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Crustal contamination, sulphide mineralization, and compaction during formation of the marginal zone… Mackie, Robin 2006

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CRUSTAL CONTAMINATION, SULPHIDE MINERALIZATION, AND COMPACTION DURING FORMATION OF THE MARGINAL ZONE OF THE M U S K O X INTRUSION, NUNAVUT, AND IMPLICATIONS FOR THE EVOLUTION OF THE 1.27 Ga MACKENZIE MAGMATIC EVENT  by ROBIN MACKIE B.Sc.H. University of Manitoba, 2003  A THESIS SUBMITTED FOR PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF SCIENCE in THE F A C U L T Y OF GRADUATE STUDIES (GEOLOGICAL SCIENCES)  THE UNIVERSITY OF BRITISH COLUMBIA April 2006  © Robin Mackie, 2006  ABSTRACT The age, petrology, geochemistry, and Hf-Nd-S isotopic compositions of basal marginal rocks at two locations (West Pyrrhotite Lake and Far West Margin) along the western margin of the large Muskox layered mafic-ultramafic intrusion, Nunavut, are used (1) to constrain the petrogenesis of the marginal zone and associated sulphide mineralization, and (2) to evaluate the genetic relationship of the Muskox intrusion with the Mackenzie dikes and Coppermine River flood basalts during the 1.27 Ga Mackenzie magmatic event. The marginal zone (1269 ± 2 Ma; U-Pb baddeleyite) consists of a lower 10 m-thick gabbronorite and upper 100-150 mthick peridotite subzone. A shift in incompatible trace element ratios and isotopic compositions at the transition from peridotite (low Th/Yb; high Nb/La; -4 to 0; 5 S = +6) to gabbronorite (e 34  Hm  = -5 to -15; e  enfrt)  = -3 to +2;  SNd(t)  =  = -1 to -13; 5 S = +7 to +10) and 34  Nd(t)  the corresponding early crystallization of orthopyroxene and appearance of granophyre within the gabbronorite indicates that the effects of crustal contamination by the adjacent country rocks (high Th/Yb; low Nb/La; e  Hm  =- -24 to -29; e  Nd  (t)  = -14 to -16; 5 S = +7 to +11) is 34  restricted to a thin (10 m) boundary zone along the contact. Silica and sulphur addition promoted local sulphide saturation within the contaminated magmas along the outer wall of the magma chamber. The low metal content of sulphides throughout the intrusion indicates that in general early solidification of this zone inhibited segregated sulphide liquid from interacting with subsequent pulses of magma (low R-factor). The overlying peridotites contain increasing proportions of postcumulus phases relative to cumulus olivine towards the base of the marginal zone, a feature that is related to the competing effects of compaction and rapid heat loss through the base of the intrusion. The marginal zone peridotites and overlying layered series rocks of Muskox intrusion and the lowermost Coppermine River basalts have the same range of Nd isotopic compositions, suggesting that they both were derived from a common relatively enriched mantle source and that this portion of the flood basalts were fed by magma that temporarily resided andfractionatedwithin the Muskox magma chamber during their final ascent through the crust.  TABLE OF CONTENTS ABSTRACT  ii  TABLE OF CONTENTS.....  iii  LIST OF TABLES  vi  LIST OF FIGURES  vii  ACKNOWLEDGEMENTS  ix  CHAPTER 1: GEOLOGIC AND EXPLORATION CONTEXT OF THE MARGINAL ZONE OF THE MUSKOX INTRUSION  1  1.1 INTRODUCTION  2  1.2 ANGLO AMERICAN EXPLORATION (CANADA) LTD. DRILL PROGRAM  7  1.3 OVERVIEW OF THE THESIS  8  1.4 REFERENCES  10  CHAPTER 2: FORMATION OF THE MARGINAL ZONE OF THE MUSKOX INTRUSION, NUNAVUT: CRUSTAL CONTAMINATION, SULPHIDE MINERALIZATION, AND COMPACTION : 13 2.1 INTRODUCTION  , 14  2.2 GEOLOGY AND EMPLACEMENT OF THE MUSKOX INTRUSION  16  2.3 MARGINAL ROCKS FROM THE WESTERN MARGIN OF THE MUSKOX INTRUSION ... 21 2.3.1 West Pyrrhotite Lake section  23  2.3.2 Far West Margin section  29  2.4 ANALYTICAL TECHNIQUES  34  2.4.1 Major element oxides and trace element concentrations 2.4.2 Olivine compositions  34 47  2.4.3 Sulphur isotopic compositions  47  2.5 GEOCHEMISTRY OF THE MARGINAL ROCKS  51  2.5.1 West Pyrrhotite Lake  51  2.5.2 Far West Margin  60  2.6 DISCUSSION  61  2.6.1 Crustal contamination and sulphide mineralization within the gabbronoritic subzone 62 2.6.2 Compaction and thermal evolution in the peridotite subzone 66 2.6.3 Implications for the formation of the marginal zone of the Muskox intrusion and the basal margins of other mafic-ultramafic intrusions '. 73 2.7 CONCLUSIONS  .'.  76  2.8 ACKNOWLEDGEMENTS  77  2.9 REFERENCES  78  CHAPTER 3: AGE AND Hf-Nd ISOTOPIC GEOCHEMISTRY OF MARGINAL ROCKS IN THE MUSKOX INTRUSION: IMPLICATIONS FOR THE CRUSTAL CONTAMINATION AND MANTLE SOURCE COMPOSITION IN THE 1.27 Ga MACKENZIE MAGMATIC EVENT 85 3.1 INTRODUCTION  86  3.2 COMPONENTS OF THE MACKENZIE MAGMATIC EVENT  87  3.2.1 Coppermine Riverfloodbasalts 3.2.2 Mackenzie dike swarm  87 89  3.23 Muskox intrusion  90  3.3 MARGINAL ROCKS OF THE MUSKOX INTRUSION  93  3.4 ANALYTICAL TECHNIQUES  95  3.4.1 U-Pb concentrations and isotopic compositions 3.4.2 Trace element and Hf-Nd isotopic compositions 3.5 RESULTS  95 ;  99 105  3.5.1 U-Pb geochronology 105 3.5.2 Trace element variations 108 3.5.3 Hf-Nd isotopic variations Ill 3.5.4 Alteration/metasomatic effects? 113 3.6 DISCUSSION 114 3.6.1 Spatial extent and degree of crustal contamination within marginal rocks of the Muskox intrusion 114 3.6.2 Temporal relationships and isotopic comositions of the Muskox intrusion, Coppermine River basalts, and Mackenzie dikes 118 3.6.3 Mantle source composition of the Muskox intrusion and other Mackenzie components... 122 3.6.4 Evolution of the Mackenzie magmatic event 124 3.7 CONCLUSIONS  126  3.8 ACKNOWLEDGEMENTS  127  3.9 REFERENCES  128  CHAPTER 4: CONTROLS ON THE CHALCOPHILE ELEMENT CONCENTRATIONS OF SULPHIDE WITHIN THE MARGINAL ROCKS OF THE MUSKOX INTRUSION, NUNAVUT 134 4.1 INTRODUCTION  135  4.2 DATASET AND RECALCULATION PROCEDURE  138  4.3 SULPHIDE COMPOSITIONAL VARIATIONS  139  4.4 DISCUSSION  142  4.5 CONCLUSIONS  150  4.6 ACKNOWLEDGEMENTS  151  4.7 REFERENCES  152  CHAPTER 5: SUMMARY AND CONCLUSIONS  156  5.1 SUMMARY AND CONCLUSIONS  157  5.2 REFERENCES  160  APPENDICES APPENDIX I: ACME Analytical Laboratories major and trace element analytical procedures  161 162  APPENDIX II: Duplicate analyses of major and trace elements from ACME Analytical Laboratories  163  APPENDIX III: All olivine core, middle, and rim compositions by EPMA  167  APPENDIX IV: Comparison of Ni abundances of olivine by different EPMA methods  183  APPENDIX V: Duplicate analyses of trace element abundances by HR-ICP-MS  184  APPENDIX VI: Trace element abundances for USGS reference materials (G-2 and DTS-2)  186  APPENDIX VII: Comparison of trace element results from PCIGR (HR-ICP-MS) and A C M E Analytical Laboratories (ICP-MS and ICP-ES)  188  LIST OF TABLES Table 2.1: Major and trace element abundances for the (a) West Pyrrhotite Lake section (DDH # MX03 -002) and (b) Far West Margin section (DDH # MX03-001) .35 Table 2.2: Representative olivine compositions from the (a) West Pyrrhotite Lake section and (b) Far West Margin section  48  Table 2.3: Sulphur isotopic compositions in marginal rocks of the Muskox intrusion  50  Table 3.1: U-Pb ID-TIMS analytical data for baddeleyite from the Muskox intrusion  97  Table 3.2: Summary of U-Pb age calculation methods  98  Table 3.3: Trace element concentrations by HR-ICP-MS for marginal rocks of the Muskox intrusion ... 100 Table 3.4: Hf and Nd isotopic compositions of marginal rocks from the Muskox intrusion  103  Table 3.5: Composition of Muskox magmas and potential contaminates used in mixing calculations  117  Table 4.1: R-factor and sulphide liquid fractionation model parameters  146  LIST OF FIGURES Figure 1.1: Regional geologic and gravity map of the Coppermine region, Nunavut  3  Figure 1.2: Geologic map of the Muskox intrusion and surrounding area  5  Figure 1.3: Photograph of (a) the eastern contact of the of the Muskox intrusion, and (b) sulphidemineralized rocks along the eastern margin of the intrusion south of McGregor Lake  6  Figure 2.1: Regional geologic and gravity map of the Coppermine region, Nunavut  17  Figure 2.2: Interpreted 3-dimensional geology map of the main body of the Muskox intrusion  18  Figure 2.3: Stratigraphic column of the Muskox intrusion based on Geological Survey of Canada deep drill holes showing the variations in crystallization order for each cyclic unit  20  Figure 2.4: Interpreted geologic cross sections of the (a) West Pyrrhotite Lake (DDH MX03-002) and (b) Far West Margin (DDH MX03-001) sections  22  Figure 2.5: Representative photomicrographs of marginal zone rocks at the West Pyrrhotite Lake section  24  Figure 2.6: Photomicrograph of a large granophyre-alkali feldspar-quartz clot within subophitic-textured gabbronorite from the West Pyrrhotite Lake section 27 Figure 2.7: Representative photomicrographs of marginal zone rocks at the Far West Margin section  30  Figure 2.8: Stratigraphic variations of major elements in the (a) West Pyrrhotite Lake and (b) Far West Margin sections of the Muskox intrusion 52 Figure 2.9: Stratigraphic variations in olivine compositions for (a) West Pyrrhotite Lake and (b) Far West Margin 53 Figure 2.10: MgO vs. A1 0 and CaO diagrams for (a) West Pyrrhotite Lake and (b) Far West Margin.... 54 2  3  Figure 2.11: Stratigraphic variations of Ni, Cu, S contents and sulphur isotopic compositions for (a) West Pyrrhotite Lake and (b) Far West Margin sections 55 Figure 2.12a: Primitive mantle-normalized trace element abundances at West Pyrrhotite Lake  56  Figure 2.12b: Primitive mantle-normalized trace element abundances at Far West Margin  57  Figure 2.13: Stratigraphic variations of incompatible trace element ratios for (a) West Pyrrhotite Lake and (b) Far West Margin  58  Figure 2.14: Incompatible trace element ratio diagram (K/Yb vs. Nb/Ti) for marginal zone rocks and adjacent crustal rocks  63  Figure 2.15: IRIDIUM results comparing the initial state of the system and that after (a) 15 years and (b) 130 years  70  Figure 2.16: Comparison of bulk chemical profiles for A1 0 and Ti02 at the end of different IRIDIUM simulations to those observed at the West Pyrrhotite Lake section 72 2  3  Figure 3.1: Geographic map showing the distribution of the major components of the 1.27 Ga Mackenzie large igneous province 88 Figure 3.2: Geologic map of the Muskox intrusion showing the location of the West Pyrrhotite Lake and Far West Margin sections 91 Figure 3.3. Interpreted cross-sections (facing north) of the (a) West Pyrrhotite Lake and (b) Far West Margin sections showing the locations and depths of drill holes  94  Figure 3.4: Concordia diagrams showing the U-Pb geochronologic results for baddeleyite fractions separated from three samples at two different locations within the Muskox intrusion  106  Figure 3.5: Parent-daughter (Sm-Nd and Lu-Hf) elemental concentrations and ratios for the (a) West Pyrrhotite Lake and (b) Far West Margin sections of the Muskox intrusion .' ".:  109  Figure 3.6: Primitive mantle-normalized trace element patterns of all samples from the (a) West Pyrrhotite Lake and (b) Far West Margin sections 110 Figure 3.7: Stratigraphic variations in Th/Yb(pm), La/Yb(pm), e f (t), and e Pyrrhotite Lake and (b) Far West Margin sections H  N d  (t) values for the (a) West 112  Figure 3.8: Initial £ f and e d isotopic compositions vs. selected incompatible trace element ratios for marginal rocks from the Muskox intrusion  116  Figure 3.9: Compilation of precise U-Pb ages for Mackenzie magmatic event samples  119  Figure 3.10: Compilation diagram showing the stratigraphic variations in initial e values for the marginal zone and layered series of the Muskox intrusion, the Coppermine River basalts, and Mackenzie dikes  121  H  N  Nd  Figure 3.11: Histograms of Nd model ages for peridotites and layered series rocks from the Muskox intrusion, basalts from Coppermine River and Husky Creek groups, and contaminated gabbronorites and crustal rocks from the margin of the Muskox intrusion 123 Figure 4.1: Geologic map of the Muskox intrusion and surrounding crustal rocks showing the location of sample regions 136 Figure 4.2: Histograms and cumulative percentages of Ni and Cu contents of sulphides from the marginal zone of the Muskox intrusion recalculated to 100% sulphide 140 Figure 4.3: Atomic ratio diagrams showing the compositional variations in marginal zone sulphides at different locations in the Muskox intrusion 141 Figure 4.4: N i and Cu contents of sulphides for the Southeast McGregor, Keel East, and Pyrrhotite Lake regions showing the modeling results with constant D / i) 144 Ni(mss  sll  Figure 4.5: N i and Cu contents of sulphides for the Southeast McGregor, Keel East, and Pyrrhotite Lake regions showing the modeling results with variable DNi(mss/sui) 145 Figure 4.6: Plot of Cu/Pd vs. Pd for mineralized samples form the Southeast McGregor, Keel East, and Pyrrhotite Lake regions of the Muskox intrusion 149  ACKNOWLEDGEMENTS Many people have thoughtfully invested their time and energy in various parts of this thesis. Firstly, I would like to thank my advisors James Scoates and Dominique Weis for their constant encouragement and support, and for all that they have taught me since my first arrival at UBC. James has devoted countless hours to the betterment of this work, especially during the final stages in the preparation of this manuscript, and for that I am very appreciative. I thank all the staff and students of the Pacific Centre for Isotopic and Geochemical Research at UBC, including Gwen Williams, Diane Hanano, Rich Friedman, Wilma Pretorius, Jane Barling, Elisa Dietrich-Sainsaulieu and Bert Mueller, who all contributed to this work. Mati Raudsepp and Elisabetta Pani are thanked for their expertise in the SEM and electron microprobe facility at UBC, as well as, Claude Maerschalk for his assistance, with column chemistry at ULB. I am appreciative for the assistance of Kelly Russell, Jon Scoates, Erik Scheel, and Steve Rowins who provided helpful reviews of this manuscript. I am grateful for the financial and logistical support provided by Anglo American Exploration (Canada) Ltd. (AAEC) throughout this study. In particular, I would like to acknowledge Dave Peck and Gary DeSchutter. Dave is responsible for the initial commencement of this project and provided helpful reviews of various drafts of this manuscript. Dave will undoubtedly continue to be a mentor in the years to come. Gary is thanked for his support during the early stages of this project and his impeccable management of both summer and winter A A E C drill programs on the Muskox intrusion. I would also like to thank friends and co-workers at A A E C , Nathan Rand in particular, for their help with sample collection and core splitting, and for making my stay at McGregor Lake Camp an unforgettable experience. My family has always supported my studies, and for that they deserve my gratitude and respect. Norm Halden is thanked for his continued encouragement and for inspiring my curiosity with many painful, yet satisfying, lectures on igneous petrology at the University of Manitoba. Caroline-Emmanuelle Morisset and Heidi Annell are thanked for their support throughout my time at UBC. Most importantly, my wife Tamara deserves my utmost appreciation and gratitude for her encouragement and patience throughout my years at university. Despite my countless absent-minded evenings and my more than occasional complete absence, Tamara has always supported my aspirations and goals and for that I am extremely grateful.  CHAPTER 1  Geologic and exploration context of the Marginal Zone of the Muskox intrusion  1.1 INTRODUCTION This study focuses on the marginal rocks at the base of the Muskox layered mafic-ultramafic intrusion located approximately 60 km south of the Coronation Gulf on the Arctic Circle in Nunavut, Canada (Fig. 1.1). The Muskox intrusion is situated within metasedimentary, metaplutonic, and metavolcanic rocks of the 1.8-1.9 Ga Wopmay Orogen and an unconformably overlying supracrustal succession containing Hornby Bay sandstones, Dismal Lake carbonates, and Coppermine River flood basalts (Smith, 1962; Baragar & Donaldson, 1973; Hoffman, 1984). The intrusion was emplaced along with the Coppermine River flood basalts and Mackenzie dikes during the 1.27 Ga Mackenzie magmatic event. The Mackenzie magmatic event represents a period of extensive tholeiitic magmatism considered to reflect the emplacement of a mantle plume at the base of the lithosphere at the outset of continental rifting (Fig. 1.1) (Fahrig, 1987; LeCheminant & Heaman, 1989; Baragar et al., 1996; Stewart & DePaolo, 1996; Griselin et al. 1997). The Muskox intrusion has been the site of numerous scientific studies and Ni-Cu-PGE exploration programs, however relatively few studies have focused on providing a comprehensive geologic and geochemical context for rocks of the marginal zone, their relationship to the layered series, and the origin of associated sulphide mineralization. The initial discovery of the intrusion (ca. 1956) was made by members of the Canadian Nickel Company (now INCO Ltd.) during aerial reconnaissance when two prominent ridges of gossan were recognized; these ridges delineated sulphide mineralization along the inward dipping walls of the intrusion (Irvine & Baragar, 1972). Numerous exploration companies have targeted this marginal zone sulphide - INCO Ltd. (ca. 1957-1959), Equinox Resources Ltd. and International Platinum Company (ca. late 1980s), Muskox Minerals Corporation (ca. 1995present) and Anglo American Exploration (Canada) Ltd. (ca. 2003-2004). Over 240 exploration holes have been drilled on the Muskox intrusion, however no economic accumulations have been found to date (DeSchutter, 2003). Sulphides within the Muskox intrusion are mostly concentrated along the basal margin of the intrusion, and sulphide is also associated with chromitite within the upper part of the layered series (Chamberlain, 1967). The Muskox chromitite typically contains an order of magnitude less platinum group elements than analogous chromite-rich horizons from the Stillwater complex, Montana, and Bushveld complex, South Africa (Barnes & Francis, 1995). The basal sulphides are sporadically distributed and typically form relatively thin bands or layers with highly variable metal contents (Barnes & Francis, 1995). Sulphur isotopic compositions of sulphide show that sulphur was  Rae Group and Coronation Sills  Dismal Lake Group  Coppermine River Group  Hornby Bay Group  Muskox Intrusion  I i  Recluse & Epworth | Groups  Akaitcho Group  +  +  +  Hepburn Batholith  . Great Bear J j Magmatic Zone  Fig. 1.1: Regional geologic and gravity map of the Coppermine region, Nunavut (adapted from Francis, 1994; geologic map compiled by Hoffman, 1984). Gravity contours (dotted lines, 10 mgl intervals) are from Irvine & Smith (1967) and are based on gravity data from Hornal (1963). The inset shows the distribution of the Mackenzie dikes (after Gibson et al., 1987), MI = Muskox intrusion. The Muskox intrusion and its underlying feeder dike are exposed for over 120 km within deformed rocks of the Wopmay orogen (Recluse, Epworth, and Akaitcho groups, Hepburn Batholith, and Great Bear Magmatic Zone) and beneath rocks of the Coppermine Homocline (Hornby Bay, Dismal Lakes, Coppermine River, and Rae groups). The Muskox intrusion plunges towards the north beneath the overlying supracrustal rocks and may, in part, be responsible for the gravity anomaly that extends northward towards the Coronation Gulf.  3  derived primarily from a crustal source indicating that interaction between the Muskox magmas and adjacent country rocks was an important factor in the formation of marginal zone sulphide (Sasaki, 1969; Barnes & Francis, 1995). Mapping and deep drilling programs by the Geological Survey of Canada (Smith, 1962; Findlay & Smith, 1965) revealed that the intrusion is exposed for over 120 km from the basal feeder in the south to the upper roof zone in the north, and plunges shallowly northward (~510°) beneath the overlying volcano-sedimentary succession where it reaches a maximum thickness of ~2000 m (Fig. 1.2). The main body of the intrusion is divided into two marginal zones that trend parallel to the inward-dipping walls of the intrusion (20-50°; Smith, 1962), a layered series that contains numerous northward dipping dunite, pyroxenite, and gabbroic layers, and a granophyric roof zone that forms a heterogeneous region along the upper contact of the intrusion (Fig. 1.2 & 1.3). A characteristic feature of the marginal zone is that it becomes progressively more evolved in composition towards the base (i.e. from peridotite to gabbronorite). This trend is opposite from that observed in the overlying layered series and that expected during differentiation of the tholeiitic parental magmas to the intrusion (Smith, 1962; Irvine & Smith, 1967; Francis, 1994). The mechanism by which the marginal zone formed and its relationship to the layered series are not well constrained. The only other study that focused on the marginal rocks of the intrusion was completed by Francis (1994), who investigated the effects of crustal contamination within the feeder dike, marginal zone, and layered series rocks based on major and trace element compositions of outcrop samples. This study indicated that contamination within the marginal zone was restricted to a thin zone along the outer margin of the intrusion and involved the selective exchange of primarily the most incompatible elements (i.e. large ion lithophile and light rare earth elements) between mafic magmas within the Muskox chamber and adjacent crustal rocks. The Muskox intrusion is considered to have formed by repeated injections of relatively undifferentiated (high MgO ~14 wt %; Irvine, 1977) basaltic magma and concurrent removal (eruption) of fractionated liquid (Irvine & Smith, 1967; Irvine, 1970). The cumulate rock layers within the intrusion record the order that minerals crystallized and accumulated from successive magma pulses. Irvine (1980) proposed that compaction of newly deposited cumulates was an important process by which fractionated interstitial melt was removed to produce the thick dunite layers (>90 vol % olivine) within the lower 2/3 of the intrusion. He also suggested that upward migrating fractionated liquid would react with cumulus minerals within the overlying cumulate pile, producing shifts in whole rock and mineral compositions. Tharp et al. (1998)  Legend Muskox Intrusion Granophyric roof zone L + ] Granophyre & gabbro Layered Series [71  Gabbro  |  Olivine pyroxenite & pyroxenite  |  Olivine gabbro & troctolite  I  I Dunite and Peridotite  Marginal zone & Feeder I  I Peridotite, feldspathic peridotite, gabbronorite  Coppermine River Homocline I  I Coppermine River Group Dismal Lake Group and sills  E3  [•':•••,•-1 Hornby Bay Group  Wopmay Orogen r~H Recluse Group I'll  Epworth Group  I  Akaitcho Group  m  Hepburn Batholith  -  \  Faults t  ' \ Mfkenzie U1K6S  • AAEC drill hole locations • GSC drill holes (N = north, S = south, & E = east)  Fig. 1.2: Geologic map of the Muskox intrusion and surrounding area showing the locations of the Anglo American Exploration (Canada) Ltd. drill holes and the historic Geological Survey of Canada drill holes (after Hulbert, 2005; mapping by Smith, 1962). Water bodies have been omitted for clarity, with the exception of McGregor and Speers lakes. The feeder dike extends off the map toward the south. The intrusion is cut by the Canoe Lake fault, which separates the Canoe Lake Block from the main body of the intrusion. This study focuses on the marginal rocks and adjacent country rocks along the western margin of the intrusion that were intersected in drill holes MX03-002 (West Pyrrhotite Lake) and MX03-001 (Far West Margin).  Fig. 1.3: (a) Aerial photograph of the eastern contact of the Muskox intrusion and the adjacent metasedimentary rocks between Speers Lake and McGregor Lake (looking southeast), (b) Photograph of oxidized, sulphide-bearing marginal rocks southeast of McGregor Lake (looking east).  modeled the compaction of olivine cumulates within the Muskox intrusion and proposed that conduction of heat through the floor of the intrusion likely played an important role in the formation of the marginal zone. Several studies have shown that compaction of igneous cumulates is an important process in the chemical and texrural evolution of mafic-ultramafic bodies (Shirley, 1987; Meurer & Boudreau, 1998a; 1998b; Boudreau & Philpotts, 2002). 1.2 ANGLO AMERICAN EXPLORATION (CANADA) LTD. DRILL PROGRAM Recent (ca. 2003-2004) Ni-Cu-PGE exploration activities within the Muskox intrusion provided a unique opportunity to investigate the marginal zone rocks of one of the world's largest known layered intrusions. Anglo American Exploration (Canada) Ltd. (joint venture with Muskox Minerals Corp. (now Prize Mining Corp.) completed eight exploration drill holes during the summer of 2003 and winter of 2004, which were designed to test conductive bodies delineated using a then proprietary Spectrem time-doman airborne electromagnetic system (Fig. 1.2) (DeSchutter, 2004; 2005). Operations were conducted from the McGregor Lake Camp on the north shore of McGregor Lake and included mainly ground-based geophysical surveys, soil sampling, and diamond drilling (~2000 m total). Drilling by A A E C intersected relatively thin zones (<0.5 m) of massive sulphide adjacent to and within host paragneiss at the base of the marginal zone within the Canoe Lake Block along the western margin of the intrusion. During employment with A A E C , the author was involved in various parts of the 6-week summer exploration during the 2003 program including prospecting, ground geophysical surveys, core logging, and sample collection. For the purposes of the present study drill core samples were collected every 6-10 m down-hole, providing exceptionally detailed chemical profiles (major element oxide and trace element concentrations) through the marginal zone rocks at different locations within the intrusion. This study focuses on two drill holes (MX03-002 and MX03001) along the western margin of the intrusion (Fig. 1.2). Examination of petrographic and geochemical variations from other drill holes provided supplementary information. The West Pyrrhotite Lake and Far West Margin sections were chosen because of distinct mineralogical and chemical characteristics of the intrusive and country rocks at each location observed during core logging. In addition, these sections occur at different locations within the Muskox intrusion, allowing for a comparison of the character of the marginal zone at different stratigraphic heights within the intrusion.  