data and Quaternary stratigraphy (Mayberry 2000). This study demonstrated the capability of the existing information to reveal several unique aquifers and their characteristics, and thereby the potential groundwater resources. In addition the study reveals that the Nechako River valley at Vanderhoof developed prior to deposition of the Miocene basalt (i.e. pre- 11-13 Ma).
The project used computer technology extensively to assist in the mapping, and the interpretation, dissemination and archiving of information. For example, digital models of topography were used to study lineaments and as a map base for lithological data (Lowe et al. 2001; Hastings et al. 1999). Aeromagnetic relief models in combination with lithology assisted in the interpretation of structures and rock distribution in covered areas (Lowe et al. 2000). The internet was used to disseminate information on the project, including reports and maps. To reach scientists outside the geoscience field, Hastings et al. (1999) produced an annotated lithology map for the Fort Fraser 1:250 000 scale map area. It discussed geoscience issues relevant to forestry, fisheries, and agriculture. Digital data sets presently available include bedrock and surficial mapping, geophysics and geochemistry of areas of the Triassic-Jurassic volcanic arc of the Quesnel Trough (Williams et al. 1996); surficial geology and till geochemistry of the Manson River and Fort Fraser map areas (Williams and Plouffe 2001); and project geochemistry and bedrock mapping as of 1998 (Struik et al. 2001a). This disk compilation contains an extensive collection of data sets produced during the course of the project. The digital products include a map and data viewer, and have reports in web browser format.
We acknowledge and thank all the 132 people who worked directly (Appendix A) and the many others who worked indirectly on the Nechako NATMAP Project, and the institutions that supported those people, and through them, supported the ideals of the project mission. We thank the Geological Survey of Canada NATMAP secretariat and committee for their support, encouragement and dedication to the principles of a National Mapping Program – a program to support all geoscientists in Canada to work together to improve our understanding of Canadian geology, and to improve our standards and techniques for accomplishing that goal. We thank Brian Jones and the Canadian Journal of Earth Sciences for supporting release of this special volume dedicated to the geology of central British Columbia as seen through the eyes of this project. Bob Anderson provided useful suggestions to improve the manuscript.
Anderson, R.G., Snyder, L.D., Wetherup, S., Struik, L.C., Villeneuve, M.E., and Haskin, M. (1998): Mesozoic to Tertiary volcanism and plutonism in Southern Nechako NATMAP area: Part 1: Influence of Eocene tectonics and magmatism on the Mesozoic arc and orogenic collapse: New developments in the Nechako River map area. In New Geological Constraints on Mesozoic to Tertiary Metallogenesis and on Mineral Exploration in Central British Columbia: Nechako NATMAP project, Edited by L.C. Struik, and D.G. MacIntyre. Geological Association of Canada, Cordilleran Section, Short Course Notes.
Anderson, R.G., Snyder, L.D., Resnick. J., Grainger, N.C., and Barnes, E.M. (1999): Bedrock geology of the Knapp Lake map area, central British Columbia. In Current Research 1999-A. Geological Survey of Canada. pp.109-118.
Anderson, R.G., Resnick, J., Russell, J.K., Woodsworth, G.J., Villeneuve, M.E., and Grainger, N.C. (2001): The Cheslatta Lake suite: Miocene mafic, alkaline magmatism in central British Columbia; in The Nechako NATMAP Project of the central Canadian Cordillera, (ed.) B. Jones; Canadian Journal of Earth Sciences, Special Volume 38, Number 4, p. 697-717.
Barnes, E.M., and Anderson, R.G. (1999): Mineralogy of amygdaloidal, mafic flow rocks of the Endako Group in the Kenney Dam area, northeastern Nechako River map area, central British Columbia. In Current research 1999-E. Geological Survey of Canada, pp. 9-20.
Bellefontaine, K., Legun, A., Massey, N., and Desjardins, P. (1995): Mineral Potential Project, Digital Geological Compilation NEBC South half, (83D, E; 93F,G, H, I, J, K, N, O, P). British Columbia Ministry of Energy, Mines and Petroleum Resources, Open File 1995-24.
Billesberger, S.M., Anderson, R.G., and Quat, M.B. (1999): Geology of four plutons in central and northern Tetachuck Lake map area, central British Columbia. In Current Research 1999-E. Geological Survey of Canada, pp. 31-43.
Carter, N.C. (1982): Porphyry copper and molybdenum deposits, west-central British Columbia. British Columbia Ministry of Energy, Mines and Petroleum Resources Bulletin 64.
Childe, F.C., and Schiarizza, P. (1997): U-Pb geochronology, geochemistry and Nd isotopic systematics of the Sitlika Assemblage, central British Columbia. In Geological Fieldwork 1996. British Columbia Ministry of Employment and Investment, Paper 1997-1, pp. 69-77.
