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Volcanostratigraphy, age and geologic setting of the Lower-Middle Jurassic Upper Hazelton Group, west-central… Gordee, Sarah Marie 2006

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VOLCANOSTRATIGRAPHY, AGE AND GEOLOGIC SETTING OF THE LOWER^MIDDLEJURASSIC JJPPERHAZELTONGROUP, WEST-CENTRAL BRITISH COLUMBIA by S A R A H M A R I E GORDEE Bachelor of Science, University of Wisconsin - Eau Claire, 2003 A THESIS SUBMITTED IN PARTIAL F U F I L L M E N T OF THE REQUIREMENTS FOR THE DEGREE OF M A S T E R OF SCIENCE in THE F A C U L T Y OF G R A D U A T E STUDIES (Geological Sciences) THE UNIVERSITY OF BRITISH C O L U M B I A January 2006 © Sarah Marie Gordee, 2006 ABSTRACT Lower and Middle Jurassic Hazelton Group rocks on the southwest margin of the Stikine Terrane (Stikinia) of the Canadian Cordillera are part of a widespread Early-Middle Jurassic arc assemblage. Upper Hazelton Group volcano-sedimentary strata host the world class, precious metal-enriched, polymetallic Eskay Creek volcanogenic massive sulphide (VMS) deposit in northwest Stikinia, as well as a number of epithermal and porphyry deposits in associated subvolcanic intrusions throughout central and northern Stikinia. Large segments of Hazelton Group strata are understudied, despite significant mineral potential. In southwest Stikinia, upper Hazelton Group strata are in part coeval with volcano-sedimentary strata that host the Eskay Creek deposit. The lithologic sequence in southwest Stikinia consists of late Early Jurassic mafic volcanic centre(s) overlain by a Middle Jurassic, sequence of volcanic vent-proximal, felsic volcanic strata, and associated reworked volcanic material. Volcanic textures, sedimentary structures and fossils together indicate dominantly shallow submarine deposition. Lithogeochemical studies indicate a normal, subduction-related affinity for Hazelton Group strata in southwest Stikinia, which contrasts with a more primitive, rift-related(?) affinity for the strata in the Eskay Creek V M S district in northwest Stikinia. Hazelton Group rocks in the Eskay Creek region and coeval rocks in southwest Stikinia were probably deposited within a broad submarine basin in the back-arc region of a Middle Jurassic oceanic island arc. Rocks of the Eskay Creek V M S district were probably deposited in a localised back-arc rift in a relatively deeper marine setting. Despite differences in the depositional environment and tectonic setting of the two regions, volcano-sedimentary sequences in southwest Stikinia demonstrate significant potential for contained V M S mineralisation. i i T A B L E O F C O N T E N T S Abstract ii List of Tables vii List of Figures viii List of Plates x Acknowledgments xi C H A P T E R 1 INTRODUCTION 1-1 INTRODUCTION 2 1 -2 PROJECT OBJECTIVES 2 1-3 METHODOLOGY 5 1-3-1 G E O L O G I C A L MAPPING, V O L C A N O S T R A T I G R A P H Y A N D S A M P L E C O L L E C T I O N 5 1-3-2 G E O C H R O N O L O G I C A L STUDIES 5 1-3-3 L ITHOGEOCHEMISTRY 6 1-3-4 P E T R O G R A P H Y 6 1 -4 PRESENTATION AND CO-AUTHORSHIP 6 1- 5 REFERENCES 7 C H A P T E R 2 TECTONIC SETTING A N D DEPOSITIONAL ENVIRONMENT OF THE L O W E R - M I D D L E JURASSIC UPPER H A Z E L T O N GROUP IN WEST-CENTRAL BRITISH C O L U M B I A : CONSTRAINTS F R O M V O L C A N O S T R A T I G R A P H Y , U-PB G E O C H R O N O L O G Y A N D LITHOGEOCHEMISTRY 2- 1 INTRODUCTION AND PURPOSE 9 2-2 THE CANADIAN CORDILLERA AND THE STIKINE TERRANE 9 2-3 THE HAZELTON GROUP 11 iii 2-3-1 PREVIOUS WORK IN THE HAZELTON GROUP 13 2-3-2 HAZELTON GROUP NOMENCLATURE 14 2-3-2-1 Hazelton Group stratigraphy and nomenclature in the Iskut River region 15 2-3-2-2 Hazelton Group stratigraphy and nomenclature in the Babine and Telkwa ranges 19 2-3-2-3 Recent chronostratigraphic and biostratigraphic adjustments to regional Hazelton Group stratigraphy.'. • 22 2-3-2-4 Hazelton Group stratigraphy and nomenclature in the central Whitesail Lake map area..22 2-3-2-5 Usage of nomenclature in the study area 26 2-4 PREVIOUS WORK AND REGIONAL GEOLOGIC SETTING 26 2-4-1 PREVIOUS WORK IN THE B E L L A COOLA AND WHITESAIL L A K E MAP AREAS 26 2-4-2 REGIONAL GEOLOGIC SETTING 27 2-5 LOCATION OF THE STUDY AREA AND GEOLOGIC MAPPING 32 2-6 VOLCANOSTRATIGRAPHY 35 2-6-1 PRINCIPAL LITHOFACIES OF THE LOWER MAFIC MEMBER (EMJHV) 35 2-6-1-1 Mafic lava flows, domes/cryptodomes, and high level intrusions (undivided emJHv) 37 2-6-1-2 Mafic volcanic-derived epiclastic rocks (undivided emJHv) 41 2-6-2 PRINCIPAL LITHOFACIES OF THE UPPER FELSIC MEMBER (MJHR) 42 2-6-2-1 Felsic to intermediate pyroclastic lithofacies (undivided mJHr) 43 2-6-2-2 Felsic lava flows (undivided mJHr) 46 2-6-2-3 Felsic domes (mJHrd) 47 2-6-2-4 Felsic volcanic-derived epiclastic rocks (undivided mJHr) 47 2-6-2-5 Felsic plutonic-derived sandstone (mJHs) 49 2-6-2-6 Calcareous epiclastic rocks and limestone (undivided mJHr) 50 2-6-2-7 Mafic domes and dyke/sill complexes (mJHb) 57 2-6-2-8 Mafic lava flows (undivided mJHr) 51 2-6-2-9 Granite (mJg) 52 2-7 DEPOSITIONAL ENVIRONMENT AND PHYSICAL VOLCANOLOGY 52 2-7-1 T H E LOWER MAFIC MEMBER 52 2-7-1-1 Depositional environment 52 2-7-1-2 Physical volcanology 53 2-7-2 T H E UPPER FELSIC MEMBER 54 2-7-2-1 Depositional environment 54 2- 7-2-2 Physical volcanology 54 2-8 A G E CONSTRAINTS 56 2-8-1 BlOSTRATIGRAPHY : 5 6 2-8 -2 GEOCHRONOLOGY '. 5 7 2-8-3 A G E OF HAZELTON GROUP STRATA AND STRUCTURES WITHIN THE STUDY AREA 63 2-9 LITHOGEOCHEMISTRY 66 2-10 REGIONAL STRATIGRAPHIC CONTEXT AND TECTONIC IMPLICATIONS 75 2-11 IMPLICATIONS FOR VMS POTENTIAL IN SOUTHWEST STIKINIA 77 2-12 DISCUSSION 77 2-13 ACKNOWLEDGMENTS 78 2-14 REFERENCES 78 CHAPTER 3 THE A G E OF THE TROITSAIA WESTERMANNI ZONE OF BRITISH C O L U M B I A : N E W GEOCHRONOLOGICAL D A T A 3-1 INTRODUCTION 86 3-2 REGIONAL GEOLOGIC SETTING 86 3-3 LITHOSTRATIGRAPHY AND DEPOSITIONAL ENVIRONMENT 89 3-3-1 VOLCANIC LITHOFACIES, PROCESSES AND DEPOSITIONAL ENVIRONMENT 91 3-3-2 SEDIMENTARY LITHOFACIES, PROCESSES AND DEPOSITIONAL ENVIRONMENT 9 3 3-4 BlOSTRATIGRAPHY 94 3-5 U-PB GEOCHRONOLOGY 94 3-6 DISCUSSION 98 3-7 ACKNOWLEDGMENTS 99 3- 8 REFERENCES 100 CHAPTER 4 S U M M A R Y , CONCLUSIONS A N D SUGGESTIONS FOR F U T U R E R E S E A R C H 4- 1 SUMMARY AND CONCLUSIONS 103 4-2 SUGGESTIONS FOR FUTURE RESEARCH 104 V 4-3 R E F E R E N C E S 106 APPENDICIES A P P E N D I X A POST HAZELTON GROUP MAGMATISM IN THE STUDY A R E A 107 A P P E N D I X B A R - A R GEOCHRONOLOGY 114 A P P E N D I X C U - P B GEOCHRONOLOGY 120 A P P E N D I X D PALEONTOLOGY REPORTS 123 A P P E N D I X E ANALYTICAL PRECISION, SAMPLE INFORMATION A N D ZIRCON SATURATION TEMPERATURES 126 A P P E N D I X F GEOLOGICAL FIELDWORK PUBLICATIONS 132 vi LIST OF TABLES C H A P T E R 2 TABLE 2-1. LOCALITIES AND LITHOLOGIC INFORMATION FOR U - P B SAMPLES COLLECTED FROM THE STUDY AREA 5 8 TABLE 2-2. U - P B ISOTOPIC DATA FOR VOLCANIC, PLUTONIC AND DETRITAL ZIRCON SAMPLES FROM THE STUDY AREA 5 9 TABLE 2-3. MAJOR ELEMENT LITHOGEOCHEMICAL DATA FOR REPRESENTATIVE SAMPLES FROM THE STUDY AREA 6 7 TABLE 2-4. T R A C E AND RARE EARTH ELEMENT LITHOGEOCHEMICAL DATA FOR REPRESENTATIVE SAMPLES FROM THE STUDY AREA 6 8 C H A P T E R 3 TABLE 3-1. CORRELATIONS OF WESTERN CANADIAN ASSEMBLAGE ZONES AND NORTHWEST EURPOEAN STANDARD ZONES IN THE PACIFIC AREA 8 7 TABLE 3-2. U - P B ISOTOPIC DATA FOR RHYOLITE TUFF SAMPLE FROM THE STUDY AREA 9 6 A P P E N D I C I E S TABLE A - l . MAJOR ELEMENT LITHOGEOCHEMICAL FOR NON-HAZELTON GROUP ROCKS FROM THE STUDY AREA 109 TABLE A-2. T R A C E AND RARE EARTH ELEMENT LITHOGEOCHEMICAL DATA FOR NON-HAZELTON GROUP ROCKS FROM THE STUDY AREA 110 TABLE B-1. DETAILED 4 0 A R / 3 9 A R STEP-HEATING RESULTS FOR SELECTED SAMPLES FROM THE STUDY AREA 116 TABLE E - l . M E A N VALUES AND DUPLICATE ANALYSES OF STANDARDS P - l AND B A S - 1 128 TABLE E-2. SAMPLE INFORMATION FOR INTRUSIVE AND EXTRUSIVE HAZELTON GROUP LITHOGEOCHEMICAL SAMPLES FROM THE STUDY AREA 129 TABLE E-3. ZIRCON SATURATION TEMPERATURES CALCULATED FOR INTRUSIVE AND EXTRUSIVE HAZELTON GROUP SAMPLES FROM THE STUDY AREA, AS WELL AS FROM THE NIFTY V M S PROSPECT IN THE EAST-CENTRAL B E L L A COOLA MAP AREA 131 vn LIST OF FIGURES CHAPTER 1 FIGURE 1-1. TERRANES AND MORPHOGEOLOGICAL BELTS OF THE CANADIAN CORDILLERA, AND LOCATION OF THE STUDY AREA 3 FIGURE 1-2. GEOLOGIC FEATURES OF STIKINIA IN CENTRAL AND NORTHERN BRITISH COLUMBIA AND LOCATION OF N T S MAP AREAS REFERRED TO IN THE TEXT 4 C H A P T E R 2 FIGURE 2-1. GEOLOGIC FEATURES OF STIKINIA IN CENTRAL AND NORTHERN BRITISH COLUMBIA AND LOCATION OF THE B E L L A COOLA, WHITESAIL L A K E , AND OTHER N T S MAP AREAS REFERRED TO IN THE TEXT 10 FIGURE 2-2. TERRANES AND MORPHOGEOLOGICAL BELTS OF THE CANADIAN CORDILLERA, AND LOCATION OF THE STUDY AREA 12 FIGURE 2-3. HAZELTON GROUP STRATIGRAPHY AND NOMENCLATURE IN THE ISKUT RIVER REGION 16 FIGURE 2-4. HAZELTON GROUP STRATIGRAPHY AND NOMENCLATURE IN THE BABINE AND T E L K W A RANGES 20 FIGURE 2-5. HAZELTON GROUP STRATIGRAPHY AND NOMENCLATURE IN THE CENTRAL WHITESAIL L A K E MAP AREA 24 FIGURE 2-6. GENERALISED GEOLOGIC MAP OF THE B E L L A COOLA AND WHITESAIL L A K E MAP AREAS 28 FIGURE 2-7. GEOLOGIC MAP OF THE EASTERN HALF OF THE TESLA L A K E 1:50 000-SCALE MAP AREA ( N T S 0 9 3 E WHITESAIL L A K E 1:250 000 MAP AREA) 33 FIGURE 2-8. IDEALIZED STRATIGRAPHIC COLUMN OF HAZELTON GROUP STRATIGRAPHY IN THE STUDY AREA 36 FIGURE 2-9. FIELD PHOTOGRAPHS OF ROCKS OF THE LOWER MAFIC MEMBER 38 FIGURE 2-10. FIELD PHOTOGRAPHS OF ROCKS WITHIN THE UPPER FELSIC MEMBER 44 FIGURE 2-11. U - P B CONCORDIA PLOTS FOR VOLCANIC, PLUTONIC AND DETRITAL ZIRCON SAMPLES FROM THE STUDY AREA 60 FIGURE 2-12. SCHEMATIC STRATIGRAPHIC CORRELATIONS OF ROCKS WITHIN THE STUDY AREA 64 FIGURE 2-13. LITHOGEOCHEMICAL DISCRIMINATE PLOTS OF INTRUSIVE AND EXTRUSIVE HAZELTON GROUP ROCKS FROM THE STUDY AREA 71 FIGURE 2-14. CHONDRITE NORMALISED TRACE ELEMENT PLOTS OF INTRUSIVE AND EXTRUSIVE HAZELTON GROUP ROCKS FROM THE STUDY AREA 72 FIGURE 2-15. PRIMITIVE MANTLE NORMALISED TRACE ELEMENT PLOTS OF INTRUSIVE AND EXTRUSIVE HAZELTON GROUP ROCKS FROM THE STUDY AREA 73 FIGURE 2-16. CHONDRITE NORMALISED RARE EARTH ELEMENT PLOTS OF INTRUSWE AND EXTRusrvE HAZELTON GROUP ROCKS FROM THE STUDY AREA 74 viii C H A P T E R 3 FIGURE 3-1 . LOCALITY MAP OF THE JUMBLE MOUNTAIN/RAMSEY PEAK AREA, NORTHEAST B E L L A COOLA MAP AREA, WEST-CENTRAL BRITISH COLUMBIA. INSET MAP IS A SIMPLIFIED MAP OF TERRANES OF THE CANADIAN CORDILLERA 88 FIGURE 3-2. MEASURED STRATIGRAPHIC SECTION OF THE LOWER JUMBLE MOUNTAIN SECTION, NORTHEAST B E L L A COOLA MAP AREA 9 0 FIGURE 3-3 . FIELD PHOTOGRAPHS OF FOSSILIFEROUS UNITS WITHIN THE LOWER JUMBLE MOUNTAIN SECTION, NORTHEAST B E L L A COOLA MAP AREA 92 FIGURE 3-4. U - P B CONCORDIA PLOT FOR RHYOLITE TUFF SAMPLE FROM THE STUDY AREA 97 A P P E N D I C E S FIGURE B-1. 4 0 A R / 3 9 A R AGE SPECTRUM DIAGRAM FOR QUARTZ DIORITE STOCK IN THE STUDY AREA 117 FIGURE B-2. 4 0 A R / 3 9 A R AGE SPECTRUM DIAGRAM FOR RHYOLITE DYKE IN THE STUDY AREA 118 i x LIST OF PLATES C H A P T E R 3 PLATE 3-1. TROITSAIA WESTERMANNI FOSSIL SPECIMENS FROM THE STUDY AREA ACKNOWLEDGMENTS In my great endeavor to call the little square of land near Bella Coola, B.C. my own, I have made and leaned on (not necessarily in that order) a great deal of friends. Throughout the project I have been incredibly privileged to work with, seek advice from, and chat over brews with many of the original and present "Cordilleran and Volcanology Gods". This thesis would not have been possible without the guidance and support of my primary supervisor, James K. Mortensen (Mort), who seems to know a little bit about every rock on Earth. Thanks for putting up with me and passing on some of your extensive knowledge. J. Brian Mahoney of the University of Wisconsin - Eau Claire (UWEC) acted as a co-supervisor throughout the project. Brian has been with me for the long haul, and continues to be a great friend, mentor, and colleague. I will miss working with you, Brian. We've had a ton of fun and done a lot of good science. Richard (Dick) M . Tosdal and J. Kelly Russell were fantastic members of my supervisory committee - each taught me a great deal of science, both in the field and out. Dick has been a great mentor with his straightforward, pragmatic advice and presents me with challenging questions. Kelly passed on some of his vast volcanological knowledge and provided much-needed "brutally honest" critique throughout the project. Thanks to he and Alison Rust for co-leading the Vancouver Volcanologists meetings. I learned a great deal from each of you and from the group, and it has been great to develop lasting bridges between us volcano-lovers. Jim Haggart was a great friend and resource throughout the project, and helped out tremendously with logistical matters, fieldwork, map editing, and writing. He also nodded sympathetically through a number of "vent sessions", for which I owe him many of pints of beer. Thanks to him and other Geological Survey of Canada (GSC) scientists Kirstie Simpson, Glenn J. Woodsworth, and Bob Anderson for their fantastic geologic expertise'. Kirstie has been extremely supportive, taught me a lot about volcanology, set. me up with numerous volcano-related experiences, and has been a huge help to me in the planning of my next step. Larry Diakow of the British Columbia Geological Survey (BCGS) is an invaluable Hazelton Group caldron of knowledge and a good friend - man, did we have some hilarious nights in Bella Coola (along with the great scientific advances). The same goes to Bob Hooper and Lori Snyder - it has been a privilege to spend some time out in the mountains with each of you. Progressing through your department (UWEC Department of Geology) was the best thing that ever happened to me, and you and your faculty and staffs are some of my best friends and mentors. xi Danny Hodson of Rainbow West Helicopters and Richard LaPointe and crew of West Coast Helicopters provided outstanding helicopter support (and fun flying) over four field seasons. Chris Kohel, Emily Hauser, Casey Bowe and Joe Nawikas were motivated and hilarious field assistants. We had some great times both in fly camp and at basecamp. Thanks to the Department of Earth and Ocean Sciences at the University of British Columbia, and the faculty, staff, and graduate students from whom I learned from through valuable scientific classes and discussions, a good plenty of them in our favourite local pubs. Claire Chamberlain in particular has been a great friend and helped me to remain positive - she is a fantastic geologist and advice giver (though she'll never give herself the credit she deserves). Rich Friedman was a great teacher, scientific resource and provided endless conversation that made those long geochron lab hours fly by. Thanks to my family, Harold, Susan, Lola, Scott, Reed, Abby and Josie, whom without this could never have been possible. Your constant encouragement and support and patience have helped me tremendously. M D & L : thanks for guiding and supporting me in my quest to do something I love. And finally, more thanks than I can give to a very special friend of mine, who has stood behind me in the pursuit to find "the grin from within". You know who you are...thanks for always being there, and don?t give up on me. To my "oldfriends " Anna, Em and Uvo: thanks for always sticking by my side, humoring me with your life adventures, and helping me keep things into perspective. x i i CHAPTER ONE INTRODUCTION 1-1 INTRODUCTION The Lower to Middle Jurassic Hazelton Group is an accreted island arc complex within the Stikine Terrane (Stikinia) of the Canadian Cordillera (Fig. 1-1). The arc succession is host to a number of significant mineral deposits, including the Eskay Creek volcanogenic massive sulphide (VMS) deposit (Fig. 1-2) and other epithermal and porphyry systems associated with sub volcanic intrusions. The volcano-sedimentary sequence has been well mapped and characterized with respect to depositional environment and tectonic setting in the immediate areas of the main mineral deposits, which are located mainly in the Iskut River and Toodoggone River areas of northwestern and north-central British Columbia, respectively (Fig. 1-2). Numerous studies focused on describing and refining the volcanostratigraphy of the sequence have been completed in those and other map areas in northern and central Stikinia, and the region-specific nomenclature has been erroneously applied widely on less studied Hazelton Group successions throughout southern Stikinia. This study is focused in southwest Stikinia, in the Bella Coola and Whitesail Lake map areas (Fig. 1-2), where thick sequences of volcano-sedimentary strata of the upper Hazelton Group have not been previously investigated in detail. The study integrates bedrock geologic mapping, volcanostratigraphic studies, lithogeochemistry and geochronology to provide a comprehensive first order assessment of the age, depositional environment and tectonic setting of Hazelton Group rocks in southern Stikinia. 1-2 PROJECT OBJECTIVES The primary objective of this project was to thoroughly examine a thick and well exposed package of upper Hazelton Group volcanic and sedimentary strata exposed in the northeast corner of the Bella Coola (NTS 093D) and Whitesail Lake (NTS 093E) 1:250 000-scale maps (Fig. 1-2; Kimsquit (093D/15) and Tesla Lake (093E/02) 1:50 000-scale maps, respectively). Geologic mapping and volcanostratigraphic field studies were integrated with lithogeochemistry and dating laboratory studies to provide a complete first order assessment of the physical volcanology, sedimentology, depositional environment, and tectonic setting and of the belt of Hazelton Group strata. Results of the study were synthesized with other regional studies of the Hazelton Group to provide insight into the regional tectonic setting and depositional environment framework of the volcanic arc succession and to speculate on the V M S potential of southwest Stikinia. Field, lithogeochemical, and dating studies of other non-Hazelton Group rocks in the study area have also been completed to better understand the comprehensive geologic evolution of that segment of the Canadian Cordillera. 2 Figure 1-1. Simplified map of terranes and morphogeological belts of the Canadian Cordillera (after Wheeler and McFeely, 1991), showing location of Stikinia and the N E Bella Coola/SE Whitesail Lake map area. Terranes that are referred to in the thesis are labeled. 3 Skeena and Sustut groups Figure 1-2. Geologic features of Stikinia in central and northern British Columbia and location of the Bella Coola, Whitesail Lake, and other NTS map areas referred to in the text. Modified from Evenchick and Thorkelson (2005), after Wheeler and McFeely (1991). 4 1-3 METHODOLOGY 1-3-1 Geological mapping, volcanostratigraphy and sample collection Geologic mapping and volcanostratigraphic studies were completed during the summers of 2003 and 2004. Approximately 13 weeks of fieldwork were carried out via helicopter-assisted fly camps and spot checks, based out of the town of Bella Coola, British Columbia. The distribution of lithologies and structures were mapped at a 1:50 000-scale, and the volcano-sedimentary stratigraphic sections were measured and described at a 1 to 10 metre-scale, depending on their degree of exposure and accessibility. Hazelton Group volcanic and sedimentary units were examined for lateral and vertical lithofacies variations, and for textural and structural information providing insights to the volcanic and sedimentary processes and depositional environment of each unit. Samples were collected for lithogeochemical and dating studies from each lithology represented on the geological insert map. Representative samples from all Hazelton Group lithologies in the study area were collected for petrographic studies to augment the macroscopic rock sample description and interpretation of the nature and origin of the individual rock units. Several lithogeochemical samples were collected from each type of unit in the study area. These samples were selected on the basis of the lowest degree of hydrothermal alteration and lowest abundance of lithic fragments; however, due to localised hydrothermal alteration in certain rock units and portions of the study area, as well as the prevalence of lithic fragments in some types of units (e.g., ignimbrites), the sampling process was clearly biased in favour of more homogeneous rock types. Fossils were collected from all fossiliferous units for biostratigraphic studies. A l l primary volcanic and intrusive units were collected for geochronologic studies; however, again because of the prevalence of lithic fragments in some extrusive units, that sampling process was also biased to more homogeneous rock types. A l l intrusive rock units with suitable mineral assemblages were sampled for Ar-Ar dating, and all other units were sampled for U-Pb zircon dating. 1-3-2 Geochronological studies Geochronological studies were carried out to temporally characterize rock units in the study area and to facilitate stratigraphic correlations within upper Hazelton Group strata in the study area and elsewhere in Stikinia. The cooling history of two post-Hazelton Group intrusive phases in the study area was investigated by dating biotite and hornblende samples using Ar-Ar techniques. Twenty-one primary volcanic samples were processed for U-Pb zircon dating. Of those, zircons were recovered from only nine, and ages obtained from only five. A l l U-Pb and Ar-Ar sample preparation, chemical preparation, and mass spectrometry were completed in the 5 Pacific Centre for Isotopic and Geochemical Research (PCIGR) in the Department of Earth and Ocean Sciences at The University of British Columbia. Ar-Ar dating methods, isotopic data, and results are presented in Appendix B . U-Pb zircon dating methods are presented in Appendix C and isotopic data and results are presented in Chapter 2. 1-3-3 Lithogeochemistry A total of 63 lithogeochemical samples of various rock units in the study area were analyzed for major, trace, and rare earth element (REE) compositions by A L S Chemex Laboratories of North Vancouver. The results were used to investigate the lithogeochemical signatures, petrology, and tectonic affinity of the rock units in the area. Lithogeochemical data and results for intrusive and extrusive Hazelton Group rocks in the study area are presented in Chapter 2. Lithogeochemical data for non-Hazelton Group rocks are presented in Appendix A . Lithogeochemical preparation methods, sample lithologies and location information, duplicate standard analyses, and calculated zircon saturation temperatures are presented in Appendix E. 1-3-4 Petrography Petrographic studies of the various rock units in the study area were carried out to augment field descriptions of lithology, primary and alteration mineralogy, and microscopic volcanic and sedimentary textures and structures. A total of 108 polished and standard thin sections of selected samples were prepared by Vancouver Petrographies Ltd., and were examined using standard transmitted and reflected light microscopy. 1-4 PRESENTATION AND CO-AUTHORSHIP This thesis is presented as two main chapters (Chapters 2 and 3), each of which represents a manuscript to be submitted to a refereed journal for publication. We intend to publish Chapter 2 as a Geological Society of America Bulletin paper, and Chapter 3 as a communication (i.e. short manuscript) in the Canadian Journal of Earth Sciences. The geological map insert is currently in review for publication as a Geological Survey of Canada Open File map. Chapter 2 presents the majority of field- and laboratory-based work completed during this study, and includes significantly more information than will ultimately be published; the extra information has been included for the clarity of the purpose and results of the study. Omission of that information - mostly under section 2-3 - wil l appreciably shorten the manuscript prior to submission to the journal. Chapter 2 discusses the volcano-sedimentary evolution of the upper 6 Hazelton Group in southwest Stikinia. Results from geologic mapping and detailed volcanostratigraphic studies are presented together with lithogeochemical, U-Pb zircon, and paleontological data. The data have been used to develop a model for the tectonic setting and depositional environment for Hazelton Group rocks within the study area, and to postulate on the V M S potential of the upper Hazelton Group in southwest Stikinia. J. Brian Mahoney, James W. Haggart, and Robert L . Hooper assisted in geologic mapping and sample collection for the study and in the development of ideas for the interpretation of rocks in the study area. James K . Mortensen provided assistance in preparation, final analyses, and write-up of U-Pb zircon geochronology and thoughtful scientific insight towards the final product. James W. Haggart and Terry P. Poulton examined the fossils for the study, and portions of Haggart's field reports were cited in the biostratigraphy and depositional environment discussion. Chapter 3 presents results from a study of the age of an ammonoid species endemic to British Columbia, and includes a short but detailed summary of the volcano-sedimentary stratigraphic section in the study area from which the ammonoids were collected and ages were obtained. Results from the biochronologic study have been integrated with 1 U-Pb zircon age from the section, and together the two data sets have important implications for the calibration of the Early Jurassic Toarcian-Aalenian boundary in southwest British Columbia. Terry P. Poulton and James W. Haggart examined the fossils for the study and provided the paleontology-related portions of the written text. J. B . Mahoney and James W. Haggart assisted in the detailed field study of the volcano-sedimentary sequence. Richard M . Friedman processed the sample for U-Pb zircon dating. A l l of these researchers will appear as co-authors in the final submitted manuscript. A l l of the authors of the geological map insert were involved in mapping portions of the map and in the final editing process. James W. Haggart provided numerous, thorough edits to produce the final product. Although all contributions focus on different aspects of the geology of the N E Bella Coola/SE Whitesail Lake study area, each has been prepared as a stand-alone publication, which has resulted in some inevitable repetition and overlap between them. 1-5 REFERENCES Evenchick, C.A. , Thorkelson, D.J., 2005. Geology of the Spatsizi River map area, north-central British Columbia. Geological Survey of Canada Bulletin 577, 276 pages. Wheeler, J.O., McFeely, P., 1991. Tectonic assemblage map of the Canadian Cordillera and adjacent parts of the United States of America. Geological Survey of Canada Map 1712A, scale: 1:2 000 000. 7 CHAPTER 2 TECTONIC SETTING A N D DEPOSITIONAL ENVIRONMENT OF THE LOWER-MIDDLE JURASSIC UPPER H A Z E L T O N GROUP IN WEST-CENTRAL BRITISH COLUMBIA: CONSTRAINTS F R O M VOLCANOSTRATIGRAPHY, U-PB GEOCHRONOLOGY A N D LITHOGEOCHEMISTRY 8 2-1 I N T R O D U C T I O N A N D P U R P O S E The Hazelton Group is one of the most widespread of numerous Paleozoic to recent volcanic "arc" successions in the Canadian Cordillera. It is one of the major components of the Stikine Terrane, which is the largest of the accreted terranes in the northern Cordillera (Figs. 2-1 and 2-2). Jurassic volcanic and sedimentary strata of the Hazelton Group host a number of significant mineral deposits, including the precious metal-rich, polymetallic Eskay Creek volcanogenic massive sulphide (VMS) deposit, as well as epithermal gold and copper-gold porphyry deposits associated with subvolcanic intrusions (Diakow et al., 2002). Despite its volumetric importance to the Canadian Cordillera and significant mineral potential, there have been relatively few regional studies focused on the nature of Hazelton Group magmatism outside of the immediate vicinity of the main mineral deposits, most of which are located in the Iskut and Toodoggone River areas of northwestern and north-central British Columbia, respectively (Fig. 2-1). Large segments of the Hazelton Group have only been mapped on a reconnaissance scale, owing in part to the remote setting and difficult access of many exposures within and adjacent to the rugged Coast Mountains. This study is focused on the Bella Coola and Whitesail Lake map areas in west-central British Columbia (Figs. 2-1 and 2-2), where widespread exposures of Lower and Middle Jurassic volcano-sedimentary strata of the upper Hazelton Group are considered to have significant mineral potential but have not previously been investigated in detail. The research focuses in part on Middle Jurassic portions of the Hazelton Group in the area, because previous U-Pb zircon dating has demonstrated that these rocks are broadly coeval with host rocks of the Eskay Creek V M S deposit. The main goal of the study is to refine our understanding of the tectonic setting and specific depositional environment(s) of rocks emplaced during the final stages of volcanism and sedimentation in this portion of the Hazelton arc. Results of the study provide constraints on tectonic and depositional variations along-strike within the arc system and help to refine genetic models for potential styles of mineralisation (specifically Eskay Creek-type V M S deposits) and mineral exploration strategies to employ within the study area. 2-2 T H E C A N A D I A N C O R D I L L E R A A N D T H E STIKINE T E R R A N E The Canadian Cordillera (Fig. 2-2) comprises a collage of autochthonous and allochtonous continental, pericrationic, marginal basin, oceanic and island arc terranes that were amalgamated, and accreted to the western margin of North America. Several of the terranes are considered to be 'suspect' (e.g., Monger and Price, 2002), having originated at more southerly and perhaps more westerly locations with respect to Ancestral North America, as indicated by the 9 Skeena and Sustut groups Bowser Lake Group Hazelton Group Stuhini Group Cache Creek Boundary between Insular. Coast, and Intermontane belts Eskay Creek deposit CRY LAKE 1041 104 G j 104H Bmtaeram RIVER f N 8 0 .104 B \ j j ... and \ /rl I Sustut basin BOWSER McCONNELL LAKE CREEK 04 A 94 Dr [ ^ASS.RIVER HAZELTON yo\p-o FORT TERRACE SMITHERS FRASER WHITESAIL NECHAKO LAKE R'VER » 3 E 9 3 F BELLA ANAHIM JCOOLA LAKE ,93*0 93 c Babine and Telkwa ranges 1 2 8 ° W 126°W 1 2 4 ° W Figure 2-1. Geologic features of Stikinia in central and northern British Columbia and location of the Bella Coola, Whitesail Lake, and other NTS map areas referred to in the text. Modified from Evenchick and Thorkelson (2005) after Wheeler and McFeely (1991). 10 presence of exotic fauna and paleomagnetic aberrances. These terranes, notably the Cache Creek, Stikine, Quesnel, Wrangellia and Alexander terranes (Fig. 2-2), consist of volcanic successions of mainly oceanic and island-arc affinity, implying the former presence of intervening subduction zones and oceanic lithosphere (Evenchick and Thorkelson, 2005, and references therein). The Stikine Terrane (Stikinia) is the largest of the accreted terranes in the northern Cordillera, and consists mainly of weakly deformed stratified and intrusive rocks metamorphosed to zeolite to greenschist metamorphic grades. It is 1500 km long, extending from south-central British Columbia to the south-central Yukon Territory, and 300,km wide at its maximum width at approximately 56°N (Fig. 2-2). Stikinia is juxtaposed against the Cache Creek terrane in the east, and, together with Quesnellia and the Cache Creek terrane makes up the Intermontane morphogeological belt. The Coast morphogeological belt, which consists of mainly crystalline rocks of the Coast Plutonic Complex, encompasses the western margin of Stikinia as well as the suture zone between Stikinia and Wrangellia and the Alexander Terrane of the Insular morphogeological belt to the west (Wheeler and McFeely, 1992; Fig. 2-2). Stikinia consists of three main lithotectonic assemblages (Wheeler and McFeely, 1992): 1) metavolcanic and metasedimentary rocks of the Upper Paleozoic Stikine Assemblage; 2) arc-related volcano-sedimentary complexes and related intrusions of the Upper Triassic Stuhini Group and Lower to Middle Jurassic Hazelton Group; and 3) basinal sediments of the overlying Middle Jurassic to middle Cretaceous Bowser Lake Group (e.g., Evenchick and Thorkelson, 2005). 2-3 THE HAZELTON GROUP The Hazelton Group sequence is interpreted to mainly represent an oceanic island arc that formed as a result of subduction-related magmatism in more southerly latitudes in the paleo-Pacific Ocean. The Hazelton Group is exposed throughout much of central and northern Stikinia, extending for approximately 800 km from latitude 51° to latitude 58°30"N, and across the entire width of the terrane (Figs. 2-1 and 2-2). Restoration of post-depositional shortening associated with the Skeena Fold Belt (e.g., Evenchick, 1991) reveals that the width of the volcanic belt at the time of deposition was on the order of 450-550 km (Thorkelson et al., 1995, and references therein). The Hazelton Group unconformably or disconformably overlies mafic to intermediate arc volcanic and associated sedimentary rocks of the Stuhini Group in the northern part of Stikinia, where the base is characterized by granitoid clast conglomerate interbedded with fossiliferous limy sandstone and siltstone bearing Late Hettangian to Early Sinemurian (Early Jurassic) 11 Figure 2-2. Simplified map of terranes and morphogeological belts of the Canadian Cordillera (after Wheeler and McFeely, 1991), showing location of Stikinia and the N E Bella Coola/SE Whitesail Lake map area. Terranes that are referred to in the text are labeled. 12 ammonites (Nadaraju, 1993; Lewis et al., 2001; Okulitch, 2001). The nature of the Hazelton Group basement is poorly constrained in southern Stikinia, but is thought to consist of Stuhini Group or older strata, as evidenced by the presence of rafts of volcanic rocks interpreted to be Stuhini within the Coast Belt immediately to the southwest (Fig. 2-1). The waning stage of Hazelton arc magmatism is best recorded in the strata of the Bowser Basin (Fig. 2-1), where it coincided with the initiation of deposition of the Middle Jurassic and younger Bowser Lake Group. The contact between uppermost Hazelton Group and overlying Bowser Lake Group strata is locally conformable. The Bowser Lake Group generally includes a sequence of early Middle Jurassic (Bajocian) to middle Cretaceous marine and nonmarine turbiditic shale and siltstone with sandstone and chert-rich conglomerate intervals. These strata were deposited within the broad, sub-circular Bowser Basin, which formed between topographic highs within the Hazelton arc, including the Skeena Arch (Fig. 2-1; Lewis et al., 2001; Evenchick and Thorkelson, 2005). Chert clasts found within conglomerates of the Bowser Lake Group were derived from the Cache Creek Terrane, which lies to the northeast of the Bowser Basin (Fig. 2-1), and are therefore a provenance link between Stikinia and the Cache Creek Terrane (Evenchick and Thorkelson, 2005). This deposition occurred as a result of amalgamation of the two terranes as the Cache Creek Ocean closed between Stikinia and Quesnellia, and with the obduction of the entire landmass onto the western margin of North America (Monger and Price, 2002). The gradational contact between the final eruptive products of Hazelton arc magmatism and oldest sedimentary strata of the Bowser Lake Group in the early Middle Jurassic is therefore coincident with a major tectonic reconfiguration, and records the dramatically changing depositional environment during which mineralisation associated with the latest stages of Hazelton Group magmatism the Eskay Creek deposit was formed. 2-3-1 Previous work in the Hazelton Group Leach (1910) first applied the term Hazelton Group to a succession of lower Sinemurian to Callovian volcanic and sedimentary rocks in northwest British Columbia. Tipper and Richards (1976) adopted this terminology, and used it to classify rocks in the Smithers, Hazelton, and McConnell Creek areas of north-central British Columbia (Fig. 2-1). The term Hazelton Group has subsequently been applied to volcano-sedimentary strata from other regions of central and southern Stikinia (e.g., Diakow and Koyanagi, 1988; Britton and Alldrick, 1988; Brown et al., 1990; Fig. 2-2). Marsden and Thorkelson (1992) and Thorkelson et al. (1995) used bio- and chronostratigraphic age, lithostratigraphic associations, and geochemical characteristics of portions of the Hazelton Group to constrain some aspects of the tectonic setting of the arc 13 sequence. Their work represents the most comprehensive study of the depositional environment and tectonic setting of the Hazelton Group, which was subsequently summarized and refined by Evenchick and Thorkelson (2005). Evenchick and Thorkelson (2005) adopted the terminology developed by Thorkelson (1992), and define the Hazelton Group as all of the Lower and Middle Jurassic volcanic and related volcanogenic sedimentary strata within Stikinia Tipper (1978) documented the age of the sequence as part of a regional study on Cordilleran Jurassic stratigraphy. Palfy and others (1995a) later conducted biostratigraphic and geochronologic studies of specific formations within the Hazelton Group, and results of their study were subsequently integrated into a timescale calibration of the Jurassic (e.g., Palfy et al., 1995b). Studies related to mineral deposits hosted in the Hazelton Group include: 1) studies of epifhermal deposits hosted in subvolcanic intrusions of the Hazelton Group in the Toodoggone River area (e.g., Diakow et al., 1991); 2) syntheses of the metallogeny of the Hazelton arc in the Iskut River region (e.g., Macdonald et al., 1996); 3) detailed studies of the physical and chemical constraints on mineralisation of Hazelton Group strata hosting the Eskay Creek deposit (e.g., Roth, 2002); and 4) ongoing mapping concentrated on revising local stratigraphic position and interpretations of Hazelton Group volcanic lithofacies in the vicinity of the Eskay Creek deposit in the Telegraph Creek and Iskut River regions (e.g., Simpson and Nelson, 2004; Fig. 2-1). Studies focused on redefining or refining local and regional stratigraphy of the Hazelton Group have been conducted by Gabrielse and Tipper (1984), Grove (1986), Thompson et al. (1986), Diakow and Mihalynuk (1987), Alldrick (1989), Maclntyre et al. (1989), Read and Psutka (1990), Anderson (1993), and Lewis et al. (2001). The impetus for the majority of stratigraphic studies in the Hazelton Group was to aid in the evaluation of the mineral potential of the various areas, and nearly all of the studies were concentrated in northern Stikinia due to the abundance of mineral showings and road access in those areas. Particular attention has been given to the Iskut River region, in part because of the presence of very valuable syngenetic deposits such as the Eskay Creek deposit within the local Hazelton Group sequence in this region (Fig. 2-1). A thorough understanding of the local stratigraphic sequences is a critical component to exploration programs within structurally disrupted mineral districts (Lewis et al., 2001). 2-3-2 Hazelton Group nomenclature The Hazelton Group in central and northern Stikinia has conventionally been divided into four or five formations (e.g., Grove, 1986; Alldrick, 1991; Anderson, 1993; Lewis et al., 2001). Most of the existing formational nomenclature of the Hazelton Group comes from the Iskut River 14 (e.g., Lewis et al., 2001), Spatsizi River (e.g., Evenchick and Thorkelson, 2005), and Toodoggone River (e.g., Diakow et al., 1991) map areas, and from the Babine and Telkwa ranges (e.g., Maclntyre et al., 1989; Fig. 2-1). The summary of Hazelton Group stratigraphy in the Iskut River region by Lewis and others (2001), together with the stratigraphic assessment of the north-central Smithers map area and the central Whitesail Lake map area by Maclntyre et al. (1989) and Diakow and Koyanagi (1988), respectively, forms the basis on which discussions of regional formational equivalents in this study are based. Schematic stratigraphic columns summarizing the results of these various investigations are presented in Figures 2-3, 2-4, and 2-5 respectively. 2-3-2-1 Hazelton Group stratigraphy and nomenclature in the Iskut River region Hazelton Group stratigraphy in the Iskut River region has received much attention since the discovery of the Eskay Creek deposit in the mid-1980s (e.g., Barrett and Sherlock, 1996). The initial Hazelton Group formational nomenclature for the Iskut River region defined by Grove (1986) has been subsequently revised several times. Lewis et al. (2001) provided the most recent comprehensive synthesis of Hazelton Group stratigraphy of the Iskut River region. Their results include concise and simplified local stratigraphic sequence with the potential for broader regional applications. They define four formations within Hazelton Group strata in the Iskut River region, including, from base to top, the Jack Formation, Betty Creek Formation, Mount Dilworth Formation, and Salmon River Formation (Fig. 2-3). The Jack Formation is synonymous with the informally named "transitional unit" (e.g., Anderson and Thorkelson, 1990), which regionally unconformably to disconformably overlies arc-related strata of the Stuhini Group (Fig. 2-3). The formation consists of granitoid and volcanic clast conglomerate interbedded with fossiliferous limy sandstone and siltstone (Lewis et al., 2001). As lithologically indistinguishable conglomerate units occur in the underlying Stuhini Group in the region, the first occurrence of fossiliferous limy units is considered to define the base of the Jack Formation. Lower Jurassic faunas recovered from the interbedded marine units indicate a Late Hettangian to Early Sinemurian age range for the Jack Formation. The Jack Formation is conformably overlain by the Betty Creek Formation in the Iskut River region (Lewis et al., 2001; Fig. 2-3). The contact between the two formations is at the first occurrence of relatively proximal volcanogenic material. The Betty Creek Formation, as redefined by Lewis et al. (2001) to include the "Unuk River Formation", consists of one formation that ranges in age from Hettangian/Sinemurian to Pliensbachian (Fig. 2-3). Previous workers noted a sharp colour change in the stratigraphic sequence from greenish, chloritic, 15 Hazelton Group Stratigraphy of the Iskut River Region t (-1 <L> n, Kimme-ridgian a  P Oxfordian lovian CO O u u T3 Bathonian JRASSI Bajocian >-> Aalenian Toarcian Pleins-bachian O Sinemurian ttangian tu X c .2 U s RIASSI Upper Norian Carnian Bowser Lake Group (Bathonian-Kimmeridgian) S PL, pa S o CS A A A A Salmon River Formation (Toarcian-Bathonian/ Callovian) Mount Dilworth Formation (Pleinsbachian/ Toarcian-Bajocian) Betty Creek Formation (Including Unuk River Formation; Hettangian/ Sinemurian-Pleinsbachian Jack Formation ("Transitional Unit") L Hettangian-E Sinemurian X > N W o O o Stuhini Group (M-L Triassic) Figure 2-3. Idealized stratigraphic column of Hazelton Group stratigraphy in the Iskut River region of northwest Stikinia, summarized from Lewis et al. (2001). Note that intraformational lithofacies associations and unit thicknesses are necessarily somewhat simplified and idealised. 16 Explanation to Lithologies for Hazelton Group Stratigraphic Columns Sedimentary Rock Units Shale, argillite, marlstone, and greywacke Tuffaceous mudstone and argillite ("Pajama beds") Limestone and cherry limestone; subordinate chert — • •' H Siltstone and mudstone Fossiliferous limey sandstone and siltstone Sandstone and feldspathic sandstone o- • -o Polymict conglomerate Volcanic Rock Units Mafic to intermediate massive flow Intermediate to felsic silicified and/or flow-banded lava flow, tuff, lapilli tuff, or tuff breccia; local felsic domes Mafic to intermediate pillowed lava Mafic to intermediate plagioclase-porphyritic flow Mafic to intermediate and felsic, monolithic to heterolithic, volcanogenic breccia, autobreccia, broken pillow breccia, or hyajoclastite breccia Pumice- and rhyolite-rich breccia Figure 2-3 (cont). Explanation to lithologies represented in Hazelton Group stratigraphic columns. Refer also to this explanation for Figures 2-4,2-5 and 2-8. 