1.3 OVERVIEW OF THE THESIS This thesis contains three distinct and complimentary studies of the marginal rocks of the Muskox intrusion that are presented in Chapters 2, 3, and 4, respectively. This study provides the first combined mineralogical, chemical, isotopic, and geochronological investigation of marginal zone rocks within the Muskox intrusion. The objectives of this study are (1) to characterize the mineralogical and chemical variations of the marginal zone of the Muskox intrusion, (2) to provide constraints on the character and extent of crustal contamination along the base of the intrusion and its relationship to the formation of sulphide mineralization, (3) to generate a petrogenetic model for the formation of the marginal zone, and (4) to constrain the relationship between the Muskox intrusion and the other components of the Mackenzie magmatic event. Chapters 2 and 3 utilize drill core samples collected during the summer A A E C drill program at the West Pyrrhotite Lake and Far West Margin sections, whereas Chapter 4 employs a previously compiled dataset of sulphide-mineralized samples from various locations along the margin of the intrusion (provided by A A E C and Muskox Minerals Corporation). Chapters 2, 3, and 4 were prepared in a manuscript format appropriate for submission to international scientific journals. As such, there are some areas of overlap between the chapters mainly regarding introductory figures and background material, however each of the background sections is described within a context relevant to the individual chapter. Chapter 5 is a summary of the major findings of this thesis. Chapter 2 involves a detailed characterization of the mineralogical, textural, and chemical variations of marginal rocks and adjacent country rocks at the West Pyrrhotite Lake and Far West Margin sections. Major and trace element results from 82 drill core samples combined with petrographic observations provide the framework for investigating the formation of the marginal zone of the Muskox intrusion. Sulphur isotopic compositions (23 samples) and trace element abundances of marginal zone rocks and adjacent wall rocks constrain the nature and extent of crustal contamination along the basal margin of the intrusion, which has important implications for the formation of marginal zone sulphide mineralization. Olivine compositions from peridotites (180 individual analyses from 10 samples) within the upper part of the marginal zone, although originally acquired to calculate parent magma compositions, appear to record varying degrees of re-equilibration with interstitial liquid. The IRIDRJM program (Boudreau, 2003) is used to model compaction of olivine cumulates within a thermal gradient to asses the role of compaction in producing the observed mineralogical and chemical variations within marginal zone rocks.  Chapter 3 evaluates the U-Pb geochronology of marginal zone rocks, and Hf and Nd isotopic compositions and trace element abundances of marginal rocks and the adjacent country rocks. U-Pb dating of baddeleyite from two peridotites and one gabbronorite at the two studied regions constrains the crystallization age of the marginal zone and confirms the temporal relationship between the Muskox intrusion and the Mackenzie dikes (1267 ± 2 Ma; LeCheminant & Heaman, 1989). The Hf and Nd isotopic compositions and high-precision trace element abundances of peridotites, gabbronorites and country rock gneisses (17 samples) not only constrain the spatial extent and degree of crustal contamination, but also provide a link between the marginal zone and layered series of the intrusion. A compilation of Nd isotopic compositions from this study and previous investigations of the Muskox intrusion (Stewart & DePaolo, 1992; 1996), Mackenzie dikes (Dundas & Peterson, 1992 (unpublished)), and Coppermine River basalts (Griselin et al. 1997) provide unique insights into the relationship between each of these bodies and the mantle source for the Mackenzie magmatic event. Chapter 4 documents the compositional variations of sulphide within marginal rocks at various locations within the Muskox intrusion. Recalculation of whole rock Ni, Cu, Pd, and S values (330 samples) to 100% sulphide allows for comparison of the metal contents from samples with varying amounts of sulphide. The compositions of magmatic Ni-Cu-PGE sulphides are considered to reflect variations in the metal contents of the magma from which a sulphide liquid segregates, the mass of silicate magma with which the liquid equilibrates, and subsequent fractionation of the sulphide liquid during cooling (e.g. Campbell & Naldrett, 1979; Naldrett et al., 1997). Numerical modeling of the compositional variation produced by these effects help constrain the formation and relationship of sulphides at different locations within the intrusion. Finally, the appendix contains tables summarizing: 1) the analytical methods and procedural duplicates for major and trace element results from A C M E Analytical Laboratories Ltd., 2) complete olivine compositions by electron microprobe, 3) a comparison of the Ni abundance of olivine by different electron microprobe methods, 4) duplicate analyses of trace element abundances by high-resolution ICP-MS at the Pacific Centre for Isotopic and Geochemical Research (PCIGR), 5) a comparison of trace element abundances for USGS reference materials, and 6) a comparison of trace element results from PCIGR and A C M E Ltd.  1.4 REFERENCES Baragar, W.R.A. & Donaldson, J.A. (1973). Coppermine and Dismal Lakes map areas. Geological Survey of Canada Paper 71-39, 20 pp. Baragar, W.R.A., Ernst, R.E., Hulbert, L. & Peterson, T. (1996). Longitudinal petrochemical variation in the Mackenzie dike swarm, Northwestern Canadian Shield. Journal of Petrology 37-2,317-359. Barnes, S.J. & Francis, D. (1995). The distribution of platinum-group elements, nickel, copper, and gold in the Muskox Layered Intrusion, Northwest Territories, Canada. Economic Geology 90, 135-154. Boudreau, A.E. (2003). IRIDIUM- a program to model reaction of silicate liquid infiltrating a porous solid assemblage. Computers & Geosciences 29, 423-429. Boudreau, A.E. & Philpotts, A.R. (2002). Quantitative modeling of compaction in the Holyoke flood basalt flow, Hartford Basin, Connecticut. Contributions to Mineralogy and Petrology 144, 176-184. Campbell, I.H. & Naldrett, A.J. (1979) The influence of silicate:sulfide ratios on the geochemistry of magmatic sulphides. Economic Geology 74, 1503-1506. Chamberlain, J. A. (1967). Sulfides in the Muskox intrusion. Canadian Journal of Earth Sciences 4, 105-153. DeSchutter, G. (2004). Muskox intrusion project, Kitikmeot Region, Nunavut. Anglo American Exploration (Canada) Ltd. 2003 Work Report, 52 pp. DeSchutter, G. (2005). Muskox intrusion project, Kitikmeot Region, Nunavut. Anglo American Exploration (Canada) Ltd. 2004 Work Report, 52 pp. Dudas, F.O. & Peterson, T.D. (1992). Nd isotopic composition of Mackenzie Dikes, Northwest Territories, Canada (Abstract). EOS, Transactions of the American Geophysical Union, Spring Meeting Supplement 339. Fahrig, W.F. (1987). The tectonic settings of continental mafic dyke swarms: Failed arm and early passive margins. Geological Association of Canada Special Paper 34, 331-348. Francis, D. (1994). Chemical interaction between picritic magmas and upper crust along the margins of the Muskox intrusion, Northwest Territories. Geological Survey of Canada Paper 92-12, 94 pp. Gibson, I.L., Sinah, M.N. & Fahrig, W.F. (1987). The geochemistry of the Mackenzie Dike Swarm, Canada. In: Halls, H.C. & Fahrig, W.F. (eds) Mafic Dyke Swarms. Geological Association of Canada, Special Paper 34, 109-121.  Griselin, M . , Arndt, N . & Baragar, W.R.A. (1997). Plume-lithosphere interaction and crustal contamination during formation of Coppermine River basalts, Northwest Territories, Canada. Canadian Journal of Earth Sciences 34, 958-975. Hoffman, P.F. (1984). Geology, Northern Internides of Wopmay Orogen, District of Mackenzie, Northwest Territories. Geological Survey of Canada, Map 1576A. Hornal, R.W. (1968). The gravity anomaly field in the Coppermine area of the Northwest Territories (Canada). Dominion Observatory Gravity Map Series, 45. Hulbert, L. (2005). Geology of the Muskox intrusion and associated Ni and Cu occurrences. Geological Survey of Canada, Open File 488J CD-ROM. Irvine, T.N. (1970). Crystallization sequences in the Muskox intrusion and other layered intrusions - 1 . Olivine-pyroxene-plagioclase relations. In: Visser, D.J.L. & Von Gruenewaldt, G. (eds) Symposium on the Bushveld Igneous Complex and Other Layered Intrusions. Geological Society of South Africa, Special Publication 1,441-476. Irvine, T.N. (1977). Definition of primitive liquid compositions for basic magmas. Carnegie Institute of Washington Year Book 76, 454—461. Irvine, T.N. (1980). Magmatic infiltration metasomatism, double-diffusive fractional crystallization, and adcumulus growth in the Muskox intrusion and other layered intrusions. In: Hargraves, R.B. (ed.) Physics of Magmatic Processes. Princeton: Princeton University Press, pp. 325-383. Irvine, T.N. & Smith, C H . (1967). The ultramafic rocks of the Muskox intrusion, Northwest Territories, Canada. In: Wyllie, P.J. (ed.) Ultramafic and Related Rocks. New York: John Wiley & Sons, Inc., pp. 38^49. Irvine, T.N. & Baragar, W.R.A. (1972). Muskox intrusion and Coppermine River lavas, Northwest Territories, Canada. International Geological Congress Field Excursion A29, 70 pp. LeCheminant, A.N. & Heaman, L . M . (1989). Mackenzie igneous events, Canada: Middle Proterozoic hotspot magmatism associated with ocean opening. Earth and Planetary Science Letters 96, 38-48. Naldrett, A.J., Ebel, D.S., Asif, M . , Morrison, G. & Moore, C M . (1997). Fractional crystallization of sulfide melts as illustrated at Noril'sk and Sudbury. European Journal of Mineralogy 9, 629-635.  Meurer, W.P. & Boudreau, A.E. (1998a). Compaction of igneous cumulates part I: geochemical consequences for cumulates and liquid fractionation trends. Journal of Geology 106, 281— 292. Meurer, W.P. & Boudreau, A.E. (1998b). Compaction of igneous cumulates part II: compaction and the development of igneous foliations. Journal of Geology 106, 293-304. Sasaki, A. (1969). Sulphur isotope study of the Muskox intrusion, District of Mackenzie (86 J/13, 0/3). Geological Survey of Canada Paper 68-46, 68 pp. Shirley, D.N. (1987). Differentiation and compaction in the Palisades sill, New Jersey. Journal of Petrology 28, 835-865. Smith, C H . (1962). Notes on the Muskox Intrusion, Coppermine River area, District of Mackenzie. Geological Survey of Canada Paper 61-25, 16 pp. Smith, C H . & Kapp, H.E. (1963). The Muskox intrusion, a recently discovered layered intrusion in the Coppermine River area, Northwest Territories, Canada. Mineralogical Society of America, Special Paper 1, 30-35. Tharp, T.M., Loucks, R.R. & Sack, R.O. (1998). Modeling compaction of olivine cumulates in the Muskox intrusion. American Journal of Science 298, 758-790.  CHAPTER 2  Formation of the Marginal Zone in the 1.27 Ga Muskox intrusion, Nunavut: crustal contamination, sulphide mineralization, and compaction  2.1 INTRODUCTION Basal marginal zones are an important subdivision of mafic-ultramafic intrusions that potentially provide information on the processes of magma emplacement, crustal contamination and cooling along the basal contacts and outer walls of magma chambers. These marginal zones, or border series, are observed in many differentiated mafic-ultramafic sills (e.g. Partridge River intrusion, Duluth complex, Minnesota, USA) and layered intrusions (e.g. Great Dyke, Zimbabwe; Stillwater Intrusion, Montana, USA) and are generally characterized by a downward differentiation trend in terms of whole rock and mineral chemistry (Wilson, 1982; Raedeke & McCallum, 1984; Page et al., 1985; Hoover, 1989; Grant & Chalokwu, 1992; Laytpov, 2003; Gibb & Henderson, 2006). This trend is typically opposite from that observed in the overlying rocks and from that expected during fractionation of basaltic magma. Previous studies on the Muskox intrusion, Nunavut, demonstrated that compaction of cumulates and migration of intercumulus liquid may have been an important differentiation mechanism in the development of the inverted character of the marginal zone (Irvine, 1980; Tharp et al., 1998). The Muskox intrusion, one of the world's largest known mafic-ultramafic layered intrusions, contains a marginal zone that has been the focus of numerous Ni-Cu-PGE exploration programs since the discovery of the intrusion in 1956 by the Canadian Nickel Company (Smith & Kapp, 1963; Irvine, 1988). Over 240 exploration drill holes have targeted Ni-Cu-PGE-enriched sulphide mineralization along the basal margin of the intrusion, however to date no economic accumulations have been found (Chamberlain, 1967; Barnes & Francis, 1995). Despite this ongoing exploration interest, relatively few scientific studies have been completed on marginal zone rocks. Mapping and deep drilling (>3000 m combined) programs completed by the Geological Survey of Canada in the early 1960's provided an understanding of the morphology and internal structure of the intrusion and revealed that the marginal zone is a structurally distinct unit that extends throughout the entire stratigraphic height of the intrusion (Smith, 1962; Findlay & Smith, 1965; Smith, 1967). A study of the variations in the sulphur isotopic compositions from sulphides along the basal contact of the intrusion by Sasaki (1969) indicated that the sulphur was largely derived from the local crustal rocks. This led Barnes and Francis (1995) to suggest that the sporadic distribution of sulphide along the margin of the intrusion was the result of limited availibility of a local sulphur source. Francis (1994) evaluated compositional variations from a number of exposed sections of the marginal 14  zone rocks along mainly the eastern side of the intrusion and proposed that the interaction between the Muskox magmas and the adjacent crustal rocks, which is recorded in only the outer few metres of the intrusion, was a selective process involving mainly the most incompatible trace elements (large ion lithophile and light rare earth elements). In this study we examine new drill core samples collected at two different regions along the western margin of the intrusion (West Pyrrhotite Lake and Far West Margin) during a recent Anglo American Exploration (Canada) Ltd. (AAEC) drill program. Detailed petrographic observations combined with an evaluation of major and trace element abundances, olivine chemistry, and sulphur isotopic compositional variations provide a framework for investigating the origin and evolution of the marginal zone of the Muskox intrusion. The main goals of the study are (1) to classify the mineralogical, textural, and chemical variations that define the marginal zone at different locations within the intrusion, (2) to determine the character and spatial extent of contamination along the basal margin of the intrusion and its relationship to observed sulphide mineralization, (3) to develop a conceptual and a quantitative model for the formation of the marginal zone of the Muskox intrusion. We demonstrate that local crustal contamination is restricted to a very thin zone of gabbronoritic rocks at the base of the marginal zone, and that the downward differentiation trend in the marginal zone of the Muskox intrusion corresponds mainly to an overall downward increase in the proportion of intercumulus phases within overlying peridotites. Sulphides at the base of the marginal zone formed as a result of local addition of crustal sulphur and silicate material derived from the directly adjacent wall rocks. Comparison of the mineralogical and chemical characteristics of marginal rocks at the different sections indicates that their character changes at different locations within the intrusion, which indicates that the marginal zone likely formed at different stages during the evolution and growth of the Muskox magma chamber. Finally, using the IRIDUM software (Boudreau, 2003), we show that the mineralogical and chemical variation observed within the peridotites can be readily explained by crystallization of varying amounts of intercumulus liquid during compaction of a cumulate pile within a thermal gradient at the base of the intrusion, supporting the original proposals of Irvine (1980) and Tharp et al. (1998).  15  2.2 GEOLOGY AND EMPLACMENT OF THE MUSKOX INTRUSION The Muskox intrusion (1270 ± 4 Ma, U-Pb baddeleyite/zircon; LeCheminant & Heaman, 1989) is located -60 km south of the Coronation Gulf in the Coppermine region of Nunavut, Canada (Fig. 2.1). The main body of the intrusion and underlying feeder dike are exposed for over 120 km within early Proterozoic rocks of the Wopmay orogen and an overlying late Proterozoic supracrustal succession containing the Hornby Bay sandstones, Dismal Lake carbonates, and Coppermine River flood basalts (Hoffman, 1980; Hoffman, 1984; Hoffman & Bowring, 1984; Hoffman & Hall, 1993). Based on gravity data, the exposed part of the intrusion may only represent a portion of a much larger body that extends northward beneath the overlying supracrustal rocks (Irvine, 1970). The Muskox intrusion, along with the Mackenzie dike swarm and Coppermine River basalts, was emplaced during the 1.27 Ga Mackenzie magmatic event, which represents a period of extensive tholeiitic magmatism considered to be related to the emplacement of a mantle plume (Baragar, 1969; Fahrig, 1987; LeCheminant & Heaman, 1989; Dupuy et al., 1992; Baragar et al., 1996; Stewart & DePaolo, 1996; Griselin et al., 1997). The intrusion has been divided into a feeder dike, marginal zone, layered series, and granophyric roof zone (Fig. 2.2 & 2.3; Smith, 1962; Smith & Kapp, 1963; Findlay & Smith, 1965). The feeder is exposed south of the Coppermine River (Fig. 2.1) and consists of a -100150 m wide, steeply-dipping, gabbronorite and norite dike that is considered to represent part of the conduit through which the initial magmas entered the chamber; later influxes may have been injected from the north (Irvine, 1980). The 100-200 m thick marginal zone trends parallel to the inward-dipping walls of the intrusion and is discordant to the layering within the layered series (Smith, 1962). The overlying 1800 m-thick layered series contains numerous rock layers that are composed of principally olivine-chromite and olivine-clinopyroxene cumulates within the lower 1300 m of the intrusion, and pyroxene and plagioclase cumulates within the upper 600 m (Fig. 2.3; Findlay & Smith, 1965; Irvine & Smith, 1967; Bedard & Taner, 1992; DesRoches, 1992). The granophyric roof zone consists of granophyric gabbro and granophyre with abundant roof rock xenoliths and is considered to represent a layer of low-density, Si02-rich liquid that was produced during partial melting of the overlying wall rocks (Stewart & DePaolo, 1992). Petrologic investigations of layered series rocks from the Muskox intrusion (Irvine & Smith, 1967; Irvine, 1970; 1975; 1977a) have shown that the intrusion formed through  Coronation Gulf  20 km  R a e Group and Coronation Sills  Dismal Lake Group  Coppermine River Group Muskox Intrusion  ; • 1 Hornby B a y Group  j  I Recluse & Epworth | Groups  Akaitcho Group +  \ Hepburn Batholith n Great Bear jj Magmatic Z o n e  Fig. 2.1: Regional geologic and gravity map of the Coppermine region, Nunavut (adapted from Francis, 1994). Gravity contours (dotted lines, 10 mgl intervals) are from Irvine & Smith (1967) and are based on gravity data from Hornal (1963). The inset shows the distribution of the Mackenzie dikes (after Gibson et al., 1987), MI = Muskox intruison. The Muskox intrusion was emplaced below an unconformity at the base of Hornby Bay and Dismal Lake group sediments, and along the boundary between metasedimentary and granitic rocks of Wopmay orogen (Irvine, 1970; 1980).  17  Muskox Intrusion Granophyric  Roof  Zone  Granophyre and gabbro Layered  Series  LT3  G a b b r o and anorthosite  •  Olivine pyroxenite, pyroxenite  ^ |  O l i v i n e g a b b r o a n d troctolitic  and websterite peridotite I  I  D u n i t e , peridotite, a n d f e l d s p a t h i c peridotite  Marginal I  I  Zones  & Feeder  dike  Peridotite, feldspathic peridotite, a n d gabbronorite  Coppermine River Group F  T  1  Husky Creek and  Coppermine River F  Country Rocks r^-TJ Dismal Lake Group t'.yy.vj Hornby Bay Group [f  1 Hepburn Intrusive Suite and Akaitcho Group Recluse and Epworth Groups Faults  o to  Fig. 2.2: Interpreted 3-dimensional geology map of the main body of the Muskox intrusion (after Irvine, 1980; based on mapping by Smith, 1962 and drill core descriptions by Findlay & Smith, 1965). The intrusion forms an elongate funnel-shaped body that plunges towards the north beneath the Hornby Bay and Dismal Lake Group sediments. A major north-trending fault, the Canoe Lake Fault, displaces the Canoe Lake Block (CBL) southward along the western margin of the intrusion. The feeder dike, which is exposed off the map to the south, is projected beneath the main body of the intrusion. Note the location of the two study regions (WPL = West Pyrrhotite Lake; F W M = Far West Margin) and the historic Geological Survey of Canada drill holes (GSC south, north, and east).  2050  CYCLIC UNITS  CRYSTALLIZATION ORDER (1) (2) (3) LEGEND  1800H  Layered Series & Roof Zone jj^h  Granophyre & Granophyric gabbro Gabbro & Anorthosite Orthopyroxenite  1500-  19  Websterite Troctolitic peridotite & Olivine gabbro Olivine clinopyroxenite  12000) OT  (0  Dunite & Peridotite  Marginal Zone  900-  Dunite & peridotite Feldspathic peridotite Olivine gabbronorite ("Picrite") Gabbronorite ("Bronzite gabbro")  600-  Crystallization Order 300H  < 1n  (1)  OL-CPX-PL-OPX  (2)  OL-CPX-OPX-PL  (3)  OL-OPX-CPX-PL  Fig. 2.3: Stratigraphic column of the Muskox intrusion based on Geological Survey of Canada drill holes (Findlay & Smith, 1965) showing the variations in the crystallization order for each cyclic unit defined by Irvine & Smith (1967). The division of the layered series into four megacycles (Francis, 1994) reflects larger-scale changes in the evolution of the Muskox magma chamber. Cyclic units are defined by both shifts to less differentiated compositions in the accumulating mineral assemblage and cryptic chemical variations within thick dunitic sections (Irvine & Smith, 1967). There is an overall progression to more evolved compositions upwards with dunite, peridotite, and feldspathic peridotite, and olivine clinopyroxenite forming most of the lower 1500 metres; and websterite, orthopyroxenite, and gabbro forming the upper 500 metres of stratigraphy. The marginal zone shows the opposite trend and becomes more evolved in composition towards the base, as described in detail in the text. This downward trend in differentiation is observed in both cyclic unit 1 (feldspathic peridotite to gabbronorite) and the lower part of cyclic unit 2 (peridotite to gabbronorite) which indicates that locally the marginal zone contains multiple sequences.  numerous injections of basaltic magma and concurrent removal (eruption) of fractionated residual liquid. Irvine and Smith (1967) grouped the cumulate rock layers within the intrusion into 25 cyclic units, each of which represents the minerals removed and deposited from a single magma batch (Fig. 2.3). The rocks within a cyclic unit become more evolved in composition with increasing stratigraphic height. The transition from relatively evolved cumulates at the top of one cyclic unit to less differentiated cumulates at the base of the overlying cyclic unit is considered to record the influx of higher temperature, less fractionated magma and removal of fractionated residual magma (Irvine, 1970). A change in the order of crystallization within the upper part of the intrusion (i.e. advanced crystallization of orthopyroxene) reflects a change to a more SiOrrich magma, potentially as a result of mixing relatively evolved and primitive magmas within the chamber (Irvine & Smith, 1967; Irvine, 1970; Stewart & DePaolo, 1992; 1996). A similar mechanism was proposed for the formation of two chromitite seams that occur within peridotite at the base of cyclic units 21 and 22 (Irvine, 1975; 1977a; Roach et al., 1998). Irvine (1980) and Tharp et al. (1998) proposed that crystals accumulated at the base of the Muskox chamber would compact under their own weight, such that much intercumulus liquid was continuously recycled into the overlying magma column. Thus, the rocks within the intrusion are considered to have formed through the initial accumulation of minerals at the base of the magma chamber, and concurrent removal of intercumulus liquid during compaction of the cumulate pile.  2.3 MARGINAL ZONE ROCKS FROM THE WESTERN MARGIN OF THE MUSKOX INTRUSION The two regions studied represent sections across the marginal zone at stratigraphically low (West Pyrrhotite Lake) and high (Far West Margin) positions along the western margin of the Muskox intrusion (Fig. 2.2). The following is a detailed description of the mineralogical and textural variations of marginal zone rocks and adjacent country rocks from drill holes MX03002 (total depth = 200 m) for the West Pyrrhotite Lake section and MX03-001 (total depth = 175 m) for the Far West Margin section (Fig. 2.4). Observations from two additional drill holes located 400 m (MX04-001) and 1000 m (MX04-002) north of the Far West Margin section provide supplementary information and indicate that the lithologic units described below can be traced along strike for >1 km north of the Far West Margin section. As described by Irvine (1970) the rocks within the Muskox intrusion are mainly cumulates, 21  (a) West Pyrrhotite Lake MX03-002 Dunite  Peridotite  Gabbronorite  50 m  o 3  Qtz-feld-bio Gneiss  Feldspathic Peridotite  Olivine Gabbronorite EOH 198 m  Fig. 2.4: Interpreted geologic cross-sections of the (a) West Pyrrhotite Lake (drill hole MX03-002; Az. 270/70°) and (b) Far West Margin (drill hole MX03-001; Az. 279/70°) sections. Geologic contacts are based on petrographic and chemical variations observed in drill core and are extended to the surface from mapping by Smith (1962). The West Pyrrhotite Lake section contains the typical marginal zone sequence, grading from peridotite at the innermost part, to feldspathic peridotite, olivine gabbronorite, and gabbronorite at the outer contact. The Far West Margin section is distinct and consists of chromite-rich peridotite, feldspathic peridotite, and gabbronorite. EOH = end of hole, referring to the termination of each diamond drill hole.  composed of early-forming cumulus minerals that are enveloped by late-forming postcumulus minerals. The cumulate terminology is used here to describe the mineralogy and texture of the marginal rocks and does not imply any specific mechanism of formation. 2.3.1 West Pyrrhotite Lake section The marginal zone rocks at West Pyrrhotite Lake grade downwards from peridotite to feldspathic peridotite, olivine gabbronorite, gabbronorite, and granophyre-bearing gabbronorite (Fig. 2.4a). This succession is consistent with that of the typical marginal zone sequence as mapped by Smith (1962) throughout most of the length of the intrusion and that described by Francis (1994) along the eastern margin of the intrusion (Fig. 2.2). Representative photomicrographs of the textural and mineralogical variations within the West Pyrrhotite Lake section are shown in Fig. 2.5. The uppermost unit of the marginal zone at West Pyrrhotite Lake consists of an 80 mthick homogeneous peridotite unit that is composed of closely-packed 0.5-0.8 mm cumulus olivine (70-80 vol %) and <0.1 mm chromite (~1 vol %) that are enclosed within 0.3-0.8 cm orthopyroxene and clinopyroxene (20-30 vol %), plagioclase (<5 vol %), and phlogopite (2-3 vol %) oikocrysts (Fig. 2.5a). Ilmenite, pyrrhotite, apatite, and trace monazite are accessory minerals that are associated with phlogopite in the interstitial regions between cumulus olivine grains. Individual olivine grains are typically 50-100% altered to serpentine and magnetite, although clusters of unaltered olivine commonly occur within orthopyroxene oikocrysts (Fig. 2.5a). Plagioclase is completely altered, but can be distinguished because of prominent internal fracturing and rarely preserved albite twinning. A progressive increase in the amount of postcumulus plagioclase marks the transition (over 5-10 m) from peridotite to feldspathic peridotite. The feldspathic peridotite unit (-60 m thick) consists of 0.5-0.8 mm closely-packed cumulus olivine (50-70 vol %) that is enclosed within plagioclase (5-20 vol %) and clinopyroxene oikocrysts (10-20 vol %) (Fig. 2.5b). The plagioclase content within this unit increases towards the base where it becomes the dominant interstitial phase over pyroxene. Orthopyroxene (-10-20 vol %) rarely encloses olivine and has sharp grain boundaries with plagioclase. A further increase in the amount and grain size of plagioclase and a significant decrease in the amount of olivine marks the transition to olivine gabbronorite.  