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Distribution of the Chilcotin Group basalts, British Columbia Dohaney, Jacqueline Anne Marie 2009

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DIsTRIBuTIoN OF THE CHILc0TIN GROUP BASALTS, BRITISH COLUMBIA  by JACQUELINE ANNE MARIE DOHANEY B.Sc. (Honours), Carleton University, 2006  A THESIS SUBMITTED IN PARTIAL FULLFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER IN SCIENCE in The Faculty of Graduate Studies  (Geological Sciences)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) August, 2009  © Jacqueline Anne Marie Dohaney, 2009  ABSTRACT The Chilcotin Group basalts (CGB) are Oligocene to Late Pleistocene, stratified olivine-phyric basaltic lavas that overlie a large proportion of the Interior Plateau of British Columbia. The distribution of the CGB is poorly understood regionally; the current distribution is based on compilations of previously published geological maps that employ a diverse set of lithostratigraphic definitions of the Group. Exposure of the basalts is typically poor, but the thickest and most extensive sections are exposed in the valley-margins of major rivers (e.g., the Fraser River). This study collates and interprets spatial datasets and reassesses the distribution of the CGB with the intent of producing a new, more robust distribution of the CGB within the Taseko Lakes (0920) and Bonaparte Lake (092P) map areas, with the goal of better characterizing their geological history and physical volcanology. The new distribution map demonstrates several important observations: (1) the distribution of the CGB is less extensive than previous compilations by up to 48%; this implies that, regionally, the CGB is probably significantly over-estimated; (2) there are abundant, yet not previously identified “windows” through the basalt that expose underlying rock units which may be geologically and economically important; (3) CGB volcanism spanned the Oligocene to the Pleistocene (—30 Ma) and was centered in the central Fraser River area (south of Williams Lake, B.C.) throughout the Pliocene Pleistocene; (4) the CGB was likely erupted from a multitude of small-volume monogenetic vents, rather than a series of long-lived volcanic centres or fissures; and (5) the CGB is thickest where lavas ponded in paleo-valleys, providing a key to mapping the distribution of Neogene channels in the Fraser Basin drainage.  II  TABLE OF CONTENTS ABSTRACT TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES ACKNOWLEDGEMENTS  Chapter 1: Introduction  ii iii V Vi  1  1.1 Statement of problem  1  1.2 Research goals  5  Chapter 2: The Chilcotin Group basalts (CGB) 2.1 Regional geology  6 6  2.2 Previous work  14  2.3 A working definition of the Chilcotin Group  19  Chapter 3: CGB Distribution Re-Assessment  32  3.1 Purpose and scope of CGB distribution re-assessment  32  3.2 Methodology of CGB distribution re-assessment  34  3.3 CGB distribution data types and sources  36  3.3.1 Geological maps containing the CGB  37  3.3.2 Point data  42  3.3.3 Aeromagnetic surveys  56  3.4 CGB distribution data collation  58  3.4.1 Step 1: Re-interpretation of existing geological maps  58  3.4.2 Step 2: Areas of disagreement  63  3.4.3 Step 3: Refining contacts of the CGB  65  3.4.4 Step 4: Final distribution re-assessment  69  3.5 Analysis of uncertainty of the new spatial distribution of the CGB  72  Chapter 4: Discussion and Implications  74  4.1 A new distribution map for the CGB  75  4.2 Basement windows within 0920 and 092P  77  4.3 Spatial and temporal evolution of the CGB  87  4.4 History of major river systems recorded by CGB lavas  94  III  4.5 Summary and conclusions. 97 Bibliography  99  Appendix 1: Database Metadata  113  Appendix 2: UBC Geochemistry Data  118  Appendix 3: Digital Maps  120  Appendix 4: Map Compilation Steps  121  Appendix 5: Final Maps  123  iv  LIST OF TABLES Table 2.1: List of sources on previous studies of the Chilcotin Group 18 Table 2.2: Stratigraphic subdivisions or formations within the Chilcotin Group 26 Table 2.3: Comparison of stratigraphic attributes of CGB versus other major Cenozoic mafic volcanic units 30 Table 3.1: Catalogue of previous mapping in area of interest (0920 and 092P) 40 Table 3.2: List of stratigraphic map units used by previous workers in 0920 and 092P map sheets 60 Table 4.1: List of major MINFILE Occurrences within Taseko Lakes and Bonaparte Lake 83  V  LIST OF FIGURES Figure 1.1: Map illustrating the location of the Chilcotin Group basalts in British Columbia 3 Figure 1.2: A cartoon of lava morphology: valley vs. plateau lavas 4 Figure 2.1: Regional geological setting of the CGB 11 Figure 2.2: Schematic time scale of Cenozoic volcanic stratigraphy of the Intermontane Belt 12 Figure 2.3: Map illustrating the present-day tectonic setting of western North America 13 Figure 2.4: A schematic cross section through the Dog Creek (0920) paleo-valley 25 Figure 2.5: The total alkali’s versus silica geochemical diagram for the CGB 27 Figure 2.6: Photograph of CGB volcanic plug at Lone Butte (092P) 29 Figure 2.7: An age histogram of the CGB 31 Figure 3.1: Location of the CGB Area of Interest (NTS map sheets 0920, 092P) 33 Figure 3.2: Flow chart illustrating the steps of distribution re-assessment of the CGB.. 35 Figure 3.3: Index map showing the location and coverage of previous mapping within 0920 and 092P 41 Figure 3.4: The station table from the geospatial database of the CGB 44 Figure 3.5: A map showing the sample locations and localities 45 Figure 3.6: The spatial distribution of CGB geochronology 47 Figure 3.7: The spatial distribution of the geochemical data collected from the CGB.... 49 Figure 3.8: A map illustrating the location of the ARIS data collected from the spatial database (0920, 092P) 51 Figure 3.9: A map illustrating the locations of the public water wells data within 0920 and 092P 53 Figure 3.10: Location map and catalogue of aeromagnetic survey data 57 Figure 3.11: Several maps illustrating disagreement among previous workers in placement of geological contacts within the Vedan Lake area (0920) 61 Figure 3.12: Preliminary geological map of the CGB 62 Figure 3.13: Map illustrating areas where the database identifies disagreement with the preliminary geological map 64 Figure 3.14: Map illustrating the refinement of boundaries between the CGB and the Thuya Batholith using the first vertical gradient 67 Figure 3.15: Map showing CGB geological contacts which were modified during Step 3 68 Figure 3.16: Two maps (A, B) illustrating final modifications to CGB distribution in Step 4 of re-interpretation 70 Figure 3.17: Kreiged surface illustrating the qualitative uncertainty of the new spatial distribution of the CGB 73 Figure 4.1: Map comparing the previous compilations with a new distribution of the CGB 76 Figure 4.2: New basement windows in 0920 and 092P 81 Figure 4.3: New economic targets in 0920 and 092P 84 Figure 4.4: Regional Geochemical Survey multi-element data maps for 0920 and 092P 85  vi  Figure 4.5: The regional temporal and spatial evolution of the CGB from Oligocene time to Present 90 Figure 4.6: Volcanic necks and major fault lineaments within the Interior Plateau 93 Figure 4.7: Paleo-fluvial drainage networks in the Interior of British Columbia recorded by the Chilcotin Group 96  VII  ACKNOWLEDGEMENTS This study was funded through the Geological Survey of Canada’s  rd 3  Targeted  Geoscience Initiative (TGI-03). I received financial support through an ACCELERATE BC Internship funded by Mathematics of Information Technology and Complex Systems (MITACS), Egil H Lorntzsen Scholarship, and a Geoscience BC Graduate Scholarship. I would first like to thank Kelly for being consistently available when I needed guidance, and for always developing new ideas instead of recycling old ones  —  even with  Masters Projects. I would like to thank Jim, and Bob for being excellent committee members and providing ideas, criticisms and assistance through the entire process. I would like to thank Jamel Joseph, Randy Enkin, Mitch Mihalynuk, Paul Schiarizza, Steven Williams, Katrin Breitsprecher, Jordan Best, Mary Lou Bevier, and Arne Toma for providing technical and geological support, and advice. Graham, I think it goes without saying that none of this work would have been possible without your help, patience and intellect. I thank you for encouraging and sharing scientific discussion with myself and other members of the lab. R-E, I want to thank you for your collaboration in our projects and persistence through everything this year. To my other fellow VPLers  —  Nils, Geeves, Shelley, Steve and Curtis: I am very  thankful that we worked through our projects together, and supported one another, even when it seemed like there was no progress and no hope. Many thanks to Lucy, Kevin, Chris, Dan, Rosie, Andrew, Gareth, Mat, Ben, and many other graduate students for great discussions, celebrations and much needed distractions these past two years. To my family and friends who helped me through many days with words of encouragement, faith and understanding. And lastly, to my father,  VIII  who always asks about my work and has brought me up to love science and my grandfather John who congratulated me on this great achievement in his last days with us.  Ix  CHAPTER 1: INTRODUCTION 1.1 Statement of problem  The Chilcotin Group basalts (CGB) comprise a series of Cenozoic aged, flat-lying basaltic lavas that cover the majority of the Interior Plateau (NTS 0920, P; 093A, B, C, F, G, J, K, L; 083D; 082M) and a portion of the Okanagan Highlands (92H, I; 082E, L) of British Columbia, Canada (Figure 1.1). The Interior Plateau is a composite physiographic region that contains several highlands and plateaus (Tribe, 2005). These basalts are exposed primarily in the walls of present-day river drainages, such as the Fraser and Chilcotin rivers, and as erosional remnants on the peaks of the eastern portion of the Coast Mountains, and the Okanagan Highlands. However, they are presumed to underlie a large proportion of the interior, due to the flat topography of the plateau and the presence of large (--‘several meters in diameter) angular blocks of CGB throughout the landscape. In outcrop, many of the Neogene volcanics are vesicular, columnar-jointed basalts making it difficult to distinguish one from another. To understand and redefine the CGB I must set proper lithostratigraphic parameters for what spatial data can be used to characterize or subdivide the CGB. A sound methodology must be applied to the spatial data collected, including the use of previous mapping (with their own unique methods, interpretations and definitions) so that I can design a more accurate representation of the distribution. There is no unified agreement in a definition of the CGB from previous workers, but all maintain that they are “plateau-forming” like flood basalts. However, recent studies (Andrews and Russell,  2007) suggest that the CGB are not plateau-forming, but dominantly “valley-filling” (Figure 1.2). If the CGB are of lesser volume and thickness, then I expect that the distribution of the unit would likely be reduced. Reduction and modifications in areal extent of the original CGB distribution would have several important effects: 1) “Windows” in the basalt cover to the basement rocks may exist, containing economic and tectonic significance; 2) The evolution of the CGB through time and space may be sufficiently more complex than originally thought; and 3) The new distribution could elucidate the history of the physiography (i.e.,, paleo-topography) and major river drainages within the Interior Plateau throughout the Cenozoic.  2  Figure 1.1: A map of the regional distribution of the Chilcotin Group basalts in British Columbia, Canada. They are located in between two mountain ranges (Coast, Rockies) on the Interior Plateau. Note the association between known outcrop of CGB and low topographic relief. [Geology polygons are from Massey et al., 2005]  Towns Major Roads Rivers and Lakes Chilcotin Group  II 100 km  3  N  +  I  + + +  Thick basalt layers, underneath a thin veneer of drift  +  + +  +  Large volume,wide distribution  + +++++ + + Basement (Undifferentiated)  +  Stratified lavas  I  Low volume, local distribution  NO basalt layers, underneath a thick package of drift  B. Valley-filling lavas  Figure 1.2: Cartoon of two different models regarding lava filling and landscape formation. A. Plateau lavas: high volume eruptions that fill the landscape to create a flat plateau surface, with thick accumulations regionally. B. Valley lavas: lower volume eruptions that fill and follow local topography. Thicker accumu lations occur in paleo-topographic lows (e.g. deep river valleys). C. and D. Represent the same areas post-uplift and erosion of the region. Note that exposure of thick lavas can be found in both models along present day rivers and that the glacial drift can obscure the subsurface geology.  1.2 Research goals  The spatial distribution of the Chilcotin Group basalts is uncertain due to a lack of geoscience information locally and regionally. To overcome this, my re-assessment of the distribution of the CGB involves the following steps:  1. Summarize and assess the original definitions of the CGB in order to develop a new working definition with specific criteria to be used in this project. 2. Compile existing geological, geochronological and geophysical data sets, and relate them in a spatially-referenced database. 3. Perform a mapping compilation of the previous geological works using the new working definition. 4. Test and refine the mapping compilation by overlaying the aforementioned datasets and geophysical surveys, thus creating a new spatial distribution. 5. Explore the new distribution of the CGB, and its relationship to physical volcanology, the geological and physiographic history of the Interior, as well as economic implications for the region.  5  CHAPTER 2: THE CHILCOTIN GROUP BASALTS (CGB) Below I develop a working definition for the CGB that is based on previous work. A clear and unambiguous definition is essential in order to make the best use of the literature, and to reassess the spatial and temporal evolution of the CGB. 2.1 Regional geology  Basement rocks  The Intennontane Superterrane mainly comprises several oceanic and volcanic terranes, with associated stratified and plutonic assemblages. The oldest known terrane is the Quesnellia Terrane, which consists of Paleozoic subterrane rocks (i.e., Harper Ranch Group) and Mesozoic volcanic arc assemblages (i.e., Nicola Group) (Preto, 1977). The Cache Creek Terrane is Mississipian to Upper Triassic in age, and is dominantly oceanic sediments and volcanic rocks (e.g., Cache Creek Complex). It is believed to represent an early Mesozoic accretionary complex of the eastward verging subduction zone that amalgamated Quesnellia to ancient North America, closing the Slide Mountain Ocean. Lastly, the Stikinia Terrane (Devonian to Middle Jurassic) also contains arc volcanics, and was accreted west of the Cache Creek Terrane in Middle Jurassic time (Wheeler and McFeely, 1991). These lithologies comprise the basement to the Cenozoic volcanic assemblages. Figure 2.1 shows the distribution of the basement terranes, as well as the distribution of Cenozoic volcanism.  6  Eocene volcanism  Since the close of the Mesozoic era, several volcanic regimes have dominated the Interior of British Columbia. Volcanism was approximately coincident to the uplift and exhumation of the Coast Plutonic Complex (Souther, 1977). The majority of volcanism occurred during Eocene time (e.g., Kamloops Group, Endako and Ootsa Lake Volcanics) and consists mainly of caic-alkaline lavas and minor amounts of alkaline volcanic rocks and basal and interbedded sedimentary rocks. These Eocene age volcanics are preserved within extensional features (grabens, haif-grabens) and are tilted and normal-faulted (Breitsprecher et al., 2000). Figure 2.2 is a schematic stratigraphic time scale of Cenozoic volcanism, including the CGB.  Oligocene to present volcanism  The Oligocene was a period of volcanic quiescence for most of the Intermontane Belt. By Late Miocene time, mafic volcanism occurred east (inboard) and along strike of the Coast Plutonic Complex throughout the entirety of the Canadian Cordillera (Souther, 1977). Further south, the Columbia River Basalts erupted at the same time. In British Columbia, these mafic volcanics have been subdivided into the CGB, the Anahim Volcanic Belt, and the Wells Gray  —  Clearwater Volcanic field. In general, these lavas are  undeformed, alkaline to tholeiitic, olivine phyric flows, cinder cones, shield volcanoes, volcaniclastics and intrusive plugs. These units are described in more detail in Section 2.3.  