17 andesitic tuffs to maroon clastic sedimentary rocks, and have previously used this to define and differentiate the "Unuk River Formation" from the Betty Creek Formation (e.g., Anderson and Thorkelson, 1990; Alldrick, 1991). Lewis et al. (2001) consider this distinction to be unreliable and attribute the colour change mainly to diagenetic phenomena. The Betty Creek Formation includes the following lithotypes (no stratigraphic order implied): 1) shale dominated packages intercalated with minor feldspathic sandstone and limestone; 2) volcaniclastic/pyroclastic dominated packages of intermediate composition; and 3) massive, brecciated, or pillowed, intermediate to mafic composition, porphyritic to aphyric flows (Lewis et al., 2001). The Mount Dilworth Formation is a distinct package of proximal felsic and less commonly intermediate tuff, breccia, and lava flows. The lower stratigraphic contact is defined at the stratigraphic position where felsic volcanic lithofacies predominate over more distal and intermediate composition units of the Betty Creek Formation (Fig. 2-3). The regionally discontinuous Betty Creek Formation is locally absent, and the Mount Dilworth Formation in some areas rests directly on conglomeratic and finer grained marine units of the Jack Formation. The maximum age of this formation is Pleinsbachian/Toarcian, and overlying strata of the Salmon River Formation yield radiolarian of Toarcian to Bajocian age (Lewis et al., 2001). This formation is laterally extensive in the Iskut River region (Fig. 2-1), where it occurs in the footwall of the Eskay Creek 21 Zone deposits (e.g., Roth, 2002). The association of the Mount Dilworth Formation with the Eskay Creek deposits, combined with its distinctiveness within the stratigraphic sequence, have led to its widespread usage as a guide in exploration programs (Lewis etal, 2001). The base of the Salmon River Formation is defined by Lewis et al. (2001) where a significant change in style of sedimentation and volcanism from underlying units is first observed. The Salmon River Formation includes the distinctive fine grained, tuffaceous turbidite sequences that have been informally dubbed "pajama beds". The pajama beds interfinger with the uppermost felsic volcanic flows of the Mount Dilworth Formation, and the contact between the formations is thus considered to be gradational (Fig. 2-3). Lower, thin, fossiliferous, calcareous sandstone units and turbidites of the lower Salmon River Formation pass up into a regionally extensive sequence of pillowed to brecciated mafic lavas, possibly laterally equivalent subaerial andesite flows, and local accumulations of felsic flows, flow domes and pyroclastic rocks. The formation ranges in age from Pleinsbachian/Toarcian to Bathonian/Callovian (Lewis etal., 2001). The contact between the Salmon River Formation and the overlying Bowser Lake Group, as defined by Lewis et al. (2001), is located immediately above the stratigraphically highest 18 volcanic units; in the Iskut River region, this interval occurs in the Bathonian/Callovian (Fig. 2-3). The Bowser Lake Group includes a thick succession of shale and greywacke with lesser amounts of interbedded chert-rich conglomerate, and the minimum age of the group is constrained by Kimmeridgian faunas. Uppermost Hazelton Group strata hosting the Eskay Creek V M S deposit consists of dominantly submarine, interstratified dacitic to rhyolitic flows and tuff and pillowed basaltic flows and breccia with mudstone intervals. The units are characterized by locally large variations in unit thicknesses, and mapping studies of the units indicates evidence for syn-depositional faulting. A rhyolite unit in the immediate footwall of the main ore zones at Eskay Creek yielded a U-Pb zircon age of ca. 173 Ma (Childe, 1994), and intercalated mudstone beds within a basaltic hanging wall unit yield Aalenian and possibly Lower Bajocian radiolarian (Roth et al., 1999). Despite the age correlation with the Mount Dilworth and Salmon River formations, these terms are not preferred lithostratigraphic terms at Eskay Creek, as in that region the stratigraphic relationships are more complex and are commonly reversed (Roth et al., 1999). To accommodate these problems, the entire bimodal volcanic suite and associated sediments are mapped as a single unit, within which local compositional and textural facies have been mapped (MacDonald et al., 1996). 2-3-2-2 Hazelton Group stratigraphy and nomenclature in the Babine and Telkwa ranges Relatively little attention has been given to Hazelton Group strata in the Babine and Telkwa ranges of the Smithers map area in east-central Stikinia, as compared to the well-studied strata of the Iskut River region (Fig. 2-1). However, the formational nomenclature that was developed in the Babine and Telkwa ranges by Tipper and Richards (1976) and further refined by Maclntyre et al. (1989) is the most widely applied nomenclature of all of the type areas of Hazelton Group strata. Despite the position of the region on the northern side of the Skeena Arch (Fig. 2-1), all Hazelton Group strata south of the region, including the Bella Coola and Whitesail Lake map areas, have been described using this nomenclature. Maclntyre et al. (1989) provide detailed descriptions of four formations within Hazelton Group strata in the region, including, from base to top: the Telkwa Formation, Nilkitkwa Formation, Smithers Formation, and Ashman Formation (Fig. 2-4). In this region, the Telkwa Formation rests unconformably atop marine, calc-alkaline to alkaline arc sequences of the Late Triassic Takla Group. Maclntyre et al. (1989) define four major lithofacies in the Telkwa Formation including, in ascending stratigraphic order: 1) poorly sorted, heterolithic basal conglomerate; 2) fining upward sequences of volcanic breccias, maroon feldspathic tuffs, and epiclastic rocks intercalated 19 Hazelton Group Stratigraphy of the Babine and Telkwa Ranges Trout Creek Assemblage and Bowser Lake Group (L Bajocian-Kimmeridgian) Ashman Formation and Smithers Formation (M Toarcian?-Callovian) Nilkitkwa Formation (L Sinemurian-Toarcian) Telkwa Formation (Sinemurian or older) • N W O O O Takla Group (L Triassic) Figure 2-4. Idealized stratigraphic column of Hazelton Group stratigraphy in the Babine and Telkwa Ranges of east-central Stikinia, summarized from Maclntyre et al. (1989). Note that intraformational lithofacies associations and unit thicknesses are necessarily somewhat simplified and idealised. **The age span of several formations has been adjusted using results from Palfy et al. {1995). 20 with aphyric to feldspar-phyric basalt and andesite flows; 3) massive aphyric to augite- and feldspar-phyric, amygdaloidal basalt flows and interbedded red air-fall tuffs and tuffaceous mudstone; and 4) cream to grey coloured, rhyolite flows, felsic ignimbrite units, rhyolite domes, and minor red tuffs and basalt flows. The age of the Telkwa Formation in the Babine and Telkwa ranges is constrained to be Sinemurian or older based on fossil collections from the overlying Nilkitkwa Formation (Maclntyre et al., 1989; Fig. 2-4). The Nilkitkwa Formation includes a lower, thin-bedded marine sedimentary lithofacies and an upper red tuff lithofacies with minor basalt flows and felsic ash flow tuffs. The lower marine sedimentary member includes a basal coarse conglomerate with granitic and felsic volcanic clasts, suggesting an intraformational hiatus between the Nilkitkwa Formation and the underlying upper felsic pyroclastic lithofacies of the Telkwa Formation (Fig. 2-4). Conglomerate beds grade upward into the thin bedded argillite and siltstone and intercalated limestone and chert beds that characterize the marine sedimentary member (Maclntyre et al., 1989). The Red Tuff member of the Nilkitkwa Formation includes several cycles of fining upward medium to thin bedded, red to maroon lapilli tuff, crystal tuff, and tuff beds and related epiclastic rocks with subordinate beds of grey ash flow tuff and amygdaloidal basalt (Maclntyre et al., 1989). Both the lower marine sedimentary member and the Red Tuff member show extreme lateral lithofacies thickness variations in the Babine and Telkwa ranges and are locally absent from the stratigraphic sequence (Maclntyre et al., 1989). The Nilkitkwa formation ranges in age from Late Sinemurian through Toarcian (late Early Jurassic), and probably includes several intraformational hiatuses (Maclntyre et al., 1989; Fig. 2-4). The Smithers Formation conformably overlies the Nilkitkwa Formation (Fig. 2-4), and consists of sequence of interbedded marine sandstone and pebble conglomerate, which contain predominantly Bajocian (Middle Jurassic) fossil fauna (Maclntyre et al., 1989). Coarse sedimentary rocks of the Smithers Formation grade up section into finer grained, marine, grey siltstone and shale intercalated with subordinate arenaceous sandstone and pebble conglomerate beds of the Ashman Formation (Fig. 2-4). Fauna collected from the Ashman Formation in the Smithers and Telkwa ranges indicate a predominantly Callovian (late Middle Jurassic) age for deposition of the Ashman Formation (Maclntyre et al., 1989). The Smithers and Ashman formations together form a continuous sedimentary rock package that is interpreted to represent a southerly prograding marine transgression from Bajocian through Callovian time. Fossil collections from the Smithers Formation made by Tipper and Richards (1976) indicate that deposition of the formation (and thus the marine transgression) may have initiated as early as Middle Toarcian (late Early Jurassic). Tipper and Richards (1976) include the Ashman 21 Formation with the Middle to Late Jurassic Bowser Lake Group, but the results of the studies by Maclntyre et al. (1989) demonstrate stratigraphic continuity between the Smithers and Ashman formations, and they therefore suggest that the Ashman Formation be included within the Hazelton Group (Fig. 2-4). Hazelton Group strata in the Babine and Telkwa ranges are conformably to disconformably overlain by coarse-grained, poorly sorted, chert-pebble conglomerate, sandstone, and siltstone of the Late Oxfordian to Early Kimmeridgian Bowser Lake Group (Fig. 2-4). 2-3-2-3 Recent chronostratigraphic and biostratigraphic adjustments to regional Hazelton Group stratigraphy Palfy et al. (1995a) studied Hazelton Group rocks in the Babine and Telkwa ranges as part of their global study of the chronostratigraphic (U-Pb) and biostratigraphic (ammonoid) Jurassic timescale. As part of their study, Palfy et al. (2005) employed the regional stratigraphic nomenclature for the Hazelton Group developed by Maclntyre et al. 1989, and their results have helped to refine the stratigraphic position of the various rock units in the area. Three main results related to the present study arise from their investigation: 1) new biostratigraphic data demonstrates that the minimum age of the Telkwa Formation is expanded through the early Pleinsbachian; 2) their results define a possible contact between the Smithers and Ashman formations in east-central Stikinia at the Bajocian/Bathonian boundary and demonstrate that the "pajama beds" that characterize the base of the Salmon River Formation in the Iskut River region (Fig. 2-1) potentially represent a regionally correlative, stratigraphically diagnostic unit; and 3) possibly expands the upper contact of the Ashman formation to ca. 158 Ma (Middle Oxfordian). 2-3-2-4 Hazelton Group stratigraphy and nomenclature in the central Whitesail Lake map area Early workers in the Whitesail Lake and Bella Coola map areas (Fig. 2-1) traditionally assigned Hazelton Group strata in those areas to the Telkwa and Smithers formations (e.g., Baer, 1965; Woodsworth, 1979; Woodsworth, 1980). A l l Hazelton Group rocks in the Bella Coola map area were previously mapped as Telkwa Formation (Baer, 1965). Woodsworth (1980) mapped most of the rocks in the study area in the southeast corner of the Whitesail Lake map as Sinemurian or older (Early Jurassic) Telkwa Formation overlain in the east by Middle Jurassic Smithers and Ashman formations. He placed strata underlying the regionally prominent Tsaydaychuz Peak in the Hauterivian (Early Cretaceous) Gambier Group, invoking a structure 22 which he believed had locally down-dropped and preserved a sequence of much younger volcanic strata (Fig. 2-6). Diakow and Koyanagi (1988) refined the Hazelton Group stratigraphy of the central Whitesail Lake map area as part of their investigation focused on characterizing the geologic setting of known mineral occurrences in the region. They integrated results of Diakow and Mihalynuk (1987) and Woodsworth (1979, 1980) into their refinement of the local Hazelton Group stratigraphy (Fig. 2-5). Diakow and Koyanagi (1988) subdivide Hazelton Group strata in the central Whitesail Lake map area using the formational nomenclature developed by Tipper and Richards (1976; further refined by Maclntyre et al., 1989). They recognize the Telkwa and Smithers formations in the central Whitesail Lake map area. The Nilkitkwa Formation is apparently absent in the central Whitesail Lake map area. The Ashman Formation is also present, but is included within the Bowser Lake Group (e.g., Tipper and Richards, 1976; Fig. 2-5). The base of the Telkwa Formation is not observed in the central Whitesail Lake map area; however, in the west-central portion of the map area, Woodsworth (1979) notes a granite boulder conglomerate comprising the base of the Hazelton Group resting unconformably atop a Paleozoic(?) mafic crystalline complex. The Telkwa Formation may also locally unconformably overlie the Upper Triassic or older Gamsby Group (Fig. 2-5). Diakow and Koyanagi (1988) subdivide the Telkwa Formation in the central Whitesail Lake map area into two map units comprising a cumulative thickness of approximately 2000 m, including a lower succession of layered maroon volcanics and an upper succession of foliated green volcanics (Fig. 2-5). The maroon volcanics are characterized by distinctly bedded maroon, brick red, and lesser green pyroclastic rocks and volumetrically subordinate, aphyric to porphyritic, locally flow-banded basalt, andesite, and rhyolite flows. The lower maroon volcanic sequence is overlain by locally pervasively foliated, dark green, aphyric and porphyritic basalt and andesite lava flows that are intimately intercalated with tuff and lapilli tuff and local marlstone and pebble conglomerate. Ubiquitous chlorite and epidote and irregular quartz veins are widespread within the mafic flows, and the pyroclastic beds are commonly graded, laminated, and rarely cross-laminated (Diakow and Koyanagi, 1988). The age of the Telkwa Formation is poorly constrained in the Whitesail Lake area; an Early Jurassic age is estimated for the formation based on fossil collections from the east-central portion of the map sheet (e.g., Diakow and Koyanagi, 1988, and references therein; Figs. 2-1 and 2-5). Woodsworth (1979, 1980) and Tipper (1979) suggest a Sinemurian age based on lithologic similarities with the type section of the Telkwa Formation in the Smithers map area to the north (Fig. 2-1); however, their assumption is not corroborated with fossil ages in the Whitesail Lake map area. 23 Hazelton Group Stratigraphy of the Central Whitesail Lake Area t CD CX Kimme-ridgian O. P Oxfordian lovian rt O u T3 Bathonian JRASSI Bajocian *n Aalenian Toarcian t-c & Pleins-bachian o Sinemurian ttangian <u X U Rhaetian RIASSI Upper Norian Carnian Kasalka Group (Upper Cretaceous) Bowser Lake Group (Ashman Formation; Bajocian-E Oxfordian) Smithers Formation (Aalenian-L Bajocian) Telkwa Formation (E Jurassic -Sinemurian?) a > N W o o O ^ Paleozoic? mafic crystalline complex or Gamsby Group (U Triassic or older) Figure 2-5. Idealized stratigraphic column of Hazelton Group stratigraphy in the central Whitesail Lake area of southwest Stikinia, summarized from Woodsworth (1979, 1980), Tipper (1979), Diakow and Koyanagi (1988), and references therein. Note that intraformational lithofacies associations and unit thicknesses are necessarily somewhat idealised. Reported formational thicknesses represent the minimum values reported from these investigations. 24 The Smithers Formation conformably overlies the Telkwa Formation in the Whitesail Range of the central Whitesail Lake map area (Diakow and Koyanagi, 1988; Fig. 2-5). Diakow and Koyanagi (1988) subdivide the Smithers Formation in the central Whitesail Lake map area into a lower sedimentary rock division and an upper pyroclastic division, with a combined minimum thickness of approximately 1700 m (Diakow and Mihalynuk, 1987; Fig. 2-5). The lower sedimentary rock division mainly consists of grey-green siltstone, sandstone, arkosic wacke, and minor granule to pebble conglomerate with rare limestone and chert beds. Sedimentary structures include parallel laminations within otherwise structureless beds (Diakow and Koyanagi, 1988). The lower sedimentary rock division grades into the upper pyroclastic division, which comprises alternating maroon and green beds of tuff, lapilli tuff, and less common flows. Thin, parallel laminated and graded tuff is locally diagnostic of this division. Rare accretionary tuff beds are locally intercalated with fossiliferous clastic rocks. The lower sedimentary rock division is a laterally continuous unit; however, where not observed in a clear stratigraphic sequence, the upper pyroclastic division is lithologically indistinguishable from the lower layered maroon volcanic division of the Telkwa Formation (Diakow and Koyanagi, 1988). Ammonite fauna indicate an age of Middle Toarcian to Late Bajocian for the Smithers Formation in the central Whitesail Lake map area. Diakow and Koyanagi (1988) suspect local erosional disconformities in the Smithers Formation based on the irregular regional distribution of similar fauna. In the east-central Whitesail Lake area (Fig. 2-1), Woodsworth (1979, 1980) and Tipper (1979) describe a sequence of cream coloured, reddish, and dark grey rhyolitic flows, breccia, and tuff intercalated with minor fossiliferous marine siltstone and sandstone. Locally abundant ammonite fauna in the sequence indicate an Upper Toarcian to Lower Bajocian age for the sequence, which they term the "Whitesail formation". The age of the sequence significantly overlaps in age with the Smithers Formation as defined by Diakow and Koyanagi (1988) in the central Whitesail Lake map area. The reported lithologies of the "Whitesail formation" are consistent with what Diakow and Koyanagi (1988) describe as the upper pyroclastic division of the Smithers formation. This indicates that the lower sedimentary rock division of the Smithers Formation as defined by Diakow and Koyanagi (1988) may represent the distal lithofacies equivalents of the proximal felsic deposits of the "Whitesail formation", which were apparently time transgressive to the west. Tipper (1979) suggests a possible correlation of the "Whitesail formation" with the Nilkitkwa Formation based on similar age and lithologies, which would also suggest that felsic volcanism that characterizes the Nilkitkwa Formation, which is generally older in the north, is time transgressive to the south (Figs. 2-3 and 2-5). 25 Diakow and Koyanagi (1988) describe an approximately 300 metre thick sequence black and grey argillite and siltstone intercalated with less abundant feldspathic sandstone, arenaceous sandstone, accretionary lapilli tuff, chert, and rare coralline limestone lenticles overlying the Smithers Formation in the central Whitesail Lake area (Figs. 2-1 and 2-5). They classify the strata as part of the Ashman Formation of the Bowser Lake Group (redefined as part of the Hazelton Group by Maclntyre et al., 1989), and distinguish the strata from the Smithers Formation on the basis of more thinly spaced bedding and less prolific fossil fauna. They describe the strata as a continuation of marine deposits representative of the Smithers Formation and observe that no major hiatus separates the successions, further supporting the inclusion of the Ashman Formation within the Hazelton Group (e.g., Maclntyre et al., 1989; Fig. 2-5). 2-3-2-5 Usage of nomenclature in the study area Although assigning formational nomenclature is a useful practice for the purposes of geologic mapping and tectonic interpretation, it is in some cases counterproductive to employ locally developed formational nomenclature to volcanic arc sequences on a regional scale due to extreme vertical and lateral lithofacies transitions within such settings. In particular, the paucity of age data from most portions of the Hazelton Group makes this process speculative and somewhat misleading. Mapping and stratigraphic studies in the Hazelton Group in southern Stikinia are still too limited to be able to construct detailed stratigraphic sections for this portion of the terrane; therefore, in this contribution, regional correlations are made on the basis of temporal and lithologic characteristics between rocks in the study area and possible formational equivalents to the north, and the use of formational nomenclature is avoided. This study represents the first comprehensive stratigraphic study of the volcanic and sedimentary lithofacies architecture of the Hazelton Group in southwestern Stikinia. U-Pb dating and biostratigraphic studies have provided important temporal constraints on the timeframe represented by volcanic and sedimentary deposition in this region, have helped to decipher strata of the Hazelton Group from locally similar arc formations, and have helped to refine the relative stratigraphic position of Hazelton Group strata in this region with respect to the regionally established stratigraphic and tectonic framework. 2-4 PREVIOUS W O R K A N D R E G I O N A L G E O L O G I C S E T T I N G 2-4-1 Previous work in the Bella Coola and Whitesail Lake map areas The geologic framework of the Bella Coola (NTS 093D), Whitesail Lake (NTS 093E; Fig. 2-6), and surrounding map areas has been established through l:250,000-scale mapping by 26 Duffell (1959), Roddick (1970), Baer (1973), Woodsworth (1980), and Hutchison (1982). Recent studies specifically focused on Hazelton Group exposures within the areas include: (1) lithostratigraphic studies of Hazelton Group strata within the Whitesail Lake map area by Tipper (1979); (2) examination of mineral occurrences and Hazelton Group stratigraphy within the Whitesail Reach, Troitsa Lake, and Chikamin Mountain map areas in the central Whitesail Lake map area (Diakow and Mihalynuk, 1987; Diakow and Koyanagi, 1988); and (3) age and geochemical characterization of the Nifty V M S prospect in the east-central Bella Coola district (Ray etal., 1998; Fig. 2-6). Recent 1:50,000-scale mapping programs led by Haggart et al. (2004) and Mahoney et al. (2005) remapped large portions of the eastern and central Bella Coola map and the southeastern Whitesail Lake map, respectively, in order to reassess the mineral potential of crystalline rocks of the Coast Belt and stratified rocks of southwestern Stikinia in these areas. Importantly, these workers developed a regionally applicable mapping model of volcanic and plutonic suites and structural history within the areas. As part of this, they demonstrated that the map units and structural history recorded within rocks of the Bella Coola area can be traced to the north at least as far as the central Whitesail Lake area. 2-4-2 Regional Geologic Setting The Bella Coola and Whitesail Lake map areas are located within a rugged part of the west-central Coast Mountains near the southwestern edge of Stikinia (Fig. 2-2). The area straddles the transition from stratified rocks of Stikinia in the Intermontane morphogeological belt on the east into crystalline rocks of the eastern margin of the Coast Plutonic Complex of the Coast morphogeological belt on the west. The Stikine Terrane in this area comprises the western portion of the Intermontane Superterrane, which, at the latitude of Bella Coola, is juxtaposed against rock units of Wrangellia and possibly Alexander Terrane (which together make up the Insular Superterrane; Fig. 2-2). The contact between the Intermontane and Insular superterranes is the Coast Mountain Shear Zone, a 1200 km-long shear zone that is postulated to have accommodated 1000s of kilometres of displacement between 65 and 55 Ma (Andronicos et al., 1999; Rusmore et al., 2000, and references therein). Two Jurassic and Cretaceous volcano-sedimentary assemblages form broad northwest-trending belts throughout the eastern Bella Coola and Whitesail Lake areas (Fig. 2-6). The Early-Middle Jurassic Hazelton Group forms the eastern arc sequence, and is unconformably overlain by the Early Cretaceous Monarch assemblage, which makes up the western belt. Hazelton Group strata generally consists of weakly bimodal, lithologically heterogeneous strata, whereas strata of 27 128°00' 127°00' 126°00' Figure 2-6. Generalised geologic map of the Bella Coola (93D) and Whitesail Lake (93 E) map areas, British Columbia, illustrating the N E Bella Coola/SE Whitesail Lake study area and other localities referred to in the text. Contacts have been removed for simplicity and some geographic localities are approximated. Modified after Wheeler and McFeely (1991). Abbreviations: C M , Chikamin Mountain; MP, Mount Preston; TP, Tsaydaychuz Peak; RP, Ramsey Peak; J M , Jumble Mountain; KP, Kalone Peak. The dashed grey line represents the approximate boundary between the Coast and Intermontane morphogeological belts and the continental divide. 28 Legend to Geologic Map of the Bella Coola and Whitesail Lake Areas CENOZOIC Stratified Rocks T Q A NTC • P T K Anahim Group plume volcanics Chilcotin Group back-arc volcanics Kamloops Group transtensional arc volcanics MESOZOIC Stratified Rocks mKS KS JKG JBL J H m A South Fork Group transtensional cauldron-subsidence and arc volcanics Skeena Group easterly derived back-arc elastics Gambier Group arc, and locally, rift volcanics Bowser Lake Group back-arc (?) and foredeep clastic wedge on Stikinia Hazelton Group volcanic arc complexes in Stikinia Atnarko Complex metamorphic equivalents Stuhini Group arc volcanics in Stikinia Crystalline Rocks Undivided granodiorite plutons MTg ETq LKg mKg Mjg EJdB Undivided granite plutons Undivided granodiorite and quartz monzonite plutons Coast Plutonic Complex southwestern portion Undivided foliated quartz diorite and granodiorite plutons Gamsby Complex Black Dome Pluton PALEOZOIC Stratified Rocks O T A D P A Undivided phyllite in Alexander Terrane Asitka Group arc volcanics and platform carbonates; basement of Stikinia Crystalline Rocks Central Gneiss Complex undivided metamorphic rocks of variable protolith age Figure 2-6 (cont). Legend to geologic map. Map and legend modified from Wheeler and McFeely (1991). 29 the Monarch assemblage are mafic-intermediate and generally lithologically homogenous. Physical volcanology, sedimentology, and lithogeochemistry suggest arc-related, dominantly submarine deposition for both arc sequences. A localised exposure of very young (ca. 164 Ma), felsic, upper Hazelton Group volcanic strata in the east-central Bella Coola map area (e.g., Haggart et al., 2004) host the small, subeconomic Nifty V M S prospect (Fig. 2-6). Northeast of the continental divide (Fig. 2-6), Hazelton Group strata are cut and/or unconformably overlain by volcanic rocks of the Paleogene and Neogene Ootsa Lake and Chilcotin groups. Scattered exposures the Ootsa Lake Group include small, high level, mainly felsic dykes, plugs and domes and minor nonmarine lava flows and volcaniclastic rocks (Woodsworth, 1979). Several columnar jointed basaltic necks and at least one mantle xenolith-bearing basalt dyke cut Hazelton Group strata in the eastern Whitesail Lake area, and are thought to represent feeders to the Chilcotin Group plateau basalts. East-northeast of Bella Coola, exposures of the Hazelton Group are unconformably overlain by remnants of a moderately dissected Miocene peralkaline shield volcano which forms the Rainbow Range (Diakow et al., 2002, and references therein). The high, jagged massifs forming the continental divide and the western boundary of Tweedsmuir Provincial Park are underlain by laterally continuous, dominantly eastward-younging successions of the Hazelton Group (Fig. 2-6). Throughout the central Bella Coola and Whitesail Lake areas Hazelton Group strata area separated by an angular unconformity from volcanic and sedimentary rocks of the overlying Early Cretaceous (Valanginian-Albian) Monarch assemblage. This erosional surface is locally marked by a granite boulder conglomerate where the Cretaceous Monarch succession rests atop a suite of Late Jurassic granitic rocks (Haggart et al., 2004). The two volcanic belts are intruded by westerly-increasing volumes of Jurassic to Eocene plutons of the Coast Plutonic Complex. Gordee et al. (in prep.) subdivide intrusive bodies of the Bella Coola area into a series of plutonic suites on the basis of age, cross-cutting relationships, and lithologic, petrograpic, lithogeochemical and isotopic characteristics, and recent mapping in the north (e.g., Mahoney et al., 2005; Gordee et al., 2005) has demonstrated that the suite terminology can also be used to accurately classify intrusive bodies of the southern Whitesail Lake area. Intrusions in the western Whitesail Lake area are dominated by Late Paleozoic to Early Mesozoic bodies, including the Jurassic "Topley Intrusions" and the Central Gneiss Complex (Woodsworth, 1979; Woodsworth, 1980; Fig. 2-6). In contrast, the western Bella Coola area is dominated by Late Cretaceous to Paleocene intrusions with subordinate Middle Jurassic to Early Cretaceous suites (e.g., Gordee et al., in prep.; Fig. 2-6). 30 Jurassic plutonic suites in the Bella Coola and Whitesail Lake areas range from intermediate to felsic in composition and are probably analogous to the Topley and Black Lake intrusive suites (Woodsworth, 1979; Woodsworth et al., 1991). These suites are aerially restricted around the margins of the Bowser Basin, and in particular along the Skeena Arch (Fig. 2-1), where most are coincident with the thickest and most felsic piles of the Sinemurian Telkwa Formation of the Hazelton Group. Most of the Topley Intrusions are epizonal, calc-alkaline, massive to weakly foliated, granitic to quartz dioritic stocks and batholiths of Late Triassic to Middle Jurassic in age (Woodsworth et al., 1991). In the northwestern Whitesail Lake area they include pink granite, monzonite, and syenite (Woodsworth, 1979, and references therein). The Trapper pluton in the southern Whitesail Lake area (Fig. 2-6) is a large, medium to coarse grained, granitic body from which a U-Pb age of 170.5 ± 0.7 Ma has been obtained that is likely related to the Topley Intrusions, (J.K. Mortensen and J.B. Mahoney, unpublished data). In the southwestern Whitesail Lake area, a pluton that is spatially associated with extensive Upper Toarcian-Lower Bajocian felsic volcanic rocks of the Hazelton Group gives a ca. 181 Ma K - A r age (G.J. Woodsworth and P. van der Heyden, unpublished data; Woodsworth et al., 1991). A layered mafic intrusion in that same area is also associated with a volcano-sedimentary succession that has yielded Jurassic ammonoids (J.W. Haggart, personal communication, 2004), and, although undated, could therefore potentially represent the deep plutonic roots for local mafic lithofacies of the Hazelton Group. The Central Gneiss Complex (Fig. 2-6) consists mainly of banded amphibolite, gneisses, agmatite, plutonic rock, and minor schist, skarn and marble, which was, at least in part, derived by increasing migmatisation of the Gamsby Group, a probable Paleozoic volcano-sedimentary assemblage that is widespread throughout the west- and south-central Whitesail Lake map area (Woodsworth, 1979). Late Cretaceous to Paleocene intrusive suites in the Bella Coola area include lithologically and geochemically distinct tonalite, granodiorite, and granite. These suites overlap in age and display complex and locally ambiguous cross-cutting relationships. They include both subduction-related and crustally-derived components, and their emplacement is partly coincident with and is thought to be associated with the transpressional regime developed with dextral (?) movement along the Coast Mountain Shear Zone (Gordee et al., in prep.; Fig. 2-6). A n east-west-trending crustal extension event during emplacement the of Late Jurassic and earliest Cretaceous intrusive suites is inferred from swarms of north-trending, late-stage diabase, and granite dykes in the area. A younger contractional episode is recorded within a broad region mainly underlain by strata of the Monarch assemblage. This deformation produced 31 northeast-vergent, asymmetric, isoclinal to upright folds and local thrust faults (Mahoney et al, 2002). In contrast, Hazelton Group volcanogenic strata along the continental divide to the east are comparatively undeformed, and generally form bedded sections that are locally disrupted by high-angle faults (Diakow et al., 2003; Fig. 2-6). The age of the contractional deformation is not well constrained; however, it is believed to coincide with Late Cretaceous deformation in the eastern Waddington fold and thrust belt to the southeast (Rusmore and Woodsworth, 1994; Rusmore et al., 2000). A series of wide, northwest-trending, en echelon high strain zones marked by protomylonite and mylonite are developed in Lower Cretaceous volcanic and plutonic rocks in the western portion of the Bella Coola area. These zones overprint contractional structures in the area. Although the precise age of shear deformation is uncertain, the shear zones apparently pre-date major translation on the Coast Mountain Shear Zone (Fig. 2-6). Shearing is bracketed by U -Pb ages of ca. 123 Ma and 73 M a for pre- and syn-kinematic intrusions, respectively (Diakow et al., 2003). Mid-crustal rocks of the Atnarko Complex (Fig. 2-6) have been exhumed within southeastern Bella Coola map area, and are currently the focus of a separate structural and stratigraphic study by Israel and Kennedy (2002, and work in progress). 2-5 L O C A T I O N O F T H E STUDY A R E A AND G E O L O G I C M A P P I N G The N E Bella Coola/ SE Whitesail Lake map area (hereafter referred to as the study area) represents the northern continuation of a belt of Early and mostly Middle Jurassic upper Hazelton Group strata that is well-exposed throughout the eastern Bella Coola map sheet (Fig. 2-6). The study area includes the eastern half of the Tesla Mountain (093E/02) 1:50,000 map sheet between Mount Preston and Ramsey Peak, and the area roughly north and northeast of Jumble Mountain on the Kimsquit (093D/15) 1:50,000 map sheet (Fig. 2-7; see geological map insert). The area is accessible by helicopter from the town of Bella Coola, which lies approximately 80 km south of the southern extent of mapping (Fig. 2-6). Traverse coverage of the remote area was completed via fly camps and helicopter-assisted spot-checking of areas of extreme relief that are inaccessible by foot. Mapping focused specifically in the glacially sculpted subalpine regions above treeline where rock exposures are continuous and ideal for detailed examination of volcanostratigraphic sections. A total of approximately 13 weeks of mapping formed the basis for this study. As part of this study, a revision of the bedrock geology of the NTS 093E/02 Tesla Mountain 1:50 000-scale map sheet in the Whitesail Lake map area was completed. Figure 2-7 includes the segment of the map representing the study area and the geological map insert shows a draft of the entire map which is currently under review for publication as a Geological Survey 32 L E G E N D S Y M B O L S - STRATIFIED ROCKS • PLEISTOCENE TO RECENT Qg Geological contact (defined, approximate) Fault, normal (daHnad, appmxknan, assumed) FmA. normal. denrteti. approximate, assumed (down dropped on tide with Orbs) Fault, compresskmal. defined, approximate, assumed (teeth on upthrust aide) Park Boundary Stwar zona boundary . Light gray to yttow rhyoBOc OrOck-isplB tuft EARLY CRETACEOUS MONARCH ASSEMBLAGE VALANQINIAN TO ALB LAN >SOHvoa]evacroclax anwpltouad IKMv | tncda.**, and M f bmxla;kKatylnmn*laMwimma^baddadal Ught cokurrad, aphanarc to pi EARLY TO MIDDLE JURASSIC (Sinemurian to Bathonian) HAZELTON GROUP n Group undH*rantiatad(U/Ptoa. 191, 776,171 Ua) Anoclina (defined and approxmata) SyncUna (defined and approximate) UPC (Mkxana-PUooanm ChOcodn) wMM rttyotaa dyke) nvafin Fold axis AoWptam Fat* y x ^ AphsnMc to iocxsly pisorrxtsmr- and laaaar o u w t r t f ^ ± v * f c ± ( y ) ^ i a tK/ f t y o^a^ ,/ ^ t u # a ^ B, cooling joints and gas-escape w d u occur tocaMy; locally up to 50** C vobtfrMc btftccia, block hilt, po/yrnictk: volcanic jranute-cobfite cangkvnenria. antf mixfrftx>«, rt>o«» tev* Aowa. baaa* artfiwaa/fc *?dfl*rni /BVB SO-TI wtth local pth» ttructmx, plugs, oykm end alaa Tan, coarse-grained, poorty-aortad. n *wmmuh*otaltoKjbtoundadcvaru arxdetjierdraltobnaamenda^ sutroundQijsrtz-sndrdagkjckte t j — i II in i|aMia»>jpiij^  « « * V unnxwW QFPltrtruaion Dark green-grey, aphan/Oc to sttgtvty plegiociaee-porphyritkz basalt to t> ooffjp<M^Wy*)pa»tig/)i)!iaft|>aaw>tWiwt<ia.anrf»><nd<^ Bicf I 'oasir iooaNywtf i 'O/wmter Ar-Ar aga oatamMnaHon locality with ID numbv U-Pb aga determination tacaitty with ID number MIN FILE with ID number •® 7cy) 4 ft contains minor rtiyoUBc Mf brace! as. lapWt tuft, tut! and red mudstone sarioairaO and MUrdlkKt rrryoiam wsh rara quart* phanoorystx O r ^ J « W , oolirmnar jorms snd oerepaoe Orvccla occur iocatty INTRUSIVE ROCKS IMNFILE tsars MINFlCwC NAME STATIM eoaawerrv DB* C O M 1 ant m sees •bMM CU. AO D01UJ1 I ease art mem *™«, CU, AO 101.DIM 3 OWE OM HEME. JAW CU.AO L01.DTO 4 one on JMfT aMMM CU, AG LB1TXB s B M OTS IUNU CU.AO i n • :wi B m m WW' »Lli>U N M waxoi 7 one OM CU.AO DQ3 B 0*31 0*1 MOM* ; i «; L01JDO3 ( a a i BM WOW10 CU. AO AU 10 owe OM =OKD Itmuini CU LM.LD6 11 M OK TWOWARHU. cu UM 11 OWI; OH CH*l.COPYRfTT£ «*BM« CU.AO,?* 101.IDE 13 one OH TETRAHEDBfrC • il ||U AG. CL LDI.IDfi 1* OWE 0*1 DOLLYD cu LO1J0* -P>>|hrnrU>[UMF«H»| hombkMtoe-bkrrMto brk^ sham torm$ prarrwOmnt outcrops with distinct srctoHstion plans*. y M » abundant wKaa rttyoHts porphyry fins to aa— iflnwf. aajijaMMlM. inlrrtaaarf. asaaUeammm fmulwmlo )I)IIIII«IHIIJIH)(I il toc*#y-04£brofcailDnvrn*n^ ratrockf?) xwnoUths; krcsMy, spsttstty sssocistad wen and forms LATE JURASSIC TO CRETACEOUS Ught green to paik. ana- to LATE JURASSIC Wrrt« to light tan, vary trbcaout. oonvokstaiy tow-banded to masstvs, ± quarU- and ptagkxJasa-pnyric, variably bncdamitttyoaat tod • wV> EKqd MIDDLE JURASSIC M J g Pink. medum-Qraaxsd. aQUtgrarurlar to kx^y porphyritic tjrotlta-tiorribianom granttw stock: kxaily matte margins: may be subvolcankz to MJHrtt may be enalagous to Toptey itWvekme EARLY TO MIDDLE JURASSIC Trapper Peak phnon (ea. 177 Ma} EMJTP I wwrpanisar. asttnet IrgH tookaatkttxa^aasmavratiadto GEOCHRONOLOGY MAP * FltLD | AGE (Ma) | MMERAL METHOD 1 .",:,:>.'.C.l).! 51.871 0 a •Ma Ar-Ar 2 03M-? 136.* « 1 S Hombtond* AWkr S •:;'SMG33 175.4 tO.B Zrnxm U-Pb 4 29SMQ03 1 ma 131 U-Pb 5 IB4JBMW 175.0 tO.B L.-Pb BA WJ6M04 172.7 ±0.8 ircofi (D2! u-Pb BB 24JBM04 174.4 an ZJroon (DZ) u-Pb 6C 24JBM04 175 4 11.8 ZlR»n(DZ) U-Pb 7 1078MO03 176.7*0.8 Zircon U-Pb 8 HFBM02-1406-1 17B.S1D6 Zjicon u-Pb 9 136JBM04 122 9 1 0B Zlraen L.-PTJ MMERAL abb eeaatanm DZ • devm 2*000 Figure 2-7 (cont). Geologic map and explanation to geologic map of the N E Bella Coola/SE Whitesail Lake study area. Map represents approximately the eastern half of the Tesla Mountain (093E/02) 1:50 000-scale Geological Survey of Canada Open File geology map. See geological map insert for the full map sheet and for any units or other features from this legend that are not shown on this map. of Canada Open File map. Hereafter, unless otherwise specified, references in the text to Figure 2-7 include both the figure itself and the geological map insert. 2-6 VOLCANOSTRATIGRAPHY Detailed geologic mapping of volcanogenic lithofacies and lithofacies associations of Hazelton Group strata within the study area has aided in the subdivision of two members, a lower mafic member (emJHv) that is gradationally overlain by an upper felsic member (mJHr; Fig. 2-7). Lithofacies of the lower mafic member have been identified, but are not subdivided on the geologic map of the study area, due to difficulties in representing the extremely laterally and vertically discontinuous lithofacies at a l:50,000-scale (Fig. 2-7). Unless otherwise indicated, lithofacies of the upper felsic member are also undivided. Units in the upper felsic member that are shown on the map are distinct enough to warrant the subdivision and/or are large enough (in plan view) to be mappable at a l:50,000-scale. Figure 2.8 is a schematic stratigraphic section illustrating the lithofacies and lithofacies associations of units within the lower mafic member and the upper felsic member in the study area. 2-6-1 Principal lithofacies of the lower mafic member (emJHv) Rocks of the lower mafic member underlie Tsaydaychuz Peak and Tesla Mountain in the southwestern portion of the study area, where volcanogenic strata broadly strike north-south and dip gently to moderately to the east (Fig 2-7). The extremely rugged Tsaydaychuz Peak was not traversed, but the strata underlying the peak are interpreted to represent the same stratigraphic interval as the strata underlying Butler Peak. Rocks of the lower mafic member overlie mafic to intermediate, dominantly fragmental Hazelton Group successions west of South Creek (Fig. 2-7). East-dipping stratigraphic successions in that area are cut by granitic intrusions, but are otherwise undisrupted, and are probably stratigraphically continuous with rocks of the lower mafic member. South of Tsaydaychuz Peak (Fig. 2-7), mafic lithofacies of the lower mafic member pass into a broad belt of aphyric and very fine to medium grained diorite ("microdiorite") that has been mapped in the northern Bella Coola region (Haggart et al., 2004). Rocks of the lower mafic member are truncated to the north by a post-depositional high-angle fault underlying Tesla Lake, and the eastern contact is gradational into rocks of the upper felsic member west and south of the Chezko River (Fig. 2-7). A minimum thickness of 7 km is indicated based on structural cross sections through the lower mafic member. 3 5 Hazelton Group Stratigraphy of the NE Bella Coola/SE Whitesail Lake Study Area t Ul 4) Oi Kimme-ridgian D. Oxfordian Callovian u Bathonian JURASSI Bajocian JURASSI Aalenian Toarcian Ul <u Ss Pleins-bachian o i—1 Sinemurian angian e X .1 u Rhaei RIASSI Upper Norian Camian 3 & O . 3 s a c o V V v vs^>yi v v v v v v v v v v v i kilometres Ashman Formation? (L Bathonian-E Callovian and younger?) a i-i o' 3 3 i-t o CD i-t 3 »? o 3 CD 3 cr ss N W o o o older Hazelton Group strata west of South Creek Figure 2-8. Idealized stratigraphic column of Hazelton Group stratigraphy in the N E Bella Coola/SE Whitesail Lake study area in southwest Stikinia. Note that the base of the lower mafic member and the top of the upper felsic member are not exposed within the study area, and therefore the thicknesses represented by the members represents the minimum thickness of the stratigraphic sequence along this transect. Ages of the Ashman Formation and older Hazelton Group strata are estimated from local fossil collections/identifications made by H.W. Tipper/H. Frebold and ages reported in Haggart etal. (2004), respectively. 36 The lower mafic member appears to be crudely thickly bedded from a distance (Fig. 2-9a), but no bedding is observable at an outcrop scale. Rocks of the lower mafic member are characteristically dark grey-green and include several distinct, compositionally similar, mafic, primary volcanic and reworked volcanogenic lithofacies. Primary lithofacies include mafic coherent and fragmental lava flows, domes/cryptodomes, and high level intrusions. Lithofacies that represent reworked primary volcanic material include volcanogenic breccia and conglomerate, as well as sandstone, siltstone and mudstone sequences. 2-6-1-1 Mafic lava flows, domes/cryptodomes, and high level intrusions (undivided emJHv) Mafic lava flows, domes, and high level intrusions together comprise nearly 90% of rock exposures in the Butler Peak region. The prevalence of these lithofacies at this stratigraphic level collectively defines the lower mafic member (Fig. 2-7). There is very little compositional and textural variability between individual units of these lithofacies; this, as well as a general lack of structures indicative of an intrusive or extrusive origin, makes discerning between them nearly impossible. A l l lava flows, domes, and most high level intrusions of the lower mafic member are aphyric to finely plagioclase- and less commonly pyroxene-phyric, variably flow-banded and vesicular basalt to andesite. Vesicles range from 0.1 to 2 cm, and are either evenly distributed or are arranged in layers parallel to the contact margins of the unit. Vesicles are spherical, elongate, or irregularly-shaped, and are infilled by carbonate, chlorite, quartz, and/or epidote. Both mafic lava flows and domes have been intensely hydrothermally altered as evidenced by pervasive epidotisation and chloritisation of mafic minerals and extensive epidote and quartz veining. Large, amorphous clots of epidosite and jasper also occur locally (Fig. 2-9b). Mafic intrusions of the lower mafic member most commonly occur as domes and irregular-shaped masses, but also occur as dome/cryptodome complexes with associated dykes and sills that locally thicken and deform well bedded strata. Along the ridge north of Butler Peak and in the Tesla Mountain region, what are assumed to be mafic cryptodomes deform felsic volcanogenic strata along or just stratigraphically above the gradational contact between the lower mafic and upper felsic members, which explains the inconsistent and irregular bedding orientations found in those areas (Fig. 2-7). Mafic intrusions display ambiguous intrusive contacts, which are characterized by subtle, anastomozing chill margins occurring between units of only slightly differing colour, composition, and texture. These contacts range from sharp and planar with localised flow-banding to highly irregular and diffuse. In one locality south of Butler 37 Figure 2-9. a) Typical outcrop expression of lithofacies within the lower mafic member. Peak in center of panorama is Butler Peak, as viewed from the west. Field of view from north to south (left to right) is approximately 4.5 km; b) Epidosite clots within subvolcanic intrusion of the lower mafic member. Hammer is 35 cm; c) Columnar jointed valley fill lava flow within the lower mafic member. Hourglass shape displayed by the joints is probably due to overflowing of the valley walls. Geologist is <2 m tall; d) Pillow structures within purple, finely plagioclase-phyric mafic lava flows of the lower mafic member. Field of view from left to right is approximately 5 m; e) Green, monolithic, mafic basal autobreccia of a lava flow within the lower mafic member. 