23  Figure 2.5  24  Fig. 2.5: Representative photomicrographs (crossed polars) of marginal zone rocks at the West Pyrrhotite Lake section. The field of view is 5 mm for each photomicrograph. OL = olivine; OPX = orthopyroxene; CPX = clinopyroxene; PL = plagioclase; CHR = chromite; PHL = phlogopite; BIO = biotite; SUL = sulphide; ILM = ilmenite; GRN = granophyre; KFS = alkali feldspar; QTZ = quartz, (a) Peridotite (Sample: RMX02-4). Euhedral to round serpentinized olivine crystals enclosed within an orthopyroxene oikocryst (white to grey) and several clinopyroxene oikocrysts (green and blue) in the left and right side of the photo, respectively, (b) Feldspathic peridotite (Sample: RMX02-5). Partially serpentinized olivine enclosed within altered plagioclase (black to brown) and a single clinopyroxene oikocryst (blue to purple). A large (2-4 mm) subhedral orthopyroxene grain occupies the upper left corner and is nearly devoid of olivine, (c) Olivine gabbronorite (Sample: RMX02-8). Loosely-packed, euhedral to round olivine crystals enclosed within mainly plagioclase oikocrysts (heavily fractured; rare albite twinning) and to a lesser extent within clinopyroxene (red to yellow). Olivine is preserved within plagioclase, but completely altered to serpentine within clinopyroxene. A large (2-4 mm) subhedral orthopyroxene crystal occupies the upper left corner of the photo, (d) Gabbronorite (Sample: 71138). An equigranular-textured rock with euhedral orthopyroxene and clinopyroxene, and interstitial plagioclase. Rare ovoid-shaped serpentine grains within a clinopyroxene crystal at the bottom of the slide likely represent early-formed olivine, (e) Granophyre-bearing gabbronorite (Sample: 71139). Subophitic-textured rock containing sericitized plagioclase laths that are partially enclosed within orthopyroxene. Anhedral masses of quartz, alkali feldspar, and granophyre enclose plagioclase and orthopyroxene. (f) Granophyre-bearing gabbronorite (Sample: RMX02-9). Large (4-5 mm) composite alkali feldspar (with apatite inclusions) and ilmenite clot surrounded by a finer-grained portion composed of mainly subhedral plagioclase laths that are partially enclosed within subhedral orthopyroxene (grey to white) and clinopyroxene (purple to blue). Phlogopite (orange to green) and associated sulphide form clots within the finer grained region.  The olivine gabbronorite unit (-15 m thick) consists of 0.5-0.8 mm cumulus olivine (40-50 vol %) enclosed within 2-4 mm plagioclase oikocrysts (20-30 vol %) and to a lesser extent within 2-3 mm clinopyroxene oikocrysts (10-15 vol %) (Fig. 2.5c). Orthopyroxene (2030 vol %) forms large (3-8 mm), irregular-shaped to subhedral grains that only rarely enclose cumulus olivine. This unit is considered to be equivalent to the "picrite" described by Smith (1962). In accordance with IUGS classification, and to avoid confusion with chemical and volcanological terminology, the term olivine gabbronorite is used throughout this paper for this rock type. The transition to gabbronorite occurs within -8 m from the contact with the country rocks, and is marked by a sharp decrease (over a 1 m interval) in the amount of olivine. The gabbronorite unit (-8 m thick) is distinctly more equigranular that the overlying olivine-rich units and is composed of 1-2 mm cumulus orthopyroxene (40 vol %) and clinopyroxene (10-20 vol %), and 1-2 mm postcumulus plagioclase (20-30 vol %) and phlogopite (5-10 vol %) (Fig. 2.5d). Olivine is rare (<5 vol %) and occurs exclusively as serpentine pseudomorphs within pyroxene. The gabbronorite unit also marks the first appearance of quartz, alkali feldspar, and minor granophyre (2-3 vol %), which occur interstitial to cumulus pyroxene. This unit is considered to be analogous to the "bronzite gabbro" unit of Smith (1962). A distinct change in texture and an increase in the abundance of granophyre marks the transition from gabbronorite to granophyre-bearing gabbronorite within 4 m of the contact (Fig. 2.5e & 2.5f). The granophyre-bearing gabbronorite (-1 m thick) has a subophitic to ophitic texture where 1-2 mm plagioclase laths (40 vol %) are partially or completely enclosed within 0.8-1.2 mm subhedral orthopyroxene (30 vol %) and clinopyroxene (-10 vol %). Granophyre, quartz, and alkali feldspar are abundant (10-30 vol %) and form large clots up to 10 mm in diameter (Fig. 2.6). These large clots also contain blocky ilmenite, abundant needle-shaped apatite, and minor euhedral and hopper-textured zircon crystals (Fig. 2.6). Phlogopite (5 vol %) forms anhedral grains and is intergrown with blades of ilmenite. Directly adjacent to the contact (within 0.5 m) the gabbronorite contains 2-5 cm ellipsoid fragments of the adjacent country rocks. Sulphides occur as rare 2-10 mm blebs that are composed of mainly pyrrhotite and minor chalcopyrite. The country rock at West Pyrrhotite Lake consists of variably contact metamorphosed quartz-feldspar-biotite gneiss. Near the contact with the intrusion the host rock has a  Fig. 2.6: Photomicrograph of a large granophyre-alkali feldspar-quartz clot within subophitictextured gabbronorite from the West Pyrrhotite Lake section (Sample 71139). These clots are abundant within the outer 4 m of the intrusion at this location. Granophyre (intergrowths of alkali feldspar and quartz) forms 2/3 of the clot and individual anhedral grains of alkali feldspar and quartz form the remaining 1/3. The clot contains abundant acicular apatite and minor hopper-textured (skeletal) zircon, which are shown in backscatter electron images in insets B and C. The red box outlines the area show in B (rotated 45°). Apatite occurs in both granophyre and granular regions and commonly transects grain boundaries. The hoppertextured zircons form equant crystals about 60-70 microns in length. The outer boundary of the clot is curvilinear and is rimmed, in places, by sericitized plagioclase laths that separate it from the subophitic intergrowths of orthopyroxene and plagioclase. The clot appears to represent a partial melt of the adjacent crust incorporated into the marginal zone that did not mix with the mafic melt.  heterogeneous texture and banding is not well-developed. It is composed of 2-3 mm anhedral quartz (40-50 vol %), 2-3 mm anhedral alkali feldspar (30-40 vol %), and 1-2 mm subhedral clinopyroxene (10-15 vol %). Accessory phases include rare granophyric patches, acicular ilmenite, and euhedral apatite and zircon. Away from the contact (>20 m), the gneiss is strongly banded and composed of alternating biotite-rich (30 vol %) and biotite-poor (<5 vol %) bands. The gneiss is composed of 2-3 mm anhedral quartz and subhedral feldspar (40-60 vol %), which occur as discrete individual grains as well as granophyric intergrowths, and 1-2 mm subhedral biotite (5-30 vol %). Pyrrhotite, chalcopyrite, and acicular ilmenite occur as accessory phases within the biotite-rich bands. The granophyre likely represents pockets of partial melt that formed as a result of heating during the emplacement of the Muskox intrusion. The lack of biotite and granophyre within the country rocks directly adjacent to the intrusion could be the result of dehydration and melt extraction during the emplacement of the intrusion.  2.3.2 Far West Margin section The marginal zone rocks at the Far West Margin (Drill hole: MX03-001, 175 m) are distinct from those at the West Pyrrhotite Lake section and consist of variably sulphide-mineralized feldspathic peridotite, chromite-rich peridotite, and gabbronorite (Fig. 2.4b). Representative photomicrographs of the textural and mineralogical variations within the Far West Margin section are shown in Fig. 2.7. The peridotites at Far West Margin contain coarse-grained olivine (1.0-1.5 mm) that is not observed at West Pyrrhotite Lake and has only been documented in the upper parts of the layered series (Irvine & Smith, 1969), which is broadly consistent with relative stratigraphic position of the Far West Margin section (Fig. 2.2). The chromite-rich peridotite horizons consist of 0.8-1.2 mm cumulus olivine (50-60 vol %) and 0.1 mm chromite (2-10 vol %) that are enclosed within 0.8-1.5 cm orthopyroxene (20 vol %) and clinopyroxene (10 vol %) oikocrysts, and anhedral plagioclase (10 vol %) (Fig. 2.7a & 2.7b). Pyroxene is commonly altered to biotite (and chlorite) along fractures and grain boundaries. Chromite grains occur in clusters within orthopyroxene and plagioclase, and rarely phlogopite. The clusters form ellipsoidal outlines that may have originally rimmed olivine grains and which were subsequently replaced by orthopyroxene (Irvine & Smith, 1969). Phlogopite is abundant (8-10 vol %) and forms 2-3 mm postcumulus crystals associated with ilmenite and sulphide (pyrrhotite and minor chalcopyrite). Olivine is 50-100% altered to serpentine and magnetite. Plagioclase is completely altered, but can be distinguished  29  Figure 2.7  30  Fig. 2.7: Representative photomicrographs (crossed polars)of marginal zone rocks for the Far West Margin section. Field of view is 10 mm for a-d and 5 mm for e-f. Abbreviations as in Fig. 2.5. (a) Chromite-rich peridotite (sample: RMX01-1). Olivine and clusters of chromite crystals enclosed within a single orthopyroxene oikocryst that occupies the entire field of view (10 mm). Secondary biotite occurs along fractures within pyroxene, (b) Chromite-rich peridotite (sample: RMX01-1). Large (1.5 mm) partially serpentinized olivine crystals surrounded by heavily fractured and sericitized plagioclase. Clusters of chromite crystals occur within interstitial plagioclase. (c) Feldspathic peridotite (sample: RMX01-4). Plagioclase, the most abundant interstitial phase, has well-developed albite twining and a heavily fractured appearance, and separates closely-packed serpentinized olivine crystals in the upper and right side of the view. Orthopyroxene is also interstitial and contains relatively few olivine crystals as shown in the left side of view. Clinopyroxene forms a minor wedge-shaped interstitial phase at the bottom of the photomicrograph, (d) Feldspathic peridotite (sample: RMX01-5). Anhedral plagioclase (white and dark grey) and clinopyroxene (red to purple) occurs in between closely-packed partially serpentinized olivine, (e) Gabbronorite (sample: RMX01-8). Subhedral sericitized plagioclase laths partially enclosed within an anhedral orthopyroxene crystal. Phlogopite is anhedral and associated with sulphide blebs within the upper right corner of the view, (f) Gabbronorite (sample: 71088). Alkali feldspar (dark grey) is interstitial to cumulus orthopyroxene.  31  by its heavily fractured appearance and rarely preserved albite twinning as noted within the West Pyrrhotite Lake section above. The abundance of chromite (2-8 vol %) and the coarseness of orthopyroxene oikocrysts (up to 1.5 cm) are distinguishing features of this unit. The chromite-rich horizons have been traced for over 1 km to the north in other drill holes. A sharp decrease in the abundance of chromite and a progressive increase in the abundance of feldspar mark the transition to feldspathic peridotite. The feldspathic peridotite consists of 1.0-1.5 mm cumulus olivine (60-70 vol %) that is partially enclosed within 1.5-3.0 mm orthopyroxene (10-20 vol %) and clinopyroxene (5-10 vol %), and 1.5-2.0 mm plagioclase (10-30 vol %) (Fig. 2.7c & 2.7d). The abundance of plagioclase increases towards the base of the unit, where it forms equant subhedral crystals that are interstitial to olivine (Fig. 2.7d). This plagioclase-rich zone (30 vol %) likely is analogous to the "picrite" unit mapped on surface (Smith, 1962). Underlying the feldspathic peridotite is a second chromite-rich horizon that is comparable to the upper chromite-rich horizon and also contains secondary biotite. At ~9 m from the contact, there is a sharp change in lithology at a thin (<30 cm) breccia zone that contains ellipsoid gabbronoritic and granitic fragments (~10 cm in diameter). Gabbronorite forms the contact phase at the Far West Margin and has an intergranular to subophitic texture with 1.0-2.0 mm subhedral calcic-plagioclase laths (20-30 vol %) and 1-4 mm subhedral orthopyroxene (30-40 vol %) (Fig. 2.7e & 2.7 f). Interstitial to orthopyroxene and plagioclase are 1-4 mm anhedral phlogopite (5-10 vol %), sulphide (10-15 vol %), and rare sodic feldspar. Olivine (<5 vol %) occurs within plagioclase and orthopyroxene and is completely altered to serpentine and chlorite. Analogous to that observed at West Pyrrhotite Lake, the gabbronorite at the Far West Margin contains blebs of granophyre, quartz, and alkali feldspar (-10 vol % combined) that fill interstitial regions between orthopyroxene (Fig. 2.7f). The gabbronorite is not mapped at surface at the Far West Margin, likely due to poor exposure. This unit is not intersected 1000 m north of the Far West Margin section (DDH MX03-002), which is consistent with the observations of Smith (1962), who noted that the gabbronorite is not typically found north of Speers Lake. Sulphide mineralization occurs throughout the Far West Margin section and is concentrated within the gabbronorite and the adjacent country rocks. The peridotites are variably mineralized, containing <l-5 vol % sulphide, which consists of 1-3 mm composite grains of pyrrhotite and pentlandite that are interstitial to olivine. Pentlandite forms globules 32  within the outer portions of pyrrhotite blebs and is associated with magnetite. The gabbronorite contains 5-15% sulphide, which occurs as 0.5-1.0 cm blebs and 1-3 mm anhedral clots of pyrrhotite and chalcopyrite, and minor pentlandite. Pyrrhotite forms the core of most blebs, whereas chalcopyrite occurs along the outer edge. Pentlandite within the gabbronorite occurs as exsolution lamellae within pyrrhotite, and rarely forms sub-millimetre blebs associated with chalcopyrite. Massive sulphide occurs as thin (30 cm) layers or lenses within gabbronorite and within the country rocks and was intersected in drill hole MX03-001 and 400 m towards the north in drill hole MX04-001. At the contact, massive sulphide consists of 1-4 mm polygonal pyrrhotite grains (70-80 vol %), which are rarely separated by lens-shaped chalcopyrite (15-20 vol %) and associated <1 mm equant pentlandite grains (<5 vol %). Sulphide also occurs as 5-10 mm wide veins within the matrix of a brecciated, biotite-rich section of the footwall rocks 15-20 m from the intrusive contact. The matrix consists of quartz-feldspar-(granophyre)-sulphide veins that contain a relatively high abundance of pentlandite and chalcopyrite and likely represent the remobilization of sulphide during hydrothermal fluid circulation within the wall rocks during the emplacement of the intrusion. The country rocks at the Far West Margin are lithologically variable and typically consist of fine-grained hornfels with lenses of granitic material adjacent to the contact, and banded sulphidic metasediments and biotite-garnet-quartz schists further from the contact (as observed in drill holes MX03-002, MX04-001, and MX04-002). This is consistent with surface mapping, which indicates that the wall rocks in this region are biotite-rich paragneiss of the Recluse and Epworth groups (Smith, 1962). Directly adjacent to the intrusion the host rock is a fine-grained and intensely altered hornfels, consisting mainly of secondary mica and acicular ilmenite enclosed within pyroxene, quartz, and biotite poikiloblasts. The granitic lenses, which likely represent veins of partial melt formed during emplacement of the intrusion, are composed predominantly of 0.5-1.5 mm anhedral quartz (40-50 vol %) and alkali feldspar (30-40 vol %) that form individual grains and granophyric intergrowths, and anhedral biotite (10 vol %) and sulphide (2-3 vol %). A contact metamorphosed and altered gabbro was intersected within the footwall only in drill hole MX03-001 and consists of equant feldspar enclosed within poikiloblastic pyroxene and biotite. The extent of this gabbroic unit is unknown as it was not observed in other drill holes. Further from the contact (>20 m), the host rocks have a well-defined, but variably oriented fabric. These rocks consist mainly of equant quartz (40-50 vol %), altered plagioclase (30 vol %), varying amounts of anhedral 33  biotite (25-30 vol %) and granular pyrrhotite and chalcopyrite (2-5 vol %). Several metrethick biotite-rich zones contain 0,5-0.8 cm garnet porphyroblasts, which occur 20-30 metres from the contact. As will be discussed below, these sulphidic sediments likely played an important role in the formation of sulphide mineralization at the Far West Margin section of the Muskox intrusion. 2.4 ANALYTICAL TECHNIQUES 2.4.1 Major element oxides and trace element concentrations Major element oxides and trace element concentrations of 82 samples were determined at A C M E Analytical Laboratories Ltd., Vancouver. Each sample represents a 0.5-1.5 m interval of split drill core collected during an Anglo American Exploration (Canada) Ltd. diamond drilling program on the Muskox intrusion in 2003. Samples were crushed to 70% passing 2 mm mesh using a T M Engineering Rhino Jaw Crusher with chrome-steel plates; and a 250 g sub-sample was subsequently powdered to 95% passing 100 micron mesh using a T M Engineering TM/G ring pulverizer with case-hardened steel bowl. The A C M E analytical procedures are summarized in Appendix I. Major element oxides and trace elements were analyzed by ICP-ES following LiBC^ fusion and digestion of 200 mg of sample in 5% HNO3. Loss-on-ignition was determined from the weight difference after ignition at 1000°C and total sulphur was determined by Leco analysis. Relative errors (la) based on five duplicate digestions are typically less than 5% for major elements. Low contents of Na20 and P2O5 in peridotite samples gave larger relative errors of 8% and 12%, respectively. Transition metals (including Cu, Pt, and Pd) were determined by ICP-MS following digestion of 30 grams of sample in HNO3, HC1, and H2O (2:2:2). Total nickel concentration was determined by ICP-ES following digestion of 500 mg of sample in H 0, HF, HC10 and HNO3 (18:10:3:6). 2  4  Analytical reproducibility is estimated from five procedural duplicates, which give relative errors of <10% for most rare earth elements (REE) and high field strength elements, and 1020% for Cs, Th, Nb, and Gd (Appendix II). Relative errors (la) for copper, nickel, cobalt, and chromium are less than 7%, and for platinum and palladium are less than 17%. Multiple analyses of an internal basalt standard (BAS2) are within error (2a) of the accepted value. Raw data is shown in Table 2.1, and all diagrams use results after recalculation on an anhydrous basis.  34  Table 2.1a : Major and trace element abundances for the West Pyrrhotite Lake section (DDH # MX03-002) Rock type  Peridotite Peridotite Peridotite Peridotite Altered Altered Peridotite Peridotite Peridotite Peridotite Peridotite Peridotite Peridotite Peridotite Feldspathic Peridotite Peridotite Peridotite  Sample ID  71104  71105  71106  71107  71108  71111  71112  71113  71114  71115  71116  71117  71118  71119  From (m)  16.6  23.5  30.8  38.0  43.5  49.2  53.7  58.9  66.2  72.5  76.9  82.6  88.4  95.6  101.4  To(m)  17.6  24.5  31.8  39.0  44.5  50.2  54.7  59.9  67.2  73.5  77.9  83.6  89.4  96.6  102.4  Distance (m)  160.4  153.5  146.2  139.0  133.5  127.9  123.3  118.1  110.8  104.5  100.2  94.4  88.6  81.4  75.6  71120  Major elements (wt%) Si0  2  35.23  35.41  35.61  35.97  34.69  35.55  35.76  35.63  36.42  36.62  36.76  36.41  36.58  37.64  Ti0  2  0.29  0.32  0.33  0.34  0.36  0.35  0.35  0.35  0.39  0.38  0.38  0.39  0.39.  0.41  0.40  2.59  2.57  2.65  2.80  2.88  2.86  2.96  2.92  3.06  3.20  3.18  3.15  3.12  3.21  3.55  14.93  14.96  14.80  14.66  13.68  13.93  14.29  14.34  14.41  14.62  14.50  14.62  14.88  14.28  14.63  Al 0 2  3  Fe 0 * 2  3  36.76  MnO  0.15  0.17  0.16  0.17  0.16  0.17  0.16  0.16  0,16  0.16  0.16  0.16  0.16  0.17  0.16  MgO  32.83  32.75  33.08  32.48  32.80  32.82  31.85  32.02  31.45  31.16  31.29  31.74  32.16  31.24  31.23  CaO  0.69  1.29  1.57  1.51  0.62  1.03  1.98  1.86  2.30  2.50  2.49  2.24  2.37  2.33  2.69  Na O  0.02  0.08  0.02  0.02  0.02  0.03  0.02  0.07  0.02  0.01  0.02  0.10  0.05  0.12  0.06  K 0  0.08  0.10  0.09  0.15  0.17  0.17  0.11  0.10  0.12  0.12  0.12  0.13  0.13  0.13  0.13  P2O5  0.05  0.08  0.09  0.08  0.06  0.06  0.06  0.06  0.05  0.08  0.07  0.07  0.09  0.07  0.10  0.46  0.48  0.48  0.49  0.52  0.53  0.51  0.51  0.54  0.55  0.51  0.52  0.57  0.57  0.56  12.2  10.8  10.4  11.1  12.6  12.0  10.8  10.9  10.5  10.1  9.7  9.4  8.7  9.9  8,6  0.07  0.03  0.03  0.02  0.08  0.04  0.03  0.03  0.06  0.02  0.02  0.02  0.01  0.04  0.04  99.75  99.24  99.5  100.0  98.79  99.72  99.08  99.16  99.66  99.73  99.41  99.17  99.62  99.25  99.99  z  2  Cr 0 2  LOI  3  1  S Total mg-number FeO"  2  0.813  0.813  0.816  0.814  0.826  0.824  0.815  0.816  0.812  0.809  0.810  0.811  0.811  0.813  0.809  13.43  13.46  13.32  13.19  12.31  12.53  12.86  12.90  12.97  13.16  13.05  13.16  13.39  12.85  13.16  Chalcophile elements (pom) Cu  60  61  61  46  148  8  27  56  320  40  43  61  54  83  75  Ni  1842  1758  1714  1752  1775  1689  1780  1823  1878  1782  1782  1817  1864  1919  1852  Co  115  102  103  102  126  104  99  98  103  95  97  104  99  103  102  Pd (ppb)  12  17  44  44  41  19  11  51  96  10  41  29  12  25  20  Pt (ppb)  15  16  44  26  21  11  7  23  28  6  31  10  6  9  5  Au (ppb)  0.9  1.0  1.3  2.4  1.4  0.6  0.4  1.0  6.1  0.4  2.0  1.5  0.4  1.2  <.2  Table 2.1b (continued): Rock type  Peridotite Peridotite Peridotite Peridotite Altered Altered Peridotite Peridotite Peridotite Peridotite Peridotite Peridotite Peridotite Peridotite Feldspathic Peridotite Peridotite Peridotite  Sample ID  71104  71105  71106  71107  71108  71111  71112  71113  71114  71115  71116  71117  71118  71119  From (m)  16.6  23.5  30.8  38.0  43.5  49.2  53.7  58.9  66.2  72.5  76.9  82.6  88.4  95.6  101.4  To(m)  17.6  24.5  31.8  39.0  44.5  50.2  54.7  59.9  67.2  73.5  77.9  83.6  89.4  96.6  102.4  Distance (m)  160.4  153.5  146.2  139.0  133.5  127.9  123.3  118.1  110.8  104.5  100.2  94.4  88.6  81.4  75.6  Sc  7  5  5  5  10  7  5  6  5  4  5  5  4  5  4  V  101  102  98  102  115  102  105  109  117  114  108  114  114  118  128  Cr  334  217  204  283  660  445  248  272  238  187  201  214  211  281  193  Se  0.4  0.3  0.2  0.2  0.3  0.3  0.2  0.3  0.5  0.2  0.3  0.3  0.3  0.4  0.3  Rb  4  5  4  6  6  6  5  5  5  5  5  6  6  6  6  Sr  9  10  10  11  7  7  9  8  11  14  15  21  25  18  35  Y  4.2  4.2  4.4  4.4  4.9  4.5  4.7  4.5  5.6  5.2  5.1 '  5.7  5.5  5.3  5.5  Zr,  20  19  21  23  24  20  23  21  31 ,  24  25  27  25  29  25  Nb  1.3  1.7  1.6  1.8  1.8  1.7  1.6  1.9  2.0  2.0  2.0  2.0  2.0  0.2  0.3  0.2  0.4  0.3  0.6  0.3  -5 0.3  2.0  Cs  0.3  0.3  0.3  0.3  0.4  0.4  0.2  Ba  18  22  20  37  44  29  34  27  25  27  33  36  38  24  43  La  2.3  2.6  2.6  2.9  2.4  2.3  3.1  3.1  3.7  3.5  3.4  3.3  3.3  3.5  3.6  Ce  5.4  6.2  5.8  6.8  6.0  5.0  6.8  6.7  7.7  7.4  7.2  7.4  7.4  7.5  7.7  Pr  0.69  0.73  0.71  0.83  0.82  0.70  0.88  0.85  1.03  0.97  - 0.96  1.00  0.92  0.96  0.96  Nd  3.3  3.6  4.0  4.5  3.8  3.4  4.3  3.4  5.0  5.3  4.7  5.0  4.3  4.9  4.0  Sm  0.9  0.8  0.9  0.8  1.0  0.9  1.1  1.1  1.0  1.1  1.0  1.0  1.0  1.1  1.1  Eu  0.22  0.24  0.24  0.32  0.28  0.23  0.27  0.30  0.34  0.34  0.27  0.33  0.37  0.33  0.35  Gd  0.90  0.84  0.85  1.16  0.84  0.90  1.02  1.06  1.05  0.89  1.21  1.15  1.09  1.24  1.22  Tb  0.13  0.14  0.13  0.17  0.20  0.17  0.19  0.17  0.19  0.20  0.17  0.19  0.17  0.16  0.17  Dy  0.72  0.72  0.70  0.83  0.92  0.78  0.89  0.89  1.06  1.05  0.90  0.85  0.96  1.07  0.93  Ho  0.13  0.15  0.13  0.18  0.17  0.17  0.17  0.19  0.21  0.19  0.17  0.21  0.19  0.19  0.20  Er  0.39  0.41  0.45  0.45  0.55  0.48  0.50  0.41  0.50  0.53  0.47  0.52  0.45  0.50  0.56  Tm  <.05  0.06  0.06  0.09  0.07  0.06  0.07  0.07  0.08  0.09  0.08  0.07  0.08  0.07  0.07  Yb  0.34  0.37  0.36  0.45  0.47  0.44  0.46  0.48  0.46  0.44  0.47  0.58  0.41  0.58  0.48  Lu  0.05  0.06  0.06  0.07  0.08  0.05  0.07  0.07  0.07  0.08  0.06  0.08  0.06  0.07  0.09  Hf  0.5  0.6  0.6  0.5  0.8  0.7  0.6  0.8  0.8  0.8  0.7  0.8  0.7  0.8  1.0  Ta  0.1  <.1  <.1  0.1  <.1  0.1  0.1  0.1  0.1  <.1  <.1  0.1  0.1  0.1  0.1  Th  0.2  0.2  0.5  0.9  0.4  0.6  0.6  0.2  0.7  0.3  0.8  0.7  0.7  0.7  0.7  71120  Trace elements (ppm)  1  Ol Gbnr = olivine gabbronorite; Qtz-feld-bio = quartz feldspar biotite; * Total Fe as Fe203;** Total Fe as FeO; 'LOI = loss on ignition; mg-number = Mg/(Mg+Fe *); < = below detection limit 2  2  Table 2.1a (continued): Major and trace element abundances for the West Pyrrhotite Lake section (DDH # MX03-002) Rock type  Feldspathic Peridotite  Feldspathic Peridotite  Feldspathic Peridotite  Feldspathic Peridotite  Feldspathic Feldspathic Feldspathic Peridotite Peridotite Peridotite  Feldspathic Ol-Gbnr Peridotite  Ol-Gbnr  Ol-Gbnr  Ol-Gbnr  Gouge  Gouge  Sample ID  71121  71122  71123  71124  71125  71126  71127  71128  71131  71132  71133  71134  71135  71136  From (m)  107.0  113.0  118.8  124.7  130.8  136.9  142.6  148.3  154.5  158.5  162.8  165.9  169.5  171.7  To(m)  108.0  114.0  119.8  125.7  131.8  137.8  143.0  149.3  155.5  159.5  163.3  166.9  171.0  172.1  Distance (m)  70.0  64.0  58.2  52.3  46.2  40.2  35.0  28.7  22.5  18.5  14.7  11.1  7.0  5.9  Major elements (wt%) Si0 Ti0  2  37.07  37.90  38.15  38.98  39.97  39.34  39.60  40.78  40.74  42.88  43.72  44.20  39.71  41.17  2  0.46  0.45  0.49  0.50  0.58  0.64  0.65  0.72  0.80  0.89  0.99  1.07  0.95  0.75  3.29  3.82  4.01  4.16  4.77  4.90  5.11  5.85  6.26  7.18  7.77  8.29  8.43  7.36  15.17  14.67  14.46  14.35  14.27  14.53  14.66  14.78  14.57  14.90  14.51  14.23  14.30  13.58  Al 0 2  3  Fe 0 * 2  3  MnO  0.16  0.17  0.18  0.16  0.16  0.17  0.17  0.17  0.17  0.17  0.16  0.15  0.12  0.12  MgO  30.71  30.23  29.25  28.28  26.94  26.11  26.05  25.24  24.35  22.75  21.66  20.89  24.99  24.23  CaO  2.42  3.10  2.55  3.07  3.65  3.83  3.05  4.08  4.12  5.19  5.40  5.35  0.84  1.56  Na 0  0.11  0.12  0.04  0.13  0.19  0.23  0.39  0.52  0.56  0.67  0.91  0.83  0.18  0.27  K 0  0.18  0.15  0.16  0.17  0.22  0.27  0.29  0.37  0.41  0.55  0.59  0.55  0.42  0.41  0.12  0.07  0.07  0.10  0.09  0.08  0.08  0.09  0.13  0.13  0.15  0.15  0.13  0.13  0.54  0.53  0.53  0.48  0.50  0.46  0.36  0.34  0.30  0.30  0.29  0.28  0.34  0.36  2  2  P O 2  6  Cr 0 2  LOI  3  1  8.8  8.5  9.8  8.6  8.5  8.0  8.4  6.7  7.5  4.2  3.7  4.0  9.2  9.2  0.13  0.09  0.04  0.06  0.03  0.15  0.19  0.02  0.02  0.02  0.03  0.07  0.19  0.18  99.30  99.95  99.90  99.20  100.0  98.79  99.02  99.80  100.1  99.97  100.0  100.2  99.79  99.32  S Total mg-number FeO"  2  -  0.800  0.803  0.800  0.796  0.789  0.781  0.779  0.772  0.768  0.752  0.747  0.744  0.776  0.780  13.65  13.20  13.01  12.91  12.84  13.07  13.19  13.30  13.11  13.41  13.06  12.80  12.87  12.22  665  Chalcophile elements (ppm)  ^1  Cu  577  324  86  255  83  636  636  95  154  160  103  311  898  Ni  2066  1942  1676  1701  1579  1701  1586  1200  1203  1144  1055  1059  1376  1262  Co  105  99  95  92  84  92  95  90  82  80  71  69  100  96  Pd (ppb)  75  53  25  30  30  57  92  20  59  70  17  32  152  82  Pt (ppb)  13  8  6  9  8  13  15  9  20  14  5  4  7  5  Au (ppb)  6.8  3.3  1.3  2.1  1.5  5.0  6.7  1.2  3.7  3.0  2.0  2.1  6.4  5.3  Table 2.1b (continued): Rock type  Feldspathic Peridotite  Feldspathic Peridotite  Feldspathic Peridotite  Feldspathic Peridotite  Feldspathic Peridotite  Feldspathic Peridotite  Feldspathic Peridotite  Feldspathic Peridotite  Ol-Gbnr  Ol-Gbnr  Ol-Gbnr  Ol-Gbnr  Gouge  Gouge  Sample ID  71121  71122  71123  71124  71125  71126  71127  71128  71131  71132  71133  71134  71135  71136  From (m)  107.0  113.0  118.8  124.7  130.8  136.9  142.6  148.3  154.5  158.5  162.8  165.9  169.5  171.7  To(m)  108.0  114.0  119.8  125.7  131.8  137.8  143.0  149.3  155.5  159.5  163.3  166.9  171.0  172.1  Distance (m)  70.0  64.0  58.2  52.3  46.2  40.2  35.0  28.7  22.5  18.5  14.7  11.1  7.0  5.9  Sc  5  5  5  4  4  4  5  4  4  3  3"  5  16  13  V  120  117  123  129  139  149  144  165  168  182  200  214  202  175  Cr  223  199  213  184  207  236  303  239  275  223  259  366  Se  0.6  0.4  0.3  0.4  0.2  0.6  0.6  0.2  0.2  0.2  0.1  0.3  Trace elements (ppm)  '  1313  1100  0.7  0.5  Rb  8  6  7  7  8  9  8  11  13  15  16  16  17  15  Sr  36  35  24  34  43  48  80  117  112  125  150  134  30  51  •12,2  Y  6.5  6.2  6.3  6.9  7.1  8.9  8.2  10.5  11.5  12.5  14.4  15.9  Zr  36  27  31  32  35  45  44  48  56  62  73  74  65  53  12.2  Nb  2.4  2.0  2.4  2.3  3.0  3.1  3.3  3.5  4.3  4.6  5.0  6.0  5.5  4.5  Cs  0.5  0.3  0.5  0.7  0.6  0.8  1.1  1.3  1.3  2.5  2.5  1.2  1.0  1.5  Ba  57  47  47  58  62  92  94  107  129  129  162  191  90  143  La  4.6  3.7  3.9  4.2  4.9  5.4  5.2  6.4  7.0  7.6  8.8  9.2  7.3  8.9  Ce  10.1  7.9  9.1  9.2  11.3  12.9  12.0  13.9  16.1  17.3  19.4  20.9  16.9  17.7  Pr  1.37  1.02  1.21  1.28  1.52  1.59  1.57  1.81  1.97  2.29  2.60  2.76  2.27  2.25  Nd  6.5  5.1  5.3  5.9  7.7  8.1  7.2  8.5  10.4  10.3  12.4  12.4  9.4  10.7  Sm  1.2  1.2  1.2  1.4  1.6  1.9  1.7  2.1  2.5  2.5  2.7  3.0  2.5  2.4  Eu  0.33  0.37  0.40  0.46  0.51  0.53  0.58  0.56  0.67  0.72  0.77  0.86  0.52  0.52  Gd  1.21  1.29  1.19  1.3  1.77  2.03  1.83  1.92  2.34  2.44  2.6  3.21  2.48  2.65  Tb  0.23  0.19  0.22  0.23  0.29  0.32  0.31  0.33  0.32  0.36  0.45  0.49  0.37  0.39  Dy  1.14  1.14  1.15  1.27  1.43  1.62  1.61  2.10  2.10  2.24  2.66  2.75  2.29  2.20  Ho  0.23  0.21  0.25  0.25  0.29  0.32  0.33  0.34  0.44  0.40  0.51  0.54  0.43  0.37  Er  0.64  0.56  0.53  0.63  0.70  0.85  0.78  1.03  1.03  1.27  1.32  1.47  1.14  1.14  Tm  0.09  0.09  0.09  0.11  0.13  0.13  0.13  0.13  0.15  0.15  0.17  0.20  0.18  0.16  Yb  0.49  0.48  0.62  0.55  0.70  0.85  0.76  1.03  1.05  1.14  1.31  1.27  1.33  1.09  Lu  0.10  0.06  0.09  0.09  0.10  0.10  0.12  0.13  0.15  0.17  0.18  0.19  0.16  0.15  Hf  1.1  0.7  1.0  0.7  1.2  1.5  1.4  1.3  1.9  1.9  2.2  2.4  2.1  1.7  Ta  0.1  0.1  0.1  0.1  0.2  0.2  0.2  0.3  0.3  0.3  0.3  0.4  0.4  0.3  Th  1.3  0.7  0.4  0.9  1.2  0.8  1.1  1.1  1.6  1.6  1.8  1.6  1.1  1.0  Ol Gbnr = olivine gabbronorite; Qtz-feld-bio = quartz feldspar biotite; * Total Fe as F e 2 0 3 ; " Total Fe as FeO; LOI = loss on ignition; mg-number = Mg/(Mg+Fe *); < = below detection limit 1  00  2  2  Table 2.1a (continued): Major and trace element abundances for the West Pyrrhotite Lake section (DDH # MX03-002) Rock type  Gabbronorite  Gabbronorite  Gabbronorite  Qtz-feld-bio Gneiss  Qtz-feld-bio Qtz-feld-bio Gneiss Gneiss  Qtz-feld-bio Qtz-feld-bio Qtz-feld-bio Qtz-feld-bio Qtz-feld-bio Qtz-feld-bio Qtz-feld-bio Gneiss Gneiss Gneiss Gneiss Gneiss Gneiss Gneiss  Sample ID  71137  71138  71139  71140  71141  71151  71142  71143  71144  71145  71146  71148  71147  From (m)  172.1  173.6  174.8  178.0  179.3  181.5  182.7  183.8  187.1  187.9  191.9  202.2  200.9  To(m)  173.6  Distance (m)  4.4  .  