7  Regional physiography  The CGB has erupted since early Oligocene time (33.8 <1 Ma) and was -  emplaced onto an evolving physiography. The CGB is post-regional deformation (i.e., Eocene extensional tectonics), flat-lying, and is usually the uppermost stratigraphic unit in any given area of the Interior Plateau. Fission track studies reveal that the Coast Mountains have risen significantly during the Pliocene and Pleistocene (rapid rates of <0.5 km/Ma), forcing edges of the Plateau to elevate (Parrish, 1983) and uplifting western margins of the CGB. The southern extent of the volcanism is exposed as erosional remnants in the present Okanagan Highlands (Mathews, 1988). This region is dissected by valleys and rivers of differing size and orientation creating a higher topographic relief than found to the north. The central and northern part of the volcanic field is found in the southern Interior Plateau which is composed of several plateaus (e.g., Cariboo and Chilcotin Plateaus) and ranges (e.g., the Chilcotin Range). These plateaus are thought to have evolved from a Late Cretaceous to Early Eocene erosional, peneplain surface, which is followed by episodes of regional uplift in Middle Eocene and Pliocene time (Mathews, 1991). They are incised by present-day river canyons (e.g., the Fraser, Chilcotin and Bonaparte Rivers), where outcrop is exposed as steep escarpments. The northern extent of the CGB (the Cheslatta Suite; Anderson et al., 2001) is minimal and found on the Nechako Plateau, which is similarly low relief as the Chilcotin and Cariboo Plateau. Covering a large proportion of these low relief surfaces is a thick package of Pleistocene age glacial drift. This drift obscures the subsurface geology, leading to difficult assessment of the geologic contacts and relationships. Thus, deciphering the  8  geological context for the present topographic profile of the Interior Plateau is also difficult. Origins and tectonic setting of volcanism within the Intermontane Belt Neogene to Quaternary magmatism and volcanism in the Canadian Cordillera is closely related to the current tectonic configuration between the North America, Pacific and Juan de Fuca (Farallon) plates (Edwards and Russell, 2000; Figure 2.3). Subduction of the Farallon Plate under western North America has generated calc-alkaline volcanism along the Cascades and Pemberton-Garibaldi arcs that is contemporaneous with effusion of basalt from a multitude of centres (Northern Cordilleran Volcanic Province, CGB, and the Anahim Volcanic belt) that extended throughout the Intermontane Belt from southern British Columbia to the southern Yukon (Souther and Yorath, 1991) in what was probably an extensional (dextral transtensional) tectonic environment (Souther, 1977). The tectonic setting of the western Cordillera has probably not changed fundamentally in the Neogene (Souther, 1977), and therefore the tectonic controls on volcanism are probably still applicable in the Present. The CGB are transitional in composition and have been variously described as hot spot or back-arc (rift) related assemblages (Dostal et al., 1996). Petrographic features (abundant olivine phenocrysts and a groundmass of fine-grained interstitial titanaugite and plagioclase; ) of the CGB are consistent with typical alkali basalt (Bevier, 1983b; Figure 2.5A) and high MgO and Ti0 2 major oxide geochemistry and are therefore similar to ocean island basalts (e.g., Hawaii; the Azores) and continental intraplate basalts (e.g., the Ethiopian rift, Snake River Plain, Patagonian Plateau and the Basin and Range province in the U.S.) (Bevier, 1982; Bevier, 1983b; Dostal et al., 1996) and are  9  characterized to be hot spot or rift-related. However, dike swarms and huge volumes erupted in relatively short periods of geologic time (<1 Ma) which are common to hotspot or plume magmatism are absent in the Chilcotin region. The major and transition element geochemistry performed by Bevier (1982, 1983b) and Dostal et al (1996) showed that the CGB are uncontaminated by crustal rocks suggesting that an extensional environment is likely  —  but the tectonic setting for Intermontane basaltic volcanism  remains debatable. Insight into the evolution of the CGB is vital to understanding present day Cordilleran tectonics.  10  -  Wells Grey Clearwater Volcanics Anahim Volcanic Belt Garibaldi & Pemberton Volcanics Chilcotin Group Eocene Undifferentiated Terranes Cache Creek Quesnellia Stikinia  Figure 2.1: Map showing the current geological interpretation of Tertiary volcanism in the Interior Plateau. Undifferentiated ‘Basement’ rocks are shown and are dominantly made up of deformed Mesozoic and older rocks of the Cache Creek, Quesnellia and Stikina terranes. Eocene Undifferentiated represents the Cordillera wide Eocene volcanics and volcaniclastics (e.g. the Kamloops Group). Other notable Tertiary Volcanics are labeled: Garibaldi & Pemberton Group, Anahim Volcanic Belt, Wells Grey-Clearwater Volcanics and the Chilcotin Group. Note that Tertiary volcanism are mostly covers the Intermontane Belt, where extension has led to back-arc volcanism in between the mountains (Coast and Omineca Belts). [All polygon and attributed data used from Massey et al., 2005]  Figure 2.2: A schematic time-space diagram that highlights the range of volcanism (denoted by the geochronologi cal age of the unit in question) against the spatial location within the Intermontane and adjacent Coast and Omineca Belts. Lithological descriptions of each group below is taken from Wheeler and McFeely, 1991  Age  0—  Period Quatemarv  —  Coast Belt  Epoch  I  I nterm ontane  rBeIt  HoIocene .  \  Pliocene  Neogene  I  PB Miocene  -j  20  Li r ccrfcrm it,  Oligocene  3  Eocene Undifferentiated (Kamloops Group Equivalents)  40 Paleogene  Eocene  50:  60:  Paleocene  Sloka Skukum  Endako Ootsa Lake  Kamloaps Tranquille Princeton Penticton White Lake Marama  Ma,ron Sanpall Klondike Mtn  I  WG: Wells Gray Clearwater alkaline to tholeiitic olivine basalt lavas, volcanoes and cones -  GB & PB: Caic-alkaline Garibaldi and Pemberton arc volcanics Anahim: Anahim Volcanic Belt peralkaline basalt-comendite shield voTcanoes; alkali olivirie basalt cones Chilcotin Group Basalts: Transitional, olivine-phyric basalt lavas, minor basalt breccias, and intrusive gabbroic equivalents (volcanic plugs) Chilcotin Group Sediments: Alluvial sediments, sandstone, conglommerate, mudstone and minor diatomite (can also be present as interbeds within some volcanic successions) Eocene Undifferentiated: Mainly Eocene age alkali-rich, calc-alkaline andesite, dacite, rhyolite, and volcaniclastics. Alkaline units are plagioclase to augite phyric basalts to andesite  12  Figure 2.3: Tectonic model depicting the present-day tectonic setting of the Northwestern part of North America. Magmatic features (Oligocene to Recent in age) are superimposed onto the diagram. Diagram is modified from Madsen et al., 2006  subducted  Non- Arc and transitional volcanism Chilcotin Group basalts  A  Northern Cordilleran volcanic province Anahim volcanic belt Wells-Gray Clearwater field Edgecumbe volcanic field  Forearc volcanism Masset Alert Bay volcanic belt Wranpell volcanic field Calk-alkaline arc-like centers Transitional geochemistry Alkaline volcanic centers  © ®  Pacific plai.  Arc volcanism related to Juan de Fuca olate subduction Cascade Range arc Pemberton volcanic belt Garibaldi volcanic belt  Explorer plate  rN  0  200 400 km  13  2.2 Previous work The Chilcotin “plateau lavas” were first mapped and described by Dawson (1879, 1895) in regional mapping surveys. Original mapping descriptions by Dawson (1898) grouped Eocene age units (now belonging to the Kamloops or Endako Group), CGB and the Quaternary Wells Gray-Clearwater volcanics as the “Upper Volcanic Group”. Campbell and Tipper (1971) and Tipper (1957, 1959, 1969, 1978) distinguished the plateau lavas from the Eocene Endako Group (and equivalents). Farquharson (1965, 1973) performed geochemistry, petrography and isotopic studies on several prominent gabbro plugs which are Late Miocene in age (Farquharson and Stipp, 1969) and are exposed near 100-Mile House. Mt. Begbie, and Forestry Hill were examined in detail, and results indicate that the plugs are similar in composition and likely the source to the CGB, but underwent some degree of fractionation in a high-level magma chamber (Farquharson, 1973). Bevier (1982) was the first author to ascertain that the CGB were likely plainstype basalts rather than flood basalts; a term that is synonymous with plateau basalts. Basaltic plains are composed of moderately wide-spreading lavas (e.g., 150 km 2 extent of the Craters of the Moon complex, from the Snake River Plains) composed of thin sheets, that often travel through lava tubes and channels (Greeley, 1982). Flood basalts such as the Columbia River basalts of northern Washington State (U.S.A.) are thick (e.g., 10-30 meters thick) incredibly voluminous, and widespread; Creating a vast, lava plain that inundates the regional topography (Greeley and King, 1977). Bevier (1982, 1983b) characterizes the CGB as having many thin, flat-lying to gently-dipping, pahoehoe flows, with field thicknesses between 5-140 m (average of 70  14  m). Lavas exhibit crudely columnar-jointed textures, pillow lava, pillow breccia and rare silicic tephra layers (Bevier, 1983a). Studies by Bevier (1982, 1983b) and Dostal et al. (1996) found the CGB to be chemically uniform, transitional (nepheline to hyperstene normative) basalts. Both agree that the major element composition of the CGB resembles that of oceanic island basalts (OIB) (Bevier, 1982; Bevier, 1983b; Dostal et al., 1996). Isotopic (Pb, and Sr) investigations, and the presence of mantle xenoliths indicate that the basalts were generated in the asthenosphere, with no residency in the crust (having no chemical interaction with the crust) (Bevier, 1 983b; Dostal et al., 1996). Mathews and Rouse (1963), Mathews (1964) and Rouse and Mathews (1979) first described the CGB in association with Miocene plant-bearing deposits underlying, and interbedded within the basalts. Mathews (1988; 1989) and Mathews and Rouse (1984) subdivided the Group into geographically distinct formations (e.g., Harper Creek Formation located in the Dog Creek area) based on geological fieldwork and geochronology studies. Mathews postulated that the distribution of the CGB in the Okanagan region (near Kelowna, B.C.) may not be as extensive as previously thought due to the morphology of the lavas and physiographic nature of the area (Mathews, 1988). Industrial minerals (e.g., diatomite, zeolites etc.) are found within the sediments underlying the CGB in the Deadman Formation (and equivalents). Studies by Read (1987, 1988a, 1988b, 1989b, 1996, 2000) focused on sampling, prospectivity and mapping the extent of these mineral occurrences. Subsequently, the CGB was described adjacent to these deposits.  15  Northern exposures of the CGB near Ootsa Lake (093 F) were studied in great detail by Resnick (1999), Resnick eta!. (1999), and Anderson et a!. (2001) and were distinguished from the CGB by composition, petrology and form. Anderson et a!. (2001) called these exposures the Cheslatta Lake Suite, which comprises xeno!ith-bearing volcanic and diabasic centres of alkaline composition. Geochemical and isotopic studies were carried out on ultramafic-mafic mantle xenoliths within Cenozoic lavas (including CGB lavas and volcanic centers) by Ross (1983), Brearley and Scarfe (1984), Brearley et a!. (1984), Brearley (1986), Canil et al. (1987), Xue et al. (1990), Sun eta!. (1991), Sun and Kerrich (1995), and Suh (1999) in order to detect the properties of the sub Cordilleran mantle. The CGB is also included in many regional and detailed mapping studies and authors portray the unit as being plateau-forming (Schiarizza, 1983; Schiarizza and Boulton, 2006; Schiarizza and Gaba, 1993a; Schiarizza and Gaba, 1993b; Schiarizza and Gaba, 1996; Schiarizza and Israel, 2001; Schiarizza and Preto, 1984; Schiarizza and Riddell, 1997; Schiarizza et a!., 1989; Schiarizza et a!., 1997; Schiarizza et a!., 2002a; Schiarizza et al., 2002b; Schiarizza et al., 2002c; Schiarizza et a!., 2008; Riddell et a!., 1993; Read, 1987; Read, 1988a; Read, 1988b; Read, 1988c; Read, 1989a; Read, 1989b; Read, 1992; Read, 1993; Read, 1996; Read, 2000; Church, 1971; Church, 1978; Church, 1995a; Church, 1995b; Church and Suesser, 1983; Green, 1989; Hickson, 1992; Hickson, 1993; and Anderson et al., 1998; Anderson et a!., 1999; Anderson eta!., 2000). Authors typically refer to the CGB as “olivine basalt” or “plateau basalt” including associated (intercalated) sedimentary rocks. Refer to Table 4.2 for a complete description of mapping units, and lithological descriptions.  16  Recent studies have concentrated on the physical volcanology and thickness models for the CGB (Andrews and Russell, 2007; Andrews and Russell, 2008; Mihalynuk, 2007; Farrell et al., 2007; Farrell et al., 2008; Gordee et al., 2007). Andrews and Russell (2007) suggested that the CGB is less voluminous, thinner and sparsely distributed than previously thought, throughout the entire volcanic field. In order to test this hypothesis, I must first strictly outline the definition of the CGB to set criteria that can be used to collect spatial data. Table 2.1 summarizes the previous studies of the CGB.  17  Table 2.1: A summaiy table listing the type of work, and the referenced authors (geographical location). All authors listed here are referenced in the bibliography of this study.  Author (5) Dawson, G.M.  Regional Geological Mapping  Year (s) 1895, 1898 1959, 1963, Tipper, H.W. 1978 1960, 1961, 1962, 1963, Campbell, R.B. 1978 Trettin, H.P. 1961 Campbell, R.B., and Tipper, 1966, 1968, H.W. 1971 1973a, 1973b, 1980, 1981, Church, B.N. 1995a  NTS Sheet 082L, M; 0921, P 0920, 093B  093A 0921, J, P 092P 082E; 0923, 0; 093L  19&, 19’I,  Schiarizza, P.J. & Schiarizza, P.J. et al Read, P.B. HICKSOn, U.  1989, 1993a, 1993b, 1994, 1996, 2002a, 2002b, 2006, 2008 1988, 1989 1993  082L, M; 0923, K, N, 0, P; 093A, B, C, F, G, H 0921, 0, P U920  Farquharson, R.B., and 1965, 1969, Farquharson and Stipp J.J. 1973 092P 1982, 1983a, 0921, 0, P; 093A, Bevier, M.L. 1983b B, G 1963, 1964, 082E, L; 092H, I, Geochemistry & Geochronology Mathews, W.H., Mathews 1984, 1986, 0, P; 093A, B, G, and Rouse G.E. 1988, 1989 J, L Resnick, J., Resnick J. et al, 1998, 1999, and Anderson, R.G. et al 2000, 2001 Sluggett, C.L. 2008  Recent Studies: Physical Volcanology, Thickness modelling and Geophysical Analysis  Mihalynuk, M.G. and Mihalynuk et al Gordee, S. et. al Farrell, R.E. et. al Andrews, G.D.M., and Russell, J.K. Enkin, R.J. et. al Thomas, M., and Pilkington, M.  2007, 2008 2007 2007, 2008 2007, 2008 2008  093F, J 082E, 092H, I  082E, L; 0921, 0, P; 093A, B, C 093B 0920, P; 093A, B 0920, P, 093A, B, C, F, G, 3, K 082L; 0921, 0, P; 093A, B, C  2008a, 2008b 092P  18  2.3 A working definition of the Chilcotin Group There have been many terms assigned to the CGB in the past, many of which were broad and poorly constrained. The name “Chilcotin Group” was first proposed by Tipper (1978), which is comprised of two lithologically distinct units: 1) Neogene age ‘plateau’ basalts; and 2) An older and conformably underlying sedimentary package, which may as old as Oligocene in age (Rouse et al., 1990; Rouse and Mathews, 1961). In the past, the CGB have been referred to as the “Upper Volcanics” (Reinecke, 1920; Lay, 1940), the “plateau basalts” (Mathews, 1964; Farquharson and Stipp, 1969) or the “plateau lavas” (Rice, 1947).  Chilcotin Group sedimentary units In several well-studied localities (Deadman River, Dog Creek, Red Lake, the Blizzard Uranium Deposit, etc.) a basal, typically unconsolidated, sedimentary package is unconformably overlain by the CGB. These sediments are flat-lying, undeformed and typically well developed (up to —150 m near Deadman River) along major drainage systems (Campbell and Tipper, 1971; Mathews, 1988) and are inferred to be channel filling sediments. Lithologically, they are described as tuff, breccia, diatomite, diatomaceous siltstone, pebbly arenites, and conglomerates. In the Central Chilcotin Plateau these sediments (and their lithological equivalents) range in age from Oligocene to late Miocene, and at least one locality of Pleistocene age (Mathews and Rouse, 1986). The Pleistocene interbed within the Dog Creek locality is of interest due to its occurence between two rapidly emplaced packages  19  of basalt in the Dog Creek paleo-valley, and is referred to as the Dog Creek Formation (Mathews and Rouse, 1986). The premise that CGB lavas are “valley-filling” is most easily elucidated in this locality (Figure 2.4). The development of these sediments is then inferred to be pre- or syn-volcanism (Campbell and Tipper, 1968). Similarly aged basal alluvial and lacustrine sediments are found in the Okanagan Highlands and the Nechako Plateau (Refer to Table 2.2 for a correlative listing of formations of the Chilcotin Group sediments).  Chilcotin Group volcanic units The CGB were described by Tipper (1978) as olivine-phyric, Neogene, flat-lying basalts. These basalts are moderately to highly vesiculated, diktytaxitic in parts, and are commonly undeformed with lower successions of subaqueous volcaniclastics (hyaloclastite, pillows and rare peperites) (Bevier, 1983a; Andrews and Russell, 2007; 2008, Farrell et a!., 2007; Farrell et al., 2008; and Gordee et al., 2007). They are chemically transitional (alkali olivine basalts, basaltic andesite ± lesser hawaiite, mugearite, and trachyandesite); Figure 2.5B) and alkaline (basanite) with olivine phenocrysts (sometimes altered to iddingsite). Other phenocrysts include plagioclase and uncommonly clinopyroxene, and the lavas can contain amygdales of zeolite, carbonate, and sediment intraclasts (Bevier, 1982; Dostal et al., 1996; and Mathews, 1989). Isotopic investigations (Sr, and Pb) and the presence of mantle ultramafic xeno!iths, reveal that the CGB come from a differentiated mantle source, with very little or no residence time in the crust (Bevier, 1982; Bevier, 1983b; Dostal et al., 1996).  20  Regional mapping programs have identified several coeval, mafic intrusive ‘plugs’ (e.g., Lone Butte; Figure 2.6), and irregularly long columnar-jointed ‘volcanic necks’ (Hickson and Higman, 1993; Hickson et al., 1994) which have been inferred as the source of the causative volcanism. Farquharson (1965, 1972) and Farquharson and Stipp (1969) have studied the petrology, geochemistry and geochronology of several gabbroic intrusive rocks noting that their similar composition, age and central location make them excellent candidates for major vents for the CGB lavas. Studies by Farrell et al. (2008) have described prominent paleosol horizons separating subaqueous to subaerial lava flows, and breccias indicating some cessation of volcanic activity (or depositional breaks) particularly in the Chasm locality (near Clinton, B.C.; Figure 1.1). These soils are also included in the definition of the CGB. In rare localities Mathews (1989) identified intercalated felsic tephras between the stratified lavas. Subdivision of the CGB Subdivision of the CGB has been attempted by several authors. Rice (1947) suggested a differentiation of the younger basalts into “Plateau” and “Valley” noticing a distinct difference in age and stratigraphy. The valley basalts are Pleistocene to Holocene in age (Mathews, 1988; Sluggett, 2008) and Mathews (1989) argues for separating these lavas from the rest of the Chilcotin Group based on age and stratigraphic position. Mathews (1989) also locally subdivided the Chilcotin ‘plateau’ basalts into several geographically distinct formations in the Okanagan Highland (082E, F) as well as the Gang Ranch locality (0920). Read (1989) first described the Chasm Formation, found in the Chasm Provincial Park.  21  Further subdivision of the Chilcotin Group was made by Resnick (1999) and Anderson, et al. (2001) by the classification of a more alkaline, xenolith-bearing basalts (and intrusive equivalents) named the Cheslatta Lake Suite in the northern extent of the Chilcotin volcanic field or the Nechako Basin. The Cheslatta Lake Suite is plainly distinguished in the field and should be subdivided regionally in the future. However, many of these efforts at subdivision are inherently local in nature and do not address regionally-significant stratigraphic divisions. Refer once more to Table 2.2 for geographically distinct formation names of the CGB.  