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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 ii TABLE OF CONTENTS iii LIST OF TABLES V LIST OF FIGURES Vi ACKNOWLEDGEMENTS Chapter 1: Introduction 1 1.1 Statement of problem 1 1.2 Research goals 5 Chapter 2: The Chilcotin Group basalts (CGB) 6 2.1 Regional geology 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 andconclusions.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 3rd 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 II100 km 3 Fi gu re 1.2 :C ar to on o ft w o di ffe re nt m o de ls re ga rd in g lav a fil lin g an d la nd sc ap e fo rm at io n. A. Pl at ea u lav as :h ig h v o lu m e er u pt io ns th at fil l t he la nd sc ap e to cr ea te a fla tp la te au su rfa ce ,w ith th ic k ac cu m u la tio ns re gi on al ly .B .V all ey lav as :l ow er v o lu m e er u pt io ns th at fil l a nd fo llo w lo ca lt op og ra ph y. Th ic ke ra c c u m u lat io ns o cc u r in pa le o- to po gr ap hi c lo ws (e. g. de ep riv er v al le ys ). C. an d D. Re pr es en tt he sa m e ar ea s po st- up lif t a n d er o sio n o ft he re gi on .N ot e th at ex po su re o f th ic k lav as ca n be fo un d in bo th m o de ls al on g pr es en td ay riv er s an d th at th e gl ac ia ld rif tc an o bs cu re th e su bs ur fa ce ge ol og y. IThic k ba sa lt la ye rs , u n de rn ea th a th in v e n e e r o fd rif t INO ba sa lt la ye rs ,u n de rn ea th a th ic k pa ck ag e o fd rif t St ra tif ie d la va s N + La rg e v o lu m e, w id e di str ib ut io n + + + B as em en t ( Un di ffe re nt iat ed ) + + + + + + + + + + + + + B. V al le y- fil lin g la va s Lo w v o lu m e, lo ca ld ist rib ut io n 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 Ti02 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 Fi gu re 2. 1: M ap sh ow in g th e cu rr en tg eo lo gi ca li nt er pr et at io n o fT er tia ry v o lc an ism in th e In te rio r P la te au .U nd iff er en tia te d ‘ Ba se m en t’ ro ck s ar e sh ow n an d ar e do m in an tly m ad e up o fd ef or m ed M es oz oi c an d o ld er ro ck s o ft he Ca ch e Cr ee k, Qu esn ell ia an d St ik in a te rr an es . E oc en e U nd iff er en tia te d re pr es en ts th e C or di lle ra w id e Eo ce ne v o lc an ic s an d v o lc an ic la sti cs (e. g. th e K am lo op s Gr ou p). O th er n o ta bl e Te rti ar y Vo lca ni cs ar e la be led :G ar ib al di & Pe m be rto n Gr ou p, A na hi m Vo lca ni c Be lt, W ell s G re y- Cl ea rw at er Vo lca ni cs an d th e Ch ilc ot in Gr ou p. N ot e th at Te rti ar y v o lc an ism ar e m o st ly co v er s th e In te rm on ta ne Be lt, w he re ex te ns io n ha s led to ba ck -a rc v o lc an ism in be tw ee n th e m o u n ta in s (C oa st an d O m in ec a Be lts ). [A llp ol yg on an d at tr ib ut ed da ta u se d fro m M as se y et al. , 2 00 5] W el ls G re y - C le ar w at er V ol ca ni cs A na hi m V ol ca ni c Be lt G ar ib al di & Pe m be rto n V ol ca ni cs Ch ilc ot in G ro up Eo ce ne U nd iff er en tia te d T er ra ne s Ca ch e Cr ee k Qu esn ell ia St ik in ia 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 Period Quatemarv Epoch HoIocene . \ Pliocene I Coast Belt I Neogene I ntermontane rBeIt Miocene PB 0— — 20 3 40 50: 60: -j Oligocene Paleogene Li r ccrfcrm it, Eocene Eocene Undifferentiated (Kamloops Group Equivalents) Kamloaps Sloka Endako Tranquille Ma,ron Skukum Ootsa Lake Princeton Sanpall Penticton Klondike Mtn White Lake Marama Paleocene 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 Northern Cordilleran volcanic province Anahim volcanic belt A 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 Arc volcanism related to Juan de Fuca olate subduction Cascade Range arc Pemberton volcanic belt Garibaldi volcanic belt rN 0 200 400 km Pacific plai. Explorer plate 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 plains- type 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 km2 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 (093F) 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. Regional Geological Mapping Author (5) HICKSOn, U. Year (s) NTS Sheet 1993 U920 Dawson, G.M. 1895, 1898 082L, M; 0921, P 1959, 1963, Tipper, H.W. 1978 0920, 093B 1960, 1961, 1962, 1963, Campbell, R.B. 1978 093A Trettin, H.P. 1961 0921, J, P Campbell, R.B., and Tipper, 1966, 1968, H.W. 1971 092P 1973a, 1973b, 1980, 1981, 082E; 0923, 0; Church, B.N. 1995a 093L 19&, 19’I, 1989, 1993a, 1993b, 1994, 1996, 2002a, 082L, M; 0923, K, Schiarizza, P.J. & 2002b, 2006, N, 0, P; 093A, B, Schiarizza, P.J. et al 2008 C, F, G, H Read, P.B. 1988, 1989 0921, 0, P 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 093F, J Sluggett, C.L. 2008 082E, 092H, I Mihalynuk, M.G. and 082E, L; 0921, 0, Mihalynuk et al 2007, 2008 P; 093A, B, C Recent Studies: Physical Gordee, S. et. al 2007 093B Volcanology, Thickness Farrell, R.E. et. al 2007, 2008 0920, P; 093A, B modelling and Geophysical Andrews, G.D.M., and 0920, P, 093A, B, Analysis Russell, J.K. 2007, 2008 C, F, G, 3, K 082L; 0921, 0, P; Enkin, R.J. et. al 2008 093A, B, C Thomas, M., and Pilkington, M. 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 Fi gu re 2. 4: A. Sc he m at ic cr o ss se ct io n ta ke n fro m M at he w s an d R ou se (19 86 ) e as t- w es t, th ro ug h th e D og Cr ee k lo ca lit y, w he re Pl io ce ne (H arp er’ sC re ek Fm )t o Pl ei sto ce ne ag e la va s (D og Cr ee k Fm )a re se pa ra te d by se di m en ts (ve rti ca l e x ag ge ra tio n is tim es fo ur ). Th e pa le o v al le y su rfa ce is tr ac ed o n to th e di ag ra m , w ith th e cu rr en tF ra se r R iv er ca n yo n to th e fa rl ef t. D og Cr ee k is a cl ea re x am pl e o ft he CG B la va s flo w in g in to pa le o- to po gr ap hy . B .P ho to ta ke n fro m th e w es te rn ex te nt o ft he D og Cr ee k ex po su re , l oc at io n n o te d o n cr o ss se ct io n. Gr ey be ds ; sa n ds to ne , c o n gl om er at e, sil tst on e, til l Ta n be ds ; sa n ds to ne , c o n gl om er at e, sil tst on e 10 00 15 00 12 50 10 00 75 0 50 0 a, a, E z 0 I.. > UI UI Lo ok in g N or th Ba sa lt ca p D og Cr ee k J Fo rm at io n L• H ar pe rs C re ek Ba sa lt Fo rm at io n — — — Ba se m en t p al eo -s ur fa ce C ac he C re ek Li m es to ne ,a rg ill ite ,c he rt G ro up K- Ar D at e (M a) I’2 01 Ta bl e 2. 