Cook, S., Jackaman, W., Lett, R.E., McCurdy, M.W., and Day, S.J. (1999): Regional Lake Water Geochemistry of parts of the Nechako Plateau, Central British Columbia (NTS 93F/2,3; 93K/9,10,15, 16; 93L/9,16; 93M/1,2,7,8). British Columbia Ministry of Energy and Mines, Open File 1999-05.
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Figure 1. Simplified terrane map of the Canadian Cordillera with the location of the five geomorphological belts and the project area.
Figure 2. Identification of the NTS map area of the Nechako NATMAP Project and the location of some geographic features mentioned in the text. The location of these map areas is shown in Fig. 1. NTS map areas are Manson River (93N), Smithers (93M), Hazelton (93L), Fort Fraser (93K), Nechako River (93F) and Prince George (93G).
Figure 3. Summary time chart of stratigraphic, magmatic, and tectonic events for central British Columbia, as seen by the Nechako NATMAP Project. U, Upper; M, Middle; L, Lower. Numbers on the chart indicate ages (in Ma).
List of geologists, technicians, and field assistants who worked on the Nechako NATMAP Project 1994-2001
A project like Nechako is an enormous task touching many people. This list fails to reflect everyone who contributed to this project. Many people in the managerial and administrative units of the institutions involved in this project are not catalogued here. These people laid out foundations of our processes, did our staffing, paid our bills, initiated and followed through on the contracts, supplied the field gear, ran the lab equipment, shipped the samples, did the archiving of materials, supplied library services, prepared and published the formal publications and did so many other things. Out of these people I would like to highlight Mike Cherry and Dan Richardson, who headed the NATMAP secretariat, and who worked very hard to enable the NATMAP program and the Nechako Project to be successful.
In addition staff at the forest district offices and local forestry companies in Vanderhoof, Fort St. James, Burns Lake, and Houston were generous with information and maps for their respective areas. Staff at the Endako, Pinchi, Bell, and Huckelberry mines enthusiastically provided guided tours of their mine sites.
Bob Anderson, Chris Anderson, Nancy Anderson, Judith Baker, Bruce Ballantyne, Wayne Bamber, Elspeth Barnes, Kim Bellefontaine, Aaron Best, Mel Best, Mary Lou Bevier, Selena Billesberger, Jean Bjornson, Andy Blair, Anthony Bond, John Bryant, D. Bosch, Bruce Broster, John Cassidy, Fiona Childe, Matthew Clapham, Steve Cook, Fabrice Cordey, Rob Creaser, Pat Desjardins, Larry Diakow, J. Dubois, Colin Dunn, Ben Edwards, Grant Edwards, Randy Enkin, Phillipe Erdmer, Karen Fallas, Juliano Ferreria, Claire Floriet, Kelly Franz, Richard Friedman, Peter Friske, Sharon Gardner, Ed Ghent, Nancy Grainger, Eric Grunsky, Andrew Harries, Michelle Haskin, Nicky Hastings, Larry Heaman, Catherine Hickson, Jennifer Hobday, Dan Hora, Mike Hrudey, Dave Huntley, Crystal Huscroft, Glenn Johnson, Daniella Jost, Angelique Justason, K. Kanmera, Holly Keyes, Ed Kimura, Walter Kuit, Robert Kung, Bob Lane, Henriette Lapierre, Michele Lepitre, Janice Letwin, Vic Levson, Samara Lewis, Carmel Lowe, Rob L’Heureux, Amber McCoy, Bill McMillan, Brian Mahoney, Nick Massey, Dave Mate, Zohrab Mawani, Jennifer Mayberry, Ryanne Metcalf, Sheldon Modland, Jim Mortensen, Stephen Munzar, Erin O'Brien, Mike Orchard, Ruth Paterson, Garry Payie, Tina Pint, Alain Plouffe, Jennifer Porter, Terry Poulton, Marianne Quat, Pat Rasmussen, K-H. Reitz, Jonah Resnick, Louis Robertson, Kika Ross, Lin Rui, Kelly Russell, Hiroyoshi Sano, Rob Scagel, Paul Schiarizza, Tom Schroeter, Stephen Sellwood, Rob Shives, Shin Yi Siew, George Simandl, Andy Stewart, Andy Stumpf, Lori Snyder, Christina Struik, Gary Taccogna, Deanne Tackaberry, Marc Tardy, Hillary Taylor, Francois Therrien, Derek Thorkelson, Brian Traub, Shelton Udayakumara, Mike Villeneuve, Brian Ward, Shireen Wearmouth, Gordon Weary, Ian Webster, Ralph Westera, Stephen Wetherup, Joe Whalen, James White, Roger White, Sue Wiebe, Stephen Williams, Glenn Woodsworth, Paul Wojdak, Hani Zabaneh.