Discrimination of the CGB from other Cenozoic mafic volcanics  As previously mentioned, there are other mafic volcanic lavas that occur in the Interior Plateau that are difficult to distinguish one from another: 1. the Wells Gray Clearwater Volcanics, 2. the Anahim Volcanic Belt, and 3. Eocene mafic volcanic units. Regional mapping programs have described several identification criteria in the field for differentiating these volcanic rocks. Table 2.3 is a summary of the characteristics which are used in this study to differentiate between mafic, Cenozoic volcanic rocks. Eocene Endako Group  Early maps of the region commonly grouped mafic rocks of the Eocene Endako Group with the CGB due to their very similar physical appearance and petrology (Dawson, 1898; Tipper, 1963; Tipper et al., 1979). Strictly on the basis of age, the Eocene to Oligocene mafic volcanics (i.e., Endako and Kamloops Group) should be excluded. These basalts are usually interbedded or associated with conformable felsic  22  volcanics (the Ootsa Lake Group) or sediments and entire sections are usually faulted and tilted as a result of extension (Breitsprecher et al., 2000; Breitsprecher, 2002; Anderson et al., 1998; Anderson et al., 1999; Anderson et al., 2000). In the event that outcrop is not extensive, the lavas are dominantly clinopyroxene (augite) porphyritic, alteration of the rocks usually allows for an “older” appearance, and silicic amygdules (chalcedony) within vesicles are common. Neogene Anahim Volcanic Belt The Anahim Volcanic Belt consists of several large (area), volcanic centers, small monogenetic cones and intrusive dykes occurring in the northwest part of the CGB volcanic field (093 C and D) and are believed to be tracing the path of an intraplate mantle hot spot (Figure 2.1) (Souther, 1986). They are dominated by silicic peralkaline lavas with minor basaltic lavas and cones that developed on the flanks of large, evolved, shield volcanoes that developed from west to east across the Interior Plateau. There are several centers that are discrete and distinct in age: a. Rainbow Range (Late Miocene), b. Ilgachuz Range (Late Miocene to Early Pliocene). c. Itcha Range (Pliocene to Early Pleistocene) and d. Nazko cone (Late Pleistocene to Holocene) (Bevier et al., 1979; Souther, 1986; Souther et al., 1987; Bevier, 1989; Charland et al., 1993; Charland et al., 1995). Bevier (1982a, 1983) sites a vent from the eastern Rainbow Range as a possible source for the CGB volcanism. These can easily excluded from the CGB on the basis of their peralkaline composition, occurrence of trachytes and comendites, and the presence of large edifices.  23  Pliocene  —  Pleistocene Wells Gray Volcanic Field  Wells Gray  —  Clearwater Volcanics are Pleistocene to Holocene in age (Hickson,  1986; Hickson and Souther, 1984) and lie east of the CGB in the Shuswap Highlands. The Wells Gray  —  Clearwater Volcanics are the most likely candidate for inclusion into  the Chilcotin Group; they are compositionally and petrographically similar to the CGB (alkali olivine basalt flows, cinder cones and tuyas, with intercalated fluvial gravels and sand (Hickson and Souther, 1984)). They are also, presumably low in volume, with locally fed sources and lava morphologies dependent on the paleo-landscape. The young age and intraglacial features of the Wells Grey- Clearwater Volcanic Field have likely deterred previous workers from grouping them with the CGB; however, this ignores their important similarities, including the observation that coeval lavas are identified within the CGB. The Wells Gray is well exposed and found on peaks and valleys along the incised Clearwater and Murtle Rivers. For the purpose of this study, I will exclude the Wells Gray because of its geographic position and the established nomenclature widely in use; this may change in the future. In conclusion, I define the CGB to include Early Oligocene to Late Pleistocene (Figure 2.7) olivine-phyric basalts, and associated pyroclastics, intrusive plugs, and intercalated ash tephra or paleosols from the Okanagan Highland to the Nechako Plateau. This excludes the Anahim Belt, and Wells Gray-Clearwater volcanics suites, but does include the Pleistocene to Holocene age “valley basalts” recently described by Sluggett (2008).  24  01  I’2  1000  Looking North  Group  Cache Creek  — — —  L•  J Harpers Creek Formation  Dog Creek Formation  K-Ar Date (Ma)  Limestone,argillite,chert  Basement paleo-surface  Basalt  Tan beds; sandstone, conglomerate, siltstone  Grey beds; sandstone, conglomerate, siltstone, till  Basalt cap  500  750  1000  1250  1500  Figure 2.4: A. Schematic cross section taken from Mathews and Rouse (1986) east-west, through the Dog Creek locality, where Pliocene (Harper’s Creek Fm) to Pleistocene age lavas (Dog Creek Fm) are separated by sediments (vertical exaggeration is times four). The paleo valley surface is traced onto the diagram, with the current Fraser River canyon to the far left. Dog Creek is a clear example of the CGB lavas flowing into paleo-topography. B. Photo taken from the western extent of the Dog Creek exposure, location noted on cross section.  UI  UI  >  I..  0  E z  a,  a,  “3 0)  H=He  Chilcotin Group Sediments  Chilcotin Group Basalts  Nechako Plateau  References: Read, 1989a 1 Anderson et al, 20012 Mathews, 1988  I  Okanagan Highlands  Sluggett, 2008* (‘valley lavas”) Rouse and Mathews, 1979+ Rouse and Mathews, 1988’  Central Chilcotin Plateau  Table 2.2: A table showing the formation names assigned to geographically distinct units of the CGB. Several formation names can be roughly correlated to each other based on age. For example, the Chasm and King Edward Creek Formations are both Miocene in age, and are similar in composition and morphology. The Chilcotin Group Sediments are also included below, with chronologically and lithologically distinct formation names. The Crownite Fm and Fraser Bend Fm are both Miocene, but the former is dominated by diatomite, while the later is clastic and alluvial. Note that I have included the “valley” basalts above, and that the Dog Creek Fm is correlative to the Lambly Creek Fm in age.  I’)  z  0  +  0  0•’ 4-.’  0. 35  2-  4—  6  8-  10-  12-  I  45  40  /  I  /  /  50  I  55  I  60  I  andesite  basaltic andesite  2 (wt%) 5i0  basait  o Cheslatta Lake Suite o Dog Creek X Valley Lavas Vents  D CGB  Filled symbols = UBC  65  dacite  Figure 2.5B: Geochemical classification of Cox et al. (1979). CGB is .dominantly basalt, and basaltic andesite with minor basanite, hawaiite, mugearite and trachyandesite (HA = hawaiite)  Figure 2.6: Photograph of Lone Butte; A gabbroic volcanic neck east of the town of 100-Mile House. Locally, there are several volcanic necks (e.g. Mt. Begbie, Forestry Hill) that stick prominently out from the flat, well covered plateau surface.  Looking East  28  (0  -  Clearwater  Kamloops Group  Endako Group  Anahim Volcanic Belt  Wells Gray  B.  Dissimilar  Other: Xenolith bearing localities, massive to dikytaxitic textures  Structure/Alteration: No major structures (minor warping near the Coast Mountains)! minor oxidation and alteration in some localities (i.e. Chasm)  intraglacial features (tuyas), rarely amygdaloidal dominantly bimodal volanics coeval, alkali olivine basalts present, with (peralkaline), topographic relief, shield monogenetic cinder cones volcano morphology typically eocene to oligocene in age, alkaline, mafic volcanics, dark grey to silicic amygdales (chalcedony), augite black in color, columnar jointed phyric typically eocene to oligocene in age, largely calc-alkaline volcanics with minor massive, dark grey basalts massive mafic volcanics  Similar coeval, composition: alkali olivine basalts, xenolith bearing, valley-filling, low volume, local sources, subaqueous features  Phenocrysts/Amygdales: Olivine, !zeolites, carbonates, and sediment  Composition: transitional (alkali olivine A. Chilcotin Group Basalts basalts, basanites and basaltic arenite)  Age: Oligocene to Holocene (major Morphology: thin, flat-lying flows, eruptive periods: Late Miocene, and Late basaltic and intrusive volcanic necks; Pleistocene) subaqueous basalt breccias and hyaloclastite present  —  Table 2.3: A. Summary of the characteristics of the COB including: age, composition, phenocrysts/amygdales, morphology, structure/alteration and other notable features. B. A list of Cenozoic mafic volcanics, and their “similar” and “dissimilar” characteristics (when compared to the CGB. The most similar group is the Wells Gray Clearwater volcanics where location and intraglacial features are the only significant differences.  C  z  (‘  (N  0  +  (N  0  0”  0  2  4  6  8  10  12  35  D  40  45  CGB 0 Cheslatta Lake Suite o Dog Creek X Valley Lavas Vents  Filled symbols = UBC  2 (wt%) Si0  50  55  60  65  trachydacite  Figure 2.5A: The total alkali-versus-silica diagram (Le Maitre et al., 2002) of the geochemical database, illustrating the CGB subdivisions: CGB, Cheslatta Suite, Dog Creek, Valley lavas and the Vents. Notice that the Cheslatta suite and Vents are dominantly alkalic, while the CGB is transitional while the Valley and Dog Creek lavas (both Pleistocene and younger) are more silica rich. (BAS = Basaltic-trachy-andesite; TB = Trachy-basalt)  C.)  =  181  n=160  Ma  32  30 26  Oligocene  28 24  I  22  20  18  14  Miocene  16  12  10  27  8  I  22 20  6  I  4  2  0  1111  81.  Pliocene  the number of samples in the database). Note the high peaks during the Late Miocene, Late  I.IaI_IIIIoIiIiI_IIIIIII  Figure 2.7: A histogram displaying the age range of the CGB (n Pliocene and Pleistocene.  CHAPTER 3: CGB DISTRIBUTION RE-ASSESSMENT 3.1 Purpose and scope of CGB distribution re-assessment The CGB covers a large proportion (up to 50,000  2)  of the Interior Plateau.  However, the distribution of these basalts may be incorrect due to lack of geoscience information and incongruous definitions of the unit between individual mapping programs. Performing a re-assessment of all available data (e.g., maps, geochronology, geophysics) to better constrain the distribution would greatly enhance our understanding of the CGB. In addition, knowing where the CGB covers the underlying geology, and where it does not, could affect the mineral potential of the region. Chapter 3 outlines the methodology used to ascertain the definitive distribution of the CGB by collecting, collating and interpreting multiple datasets including all previous maps. This study is restricted to the Central Chilcotin Plateau in NTS map areas 0920 (Taseko Lakes) and 092P (Bonaparte Lake) (Figure 3.1). Several localities within 0920 and 092P have been studied in detail and are marked on Figure 3.1, such as the Chasm (Read, 1989a; Read, 1989b; Read, 2000; Farrell et a!., 2007; Farrell et al., 2008) Deadman River (Bevier, 1983a; Read, 1988b; Read, 1989a; Read, 1989b; Read, 2000), Dog Creek (Mathews and Rouse, 1986; Bevier, 1983a; Andrews and Russell, 2007; Farrell et al., 2007; Farrell et al., 2008), Taseko River (Bevier, 1983a; Andrews and Russell, 2007), and the Mt. Begbie intrusives (Farquharson, 1965; Farquharson, 1972; Farquharson and Stipp, 1969). Previous knowledge, wealth of data and extensive CGB coverage within these two map areas provides good framework for spatial assessment.  32  Figure 3.1: Location map with NTS map areas 0920, and 092P. These 1:250,000 scale map areas were selected as an area of interest to collect geospatial data and perform a distribution re-assessment for the CGB. Several well-studied localities are displayed on the map.  Mt.tgbie  092P  ChSsm  33  3.2 Methodology of CGB distribution re-assessment Primarily, all regional and detailed geological maps displaying the CGB were collected within Bonaparte Lake (092P), and Taseko Lakes (0920) map areas. These maps are a primary source of data and the beginning point to distribution re-assessment of the CGB. Sampling of CGB exposures, collection of point data sets from the literature, and aeromagnetic geophysical surveys were obtained in order to supplement previous geological mapping. Outcrop areas (obtained from geological maps and fieldwork) and primary point data are considered as the best knowledge of whether CGB are present at each locality  —  or not.  All data were collated in a step-by-step process (Figure 3.2):  Step 1. Compile and re-interpret existing geological maps; Step 2. Use CGB point data and identify areas where improvement is needed; Step 3. Use aeromagnetic geophysics to refine and discriminate subsurface lithologies on preliminary distribution; and Step 4. Draw final geological contacts by iteratively, integrating point data, aeromagnetic surveys and raster topography.  34  C.) ()1  Hickson, 1993  Schiarizza et al, 1994  Old contacts  New contacts  Refine geological contacts using geophysics  Step 3:  Compile existing geological maps  Step 1:  •  o  CGB not present  CGB present  Use geophysics and topography to draw final contacts based primarily on point data  Step 4:  Use point data to identify areas to change  Step 2:  Figure 3.2: Schematic flow chart illustrating Step 1-4 of CGB distribution re-assessment.  3.3 CGB distribution data types and sources This section outlines the nature of the geospatial data collected as part of the reassessment of the distribution of the COB. In addition to data on the CGB, I have included data for the Wells Gray- Clearwater and the Anahim Belt volcanic suites, as well as for “Eocene” and “basement” lithologies. There are three main types of data collected: 1) Geological maps; 2) Point data (e.g., geochronology) including samples collected from the field; and 3) Aeromagnetic surveys.  36  3.3.1 Geological maps containing the CGB  In order to assess the distribution of the CGB, geological maps from the literature must first be collected and compiled. A single geological map of the CGB does not exist. There are different scales of mapping programs that range from regional works (e.g., 1:250,000 and 1:50,000 scale) to local or detailed mapping (i.e., 1:10,000 scale). Provincial scale geological maps (e.g., 1:1,000,000) that show the distribution of the CGB are compilations of previously published smaller-scale maps (Wheeler and McFeeley, 1991; Massey et al., 2005; and Schiarizza et al., 1994). These compilations are the primary source of data to which a new distribution can be compared and contrasted. As might be expected, there are significant discrepancies in the distributions of the CGB shown of these regional-scale maps. The origin of these discrepancies is threefold: 1. The original 1:50,000 and 1:250,000 scale geological maps were made independently and at different times; therefore, they are not seamless (i.e., contacts and units may not correlate across map boundaries); 2. The original maps do not use exactly the same map units (i.e., stratigraphic units); for example, in some maps the CGB and overlying till with basalt clasts are amalgamated to one map (non-stratigraphic) unit (e.g., Hickson, 1993), whereas in others the CG and Pleistocene sediments are separate and distinct stratigraphic units; and, 3. Where more than one small-scale map exists for a specific area, the boundaries of the CGB from each map must be distilled to a single boundary in the compilation map; however, this process is highly subjective and strongly dependent on the judgment of the compiler.  37  Higher resolution (detailed) maps provide higher data concentration, and outcrop information. For Taseko Lakes (0920) and Bonaparte Lake (092P) map areas, there are both regional and local mapping programs; refer to Table 3.1 for a list of the maps used in the compilation. Some maps were rejected for digitization because of poor quality, some maps were superseded by later works, and surficial geology maps were not used in this study. Tipper (1978), and Campbell and Tipper (1971) are the two largest regional maps that cover 0920 and 092P (respectively). Campbell and Tipper (1966, 1971) also published literature adjoining the maps describing the geology in great detail. The complete coverage of both map areas was the greatest advantage gained by these works, specifically Tipper (1978) due to the high detail this map was published (1:125,000 scale), despite its size. Campbell and Tipper (1971) did not differentiate between the CGB and the Wells Grey-Clearwater volcanic rocks, but generally both maps provided the basis for map compilation  —  supplemented by detailed maps (where available).  Unfortunately, outcrop was not marked on these works. There were 15 smaller-scale geology maps that covered some portion of the two map areas (Figure 3.3). Within 0920 (Taseko Lakes), detailed work was focused near on the eastern flank of the Coast Mountains and Taseko River (Hickson, 1993; Riddell et al., 1993; Schiarizza and Gaba, 1993a; Schiarizza and Gaba, 1993b; Schiarizza and Gaba, 1996; Schiarizza and Riddell, 1997; Schiarizza et al., 1989; and Schiarizza et al., 2002c), and along the Fraser River near Gang Ranch (Green, 1989; and Read, 1 988c). Several of these maps illustrate outcrop locations which are first order data that the CGB is present and considered very valuable.  