174.8  175.8  179.0  180.3  182.5  183.2  185.4  187.9  188.9  192.9  202.9  201.9  3.2  2.2  -1.0  -2.3  -4.5  -5.2  -7.4  -9.8  -10.9  -14.9  -24.9  -23.9  Major elements (wt%) Si0  2  43.86  47.92  50.49  67.23  69.13  70.28  69.20  58.72  36.76  56.70  58.49  65.86  Ti0  2  0.80  0.76  0.47  0.36  0.35  0.30  0.21  0.61  0.39  0.41  0.58  0.52  0.56  9.68  8.94  10.19  8.89  11.60  10.57  13.93  15.88  9.93  12.46  15.57  15.41  15.38 4.86  Al 0 2  3  65.53  14.78  17.77  18.32  11.37  5.62  5.86  3.53  8.93  38.60  17.27  10.47  4.89  MnO  0.15  0.34  0.49  0.13  0.13  0.11  0.06  0.08  0.10  0.07  0.04  0.08  0.04  MgO  17.43  15.00  11.90  3.89  2.60  3.02  1.55  3.35  1.69  2.28  2.91  2.69  2.51  CaO  6.13  2.73  2.26  1.79  2.59  1.66  1.25  1.20  0.90  1.13  0.45  0.74  0.47  Na 0 2  0.74  0.58  0.89  1.21  2.33  1.68  2.47  2.45  1.54  1.64  1.00  2.93  2.00  K 0  0.91  1.75  2.54  2.13  2.91  3.21  5.82  4.90  3.19  3.72  5.80  4.30  5.50  P2O5  0.13  0.11  0.10  0.05  0.07  0.06  0.19  0.07  0.08  0.06  0.06  0.06  0.06  Cr 0  0.25  0.14  0.09  0.02  0.00  0.01  0.01  0.01  0.01  0.01  0.01  0.01  0.01  4.0  2.9  2.0  2.8  2.6  2.8  1.7  3.5  6.2  4.2  4.4  2.7  3.1  1.18  1.06  1.58  3.45  1.42  1.27  0.98  2.45  12.51  5.54  3.3  0.63  0.81  99.08  99.11  99.86  100.0  100.1  99.65  100.1  99.90  100.1  100.3  100.0  100.3  100.1  Fe 0 * 2  3  2  2  LOI  3  1  s Total mg-n umber FeO"  2  .  0.700  0.626  0.563  0.404  0.478  0.505  0.465  0.426  0.080  0.207  0.355  0.522  0.506  13.30  15.99  16.48  10.23  5.06  5.27  3.18  8.04  34.73  15.54  9.42  4.40  4.37  Chalcophile elements (ppm) Cu  2002  1199  1045  1507  2312  829  1510  1310  8284  6188  2437  43  46  Ni  1465  945  655  878  975  438  616  749  4623  1820  1039  43  49  Co  115  82  59  106  54  38  28  76  554  197  87  12  13  Pd (ppb)  164  129  32  <10  159  39  136  <10  327  121  104  <10  <10  Pt (ppb)  5  3  3  2  9  2  6  2  18  8  3  <2  <2  Au (ppb)  10.8  5.7  3.0  3.5  12.4  2.9  6.5  4.0  19.8  8.2  4.4  1.2  0.4  Table 2.1b (continued): Rock type  Gabbronorite  Gabbronorite  Gabbronorite  Qtz-feld-bio Qtz-feld-bio Qtz-feld-bio Gneiss Gneiss Gneiss  Qtz-feld-bio Qtz-feld-bio Gneiss Gneiss  Qtz-feld-bio Qtz-feld-bio Qtz-feld-bio Qtz-feld-bio Gneiss Gneiss Gneiss Gneiss  Qtz-feld Gneiss  Sample ID  71137  71138  71139  71140  From (m)  172.1  173.6  174.8  178.0  To(m)  173.6  174.8  175.8  Distance (m)  4.4  3.2  2.2  Sc  5  9  V  208  371  Cr  368  418  228  Se  1.6  1.5  1.9  Rb  26  54  Sr  139  Y  71141  71151  71142  71143  71144  71145  71146  71148  71147  179.3  181.5  182.7  183.8  187.1  187.9  191.9  202.2  200.9  179.0  180.3  182.5  183.2  185.4  187.9  188.9  192.9  202.9  201.9  -1.0  -2.3  -4.5  -5.2  -7.4  -9.8  -10.9  -14.9  -24.9  -23.9  6  3  2  4  5  9  280  73  34  46  26  108  83  31  47  32  3.4  2.2  1.4  1.4  69  73  73  84  179  183  143  203  13.2  12.3  11.6  13.4  Zr  60  67  73  213  ^  Trace elements (ppm) 6  6  9  8  8  . 87  59  112  83  88  97  37  48  74  70  68  2.7  28.4  9.8  4.8  1.0  0.9  140  144  92  120  198  158  182  201  302  261  128  154  116  134  100  16.8  13.1  13.6  19.5  12.8  15.5  21.3  23.1  17.5  285  222  189  222  127  181  160  287  249  Nb  4.5  5.2  4.9  5.7  7.4  6.3  6.0  11.4  7.8  8.8  10.9  11.5  10.3  Cs  1.9  2.1  2.7  3.4  2.0  2.6  2.5  4.5  2.4  3.1  5.1  4.8  4.8  Ba  301  394  409  420  435  338  1031  924  724  919  753  661  594  La  8.9  10.7  15.4  23.9  28.6  28.3  24.3  49.9  32.7  32.2  45.1  36.9  35.0  Ce  18.9  22.4  29.9  45.0  53.5  52.2  44.5  90.6  62.7  59.7  87.8  75.5  69.7  Pr  2.47  2.61  3.37  4.73  5.77  5.24  4.60  9.43  6.55  6.42  9.51  8.25  7.70  Nd  11.0  10.9  12.6  17.3  20.5  18.7  16.9  31.8  • 22.6  22.9  34.1  29.1  30.6  Sm  2.5  2.5  2.4  3.3  3.9  3.2  3.1  5.7  3.7  4.0  6.3  5.6  5.0  Eu  0.89  0.70  0.65  0.73  1.12  1.08  1.30 '  1.63  1.00  0.91  1.29  1.04  0.98  Gd  2.41  2.03  1.88  2.41  2.68  2.41  1.99  3.75  2.86  3.17  4.12  4.45  3.79  Tb  0.43  0.39  0.36  0.34  0.46  0.38  0.35.  0.62  0.45  0.48  0.62  0.74  0.53  Dy  2.28  2.17  1.99  2.20  2.39  2.17  2.07  3.19  2.08  2.38  3.74  3.58  2.88  Ho  0.44  0.40  0.36  0.41  0.49  0.41  0.43  0.63  0.40  0.45  0.66  0.70  0.59  Er  1.21  1.18  1.19  1.21  1.53  1.15  1.30  1.91  1.20  1.39  1.83  2.18  1.53  Tm  0.17  0.17  0.15  0.16  0.20  0.17  0.24  0.27  0.16  0.19  0.26  0.29  0.23  Yb  1.16  1.14  1.22  1.31  1.48  1.48  1.53  1.82  1.18  1.41  1.55  1.97  1.53  Lu  0.17  0.19  0.19  0.20  0.25  0.21  0.27  0.29  0.18  0.21  0.27  0.33  0.25  •  Hf  1.7  1.8  2.4  5.8  8.0  6.5  5.5  6.6  - 4.1  5.2  4.7  8.3  7.6  Ta  0.4  0.4  0.4  0.4  0.6  0.7  0.7  1.0  0.6  0.7  0.9  1.1  1.0  Th  2.1  3.0  4.2  8.8  15.0  9.3  9.5  19.5  11.5  13.6  17.8  17.6  14.6  Ol Gbnr = olivine gabbronorite; Qtz-feld-bio = quartz feldspar biotite; * Total Fe as Fe203;** Total Fe as FeO; LOI = loss on ignition; mg-number = Mg/(Mg+Fe *); < = below detection limit 1  o  2  2  Table 2.1b: Major and trace element abundances for the Far West Margin section (DDH # MX03-001) Rock type  Chr. Peridotite  Chr. Peridotite  Sample ID  71061  71062  From (m)  11.7  19.8  To (m)  10.7  18.8  Distance (m)  106.3  98.2  Chr. Peridotite  Chr. Peridotite  Chr. Peridotite  Chr. Peridotite  71063  71064  71065  25.1  28.7  32.3  24.2  27.7  92.9  89.3  Feldspathic peridotite  Feldspathic peridotite  Feldspathic peridotite  Feldspathic peridotite  Feldspathic peridotite  Feldspathic peridotite  71066  71067  71068  71071  71072  71073  71074  38.5  45.9  48.9  51.9  58.9  66.2  71.0  31.3  37.5  44.8  47.4  50.9  57.8  65.2  70.0  85.7  79.5  72.2  69.6  66.1  59.2  51.9  47.0  Major elements (wt%) Si0  2  35.43  38.35  36.95  36.80  36.14  38.41  37.32  38.13  38.92  38.50  39.19  Ti0  2  0.56  0.54  0.31  0.29  0.37  0.34  0.39  0.42  0.31  0.41  0.41  0.41  5.22  5.23  3.71  3.90  3.83  3.81  3.99  4.13  4.20  4.00  4.27  4.74 11.36  Al 0 2  3  Fe 0 *  39.14  14.85  11.96  13.39  15.11  14.06  11.59  10.91  11.15  10.67  10.93  10.55  MnO  0.10  0.15  0.11  0.13  0.12  0.13  0.13  0.13  0.13  0.13  0.14  0.13  MgO  30.49  29.81  32.20  30.67  31.92  32.99  33.17  32.21  32.23  32.31  31.53  29.84  CaO  0.82  3.08  1.51  1.79  1.39  2.70  2.08  2.73  2.90  2.87  2.82  3.06  Na 0 2  0.10  0.23  0.07  0.07  0.01  0.05  0.11  0.13  0.12  0.09  0.18  0.21  K 0  1.33  0.70  0.90  0.94  0.68  0.53  0.29  0.28  0.31  0.23  0.20  0.27  P2O5 Cr 0  0.10  0.12  0.08  0.10  0.09  0.08  0.09  0.08  0.09  0.06  0.09  0.06  3.98  1.17  2.01  1.28  1.46  0.52  0.38  0.32  0.32  0.29  0.35  0.34  7.0  8.5  8.7  8.8  9.8  9.0  10.8  10.2  9.8  9.9  10.2  10.2  0.18  0.19  0.89  1.47  0.88  0.30  0.47  0.37  0.04  0.07  0.05  0.46  100.2  100.1  100.2  100.2  100.2  100.4  99.97  100.2  100.3  99.95  100.2  100.0  2  3  2  2  LOI  3  1  S Total mg-number FeO"  2  0.803  0.832  0.827  0.801  0.818  0.849  0.858  0.851  0.857  0.854  0.856  0.839  13.36  10.76  12.05  13.60  12.65  10.43  9.82  10.03  9.60  9.83  9.49  10.22  Chalcophile elements (ppm) Cu  50  180  328  1121  350  142  532  265  31  21  18  433  Ni  1623  1583  2254  2024  2605  2044  2376  2086  1781  1783  1803  1990  Co  84  101  129  177  155  110  127  115  96  96  89  110  Pd (ppb)  23  19  41  131  71  29  39  14  <10  <10  <10  51  Pt (ppb) Au (ppb)  2  <2  <2  <2  3  3  12  2  4  <2  <2  6  2.6  2.8  2.3  7.3  3.3  2.3  4.8  2.3  1.5  <2  <.2  3.3  Table 2.1b (continued): Rock type  Chr. Peridotite  Chr. Peridotite  Sample ID  71061  71062  From (m)  11.7  19.8  To(m)  10.7  18.8  Distance (m)  106.3  Sc V Cr  Chr. Peridotite  Chr. Peridotite  Chr. Peridotite  Chr. Peridotite  71063  71064  71065  25.1  28.7  32.3  24.2  27.7  98.2  92.9  9  6  218  145  1131  541  Se  0.5  Rb  48  Sr  Feldspathic peridotite  Feldspathic peridotite  Feldspathic peridotite  Feldspathic peridotite  Feldspathic peridotite  Feldspathic peridotite  71066  71067  71068  71071  71072  71073  71074  38.5  45.9  48.9  51.9  58.9  66.2  71.0  31.3  37.5  44.8  47.4  50.9  57.8  65.2  70.0  89.3  85.7  79.5  72.2  69.6  66.1  59.2  51.9  47.0  6  6  8  6  7  6  6  6  6  8  127  121  133  88  102  107  101  108  118  116  916  882  772  594  530  400  396  391  395  481  0.5  1.0  2.0  1.1  0.7  1.0  0.6  0.2  0.3  0.2  0.7  20  36  38  23  20  9  9  11  8  7  8  29  100  19  28  19  24  42  64  61  50  70  85  Y  4.4  8.6  5.7  5.8  5.7  6.4  6.4  5.9  4.2  6.4  6.9  6.6  Zr  33  39  24  22  23  24  22  21  12  23  28  27  Trace elements (ppm)  Nb  2.1  2.7  1.7  1.6  1.6  1.7  1.9  1.4  1.0  1.8  2.0  2.0  Cs  1.5  1.0  1.6  2.2  1.1  1.1  1.2  0.8  0.9  0.8  1.0  1.0  Ba  147  213  96  124  128  114  144  126  103  91  153  126  La  1.2  4.8  1.6  2.6  1.7  2.8  4.3  3.4  2.3  3.5  4.2  3.6  Ce  2.7  10.7  4.1  6.2  4.3  6.6  7.5  6.1  4.2  7.9  8.9  8.3  Pr  0.41  1.42  0.66  0.88  0.70  0.91  0.99  0.68  0.56  0.87  1.07  1.00  Nd  2.2  5.5  4.0  4.6  3.2  4.5  4.8  3.0  2.1  4.5  4.6  4.7  Sm  0.6  1.5  1.0  1.1  1.0  1.2  1.0  0.9  0.7  1.1  Eu  0.08  0.48  0.16  0.27  0.22  0.30  0.49  0.37  0.34  0.40  -  '  1.1  1.0  0.33  0.46  Gd  0.73  1.52  1.05  1.16  0.86  1.30  1.10  0.90  0.76  1.04  1.37  1.32  Tb  0.10  0.24  0.19  0.17  0.16  0.19  0.20  0.16  0.15  0.20  0.20  0.19  Dy  0.78  1.60  1.10  1.11  1.03  1.03  1.22  1.01  0.76  1.04  1.37  1.13  Ho  0.14  0.28  0.18  0.19  0.19  0.21  0.19  0.17  0.18  0.23  0.24  0.24  Er  0.40  0.70  0.55  0.53  0.52  0.66  0.51  0.52  0.44  0.58  0.65  0.66  Tm  0.07  0.15  0.08  0.09  0.07  0.10  0.08  0.09  0.07  0.13  0.12  0.10  Yb  0.40  0.66  0.48  0.62  0.60  0.51  0.59  0.42  0.45  0.61  0.65  0.67  Lu  0.10  0.10  0.07  0.07  0.09  0.08  0.08  0.08  0.06  0.08  0.09  0.08  Hf  0.8  1.1  0.8  0.7  0.8  0.6  0.6  0.7  0.5  0.9  0.9  0.8  Ta  0.1  0.1  0.1  0.1  0.1  0.1  0.1  0.1  <.1  0.2  0.1  0.1  Th  1.1  1.1  1.2  1.3  0.4  0.7  0.5  0.6  0.6  0.5  0.5  0.4  Chr = chromite-rich; * Total Fe as Fe203;** Total Fe as FeO; LOI = loss on ignition; mg-number = Mg/(Mg+Fe *);< = below detection limit 1  2  2  Table 2.1b (continued): Major and trace element abundances for the Far West Margin section (DDH # MX03-001) Rock type  Feldspathic peridotite  Feldspathic peridotite  Chr. Chr. Peridotite Peridotite  Chr. Peridotite  Chr. Peridotite  Chr. GabbroPeridotite norite  Sample ID  71075  71076  71077  71078  71079  71080  71081  From (m)  74.0  81.4  88.7  94.7  98.0  101.5  105.5  To(m)  72.5  79.8  87.7  93.2  96.9  100.0  Distance (m)  44.5  37.2  29.4  23.8  20.1  17.1  Gabbronorite  Gabbronorite  Gabbronorite  Massive Sulphide  Gouge  Gabbronorite  71082  71083  71084  71085  71086  71087  71088  109.1  110.3  111.8  112.5  112.8  115.3  116.5  101.5  107.6  109.1  110.3  111.8  112.5  113.7  115.3  15.6  9.4  7.9  6.7  5.2  4.5  3.3  1.8  Major elements (wt%) Si0  2  39.28  40.38  40.08  38.77  38.11  38.79  40.93  46.62  42.83  43.93  38.42  10.44  47.04  46.33  Ti0  2  0.48  0.48  0.47  0.43  0.39  0.47  0.63  0.44  0.38  0.50  0.37  0.14  0.38  0.36  4.98  5.45  5.16  4.74  4.40  5.08  5.68  7.37  5.42  6.96  6.02  2.43  5.26  6.95  12.68  13.38  12.18  12.60  13.49  13.37  13.05  15.21  17.53  20.37  26.88  68.37  18.31  23.36  Al 0 2  3  Fe 0 * 2  3  MnO  0.14  0.15  0.15  0.14  0.14  0.13  0.14  0.10  0.10  0.15  0.09  0.03  0.09  0.10  MgO  28.19  26.49  27.95  29.41  29.34  28.10  26.26  20.61  23.58  19.03  17.33  4.75  20.31  13.77  CaO  3.69  4.13  3.68  2.62  2.55  2.38  3.91  1.33  1.54  2.33  0.75  0.23  0.55  0.91  Na 0 2  0.27  0.33  0.13  0.05  0.03  0.13  0.41  0.61  0.24  0.28  0.27  0.15*  0.26  0.76  K 0  0.30  0.42  0.78  0.98  0.77  0.73  0.63  1.50  1.68  1.99  1.73  0.40  1.30  2.09  P2O5  0.09  0.09  0.08  0.08  0.07  0.09  0.10  0.07  0.10  0.08  0.07  0.04  0.05  0.05  0.31  0.47  0.86  1.10  0.81  0.62  0.32  0.11  0.30  0.12  0.11  0.07  0.15  0.08  9.2  8.1  8.4  8.9  9.8  9.5  7.4  5.9  6.3  4.2  7.7  12.7  6.1  4.6  1.12  0.78  0.18  0.40  0.82  1.21  0.97  1.80  2.33  3.15  7.53  30.90  2.92  6.19  99.97  100.1  100.2  100.1  100.2  99.77  99.83  100.0  100.2  100.1  99.94  100.3  100.0  99.63  2  Cr 0 2  LOI  3  1  S Total mg-number FeO"  2  0.815  0.797  0.820  0.822  0.812  0.806  0.799  0.729  0.727  0.649  0.561  0.121  0.687  0.539  11.41  12.04  10.96  11.34  12.14  12.03  11.74  13.69  15.77  18.33  24.19  61.52  16.48  21.02  2147  Chalcophile elements (ppm) Cu  1198  309  166  174  380  971  898  961  852  846  1511  5721  1064  Ni  2626  1379  1763  2163  2498  2828  2784  953  1284  1049  1266  4623  1361  1778  Co  139  112  93  111  123  136  116  110  173  161  225  834  155  223  Pd (ppb)  142  22  21  50  112  144  140  46  57  40  22  106  53  48  Pt (ppb)  25  5  <2  4  5  3  10  2  3  <2  <2  <2  3  3  Au (ppb)  9.1  2.8  1.9  3.4  3.8  9.7  9.1  3.8  4.0  2.6  2.8  5.7  5.3  5.5  Table 2.1b (continued): Rock type  Feldspathic peridotite  Feldspathic peridotite  Chr. Peridotite  Chr. Peridotite  Chr. Peridotite  Chr. Peridotite  Chr. Peridotite  Gabbronorite  Gabbronorite  Gabbronorite  Gabbronorite  Msv. Sulphide  Gouge  Gabbronorite  Sample ID  71075  71076  71077  71078  71079  71080  71081  71082  71083  71084  71085  71086  71087  71088  From (m)  74.0  81.4  88.7  94.7  98.0  101.5  105.5  109.1  110.3  111.8  112.5  112.8  115.3  116.5  To(m)  72.5  79.8  87.7  93.2  96.9  100.0  101.5  107.6  109.1  110.3  111.8  112.5  113.7  115.3  Distance (m)  44.5  37.2  29.4  23.8  20.1  17.1  15.6  9.4  7.9  6.7  5.2  4.5  3.3  1.8  Sc  7  6  6  8  8  10  6  8  6  5  11  4  11  7  V  127  148  145  141  140  79  155  145  125  141  145  145  69  81  Cr  404  448  696  819  790  834  537  483  745  424  594  182 .  713  365  Se  1.4  0.7  0.4  0.8  1.3  1.6  1.2  1.8  2.2  2.8  5.6  21.4  3.1  5.3  Rb  9  13  26  35  27  23  21  50  62  73  70  16  49  66  "102  124  • 50  Trace elements (ppm)  '  Sr  107  115  77  50  34  64  75  53  31  67  99  Y  7.7  7.4  8.4  7.5  6.8  8.2  10.3  16.6  13.5  16.0  17.2  5.8  24.7  19.2  Zr  33  28  35  24  33  28  50  83  91  88  107  34  110  110  Nb  2.4  2.0  2.2  1.8  1.7  1.8  3.5  6.8  8.0  8.0  8.5  3.2  10.0  8.1  Cs  1.0  1.3  1.7  1.8  1.7  1.5  1.6  2.7  3.6  3.8  4.1  1.1  2.4  3.1  Ba  175  169  197  171  165  161  177  284  194  313  281  55  231  427  La  5.1  4.2  5.1  2.2  2.4  4.2  8.1  18.9  9.2  19.2  25.3  8.4  25.0  19.8  Ce  10.1  9.4  11.2  5.8  6.0  9.8  16.4  38.8  21.0  39.3  51.6  16.2  48.4  38.0 4.46  Pr  1.18  1.12  1.43  0.94  0.95  1.31  2.01  4.56  2.70  4.72  5.80  1.75  5.53  Nd  5.6  4.8  7.3  4.2  4.7  5.8  7.8  16.4  12.1  16.9  21.1  5.8  20.8  14.7  Sm  1.2  1.1  1.5  1.3  1.3  1.6  1.9  3.5  2.9  3.6  3.9  1.2  4.1  3.6  Eu  0.53  0.48  0.31  0.24  0.25  0.42  0.62  0.65  0.42  0.59  0.56  0.15  0.64  0.68  Gd  1.30  1.30  1.25  1.32  1.44  1.48  2.21  3.19  2.85  3.65  3.55  0.88  3.92  2.98  Tb  0.25  0.21  0.24  0.19  0.19  0.26  0.33  0.43  0.41  0.53  0.54  0.15  0.69  0.50  Dy  1.48  1.41  1.54  1.30  1.38  1.41  1.86  2.93  2.32  2.80  3.13  0.87  4.17  2.87  Ho  0.28  0.28  0.31  0.25  0.27  0.30  0.36  0.59  0.47  0.57  0.60  0.20  0.89  0.65  Er  0.77  0.69  0.85  0.65  0.78  0.81  1.03  1.81  1.28  1.45  1.67  0.53  2.59  2.06  Tm  0.12  0.13  0.14  0.13  0.10  0.13  0.13  0.25  0.17  0.22  0.24  0.11  0.41  0.31  Yb  0.68  0.70  0.83  0.68  0.64  0.77  1.03  1.72  1.26  1.47  1.77  0.49  3.27  2.25  Lu  0.09  0.10  0.11  0.10  0.07  0.12  0.15  0.26  0.19  0.17  0.27  0.09  0.51  0.32  Hf  1.0  1.1  1.0  0.7  0.8  0.7  1.6  2.4  2.5  2.4  2.9  0.9  2.8  3.2  Ta  0.1  0.1  0.2  0.2  0.2  0.1  0.2  0.5  0.5  0.5  0.5  0.2  0.6  0.5  Th  0.8  0.5  1.0  0.9  1.1  1.2  1.6  5.1  5.7  6.6  6.1  1.8  5.0  6.2  Chr = chromite-rich; * Total Fe as Fe203;** Total Fe as FeO; LOI = loss on ignition; mg-number = Mg/(Mg+Fe *);< = below detection limit 1  2  2  Table 2.1b (continued): Major and trace element abundances for the Far West Margin section (DDH # MX03-001) Rock type  Gabbronorite  Massive Sulphide  Hornfelsed paragneiss  Hornfelsed paragneiss  Massive Sulphide  Granitic pod  Granitic pod  Metagabbro  Metagabbro  Metagabbro  Metagabbro  Metagabbro  Sulphide Breccia  Sample ID  71091  71092  71093  71094  71095  71096  71097  71098  71099  71100  71101  71102  71103  From (m)  117.0  117.5  119.0  120.1  120.3  120.8  121.8  126.0  127.7  128.1  128.6  133.2  133.9  To(m)  116.5  117.0  117.5  119.0  120.1  120.3  120.8  125.7  127.3  127.7  128.3  132.8  133.3  Distance (m)  0.5  0.0  -0.5  -2.0  -3.1  -3.3  -3.8  -8.7  -10.3  -10.7  -11.3  -15.8  -16.3  Major elements (wt%) Si0  2  48.81  9.08  45.72  54.23  10.58  52.87  67.41  48.30  49.76  53.14  59.67  40.01  Ti0  2  0.40  0.09  0.82  0.91  0.07  0.29  0.32  2.04  1.41  1.21  0.64  1.94  1.30  7.73  1.87  15.91  14.19  2.60  11.86  11.49  12.54  14.10  14.90  10.84  15.59  10.18  Al 0 2  3  43.41  23.75  73.28  15.54  13.76  72.67  20.02  6.82  17.74  15.57  11.70  11.85  18.54  22.81  MnO  0.09  0.02  0.10  0.12  0.02  0.05  0.05  0.22  0.17  0.13  0.10  0.17  0.16  MgO  8.73  2.66  8.05  5.44  0.94  3.05  3.09  5.62  5.59  5.42  7.47  7.84  7.32  CaO  0.62  0.12  2.16  2.49  0.36  1.47  1.43  7.26  6.85  5.08  1.88  3.63  4.22  Na 0  0.88  0.10  1.16  1.47  0.32  2.13  2.13  2.10  2.47  2.66  1.65  1.08  1.01  K 0  2.99  0.25  3.68  3.09  0.61  3.21  4.00  1.82  1.36  2.75  1.39  4.58  2.52  0.07  0.02  0.09  0.07  0.02  0.06  0.06  0.23  0.16  0.12  0.06  0.20  0.15  0.07  0.04  0.02  0.01  0.04  0.03  0.02  0.00  0.01  0.01  0.01  0.01  0.01  5.1  12.5  6.0  3.5  11.6  3.9  2.3  1.0  1.4  2.0  3.8  4.7  5.9  6.89  31.10  3.24  2.47  29.55  6.56  0.86  1.06  1.68  0.63  0.35  3.37  5.92  99.52  100.9  99.37  99.41  101.2  99.34  99.24  99.08  99.14  99.29  99.44  99.21  Fe 0 * 2  3  2  2  P 0 Cr 0 2  5  2  LOI  3  1  S Total mg-number FeO"  2  100.4 '  0.421  0.067  0.507  0.439  0.025  0.232  0.473  0.386  0.416  0.479  0.555  0.456  0.389  21.37  65.94  13.98  12.38  65.39  18.01  6.14  15.96  14.01  10.53  10.66  16.68  20.52  7460  Chalcophile elements (ppm) Cu  2026  8362  1335  829.3  8016  2072  394.2  1732  1311  1111  1097  10189  Ni  1672  6624  697  647  10278  2447  284  1187  2067  912  524  6568  10672  Co  221  793  113  80  996  206  33  63  85  38  28  145  224  Pd (ppb)  55  251  59  47  449  79  <10  142  135  111  88  1836  1247  Pt(ppb)  2  13  7  6  36  <2  <2  6  3  5  2  152  105  Au (ppb)  6.9  40.9  3.9  6.9  55.3  12.0  1.3  22.6  27.7  37.0  34.3  203.9  296.0  .  Table 2.1b (continued): Rock type  Gabbronorite  Msv. .. Sulphide  Hornfelsed paragneiss  Hornfelsed paragneiss  Msv. Sulphide  Granitic pod  Granitic pod  Metagabbro  Metagabbro  Metagabbro  Meta gabbro  Metagabbro  Sul. Breccia  Sample ID  71091  71092  71093  71094  71095  71096  71097  71098  71099  71100  71101  71102  71103  From (m)  117.0  117.5  119.0  120.1  120.3  120.8  121.8  126.0  127.7  128.1  128.6  133.2  133.9  To(m)  116.5  117.0  117.5  119.0  120.1  120.3  120.8  125.7  127.3  127.7  128.3  132.8  133.3  Distance (m)  0.5  0.0  -0.5  -2.0  -3.1  -3.3  -3.8  -8.7  -10.3  -10.7  -11.3  -15.8  -16.3  Sc  12  5  15  8  3  9  7  5  6  6  9  15  14  V  158  141  342  244  129  94  77  389  301  236  118  367  244 39  :  Trace elements (ppm)  Cr  386  177  88  58  64  108  97  7  25  32  34  66  Se  8.5  28.4  3.5  2.4  33.6  8.3  1.4  1.9  3.5  1.2  0.8  9.4  15.6  Rb  85  9  113  89  15  70  96  62  46  76  28  162  89  Sr  127  17  245  216  38  234  263  263  223  289  71  240  167  Y  21.1  4.7  23.0  27.9  2.6  15.9  23.1  37.7  32.0  23.9  18.8  31.9  23.0  Zr  126  18  111  156  17  70  148  111  73  85  72  123  83  Nb  8.8  1.9  10.5  13.5  0.9  5.2  6.4  15.9  10.3  11.7  7.6  12.9  7.9  Cs  3.0  0.5  2.9  2.9  0.6  2.1  2.2  3.0  2.3  2.6  1.0  6.0  1.9  Ba  578  27  274  384  130  784  740  504  251  493  99  761  393  La  30.7  4.3  28.1  53.3  4.3  17.9  29.8  19.4  9.6  12.1  8.1 •..  16.1  15.5  Ce  59.0  8.0  52.6  98.6  7.2  29.2  53.2  40.1  21.9  24.7  16.0  35.2  33.9  Pr  6.56  0.94  6.30  11.25  0.77  3.22  5.93  4.74  2.93  2.89  1.81  4.49  4.09  Nd  24.3  3.4  23.3  35.7  2.7  10.8  20.0  22.4  15.1  13.5  7.8  20.0  18.1  Sm  4.7  0.7  4.7  6.0  0.5  2.1  4.1  5.5  4.3  3.1  2.2  5.3  4.2  Eu  0.8  0.1  1.2  1.4  0.2  1.2  1.0  2.0  1.4  Gd  3.68  0.73  4.26  5.58  0.49  2.52  3.65  6.36  5.26  Tb  0.58  0.14  0.69  0.89  0.09  0.45  0.67  1.24  Dy  3.92  0.85  4.09  4.70  0.37  2.63  4.08  6.86  Ho  0.77  0.16  0.73  0.84  0.07  0.58  0.79  Er  2.27  0.50  2.19  2.68  0.29  1.45  Tm  0.37  0.08  0.33  0.34  0.05  Yb  2.71  0.50  2.33  2.56  Lu  0.35  0.08  0.35  1.4  0.9  1.4  1.2  3.92  2.29  5.74  4.75  0.95  0.67  0.54  1.08  0.72  5.16  3.89  2.94  5.87  3.88  1.42  1.09  0.78  0.65  1.16  0.85  2.44  -3.87  3.16  2.30  1.77  3.08  2.22  0.24  0.41  0.58  0.57  0.35  0.33  0.53  0.37  0.25  1.55  2.52  3.54  3.30  2.28  2.11  2.84  2.13  0.36  0.05  0.26  0.40  0.53  0.55  0.34  0.25  0.42  0.31  .  Hf  3.1  0.7  3.2  4.7  0.6  1.9  4.4  3.2  1.9  2.3  2.2  3.6  2.4  Ta  0.6  0.1  0.8  0.8  <.1  0.6  1.0  1.1  0.9  1.0  0.6  0.7  0.5  Th  7.9  1.1  7.7  10.5  0.9  4.7  11.9  1.9  1.4  2.3  3.4  2.3  3.0  Chr = chromite-rich; * Total Fe as F e 2 0 3 ; " Total Fe as FeO; LOI = loss on ignition; mg-number = Mg/(Mg+Fe *);< = below detection limit 1  2  2  2.4.2 Olivine compositions Olivine compositions from 10 samples were determined by wavelength-dispersion spectrometry (WDS) using the Cameca SX50 Electron Microprobe at the University of British Columbia. The olivine compositions were measured with an accelerating voltage of 15 KeV, a beam current of 20 nA, and a beam size of 5 pm. Counting times for peak and background were 20 and 10 seconds, respectively. In order to precisely determine nickel contents, each analysis was repeated using the fixed-matrix mode and a beam current and counting time of 100 nA and 100 seconds, respectively. Natural and synthetic standards were used for calibration and procedural set-up. The "PAP" O(pZ) data reduction procedure of Pouchou & Pichoir (1991) was applied to all analyses. Relative errors (la) for Si02 and MgO, and for FeO are less than 1% and 2.5%, respectively. Low abundances of MnO and NiO gave higher relative errors of 10-30% using the standard method. CaO, Cr203, and Ti02 abundances were at or below detection limits. Using the higher beam current and counting times, as described above, the analytical error on nickel analyses was reduced to <5% relative. Olivine in the studied samples is strongly serpentinized (20-80 vol %); analyzed grains were chosen within clusters of relatively unaltered olivine. Each grain was analyzed in the core, in an intermediate spot, and on the rim, unless one of these areas was serpentinized, in which case only two analyses were determined. The olivine grains were not visibly zoned and all analyses from an individual grain are within error, with the exception of two samples from the Far West Margin that were clearly zoned. Two to four grains were measured in each cluster and 2-3 clusters were measured on each thin section for a total of 185 measurements. Representative core analyses are summarized in Table 2.2 and all data are reported in Appendix III. A l l analyses reported are consistent with mineral stoichiometry. Comparison of the two methods described above for Ni determination is shown in Appendix IV.  2.4.3 Sulphur isotopic compositions Sulphur isotopic compositions were measured for 23 samples and 3 duplicates (71092, 71095 and 71145) at the Queen's Facility for Isotopic Research (QFIR) in the Department of Geological Sciences and Geological Engineering at Queen's University in Kingston, Ontario. The analyses were completed on a Finnigan MAT 252 isotope-ratio mass spectrometer using continuous-flow technology and online sulphur extraction. The measured sulphur isotopic compositions are reported in Table 2.3. All values were corrected using the NIST 8556 47  Table 2.2a: Representative olivine compositions from the West Pyrrhotite Lake section . 1  Region / Drillhole Rock type* Thin Section Sample no. Site  West Pyrrhotite Lake / MX03-002 Peridotite Peridotite RMX02-3A RMX02-4 71112 71115 rim mid interm  rim  F. Peridotite RMX02-5 71123 , core  mid  F. Peridotite RMX02-6 71127 mid  38.97 0.03 18.29 0.30 42.49 0.04 0.00 0.29 100.41  Ol-Gbnr  mid  RMX02-8 71133 mid  core  38.61 0.04 . 