3 8 Figure 2-9 (cont). f) Monolithic, mafic hyaloclastite autobreccia within the lower mafic member. Breccia is comprised of entirely cuspate, fluidally-shaped clasts; g) Well bedded, parallel laminated tuffaceous mudstone sequence within the lower mafic member. Rusty color is the result of stratiform pyrite within the sequence. These strata are locally deformed around mafic cryptodomes north of Butler Peak. Cliff is 8 m high. 39 Peak, an intrusion breccia separates compositionally and texturally identical aphyric mafic intrusions of this lithofacies. A less common but texturally distinct group of high level intrusions are made up of crowded plagioclase-phyric andesite. Plagioclase is boxy and "bladed", white, euhedral, and up to 6mm in length, and the intrusions are non-vesicular. The intrusions display very sharp and anastomozing intrusive contacts which are evenly porphyritic throughout. Andesite porphyry intrusions post-date aphyric mafic flows and other intrusions of the lower mafic member. Mafic lava flows in the sequence are difficult to distinguish from mafic intrusions. Rare exposures comprising columnar jointed or pillowed lava flows, and units containing sublithofacies such as hyaloclastite are the only definitively extrusive units. Columnar jointing was observed in one locality west of Butler Peak, where the presence of a channel-fill lava flow is inferred by the presence of well-developed cooling joints radiating inward from a paleo-channel (Fig. 2-9c). Several exposures comprising pillowed mafic lava flows and broken pillow breccia were observed low in the stratigraphic section, west of Butler Peak (Fig. 2-7). Pillows are spherical to elliptical, range from <10 cm to 4 metres in diameter; the exposures probably represent oblique cross sections through the flows (Fig. 2-9d; cf. Cas and Wright, 1987, Figure 4.13). Individual pillows commonly possess up to 1 cm chill margins. Matrix material includes purple to maroon, spheroidally-weathering, weakly calcareous mudstone with angular broken pillow fragments (e.g., Photo 1, Gordee et al., 2005, Appendix F). Mafic lava flows are mainly coherent, but rare autoclastic sub-lithofacies such as carapace and floor autobreccia and hyaloclastite occur locally as gradational lateral lithofacies equivalents or as irregular pockets within coherent portions of flows. A general lack of marginal or intercalated lithofacies within and between flows makes the morphology, lateral extent and aspect ratio of lava flows difficult to discern. Rare carapace and floor breccias are medium- to very coarse-grained, poorly-sorted, clast-supported, and monomictic, with locally abundant calcite veining and cement (Fig. 2-9e). They are compositionally and texturally identical to the flows from which they were derived. Vesicle grading is locally present within clasts, where larger, more abundant vesicles in the center of clasts grade to smaller, less abundant vesicles along clast margins. Hyaloclastite occurs as isolated lenses of material within or at the margins of homogeneous and coherent mafic lava flows. Hyaloclastite contains variably equant and blocky to cuneiform clasts, which commonly possess curviplanar margins and display a jigsaw-fit texture. This texture is inferred to reflect in situ quench fragmentation of the lava. Matrix material consists of splinters of lava. Although the transition from hyaloclastite to coherent lava is gradational, local structures within coherent units, such as vesicles and flow-banding, do not 40 penetrate the gradational contact. Several exposures of hyaloclastite south of Butler Peak are entirely made up of fluidally-shaped clasts (Fig. 2-9f). 2-6-1-2 Mafic volcanic-derived epiclastic rocks (undivided emJHv) Lava flows and intrusions of this member are intercalated with volumetrically minor mafic volcanic breccia/conglomerate, as well as sandstone, siltstone, and mudstone sequences, which together represent 15% or less of observed outcrop within the lower mafic member. Volcanogenic breccia and conglomerate of this lithofacies are present as laterally discontinuous lenses intercalated with massive mafic lava flows. Breccia is dark green-grey in colour and comprises massive, clast supported, and poorly sorted, with monomictic, angular to subangular, block- to lapilli-sized clasts of mafic volcanic rock. Matrix material consists of fine-grained mafic volcanic and plagioclase fragments. Isolated exposures of crudely stratified, normally graded breccia with moderately well-sorted, angular to subrounded clasts may represent resedimented autobreccia or hyaloclastite. The distinction between volcanogenic breccia and conglomerate in this lithofacies is simply a difference in clast morphology - matrix material is identical in both. Conglomerate units are similarly monomictic, and clasts are subangular to subround, cobble- to pebble-sized. Intercalated sandstone, siltstone, and mudstone occur as laterally discontinuous sequences within this lithofacies. Sandstone ranges from fine to coarse grained lithic arkose to feldspathic lithic wacke, and locally contains granules and pebbles and grades into matrix-supported granule to pebble conglomerate. Sandstone, siltstone, and mudstone consist of varying proportions of angular to subangular particles of chloritised mafic rock and broken plagioclase. In mudstone units, sparse particles are set in a dark grey to green mudstone matrix. Sandstone and siltstone units are thin to medium bedded and moderately well sorted, and conglomerate and locally granule- and pebble-rich mudstone units are poorly sorted. Beds are either massive or parallel laminated, ungraded to crudely normally graded. No cross bedding or other paleocurrent direction indicators were observed. Mudstone beds always gradationally overlie a fining upward sequence of sandstone-siltstone, and are commonly scoured by overlying sandstone beds. A n approximately 10 m thick sequence of grey and rusty, parallel laminated, internally massive to locally normally graded, pyritic tuffaceous mudstone and siltstone unit is restricted to the west Tesla Mountain area (Figs. 2-7 and 2-9g; e.g., Photo 2, Gordee et al., 2005, Appendix F). 41 2-6-2 Principal lithofacies of the upper felsic member (mJHr) Rocks of the upper felsic member are exposed between Rivers Peak and Mount Preston in the structural block north of Tesla Lake, on the eastern flanks of Tesla Mountain, and in the southernmost portion of the study area roughly between Jumble Mountain and western Oppy Lake (Fig. 2-6). Volcanic and sedimentary strata of this member strike north-south between Rivers Peak and Mount Preston (Fig. 2-7). In that region the sequence is block-faulted and has been tilted to the west, a reversed orientation from the overall regional trend. The northern fault of this rotated block has not been mapped, but probably lies beneath Eutsuk Lake to the north of Mount Preston. A north-south-trending fault is inferred to exist between this portion of the study area and similar, subvertical, east-dipping strata underlying Mount Pondosy to the west (see insert map). Woodsworth (1980) mapped east-dipping strata underlying Wahla Mountain and Two Bear Hi l l that are also probably part of the upper felsic member; therefore one or more subvertical structures are inferred to exist in the linear drainages east of Rivers Peak to account for this discordance (Fig. 2-7). A fault beneath Tesla Lake separates strata of the upper felsic member in the north from east-dipping strata in the south, where the gradational contact between strata of this member and the underlying lower mafic member is well documented on the east flanks of Tesla Mountain and east of Butler Peak (Fig. 2-7). The contact is also observed south of the Chezco River, and is characterized by mafic lava flows and subvolcanic intrusions intercalated with, and subsequently overlain by tuff and lapilli tuff, mass flow deposits, and shallow marine fossiliferous sandstone and siltstone representing the oldest strata of the upper felsic member. The precise stratigraphic boundary between the two members is taken at the first occurrence of felsic rocks of the upper member. South of Tesla Lake, the stratigraphic sequence continues, apparently uninterrupted, to the east beyond the eastern edge of Oppy Lake (Woodsworth, 1980; Fig. 2-6). The true stratigraphic thickness of the upper felsic member between the lower contact south of Ramsey Peak and Oppy Lake is at least 5 km. The upper felsic member is distinctly well-bedded (e.g., Fig. 4b, Mortensen et al., 2004, Appendix F) and characteristically maroon and purple in colour. Rocks in this member consist of a texturally heterogeneous but compositionally similar assemblage of very coarse to fine grained, primary volcanic, felsic lithofacies intercalated with subequal amounts of coarse to fine grained, heterolithic, epiclastic lithofacies. Primary volcanic lithofacies include felsic pyroclastic fall, flow, and possibly surge deposits, felsic lava flows and domes, and subordinate mafic lava flows, domes, and dyke/sill complexes. Lithofacies that represent reworked volcanic material include heterolithic volcanic breccia and conglomerate and sandstone, siltstone, and mudstone sequences. 42 2-6-2-1 Felsic to intermediate pyroclastic lithofacies (undivided mJHr) In total, rocks of pyroclastic origin account for approximately one-third of stratified rocks in the upper felsic member, and rocks representing fall and surge deposits together account for <30% of that. In general, pyroclastic rocks of the upper felsic member include massive, unstructured, rhyolitic to dacitic lapilli tuff and subordinate tuff, with local laterally discontinuous tuff breccia and breccia units. Lithofacies representing pyroclastic fall deposits in the study area dominantly consist of thin, unstructured, laterally continuous veneers of siliceous tuff (ash-fall deposits) intercalated with other felsic volcaniclastic units. Tuff layers are typically <10 cm thick, and are not spatially or temporally associated with any intervening pyroclastic flow-related units. Rare, thinly bedded, parallel laminated, normally graded, or internally massive lapillistone units are restricted to the northern portion of the study area. Several sequences display asymmetric and locally chaotic bomb sag structures that are the result of lapilli and block ballistics falling into maroon, massive to thinly laminated volcanogenic mudstone units (Figs. 2-10a and 2-10b). Bombs are subround, vesicular, intermediate in composition, and always immediately precede or supersede compositionally similar crystal-lithic tuff to lapilli tuff units. Several accretionary lapilli tuff horizons are present within strata of the upper felsic member. Accretionary lapilli are cored with ash and are always armoured with 1-3 mm of unstructured ash, which aids in their preservation when they are reworked. Primary accretionary lapilli deposits are characterized by <10 cm thick, display crudely planar stratified, ungraded to distinctly normally graded, monolithic lapillistone units that are always succeeded by lithic-crystal tuff and lapilli tuff units (e.g., Photo 4, Gordee et al., 2005, Appendix F). The stratified nature of unsorted armoured accretionary lapilli horizons, together with the close spatial and temporal association with overlying tuffaceous units, suggests that they in part may represent base-surge deposits (e.g., Cas and Wright, 1987). None of the sedimentary bedforms that Cas and Wright (1987) define as characteristic distinguishing features of surge deposits, including low angle cross-stratification, dune- and climbing-dune-forms, and pinch and swell structures, and shoot and pool structures, have been observed within the pyroclastic rocks in the study area, but the existence of such accretionary lapilli horizons is suggestive of this type of deposit. Ignimbrite units are the most volumetrically abundant lithotype in the upper felsic member, together comprising approximately one-third to one-half of all rock exposures in the 43 Figure 2-10. a) Asymmetric ballistic lapilli sag structures within tuffaceous mudstone of the upper felsic member. Pencil is 8 cm; b) Chaotic ballistic block sag structure within pebbly mudstone of the upper felsic member. Chaotically distributed white fragments are silicified pumice and lithic fragments from underlying felsic lapilli tuff; c) View to S across prominent rhyolite dome knob. Peak in right, center (foreground) is Rivers Peak, which is a dip-slope to the west; d) Pink, monolithic, rhyolitic carapace breccia of extrusive flow dome cutting volcanic strata of the upper felsic member. Hammer is 40 cm; e) Very coarse grained, heterolithic, felsic pumice breccia within the upper felsic member. Largest clasts are green and pink, variably chloritized, flow banded, and flattened pumice clasts with wispy margins. Scale is 10 cm; f) Typical maroon and purple, parallel laminated mudstone sequences of the upper felsic member. 4 4 member. These units range from moderately to highly silicified, and tend to form erosion resistant rock exposures. Ignimbrite units can be subdivided into two principal types based upon characteristic unit morphologies, classification based on proportions of pyroclasts, and welding characteristics. Type one units are characterized by relatively thin, poorly welded, lithic-rich and vitric-poor rhyolite to dacite units. Type two ignimbrite units are characterized by thick, very densely welded, lithic-poor and vitric-rich rhyolite units. Type one units are the most commonly occurring type of ignimbrite, and include pink to purple, massive, locally crudely parallel laminated, poorly to moderately well welded, rhyolitic to dacitic vitric-crystal- to crystal-vitric-lithic lapilli tuff. Locally lithic-rich units grade into lapillistone. Type one units are typically <1 to 10 metres thick, but are locally up to 30 metres thick. Crude columnar jointing is rare (e.g., Fig. 4c, Mortensen et al., 2004, Appendix F). Pumice fragments are either white to maroon to brown in colour, non-flattened to moderately flattened, and silicified, or flattened (approximately 5:1 flattening ratio) and chloritised, resulting in deep green coloured, wispy fiamme that rarely exceed 2 cm in length. Crystals include plagioclase and less commonly quartz. Plagioclase is clear and colourless to white and sericitised, euhedral and boxy or broken, and is <3 mm. Quartz (when present) is clear and colourless, vitreous, anhedral, and typically <1 mm. Lapilli-sized lithics rarely exceed 2 cm in diametre, are subangular to subround, multicoloured (pink, grey, green, or maroon), angular to subround, finely to coarsely plagioclase-phyric, and are intermediate to felsic in composition. One ridge-capping unit southeast of Mount Preston contained syenitic accidentals. Matrix material consists of indurated ash with minor amounts of plagioclase and quartz crystals. Several lithic- and crystal-rich sandstone units within the upper felsic member are probably derived from this type of ignimbrite unit. In the Mount Preston area, several ignimbrite units of this type display abundant silicified lithophysae that result in a weathered appearance of close-packed billiard balls. One unit south of Ramsey Peak contains silicified gas segregation pipes up to 2 metres in length, and other similar units in the Ramsey Peak area contain siliceous nodules! The second type of ignimbrite in the upper felsic member comprises distinctive purple-and white-striped, massive, very densely welded, rhyolitic lithic-crystal-vitric tuff to lapilli tuff (e.g., Photo 3, Gordee et al., 2005, Appendix F). Three of these units - one capping the stratigraphic sequence west-southwest of Mount Preston and two underlying the Ramsey Peak massif - have been mapped within the study area. The unit in the Mount Preston area is lithologically indistinguishable from the units underlying Ramsey Peak. Type 2 ignimbrite units are quite lithologically distinct compared to other rocks in the upper felsic member in several 45 ways: 1) they are the most felsic rocks in the study area in terms of mineralogy and chemistry (see discussion below); 2) they display distinct welding horizons, including a very densely welded "high grade" interior; and 3) they are very thick - each unit is in excess of 100 metres thick, and one unit exceeds 300 metres in thickness. Lithics and crystals are the same morphology and composition as type one ignimbrite units, with slightly more quartz as a modal phase. Pumice/fiamme is more abundant in ignimbrite units of this type, as well as much larger in size. The lenticular fragments are white, pink and blue in colour, display a flattening ratio ranging from approximately 5:1 to greater than 25:1, and decrease significantly in abundance near the top of the units. Welding horizons are characterized by a non-welded to moderately welded, distinctly parallel laminated base, which passes into a very densely welded interior, which then grades into a poorly welded to non-welded horizon at the top of the unit. The very densely welded interior of these units displays complex flow foliations and flow folds, and probably indicate that the units retained sufficient heat to undergo non-particulate flowage (rheomorphism) during and after deposition (cf. Plate 26.3, McPhie et al., 1993). These flow features closely resemble those in coherent lavas and in some cases obscures primary evidence for a pyroclastic origin. The rapidly cooled, less welded bases of such ignimbrites are most likely to record their pyroclastic character (McPhie et al., 1993). The thickest unit is reversely graded at the base, and all units are normally graded at the top. A third, volumetrically subordinate type of ignimbrite consists of maroon, thin bedded, densely welded, distinctly quartz-eye-phyric rhyolitic lithic-crystal-vitric tuff to lapilli tuff. Pumice fragments are completely flattened to fiamme and wispy. The fragments are wholly altered to chlorite, resulting in a dark green colour. These units are always intercalated with maroon mudstone sequences. 2-6-2-2 Felsic lava flows (undivided mJHr) Felsic lava flows are rare within the upper felsic member, and are spatially restricted to the Ramsey Peak area within the study area. They are highly silicified and resistant to weathering and form cream coloured, steep, prominent, laterally discontinuous but stratabound cliffs up to 15 metres thick in the stratigraphic section underlying Ramsey Peak. Flows consist of aphyric to finely plagioclase-phyric rhyolite and dacite; all flows have complexly flow banded interiors, and some display autobrecciated margins. 46 2-6-2-3 Felsic domes (mJHrd) Felsic domes are spatially restricted to the northernmost portion of the study area, south of Mount Preston (Fig. 2-7). Domes are roughly circular in plan view and occur as individual or coalesced bodies up to 50 metres wide that crop out in a roughly linear, east/west-trending flow-dome complex along the trace of a low-angle extensional fault south of Mount Preston (e.g., Photo 6, Gordee et al., 2005, Appendix F). This fault is characterized by zones of intense fracturing with abundant slip surfaces and well developed ferricrete overlying fault breccia. Impressive gossans in this area are characterized by finely disseminated pyrite and small bodies of chalcopyrite ± bornite-bearing vein breccia along the trace of this fault; however, the domes themselves are unmineralised, and their emplacement may post date the mineralisation. Felsic domes are aphyric to sparsely plagioclase- and lesser quartz-phyric, massive, and variably vesicular rhyolite and dacite. The domes are highly silicified and fractured, and form prominent pink-coloured knobs that visibly crosscut stratified rocks in the study area (Fig. 2-10c). Zones of carapace breccia up to several metres thick locally occur along the margins of the domes (Fig. 2-10d). These breccia zones indicate that the domes were probably in part extrusive. Differential nodular devitrification commonly produces a breccia-like or fragmental-looking texture within the coherent interior of these domes. The coalescence of these devitrified nodules along individual flow-bands, combined with overprinting silicification produces boudin-like structures (e.g., Plate 4.2, McPhie et al., 1993). Spherical to elliptical vesicles are commonly filled with chlorite or a combination of quartz and epidote, and are arranged in trains parallel to the dome margins. Plagioclase is occurring sericite-altered, silicified, white, euhedral grains that are 1-2 mm in length. Cryptic, anhedral, 1-3 mm spots may represent ghost quartz phenocrysts, but the mineral has been completely overprinted by later silicification. 2-6-2-4 Felsic volcanic-derived epiclastic rocks (undivided mJHr) Epiclastic rocks are intimately associated with felsic pyroclastic rocks in the upper felsic member; nearly every ignimbrite unit is stratigraphically preceded and succeeded by intervening epiclastic lithofacies. Epiclastic rocks in the upper felsic member include volcanogenic breccia, conglomerate, sandstone, siltstone, and mudstone; all of these lithofacies represent reworked volcanic material. Volcanic breccia units are common within the upper felsic member. These units consist of heterogeneous, laterally discontinuous, massive, unstructured, medium to very coarse grained, heterolithic, clast- and matrix-supported volcanic breccia. These epiclastic units are distinguished from lithologically similar primary volcanic units based upon a lack of the characteristic features 47 indicative of a hot state of emplacement (i.e. columnar jointing, gas segregation pipes, or welding textures) as defined by Cas and Wright (1991). Clasts are grey, green, maroon, and purple in colour, angular to subround, aphyric to less commonly plagioclase-phyric, and felsic to intermediate in composition. Mafic clasts are rare within breccia units. Some clasts within these units possess up to 3 mm siliceous, alteration rinds that may indicate hot deposition; however, such features can be preserved during reworking and are unreliable indications of hot emplacement in the absence of the aforementioned features. One approximately 10 metre thick, laterally discontinuous unit underlying Ramsey Peak consists of heterolithic volcanic breccia with pumice blocks up to 30 cm in length (Fig. 2-10e). The unit is clast-supported with subequal quantities of lapilli-sized felsic clasts and lapilli- and block-sized pumice fragments. Felsic clasts include white to pink, angular to subround, aphyric rhyolite with up to 2 mm alteration rinds. Pumice is dark green to light pink in colour, aphyric to plagioclase-phyric, and ungraded throughout the unit. The dark green colour is due to intense chloritisation of the pumice fragments. Pumice is variably flattened (1:1 to 5:1 flattening ratio); however, they are not parallel aligned. Eutaxitic textures are absent and the unit is internally massive. Wispy margins of numerous pumice fragments may reflect diagenetic processes. Matrix material is the fine grained equivalent of pumice and felsic clasts, and is pervasively chloritised. At least one heterolithic, matrix-supported volcanic breccia unit underlying Ramsey Peak is sparsely fossiliferous, containing large, robust and thick-shelled, articulated coquina and fossil fragments. The unit is typically internally massive, but thick, parallel laminations and high-angle, planar, cross-stratification occurs locally. Several volcanic conglomerate units exist throughout the upper felsic member. These units are always intercalated with finer-grained epiclastic successions and are not interpreted to reflect significant intraformational hiatuses. The units comprise thick to massively bedded, internally massive to locally normally graded, poorly sorted, matrix supported, granule to cobble conglomerate. Clasts are maroon, purple, green, and grey in colour, subangular to round, aphyric to plagioclase phyric, felsic to intermediate volcanic rock and subordinate maroon mudstone and pebbly mudstone. Salt-and-pepper textured medium-grained diorite clasts are rare. Matrix material consists of maroon mudstone. South of Ramsey Peak, several conglomerate units are normally graded, forming conglomerate-sandstone-mudstone triplets. Sparse sedimentary structures in these sequences include crude parallel laminations. 48 Relatively finer grained epiclastic rocks in the upper felsic member include, in order of increasing abundance, volcanogenic sandstone, siltstone, and mudstone. These lithofacies are intimately intercalated and occur in characteristically distinctly bedded maroon units. Sandstone units are quite rare and include white to grey, thin to medium bedded, medium grained, internally massive to locally normally graded, well sorted lithic feldspathic and feldspathic lithic arenite. These sandstone units are particularly crystal rich, containing abundant white, angular to subround plagioclase, and clear, colourless, vitreous, rounded quartz. Lithic fragments are dark green, grey, purple, and maroon, aphyric, and are rhyolitic to basaltic in composition. Sandstone units locally normally grade into lithologically similar siltstone. Mudstone units are the most abundant type of epiclastic rock in the upper felsic member. Mudstone beds are commonly intercalated with thin bedded lithic- and crystal-rich tuff and lapilli tuff units. Mudstone units are maroon, purple, and red, thinly to medium bedded, massive to locally thinly parallel and wavy laminated, well to locally poorly sorted tuffaceous mudstone and granule to pebbly mudstone (Fig. 2-10f). Granule and pebble fragments consist of white, broken, angular to round plagioclase and lesser pink, purple, green, and grey, subangular to subround, aphyric to plagioclase-phyric, felsic to intermediate volcanic rock fragments. Matrix material is maroon clay, and unstructured mudstone units may in part represent pyroclastic ash-fall deposits. The rare presence of articulated armoured accretionary lapilli within several mudstone units is evidence to support the possibility of at least some of these units representing pyroclastic fall deposits. However, the accretionary lapilli are randomly dispersed, and are in part broken/inarticulated, suggesting a small amount of reworking. Mudcracks were observed in one mudstone unit south of Mount Preston, and a fossil leaf was collected from a mudstone unit further up section in the same area. 2-6-2-5 Felsic plutonic-derived sandstone (mJHs) One very spatially localised sandstone unit is unlike any other sedimentary rock in the study area. The unit is approximately 10 metres thick and is discontinuously exposed in a topographic bowl immediately adjacent to an east-west trending normal(?) fault over an approximately 500x200 metre area northwest of Rivers Peak. The unit is light grey in colour and consists of massive, unstructured, poorly to moderately well sorted, coarse grained, crystal-rich, lithic-feldspathic sandstone (e.g., Photo 5, Gordee et al, 2005, Appendix F). Crystal fragments include clear, colourless, euhedral to subhedral and subround, 1-4 mm quartz, and white, euhedral and broken to subround, 1-5 mm plagioclase laths. Scattered granule- and pebble-sized clasts are locally sufficiently abundant to classify the unit as a matrix-supported granule to pebble 49 conglomerate. They include light green, angular to subround, aphyric andesite, and light pink, quartz- and plagioclase-porphyritic (QFP) rhyolite. The clasts are only present at the base of the unit and define very crude normal grading within the sandstone sequence. The sandstone apparently represents a very proximal epiclastic derivative of the QFP rhyolite clasts contained within the unit; however, the morphology and abundance of the crystals contained within clasts are entirely unlike any other Hazelton Group volcanic units within the study area. The source of the unit is interpreted to be a locally unroofed, shallow level QFP intrusion. 2-6-2-6 Calcareous epiclastic rocks and limestone (undivided mJHr) Calcareous epiclastic rocks are rare within the study area. One succession is exposed south of Ramsey Peak near the contact with the lower mafic member, where limey sandstones and siltstones are intercalated with felsic tuffaceous units, coarse volcanogenic breccia, and minor mafic flows. Two similar, thinner successions are exposed southwest of Rivers Peak near the top of the stratigraphic sequence in that area, where they are intercalated with maroon tuffaceous mudstones and felsic crystal and lapilli tuffs. The calcareous epiclastic sequences south of Ramsey Peak are not stratigraphically correlative with those in the Rivers Peak area. In general, these units consist of thin to medium bedded, massive to locally thinly parallel, wavy and cross laminated, well to moderately well sorted, subangular to round, limey lithic-feldspathic arenite and subordinate limey feldspathic litharenite sandstone and siltstone. Sandstone and siltstone beds are commonly normally graded; coarse to medium grained, parallel and cross laminated sandstone grades into fine grained, internally massive to crudely thinly parallel laminated sandstone and siltstone. The coarse grained bases of these sequences locally comprise poorly sorted granule to pebble conglomerate, which commonly scour into the siltstone tops of preceding sandstone-siltstone couplets. Siltstone beds commonly contain sandstone lenses 1-3 cm in thicknesses and up to 20 cm in length. Limey sandstone and siltstone units are commonly fossiliferous, containing an assemblage of gastropod, bivalve, and mollusk coquinas. Belemnoids and ammonoids are rare. A l l fossils are robust and thick-shelled, range from broken to articulated, and are present as unfilled or carbonate infilled molds in laterally continuous, locally normally graded coquina beds. Most bivalve fragments are oriented subparallel to bedding. Locally abundant weathered, hollow or carbonate infilled pits commonly oriented oblique to bedding may represent fossil molds or solution pits developed along incipient fractures (J.W. Haggart, personal communication, 2005). One unit is characterized by coarse grained sandstone and granule conglomerate with abundant, irregular-shaped, carbonate infilled pits that in part consist of fossil molds. Large, 50 robust, high-spired gastropods have been collected from this unit, which is interpreted to represent a shallow marine lag deposit (e.g., Fig. 3c, Mortensen et al., 2004, Appendix F). The only true limestone lithofacies in the study area is exposed in a saddle northeast of Rivers Peak, where it is immediately stratigraphically overlain by the quartz-feldspar sandstone unit (mJHs). The limestone unit is very spatially localised, less than three metres thick, and comprises blue-grey- and tan-striped in colour, scalloped, very thinly to thinly bedded, parallel and wavy laminated interbedded limestone and sandy limestone. The unit does not contain macro or microfossils. 2-6-2-7 Mafic domes and dyke/sill complexes (mJHb) Mafic domes and dyke/sill complexes are uncommon within the upper felsic member. They are restricted to the Rivers Peak and Mount Preston areas, where they are in spatial proximity to undivided mafic lava flows that are intercalated with thick sequences of felsic volcanogenic strata of the member (undivided mJHr; see discussion below). Most mafic domes cutting the upper felsic member are lithologically indistinguishable from those cutting strata of the lower mafic member, comprising dark green-grey, coherent, variably amygdaloidal basalt and basaltic andesite. These plugs are roughly circular in plan view and are typically less than 100 m 2 (several are too small to be represented at the 1:50 000-scale of mapping). One plug dome comprising the northwestern wall of a cirque southeast of Mount Preston forms a prominent knob - roughly triangular in cross section - that probably represents the erosional remnants of a volcanic conduit (e.g., Fig. 5b, Mortensen et al., 2004, Appendix F). The plug dome is dark grey-brown, flow banded, finely plagioclase-phyric basalt. Numerous lithologically similar dykes and sills originating from this plug dome cut the surrounding strata, and at least one displays peperitic margins where it is in contact with a sequence of red mudstones. Peperite, or intrusive hyaloclastite, indicates that emplacement of the plug dome was coeval with deposition of the Hazelton Group strata. At least one mafic dome cuts an east-west trending normal(?) fault northeast of Rivers Peak. • 2-6-2-8 Mafic lava flows (undivided mJHr) Mafic lava flows are infrequent in the upper felsic member; however, where present, they are spatially and temporally associated with mafic domes and dyke/sill complexes (mJHb), from which they probably erupted. They typically range from 5 to 10 metres thick, though one flow underlying Ramsey Peak exceeds 20 metres in thickness. Flows are dark green-grey or dark maroon-grey in colour, aphyric to sparsely plagioclase.phyric, strongly to weakly flow banded 51 and vesicular basalt and basaltic andesite. Vesicles are 1-10 mm, round to elliptical to irregularly shaped, infilled with chlorite or quartz/epidote, and commonly parallel the stratabound margins of the flows. Several flows with floor breccias were observed; floor breccias are very coarse to medium grained, monomictic, and consist of dark green-grey coloured, angular mafic clasts in a very fine grained maroon coloured matrix. One approximately 10 metre thick flow southeast of Mount Preston contains pillow structures. Several amygdaloidal, crowded plagioclase-phyric andesite flows occur in stratigraphic proximity to the pillowed flow in that region. These flows are lithologically identical to the crowded plagioclase-phyric high level intrusions in the lower mafic member; however, no intrusive equivalents to these flows were observed within the upper felsic member. 2-6-2-9 Granite (mJg) One phaneritic stock has been recognized within the study area that is demonstrably coeval with and probably subvolcanic to spatially and temporally related Hazelton Group volcanogenic strata in the region. The stock, which has yielded a ca. 175 Ma U-Pb zircon age (see geochronology discussion below) intrudes the hanging wall of the aforementioned mineralised fault zone south of Mount Preston (e.g., Photo 6, Gordee et al., 2005, Appendix F), thereby constraining the age of the extensional structure and the rhyolite domes in that region. The stock is dark pink to grey, fine grained, equigranular to locally porphyritic hornblende-biotite granite. The exposed area of the stock is less than 250 m 2 , and a five metre wide aureole around the stock consists of fine grained leucogabbro. The stock provides an important "window" into the subvolcanic roots to the upper felsic member. 2-7 DEPOSITIONAL ENVIRONMENT AND PHYSICAL VOLCANOLOGY 2-7-1 The lower mafic member 2-7-1-1 Depositional environment Rocks of the lower mafic member are interpreted to have been deposited subaqueously. Pillow lavas are generally regarded as the most distinctive feature of basaltic lavas erupted under water (Cas and Wright, 1987); the few mafic pillowed lava units, together with localised hyaloclastite facies in rocks of the lower mafic member, suggest subaqueous deposition. Epiclastic lithofacies of the lower mafic member probably represent the reworking of mafic lava flows and intrusions of the lower mafic member. The relatively finer grain size of the sandstone, siltstone, and mudstone sequences with respect to primary volcanic rocks within the lower mafic member suggests rapid disintegration of primarily fragmented material, and the 52 compositionally and texturally immature nature of the rocks suggests a proximal source. The mudstone caps of the sedimentary sequences may have been derived from the glassy and clay-rich margins of hyaloclastite breccia or pillows. Repeated couplets of internally graded epiclastic rocks suggest subaqueous deposition. The distinctly laterally discontinuous volcanogenic sediments were probably deposited in relatively shallow water environment above normal wave base in a subtidal environment. 2-7-1-2 Physical volcanology The high proportion of lava flows to epiclastic rocks in the lower mafic member implies relative proximity to one or more volcanic vents. Submarine mafic lavas are erupted either along fissures (e.g., mid-ocean ridges) or from central vents at seamounts (Cas and Wright, 1987). Fissure eruptions are characterized by quiet effusion of pillow and sheet lava flows. Relatively little quench shattering and autobrecciation occurs in fissure environments due to minimal physical interaction between lava and sea water; therefore, fragmental volcaniclastic material is rarely produced (Cas and Wright, 1987, and references therein). The generally subordinate amount of fragmental material to coherent material in rocks of the lower mafic member suggests that the morphology of the volcanic edifices more closely resembled subaqueous fissures than seamounts (Cas and Wright, 1987). Furthermore, localised exposures of fluidal clast breccia within the lower mafic member may indicate eruption from subaqueous fissures (cf. spatter cones in subaerial environments). The fluidally-shaped clasts resemble blocks and fluidal lapilli that form by tearing apart of relatively low-viscosity lava ribbons jetted upward from vents during Hawaiian-style fire-fountain eruptions (e.g., Macdonald, 1972; Allen et al., 1997; Simpson and McPhie, 2001; cf. McPhie et al., 1993, plate 13.1).). In subaqueous environments, dispersal is likely to be restricted, with most fall-out occurring in the immediate vicinity of the vent (Simpson and McPhie, 2001, and references therein). Therefore, exposures of fluidal clast breccia south of Butler Peak likely represent the vestiges of one or more subaqueous volcanic edifices that erupted some of the pillow and sheet lava flows within the lower mafic member. The transition from pillowed to massive morphology, within a single flow or between flows, could reflect fluctuating discharge rates (Cas and Wright, 1987). Minor intercalated epiclastic lithofacies may indicate brief intraformational pauses in eruptive activity. 53 2-7-2 The upper felsic member 2-7-2-1 Depositional environment Most indications of the environment of deposition of rocks of the upper felsic member suggest submarine deposition. The most obvious indications of submarine deposition are the fossiliferous beds, which are generally restricted to stratigraphically low sections (e.g., the south Ramsey Peak area). Most of the fossils found in the coquinas south of Ramsey Peak include robust, shallow-marine forms that characterize the sublittoral region and that have been abraded due to high-energy post-mortem processes. The grading of shells and the distinct lateral continuity of several coquina units suggests that some of the fossiliferous beds represent storm deposits. This is consistent with the occurrence of shallow-marine molluscan forms found singly in the matrix in underlying units. The articulated nature of many of the shells implies a rapid sedimentation rate. Stratigraphically higher in the upper felsic member, indications of the environment of deposition are consistent with the fossiliferous, sedimentary-dominated rock units lower in the section. Again, rare fossiliferous beds contain robust, shallow-marine coquinas that characterize the sublittoral region. Abundant, coarse grained, heterolithic volcanic breccia units may represent periodic slumping of the volcanic apron on the steep flanks of a volcano into the sea. Oxidised clasts in these units were probably derived from the subaerial flanks of the volcano. Submarine reworking of these deposits in a subtidal region is evidenced by local high angle cross stratification and fossils. Peperitic textures and mafic pillow lavas also suggest subaqueous volcanism and/or deposition. Siliceous nodules and subordinate gas segregation pipes represent infilled original vesicles which formed as a result of upward migration of large amounts of steam (Cas and Wright, 1987), again suggesting hot, subaqueous deposition. Leaves suggest a near-shore environment, and stratigraphically associated syneresis cracks suggest periodic exposure and desiccation, perhaps in a tidal flat region. Lava flows and coarse grained fragmental units locally contain oxidised clasts at this stratigraphic interval, which indicate subaerial transport, at least in part. Collectively, these features indicate a fluctuating environment, ranging from tidal to subtidal or deltaic and possibly brief periods of subaerial deposition or subaerially reworked fragments being deposited in a those environments. 2-7-2-2 Physical volcanology Pyroclastic deposits in the upper felsic member probably formed as a result of subaerial phreatomagmatic eruptions from oceanic island volcano(es) that created a plinian column from which pyroclastic fall deposits (ash- and pumice-fall) formed. Collapse of the eruption column 54 probably spawned pyroclastic flows (± surges) that passed into the sea. Typically poorly welded pyroclastic units with chloritised pumice and fiamme of the upper felsic member suggest subaqueous deposition. Ambient heated water likely contributed to the rapid disintegration or alteration of variably porous pumice/fiamme fragments to chlorite. Thin pyroclastic units deposited subaqueously probably did not retain sufficient heat to weld. Alternatively, very thick and very densely welded units such as the ones underlying Ramsey Peak and Mount Preston may have been formed as a result of very large and high energy eruptions that retained sufficient heat to weld through localised shoaling of the already shallow sea water. Ash-cored and -armoured accretionary lapilli may have formed as a result of fine ash from a subaerial eruption accumulating around water droplets that then dropped into water. As the lapilli fell through the water column, some of them were effectively sorted according to size and/or reworked by normal epiclastic processes. The stratigraphic association of normally graded accretionary lapilli tuff units succeeded by unwelded ignimbrite units indicates that the accretionary lapilli likely formed by ash elutriating out of a pyroclastic flow (e.g., ash-cloud-derived; cf. Cas and Wright, 1987) moving over - and possibly ingesting - water. Primary volcanic units and secondary reworked deposits are thicker, more widespread, and coarser grained in the Ramsey Peak area than in the northern portion of the study area. Intercalated epiclastic, finer-grained lithofacies, which are locally subequal to volcanic units in the north are rare or absent throughout much of the top half of the stratigraphic sequence in the south. This suggests a generally more vent-proximal setting for rocks in the Ramsey Peak area; however, no vent areas have been identified. Very thick lapilli tuff units may represent intracaldera facies. Local extensional faults with minimal displacement offsetting strata underlying the Ramsey Peak massif (Mortensen et al., 2004; see appendix F) may represent caldera-bounding structures. Ballistic sag structures, which occur in both the northern and southern exposures of the upper felsic member, suggest a near-vent (within hundreds of metres) setting (Cas and Wright, 1987). The association of some pyroclastic fall tuff units with ballistic pyroclasts suggests that they represent true "ash-fall" deposits, resulting from ash-sized pyroclasts falling from an expanding plume of tephra. Possible surge deposits probably represent base surge deposits based on the stratigraphic association with ignimbrite units. South of Mount Preston, the linear arrangement of felsic domes along an extensional fault suggests a fissure-like vent where each individual extrusive dome represented a point source where periodic dome collapse may have spawned pyroclastic flows and surges. However, no observable thinning of pyroclastic units occurs moving away from the vents, therefore, the possibility that pyroclastic units in that region having formed as a result of eruption column collapse cannot be precluded. 55 2-8 AGE CONSTRAINTS Volcanic and fossiliferous sedimentary Hazelton Group rocks throughout the study area were sampled extensively for isotopic and fossil dating during the 2003 and 2004 field seasons in attempt to precisely constrain the age of the volcanostratigraphic sequences for comparison with regional Hazelton Group ages. Biostratigraphic and U-Pb geochronologic data from this investigation have been combined with fossil collections and U-Pb ages from other studies in the area (e.g., Haggart et al., 2004; Mahoney et al., 2005; Diakow and Koyanagi, 1988; G J . Woodsworth and P. van der Heyden, unpublished data) to assist in constraining the age of the base of the lower mafic member and the top of the upper felsic member, which are not exposed within the study area. 2-8-1 Biostratigraphy Macrofossils are generally very rare within the Hazelton Group strata in the study area, and fossiliferous units are restricted to marine volcanogenic sedimentary rocks of the upper felsic member. Fossil collections in the upper felsic member have been made from strata south of Ramsey Peak and west-southwest of Rivers Peak (Fig. 2-7). Fossils from these collections generally include a diverse assemblage of bivalve taxa, including trigoniids, ostreids, pectinids, and Pleuromya sp., as well as high-spired gastropods and belemnoids, but most of the material is indeterminate and/or non-diagnostic (J.W. Haggart, personal communication, 2004). South Ramsey Peak area biostratigraphy South of Ramsey Peak (Fig. 2-7), a section of marine volcanogenic sedimentary rocks and interbedded felsic tuffaceous units is the most richly fossiliferous sequence of Hazelton Group strata within the study area. The fossiliferous sequence is approximately 100 metres thick and contains, in addition to the assorted aforementioned species, the ammonoid species Troitsaia westermanni, which is considered to be a diagnostic species of the basal Aalenian (early Middle Jurassic) in western British Columbia (T. Poulton, personal communication, 2005; Gordee et al., in prep.; see Chapter 3). Two fossil collections from midway up the southern flank of Ramsey Peak consist of large and coarsely ribbed bivalves of Trigonia sp. that are almost certainly Early Bajocian (Middle Jurassic) in age, but may range from Middle Toarcian through Early Callovian (late Early Jurassic through Middle Jurassic; T. Poulton, personal communication, 2005). 