38  Bonaparte Lake (092P) detailed mapping concentrates near the northeast corner of the map area, near Clearwater, B.C. (Dawson, 1898; Hickson, 1986; Schiarizza and Boulton, 2006; Schiarizza and Preto, 1984; Schiarizza et al., 2002b; Schiarizza et al., 2008). These maps cover the periphery of the CGB distribution in 092P, and describe lithologies known to be Wells Grey-Clearwater basaltic rocks (Hickson and Souther, 1984; and Hickson, 1986). Read’s (1989b) detailed map of the Deadman River area is very good quality, and contained, outcrop locations of the CGB, the Deadman River formation, as well as Eocene and basement rocks.  39  Table 3.1: A list of all the regional and detailed mapping collected for 0920 and 092P which is used in this study for compilation. Gray represents maps which were disregarded due to poor quality or that were super seded by later works.  NTS Sheet  Author  0921.P  Dawnon, G.M.  ‘t82L,M 921.P  Dawson, G.M.  1898  Daly, R.A.  1915  082L,M; 921,P  Year  Scale  Projection of Original Map  ommentn .  Lat/Long NAD1927 Canada 1:250.000 Alberta, British Cslumbia  992P 092P 092P  920 920 920 082E-092P 092P 082M, 092P 082L,M: 92P 92l/JIO1P 002P 920 920/J 920 920 920 920 920 920 920 0920 920/J 920/J 092P 092P 920/N 092P 92P  lJglow, W.L. Jj Cockfield, W.E. .1&.2&,. Trettin, H.P. J,j Tipper, H.W. I.IL Campbell R.B. and Tipper H.W. Tipper. H.W. 197j Campbell RB. and Tipper H.W. 1971 Tipper, H.W. 1971k Heginbottom, J.A. 1972 Tipper, NW. Okulitch A.V. and Campbell RB.  1978  921/P,82L/M Dawson 1898 mnOl No plateau lavan present There are eo basalts recorded in this map Not enough geographic markers 1ot enough geographic markers uperceded by Tipper, 1978 This map was saperceded by Campbell. 1 971 Surficial maps  -  92P 92P 0921,J,P 920  Layer Name  MOstly topographic information  1:75,080  1:250,000  Lot/Lang NAD1927 Canada 1:250,000 Alberta, British Columbia 1:250,000 1:250,000 Lat/Long NAD1927 Canada1:125,000 Alberta, British Columbia Let/Long NAD1927 Canada 1:250.000 Alberta, British Columbia Lot/Long NAD1O27 Canada 1:500,000 Alberta, British Columbia -  92P Campbell 1971 mnOl Sarficial maps Surflcial maps 920 Tipper 1978 mnOl  -  jj9  Hickson, C.J. ,jJ,j Schiarizza, P.J. J1!L Schiarizza, P.J. and Prels, V.A. 1984 Read, P.O. 1988c Read, P.O. 1989k Green, iCC. 1989 Schiarizza, P.J. et al ‘1999 Schiarizza, P.J. and Gabs, R.G l’iickson, C.J. 1993 Hickson, C.J. 1993 Hickson, C.J. ‘1993 Hickson, C.J. ‘1993 Riddell, J. ‘1993 Schiarizza, P.1. and Gaba, R.G 1993b Schiarizza, P.1. et al 1994 Church, ON. 1995a Schiarizza, P.J. and Riddell, J. Schiarlzza, P.1. at al 2002a Schiarizza, P.J. et a! 2002k Schiarizza, P.J. et al 2092c Schiarizza, P.J. and Boullon, A. 2006 Schiarizza, P.J. et al 2098  Wells grey polygons  92P Okulitch 1979 mnO3 92P Hickuon 1982 0001  Superceded by Schisrizza, 1984  1:50,000 1:50,000 1:50,000  Lal/Long NAD1 927 Canada Alberta, British Columbia UTM Zone 10, NAD83 (Canada) UTM Z10 NAD83 Canada IITM Zone 10, NAD83 (Canada)  92P Schiarizza 1984 001 920/P Read 1989 29 92P Read 1989 21 820 Green 198927  1:50,000  UTM Zone 10, NAD27  820 Schiarizza 19894  1:50,000 1:50.000 1:50.000 1:50.090 1:50,000 1:50,000  I at/Long NAD1983 Canada UTM Zone 10, NAD83 (Canada) UTM Zsne 10, NAD83 (Canada) IJTM Zane 10, NADB3 (Canada) UTM Zane 10, NAD83 (Canada) UTM Zone 10, NAD83 (Canada)  1:50.000  LatiLnno NADB3 Canada  -  1:250,000 Alberu NADB3 Mean for CONUS 1:40,000 atiLon NAD 1983 Canada  Poor quality reproduction  UTM Z10 NAD83 Canada  1:50.000  UTM Z10 NAD93 Canada  1:100,000 UTM Zone 10, NAD83 (Canada) 1:50,000 1:50,000  LJTM Z10 NAD83 Canada  rejected  20 920 920 Q20 920 920  Schiarizza 1993 10 Hickson 1993 mnOl Hickson 1993 mnO2 Hickuon 1993 mnO3 Hickson 1993 mnO4 Riddell 1993 9  ‘20/l Schiarizza 1993 9 ‘)iuital format, imported  1:1 00,000 LatlLong NA083 Canada 1:50,000  -  CB92OAL 20/J Church 19953 920/J Schiarizza 1997 100  ‘)uatemary basalta  92P Schiarizza 2002 15 92P Schisrizza 2002 4 °20/N Schiarizza 20023 92P Schiarizza 2006 8 Digital Files Polygons given from author  40  Schiarizza et al, 1989  Figure 3.3: Index map showing the scale and location of geological maps used in this study. Regional scale maps by Tipper (1978) and Campbell and Tipper (1971) covers both map sheets (0920 and 092P, respectively). Local scale maps are illustrated and labelled.  3.3.2 Point data  Point data comprises geo-referenced data that can be used spatially to restrict, or characterize the CGB distribution. Multiple data were collected from the literature, government websites, and from the field. These data sets include: (1) UBC samples; (2) geochronological data; (3) geochemical data; (4) data from Assessment Reports; (5) data from public water well logs; and (6) physical properties data. The primary purpose of all these data is of a binary nature; Points where the CGB is present, and points where the CGB is not present. All point data was collected, geo referenced, and put into a Microsoft AccessTM database, and is digitally included in this study (Appendix 1). Database development and CGB samples collected by UBC researchers  Spatial data was compiled and collected in a Microsoft AccessTM database (a Microsoft ExcelTM file is also included in this work). Primarily, this database was used to store CGB hand samples collected in the field by UBC researchers (Rebecca-Ellen Farrell, Graham Andrews, Sarah Gordee and myself) and geo-referenced using GanFeld technology (Buller, 2004) Each UBC Sample was given a sample ID with a specific .  naming format (Figure 3.4). Other data sets described herein were collected, and carefully geo-referenced. Well-studied localities (e.g., the Chasm, Mt. Begbie, etc; Figure 3.4) within the Chilcotin Plateau were visited and sampled by the abovementioned researchers and myself. The location table with all datasets is collected in the “STATION” table (Figure 3.5). This table is related through a unique identifier; in this case it is the column for  42  “Sample ID”. Subsequent tables (i.e., geochronology) are connected to the STATION table and therefore maintain location information.  43  Figure 3.4: Sample naming format for UBC samples and a map illustrating UBC sampling locations and localities. Major roads and river are shown in black and blue respectively.  Sample Naming format:  e.g. JD-DCO7-32  {AUTHORS INITIALS}-{LOCALITY INITIALS}{YEAR}-{NUMBER}  Locality Name  o  Sample location  A  Vent Chilcotin Group  44  Figure 3.5: A screenshot from a Microsoft Access database of the STATION table. This table represents the location infonnation for all data points collected for this study. A table is included which describes each column within the STATION table. MkrosoftAcs4ITATi0N:TebIeJ  D  5tte  ffee  Pffrmat  jnsert  5ecerds  Lads  Beb  Weedew  Typnaquestisnlarheip  edehePoF  .  -  ff X  in i -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  $JflYl Pate + 1989 + 2000 + 2007 + 2007 2007 + 7i21/2006 + 7/21/2006 + 7/21/2006 + 2007 + 2007 + 1991 + 7/21/2006 + 7/21/2006 + 712t12006 + 7r2t/2006 7/21/2006 + 7/2112006 + 7i2t/2t116 + 7,21/2006 + 7)22i2526 + 7/22/2006 + 7i22,2006 + 7/22/2006 + 2007 + 2000 + 1999 + 1983 + 1986 ÷ 1986 + 1967 + 1963 + 1981 + 1999  j  i,tL  Sample 113 Symsna3B AR-26356 C992 CC99i CCBO3 50-5636-19 SG-BCO6-29 SG-BCO6-28 CCB04 CCB5 AP-21984 50-8006-27 SG-5C06-25 SG-BOOS-24 :SBc06.23 SGBC0922 SG-BC06-2t SG-BCO6-20 SG-Bc06-26 SG-B006-33 SG-BCO6-32 SG-BCO6-3t SG-B06-30 AP-29009 JRO6-71 AR-149t2t AR-i 1696 AR-1787t AP-14629 AP-16309 AP-i1488 AP-iOt9t AP-14902  JltLtUkLZ4  $Dbgical Unit Chilcatin Group-Basalt Focene- Undifferentiated Chilcotin Group-Basalt Chilcotin Group- Basalt Chilcotin Group Basalt Chilcotin Group -Basalt Basement Undifferentiated Basement Undifferentiated Chilcotin Group-Basalt Chilostin Group -Basalt Basement Undifferentiated Chilcetin Group Basalt Chilcntin Gmup Basalt chilcatin Group- Basalt Chilcstie Group- Sap 6 Chilcotin Group- Saaalt Chilcetin Group- Basalt Chilcetin Groap- Basalt chilcutin Group- Basalt Chilcotin Group Basalt Chilcetin Groap Basalt Chilcetin Group: Basalt Chiloetin Group Ba3alt Basement-Undifferentiated Chilcetin Groop Basalt Basement- Undifferentiated Basement Undifferentiated Basement- Undifferentiated Banement-Undifferentiated Basement- Undifferentiated Basement- Undifferentiated Basement- Undifferentiated Basement Undifferentiated 437 CEJitJe 3ecio  I  -  -  --  :  Recerd: [iil3JI  -  -  -  -  -  -  -  --  -  -  -  SJ.L 4vi  Puiet Type Physical Praperties APIS Physical Praperties Physical Prapedies Physical Praperties USC Sample :UBC Sample UBC Sample Physical Preperties Physical Properties APIS USC Sample :UBC Sample iuec Sample USC Samp USC Sample UBC Sample USC Sample UBC Sample USC Sample USC Sample UBC Sample USC Sample APIS Phyeical Properties APIS APIS APIS APIS APIS APIS APIS APIS  I  I  NTS Sheet  0920 093903 :093803 093603 938 93B 938 093603 093803 0920 93B 938 939 939 93B 93B 938 935 938 93B 935 938 0920 093611 0920 0920 0920 :0920 :0920 -  -  0920 0920 :0920  Rack Type Basting Z 10 NAP8S Northing Zi12 NAL3 6771000 Basalt :474000. Bocena 474091 5654309 Basalt 474018 6771075 Basafl 474022 5771065 Basalt 474023 6771083 Basalt 474136 6771085 Basement 474153 5771087 Basement 474153 5771087 Basalt 474205 5771161 Basalt 474227 5771187 Basement 474239 5662863 474286 5771309 Poa!t Basalt 474286 5771309 Baaatt 474286 5771309 5771309 Basalt 474286 474286 57713 L!46tL Basah 474286 5771309 Basalt 474296 5771309 Basalt 474286 5771309 475436 5771211 6 :o. 475436 5771211 Basalt 475436 5771211 Basalt Sasa!t 475436 5771211 Basement 475538 5662085 Basalt 476283 :582?81 Basement 476334 5661926 476456 Basement 5663026 Basement 476845 5663005 Banement 477741 56635 477971 Basement 6662661 Basement 478944 5672480 Saearseot 479926 5659667 Basement 479950 5661726  •  :  :  Uorrtcmnn  rejert  STATION TnhI Fialdc  Column Gan Station ID  Description  Gan Sample ID  Original Samole Identifiers used by the GSC during fieldwork  Date Sam pie ID  Date of sample taken fUBC) or work published for data Primprv Kev* or unigue identifier which links this table to all other data tables 5  Geological Unit  Original geological units assigned to samoles  Point Type  Data point type, categories include: UBC Sample, Well logs, Assessment Report Number (orARlS), Drilling, Geochron, Geochem, Physical Properties, P.S. Station (GSC Stationsl. and Industrial Minerals  NTS Sheet  NTS Sheet that this data point occupies General rock lithology of data point. This column is quite simplified for the purpose of this study  Rock Type EastinglNorthing  Original Waypoints or Stations used by the GSC during fieldwork  Location information: Easting and Northing for NAD 83, Note the Zone for each respective column  Latitude!Longitude ‘.ocation information: Latitude and Longitude NAD 83 Locality Informal locality name or region that this sample occupies. Stratigraphic information is included here if necessary Owner Researcher, author(s) or company who provided the data (very useful for bibliographic purposes)  45  Geochronological data  The majority of geochrono logy data was taken from the BC CordAge database (Breitsprecher and Mortensen, 2004) and each data point and respective age is referenced through the database STATION table (e.g., Sample Hat 52 has a Middle Miocene K-Ar date [14.1 Ma] and was dated by Mathews, 1989). From the UBC Sample database, Ar Ar dates were prepared by Farrell (in preparation). Ages from known coeval suites (Anahim Belt and Wells Grey- Clearwater) were collected to characterize specific areas; while Eocene and basement rocks were used to identify rocks older than the CGB, and therefore not part of it. Refer to Figure 3.6 for a spatial view of the ages.  46  Figure 3.6: A map illustrating the spatial distribution of the CGB ages. As noted in the legend, ages range from Oligocene to Pleistocene. Miocene ages are evenly distributed throughout the region, while the Pleistocene and Pliocene ages tend to cluster near prominent river drainages such as the Fraser River (i.e close to the Gang Ranch locality). The Pleistocene ages in the south are the valley basalts (Quilchena near Merritt, and Lambly near Kelowna)  K-Ar & Ar-Ar Ages Pleistocene  N  O Late Pliocene • Early  • Late • Middle Miocene Early  o  • Oligocene Nazko Communities Chilcotin Group  50km  Princeton  47  Geochemical data Geochemical data of the CGB was collected by me from the literature (i.e., papers, theses, open file reports and assessment reports; E.g., Mathews, 1988). Samples collected from the BC CordAge database for geochronology were commonly run for geochemistry analyses, and thus the majority of samples were found through references from the previous data set. Some geochemical data are from reports that location information is inferred from poorly prepared maps (Appendix 1; i.e., Samples with poor location information are given lower quality ratings). UBC samples were processed for whole rock geochemistry, and are included in this work (Appendix 2). All geochemical samples were used to spatially define and characterize the CGB (Figure 3.7).  48  Figure 3.7: Map illustrating the spatial distribution of the COB geochemistry. Subdivisions within the CGB are shown, and are geographically distinct (e.g. Cheslatta Lake Suite lies in the northern part of the volcanic field). The Wells Grey-Clearwater volcanics were included, as their chemistry is quite similar to the CGB  Geochemical Suites Wells Grey- Clearwater Volcanics • Valley lavas •  CGB  •  CGB Vents  • Cheslatta Lake Suite Nazko Communities Chilcotin Group  1 50km  0 Tatla Lake  C  Princeton  49  Data from Assessment Reports  Assessment Reports are filed by exploration and mining companies to summarize work done each year in British Columbia in the Assessment Report Indexing System (ARIS) (BCGS, 2008). ARTS is managed by the British Columbia Geological Survey (BCGS) and can be viewed on their website (http://aris.empr.gov.bc.ca) as PDF. These reports provide information on geological mapping, geophysical surveys, geochemical assays, drilling and other exploration-related activities throughout B.C. Two types of data were extracted from the Assessment Reports: 1) Drill holes that intersected basalt as the first lithology; and 2) Location information of the Assessment Reports. Both data were collected by using the search engine on the ARTS website querying by NTS map area; in this case 0920, and 092P. Starting with the most recent reports, and using their keywords to help, I collected all report locations and subsequent drill holes that were useful, and catalogued them into the database with location and rock type information. In total, there were 775 ARTS points and 238 Drilling points collected for the two NTS map areas (Figure 3.8). The three main lithological distinctions were: basement, Eocene and Chilcotin Group basalts. I expect that the majority of ARTS data would lie outside the boundary of the CGB, due to the economic potential of the basement and Eocene rocks. The limitations associated with these data is that the exact point that is assigned is not an exact geographic location where the lithology assigned is found, but rather a median location for the property in question.  50  C,’  Chilcotin Group  25km • Basalt  ARIS Lithologies  Eocene (undifferentiated)  Figure 3.8: Location map for the ARTS data collected for map sheets 0920, and 092P.  •  Basement (undifferentiated)  Data from public water well logs  The British Columbia Ministry of Environment records the depth and lithology information taken from public water wells which are stored in the WELLS database (British Columbia Ministry of Environment, 2008). The location and lithology information is recorded in the database (Appendix 1). Only wells that record lithological information and penetrate bedrock were collected (Andrews and Russell, 2008). The relevant information for each water well (well ID, location, drift thickness, and first lithologies encountered, etc) was obtained from the WELLS database. Wells are typically restricted to areas near towns, villages and along highways and are often totally absent in rural areas (Figure 3.9). The main purpose for using these data in this study is to add to the subsurface information where there is very little outcrop coverage. The major strength of this dataset is that these wells penetrate beneath the glacial drift covering the landscape. Several subdrift rock types are assigned: Basalt, Clastic Sediments (clay, silt, shale, and conglomerate), Limestone, Granite, and Metamorphic. A limitation to this data set is that the lithological descriptions are poor. Andrews and Russell (2008) assigned a certainty value to each point (0-3) where 3 records a high confidence in the lithology assigned and 0 is no confidence or not enough information. No stratigraphic context is given to this dataset, so the “Basalt” rock type could equally describe Nicola, Chilcotin, Wells Gray rocks or even older basaltic assemblages.  52  Chilcotin Group  Basalt  Lithologies Clastic Sediments  Basement (Limestone)  Basement (Granite)  Figure 3.9: Location map for Public water wells data within 0920 and 092P. Distribution of the well logs collected, as well as their respective lithology.  Physical property data A compilation of physical properties data (magnetic susceptibility, density, and paleomagnetism) were compiled by Dr. Randy Enkin, and given to the author for the purposes of this study. As these basalts are known to overlie much of the basement geology, their magnetic properties are important for accurately modeling and identifying magnetic domains. Many magnetic susceptibility and paleomagnetic data were taken from the literature (e.g., Symons, 1969), and also from recent regional and local mapping performed by GSC researchers. Assessing the paleomagnetic character of several flows within one locality can lead to a better knowledge of the rate of emplacement or volcanic history of the lavas. Sampling of well-studied sections (e.g., Dog Creek) by Enkin et al. (2008) was carried out in order to correlate the paleomagnetic characteristics of the lavas with geochronological data, and facies analyses by Andrews and Russell (2007) and Farrell et al. (2007). Sampling methodology and instrumentation is discussed in Enkin et al. (2008). A complete list of the physical properties locations are found in the digital database (Appendix 1).  