20.31 0.26 40.75 0.07 0.08 0.29 100.42  38.48 0.04 19.12 0.27 41.52 0.02 0.04 0.32 99.82  38.32 0.02 22.78 0.32 39.07 0.07 0.00 0.26 100.84  38.51 0.02 21.03 0.28 40.09 0.07 0.03 0.25 100.28  Oxide wt % Si0 Ti0 FeO MnO MgO CaO Cr 0 NiO total 2  2  2  3  Cation (p.f.u.) Si Ti Fe * 2  Mn Mg Ca Cr Ni Sum Endmembers % Fo Fa  39.22 0.07 17.75 0.19 42.76 0.02 0.02 0.30 100.35  39.11 0.01 16.95 0.27 43.10 0.08 0.11 0.31 99.93  39.08 0.03 18.01 0.27 43.15 0.05 0.00 0.31 100.90  0.00 0.33 100.71  42.20 0.05 0.12 0.30 101.22  0.995 0.001  0.993 0.000  0.989 0.001  0.994 0.001  0.993 0.001  0.992 0.001  0.991 0.001  0.990 0.001  0.992 0.000  0.994 0.000  0.377 0.004 1.618 0.001 0.001 0.006 3.003  0.360 0.006 1.631 0.002 0.005 0.006 3.004  0.381 0.006 1.627 0.001 0.000 0.006 3.011  0.368 0.006 1.629 0.001 0.000 0.007 3.005  0.401 0.006 1.590 0.001 0.006 0.006 3.004  0.389 0.006 1.612 0.001 0.000 0.006 3.007  0.436 0.006 1.560 0.002 0.004 0.006 3.006  0.411 0.006 1.592 0.001 0.002 0.007 3.009  0.493 0.007 1.508 0.002 0.000 0.005 3.008  0.454  81.1 18.9  81.9 18.1  81.0 19.0  81.6 18.4  79.9 20.1  80.6 19.4  78.2 21.8  79.5 20.5  75.4 24.6  77.3 22.7  39.36 0.04 17.42 0.26 43.27 0.04  39.27 0.04 18.97 0.27  ' Reported values are for minimum and maximum forsterite contents in each thin section. 2  F.Peridotite = Feldspathic peridotite; Ol-Gbnr = olivine gabbronorite; Cr. Peridotite = chromite-rich peridotite  0.006 1.542 0.002 0.002 0.005 3.005  Table 2.2b: Representative olivine compositions from the Far West Margin section . 1  Region / Drillhole Rock type Thin Section Sample no. Site  Far West Margin / MX03-001 Cr. Peridotite Cr. Peridotite RMX01-1 RMX01-3 71061 71063 rim mid core  rim  Peridotite RMX01-4 71072 rim  core  F. Peridotite RMX01-5 71075 rim  Cr. Peridotite RMX01-6 71078 mid core  rim  Oxide wt % Si0 Ti0 FeO MnO MgO CaO Cr 0 NiO total 2  2  2  3  Cation (p.f.u.) Si Ti Fe * 2  Mn Mg Ca Cr Ni Sum Endmembers % Fo Fa  39.28 0.01 18.54 0.14 42.33 0.01 0.13 0.17 100.62  40.59 0.01 11.69 0.18 47.85 0.05 0.04 0.30 100.71  40.01 0.03 13.04 0.17 46.20 0.11 0.05 0.16 99.76  40.24 0.00 12.17 0.17 47.22 0.04 0.05 0.15 100.04  40.01 0.02 14.80 0.21 45.41 0.08 0.04 0.33 100.90  39.50 0.04 14.26 0.22 45.19 0.07 0.00 0.35 99.63  39.51 0.02 17.01 0.24 43.81 0.08 0.03 0.25 100.95  0.26 43.96 0.13 0.07 0.26 99.94  45.89 0.07 0.03 0.26 101.10  39.67 0.01 13.89 0.25 45.80 0.06 0.05 0.24 99.97  0.996 0.000  0.997 0.000  0.998 0.001  0.997 0.000  0.996 0.000  0.994 0.001  0.993 0.000  1.001 0.000  0.990 0.001  0.993 0.000  0.393 0.003 1.599 0.000 0.006 0.003 3.001  0.240 0.004 1.752 0.001 0.002  0.252 0.004 1.744  0.300 0.005 1.696 0.002 0.000 0.007 3.005  0.327 0.006 1.651 0.004  0.307  0.001 0.002 0.003 3.002  0.308 0.004 1.684 0.002 0.002 0.007 3.003  0.357 0.005 1.641 0.002  0.006 3.002  0.272 0.004 1.718 0.003 0.002 0.003 3.000  0.001 0.005 3.006  0.003 0.005 2.997  0.003 1.699 0.002 0.001 0.005 3.008  0.291 0.005 1.708 0.002 0.002 0.005 3.006  80.3 19.7  87.9 12.1  86.3 13.7  87.4 12.6  84.5 15.5  85.0 15.0  82.1 17.9  83.5 16.5  84.7 15.3  85.5 14.5  ' Reported values are for minimum and maximum forsterite contents in each thin section. 2  F.Peridotite = Feldspathic peridotite; Ol-Gbnr = olivine gabbronorite; Cr. Peridotite = chromite-rich peridotite  39.72 0.01 15.54  39.86 0.06 14.79 0.14  Table 2.3: Sulphur isotopic compositions in marginal rocks of the Muskox intrusion Host rock  Sample no.  Far West Margin (DDH #  Chr. Peridotite F. Peridotite F. Peridotite Chr. Peridotite Gabbronorite Gabbronorite Gabbronorite Gabbronorite Gabbronorite Paragneiss Paragneiss Paragneiss Paragneiss Breccia Paragneiss Paragneiss West  71064 71067 71076 .-• 71080 71085a 71085b 71088 71092a 71092b 71095a 71095b 71096 GD 04-03 71103 141 149.2  Pyrrhotite Lake  Gabbronorite Gabbronorite Feld-Bio-Qtz Gneiss Pegmatite Vein Feld-Bio-Qtz Gneiss Feld-Bio-Qtz Gneiss Feld-Bio-Qtz Gneiss  1  Drilled  Distance Mineralogy Texture/grain Whole rock 5 s  depth (m)  ( )2  3  m  M  s i z e  i  S (wt%)  28.7 45.9 81.4 101.5 112.5 112.5 , 116.5 117.5 117.5 120.3 120.3 120.6 120.9 133.9 141 149.2  (DDH #  88.4 71.2 35.7 15.6 4.6 4.6 0.5 -0.5 -0.5 -3.3 -3.3 -3.6 -3.9 -16.9 -24.0 -32.2  po po. po po po po PO po po po po po po po.cpy po po  D, BL D BL D, BL BL, NT BL/0.8 cm D, BL MSV MSV MSV MSV BL / 0.8 cm MSV vein MSV vein D D  1.47 0.47 0.78 1.21 7.53 7.53 6.19 31.1 31.1 29.6 29.6 6.56  3  4  5  D  T  -  6.5 6.4 6.3 7.9 9.1 7.9 7.2 7.9 7.9 8.7 8.5 11.6 9.4 7.8 7.5 7.9  -  5.92  -  MX03-002)  71138 71139 71141  174.8 175.8 180.2  3.2 2.2 -2.2  po po po.cpy  BL / 0.5 cm BL / 0.5 cm D  1.06 1.58 1.42  6.7 6.1 7.6  RM02-10  182.7  -4.7  cpy.po  BL / 0.5 cm  -  7.3  71145  188.8  -10.8  po.cpy  71145b  188.8  -10.8  po.cpy  71146  192.9  -14.9  po.cpy  MSV, 3.5 cm 5.54 wide vein MSV, 3.5 cm 5.54 wide vein STR, 0.5 cm, 3.30 along foliation  Procedural duplicates are denoted "a" and "b"; with the exception of sample 71085 in which two distinct textured grains were analyzed.  Drilled distance from the outer intrusive contact. po = pyrrhotite; cpy = chalcopyrite D = disseminated; BL = blebby; NT = net-textured; MSV = massive; STR = stringer CDT = Canyon Diablo Troilite  2  C  MX03-001)  F. Peridotite = feldspathic peridoite; Chr. Peridotite = chromite-rich peridotite; Feld = feldspar; Bio = biotite; Qtz = quartz. 1  (  7.0 7.4 7.7  )  5  standard and are reported relative to Canyon Diablo Troilite (CDT). Analytical precision is ± 0.3%o and results from the three procedural duplicates are within 0.5%o (Table 2.3). 2.5 GEOCHEMISTRY OF THE MARGINAL ROCKS The following section summarizes stratigraphic variations at the West Pyrrhotite Lake and Far West Margin sections in (1) major and trace element abundances, which primarily record changes in the modal abundance of cumulus and postcumulus phases; (2) olivine composition, which in the case of the Muskox marginal samples records mainly varying degrees of reequilibration with intercumulus liquid during cooling (e.g. Barnes, 1986); (3) chalcophile elements, which are typically controlled by the distribution of sulphide minerals owing to their high partition coefficients between sulphide and silicate liquids (e.g. Rajamani & Naldrett, 1978; Fleet et al., 1991; Peach et al., 1994); (4) primitive mantle-normalized trace element diagrams; and (5) incompatible trace element ratios and sulphur isotopic compositions, which provide an index of contamination along the basal margin of the intrusion (Fig. 2.8-2.13). Select major elements are also plotted against MgO to compare results from the two sections with those of a previously studied section along the eastern margin of the intrusion (Francis, 1994; Pyrrhotite Lake section) and of an additional drill hole north of the Far West Margin (MX04-001). 2.5.1 West Pyrrhotite Lake The peridotites (peridotite, feldspathic peridotite, and olivine gabbronorite) become progressively lower in MgO (38 to 22 wt %) and C r 0 (0.5 to 0.3 wt %), and higher in CaO 2  3  (0.8 to 5.6 wt %), and A1 0 (3.2 to 8.6 wt %) towards the contact with the country rocks (Fig. 2  3  2.8a). Stratigraphic trends of Si0 , Ti02, K 0 , Na20, and incompatible trace elements 2  2  correlate with A I 2 O 3 and progressively increase towards the margin, which corresponds to a progressive decrease in olivine abundance and increase in postcumulus pyroxene, plagioclase, and phlogopite abundances. The trend of decreasing whole-rock MgO contents correlates with a progressive decrease in the forsterite content of olivine (Fog2 to Fo ; Fig. 2.9a). Olivine 74  accumulation exhibits a strong control on the overall geochemical variation within the peridotites (Fig. 2.10a). The peridotites at West Pyrrhotite Lake contain only rare sulphide and therefore have relatively low abundances of chalcophile elements, with N i concentrations being largely controlled by olivine (Fig. 2.1 la). The olivine cumulates have the lowest 51  (a) West Pyrrhotite Lake 160'  160 X  -§•120  120  Peridotite r  a VI  sr •  c o  O  o 80 E  80 Feldspathic Peridotite  2  H<D O C  40  3  Ol Gbnr  in  Gbnr  _ _  15^  56  /*"  U0  5  • T  M r  Feld-BioQtz Gneiss -40'  sr  20  40 0  MgO  0.0 20  10  2.0  Al 03  4.0 0  3  6.0  8.0 0.0  o  J**  i  -40 0.2  0.4  0.8  0.6  0203  0  2  (b) Far West Margin  120 100 B r 804  120 4.3, Chr-rich Peridotite  100  2.2  80  as:  3  o  60H Feldspathic  60 %  o  Peridotite 79  40 A Chr-rich o I 20 Peridotite in Gbnr a  -20  Sulphidic Paragneiss  Mo § sr  20 a ••  1A  A  20  MgO  40 0  A  10 AI203  •  AA  A o 0.0 20  2.0  4.0  CaO  -20 6.0  8.0 0.0  1.0  2.0  O2O3  Fig. 2.8: Stratigraphic variations of major elements (all in wt %) at the (a) West Pyrrhotite Lake and (b) Far West Margin sections of the Muskox intrusion. Solid circles are marginal zone rocks, squares are gneissic host rocks, triangles are gabbroic host rocks, open circles are sulphide-rich (>5 wt % sulphur) samples, and crosses are intensely altered samples or gouge material. Ol Gbnr = olivine gabbronorite and Gbnr = gabbronorite. Note the difference of scale in Cr203 for the two sections. Arrows in the Far West Margin Cr203 plot point towards very Cr-rich peridotites. The numbers in the MgO plots give the calculated Mg# of the indicated sample (Mg# = (Mg2+/(Mg2++Fe2+)) x 100). The rocks at West Pyrrhotite Lake become progressively more evolved in composition (e.g. decreasing MgO and increasing AI2O3) towards the margin, which corresponds to a systematic increase in abundance of postcumulus pyroxene and plagioclase. A similar variation is observed within the feldspathic peridotite horizon at the Far West Margin.  52  (a) W e s t Pyrrhotite L a k e 140  140  mm  120  120  -  Peridotite % 100  g to'  100 §  80  80  o  60 " Feldspathic Peridotite  60  .se  40 -  o CD  —*  3 0)  mtm  Q  20 -  40  • mam  Ol Gbnr  74  1  1  78  1  1  1  82  3 o o  «-»01  o  20  1  86. 1000  2000  Fo olivine  3000  Ni (ppm)  (b) Far W e s t Margin 120  120  tmm 100 .  Chr-rich Peridotite  _  100 D  co' .—*  V  80  mmmm60  60 - Feldspathic Peridotite 40 -i  80 3 O CD  -  —  40  —  mmmm  - Chr-rich 20 ^  V  Peridotite  74  —i 1 78  1  1  82  Fo olivine  1  1  86  1000  1  2000  —*  a o 3 o 3 ST o  20  1 3000  Ni (ppm)  Fig. 2.9: Stratigraphic variations in olivine compositions for (a) West Pyrrhotite Lake and (b) Far West Margin peridotites. Abbreviations as in Fig. 2.8. The olivine grains are typically unzoned, with the exception of the upper chromite-rich horizon at the Far West Margin. At West Pyrrhotite Lake, the forsterite content, and to some extent the Ni content, decreases progressively towards the margin. The correlation between decreasing forsterite content and increasing abundance of postcumulus phases is consistent with the shift expected from re-equilibration with intercumulus liquid during solidification (see text for discussion). At the Far West Margin, a similar variation is observed within the feldspathic peridotite unit. The olivine grains within sulphide-bearing chromite-rich peridotites and the lower feldspathic peridotite sample however have relatively low N i contents which may record the crystallization of olivine in the presence of a sulphide liquid.  (a) West Pyrrhotite Lake 12  18 16 Norite & Gabbronorite  14  • • •  Peridotite F. Perid Ol-Gbnr  •  Gabbrnorite  \ i  ?  12 r  « 9i  ~- , Olivine  10  A ^  J  Gabbronorite  i  8  I  O  Feldspathic Peridotite  8  i Olivine ' Gabbronorite  10 r  Feldspathic ~ ; \ Peridotite  6  '  <3  "¥\ Norite &'"' Gabbronorite A  ''m''-m • t •  Olivine 10  20  30  10  50  40  20  30  Olivine 40  50  MgO (wt %)  MgO (wt%)  (b) Far West Margin 12  10 h  v Norite  k  \  \ \  \ \  Chr. Perid F. Perid Chr. Perid Gabbronorite  -  A  -  ,  v v  O  \  '  o  Peridotite & ^Feldspathic peridotiter]  x  v  \ \  y -  • • o A  Peridotite & \ Feldspathic peridotite  ^ %  o  4  Norite /  \  \l  j  3  1/  ra O  6 h  \  A  \ o •• Chromite-ricrT.. peridotite \. \ v  i  N  i  D  t  v  1  i ,* i  Chromite-rich;« peridotite  Olivine  Olivine  • PE^l 10  20  30  MgO (wt%)  40  50  10  20  30  40  MgO (wt%)  Fig. 2.10: MgO vs. A1203 and CaO diagrams for (a) West Pyrrhotite Lake and (b) Far West Margin samples. Note the difference in scale of the Y-axis for the two sections. The range in analyzed olivine compositions is shown for each section. The labeled fields are for equivalent lithologies from a previously studied section along the eastern margin of the intrusion (Pyrrhotite Lake section; Francis, 1994) for the West Pyrrhotite Lake diagrams, and unpublished data from drill core collected ~1 km north of the Far West Margin section (DDH MX04-002) for the Far West Margin diagrams. In general, peridotite samples from all sections plot along an olivine control line, indicating that the rocks represent mixtures of olivine and some proportion of residual liquid that crystallized as postcumulus minerals. Peridotites from the eastern margin (Francis, 1994) are displaced to higher CaO and A1203, which could reflect a higher proportion of postcumulus phases at this location. The scatter within the Far West Margin peridotites reflects abundant orthopyroxene and chromite within the chromite-rich peridotites. The contaminated gabbronorite samples in all sections plot off the overall trend and are displaced towards lower CaO.  I  50  (a) West Pyrrhotite Lake 160  160  •g-120  Peridotite  L  120  g  </>'  B 3  c o o E  40  40  s  O * o 3 o  Feldspathic Peridotite  $  8 c  80  80  § 5  Ol Gbnr  </>  "Gbnr Feld-BioQtz Gneiss -40  -40 1000  o  2000 5000  Ni (ppm)  10  10000  S (wt%)  Cu (ppm)  4  6  8  10  12  (CDT)  6  (b) Far West Margin 120  120 100  Chr-rich  100  Peridotite  o 80 5'  E. 80  sr =  o  2  c o o  60  E o  40  8  Feldspathic  60  *  40  f  20  S  Peridotite  20  Chr-rich Peridotite  ~Gbhr~  !2  b  -20  Sulphidic  0  o  3.  wt% .  A* A  h-20  Paragneiss  -40  -40 5000  o  10000 5000  Ni (ppm)  Cu (ppm)  10  10000  4  S (wt%)  6  5  8  10  12  (CDT)  Fig. 2.11: Stratigraphic variations of Ni, Cu, S contents and sulphur isotopic compositions for (a) West Pyrrhotite Lake and (b) Far West Margin sections. Symbols and abbreviations as in Fig. 2.8. CDT = canyon Diablo troilite. As expected from the high partition coefficients between sulphide and silicate liquids, samples that contain sulphide have elevated Ni and Cu contents. Pd and Pt contents (not shown) are also elevated in the mineralized samples. Ni also strongly partitions into olivine and therefore its variation is controlled, in part, by the distribution of olivine. Sulphur isotopic compositions within the gabbronoritic marginal rocks and olivine cumulates are well above the accepted values for mantle-derived sulphur (-2 to +2 per mil; Ripley & Li, 2003) and are comparable to those of the wall rocks, suggesting that the sulphur was derived from the adjacent crust. The 834S values determined in this study are within the range of previous results from Sasaki (1969) for marginal zone (outer marginal zone 834S = 4-10 per mil) and crustal rocks (western margin 834S = 7-9 per mil).  55  0.1 u  i  i  i  i  i  i  i  I  I  I  I  I  I  I  I  I  I  I  I  I  I  i  i  U  CsRbBaTh K NbTa La Ce Pr Sr Nd Zr Hf SmTi BuGdTbDyHoErYbY Lu 1000 i - | — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — r  0.1 L i  i  i  i  i  i  i  i  i  i  i  i  i  i  i  i  i  i  i  i  i  i  i  i  i I  CsRbBaTh K NbTa La Ce Pr Sr Nd Zr Hf SmTi Eu Gd Tb Dy Ho Er Yb Y Lu Fig. 2.12a: Primitive mantle-normalized trace element abundance patterns in the West Pyrrhotite Lake section of the Muskox intrusion. Elements are arranged, from right to left, in order of increasing incompatibility and normalizing values are from McDonough & Sun (1995). Tantalum abundances within peridotites are below detection limits and therefore are excluded. There is a progressive increase in the abundance of incompatible trace elements towards the margin. Both marginal zone and crustal rocks are relatively enriched in the most incompatible elements and have prominent Nb-Ta depletions. The gabbronoritic marginal rocks contain distinctly higher abundances of large ion lithophile elements, and La and Ce, than the overlying olivine gabbronorite, while the abundance of heavy rare earth elements remains relatively constant in both groups.  56  J I I I I I I I I I I I I I I I I 1_ 0.1 J l_ Cs Rb BaTh K Nb Ta La Ce Pr Sr Nd Zr Hf SmTi Eu GdTb Dy Ho Er Yb Y Lu  1000 T — r  -i—i—i—r  ~i—i—i—i—i—i—i—i—i—i—i—i—r  - ° - Feldspathic Peridotite -A- Gabbronorite 100 c <o E  Country rocks ••-  Hornfels Gabbro  0)  > 'J  E  10  *c D. «  a.  £  (0  1k  0.1 Li i i i i i i i i i i i i i i i i i i i i i i i u Cs Rb BaTh K NbTa La Ce Pr Sr Nd Zr Hf SmTi Eu Gd Tb Dy Ho Er Yb Y Lu Fig. 2.12b: Primitive mantle-normalized trace element abundance patterns in the Far West Margin section of the Muskox intrusion. Elements are arranged, from right to left, in order of increasing incompatibility and normalizing values are from McDonough & Sun (1995). Tantalum abundances within peridotites are below detection limits and therefore are excluded. A l l peridotites have similar abundances of trace elements, but the chromite-rich peridotites have positive K. anomalies which are likely related to the presence of secondary biotite. The gabbronoritic marginal rocks contain similar abundances of trace elements as the adjacent country rocks. The different country rocks have distinct incompatible trace element patterns, with the hornfelsed paragneiss and granitic pods being more enriched in incompatible elements than the gabbro. Paragneiss samples from other drill holes have similar enriched trace element patterns.  57  (a) West Pyrrhotite Lake 160  •160  120H  80  s  Peridotite  if  •120 sr fil  A  L 80  Feldspathic Peridotite 40  a u c  I.  Ol Gbnr  5  Gbnr  M Q  Feld-BioQtz Gneiss -40 10  Th/Yb  0.0  15 0  5  10  Nb/La  La/Sm  -40  1.0  0.5  o  5  10  Km  (b) Far West Margin 120100  r o  •100  Chr-rich Peridotite  D  5' • 80 §f  son  c o  60  J  40  S  •120  20  I  AFeldspathicj  r-60  Peridotite  -40 Chr-rich Peridotite |"  •20  »  Gbnr 0^0  -20  Sulphidic Paragneiss  &  A  0  A  A  As 2  o.o  4  Th/Yb  5  La/Sm  10  0.5  1.0  Nb/La  -20 1.5 0  10  20  Km  Fig. 2.13: Stratigraphic variations of incompatible trace element ratios for (a) West Pyrrhotite Lake and (b) Far West Margin. Symbols and abbreviations as in Fig. 2.8. The grey shaded region in the Far West Margin section represents the range of values from paragneiss samples collected in other drill holes at this location (unpublished data). Incompatible trace element ratios are not affected by olivine fractionation owing to the extremely small partition coefficients for trace elements in olivine (e.g. D R E E <0.01). These ratios provide an index of crustal contamination, owing to the distinct compositions of crustal rocks compared to mantle-derived magmas. The shift in incompatible element ratios at the transition from peridotite to gabbronorite is consistent with a progressive increase in the amount of contamination within the outer -10 metres of the intrusion. The chromite-rich peridotite samples have somewhat anomalous compositions (high Th/Yb, Nb/La, K/Ti, and low La/Sm) compared to those of the intervening feldspathic peridotite and the peridotites at West Pyrrhotite Lake, which may be the result of post-magmatic metasomatism. The gabbroic samples within the wall rock at Far West Margin have distinct Nb/La values from of the marginal zone rocks, which may indicate that the gabbroic body is unrelated to the Muskox intrusion. =  58  abundances of trace elements, relatively enriched incompatible element patterns, and pronounced negative Nb-Ta anomalies in primitive mantle-normalized trace element diagrams (Fig. 2.12a). Incompatible element ratios are constant throughout the peridotites, indicating that the amount of enrichment in the most incompatible elements (Th/Yb, La/Sm, and K/Ti) and the magnitude of the Nb depletion (Nb/La) remain the same throughout most of the marginal zone (Fig. 2.13a). The stratigraphic trends within the underlying gabbronoritic rocks show a continued and somewhat more pronounced decrease in MgO (18-12 wt %), Cr203 (0.3-0.05 wt %), and N i (1460 to 550 ppm), and increase in AI2O3, LILE, and LREE towards the margin (Fig. 2.82.13). The stratigraphic trend of CaO, however, is reversed and progresses to lower values towards the contact (Fig. 2.8a). A similar reversal is observed for Ti02 and HREE, while the trend of increasing Si0 , 2  AI2O3,  K 0 , and Na20 observed within the olivine cumulates 2  continues through to the contact with the country rocks. Elevated Cu and S abundances occur within the gabbronorite as expected from the appearance of blebby sulphide (Fig. 2.1 la). The 8 S values from the sulphides within the gabbronorite are high compared to mantle-derived 34  sulphur (-2 to + 2 % ; Ripley, 1999; Ripley & Li, 2003) which indicates that sulphur was 0  largely derived from a crustal source (Fig. 2.11a). The gabbronoritic rocks have enriched incompatible element patterns like those of the overlying peridotite. However the level of enrichment is considerably higher shown by relatively high La/Sm, Th/Yb and K/Ti values. This increased level of enrichment in the most incompatible elements is consistent with the incorporation of crustal material (Fig. 2.12 & 2.13). Similarly, the increased magnitude of the Nb-depletion (low Nb/La values) is likely also the result of crustal contamination. As expected, the country rock gneisses at the West Pyrrhotite Lake section are highly evolved in composition, and contain higher abundances of A I 2 O 3 , Cu, S, and most incompatible trace elements, and lower abundances of MgO, Ni, CaO, Cr203, Ti and Sr than the intrusive rocks (Fig. 2.8a-2.1 la). The quartz-rich rocks directly adjacent to the intrusion have typically lower abundances of A I 2 O 3 (and K2O, TW2) and incompatible trace elements, and higher abundances of CaO than the banded gneiss further from the contact (the abundance of MgO remains relatively constant). The country rocks have highly enriched trace element patterns and prominent negative Nb-Ta, Sr, and Ti anomalies (Fig. 2.12a & 2.13a).  2.5.2 Far West Margin Unlike the systematic progression to more evolved composition towards the margin observed at the West Pyrrhotite lake section, the peridotites at Far West Margin are characterized by distinct reversals in major element trends (Fig. 2.8b). The chromite-rich peridotite horizons have high C r 0 contents (up to 4 wt %) and have relatively low CaO contents compared to the 2  3  intervening feldspathic peridotite unit, which is consistent with the distribution of cumulus chromite and postcumulus plagioclase. Towards the base of the feldspathic peridotite unit the MgO content decreases progressively and CaO and A1 0 contents increase, consistent with 2  3  the observed distribution of cumulus olivine and intercumulus plagioclase. These trends have been traced for over 1 km towards the north in other drill holes. The Fo content of olivine within the feldspathic peridotite decrease towards the basal contact, analogous to that observed throughout the West Pyrrhotite Lake section (Fig. 2.9b). Unlike the olivine accumulation trend of the West Pyrrhotite Lake section, the geochemical variation of the peridotites at the Far West Margin is likely controlled by the accumulation/fractionation of olivine, orthopyroxene, and chromite (Fig. 2.10b). Elevated Cu and Ni contents within peridotites occur in three separate horizons and are coincident with elevated S contents (Fig. 2.1 lb). Sulphur isotopic compositions of sulphide within the peridotites are within the range of those for sulphides within the layered series (+3 to + 7 % ; Sasaki, 1969). The peridotites have 0  enriched incompatible trace element patterns and variably negative Nb anomalies (Fig. 2.12b). The chromite-rich horizons have positive K anomalies, which are interpreted to be the result of metasomatism as manifested by the appearance of secondary biotite (Fig. 2.13b). The gabbronoritic rocks at the Far West Margin are variably sulphide-mineralized and therefore the chemical trends across this zone are irregular. The relatively unmineralized (<5 wt % S) samples have relatively low MgO (19-22 wt %), CaO (1-5 wt %), and C r 0 contents 2  3  and high incompatible trace element abundances compared to the overlying peridotites, which is analogous to the variation previously described within the contact region at the West Pyrrhotite Lake section (Fig. 2.8). The mineralized samples, as expected, have elevated Ni, Cu, and S contents (Fig. 2.11). Sulphur isotopic compositions of sulphide within the gabbronoritic rocks are shifted from those of the overlying peridotite-hosted sulphide towards the compositions of the adjacent wall rocks. As with the West Pyrrhotite Lake section, the gabbronoritic rocks have elevated La/Sm, Th/Yb, and K/Ti values compared to the overlying peridotites, suggesting that they crystallized from a hybrid magma (Fig. 2.12).  As expected from their lithologic variations, the country rocks at Far West Margin are variable in composition and contain relatively low abundances of MgO and CaO, and high abundances of Si02, A I 2 O 3 , and incompatible trace elements compared to the marginal zone rocks (Fig. 2.8b). The fine-grained hornfelsed sediments, granitic lenses, and paragneiss samples have high Th/Yb, La/Sm, and K/Ti values, and low Nb/La values, similar to the country rocks at West Pyrrhotite Lake (Fig. 2.13b). The gabbroic wall rocks are chemically distinct from the other country rocks and have low Th/Yb, La/Sm, and K/Ti and high Nb/La values.  2.6 DISCUSSION Although there are some distinct differences in the mineralogical and chemical variations between the two studied sections, the marginal zone of the Muskox intrusion broadly consists of an upper peridotite subzone (including peridotite, feldspathic peridotite, chromite-rich peridotite, and/or olivine gabbronorite), within which there is an overall increase in the abundance of postcumulus minerals towards the base, and a lower gabbronorite subzone that contains variable amounts of granophyre and sulphide. Sulphide is significantly more abundant at the Far West Margin, which is likely related to the presence of the variably sulphidic paragneiss forming the wall rock at this location. The trace element and sulphur isotopic compositions of the gabbronoritic marginal zone rocks clearly indicate that they have incorporated crustal material, whereas the compositional variations within the overlying peridotites appear to be primarily related to variable proportions of cumulus and postcumulus phases. Below, we examine the relationship between crustal contamination and sulphide mineralization within the gabbronoritic marginal rocks at the two studied regions, which provides important constraints on the potential for forming sulphide mineralization throughout the marginal zone of the Muskox intrusion. We then present a conceptual framework for the formation of the peridotite part of the marginal zone involving the accumulation and compaction of a cumulate pile during cooling through the base of the intrusion. To investigate the role of compaction in producing the observed mineralogical and chemical variation observed in the marginal zone, we use the forward modelling capabilities of IRIDIUM (Boudreau, 2003). Finally, we address the implications for the formation of the marginal zone throughout the evolution of the Muskox chamber, and the formation of similar features at the base of other mafic and ultramafic intrusive bodies.  