56 West Rivers Peak area biostratigraphy West of Rivers Peak, a succession of fossiliferous marine sandstone is intercalated with medium bedded tuff and lapilli tuff. Fossil collections from the sequence comprise fragments of mostly indeterminate material; however, one belemnite, bivalve, or ammonite fragment (Trigonia sp.?) is probably Middle Toarcian through Middle Callovian (late Early Jurassic through Middle Jurassic) in age (T. Poulton, personal communication, 2005). Other local biostratigraphy age constraints West of Oppy Lake (Fig. 2-6), ammonoid collections from H.W. Tipper have been identified as Late Bathonian or Early Callovian Lilloettia sp. by H . Frebold (G.J. Woodsworth, personal communication, 2004), and indicate that the east-dipping stratigraphic sequence that underlies Ramsey Peak is probably structurally undisrupted and youngs at least that far to the east. 2-8-2 Geochronology Volcanic rocks of felsic and intermediate compositions in the study area were sampled extensively for U-Pb zircon dating; however, nearly all of the samples were barren of zircons. These rocks have normal Zr concentrations (Table 2-1), and it is assumed that at least some zircon was present in the samples, but was too fine-grained to be recovered in the mineral separation process. Table 2-1 lists all samples processed for zircon in this study. A l l rocks collected from the lower mafic member were barren of zircons; therefore, all reported ages are from rocks within the upper felsic member. Three single detrital zircon ages are reported from one sedimentary rock (mJHs) sample and therefore represent the maximum age of deposition of that unit. U-Pb dating of zircon recovered from all samples was conducted at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) in the Department of Earth and Ocean Sciences at The University of British Columbia. Mineral separation and U-Pb dating techniques are as described by Friedman et al., 2001. U-Pb isotopic data are listed in Table 2-2 and are plotted on conventional concordia diagrams in Figure 2-11. Rhyolitic lapilli tuff southeast of Mount Preston (undivided mJHr) Flaggy weathering, maroon, rhyolitic, lithic-crystal-vitric tuff to lapilli tuff southeast of Mount Preston lies near the base of the measured volcanostratigraphic sequence in the Mount 57 Table 2-1. Summary of geochronology sample locality and information. U T M ' Zr Field no. 1:50 000 NTS Easting Northing Locality Map unit Rock type2 Modal mineralogy1 Textnres/itructurcs Justification Daring method Yield DM* (ppm) Layered Hazelton Group rocks 04 SMG 03 093D/15 666487 5874528 S of Ramsey Peak mJHr green and white, un-welded, rhy xl tuff aphanitic; rare pig Constrain age of volcanic strata in Jumble Mountain region U-Pb very few I2SMG03 093E/02 652885 5898500 SE of Mount Preson mJHr pink syneite clast IN purple, moderately welded, rhy ksp medium grained, equigranular Constrain age of subsurface intrusive body and provide maximum age U-Pb few vit-xl lapilli tuff of volcanic strata hostina the ctast 20 SMG 03 O93E/02 652292 5897847 SE of Mount Preson mJHrd rhy dome rare qtz + pig flow banded, vesicular Determine if extrusive felsic dome field is coeval with Hazelton U-Pb very few -Group volcanism 29 SMG 03 O93E/02 653687 5897387 SE of Mount Preson mJHr maroon, chloritized, densely welded, rhy xl-vit pig > qtz Constrain maximum age of section measured at Mount Preston U-Pb few lapilli tuff 39B SMG 03 O93E/02 650897 5898972 Mount Preston mJHr grey, moderately welded, dac vit-xl-lit lapilli tuff pig Constrain age of volcanic strata in Mount Preston region U-Pb none? 47 SMG 03 093E/02 650819 5898147 Mount Preston mJHr grey, poorly welded, rhy vit-lit-xl lapilli tuff pig Constrain minimum age of section measured at Mount Preston U-Pb few 107 SMG 03 O93E/02 665773 5875662 SSW of Ramsey Peak mJHr pink, densely welded, dac xl-vit-lit lapilli tuff pig Constrain maximum age of section measured at Ramsey Peak U-Pb very few 24 JBM 04 093E/02 653237 5893280 N of Rivers Peak mJHs grey, massive. QFP sandstone with rhy QFP clasts qtz + pig poorly sorted, angular to subround, coarse Comment on age and types of detritus being deposited during DZ' many Brained Hazelton Group volcanism and sedimentation 26 JBM 04 093E/02 653787 5895178 N of Rivers Peak mJHr purple, rhy vit-xl lapilli tuff pig > qtz parallel laminated, normally graded Constrain age of volcanic strata in Rivers Peak region U-Pb none? 223.0 01 SMG 04* 093E/02 666192 5875688 S of Ramsey Peak mJHr white and purple, very densely welded, rhy lil-xl-vit pig » qtz high-grade rheomorphic flow banding with Constrain maximum age of section measured at Ramsey Peak U-Pb none 332.0 ruff to lanilli tuff folding, distinct vertical welding zones 31 SMG 04 093E/02 663477 5883072 E of Butler Peak mJHr tan, very densely welded, rhy lit-xl-vil lapilli tuff pig Constrain minimum age of section measured at Butler Peak U-Pb none 211.0 66 SMG 04 093E/02 653496 5897049 N of Rivers Peak mJHrd tan rhy dome rare qtz columnar jointed, sucrosic Determine if extrusive felsic dome field is coeval with Hazelton U-Pb none 344.0 Group volcanism 91 SMG 04 093E/02 655286 5882377 W of Butler Peak emJHv grey, siliceous, rhy tuff devitrification textures, thinly wavy and Constrain maximum age of section measured at Butler Peak U-Pb none? 243.0 convolutelv laminated 94 SMG 04 093E/02 656121 5881387 WSW of Butler Peak emJHv grey rhy tuff aphanitic thinly laminated Constrain maximum age of section measured at Butler Peak U-Pb few 327.0 102 SMG 04 093E/02 666753 5877461 NNE of Ramsey Peak mJHr grey, very densely welded, rhy xl-vit lapilli tuff pig Constrain minimum age of section measured at Ramsey Peak U-Pb none? 392.0 121 SMG 04 O93E/02 667628 5878650 E of Ramsey Peak mJHr grey, thick bdd, rhy lit-xl tuff to lapilli tuff aphanitic: rare pig Constrain minimum age of section measured at Ramsey Peak U-Pb none? 853.0 140 SMG 04 O93E/02 653545 5893519 N of Rivers Peak mJHr pink, rhy flow pig > qtz flow banded, auto-brccciated zones Constrain age of volcanic strata in Rivers Peak region U-Pb none? 190.0 Subvolcanic Intrusions to the Hazelton Group and post-Hazelton Group intrusions 03 M - 2 O93E/02 665623 5878291 N of Ramsey Peak EKqd heterogeneous px-hbl qtz diorite pig > qtz > hbl > px medium grained, equigranular. abundant Constrain age of younger magmatism in the study area Ar-Ar (hbl) abundant 25 SMG 03 093E/02 652425 5898275 SE of Mount Preson Erp grey, hbl-bi-qtz rhy porphyry dyke qtz > bi > hbl xenoliths 1 Constrain age of younger magmatism in the study area Ar-Ar (bi) abundant 164 JBM 047 O93E/02 653979 5896213 N of Rivers Peak mJg pink, bi-hbl granite (pig =ksp=qtz) medium grained, equigranular to locally Constrain age of younger magmatism in the study area; cross-cuts 66 U-Pb few 257.0 hbl > bi ineaui granular SMG 04 21 SMG 04 093E/02 666288 5875997 Ramsey Peak Ur? white rhy dome pig > qtz flow banded Determine if rhyolite plug is coeval with Hazelton Group volcanism U-Pb none 264.0 or represents vouneer magmatism: is cross-cut bv 03 M-2 36 SMG 04 093E/02 659050 5881579 N of Butler Peak emJHv grey, pyritiferous, px-hbl microdiorite pig > hbl > px amygdaloidal (cbloritc-filled), qtz-eptdote- Determine if extensive mafic intrusive complex is coeval with mafic U-Pb none 152.0 vetned flows in Butler Peak reeion 100 SMG 04 093E/02 665609 5877393 N of Ramsey Peak Ur? grey, rhy dome rare pig locally flow banded, vesicular Determine if rhyolite plug is coeval with Hazelton Group volcanism U-Pb none 374.0 or represents vouneer masmatism 'UTMs are reported in North American Datum. 1927 (NAD 27). Rock type abbreviations: rhy, rhyolite; dac, dactte; and, andesite; has, basalt; QFP, quartz feldspar porphyry: vit. vitric; xl, crystal; lit, lithic. Mineral abbreviations: pig, plagioclase: ksp. alkali feldspar; qtz, quartz: bt, biotitc; hbl, hornblende; px, pyroxene. Vield DM: yield of mineral used to date rock. 5Detrital zircon study; U-Pb dating of representative zircons from each present morphological population. *Sample is from same unit as geochemical sample 112 SMG 03, from which the reported zirconium concentration was taken (see Table 2-4). 7Sample is from same intrusion as geochemical sample 61 SMG 04. from which the reported zirconium concentration was taken (see Table 2-4). Table 2-2. U-Pb analytical data for volcanic, plutonic and detrital zircon samples. Sample Wt U Pb ! m P b / J M P b total % " W u 4 2 0 7 p h / 2 0 6 p b . * W ! , U age 2 0 7 p W 2 0 6 p b a g ( , Description1 (mg) (ppm) (ppm) (meas.)J common ( ± % l o ) ( ± % l a ) ( ± % l o ) (Ma; ± % 2 a) (Ma; ± % 2o) Pb(PB) Sample 29-SMG-03 A: N 10,62-104 0.008 1565 51 8369 3 22.8 .02760(0.19) 0.1895(0.25) 0.04979(0.16) 175.5(0.7) 185.4(7.4) B: N 10,-62 0.013 670 21 337 46 20.2 0.02730(0.21) 0.1865(0.66) 0.04956(0.53) 173.6(0.7) 174.3(24.6) D: N10.-62 0.013 369 II 1104 7 22.9 0.02423(0.15) 0.1661(0.44) 0.04961(0.37) 154.7(0.5) 176.9(17.1) E: N 10,-62 0.005 41 1.3 258 1 19.0 0.02784(0.73) 0.1898(4.45) 0.4945(4.24) I77..0(2.5) 169.1(192) Sample 47-SMG-03 A: N5.+I34 0.007 116 3.3 460 3 14.1 0.02713(0.27) 0.1898(1.63) 0.05075(1.55) 172.6(0.9) 229.4(71.4) B: N5.+134 0.007 300 8.7 949 4 15.3 0.02718(0.24) 0.1852(0.67) 0.04942(0.60) 172.9(0.8) 168.0(27.9) C: N5.+134 0.006 376 11 1343 3 16.6 0.02758(0.25) 0.1877(0.60) 0.04935(0.53) 175.4(0.9) 164.6(24.9) Sample I07-SMG-0S A: N5.+134 0.008 628 18 1255 7 13.8 0.02718(0.17) 0.1858(0.68). 0.04958(0.64) 172.9(0.6) 175.5(29.5) B: N5.+134 0.010 441 13 902 8 14.8 0.02744(0.17) 0.1874(1.13) 0.04955(1.06) 174.5(0.6) 173.7(49.2) E: N5.+134 0.003 431 13 214 II 14.2 0.02763(0.27) 0.1883(3.33) 0.04943(3.25) 175.7(0.9) 168.2(149) Sample 164-JBM-04 A: N2.+134 0.020 148 4.3 1131 4 13.3 0.02751(0.26) 0.1878(1.01) 0.04949(0.93) 175.0(0.9) 171.3(43.5) D: N2.+134 0.036 179 5.1 951 11 13.9 0.02725(0.15) 0.1826(1.16) 0.04862(1.10) 173.3(0.5) 129.4(51.3) Sample 24-JBM-04 A:N2,+ 149 0.011 58 1.6 228 5 13.5 0.02715(0.27) 0.1857(2.41) 0.04961(1.27) 172.7(0.9) 176.8(106) B: N2.+149 0.007 82 2.4 277 4 16.9 0.02742(0.33) 0.1875(2.43) 0.04958(2.29) 174.4(1.1) 175.3(107) C: N2.+I49 0.010 58 1.7 267 4 13.3 0.02758(0.51) 0.1882(4.33) 0.04949(4.10) 175.4(1.8) 171.0(187) N2, N5, N10 - non-magnetic at 2, 5, 10 degrees side slope on Frantz magnetic separator; grain size given in microns. radiogenic Pb; corrected for blank, initial common Pb, and spike corrected for spike and fractionation corrected for blank Pb and U, and common Pb 59 Figure 2-11. U-Pb concordia diagrams for a) rhyolite lapilli tuff southeast of Mount Preston; b) rhyolite lapilli tuff south of Ramsey Peak; c) rhyolite lapilli tuff south of Mount Preston; d) granite stock southeast of Mount Preston; and e) detrital zircon from sandstone northwest of Rivers Peak. 60 Preston area (sample 29 S M G 03; Fig. 2-7; Table 2-1), where it is intercalated with maroon mudstone and pebbly mudstone and subequal aphyric to plagioclase-phyric mafic flows. The tuff lies in the footwall of the extensional fault south of Mount Preston. The sample yielded a small amount of relatively fine grained zircon, mainly comprising clear, colorless, stubby euhedral prisms with rare opaque inclusions. Three strongly abraded fractions were analyzed (Table 2-2). Two of the analyses (B and E) are concordant with non-overlapping errors, and the third fraction (A) is slightly discordant (Fig. 2-1 la). Fraction E gives an older 2 0 6 P b / 2 3 8 U age than fraction, but is considerably less precise than B, and we cannot preclude the possibility that fraction E also contained a minor inherited zircon component. An age of 176.3 ± 3.3 M a is assigned to the sample based on the total range of 2 0 6 P b / 2 3 8 U ages for fractions B and E. Rhyolitic lapilli tuff south of Ramsey Peak (undivided mJHr) Light pink, massive, densely welded, dacitic crystal-vitric-lithic lapilli tuff exposed at the southern base of the Ramsey Peak massif (sample 107 SMG 03; Fig. 2-7; Table 2-1). The tuff is intercalated with similar felsic ignimbrite units, and immediately stratigraphically underlies the very thick, very densely welded, rhyolitic lapilli tuff unit in that region. Zircon recovered from this sample is similar in appearance to that in the previous sample, and was mostly relatively fine grained. One coarser grained fraction (A) and two finer grained fractions were analyzed, after strong abrasion. A l l three fractions are concordant (Table 2-2; Fig. 2-1 lb), and the oldest Pb/ U age of 175.7 ± 0.9 Ma is taken as the best estimate for the crystallization age of the sample. Rhyolitic lapilli tuff south of Mount Preston (undivided mJHr) Light grey, poorly welded, rhyolitic vitric-lithic-crystal lapilli tuff exposed at the base of the western cirque wall south of Mount Preston lies near the top of the measured volcanostratigraphic sequence in the Mount Preston area (sample 47 S M G 03; Fig. 2-7; Table 2-1). The tuff is intercalated with other similar ignimbrite units and subordinate maroon mudstone and pebbly mudstone, and closely stratigraphically underlies the very densely welded rhyolitic lapilli tuff that caps the stratigraphic sequence in the area. Zircon from the sample was similar in appearance to that in the previous two samples but was somewhat coarser grained. Three strongly abraded fractions were analyzed after strong abrasion, and all three fractions yielded concordant analyses (Table 2-2; Fig. 2-1 lc). The oldest 2 0 6 P b / 2 3 8 U age of 175.4 ± 0.9 M a is taken as the best estimate for the crystallization age of the sample. 61 Granite stock southeast of Mount Preston (mJg) Sample 164 I B M 04 was collected from the granite stock south of Mount Preston that intrudes the hanging wall of the extensional fault in that region (Fig. 2-7; Table 2-1). Abundant clear, pale yellow, stubby to elongate prismatic zircons were recovered from the sample. Two fractions were analyzed (Table 2-2, Fig. 2-1 Id). Fraction A is concordant with a 2 0 6 P b / 2 3 8 U age of 175.0 ± 0.9 Ma, which is taken as the best estimate for the crystallization age of the sample. The second fraction (D) gives a slightly reversely discordant analysis; the reason for this discordance is uncertain. Sandstone northwest of Rivers Peak (mJHs) The crystal-rich sandstone unit northwest of Rivers Peak was sampled for detrital zircons to constrain the maximum age of deposition of the unit (sample 24 I B M 04; Fig. 2-7; Table 2-1). The sample yielded a moderate amount of what appears to be a single population of zircon, comprising relatively coarse, clear, pale pink, euhedral, stubby square prisms, some of which displayed evidence for magmatic resorption on the surfaces. Three single grains were analyzed and all yielded concordant analyses (Table 2-2, Fig. 2-1 le). The 2 0 6 P b / 2 3 8 U ages of the individual grains range from 175.4 ± 1.8 Ma to 172.7 ± 0.9 Ma (Table 2-2). The grains are high quality and had low U-contents (57-82 ppm), and the strong abrasion prior to analysis should have removed any post-crystallization Pb-loss effects. The youngest 2 0 6 P b / 2 3 8 U age of 172.7 ± 0.9 Ma should therefore provide a maximum age for deposition of the sandstone unit. Other local geochronological constraints A crystal tuff from the stratigraphic succession south of Ramsey Peak that immediately stratigraphically overlies the gradational contact zone between the lower mafic member and the upper felsic member yielded a U-Pb zircon age of 176.5 ± 0.6 M a (Gordee et al., in prep.; see Chapter 3). South-southwest of Sakumtha Pass (Fig. 2-7) in the north-central Bella Coola map area, U-Pb zircon dating of a quartz-phyric dacite breccia indicates an age of 191 ± 12 M a (Haggart et al., 2004; R . M . Friedman, unpublished data). A more precise age of 181.6 ± 1.0 M a has been obtained from a quartz-rich crystal tuff in the same outcrop belt to the south in the east-central Bella Coola map area (Haggart et al., 2004; R . M . Friedman, unpublished data). Approximately 30 km to the west of the study area, the Trapper pluton is the closest large granitic batholith of early Middle Jurassic age. At 170.5 ± 0.7 Ma (J.K. Mortensen and J.B. 62 Mahoney, unpublished data), the body is ca. 5 m.y. younger than the majority of strata within the upper felsic member. However, the age of the Trapper pluton more closely corresponds with the age of the proposed shallower level QFP intrusion from which the QFP sandstone unit (MJHs) northeast of Rivers Peak was derived. The two broadly coeval intrusions are probably analogous to the Topley Intrusions, and may demonstrate that the extensive felsic volcanism that characterizes the upper felsic member continued until at least ca. 170 Ma. 2-8-3 Age of Hazelton Group strata and structures within the study area No depositional or intrusive ages have been obtained from the lower mafic member. However, because of the assumed lower stratigraphic position of the east-dipping stratigraphic succession west of the East Sakumtha River, the ca. 181 Ma age west of Kalone Peak in the same outcrop to the south can be taken as a very crude estimate of the maximum age of the base of the lower mafic member (Fig. 2-12). Separating the dated section west of Kalone Peak from rocks of the lower mafic memberis a microdiorite complex that is interpreted to represent a sequence of recrystallized mafic lava flows and subvolcanic intrusions (Haggart et al., 2004). The complex probably represents the along-strike equivalent to rocks in the lower mafic member (Fig. 2-12), and importantly may represent the initial stages of widespread mafic magmatism that characterizes the lower mafic member. The contact between the lower mafic member and the upper felsic member is best documented south of Ramsey Peak. At that locale, mafic lava flows of the lower mafic member are intercalated with felsic tuff and lapilli tuff, volcanic breccia, and fossiliferous marine epiclastic rocks of the upper felsic member in a broad transition zone. The ca. 176 Ma age obtained from a felsic tuff in that stratigraphic section is interpreted to represent the top of the lower mafic member and the earliest stages of felsic volcanism and sedimentation of the upper felsic member. The Lower Aalenian ammonites collected from the same stratigraphic interval reinforce that chronostratigraphic position, and the geochronologic and biostratigraphic controls together indicate that the contact between the two members lies just below or at the Lower-Middle Jurassic boundary (Fig. 2-12; see Chapter 3 for more details). Assuming no obscured structural complexities or significant intraformational unconformities exist within the mafic package, approximately 7 km thickness of mafic volcanic strata and subvolcanic intrusions were erupted/emplaced between ca. 181 and 176 Ma. The felsic tuff near the base of the stratigraphic sequence southeast of Mount Preston yielded an imprecise age of ca. 176 Ma, which provides a maximum age of the upper felsic member in the northern structural block (Figs. 2-7 and 2-12). The dated tuff in that stratigraphic 63 P - f ] Basaltic to andesitic flow 1- 1 Basalt to andesite pillowed lava I J I Basalt to andesite intrusion I * I Mafic breccia r~T| Dacite tuff and lapilli tuff \r I Rhyolite tuff, lapilli tuff or dome C 3 Rhyolite flow 17^ 1 Pumice- and rhyolite-rich breccia f - 1 Tuffaceous mudstone [•. • I Lithic-feldspathic sandstone I-. -I Mudstone to pebbly mudstone m Limey siltstone, sandstone and limestone O H Polymictic volcanic conglomerate I • I Dioritic stock ^ Fossil age U-Pb zircon age •Thicknesses arc approximate Km ! 0 Figure 2-12. Schematic stratigraphic correlations of rocks in the study area based on lithologies and ages. Stratigraphically lowest correlations are based on ages from Hazelton Group rocks in the central Bella Coola map area (e.g., Haggart etal., 2004). succession is intercalated with subordinate mafic flows and sills, and may in fact represent the uppermost portion of the gradational contact between the lower mafic member and upper felsic member. Further up section to the west, the ca. 175 Ma age obtained from another felsic tuff represents a close approximation of the minimum absolute age of the stratigraphic sequence in the northern portion of the study area (Fig. 2-12). Due to the large (± 3.3 Ma) error associated with the age constraining the base of the package of upper felsic member strata in the northern portion of the study area, it is difficult to estimate the timeframe of deposition represented by the approximately 5 km thick stratigraphic sequence. The most conservative depositional rate is at least 5 km in 4.5-5.5 m.y.; however, a shorter timeframe of 1-2 m.y. is a more likely scenario. The ca. 175 M a locally porphyritic granite stock that cuts the extensional fault south of Mount Preston (Fig. 2-7) provides three important age constraints: 1) it constrains the minimum age of the fault to pre-ca. 175 Ma; 2) it further constrains the age of the stratigraphic sequence to pre-ca. 175 Ma; and 3) it establishes that the stratigraphic sequence was buried to a sufficient depth to be intruded by a fine grained, porphyritic stock by ca. 175 Ma. The three detrital zircon ages (ca. 175, 174, and 172 Ma) obtained from the crystal-rich sandstone unit northwest of Rivers Peak demonstrate that the unit is at least 3 m.y. younger than the stratigraphic package on which it rests, suggesting that the unit rests on a localised unconformity within the stratigraphic succession (Fig. 2-12). The period of erosion must span approximately 3 m.y. or more, but is probably contained within the timeframe of continued early Middle Jurassic Hazelton Group magmatism, as indicated by the one population of Middle Jurassic zircons. Because the unit contained a moderate amount of good quality zircons (which is unlike any other stratified (volcanic) unit in the study area), the previously discussed suggestion that the unit represents the proximally deposited epiclastic derivative of a Hazelton Group subvolcanic QFP intrusion is reinforced. That situation requires that rapid uplifting of the local stratigraphic sequence occurred between ca. 172 Ma and the early Middle Jurassic(?) deposition of the crystal-rich sandstone unit. Rocks of the upper felsic member in the Ramsey Peak area comprise the thickest, and most well dated stratigraphic sequence in the study area. The ca. 175 Ma felsic tuff immediately south of Ramsey Peak is approximately 1 km up section from the ca. 176 Ma tuff approximately 3 km further to the south (Figs. 2-7 and 2-12). Early Bajocian(?) fossils collected from near the summit of Ramsey Peak stratigraphically overlie the ca. 175 Ma age near the southern base of the mountain, indicating a depositional rate in the southern exposures of the upper felsic member of at least ~1 km in ca. 6 m.y. These data, together with the Bathonian/Callovian fossils collected from the west Oppy Lake region another approximately 4 km up section to the east, indicate a 65 minimum depositional rate of 5 km in ca. 15 m.y. in that region (again, assuming no obscured structural complexities). The two ca. 175 Ma ages assist in a crude stratigraphic correlation the upper felsic member between the very densely welded tuff exposed on the southern flanks of Ramsey peak and the similar one capping the stratigraphic sequence in the Mount Preston area (Fig. 2-12). 2-9 LITHOGEOCHEMISTRY A lithogeochemical study was carried out in order to broadly characterize the nature and petrotectonic setting of erupted and non-erupted magmas of Hazelton Group rocks in the study area. Lithogeochemical analyses from 19 felsic lithic-poor or lithic-free tuff, lapilli tuff, and lava flow units, as well as 11 subvolcanic intrusions have been obtained from rocks in the lower mafic and upper felsic members in the study area. A total of 22 samples belong to the lower mafic member and 18 samples belong to the upper felsic member. Lithogeochemical data are listed in Tables 2-3 and 2-4. Rocks in the study area - particularly mafic rocks of the lower mafic member - contain mineral assemblages (e.g., chlorite + epidote) typical of lower greenschist facies metamorphism and/or low-grade hydrothermal alteration. This alteration is attributed mainly to background seawater alteration based on the non-pervasive and highly localised nature of the altered zones. Relatively soluble major elements, such as Si, Fe, Mg, Ca, Na, and K , may have been mobilized in the conversion of volcanogenic material to chlorite and epidote during one or more hydrothermal events. Therefore, more emphasis in the lithogeochemical characterization has been placed on rare earth elements (REE) and high field strength (HFS) elements, which are immobile under low grade hydrothermal alteration and metamorphism (Gifkins et al., 2005). The samples are characterized by variable S i 0 2 contents and total alkali (Na 2 0+K 2 0) contents (Fig. 2-13a), which may reflect silica and alkali mobility during alteration. Samples from the lower mafic member straddle the alkaline-subalkaline boundary of Irvine and Baragar (1971; Fig. 2-13a). A l l samples from the upper felsic member plot in the subalkaline field on the same plot. On the total alkali versus silica (TAS) plot (LeBas et al., 1986), samples from the lower mafic member have broadlybasalt, trachybasalt, and basaltic andesite compositions, and samples from the upper felsic member are dacitic to rhyolitic in composition (Fig. 2-13a). The weak bimodality of the samples on the TAS plot (Fig. 2-13a) is not evident on MacLean and Barrett's (1993) Ti0 2 -Zr plot (Fig. 2-13b). Most notably, rocks of andesitic composition are absent on the TAS plot of Figure 2-13a, but several samples plot as andesite on the incompatible element volcanic rock classification scheme (Fig. 2-13b). Several samples that plot in the 66 Table 2-3. Major element Uthogeochemical data1 for representative Hazelton Group samples in the study area. Field no.z SIQ| AI^Oj FeO(T) Fe2Q3 FeO CaO MgO Na t O K 2 Q C r 2 Q 3 TO, M n O P;Q 5 SrO BaO L O l Tolal Fe 2Oj/FeO Stratified rocks 05 SMG 03 71.71 12.31 4.96 2.64 2.32 1.87 1.61 5.13 0.10 <0.01 0.47 0.11 0.07 0.01 0.02 1.11 99.47 1.14 06 SMG 03 73.98 13.53 2.81 1.16 1.65 0.48 0.71 4.72 1.18 <0.0I 0.42 0.03 0.08 <0.01 0.02 1.05 99.00 0.70 09 SMG 03 53.48 14.33 12.86 5.42 7.44 6.82 3.74 2.48 1.02 <0.01 1.30 0.27 0.20 0.03 0.08 1.73 98.34 0.73 10 SMG 03 67.67 13.56 5.42- 4.44 0.98 2.18 1.14 4.95 1.01 <0.0I 0.73 0.08 0.21 0.01 0.03 2.81 99.80 4.53 14a SMG 03 66.69 13.82 6.49 3.17 3.32 0.86 1.53 4.26 2.36 <0.01 0.78 0.17 0.24 0.03 0.07 1.68 98.98 0.95 14b SMG 03 65.67 13.84 6.34 •, 3.30 3.04 1.39 1.36 4.53 2.05 <0.0I 0.78 0.22 0.25 0.02 0.07 2.02 98.53 1.09 15 SMG 03 47.94 14.54 7.73 ' 2.92 4.81 8.86 2.61 3.44 2.91 <0.01 0.86 0.57 0.14 0.02 0.13 8.81 98.55 0.61 16 SMG 03 48.18 16.75 11.10 4.46 6.64 9.25 6.48 3.17 0.98 <0.0I 0.83 0.25 0.10 0.06 0.04 2.38 99.58 0.67 17 SMG 03 53.90 14.52 9.98 5.91 4.07 4.44 3.54 4.98 0.56 <0.0I 1.05 0.23 0.21 0.02 0.02 5.26 98.71 1.45 21 SMG 03 45.69 16.70 11.24 4.81 6.43 8.29 6.80 2.62 1.81 0.01 0.79 0.39 0.10 0.04 0.04 4.36 98.89 0.75 34 SMG 03 46.75 16.30 10.14- 4.48 5.66 9.02 8.12 1.77 1.79 0.04 0.87 0.30 0.17 0.04 0.05 3.16 98.51 0.79 43a SMG 03 47.88 17.15 10.99 5.54 5.45 7.62 6.02 3.21 1.99 0.02 0.89 0.20 0.22 0.10 0.05 3.31 99.63 1.02 44 SMG 03 70.12 . 15.39 3.13 2.80 0.33 0.37 0.36 4.56 3.56 <0.01 0.82 0.03 0.11 0.03 0.11 1.04 99.62 8.48 45 SMG 03 46.83 16.74 11.09 5.04 6.05 7.95 7.98 2.22 2.12 0.03 0.85 0.23 0.17 0.08 0.11 2.92 99.32 0.83 48 SMG 03 48.89 i 16.23 12.72 10.15 2.57 3.10 4.83 5.75 0.37 <0.01 1.23 • 0.20 0.29 0.02 0.02 4.50 98.13 3.95 112 SMG 03 74.82 '• 13.31 3.39 2.41 0.98 0.24 0.49 5.80 0.31 <0.01 0.43 0.03 0.04 0.03 0.02 0.70 99.60 2.46 113 SMG 03 49.99 17.08 11.44 4.42 7.02 9.37 4.49 2.53 0.55 0.01 1.04 0.21 0.13 0.04 0.04 2.03 98.96 0.63 114 SMG 03 70.78 12.72 5.29 2.28 3.01 1.07 1.65 4.79 0.67 <0.01 0.75 0.09 0.23 0.01 0.03 1.73 99.80 0.76 26 JBM 04 73.22 14.59 2.25 1.99 0.26 1.10 0.27 2.35 3.22 <0.01 0.36 0.03 0.04 0.01 0.02 2.53 99.97 7.65 13 SMG 04 48.05 16.05 11.59 4.58 7.01 8.17 6.39 3.50 1.25 0.01 0.71 0.51 0.07 0.03 0.04 2.59 98.97 0.65 15 SMG 04 60.10 13.88 9.26 5.98 3.28 1.87 2.68 5.94 0.14 <0.01 1.03 0.22 0.32 0.02 0.01 2.73 98.20 1.82 29 SMG 04 52.40 17.58 7.70 2.81 4.89 7.35 4.44 4.54 1.87 0.01 1.04 0.13 0.33 0.05 0.05 2.37 99.87 0.57 31 SMG 04 67.55 12.71 7.50 4.09 3.41 0.69 1.42 1.43 5.61 <0.01 0.49 0.17 0.04 0.02 0.21 1.92 99.76 1.20 33 SMG 04 47.25 18.50 10.27 3.07 7.20 8.79 6.16 2.49 2.00 0.01 0.86 0.48 .0.11 0.03 0.08 2.80 99.84 0.43 66 SMG 043 98.21 0.35 0.18 . 0.19 0.07 0.01 0.09 0.05 <0.01 0.65 <0.01 0.01 <0.01 0.01 0.24 99.86 -91 SMG 04 71.85 14.43 2.95 0.70 2.25 0.91 0.85 6.41 0.76 <0.01 0.45 0.07 0.06 0.05 0.04 1.00 99.82 0.31 92 SMG 04 54.50 19.44 7.87 6.00 1.87 4.15 4.87 4.42 0.34 <0.01 0.77 0.19 0.31 0.14 0.03 2.83 99.86 3.21 102 SMG 04 70.48 14.08 2.90 2.71 0.19 1.31 0.05 3.51 5.23 <0.01 0.44 0.06 0.06 <0.01 0.14 1.55 99.81 14.26 109 SMG 04 65.85 13.21 6.36 1.41 4.95 3.09 1.82 2.15 3.42 <0.01 0.80 0.23 0.18 0.03 0.11 2.08 99.33 0.28 121 SMG 04 73.50 12.72 3.81 1.88 1.93 1.07 0.61 4.75 1.58 <0.01 0.38 0.07 0.08 0.01 0.04 1.14 99.76 0.97 140 SMG 04 65.00 13.50 4.25 3.03 1.22 4.49 2.06 4.34 1.88 <0.01 0.63 0.08 0.13 0.02 0.02 3.13 99.52 2.48 145 SMG 04 66.66 15.36 4.62 2.56 2.06 3.29 0.99 4.76 1.80 <0.01 0.70 0.19 0.24 0.05 0.10 1.16 99.92 1.24 ubvolcanic intrusions 08 SMG 03 50.93 17.43 11.97 5.77 6.20 4.52 3.88 4.81 0.45 <0.0I 1.13 0.16 0.15 0.03 0.05 3.82 99.32 0.93 22 SMG 03 55.16 15.31 9.45 4.33 5.12 3.50 3.62 4.58 1.13 <0.01 0.90 0.15 0.20 0.01 0.03 5.05 99.07 0.85 23 SMG 03 46.59 16.70 10.26 . 4.08 6.18 8.48 6.70 3.87 0.35 0.01 0.84 0.31 0.16 0.03 0.01 4.74 99.06 0.66 JBM 0505 48.00 17.83 9.40 4.25 5.15 8.16 5.42 3.36 1.11 0.01 1.32 0.12 0.39 0.04 0.05 4.11 99.32 0.83 21 SMG 04 73.50 13.17 2.04 . 1.46 0.58 1.10 0.21 5.22 2.39 <0.01 0.39 0.05 0.05 0.02 0.04 1.46 99.63 2.52 36 SMG 04 52.51 16.13 8.39 , 2.79 5.60 5.16 6.64 3.90 1.39 0.02 0.97 0.13 0.31 0.04 0.05 4.05 99.69 0.50 46 SMG 04 49.50 17.60 10.01 4.54 5.47 7.35 4.84 3.56 2.17 0.01 1.57 0.15 0.47 0.07 0.05 2.52 99.85 0.83 61 SMG 044 68.21 14.23 4.30 2.56 1.74 2.06 1.18 3.87 2.96 <0.01 0.50 0.09 0.10 0.02 0.07 1.91 99.48 1.47 93 SMG 04 39.02 15.68 9.16 5.75 3.41 13.45 3.68 2.33 1.78 <0.01 1.29 0.18 0.35 0.05 0.06 12.85 99.88 1.69 100 SMG 04 77.30 12.36 1.45 0.81 0.64 0.25 0.38 5.39 1.67 <0.01 0.35 0.04 0.05 0.01 0.03 0.66 99.94 1.27 143 SMG 04 54.70 17.14 6.27 2.15 4.12 7.25 3.35 3.36 1.46 0.01 0.91 0.09 0.24 0.05 0.07 4.85 99.75 0.52 All major element analyses are reported as weight % oxides and were completed using X-Ray Fluorescence Spectroscopy (XRF). :See Appendix E for sample information, including rock types. 3Highry silicified sample. 4Sample is from same intrusion as U-Pb sample 164 JBM 04 (sec Table 2-1). T a b l e 1-4, Trace and rare earth element ( R E E ) lithogeochemical data 1 for representative Hazelton Group samples in the study area. F i e l d no . 2 B a C e C o C r Cs C o B y E r E n G a G d H f H o L a L n M o N b N d N i P b P T R b S m ratified rocks 05 S M G 03 <1 108.5 32.7 5.7 20 0.1 <5 6.3 4.3 1.1 15 4.9 7 1.4 14.9 0.8 <2 4 19.7 8 <5 4.3 1.0 5.2 06 S M G 03 <1 125.5 28.5 3.2 <10 1.0 <5 3.5 2.7 0.6 15 3.2 7 0.8 12.6 0.6 <2 4 15.4 5 <5 3.5 22.9 3.6 09 S M G 03 <1 573.0 19.5 35.0 30 1.0 22 6.0 3.9 1.2 19 4 . 6 4 1.3 9.7 0.6 2 2 13.1 23 II 2.7 18.6 4.2 10 S M G 03 <! 278.0 38.4 5.5 10 1 . 3 29 4.9 3.2 1.0 14 5.0 6 1.0 17.6 0.5 <2 4 21.6 6 8 4.7 17.2 5.3 14a S M G 03 <1 592.0 26.8 11.4 10 0.6 <5 6.2 • 4.4 0.8 18 4.8 6 1.4 11.2 0.8 3 4 16.6 7 8 3.5 47.1 4.5 14b S M G 03 <1 536.0 24.4 9.0 <10 0.5 <5 7.2 4.9 I.I 16 5.4 6 1.6 10.8 0.8 <2 4 1S.7 <5 7 3.2 40.1 4.9 15 S M G 03 <1 1270.0 19.1 27.5 <10 0.8 139 3.7 2.3 1.3 14 3.3 2 0.8 9.7 0.4 <2 1 10.9 10 30 2.2 69.8 2.9 16 S M G 03 <1 344.0 10.8 41.0 100 0.4 108 2.8 1.8 0.8 18 2.3 2 0.6 4.7 0.3 <2 1 7.0 37 6 1.4 20.0 2.1 17 S M G 03 <1 77.1 16.4 25.3 20 1.0 10 4.0 2.8 1.0 16 3.4 3 0.9 7.8 0.5 <2 2 10.1 16 7 2.1 6.8 3.1 21 S M G 03 <1 380.0 9.7 40.2 100 4.4 15 2.7 1.6 0.7 18 2.1 1 0.6 4.2 0.3 <2 1 6.4 36 6 1.3 52.1 1.9 34 S M G 03 < 1 471.0 13.7 39.1 360 4.8 14 2.7 1.8 0.8 17 2.4 2 0 . 6 6.5 0.3 <2 1 8.3 81 6 1.8 43.8 2.4 43a S M G 03 <1 372.0 15.7 41.8 230 2.4 9 3.2 1.8 0.9 17 2.8 2 0.7 7.1 0.3 <2 2 9.7 72 10 2.0 54.2 2.8 44 S M G 03 <1 1010.0 45.5 1 .4 20 4.0 10 8.2 5.4 1 . 9 18 6.9 7 1.8 20.6 0.9 <2 5 26.8 5 23 6.0 61.6 6.6 45 S M G 03 < 1 1075.0 12.9 41.2 310 3.0 33 2.8 1.7 0.8 17 2.4 2 0.6 5.9 0.3 <2 1 8.1 77 5 1.7 51.0 2.2 48 S M G 03 <1 67.8 13.0 36.3 80 0.2 116 3.6 2.2 1.0 19 3.2 2 0.8 5.9 0.3 <2 1 10.4 52 8 2.0 8.3 3.0 112 S M G 03 < 1 40.7 29.8 2.2 10 0.2 <5 10.9 7.7 1.1 16 6.3 9 2.4 12.7 1.3 <2 5 17.7 5 9 3.8 5.2 5.3 113 S M G 03 <! 330.0 12.8 35.2 80 0.3 85 4.3 2.8 1.0 18 3.1 3 0.9 5.5 0.5 <2 1 8.6 32 13 1.7 8.3 2.7 114 S M G ( 1 3 <1 164.5 18.9 5.2 <10 0.1 <5 6.7 4.3 0.9 14 4.4 5 1.4 8.0 0.7 2 2 11.6 <5 8 2.5 9.5 3.6 26 J B M 04 < 1 163.5 30.4 1.9 10 2.4 <5 5.5 4.0 0.8 15 4.0 7 1.1 14.9 0.6 <2 4 16.9 <5 10 3.7 63.7 4.0 13 S M G 04 < 1 360.0 7.3 42.7 80 0.8 34 2.5 1.6 0.7 17 2.0 1 0.6 3 . 1 0.2 <2 1 4.9 34 14 1.0 27.5 1.7 15 S M G 04 < 1 61.0 27.1 1 1 . 7 10 0.2 <5 6.5 4.3 1 . 4 18 5.6 5 1.5 11.4 0.7 <2 3 18.0 5 14 3.6 2.4 4.9 29 S M G 04 < 1 400.0 38.2 27.2 110 0.9 54 4.4 2.9 1.6 20 5.2 4 1.0 15.6 0.4 <2 4 22.4 42 7 4.8 27.1 5.0 31 S M G 04 <! 1900.0 22.0 4.1 60 0.2 14 6.9 4.9 1.1 16 5.2 6 1.6 8.2 0.8 <2 4 13.4 27 6 2.7 73.8 4.3 33 S M G 04 <! 728.0 12.4 40.7 170 0.5 71 3.1 2.0 0.9 18 2.4 8 0.6 5.0 0.3 <2 1 7.3 36 6 1.5 31.4 2.3 66 S M G 0 4 1 , | 18.4 1.2 1.0 30 0.2 9 0.1 0.1 <0.1 1 0.1 8 <0.1 <0.5 <0.1 2 1 <0.5 5 5 0.1 0.9 0.1 91 S M G 04 <1 302.0 33.4 6.5 20 0.2 60 3.7 2.8 0.5 13 3.6 7 0.9 15.4 0.5 <2 6 17.8 7 24 4.1 17.0 3.3 92 S M G 04 <1 282.0 37.1 29.4 20 2.3 17 2.7 1.6 1.4 22 3.9 3 0.6 14.9 0.2 <2 2 22.5 22 16 4.7 5.7 4.5 102 S M G 04 ' < 1 1190.0 45.6 1.5 10 0.8 <5 7.8 5.4 1 . 6 17 6.7 II 1.6 21.7 0.8 <2 5 25.6 <5 10 5.6 79.5 6.1 109 S M G 04 <I 1130.0 26.6 9.5 20 0.3 7 7.1 4.8 2.0 20 5.8 4 1.6 9.9 0.8 2 3 17.2 5 8 3.2 54.8 5.3 121 S M G 04 <1 376.0 37.2 10.2 20 0.2 21 6.7 5.0 1.1 16 6.2 20 1.6 16.0 0.9 2 5 20.5 5 7 4.4 18.0 5.3 140 S M G 04 <1 161.5 22.1 6.0 10 1.8 <5 4.8 3.4 0.8 15 4.1 5 1.2 10.0 0.6 <2 3 14.2 <5 10 2.9 43.6 3.7 145 S M G 04 <1 822.0 41.3 3.7 20 0.5 <5 7.3 5.1 1.8 18 7.0 6 1.8 18.1 0.8 <2 4 25.0 <5 16 5.1 32.8 6.3 tbvolcanic intrusions 08 S M G 03 <1 366.0 13.9 33.5 30 0.1 16 4.6 3.0 I.I 18 3.6 3 1.1 6.1 0.5 <2 1 10.5 21 8 2.0 7.1 3.3 22 S M G 03 <1 252.0 20.3 22.5 10 1.1 <5 4.9 3.2 1.2 18 4.0 3 1.1 8.7 0.5 <2 2 13.0 8 18 2.7 18.0 3.9 23 S M G 03 <1 81.3 12.0 38.4 170 2.3 48 2.7 1.7 0.7 17 2.2 1 0.5 5.3 0.3 2 1 7.3 62 60 1.6 11.3 2.1 J B M 0505 <] 386.0 36.8 32.5 130 0.9 34 5.0 3.0 1.7 21 5.1 4 1.1 15.2 0.5 <2 5 23.9 72 7 5.2 24.4 5.6 21 S M G 04 <1 363.0 29.4 2.4 20 0.3 <5 4.8 3.4 0.9 13 4.1 7 1.2 12.2 0.7 <2 4 14.0 5 11 3.2 25.1 3.6 36 S M G 04 <1 • 440.0 39.6 37.3 210 0.4 50 4.1 2.4 1.3 17 4.8 4 0.9 16.7 0.4 <2 5 21.2 121 8 4.6 19.4 4.4 46 S M G 04 <1 457.0 38.5 34.1 90 1.0 60 5.6 3.4 1.8 19 6.1 5 1.3 15.0 0.5 <2 6 24.3 44 6 5.2 52.7 5.9 61 S M G 0 4 ' <1 639.0 24.4 9.1 20 0.9 20 3 . 6 2.5 0.7 14 3.4 7 0.8 10.8 0.5 2 3 11.7 10 8 2 . 6 50.8 2.8 93 S M G 04 <1 485.0 34.4 25.6 50 2.4 39 4.5 2.8 1.4 18 4.6 4 0.9 12.8 0.4 <2 6 20.3 25 7 4.1 33.3 4.9 100 S M G 04 <1 304.0 23.1 2.4 30 0.3 <5 4.4 3.5 0.7 II 3.3 8 1.1 9.0 0.7 <2 4 11.3 <5 7 2.5 19.7 2.8 143 S M G 04 <1 621.0 37.9 23.1 90 1.6 52 3.7 2.4 1.2 21 Vo 5 0.8 17.1 0.3 <2 5 19.9 52 13 4.4 21.4 4.2 ' A l l trace and rare earth element analyses are reported in parts per mi l l ion (ppm) and were completed using Inductively Coupled Plasma - Atomic Emission Spectroscopy ( I C P - A E S ) and/or Inductively Coupled Plasma - Mass Spectrometry ( I C P - M S ) . 1 See Appendix E for sample information, including rock types. ' H i g h l y si l icif ied sample. 'Sample is from same intrusion as U - P b sample 164 J B M 04 (see Table 2-1). Table 2-4 (continued). Trace and rare earth element (REE) lithogeochemica! data1 for representative Hazelton Group samples in the study area. Field no.1 Sn Sr Ta Tb Th T l Tm U V W Y Yb Zn Zr ratified rocks 05 SMG 03 , 79.0 <0.5 1.0 4 <0.5 0.8 1.6 33 1 38.8 4.7 108 265.0 06 SMG 03 1 40.4 <0.5 0.6 6 <0.5 0.5 2.3 14 1 24.0 3.3 77 265.0 09 SMG 03 1 277.0 <0.5 0.8 2 <0.5 0.6 0.8 405 <1 37.2 3.8 278 115.0 10 SMG 03 <1 67.1 <0.5 0.8 3 <0.5 0.5 1.4 67 <1 30.1 3.3 53 206.0 14a SMG 03 1 112.5 <0.5 0.9 3 <0.5 0.7 1.1 45 <1 38.6 4.5 252 199.0 14b SMG 03 1 115.5 <0.5 1.0 3 <0.5 0.8 1.2 43 1 46.4 4.9 160 195.0 15 SMG 03 1 94.9 <0.5 0.5 1 0.5 0.3 0.5 262 <1 21.8 2.2 358 83.9 16 SMG 03 1 485.0 <0.5 0.4 1 <0.5 0.3 <0.5 355 <1 16.9 1.7 132 52.7 17 SMG 03 1 78.6 <0.5 0.6 2 <0.5 0.5 0.7 265 1 25.3 2.9 173 114.5 21 SMG 03 1 360.0 <0.5 0.4 1 <0.5 0.3 <0.5 355 <1 16.0 1.6 193 48.1 34 SMG 03 1 364.0 <0.5 0.4 1 <0.5 0.3 <0.5 337 <1 16.2 1.6 180 55.4 43a SMG 03 1 805.0 <0.5 0.5 1 <0.5 0.3 <0.5 307 <1 18.0 1.7 104 59.8 44 SMG 03 1 90.5 <0.5 1.2 4 <0.5 0.8 1.6 47 <1 53.5 5.1 83 255.0 45 SMG 03 1 790.0 <0.5 0.4 1 <0.5 0.2 <0.5 336 <1 15.7 1.6 106 53.7 48 SMG 03 I 147.5 <0.5 0.5 <1 <0.5 0.3 <0.5 382 <1 21.6 1.9 386 61.2 112 SMG 03 75.5 <0.5 1.4 5 <0.5 1.2 2.0 9 <1 70.4 7.5 55 332.0 113 SMG 03 1 271.0 <0.5 0.6 1 <0.5 0.4 <0.5 362 <1 26.2 2.6 284 83.6 114 SMG 03 1 63.6 <0.5 0.9 2 <0.5 0.7 1.1 26 <1 40.8 4.2 52 180.0 26 JBM 04 57.0 <0.5 0.8 4 <0.5 0.5 1.1 13 7 33.1 4.2 34 223.0 13 SMG 04 1 266.0 <0.5 0.4 <l <0.5 0.2 <0.5 378 1 15.9 1.6 440 41.7 15 SMG 04 1 109.5 <0.5 1.0 3 <0.5 0.6 0.6 136 3 43.0 4.2 242 152.5 29 SMG 04 1 375.0 <0.5 0.9 2 <0.5 0.4 0.5 181 2 25.7 2.6 72 160.0 31 SMG 04 1 21.4 <0.5 1.1 4 <0.5 0.7 1.2 37 2 44.1 4.8 79 211.0 33 SMG 04 1 258.0 <0.5 0.5 1 <0.5 0.3 <0.5 288 1 16.8 1.7 144 353.0 66 SMG 04J 15.8 <0.5 <0.1 <l <0.5 <0.1 <0.5 6 2 1.0 0.1 8 344.0 91 SMG 04 291.0 <0.5 0.6 4 <0.5 0.4 1.6 32 1 25.9 3.1 70 243.0 92 SMG 04 1 1005.0 <0.5 0.6 1 <0.5 0.2 <0.5 172 1 15.6 1.4 105 96.9 102 SMG 04 1 42.7 <0.5 1.2 5 <0.5 0.7 1.5 37 3 42.7 5.5 30 392.0 109 SMG 04 2 296.0 <0.5 1.1 2 <0.5 0.7 0.6 75 2 43.6 4.6 158 137.5 121 SMG 04 2 110.5 <0.5 1.1 5 <0.5 0.8 1.7 10 2 44.3 5.3 37 853.0 140 SMG 04 1 75.8 <0.5 0.8 4 <0.5 0.5 1.1 68 16 32.1 3.7 46 190.0 145 SMG 04 2 413.0 <0.5 1.3 4 <0.5 0.8 1.2 19 2 47.6 5.1 116 221.0 ibvolcanic intrusions 08 SMG 03 1 275.0 <0.5 0.7 1 <0.5 0.5 0.5 359 2 28.1 2.9 301 87.5 22 SMG 03 1 113.5 <0.5 0.7 1 <0.5 0.5 0.5 203 <1 29.0 3.0 168 95.9 23 SMG 03 1 184.5 <0.5 0.4 1 <0.5 0.2 <0.5 311 < | 15.7 1.6 393 48.4 JBM 0505 1 406 <0.5 0.9 1 <0.5 0.5 0.5 231 1 30 2.7 53 164.5 21 SMG 04 1 56.2 <0.5 0.8 6 <0.5 0.6 1.9 8 1 34.0 3.9 56 264.0 36 SMG 04 1 257.0 <0.5 0.8 2 <0.5 0.4 0.7 156 1 24.0 2.3 79 152.0 46 SMG 04 2 568.0 <0.5 1.0 1 <0.5 0.5 <0.5 242 1 32.5 3.2 83 190.5 61 SMG 04* 1 152.5 <0.5 0.6 7 <0.5 0.4 1.8 87 2 22.8 2.8 42 257 93 SMG 04 2 476.0 <0.5 0.8 1 <0.5 0.4 0.5 192 2 25.9 2.5 74 154.5 100 SMG 04 1 72.1 <0.5 0.6 5 <0.5 0.5 2.0 5 <1 27.8 3.7 48 374.0 143 SMG 04 2 519.0 <0.5 0.7 4 <0.5 0.3 1.3 152 2 20.9 2.2 77 178.5 All trace and rare earth element analyses are reported in parts per million (ppm) and were completed using Inductively Coupled Plasma - Atomic Emission Spectroscopy (ICP-AES) and/or Inductively Coupled Plasma - Mass Spectrometry (ICP-MS). 2See Appendix E for sample information, including rock types. 3Highly silicified sample. 4Sample is from same intrusion as U-Pb sample 164 JBM 04 (see Table 2-1). rhyolite and dacite fields on the TAS plot (Fig. 2-13a) plot as rhyodacite to dacite or andesite, respectively, on the incompatible element plot (Fig. 2-13b). These disparities are attributed to the commonly observed silicification of the felsic samples. Mafic and felsic samples typically plot in the calc-alkaline to transitional fields on the A F M plot of Irvine and Baragar (1971; Fig. 2-13c); however, on the Zr-Y plot of MacLean and Barrett (1993), the samples span the tholeiitic, transitional and calc-alkaline fields (Fig. 2-13d). Mafic samples typically plot as tholeiitic to transitional, and felsic rocks evenly span each field (Fig. 2-13d). Outlier felsic samples with high Zr contents on Figure 2-13 are the same silicified samples as in Figs. 2-13a and 2-13b. Figure 2-13e displays a plot of Ba/La versus S i 0 2 from Kay and Gordillo (1994), which distinguishes between rocks of arc and back-arc affinity. Mafic and felsic samples, again, display the weak bimodality in S i 0 2 content, and show distinct vertical patterns of increasing Ba/La ratio, spanning the arc and back-arc fields. There is no apparent spatial or temporal trend in the Ba/La ratio of rocks of the lower mafic member or in the upper felsic member. Rocks of the lower mafic and upper felsic members are clearly distinguished on Shervais's (1982) V-Ti/1000 plot (Fig. 2-13f). Felsic samples plot in a tight cluster below the alkaline boundary, whereas mafic rocks are characterized by highly variable V concentrations and, as in Figure 2-13e, the samples span the back-arc basalt (BAB) and island arc tholeiite (IAT) fields (Fig. 2-13f). The samples are plotted on chondrite- and primitive mantle-normalized plots on Figures 2-14a-d and 2-15a-d. Mafic and felsic samples display similar relative abundances of trace elements. A l l samples are characterized by variable large-ion lithophile element (LTLE) concentrations, which were likely easily mobilized during one or more hydrothermal alteration events. The samples display distinct Nb depletions characteristic of subduction-related magmas (Ta is below the detection limit in every sample). The sample with distinctly low trace element concentrations relative to the other samples is an extremely silicified felsic dome from the south Mount Preston area (Figs. 2-7, 2-14d and 2-15d). Mafic and felsic samples are plotted on chondrite normalised rare earth element (REE) plots in Figure 2-16a-d. The samples display similar relative abundances of REEs, although felsic rocks are slightly enriched overall in the lightest and heaviest REEs relative to mafic rocks. A l l samples are slightly light REE-enriched relative to heavy REEs (Fig. 2-16a-d); however, the overall patterns are relatively flat, indicative of a primitive source of the magmas. Some mafic samples and all felsic samples display moderate negative Eu anomalies (Fig. 2-16a-d). Again, the sample with low REE concentrations was collected from an extremely silicified felsic dome. 70 Figure 2-13. Lithogeochemical discriminate plots of intrusive and extrusive Hazelton Group rocks from the study area, a) Total alkali versus silica (TAS) plot of LeBas et al. (1986); b) T i 0 2 versus Zr plot after MacLean and Barrett (1993); c) A F M plot of Irvine and Baragar (1971); d) Zr versus Y plot from Gifkins et al. (2005), modified after MacLean and Barrett (1993); e) Ba/La versus Si0 2 plot from Kay and Gordillo (1994); f) V versus Ti/1000 plot of Shervais (1982). Purple symbols represent samples from the lower mafic member. Open diamonds represent mafic lava flows and closed diamonds represent subvolcanic intrusions. Blue symbols represent samples from the upper felsic member. Open squares represent felsic pyroclastic rocks and closed squares represent felsic domes. The red circle is a sample from the granite stock from the south Mount Preston area and the black cross is a sample from the microdiorite complex in the N E Bella Coola map area (e.g., Haggart et al. (2004)). 7 1 Rb Ba Th U Nb Ta K La Ce Sr Nd Sm Zr Ti Gd Y Rb Ba Th U Nb Ta K La Ce Sr Nd Sm Zr Ti Gd Y L E G E N D Upper felsic member • felsic pyroclastic rocks • felsic domes 0 granite stock Lower mafic member § mafic flows ^ mafic intrusions + microdiorite Figure 2-14. a-d) Chondrite normalised trace element plots of intrusive and extrusive Hazelton Group rocks from the study area. From Sun (1980). 72 Ca Rb Ba Tfa U Nb Ta K La Cc Pb PT Sr P Nd Zr So) Eu Ti Dy Y Y b Lu Cs Rb Ba Th U Nb Ta K La Ce Pb PT Sr P N d Zr Sm Eu T i Dy Y Yb Lu LEGEND Upper felsic member PI felsic pyroclastic rocks H felsic domes 0 granite stock Lower mafic member § mafic flows ^ mafic intrusions + microdionte Figure 2-15. a-d) Primitive mantle normalised trace element plots of intrusive and extrusive Hazelton Group rocks from the study area. From Sun and McDonough (1989). La Ce PT Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yh I.u La Ce FT Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu L E G E N D Upper felsic member • felsic pyroclastic rocks • felsic domes 0 granite stock Lower mafic member 0 mafic flows ^ mafic intrusions + microdiorite Figure 2-16. a-d) Chondrite normalised rare earth element (REE) plots of intrusive and extrusive Hazelton Group rocks from the study area. From Sun and McDonough (1989). 74 2-10 REGIONAL STRATIGRAPHIC CONTEXT AND TECTONIC IMPLICATIONS Our work, together with recent work completed to the south and southwest by Haggart et al. (2004) and to the west and northwest by Mahoney et al. (2005), demonstrates that a predictable sequence of upper Hazelton Group strata is stratigraphically correlative throughout much of southwestern Stikinia. The sequence is bracketed by latest Early Jurassic to early Middle Jurassic ages in the vicinity of the study area, but may include a broader range of ages, from middle Early Jurassic through the Middle Jurassic (e.g., Haggart et al., 2004). Rocks of the upper felsic member lithologically resemble and are age correlative with the upper pyroclastic division of the Smithers Formation in the central Whitesail Lake map area, as described by Diakow and Koyanagi (1988; Fig. 2-5). Volcanic-dominated, more vent-proximal sections, such as the upper Ramsey Peak section may be analogous to the "Whitesail Formation" (e.g., Woodsworth, 1979, 1980 and Tipper, 1979; Fig. 2-5). Diakow and Koyanagi (1988) do not describe any rock packages in the central Whitesail Lake map area that could be potentially lithologically correlative with the lower mafic member, and the lower sedimentary rock division of the Smithers Formation that they define is not present in the southeast Whitesail Lake map area. The stratigraphic sequence in the study area is age correlative with the top of the Nilkitkwa Formation and the base of the Smithers Formation in the Babine and Telkwa ranges in the Smithers map area, south of the Skeena Arch (Figs. 2-1 and 2-4). In the Iskut River region, age equivalent units include the Mount Dilworth and Salmon River formations (Figs. 2-1 and 2-3). However, the stratigraphic sequence in the study area is not lithologically correlative with the stratigraphic successions in central and northern Stikinia, and, despite the obvious age similarities, we choose not to apply the nomenclature developed for those successions to underscore the region-specific characteristics of upper Hazelton Group strata in southwest Stikinia. The most widely accepted tectonic model for the Hazelton arc was first proposed by Thorkelson (1992) and was further developed by Marsden and Thorkelson (1992) and Thorkelson et al. (1995). Thorkelson proposes that the widespread and protracted Hazelton arc formed as a result of two opposing subduction zones - one east- and one west-dipping - beneath Stikinia. The two subduction zones in his model produced two parallel, dominantly subaerial volcanic arcs separated by a broad, dominantly submarine basin. The basin, which he terms the Hazelton Trough, is a region of back-arc extension and subsidence common to both arcs (Thorkelson, 1992). Both the Iskut River region and the study area are located along the axis of the western Hazelton arc (Fig. 2-1; e.g., Marsden and Thorkelson, 1992). Early Jurassic Hazelton arc 75 magmatism and sedimentation is widespread throughout west-central and northwest Stikinia, but is apparently less voluminous in southwest Stikinia during that period, although this may mainly reflect a paucity of age data in that region. By Middle Jurassic time, Hazelton arc magmatism and deposition was apparently restricted to the Iskut River and Telegraph Creek regions of northwest Stikinia and the Whitesail Lake and Bella Coola regions of southwest Stikinia (although again, that may only reflect a paucity of age data in west-central Stikinia; Fig. 2-1). Physical and lithogeochemical characteristics of most studied portions of the Hazelton Group are consistent with a subduction-related setting (e.g., Tipper and Richards, 1976; Brown, 1987; Mihalynuk, 1987; Alldrick, 1991; Souther, 1991; Thorkelson, 1992); however, in northwest Stikinia upper Hazelton Group strata hosting the Eskay Creek deposit display more primitive lithogeochemical signatures (e.g., Macdonald et al., 1996; Barrett and Sherlock, 1996; Roth, 2002; Evenchick and Thorkelson, 2005). Field relations and indications of depositional environment of Hazelton Group strata in the Eskay Creek region, together with lithogeochemical and radiogenic isotopic signatures, are consistent with the involvement of primitive magmas thought to be related to a rifting environment (Roth et al., 1999, and references therein; e.g., Alldrick et al., 2004). The rift-related (?), submarine Hazelton Group volcano-sedimentary succession in the Eskay Creek area may have been derived in the back-arc region of the western Hazelton arc, along the northwestern margin of the Hazelton Trough. Lithologic characteristics of upper Hazelton Group strata in the study area and in the Bella Coola map area to the south indicate submarine deposition in relative proximity to one or more Middle Jurassic volcanic centres. These strata, possibly like those in the Iskut River region, may have been deposited along the western margin of the Hazelton Trough, with volcanic rocks derived mainly from volcanoes of the western Hazelton arc to the west. However, lithogeochemical signatures of upper Hazelton Group strata in southwest Stikinia are consistent with a subduction-related origin, suggesting that the coeval Hazelton Group strata to the north that host the Eskay Creek V M S deposit were deposited in a spatially isolated, rather than widespread, rifted (?) zone. Limited studies of Hazelton Group strata in west-central Stikinia (e.g., Marsden and Thorkelson, 1992) suggest possibly subaerial volcanism throughout that region, and pillow lavas found within the study area are the only occurrences that have been documented south of the Iskut River region (G.J. Woodsworth, personal communication, 2004). Together, these features suggest that the Hazelton Trough marine basin in central Stikinia may have been locally dissected by uplifted, subaerial regions (e.g., the Skeena Arch?), further reinforcing the idea of a spatially restricted tectonic structure to the north. 