2: A ta bl e sh ow in g th e fo rm at io n n am es as sig ne d to ge og ra ph ic al ly di sti nc tu n its o ft he CG B. Se ve ra lf or m at io n n am es ca n be ro u gh ly co rr el at ed to ea ch o th er ba se d on ag e. Fo re x am pl e, th e Ch as m an d K in g Ed w ar d Cr ee k Fo rm at io ns ar e bo th M io ce ne in ag e, an d ar e sim ila ri n co m po sit io n an d m o rp ho lo gy .T he Ch ilc ot in G ro up Se di m en ts ar e als o in cl ud ed be lo w, w ith ch ro no lo gi ca lly an d lit ho lo gi ca lly di sti nc tf or m at io n n am es . Th e Cr ow ni te Fm an d Fr as er Be nd Fm ar e bo th M io ce ne ,b ut th e fo rm er is do m in ate d by di ato m ite ,w hi le th e la te ri s c la sti c an d all uv ial .N ot e th at Ih av e in cl ud ed th e “ v al le y” ba sa lts ab ov e, an d th at th e D og Cr ee k Fm is co rr el at iv e to th e La m bl y Cr ee k Fm in ag e. C hi lc ot in G ro up B as al ts C hi lc ot in G ro up Se di m en ts N ec ha ko Pl at ea u C en tra lC hi lc ot in Pl at ea u I O ka na ga n H ig hl an ds H = H e R ef er en ce s: Re ad ,1 98 9a 1 Sl ug ge tt, 20 08 * (‘v all ey lav as ”) A nd er so n et al, 20 01 2 Ro us e an d M at he w s, 19 79 + M at he w s, 19 88 Ro us e an d M at he w s, 19 88 ’ “ 3 0) 0• ’ 4- .’ 0 + 0 z Fi gu re 2. 5B :G eo ch em ic al cl as sif ic at io n o fC ox et al. (19 79 ). CG B is . do m in an tly ba sa lt, an d ba sa lti c an de sit e w ith m in or ba sa ni te, ha w ai ite , m u ge ar ite an d tr ac hy an de sit e (H A = ha w ai ite ) Fi lle d sy m bo ls = UB C D CG B o C he sl at ta La ke Su ite o D og C re ek X V al le y L av as V en ts 12 - 10 - 8- 6 4— 2- 0. da ci te an de si te b as ai t / / / ba sa lti c an de si te I I I I I 35 40 45 50 55 60 65 5i 0 2 (w t% ) I’) 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 Ta bl e 2. 3: A . S um m ar y o ft he ch ar ac te ris tic s o ft he CO B in cl ud in g: ag e, co m po sit io n, ph en oc ry sts /a m yg da le s, m o rp ho lo gy ,s tr uc tu re /a lte ra tio n an d o th er n o ta bl e fe at ur es . B .A lis to fC en oz oi c m af ic v o lc an ic s, an d th ei r “ sim ila r” an d “ di ss im ila r” ch ar ac te ris tic s ( wh en co m pa re d to th e CG B. Th e m o st sim ila rg ro up is th e W ell sG ra y — Cl ea rw at er v o lc an ic s w he re lo ca tio n an d in tra gl ac ia l f ea tu re s ar e th e o n ly sig ni fic an td iff er en ce s. C om po si tio n: tr an sit io na l ( alk ali ol iv in e St ru ct ur e/ A lte ra tio n: No m ajo r ba sa lts ,b as an ite s an d ba sa lti c ar en ite ) st ru ct ur es (m ino r w ar pi ng n ea r th e Co as tM ou nt ai ns )! m in or o x id at io n an d al te ra tio n in so m e lo ca lit ies (i.e .C ha sm ) B. Si m ila r D is si m ila r co ev al ,c o m po sit io n: alk ali ol iv in e ba sa lts , x en o lit h be ar in g, va lle y- fil lin g, lo w v o lu m e, lo ca ls o u rc es , su ba qu eo us in tra gl ac ial fe at ur es (tu ya s), ra re ly W el ls G ra y - C le ar w at er fe at ur es am yg da lo id al do m in an tly bi m od al v o la ni cs co ev al ,a lk ali ol iv in e ba sa lts pr es en t, w ith (pe ral ka lin e), to po gr ap hi c re lie f, sh ie ld A na hi m V ol ca ni c B el t m o n o ge ne tic ci nd er co n es v o lc an o m o rp ho lo gy ty pi ca lly eo ce n e to o lig oc en e in ag e, alk ali ne ,m af ic v o lc an ic s, da rk gr ey to sil ici c am yg da le s (ch alc ed on y), au gi te E nd ak o G ro up bl ac k in co lo r, co lu m na r jo int ed ph yr ic ty pi ca lly eo ce n e to o lig oc en e in ag e, la rg el y ca lc -a lk al in e v o lc an ic s w ith m in or K am lo op s G ro up m as siv e, da rk gr ey ba sa lts m as siv e m af ic v o lc an ic s A ge : Ol ig oc en e to H ol oc en e (m ajo r er u pt iv e pe rio ds : La te M io ce ne ,a n d La te Pl ei sto ce ne ) A. C hi lc ot in G ro up B as al ts M or ph ol og y: th in ,f lat -ly in g flo ws , ba sa lti c an d in tru siv e v o lca ni c n ec ks ; su ba qu eo us ba sa lt br ec ci as an d hy al oc la sti te pr es en t Ph en oc ry st s/ A m yg da le s: Ol iv in e, !z eo lit es ,c ar bo na te s, an d se di m en t O th er : X en ol ith be ar in g lo ca lit ies , m as siv e to di ky tax iti c te xt ur es (0 0 ” 0 (N + 0 (N (‘ z Fi gu re 2. 5A : T he to ta l a lk al i-v er su s- sil ic a di ag ra m (L eM ai tre et al. ,2 00 2) o ft he ge oc he m ic al da tab as e, ill us tra tin g th e CG B su bd iv isi on s: CG B, Ch es la tta Su ite , D og Cr ee k, Va lle y lav as an d th e Ve nt s. N ot ic e th at th e Ch es la tta su ite an d Ve nt s ar e do m in an tly al ka lic , w hi le th e CG B is tr an sit io na l w hi le th e Va lle y an d D og Cr ee k lav as (bo th Pl ei sto ce ne an d yo un ge r) ar e m or e sil ic a r ich . (B AS = Ba sa lti c- tra ch y- an de sit e; TB = Tr ac hy -b as alt ) Fi lle d sy m bo ls = UB C D CG B 0 C he sl at ta La ke Su ite o D og C re ek X V al le y L av as V en ts tr ac hy da ci te 12 10 8 6 4 2 0 35 40 45 50 55 60 S i0 2 (w t% ) 65 C Fi gu re 2. 7: A hi sto gr am di sp la yi ng th e ag e ra n ge o ft he CG B (n = th e n u m be r o fs am pl es in th e da tab as e). N ot e th e hi gh pe ak s du rin g th e La te M io ce ne ,L at e Pl io ce ne an d Pl ei sto ce ne . 27 22 n = 16 0 20 Pl io ce ne 18 1 81 . I. Ia I_ II II o Ii Ii I_ II II II I I 1 1 1 1 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 M a O lig oc en e I M io ce ne I C. ) 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 Fi gu re 3. 2: Sc he m at ic flo w ch ar ti llu str at in g St ep 1- 4 o fC GB di str ib ut io n re -a ss es sm en t. Sc hi ar iz za et al ,1 99 4 R ef in eg eo lo gi ca l c o n ta ct s u si ng ge op hy si cs o CG B pr es en t • CG B n o t pr es en t St ep 1: St ep 2: H ic ks on ,1 99 3 Co m pi le e x is tin g ge ol og ic al m a ps St ep 3: U se po in td at a to id en tif y a re a s to c ha ng e St ep 4: Ol d co n ta ct s Ne w co n ta ct s U se ge op hy si cs a n d to po gr ap hy to dr aw fin al c o n ta ct s ba se d pr im ar ily o n po in t da ta C. ) ()1 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 Year Scale Projection of Original Map ommentn Layer Name 0921.P Dawnon, G.M. . MOstly topographic information Lat/Long NAD1927 Canada ‘t82L,M 921.P Dawson, G.M. 1898 1:250.000 Alberta, British Cslumbia 921/P,82L/M Dawson 1898 mnOl 082L,M; 921,P Daly, R.A. 1915 No plateau lavan present - There are eo basalts recorded in this 92P lJglow, W.L. Jj 1:75,080 map 92P Cockfield, W.E. .1&.2&,. Not enough geographic markers 0921,J,P Trettin, H.P. J,j 1ot enough geographic markers 920 Tipper, H.W. I.IL 1:250,000 uperceded by Tipper, 1978 Campbell R.B. and This map was saperceded by 992P Tipper H.W. Campbell. 