61  2.6.1 Crustal contamination and sulphide mineralization within the gabbronorite subzone Crustal contamination is an important process by which a basaltic magma can become saturated with respect to sulphide and is a key factor in the genesis of many Ni-Cu-PGE sulphide deposits (e.g. Keays, 1995; Naldrett, 1997; Mavrogenes & O'Neill, 1999; Lesher et al., 2001; Naldrett, 2004). Sulphide saturation can be initiated through high degrees of fractional crystallization, magma mixing, and/or assimilation of both crustal sulphur and silica (e.g. L i & Naldrett, 1993; Li & Ripley, 2005). The occurrence of sulphide mineralization at the base of the marginal zone of the Muskox intrusion is undoubtedly related to the interaction between basaltic magma within the chamber and the adjacent country rocks. Below, we investigate the genetic link between crustal contamination and the presence of variable amounts of sulphide within the gabbronoritic rocks at the two studied sections. In Chapter 3, the degree of contamination recorded within the marginal rocks and the potential influence of contamination on parental magma composition prior to emplacement within the Muskox chamber (e.g. Nb-Ta depletion in peridotites) will be addressed. The shift in incompatible trace element ratios (e.g. Th/Yb, La/Sm, Nb/La, K/Ti) at the base of the marginal zone at both sections indicates that the effect of crustal contamination by the adjacent wall rocks is restricted to the thin zone (<10 m) of gabbronoritic rocks directly adjacent to the contact (Fig. 2.13). This change in incompatible element ratios coincides with the physical appearance of granophyre, which records the addition of partial melts derived through melting of the adjacent wall rocks (Fig. 2.6), and euhedral orthopyroxene, which likely formed from relatively silica-rich hybrid magmas along the outer wall of the intrusion. This limited spatial extent of contamination was also observed by Francis (1994) along the eastern margin of the intrusion and indicates that the thickness of the contaminated zone remains relatively constant throughout the intrusion. The sulphur isotopic compositions of sulphide at the Far West Margin also shift towards more crustal values within the outer 10-15 m of the marginal zone (Fig. 2.1 lb). As shown in Fig. 2.14, the gabbronoritic rocks at the two studied sections have distinct incompatible trace element ratios that trend towards those of the adjacent host rocks, clearly indicating that the contaminant was locally derived. From the overlapping incompatible trace element ratios between the gabbronorite at the Far West Margin and the adjacent wall rocks, it appears that a significant amount of the host paragneiss 62  50 45  FWM contaminant  40 35  •  30  •  H  !B Z  •  25 20  WPL contaminant  15 10 5  K-metasomatism  (?)  2  K/Yb Far • A o  West Margin Peridotites Gabbronorite Hornfels & Paragneiss  West Pyrrhotite Lake • Peridotites A Gabbronorite • Qtz-feld-bio gneiss  Fig. 2.14: Incompatible trace element ratio diagram (K/Yb vs. Nb/Ti) for marginal zone rocks and adjacent crustal rocks used to discriminate between the chemical effects of contamination and alteration. Nb/Ti is used because they are both high field strength elements and are considered to be relatively immobile during alteration, whereas K/Yb is sensitive to both crustal contamination and alteration effects. Both ratios are not greatly affected by olivine fractionation as demonstrated by the tight cluster formed by the peridotites at West Pyrrhotite Lake despite the 20 wt % change in MgO content. Paragneiss includes samples from both MX03-001and MX03-002 drill holes at the Far West Margin section. The gabbronoritic marginal rocks at each section have distinct compositions that plot towards those of the respective country rocks. This feature is consistent with crustal contamination and suggests that the contaminant was locally derived. Given the scatter of the country rock compositions and the fact that the actual composition of the contaminant is unknown, curvilinear mixing trends have not been included. The chromite-rich peridotites form a horizontal trend towards high K/Yb values which, given the appearance of secondary biotite in these samples, is consistent with the effects of K-metasomatism.  63  was assimilated at this location. In contrast, the progressive and subtle shift in incompatible trace element ratios at West Pyrrhotite Lake indicates that only minor amounts of the quartzfeldspar-biotite gneiss were incorporated into the magma along the outer wall of the chamber. Sasaki (1969) showed that the sulphur isotopic compositions of sulphides within the outer 50 m of the marginal zone of the Muskox intrusion correlate with those of the adjacent wall rocks, and suggested that the addition of sulphur was also a local phenomenon. The anomalous trace element ratios of the chromite-rich peridotites at the Far West Margin (high K/Ti and Th/Yb; Fig. 2.13) correlate with the appearance of secondary biotite, suggesting that this signature is likely related to alteration/metasomatism as opposed to contamination (Fig. 2.14). We propose that this limited extent and local nature of contamination is likely the result of rapid cooling and solidification of a thin hybrid zone along the outer wall of the intrusion. Rapid solidification of this zone would have effectively prevented overlying magmas from interacting with the surrounding crustal rocks, resulting in the uncontaminated signatures of the overlying peridotites. It is important to note that the contaminated gabbronorite may not be present everywhere within the upper part of the intrusion (Smith, 1962). This indicates that this thin boundary zone may have been locally resorbed, or eroded during active convection within the chamber early in its history, as proposed by Francis (1994), or during subsequent periods of magma replenishment. The presence of sulphide within the contaminated gabbronorite at both studied sections indicates that the magmas along the outer wall of the chamber became sulphidesaturated. Because of the local nature of the contamination, we might expect that the abundance of sulphide produced was controlled by the availability of sulphur within the adjacent wall rocks. The formation of relatively abundant sulphide at the Far West Margin may reflect the assimilation of a large amount of the host paragneiss, which through the addition of silica and sulphur promoted sulphide saturation in the magma directly adjacent to the contact. The lack of sulphide at West Pyrrhotite Lake appears to reflect the limited ability of the magma to assimilate large quantities of the country rock at this location. This limited interaction resulted in only minor incorporation of crustal sulphur and consequently a relatively small amount of sulphide liquid was produced, represented by the appearance of only minor pyrrhotite blebs within the gabbronorite at this location. Rapid solidification of the contaminated magmas adjacent to the contact may have prevented segregated sulphide droplets from interacting with large volumes of magma, which 64  would have a significant affect on the metal content of the sulphides. The metal content of sulphide (i.e. Ni-Cu-PGE tenor) is strongly controlled by the mass ratio between a silicate magma and a coexisting sulphide liquid that it can equilibrate with (R-factor; Campbell and Naldrett, 1979; Lesher & Burnham, 1999). The physical mechanics behind this interaction are still imperfectly understood, however this relationship can be effectively used to compare the composition of sulphide ores found within and between different intrusions (e.g. Barnes & Francis, 1995; Barnes et al. 1997; Theriault et al. 1997; Lesher et al., 2001). For example, the metal contents in 100% sulphide within gabbronoritic rocks at the Far West Margin are relatively low with Niioo =1.0 wt'% and Cuioo = 1.0 wt % (calculation procedure described in detail in Chapter 4). As will be shown in Chapter 4, this is typical of marginal zone sulphide in the Muskox intrusion. These low metal contents indicate that the sulphide in the gabbronoritic rocks formed at low R-factors (-100). Such low values are likely the combined result of the addition of relatively large amounts of sulphur from the host paragneiss and the overall small volume of silicate magma the segregated sulphides interacted with, subsequently preserved as a thin contaminated horizon at the base of the marginal zone. This indicates that the typical marginal zone environment (i.e. relatively rapid solidification of the thin contaminated zone) is not optimal for formation of significant quantities of metal-rich sulphide. Sulphide is also observed within the two chromite-rich peridotite and feldspathic peridotite horizons at the Far West Margin. The sulphur isotopic composition of sulphide within the lower chromite-rich peridotite is equivalent to that of underlying gabbronorite and adjacent wall rocks suggesting that sulphur was externally derived (Fig. 2.1 lb). The anomalous trace element ratios of this horizon are considered to reflect alteration (Fig. 2.14), and thus the relatively high 8 S values may indicate that the sulphides migrated upwards (1034  15 m) from the underlying gabbronorite zone owing to the high mobility of sulphide liquids (Mungall, 2002). Alternatively, the addition of crustal sulphur may have been decoupled from the addition of silicate material, which would result in only high 8 S values. The sulphur 34  isotopic compositions of sulphides from the upper chromite-rich horizon and feldspathic peridotite (5 S = +6%o) are distinct from those within the underlying rocks and are within the 34  range of values documented throughout the layered series (5 S = +3 to +7 % ; Sasaki, 1969) 34  0  suggesting that the addition of crustal sulphur from the adjacent wall rocks was minimal. The occurrence of relatively thin disseminated sulphide horizons associated with olivine that has  low Ni contents (Fig. 2.9) suggests that sulphide saturation occurred locally during in situ crystallization of olivine (e.g. L i & Naldrett, 1999; L i et al., 2002). The relatively high 6 S 34  values of the sulphide within these peridotites (8 S = +6) compared to those estimated for 34  mantle-derived sulphur (8 S = -2 to +2; Ripley, 1999) may indicate that crustal sulphur was 34  added to the parental magmas prior to emplacement within the Muskox chamber. Thus, the sulphides within the peridotite appear to have formed by a distinct mechanism from the sulphides within the underlying gabbronorite and lower chromite-rich peridotite.  2.6.2 Compaction and thermal evolution in the peridotite subzone of the marginal zone Compaction is an important process in the textural and compositional evolution of maficultramafic flows, sills, and layered intrusions (e.g. Irvine, 1980; Shirley, 1987; Meurer & Boudreau, 1996; Tharp et al., 1998; Meurer & Boudreau, 1998a; 1998b; Boudreau & Philpotts, 2002). Layered mafic-ultramafic intrusions can be considered to form through the effective removal and accumulation of dense crystals (olivine, chromite, pyroxene) at the base of a magma chamber, and may be constructed by repeated injections of crystal-bearing magmas (e.g. Raedeke & McCallum, 1984; Marsh, 2000). The accumulated crystals initially build a cumulate pile composed of cumulus mineral grains and evolved interstitial melt (with 50-60 vol % porosity; Irvine, 1980; Shirley, 1986; Tharp et a l , 1998). Given the relatively high density contrast between olivine and pyroxene (3.2-3.5 g/cm ) and basaltic liquids (-2.7 3  g/cm ), compaction within the consolidating cumulate pile will aid in the differentiation 3  process by forcing relatively buoyant interstitial melt upward through the pile. Below, we examine the role of compaction within a temperature gradient along the base of an intrusion in producing the downward differentiation trend within the marginal zone of the Muskox intrusion, a mechanism that has been previously explored for the formation of the overlying layered series by Irvine (1980) and Tharp et al. (1998). As described earlier, the proportion of postcumulus phases within the marginal zone progressively increases towards the basal margin of the intrusion (-20 vol % to 50 vol %), which corresponds to a systematic decrease in MgO (a proxy for olivine abundance) and increase in A I 2 O 3 (a proxy for the abundance of postcumulus plagioclase) and other elements not compatible in olivine (Fig. 2.8). This trend is observed throughout the peridotites of the West Pyrrhotite Lake section and the feldspathic peridotite at the Far West Margin section, and is consistent with the mineralogy of marginal zone rocks throughout most of the intrusion as 66  originally mapped by Smith (1962). This distribution of postcumulus material can be explained by the crystallization of varying amounts of intercumulus liquid during compaction of the cumulate pile and cooling through the base of the intrusion. In the relatively rapidly cooled region near the margin of the intrusion, significant quantities of intercumulus liquid crystallized, whereas in the more slowly cooled interior of the intrusion, compaction forced intercumulus liquid to percolate upwards through the cumulate pile before it could crystallize (see modeling below). The majority of the layered series of the Muskox intrusion is composed of olivine cumulates with 7-10 vol % postcumulus phases (Irvine, 1980), whereas the marginal zone peridotites can contain up to 50 vol % postcumulus phases as noted above. Tharp et al. (1998) successfully modeled this distribution of postcumulus material in the Muskox intrusion, including the combined effects of compaction, porous medium flow, thermal conduction, advection of heat, and crystallization. In their model, compaction involved both grain boundary diffusion creep and power law creep, which allowed for compaction to be monitored from initial deposition (50-60% porosity) to nearly zero porosity. The fractions of liquid and crystalline phases were calculated during cooling and fractional crystallization using MELTS (Ghiorso & Sack, 1995). Their results indicated that rapid cooling at the upper and lower boundaries resulted in reduced compaction (i.e. high proportion of crystallized interstitial liquid) due to the conduction of heat to the bounding wall rocks. Based on the available petrographic and geochemical information on the marginal zone (unpublished data for the GSC South drill hole summarized in graphical form in Irvine, 1980), Tharp et al. (1998) proposed that this interplay between compaction and cooling could also potentially explain the progressive increase in the amount of postcumulus material within the marginal zone of the Muskox intrusion. To address the extent to which a compaction process can explain the range of mineralogical and geochemical variations observed within the marginal zone peridotites in this study, we have used the forward modeling capabilities of IPJDKJM (Boudreau, 2003). The IRIDIUM program combines a mineral-liquid equilibration routine based on the free energy minimization techniques used in the MELTS program (Ghiorso & Sack, 1995), with the 1dimensional mass and heat transport equations of Mackenzie (1984) as implemented by Shirley (1986) to quantitatively model compaction within crystal-liquid mixtures (Boudreau, 2003). Detailed descriptions of the program operation are given in Boudreau and Philpotts 67  (2002) and Boudreau (2003) and will only be briefly summarized below. The program assumes that during compaction, the bottom is closed to mass transfer and the overlying assemblage compacts under its own weight. The initial conditions (temperature, pressure, and bulk composition) are specified by the user for each node (i.e. height) in the system and the program calculates the equilibrium mineral-liquid assemblage and various physical parameters (including heat capacity, enthalpy, and liquid viscosity). The program calculates new equilibrium mineral-liquid assemblages at each node after some change in the bulk composition resulting from advection and diffusion of heat and mass during compaction at successive time-steps. IRIDIUM, unlike the model of Tharp et al. (1998), does not explicitly deal with grain boundary or power law creep, but instead the deformation of the solid matrix is approximated using a term for the effective viscosity of the matrix (assumed constant at 5 x 10 Pa s; Shirley, 1986). Given that we are not attempting to produce results below liquid 11  fractions of 10% this difference likely does not affect our results. The boundary conditions are also different in these two models: the Tharp et al. (1998) model assigns specific thermal conductivities and initial temperatures for the bounding wall rocks, whereas IRIDIUM simulates conduction by progressively decreasing the temperature of the bottom and/or top nodes. Our purpose is not to compare in detail the results generated by these different numerical models, but instead is to provide constraints on the role of compaction in producing the observed chemical variations within the marginal zone of the Muskox intrusion. The compaction parameters used (e.g. solid viscosity and permeability constant) are those from Shirley (1987) with the exception of cumulus mineral grain size, which in the case of the outermost marginal zone rocks of the Muskox intrusion is -0.05 cm. A n olivine gabbronorite from the base of the peridotite subzone at the West Pyrrhotite Lake section (Sample 71133: MgO = 22 wt %) was used as the bulk starting composition. This sample does not represent a liquid composition, but is used to construct a cumulate pile containing olivine and fractionated liquid (justification given below). The pressure was set at 1000 bars which is consistent with estimates for emplacement depth of the intrusion (Irvine, 1980; Tharp et al. 1998). The initial temperature of the system and the porosity of the cumulate pile were defined at 1200°C and 50 vol %, respectively. Based on these parameters, IRIDIUM constructed a cumulate pile composed of olivine and interstitial liquid, and an overlying liquid layer (see below). To simulate heat conducted to the underlying host rocks we incrementally decreased the temperature of the bottom node from 1200°C to 400°C at a specified rate (e.g. 68  0.01°C/day; -220 yr cooling interval). The upper boundary was kept at a relatively high temperature (1200°C to 1000°C), which is justified by the fact that the upper boundary would have been separated from the roof rocks by a continually building cumulate pile (Tharp et al., 1998). The olivine gabbronorite used as the bulk starting composition occurs at the base of the West Pyrrhotite Lake section and is composed of cumulus olivine (40-50 vol %) and postcumulus plagioclase and pyroxene. We consider this to represent a mixture of accumulated olivine and fractionated intercumulus liquid that approximates the initial cumulate pile prior to, or at the early stages of compaction (i.e. contains a high proportion of crystallized intercumulus liquid), as proposed by Irvine (1980). Support for using this starting composition comes from examining the composition of the interstitial liquid within the initial cumulate pile constructed at the beginning of the IRIDIUM run. Under the present conditions, the interstitial liquid contains -7.5 wt % MgO. Using MELTS (Ghiorso & Sack, 1995), this MgO content is comparable to a residual liquid formed after -15% fractional crystallization of olivine from an estimated primary magma composition for the Muskox intrusion (Irvine, 1977b), and thus indeed represents a fractionated composition expected within a cumulate pile. The mineralogical and chemical changes during an IRIDIUM simulation are summarized in Fig. 2.15. The initial state of the system (1200°C throughout) contained a 180 m-thick cumulate pile composed of olivine, spinel, and interstitial liquid (-7.5 wt % MgO), and an overlying 20 m-thick liquid layer (Fig. 2.15). As the temperature was decreased at the base of the column (i.e. simulating the conduction of heat to the underlying wall rocks), plagioclase and clinopyroxene, and then orthopyroxene, began to crystallize, and the lower 5 m of the pile became almost completely solidified within 15 years (Fig. 2.15). Within the hotter interior, the cumulate pile had already begun to compact and the solid components moved downwards relative to the surrounding interstitial liquid, as demonstrated by a decrease in modal olivine abundance within the upper portion of the column. The increase in the amount of olivine near the base is due to both compaction and crystallization. During continued cooling, compaction proceeded to force liquid upwards within the hotter interior, whereas the liquid at the bottom of the column crystallized before it could be expelled due to the thermal gradient that had developed. After 130 years, during which time the temperature of the bottom node decreased from 1200°C to 500°C, the thickness of the solidified zone (<10 % liquid remaining) increased to 90 m (Fig. 2.15b). At this point the model simulation was 69  (a) 15 years p200  -I  •  180 •  : \  140 -  -180  oi  80 • 60 40 • 20-  :  Sp(i)  L  I Sp>*  0 • 0  .  /  t= 0  solid-liquid mixture  i I  I I I I I I l  (  t= o t = 15yrs  \X  C p x r t  600  50 100 400 Cumulative Mass (grams)  800  /  /  / •  t=15yrs  ^  /  ::  I  -120  -80  •40 •20 -0 2.0  1.0  Temp(°C)  -100  •60  (/ 0.0  -160 -140  / 1 1 1 1 1 • |  •  j  1000 1200 1400  /  / 1 1 1 1 1  !  •  •  Height  120 • 100 •  X  | 1  OKI)  160 •  E  liquid  (UJ)  200  Ti02(wt%)  (b) 130 years 200 liquid i J  i  solid-liquid mixture  i i  i  j  t = 130 yrs  \/ I  '  /  140  100  ,'t-o  l  /  160  120  V  t = 130 yrs /  180  \  \  I  iI\  t= 0  J.  60 40  \  \  80  X  ro to'  \ \  20  \ \ \  -Y-  50 100 400 Cumulative Mass (grams)  600  800 1000 1200 1400 Temp(°C)  0.0  1.0  2.0  Ti02 (wt%)  Fig. 2.15: IRIDIUM results comparing the initial state of the system and that after (a) 15 years and (b) 130 years, using an initial porosity of 60% and a bottom cooling rate of 0.05 °C/day. Reported results are the cumulate mass of crystallized phases, the temperature profiles, and bulk Ti02 (wt %). The initial state of the system (dotted line) is at constant temperature and contains a ~20 m-thick liquid layer and an underlying -180 m-thick cumulate pile with olivine and spinel. An olivine gabbronorite sample (71133) from the West Pyrrhotite Lake section was used as the bulk starting composition. See text for discussion.  70  halted because under the present setup conditions the temperature within the upper part of the system remained too high for crystallization to proceed. The competition between liquid expulsion during compaction and crystallization of interstitial liquid during cooling resulted in an upward increase in the amount of olivine and a corresponding decrease in the abundance of plagioclase and pyroxene. This variation is analogous to that observed in the marginal zone peridotites of the Muskox intrusion. The final chemical profiles predicted by a number of different IRIDIUM simulations are compared to the observed profile in the peridotites at West Pyrrhotite Lake in Fig. 2.16 for AI2O3,  Ti02, and CaO (measure the of abundance of crystallized interstitial liquid) and MgO  (measure of the abundance of olivine). Only the solidified portion (<10 % liquid remaining) at the base of the column for each simulation is shown. The simulations were completed at different initial porosities (50% and 60%) and bottom cooling rates (0.05°C/day and 0.1°C/day) to asses their effect on the final compositional profiles. All simulations reproduced the overall downward differentiation trend observed within the marginal zone (Fig. 2.16). As expected, the compositional profiles change depending on the values for initial porosity and bottom cooling rate, which can be described in terms of the proportion of liquid that crystallized at the base of the column before it can percolate upwards through the cumulate pile. By either decreasing the porosity or increasing the cooling rate, relatively high proportions of liquid crystallize at the base of the column. Increasing only one of these parameters affects the overall curvature of the profile, because this influences the height within the column where significant compaction occurs. This is apparent from the crossover points A and B shown in Fig. 2.16. Increasing only the initial porosity results in an increased amount of crystallization at the base, but due to the high porosity, compaction occurs more rapidly and therefore the site of compaction is relatively close to the bottom. Conversely at low initial porosities, the amount of crystallization at the base is limited and compaction occurs higher up in the column. This trade-off results in the crossover observed between the profiles for simulations with 50% and 60% porosity at approximately 30 m from the base (point A; Fig. 2.16). The effect of changing only the cooling rate results in a similar crossover that occurs higher up in the column at point B. The IRIDIUM results confirm that cumulate pile compaction during cooling through the base of the intrusion can explain the overall mineralogical and chemical trends observed in the peridotite subzone of marginal zone of the Muskox intrusion, a mechanism originally 71  F i g . 2.16: Comparison of bulk chemical profiles for AI2O3, Ti02, CaO, and M g O at the end of different I R I D I U M simulations to those observed at the West Pyrrhotite Lake section. Adjusted parameters are initial porosity (50-60%) and cooling rate (0.05-0.1°C). The 60% porosity simulation is that summarized in Fig. 2.15. The inset shows schematically the effect of changing different parameters. See text for discussion.  72  proposed by Irvine (1980) and evaluated by Tharp et al. (1998). As expected, the final compositional profile varies as a function of initial porosity of the cumulate pile and bottom cooling rate (Fig. 2.16). We would also expect that if solidification occurred during accumulation, the proportion of crystallized interstitial liquid along the lower contact would be higher than that in the model simulations, and would therefore result in a significantly more exaggerated (curved) chemical profile. In addition, if heat loss occurred both from the top and bottom we would expect more vertical chemical profiles. Increased loading from a thicker cumulate pile would likely enhance compaction and result in a lower proportion of crystallized interstitial liquid at the base than that observed in the model simulations. Thus, it is possible to produce a wide range of compositional profiles.  