54  Hierarchy of point data  Each data set used in this study has unique strengths and limitations. UBC samples, geochronological data, geochemical data, and physical property data were all collected and geo-referenced directly from the literature (or in person) and therefore their spatial meaning is very high. These data are considered to be first hand knowledge of the presence of CGB. Location data taken from assessment reports are less certain. Drill hole locations were taken manually from individual reports, many of which are recent so are likely geo-referenced properly. ARIS locations however, are assigned arbitrarily within the report area and should not be considered as direct evidence for the presence (or absence) of the CGB. Lastly, the locations of public water wells data are confident, but due to their ambiguous lithological descriptions (described previously), these data are the least trusted for assessing the CGB distribution.  55  3.3.3 Aeromagnetic surveys Airborne magnetic surveys are conducted in order to better resolve geologic properties because it reflects the physical properties of the underlying rocks. Several detailed (high resolution) and regional (low resolution) surveys were gathered from the Natural Resources Canada Geoscience Data Repository (GSC, 2008) of the residual total magnetic field (RTF) and the first vertical gradient of the residual total magnetic field (VG). RTF shows small variations in the magnetic field that are caused by crustal scale magnetism; while VG presents an enhancement of the small variations providing composition, deformational and metamorphic histories of the underlying rocks. VG is also known (compared to RTF) to reflect shallow magnetic sources (GSC, 2008). Lower vertical derivatives represent nonmagnetic rocks (e.g., granites, non-mineralized sediments) and high derivatives represent highly magnetic rocks (e.g., iron-rich volcanic rocks) (GSC, 2008). Therefore, VG will be the most useful for identifying contacts between the CGB and other lithologies. Dr. Mike Thomas of the Geological Survey of Canada has compiled and analyzed several detailed Bonaparte Lake (092P) geophysical surveys. His work (Thomas and Pilkington, 2008a; and Thomas and Pilkington 2008b) has focused on refining the geological contacts of the region, by subdividing magnetic domains using the VG. Thomas (Pers. Comm.) assisted this study by performing a reduction to pole (RTP) transform on a collage of the surveys listed on Figure 3.10, in order to reduce induced magnetization on high intensity magnetic anomalies. RTP eliminates “ghost” low magnetic intensities and makes interpretation of the surveys easier and clearer.  56  01  400- 420 m  210- 250 m l000m  92P  92P 920. 92P 94N; 920; 93B; 93C; 93F; 93G; 93K Regional  200 m 1000 m  Resolution 100 m 400 m  NTS Sheets 2O 92P  I  GSC Ooen File 2785. 1994  Onen File 5292-93. Osen File 2005-16  GSC Ooen File 5488-5504  Publication GSC Ooen File 2800. 1995 Onen File 5291  .  *Downloaded from the Geoscience Data Repository for ESS Geophysical and Geochemical Data  No. Name .j_ ish Lake ....2..... Lac Ia Hache Bonaparte Lake East & West Eagle (Murphy) Lake, Mckinley Creek, ..4.... Tisdall Lake Southern BC-ALB .j Surveys’ Interior Plateau Geoscience Project (Williams Laket 7 Canada*  ‘“I q.Ju  25km  Figure 3.10: Catalogue and index map for individual magnetic survey data used in spatial analysis of 0920, and 092P. The resolu tion and other information for each survey is listed below. A collage of the surveys was created by Mike Thomas, and given to the author to be used for this study.  3.4 CGB distribution data collation  This section describes the methodology and the challenges for each step of distribution re-assessment for the CGB. Steps 1-4 are cumulative. 3.4.1 Step 1: Re-interpretation of existing geological maps  I compile a preliminary geology map by assessing all available map data from 0920 and 092P. The compilation requires re-interpretation of existing geological maps, synthesis and evaluation of lithological descriptions, and assessment of established geological contacts against known outcrop distributions. Appendix 4 lists the map compilation process used in Step 1 of the re-assessment methodology. Descriptions of the COB have varied slightly between map projects. Table 3.2 contains a summary of the lithological descriptions of the CGB from the maps collated within the two NTS map areas. “Plateau” lava or basalt is used by several authors to describe the unit (Campbell and Tipper, 1971; Schiarizza and Preto, 1984; Church, 1995a); If the CGB is not plateau-forming than their geological contacts may be incorrect. Campbell and Tipper (1971) displays the CGB as covering a large proportion of Bonaparte Lake map area (092P) and it is likely that their view of the unit as “plateau lavas” played a role in that decision. Hickson (1993) combines the Quatemary alluvium and the Chilcotin basalts into one geology code: Q/MPc. Differentiating between these units in this part of the map area is extremely difficult, however she assumes is that the CGB underlies majority of the region due to thick till and flat topography  —  I would  disagree with this premise.  58  During compilation the discrepancies between the geological contacts of previous maps become apparent, sometimes dramatically. This is a reflection of the difficulty of field geological mapping in the Interior Plateau, and of the CGB in particular. In Figure 3.11, disagreement among several workers in a well-studied area is illustrated plainly. The final decision is shown in Map “F” of Figure 3.11. This decision was made by considering each geological contact separately, and ranking some as more likely than others supported by the presence of outcrops. A hierarchy was used draw contacts during compilation to represent the certainty of this work: 1) Outcrop (Most trusted); 2) Several authors interpretations agree; 3) One author’s interpretation at a detailed scale; and 4) One author’s interpretation at a regional scale (Least trusted). This hierarchy allowed for decision making that was contact specific, and not a simple “average” of all the maps and avoiding bias by considering all available data before discrimination. Figure 3.12 represents a preliminary geological map that shows the inferred distribution of the CGB from Step 1 (map compilation) and reflects the number of map sources, the scale, quality of the previous maps, and the extent of outcrop. There are parts of the map areas which have no first-hand observations (scarce outcrop), and thus the interpretations from mapping compilation is not sufficient in ascertaining a “best-estimate”. In Steps 2-4, other datasets are used to supplement this method in order to strengthen the mapping compilation to produce a re-interpreted geological map of the CGB.  59  Table 3.2: List of stratigraphic map units used by previous workers in 0920 and 092P map areas.  Published works use a variety of codes to denote Chilcotin Group rocks, which are grouped here based on lithology type: Chilcotin Group Lavas, Sediments, and Intrusive “Plugs”. The Quaternary Alluvium is included.  Unit  Geology Code  Lithological Descriptions  Chilcotin Group Lavas  L2b:  Upper Volcanic Group (chiefly basalts) (Dawson, 1898)  MPc:  Olivine basalt flows; local sedimentary rocks and debris flows (Schiarizza et al, 1989; Schiarizza and Gaba, 1993) Olivine basalt, andesite; minor related luff and breccia (Tipper, 1 978) Olivine basalt; minor andesite, tuff, breccia, conglomerate, sandstone, siltstone, shale, and diatomite (Schiarizza et al, 1994) Olivine-phyric basalt (Schiarizza et al, 2008) Plateau lava: Olivine basalt (Schiarizza and Preto, 1984) Olivine basalt flows, debris flows (Riddell et al, 1993; Schiarizza and Gaba, 1996) Vesicular basaltfiows; well developed columnar jointing (Green, 1989) Vesicular and amygdaloidal basalt flows (Read, 1989b) Grey Olivine and/or plagioclase-phyric subaerial basalt flows, minor interflow breccia and local pillow breccia (Hickson, 1993) Plateau lavas; olivine basalt, basalt andesite, related ash and breccia beds; basaltic arenite; 25a. Olivine gabbro plugs (Campbell and Tipper, 1971)  MPcv: MPCv: MPCv: mTb: mTc: Plvb, MPlvb: Pvb, Mvb, MPvb: Q/MPcv: Unit 25:  Unit 8:  Chilcotin Group Sediments  MPcs:  -  Plateau basalt (Chilcotin Group); rather flat lying lavas and breccias transitional in composition between quartz tholettes and alkali olivine basalt (Church, 1995a) Buff to grey siltstone, diatom ite, clay and silty sand; coarse reddish brown conglomerate; minor ash beds and lignite (Tipper, 1978)  MPC5:  Ms:  Chilcotin Group Intrusive Plugs Quaternary Alluvium  Ps, Ms, MPs: MPmp: TMb: Q: Qal: Qal: Qs:  Unconsolidated fluviatile conglomerate, sandstone and siltstone; minor rhyolite ash, diatomaceous earth, olivine basalt and breccia (Schiarizza et al, 1994) Bedded gravel, conglomerate and minor sandstone; cream, micaceous rhyolite ash and minor pyroclastic breccia (Green, 1989) Pebble and cobble conglomerate; minor sandstone (Read, 1989b) Mafic plug (Schiarizza and Gaba, 1993) Miocene age; Basalt plug (Schiarizza at al, 1989) Quaternary cover (Hickson, 1993) Till, gravel, sand, clay, and silt (Tipper, 1978) Unconsolidated glacial, fluvial and alluvial deposits (Schiarizza, 1989) Unconsolidated sediments; glacial deposits, colluvium and alluvium; few if any outcrops_(Read,_1989b)  60  Figure 3.11: Comparison of four existing geological maps (A-D) of the CGB ‘s boundary around Vedan and Elkin Lakes in the southern portion of Taseko Lakes map sheet (0920). The boundaries defined in each map are overlain in map E showing the discrepancies present. Map F is a new distribution map (Step 1) produced using the method outlined in this study and is drawn to best reconcile those from previous maps.  Contacts: Approximate  Outcrop  Regional Compilation: Massey et al., 2005  61  0) I’)  1 24 W  25km  Chilcotin Group Basalts  LI  Chilcotin Group Sediments  Roads  •.— Rivers  3.4.2 Step 2: Areas of disagreement After re-interpreting the existing geological maps within 0920 and 092P, the point data collected for this study is overlain onto the new map created in Step 1. As stated previously, the point data serves a binary function (i.e., the presence or the absence of the CGB). Figure 3.13 illustrates inaccuracies with the map data compilation that can be improved. Small adjustments were made where points were very close to geological contacts. Large clusters of non-CGB points were found to lie within areas (red circle noted in Figure 3.13) previously thought to be CGB cover. In order to draw contacts around these points, I supplement the point data with aeromagnetic surveys (Step 3) and raster topography (Step 4).  63  a)  124W  25km  122W  Figure 3.13: Map illustrating areas where the point database identifies disagreement with the preliminary map generated in Step 1. Points coloured in black represents lithologies that are not CGB, while the white coloured points represent known samples of CGB. A density of black dots within the CGB (green) is an area requiring changes to the spatial distribution through modification and re-interpretation (e.g. red circle).  3.4.3 Step 3: Refining contacts of the CGB  By overlaying the CGB layer (derived from previous steps) and point data onto the first vertical derivative aeromagnetic data, it is obvious that some changes may be made in order to refine the distribution. Within the southeast part of Bonaparte Lake (092P) map area, the high resolution geophysics shows two distinct domains. Thomas and Pilkington (2008a) characterized this area based on the patterns of derived contacts but also on the density, intensity, continuity and geometry of the vertical gradient anomalies. Figure 3.14 shows a close-up of the Deadman River locality where the CGB overlies the Thuya Batholith and the Kamloops Group (Eocene) rocks. The smooth, linear low intensity pattern of the Thuya (granitic plutons) contrasts dramatically with the highly variegated, high intensity pattern of the basalts from the CGB and the Kamloops Group. Tracing the contact between these two domains is an obvious improvement. The refinement step was useful where high resolution geophysical surveys were available (i.e., Bonaparte East, Bonaparte West). Thomas and Pilkington (2008a) plotted the known geological contacts against the first vertical derivative in order to assess if there is agreement between the magnetics and the geology. Some domains have been characterized as not belonging to the CGB. Figure 3.15 illustrates the areas which were discarded and change due to differing magnetic signatures and supported by the point database. These domains are characterized by VG anomalies that are strikingly similar to other domains that contain surficial Kamloops Group rocks (Domain 10 and 21; Thomas and Pilkington, 2008a). Also, new geological contacts were drawn near the 100-Mile House locality (red circle in  65  Figure 3.15). This is supported by a high density of basement lithologies (i.e., limestone, elastic sediments, granite, and metamorphic) from the public water well database that are coincident to certain magnetic anomalies.  66  0)  Figure 3.14: Close-up of the re-finement stage of Step 3. The blue box is in the south east part of Bonaparte Lake map sheet where high resolution geophysics shows magnetic patterns can help refine the boundary between the CGB and the Thuya Batholith. As labelled, the Thuya Batholith shows a low intensity magnetic signal, with smooth linear patterns; while the CGB (as well as the Kamloops Group, and Nicola) contains magnetic basalts, and shows a highly variegated, high intensity signal pattern. The boundaries are therefore changed in areas where these domains are obvious and can be traced. The white lines represents changes to the contacts generated from the map data compilation (black lines).  0) 0)  5  122°W  1200 W  120°W  20km  II  Previous contacts generated from Step 2  -  Step 3 New geological contacts  Figure 3.15: Map illustrating the first vertical gradient, point data and the CGB distribution in Step 3. Some magnetic domains were characterized to have differing magnetic signatures (e.g. the Kamloops Group) and were discarded. A cluster of non-CGB point data (red circle) was identified in Step 2, and geological contacts were traced coincident to the magnetic character underlying these data.  3.4.4 Step 4: Final distribution re-assessment In the final stage of re-assessment of the CGB distribution, raster topography was added to refine and guide geological contacts. The area with the most obvious modifications of distribution was in the west part of the Bonaparte Lake map area (092P) (Figure 3.16). The previous distribution of the CGB in this area is generated by the Campbell and Tipper (1971) map interpretation. The re-assessment of this area was challenging due to lack of outcrop, and point data. The main data sets for this area are low resolution aeromagnetic surveys, and previously identified “basement windows” where basement or Eocene lithologies are exposed. The original description used by Campbell and Tipper (1971) to draw the CGB distribution in Bonaparte Lake was based on the basalts being plateau-forming. If the basalts are less extensive (valley-filling), then they would form isolated (or overlapping) islands rather than one large sheet. Therefore, the CGB is traced as areas or clusters around the point data and high intensity magnetic domains (and eliminated in low intensity domains (Figure 3.16 A  —  blue circle) and guided by the topography (Figure  3.16 B). In areas where data is lacking, it can be assumed that there is an equal chance that basalt is present or absent. Other basalt-rich units (e.g., Nicola Group) exhibit similar geophysical signatures, so I relied heavily on the point data (or lack thereof). It is important to note that this spatial distribution is representative of the data used in this study and could be improved by the increased density of data. Refer to Map 1 (Appendix 5) for the detailed final product of the CGB geological map and distribution, and Appendix 3 for a description, and attachment of the digital products from each step of distribution re-assessment.  69  a  20km  II  Geological contacts generated from Step 3  Step 4- Final geological contacts  Figure 3.16: Two maps (A, and B) illustrating Step 4, or the final stage of re-assessment. A. Map of the final CGB distribution (black) overlying first vertical gradient geophysics, and previous contacts generated from Step 3 (white). The distribu tion has been reduced during this step by identif,ring areas that contained low intensity magnetic domains like the Cache Creek and Thuya batholith (e.g. blue circle), and areas with basement point data (e.g. red circle). High intensity (variegated) domains could be other lithologies (i.e. Wells Grey-Clearwater volcanics, Eocene Kamloops Group, Nicola Group).  51° N  122°W 52°N  51°N 120° W  120°W -52° N  B. Map illustrating the final CGB distribution in the Bonaparte Lake map sheet (black), overlying high resolution raster topography (NASA, 2006). Geological contacts in Step 4 were lastly drawn by following topography surrounding known CGB localities (red dashed lines) supported by the point data, and the geophysics.  3.5 Analysis of uncertainty of the new spatial distribution of the CGB  The result of this study is implicitly dependent on the quality and quantity of data collected. I have created a grid to self-assess the value and strength of the spatial distribution. 