1 971 092P Tipper. H.W. 197j Surficial maps Campbell RB. and Lot/Lang NAD1927 Canada - 092P Tipper H.W. 1971 1:250,000 Alberta, British Columbia 92P Campbell 1971 mnOl 920 Tipper, H.W. 1971k 1:250,000 Sarficial maps 920 Heginbottom, J.A. 1972 1:250,000 Surflcial maps Lat/Long NAD1927 Canada- 920 Tipper, NW. 1978 1:125,000 Alberta, British Columbia 920 Tipper 1978 mnOl Okulitch A.V. and Let/Long NAD1927 Canada - 082E-092P Campbell RB. jj9 1:250.000 Alberta, British Columbia Wells grey polygons 92P Okulitch 1979 mnO3 Lot/Long NAD1O27 Canada 092P Hickson, C.J. ,jJ,j 1:500,000 Alberta, British Columbia 92P Hickuon 1982 0001 082M, 092P Schiarizza, P.J. J1!L Superceded by Schisrizza, 1984 Schiarizza, P.J. Lal/Long NAD1 927 Canada - 082L,M: 92P and Prels, V.A. 1984 Alberta, British Columbia 92P Schiarizza 1984 001 92l/JIO1P Read, P.O. 1988c 1:50,000 UTM Zone 10, NAD83 (Canada) 920/P Read 1989 29 002P Read, P.O. 1989k 1:50,000 UTM Z10 NAD83 Canada 92P Read 1989 21 920 Green, iCC. 1989 1:50,000 IITM Zone 10, NAD83 (Canada) 820 Green 198927 Schiarizza, P.J. et 920/J al ‘1999 1:50,000 UTM Zone 10, NAD27 820 Schiarizza 19894 Schiarizza, P.J. 920 and Gabs, R.G 1:50,000 I at/Long NAD1983 Canada Poor quality reproduction - rejected 20 Schiarizza 1993 10 920 l’iickson, C.J. 1993 1:50.000 UTM Zone 10, NAD83 (Canada) 920 Hickson 1993 mnOl 920 Hickson, C.J. 1993 1:50.000 UTM Zsne 10, NAD83 (Canada) 920 Hickson 1993 mnO2 920 Hickson, C.J. ‘1993 1:50.090 IJTM Zane 10, NADB3 (Canada) Q20 Hickuon 1993 mnO3 920 Hickson, C.J. ‘1993 1:50,000 UTM Zane 10, NAD83 (Canada) 920 Hickson 1993 mnO4 920 Riddell, J. ‘1993 1:50,000 UTM Zone 10, NAD83 (Canada) 920 Riddell 1993 9 Schiarizza, P.1. 920 and Gaba, R.G 1993b 1:50.000 LatiLnno NADB3 Canada ‘20/l Schiarizza 1993 9 Schiarizza, P.1. et 0920 al 1994 1:250,000 Alberu NADB3 Mean for CONUS ‘)iuital format, imported CB92OAL 920/J Church, ON. 1995a 1:40,000 atiLon NAD 1983 Canada 20/J Church 19953 Schiarizza, P.J. 920/J and Riddell, J. 1:1 00,000 LatlLong NA083 Canada 920/J Schiarizza 1997 100 Schiarlzza, P.1. at 092P al 2002a 1:50,000 UTM Z10 NAD83 Canada ‘)uatemary basalta 92P Schiarizza 2002 15 Schiarizza, P.J. et 092P a! 2002k 1:50.000 UTM Z10 NAD93 Canada 92P Schisrizza 2002 4 Schiarizza, P.J. et 920/N al 2092c 1:100,000 UTM Zone 10, NAD83 (Canada) °20/N Schiarizza 20023 Schiarizza, P.J. 092P and Boullon, A. 2006 1:50,000 LJTM Z10 NAD83 Canada 92P Schiarizza 2006 8 Schiarizza, P.J. et Digital Files Polygons given from 92P al 2098 1:50,000 author 40 Fi gu re 3. 3: In de x m ap sh ow in g th e sc ale an d lo ca tio n o fg eo lo gi ca l m ap s u se d in th is st ud y. Re gi on al sc al e m ap s by Ti pp er (19 78 )a n d Ca m pb ell an d Ti pp er (19 71 ) c o v er s bo th m ap sh ee ts (0 92 0 an d 09 2P , r es pe ct iv el y). Lo ca l s ca le m ap s ar e ill us tra te d an d la be lle d. Sc hi ar iz za e t a l, 19 89 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. STATION TnhI Fialdc Column Description Gan Station ID Original Waypoints or Stations used by the GSC during fieldwork Gan Sample ID Original Samole Identifiers used by the GSC during fieldwork Date Date of sample taken fUBC) or work published for data Sam pie ID 5Primprv Kev* or unigue identifier which links this table to all other data tables 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 Rock Type General rock lithology of data point. This column is quite simplified for the purpose of this study EastinglNorthing 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) MkrosoftAcs4ITATi0N:TebIeJ D 5tte ffee jnsert Pffrmat 5ecerds Lads Weedew Beb edehePoF Typnaquestisnlarheip . - ff X in i $JflYl i,tL JltLtUkLZ4 SJ.L 4vi - j Pate Sample 113 I $Dbgical Unit I Puiet Type I NTS Sheet Rack Type Basting Z 10 NAP8S Northing Zi12 NAL3 • - + 1989 Symsna3B Chilcatin Group-Basalt Physical Praperties Basalt :474000. 6771000 + 2000 AR-26356 Focene- Undifferentiated APIS 0920 - Bocena 474091 5654309 - + 2007 C992 Chilcotin Group-Basalt Physical Praperties 093903 Basalt 474018 6771075 - + 2007 CC99i Chilcotin Group- Basalt Physical Prapedies :093803 Basafl 474022 5771065 2007 CCBO3 Chilcotin Group Basalt Physical Praperties 093603 Basalt 474023 6771083 - + 7i21/2006 50-5636-19 Chilcotin Group -Basalt USC Sample 938 Basalt 474136 6771085 - + 7/21/2006 SG-BCO6-29 Basement - Undifferentiated :UBC Sample 93B Basement 474153 5771087 + 7/21/2006 SG-BCO6-28 Basement - Undifferentiated UBC Sample 938 Basement 474153 5771087 - + 2007 CCB04 Chilcotin Group-Basalt Physical Preperties 093603 Basalt 474205 5771161 - + 2007 CCB5 -- Chilostin Group -Basalt Physical Properties 093803 : Basalt 474227 5771187 - + 1991 AP-21984 Basement - Undifferentiated APIS 0920 Basement 474239 5662863 - + 7/21/2006 : 50-8006-27 Chilcetin Group - Basalt USC Sample 93B Poa!t 474286 5771309 - + 7/21/2006 SG-5C06-25 Chilcntin Gmup - Basalt :UBC Sample 938 Basalt 474286 5771309 - + 712t12006 SG-BOOS-24 chilcatin Group- Basalt iuec Sample 939 Baaatt 474286 5771309 - + 7r2t/2006 :SBc06.23 Chilcstie Group- Sap 6 USC Samp 939 Basalt 474286 5771309 - 7/21/2006 SGBC0922 Chilcotin Group- Saaalt USC Sample 93B L!46tL 474286 57713 - + 7/2112006 SG-BC06-2t Chilcetin Group- Basalt UBC Sample 93B Basah 474286 5771309 - + 7i2t/2t116 SG-BCO6-20 Chilcetin Groap- Basalt USC Sample 938 Basalt 474296 5771309 - + 7,21/2006 SG-Bc06-26 chilcutin Group- Basalt UBC Sample 935 Basalt 474286 5771309 - + 7)22i2526 SG-B006-33 Chilcotin Group - Basalt USC Sample 938 :o.6 475436 5771211 - + 7/22/2006 SG-BCO6-32 Chilcetin Groap - Basalt USC Sample 93B Basalt 475436 5771211 - + 7i22,2006 SG-BCO6-3t Chilcetin Group: Basalt UBC Sample 935 Basalt 475436 5771211 - + 7/22/2006 SG-B06-30 Chiloetin Group - Ba3alt USC Sample 938 Sasa!t 475436 5771211 - + 2007 AP-29009 Basement-Undifferentiated APIS 0920 Basement 475538 5662085 - + 2000 JRO6-71 -- Chilcetin Groop - Basalt - Phyeical Properties 093611 Basalt 476283 :582?81 - + 1999 AR-149t2t Basement- Undifferentiated APIS 0920 Basement 476334 5661926 - + 1983 AR-i 1696 Basement - Undifferentiated APIS - 0920 Basement 476456 5663026 + 1986 AR-1787t Basement- Undifferentiated APIS 0920 Basement 476845 5663005 - ÷ 1986 AP-14629 Banement-Undifferentiated APIS :0920 Banement 477741 56635 - + 1967 AP-16309 Basement- Undifferentiated APIS :0920 Basement 477971 6662661 + 1963 AP-i1488 Basement- Undifferentiated APIS 0920 Basement 478944 5672480 - + 1981 AP-iOt9t Basement- Undifferentiated APIS 0920 Saearseot 479926 5659667 - + 1999 AP-14902 Basement - Undifferentiated APIS :0920 Basement 479950 5661726 Recerd: [iil3JI 437 CEJitJe 3ecio : Uorrtcmnn rejert 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 N Pleistocene O Late Pliocene • Early • Late • Middle Miocene o Early • 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 50km1 0 C Tatla Lake 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 Fi gu re 3. 