2.6.3 Implications for the formation of the marginal zone of the Muskox intrusion and the basal margins of other mafic-ultramafic intrusions A number of additional constraints on the formation of the marginal zone of the Muskox magma chamber can be made based on the results presented in this study. Firstly, the solidification of varying amounts of intercumulus liquid with distance from the base of the marginal zone may also explain the systematic decrease in the forsterite content of olivine observed in peridotites at West Pyrrhotite Lake and the feldspathic peridotite at the Far West Margin section of the Muskox intrusion. Several studies (e.g. Barnes, 1986; Chalokwu & Grant, 1987; Grant & Chalokwu, 1992) have shown that the cumulus minerals in maficultramafic intrusions may re-equilibrate with the surrounding fractionated intercumulus liquid during cooling. This results in a shift towards more evolved mineral compositions (i.e. reequilibrated olivine is more Fe-rich); the higher the proportion of intercumulus liquid present, the higher the magnitude of this shift. Barnes (1986) demonstrated that the composition of olivine within an olivine cumulate with -10% intercumulus liquid will show a 2 mol % shift, whereas an olivine cumulate with -50% intercumulus liquid will show a 5-7 mol % shift. This magnitude of shift in the composition of olivine and variation in amount of interstitial liquid is comparable to that observed for the olivine cumulates at West Pyrrhotite Lake (Fig. 2.9). The N i content of olivine is relatively unaffected during re-equilibration as a result of the low Ni abundance within the intercumulus liquid, which may explain the relatively constant Ni content of olivine within the peridotites at the West Pyrrhotite Lake section (Fig. 2.9). This reequilibration process must be a relatively rapid process (e.g. Cawthorn et al., 1992)  considering that it is recorded in mineral grains within a few metres from the basal contact of the Muskox intrusion, which would have undoubtedly solidified soon after emplacement. The distinct mineralogical and chemical characteristics of the peridotites at the West Pyrrhotite Lake and Far West Margin demonstrate that the character of the marginal zone changes at different positions within the intrusion. Because the compaction model is mainly temperature-controlled, the change in the character of the marginal zone may reflect changes in the minerals that accumulated at different stages during the emplacement of the Muskox intrusion (i.e. the entire marginal zone of the Muskox intrusion was likely not formed from a single, early magma injection). In particular, chromite becomes an important phase within the upper part of the layered series (Fig. 2.4; Smith, 1962; Findlay & Smith, 1965; Irvine & Smith, 1969), which broadly correlates with the appearance of chromite within the marginal zone at the Far West Margin section. In addition, the peridotites at the Far West Margin contain coarse-grained olivine which has only been documented within the upper part of the layered series (Irvine & Smith, 1969). These features suggest that the marginal zone formed at different stages during the evolution (growth) of the Muskox magma chamber and may represent, in part, a lateral extension of the rocks within the layered series. Changes in the thermal conditions during evolution of the chamber could also have had an impact on the formation of the marginal zone. The initial magmas introduced into the Muskox chamber would have been in contact with relatively cool country rocks, whereas later magmas would have been emplaced into rocks that were progressively heated by previous magma inputs. This would affect the cooling rate along the outer walls of the chamber during the later stages of its evolution, which could produce a more subdued downward trend in differentiation across the marginal zone. It is important to note that the GSC South drill hole intersected two individual downward differentiation cycles in the marginal zone (Fig. 2.3). We speculate that each of these cycles could represent the minerals separated and crystallized from two different magma injections, both of which cooled through the base of the intrusion and contain the predicted downward increase in postcumulus material. The downward trends in the proportion of postcumulus material and cumulus mineral compositions observed within the marginal zone peridotites in the two studied sections are not unique to the Muskox intrusion. Similar trends are observed along the basal margins of other mafic-ultramafic layered intrusions (e.g. Great Dyke, Zimbabwe, Wilson, 1982; Stillwater complex, Montana, Raedeke & McCallum, 1984), and troctolititc intrusions (e.g. Partridge 74  River intrusion in the Duluth complex, Minnesota; Grant & Chalokwu, 1992). Thus, compaction may well have played an important role in generating the mineralogical and chemical variations at the base of these other bodies that formed from compositionally distinct parental magmas from that of the Muskox intrusion. Finally, Latypov (2003) recently proposed that the reversal in differentiation trends at the base of many mafic-ultramafic intrusions and layered intrusions is produced through the diffusion of components within magma along the outer wall of a chamber owing to the presence of a steep thermal gradient across the contact region (Soret diffusion). The main evidence presented by Latypov (2003) against any gravitational mechanism for the formation of marginal zone reversals was that marginal zones are apparently "mirror images" of the overlying layered series with respect to their order of crystallization. According to this proposal, the marginal zone of the Muskox intrusion should record the crystallization sequence preserved within the overlying layered series, which throughout most of the intrusion is olivine-clinopyroxene-plagioclase-orthopyroxene (Fig. 2.3). This progression is not observed within the marginal zone of the Muskox intrusion, and in addition the appearance of cumulus pyroxene (mainly orthopyroxene and minor clinopyroxene) occurs only within the contaminated zone along the outer contact, which has a consolidation history distinct from that of the overlying peridotite subzone of the marginal zone as documented in this study. Strong mineralogical and chemical variations within the marginal zone of the Muskox intrusion mainly occur within a section of olivine cumulates that were isolated physically and geochemically from the underlying crustal rocks by a thin contaminated gabbronorite subzone, and can be appropriately explained by the re-distribution of intercumulus liquid during compaction of a dense cumulate pile during rapid cooling through the base of the intrusion.  75  2.7 CONCLUSIONS This detailed petrographic and geochemical study of marginal zone rocks at stratigraphically low (West Pyrrhotite Lake) and high (Far West Margin) positions within the large Muskox layered mafic-ultramafic intrusion reveals that the marginal rocks consist of two distinct parts, a lower gabbronorite subzone and an upper peridotite subzone. The gabbronoritic rocks at the base of the marginal zone crystallized from magmas that were contaminated by partial melts derived from the directly adjacent wall rocks. Rapid solidification of this contaminated zone prevented overlying magmas from interacting with the surrounding crustal rocks, such that the overlying peridotites crystallized from relatively uncontaminated magma. The addition of sulphur and silica to magmas along the outer wall of the chamber promoted local sulphide saturation, however rapid cooling of the thin contaminated zone inhibited segregated sulphide from interacting with large volumes of magma and therefore resulted in metal-poor sulphides. The mineralogical and geochemical variations within the marginal zone peridotites were successfully modeled with the IRIDIUM software and are the result of crystallization of varying amounts of intercumulus liquid during compaction within a thermal gradient at the base of the magma chamber. The distinct mineralogical and geochemical variations observed at the two studied sections correlate with changes in the accumulated minerals within the layered series, indicating that the marginal zone of the Muskox intrusion formed throughout the evolution of the Muskox chamber rather than representing a single initial magma injection. This interplay between the expulsion of interstitial liquid during accumulation and compaction, and solidification of interstitial liquid as a result of cooling through the base of the chamber, likely played an important role in the formation of downward differentiation trends in the basal margins of other mafic-ultramafic bodies.  2.8 ACKNOWLEDGEMENTS This project would not have been possible without the assistance of Gary De Schutter (Senior Project Geologist, Anglo American Exploration Canada Ltd. (AAEC)) during A A E C summer and winter drill programs on the Muskox intrusion in 2003 and 2004. The author would also like to thank Nathan Rand for his help with sample collection. Mati Raudsep and Elisabetta Pani are thanked for their support in the SEM/Electron microprobe facility at the University of British Columbia. R A M was supported by an NSERC Industrial Postgraduate Scholarship (IPS). Funding for this research was provided by Anglo American Exploration Ltd. (Canada), by a Collaborative Research Development (CRD) grant from NSERC and A A E C , and by an NSERC Discovery Grant to JSS.  77  2.9 REFERENCES Baragar, W.R.A. (1969). The Geochemistry of the Coppermine River Basalts. Geological Survey of Canada Paper 69-44, 43 pp. Baragar, W.R.A., Ernst, R.E., Hulbert, L. & Peterson, T. (1996). Longitudinal petrochemical variation in the Mackenzie dike swarm, Northwestern Canadian Shield. Journal of Petrology 37-2, 317-359. Barnes, S.J. (1986). The effect of trapped liquid crystallization on cumulus mineral compositions in layered intrusions. 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Journal of Petrology 23, 240-292.  CHAPTER 3  Age and Hf-Nd isotopic geochemistry of marginal rocks in the Muskox intrusion: implications for crustal contamination and mantle source composition in the 1.27 Ga Mackenzie magmatic event  3.1 INTRODUCTION The 1.27 Ga Mackenzie magmatic event represents a period of extensive tholeiitic magmatism that resulted in the emplacement of the large Muskox layered mafic-ultramafic intrusion and Mackenzie dike swarm, and the eruption of the Coppermine-River flood basalts (LeCheminant & Heaman, 1989; Griselin et al., 1997; Baragar et al., 1996). Previous petrologic, paleomagnetic, and geochronologic studies have indicated that all components of the Mackenzie magmatic event were emplaced within a relatively short time-span of only a few million years, and that they are genetically related and considered to be the products of a mantle plume (Wandless & Loveridge, 1972; Fahrig, 1987; LeCheminant & Heaman, 1989; Baragar et al., 1996; Griselin et al., 1997). An important aspect in the geochemical evolution of these bodies is that the tholeiitic parental magmas ascended through ~40 km of continental crust, which may have imparted distinct trace element and isotopic signatures within both the extrusive and intrusive components (e.g. Siberian flood basalts and associated sills, Noril'sk region, Russia; Wooden et al., 1993; Arndt et al., 2003). Because of the highly enriched incompatible trace element contents of most middle and upper crustal rocks compared to basaltic magmas, the extent to which these magmas interacted with the crust during transit and emplacement can be assessed using radiogenic isotopic compositions and incompatible trace element ratios. Previous investigations of the trace element and isotopic compositional variations within the Coppermine River basalts (Griselin et al., 1997; Dupuy et al., 1992) indicate that the lowermost basalts were contaminated by continental crust during their ascent to the surface, whereas the uppermost basalts emplaced with little or no interaction with crustal material. A previous Nd and Sr isotopic investigation within the Muskox intrusion (Stewart & DePaolo, 1992; 1996) focused on the layered series and roof zone, and suggested that only minimal crustal contamination occurred within the Muskox chamber as a result of the buoyancy and viscosity contrast between mafic magma within the chamber and overlying silicic magma derived through melting of the roof rocks. In this study, we first present precise U-Pb ages from baddeleyite in marginal zone peridotite and gabbronorite at stratigraphically low and high positions within the Muskox intrusion to constrain the absolute crystallization age of the marginal zone rocks and their temporal relationship with the overlying layered series (1270 ± 4 Ma, U-Pb baddeleyite/zircon; LeCheminant & Heaman, 1989) and the Mackenzie dikes (1268 ± 2 Ma, U-Pb baddeleyite; LeCheminant & Heman, 1989). We then evaluate variations in the Hf-Nd isotopic and trace 86  element concentrations of the marginal rocks to determine the spatial extent and degree of crustal contamination along the basal margin of the intrusion. Finally, we compare available Nd isotopic compositions from the Muskox intrusion, Coppermine River flood basalts, and Mackenzie dikes to constrain the petrogenetic relationship between these bodies and possible variations in the mantle source composition during the Mackenzie magmatic event. Our results indicate that the Muskox intrusion was emplaced over a geologically restricted time span at 1269 ± 2 Ma (U-Pb baddeleyite) which correlates precisely with the emplacement of the Mackenzie dikes. The effects of local crustal contamination within the marginal zone are restricted to a thin zone (<10 m) of gabbronoritic rocks directly adjacent to the contact with country rocks. The Nd isotopic compositions of overlying marginal zone peridotites are entirely within the range of published values from the layered series cumulates (Stewart & DePaolo, 1996), thus the majority of the marginal zone rocks record the isotopic composition of the magmas that progressively entered the Muskox chamber. An important conclusion from this study is that the Nd isotopic compositions of the marginal zone peridotites and layered series rocks of the Muskox intrusion are comparable to only the lowermost Coppermine River basalts, which indicates that the majority of the basalts bypassed the Muskox magma chamber and were erupted after travelling through a separate conduit system.  3.2 COMPONENTS OF THE MACKENZIE MAGMATIC EVENT Below we briefly review the essential characteristics and geochemistry of the main components of the 1.27 Ga Mackenzie magmatic event: the Coppermine River flood basalts, the Mackenzie dike swarm, and the Muskox intrusion.  3.2.1 Coppermine River flood basalts The Copper Creek Formation and overlying Husky Creek Formation comprise the Coppermine River Group and form a northward dipping (5-8°) succession of continental flood basalts and interflow sandstones that are exposed for 250 km south of the Coronation Gulf (Fig. 3.1) (Baragar, 1969; Baragar & Donaldson, 1973; Dostal et al., 1983). The Ekalulia basalts, which are exposed along the northwestern shore of Bathurst Inlet, are thought to be correlative to the Coppermine River basalts indicating that the total east-west extent of the flood basalt succession may have been >500 km (Baragar et al., 1996). The Coppermine River basalts erupted primarily on fluvial to shallow marine sediments of the Dismal Lake and Hornby Bay  110°W  —I  90°W  L_  Fig. 3.1: Geographic map showing the distribution of the major components of the 1.27 Ga Mackenzie large igneous province, including the Coppermine River basalts, Mackenzie dike swarm, and Muskox intrusion (modified from LeCheminant & Heaman, 1989; after Gibson et al., 1987). CG = Coronation Gulf; B = Bathurst Inlet.  groups that unconformibly overlie deformed rocks of the 1.8-1.9 Ga Wopmay Orogen (Baragar & Donaldson, 1973; Hoffman, 1984; Hoffman & Bowring, 1984). The flows are typically aphyric and plagioclase microphyric, however olivine or orthopyroxene phenocrysts are present within the lowermost flows (Baragar, 1969). Low Mg/Fe, MgO, and Ni contents and high incompatible element abundances indicate that the lavas fractionated extensively at depth and do not represent primary magma compositions (Dostal et al., 1983). Nd isotopic and trace element compositional variations throughout the flood basalt succession show that the degree of crustal contamination decreased through time with the lower Copper Creek basalts having initial e d values of -5 to +1, and upper Copper Creek and overlying Husky N  Creek basalts having initial e d values of+1 to +5 (Dupuy et al., 1992; Griselin et al., 1997). N  3.2.2 Mackenzie dike swarm The Mackenzie dikes (1267 ± 2 Ma; LeCheminant & Heaman, 1989) form a series of nearvertically dipping diabase dikes that radiate outwards from the Coronation Gulf towards the south and east for a distance of over 2400 km (Fig. 3.1; Gibson et al., 1987; Baragar et al., 1996). The dikes terminate within the lower Copper Creek basalts, which along with petrological and geochemical considerations, suggests that they represent the feeder system through which the basalts were emplaced (Baragar & Donaldson, 1973; Dostal et al., 1983; Baragar et al., 1996). Two distinct chemical groups, or subswarms, have been identified based on variations in Ce/Yb, which primarily reflects changes in the degree of mantle melting (Baragar et al., 1996; Gibson et al., 1987). Crustal contamination within the dikes is more pronounced closer to the focus of the swarm based on incompatible element ratios (e.g. K/Ti; Baragar et al., 1996). Magma flow direction in the dikes is considered to be near-vertical within 500 km of the focal point of the dike swarm and near-horizontal at greater distances (Ernst & Baragar, 1992). An unpublished Nd isotopic study (Dundas & Peterson, 1992) indicates that in all the dikes sampled, including those from each subswarm, the initial em values range from -2.8 to +4.9, which is consistent with the range observed in the Coppermine River basalts. Dikes of a similar age and composition (Bear River dikes, Yukon) have recently been identified and may represent part of the Mackenzie dike swarm, broadening the extent of the swarm by approximately 50° towards the west (Schwab et al., 2004).  89  3.2.3 Muskox intrusion The Muskox intrusion is a layered mafic-ultramafic intrusion that was emplaced within rocks of the 1.8-1.9 Ga Wopmay Orogen along the western margin of the Slave Craton (Fig. 3.2) (Smith, 1962; Hoffman, 1984; Hoffman & Bowring, 1984; Gandhi et al., 2001). The intrusion and underlying feeder dike are exposed for over >100 km south of the Coronation Gulf near the focal point of the Mackenzie dike swarm. The main body of the intrusion is funnel-shaped in cross-section and forms an elongate body that plunges shallowly (4-8°) northward beneath the overlying Hornby Bay sandstones, Dismal Lake carbonates, and Coppermine River basalts (Smith, 1962; Findlay & Smith, 1967; Baragar & Donaldson, 1973). The northward-plunging attitude of the intrusion provides an oblique section through its entire stratigraphy from the basal feeder and margin in the south to the upper roof zone in the north. The surrounding crustal rocks consist of metasedimentary rocks of the Recluse and Epworth groups to the east and metavolcanic, metasedimetary, and metaplutonic rocks of the Akaitcho Group and Hepburn Intrusive Suite to the west. The Muskox intrusion is divided into a feeder dike, marginal zone, layered series, and granophyric roof zone (Fig. 3.2) (Smith, 1962; Smith & Kapp, 1963). The feeder dike is exposed south of the main body of the intrusion and consists of mainly gabbronorite (bronzite gabbro) and norite with minor olivine-bearing units near the base of the intrusion. The dike is considered to represent a feeder through which the initial magmas entered the Muskox magma chamber; subsequent magma pulses may have been injected from an unexposed feeder to the north (Irvine, 1980). The marginal zone forms a sheath along the inward-dipping walls of the intrusion, separating the layered series rocks from the surrounding crustal rocks (Smith, 1962; Findlay & Smith, 1967; Francis, 1994). The layered series is composed of numerous northward-dipping layers of mainly olivine-chromite cumulates, and olivine-pyroxene cumulates in the lower part of the intrusion, and pyroxene and plagioclase cumulates within the upper part of the intrusion (Smith, 1962; Bedard & Taner, 1992; DesRoches, 1992; Francis, 1994). The upper part also hosts two chromite-rich layers that are similar to those of the lower part of the Bushveld Complex, South Africa, but contain an order of magnitude less PGE (Irvine & Smith, 1969; Irvine, 1988; Barnes & Francis, 1995; Roach et al., 1998). The granophyric roof zone is a heterogeneous zone composed of granophyric gabbro and granophyre with varying abundances of host rock xenoliths and is considered to represent both  90  M  v v w v V W 'v v o r v v v v v v v v v v / /  ,  1  v v v «rv v v \ \ ^ J r - ^ v v v v v v v v v v v ^VVVVrfVVVVVVVVVVVVVVVVVJ  V V V v vY  ;£/  / J ' /  vvvvvvvvvvvvvvvv/  ( / W W V»V V V V V V V V V V V V V V , V < V V V V V \fV V V V V V V V V V V V V 1  Legend  VVVVVVVVVVVVVVVVVVVJ |*VVVVVVVVVVVVVVVVVV' V V V V V W W V V V V V V vv v vv I |f V V V V V V \| V V V V V V V V V V V  Coppermine Homocline  |/ V V V V V v\v v v v v v v v v v v v v ^ v ,  1  v v v v v v viv v v v v v v v v v v v1 i  ^  1  i ' i  Coppermine River Group  vvvvvvvvvv  V V V/ffy  ^^P^T^'r'^v v v v v v v v v v v l r i  >v V V V V V V V V "  I |  x  "| Husky Creek Formation  v v v  | Copper Creek Formation Dismal Lake Group Hornby B a y Group  Muskox Intrusion Upper border zone Granophyre, gabbro Layered series  LZ1 Gabbro, anorthosite I Olivine pyroxenite, pyroxenite, websterite I Olivine gabbro, troctolitic peridotite |  | Dunite, peridotite, feldspathic peridotite Marginal zone  I pm  I Peridotite, feldspathic peridotite, gabbronorite Mackenzie Dikes  Wopmay Orogen Hepburn Intrusive Suite [ * \ \ Recluse Group |' i ' ' ,| Epworth Group j ['-1 Akaitcho Group N v Major Faults  Figure 3.2  Fig. 3.2: Geologic map of the Muskox intrusion showing the location of the West Pyrrhotite Lake and Far West Margin sections (after Hulbert, 2005; mapping by Smith, 1962). The intrusion plunges shallowly to the north (4-8°) exposing a large section of the stratigraphy from a basal feeder zone in the south to the granophyric roof zone in the north. The West Pyrrhotite Lake section is near the base of the intrusion, while the Far West Margin section is at a stratigraphically higher position near the roof of the intrusion. The Muskox feeder dike, extends to the south (off the map) for ~60 km. Rivers and lakes have been omitted for clarity, with the exception of McGregor and Speers lakes.  extremely fractionated liquid within the chamber and siliceous melt derived by melting of the overlying roof rocks (Irvine & Smith, 1967; Stewart & DePaolo, 1996). The cumulate rocks within the intrusion are considered to have formed through the fractionation and accumulation of mineral grains from multiple magma injections and subsequent compaction within a cumulate pile (Irvine & Smith, 1967; Irvine, 1970; Irvine, 1980; Tharp et al., 1998). Irvine and Smith (1967) divided the layered series into 25 cyclic units, each of which represents an influx of relatively undifferentiated magma and removal (eruption) of fractionated residual liquid. The appearance of pyroxenite layers within the upper part of the intrusion marks a change in the order of crystallization, which reflects a change to a more evolved magma composition during the later stages of the evolution of the Muskox chamber. Irvine (1970) postulated that this advanced crystallization of orthopyroxene was the result of contamination of the magma within the chamber by silicic material derived from melting of the roof rocks. Irvine (1975) initially suggested that the chromite-rich horizons formed by the same mechanism, however he later proposed (Irvine, 1977) that mixing between primitive and evolved magmas within the chamber was a more viable process to explain the formation of the chromite-rich horizons. Nd isotopic compositions of the Muskox intrusion (Stewart & DePaolo, 1996) show relatively limited variation throughout the layered series (initial eNd -2.5 to 0.5), which supports the magma mixing model for the =  formation of the chromite-rich horizons and suggests that the early crystallization of orthopyroxene may have also resulted from magma mixing as opposed to crustal contamination.  3.3 MARGINAL ROCKS OF THE MUSKOX INTRUSION The marginal zone is a structurally distinct unit within the Muskox intrusion that separates the rocks of the overlying layered series from the adjacent crustal rocks, trends parallel to the inward dipping walls, and extends throughout the entire stratigraphic height of the intrusion (Fig. 3.2 & 3.3) (Smith, 1962; Francis, 1994). In this study, we evaluate the trace element and isotopic compositions of drill core collected in 2003 from stratigraphically low (West Pyrrhotite Lake) and high (Far West Margin) positions along the western margin of the intrusion (Fig. 3.2 & 3.3). As described in Chapter 2, the marginal zone at both sections is composed of a thick upper subzone (~ 100-150 m) of olivine and olivine-chromite cumulates and a relatively thin (<10 m) lower subzone containing granophyre-bearing gabbronoritic 93  (a) West Pyrrhotite Lake  Fig. 3.3: Interpreted cross-sections (facing north) of the (a) West Pyrrhotite Lake and (b) Far West Margin sections showing locations and depths of drill holes. Surface geologic contacts and topography are from Smith (1962) and down-hole contacts are based on drill core and petrographic observations and stratigraphic shifts in major element chemistry (see Chapter 2). EOH = end of hole. Qtz-feld-bio = quartz-feldspar-biotite.  rocks at the contact with the adjacent gneisses (Fig. 3.3). The peridotite part of the marginal zone becomes progressively more evolved in composition towards the margin owing to a systematic increase in the proportion of postcumulus pyroxene, plagioclase, and phlogopite relative to cumulus olivine. This downward trend to more evolved compositions is the result of rapid cooling and solidification of intercumulus liquid near the margin of the intrusion and expulsion of intercumulus liquid during compaction within the relatively slowly cooled interior (see Chapter 2). The gabbronoritic rocks at the base of the marginal zone contain granophyre and have distinct incompatible trace element ratios (Th/Yb, La/Sm, Nb/La, and K/Ti) indicating that they were contaminated by the adjacent wall rocks during emplacement. The H f and Nd isotopic compositions determined in this study, not only allow us to confirm the extent of contamination predicted by trace element ratios, but provide a link between the marginal zone and layered series rocks (Stewart & DePaolo, 1996; Purves, 2005 (unpublished)), as well as the other components of the Mackenzie magmatic event (Griselin et al., 1997; Dundas & Peterson, 1992 (unpublished)) for which there is available isotopic data.  3.4 ANALYTICAL TECHNIQUES 3.4.1 U-Pb concentrations and isotopic compositions Mafic and ultramafic cumulate rocks typically contain low concentrations of incompatible elements (e.g. 20-40 ppm Zr in marginal zone peridotites of the Muskox intrusion) and therefore contain only trace amounts of U-rich minerals suitable for U-Pb geochronology. Baddeleyite ( Z 1 O 2 ) , however, which can crystallize from fractionated interstitial liquid, contains high concentrations of U (-500 ppm) and can be used to precisely date mafic rocks (Heaman & LeCheminant, 1993). In the Muskox intrusion, baddeleyite occurs not only in marginal gabbronorite, but also in peridotite with MgO contents up to 38 wt %. A total of 15 fractions of baddeleyite were separated from peridotite (71112) from the West Pyrrhotite Lake section, and from chromite-rich peridotite (71064) and gabbronorite (71084) from the Far West Margin section (Fig. 3.3). All separation and analytical procedures were completed at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the University of British Columbia, Vancouver. Samples 71064 and 71084 represent a one metre interval of halved drill core, whereas sample 71112 represents a composite sample of four one metre intervals taken over a 20 m-wide zone of homogeneous peridotite.  Two different baddeleyite separation procedures were used for the three samples. For samples 71112 and 71084, a heavy mineral concentrate was obtained from 5-10 kg of crushed sample following standard density and magnetic separation procedures. For sample 71064, baddeleyite was hand-picked following only magnetic separation procedures. The density separation procedure involved both Wilfley table and heavy liquid techniques. Magnetic separation was completed on a model LI Frantz Isodynamic Separator by progressively decreasing the side tilt (20°, 5°, and 2°) and increasing the amperage (0.6 and 1.8 amps). The highest yield of baddeleyite was typically under the 5° side tilt and 1.8 amps settings. Baddeleyite grains within the Muskox samples are light brown to tan and form euhedral, blade- and needle-shaped crystals with striated crystal faces. They are typically <20 x 50 pm, but smaller fragments can also be observed. Approximately 60-80 individual grains (70-90% of total yield) were hand-picked from each sample using a binocular microscope and -2-30 grains were selected for each fraction to ensure only the clearest and inclusion-free grains were analyzed. Ion exchange column techniques were used to separate U and Pb for 13 fractions, and the remaining two fractions were analyzed without column chemistry to assess whether or not the column chemistry procedure would produce more precise results (Table 3.1). Each fraction was dissolved in concentrated HF and HNO3 with a mixed  233  " 2 3 5 TJ- Pb 205  tracer. Ion  exchange column techniques are those of Parrish et al. (1987). U and Pb were eluted separately and loaded together on a single Re fdament using a phosphoric acid-silica gel emitter. U and Pb isotopic compositions were measured on a modified single collector V G 54R thermal ionization mass spectrometer fitted with a Daly photomultiplier. U and Pb concentrations, isotopic ratios, and apparent ages are shown in Table 3.1. During the analyses, procedural blanks for U and Pb were in the range of <1 pg and 2-5 pg, respectively. The amount of U fractionation was determined directly on individual runs using a double  2 3 3  U-  2 3 5  U  tracer. The Pb isotopic ratios were corrected for a fractionation of 0.0027-0.0037%/amu based on replicate analyses of the NBS-982 Pb standard. All analytical errors were propagated through the age calculations using the method described by Roddick (1987). Concordia intercept ages and associated errors were calculated using Isoplot/Ex 3.00 (Ludwig, 1980; 2003; York, 1969) by both free-fit and forced-zero regression methods and are reported with and without uncertainties in the decay constant in Table 3.2.  