76 2-11 IMPLICATIONS FOR VMS POTENTIAL IN SOUTHWEST STIKINIA Several volcanological and compositional characteristics of volcanogenic strata within the study area and surrounding portions of the Whitesail Lake and Bella Coola map areas emphasize the potential for V M S mineralisation within the Hazelton Group in southwest Stikinia. First, submarine-deposited, volcanic vent-proximal lithofacies coincide with syn-volcanic heat sources and fracture networks required for circulation of hydrothermal fluids. Fluidal clast breccia, thick sections of mafic flows, abundant subvolcanic intrusions and domes/cryptodomes of the lower mafic member are all independent indications of proximity to one or more volcanic vents. Fluidal clast breccia units probably represent submarine fire-fountain breccias, which have been identified in several V M S districts (e.g., Allen et al., 1996; Cas et al., 1996; Allen et al., 1997; Simpson and McPhie, 2001). Domes with hyaloclastite carapace breccias and peperites within the upper felsic member also indicate proximity to volcanic vents, and are common features within massive sulphide districts (e.g., Kuroko-type). Syn-volcanic normal faulting, together with locally thick volcanic and sedimentary rock facies with rapid lateral thickness variations suggest an actively extending volcanic environment. Submarine fire-fountain breccias may also occur in extensional, fissure-like environments on the seafloor (Simpson and McPhie, 2001). Second, the Nifty V M S prospect in the east-central Bella Coola map area is hosted within the youngest observed Hazelton Group strata in southwest Stikinia (ca. 164 Ma; Haggart et al., 2004). Although younger than rocks in the study area, the existence of the deposit is certainly a good indication that processes favourable for the formation of V M S deposits were acting during the latest stages of Hazelton arc activity in southwest Stikinia. Finally, despite the fact that an analogy to the proposed "Eskay Rift" in the Iskut River area (e.g., Alldrick et al., 2004) does not appear to exist in the study area, there is no reason to preclude the possibility of another such feature in other back-arc regions along either of the Hazelton arcs. Widespread exposures of Hazelton Group strata throughout central and southern Stikinia have not been examined in detail, and the potential for one or more Eskay Creek-type V M S deposits within these regions cannot be ruled out. 2-12 DISCUSSION Results of this study demonstrate that magmatism and sedimentation related to the western Hazelton arc was continuous and voluminous well into the early Middle Jurassic in southwestern Stikinia. In that region, a diverse assemblage of vent-proximal volcanic and associated sedimentary lithofacies were deposited in a dominantly shallow submarine 77 environment, probably along the southwest margin of the Hazelton Trough, adjacent and to the east of subaerial volcanic centres of the western Hazelton arc. The stratigraphic sequence can be used as a geologic mapping tool to reliably predict the stratigraphic position throughout portions of southwest Stikinia. Although different from the largely coeval upper Hazelton Group strata hosting the Eskay Creek V M S deposit, the geologic setting of Hazelton Group rocks in southwest Stikinia is favourable for the formation of economic V M S deposits, and further exploration in the understudied arc sequence is recommended. 2-13 ACKNOWLEDGMENTS Funding for this study was provided by the Rocks to Riches Program, which is administered through the British Columbia & Yukon Chamber of Mines, as well as four mining companies (Barrick Gold Corp., Heritage Exploration Inc., Kenrich-Eskay Mining Corp., and Placer Dome Inc.). Danny Hodson of Rainbow West Helicopters and Richard Lapointe of West Coast Helicopters provided excellent and entertaining helicopter support. Christopher Kohel, Emily Hauser, Casey Bowe, and Joe Nawikas provided excellent assistance in the field. This project benefited greatly from the senior assistance in geologic mapping from J.B. Mahoney, R.L. Hooper, J.W. Haggart, and L .D. Snyder. Thanks to J.W. Haggart, L .J . Diakow, G.J. Woodsworth, and R.L. Anderson for ongoing valuable discussions about general geology of the Canadian Cordillera, Hazelton Group stratigraphy, and biostratigraphy. Thanks to K . A . Simpson and J.K. Russell for sharing some of their expertise in physical volcanology in ancient and modern volcanic terrains. R.L. Friedman provided assistance with U-Pb dating. A special thanks to J.K. Mortensen, J.B. Mahoney and J.W. Haggart for continued support and guidance throughout the project. 2-14 REFERENCES Alldrick, D.J., 1989. Volcanic centres in the Stewart Complex (103P and 104A, B). In: Geological Fieldwork 1988, British Columbia Ministry of Energy, Mines and Petroleum Resources, Paper 1989-1, pp. 233-240. Alldrick, D.J., 1991. Geology and ore deposits of the Stewart Mining Camp. The University of British Columbia, Unpublished Ph.D. thesis, 355 pages. Alldrick, D.J., Stewart, M.L., Nelson, J.L., Simpson, K.A., 2004. 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In: Geological Fieldwork 1997, British Columbia Ministry of Energy, Mines and Petroleum Resources, Paper 1998-1, pp. 20-1 - 20-28. Roddick, J.A., 1970. Douglas Channel-Hecate Straight map-area, British Columbia. Geological Survey of Canada Paper 70-42, 56 pages. Roth, T., 2002. Physical and chemical constraints on mineralization in the Eskay Creek deposit, northwestern British Columbia: evidence from petrography, mineral chemistry, and sulfur isotopes. The University of British Columbia, Unpublished Ph.D. thesis, 401 pages. Roth, T., Thompson, J.F.H., Barrett, T.J., 1999. The precious metal-rich Eskay Creek Deposit, northwestern British Columbia. In: Barrie, C.T. , Hannington, M.D. (Eds.), Volcanic-associated massive sulfide deposits: processes and examples in modern and ancient settings, Reviews in Economic Geology, vol. 8, pp. 357-373. Rusmore, M . E . , Woodsworth, G.J., Gehrels, G.E. , 2000. Late Cretaceous Evolution of the eastern Coast Mountains, Bella Coola, British Columbia. 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In: Current Research, Part A , Geological Survey of Canada, Paper 2004-A1, pp. 1-8. Souther, J.G., 1991. Volcanic regimes, Chapter 14. In: Gabrielse, H. , Yorath, C.J. (Eds.), Geology of the Cordilleran Orogen in Canada, Geology of Canada, no. 4, pp. 457-490 (also Geological Society of America, The Geology of North America, vol. G-2). Sun, S.S., 1980. Lead isotopic study of young volcanic rocks from mid-ocean ridges, ocean islands and island arcs. Philosophical Transactions of the Royal Society of London, Series A. , vol. 297, pp. 409-445. Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. Geological Society Special Publications, vol. 42, pp. 313-345. 83 Thompson, R . C , Smith, P.L., Tipper, H.W., 1986. Lower to Middle Jurassic (Pleinsbachian to Bajocian) stratigraphy of the northern Spatsizi area, north-central British Columbia. Canadian Journal of Earth Sciences, vol. 23, pp. 1963-1973. Thorkelson, D.J., 1992. Volcanic and tectonic evolution of the Hazelton Group in Spatsizi River (104H) map-area, north-central British Columbia. Carlton University, Unpublished Ph.D. thesis, 281 pages. Thorkelson, D.J., Mortensen, J.K., Marsden, H. , Taylor, R.P., 1995. Age and tectonic setting of Early Jurassic episodic volcanism along the northeastern margin of the Hazelton Trough, northern British Columbia. In: Miller, D . M . , Busby, C. (Eds.), Geological Society of America Special Paper 299, pp. 83-94. Tipper, H.W., 1978. Jurassic biostratigraphy, Cry-Lake map area, British Columbia. In: Current Research, Part A , Geological Survey of Canada, Paper 78-1 A, pp. 25-27. Tipper, H.W., 1979. Jurassic stratigraphy of the Whitesail Lake map area, British Columbia. In: Current Research, Part A, Geological Survey of Canada, Paper 79-1 A , pp. 31-32. Tipper, H.W., Richards, T.A. , 1976. Jurassic stratigraphy and history of north-central British Columbia. Geological Survey of Canada, Bulletin 270, 73 pages. Van der Heyden, P. (1982). Tectonic and stratigraphic relations between the Coast Plutonic Complex and Intermontane Belt, west-central Whitesail Lake map area, British Columbia. The University of British Columbia, Unpublished M.Sc. thesis, 172 pages. Wheeler, J.O., McFeely, P., 1991. Tectonic assemblage map of the Canadian Cordillera and adjacent parts of the United States ofAmerica. Geological Survey of Canada Map 1712A, scale: 1:2 000 000. Winchester, J.A., Floyd, P.A., 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology, vol. 20, pp. 325-343. Wood, C.A. , 1980. Morphometric evolution of cinder cones. Journal of Volcanology and Geothermal Research, vol. 7, pp. 387-413. Woodsworth, G.J., 1980. Geology of Whitesail Lake (93E) map area, British Columbia. Geological Survey of Canada, Open File 708, scale: 1:250 000. Woodsworth, G.J., 1979. Geology of Whitesail Lake (93E) map area, British Columbia. In: Current Research, Part A , Geological Survey of Canada, Paper 79-1 A , pp. 25-29. Woodsworth, G.J., Anderson, R.G., Armstrong, R.L. , 1991. Plutonic regimes, Chapter 15. In: Gabrielse, H . , Yorath, C.J. (Eds.), Geology of the Cordilleran Orogen in Canada. Geological Survey of Canada, Geology of Canada, no. 4, pp. 491-531 (also Geological Society of America, The Geology of North America, vol. G-2). 84 CHAPTER 3 THE A G E OF THE TROITSAIA WESTERMANNI ZONE OF BRITISH COLUMBIA: NEW GEOCHRONOLOGICAL D A T A 85 3-1 INTRODUCTION The genus Troitsaia was created (Poulton and Tipper, 1991) to accommodate ammonites that are found in British Columbia in association with the Aalenian ammonite Tmetoceras and that closely resemble the genus Dumortieria of the Subfamily Grammoceratinae, from which they were undoubtedly derived. Dumortieria is a widely used guide fossil for the Late Toarcian globally (e.g. Arkell, 1957), including British Columbia (Jakobs, 1997), although certain uncommon species may extend into the lowest Aalenian in Europe. Troitsaia differs from Dumortieria in having small spines or nodes on the ribs around the umbilical margin, and in being more evolute, with a slightly lower whorl height in the juvenile and intermediate growth stages. It is apparently endemic to North America, known so far only from western British Columbia, from the Methow Trough and the Hazelton Group resting on the Stikine tectonostratigraphic terrane (Fig. 3-1 inset). Poulton and Tipper (1991) concluded that Troitsaia is a good index species for the basal Aalenian in Canada even in the absence of other diagnostic Aalenian ammonites, and created the Troitsaia westermanni Assemblage Zone to recognize its regional utility (Table. 3-1). Troitsaia and Dumortieria are found mutually exclusively in British Columbia as far as we know, so that their morphological differences provide a ready means to differentiate between the strata in which they are found. (Note, however, that certain ammonites now identified as Troitsaia were called Dumortieria and assigned a Toarcian age in some fossil reports prepared before 1991.) Unfortunately, however, the precise relationships of Troitsaia-bearmg Aalenian beds with underlying Toarcian strata are nowhere entirely clear, because of the lack of richly fossiliferous sequences across the stage boundary. Consequently, the precise position of the Troitsaia westermanni Assemblage Zone with respect to the Toarcian/Aalenian stage boundary has remained uncertain. In this report, we document new paleontological collections and associated geochronological data from west-central British Columbia that confirm the latest Toarcian to lowermost Aalenian age of the zone (Table 3-1). 3-2 REGIONAL GEOLOGIC SETTING The Bella Coola map area (NTS 93D) is situated on the southwest margin of the Stikine Terrane (Stikinia; Fig. 3-1 inset), and includes the boundary between the Intermontane and the Insular superterranes. Intrusive and metamorphic rocks of the Coast Plutonic Complex dominate the central and western portions of the region and separate allochtonous rocks of Stikinia to the east from those of Wrangellia and possibly Alexander terrane to the west (Fig. 3-1 inset). At the latitude of Bella Coola, Stikinia comprises two distinct, northwest-trending volcano-sedimentary 86 Table 3-1. Correlations of western Canadian assemblage zones and northwest Eurpoean standard zones in the Pacific area. NORTHWEST EUROPEAN STANDARD ZONES SOUTH AMERICA EASTERN AND NORTHERN USSR OREGON SOUTHERN ALASKA WESTERN CANADA C O N C A V U M z < z u -1 < < M U R C H I S O N A E a z J < O Eudmetoceras Eudmetoceras amplectens Puchenquia malarguensis Pseudolioceras tugurense Tmetoceras tenue Zurcheria groeberi / / / Erycitoides unnamed (with Tmetoceras) unnamed (with Tmetoceras scissum) Bredyia manflasensis Pseudolioceras mclintocki absent? absent? Pseudolioceras (P.) rosenkrantzi Z < 0 < o Erycitoides howelli Tmetoceras scissum Y A K O U N E N S I S Dumortieria Troitsaia westermanni Hammatoceras n . sp. oo Toarc ian assemblage zones from Jakobs et al. (1994). 2 A a l e n i a n assemblage zones from Poul ton and Tipper (1991). 53°03 53°00' 52°58 126°34' 126°30' Scale 1:50 000 kilometres 1 — . — „ — 0 1 ? ? 4 Figure 3-1. Locality map of the E N E Jumble Mountain/S Ramsey Peak area, northeast Bella Coola map area (NTS 093D), British Columbia. The dotted line represents the stratigraphic section measured for this study that is schematically illustrated in Figure 3-3. Inset is a simplified map of terranes of the Canadian Cordillera (after Wheeler and McFeely, 1991). Some structural data has been removed or simplified. Features referred to in the text are labeled. Same explanation as in Figure 2-7, but with approximate Troitsaia (T) sample locations added. 88 sequences - the Lower-Middle Jurassic Hazelton Group and the informally-named Lower Cretaceous Monarch assemblage - each representing remnants of Mesozoic arcs. The Hazelton Group is an accreted island arc complex that formed as a result of subduction-related magmatism in more southerly latitudes in the paleo-Pacific Ocean. In the Bella Coola region, it is separated from the overlying continental arc-related Monarch assemblage by one or more locally recognized unconformities. Exposures of Jurassic Hazelton Group rocks in this region are part of a semi-continuous belt of Hazelton Group strata that extends northwestward to near the British Columbia/Yukon Territory border (58°30"N), and pinches out south of Bella Coola (approximately 52°N; Marsden and Thorkelson, 1992). The study section is located 2.5 km northeast of Jumble Mountain in the NTS 93D/15 Kimsquit 1:50 000-scale map sheet (Bella Coola map area), and 4 km south of Ramsey Peak in the NTS 93E/02 Tesla Lake 1:50 000-scale map sheet (Whitesail Lake map area; Fig. 3-1). The section is centered on a prominent unnamed peak that splits into two, parallel, east-trending ridges that terminate at a major Ramsey Creek drainage (Fig. 3-1). The main Jumble Mountain massif is underlain by alternating red and cream-colored, well-bedded, felsic? volcanic and sedimentary strata; however, these beds have not been examined in detail, due to the extreme topography of the mountain and difficult access. The strata are similar in appearance to the study section, and the two sections are probably correlative. The study section is located at a major facies transition of a very thick and well-exposed stratigraphic sequence of dominantly subaqueous Hazelton Group strata that extends at least 30 km to the north (e.g., Gordee et al., in prep.). Vent-proximal mafic flows and subvolcanic intrusions of a lower mafic member gradationally transition into vent-proximal to -intermediate zone felsic tuffaceous rocks and associated epiclastic derivatives of an upper felsic member (Fig. 3-1). At the gfadational facies boundary, flows of the mafic package are intercalated with volcaniclastic rocks of the upper felsic package. The base of the lower mafic member is constrained to post-ca. 181 Ma (Haggart et al., 2004), and top of the upper felsic member is ca. 172 Ma or younger (Gordee et al., in prep.). Difficulties arise in trying to correlate rock units defined in the study area with those of other localities; consequently, Gordee et al. (in prep.) have chosen not to apply regionally developed formational nomenclature assigned to Hazelton Group strata in other regions to strata in the Bella Coola map area. 3-3 LITHOSTRATIGRAPHY AND DEPOSITIONAL ENVIRONMENT Figure 3-2 displays a measured stratigraphic section of the basal 175 metres of the northeast Jumble Mountain section. Beds in the section dip gently down-slope to the east-89 80 60 40 -\ 20 —I—-» • !_ta r-^.! i _ o C=s*l i _ C o metres F F + 176.5 ±0 .6 Ma a s s W F = w Volcanic Lithofacies ~A— 1 £• J T Basalt and basaltic-andesite sills and dykes Dacite lapilli tuff and flow-banded domes Rhyolite tuff and lapilli tuff Heterolithic tuff breccia and volcanic-derived breccia Sedimentary Lithofacies Mudstone and granule to pebble mudstone Feldspathic-lithic sandstone Calcareous feldspathic-lithic sandstone and siltstone Volcanic-derived pebble-to cobble-conglomerate Symbols + F/F I U-Pb age Planar laminations Wavy laminations Normally graded bedding Planar cross-bedding Fossils noted in unit/ fossil collection Gas segregation pipes Figure 3-2. Measured stratigraphic section of the lower 175 metres of the E N E Jumble Mountain/S Ramsey Peak section, northeast Bella Coola map area (NTS 093D), British Columbia. Note that intraformational lithofacies associations are necessarily somewhat simplified and idealised. 90 southeast in a continuous homoclinal succession (Fig. 3-3a), and are locally folded within low-amplitude open folds (Fig. 3-1). The section is truncated by porphyritic andesite and quartz diorite stocks on both the northern and southern limits, and is structurally continuous for 1.5 km (approximately 1 km of true stratigraphic thickness; Fig. 3-1). Numerous mafic sills thickening the section may be related to the strata-bounding stocks. Of the 1000 metres of preserved section, only the basal 175 metres contain fossiliferous strata and are therefore the focus of this discussion. In general, the stratigraphically lower two-thirds of the study section consists of subequal proportions of volcanogenic sandstone and conglomerate units, intercalated with subordinate felsic volcanic breccia, lapilli tuff, tuff, siltstone, and mudstone (Fig. 3-2). The stratigraphic sequence displays a general fining-upward trend; thicker-bedded, pebble to cobble, volcanic conglomerate and coarse volcanogenic sandstone in the lower part of the study section transition to thinner beds of fine- to medium-grained sandstone and mudstone in the middle part (Fig. 3-2). A thick unit comprising grey, monolithic, felsic, clast-supported, pebble to boulder conglomerate caps the relatively finer grained study section of fossiliferous units (Fig. 3-2). Relatively thinner bedded tuff units that characterize the upper portion of the study section are rare to absent throughout the lower portion of the section (Fig. 3-2). 3-3-1 Volcanic lithofacies, processes and depositional environment Rare primary volcanic units in the study section include felsic tuff and felsic to intermediate lapilli tuff. Brown, massive, poorly welded, rhyolitic? to dacitic vitric-crystal-lithic lapilli tuff units are common throughout the entire study section. Rare flattened pumice is green and chloritised. One unit contains silicified gas segregation pipes up to 2 m in length. Relatively finer grained units include pink or green, thin bedded, massive, non-welded, rhyolitic crystal tuff with plagioclase and rare quartz. Primary volcanic units in the study section likely formed as a result of subaerial phreatomagmatic (phreatoplinian) eruptions - non-welded tuff units probably represent air-fall deposits and typically poorly welded lapilli tuff units probably represent pyroclastic flow deposits that formed through collapse of the eruption column. Poorly welded units with chloritised pumice, together with gas segregation pipes and the close stratigraphic association with fossiliferous units suggests submarine deposition for volcanic units. Many of the units were subsequently reworked via normal epiclastic processes, forming finer grained, volcaniclastic units. 91 Figure 3-3. a) Outcrop of top half of fossiliferous section in the south Ramsey Peak area. Mountain peak in background is south face of Ramsey Peak. Hammer is 40 cm; b) Coquinoid lag deposit. Lens cap is ~3 cm; c) Closeup of fossiliferous unit, with fossils (F) preserved as unfilled molds; d) Brown sandstone unit south of Ramsey Peak from which one Troitsaia collection was made. Knapsack is ~40 cm. 92 3-3-2 Sedimentary lithofacies, processes and depositional environment Sedimentary rocks predominate over volcanic rocks in the study section and include a wider range of lithologies, including volcanic conglomerate and breccia, sandstone, siltstone and mudstone (Fig. 3-2). With the exception of the conglomerate unit that caps the study section, conglomerate units in the study section are polymictic, matrix supported, and locally contain discontinuous lenses of sandstone. Clasts are angular to subrounded, range from granule- to cobble-sized, and comprise predominantly felsic lapilli tuff and andesite porphyry. Matrix material consists of maroon sandstone and mudstone with broken plagioclase crystal fragments. Local finer-grained lenses consist of thin-bedded and -laminated, normally graded sandstone, siltstone, and mudstone that are compositionally identical to the matrix material. Conglomerate units commonly channels into underlying beds. Subordinate volcanic breccia units are immature variations of conglomerate units with more homogeneous clast compositions. Clasts are predominantly angular and the units are locally clast supported. Matrix material is coarser grained, and sandstone lenses and interbeds are absent. Relatively finer-grained volcanogenic epiclastic units include thin to medium bedded, parallel and locally high-angle cross laminated, massive to normally graded, feldspathic-lithic wacke sandstone, siltstone and pebbly to granule mudstone. Siltstone units locally contain discontinuous lenses of coarser grained sandstone. Mudstone units are identical in composition to the finest-grained matrix material of conglomerate units. Fossils have been found at several levels within the stratigraphic section (Fig. 3-2). They occur as unfilled or carbonate-filled molds singly in the matrix of sedimentary units, as well as in coquinoid lag deposits (Figs. 3-3b and 3-3c; e.g., Fig. 3c, Mortensen et al., 2004, Appendix F). Brown, fine-grained sandstone units yielded the most fossils (Fig. 3-3d). Coquinas are variable in thickness, although laterally continuous. Fossil present in the coquinas include a diverse assemblage of bivalve taxa, including trigoniids, ostreids, pectinids, and Pleuromya sp., as well as high-spired gastropods and rare belemnoids. Bivalve fossils are typically broken fragments and articulated valves in multiple orientations, but with the majority subparallel to bedding. Other fossils are commonly found singly in the matrix, including Pleuromya sp., trigoniids, and other bivalves, as well as belemnoids and ammonoids (Troitsaia). Several taxa of large, inflated, and high-spired gastropods are found here as well. The articulated nature of many of the shells implies a rapid sedimentation rate. Most of the fossils found in the coquinas are robust, thick-shelled, shallow-marine forms that characterize the sublittoral region and that have been abraded due to high-energy post-mortem processes. The grading of shells and the distinct lateral continuity of the coquina unit suggest that these beds are 93 likely storm deposits. This environmental interpretation is in harmony with sedimentary structures, which also indicate shallow submarine deposition. 3-4 BIOSTRATIGRAPHY The Early Aalenian age of the strata (Haggart et al., 2004) is suggested from the presence of the ammonite Troitsaia westermanni Poulton & Tipper at GSC Loc. C-404725 and C-404726 (Poulton and Tipper, 1991; Plate 3-la-f). In addition to the ammonite taxa, the fossil localities also contain poorly preserved moulds of the bivalves Myophorella sp., Vaugonia(l) sp. cf. V.(?) yukonensis Poulton, Coelastarteil), Isognomon(1), Grammatodon(T), and Lima(T), as well as a variety of unidentified gastropods. Based on the occurrence of T. westermanni, the strata are correlated with the Troitsaia westermanni Assemblage Zone of the Canadian Cordillera. 3-5 U-PB GEOCHRONOLOGY U-Pb dating of zircon from pink, massive, unwelded crystal-lithic lapilli tuff sampled from the study section (Fig. 3-2) was conducted at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) in the Department of Earth and Ocean Sciences, The University of British Columbia. Mineral separation and U-Pb dating techniques are detailed in Friedman et al. (2001). U-Pb data are listed in Table 3-2 and are plotted on a standard concordia diagram in Figure 3-4 (at the 2o confidence level). A modest quantity of good quality zircon was separated from an approximately 20 kg sample of tuff. Zircons are clear, colorless to pale pink prisms, many of which were broken; some appear to have been slightly resorbed. Unbroken grains have aspect ratios of 2-3. No evidence of cores was observed during sample selection in ethanol under a binocular microscope. The coarsest available grains (n ~ 40) were selected and air abraded following the methods of Krogh (1982). Due to the limited amount of material available, the selected grains were abraded only lightly, just to remove facets. These grains were then split on the basis of size into four fractions of approximately equal mass (6-9 each; Table 3-2). Of the four prepared fractions, only three yielded U-Pb results. These indicate a restricted range of U concentrations (137-162 ppm) and model Th/U ratios (0.51-0.59). U-Pb age results all intersect concordia; the two coarser fractions yielded slightly older, overlapping results. A n assigned age of 176.5 ± 0.6 Ma for the crystallization of primary igneous zircon in this tuff is based on the weighted 2 0 6 P b / 2 3 8 U age of fractions B and C. We interpret the younger 2 0 6 P b / 2 3 8 U age of fraction D to be indicative of minor Pb loss. 94 Plate 3-1. a) Oblique lateral view, latex mould, septate fragment, figured specimen G S C 124088 from G S C locality C-404726. b) Ventral view, same latex mould as in 3-1 a. c) Lateral view, latex mould, figured specimen GSC 124089 from GSC locality C-404725. d) Lateral view, latex mould, figured specimen GSC 124090 from G S C locality C-404725. e) Ventral view, same latex mould as in 3-ld. f) Lateral view, latex mould, reverse side of specimen shown in 3-ld and 3-le. See Appendix D for fossil locality information. Table 3-2. U-Pb analytical data for rhyolitic crystal-lithic lapilli tuff N E of Jumble Mountain. Fraction Wt (ug) U 2 (ppm) Pb*3 (ppm) 2 0 6 p b 4 Pb5 (pg) 2 0 8 Pb 6 Isotopic Ratios (lo, %)7 Apparent ages (2a, Ma) 7 2 0 4 p | j (%) 2 0 6 Pb/ 2 3 8 U 2 0 7 Pb/ 2 3 5 U 2 0 7 p b / 2 0 6 p b 2 0 6 p b / 2 3 8 ) J 2 0 7 Pb/ 2 3 5 U 2 0 7 p b / 2 0 6 p b HFBM02- 1405-1: 176.5 ± 0.6 Ma; map sheet 93D/15; U T M 664895E, 5872855N B, 6 9 137 4.0 960 2.2 15.1 0.02777(0.19) 0.1906(0.97) 0.04978 (0.92) 176.6 (0.7) 177.1 (3.2) 185 (42/43) C, 11 6 163 4.8 254 7.1 15.0 0.02773 (0.31) 0.1927(2.2) 0.05040 (2.1) 176.3(1.1) 179.0 (7.2) 214(93/98) D, 17 6 162 4.7 745 2.2 14.3 0.02722(0.38) 0.1875 (1.3) 0.04996(1.2) 173.1 (1.3) 147.5 (5.2) 193 (57/59) 'All zircon grains selected for analysis were air abraded prior to dissolution. Capital letter designation is fraction identifier, also shown on concordia plot (Fig. X), followed by the number of grains analyzed. Analyzed zircon grains are clear, very pale pink, euhedral to slightly resorbed prisms. Unbroken grains have aspect ratios of 2-3. There were no cores detected during grain selection under a binocular microscope in ethanol. 2 233 235 U blank correction of 1 pg ± 20%; U fractionation corrections were measured for each run with a double " J U - U spike. 3Radiogenic Pb. 4Measured ratio corrected for spike and Pb fractionation of 0.0037/amu ± 20% (Daly collector) which was determined by repeated analysis of NBS Pb 981 standard throughout the course of this study. 5Total common Pb in analysis based on blank isotopic composition. 6Radiogenic Pb. 7Blank and common Pb corrected; Pb procedural blanks were about 2 pg; <1 pg (U). Common Pb concentrations are based on Stacey-Kramers model Pb (Stacey and Kramers, 1975) at the interpreted age of the rock or the 2 0 7 Pb/ 2 0 6 Pb age of the rock. as HFBM02-1405-1 0 . 1 7 0 . 1 9 0 . 2 1 Figure 3 - 4 . Concordia plot for geochronology sample of rhyolitic crystal-lithic lapilli tuff from E N E Jumble Mountain section (approximately 4 km S of Ramsey Peak), sample HFBM02-1405-1. 9 7 3-6 DISCUSSION The endemic genus Troitsaia was established by Poulton and Tipper (1991) for characteristic ammonite taxa found at a number of localities in British Columbia. Since that time, examples of the genus have been identified by one of us (TPP) in fourteen fossil collections from British Columbia, in Whitesail Lake (NTS 93E), Smithers (93L), Spatsizi (104H), Hope (92H), and now Bella Coola map-areas. At four of these localities, specimens of Troitsaia are associated with the globally-distributed Aalenian ammonite Tmetoceras scissum (Benecke); at others, they are found with the Aalenian ammonites Tmetoceras kirki Westermann(?), poorly preserved Tmetoceras sp. indet., and Planammatoceras(T). Other associated ammonites - poorly preserved Euhoploceras(T) and Phylloceras(T) - and a variety of other invertebrates found with Troitsaia in British Columbia are not stratigraphically diagnostic. Bivalve faunas associated with Troitsaia and the other Aalenian ammonites contain distinctive elements which are not discussed in detail because they have not yet been described nor their stratigraphic ranges firmly established. However, some of them have been found useful to support local correlations within western British Columbia. Poulton and Tipper (1991) favoured correlation of the Troitsaia westermanni Assemblage Zone of British Columbia with the lowest Aalenian of the European type section (Table. 3-1), based on association with other taxa found in that region. Given its endemic nature, however, the precise stratigraphic level of the Troitsaia westermanni Assemblage Zone within the lower Aalenian of British Columbia has been considered uncertain. Our geochronological dating of volcanic strata immediately adjacent to the Troitsaia-bearing fossiliferous strata have provided a U-Pb age of 176.5 ± 0.6 Ma, suggesting that these fossil collections can be assigned to latest Toarcian (Gradstein et at., 2004), although the uncertainty surrounding the dating of both our sample and the Toarcian/Aalenian boundary of Gradstein et al. (2004) does not preclude an earliest Aalenian age. The radiometric age clearly indicates that the zone of Troitsaia westermanni ranges well down in the lowermost Aalenian, possibly into the uppermost Toarcian. The correlation of the British Columbia Troitsaia westermanni Assemblage Zone with the lowest zone of the Aalenian stage in Europe (Table 3-1), as favoured by Poulton and Tipper (1991) requires elaboration because of the provincial character of the nominal guide fossils in both British Columbia and Europe. The Aalenian has only been widely accepted as an independent stage since the 1960s (see discussion by Westermann, 1979) and in Canada since the early 1980s. It has replaced the Early Bajocian of earlier publications, and what was previously called the Middle Bajocian is now the Early Bajocian. The Aalenian in current usage is the lowest stage of the Middle Jurassic, and its base is the base of the Middle Jurassic. Its base was 98 defined at a Global Boundary Stratotype Section and Point (GSSP) in Spain in 2000 (Cresta et al., 2001), at the base of the Leioceras opalinum Standard Zone. The Opalinum Standard Zone recognizes the stratigraphic range of the ammonite Leioceras opalinum (Reinecke) and related species at the base of the Aalenian beds in Europe. The lower occurrences of Tmetoceras scissum lie within the Opalinum Zone, which also contains Planammatoceras as well as other ammonite species not known in North America (e.g. Cresta, 1996; Henriques et al., 1996). Leioceras has not been firmly identified in western Canada or US, although it is abundant in Arctic Canada. In other areas of the eastern Pacific where the Late Toarcian and Early Aalenian are seen in apparent sequence, Troitsaia has not been recognized. In some areas, a disconformity separates the two stages, e.g. eastern Oregon (Smith and Taylor, 1993) and southern Alaska (Westermann, 1964; Detterman and Westermann, 1993). In others, a disconformity is likely or possible, e.g. Queen Charlotte Islands (Poulton et al., 1991; Jakobs, 1997) and Argentina and Chile (von Hillebrandt and Westermann, 1985; Riccardi et al., 1993). In these areas, Bredyia manflasensis Westermann is amongst the lowest of the Aalenian ammonites identified, and it probably represents a higher than basal level in the Aalenian (Poulton and Tipper, 1991). Thus, the Troitsai westermanni Zone may has been considered to represent a basal Aalenian interval unique to parts of western British Columbia, that is absent by disconformity in other areas or is so far unrecognized within poorly fossiliferous beds. Tmetoceras scissum is found commonly in both Europe and western Canada, ranging through much of the Aalenian stage, with an interval in the lower part of its range distinguished by the presence of Leioceras opalinum in Europe. Like the T. westermanni Assemblage Zone of western British Columbia, the L . opalinum Standard Zone lies above strata with Late Toarcian species of Dumortieria and other ammonites, and below strata with Tmetoceras and other Aalenian ammonites. Any error within this biostratigraphic correlation would likely fall within the approximately 1 million year range implied by the Opalinum Zone and the Troitsaia westermanni zones occupying a small part of the 4 million year Aalenian interval bracketed by radiometric dates 171.6 and 175.6 Ma shown on the recent time scale of Gradstein et al. (2004). 3-7 ACKNOWLEDGMENTS This study was funded by a Geological Survey of Canada Targeted Geoscience Initiative (TGI), the Rocks to Riches Program, which is administered through the British Columbia & Yukon Chamber of Mines, as well as four mining companies (Barrick Gold Corp., Heritage Exploration Inc., Kenrich-Eskay Mining Corp., and Placer Dome Inc.). We acknowledge 99 logistical support of Danny Hodson and Richard LaPointe of Rainbow West and West Coast Helicopters, respectively, Bella Coola, British Columbia. Lori Snyder lent her time and expert eyes on the outcrop and provided thoughtful ideas. Casey Bowe provided excellent assistance in the field. 3-8 REFERENCES Arkell, W.J., Furnish, W . M . , Kummel, B., Miller, A .K. , Moore, R . C , Schindewolf, O.H. , Sylvester-Bradley, P.C., Wright, C.W., 1957. Treatise on Invertebrate Paleontology, Part L, Mollusca 4, Cephalopoda, Ammonoidea. 490 pages. Cresta, S., 1996. Aalenian ammonite biostratigraphy in northern Apennines (Italy). GeoResearch Forum, vols. 1/2, pp. 135-138. Cresta, S., Goy, A. , Ureta, S., Arias, C , Barron, E . , Bernad, J., Canales, M . L . , Garcia-Joral, F., Garcia-Romero, E . , Gialanella, P.R., Gomez, J.J., Gonzalez, J.A., Herrero, C , Matinez, G. , Osete, M . L . , Perilli, N. , Villalain, J.J., 2001. The Global Boundary Stratotype Section and Point (GSSP) of the Toarcian-Aalenian boundary (Lower-Middle Jurassic). Episodes, vol. 24, no. 3, pp. 166-175. Detterman, R.L. , Westermann, G.E.G. , 1993. Southern Alaska. In: Westermann, G.E .G. (Ed.), The Jurassic of the Circum-Pacific, Cambridge University Press, pp. 49-57. Friedman, R .M. , Diakow, L.J . , Lane, R.A., Mortensen, J.K., 2001. U-Pb age constraints on latest Cretaceous magmatism and associated mineralization in the Fawnie Range, Nechako Plateau, central British Columbia. Canadian Journal of Earth Sciences, vol. 38, pp. 619-637. Gordee, S.M., Mahoney, J.B., Haggart, J.W., Mortensen, J.K., Friedman, R . M . , in prep. Tectonic setting and depositional environment of Lower-Middle Jurassic Hazelton Group, west-central British Columbia: constraints from volcanostratigraphy, U-Pb geochronology, and lithogeochemistry. Gradstein, F . M . , Ogg, J.G., Smith, A . G . (Eds.), 2004. A geologic time scale 2004. Cambridge University Press, 589 pages. Haggart, J.W., Diakow, L.J . , Mahoney, J.B., Struik, L . C . , Woodsworth, G.J., Gordee, S.M., 2004. Geology, Bella Coola area (parts of93D/01, D/02, D/06, D/07, D/08, D/09, D10, D/ll, D/15 andD/16), British Columbia. Geological Survey of Canada, Open File 4639 and British Columbia Geological Survey and Development Branch, Open File 2004-13, 1 sheet, scale: 1:150 000. Henriques, M . H . , Linares, A. , Sandoval, J., Ureta, M.S., 1996. The Aalenian in the Iberia (Betic, Lusitanian and Iberian basins). GeoResearch Forum, vols. 1/2, pp. 139-150. von Hillebrandt, A. , Westermann, G.E.G. , 1985. Aalenian (Jurassic) ammonite faunas and zones of the southern Andes. Zitteliana, vol. 12, pp. 3-55. Jakobs, G.K. 1997. Toarcian (Early Jurassic) ammonoids from western North America. Geological Survey of Canada, Bulletin 428, 137 pages. Krogh, T .E . 1982. Improved accuracy of U-Pb zircon ages by the creation of more concordant systems using an air abrasion technique. Geochimica et Cosmochimica Acta, vol. 46, pp. 637-649. Marsden, H. , Thorkelson, D.J., 1992. Geology of the Hazelton volcanic belt in British Columbia: implications for the Early to Middle Jurassic Evolution of Stikinia. Tectonics, vol. 11, pp. 1266-1287. 100 Mortensen, J.K., Gordee, S.M., Mahoney, J.B., Tosdal, R . M . , 2004. Regional studies of Eskay Creek-type and other volcanogenic massive sulphide mineralization in the upper Hazelton Group in Stikinia. In: Geological Fieldwork 2003, British Columbia Ministry of Energy, Mines and Petroleum Resources, Paper 2004-1, pp. 249-262. Poulton, T.P., Tipper, H.W., 1991. Aalenian ammonites and strata of western Canada. Geological Survey of Canada, Bulletin 411,71 pages. Poulton, T.P., Hall, R.L. , Tipper, H.W., Cameron, B.E.B. , Carter, E.S., 1991. Current status of Middle Jurassic biostratigraphy of the Queen Charlotte Islands, British Columbia. Geological Survey of Canada, Paper 90-10, pp. 237-252. Riccardi, A . C . , Gulisano, C.A. , Mojica, J., Palacios, O., Schubert, C , Thomson, M.R.A. , 1993. Western South America and Antarctica. In: G.E.G. Westermann (Ed.), The Jurassic of the Circum-Pacific, Cambridge University Press, pp. 122-161. Smith, P.L., Taylor, D.G. , 1993. Eastern Oregon and adjacent areas. In: G.E.G. Westermann (Ed.), The Jurassic of the Circum-Pacific, Cambridge University Press, pp. 67-77. Stacey, J.S. and Kramers, J.D., 1975. Approximation of terrestrial lead isotope evolution by a two-stage model. Earth and Planetary Science Letters, vol. 26, pp. 207-221. Westermann, G.E .G. , 1964. The ammonite fauna of the Kialagvik Formation at Wide Bay, Alaska Peninsula, Part I. Lower Bajocian (Aalenian). Bulletins of American Paleontology, vol. 47, pp. 325-503. Westermann, G.E.G. , 1979. Troublesome definition of the Lower/Middle Jurassic boundary. Canadian Journal of Earth Sciences, vol. 16, no. 10, pp. 2060-2062. Wheeler, J.O., McFeely, P., 1991. Tectonic assemblage map of the Canadian Cordillera and adjacent parts of the United States of America. Geological Survey of Canada Map 1712A, scale: 1:2 000 000. 