8: Lo ca tio n m ap fo rt he AR TS da ta co lle ct ed fo rm ap sh ee ts 09 20 ,a n d 09 2P . Ch ilc ot in G ro up • Ba sa lt Eo ce ne (un dif fer en tia ted ) • B as em en t( un dif fer en tia ted ) 25 km AR IS Li th ol og ie s C, ’ 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 sub- drift 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 Fi gu re 3. 9: Lo ca tio n m ap fo rP ub lic w at er w ell s da ta w ith in 09 20 an d 09 2P .D ist rib ut io n o ft he w ell lo gs co lle ct ed , a s w el la s th ei r r es pe ct iv e lit ho lo gy . Ch ilc ot in G ro up Ba sa lt Cl as tic Se di m en ts B as em en t( Li me sto ne ) B as em en t ( Gr an ite ) Li th ol og ie s 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 Fi gu re 3. 10 :C at al og ue an d in de x m ap fo ri nd iv id ua l m ag ne tic su rv ey da ta u se d in sp at ia la n al ys is o f0 92 0, an d 09 2P .T he re so lu tio n an d o th er in fo rm at io n fo re ac h su rv ey is lis te d be lo w. A co lla ge o ft he su rv ey s w as cr ea te d by M ik e Th om as ,a nd gi ve n to th e au th or to be u se d fo rt hi ss tu dy . ‘ “ I q .J u . I N o. N am e N TS Sh ee ts R es ol ut io n Pu bl ic at io n . j_ is h La ke 2O 10 0 m G SC O oe n Fi le 28 00 . 19 95 . . . . 2.... . La c Ia H ac he 92 P 40 0 m O ne n Fi le 52 91 B on ap ar te La ke Ea st & W es t 92 P 40 0- 42 0 m G SC O oe n Fi le 54 88 -5 50 4 Ea gl e (M urp hy )L ak e, M ck in le y C re ek , . . 4.... Ti sd al l La ke 92 P 21 0- 25 0 m O ne n Fi le 52 92 -9 3. O se n Fi le 20 05 -1 6 So ut he rn BC -A LB . j Su rv ey s’ 92 0. 92 P l0 00 m In te rio r Pl at ea u 94 N; 92 0; 93 B; G eo sc ie nc e Pr oje ct 93 C; 93 F; 93 G ; (W illi am s L ak et 93 K 20 0 m G SC O oe n Fi le 27 85 . 19 94 7 C an ad a* R eg io na l 10 00 m 25 km * D ow nl oa de d fro m th e G eo sc ie nc e D at a R ep os ito ry fo r ES S G eo ph ys ic al an d G eo ch em ic al D at a 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) MPcv: Olivine basalt, andesite; minor related luff and breccia (Tipper, 1 978) MPCv: Olivine basalt; minor andesite, tuff, breccia, conglomerate, sandstone, siltstone, shale, and diatomite (Schiarizza et al, 1994) MPCv: Olivine-phyric basalt (Schiarizza et al, 2008) mTb: Plateau lava: Olivine basalt (Schiarizza and Preto, 1984) mTc: Olivine basalt flows, debris flows (Riddell et al, 1993; Schiarizza and Gaba, 1996) Plvb, MPlvb: Vesicular basaltfiows; well developed columnar jointing (Green, 1989) Pvb, Mvb, MPvb: Vesicular and amygdaloidal basalt flows (Read, 1989b) Q/MPcv: Grey Olivine - and/or plagioclase-phyric subaerial basalt flows, minor interflow breccia and local pillow breccia (Hickson, 1993) Unit 25: Plateau lavas; olivine basalt, basalt andesite, related ash and breccia beds; basaltic arenite; 25a. Olivine gabbro plugs (Campbell and Tipper, 1971) Unit 8: Plateau basalt (Chilcotin Group); rather flat lying lavas and breccias transitional in composition between quartz tholettes and alkali olivine basalt (Church, 1995a) Chilcotin Group Sediments MPcs: Buff to grey siltstone, diatom ite, clay and silty sand; coarse reddish brown conglomerate; minor ash beds and lignite (Tipper, 1978) MPC5: Unconsolidated fluviatile conglomerate, sandstone and siltstone; minor rhyolite ash, diatomaceous earth, olivine basalt and breccia (Schiarizza et al, 1994) Ms: Bedded gravel, conglomerate and minor sandstone; cream, micaceous rhyolite ash and minor pyroclastic breccia (Green, 1989) Ps, Ms, MPs: Pebble and cobble conglomerate; minor sandstone (Read, 1989b) Chilcotin Group Intrusive Plugs MPmp: Mafic plug (Schiarizza and Gaba, 1993) TMb: Miocene age; Basalt plug (Schiarizza at al, 1989) Quaternary Alluvium Q: Quaternary cover (Hickson, 1993) Qal: Till, gravel, sand, clay, and silt (Tipper, 1978) Qal: Unconsolidated glacial, fluvial and alluvial deposits (Schiarizza, 1989) Qs: 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 Assumed Outcrop Regional Compilation: ____ Massey et al., 2005 61 0) I’) LI Ch ilc ot in G ro up Se di m en ts Ro ad s 12 4 W 25 km Ch ilc ot in G ro up Ba sa lts • . — Ri ve rs 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) Fi gu re 3. 13 : M ap ill us tra tin g ar ea s w he re th e po in t d ata ba se id en tif ies di sa gr ee m en t w ith th e pr el im in ar y m ap ge ne ra te d in St ep 1. Po in ts co lo ur ed in bl ac k re pr es en ts lit ho lo gi es th at ar e n o tC GB ,w hi le th e w hi te co lo ur ed po in ts re pr es en t k no w n sa m pl es o fC GB .A de ns ity o fb lac k do ts w ith in th e CG B (gr een ) i sa n ar ea re qu iri ng ch an ge st o th e sp at ia ld ist rib ut io n th ro ug h m o di fic at io n an d re -in te rp re ta tio n (e. g. re d ci rc le ). 12 4W 12 2W 25 km 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 Fi gu re 3. 14 :C lo se -u p o ft he re -fi ne m en ts ta ge o fS tep 3. Th e bl ue bo x is in th e so u th ea st pa rt o fB on ap ar te La ke m ap sh ee tw he re hi gh re so lu tio n ge op hy sic s sh ow s m ag ne tic pa tte rn s ca n he lp re fin e th e bo un da ry be tw ee n th e CG B an d th e Th uy a Ba th ol ith .A s la be lle d, th e Th uy aB at ho lit h sh ow s a lo w in te ns ity m ag ne tic sig na l, w ith sm o o th lin ea r p at te rn s; w hi le th e CG B (as w ell as th e K am lo op sG ro up ,a nd N ic ol a) co n ta in sm ag ne tic ba sa lts ,a nd sh ow s a hi gh ly v ar ie ga te d, hi gh in te ns ity sig na lp at te rn .T he bo un da rie s ar e th er ef or e ch an ge d in ar ea s w he re th es e do m ain s ar e o bv io us an d ca n be tra ce d. Th e w hi te lin es re pr es en ts ch an ge st o th e co n ta ct s ge ne ra te d fro m th e m ap da ta co m pi la tio n (bl ack lin es ). 0) Fi gu re 3. 15 : M ap ill us tra tin g th e fir st v er tic al gr ad ien t, po in td ata an d th e CG B di str ib ut io n in St ep 3. So m e m ag ne tic do m ain sw er e ch ar ac te riz ed to ha ve di ffe rin g m ag ne tic sig na tu re s (e. g. th e K am lo op s G ro up )a nd w er e di sc ar de d. A cl us te r o fn o n -C G B po in t d ata (re dc irc le) w as id en tif ied in St ep 2, an d ge ol og ic al co n ta ct s w er e tr ac ed co in ci de nt to th e m ag ne tic ch ar ac te ru n de rly in g th es e da ta. St ep 3- Ne w ge ol og ic al co n ta ct s Pr ev io us co n ta ct s ge ne ra te d fro m St ep 2 I I 20 km 12 0° W 5 0) 0) 12 2° W 12 00 W 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 St ep 4- Fi na l ge ol og ic al co n ta ct s G eo lo gi ca l c o n ta ct s ge ne ra te d fro m St ep 3 I I 20 km Fi gu re 3. 