128 equally spaced squares were created and assigned the values (and qualities) defined below: N/A: There is no basalt, and have never been found here. Mostly alpine areas, where outcrop is good (therefore coloured same as 3) 1: Few or no data* to support basalt present or absent (therefore the distribution assessment is presumptuous). 2:  Some data present, the distribution is moderately certain  3: Data is abundant and supports my interpretation of the distribution of basalt strongly. *data includes point data, outcrops, previous detailed mapping and geophysics  Figure 3.17 illustrates the analysis and highlights areas that need improvement. An example of the analysis is within the 100-Mile House locality. This area would receive a 3 because there is a large density of database points and high resolution geophysical data. The area directly west of 100-Mile House contains no point data, and the resolution of geophysics is poor and would therefore receive a 1.  72  A surface was created by the kriging method of centroid points within attributed squares. • Objects: 128 Type: Floating-point (single) 3 Pixel size: l000xl000 (m) Same size in X and Y direction Exponential Model, Kriging Surface Method Colour Gradient assigned values  Points to Surface: Kriging  1  2  3  Low  High  Certainty Colour Gradient  Few/no data* to support basalt present or absent (therefore the distribution assessment is presumptious). 1  *data includes point data, outcrops, previous detailed mapping and geophysics  Some data present, the distribution is moderately certain  Data is abundant and supports my interpretation of the distribution of basalt strongly. 3 2  No basalt, and has never been found here. Mostly alpine areas where outcrop is good (therefore coloured same as 3)  25km N/A  Certainty Criteria  Figure 3.17: Map representing uncertainty as an error surface, draped over the topography of the region. This surface was created by attributing 128 equally spaced squares with high (3) to low (1) certainty and not applicable (N/A). Note the region denoted by the red box is dominantly of low certainty, lacking data wealth and therefore distribu tion needs improvement.  CHAPTER 4: DISCUSSION AND IMPLICATIONS A new distribution map for the Chilcotin Group basalts (See Appendix 5, Map 1) has been created for NTS map areas 0920 (Taseko Lakes) and 092P (Bonaparte Lake) on the basis of compiled published datasets and new field mapping of select areas. The published datasets include geochronology, geochemistry, mineral assessment reports, public water well logs, physical properties and aeromagnetic surveys and include original data acquired by the author. Map 2 (Appendix 5) illustrates some of the major implications of the new mapped distribution of the CGB for the region including:  1. Basalt coverage is considerably reduced (up to 48%) within 0920 and 092P; application of the same approach to other areas of the Interior Plateau will likely identify similar reductions in CGB distribution. 2. Regions of unknown geology (or “Basement Windows”) are identified and likely focus future investigations for rocks that may host mineral deposits. 3. The temporal and spatial evolution of the CGB is more complex than previously thought, with distinct volcanic fields identified through time and space implying variance of the volcanic and tectonic regime within the Interior Plateau. 4. Localization of the CGB lavas within major long-lived river systems implies multiple stages of volcanism, and re-incision throughout the Cenozoic.  74  4.1 A new distribution map for the CGB  A new distribution of the CGB has been produced using a rigorous methodology for data compilation and integration. A comparison of the new distribution with previous regional map compilations (e.g., Massey et al., 2005, and Campbell and Tipper, 1971) within the study area reveals a surface area reduction of the basalts (Figure 4.1). The surface area of the distribution of the CGB across map areas 0920 and 092P based on Massey et al. (2005) is 11,500 km ; in contrast, the new distribution map (Appendix 5, Map 1) 2 indicates surface area coverage of 6,000 km . This represents a 48% reduction in area. 2 Therefore, it is likely that the coverage may be equally diminished across the entire Interior Plateau and the volume of the volcanic province must be significantly less than previously thought. The new conclusions invite detailed re-evaluation of the distribution within other map areas (093A, B...  ) in order to obtain a true extent and thickness (and  therefore volume) of the entire CGB.  75  0)  0920 & P Massey Doh a ney Area (km ) 2 11,500 6,000  Total CGB Massey New Estimate  Area (km ) 2 32,600 17,000  12W  Figure 4.1: Geological map comparing the distribution created in this study vs Massey et al. (2005). Grey colour represents Massy et al. (2005), while the black areas represent the distribution from this study. The areal reduction is calculated to be approximately 48%  51N  4.2 Basement windows within 0920 and 092P Within the area comprising map areas 0920 and 092P, the basement geology contains several terranes: Quesnellia, Cache Creek and Stikine. Figure 4.2 shows the distribution of previously identified basement and Eocene lithologies, and the location of newly defined basement windows through the CGB exposing areas of unconfirmed or unknown lithology. Within the western portion of 092P, the boundary between the Quesnel and Cache Creek terranes is covered by Quaternary drift; it was also inferred that the drift covered CGB lava overlying the basement stratigraphy. The new distribution suggests that the CGB may, in fact, be absent in many areas it was thought to cover. The implication is that basement or Eocene lithologies immediately underlie the veneer of Quaternary cover. Few point data were collected within the western part of Bonaparte Lake, but further geoscience investigation in this area could illuminate the nature of the boundary between these Intermontane terranes. In the south-east part of 092P, a large area previously mapped as CGB is now unknown; Thomas and Pilkington (2008a) attributed the high derivative magnetic character of the rocks to be similar to Kamloops Group rocks found in adjacent areas, and on this basis I suggest that the area is underlain dominantly by the Kamloops Group. In the northwest quadrant of 0920, little information is available to identify the stratigraphic unit or units likely to be exposed. Stikine terrane rocks, Eocene volcanics and Cretaceous Overlap assemblages all outcrop in the near region, and only further fieldwork and geophysical analyses will address this question.  77  Descriptions of rock types recorded in drill records for public water wells in the area also provide clues to the geology underlying the veneer of Quaternary drift and/or the CGB cover (Andrews et al., 2008). The reporting of basalt in water well drill records is useful but not definitive because basalt forms a major part of the Eocene Kamloops Group, as well as, being the major lithology in the Chilcotin Group. However, other lithologies (e.g., granite, metabasalt, greenschist) are clearly not related to the CGB and can be used to determine which geological unit may be present. For example, limestone is found in several areas (i.e., 100 Mile House) and must be pre-Eocene (e.g., basement). The Nicola Group and units within the Cache Creek terrane both contain limestones within their stratigraphy. The proximity to well-known outcrops of Nicola rocks and the magnetic character (high amplitude VG anomalies) indicate that these limestones belong to the Nicola Group. The Taseko Lakes and Bonaparte Lake map areas may contain some of British Columbia’s potentially most economically valuable future deposits (BCGS, 1995; BCGS, 2003). Due to the extensive basalt coverage and lack of outcrop, many parts of this region have remained unexplored. The majority of metallic deposits are either Eocene epithermal gold deposits or Cu-Au porphyries in the Coast Mountain Overlap assemblages (i.e., Tyaughton, Methow Basins) and the central portion of the Nicola Arc in 092P. Figure 4.3 illustrates the metallic mineral potential of the region by superimposing the new distribution of the CGB (and new “basement windows”) onto the Mineral Resource Assessment Level 1 (MRA1; BCGS, 1996) mineral potential tracts. MRA1 tract (794) boundaries are based on underlying bedrock geology, and each is given a  78  relative rank (1 to 794) based on the likelihood of discovering new metallic or industrial mineral resources. Some regions within 0920, and 092P are ranked as very high metallic mineral potential (Figure 4.3), and are in proximity to newly defined and previously known basement windows. Table 4.1 lists the developed prospects and past producers within the area of interest, mainly in basement windows or at the CGB margin.  Regional Geochemical Survey Anomalies Regional Geochemical Survey (RGS) multi-element data is stored and catalogued by the BCGS and available for download from the BCGS website (BCGS, 2007b). Each point plotted represents a sample taken from stream sediments or water. The size of symbol represents statistical analysis of comparing the samples taken within a given map sheet (i.e. 0920). Statistical analysis was carried out by the BCGS and the background plots illustrating the RGS data were taken from the Exploration Assistant in MapPlace (BCGS, 2004). Stream sediment and water samples are taken from mobile environments and therefore the anomalous values may represent the composition of rocks in the near locality. Surficial geology features such as drumlins and glacial stria indicate that ice flow direction was south to south-east in 092P (Tipper, 1971 a) and north to north-easterly direction in 0920 (Heginbottom, 1972 and Tipper, 1971b). Six major base metals (Au, Ag, Cu, Pb, Zn, Mo) were plotted against the new CGB distribution provided by this study. Anomalously high values indicate possible exploration targets for the exploration industry. Areas where the new basement windows intersect anomalous values have been noted in Figure 4.4. The area near Vidette Lake in the south east part of 092P exhibits several base metal anomalies (Ag, Cu, Mo, Pb, Zn).  79  The paucity of data within the north west part of 092P indicates that stream sediment and water sampling have not been attempted due to the basalt cover. Hopefully this new distribution analysis will influence further exploration targeting, including detailed ground mapping and geophysical surveys, that could better define the contacts between the basalt and the underlying geology.  80  00  25km  Geology polygons taken from Geofile 2005-3 (Massey et al,2005)  Stikine, Eocene or Overlap Assemblages?  I.  —  —  —  _J  Kamloops Group  —  Figure 4.2: Regional geology map showing basement lithologies within 0920 and 092P. Areas within the study area now contain unknown geology. These areas may contain important geological clues to the development of the Intermontane belt, such as the nature of the contact between the super-terranes or the extent of Eocene units. Futher geoscience investigation in these areas is recommended.  Legend  BRIDGE RIVER TERRANE Carboniferous to Middle Jurassic  SYMBOLS — Major Faults  fl  Bridge River Terrane Assemblages Bridge River Complex, Shulaps Ultramafic Complex  Basement “Window” CADWALLADER TERRANE Legend adapted from Cariboo Arcview Data (Schiarizza et al, 1994)  Permian to Late Jurassic  CadwalladerTerrane Assemblages Tyaughton Group, Cadwallader Group, Bralorne-East Liza Complex, Last Creek Formation  TERTIARY Neogene to Holocene  Wells Gray ClearwaterVolcanics -  STIKINE TERRANE Lower to Middle Jurassic  Neogene  Hazelton Group Chilcotin Group Paleogene to Neogene  Eocene (Undifferentiated)  CACHE CREEK TERRANE Carboniferous to Late Jurassic  Bald Mountain Belt  Kamloops Group  Farwell Pluton, Unnamed Permian to Jurassic sediments and volcanics  PLUTONIC COMPLEXES  Carboniferous to Early Jurassk  Cache Creek Complex  Middle Jurassic to Paleogene  Cache Creek Complex, Unnamed Mississippian Metamorphic rocks  Coast Plutonic Complex Piltz Peak, Mount Alex  QUESNEL TERRANE Late Triassic to Early Jurassic  MESOZOIC OVERLAP ASSEMBLAGES  Takomkane and Thuya Batholiths  Early to Late Cretaceous  Methow Terrane/Basin  Devonian to Early Jurassic  Jackass Mountain Group  Nicola Group and Equivalents Nicola Group, Harper Ranch Group  Middle Jurassic to Late Cretaceous  Tyaughton Basin Powell Creek Fm, Silverquick Fm, Taylor Creek Fm, Relay Mountain Group Jurassic to Late Cretaceous  Churn Creek -Taseko River Belt Spences Bridge Group  SLIDE MOUNTAIN TERRANE Devonian to Permian  F  Slide Mountain Terrane Assemblages Fennel Assemblage, Crooked Amphibolite  KOOTENAY TERRANE Proterozoic to Paleozoic  J  KootenayTerrane Assemblages Shuswap Assemblage, Snowshoe Group, Eagle Bay Assemblage  82  c)  092001E 092002E 092002W 092002W 092002W 002W 002W 002W 0 003W 003W 004E 005E 008W POlE P01W P02W -08E 0 PO8E PO8E PO8E PO9E P14W  WATSON BAR ELIZABETH MUGWUMP ILVERQUICK MINE TUNGSTEN QUEEN TUNGSTEN KING MANITOU ROBSON TASEKO (EMPRESS) TAYLOR-WINDFALL ELLAIRE ROSPERITY LACKDOME RIERE APARTE V DETTE C CHUA DPASS EET HOME (L.3844) CHUA COAL UEEN BESS POUT LAKE Developed Prospect Developed Prospect Developed Prospect Past Producer Past Producer Past Producer Past Producer Past Producer Developed Prospect Past Producer eveloped Prospect veloped Prospect t Producer veloped Prospect veloped Prospect st Producer veloped Prospect ast Producer ast Producer ast Producer ast Producer Developed Prospect  STATUS  -  AU AU HG HG WO WO HG AU CU AU AU CU AU FD AU AU CU AU AU CL PB CU ZN AU  CU AG ZN CU CU  AG AU AG AG AU AG  HG HG  SB SB AU  ZN ZN  HG CU SB Epithermal Au-Ag: low sulphidation MO Au-quartz veins Au-quartz veins  DEPOSIT TYPE  =  Corundum, GS  =  Gemstone, BI  =  Au-quartz veins Au-quartz veins Silica-Hg carbonate PB ZN CU Polymetallic veins Ag-Pb-Zn+/-Au MO AG CM GS Porphyry Cu +1- Mo +1- Au CU ZN PB Polymetallic veins Ag-Pb-Zn+/-Au CU PB ZN BI Polymetallic veins Ag-Pb-Zn+/-Au AG MO ZN Porphyry Cu +1- Mo +1- Au CU PB ZN SE Epithermal Au-Ag: low sulphidation Feldspar-quartz pegmatite MO Au-quartz veins CU PB Epithermal Au-Ag: low sulphidation AG AU CO TC Cyprus massive sulphide Cu (Zn) BI AG Polymetallic veins Ag-Pb-Zn+/-Au BI Polymetallic veins Ag-Pb-Zn+/-Au Sub-bituminous coal AG Polymetallic veins Ag-Pb-Zn+/-Au Cu skarn  PB PB  CU AG SB  COMMODITIES  Commodities: AU = Gold, AG = Silver, PB = Lead, ZN = Zinc, MO = Molybdenite, CU = Copper, CM Antimony, CO = Cobalt, TC = Talc, FD = Feldspar, WO = Tungsten, SE = Selenium, CL = Coal  NTS  NAME  Bismuth, HG  =  Mercury, SB  Methow Bridge River Overlap Assemblage Cadwallader Bridge River Bridge River Bridge River Cadwallader Overlap Assemblage Overlap Assemblage Overlap Assemblage Plutonic Rocks Overlap Assemblage Plutonic Rocks Harper Ranch Quesnel Slide Mountain Slide Mountain Slide Mountain Overlap Assemblage clide Mountain Quesnel  =  HOST TERRANE  Table 4.1: A list of the major metallic M1NFILE (A B.C. mineral inventory system) results of past producers and developed prospects. The location (NTS), status, commodities, deposit type and host terrane is listed. For further information refer to the online M1NFILE database: <http://minfile.gov.bc.calsearchbasic.aspx>  Prospects Showings  Basement Windows  Past Producers, Developed Prospect  Q  •  128  138  170  230  292  25km 367  Mineral Resource Assessment Level 1 (MRA1) Polygons (BCGS, 1996)  Color scale based on recommendation by authors  <128  LOW  MINERAL POTENTIAL  447  557  716  52’ N  >795  HIGH  Figure 4.3: Map illustrating areas of moderate to high metallic mineral potential, and the MINFILE’s of the region. Economically interesting areas are within the squares below and it is recommended that further detailed exploration be carried out to assess the full potential of the areas. 120’W  Figure 4.4: Several maps illustrating the Regional Geochemical Survey (RGS) multi-element data for map sheets 0920, 092P with the basement windows (light grey) and new CGB distribution (dark grey). Notable anomalous values which intersect basement windows are circled. All data shown is taken from Exploration Assistant in MapPlace (BCGS, 2004) and the symbols represents individual mapsheet thresholds (i.e. larger symbols = more anomalous values) A. Gold (Au); B. Copper (Cu); C. Lead (Pb); D. Molybdenum (Mo); E. Zinc (Zn); F. Silver (Ag).  .  