101 CHAPTER 4 S U M M A R Y , CONCLUSIONS A N D SUGGESTIONS FOR FUTURE RESEARCH 4-1 SUMMARY AND CONCLUSIONS The main goal of this study was to investigate the volcanic and sedimentary stratigraphy, age, and lithogeochemical characteristics of Hazelton Group exposures in an understudied portion of west-central British Columbia to develop a model for the depositional environment, tectonic setting, and volcanogenic massive sulphide (VMS) mineralisation potential of the upper Hazelton Group in southwest Stikinia. Prior to this study, little detailed work had been completed on the thick and spectacularly exposed volcano-sedimentary successions in the northeast Bella Coola and southeast Whitesail Lake map areas. These strata had only been characterized on a reconnaissance scale, largely due to the difficult access to the areas. Nomenclature from better studied Hazelton Group successions in central and northern Stikinia had been applied to the sequences, carrying along with it genetic connotations about the character and environment of volcanic centres, associated sedimentation, and tectonic setting. Results from this study include a revised, more region-specific characterization of the Hazelton Group stratigraphic sequence in the northeast Bella/southeast Whitesail Lake study area, as well as a more thorough understanding of the depositional environment, age, tectonic setting, and mineralisation potential of the thick volcano-sedimentary accumulations in the region. Additional results include a more thorough understanding of the geologic evolution of this portion of the Canadian Cordillera by means of a revised geologic map of the southeastern Whitesail Lake map area. Two lithologically and temporally distinct members have been defined within Hazelton Group strata in the study area. A lower mafic member consisting of vent-proximal mafic flows, subvolcanic intrusions, and associated intercalated mafic, volcanic-derived epiclastic rocks is bracketed by ca. 181 Ma (Haggart et al., 2004) and ca. 176 Ma U-Pb zircon ages. The lower mafic member is gradationally overlain by an upper felsic member, which is characterized by variable proportions of felsic pyroclastic rocks and associated intercalated felsic, volcanic-derived, sparsely fossiliferous epiclastic rocks, with subordinate felsic and mafic domes/plugs and flows. The base of the upper felsic member is well constrained by a ca. 176 M a U-Pb zircon age. That date, together with ammonoid species collected from the same stratigraphic interval, demonstrates that the range of the ammonoid species extends into the early Aalenian. These data also indicate that a dramatic change in the nature and style of volcanism in southwest Stikinia occurred at the Lower-Middle Jurassic boundary. Detrital zircon U-Pb ages from a unit near the top of the upper felsic member indicate that the top of the member was deposited no earlier than ca. 173 Ma. The age of rocks in the study area corresponds with the age of the Nilkitkwa and Smithers formations in central Stikinia (e.g., Maclntyre et al., 1989) and with the Mount Dilworth 103 and Salmon River formations in northwest Stikinia (e.g., Lewis et al., 2001), although no clear lithologic correlations can (or should) be made with strata in those regions. Volcanic textures, sedimentary structures, and fossils collectively indicate that the rocks were deposited in a shallow marine (subtidal to tidal or deltaic) setting, subject to periodic storm deposits and desiccation. Volcanic rocks of the lower mafic member were probably erupted in part from submarine fissures, with localised fire fountaining. Dominantly pyroclastic units of the upper felsic member were probably sourced from subaerial island volcanoes but were in part deposited in shallow water. Periodic dome collapse also may have generated some ignimbrite units. Some pyroclastic deposits were subsequently reworked to form sandstone, siltstone, and mudstone units, and periodic slumping of steep subaerial or subaqueous flanks of the volcano(es) may have produced coarse-grained, heterolithic mass flow deposits. Volcanic and intrusive Hazelton Group rocks in the study area exhibit lithogeochemical characteristics consistent with their development in a primitive, subduction-related arc to back-arc region. Normal subduction-related lithogeochemical signatures are common throughout many portions of the Hazelton arc system, and they contrast with lithogeochemical signatures of Middle Jurassic magmatic arc rocks of the upper Hazelton Group in northwest Stikinia, where lithogeochemical affinities in the Eskay Creek V M S district are more consistent with the involvement of more primitive, rift-related(?) magmas (Barrett and Sherlock, 1996). Vent-proximal volcanic and associated submarine sedimentary rocks of the Middle Jurassic upper Hazelton Group rocks in southern and northern Stikinia were probably derived from the western Hazelton arc and deposited in the back-arc region of the western portion of the Hazelton Trough. Although rocks in the study area are coeval with strata hosting the Eskay Creek deposit, the proposed "Eskay Rift" (e.g., Alldrick et al, 2004) is probably spatially restricted to the Iskut River region. However, the broad back-arc regions associated with Hazleton arc magmatism may include more rift-like structures akin to the "Eskay Rift", and these structures are not necessarily exclusive to the latest stages of the large and protracted arc system. Additionally, exploration strategies should not be limited to Eskay Creek-type V M S deposits, as specific features of rocks indicative of more typical Kuroko-type V M S mineralisation have been observed in many parts of the study area. 4-2 SUGGESTIONS FOR FUTURE RESEARCH Most areas in central and southern Stikinia that are underlain by Hazelton Group strata have been broadly characterized, mostly for the purposes of tectonic reconstructions. Volcano-sedimentary successions throughout these regions remain understudied in terms of their physical 104 volcanology and sedimentology and/or intrusive and lithogeochemical characteristics. Nor have the age relationships within these successions been studied in sufficient detail to permit the age(s) or duration of specific magmatic or depositional events to be assessed. Thorough investigations of understudied regions would provide an excellent contribution to the understanding of the overall character of the Hazelton arc sequence. Also, ancient arc sequences provide important contributions to the understanding of physical, chemical and temporal processes within modern arc sequences, and the widespread and protracted Hazelton arc sequence would make an ideal ancient analogue for modern-ancient analogue studies (e.g., Marsden and Thorkelson, 1992). On a smaller scale, results of this study provide a framework on which future research of the Hazelton Group in southwest Stikinia can be based. Numerous aspects of the physical volcanological interpretations of rocks in the region could potentially be expanded. Further development of the idea of fire fountaining from submarine fissures as eruptive centres for rocks of the lower mafic member via further mapping within the sequence (within or outside of the study area) would make an interesting study and would contribute to the understanding of this thick package of volcanic strata. Also, stable isotopic, mineralogical and lithogeochemical studies of the abundant subvolcanic intrusions and semiconformable altered zones within the lower mafic member may elucidate some aspects of the hydrothermal systems that operated during the voluminous volcanism in the region. Lateral lithofacies mapping should be expanded to the north (and to some degree, the south; however, the reader should be cautioned that the access to the very rugged Tsaydaychuz Peak and Jumble Mountain areas is difficult). In the upper felsic member, such work would contribute to the understanding of the location of eruptive centres to the voluminous felsic pyroclastic rocks, and would possibly assist in delineating bounding structures to the proposed caldera structure(s) that locally excessively thick ignimbrite units may have been deposited within. Petrographic and lithogeochemical studies of Early and Middle Jurassic plutons in the region (e.g., Haggart et al., 2004; J.K. Mortensen and J.B. Mahoney, unpublished data) may provide interesting insight to the deeper roots of local Hazelton arc volcanoes. Although the potential for V M S mineralisation is not necessarily limited to Hazelton Group rocks of early Middle Jurassic age, tectonic and hydrothermal processes favourable for the formation of V M S deposits were demonstrably operating in northwest Stikinia during that time period. It is unlikely that those processes were unique to the spatially very restricted Eskay Creek V M S district of northwestern Stikinia. Volcanic sequences stratigraphically lower in the Hazelton Group should also be considered as favourable exploration targets, since the actively extending tectonic regime common to many V M S districts is not necessarily restricted to the 105 latest stages of back-arc extension. Rocks in the study area were deposited in an actively extending environment ideal for the formation of V M S deposits; however, for the most part they appear to have been deposited in too shallow a marine setting to permit V M S formation. A thorough documentation of the depositional environment and lateral facies characteristics of the Hazelton Group volcano-sedimentary successions in the study area may lead to the recognition of volcanic and sedimentary facies more characteristic of deeper water and subsequently more quiescent deposition and hence better potential for V M S deposit formation and preservation. Potential also exists for epithermal mineralisation in shallow marine and subaerially deposited sections of the Hazelton Group, and the possibility of porphyry-style mineralisation in subvolcanic intrusions cannot be precluded. 4-3 REFERENCES Alldrick, D.J., Stewart, M.L., Nelson, J.L., Simpson, K.A., 2004. Tracking the Eskay Rift through northern British Columbia - geology and mineral occurrences of the upper Iskut River area. In: Geological Fieldwork 2003, British Columbia Ministry of Energy, Mines and Petroleum Resources, Paper 2004-1, pp. 1-18. Barrett, T.J., Sherlock, R.L., 1996. Geology, lithogeochemistry and volcanic setting of the Eskay Creek Au-Ag-Cu-Zn deposit, northwestern British Columbia. Exploration and Mining Geology, vol. 5, pp. 339-368. Haggart, J.W., Diakow, L.J., Mahoney, J.B., Struik, L.C., Woodsworth, G.J., Gordee, S.M., 2004. Geology, Bella Coola area (parts of93D/01, 93D/02, 93D/06, 93D/07, 93D/08, 93D/09, 93D/10, 93D/1I, 93D/15, and93D/16), British Columbia. Geological Survey of Canada, Open File 4639, British Columbia Ministry of Energy and Mines, Open File 2004-13, scale: 1:150 000. Lewis, P.D., Macdonald, A.J., Bartsch, R.D., 2001. Hazelton Group/Bowser Lake Group stratigraphy in the Iskut River area: progress and problems. In: Lewis, P.D., Toma, A., Tosdal, R.M. (Eds!), Metallogenesis of the Iskut River area, northwestern British Columbia, Mineral Deposit Research Unit, Special Publication no. 1. Maclntyre, D.G., Desjardins, P., Tercier, P., 1989. Jurassic stratigraphic relationships in the Babine and Telkwa ranges (93L/10, 11, 14, 15). In: Geological Fieldwork 1988, British Columbia Ministry of Mines, Energy and Petroleum Resources, Paper 1989-1, pp. 195-208. Marsden, H., Thorkelson, D.J., 1992. Geology of the Hazelton volcanic belt in British Columbia: implications for the Early to Middle Jurassic evolution of Stikinia. Tectonics, vol. 11, no. 6, pp. 1266-1287. 106 APPENDIX A POST HAZELTON GROUP MAGMATISM LN THE STUDY AREA 107 A-l POST HAZELTON GROUP MAGMATISM IN THE STUDY AREA Despite its position along eastern margin of the Coast Plutonic Complex, intrusive rock units are relatively rare in the study area. Immediately west of Pondosy Pass and South Creek plutonic rocks of Late Jurassic to Eocene age of the Coast Plutonic Complex locally intrude Hazelton Group rocks, and comprise up to half of rock exposures in the western half of the Tesla Lake map area (see geological map insert). Younger rocks that cut Hazelton Group strata in the study area are limited to small, equigranular to aphanitic stocks, dykes and sills. The age of these units has either been determined by Ar-Ar dating during the course of this study or is inferred on the basis of similarities with regionally recognized units of known age. These units are shown on Fig. 2-7, and include Late Jurassic(?) rhyolite (and dacite) domes (LJr), Early Cretaceous quartz diorite stocks and dykes (EKqd), Eocene quartz-feldspar porphyry (QFP) rhyolite stocks and dykes, and undivided and Miocene to Pliocene mafic dykes, dyke swarms and sills. These units have not been described in the main body of the thesis and have been omitted from the lithogeochemical study. Lithogeochemical analyses were obtained from samples of these units to compare and contrast their signatures with other regional magmatic suites that have been geochemically characterized. Lithogeochemical data for these units are presented in Tables A - l and A-2. Lithogeochemical sample locations and lithologic information are presented in Appendix E. A-l-1 Felsic domes (LJr) Several felsic domes intrude the volcano-sedimentary sequences that are physically and chemically distinct from other Hazelton Group-related felsic domes in the study area (e.g., mJHrd). These domes are spatially restricted to the southern half of the study area. They cut mafic lava flows and intrusions of the lower mafic member in the Butler Peak region, and similar bodies cut felsic volcano-sedimentary strata of the upper felsic member at and south of Ramsey Peak (Fig. 2-7). The domes are white to light pink in colour, aphanitic to finely quartz-phyric, silicified, flow banded to locally unstructured rhyolite and dacite. In the Ramsey Peak area, several domes form complexly interfingering and ambiguous cross-cutting relationships with unit EKqd. The domes may represent the shallow level equivalents of a Late Jurassic suite of granitic bodies exposed west of South Creek (e.g., Mahoney et al., 2005; see geological insert map) and to the south in the Bella Coola map area (e.g., Gordee et al., in prep.). 1 0 8 Table A-l . Major element lithogeochemical data1 for samples in the study area that represent post-Hazelton Group magmatism, and/or which have been omitted from the study. Field no.* SiOt A12Q3 FeOlT) Fe203 FeO CaO MgO Na,0 K 2Q Cr 2 Q 3 TIP, MnO PjOs SrO BaO LOI Total FcaQa/PcO Felsic intrusions (undivided and divided Ur) 118 SMG 03 65.12 16.38 3.44 1.64 1.80 3.17 1.36 4.69 2.15 <0.01 0.56 0.04 0.21 0.09 0.14 2.18 99.51 0.91 126 SMG 03 66.95 14.21 6.46 2.21 4.25 0.82 2.72 5.07 0.10 <0.01 0.86 0.14 0.26 0.02 0.01 1.87 99.49 0.52 124 SMG 04 70.20 15.13 1.78 0.82 0.96 1.70 0.64 4.17 3.88 <0.01 0.32 0.03 0.09 0.04 0.14 1.69 99.81 0.85 Diorite and quartz diorite stocks and dykes (EKqd) 115 SMG 03 53.29 17.37 8.08 3.09 4.99 6.88 4.36 3.30 1.72 <0.01 1.10 0.12 0.29 0.05 0.07 2.59 99.23 0.62 116 SMG 03 50.50 15.22 11.81 5.38 6.43 7.24 3.21 3.38 0.26 <0.01 1.13 0.20 0.14 0.03 ' 0.03 5.21 98.37 0.84 22ASMG04 45.25 16.62 10.85 4.87 5.98 9.75 5.64 3.43 0.59 0.02 1.76 0.23 0.50 0.05 0.03 5.01 99.72 0.81 Mafic dykes (MPC and undivided) 07 SMG 03 52.48' 16.70 9.21 3.34 5.87 7.99 4.36 3.16 1.38 <0.01 1.40 0.14 0.39 0.07 0.07 1.73 99.09 0.57 11 SMG 03 45.56 16.18 9.28 3.08 6.20 6.73 6.29 2.90 2.49 <0.01 0.66 0.37 0.08 0.04 0.20 7.87 98.67 0.50 19 SMG 03 47.68 15.56 11.09 4.86 6.23 6.25 3.39 4.87 ' 1.26 <0.01 1.17 0.59 0.20 0.02 0.06 6.87 99.00 0.78 28 SMG 03 48.95 18.03 8.28 3.01 5.27 5.69 4.38 4.22 0.86 <0.01 1.17 0.08 0.30 0.05 0.05 6.62 98.68 0.57 41 SMG 03 51.49 15.79 9.95 5.19 4.76 3.98 4.02 4.44 2.24 <0.01 2.06 0.15 0.65 0.04 0.05 4.02 98.88 1.09 46 SMG 03 45.12 17.26 10.53 4.35 6.18 7.46 7.41 3.17 0.98 <0.01 0.80 0.39 0.11 0.02 0.03 5.61 98.88 0.70 68 SMG 03 47.53 16.53 10.97 3.82 7.15 8.45 7.55 2.81 0.95 0.03 0.82 0.18 0.15 0.07 0.03 3.32 99.40 0.53 73 SMG 03 50.34 17.14 8.69 4.19 4.50 3.49 5.01 4.83 2.15 <0.01 1.30 0.15 0.41 0.05 0.08 4.72 98.36 0.93 83 SMG 03 51.92 14.90 14.01 7.24 6.77 7.12 4.18 2.80 0.54 <0.01 1.26 0.28 0.14 0.03 0.04 2.49 99.71 1.07 95 SMG 03 45.06 16.30 10.40 4.53 5.87 8.93 6.89 2.72 0.75 0.02 1.57 0.18 0.41 0.03 0.04 4.89 98.19 0.77 108 SMG 03 58.51 18.01 5.52 2.25 3.27 3.27 2.26 5.61 2.78 <0.01 0.94 0.09 0.26 0.03 0.12 1.92 99.31 0.69 Pyrophyllite (undivided)' 18a SMG 03 11.19 70.15 0.18 _ 0.21 0.25 0.14 0.06 2.28 0.03 <0.01 <0.01 1.23 0.67 0.12 13.25 99.56 18b SMG 03 17.94 65.24 • 1.52 0.98 0.54 0.11 0.13 0.06 0.73 0.04 <0.01 <0.01 0.72 0.66 0.07 12.55 99.78 1.81 Sample omitted from study" 94 SMG 04 75.25 13.06 1.29 1.03 0.26 1.74 0.13 3.16 3.97 <0.01 0.26 0.03 0.03 0.01 0.12 0.73 99.77 3.96 1 All major element analyses are reported as weight % oxides and were completed using X-Ray Fluorescence Spectroscopy (XRF). 2See Appendix E for sample location and specific lithologic information. Table A-2. Trace and rare earth element (REE) lithogeochemical data1 for samples in the study area that represent post-Hazelton Group magmatism, and/or which have been omitted from the study. Field no.2 Ag Ba Ce Co Cr Cs Cu F> Eu Ga Gd Hf Ho La Lu Mo Nb Nd Felsic intrusions (undivided and divided LJr) 118 SMG 03 <1 1270.0 37.4 10.8 10 0.4 <5 1.7 0.8 0.9 22 2.8 5 0.3 17.8 0.1 2 6 18.4 126 SMG 03 <1 46.4 30.2 6.6 <10 0.1 <5 6.2 4.5 1.3 18 5.3 9 1.4 13.8 0.8 <2 3 17.8 124 SMG 04 <1 1205.0 49.6 3.7 10 1.8 23 1.2 0.7 0.7 22 2.7 7 0.2 25.6 0.1 <2 7 19.6 Diorite and quartz diorite stocks and dykes (EKqd) 115 SMG 03 <1 644.0 40.0 212 60 0.8 46 4.7 2.8 1.4 19 4.9 5 1.0 18.0 . 0.4 <2 7 21.5 116 SMG 03 <I 182.0 12.6 33.0 <10 0.4 25 4.4 2.9 1.0 20 3.3 2 1.0 5.6 0.5 <2 1 8.7 22A SMG 04 <1 252.0 38.2 40.8 200 0.9 53 6.1 3.7 2.0 18 6.5 4 1.3 13.6 0.5 2 7 24.3 afic dykes (MPC and undivided) 07 SMG 03 <1 629.0 46.5 28.0 70 0.9 48 5.3 3.1 1.8 20 5.4 5 1.1 22.0 0.5 <2 8 27.4 11 SMG 03 <1 2000.0 8.9 36.4 110 8.1 51 2.4 1.6 0.7 15 2.0 1 0.5 4.1 0.3 <2 1 5.9 19 SMG 03 <1 500.0 15.8 31.9 20 0.3 46 3.9 2.6 0.9 20 3.2 3 0.9 6.7 0.4 <2 2 10.6 28 SMG 03 <l 377.0 29.7 24.2 50 14.1 46 3.9 2.3 1.2 19 3.9 4 0.7 12.8 0.4 2 5 17.2 41 SMG 03 <1 365.0 55.1 20.6 20 1.4 19 7.1 4.3 2.2 19 7.5 6 1.5 23.4 0.6 <2 9 32.7 46 SMG 03 1 216.0 9.4 37.4 80 6.3 112 2.3 1.5 0.7 21 2.0 1 0.5 4.5 0.2 <2 1 6.0 68 SMG 03 <1 259.0 13.0 44.5 370 2.9 61 2.7 1.6 0.8 18 2.4 1 0.6 6.0 0.3 <2 1 8.1 73 SMG 03 <1 751.0 44.3 26.5 70 0.5 42 5.0 3.0 1.8 20 5.3 5 1.1 19.6 0.5 <2 8 24.7 83 SMG 03 <1 199.0 11.8 38.2 10 0.4 <5 3.8 2.6 0.9 20 3.0 2 0.8 5.2 0.5 2 1 8.2 95 SMG 03 <1 227.0 32.8 39.8 240 0.6 45 5.2 3.2 1.7 18 5.3 4 1.1 13.2 0.5 2 6 20.6 108 SMG 03 <1 1175.0 50.2 12.4 30 0.2 14 5.6 3.5 1.9 18 5.7 9 1.2 22.6 0.6 <2 10 26.0 r^ophyllite (undivided)* 18a SMG 03 <1 234.0 34.6 <0.5 280 1.0 <5 1.9 0.8 0.8 75 3.1 5 0.3 17.9 0.2 4 3 12.3 18b SMG 03 1 232.0 72.2 7.3 270 0.2 26 0.7 0.4 0.6 72 2.7 4 0.1 31.5 0.1 146 3 32.4 imples omitted from study4 94 SMG 04 <1 976.0 31.3 1.2 10 0.5 6 2.0 1.4 0.4 12 2.1 8 0.4 16.2 0.3 <2 4 11.5 1 All trace and rare earth element analyses are reported in parts per million (ppm) and were completed using inductively coupled plasma mass spectrometry (ICP-MS). 2See Appendix E for sample location information. Table A-2 (continued). Trace and rare earth element (REE) lithogeochemical data1 for samples in the study area that represent post-Hazelton Group magmatism, and/or which have been omitted from the study. Pb Rb Sm Sn Felsic intrusions (undivided and divided Ur) 118 SMG 03 9 21 4.4 32.4 3.5 1 882.0 <0.5 126 SMG 03 <5 8 3.8 1.3 4.8 1 119.0 <0.5 124 SMG 04 <5 31 5.1 133.5 3.2 2 373.0 0.6 Diorite and quartz diorite stocks and dykes (EKqd) 115 SMG 03 116 SMG 03 22A SMG 04 47 9 96 12 10 4.9 1.7 4.8 23.7 5.3 7.3 4.8 2.7 6.2 Mafic dykes (MPC and undivided) Pyrophyllite (undivided) 18a SMG 03 <5 18b SMG 03 8 Samples omitted from study 94 SMG 04 <5 10 46 3.5 8.8 29.2 10.9 2.1 3.2 473.0 290.0 410.0 1 6730.0 I 6600.0 0.5 <0.5 <0.5 <0.5 <0.5 0.3 0.9 0.3 0.7 0.6 1.1 07 SMG 03 29 5 6.1 22.9 6.2 1 559.0 0.5 1.0 11 SMG 03 53 42 1.2 57.7 1.8 1 325.0 <0.5 0.4 19 SMG 03 12 32 2.2 20.4 3.0 1 113.0 <0.5 0.6 28 SMG 03 25 7 3.8 23.4 4.0 1 358.0 <0.5 0.6 41 SMG 03 11 12 7.3 32.9 7.8 2 329.0 0.6 1.2 46 SMG 03 36 171 1.2 25.8 1.7 1 116.5 <0.5 0.3 68 SMG 03 99 <5 1.7 18.0 2.3 1 771.0 <0.5 0.4 73 SMG 03 29 10 5.5 37.4 5.6 1 421.0 0.5 0.8 83 SMG 03 8 12 1.6 8.9 2.6 1 241.0 <0.5 0.5 95 SMG 03 133 10 4.4 16.8 5.2 2 370.0 <0.5 0.9 108 SMG 03 21 10 6.1 23.6 5.7 2 258.0 0.7 0.9 0.4 0.2 3 2 15 3 I <l <0.5 <0.5 0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 0.1 8.7 0.7 158.0 0.7 1.2 26 <l 40.2 4.6 74 320.0 0.1 4.4 27 3 6.2 0.5 62 259.0 0.4 1.4 201 <1 27.3 2.6 90 210.0 0.5 0.5 480 <l 26.5 2.8 156 74.4 0.5 <0.5 233 1 34.7 3.2 93 191.0 0.5 1.0 263 1 30.3 2.8 93 208.0 0.2 <0.5 284 <1 14.9 1.5 379 44.2 0.4 <0.5 452 1 25.0 2.5 926 92.0 0.3 0.8 240 <1 21.8 2.2 81 134.0 0.6 1.1 230 <1 41.8 3.8 106 224.0 0.2 <0.5 329 <1 13.8 1.4 267 38.2 0.2 <0.5 344 <1 15.6 1.5 87 47.1 0.5 0.7 216 <1 29.7 2.7 97 204.0 0.4 <0.5 467 <1 24.5 2.5 193 81.1 0.5 <0.5 238 <1 31.0 2.9 93 172.5 0.5 1.0 84 1 32.7 3.3 72 414.0 0.1 0.6 651 3 6.4 0.9 30 131.0 <0.1 0.5 1375 5 2.5 0.3 26 136.5 0.2 1.8 17 2 13.0 1.6 " 26 327.0 1 All trace and rare earth element analyses are reported in parts per million (ppm) and were completed using inductively coupled plasma mass spectrometry (ICP-MS). 2Sce Appendix E for sample location information. A-l-2 Dioritic stocks (EKqd) The upper Ramsey Peak section is cut by a small pyroxene-hornblende quartz diorite stock, which is texturally and compositionally similar to other small dioritic stocks and dykes documented in the western Tesla Mountain region. The bodies consist of fresh, medium to coarse grained, equigranular, biotite-hornblende diorite to quartz diorite with a distinct salt and pepper texture. Ar-Ar (hornblende) dating of the stock at Ramsey Peak indicates a cooling age of 136.4 ± 1.5 Ma, which is temporally consistent with a ca. 139-132 Ma intrusive suite documented immediately to the south in the Bella Coola area (T.D. Ullrich, unpublished data; Haggart et al., 2004; Table B-1 and Fig. B-1). A-l-3 Quartz-feldspar porphyry intrusions and related dykes (Erp) Quartz-feldspar porphyry (QFP) intrusions and deeper level (?) granitic equivalents are abundant within the southeast portion of the Tesla Lake map area (Fig. 2-7). The large body east of Mount Preston (Erp?) and the smaller bodies east of Tesla Lake (all Eg?) were mapped by Woodsworth (1980), and are inferred to exist based on air photo examination. The body immediately NE of Mount Preston comprises dark grey, massive QFP rhyolite, and includes four Cu-Au MINTTLE occurrences along its contact margins with the upper felsic member of the Hazelton Group (see geological insert map). That body is assumed to represent a shallower level equivalent to other, more equigranular granitic bodies to the west mapped by Mahoney et al. (2005). A biotite-quartz-porphyry dyke that cuts Hazelton Group strata in the southeast Mount Preston area and is presumed to be associated with the QFP bodies yields an Ar-Ar biotite cooling age of 51.87 ± 0.8 Ma (T.D. Ullrich, unpublished data; Table B-1 and Fig. B-2). A-l-4 Mafic dykes and dyke swarms (undivided and MPC) Mafic dykes and dyke swarms are abundant within the study area. The dykes intrude along regionally well developed orthogonal sets of north-south and east-west trending fractures within Hazelton Group strata in the area. All dykes are mafic, ranging in composition from basalt to andesite, and three lithologically distinct groups of dykes can be broken out (no age relationship implied). One group of dykes consists of dark grey-green, amygdaloidal (chlorite ± epidote/quartz), aphanitic basalt. A second very distinct set of army green dykes that are restricted to the Ramsey Peak area consist of plagioclase-porphyritic basaltic-andesite to andesite. Plagioclase occurs in acicular laths up to 1 cm in length that are commonly traychytic parallel to the dyke margins. Based on cross-cutting relationships, in the southern portion of the study area the distinctly plagioclase-porphyritic dykes are apparently the youngest phase. However, in the 112 central and northern portions of the study area, the dykes are cut by a younger set of dykes, which consist of dark grey, aphanitic to very finely plagioclase-phyric basalt locally with distinctly flow-banded margins. One north-south-trending swarm of these dykes cuts the ridge southeast of Mount Preston. At least one of the dykes yields abundant peridotite xenoliths, and the dykes may represent feeders to the Miocene-Pliocene Chilcotin Group lavas east and northeast of the study area (Fig. 2-6). A-2 R E F E R E N C E S Gordee, S.M., Mahoney, J.B., Friedman, R .M. , Haggart, J.W., Diakow, L.J . , Woodsworth, G.J., Villeneuve, M . , in prep. Magmatic evolution of the eastern Coast Plutonic Complex, Bella Coola Region, west-central British Columbia. Haggart, J.W., Diakow, L.J . , Mahoney, J.B., Struik, L . C . , Woodsworth, G.J., Gordee, S.M., 2004. Geology, Bella Coola area (parts of93D/01, 93D/02, 93D/06, 93D/07, 93D/08, 93D/09, 93D/10, 93D/11, 93D/15, and 93D/16), British Columbia. Geological Survey of Canada, Open File 4639, British Columbia Ministry of Energy and Mines, Open File 2004-13, scale: 1:150 000. Mahoney, J.B., Hooper, R.L. , Gordee, S.M., Haggart, J.W., Mortensen, J.K., 2005. Initial evaluation of bedrock geology and economic mineralization potential of the southern Whitesail Lake map area (093E/02 and /03), west-central British Columbia. In: Geological Fieldwork 2004, British Columbia Ministry of Energy, Mines and Petroleum Resources, Paper 2005-1, pp. 291-300. 113 APPENDIX B AR-AR GEOCHRONOLOGY B-1 SAMPLING 4 0 A r / 3 9 A r geochronology was used to constrain the age and/or cooling history of rock units that cross-cut Hazelton Group strata in the study area. Only two units in the study area contained the appropriate mineralogy for the study - a pyroxene-hornblende quartz diorite stock in the Ramsey Peak area (EKqd) and a biotite-quartz-porphyry dyke in the south Mount Preston area (Cenozoic rhyolite dyke; Fig. 2-7). Sample locations and isotopic data area shown on Table B-1 and results are shown on Figures B-1 and B-2 for each sample, respectively. B-2 METHODOLOGY Each sample was crushed and sieved to obtain fragments ranging in the size range from 0.3 to 2 mm. A hand magnet was passed over the samples to remove magnetic minerals and metallic crusher fragments/spall. The samples were wash ed in deionized water, rinsed, and then air-dried at room temperature. Mineral separates were hand-picked, wrapped in aluminum foil and stacked in an irradiation capsule with similar-aged samples and neutron flux monitors (Fish Canyon Tuff sanidine; 28.02 Ma (Renne et al., 1998)). The samples were irradiated on May 27 and 28, 2004, at the McMaster Nuclear Reactor in Hamilton, Ontario, for 56 M W H , with a neutron flux of approximately 3 x l 0 1 6 neutrons/cm2. Analyses (n=54) of 18 neutron flux monitor positions produced errors of <0.5% in the calculated J value. The samples were analyzed on July 27 and 28, 2004, at the Noble Gas Laboratory of the Pacific Centre for Isotopic and Geochemical Research (PCIGR) in the Department of Earth and Ocean Sciences at The University of British Columbia. The separates were step-heated at incrementally higher power in the defocused beam of a 10W C 0 2 laser (New Wave Research MIR 10) until fused. The gas evolved from each step was analyzed by a VG5400 mass spectrometer equipped with an ion-counting electron multiplier. A l l measurements were corrected for total system blank, mass spectrometer sensitivity, mass discrimination, radioactive decay during and subsequent to irradiation, as well as interfering Ar from atmospheric contamination and the irradiation of Ca, C l and K (Isotope production ratios: ( 4 0Ar/ 3 9Ar)K=0.0302, (37Ar/39Ar)Ca=1416.4306, (3 6Ar/3 9Ar)Ca=0.3952, Ca/K=1.83 ( 3 7 ArCa/ 3 9 ArK).) . Plateau and correlation ages were calculated using Isoplot v. 3.09 (Ludwig, 2003). Errors are quoted at the 2-sigma (95% confidence) level and are propagated from all sources except 115 Table B-1. Detailed 4 0 Ar/ 3 9 Ar step-heating results1 for selected samples from the study area. Laser intensity (%)* ^ A r ^ A r ±2o 3 1 W A r ±2a ^Ar/^Ar ±2a ^ A r / ' A r ±2o Ca/K Cl/K % 4 t t A r * 3 %3VAr 4 0 A r * / 3 y A r K ±2q Age (Ma) ±2q 25 SMG 03 (biotite- and quartz-phyric rhyolite dyke; Erp; Mount Preston area4) - biotite 2J = 0.006875 ± 0.0000203; volume6 3 9 A r K = 2485.07; integrated age = 51.74 ± 0.55 Ma7; low T plateau age = 51.87 ± 0.79 Ma; high T plateau age = 50.04 ± 0.57 Ma 1.8 69.377 0.015 0.205 0.033 0.040 0.060 0.216 0.022 0.185 0.034 90.71 0.75 6.411 1.421 77.82 33.76 1.9 38.218 0.018 0.199 0.028 0.038 0.077 0.121 0.032 0.139 0.037 92.11 0.58 2.965 1.117 36.40 27.14 2.0 30.381 0.017 0.181 0.089 0.019 0.041 0.090 0.024 0.097 0.034 86.46 1.74 4.078 0.672 49.88 16.22 2.1 21.987 0.017 0.166 0.103 0.014 0.051 0.061 0.027 0.078 0.032 80.80 3.03 4.190 0.538 51.24 12.98 2.2 14.261 0.013 0.169 0.018 0.011 0.042 0.034 0.019 0.062 0.034 69.65 3.98 4.294 0.229 52.49 5.52 2.3 9.262 0.013 0.165 0.030 0.009 0.034 0.017 0.023 0.053 0.034 53.31 5.24 4.287 0.139 52.40 3.34 2.4' 7.538 0.019 0.176 0.073 0.009 0.047 0.012 0.032 0.051 0.037 44.92 4.02 4.102 0.157 50.17 3.80 2.5 . 7.300 0.020 0.155 0.080 0.009 0.044 0.011 0.026 0.053 0.032 42.32 4.63 4.164 0.142 50.92 3.42 2.6 8.758 0.021 0.142 0.061 0.011 0.032 0.015 0.033 0.062 0.029 50.36 4.55 4.305 0.198 52.62 4.78 2.7 9.531 0.021 0.161 0.029 0.012 0.058 0.018 0.033 0.075 0.033 53.64 4.17 4.377 0.220 53.48 5.30 2.8 9.307 0.023 0.156 0.055 0.014 0.063 0.017 0.028 0.087 0.032 52.71 3.76 4.355 0.218 53.23 5.24 2.9 8.941 0.020 0.171 0.023 0.015 0.076 0.016 0.033 0.090 0.035 51.84 3.02 4.251 0.193 51.97 4.66 3.0 8.373 0.013 0.181 0.051 0.025 0.022 0.013 0.033 0.180 0.038 44.12 7.32 4.646 0.150 56.72 3.62 3.2 6.427 0.023 0.219 0.050 0.094 0.027 0.008 0.031 0.729 0.047 33.13 9.10 4.265 0.128 52.13 3.08 3.4 5.633 0.018 . 0.187 0.027 0.044 0.026 0.005 0.043 0.334 0.039 24.43 9.21 4.221 0.107 51.61 2.58 3.6 5.072 0.015 0.166 0.029 0.017 0.031 0.003 0.049 0.123 0.035 18.55 10.38 4.096 0.084 50.10 2.02 3.8 5.007 0.017 0.158 0.053 0.016 0.044 0.003 0.036 0.114 0.033 17.43 7.09 4.089 0.086 50.02 2.08 4.0 4.867 0.014 0.149 0.099 0.016 0.029 0.003 0.055 0.112 0.031 15.31 8.59 4.081 0.078 49.93 1.88 4.3 4.752 0.019 0.124 0.124 0.013 0.036 0.002 0.042 0.090 0.025 12.94 8.84 4.097 0.092 50.12 2.22 (pyroxene-hornblende quartz diorite stock; EKqd; Ramsey Peak area4) hornblende 6846 ± 0.000020; volume 3 9 A r K = 203.74; integrated age = 142.82 ± 2.35 Ma; plateau age = 36.4 ± 1.5 Ma 2.0 282.906 0.030 0.545 0.114 1.884 0.037 0.822 0.037 13.711 0.087 83.87 1.03 45.498 7.787 489.19 146.66 2.2 142.948 0.029 0.214 0.062 1.208 0.044 0.448 0.036 8.846 0.027 90.47 1.74 13.512 4.276 159.61 96.68 2.4 112.536 0.024 0.167 0.060 0.882 0.032 0.342 0.032 6.406 0.020 87.64 2.21 13.792 2.590 162.77 58.46 2.6 123.400 0.018 0.241 0.073 1.481 0.032 0.384 0.047 11.013 0.036 89.66 1.69 12.639 5.065 149.72 115.16 2.8 74.564 0.040 0.451 0.082 2.460 0.041 0.214 0.052 18.512 0.091 81.00 1.17 13.810 3.162 162.97 71.36 3.1 26.285 0.026 0.709 0.074 2.992 0.030 0.051 0.033 23.779 0.158 50.78 5.73 12.822 0.545 151.79 12.38 3.4 16.837 0.024 0.774 0.040 2.466 0.027 0.022 0.045 19.683 0.175 32.31 16.40 11.374 0.400 135.28 9.16 3.6 17.954 0.012 0.888 0.065 2.516 0.020 0.025 0.030 20.055 0.201 34.85 11.86 11.639 0.283 138.31 6.48 3.8 14.644 0.008 0.715 0.023 2.240 0.015 0.015 0.034 17.895 0.161 22.45 29.19 11.366 0.181 135.19 4.16 4.0 16.107 0.017 0.687 0.047 2.321 0.020 0.019 0.049 18.601 0.154 27.90 8.97 11.475 0.361 136.44 8.28 4.4 15.128 0.020 0.582 0.168 2.402 0.019 0.016 0.025 19.354 0.130 23.21 19.99 11.602 0.301 137.89 6.90 'Measured values of 4 0 Ar/ 3 9 Ar, 3 8 Ar/ 3 9 Ar, 3 7 Ar/ 3 9 Ar, 3 6 Ar/ 3 9 Ar, Ca/K, Cl/K, % ^Ar*, % 3 9 A r , and 4 0 Ar*/ 3 9 Ar, as well as calculated ages, are shown for each increment of step-heating. All measurements were corrected for interfering Ar from irradiation of Ca, Cl and K using measured isotope production ratios: C°AT/39AT)K = 0.03 02, ( 3 7Ar/ 3 9Ar) C a ~ 1416.4306, ( 3 6Ar/ 3 9Ar)C a = 0.3952, and Ca/K = 1.83( 3 7Ar c/ 9ArK). 2Intensity in the defocused beam of a 10-W C0 2 laser. 3Asterisks indicate radiogenic argon. 4See Table 2-1 and discussion in Appendix A for sample localities and lithologic information. 5The J-value (-0.5%) indicates the irradiation flux for each sample, which was calculated relative to neutron flux monitors (Fish Canyon Tuff sanidine; 28.02 Ma; Renne et al., 1998). 6Volumes are IE-13 cm3 N P T . 7A!1 errors on calculated ages are 2a. 03-M-02 Hornblende Plateau steps are filled, rejected steps are open 03 280 h 240 200 160 DX) « < 120 80 r 40 r 20 ^ Plateauage = 136.4±l .5Ma ^ (2a, including J-error of .5%) MSWD = 0.93, probability=0.44 Includes 86.4%'of the M A r 40 60 box heights are 2o 80 100 Cumulative Ar Percent Figure B-1. Step-heating spectra and inverse isochron diagram for a pyroxene-hornblende quartz diorite sample (03-M-02) from the study area dated by the 4 0 Ar/ 3 9 Ar method. Crystallization age cited within the text is calculated from an age spectra plateau, which is defined by at least three consecutive steps that represent >50% of the total Ar released that have ages that agree within 2a. Plateau steps used in the age calculations are filled, and rejected steps are open. All heating steps were used in the inverse isochron age calculations. The 3 6 Ar/ 4 0 Ar intercept indicates the initial ratio of 4 0 Ar/ 3 6 Ar in the sample, which is within error of the atmospheric value (295.5 ± 1; McDougall and Harrison, 1999). Analytical data from this study are presented in Table B-1. 117 25-SMG-03 Biotite, low-7" Plateau steps are filled, rejected steps are open hox heights are 2o 100 r 80 s CD 60 40 20 Plateau age = 51.87±0.79 Ma (2o, including J-error of .5%) MSWD = 0.92, probability=0.51 Includes 38.1% of the 3*Ar 20 40 60 SO 100 39 Cumulative Ar Percent Figure B - 2 . Step-heating spectra and inverse isochron diagram for a biotite-quartz rhyolite porphyry sample (25 S M G 03) from the study area dated by the 4 0 A r / 3 9 A r method. Crystallization age cited within the text is calculated from an age spectra plateau, which is defined by at least three consecutive steps that represent >50% of the total Ar released that have ages that agree within 2o. Plateau steps used in the age calculations are filled, and rejected steps are open. All heating steps were used in the inverse isochron age calculations. The ^ A r / ^ A r intercept indicates the initial ratio of 4 0 A r / 3 6 A r in the sample, which is within error of the atmospheric value (295.5 ± 1; McDougall and Harrison, 1999). Analytical data from this study are presented in Table B-1. 118 mass spectrometer sensitivity and age of the flux monitor. The best statistically-justified plateau and plateau age were picked based on the following criteria: 1. Three or more contiguous steps comprising more than 50% of the 3 9 A r ; 2. Probability of fit of the weighted mean age greater than 5%; 3. Slope of the error-weighted line through the plateau ages equals zero at 5% confidence; 4. Ages of the two outermost steps on a plateau are not significantly different from the weighted-mean plateau age (at 1.8o six or more steps only); 5. Outermost two steps on either side of a plateau must not have nonzero slopes with the same sign (at 1.8a nine or more steps only). B-3 REFERENCES Ludwig, K.R., 2003. Isoplot 3.00 A Geochronological Toolkit for Microsoft Excel. Berkeley Geochronology Center, Special Publication No. 4. McDougall, I., Harrison, T . M . , 1999. Geochronology and thermochronology by the (super 40) Ar/ (super 39) Ar method. Oxford University Press, New York, 269 pages. Renne, P.R., C.Swisher, C.C. , III, Deino, A . L . , Karner, D.B., Owens, T , DePaolo, D.J., 1998. Intercalibration of standards, absolute ages, and uncertainties in ""Ar^Ar dating. Chemical Geology, vol. 145, nos. 1-2, pp. 117-152. 119 APPENDIX C U-PB GEOCHRONOLOGY C-l METHODOLOGY Field sampling methods for U-Pb samples and results of this study are discussed in Chapter 2. Zircon was separated from the volcanic rock samples using conventional crushing, grinding, and Wilfley table techniques, followed by final concentration using heavy liquids and magnetic separations. Zircon fractions for analysis were selected based on grain morphology, quality, size and magnetic susceptibility. A l l zircon fractions were abraded prior to dissolution to minimize the effects of post-crystallization Pb-loss, using the technique of Krogh (1982). A l l mineral separations, geochemical separations and mass spectrometry were done in the Pacific Centre for Isotopic and Geochemical Research (PCIGR) in the Department of Earth and Ocean Sciences at The University of British Columbia. Samples were dissolved in concentrated FTP and HN03 in the presence of a mixed 2 3 3 2 3 5 U- 2 0 5 Pb tracer. Separation and purification of Pb and U employed ion exchange column techniques modified slightly from those described by Parrish et al. (1987). Pb and U were eluted separately and loaded together on a single Re filament using a phosphoric acid-silica gel emitter. Isotopic ratios were measured using a modified single collector VG-54R thermal ionization mass spectrometer equipped with a Daly photomultiplier. Measurements were done in peak-switching mode on the Daly detector. U and Pb total procedural blanks were in the range of 1 pg and 3-5 pg, respectively, during the course of this study. U fractionation was determined directly on individual runs using the 2 3 3 " 2 3 5 u tracer, and Pb isotopic ratios were corrected for a fractionation of 0.37%/amu for Faraday and Daly runs, respectively, based on replicate analyses of the NBS-981 Pb standard and the values recommended by Todt et al. (2000). A l l analytical errors were numerically propagated through the entire age calculation using the technique of Roddick (1987). Concordia intercept ages and associated errors were calculated using a modified version the York-II regression model (wherein the York-II errors are multiplied by the MS WD) and the algorithm of Ludwig (1980). A l l errors are quoted at the 2o level. C-2 REFERENCES Krogh, T .E . , 1982. Improved accuracy of U-Pb zircon ages by the creation of more concordant systems using an air abrasion technique. Geochimica et Cosmochimica Acta, vol. 46, pp. 637-649. Ludwig, K.R., 1980. Calculation of uncertainties of U-Pb isotopic data. Earth and Planetary Science Letters, vol. 46, pp. 212-220. Parrish, R., Roddick, J . C , Loveridge, W.D., Sullivan, R.W., 1987. Uranium-lead analytical techniques at the geochronology laboratory, Geological Survey of Canada. In: Radiogenic Age and Isotopic Studies, Report 1, Geological Survey of Canada Paper 87-2, pp. 3-7. 121 Roddick, J . C , 1987. Generalized numerical error analysis with application to geochronology and thermodynamics. Geochimica et Cosmochimica Acta, vol. 51, pp. 2129-2135. Stacey, J.S. and Kramer, J.D., 1975. Approximation of terrestrial lead isotope evolution by a two-stage model. Earth and Planetary Science Letters, vol. 26, pp. 207-221. Thirlwall, M.F. , 2000. Inter-laboratory and other errors in Pb isotope analyses investigated using a 207Pb— 204Pb double spike. Chemical Geology, vol. 163, pp. 299-322. 122 APPENDIX D PALEONTOLOGY REPORTS D-l FOSSIL REPORT J4-2005-TPP Report on 2 collections of Middle Jurassic fossils from southeastern Whitesail Lake map area, British Columbia (NTS 093E), collected by Sarah M . Gordee, U B C , 2004. D-l-1 GSC Loc. No. C-307263/Field No. O6SM604 Sample is associated with [stratigraphically overlies] rhyolitic lapilli tuff dated at 176.5 ± 0.6 Ma (see Chapter 3). Identifications: Bivalves: Trigonia sp. Ctenostreon sp. Age and Remarks: Possibly Middle Toarcian through Early Callovian, but almost certainly Early Bajocian. D-l-2 GSC Loc. No. C-307268/Field No.O6SM604 Identifications: A bivalve or ammonite fragment, large, coarsely ribbed; possibly fragment of Trigonia as in C-307263. A probable belemnite fragment Age and Remarks: Probably Middle Toarcian through Early Callovian. T. Poulton June 30, 2005 124 D-2 FOSSIL REPORT 2005-TPP D-2-1 GSC Loc. No. C-404725/FieId No. HFBM02-1902-1 U T M Zone 9 N A D 27 664935E 5872765N Approximately 3 km E N E of Jumble Mountain and 4 km S of Ramsey Peak D-2-2 GSC Loc. No. C-404726/FieId No. HFBM02-2002-1 U T M Zone 9 N A D 27 665016E 5872702N Approximately 3 km E N E of Jumble Mountain and 4 km S of Ramsey Peak APPENDIX E A N A L Y T I C A L PRECISION, SAMPLE INFORMATION A N D ZIRCON SATURATION TEMPERATURES 126 E-l ANALYTICAL PRECISION VIA DUPLICATE AND STANDARD ANALYSIS The precision of lithogeochemical data obtained during the course of this study was monitored by replicate analyses of Mineral Deposit Research Unit (MDRU) in house standards P-1 (granodiorite from the Coast Plutonic Complex) and BAS-1 (basalt from near Cheakamus, British Columbia). Analytical data obtained from these samples was compared to a mean of 5 previous repeat analyses and are presented in Table E - l . Duplicate analyses of these samples are precise and are within two standard deviations of the standard values. E-2 LITHOGEOCHEMICAL SAMPLE INFORMATION AND ZIRCON SATURATION TEMPERATURES Lithogeochemical sample information, including locality, lithology, and modal mineralogy of each sample analyzed for this study is listed in Table E-2. Lithogeochemical sampling methodology is discussed in Chapter 2. Zircon saturation temperatures were calculated for each Hazelton Group lithogeochemical sample from the study area, as well as for lithogeochemical samples from the Nifty V M S deposit in the east-central Bella Coola map area (from data reported by Ray et al., 1998). The results were obtained using the calculations outlined by Miller et al. (2003), and are listed in Table E-3. E-3 REFERENCES Miller, C.F. , McDowell, S.M., Mapes, R.W., 2003. Hot and cold granites? Implications of zircon saturation temperatures and preservation of inheritance. Geology, vol. 31, no. 6, pp. 529-532. Ray, G.E. , Brown, J.A., Friedman, R.M. , 1998. Geology of the Nifty Zn-Pb-Ba prospect, Bella Coola district, British Columbia. In: Geological Fieldwork 1997, British Columbia Ministry of Energy, Mines and Petroleum Resources, Paper 1998-1, pp. 20-1 - 20-28. 127 Table E-l. Mean values and duplicate analyses standards o f P - l and B A S - 1 ' . P-l (n=5)2 mean SD3 P-l-A 4 P-l-B BAS-1 (n=5) mean SD BAS-l-A BAS-l-B tfajor elements 5 S i 0 2 70.96 0.10 69.57 69.37 53.56 0.36 52.10 51.96 T i 0 2 0.38 0.00 0.40 0.39 1.31 0.01 1.30 1.28 A 1 2 0 , 14.10 0.06 14.42 14.38 15.12 0.07 15.50 15.47 F e 2 0 3 3.90 0.00 3.82 3.79 11.16 0.05 11.11 11.08 F e 2 0 3 2.34 0.08 2.19 2.19 8.86 0.12 8.56 8.56 M n O 0.08 0.00 0.07 0.07 0.14 0.00 0.13 0.13 M g O 1.11 0.01 , 0.96 0.97 7.35 0.05 7.06 7.03 C a O 3.49 0.02 3.45 3.44 8.28 0.05 8.13 8.13 N a 2 0 3.80 0.00 3.80 3.81 3.28 0.04 3.22 3.20 K 2 0 2.12 0.01 2.03 2.02 0.56 0.02 0.54 0.54 P2O5 0.08 0.04 0.07 0.07 0.22 0.00 0.23 0.22 Total 100.56 0.22 99.10 98.83 100.96 - 99.31 99.00 frace and rare earth elements ( R E E ) 6 A g 0.3 _ <1 <1 0.3 0.1 <1 <1 B a 724.0 8.0 722.0 752.0 194.0 18.6 172.0 171.0 C e 28.0 1.3 23.1 25.0 21.8 0.8 19.4 18.8 C o 6.2 0.4 7.2 7:4 42.2 0.4 42.9 43.9 Cs 1.2 0.1 1.1 1.1 0.1 0.0 0.1 0.2 C u 15.5 5.5 9.0 10.0 59.0 0.8 65.0 58.0 D y 3.3 0.2 3.1 v 2.9 3.3 0.2 2.8 2.8 E r 2.1 0.1 2.1 2.0 1.5 0.1 1.4 1.6 E u 0.8 0.0 0.7 0.7 1.3 0.1 1.0 1.1 G a 15.0 1.1 15.0 15.0 19.6 1.0 18.0 20.0 G d 3.1 0.1 2.5 2.8 3.8 0.1 3.3 3.1 H f 3.8 0.1 4.0 3.0 2.4 0.1 2.0 2.0 Ho 0.7 0.0 0.6 0.6 0.6 0.0 0.6 0.5 L a 13.2 0.4 13.0 13.5 9.3 0.4 9.2 9.3 L u 0.4 0.0 0.3 0.3 0.2 0.0 0.1 0.1 N b 3.8 0.2 3.0 3.0 8.2 0.5 7.0 7.0 N d 13.0 0.6 11.2 11.5 13.6 0.8 12.2 11.8 N i - - 11.0 12.0 172.0 1.9 194.0 175.0 Pb 10.2 1.5 10.0 12.0 4.4 4.3 10.0 6.0 Pr 3.4 0.1 2.9 3.0 3.0 0.1 2.6 2.6 Rb 50.4 3.1 45.1 45.6 7.0 0.1 6.1 6.2 Sm 2.9 0.1 2.3 2.4 3.5 0.5 2.8 2.9 Sn 2.4 0.9 2.0 2.0 1.2 0.2 2.0 2.0 Sr 256.0 4.9 228.0 236.0 502.0 7.5 461.0 471.0 A g 0.3 0.0 O . 0 1 0.0 0.5 0.0 0.0 0.1 Tb 0.5 0.0 0.4 0.4 0.6 0.0 0.5 0.5 Th 4.4 - 4.0 4.0 0.8 0.0 1.0 1.0 RT1 0.3 - <0.5 <0.5 0.1 0.0 <0.5 <0.5 T m 0.4 0.0 0.3 0.3 0.2 0.0 0.2 0.2 U 1.5 0.1 1.4 1.4 0.3 0.0 <0.5 <0.5 V 58.2 0.4 57.0 57.0 152.0 1.1 136.0 148.0 Y 22.8 0.5 18.5 19.0 18.4 1.0 15.2 14.3 Y b 2.5 0.2 2.3 2.2 1.4 0.1 1.2 1.2 Z n 44.0 0.9 33.0 31.0 91.4 1.0 74.0 81.0 Z r 126.0 10.2 124.0 115.0 94.5 2.2 83.2 91.4 ' P - l and B A S - 1 are M D R U standards. 2 M e a n values o f P - l and BAS-1 are based on the average o f 5 previous repeat analyses. 'Standard deviation. 4P-1 - A and - B are duplicate analyses o f the standards that were used to test for precision. A l l major element analyses are reported as weight % oxides and were completed using X - R a y Fluorescence Spectroscopy ( X R F ) . 6A11 trace and rare earth element analyses are reported in parts per mi l l ion (ppm) and were completed using Inductively Coupled Plasma - Atomic Emission Spectroscopy ( I C P - A E S ) and/or Inductively Coupled Plasma - Mass Spectrometry ( ICP-MS) . Table E-2. Summary o f lithogeochemical sample locality and information. U T M ' Field no. 1:50 000 N T S Easting Northing Locality Map unit Rock type 1 Modal mineralogy1 Textures/structures and alteration4 05 S M G 03 093 E/02 666651 5874273 N of Ramsey Peak MJHr rhy tuff pig? 06 S M G 03 093E/02 666834 5874043 N of Ramsey Peak MJHr grey-purple dac x l tufT plg>qiz 07 S M G 03 093 B 0 2 665855 S874090 N of Ramsey Peak undiv. made dyke aph bas dyke 08 S M G 03 093 E/02 665640 5873637 N of Ramsey Peak undiv. MJHr amyg, pig ppy bas Pig cpidostte zones 09 S M G 03 093 E/02 665820 5873432 N of Ramsey Peak undiv. MJHr dark grey, aph, amyg bas flow 10 S M G 03 093E/02 653681 5898678 SE of Mount Preston MJHr purple, densely welded, dac vit-xl tuff Pig? 11 S M G 03 093B02 653039 5898624 SE of Mount Preston undiv. malic dyke aph bas dyke 14a S M G 03 14b S M G 03 15 S M G 03 093B02 093E/02 093E/02 652317 652317 652493 5897849 5897849 5897977 SE of Mount Preston SE of Mount Preston SE of Mount Preston MJHrd MJHrd undiv. MJHr pink, amyg. aph to finely ppy rhy dome pink, amyg, aph to finely ppy rhy dome aph bas pig > qtz pig > qtz flow banded: carapace breccia; sericite > chlorite alteration flow banded; carapace breccia; sericite > chlorite alteration pillowed 16 S M G 03 093E/02 652493 5897977 SE of Mount Preston undiv. MJHr px>p lg chlorite > sericite alteration 17 S M G 03 09315/02 652459 5897536 SE ofMount Preston undiv. MJHr amyg, finely ppy bas p]g>px hyaloclastitc; chlorite alteration 18a S M G 03 093E-02 652348 5897557 SE ofMount Preston undiv. float light tan to orange baritc? 18b S M G 03 093E/02 652348 5897557 SE ofMount Preston undiv. float light tan to orange baritc? 19 S M G 03 093H/02 652210 5897765 SE of Mount Preston undiv. mafic dyke dark grey-brown, aph bas dyke 21 S M G 03 093E/02 652190 5898051 SE of Mount Preston undiv. MJHr dark grey, aph bas flow 22 S M G 03 093E/02 652053 5897927 SE of Mount Preston MJHb finely ppy bas pig pepcritic contact! 23 S M G 03 O93E/02 652239 5898133 SE of Mount Preston MJHb brown, aph to ppy bas plug pig ± hbl eroded volcanic neck? 28 S M G 03 09315/02 653687 5897387 SE ofMount Preston undiv. mafic dyke amyg, aph to ppy bas dyke Pig chlorite; flow banded 34 S M G 03 O93IS/02 650991 5899052 SE ofMount Preston undiv. MJHr green-grey, aph bas sil l 41 S M G 03 093 E/02 650743 5899065 SE of Mount Preston undiv. mafic dyke army green, ppy bas sill/dyke pig 43o S M G 03 093 E/02 650620 5899272 SE of Mount Preston undiv. MJHr orange to grey, ppy bas sill pig > px 44 S M G 03 45 S M G 03 093E/02 093E/02 650300 650125 5898969 5898471 SE of Mount Preston SE ofMount Preston MJHr undiv. MJHr purple-pink, very densely welded, dac lit-xl-vit lapilli tuff orange to grey-green, ppy bas sil l pig px > pig perlites; sericite alteration chlorite > sericite > epidote alteration 46 S M G 03 48 S M G 03 093E/02 093E/O2 650125 650760 5898471 5898134 SE ofMount Preston S ofMount Preston undiv. mafic dyke undiv. MJHr orange to grcy-grcen, amyg. aph to ppy bas dyke grey-green, amyg, ppy bas sil l Pig Pig chlorite chlorite 68 S M G 03 093&O2 650612 5898053 S ofMount Preston undiv. mafic dyke grcy-grcen, ppy bas dyke plg>px 73 S M G 03 09315/02 651459 5897808 Mount Preston undiv. mafic dyke green-grey, aph bas dyke 83 S M G 03 093E/02 665665 5874657 S of Ramsey Peak undiv. malic dyke army green-brown, aph bas dyke 95 S M G 03 093E/02 665763 5875382 S of Ramsey Peak undiv. mafic dyke grey-green, ppy bas dyke plg>px 108 S M G 03 093E/02 665750 5875705 S of Ramsey Peak undiv. malic dyke green-grey, ppy bas pig > px > hbl 112 S M G 03 093E/02 665933 5875598 S of Ramsey Peak MJHr white and purple, very densely welded, rhy lit-xl-vit tuff to lapilli tuff pig » qtz distinct vertical welding zones; sericite > chlorite alteration ' U T M s are reported in North American Datum, 1927 ( N A D 27). : R o c k lypc abbreviations: rhy, rhyolite: dac, dacite; and. andesite; bas, basalt; v i i , vi tr ic; x l . crystal; lit, l i thic; ppy. porphyrilic or porphyry, aph, aphanitic; amyg, amygdaloidal. 3 M i n c r a l abbreviations: p ig . plagioclase: ksp. a lkal i feldspar; qtz, quartz; bt, biotite; hbl . hornblende; px. pyroxene. Sericite alteration is pervasive throughout a l l rocks in the study area, but is only reported i f verified petrographically. 