16 :T wo m ap s (A ,a nd B) ill us tra tin g St ep 4, or th e fin al st ag e o fr e- as se ss m en t. A. M ap o ft he fin al CG B di str ib ut io n (bl ack ) o v er ly in g fir st v er tic al gr ad ie nt ge op hy sic s, an d pr ev io us co n ta ct s ge ne ra te d fro m St ep 3 (w hit e). Th e di st rib u tio n ha s be en re du ce d du rin g th is st ep by id en tif ,ri ng ar ea s th at co n ta in ed lo w in te ns ity m ag ne tic do m ain s lik e th e Ca ch e Cr ee k an d Th uy a ba th ol ith (e. g. bl ue ci rc le ), an d ar ea s w ith ba se m en t p oi nt da ta (e. g. re d ci rc le ). H ig h in te ns ity (va rie ga ted ) d om ain sc o u ld be o th er lit ho lo gi es (i.e . W ell s G re y- Cl ea rw at er v o lc an ic s, Eo ce ne K am lo op s Gr ou p, N ic ol a Gr ou p). a B. M ap ill us tra tin g th e fin al CG B di str ib ut io n in th e Bo na pa rte La ke m ap sh ee t( bla ck ), o v er ly in g hi gh re so lu tio n ra st er to po gr ap hy (N AS A, 20 06 ). G eo lo gi ca lc o n ta ct s in St ep 4 w er e la stl y dr aw n by fo llo w in g to po gr ap hy su rr o u n di ng kn ow n CG B lo ca lit ie s (re dd as he d lin es )s u pp or te d by th e po in td ata , an d th e ge op hy sic s. - 52 ° N 51 °N 12 0° W 52 °N 12 2° W 12 0° W 51 ° N 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 Fi gu re 3. 17 :M ap re pr es en tin g u n ce rt ai nt y as an er ro r su rfa ce ,d ra pe d o v er th e to po gr ap hy o ft he re gi on .T hi ss u rfa ce w as cr ea te d by at tr ib ut in g 12 8 eq ua lly sp ac ed sq ua re s w ith hi gh (3) to lo w (1) ce rta in ty an d n o ta pp lic ab le (N /A ).N ot e th e re gi on de no ted by th e re d bo x is do m in an tly o fl ow ce rta in ty ,l ac ki ng da ta w ea lth an d th er ef or e di st rib u tio n n ee ds im pr ov em en t. 3 H ig h 2 1 Lo w 25 km Po in ts to Su rfa ce :K rig in g Ce rta in ty Co lo ur G ra di en t Ce rta in ty Cr ite ria A su rfa ce w as cr ea te d by th e kr ig in g m et ho d o f ce n tr oi d po in ts w ith in at tri bu ted sq ua re s. • Ob jec ts: 12 8 3 Ty pe : F lo at in g- po in t( sin gle ) Pi xe ls ize : l0 00 xl 00 0 (m ) Sa m e siz e in X an d Y di re ct io n Ex po ne nt ia l M od el, K rig in g Su rfa ce M et ho d Co lo ur G ra di en ta ss ig ne d v al ue s N /A N o ba sa lt, an d ha s n ev er be en fo un d he re .M os tly al pi ne ar ea s w he re o u tc ro p is go od (th ere for ec o lo ur ed sa m e as 3) 3 D at a is ab un da nt an d su pp or ts m y in te rp re ta tio n o f th e di str ib ut io n o f b as al ts tro ng ly . 2 So m e da ta pr es en t, th e di str ib ut io n is m o de ra te ly ce rt ai n 1 Fe w /n o da ta* to su pp or tb as al tp re se nt o r ab se nt (th ere for et he di str ib ut io n as se ss m en ti sp re su m pt io us ). * da ta in cl ud es po in td at a, o u tc ro ps ,p re vi ou s de ta ile d m ap pi ng an d ge op hy sic s 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 km2; in contrast, the new distribution map (Appendix 5, Map 1) indicates surface area coverage of 6,000 km2. This represents a 48% reduction in area. 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 Fi gu re 4. 1: G eo lo gi ca l m ap co m pa rin g th e di str ib ut io n cr ea te d in th is st ud y vs M as se y et al. (20 05 ). Gr ey co lo ur re pr es en ts M as sy et al. (20 05 ), w hi le th e bl ac k ar ea s re pr es en t t he di str ib ut io n fro m th is st ud y. Th e ar ea lr ed uc tio n is ca lc ul at ed to be ap pr ox im at el y 48 % 1 2 W M as se y D oh a n e y 09 20 & P A re a (k m 2) To ta lC GB A re a (k m 2) 11 ,5 00 32 ,6 00 17 ,0 00 6, 00 0 51 N M as se y N ew Es tim at e 0) 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 Fi gu re 4. 2: Re gi on al ge ol og y m ap sh ow in g ba se m en tl ith ol og ie s w ith in 09 20 an d 09 2P .A re as w ith in th e st ud y ar ea n o w co n ta in u n kn ow n ge ol og y. Th es e ar ea s m ay co n ta in im po rta nt ge ol og ic al clu es to th e de ve lo pm en to ft he In te rm on ta ne be lt, su ch as th e n at ur e o ft he co n ta ct be tw ee n th e su pe r-t er ra ne so r th e ex te nt o fE oc en e u n its .F ut he rg eo sc ie nc e in ve sti ga tio n in th es e ar ea s is re co m m en de d. St ik in e, Eo ce ne o r O ve rla p A ss em bl ag es ? 25 km G eo lo gy po ly go ns ta ke n fro m G eo fil e 20 05 -3 (M ass ey e ta l,2 00 5) I. — — — — _ J K am lo op s G ro up 00 Legend SYMBOLS — Major Faults Basement “Window” Legend adapted from Cariboo Arcview Data (Schiarizza et al, 1994) TERTIARY Neogene to Holocene Wells Gray - ClearwaterVolcanics Neogene Chilcotin Group Paleogene to Neogene Eocene (Undifferentiated) Kamloops Group PLUTONIC COMPLEXES Middle Jurassic to Paleogene Coast Plutonic Complex Piltz Peak, Mount Alex MESOZOIC OVERLAP ASSEMBLAGES Early to Late Cretaceous Methow Terrane/Basin Jackass Mountain 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 Carboniferous to Middle Jurassic fl Bridge River Terrane AssemblagesBridge River Complex, Shulaps Ultramafic Complex CADWALLADER TERRANE Permian to Late Jurassic CadwalladerTerrane Assemblages Tyaughton Group, Cadwallader Group, Bralorne-East Liza Complex, Last Creek Formation STIKINE TERRANE Lower to Middle Jurassic Hazelton Group CACHE CREEK TERRANE Carboniferous to Late Jurassic Bald Mountain Belt Farwell Pluton, Unnamed Permian to Jurassic sediments and volcanics Carboniferous to Early Jurassk Cache Creek Complex Cache Creek Complex, Unnamed Mississippian Metamorphic rocks QUESNEL TERRANE Late Triassic to EarlyJurassic Takomkane and Thuya Batholiths Devonian to EarlyJurassic Nicola Group and Equivalents Nicola Group, Harper Ranch Group SLIDE MOUNTAIN TERRANE Devonian to Permian F Slide Mountain Terrane AssemblagesFennel Assemblage, Crooked Amphibolite KOOTENAY TERRANE Proterozoic to Paleozoic J KootenayTerrane AssemblagesShuswap Assemblage, Snowshoe Group, Eagle Bay Assemblage BRIDGE RIVER TERRANE 82 Ta bl e 4. 