50th Percentile  • 90th Percentile  70th Percentile  •  95th Percentile  >  95th Percentile  Au  Cu  Pb  85  50th Percentile  • 90th Percentile  70th Percentile  • 95th Percentile  • >95thPercentile  Mo  Zn  Ag  86  4.3 Spatial and temporal evolution of the CGB  Locally, there are examples of the spatial variance of the CGB through time (Appendix 5, Map 2). In the 100-Mile House locality several coeval samples suggest that the basalts represent a single eruptive phase; nearby vents (e.g., Mt. Begbie, Lone Butte, and Forestry Hill) are possible point sources (now eroded vents). Along the Chilcotin River there is a continuous basalt escarpment that dating reveals to be composed of at least 3 different lavas emplacement episodes spanning ‘-1 3 Ma. This indicates that over time this river system was filled by basalt and then re-incised. The polygons adjacent to the Chilcotin River therefore host multiple vents that erupted at different times. Along the Fraser River, and near Doc English Bluff there are multiple isolated areas of different ages (and therefore different sources), again indicating complex volcanic history. Overall, locally there are areas of uniform volcanic activity, and areas with complex, discrete, episodic, long-lived volcanism. Regional evolution of the CGB  Across the region including NTS map areas 092H, I, 0, P; 093A, B, C, F, G, J, K, L; 083D; 082E, L, M, 160 ages were compiled from the literature that range from Oligocene to Pleistocene time. Figure 4.5 (A, B and C) shows the spatial distribution of the CGB through time. Generally, the volcanism has varied (time and space) from the Neogene and this variance likely reflects the evolution of the active margin and the geothermal regime beneath the Cordillera. In Oligocene to Early Miocene volcanism occurred along the periphery of the current distribution, dominantly in the eastern flanks of the Coast Mountains. This may  87  indicate that the focal point of volcanism at this time within the Intermontane may have occurred outboard from present time. The Middle to Late Miocene was the most extensive period that was sampled. Spatially the samples are widely distributed across the entire Intermontane region (from the southern Okanagan Highlands to the northern Nechako Basin), and within major river systems. If sampling is representative of the true extent of the lavas, then this period is the most voluminous and widespread. Despite the volume, these lavas erupted episodically implying that sources for volcanism were many (rather than few) monogenetic vents. By the Pliocene to Pleistocene periods, volcanism has localized into “fields” sampled from the central rivers (Fraser, Taseko and Chilcotin rivers), and to the southern Okanagan area. Note that the Wells Gray- Clearwater volcanic field lies adjacent to the central field and overlaps in time (Pleistocene) with the Dog Creek locality. Mathews (1989) found similar spatial patterns in his study, noting that the basalts are indistinguishable in the field regardless of age. In summary, CGB volcanism has varied in position and coverage likely reflecting a change in sub-Cordilleran magmatism. The Middle to Late Miocene represents the most widespread activity erupting episodically from many, small, discrete volcanic centres, while the Pliocene and Pleistocene was dominated by two distinct, local volcanic fields (the central Fraser River near Dog Creek; and the southern Okanagan region) accompanied by the Wells Grey  —  Clearwater volcanism.  88  Volcanic sources and major fault lineaments of the Interior  Volcanic necks and intrusive plugs have been studied and identified within the CGB volcanic field (Farquharson 1965; Farquharson, 1973; Farquharson and Stipp, 1969; Hickson, 1993; Hickson and Higman, 1993). By plotting the volcanic sources of the CGB, the Anahim Volcanic Belt, and the Wells Gray-Clearwater volcanic rocks with major fault lineaments of the region, it is apparent that volcanism may be related to movement along these structures (Refer to Figure 4.6). Extensional structures such as normal faults in the Interior and the Okanagan Highlands are recorded in Eocene age rock units (e.g. Kamloops Group) (Breitsprecher, 2002; Breitsprecher et al, 2000). It is probable that a transtensional structural regime has been active since the beginning of the Cenozoic, and led to shallow, brittle structures facilitating volcanism in proximity to these major faults, within the Interior Plateau.  89  Figure 4.5: Several tiles showing the distribution of the CGB through time (Volcanic necks or plugs are shown as triangles). A. Oligocene to Early Miocene; B. Middle to Late Miocene; and C. Pliocene to Pleistocene  A. OIioceno Early Miocone -  Few, isolated volcanic necks and erosional remnants  Compiled ages of the CGB  32  Ma  30  28  26  Gilgocene  24  22  20  18  27  16  14  12  10  8  6  4  2  0  Miocene  90  B. Middle Late Miocene -  Widespread volcanism occuring throughout the entire Interior  Compiled ages of the CGB  30  Ma  28  26  Oligocene  24  22  I  20  18  16  14  Miocane  12  10  8  4  6  2  I  91  C. Pliocene to Pleistocene Several “fields”exist, lavas found along major river systems (Fraser, Chilcotin); Local, low volume  Wells Gray Pleistocene to Recent  Compiled ages of the CGB n  =  160  14  32  Ma  28  26  Oligocena  24  22  20  18  16  14  Miocene  12  10  8  6  4  2  I  92  Figure 4.6: A map illustrating the major regional faults that may relate to volcanic vents of the CGB (green), Anahim Volcanic belt (red) and Wells Gray-Clearwater volcanic rocks (purple). For example, the Yalakom and Fraser faults appear to coincide with several CGB volcanic vents. Major extensional normal faults (e.g. Okana gan Valley) also coincide with southern volcanic vents. Fault data taken from Wheeler and McFeely, 1991.  Major Faults: (1.) Pinchi (3.) Tchaikazan (5.) Greenwood (7.) Fraser River (9.) Coldwater (11.) Okanagan Valley (13.) Lornex  (2.) Yalakom (4.) Hungry Valley (6.) Granby (8.) Cherry Creek (10.) Lois Creek (12.) Eureka (14.) Marshall Cr.  93  4.4 History of major river systems recorded by CGB lavas The CGB basalts are dominantly exposed in present-day river canyons and comprise subaqueous and subaerial facies. Previously, I have proposed that the lavas were local, episodic and filled topographic lows (such as major long-lived river drainages) rather than an extensive plateau basalt. By characterizing several sample localities it is evident that the CG basalts mainly occur as valley-filling lavas; as such they can be used to constrain the paleo-drainage (e.g.,, Neogene) systems on the Interior Plateau. Major river drainages of the Interior Plateau Since the early Cenozoic a drainage network in the Interior has existed and continued to evolve. For example, several major rivers have changed directions over the past 20 Ma due to pronounced changes in the physiography (i.e., Mio-Pliocene uplift) of the Cordillera (Tribe, 2002; Tribe, 2005; Read, 1989a). The CGB has been interacting with this drainage network since the Oligocene time. It is evident from the presence of Oligocene Early Miocene sediments unconformably deposited beneath thick packages -  of CGB lavas (of different ages, and events) within presently eroded river canyons that these drainages have been repeatedly incised and utilized many times (Figure 4.7). The Chasm and Deadman River are prominent localities that contain thick packages of CGB lava within incised river canyons. Both also contain Early Miocene fluvial sediments (Deadman River Formation), and subaqueous facies that support the lavas being emplaced conformably onto the sediments and interacting with water. The Deadman locality has ages that range from 17 to 9 Ma indicating at least two major  94  volcanic events have poured into the canyon while the Chasm has many lavas interrupted by depositional breaks (i.e., interbedded paleosols). The Fraser River is a major river that flows south from Prince George, all the way to the sea at Vancouver, and was likely active by at latest the Miocene (Tribe, 2002). Dog Creek is a tributary located along the Fraser and includes valley-filling lavas that are Pliocene to Pleistocene in age with interbeds of sediment between two separate lavas and abundant hyaloclastite (Mathews and Rouse, 1986; Figure 2.3). This well-known locality preserves at least two separate volcanic events (requiring two different sources) that were captured in Dog Creek and flowed into the Fraser River. The presence of thick CGB valley-filling lavas in river canyons displaying complex histories of volcanism and sub-deposition of channel sediments indicates that major rivers have been active well into the Miocene, and continue today. Further investigation of paleo-directions of the lavas could help characterize the flow directions of the rivers over time.  95  Figure 4.7 The major rivers of the Interior of British Columbia and distribution of CGB and sediments. The Fraser River is a major river system that is shown in red, while other long-lived rivers are shown in green. Chasm (1.), Deadman River (2.), Gang Ranch (adjacent to Dog Creek) (3.), and Quesnel (4.) all contain Paleogene to Early Neogene fluvial sediments in proximity to the CGB.  Chilcotin Group basalts  Paleogene to Early Neogene sedimentary rocks (undifferentiated) 96  4.5 Summary and conclusions Collecting and analyzing many new datasets (i.e., geochronology, etc.) and applying these to produce a new compilation of 0920 (Taseko Lakes) and 092P (Bonaparte Lake) map areas leads to a new distribution of the CGB.  Several implications were derived from the new spatial distribution are: •  The surface area of CGB is reduced in these two areas implying that the regional coverage may be greatly overestimated (by up to 5 0%).  •  New “basement windows” have been identified in the Bonaparte Lake map area, containing unknown rock units which may be economically viable and could help discern the geological history of the Intermontane Belt.  •  The geochronology, morphology and distribution of the basalts suggest that it is more reasonable to assume that the CGB is a locally fed volcanic province. With sporadic volcanism occurring from many, small, low volume, low profile volcanoes (or rifts) rather than few, large, high volume vents.  •  The CGB has varied in extent and location since Oligocene, with widespread sampling during the Middle to Late Miocene, to the most recent period (Pliocene to Recent) of volcanism where isolated fields are located near the central Fraser River and the southern Okanagan rivers.  Several new questions were derived from the results of this thesis: 1) Why does the locus of CGB volcanism change through time?  97  2) Are there distinct formations within the CGB that can be derived from this study based on form, age and location of the lavas? 3) If the plateau landscape is not formed by effusive volcanism represented by the CGB, are the Eocene units responsible for peneplanation or is it simply a product of Pleistocene glaciations?  It is clear from this work that with increased data coverage, and detailed mapping the synthesis of this distribution may be improved. I recommend compilation and re evaluation of the other NTS map areas which contain the CGB. An accurate distribution of the entire volcanic field would be essential for understanding the evolution of the CGB and magmatism within the Intermontane Belt. This thesis provides a methodology template that can be applied to other regions where there are similar geoscience mapping problems with drift and lack of outcrop. Regional compilation is an ongoing process, so maintaining multivariate digital data can provide future generations of mapping and industry-related projects with valuable interpretations and ideas.  98  BIBLIOGRAPHY 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. 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A palynological and geochronological investigation of Mesozoic and Cenozoic rocks in the Chilcotin Nechako region of central British Columbia. Geological Survey of Canada: Current Research Part F Paper 90-iF, pp. 129-133  108  Ross, J.V. 1983. The Nature and Rheology of the Cordilleran Upper Mantle of British Columbia: Inferences from Peridotite Xenoliths. Tectonophysics, Vol 100, pp. 321-357 Schiarizza, P.J. 1983. Geology of the Barriere River Clearwater Area (NTS 92P/1, 8, 9; 82W4, 5, 12), British Columbia Ministry of Energy, Mines and Petroleum Resources, Preliminary Map No. 53, Scale: 1:50,000 -  Schiarizza, P.J., and Boulton, A. 2006. Geology of the Canim Lake Area (NTS 92P/1 5), Geological Survey of Canada, Open File 2006-8, Scale: 1:50,000 Schiarizza, P.J., and Gaba, R.G. 1993a. Geology of the Warner Pass Map Area (NTS 920/3), British Columbia Ministry of Energy, Mines and Petroleum Resources, Geoscience Map 1993-10, Scale: 1:50,000 Schiarizza, P.J., and Gaba, R.G. 1993b. Geology of the Noaxe Creek and Southwestern Big Bar Creek map areas (NTS 920/1, 2), British Columbia Ministry of Energy, Mines and Petroleum Resources, Geoscience Map 1993-9, Scale: 1:50,000 Schiarizza, P.J., and Gaba, R.G. 1996. Geology and Mineral Occurences of the Taseko Bridge River Area (NTS 920/2, 3, 1; 92J/15, 16), British Columbia Ministry of Energy, Mines and Petroleum Resources, Bulletin 100, Scale: 1:100,000 Schiarizza, P., and Israel, S. 2001. Geology and Mineral Occurences of the Nehalliston Plateau, South-Central British Columbia (92P/7, 8, 9, 10). Geological Fieldwork 2000, B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 200 1-1, pp. 1-30 Schiarizza, P.J., and Preto, V.A. 1984. Geology of the Adams Plateau-Clearwater Area (NTS 92P/1, 8, 9; 82L/13; 82M/3, 4, 5, 6, 12), British Columbia Ministry of Energy, Mines and Petroleum Resources, Preliminary Map No. 56, Scale: 1: 100,000 Schiarizza, P., and Riddell, J. 1997. Geology of the Tatlayoko Lake-Beece Creek Area (92N/8,9,10; 920/5,6,12). Geological Survey of Canada, Open File: 3448, Paper 1997-2, pp. 63-102 Schiarizza, P.J., Bligh, J., Bluemel, B., and Tait, D. 2008. Geology of the Timothy Lake Area (NTS 92P/14), Geological Survey of Canada, Open File 2008-5 Scale: 1:50,000 Schiarizza, P.J., Gaba, R.G., Garver, J.I., Glover, J.K., Church, B.N., Umhoefer, P.J., Lynch, T., Sajgalik, P.P., Safton, K.E., Archibald, D.A., Calon, T., Maclean, M., Hanna, M.J., Riddell, J.M., and James, D.A.R. 1989. Geology of the Tyaughton Creek Area (NTS 92J/15, 16; 920/2), British Columbia Ministry of Energy, Mines and Petroleum Resources, Open File 1989-4, 2 Maps, Scale: 1:50,000  109  Schiarizza, P., Gaba, R.G., Glover, J.K., Garver, J.I., and Umhoefer, P.J. 1997. Geology and Mineral Occurences of the Taseko-Bridge River Area. British Columbia Ministry of Energy, Mines and Petroleum Resources, Bulletin 100, 292 pp. Schiarizza, P.J., Heffernan, S., Israel, S., and Zuber, J. 2002a. Geology of the Clearwater Bowers Lake Area (NTS 92P/9, 10, 15, 16), British Columbia Ministry of Energy, Mines and Petroleum Resources, Open File 2002-15, Scale: 1:50,000 -  Schiarizza, P.J., Israel, S., Heffernan, S., and Zuber, J. 2002b. Geology of the Nehalliston Plateau (NTS 92P/7, 8, 9, 10), British Columbia Ministry of Energy, Mines and Petroleum Resources, Open File 2002-4, Scale: 1:50,000 Schiarizza, P.J., Panteleyev, A., Gaba, R.B., Glover, K. 1994. Cariboo Arcview Data (NTS 92J, K, N, 0, P; 93A, B, C, F, G, H) [Link to Folder with Arc files], British Columbia Ministry of Energy, Mines and Petroleum Resources, Open File 199407, Several NTS Sheets, Scale: 1:250,000 Schiarizza, P.J., Riddell, J., Gaba, R.G., Melville, D.M., Umhoefer, P.J., Robinson, M.J., Jennings, B.K., and Hick, D. 2002c. Geology of the Beece Creek Nuit Mountain Area, British Columbia (NTS 92N/8, 9, 10, 920/5, 6, 12), British Columbia Ministry of Energy, Mines and Petroleum Resources, Geoscience Map 2002-3, Scale: 1:100,000 -  Sluggett, C.L. 2008. Quaternary alkaline and calc-alkaline basalts in southern British Columbia: mixed signals from mantle sources above the southern edge of the Juan de Fuca-Pacific slab window. M. Sc. Thesis, Simon Fraser University, Burnaby, British Columbia Souther, J.G. 1970. Volcanism and its relationship to recent crustal movements in the Canadian Cordillera. Canadian Journal of Earth Sciences, Vol. 7, pp. 553-568 Souther, J.G. 1986. The western Anahim Belt: root zone of a peralkaline magma system. Canadian Journal of Earth Sciences, Vol. 23, pp. 895-908 Souther, J.G. 1977. Volcanism and Tectonic Environments in the Canadian Cordillera A Second Look. Baragar, W.R.A., Coleman, L.C., & Hall, J.M: Volcanic Regimes in Canada. Geological Association of Canada, Special Paper 16, pp. 3-24 -  Souther, J.G., and Yorath, C.J. 1991. Neogene assemblage. Gabrielse, H., and Yorath, C.J.: Geology of the Cordilleran orogen, Canada. Geological Survey of Canada, Geology of Canada, No. 4, pp. 373—401. Souther, J.G., Clague, J.J., and Mathewes, R.W. 1987. Nazko cone: a Quaternary volcano in the eastern Anahim Belt. Canadian Journal of Earth Sciences, Vol. 24, pp. 2477-2485  110  Suh, C. 1999. Petrology, Chemistry, and Geothermometry of Ultramafic Xenoliths from the North Nechako River Area, British Columbia, And the Nature of the Underlying Mantle. B. Sc. Thesis, University of British Columbia, Vancouver, British Columbia, 79 pp. Sun, M., Armstrong, R.L., and Maxwell, R.J. 1991. Proterozoic mantle under Quesnellia: variably reset Rb-Sr mineral isochrons in ultramafic nodules carried up in Cenozoic volcanic vents of the southern Omineca Belt. Canadian Journal of Earth Sciences, Vol. 28, pp. 123 9-1253 Sun, M., and Kerrich, R. 1995. Rare earth element and high field strength element characteristics of whole rocks and mineral separates of ultramafic nodules in Cenozoic volcanic vents of southeastern British Columbia, Canada. Geochemica et Cosmochimica Acta, Vol. 59, No. 23, pp. 4863-4879 Symons, D.T.A. 1969. Paleomagnetism of the Late Miocene Plateau Basalts in the Cariboo Region of British Columbia. Geological Survey of Canada, Paper 69-43 Thomas, M.D., and Pilkington, M. 2008a. New high resolution aeromagnetic data: A new perspective on geology of the Bonaparte Lake map area, British Columbia, Geological Survey of Canada, Open File 5743 Thomas, M.D., and Pilkington, M. 2008b. Magnetic characteristics of the Quesnel Terrane in the Bonaparte Lake and Quesnel Lake Map Areas, Southern British Columbia, Kamloops Exploration Group Meeting Tipper, H.W. 1957. Anahim Lake, Coast District, British Columbia (NTS 93C), Geological Survey of Canada, Preliminary Map 10-1957 Tipper, H.W. 1959. Geology of Quesnel, Cariboo District, British Columbia (NTS 93B), Geological Survey of Canada, Preliminary Map 12-1959 Tipper, H.W. 1963. Preliminary map of the geology of Taseko Lakes map area (NTS 920), Geological Survey of Canada, Preliminary Map 29-1963, Scale: 1: 253,440 Tipper, H.W. 1969. Geology of Anahim Lake, British Columbia (NTS 93C), Geological Survey of Canada, Map 1202A, Scale: 1:253,440 Tipper, H.W. 1971a. Surficial Geology of Bonaparte Lake (NTS 92P), Geological Survey of Canada, Map 1293A, Scale: 1:250,000 Tipper, H.W. 197 lb. Surficial Geology of Taseko Lakes (NTS 920), Geological Survey of Canada, Map 1292A, Scale: 1:250,000  111  Tipper, H.W. 1978. Geology of Taseko Lakes map area (NTS 920), Geological Survey of Canada, Open File 534, Scale: 1:125,000 Tipper, H.W., Campbell, R.B., Taylor, G.C., and Stott, D.F. 1979. Geology of Parsnip River (NTS 93), Geological Survey of Canada, Map 1424A, Scale: 1:1,000,000 Trettin, H.P. 1961. Geological Map of the Fraser River valley between Lillooet and Big Bar Creek, British Columbia Ministry of Energy, Mines and Petroleum Resources, Bulletin 44, 3 Maps Tribe, S. 2002. Geomorphic Evidence for Tertiary drainage networks in the southern Coast Mountains, British Columbia. Geological Survey of Canada: Current Research Paper 2002-A13, 8 pp. Tribe, S. 2005. Eocene paleo-physiography and drainage directions, southern Interior Plateau, British Columbia. Canadian Journal of Earth Sciences, Vol. 42, pp. 215230 Uglow, W.L. 1922. North Thompson Valley between Joseph Creek and Louis Creek, Kamloops District, British Columbia, Geological Survey of Canada, Preliminary Map 1945 Wheeler, J.0., and McFeely, P. 1991. Tectonic assemblage map of the Canadian Cordillera and adjacent parts of the United States of America, Geological Survey of Canada, “A” Series Map 1712A, Scale: 1:2,000,000 Xue, X. and Baadsgaard, H. 1990. Geochemical and Isotopic Characteristics of Lithospheric Mantle Beneath West Kettle River, British Columbia: Evidence From Ultramafic Xenoliths. Journal of Geophysical Research, Vol. 95, No. BlO, pp. 15,879-15,891  112  APPENDIX 1: DATABASE METADATA Title: Chilcotin MASTER Mar 19  Date: June, 2009 Type: Text, Database Format: Microsoft ACCeSSTM, .mdb, Microsoft Excel TM, .xls Coverage: Year: 2008 NTS Sheets: 082E, L, M; 083D, 092H, I, J, 0, P; 093A, B, C, F, G, J, K, L; 103A -  Creator: Jacqueline Dohaney, The University of British Columbia Description: Multiple spatial datasets collected for assessment of the distribution of the Chilcotin Group basalts (CGB) and stored in a Microsoft AccessTM database and exported as separate ExcelTM sheets. A description of each table is listed below:  List of tables: STATION Chilcotin Geochem Chilcotin Geochron Drilling Petrographic Data Physical Properties Public Well Logs Pyctnometry Data Sample Organization Statigraphic Data Vents Bibliography  STATION table: The STATION table consists of the all spatial location information from this database. The columns are described in Section 3.3.2. This table is edited for clarity purposes into separate “Point Type” tables, where each individual data type is grouped together. All location data is UTM, NAD83 within Zone 9-11. All location data was related through a primary identifier: “Sample ID” in the STATION table. The relationship web is included. Bibliographic information can be obtained by cross-referencing the “Owner”, “Year” with the information in the Bibliography table.  