129 Tabic E-2 (continued). Summary of lithogeochemical sample locality and infom UTM' Field no. 1:50 000 NTS Easting Northing Locality Map unit Rock type' Modal mineralogy'1 Textures/structures and alteration4 113 S M G 03 093LV15 665873 5873069 N E of Jumble Mountain undiv. MJHr grey-green, ppy bas-and sill p lg>px 114 S M G 03 093D/1S 665270 5872886 N E of Jumble Mountain MJHr grey-green, ppy and sill p1g>px 115 S M G 03 093D/15 666534 5872274 N E of Jumble Mountain BKqd grey dioritc ppy plg>px fine grained; in eg ui granular 116 S M G 03 093D/15 666534 5872274 N E of Jumble Mountain BKqd greydiorite ppy plg>px fine grained; incqui granular 118 S M G 03 093D/I3 664732 5872646 N E of Jumble Mountain U r 7 tan-orange, ppy dac sil l pig 126 S M G 03 093D/15 665249 5872008 N E of Jumble Mountain U r 7 ppy dac dome pig flow banded 26 J B M 04 093EV02 N of Rivers Peak MJHr purple, rby vit-xl accretionary lapilli tuff pig > qtz laminated; internally normally graded; scricttc alteration JBM05O5 093D/1S N E Bella Coola map N A microdiorite p lg>px holocrystallinc; very fine grained; chlorite > cpidote > scricite alteration 13 S M G 04 093E/02 665365 5875830 S o f Ramsey Peak undiv. MJHr green, amyg, aph to ppy bas px>plg flow banded: chlorite > scricite alteration IS S M G 04 093&02 665934 5875931 S of Ramsey Peak undiv. MJHr red-purple bas flow px>plg flow banded; chlorite > scricite alteration 21 S M G 04 093&02 666288 5875997 S o f Ramsey Peak undiv. MJHr white ray dome pig > qtz flow banded; scricite » chlorite alteration 22ASMG04 O93E/02 666288 5875997 S o f Ramsey Peak EKqd grey microdiorite dyke pig > px > hbl fine grained; cquigranular 29 S M G 04 O93E/02 662010 5877670 E of Tsaydaychuz Peak undiv. EMJHv grey, ppy dac flow or hypabyssal intrusion pig > px scricite > chlorite » epidote alteration 31 S M G 04 093E/02 663477 5883072 E of Bullet Peak MJHr tan, very densely welded, rhy Itl-xl-vit lapilli pig » hbl? scricite » chlorite alteration 33 S M G 04 O93E/02 663498 5882199 Butler Peak EMJHv grey, ppy bas-ond flow pig > px cpidote and jasper clots; chlorite > scricite » cpidote alteration 36 S M G 04 O93E/02 659050 5881579 Butler Peak EMJHv grey, pyritifcrous, amyg px-hbl microdiorite pig > hbl > px epidote + quartz veins; chlorite alteration 46 S M G 04 O93E/02 661456 5880955 Butler Peak EMJHv green-grey, sparsely amyg, ppy and p lg>px 61 S M G 04 O93E/02 653975 5895991 N of Rivers Peak MJg pink, bi-hbl granite (pig =ksp=qtz) medium grained; inequigranular hbl > bi 66 S M G 04 O93E/02 653496 5897049 N of Rivers Peak MJHrd tan rhy dome rarcqtz? sucrosic; scricite alteration 91 S M G 04 093E/02 655286 5882377 N W of Butler Peak MJHr grey, aph, siliceous rhy tuff convolutely flow banded; scricite alteration 92 S M G 04 093 E/02 655676 5881154 W of Butler Peak EMJHv purple, ppy bas-ond flow pig pillowed; scricttc > chlorite alteration 93 S M G 04 093E.02 656121 5881387 W of Butler Peak EMJHv dark grey, amyg, ppy and plug plg>px scricite > chlorite > calcile alteration 94 S M G 04' 093E/02 656121 5881387 Butler Peak grey, aph ray tuff thinly laminated 100 S M G 04 093E/02 665609 5877393 N of Ramsey Peak undiv. M J l l r grey, vesicular rhy dome rare pig flow handed; scricttc » chlorite alteration 102 S M G 04 093E/02 666753 5877461 N of Ramsey Peak MJHr grey, very densely welded, rhyxl-vtt lapilli tuff Pl« scricite » calcitc alteration 109 S M G 04 093&02 667837 5878285 N of Ramsey Peak MJHr grey, pyritilerous, rhy tuff to xl tuff pig 121 S M G 04 093E/02 667628 5878650 NofRairaeyPeak MJHr grey, rhy l i l -x l tuff to lapilli tuff rare pig scricite > calcite alteration 124 S M G 04 093E/02 653155 5894491 N of Rivers Peak U r ? tan rhy dome qtz 140 S M G 04 093E/02 653545 5893519 Rivers Peak MJHr pink my flow Pig flow banded; aulobrccciatcd zones; scricite » chlorite alteration 143 S M G 04 093E/02 652992 5893386 Rivera Peak MJHb dark grey and ppy hypabyssal intrusion Pig 145 S M G 04 093E/02 645803 5889068 Mount Pondoscy MJHr purple, densely welded, rhy x l - l i M i t lapilli tuff pig > qtz scricite > chlorite alteration UTMs are reported in North American Datum, 1927 (NAD 27). Rock type abbreviations: rhy, rhyolite; dac, dacite; and, andesite: bas, basalt; vit, vitric; xl. crystal; lit, lithic; ppy. porphyritic or porphyry: aph, aphanitic; amyg. amygdaloidal. Mineral abbreviations: pig, plagioclase; ksp, alkali feldspar; qtz, quartz; bt, biotite; hbl, hornblende; px, pyroxene. Scricite alteration is pervasive throughout all rocks in the study area, but is only reported if verified petrographically. Sample was omitted from the geochcmical characterization study due to insufficient field information. 130 Table E-3. Zircon saturation temperatures1 calculated for intrusive and extrusive Hazelton Group rocks in the study area and for Hazelton Group rocks hosting the Nifty VMS prospect2. M-value Cation fraction 3 Z r Na+K+2*Ca Temp. 4 Field no. Si A l C a Na K (ppm) Si*Al <°C) Rocks from the study area 05 SMG 03 0.671 0.136 0.019 0.093 0.001 265.0 1.45 828 06 SMG 03 0.698 0.150 0.005 0.086 0.014 265.0 1.05 860 08 SMG 03 0.475 0.191 0.045 0.087 0.005 87.5 2.01 697 09 SMG 03 0.501 0.158 0.069 0.045 0.012 115.0 2.45 689 10 SMG 03 0.649 0.153 0.022 0.092 0.012 206.0 1.50 801 14a SMG 03 0.629 0.154 0.009 0.078 0.028 199.0 1.28 814 14b SMG 03 0.624 0.155 0.014 0.083 0.025 195.0 1.41 802 15 SMG 03 0.480 0.171 0.095 0.067 0.037 83.9 3.57 606 16 SMG 03 0.439 0.180 0.090 0.056 0.011 52.7 . 3.14 600 17 SMG 03 0.521 0.165 0.046 0.093 0.007 114.5 2.23 702 21 SMG 03 0.428 0.185 0.083 0.048 0.022 48.1 2.98 603 22 SMG 03 0.525 0.172 0.036 0.085 0.014 95.9 1.88 711 23 SMG 03 0.435 0.184 0.085 0.070 0.004 48.4 3.05 599 34 SMG 03 0.437 0.180 0.090 0.032 0.021 55.4 2.98 611 43a SMG 03 0.444 0.187 0.076 0.058 0.024 59.8 2.80 626 44 SMG 03 0.662 0.171 0.004 0.083 0.043 255.0 1.18 846 45 SMG 03 0.432 0.182 0.079 0.040 0.025 53.7 2.82 618 48 SMG 03 0.474 0.185 0.032 0.108 0.005 61.2 2.02 671 112 SMG 03 -0.700 0.147 0.002 0.105 0.004 332.0 1.11 878 113 SMG 03 o'.463 0.186 0.093 0.045 0.006 83.6 2.76 649 114 SMG 03 0.662 0.140 0.011 0.087 0.008 180.0 1.25 807 26 JBM 04 0.712 0.167 0.011 0.044 0.040 223.0 0.90 856 13 SMG 04 0.440 0.173 0.080 0.062 0.015 41.7 3.11 588 15 SMG 04 0.572 0.156 0.019 0.110 0.002 152.5 1.68 762 21 SMG 04 0.693 0.146 0.011 0.095 0.029 264.0 1.44 828 29 SMG 04 0.477 0.189 0.072 0.080 0.022 160.0 2.73 696 31 SMG 04 0.647 0.144 0.007 0.027 0.069 211.0 1.18 828 33 SMG 04 0.430 0.198 0.086 0.044 0.023 353.0 2.80 752 36 SMG 04 0.484 0.175 0.051 0.070 0.016 152.0 2.21 725 46 SMG 04 0.455 0.191 0.072 0.063 0.025 190.5 2.69 711 66 SMG 04 0.985 0.004 0.001 0.002 0.001 344.0 0.96 895 91 SMG 04 0.659 0.156 0.009 0.114 0.009 243.0 1.37 826 92 SMG 04 0.511 0.215 0.042 0.080 0.004 96.9 1.53 735 93 SMG 04 0.409 0.194 0.151 0.047 0.024 154.5 4.71 585 100 SMG 04 0.721 0.136 0.002 0.097 0.020 374.0 1.25 878 102 SMG 04 0.672 0.158 0.013 0.065 0.064 392.0 1.46 865 109 SMG 04 0.622 0.147 0.031 0.039 0.041 137.5 1.56 761 121 SMG 04 0.689 0.141 0.011 0.086 0.019 853.0 1.31 964 140 SMG 04 0.622 0.152 0.046 0.081 0.023 190.0 2.06 753 143 SMG 04 0.520 0.192 0.074 0.062 0.018 178.5 2.28 733 145 SMG 04 0.621 0.169 0.033 0.086 0.021 221.0 1.65 795 Rocks from the Nift VMS prospect in the east-central Bella Coola map area GR96 19 0.492 0.193 0.039 0.099 0.008 70.0 1.94 684 GR96 20 0.507 0.215 0.078 0.059 0.021 72.0 2.16 674 GR96 26 0.498 0.191 0.063 0.091 0.005 138.0 2.35 709 GR96 52 0.682 0.168 0.024 0.053 0.032 132.0 1.16 786 GR96 52R 0.681 0.167 0.025 0.053 0.031 128.0 1.18 783 GR96 53 0.642 0.173 0.034 0.086 0.014 94.0 1.51 734 GR96 54 0.645 0.173 0.035 0.078 0.014 128.0 1.46 762 GR96 57 0.543 0.250 0.022 0.046 0.058 100.0 1.09 768 GR96 58 0.542 0.197 0.070 0.070 0.005 83.0 2.01 693 GR96 59 0.545 0.187 0.073 0.064 0.002 92.0 2.07 696 GR96 70 0.653 0.171 0.033 0.056 0.041 152.0 1.45 777 GR96 71 0.629 0.173 0.017 0.094 0.014 169.0 1.30 798 GR96 72 0.593 0.190 0.011 0.056 0.033 98.0 0.99 774 GR96 73 0.662 0.173 0.026 0.055 0.027 134.0 1.17 787 GR96 74 0.577 0.174 0.069 0.054 0.003 94.0 1.95 705 GR96 103 0.676 0.160 0.022 0.061 0.030 155.0 1.25 794 'These results were obtained using the calculations outlined by Miller et al., 2003. 2Data obtained from full geochemical analyses reported in Ray et al., 1998. 3Cation fractions for samples were calculated using oxide values reported in Table 2-3, and in Ray etal., 1998. 4 A concentration of 497644.345 (ppm) Zr in zircon and 0% inheritance for zircons were assumed for each sample. 131 APPENDIX F GEOLOGICAL FIELDWORK PUBLICATIONS REGIONAL STUDIES OF ESKAY CREEK-TYPE AND OTHER VOLCANOGENIC MASSIVE SULPHIDE MINERALIZATION IN THE UPPER HAZELTON GROUP IN STIKINIA: PRELIMINARY RESULTS J.K. Mortensen1, S.M. Gordee1, J. B. Mahoney2 and R.M Tosdal1 KEYWORDS: Volcanogenic massive sulphide deposits, Eskay Creek, Hazelton Group, Stikinia, Early Jurassic, Bella Coola area, Whitesail Lake area, Rocks to Riches program INTRODUCTION Eskay Creek type (ECT) volcanogenic massive sulphide (VMS) deposits represent an attractive exploration target because of their substantial tonnage potential and high precious metal content. Despite numerous geological and geochemical studies of Eskay Creek and years of exploration for ECT deposits in the northern Stikinia terrane, however, deposits in the immediate area of Eskay Creek are still the only significant deposits of this type that have been discovered in British Columbia. New exploration criteria must be developed in order to improve the likelihood of success in future exploration endeavors. The British Columbia Geological Survey Branch recently completed two major syntheses that provide an excellent basis on which to build a new research project focused on developing new exploration strategies for ECT deposits. Massey (1999) compiled a summary of all known VMS deposits in B.C. and subdivided those associated with felsic volcanic rocks into Kuroko-type and Eskay Creek-type. Massey et al. (1999) undertook a detailed assessment of the potential for ECT deposits throughout British Columbia. Their report summarizes the main geological and geochemical characteristics of ECT deposits and provides brief descriptions of numerous mineral occurrences in the province that share at least some of the key characteristics of ECT deposits. Eight individual occurrences were identified that are considered to be ECT deposits, and several additional prospects were described that have potential to be ECT. A new two-year research project was initiated by the Mineral Deposit Research Unit at UBC in 2003 aimed at better understanding the geological setting in which Eskay Creek type (ECT) deposits and occurrences formed, and devising better exploration strategies for this much sought after style of mineralization. Funding for the project derives in part from the Rocks to Riches Program, which is administered by the BC & Yukon Chamber of Mines, and by a consortium of mining and exploration companies. Initial field work carried out during the 2003 field season had two main goals. First, we began a mapping based study of upper Hazelton Group strata in the southern Whitesail Lake area (and northernmost Bella Coola area) in southern Stikinia, aimed at refining our understanding of Hazelton Group stratigraphy in this region, constraining the environment(s) of deposition, and investigating the geological setting of ECT occurrences known to occur in the southern part of the area (Diakow et al., 2002; Haggart et al., 2003). Approximately five weeks of mapping was carried out in the southern Whitesail Lake area. Second, we began regional investigations of ECT occurrences in several other parts of Stikinia, including the Eskay Creek area itself, as well as the geological setting of other VMS occurrences hosted in older portions of the Hazelton Group to compare and contrast with the setting in which ECT mineralization is known to have formed. Approximately two weeks of regional reconnaissance work was directed towards this part of the study. The new research builds on previous work completed by the Mineral Deposit Research Unit (MDRU) at UBC under the auspices of the Iskut Project (results compiled in Lewis and Tosdal, 2000) and the Volcanogenic Massive Sulfide Deposits of the Cordillera Project (most results summarized in Juras and Spooner, 1996; and Roth, 2002). / - Mineral Deposit Research Unit, Earth & Ocean Sciences, UBC, Vancouver, B.C.; 2 -Department of Geology, University of Wisconsin, Eau Claire, Wisconsin, U.S.A. 133 CHARACTERISTICS OF ECT DEPOSITS IN STIKINIA AND OUTSTANDING QUESTIONS ECT deposits are polymetallic VMS deposits characterized by high precious metal contents and highly anomalous levels of "epithermal suite elements", especially Hg, Sb and As (Roth et al., 1999). Several lines of evidence indicate that the Eskay Creek deposit formed at shallow water depths (see summary in Barrett and Sherlock, 1996), although depths as great as 1500 m are permitted by the data (Ross Sherlock, oral communication, 2002). Fluid inclusion data suggest that the mineralizing fluids were relatively low temperatures (120-210°C) and that boiling occurred. Microfossil studies of sedimentary rocks that are the immediate host to ore at Eskay Creek are also consistent with shallow water depths (Nadaraju, 1993), although precise depths cannot be constrained. The high precious metal contents of the ore are considered to be typical of VMS deposits formed in shallow water settings (e.g., Hannington et al., 1999). The Eskay Creek deposit is associated with a distinctive bimodal basalt-rhyolite volcanic package (the Eskay Creek member of the Salmon River Formation; Lewis and Tosdal, 2000). The host rocks are both slightly younger (172-178 Ma vs. >181 Ma) and compositionally distinct (tholeiitic vs. mainly calc-alkaline) from volcanic rocks that comprise the rest of the Hazelton Group. Rhyolitic rocks associated with the Eskay Creek deposit are characterized by low Ti02 values, which distinguish them from felsic volcanic units elsewhere in the Hazelton Group. Their Nd isotopic compositions lie in a restricted range with 8 N d between +4 and +5.5, whereas felsic rocks of the rest of the Hazelton Group appear to have a much broader range of isotopic compositions and extend to e N d as low as +2 (Childe, 1996, 1997). A number of polymetallic Kuroko-type VMS deposits and prospects that do not share the ECT characteristics also occur within Early and Middle Jurassic sequences of Stikinia in British Columbia (Massey, 1999). Hydrothermal systems capable of generating VMS deposits were therefore active in a number of areas and at more than one time within Stikinia during the development of the Hazelton arc, and a key question is what specific factors determine which systems will produce an ECT deposit rather than a more typical polymetallic Kuroko-type VMS deposit. Resolution of this question is critical for developing exploration strategies specific to ECT deposits. Factors that may be important include (but are not limited to) the following: 1) water depth; 2) specific composition of associated volcanic rocks; 3) nature and/or depth of associated subvolcanic intrusions; 4) temperature of the associated magmas; 5) seafloor topography; and 6) nature of structural conduits controlling fluid flow in the subsurface. The new research addresses the relative importance of these and other factors with the ultimate goal of devising more effective exploration criteria for ECT deposits in Stikinia and elsewhere in the world. A broad range of investigative tools is being brought to bear on the problem, including geological mapping, petrography, micropaleontology, lithogeo-chemistry, U-Pb and Ar-Ar geochronology and Pb and Nd isotopic studies. Specific goals of the study include: 1) comparing the lithogeochemistry of volcanic units associated with other VMS occurrences (both Kuroko-type and ECT) elsewhere in Stikinia with those at Eskay Creek to determine if systematic differences occur that may be used to target areas of high ECT deposit potential; 2) assessing the magmatic temperatures of volcanic units associated with ECT and other VMS occurrences in Stikinia using zircon geothermometry to determine whether ECT deposits are associated with anomalously high temperature magmas; 3) evaluating the water depth in which each of the known VMS occurrences formed using micropaleontology of associated clastic sedimentary units; 4) carrying out a detailed Pb isotopic study of sulphides and host rocks from both ECT and Kuroko-type VMS deposits in Stikinia to determine whether there are systematic differences in metal sources between the two styles of mineralization, and to eliminate occurrences in which the "epithermal geochemical signature" may be related to overprinting by Tertiary epithermal vein systems rather than the primary VMS mineralization itself; and 5) undertaking a 1:50,000 scale mapping study and stratigraphic analysis of a portion of southern Stikinia northeast of Bella Coola (southern Whitesail Lake and northernmost Bella Coola map areas). Here, previously unrecognized upper Hazelton Group stratigraphy have recently been shown to be age equivalent to the Eskay Creek member (Ray et 134 al., 1998; Diakow et al., 2002). Furthermore, these rocks host both ECT-like and Kuroko-type VMS occurrences, including the Nifty occurrence in northern Bella Coola map area (BC MINF1LE 093D 006) ) and the Smaby occurrence in southern Whitesail Lake area (BC MINFILE 093E 025). This work is aimed at establishing a stratigraphic, geochronological and lithogeochemical framework for the upper Hazelton Group in southern Stikinia, and the position of ECT and other VMS mineralization within that framework. MAPPING STUDIES IN THE SOUTHERN WHITESAIL LAKE MAP AREA The first of two field seasons of mapping in the southern Whitesail Lake area focused on the area between Jumble Mountain in the south and Mount Preston in the north (Figures 1, 2). Hazelton Group volcanic and sedimentary rocks that are very well exposed in this area represent a northwestern continuation of the package of mainly felsic volcanic strata that host the Nifty VMS occurrence in northern Bella Coola map area (Ray et al., 1998; Diakow et al., 2002), approximately 45 km southeast of Jumble Mountain. U-Pb dating of volcanic rocks that host the Nifty occurrence (Ray et al., 1998) indicates an age of 164.2 ± 4.4 Ma. A felsic tuff horizon on the southeast side of Jumble Mountain has given a U-Pb zircon age of 176.6 ± 0.7 Ma (R.M. Friedman, unpublished data). Late Toarcian to Early Aalenian fossils have also been recovered from this locality. Together, these data confirm that the Jumble Mountain section and correlative rocks exposed between Jumble Mountain and Mount Preston, 30 km to the northwest, are roughly age equivalent to host rocks for the Eskay Creek deposit. 135 Figure 2. Regional map of the southeast Whitesail Lake and northern Bella Coola map areas. Box shows the outline of the study area and bold lines indicate measured stratigraphic sections, which are named after adjacent mountains. Several very well exposed stratigraphic sections of Hazelton Group strata between Jumble Mountain and Mount Preston were examined in detail during the 2003 field season, and measured sections were completed in both the northern and southern parts of the study area. U-Pb dating of felsic volcanic units in these sections are in progress to provide firm temporal correlations. The area between Jumble Mountain and Ramsey Peak (Figure 2) contains three-dimensional exposures of Hazelton Group strata within an area of approximately 50 km2. Layered rocks in this area trend approximately east/west and dip shallowly to the north and northeast, with very minor structural disruption. The main Jumble Mountain massif itself has superb exposures of shallowly dipping volcanogenic strata that are unfortunately largely inaccessible due to very steep topography and glacial cover. This area will be spot-checked and sampled for U-Pb dating during the 2004 field season. The base of the measured section in the Jumble Mountain area is exposed on the northeast flanks of the mountain (Figures 2, 3). The base of the section is dominated by coarse-grained, rhyolitic to dacitic fragmental rocks interbedded with massive, volcanogenic granule to pebble conglomerate, which comprises Unit A of this section (Figure 3). Conglomeratic beds generally decrease in abundance up section, becoming intercalated with finer-grained, well-bedded feldspathic-lithic wacke which forms Unit B (Figure 3). Wackes in this unit are fossiliferous, containing articulate and broken bivalves and less abundant gastropods. Ammonites recovered from this unit during previous summers have been identified as Late Toarcian to Early Aalenian (J.W. Haggart, personal communication, 2003), and a U-Pb age of 176.6 ± 0.7 Ma was obtained from a dacitic to rhyolitic crystal-lithic tuff from within this unit (R.M. Friedman, unpublished data). Fossil assemblages and sedimentary structures suggest a relatively shallow-water depositional environment. Unit C of this section is characterized by well-bedded, fine-grained tuffaceous beds intercalated with bioclastic lag deposits and less abundant feldspathic-lithic wacke (Figure 3). This unit is overlain by huge thicknesses of massive, volcanogenic, granule to boulder conglomerate. The entire measured section is intruded by a set of sparsely plagioclase-phyric to aphyric dacitic sills and dykes, which appear to be related to an aphanitic dacitic plug that intrudes the upper part of the section (Figure 3). Exposures between the Jumble Mountain section and the Ramsey Peak area have not yet been measured or examined in detail but generally comprise large thicknesses of well-bedded, feldspathic-lithic wacke and granule to pebble mudstone, which are overlain by crowded plagioclase-phyric to aphyric, amygduloidal basaltic andesite flows(?). 136 (A) Figure 3. Measured section from the Jumble Mountain study area, showing (a) the location of section shown in Figure 2, (b) a view to the southeast across well-exposed strata northeast of Jumble Mountain, and (c) an outcrop photograph of a bioclastic lag deposit within the lower Jumble Mountain section. Units A, B, and C correspond with the vertical scale beside the measured section. Late Toarcian to Early Aalenian ammonoids have been identified at the indicated fossil site, stratigraphically below a crystal-lithic lapilli tuff which has yielded a U-Pb age of 176.6 ± 0.7 Ma. Further to the north, volcanic stratigraphy in the Ramsey Peak area is dominated by three distinct groups of lithologies (Figure 4). The base of this section, which is presumed to overlie basaltic flows north of the Jumble Mountain section, is comprised of enormous thicknesses of massive, volcanogenic cobble to boulder conglomerate intercalated with very minor feldspathic-lithic wacke and thin tuffaceous beds. This comprises Unit A in the measured Ramsey Peak section (Figure 4). Overlying the massive conglomerates are moderately to poorly welded lapilli tuff and tuff breccia of felsic to intermediate composition and lesser volcanogenic wacke and mudstone (Unit B, Figure 4). The uppermost unit of measured section in the Ramsey Peak area, Unit C, comprises very thick, very densely welded, rhyolitic crystal-vitric tuff. Abundant plagioclase-phyric to aphyric basaltic dykes cut this section and are presumably related to a poorly exposed, plug-like basaltic intrusion that intrudes the conglomerates at the base of this section. Strata in this area continue northward from Ramsey Peak into the Oppy Lake basin, and will be examined during the 2004 field season. Stratigraphic units in the Jumble Mountain and Ramsay Peak area extend northward along strike past Tsaydaychuz Peak, which has been mapped by Woodsworth (1980) as the Early Jurassic Telkwa Formation, to the Mount Preston 137 Figure 4. Measured section from the Ramsey Peak study area, showing (a) the location of section shown in Figure 2, (b) a view to the north at southern flank of Ramsey Peak, and (c) a view to the southeast across Sigutlat Lake towards the Nechako Plateau. Units A, B, C, and D correspond with the vertical scale beside the measured section. The outcrop in Figure 4c displays a sharp contact between fine-grained mudstone and densely welded, columnar jointed crystal-vitric tuff within Unit B of the Ramsey Peak section (see above). area (Figure 2), where several measured sections were completed during the 2003 field season. Exposures in the Mount Preston area mainly consist of approximately northeast/southwest trending, shallowly-dipping volcaniclastic and sedimentary strata. The base of the measured section in the Mount Preston area is dominated by very fine-grained feldspathic-lithic wacke to mudstone interbedded with less abundant, chloritized, densely welded, quartz-eye bearing rhyolitic crystal-vitric tuff (Figure 5). These units are overlain by a series of plagioclase-phyric to aphyric, variably amygdaloidal basalt to basaltic andesite flows, pillow lavas and broken pillow breccia (Units A and B; Figure 5). Mafic flows are overlain by large thicknesses of feldspathic-lithic wacke and mudstone of variable bedding thickness and grain size, comprising unit C in this area (Figure 5). Interbedded within the 138 Figure 5. Measured sections from the Mount Preston study area, showing (a) locations of sections shown in Figure 2, (b) a view to the west towards Mount Preston (not visible), and (c) a view to the west into the cirque immediately south of Mount Preston. The cirque wall displays pillow basalts and broken pillow breccia (A), basaltic andesite flows (B), fine-grained volcanogenic mudstone (C), a basaltic plug (D), and a rhyolite dome (E). F and G correspond with the vertical scale beside respective measured sections. clastic sediments is a densely welded, dacitic vitric-crystal tuff which locally contains distinctive felsic plutonic clasts. These volcanic and sedimentary strata are intruded by an aphanitic basaltic plug, Unit D, which has a distinctly triangular-shaped cross section (Figure 5). The basaltic pillow lavas that form part of the base of this section are intruded by a rhyolite to rhyodacite flow-dome complex, with a well developed carapace breccia (Unit E; Figure 5). Overlying strata in measured sections F and G (Figure 5) consist of a clastic-dominated section, with abundant planar and trough cross-laminae and mudcracks (section F; Figure 5), and a more tuffaceous-dominated section (section G; Figure 5), with variably welded, rhyolitic to dacitic lapilli tuff intercalated with less abundant clastic material. 139 Preliminary petrographic studies of igneous and sedimentary rock units in the southern Whitesail Lake area show the effects of weak to locally stong chlorite and carbonate alteration. Mafic minerals present within mafic flows and intrusive bodies are pervasively altered to chlorite, and amygdules, where present, are filled with epidote, calcite, and/or quartz. Plagioclase phenocrysts are euhedral and unaltered in porphyritic samples, and groundmass material typically consists of microcrystalline plagioclase that forms a trachytic texture around phenocrysts. Felsic to intermediate composition tuffaceous rocks commonly contain euhedral and broken plagioclase phenocrysts. Welded material is partially or wholly devitrified. Plutonic lithic fragments, where present, appear to be syenitic in composition with distinctive rnyrmekitic textures. Samples from the rhyolite to rhyodacite flow-dome complex south of Mount Preston are generally aphyric, and contain locally abundant quartz-filled vesicles. Clasts in sedimentary units consist of broken plagioclase grains, fine grained basalt, and welded tuffaceous material. Ongoing petrographic and textural studies of rocks from this region will help further refine rock-unit designations and provide additional information related to the depth of water in which the various units were deposited. Mineral occurrences present within the southern Whitesail Lake study area include large and impressive gossans developed south of Mount Preston (Pond/Rivers Peak occurrence; BC MINFILE 093E 058) that are likely associated with porphyry-type systems related to small Late Cretaceous (?) porphyry intrusions. However copper mineralization in the form of small, mineralized quartz vein breccias were also noted in this area and this may represent older, possibly Hazelton-age, epigenetic mineralization. Several samples of the Cu-bearing breccias were collected for Pb isotope analysis to test this hypothesis. Numerous other mineral occurrences are also recorded in the BC MINFILE in the Mount Preston area (e.g., the Ron occurrences; BC MINFILE 093E 065, 079, 080, 081, 082); these are mainly narrow stringers, small pods and disseminations of chalcopyrite, pyrite, bornite and hematite in Hazelton Group volcanic rocks. REGIONAL STUDIES Regional studies during the 2003 field season included extensive sampling at the RDN (GOZ) property approximately 40 km northeast of Eskay Creek (BC MINFILE 104G 144; Figure 1), which is currently being explored as part of a joint venture between Barrick Gold Corporation and Rimfire Minerals Corporation. Samples were collected for U-Pb zircon dating of some of the main host rocks for mineralization on the property, and to geochemically characterize both the felsic host rocks and the intermediate^) to mafic volcanic rocks in the area. These data will permit a comparison between the age(s) and geochemistry of volcanic rocks on the RDN property and those at Eskay Creek, and will establish the paleotectonic environment in which the Early and Middle Jurassic rocks in the area formed. Drill core from a deep drill hole on "Pillow Basalt Ridge" between the Iskut River and Forest Kerr Creek approximately 12 km northeast of Eskay Creek was also examined and sampled for lithogeochemical and dating studies. Pillow Basalt Ridge is underlain by a very thick (>1.8 km) pile of mafic volcanic rocks (and minor interlayered argillite) that is thought to be correlative with the hangingwall basalts at Eskay Creek. If this correlation is correct, the section at Pillow Basalt Ridge represents a much thicker and more extensive accumulation of presumably rift-related mafic volcanics than are preserved in the immediate Eskay Creek area. This would have important implications for the geometry and extent of Eskay Creek-age rifting in this area. The Homestake Ridge property southeast of Stewart (Figure 1) was briefly visited together of personnel from the Bravo Ventures Group Inc., who are currently exploring the area. Samples of several of the main volcanic lithologies present in the Homestake Ridge area, as well as an extensive suite of sulphide samples, were collected for U-Pb dating, lithogeochemical and Pb isotopic studies to better constrain the nature and age of mineralization in the area. Several mineral occurrences hosted by Hazelton Group volcanic rocks in the southern Babine Range (Figure 1) have been interpreted by Wojdak (1998) to be potentially syngenetic in origin. Volcanic and sedimentary strata in this area have been assigned to' the Telkwa and Nilkitkwa formations by Maclntyre (1989) based on lithology and fossil age constraints, which indicate an age of Late Sinemurian to earliest 140 Toarcian for the immediate host rocks to mineralization. Syngenetic (?) mineralization in the area is therefore somewhat older than that at Eskay Creek. One of these occurrences (Harry Davis; BC MINFILE 0931 203, 204, 205 and 214), near the summit of Mt. Harry Davis north of Houston, was briefly examined and sampled for lithogeochemical analysis, Pb isotopic studies and U-Pb dating. In this area a thick section of flow-banded, quartz- and feldspar-phyric rhyolite is associated with bedded red and maroon lapilli tuffs which locally contain accretionary lapilli. Stratabound, possibly syngenetic, mineralization occurs in the form of sphalerite layers in thinly laminated chert, and epigenetic quartz-calcite-sphalerite(± fluorite) veins are also present in the area (Wojdak, 1998). GEOCHEMICAL STUDIES -PRELIMINARY RESULTS Geochemical studies of igneous rock units from the southern Whitesail Lake area and a regional sample suite are underway to characterize the geochemical affinity of each of the units and place constraints on the paleotectonic setting in which they were emplaced. Complete major, trace and rare earth element analyses have been obtained from 40 representative samples of intrusive and extrusive rock units from the southern Whitesail Lake study area and 29 samples of Hazelton Group rocks collected during regional investigations elsewhere in Stikinia. Preliminary interpretations of the data are presented in Figures 6 and 7, and discussed briefly below. Work thus far has focused on geochemically characterizing the various rock suites; detailed comparisons with volcanic host rocks for the Eskay Creek deposit have not yet been done. Data from the southern Whitesail Lake study area, together with reconnaissance data from host volcanic rocks at the Nifty VMS occurrence in the northern Bella Coola map area (from Ray et al., 1998) are shown on various geochemical discriminant plots in Figure 6. The following main observations arise from the data. Volcanic and subvolcanic rock units in southern Whitesail Lake map area geochemically closely resemble the broadly age equivalent early Middle Jurassic host volcanic rocks at the Nifty occurrence which on strike to the southeast. They are broadly bimodal in composition (mainly basalt to basaltic andesitic and dacitic to rhyodacitic). The felsic units are all subalkaline; however the mafic units include both subalkaline and alkaline compositions. Although on an A F M diagram the Whitesail Lake samples fall mainly in the calc-alkaline field (as do the Nifty samples), immobile trace element plots such as Y vs. Zr (Figure 6) indicates that they are predominantly tholeiitic to transitional in composition. A plot of Rb vs. Y+Nb suggests that all of the volcanic rocks formed in a volcanic arc setting; however immobile trace element plots such as V vs. T i 0 2 (Figure 6) indicate that the mafic volcanic and subvolcanic units include both island arc tholeiites and back-arc tholeiites. These mixed volcanic arc/back arc geochemical signatures are very similar to those described by Barrett and Sherlock (1996) at Eskay Creek, and is consistent with an overall rifted arc (intra-arc or back-arc) setting. Most of the samples collected during regional investigations during the 2003 field season were from the general vicinity of known mineralization, hence most of them show evidence of moderate to strong hydrothermal alteration. Because of this, some major and trace elements have been mobilized and cannot be used to characterize the original geochemical composition and petrotectonic affinity of the samples. Data from three of the areas examined during the regional study (Pillow Basalt Ridge north of Eskay Creek), Homestake Ridge, and the southern Babine Range) are discussed briefly here, focusing mainly on immobile trace elements. Pillow Basalt Ridge northeast of Eskay Creek comprises a thick section of basaltic flows and less abundant hyaloclastites, locally with thin interbeds of argillite. The volcanic rocks and a 28 m thick medium-grained gabbro sill that intrudes the section and is presumed to be synvolcanic range from basalt to basaltic andesite in composition. On A F M and Y vs. Zr plots the Pillow Basalt Ridge samples all fall in the tholeiitic field (Figure 7), and V vs. Ti02 and Rb vs. Y+Nb plots indicate both island arc tholeiitic and back-arc affinities (Figure 7). These geochemical characteristics are similar to those for the hangingwall basalt at Eskay Creek and support a correlation between these two volcanic packages. Two flow-banded felsic domes have been recognized at Homestake Ridge (R. MacDonald, personal communication, 2003). These domes were emplaced into a sequence of mainly intermediate^) composition volcanic breccias 141 FeO* .01 .001 Rhyolite Rhyodacite/ i Dacite Andesite A 7* ~ AndesltetBasaJt • — SubAlkallno Basalt <$) i TrachyAnd Alk-Bas .01 .1 10 Nb/Y 600 500 400 300 200 100 0 Low-T i lAT , 1 0 ARC<20>OFB ' B 0 N / 1AT / / \ A / MORB / / BAB MORB Alk MgO transitional ...JJIL. 1000 Figure 6. Geochemical discriminant diagrams for volcanic and shallow intrusive rocks in the southern Whitesail Lake study area. Closed squares indicate felsic tuffaceous and intrusive units and closed triangles indicate mafic intrusive and extrusive units. Open diamonds are analyses of felsic and mafic samples from the vicinity of the Nifty prospect (data from Ray et al., 1998). and argillite. Several bodies of plagioclase-hornblende (± biotite) porphyry also intrude the volcaniclastic and argillite package. The felsic domes and feldspar-hornblende porphyry intrusions are similar in composition (scatter on the total alkalies vs. SiC>2 and A F M diagrams likely reflects major element mobility during the strong hydrothermal alteration that has affected all of the units in the area). They are all calc-alkaline, subalkaline and range from dacite to rhyolite in composition. On a Rb vs. Y+Nb plot all of the Homestake Ridge samples fall well within the volcanic arc field; however on a V vs. T i 0 2 plot their compositions are consistent with eruption in a rifted arc setting. A single sample from a flow-banded, sparsely quartz- and feldspar-phyric rhyolite sampled immediately south of the summit of Mt. Harry Davis in the southern Babine Range yields a calc-alkaline rhyolitic composition with a volcanic arc affinity. 142 F e d * §.10 z 35 O £ ft .01 .001 600 500 400 r 300 200 100 0 -I T — r T X T T T y -[ I—[- r T i i 1TT. =- Com/Pant A Phonolite -= - Rhyolite^^ - \ / _ • V / Trachyte T " H — Rhyodacite/Dactte = TrachyAnd _ Andesite , " — -O—y^ Bsn/Nph Andesite/Basalt_.„/ Alk-Bas -SubAlkaline Basalt I .01 10 Nb/Y I - Low-TI IAT, BON j 10 ARC<20>OFB / 0 I IAT / 0 MORB / BAB MORB ,50 / °/ Alkaline -lOtT / /Aa ~ / / • / / / • 1 1 ..I Alk MgO 70 10 15 Ti/1000 20 25 Figure 7. Geochemical discrimination diagrams for volcanic and shallow intrusive rocks from regional investigations of the upper Hazelton Group. Open circles are basalts from Pillow Basalt Ridge and the single closed circle is a gabbro body that intrudes the basalts. Closed squares and closed triangles are flow-banded rhyolite and plagioclase (± hornblende) porphyry bodies at Homestake Ridge. Closed diamond is a flow-banded rhyolite ata the HD prospect on Mt. Harry Davis in the southern Babine Range. 143 GEOCHRONOLOGY AND LEAD ISOTOPIC STUDIES A number of samples are presently being processed for U-Pb zircon dating, including several felsic tuff and flow dome samples from the southern Whitesail Lake area, several samples from the RDN and Homestake Ridge properties, an intrusive diorite/gabbro from the Pillow Basalt Ridge section, and a single rhyolite unit from the southern Babine Range. An extensive suite of sulphide samples from all of the studied areas is also being prepared for Pb isotopic analysis. DISCUSSION AND PRELIMINARY CONCLUSIONS Although still at an early stage of a projected two-year project, our results thus far provide some new insights into the nature of upper Hazelton Group magmatism in several parts of Stikinia and the regional potential for additional ECT deposits. Mapping in the southern Whitesail Lake area has shown that the host stratigraphy for the Nifty VMS occurrence, which has been shown to be age equivalent to host rocks at Eskay Creek, extends at least another 75 km to the northwest. Furthermore facies analyses of these strata indicate predominantly shallow water deposition, and suggest formation in a rifted arc setting at the termination of Hazelton arc magmatism. Both of these characteristics, together with the presence of subaqueous felsic flow domes, are highly prospective for formation of ECT mineralization, similar to that at the Nifty occurrence. Several VMS prospects are known to occur farther along strike to the northwest in southwestern Whitesail Lake map area; these will be examined during the 2004 field season. Preliminary work at Pillow Basalt Ridge north of Eskay Creek supports the suggestion that these basalts are stratigraphically equivalent to the hangingwall basalt at Eskay Creek. The great thickness of basalts present on Pillow Basalt Ridge (nearly 2 km), however, indicates that the latest stage of Hazelton Group magmatism in this area occurred during much more extensive rifting and associated subsidence than was manifest at Eskay Creek. The implications of this for ECT potential in the area are still uncertain. Field examinations, preliminary geochemical studies, and discussions with industry geologists suggest that the Homestake Ridge mineralization occurs within a somewhat older portion of the Hazelton Group than Eskay Creek. In particular the plagioclase (± hornblende) porphyry bodies that intrude the section lithologically and geochemically resemble ~197-202 Ma intrusive units at the Red Mountain and Silbak Premier deposits to the northwest. Since these porphyry bodies intrude the felsic domes, intermediate volcaniclastic units and argillites that underlie much of the Homestake Ridge property, it appears unlikely that Eskay Creek stratigraphic equivalents are present in the area. U-Pb dating is underway to test this. A number of small VMS occurrences are known to be present within Betty Creek Formation-equivalent rocks of the Hazelton Group in the Kisault River valley to the south (e.g., Pinsent, 2001), however; thus the potential for syngenetic mineralization on Homestake Ridge cannot be ruled out. Work carried out at the RDN property north of Eskay Creek was done as part of the industry-funded portion of this project, and results from that work are subject to a one-year confidentiality agreement. Reconnaissance examinations of volcanic sections in the southern Babine Range and a single geochemical analysis of a flow-banded rhyolite unit in the area support the suggestion by Wojdak (1998) that these strata are somewhat older than the host rocks at Eskay Creek. U-Pb geochronology and Pb isotopic work is underway to more precisely constrain the age of the host rocks to possible syngenetic mineralization in this area and test whether the mineralization in this area is indeed syngenetic, or is epigenetic and unrelated to Hazelton Group magmatism. FUTURE WORK A considerably more extensive field season is planned for 2004, including approximately 6-8 weeks of mapping to complete the Whitesail Lake mapping project, and examination and sampling of a number of VMS (?) occurrences throughout the Hazelton Group. This regional work will be done in conjunction with industry geologists as well as BC Geological Survey 144 Branch and Geological Survey of Canada personnel. ACKNOWLEDGMENTS Danny Hodson of Rainbow West Helicopters and Richard LaPointe of West Coast Helicopters provided outstanding helicopter support during the 2003 field season. We thank Jim Haggart and the Geological Survey of Canada for providing logistical support for the mapping project, Lori Snyder for assistance and insights in the field, and Larry Diakow for valuable on-going discussions about Hazelton Group stratigraphy in the Bella Coola and Whitesail Lake areas and throughout Stikinia. Casey Bowe provided cheerful assistance in the field. We also thank Ian Dunlop and Aletha Buschman of Barrick Gold for guidance and discussions during field work in the Eskay Creek area, Rob MacDonald of Bravo Ventures Group for guidance during a visit to the Homestake Ridge property, Paul Wojdak of the BC Geological Survey Branch for valuable discussions concerning VMS occurrences in the southern Babine Range, and Paul McGuigan of Cambria Geosciences for insights into the regional VMS potential in Stikinia. Funding for this project was provided by the Rocks to Riches Program, which is administered through the BC & Yukon Chamber of Mines, as well as four mining companies (Barrick Gold Corp., Heritage Exploration Inc., Kenrich-Eskay Mining Corp. and Placer Dome Inc.). Richard Friedman is thanked for critically reading the manuscript. REFERENCES Barrett, T.J. and Sherlock, R.L. (1996): Geology, lithogeochemistry and volcanic setting of the Eskay Creek Au-Ag-Cu-Zn deposit, northwestern British Columbia; Exploration and Mining Geology, Volume 5, pages 339-368. Childe, F. (1996): U-Pb geochronology and Nd and Pb isotope characteristics of the Au-Ag-rich Eskay Creek volcanogenic massive sulfide deposit, British Columbia; Economic Geology, Volume 91, pages 1209-1224. Childe, F. (1997): Timing and tectonic setting of volcanogenic massive sulphide deposits in British Columbia: constraints from U-Pb geochronology, radiogenic isotopes and geochemistry; University of British Columbia, Unpublished Ph.D. thesis, 557 pages. Diakow, L.J., Mahoney, J.B., Gleeson, T.G. , Hrudey, M.G. , Struik, L.C. and Johnson, A.D. (2002): Middle Jurassic stratigraphy hosting volcanogenic massive sulphide mineralization in eastern Bella Coola map area (NTS 093/D), southwest British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 2001, Paper 2002-1, pages 119-134. Haggart, J.W., Mahoney, J.B., Diakow, L.J., Woodsworth, G.J., Gordee, S.M., Snyder, L.D. , Poulton, T.P., Friedman, R.M. and Villeneuve, M.E. (2003): Geological setting fo the eastern Bella Coola map area, west-central British Columbia; Geological Survey of Canada, Current Research 2003-A4, 9 pages. Hannington, M.D., Poulsen, K . H . , Thompson, J.F.H., and Sillitoe, R.H. (1999): Volcanogenic gold and epithermal-style mineralization in the V M S environment; In Barrie, C.T., and Hannington, M.D., Volcanic-Associated Massive Sulfide Deposits: Processes and Examples in Modern and Ancient Settings: Reviews in Economic Geology, Volume 8, pages 325-356. Juras, S.J. and Spooner, E.T.C. , eds. (1996): Volcanogenic Massive Sulfide Deposits of the Cordillera, Exploration and Mining Geology, Volume 5, Number 4, pages 281-458. Lewis, P.D. and Tosdal, R .M. (2000): Metallogenesis of the Iskut River area, northwestern British Columbia; Mineral Deposit Research Unit, Special Publication No. 1, 337 pages. Maclntyre, D.G., Desjardins, P. and Tercier, P. (1989): Jurassic stratigraphic relationships in the Babine and Telkwa ranges (93L/10, 11, 14,15); B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 1988, Paper 1989-1, pages 195-208. Massey, N.W.D. (1999): Volcanogenic massive sulphide deposits in British Columbia; B.C. Ministry of Energy and Mines, Open File 1999-2. Massey, N.W.D., Alldrick, D.J. and Lefebure, D.V. (1999): Potential for subaqueous hot-spring (Eskay Creek) deposits in British Columbia; B.C. Ministry of Energy and Mines, Open File 1999-14. Nadaraju, G.D. (1993): Triassic-Jurassic biochronology of the Iskut River map area, northwestern British Columbia; University of British Columbia, Unpublished M.Sc. thesis, 268 pages. Pinsent, R.H. (2001): Mineral deposits of the Upper Kitsault River area, British Columbia (103P/W); B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 2000, Paper 2001 -1, pages 313-326. Ray, G.E., Brown, J.A. and Friedman, R.M. (1998): Geology of the Nifty Zn-Pb-Ba prospect, Bella Coola district, British Columbia; B.C. Ministry 145 of Energy, Mines and Petroleum Resources, Geological Fieldwork 1997, Paper 1998-1, pages 20-1-20-28. Roth, T., Thompson, J.F.H. and Barrett, T.J. (1999): The precious metal-rich Eskay Creek deposit, northwestern British Columbia; In Barrie, C.T., and Hannington, M.D., Volcanic-Associated Massive Sulfide Deposits: Processes and Examples in Modern and Ancient Settings: Reviews in Economic Geology, Volume 8, pages 357-373. Roth, T. (2002): Physical and chemical constraints on mineralization in the Eskay Creek deposit, northwestern British Columbia: Evidence from petrography, mineral chemistry, and sulfur isotopes: University of British Columbia, Unpublished Ph.D. thesis, 401 pages. Wojdak, P. (1998): Volcanogenic massive sulphide deposits in the Hazelton Group, Babine Range, B.C.; B.C. Ministry of Energy, Mines and Petroleum Resources, Exploration and Mining in British Columbia 1998, pages C1-C13. Woodsworth, G.J. (1980): Geology of Whitesail Lake (93E) map area, British Columbia; Geological Survey of Canada, Open File 708, 1:250 000. VOLCANOSTRATIGRAPHY, LITHOGEOCHEMISTRY AND U-PB GEOCHRONOLOGY OF THE UPPER HAZELTON GROUP, WEST-CENTRAL BRITISH COLUMBIA: IMPLICATIONS FOR ESKAY CREEK-TYPE VMS MINERALIZATION IN SOUTHWEST STIKINIA S.M. Gordee1, J.K. Mortensen1, J.B. Mahoney2, R.L. Hooper2 KEYWORDS: Volcanostratigraphy, volcanogenic massive sulphide deposits, Eskay Creek, Stikinia, Early-Middle Jurassic, Hazelton Group, Bella Coola area, Whitesail Lake area, Rocks to Riches program INTRODUCTION The Hazelton Group is one of the most widely exposed Mesozoic volcanic arc successions in the Canadian Cordillera, occurring along nearly the entire length and breadth of the Stikine Terrane (Figure 1). Despite hosting a number of significant mineral deposits (e.g., Eskay Creek-type volcanogenic massive sulphide (ECT-VMS) deposits, epithermal gold and associated copper-gold porphyry deposits in subvolcanic intrusions; Diakow et al, 2002), there have been relatively few regional studies of the nature of Hazelton Group arc magmatism outside of the immediate vicinity of known deposits (e.g., Tipper and Richards, 1976; Marsden and Thorkelson, 1992; Thorkelson et al., 1995). This study investigates Hazelton Group successions in the Bella Coola and Whitesail Lake map areas of west-central British Columbia in order to constrain the evolution of the volcanic package and assess its potential for economic mineralization. This study builds upon the framework established through a joint federal-provincial Targeted Geoscience Initiative (TGI) that operated in the area from 2001-2004 (e.g., Haggart et al., 2004 and references therein), and aims to refine our understanding of the tectonic setting and specific depositional environments) of rocks emplaced during Hazelton arc volcanism and sedimentation. This could provide controls on the existence and/or nature of syngenetic mineralization within the Hazelton Group in this area. Bella Coola is located within a rugged part of the Coast Mountains, and includes the topographic divide and transition zone between the Coast and Intermontane morphogeological belts (Figure 1, inset). Specifically, the northeastern Bella Coola (093D)/southeastern Whitesail Lake (093E) map area is situated in southwestern Stikinia of the Intermontane Superterrane (Figure 1). In this area (predominantly the eastern half of 093D/15 and 093E/02), thick, laterally continuous, dominantly eastward-younging successions of Lower-Middle Jurassic Hazelton Group form the high, jagged massifs along the western boundary of Tweedsmuir Provincial Park. To the east of this area, exposures of the Hazelton Group are unconformably overlain by remnants of a moderately dissected Miocene peralkaline shield volcano forming the Rainbow Range (Diakow et al., 2002 and references therein). Exposures of Hazelton Group decrease progressively to the west, where they are unconformably overlain by the Cretaceous Monarch Assemblage and intruded by numerous Jurassic to Eocene plutons of the Coast Plutonic Complex. Volcanogenic strata within the study area is relatively structurally intact, in contrast to Hazelton Group and Monarch Assemblage exposures further to the west, which are variably deformed within the Waddington Fold and Thrust belt (Mahoney et al., 2005, this volume). PRELIMINARY RESULTS FROM GEOLOGIC MAPPING Two summers of field mapping (2003-2004) in the northeastern Bella Coola/southeastem Whitesail Lake map area focused on the area between Jumble Mountain in the south and Mount Preston in the north (Figure 2). Hazelton Group volcano-sedimentary successions in this area represent a northwestern continuation of the package of mainly felsic volcanic strata that host the Nifty VMS occurrence in the east-central Bella Coola map area (e.g., Ray et al., 1998; Diakow et al., 2002; Haggart et al., 2004). U-Pb dating of a dacite breccia that hosts mineralization at Nifty indicates an age of 163.7 ± 0.4 Ma (M. Villeneuve, unpublished data), and this, together with several ca. 176 Ma dates and Early-Middle Jurassic fossil collections from the northeastern Bella Coola map area, demonstrates that Hazelton Group rocks in this area are roughly age equivalent to host rocks of the Eskay Creek deposit. This study targeted four main areas in the 30km transect between Jumble Mountain and Mount Preston, including (from south to north): the Jumble Mountain/Ramsey Peak area, the Tsaydaychuz Peak/Butler Peak area, Tesla Mountain and the Rivers Peak/Mount Preston area (Figure 2). Fly camps were 'Minera l Deposit Research Unit , Department o f Earth and Ocean Sciences, The Universi ty o f Bri t ish Columbia , Vancouver, B . C . depar tment o f Geology, Universi ty o f Wiscons in at Eau Claire , Wisconsin , U . S . A . 