1: A lis to f t he m ajo rm et al lic M 1N FI LE (A B. C. m in er al in ve nt or y sy ste m )r es u lts o f p as tp ro du ce rs an d de ve lo pe d pr os pe ct s. Th e lo ca tio n (N TS ), st at us , c o m m o di tie s, de po sit ty pe an d ho st te rr an e is lis ted .F or fu rth er in fo rm at io n re fe r t o th e o n lin e M 1N FI LE da tab as e: < ht tp :// m in fil e.g ov .b c.c al se ar ch ba sic .as px > NA M E N TS ST AT US CO M M O D IT IE S D EP O SI T TY PE H O ST TE RR A N E W AT SO N BA R 09 20 01 E D ev el op ed Pr os pe ct AU CU PB ZN HG SB Ep ith er m al Au -A g: lo w su lp hi da tio n M et ho w EL IZ AB ET H 09 20 02 E D ev el op ed Pr os pe ct AU AG PB ZN CU M O A u- qu ar tz v ei ns Br id ge Ri ve r M UG W UM P 09 20 02 W D ev el op ed Pr os pe ct HG SB A u- qu ar tz v ei ns Ov er lap A ss em bl ag e IL VE RQ UI CK M IN E 09 20 02 W Pa st Pr od uc er HG Ca dw al la de r TU NG ST EN QU EE N 09 20 02 W Pa st Pr od uc er W O SB HG AU A u- qu ar tz v ei ns Br id ge Ri ve r TU NG ST EN KI NG 00 2W Pa st Pr od uc er W O SB HG A u- qu ar tz v ei ns Br id ge Ri ve r M AN IT OU 00 2W Pa st Pr od uc er HG Si lic a- Hg ca rb on at e Br id ge Ri ve r RO BS ON 00 2W Pa st Pr od uc er AU AG PB ZN CU Po ly m eta lli c v ei ns A g- Pb -Z n+ /-A u Ca dw al la de r TA SE KO (EM PR ES S) 0 00 3W D ev el op ed Pr os pe ct CU AU M O AG CM GS Po rp hy ry Cu +1 -M o +1 -A u Ov er lap A ss em bl ag e TA YL OR -W IN DF AL L 00 3W Pa st Pr od uc er AU AG CU ZN PB Po ly m eta lli c v ei ns A g- Pb -Z n+ /-A u Ov er lap A ss em bl ag e EL LA IR E 00 4E ev el op ed Pr os pe ct AU AG CU PB ZN BI Po ly m eta lli c v ei ns A g- Pb -Z n+ /-A u Ov er lap A ss em bl ag e RO SP ER IT Y 00 5E v el op ed Pr os pe ct CU AU AG M O ZN Po rp hy ry Cu +1 -M o +1 -A u Pl ut on ic Ro ck s LA CK DO M E 00 8W t Pr od uc er AU AG CU PB ZN SE Ep ith er m al Au -A g: lo w su lp hi da tio n Ov er lap A ss em bl ag e RI ER E PO lE v el op ed Pr os pe ct FD Fe ld sp ar -q ua rtz pe gm at ite Pl ut on ic Ro ck s AP AR TE P0 1W v el op ed Pr os pe ct AU CU M O A u- qu ar tz v ei ns H ar pe rR an ch V DE TT E P0 2W st Pr od uc er AU AG CU PB Ep ith er m al Au -A g: lo w su lp hi da tio n Qu esn el C CH UA - 08 E v el op ed Pr os pe ct CU ZN AG AU CO TC Cy pr us m as siv e su lp hi de Cu (Z n) Sl id e M ou nt ain DP AS S 0 PO 8E as t Pr od uc er - AU CU BI AG Po ly m eta lli c v ei ns A g- Pb -Z n+ /-A u Sl id e M ou nt ain EE T HO M E (L .38 44 ) PO 8E a st Pr od uc er AU CU BI Po ly m eta lli c v ei ns A g- Pb -Z n+ /-A u Sl id e M ou nt ain CH UA CO AL PO 8E a st Pr od uc er CL Su b- bi tu m in ou s c oa l Ov er lap A ss em bl ag e UE EN BE SS PO 9E a st Pr od uc er PB ZN AG Po ly m eta lli c v ei ns A g- Pb -Z n+ /-A u cli de M ou nt ain PO UT LA KE P1 4W D ev el op ed Pr os pe ct CU AU Cu sk ar n Qu esn el C om m od iti es :A U = Go ld ,A G = Si lv er , P B = Le ad ,Z N = Zi nc ,M O = M ol yb de ni te, CU = Co pp er , C M = Co ru nd um , G S = G em sto ne ,B I = Bi sm ut h, HG = M er cu ry ,S B = A nt im on y, CO = Co ba lt, TC = Ta lc, FD = Fe ld sp ar , W O = Tu ng ste n, SE = Se le ni um , C L = Co al c) Co lo rs ca le ba se d o n re co m m en da tio n by au th or s Fi gu re 4. 3: M ap ill us tra tin g ar ea s o fm o de ra te to hi gh m et al lic m in er al po te nt ia l, an d th e M IN FI LE ’s o ft he re gi on .E co no m ic al ly in te re sti ng ar ea s ar e w ith in th e sq ua re sb elo w an d it is re co m m en de d th at fu rth er de tai led ex pl or at io n be ca rr ie d o u tt o as se ss th e fu ll po te nt ia lo ft he ar ea s. 12 0’ W 52 ’N B as em en tW in do w s Pr os pe ct s • Pa st Pr od uc er s, < 12 8 12 8 13 8 17 0 23 0 29 2 36 7 44 7 55 7 71 6 > 79 5 D ev el op ed Pr os pe ct Sh ow in gs Q _ _ _ _ _ 25 km M IN ER AL PO TE NT IA L LO W HI GH M in er al R es ou rc e A ss es sm en tL ev el 1 (M RA 1) Po ly go ns (BC GS ,1 99 6) 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 Mo Zn Ag 50th Percentile 70th Percentile • 90th Percentile • 95th Percentile • >95thPercentile 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 27 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 Ma Gilgocene Miocene 90 B. Middle - Late Miocene Widespread volcanism occuring throughout the entire Interior Compiled ages of the CGB 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 Ma Oligocene I Miocane 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 28 26 24 22 20 18 16 14 12 10 8 6 4 2 Ma Oligocena Miocene 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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Report on exploration of the southern portion of British Columbia. Geological Survey Canada. Progress Report, 1877-1878, p. 1-186B Dawson, G.M. 1895. Economic Minerals of the Kamloops Sheet, British Columbia, Geological Survey of Canada, Map 557 Dawson, G.M. 1898. Geology of the Shuswap Sheet, British Columbia, Geological Survey of Canada, Map 604 Dostal, J., Hamilton, T.S., and Church, B.N. 1996. The Chilcotin basalts, British Columbia (Canada): Geochemistry, petrogenesis and tectonic significance. Neues Jahrbuch für Mineralogie Abhandlungen, Vol. 170, pp. 207-229 Edwards, B.R., and Russell, J.K. 2000. Distribution, nature, and origin of Neogene Quaternary magmatism in the northern Cordilleran volcanic province, Canada. Geological Society of America Bulletin, August 2000, Vol. 112, pp. 1280-1295 Enkin, R.J., Vidal, B.S., Baker, J., Struyk, N.M. 2008. Physical Properties and Paleomagnetic Database for South-Central British Columbia. Geological Fieldwork 2007, B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 2008-1, pp. 5-8 103 Farquharson, R.B. 1965. The petrology of several late Tertiary gabbroic plugs in the South Cariboo region, British Columbia. Ph. D. thesis, University of British Columbia, Vancouver, British Columbia, 69 pp. Farquharson, R.B. 1973. The Petrology of Late Tertiary Dolerite Plugs in the South Cariboo Region, British Columbia. Canadian Journal of Earth Sciences, Vol. 10, pp. 205-225 Farquharson, R.B., and Stipp, J.J. 1969. Potassium-argon ages of dolerite plugs in the South Cariboo region, British Columbia. Canadian Journal of Earth Sciences, Vol. 6,pp. 1468-1470 Farrell, R.E., Andrews, G.D.M., Russell, J.K., and Anderson, R.G. 2007. Chasm and Dog Creek lithofacies, Chilcotin Group basalt, Bonaparte Lake map area, British Columbia. Geological Survey of Canada: Current Research Paper 2007-AS, 11 pp. Farrell, R.E., Simpson, K.A., Andrews, G.D.M., Russell, J.K., and Anderson, R.G. 2008. Preliminary interpretations of detailed mapping in the Chilcotin Group, Chasm Provincial Park, British Columbia. Geological Survey of Canada: Current Research Paper 2008-13, 11 pp. GSC: Government of Canada, Natural Resources Canada, Earth Sciences Sector, Geological Survey of Canada. 