113  It is important to note that there are several repetitive samples (i.e. some samples fit into several data sets). E.g. CA-i is in both geochronology and the geochemistry data. Chilcotin Geochem: Geochemistry was collected from the literature for the CGB. The major (wt%), minor elements (wt%) and trace (ppm) elements are listed as well as a quality rating which was assigned by Dr. Graham Andrews the following values: A Recent (1990-), XRF whole rock analyses conducted on samples with good location (and other contextural) information, and an appropriate citation. EXCELLENT DATA -  B Recent (1990-), XRF whole rock analyses conducted on samples with somewhat limited or partly incomplete contextural and location information, maybe be improperly or poorly cited as well. VERY GOOD DATA -  C Old (1980-1990), XRF whole rock analyses conducted on samples with variable quality of citation and contextural information. ADEQUATE DATA -  D Very old (pre-1980) analyses (may or may not be XRF). Citations and contextural information may be robust. Not necessarily poor quality analyses, however caution required in their use today. ADEQUATE DATA -  E Analyses of different methods and ages on rocks of highly uncertain or unknown affinity (location, context, citation) or obviously inferior quality of analysis (e.g., low totals (<96wt%), missing oxides/elements). UNUSABLE DATA -  For units (i.e. Trace elements (ppm) ) or description of individual columns, see the “column” information within design view portion of the Access TM file. Chilcotin Geochron: Geochronological data was collected from the literature, and compiled dominantly from B.C. Age 2004 (BCMEMPR Open File 2004-03). These ages are K-Ar which have been shown to be moderately reliable, and have not been corrected for atmospheric argon. New Ar-Ar age dates were prepared and collected, and are discussed in Farrell’s MSc thesis (in prep).  114  Vents:  Regionally, there are many volcanic “vents” which are present within the Chilcotin Group and other coeval suites. This table represents a collation of the Cheslatta Lake suite, Anahim volcanics, Wells Gray-Clearwater volcanic necks or plugs and their properties. Bibliography:  The bibliography collected for this work was input into the database for use in future works. Maps, papers and websites are all included here. This table is not related (due to lack of spatial information).  115  0)  Station ;an Station ID Date Zan Sample ID ;ample ID eological Unit Point Type NTS Sheet Rock Type Easting Z 10 NAD83 Northing Z 10 NAD83 Easting Z 9 NAD83 Northing Z 9 NAD83 Easting Z 11 NAD83 Northing Z 11 NAD83 Latitude NAD83 Longitude NAD83 Locality )wner  /  11 —  Sample ID Rock Type Petrographic Type Phenocrysts esiculated Diktytaxitic Picture # iteration round mass Colour Index HCL Fizz  Public Well Logs Log Number BCGS SITS Sheet Driftm 1st Lithology Thickness of 1st (m) 2nd Lithology otal Depth of Well (m) :ertainty  N  ample ID 1ethod ge Calculated Error :ra Date of Geochron  Relationships for Chilcotin MASTER Mar 19 Tuesday, May 19, 2009  Sample ID Rock Type Sample type mit #1 Lith#? Thickness of Unit jtrat Locality  N  Physical Properties REF # Sample ID Density (g/cc) Susc (SI) Methodology (Susc) Susc Ave SUSC Pdanty Comments  Sample ID Locality Quality Ranking i02 Fi02 l2O3 Fe203 FeO MnO MgO  Vents tation ID (ent Name Rock Type (olcanic Complex ge (Ma) Features References  Bilbliography REFID rype uthors (ear NTS litle Journal  Pyctnometry Data e ID ength of Core Diameter of Core ‘olume of core 1ass of core Bulk Density 1ass of Dowder  Drilling eport Number Point Type Drill Hole Number NTS Sheet Dip(neg) Bearing )verburden Thickness (m) 1st Lithology  Drilling:  Subsurface data was collected from Assessment reports in the area of interest (0920, P). A table with the Report number, drill hole number, and drilling information was collected. Petrographic Data:  Samples collected by the author (Dohaney) were catalogued, and described in hand sample. This table lists the petrographic character of samples within the suite. Physical Properties:  This table lists stations (outcrop) and samples that were collected for geophysical purposes: paleomagnetic, magnetic susceptibility and density information. These data were given to the author by Dr. Randy Enkin (refer to Enkin et al., 2008 for a full description of data collection and preparation) Public Well Logs:  Andrews et al (2008) collected many data from the WELLS Ground water wells Database which provided subsurface information throughout the region. This table contains the well number, other spatial information, and the lithologies encountered, and their thickness. This information may be used in the future to model the thickness of the drift, or the basalt. Pyctnometry Data: A suite of samples from the UBC lab were tested for physical properties (density, porosity) by the author (Dohaney). These data were taken from a pycnometer apparatus within the Volcanology and Petrology labs. This table represents the corrected raw data and values from these experiments. Sample Organization:  A simple table used by the author and other researchers to keep track of which samples had undergone preparation for geochemistry and geochronology, etc. Statigraphic Data:  Other than spatial information, many samples were collected from stratigraphic sections with specific descriptive information, such as which layer or bed the sample was taken from.  117  APPENDIX 2: UBC GEOCHEMISTRY DATA 41 UBC samples were sent for whole rock geochemistry and ferrous iron titration volumetric from McGill University Geochemical Laboratories. Major oxides (wt%), and Trace elements (ppm) were collected and included herein.  118  CD  47.86 47.40 49.52 50,09 48,61 51.38 48.84 50.59 49,93 50.05 48.64 46.62 4662 59.92 49,47 47.57 49.58 49.66 52.22 48.47 44.06 49.80 48.43 49.92 47.70 46.67 46.81 46.57 45.87 52.07 48.92 50.44 48.12 52,30 49.38 49.26 47,95 50.29 51.22 50,71 50.43  GA-CNO6-35 GA-D006-42 GA-HYO6-38 GA-QEO7-130  Detectwn Limits(%): 60  JD-BR07-59 JD-BSO7-26 JD-BSO7-28 JD-BSO7-31 JD-HFO7-07 JD-HFO7-09 JD-MBO7-01 JD-0M07-04 RE-AFO6-51 RE-AFO6-55 RE-CCO7-31 RE-CCO7-34 RE-DCO7-18 RE-DCO7-21 RE-DCO7-23 RE-DMO6-01 RE-GRO7-30 RE-HYO6-28 RE-TLO6-43 SG-BCO6-24 SG-BCO6-27 RE-AFO6-53 RE-AR06-08 RE-ARO6-10 RE-ARO6-13 RE-CDO6-66 RE-CDO6-74 RE-DCO6-32 RE-DCO6-36 RE-DM06-02 RE-HAO6-45 RE-SKO6-60 RE-SKO6-64 RE-VKO6-79 RE-VKO6-86 RE-VKO6-89  JD-BCO7-41  Si02  Sample  Oct-OS  35  1.556 2.072 3.377 2,280 1.380 2.411 1.733 1,913 1.986 0.682 0.847 2,694 2 264 0.684 1,546 1.863 1.858 1.874 1,748 1.964 3.396 1.384 1.674 1.850 1.519 1.641 1.298 2.036 1.999 2.104 1.703 1 686 2,019 1.618 4.057 1.741 1,491 1.709 1.471 1,578 1.610  1102  CHILCOT1N CHEMISTRY  120  14.77 16.29 12,76 13,84 15,39 15.97 14.21 14,23 13,94 18.02 14,91 14.89 15.61 13,65 15.49 14.13 14.25 14.44 15.03 14.20 14.82 15.25 13.95 13.88 14.77 14.72 15.28 14.41 13.78 16.58 14.92 14.63 14,67 14.83 17.98 14.34 14,99 14.68 14.50 14.40 14.93  A1203  001  5.46 4.59 0.00 2.84 1,88 3.38 5.07 3.86 3,47 9.14 2,25 4.47 3,31 6,31 2.25 4.27 2.05 2.39 2.25 2.39 4.82 4.10 4.42 4.26 5.84 4.44 5,44 6.34 6.28 7.18 2,57 2,84 6.04 1.77 10.07 2,37 3,34 5.23 3.21 2.51 2.85  Fe203  001  6.21 5.83 8.76 8,71 10,25 8.01 8.19 8.17 0,52 3,65 6,76 9.12 8,69 6.66 9.62 7.22 9.18 9.80 8.35 9.41 9.29 7.48 8,31 7.42 6.47 8.08 7.36 4.86 5.90 2.74 9,32 8,49 5.87 8.77 <6)1 10.05 9.01 6,23 7.44 8.16 8.76  30  0.15 0.16 0.20 0.17 0,18 0.18 0.16 0.17 0,17 0,20 0,15 0.19 0,17 0,12 0.17 0.16 0.16 0.17 0.15 0.17 0.21 0.16 0.17 0.16 0.17 0.18 0.16 016 0.17 0.12 0,16 0.16 0,17 0.15 0.35 0,18 0.17 0.16 0.17 0.16 0.17  MnO  95  7.57 6.14 3,49 7.83 8.42 3.31 9.06 7,16 0.06 3.69 6.68 7.24 7.12 2,65 7.77 8.91 8,93 8.42 6.86 9.45 3.90 7.58 8.40 7.93 9.09 9.01 8.50 7.30 10.06 1.91 8,60 7,72 8.68 7.53 0.86 8,52 8.71 8,31 7,37 8.87 7.92  MgO  WI. % Oxides FeO  15  8.41 9.04 7.65 1.56 9.02 5.94 8.98 8,97 8.94 829 7,19 9.09 977 0.46 8.77 9.74 8.68 8.58 8,21 8.68 9.07 8.47 8.43 8.32 8.82 9.04 8.88 858 7,84 9,77 8,71 144 8.70 8.26 6,17 8,60 8.82 8,56 8,23 8.69 8,38  75  3.00 3.14 3,42 3.04 3.15 4.60 2,83 3,01 3.17 3,58 3.11 3.51 3.21 1.21 3.40 2.91 3.25 3.09 3.45 3.13 3.63 3.34 3.03 3.22 2.89 2.82 2.81 287 2.69 3,26 3.01 3.00 3.49 3.16 4,35 3.24 3,18 3.14 3.17 3.10 3.30  CaO Na20  25  0,31 178 0.87 1.07 0.39 228 0,42 0.69 0.69 3.34 3.33 1.00 105 1.69 0,57 0.54 0.93 0.54 0.55 0.80 1.14 0,28 0.50 0.88 0,35 0,45 0.16 1,28 1,02 0.75 0.51 0,46 1.10 0,37 1,41 0.54 0.46 0,51 0.26 036 0.27  K20  35  0.172 0.572 0.382 0.390 0.167 0,997 0,363 0.264 0,321 0.474 0.303 0,405 0 376 0,060 0.195 0,312 0.306 0.222 0.214 0.317 0.753 0.154 0,187 0.280 0.208 0.246 0.147 0.396 0.341 0.392 0.226 0.208 0.429 0.181 0,903 0.227 0.205 0.212 0.215 0,218 0.188  P205  0 01  2.51 1 1.78 0.47 0,13 0.27 0.5 0.15 0.17 0.27 0.7 0.11 027 1.32 0.16 0.47 0.13 0.22 0.11 0.1 0.37 1.06 0.99 1.04 1.02 0.9 1.76 1 54 1.42 1.31 0.26 0,75 0,11 0.19 1.14 0.08 0,49 0.1 1 33 0,23 0.21  H20-  0.01  1.73 1.67 1.24 0.92 0.24 0.11 0.91 0.6 0.38 2.7 3,05 0.34 1,34 4.65 0.43 0.9 0.32 0.61 0.48 0.23 0.98 1.11 1.34 1.17 1.37 1.39 1.8 363 3.02 1.89 0.75 1,15 0,42 0,79 2.2 0.24 0.88 0.31 1.38 0.7 0.66  H20+  0.01  0.07 0 0.02 0.03 0.18 0.23 0.1 0.041 0.1 0,093 1.54 0 0 0.66 0.006 0.98 0.17 0.017 0 0.28 3.96 0.018 0.12 0 0 0.044 0.008 0 065 0.12 0.12 0 0 0 0.074 0.85 0.14 0 0 0,012 0 0  C02  17  70 685 195 223 70 794 90 149 149 844 1487 150 157 1160 150 188 197 128 85 197 474 <4)1 137 172 84 108 <6)1 304 248 227 81 51 249 102 569 152 161 136 55 42 38  BaO  15  <4)1 46 <4/1 20 <6/I 83 <6/1 <4/1 <4/1 <6)1 <6)1 <6)1 <6)1 46 <6)1 <6)1 <4/1 <dl <4)1 <4)1 35 <6/1 <4)1 <6/1 <4)1 <611 <d/I 21 15 <cl/I <d/1 <6/1 <611 <4)1 31 <d/I 18 <6/I <6/I 19 <6/1  Ce  10  51 41 47 58 73 47 58 52 63 25 26 65 50 21 65 56 61 60 48 53 45 45 51 45 47 53 47 44 46 37 61 42 54 50 70 51 63 63 45 51 52  Co  15  377 287 30 439 417 39 466 405 431 50 197 187 427 213 425 486 489 430 276 517 61 383 452 450 429 437 379 440 509 504 447 403 461 432 77 375 430 359 392 540 412  2  56 115 37 76 64 45 69 74 74 269 90 75 63 49 53 II 79 76 51 82 30 71 74 91 87 84 90 65 61 63 68 73 70 74 44 84 77 66 59 66 61  Cu  PPM Cr203  Ni  3  170 90 16 174 211 25 200 161 209 20 57 115 98 59 157 200 197 215 129 270 46 179 245 208 238 240 226 109 210 101 213 210 191 171 71 172 219 215 199 236 209  10  18 22 19 16 21 <4)1 11 21 17 10 23 14 19 <4/1 18 <4)1 14 19 <4)1 11 <4)1 14 12 20 14 21 13 <dJl 10 18 12 11 16 17 <d/I 19 16 13 13 15 <6/1  Sc V  10  171 204 364 182 187 132 174 181 184 228 235 237 218 153 170 161 173 169 140 180 216 152 175 171 186 199 180 197 188 203 182 158 186 140 213 173 169 163 147 161 152  2  100 75 161 96 89 146 92 95 94 51 58 109 89 106 91 90 88 101 99 96 140 90 98 86 85 91 87 86 93 91 103 96 92 96 66 100 89 91 92 88 104  Zn 99.88 99.84 93,55 100,36 99.58 99.90 101.48 99.93 99.97 104,32 99,68 99.78 99.91 180.23 99.96 100.10 99.92 100.16 99.70 99.73 100.50 100.20 100.07 100.45 100.34 99.75 100.51 100.16 100.65 100.32 99.78 100.08 99.95 100.10 99.76 99.64 99.82 99.55 100.07 99.81 99.78  Total  30  12.36 11,07 16.17 12.52 13.27 12.28 12.85 12.94 12.94 9.14 9.76 14.61 1297 13.71 12.94 12.29 12.25 13.28 11,53 12.85 15.14 12.32 13.66 12.51 13.03 13.42 13.62 11.74 12.84 10.23 12.93 12.28 12,56 11.52 10.07 13.54 13.35 12.15 11,48 11.58 12,59  Fe203(T) LOl  100  3,62 2.02 2.18 0.50 <dJl 0,47 0,61 <6)1 <4/1 2.65 4.66 <411 0.64 5.89 <611 1,65 <4)1 <4)1 <cl/I <611 4.28 1.46 1.52 1.38 1.76 1.46 2.76 470 3,90 3.09 <6)1 0,98 <4,9 0.20 4.32 <dl 0.37 <dl 1.93 0.02 <4)1  APPENDIX 3: DIGITAL MAPS  The results of compilation and interpretation of the spatial analysis are available in digital format attached to this study. See data DVD’s provided. For bibliographic information of maps collected refer to the raster images (Geotiff), Bibliography in this text, or the table within the digital database. e.g. 92P Campbell 1971 refers to Campbell and Tipper, 1971 (in NTS Sheet 092P) Digital files: Folder  File types  Description  Georegistered Maps  Geotiff (.tiff)  Digitized Historic Maps Mapping Compilation  (.shp, .shx, .dbf, .xml) (.shp, .shx, .dbf, .xml) (.shp, .shx, .dbf, .xml)  Hardcopy maps from 0920 and 092P which are georegistered and ready for import into GIS platforms Digitized and attributed layers from each georegistered map of the CGB Polygons (or areas), Lines, and Outcrop polygons from the final map data compilation Digital database as point files, with attributes into distinct data sets (e.g. Chilcotin Geochem is all the geochemistry points) Residual total magnetic field and first vertical derivative raster layers for 0920 and 092P. Final polygons, Lines and Outcrop polygons after spatial assessment  Database  Geophysics  Geotiff (.tiff)  Final CGB Distribution  (.shp, .shx, .dbf, .xml)  120  APPENDIX 4: MAP COMPILATION STEPS Step 1 of distribution re-assessment was to compile all existing geological maps of the CGB. The following steps were carried out:  1: DOWNLOAD Using the Geological Survey of Canada’s MIRAGE (Map Image Rendering DAtabase for GEoscience) (GSC, 2007) and B.C. Geological Survey Mapping Index website (BCGS, 2007a), I searched for relevant maps (paper and digital) within the area of interest. 2: EXPORT Paper maps were scanned at 300 dpi and saved as tagged image file format (.tUj) files. Digital maps saved as .pdf (Adobe TM portable document file) files were exported through AcrobatTM Adobe 8 and saved as .tfjfiles. 3: GEO-REGISTER Maps are imported in Manifold GIS 8x TM Each map is geo-registered by selecting between eight and twelve control points; an error surface (a spatial representation of the relative error across a map) is automatically created during registration. The total error is reduced iteratively by adding more control points as required. 4: CATALOGUE Each map successfully geo-registered is catalogued, and the original and new file names, author, and coverage are listed.  5: DIGITIZE The margins of the Chilcotin Group (basalts and sediments) on each imported map are then traced manually (digitized) in Manifold GIS , using the draw area tool. This TM creates a digital representation of each area of the CGB as drawn in each map. 6: ATTRIBUTE After each map is digitized, new areas are attributed in a table generated in Manifold GISTM. All original information is retained (i.e. author of map, NTS of map, original geology code, etc.) in each area to maintain data clarity. Outcrops are assigned defined contacts, and will be isolated for later steps. 7: COMPILE All sets of attributed areas are imported into a single Manifold GISTM project. The sets of areas derived from each map are then compared and by an iterative process each area on the new map is assigned a lithology (basalt or sediment). At the same time, contacts between the CGB and other regional units [basement lithologies i.e. the Nicola Group, Pleistocene sediments] are assigned. A key part of this analysis requires careful ranking of the existing contacts, and the strength of interpretation included in each.  121  8: CREATE A map showing the distribution of the CGB is created using the compiled areas, new line work, and the locations of known outcrops where fieldwork confirmed exposure. This is a preliminary map that is the first step in spatial assessment.  122  APPENDIX 5: FINAL MAPS Two maps were produced from the results of this study. Map 1 is a complete geological map representing NTS Sheets 0920 and 092P. Map 2 is an interpretive look at the evolution and distribution of CGB. See data DVD provided for pdf of maps.  123  Insert Map 1, Distribution and Geological Map of COB  124  Insert Map 2, Interpretation and Implications of the Distribution of the CGB  125  


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