147 Figure 1. Distribution of Early-Middle Jurassic volcano-sedimentary strata of the Hazelton Group (shown in green) within the Stikine Terrane of British Columbia (outlined with dashed boundary), showing specific localities referred to in the text, and the northeast Bella Coola/southeast Whitesail Lake map area (black box). The inset map illustrates the morphogeologic belts of the Canadian Cordillera (modified after Wheeler and McFeely, 1991). placed in central locations within these areas, and traverses were completed in accessible, subalpine regions, where outcrop is continuous among snow and ice fields. Inaccessible areas were spot-checked with helicopter support. Field investigations focused on the identification and development of large-scale lithologic subdivisions, detailing and measuring volcanostratigraphic sections, defining large-scale structures, geochemical, isotopic and geochronologic sampling and characterization of mineral occurrences recognized within the study area. number of key observations to be made based on interpretation of large-scale lithologic subdivisions across the map area. Figure 3 shows a schematic volcanostratigraphic fence diagram of measured sections within the field area (section lines drawn in Figure 2), and can be referred to throughout this section. Horizontal and vertical distances are scaled accordingly; U-Pb, fossil ages and lithologic associations are used to correlate between the sections. Tsaydaychuz Peak and Butler Peak Areas VOLCANOSTRATIGRAPHY Geologic mapping and analysis of numerous volcanostratigraphic sections in studied areas throughout the 2003 and 2004 field seasons permits a Map patterns and cross-cutting relationships suggest that the Tsaydaychuz Peak/Butler Peak area comprises the base of the volcano-sedimentary sequence 148 127°30" 126"30" 53°00 IKfm F o u r M i l e s u i l e (ca 70 Ma) Fougner suite (ca. 70 Ma) | eKd | Desire suite (ca. 120 Ma) IJsp | Stick Pass suite (ca. 150 Ma) rnJg | Trapper pluton (ca. 177 Ma) K fT IVp volcanoplutonic KqdC quartz diorite complex Figure 2. Generalized geologic map of the northeast Bella Coola/southeast Whitesail Lake map area, showing major lithologic subdivisions, structures and physiographic features referred to in the text (modified after Mahoney et al., 2005, this volume). Location of measured sections is indicated by bold lines adjacent to encircled numbers. Basalt and basaltic andesite flow I I Tuffaceous mudslone Basalt and basaltic andesite pillow lava ITT71 Volcanic-lilhic-feldspathic sandstone Basall and basaltic andesite plug Andesite flow Dacite flow, plug or ignimbrite ] Rhyolite flow or ignimbrite Rhyolite dome or QFP intrusion I" 1 Mudslone and granule to pebble mudstone r~~l Volcanic pebble- lo cobble-conglomerate Diorite to quartz diorite plulon + U-Pb age F Fossil age 'Thicknesses are approximate J» + 175.4 ± 0 . 9 M a + 176.3 ± 3 . 3 M a 1 0 1 2 3 4 5 Rivers Peak/ Mount Preston study area © © Tesla Mountain Tsaydaychuz/ study area Butler Peak study area Jumble Mountain/ Ramsey Peak study area Figure 3. Measured volcanostratigraphic sections of the Hazelton Group within the northeast Bella Coola/southeast Whitesail Lake map area. in the map area. Rocks of this area overlie mafic to intermediate, dominantly fragmental successions west of the East Sakumtha River, where a U-Pb date from a quartz-phyric dacite breccia indicates an age of 191 ± 12 Ma (R.M. Friedman, unpublished data). Separating the two sections is a broad, NW/SE-trending belt of complexly interfingering aphanitic basalt, and very fine-to medium-grained diorite and lesser quartz diorite ("microdiorite"); the latter may represent recrystallized mafic flows and/or small pyroxene diorite plug-like intrusions (Haggart et al., 2004). Importantly, this belt of mafic-intermediate rocks may record the early stages of the widespread basaltic-andesitic volcanism that characterizes the Tsaydaychuz Peak/Butler Peak region. Tsaydaychuz Peak is the highest massif within the Whitesail Lake map sheet. At 9,085 feet (2,769 meters) in elevation, its vertical walls and extensive ice cover render the mountain completely inaccessible, and has limited us to numerous spot checks along its flanks. Extensive traversing has been completed in the Butler Peak area, and assuming no major structure exists between the two peaks, volcanogenic strata and field relationships observed at Butler Peak are presumed to extend to its sister mountain to the south. Traverses completed in the Butler Peak region encompass the subalpine region between north Tsaydaychuz Peak and north Butler Peak (Figure 2). Strata in the area generally strike north-northwesterly and dip gently to moderately to the east; exposures west of Butler Peak are dominated by volcaniclastic rocks, while further up section to the east, lithologies are dominated by intermediate and lesser mafic flows and subvolcanic intrusions. Volcanostratigraphy west of Butler Peak is dominated by orange-purple, massive, coarse-grained tuff breccia, lapilli tuff and lesser tuff. Tuff breccia and lapilli tuff units range from l-25m in thickness and are dominantly very lithic- and crystal-rich; modal phenocryst assemblages (plagioclase and rare quartz) suggest an intermediate to felsic composition for these fragmental rocks. Tuffs rare throughout this area; these <l-5m-thick units are typically very light grey to tan in color and plagioclase is locally observed as the only phenocryst phase. Pyroclastic rocks comprise about 45% volume of exposed bedrock in the west Butler Peak region, and are intercalated with lesser (~15%) sandstone and mudstone beds. Ignimbrite units commonly display a gradational upper contact with overlying sedimentary beds, which are sharply overlain by subsequent ignimbrite units. Volcaniclastic rocks are typically either a deep purple-maroon and dark green (more typical of Hazelton Group sediments throughout the Bella Coola and^Whitesail Lake map areas) or white to tan to grey in color. They generally consist of interbedded, thin to medium-bedded, dominantly parallel, wavy and locally ripple cross laminated, ± granule ± pebble mudstone and lesser conglomerate, sandstone and siltstone. Sedimentary rocks are typically immature, ranging from poorly- to moderately well-sorted, with angular to subangular clasts of aphanitic to plagioclase ± hornblende-phyric basalt, andesite, dacite and rhyolite. Fossils have not been found in this area. The remaining 40% of outcrop in the west Butler Peak region consists of mafic lava flows, which occur in two broad, N/S-trending belts across the map area. The bases and tops of these flows are commonly not exposed, but where present, occur as meter-scale brecciated zones. Flows range from dark grey-purple to dark grey-green, are aphyric to plagioclase ± pyroxene-phyric, variably amygdaloidal (epidote- and quartz-filled), and are remarkably poorly layered. Crude compositional and/or textural boundaries (on a scale of 10s of meters) within flow(s) that are approximately concordant with local strike trends may represent differences between individual flows, or may simply be variations within a single flow. One spectacular exposure of radiating cooling joints within the sequence (approximately 25m high) may represent a cross-section through a lava feeder tube. Part of the volcano-sedimentary sequence in this region is assumed to be subaqueous on the basis of an outcrop of orthogonally-dissected pillowed basaltic andesite, which is exposed along a vertical cleft on the southwestern margin of the field area (Photo 1). A number of small, bladed-plagioclase andesite porphyry plugs and associated dykes cut the volcanic successions in the area, and are interpreted to represent hypabyssal subvolcanic intrusions. Geologic mapping suggests that the Tsaydaychuz Peak region, which lies directly along strike to the south, likely represents the southern continuation of the volcanostratigraphic section documented in the Butler Peak region. Numerous spot checks and sample collections completed along the flanks of the massif yielded similar rock-types and lithologic associations, which supports this generalization. The size and abundance of basalt to basaltic andesite lava flows and bladed-plagioclase porphyry plugs increases dramatically east of Butler Peak. The area is being collectively described as the Butler Peak andesitic complex, and is characterized by a complexly interfingering assemblage of basalt to basaltic andesite lava flows, dykes and hypabyssal intrusions, gabbroic to dioritic plugs, widespread microdiorite and <10% welded lapilli tuff and intercalated volcanogenic sediments; the latter are commonly locally folded around intrusive units. As in the lower portion of the section, individual lava flows in this area are commonly difficult to subdivide; lava flow margins, where observed, are highly brecciated over a thickness of 3-5 meters. Intrusive relationships are complex and the relative timing between units is often ambiguous, and this, coupled with the compositional similarities shared between rock types, leads to the interpretation that this area comprises a mafic eruptive center. Geochemical comparisons and U-Pb dating studies are currently 151 underway to test this hypothesis and potentially confirm the coeval nature of rocks in this area. At least four rhyolite domes have been identified that intrude the volcanic sequences in the Tsaydaychuz Peak/Butler Peak area. Domes are pink to white in color, aphanitic to plagioclase ± quartz-phyric, massive to flow-banded, rarely fragmental, and are associated with gossans characterized by disseminated pyrite west of Butler Peak. It is uncertain whether these units represent intrusive and/or extrusive domes. Tesla Mountain Area The Tesla Mountain area comprises a low, E/W-trending ridge immediately south of Tesla Lake, approximately 4km north of Butler Peak (Figure 2). Structural trends suggest that this area should represent the northern continuation of the east-dipping outcrop belt in the Tsaydaychuz Peak/Butler Peak region, and although this can be assumed based upon lithologic and structural similarities between the two areas, a number of differences were noted. Important differences include: (a) a decrease in mafic volcanic rocks; (b) a subsequent increase in the proportion of volcaniclastic material, including a thick section of pyritiferous tuffaceous mudstones; (c) the existence of several mineral showings; and (d) a pervasive, well-developed deformation fabric throughout the area. The widespread mafic volcanic rocks that characterize the Tsaydaychuz Peak/Butler Peak region extend northward into the Tesla Mountain area, but decrease in volume significantly across the 4km distance; mafic flows and subvolcanic intrusions are subordinate to volcaniclastic rocks and fine-grained volcanogenic sediments in this area. In general, the western half of this mountain consists of volcanogenic sedimentary rocks and lesser welded ignimbrite sequences with interbedded mafic lava flows, which increase in thickness and number to the east across the summit of Tesla Mountain. Complex, outcrop-scale folding is developed west of Tesla Mountain, where mafic plugs intrude volcaniclastic sequences, a lithologic association that is consistent with observations made in the west Butler Peak region. Possible pillows in flow-banded basaltic flows northwest of Tesla Mountain suggest that part of this section may represent a submarine sequence. A thick section of tuffaceous mudstone exposed west of Tesla Mountain is unique to the field area. This sequence is approximately lOOm-thick and consists of interbedded thin to medium bedded, parallel laminated mudstone and rhyolitic tuffaceous mudstone and lesser siltstone and sandstone (Photo 2). Outcrops weather rusty orange in part, and upon initial examination appear to be devoid of sulphides; however, cut slabs reveal thin, conformable layers of disseminated to semi-massive pyrite. Petrographic studies are in progress to determine whether this represents syngenetic or epigenetic mineralization. Several small rhyolite plugs and associated dykes similar to those described near Butler Peak cut the volcanic sequence near the summit of Tesla Mountain. These rhyolites are highly silicified and are responsible for wide alteration haloes and minor disseminated pyrite in the surrounding country rock. At least one claim has been staked, and several prospecting pits have been excavated on or near the margins of these intrusions. Mineralization in the form of narrow veins of hematite, pyrite, chalcopyrite and malachite has been observed within mafic dykes at two locations in the west Tesla Mountain area. A zone of fracture-controlled, comb-textured quartz veins occurs near the top of Tesla Mountain; these veins are devoid of mineralization, but may be related to "rather disappointing", narrow and low grade Cu- and Au-bearing veins described in this area by Duffell (1959). The Tesla Mountain region displays a very well-developed, pervasive, E/W-trending close-spaced cleavage. This fabric extends to the south into the northwest Butler Peak region, where it is locally well-developed, but does not extend across Tesla Lake into the Rivers Peak region to the north. The nature and localization of this fabric suggests that Tesla Mountain represents a zone of localized strain associated with regional deformation. Much of the vein- and dyke-hosted mineralization observed in the Tesla Mountain area appears to be concentrated along these zones of structural weakness. It has been hypothesized that the large, linear lakes and valleys in the Tesla Lake area may represent major faults bounding large structural blocks (e.g., Duffell, 1959). South of Tesla Mountain, Lower to Middle Jurassic volcanic stratigraphy forms an east-dipping, eastward-younging homocline, based on geologic mapping, paleontology and U-Pb ages. Conversely, north of Tesla Lake between Rivers Peak and Mount Preston, strata dip and young to the west and northwest, demonstrating the existence of an E/W-trending structure that lies within the Tesla Lake basin. Uppermost Volcanostratigraphy U-Pb dating of tuffs within the Rivers Peak/Mount Preston and Jumble Mountain/Ramsey Peak areas has established that the two homoclines are of similar age, and geologic mapping suggests that they represent the youngest Hazelton Group strata in the study area. Individual units cannot be traced between the two areas; however, broadly similar lithologies on a hundreds of meter-scale, together with U-Pb dating, demonstrate that these areas represent similar volcanic and sedimentary depositional environments. 152 Photo 1. Cross-section through a stack of basaltic-andesite pillow lavas in the west Butler Peak region. Note the large pillow in the upper left corner. Ice axe (~60cm) for scale. J U M B L E M O U N T A I N A N D R A M S E Y P E A K A R E A S Detailed geologic mapping in the Jumble Mountain/Ramsey Peak area carried out during the 2004 field season has significantly expanded the area covered during the 2003 field season. Previous work concentrated on the area between NE Jumble Mountain and Ramsey Peak, whereas work during the 2004 field season focused on the area further to the north, between Ramsey Peak and Oppy Lake. Results from work completed in this area during 2003 field season are detailed in Mortensen et al. (2004). In general, the area between Jumble Mountain and Oppy Lake consists of an eastward-younging succession of thick ignimbrites intercalated with lesser marine sandstone and siltstone, mudstone, conglomerate and mafic lava flows near the base. Near Jumble Mountain, the section is cut by numerous mafic plugs, sills and dykes, which may be the source of these minor basaltic lava flows. Mafic flows are generally dark green to red, aphanitic and variably flow-banded and brecciated, whereas the intrusive equivalents are dark green to grey and range from aphanitic to plagioclase ± pyroxene ± hornblende-phyric basalt to andesite to microdiorite plugs. Mafic rocks in this area presumably represent the southern extent of the mafic eruptive center comprising the Tsaydaychuz Peak/Butler Peak area, which lies directly along strike to the north. Ignimbrites in this area are pink to purple to grey, massive, unstructured, poorly to moderately welded, lithic- and crystal-rich, and range from tuff to lapilli tuff to tuff breccia. Sedimentary rocks are variably fossiliferous and consist of fine- to coarse-grained feldspathic-lithic wacke and calcareous lag deposits. Fossils present in the coquinas include a diverse assemblage of bivalve taxa, high-spired gastropods, rare belemnoids, and possibly mollusk fragments, most of which are thick-shelled and robust and are of shallow-marine forms that characterize the sublittoral region. Many shells have been abraded due to high-energy post-mortem processes, and this, coupled with a distinct grading and lateral continuity of shell beds suggests that these beds represent storm deposits. The articulated nature of shells in some beds implies a rapid sedimentation rate. Ammonites recovered from this section during previous field seasons have been identified as probable Early Aalenian taxa (T.P. Poulton, personal communication, 2003) , and a U-Pb zircon age of 176.6 ± 0.7 Ma was obtained from an overlying rhyolitic crystal-lithic tuff (R.M. Friedman, unpublished data; Mortensen et al., 2004) . Volcanic composition changes to a more intermediate- to felsic-dominated system further up section between Ramsey Peak and Oppy Lake, as evidenced by a decrease in mafic lavas and subvolcanic intrusions and a subsequent increase in intermediate to felsic ignimbrites and associated plugs and dykes. Ignimbrites range from tuff to lapilli tuff to tuff breccia and are purple to pink to dark grey, massive, poorly to moderately welded, crystal- and lithic-rich, and typically 5-20m-thick. Several very coarse-grained volcanic units within this section may represent vent-proximal and/or intra-caldera facies. These coarse facies range from lapillistone to tuff breccia to block tuff, and commonly include lapilli- to block-size, chloritized pumice/fiamme. At least two anomalously thick tuffaceous units exist within this section, each of which includes a very thick, very densely welded facies. These units are homogeneous throughout their observed lateral extent, and are purple, massive, very densely welded, rhyolitic ± lithic-crystal-vitric tuff to lapilli tuff, with unwelded and lithic- and crystal-rich basal and upper contacts (Photo 3). The calculated thickness of one of these units exceeds 400m - a thickness that may also support an intra-caldera or near vent setting for rocks in this area. As in the Tsaydaychuz Peak/Butler Peak region, primary volcanic units in this area commonly display a gradational upper contact, transitioning into lithic- and crystal-rich wacke and mudstone units, which, in turn, are sharply overlain by succeeding ignimbrite units. Sedimentary rocks in this package are dark maroon, thin to medium-bedded to massive, parallel laminated to structureless mudstone to granule to pebble mudstone. Individual mudstone beds commonly contain up to 10%, articulate to inarticulate armored accretionary lapilli up to 1cm in diameter, which are interpreted to represent the erosional remains of a phreatoplinian eruption (Photo 4). This section also contains several thick exposures of massive, matrix-supported, polymict, pebble to cobble conglomerate. Clasts are subangular to rounded and comprise a variety of lithologies, including mafic to felsic lavas, hypabyssal intrusions and rare intermediate plutons. These conglomerate beds are massive and homogeneous, containing very few sedimentary structures. Rare parallel and locally cross laminated sandstone lenses have been observed within these conglomerate sequences. Rocks within this volcanostratigraphic section are remarkably devoid of fossils, and, where observed, fossil fragments are always associated with very coarse-grained facies. Field mapping for this study terminated at the ridgeline 3.5km north of Ramsey Peak, approximately 4km SW of Oppy Lake; however, this homoclinal volcano-sedimentary succession extends at least as far as Oppy Lake, where Late Bathonian or Early Callovian fossils have been recovered (H. Frebold, unpublished data). 154 Photo 3 Densely welded rhyolitic ignimbrite unit within the upper Ramsey Peak section. This ~400m-thick unit may represent an intra-caldera facies. Pencil (~8cm) for scale. Photo 4. Articulate armored accretionary lapilli in rhyolitic vitric-lithic-crystal tuff in the Ramsey Peak area. Accretionary lapilli are quite common throughout the entire field area, and occur as primary and reworked fragments within maroon mudstone and fine-grained tutlaceous units. Rock hammer for scale. Field of view is approximately 30cm. 155 RIVERS P E A K AND M O U N T PRESTON A R E A S The Rivers Peak/Mount Preston area comprises an isolated, west-dipping block, which is presumably separated from the Tesla Mountain block to the south by a fault beneath Tesla Lake, and from the Mount Pondosey massif to the west by a N/S-trending structure that forms the Pondosey Pass and South Creek topographic low (Figure 2). A U-Pb zircon age of 176.3 ± 3.3 Ma from a rhyolite lapilli tuff near the base of the section southeast of Mount Preston, together with a U-Pb zircon age of 175.4 ± 0.9 Ma immediately south of Mount Preston at the top of the section indicates that volcanogenic strata in this area are coeval with strata in the Jumble Mountain region. Broad-scale volcanostratigraphic similarities between the two areas reinforce this correlation. Specifically, lithologies in the Rivers Peak/Mount Preston area are consistent with those documented in the north Ramsey Peak area, which lies along strike 30km to the south. Rocks in this area are characterized by coarse-grained, intermediate to felsic volcanic facies and minor intercalated sedimentary rocks, which increase in abundance and eventually predominate over ignimbrite units near the top of the section south of Mount Preston. Primary volcanic units in this area include andesitic to rhyolitic lapilli tuff to tuff breccia units that are pink to purple to maroon in color, thick and massive, poorly to moderately welded, and notably lithic- and crystal-rich. Sedimentary rocks consist of maroon mudstone to granule to pebble mudstone and lesser feldspathic-lithic wacke intercalated with thin (10 to 30cm-thick) lithic-and crystal-rich chloritic lapilli tuff sequences. These intermediate composition tuff units are spatially and temporally associated with and may be the eruptive source of ballistic blocks which produce block sag structures within several mudstone horizons in this area. Northeast of Rivers Peak, a thin, thinly-bedded limestone unit is immediately overlain by a 25m-thick section of massive, unstructured, very coarse-grained, quartz-eye-feldspathic sandstone (Photo 5). Quartz and plagioclase grains are euhedral to subrounded and broken, respectively, and are assumed to represent detritus shedding off of a proximal rhyolite flow or granitic pluton. Rare (<1%), subangular to rounded, aphanitic mafic to intermediate and quartz-phyric rhyolite clasts occur along the base of this unit. This anomalous sandstone unit is laterally discontinuous, and may be infilling paleo-valley or channel. A collection of marine fossils recovered from a calcareous sandstone unit near the summit of Rivers Peak are currently being examined to provide additional age constraints for this section and to assist in determining the environment of deposition. Sedimentary rocks dominate in the Mount Preston area, where they are characterized by maroon mudstones intercalated with lesser rhyolitic lapilli tuff and mafic to intermediate flows and sills. The top of section in this area is marked by a thick, purple, massive, very densely welded rhyolite lapilli tuff unit, which may correlate regionally to one of the aforementioned units observed in the Ramsey Peak area. Southeast of Mount Preston, near the base of measured section in the area, mudstones and lesser rhyolitic tuffs are intercalated with a series of plagioclase-phyric to aphyric, variably amygdaloidal basalt to basaltic andesite flows, pillow lavas and broken pillow breccia, which are intruded by an aphanitic basaltic plug. These basaltic pillow lavas are intruded by a dacitic to rhyodacitic flow-dome complex with a well developed carapace breccia (refer to Mortensen et al., 2004 for photograph). Geologic mapping in this area during the 2004 field season has demonstrated the existence of numerous other extrusive felsic (dacitic to rhyolitic) domes in this area. The domes are highly fractured and silicified with well-developed carapace breccias, and are aphanitic to sparsely quartz-phyric. Geochemical analysis of several dome samples yielded 68-98% silica - this high degree of silicification makes the domes more resistant to weathering than local country rock, and they subsequently form round knobs along a linear outcrop belt. The linear distribution of these domes follows the trace of an EAV-trending extensional fault south of Mount Preston. This fault is characterized by zones of intense fracturing with abundant slip surfaces, and well developed ferricrete overlying fault breccia. It may represent a synvolcanic extensional structure - a zone of weakness through which the spatially and potentially temporally associated rhyolite domes were intruded. A small granite stock intrudes the fault/dome sequence; this intrusion is lithologically similar to a suite of ca. 148-149 Ma plutons mapped to the south in the northeastern Bella Coola map sheet (Photo 6). U-Pb dating studies of felsic dome samples and this granite stock are currently underway, and will assist in constraining the age of this extensional structure. The Pond/Rivers Peak mineral occurrence in this area (BC MINFILE 093E 058) and impressive gossans developed south of Mount Preston are characterized by finely disseminated pyrite, and occur in wallrocks immediately adjacent to this structure. Small (cm-scale) bodies of chalcopyrite ± bornite-bearing vein breccia were observed in several areas in the Mount Preston/Rivers Peak area. YOUNGER MAGMATISM The upper Ramsey Peak section is cut by a small pyroxene-hornblende quartz diorite stock, which is texturally and compositionally similar to other small dioritic stocks documented throughout the field area. 156 Photo 5. Very coarse-grained quartz-eye-feldspathic sandstone in the Rivers Peak area. Gritty-looking regions comprise euhedral to subrounded and broken quartz and plagioclase. Rusty orange and green, more coherent splotches comprise aphanitic, mafic to intermediate volcanic clasts that occur near the base of this unit. Pencil (~8cm) for scale. Photo 6. View to the north towards Mount Preston (not visible) from the north Rivers Peak region. The trace of an E/W-trending extensional fault is represented by (A), which may represent a synvolcanic extensional structure through which Jurassic (?) rhyolite domes (B) intruded along. (C) represents a small biotite-homblende granite stock that intrudes Jurassic volcanogenic strata in the area. Image represents ~5km from left to right. Ar-Ar (hornblende) dating of this pluton indicates an age of 136.4 ± 1.5 Ma, which is temporally consistent with a ca. 139-132 Ma intrusive suite documented immediately to the south in the Bella Coola area (T.D. Ullrich, unpublished data; Haggart et al., 2004). The entire field area is cut by numerous grey-green, centimeter- to meter-scale (up to 10m in width), aphanitic to plagioclase ± pyroxene ± hornblende-phyric basalt to andesite dykes. These dykes are typically randomly oriented but are locally consistently oriented where they intrude local fracture sets and faults; one such dyke swarm has been observed at Butler Peak. The aforementioned quartz diorite pluton at Ramsey Peak is cut by these dykes, suggesting that these dykes are at least partly post-ca. 136 Ma, and therefore represent a younger magmatic event in the area. The upper Mount Preston volcanostratigraphic section is cut by a biotite-quartz-phyric rhyolite porphyry dyke, which has been dated (Ar-Ar biotite) at 51.87 ± 0.79 Ma (T.D. Ullrich, unpublished data). This Early Eocene age is interpreted to represent the youngest magmatic event within the study area, and suggests correlation with the Ootsa Lake Group, which is diffusely exposed throughout the eastern half of the Whitesail Lake map sheet. GEOCHRONOLOGY In addition to the four U-Pb and Ar-Ar dates completed from samples collected during the 2003 field season (several samples yielded insufficient zircon for dating), 15 samples collected from throughout the study area in the 2004 field season are currently in the mineral separation process for U-Pb zircon dating. Several rhyolite tuff samples from the study area are being dated, which will assist in constraining the age range for each measured volcanostratigraphic section. A number of rhyolitic intrusive (?) and extrusive dome samples from the Rivers Peak and the Butler Peak areas are being dated to determine if the domes represent synvolcanic intrusions. A sample of microdiorite from the Butler Peak andesitic complex may help to constrain the age of the thick pile of mafic lavas and subvolcanic intrusions in this area. Detrital zircons studies from one or more sandstones from throughout the field area, including the quartz-eye feldspathic sandstone from the Rivers Peak section, may provide controls on the source regions that were eroding during Middle Jurassic time. LITHOGEOCHEMISTRY Geochemical studies of volcanic rock units from the northeastern Bella Coola/southeastern Whitesail Lake map area are underway to characterize the geochemical affinity of Middle Jurassic Hazelton Group volcanic rocks in this area and place constraints on the paleotectonic setting in which they were emplaced. Complete major, trace and rare earth element analyses have been obtained from a total of 64 representative samples of lava flows, ignimbrites, intrusive and extrusive domes, sills, dykes and hypabyssal intrusions from the study area. Geochemical analyses from samples collected in the 2004 field season have only recently been obtained, and has not yet been examined in detail. These new data, combined with analyses from the study area completed in 2003, together with reconnaissance data from host volcanic rocks at the Nifty VMS occurrence in the east-central Bella Coola map area (e.g., Ray et al., 1998) are shown on several geochemical discriminant plots in Figure 4. Mafic dyke samples are not included on these discriminant plots. Volcanic and subvolcanic rock units in the northeastern Bella Coola/southeastern Whitesail Lake map area geochemically resemble the broadly age equivalent Middle Jurassic host volcanic rocks at the Nifty VMS occurrence, which is on strike to the southeast. When plotted on a TAS diagram, samples from the study area are moderately bimodal in composition (mainly basaltic to basaltic andesitic and dacitic to rhyolitic), but when plotted on a discriminant plot of immobile trace element ratios (Nb/Y vs. Zr/Ti02), the samples span the basaltic to rhyolitic compositional range, and the Nifty samples show a distinctly higher Nb/Y ratio than do samples from the current study area. The felsic units are all subalkaline; however the mafic units include both subalkaline and alkaline compositions. On an A F M diagram, the Nifty samples and the felsic intrusive and extrusive samples from the study area are calc-alkaline to transitional in composition, whereas mafic intrusive and extrusive samples from the study area fall almost exclusively into the tholeiitic field. A plot of Rb vs. Y+Nb suggests that all of the volcanic rocks formed in a volcanic arc setting; however, immobile trace element plots such as V vs. T i 0 2 indicate that the mafic volcanic and subvolcanic units from the study area include both island arc tholeiites and back-arc tholeiites. These mixed volcanic arc/back-arc geochemical signatures are very similar to those described by Barrett and Sherlock (1996) at Eskay Creek, and are consistent with an overall rifted arc (intra-arc or back-arc) setting. ALTERATION AND IMPLICATIONS FOR VMS POTENTIAL Mafic rocks throughout the entire study area have undergone a high degree of alteration, which is characterized by pervasive epidotization in basaltic and basaltic andesitic flows, plugs, dykes and sills. The resulting epidosite occurs as large (up to lm in diameter) clots, and is commonly spatially associated 158 FeO* I I | I I I 1 | I I I I | I I I I | I I I I | I I I ' Phonolite Foidite l l l | l l l l | l 35 ' ' ' ' ' ' • Alk MgO O .1 t 01 .001 T — i i i 11111—r~i—i i i 111 LJ . ... Com'Pant V " » I M M H H.i'-.i. _l I • I I I I I I I I 11 I I I I I I I I I I I 01 Nb/Y 10 111111 1 I I 111111 1 I m: syn-collisional volcanic arc •'» ' ocean ridge in i l i i i 11II 10 100 Y+Nb 1000 10 15 Ti/1000 Figure 4. Geochemical discriminant diagrams for volcanic and hypabyssal rocks in the northeast Bella Coola/southeast Whitesail Lake map area. Diamonds indicate mafic to intermediate lava flows and plugs and circles indicate intermediate to felsic lava flows, ignimbrites and plugs. Triangles represent analyses of mafic to felsic samples from the vicinity of the Nifty prospect (data from Ray et al., 1998). 159 with intense quartz- and epidote-veining and large jasperite clofs, and may reflect semiconformable, synvolcanic alteration above a subvolcanic intrusion. Although no Middle Jurassic intrusions have been recognized within the study area, at least one Middle Jurassic pluton has been identified ~30km to the west-southwest; the Trapper Pluton is a large (exposed over 200km3), coarse-grained granite pluton with a U-Pb zircon age of 177.4 ± 0.7 Ma (P. van der Heyden, unpublished data; Figure 2; see Mahoney et al., 2005, this volume for more details). We speculate that the Trapper and possibly other coeval intrusions that are not exposed at the present level of erosion may have been subvolcanic equivalents of the locally abundant rhyolitic ignimbrite units that have been recognized throughout the study area and yield similar U-Pb zircon ages. These intrusions may have driven hydrothermal circulation that produced widespread, semiconformable alteration (characterized by development of epidosite and jasperoid) in more permeable portions of the sequence. Specific results of our study that emphasize the high potential for VMS mineralization in Hazelton Group volcanogenic strata in the Bella Coola/Whitesail Lake map areas include: (1) the linear arrangement of extrusive felsic domes, together with (2) indications of a synvolcanic extensional structure in the Rivers Peak/Mount Preston area; (3) evidence for shallow water, submarine deposition, as indicated by specific fossil assemblages, sedimentary structures and pillow lavas; (4) the presence of known Middle Jurassic syngeneic (e.g., Nifty) and epigenetic mineral occurrences (e.g., Mortensen, 2005, this volume); (5) stratiform pyrite locally within tuffaceous mudstones at Tesla Mountain; and (6) widespread epidosite clots that may reflect semi-conformable alteration above a buried subvolcanic intrusion. ONGOING RESEARCH Ongoing research for this study includes: (1) compilation of detailed measured volcanostratigraphic sections; (2) petrographic studies of volcanic and sedimentary rocks from the study area; (3) processing of U-Pb samples collected during the 2004 field season; (4) detailed lithogeochemical comparisons with other Hazelton Group suites available from throughout Stikinia and volcanic host rocks for the Eskay Creek deposit; and (5) studies of the specific volcanologic, sedimentologic, and large scale tectonic processes operating during deposition of Middle Jurassic Hazelton Group rocks in this area. ACKNOWLEDGMENTS Danny Hodson of Rainbow West Helicopters provided outstanding helicopter support during the 2004 field season. We thank Jim Haggart and the Geological Survey of Canada for providing mapping expertise and logistical support for the mapping project. David Gale of the Barrick Gold Corporation provided an excellent and informative tour of the Eskay Creek mine and vicinity. We thank Jim Haggart, Larry Diakow, Lori Snyder, Glenn Woodsworth, Margi Rusmore, Bob Anderson and Kirstie Simpson for valuable on-going discussions about Hazelton Group volcanostratigraphy and volcanological and sedimentological processes. Chris Kohel, Emily Hauser and Joe Nawikas provided excellent assistance in the field. Funding for this project was provided by the Rocks to Riches Program, which is administered through the BC & Yukon Chamber of Mines, as well as four mining companies (Barrick Gold Corp., Heritage Exploration Inc., Kenrich-Eskay Mining Corp. and Placer Dome Inc.). Rich Friedman provided a helpful review of the manuscript and assistance with U-Pb dating. Ar-Ar dating was carried out by Tom Ullrich ofPCIGR. REFERENCES Barrett, T.J. and Sherlock, R.L. (1996): Geology, lithogeochemistry and volcanic setting of the Eskay Creek Au-Ag-Cu-Zn deposit, northwestern British Columbia; Exploration and Mining Geology, Volume 5, pages 339-368. Diakow, L.J., Mahoney, J.B., Gleeson, T.G. , Hrudey, M.G. , Struik, L .C . and Johnson, A.D. (2002): Middle Jurassic stratigraphy hosting volcanogenic massive sulphide mineralization in eastern Bella Coola map area (NTS 093/D), southwest British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 2001, Paper 2002-1, pages 119-134. Diakow, L.J., Mahoney, J.B., Haggart, J.W., Woodsworth, G.J., Gordee, S.M., Snyder, L.D., Poulton, T.P., Friedman, R.M. and Villeneuve, M. (2003): Geology of the eastern Bella Coola map area (93 D), west-central British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 2002, Paper 2003-1, pages 65-75. Duffell, S. (1959): Whitesail Lake map-area, British Columbia; Geological Survey of Canada, memoir 299, 119 pages. Haggart, J.W., Diakow, L.J. , Mahoney, J.B., Struik, L . C , Woodsworth, G.J. and Gordee, S.M. (2004): Geology, Bella Coola area (parts of 93D/01, 93D/02, 93D/06, 93D/07, 93D/08, 93D/09, 93D/10, 93D/11, 93D/15 and 93D/16), British Columbia; Geological Survey of Canada, Open File 4639; British Columbia Geological Survey and Development Branch, BC GSDB Open File 2004-13, scale 1:150 000. Haggart, J.W., Mahoney, J.B., Diakow, L.J. , Woodsworth, G.J., Gordee, S.M., Snyder, L.D. , Poulton, T.P., Friedman, R.M. and Villeneuve, M.E. (2003): 160 Geological setting of the eastern Bella Coola map area, west-central British Columbia; Geological Survey of Canada, Current Research 2003-A4, 9 pages. Marsden, H. and Thorkelson, D.J. (1992): Geology of the Hazelton volcanic belt in British Columbia; implications for the Early to Middle Jurassic evolution of Stikinia; Tectonics, Volume 11, pages 1266-1287. Mahoney, J.B., Hooper, R.L., Gordee, S.M., Haggart, J.W. and Mortensen, J.K. (2005): Initial evaluation of the bedrock geology and economic mineralization potential of the southern Whitesail Lake map area (92E02/03), west-central British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 2004, this volume. Mortensen, J.K., Wodjak, P., Macdonald, R., Gordee, S.M. and Gabites, J.E. (2005): Regional studies of V M S mineralization and potential within the Early Jurassic Hazelton Group, British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 2004, this volume. Mortensen, J.K., Gordee, S.M., Mahoney, J.B. and Tosdal, R.M. (2004): Regional studies of Eskay Creek-type and other volcanogenic massive sulphide mineralization in the upper Hazelton Group in Stikinia: preliminary results; B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 2003, Paper 2004-24, pages 249-262. Ray, G.E., Brown, J.A., Friedman, R.M. and Cornelius, S.B. (1998): Geology of the Nifty Zn-Pb-Ba prospect, Bella Coola district, British Columbia; B.C. Ministry of energy, Mines and Petroleum Resources, Geological Fieldwork 1997, Paper 1998-1, pages 20-1 to 20-28. Thorkelson, D.J., Mortensen, J.K., Marsden, H. and Taylor, R.P. (1995): Age and tectonic setting of Early Jurassic episodic volcanism along the northeastern margin of the Hazelton Trough, northern British Columbia; In Miller, D .M. and Busby, C , Jurassic magmatism and tectonics of the North American Cordillera: Geological Society of America, Special Paper, Volume 299, pages 83-94. Tipper, H.W. (1979): Jurassic stratigraphy of the Whitesail Lake map area, British Columbia; Geological Survey of Canada, Current Research 79-1 A, pages 31-32. Tipper, H.W. and Richards, T.A. (1976): Jurassic stratigraphy and history of north-central British Columbia; Geological Survey of Canada, Bulletin 270, 73 pages. Wheeler, J.O. and McFeely, P. (1991): Tectonic assemblage map of the Canadian Cordillera and adjacent parts of the United States of America; Geological Survey of Canada, Map 1712A, scale 1:2,000,000. Woodsworth, G.J. (1980): Geology of Whitesail Lake (93E) map area, British Columbia; Geological Survey of Canada, Open File 708, 1:250,000. 

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