2007. MIRAGE: Map Image Rendering Database for Geoscience Rupert, J. ed. <http://gdr.nrcan.gc.ca/mirage/index_e.php> GSC: Government of Canada, Natural Resources Canada, Earth Sciences Sector, Geological Survey of Canada. 2008. Geoscience Data repository: Aeromagnetic and Electromagnetic data GSC ed. <http://gdr.nrcan.gc.ca/aeromag/index_e.php> Gordee, S., and Andrews, G., Simpson, K.A., and Russell, J.K. 2007. Subaqueous Channel-Confined Volcanism within the Chilcotin Group, Bull Canyon Provincial Park (NTS 093B/03), South-Central British Columbia. Geological Fieldwork 2006, B.C. Ministry of Energy, Mines and Petroleum Resources, Report 2007-1, pp. 285-290 Green, K.C. 1989. 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Industrial Minerals in Some Tertiary Basins Southern British Columbia (92H,I). Geological Fieldwork 1986, B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 1987-1, pp. 247-254 Read, P.B. 1988a. Industrial Minerals in Tertiary Rocks, Lytton to Gang Ranch, Southern British Columbia (921, 0, P). Geological Fieldwork 1987, B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 1988-1, pp. 411-415 Read, P.B. 1 988b. Industrial Minerals in the Tertiary of the Bonaparte to Deadman River Area, Southern British Columbia (921, P). Geological Fieldwork 1987, B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 1988-1, pp. 417-419 Read, P.B. 1 988c. Tertiary Stratigraphy and Industrial Minerals, Fraser River: Lytton to Gang Ranch, southwestern British Columbia (NTS 921/5, 12, 13; 92J/16; 920/1, 8; 92P/4), British Columbia Ministry of Energy, Mines and Petroleum Resources, Open File 1988-29, Scale: 1:50,000 Read, P.B. 1 989a. 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Geology and mineral deposits of the Princeton map-area, British Columbia. Geological Survey of Canada, Memoir 243. Riddell, J., Schiarizza, P.J., Gaba, R., Mclaren, G., and Rouse, J. 1993. Geology of the Mount Tatlow map area, British Columbia (NTS 920/5, 6, 12), British Columbia Ministry of Energy, Mines and Petroleum Resources, Open File 1993-8, 2 Maps, Scale: 1:50,000 Rouse, G.E., and Mathews, W.H. 1961. Radioactive Dating of Tertiary Plant-Bearing Deposits. Science, Vol. 133, No. 3458, pp. 1079-1080 Rouse, G.E., and Mathews, W.H. 1979. Tertiary Geology and Palynology of the Quesnel Area, British Columbia. Bulletin of Canadian Petroleum Geology, Vol. 27, No. 4, pp. 418-445 Rouse, G.E., and Mathews, W.H. 1988. Palynology and geochronology of Eocene beds from Cheslatta Falls and Nazko areas, central British Columbia. Canadian Journal of Earth Sciences, Vol. 25, pp. 1268-1276 Rouse, G.E., Mathews, W.H., and Lesack, K.A. 1990. 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 1994- 07, 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. 215- 230 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 R el at io ns hi ps fo r C hi lc ot in M A ST ER M ar 19 Tu es da y, M ay 19 ,2 00 9 N Lo g N um be r BC GS SIT S Sh ee t Dr ift m 1s t L ith ol og y Th ick ne ss o f 1 st (m ) 2n d Li th ol og y ot al D ep th o fW ell (m ) :e rt ai nt y Sa m pl e ID Lo ca lit y Qu ali ty Ra nk in g i0 2 Fi 02 l2 O 3 Fe 20 3 Fe O M nO M gO RE F # Sa m pl e ID D en sit y (g /cc ) Su sc (S I) M et ho do lo gy (S us c) Su sc Av e SU SC Pd an ty Co m m en ts N Sa m pl e ID Ro ck Ty pe Sa m pl e ID Pe tro gr ap hi c Ty pe Ro ck Ty pe Ph en oc ry sts Sa m pl e ty pe es ic ul at ed m it #1 Li th #? D ik ty tax iti c Th ick ne ss o fU ni t Pi ct ur e # jtr at Lo ca lit y ite ra tio n ro u n d m as s Co lo ur In de x HC L Fiz z e ID en gt h o fC or e D ia m et er o fC or e ‘ ol um e o fc o re 1a ss o f c o re Bu lk D en sit y 1a ss o fD ow de r Bi lb lio gr ap hy RE FI D ry pe u th or s (ea r NT S lit le Jo ur na l St at io n am pl e ID 1e th od ge Ca lc ul at ed Er ro r :r a Da te o fG eo ch ro n ;a n St at io n ID D at e Za n Sa m pl e ID ;a m pl e ID eo lo gi ca lU ni t Po in t T yp e NT S Sh ee t Ro ck Ty pe Ea sti ng Z 10 NA D8 3 N or th in g Z 10 NA D8 3 Ea sti ng Z 9 NA D8 3 N or th in g Z 9 NA D8 3 Ea sti ng Z 11 NA D8 3 N or th in g Z 11 NA D8 3 La tit ud e NA D8 3 Lo ng itu de NA D8 3 Lo ca lit y )w ne r Dr ill ing / 1 1 — Pu bl ic W ell Lo gs e po rt N um be r Po in t T yp e Dr ill Ho le N um be r NT S Sh ee t D ip (ne g) Be ar in g )ve rbu rde nT hi ck ne ss (m ) 1s tL ith ol og y Ph ys ica l Pr op er tie s Py ct no m et ry D at a V en ts 0) ta tio n ID (en t N am e Ro ck Ty pe (ol can ic Co m pl ex ge (M a) Fe at ur es R ef er en ce s 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 D et ec tw n L im its (% ): 60 35 12 0 00 1 00 1 30 95 15 75 25 35 0 01 0. 01 0. 01 17 15 10 15 2 3 10 10 2 30 10 0 CH IL CO T1 N CH EM IS TR Y O ct -O S W I. % O xi de s PP M Sa m pl e Si 02 11 02 A 12 03 Fe 20 3 Fe O M nO M gO Ca O N a2 0 K 20 P2 05 H 20 - H 20 + C 02 B aO Ce Co C r2 03 Cu Ni Sc V Zn To ta l Fe 20 3( T) LO l G A -C N O 6- 35 47 .8 6 1. 55 6 14 .7 7 5. 46 6.2 1 0. 15 7. 57 8.4 1 3. 00 0, 31 0. 17 2 2. 51 1.7 3 0. 07 70 <4 )1 51 37 7 56 17 0 18 17 1 10 0 99 .8 8 12 .3 6 3, 62 G A -D 00 6- 42 47 .4 0 2. 07 2 16 .2 9 4. 59 5. 83 0. 16 6. 14 9. 04 3. 14 17 8 0. 57 2 1 1. 67 0 68 5 46 41 28 7 11 5 90 22 20 4 75 99 .8 4 11 ,0 7 2. 02 G A -H Y O 6- 38 49 .5 2 3. 37 7 12 ,7 6 0. 00 8. 76 0. 20 3, 49 7. 65 3, 42 0. 87 0. 38 2 1. 78 1. 24 0. 02 19 5 <4 /1 47 30 37 16 19 36 4 16 1 93 ,5 5 16 .1 7 2. 18 G A -Q EO 7-1 30 50 ,0 9 2, 28 0 13 ,8 4 2. 84 8,7 1 0. 17 7. 83 1. 56 3. 04 1. 07 0. 39 0 0. 47 0. 92 0. 03 22 3 20 58 43 9 76 17 4 16 18 2 96 10 0, 36 12 .5 2 0. 50 JD -B CO 7- 41 48 ,6 1 1. 38 0 15 ,3 9 1, 88 10 ,2 5 0, 18 8. 42 9. 02 3. 15 0. 39 0. 16 7 0, 13 0. 24 0. 18 70 < 6/ I 73 41 7 64 21 1 21 18 7 89 99 .5 8 13 .2 7 <d Jl JD -B R 07 -5 9 51 .3 8 2. 41 1 15 .9 7 3. 38 8.0 1 0. 18 3. 31 5. 94 4. 60 22 8 0, 99 7 0. 27 0. 11 0. 23 79 4 83 47 39 45 25 <4 )1 13 2 14 6 99 .9 0 12 .2 8 0, 47 JD -B SO 7- 26 48 .8 4 1. 73 3 14 .21 5. 07 8. 19 0. 16 9. 06 8. 98 2, 83 0, 42 0, 36 3 0. 5 0. 91 0.1 90 <6 /1 58 46 6 69 20 0 11 17 4 92 10 1. 48 12 .8 5 0, 61 JD -B SO 7- 28 50 .5 9 1, 91 3 14 ,2 3 3. 86 8. 17 0. 17 7, 16 8, 97 3,0 1 0. 69 0. 26 4 0. 15 0. 6 0. 04 1 14 9 <4 /1 52 40 5 74 16 1 21 18 1 95 99 .9 3 12 .9 4 <6 )1 JD -B SO 7- 31 49 ,9 3 1. 98 6 13 ,9 4 3, 47 0, 52 0, 17 0. 06 8. 94 3. 17 0. 69 0, 32 1 0. 17 0. 38 0.1 14 9 <4 /1 63 43 1 74 20 9 17 18 4 94 99 .9 7 12 .9 4 <4 /1 JD -H FO 7- 07 50 .0 5 0. 68 2 18 .0 2 9. 14 3, 65 0, 20 3. 69 82 9 3, 58 3. 34 0. 47 4 0. 27 2. 7 0, 09 3 84 4 <6 )1 25 50 26 9 20 10 22 8 51 10 4, 32 9. 14 2. 65 JD -H FO 7- 09 48 .6 4 0. 84 7 14 ,91 2, 25 6, 76 0, 15 6. 68 7, 19 3. 11 3. 33 0. 30 3 0. 7 3, 05 1. 54 14 87 <6 )1 26 19 7 90 57 23 23 5 58 99 ,6 8 9. 76 4. 66 JD -M BO 7- 01 46 .6 2 2, 69 4 14 .8 9 4. 47 9. 12 0. 19 7. 24 9. 09 3.5 1 1. 00 0, 40 5 0. 11 0. 34 0 15 0 <6 )1 65 18 7 75 11 5 14 23 7 10 9 99 .7 8 14 .61 <4 11 JD -0 M 07 -0 4 46 62 2 26 4 15 .61 3, 31 8, 69 0, 17 7. 12 97 7 3.2 1 10 5 0 37 6 02 7 1, 34 0 15 7 <6 )1 50 42 7 63 98 19 21 8 89 99 .9 1 12 97 0. 64 RE -A FO 6- 51 59 .9 2 0. 68 4 13 ,6 5 6,3 1 6. 66 0, 12 2, 65 0. 46 1.2 1 1. 69 0, 06 0 1. 32 4. 65 0. 66 11 60 46 21 21 3 49 59 <4 /1 15 3 10 6 18 0. 23 13 .71 5. 89 RE -A FO 6- 55 49 ,4 7 1, 54 6 15 .4 9 2. 25 9. 62 0. 17 7. 77 8. 77 3. 40 0, 57 0. 19 5 0. 16 0. 43 0. 00 6 15 0 <6 )1 65 42 5 53 15 7 18 17 0 91 99 .9 6 12 .9 4 <6 11 RE -C CO 7- 31 47 .5 7 1. 86 3 14 .1 3 4. 27 7. 22 0. 16 8. 91 9. 74 2. 91 0. 54 0, 31 2 0. 47 0. 9 0. 98 18 8 <6 )1 56 48 6 II 20 0 <4 )1 16 1 90 10 0. 10 12 .2 9 1,6 5 R E- CC O 7- 34 49 .5 8 1. 85 8 14 .2 5 2. 05 9. 18 0. 16 8, 93 8. 68 3. 25 0. 93 0. 30 6 0. 13 0. 32 0. 17 19 7 <4 /1 61 48 9 79 19 7 14 17 3 88 99 .9 2 12 .2 5 <4 )1 R E- D CO 7- 18 49 .6 6 1. 87 4 14 .4 4 2. 39 9. 80 0. 17 8. 42 8. 58 3. 09 0. 54 0. 22 2 0. 22 0. 61 0. 01 7 12 8 < dl 60 43 0 76 21 5 19 16 9 10 1 10 0. 16 13 .2 8 <4 )1 RE -D CO 7- 21 52 .2 2 1, 74 8 15 .03 2. 25 8. 35 0. 15 6. 86 8,2 1 3. 45 0. 55 0. 21 4 0. 11 0. 48 0 85 <4 )1 48 27 6 51 12 9 <4 )1 14 0 99 99 .7 0 11 ,53 <c l/I RE -D CO 7- 23 48 .4 7 1. 96 4 14 .2 0 2. 39 9.4 1 0. 17 9. 45 8. 68 3. 13 0. 80 0. 31 7 0.1 0. 23 0. 28 19 7 <4 )1 53 51 7 82 27 0 11 18 0 96 99 .7 3 12 .8 5 <6 11 RE -D M O 6- 01 44 .0 6 3. 39 6 14 .8 2 4. 82 9. 29 0. 21 3. 90 9. 07 3. 63 1. 14 0. 75 3 0. 37 0. 98 3. 96 47 4 35 45 61 30 46 <4 )1 21 6 14 0 10 0. 50 15 .1 4 4. 28 R E- G RO 7- 30 49 .8 0 1. 38 4 15 .25 4. 10 7. 48 0. 16 7. 58 8. 47 3. 34 0, 28 0. 15 4 1. 06 1.1 1 0. 01 8 <4 )1 <6 /1 45 38 3 71 17 9 14 15 2 90 10 0. 20 12 .3 2 1. 46 RE -H Y O 6- 28 48 .4 3 1. 67 4 13 .9 5 4. 42 8, 31 0. 17 8. 40 8. 43 3. 03 0. 50 0, 18 7 0. 99 1. 34 0. 12 13 7 <4 )1 51 45 2 74 24 5 12 17 5 98 10 0. 07 13 .6 6 1. 52 RE -T LO 6- 43 49 .9 2 1. 85 0 13 .8 8 4. 26 7. 42 0. 16 7. 93 8. 32 3. 22 0. 88 0. 28 0 1. 04 1. 17 0 17 2 <6 /1 45 45 0 91 20 8 20 17 1 86 10 0. 45 12 .51 1. 38 SG -B CO 6- 24 47 .7 0 1. 51 9 14 .7 7 5. 84 6. 47 0. 17 9. 09 8. 82 2. 89 0, 35 0. 20 8 1. 02 1. 37 0 84 <4 )1 47 42 9 87 23 8 14 18 6 85 10 0. 34 13 .0 3 1. 76 SG -B CO 6- 27 46 .6 7 1. 64 1 14 .7 2 4. 44 8. 08 0. 18 9. 01 9. 04 2. 82 0, 45 0. 24 6 0. 9 1. 39 0. 04 4 10 8 <6 11 53 43 7 84 24 0 21 19 9 91 99 .7 5 13 .4 2 1. 46 RE -A FO 6- 53 46 .8 1 1. 29 8 15 .2 8 5, 44 7. 36 0. 16 8. 50 8. 88 2. 81 0. 16 0. 14 7 1. 76 1.8 0. 00 8 <6 )1 < d/ I 47 37 9 90 22 6 13 18 0 87 10 0. 51 13 .6 2 2. 76 R E- A R 06 -0 8 46 .5 7 2. 03 6 14 .4 1 6. 34 4. 86 01 6 7. 30 85 8 28 7 1, 28 0. 39 6 1 54 36 3 0 06 5 30 4 21 44 44 0 65 10 9 <d Jl 19 7 86 10 0. 16 11 .7 4 47 0 R E- A RO 6- 10 45 .8 7 1. 99 9 13 .7 8 6. 28 5. 90 0. 17 10 .0 6 7, 84 2. 69 1, 02 0. 34 1 1. 42 3. 02 0. 12 24 8 15 46 50 9 61 21 0 10 18 8 93 10 0. 65 12 .8 4 3, 90 RE -A RO 6- 13 52 .0 7 2. 10 4 16 .5 8 7. 18 2. 74 0. 12 1.9 1 9, 77 3, 26 0. 75 0. 39 2 1.3 1 1. 89 0. 12 22 7 <c l/I 37 50 4 63 10 1 18 20 3 91 10 0. 32 10 .2 3 3. 09 R E- CD O 6- 66 48 .9 2 1. 70 3 14 .9 2 2, 57 9, 32 0, 16 8, 60 8, 71 3. 01 0. 51 0. 22 6 0. 26 0. 75 0 81 <d /1 61 44 7 68 21 3 12 18 2 10 3 99 .7 8 12 .9 3 <6 )1 R E- CD O 6- 74 50 .4 4 1 68 6 14 .63 2, 84 8, 49 0. 16 7, 72 14 4 3. 00 0, 46 0. 20 8 0, 75 1, 15 0 51 <6 /1 42 40 3 73 21 0 11 15 8 96 10 0. 08 12 .2 8 0, 98 R E- D CO 6- 32 48 .1 2 2, 01 9 14 ,6 7 6. 04 5. 87 0, 17 8. 68 8. 70 3. 49 1. 10 0. 42 9 0, 11 0, 42 0 24 9 <6 11 54 46 1 70 19 1 16 18 6 92 99 .9 5 12 ,5 6 <4 ,9 R E- D CO 6- 36 52 ,3 0 1. 61 8 14 .8 3 1. 77 8. 77 0. 15 7. 53 8. 26 3. 16 0, 37 0. 18 1 0. 19 0, 79 0. 07 4 10 2 <4 )1 50 43 2 74 17 1 17 14 0 96 10 0. 10 11 .5 2 0. 20 R E- D M 06 -0 2 49 .3 8 4. 05 7 17 .9 8 10 .0 7 <6 )1 0. 35 0. 86 6, 17 4, 35 1,4 1 0, 90 3 1. 14 2. 2 0. 85 56 9 31 70 77 44 71 <d /I 21 3 66 99 .7 6 10 .0 7 4. 32 RE -H A O 6- 45 49 .2 6 1. 74 1 14 .3 4 2, 37 10 .0 5 0, 18 8, 52 8, 60 3. 24 0. 54 0. 22 7 0. 08 0. 24 0. 14 15 2 < d/ I 51 37 5 84 17 2 19 17 3 10 0 99 .6 4 13 .5 4 < dl RE -S K O 6- 60 47 ,9 5 1, 49 1 14 ,9 9 3, 34 9.0 1 0. 17 8. 71 8. 82 3, 18 0. 46 0. 20 5 0, 49 0. 88 0 16 1 18 63 43 0 77 21 9 16 16 9 89 99 .8 2 13 .3 5 0. 37 RE -S K O 6- 64 50 .2 9 1. 70 9 14 .6 8 5.2 3 6, 23 0. 16 8, 31 8, 56 3. 14 0, 51 0. 21 2 0.1 0. 31 0 13 6 < 6/ I 63 35 9 66 21 5 13 16 3 91 99 .5 5 12 .1 5 < dl RE -V K O 6- 79 51 .2 2 1. 47 1 14 .5 0 3. 21 7. 44 0. 17 7, 37 8, 23 3. 17 0. 26 0. 21 5 1 33 1. 38 0, 01 2 55 < 6/ I 45 39 2 59 19 9 13 14 7 92 10 0. 07 11 ,4 8 1.9 3 RE -V K O 6- 86 50 ,71 1, 57 8 14 .4 0 2. 51 8. 16 0. 16 8. 87 8. 69 3. 10 03 6 0, 21 8 0, 23 0. 7 0 42 19 51 54 0 66 23 6 15 16 1 88 99 .8 1 11 .58 0. 02 RE -V K O 6- 89 50 .4 3 1. 61 0 14 .93 2. 85 8. 76 0. 17 7. 92 8, 38 3. 30 0. 27 0. 18 8 0.2 1 0. 66 0 38 <6 /1 52 41 2 61 20 9 <6 /1 15 2 10 4 99 .7 8 12 ,5 9 <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) Hardcopy maps from 0920 and 092P which are georegistered and ready for import into GIS platforms Digitized Historic (.shp, .shx, Digitized and attributed layers from each Maps .dbf, .xml) georegistered map of the CGB Mapping Compilation (.shp, .shx, Polygons (or areas), Lines, and Outcrop .dbf, .xml) polygons from the final map data compilation Database (.shp, .shx, Digital database as point files, with attributes .dbf, .xml) into distinct data sets (e.g. Chilcotin Geochem is all the geochemistry points) Geophysics Geotiff (.tiff) Residual total magnetic field and first vertical derivative raster layers for 0920 and 092P. Final CGB Distribution (.shp, .shx, Final polygons, Lines and Outcrop polygons .dbf, .xml) after spatial assessment 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(AdobeTM portable document file) files were exported through Adobe AcrobatTM 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 GISTM,using the draw area tool. This 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 ofCOB 124 Insert Map 2, Interpretation and Implications of the Distribution of the CGB 125  

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