Table 3.1: U-Pb ID-TIMS analytical data for baddeleyite from the marginal rocks of the Muskox intrusion Fraction  1  Mass (mg)  U  2  (ppm)  Pb'  3  (ppm)  2 0 6  Pb  204  4  pb  Pb  5  10 2 2  773 843 324  158 171 66  1048 4104 1269  71084 (Far West Margin Gabbronorite) B1,1 4 444 90 5514 440 90 B3, 1 4 4225 257 52 B5, 1 2 2646 272 55 B6, 1 3 2505 B7,2  2  378  71112 (West Pyrrhotite Lake B1,2 3 172 B2-2,3 2 627 B3,5 2 270 B4-1.6 4 317 B5-1.12 2 444  77  2978  Peridotite) 2304 35 127 4612 55 2692 64 6020 3137 90  6  0.02 0.02 0.03 0.03  4.2  0.04 0.07  3.0 3.6 2.7 2.8 3.8  0.03  0.03 0.01 0.04  0.02 0.02 0.02 0.02 0.02  7  Discordance  7  .  ^Pb/^Pb  ^Pb/^U  0.21400 (0.16) 0.21548 (0.08) 0.21771 (0.19)  2.4467 (0.19) 2.4679 (0.14) 2.4945 (0.28)  0.08292 (0.09) 0.08306 (0.08)  1250.1 (3.7) 1258.0(1.9)  1256.5(2.8) 1262.7 (2.0)  1267.3 (3.3) 1270.7 (2.9)  0.21538 (0.09) 0.21712(0.17)  2.4618(0.16) 2.4850 (0.29)  0.08310(0.18) 0.08290 (0.09) 0.08301 (0.21)  1269.8(4.3) 1257.4 (2.0) 1266.6 (3.9)  1270.5 (4.0) 1260.9 (2.3) 1267.7 (4.2)  1271.6 (7.1) 1266.9 (3.7) 1269.5 (8.0/8.1)  0.21516(0.11) 0.21670 (0.11) 0.21499(0.18) 0.21562(0.14) 0.21540 (0.18)  2.4615(0.18) 2.4795 (0.20) 2.4591 (0.33) 2.4663 (0.29)  0.08298(0.11) 0.08298(0.16) 0.08296 (0.26)  1256.2(2.6) 1264.4 (2.6) 1255.4(4.1) 1258.7 (3.2)  1260.8 1266.1 1260.1 1262.2  1268.6 (4.5) 1268.8 (6.2) 1268.2(10.2)  1.1 0.4 1.1  1257.5(4.2)  1261.9(3.6)  1268.2 (9.0/9.1) 1269.3 (7.4)  0.8 1.0  0.21764 (0.24) 0.21611 (0.14)  2.4896 (0.40)  1269.4 (5.6)  1269.0(5.9) 1265.4 (3.6) 1268.8 (5.2) 1258.9 (2.9) 1264.8 (3.9)  1268.3(12.2/12.3) 1272.2 (7.5) 1272.2 (7.5) 1271.7 (5.9) 1270.9 (8.3)  -0.1 0.9 0.2 1.8 0.8  u  0.21735 (0.21) 0.21423 (0.13) 0.21608 (0.13)  m  VB  2.4651 (0.25)  2.4771 2.4888 2.4548 2.4750  (0.25) (0.36) (0.20) (0.27)  0.08296 (0.23) 0.08300 (0.19)  0.08296(0.31) 0.08313(0.19) 0.08305 (0.28) 0.08311 (0.15) 0.08307 (0.21)  1261.3(3.3) 1267.9(4.8) 1251.3(3.0) 1261.1 (3.1)  1  Baddeleyite fraction followed by the number of grains or fragments analysed. N C signifies "no chemistry" fraction.  2  U blank correction of 1 pg ± 20%; U fractionation corrections were measured for each run with a double  3  Apparent ages (±2s,Ma) 207 206 Pb/ U  Pbt V  pb/  100 5.4 6.9  5.6 2.6 4.4 3.4  Isotopic ratios ( ± 1 s , % ) 206 238  (pg)  7*064 (Far West Margin Chromite-rich peridotite) B1.13 13 606 121 15528 6.6 B2, 13 13 347 70 11032 5.4 B3, - 3 0 B5 NC, 4 B6 NC, 5  Th/U  2 3 3  U-  2 3 5  2 0 7  2 3 5  (2.6) (3.0) (4.7) (4.2)  pb/  pb  (%)  1.5 1.1 0.2 0.8 0.2  U spike.  Radiogenic Pb  Measured ratio corrected for spike and Pb fractionation of 0.0028-0.0032/amu ± 20% (Daly collector) determined by repeated analysis of the N B S Pb 982 standard throughout the course of this study. 4  ^ o t a l common Pb in analysis based on blank isotopic composition. 6  Model Th/U; Th derived from radiogenic ^ P b and ^ P b / ^ P b age of fraction.  7  Blank and common Pb corrected; P b procedural blanks were 2-5 pg and U <1 pg. Common Pb isotopic compositions are based on Stacey and Kramers (1975) model P b at the  interpreted age of the rock or the ^ P b / ^ P b age of the fraction.  Table 3.2: Summary of U-Pb age calculation methods Upper intercept (Ma)  2a  free-fit linear regression  1271  6.1 (8.8)  fixed-zero linear regression weighted-mean (2 fractions)  1269 1269  1.7 (5.5) 2.7 (2.9)  71084  free-fit linear regression fixed-zero linear regression  1269 1269  9.7(11) 2.9 (5.9)  63  71112  free-fit linear regression fixed-zero linear regression weighted-mean (2 fractions)  1270 1271 1269  6.4 (7.9) 3.6 (6.3) 3.4 (3.5)  All Samples  free-fit linear regression  1271  fixed-zero linear regression weighted-mean (4 fractions)  1269 1269  4.1 (7.2) 1.4 (5.4) 2.1 (2.4)  Sample  Method  71064  1  2  Lower intercept (Ma)  2a  299  500  MSWD  3  Probability  1.05  0.37  1.06 0.53  0.37  1500  0.01 0.01  0.99 1.00  -204  1100  0.07 0.09 0.09  0.97 0.99 0.97  194  430  0.43 0.45 0.26  0.96 0.96 0.97  4  0.66  All calculations methods are described by Ludwig (2003) and calculated using the Isoplot/Ex 3.00 software. Linear regression methods were completed using the algorithm of York (1969); Weighted mean ("concordia age") method is based on Ludwig (1998). 1  2  The calculated 2 a errors are shown with (in brackets) or without the uncertainty in U-decay constants.  M S W D = mean square weighted deviates. For weighted mean method M S W D is for both concordance and X - Y equivalence of multiple data points. 3  4  Probablity of fit for regression methods; and probability of concordance and X - Y equivalence for weighted mean method.  3.4.2 Trace element and Hf-Nd isotopic compositions Trace element concentrations and Hf-Nd isotopic compositions of 17 samples and 3 duplicates were measured at the PCIGR, University of British Columbia. A l l samples were previously analyzed for major and trace element compositions at A C M E Analytical Laboratories Ltd. and are a subset of the 81 drill core samples discussed in Chapter 2. Samples were selected for trace element and isotopic ratio determination based on the detailed chemical profiles provided in Chapter 2 and thin section observations to include those least affected by post-magmatic alteration or serpentinization. The original sample powders, which were ground at A C M E Laboratories, Vancouver, were re-ground by hand with an agate mortar and pestle to ensure a uniform particle size less than 60 microns. Procedural duplicates were made for three Muskox peridotite samples (71072, 71078, and 71128) to monitor data reproducibility. In addition, two USGS reference materials (G-2 granite; DTS-2 dunite) were analyzed to monitor the accuracy of the concentration results. Both trace element and isotopic compositions for each sample were determined from a single digestion procedure. A l l samples, duplicates, and reference materials were digested within Teflon bombs enclosed in metallic bombs (modified Krogh design) and placed in an oven at 190°C for 120 hrs in HF-HN0 -HC10 (7:1:1) and 24 hrs in 3  4  HC1. Sample weights were 100 mg for rocks with >1 ppm Hf and 150 mg for rocks with <1 ppm Hf. Following this initial multi-acid digestion, the sample solutions were transferred to Savillex™ and dried on a hotplate. Each sample was then re-dissolved in HC1 (4 g) on a hotplate and an aliquot (0.8 g) was removed and placed in a separate Savillex™ for trace element analysis. The remaining sample solution (3.2 g) was kept for isotope ratio determination (see column chemistry procedures below). In preparation for the dilution procedure, the trace element fraction was re-dissolved in HNO3 and then dried. Taking into account the exact weight of the trace element aliquot removed, each sample was diluted by 800 to 2000 times in 1% HNO3 with 1 ppb In depending on the expected elemental concentrations. Trace element concentrations were analyzed on a Thermo Finnigan Element2 highresolution inductively coupled plasma mass spectrometer (HR-ICP-MS). Rare earth elements were measured in high resolution for gabbronorite and country rock samples and low resolution for peridotite samples. U , Pb and Ta were measured in low resolution and all remaining elements in medium resolution for all samples. A l l trace element concentrations are shown in Table 3.3. External calibration and concentration calculations were achieved using a series of six standards obtained from sequential dilution of 1000 ppm High Purity® stock 99  Table 3.3: Trace element concentrations by HR-ICP-MS for marginal rocks of the Muskox intrusion. Sample Site Rock type  Far West Margin (MX03-001) Chromite- FeldFeldrich spathic spathic Peridotite Peridotite Peridotite  Feldspathic Peridotite  Chromite- Chromite- Gabbro- Gabbro- Hornfe rich rich norite norite paragr Peridotite Peridotite  Sampe N o .  71064 28.7  71072a  71072b  71078a 94.7  71082  71084  71094  58.9  71076 81.4  71078b  58.9  94.7  109.1  111.8  120.1  150 1.76  150 0.55 7 na 0.5 0.15 0.093 1.4 2.7  150 0.56 7 na 0.5 0.15 0.095 1.4 2.7  150 1.67  150 1.57  100 2.70  100 • 3.59  30 148 0.2 0.23 0.072 1.1  30 na 0.7 0.21 0.117  45 na 4.6 0.95 0.425 5.9 17.2  64 na 5.9 1.16 0.516 7.2 15.7  100 2.88 82 na 8.3 1.29 0.818 12.0 42.6  6.1 0.8 3.44 4 41 21 0.59 0.89 0.41  100 1.25 13 165 0.6 0.18 0.091 1.4 3.8 8.7 1.1 4.78 19 107 30 0.91 1.20 0.49  30.7 3.8 14.25 70 103 74 2.04 2.88 0.60  31.4 3.8 14.58 22 65 88 2.35 2.95 0.56  76.1 8.6 31.08 38 174 156 3.98 5.20 1.20 4.8 0.74 4.44  1  Depth (m) Weight (mg) C s (ppm)  2  Rb Ba Th U Ta Nb La Ce Pr Nd Pb Sr Zr Hf Sm Eu  25 20 0.54 0.94 0.22  6.0 0.8 3.45 4 42 21 0.60 0.89 0.41  Gd Tb Dy Ho  1.0 0.17 0.91 0.19  1.0 0.18 1.00 0.22  1.0 0.18 1.00 0.22  1.3 0.22 1.40 0.28  Er  0.50 0.44  0.58 0.53 4.5  0.58 0.53 4.6  0.09  Yb Y  30 na 1.1 0.30 0.095 1.2 2.1 5.5 0.8 3.62 17  1.8 5.9 0.9 4.29 44  1.8 1.9 5.7 0.8 4.07 41  46 19 0.65  43 23 0.68  1.13 0.21 1.2 0.22 1.23 0.26  1.10 0.25 1.2 0.21 1.18 0.26  2.6 0.41 2.54 0.51  2.8 0.43 2.58 0.47  0.84 0.74 6.9  0.74 0.61  1.50 1.61 13.1  1.28 1.32 12.7  2.30 2.40  5.1  0.68 0.61 5.5  0.09  0.11  0.08  0.10  0.23  0.18  0.33  0.79  Lu  4.1 0.07  Sc V Co  9.51 85 145  12.2 81 80  10.8 85 79  17.8 139 133  4.30 131 125  9.02 121 100  7.53 64 56  7.77 65  14.0 101  76  40  Cu Zn Ga  702 104 4.5  15 57 4.4  16 55 4.3  270 107 6.9  149 131 6.1  128 105 5.4  373 74 4.9  328 63 4.2  312 57 8.3  na = not analysed <lod = below limit of detection. 1  Sample numbers with " a " and "b" denote complete procedural duplicates.  2  Approximate sample powder weight in milligrams.  22.8  Table 3.3 (continued):Trace element concentrations by HR-ICP-MS for marginal rocks of the Muskox intrusion. Sample Site Rock type  Granitic pod  West Pyrrhotite Lake (MX03-002) Peridotite Peridotite FeldFeldFeldspathic spathic spathic Peridotite Peridotite Peridotite  Olivine Gabbronorite  Gabbro- Gneiss norite  71097  71106  121.8  31.8  C s (ppm)  100 2.03  150 0.21  Rb Ba Th U  91 na 10.0 3.76  5 25 0.3 0.12  Ta Nb La Ce Pr Nd Pb Sr Zr Hf Sm Eu Gd Tb Dy  0.963 6.2 24.9  0.093 1.4 2.2 6.1 0.8 3.58 3 10 21  Sampe N o .  1  Depth (m) Weight (mg)  Ho Er  2  46.1 5.1 18.19 19 245 147 3.68 3.43 0.90 3.2 0.56 3.86 0.73  Lu  2.17 2.47 20.4 0.34  Sc V  7.46 41  Co  17  Cu Zn  174 29 6.4  Yb Y -  Ga  71115 72.5  71122  150 0.28 4 na 0.5 0.14  150 0.36 5 na 0.6 0.15  0.069 1.1 2.7  0.120 1.9 3.4  6.8 0.9 3.88 2 11 21 0.59 0.95 0.35  8.1 1.0 4.38 5 33 25 0.70 1.08 0.41  1.0 0.18 0.97 0.20  1.2 0.20 1.08 0.23  0.63 1.8 0.32 1.93 0.38  0.53 0.47 4.2  0.60 0.53 4.8  1.07 0.97 8.6  0.08  0.08  7.74 108 132  10.3 92  11.5 118  102  103  0.13 17.2 168 110  64  37 62 4.2  238 85 4.8  96 82 8.4  0.63 0.83 0.27 0.8 0.14 0.88 0.17 0.46 0.42 3.8 0.06  90 4.2  113.0  Gneiss  71128a 149.3  71128b  71133  71147  162.8  71138 173.6  71141  149.3  179.3  200.9  100 1.30 11 104  100 1.28  100 2.35  100 1.83  100 1.71  100 4.94  11 99 1.0 0.26  15 na 1.6 0.37  48 na 3.0 0.71  174 na 12.2  0.176 2.9 5.5 13.7 1.8 7.98 3  0.208 3.6 8.3  0.289 3.9 9.3 18.7 2.4 9.52 62 141 61  69 na 11.2 3.28 0.564 6.6 26.3 48.2 5.2 19.62 173  1.0 0.26 0.180 2.9 5.5 13.8 1.8 7.88 3 109 53 1.49 1.94  108 50 1.46 1.87 0.62 1.9 0:32 1.98 0.38 1.05 0.93 8.5 0.14 16.5 164 109  17.8 2.4 10.38 3 120 57 1.49 2.52 0.79 2.7 0.40 2.61  1.66 1.96 0.60  0.48 1.34  0.39  1.20 11.6 0.18 9.88 77  94  46 54  79 7.8  43 4.6  na = not analysed <lod = below limit of detection. 1  Sample numbers with " a " and "b" denote complete procedural duplicates.  2  Approximate sample powder weight in milligrams.  1.9 0.29 1.92 1.06 1.09 9.4 0.17 13.7 167 48 427 124 4.9  166 250  3.56 0.870 9.5 31.3 60.4 7.3 25.84 207 97 248  6.95 3.38 1.03 2.8 0.41 2.53 0.47  6.61 4.41 0.94 3.4  1.44 1.58  1.45 1.62 14.9  13.5 0.23 2.66 19 25  0.48 2.87 0.51  0.24 5.17 47 6  981  21  248 5.8  180 8.8  standard solutions of 1% H N O 3 with 1 ppb In. Data reproducibility was determined from the three procedural duplicates and is shown in Appendix V. Results for USGS reference materials (G-2 and DTS-2) are within error (2a) of the range of previously published values (see Appendix VI) (Robinson et al., 1986; Totland et al., 1992; Govindaraju, 1994; Liang et al., 2000; Raczek et al., 2000; Meisel et al., 2001; Pretorius et al., in press). For comparison of trace element results determined at PCIGR and A C M E Analytical Laboratories Ltd. see Appendix VII. Relative standard deviations for each pair of analyses are typically less than 5% for most elements, however deviations are between 5-15% for Pb, Y, Zr, Nb, and Ta, and up to 20% for Sc. These relatively high uncertainties are the result of a poor analysis of one duplicate (71078a) where the standard deviation determined during the analysis was considerably larger than all other analyses, which may reflect sample inhomogeneity. As a result, this sample has been removed from all plots. The REE (including Nd) were separated from Hf using a Teflon column with Biorad A G 50W-X8 100-200 mesh resin and a progressively increasing concentration of HC1 from 1.5 N to 4.0 N . The Hf separate was then passed through a polypropylene column and a Savillex™ column, using a 0.1 N HF / 0.5 N HC1 solution and Biorad A G 1-X8 100-200 mesh resin, and a 0.3 N HF / 2.5 N HC1 solution and Biorad A G 50W-X8 200-400 mesh resin, respectively. Nd was separated from the REE in a separate quartz column using 0.16 N HC1. The Nd isotopic measurements were made on a Thermo Finnigan Triton-TI thermal ionization mass spectrometer (TIMS) in static mode with relay matrix rotation. The results are shown in Table 3.4. The measured compositions of each sample are the mean of 125-130 analyses. Samples were measured in two separate batches. During the analysis of each batch the La Jolla Nd standard was measured six times giving a mean value of N d / N d = l43  144  0.511857 ± 0.000008 (2a) and 0.511858 ± 0.000006 (2a) for the first and second batch, respectively. The three procedural duplicates are all within analytical error (2a). A l l measurements were corrected for internal mass fractionation using N d / N d = 0.7219. The 146  l44  Nd isotopic compositions of the USGS G-2 reference material are within analytical error (2a) of previously reported results (Weis et al., submitted). Due to very low Nd concentrations (0.01 ppm), the Nd isotopic composition of the DTS-2 reference material was not determined. The Hf isotopic compositions were analyzed in static mode on the PCIGR Nu Plasma multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) in the "dry" plasma mode using a desolvating nebulizer (DSN). Measured ratios and age-corrected values 102  Table 3.4: Hf and Nd isotopic compositions of marginal rocks from the Muskox intrusion. Drillhole  MX03-001 (Far West Margin)  Rock type  Chromite-rich Peridotite  Feldspathic Peridotite  Feldspathic Peridotite  Feldspathic Peridotite  Sample no.  Chromite-rich Peridotite  Chromite-rich Peridotite  Gabbronorite  Gabbronorite  Hornfelsed paragneiss  Granitic pod  71064  71072a  71072b  71076  71078a  71078b  71082  71084  71094  71097  Drilled depth (m)  28.7  58.9  58.9  81.4  94.7  94.7  109.1  111.8  120.1  121.8  Distance (m)  88.3  58.1  58.1  35.6  22.3  22.3  7.9  5.2  -3.1  -4.8  Lu (ppm)  0.07  0.09  0.09  0.11  0.08  0.10  0.23  0.18  0.33  0.34  Hf(ppm)  0.54  0.60  0.59  0.91  0.65  0.68  2.04  2.35  3.98  3.68  Lu/Hf  0.130  0.145  0.147  0.116  0.129  0.145  0.115  0.075  0.082  0.091  0.0184  0.0206  0.0209  0.0164  0.0184  0.0206  0.0163  0.0106  0.0116  0.0130  0.282088  0.282364  0.282375  0.282363  0.282373  0.282369  0.281911  0.281816  0.281646  0.281504  0.000004  0.000016  0.000014  0.000019  0.000008  0.000005  0.000008  0.000006  0.000007  0.000008  0.28163  0.28185  0.28186  0.28196  0.28192  0.28186  0.28151  0.28155  0.28136  0.28118  -11.2  -3.4  -3.3  0.3  -1.1  -3.2  -15.6  -14.0  -20.9  -27.2  tcHUR ( )  2.34  1.65  1.65  1.25  1.37  1.63  2.57  2.15  2.63  3.15  t (Ga)  2.93  2.52  2.53  2.05  2.22  2.50  3.04  2.61  3.01  3.44  Sm (ppm)  0,94  0.89  0.89  1.20  1.13  1.10  2.88  2.95  5.20  3.43  Nd (ppm)  3.62  3.44  3.44  4.78  4.29  4.07  14.25  14.58  31.07  18.19  176  1  2  Lu/ Hf ,77  176  H f /  177  H f  (  m  )  2a 176  H f /  177  H f  (  j  )  Ga  D M  0.259  0.258  0.258  0.251  0.264  0.270  0.202  0.202  0.167  0.188  147  Sm/Nd Sm/ Nd  0.1564  0.1559  0.1559  0.1517  0.1597  0.1634  0.1221  0.1223  0.1011  0.1138  143  Nd/  0.511948  0.512196  0.512188  0.512118  0.512171  0.512177  0.511319  0.511378  0.511088  0.511086  0.000006  0.000011  0.000007  0.000008  0.000012  0.000010  0.000007  0.000006  0.000006  0.000006  0.51064  0.51090  0.51089  0.51085  0.51084  0.51081  0.51030  0.51036  0.51024  0.51014  ENd (0  -6.9  -2.0  -2.1  -2.8  -3.1  -3.6  -13.6  -12.5  -14.7  -16.8  tcHUR (Ga)  2.59  1.65  1.68  1.76  1.92  2.10  2.68  2.57  2.46  2.84  toM(Ga)  '3.17  2.50  2.52  2.53  2.75  2.93  3.03  2.93  2.78  3.13  ,44  144  N d (m)  2a ,43  Nd/  144  N d (i)  All Hf ratios determined by M C - I C P - M S , N d ratios determined by TIMS, and concentration data by H R - I C P - M S at the P C I G R , U B C . Initial ratios calculated a 1270 M a using A144Nd = 6.54x10-12 (Lugmair & Marti, 1978) and A176Lu = 1.93x10-11 y-1 (Sguigua et al., 1982). Epsilon values and model ages calculatec using 177Hf/176Hf R = 0.282772 and 176Lu/177Hfc uR= 0.0332 (Blichert-Toft & Albarede, 1997), 177Hf/176Hfc = 0.28325 and 176Lu/177Hfb = 0.0384; and 143Nd/144NdcHUR = 0.512638 and 147Sm/144Ncb uR = 0.1967 (DePaolo & Wasserburg, 1976), 143Nd/144Ncb = 0.51314 and 147Sm/144Ncb = 0.2137. CHU  H  M  H  'Procedural duplicates are denoted ' a ' and 'b'. 2  Drilled distance in metres from the outer intrusive contact.  M  M  M  Table 3.4 (continued): Hf and Nd isotopic compositions of marginal rocks from the Muskox intrusion. Drillhole Rock type Sample no.  a  Drilled depth (m) Distance (m)  MX03-002 (West Pyrrhotite Lake) Feldspathic Peridotite Peridotite Peridotite  Feldspathic Peridotite  Feldspathic Peridotite  Olivine gabbronorite  Gabbronorite  Gneiss  71106  71115  71122  71128a  71128b  71133  71138  71141  31.8  72.5  113.0  149.3  149.3  162.8  173.6  179.3  200.9  Gneiss .  71147  145.2  104.5  64.0  27.7  27.7  14.2  3.4  -2.3  -23.9  Lu (ppm)  0.06  0.08  0.08  0.13  0.14  0.18  0.17  0.23  0.24  Hf(ppm)  0.63  0.59  0.70  1.49  1.46  1.49  1.66  6.95  6.61  Lu/Hf  0.097  0.132  0.121  0.088  0.094  0.119  0.102  0.033  0.036  0.0137  0.0187  0.0171  0.0125  0.0134  0.0168  0.0145  0.0047  0.0051  0.282340  0.282313  0.282350  0.282317  0.282318  0.282292  0.282157  0.281246  0.281394  0.000005  0.000008  0.000004  0.000008  0.000009  0.000009  0.000018  0.000004  0.000004  0.28200  0.28185  0.28192  0.28201  0.28199  0.28187  0.28180  0.28113  0.28127  ,76  Lu/  176  1T7  b  Hf  H f /  17?  H f  H f /  177  H f  (  m  )  2a 176  (  j  )  E fO)  1.8  -3.5  -0.8  2.1  1.4  -2.6  -5.3  -29.0  -24.1  W(Ga)  1.14  1.61  1.34  1.13  1.17  1.50  1.67  2.70  2.48  tDM (Ga)  1.88  2.41  2.15  1.83  1.89  2.25  2.31  2.99  2.81  Sm (ppm)  0.83  0.95  1.08  1.87  1.87  2.52  1.96  3.38  4.41  Nd (ppm)  3.58  3.88  4.38  7.98  7.98  10.38  9.52  19.62  25.84  Sm/Nd  0.232  0.244  0.246  0.234  0.234  0.243  0.206  0.172  0.171  0.1402  0.1476  0.1490  0.1413  0.1413  0.1469  0.1243  0.1041  0.1031  0.512195  0.512190  0.512190  0.512168  0.512185  0.512167  0.511754  0.511086  0.511121  2a  0.000008  0.000006  0.000006  0.000006  0.000006  0.000006  0.000006  0.000007  0.000006  " W ' N d (i)  0.51103  0.51096  0.51095  0.51099  0.51101  0.51094  0.51072  0.51022  0.51026  E d (i)  0.5  -0.8  -1.0  -0.2  0.2  -1.1  -5.5  -15.3  -14.4  Uur(Ga)  1.20  1.39  1.43  1.29  1.25  1.44  1.86  2.54  2.46  toM (Ga)  1.98  2.20  2.25  2.06  2.03  2.23  2.37  2.85  2.78  H  Sm/ Nd  1 4 7  w  i «  N  d  /  « 4  N  N  d  (  m  )  All Hf ratios determined by M C - I C P - M S , Nd ratios determined by TIMS, and concentration data by H R - I C P - M S at the P C I G R , U B C . Initial ratios calculated a 1270 M a using A144Nd = 6.54x10-12 (Lugmair & Marti, 1978) and A176Lu = 1.93x10-11 y-1 (Sguigua et al., 1982). Epsilon values and model ages calculate using 1 7 7 H f / 1 7 6 H f = 0.282772 and 176Lu/177Hfc uR= 0.0332 (Blichert-Toft & Albarede, 1997), 177Hf/176Hfc = 0.28325 and 176Lu/177Hfc = 0.0384; and 143Nd/144NdcHUR = 0.512638 and 147Sm/144Ncfc uR = 0.1967 (DePaolo & Wasserburg, 1976), 143Nd/144Ncb = 0.51314 and 1 4 7 S m / 1 4 4 N c b = 0.2137. CHUR  H  M  H  'Procedural duplicates are denoted 'a' and 'b'. 2  Drilled distance in metres from the outer intrusive contact.  M  M  M  are shown in Table 3.4. The measured compositions of each sample are the mean of 25-30 cycles. The measured Hf isotopic ratios were corrected for interferences by monitoring Lu and Yb beams throughout each analysis. Samples were measured in three separate batches. Replicate measurements of the Hf JMC 475 in-house standard gave a mean value of 176  Hf7 Hf = 0.282148 ± 0.000006 (2a on 10 measurements) for the first batch and 0.292151 ± l77  0.000007 (2a on 11 measurements) for both the second and third batches; the values are within the range of previously published values (Blichert-Toft et al., 1997; Chauvel & Blichert-Toft, 2001; Goolaerts et al., 2004). The three procedural duplicates are within analytical error (2a). All reported values were normalized to H f / H f = 0.282160 as suggested by Vervoort & 176  177  Blichert-Toft (1999). The Hf isotopic compositions of the USGS G-2 reference material are within analytical error (2a) of previously reported results (Weis et al., submitted). As a result of the very low Hf concentrations (<0.004 ppm) of the DTS-2 reference material, its Hf isotopic compositions have not been previously published and therefore the accuracy of the results for this material cannot be verified.  3.5 RESULTS 3.5.1 U-Pb geochronology The U-Pb concentrations and isotopic compositions of baddeleyite from two peridotites and one gabbronorite sample from the marginal rocks of the Muskox intrusion are shown in Table 3.1 and displayed on concordia diagrams in Fig. 3.4. The concentrations of U and Pb for each fraction range from 170-840 ppm to 55-160 ppm, respectively. The high Pb/ Pb values 206  204  (1000 to 15,000) indicate a negligible contribution of initial common Pb. The U-Pb data for all fractions from all three samples plot near concordia (<2% discordance), which is consistent with closed-system behavior with respect to U-loss or Pb-gain since the time of crystallization (Fig. 3.4). Table 3.2 summarizes the different U-Pb age calculation methods applied to each sample as discussed below. Sample 71064 was collected from a chromite-rich peridotite layer within the layered series at the Far West Margin section (Fig. 3.2 & 3.3). The chromite-rich peridotite consists of cumulus olivine and chromite enclosed within orthopyroxene oikocrysts (up to 2 cm across) and minor interstitial plagioclase and phlogopite. The U-Pb data for five fractions of baddeleyite are nearly concordant (<1.5% discordance) with apparent  Pb/ Pb ages ranging  from 1267 to 1271 Ma (Table 3.1). Linear regression through the data points results in an 105  0.220  0.220 (a) 71064 Chromite-rich Far West Margin  (b) 71084 Gabbronorite Far West Margin  Peridotite  280  0.218  H  0.216  H 0.216  0.214  0.218  1  0.214  Free-regression Fixed-regression 0.212 2.42  2.44  2.46  2.48  207  Pb/  235  2.50  2.52 2.42  2.44  U  2.46 2 0 7  2.48  Pb/  2 3 5  2.50  0.212  2.52  U  0.220  0.220 (d) All fractions 71064, 71084, 8. 71112^  0.218  0.216  0.218  V  H  0.214  0.216  H 0.214  0.212 2.42  2.44  2.46 M 7  2.48  Pb/  2 3 5  U  2.50  2.52 2.42  2.44  2.46 2 0 7  2.48  Pb/  2 3 5  2.50  2.52  U  Fig. 3.4: Concordia diagrams showing U-Pb geochronologic results for baddeleyite fractions separated from three samples at two different locations within the Muskox intrusion, (a) Chromite-rich peridotite (71064), Far West Margin; (b) Gabbronorite (71084), Far West Margin; (c) Peridotite (71112), West Pyrrhotite Lake; (d) All samples (71064, 71084 & 71112). Individual fractions are represented by a 2a error ellipse and are labelled B l , B2, etc. Diagrams were made with Isoplot/Ex 3.0 including the error on concordia and using both free-fit and fixed-zero regression methods, as indicated. See text for interpretation of results.  0.212  upper intercept with concordia at 1271 ± 6 Ma (2c) using a free-fit regression method and 1269 ± 2 (2a) Ma using a forced-zero regression method (Table 3.2; Fig. 3.4a). The weightedmean of two concordant fractions gives an apparent age of 1268 ± 3 Ma (2a), which is considered the best estimate for the crystallization age of this chromite-rich layer in the Muskox intrusion. Sample 71084 was collected from a gabbronorite unit within the marginal zone of the intrusion at the Far West Margin (Fig. 3.2 & 3.3). The gabbronorite consists of cumulus orthopyroxene (and minor clinopyroxene) that partially enclose subhedral calcic-plagioclase laths and interstitial phlogopite, sodic-plagioclase, and minor granophyre. The U-Pb data for five baddeleyite fractions are nearly concordant (<1.0% discordance) and all give apparent "?fi7 zu  7fl/i  'Pb/ Pb ages of 1268 Ma. Linear regression through the data points intercepts concordia at zuo  1269 ± 9 Ma (2a) using a free-fit regression and 1269 ± 3 (2a) Ma using a forced-zero regression (Table 3.2; Fig. 3.4b). Because all data points are nearly equivalent and plot close to concordia, the free-fit regression results in large uncertainties. Therefore, the intercept with concordia using the forced-zero regression method is interpreted as the crystallization age of the sample, which is within error of the interpreted crystallization age of the chromite-rich peridotite layer (sample 71064). Sample 71112 was collected near the base of the intrusion from the innermost part of the marginal zone at West Pyrrhotite Lake (Fig. 3.2 & 3.3). The peridotite consists of closelypacked cumulus olivine enclosed within orthopyroxene and clinopyroxene oikocrysts. Plagioclase and phlogopite are minor interstitial phases. The U-Pb data for five fractions of ?(Y7  baddeleyite are nearly concordant (<2.0% discordance) with apparent  70ri  Pb/ Pb ages ranging  from 1268 to 1272 Ma (Table 3.1). Linear regression through the data points gives an upper intercept with concordia at 1270 ± 6 Ma (2a) using a free-fit regression and 1271 ± 4 Ma (2a) using a forced-zero regression (Table 3.2; Fig. 3.4c). The weighted-mean of two concordant fractions gives an apparent age of 1269 ± 3 Ma (2a), which is considered the best estimate for the crystallization age of the peridotite and is within error of the interpreted crystallization ages of both the gabbronorite and chromite-rich peridotite samples discussed above. The interpreted crystallization ages of each sample are within analytical uncertainty and therefore all data can be treated together. Linear regression through all 15 baddeleyite fractions gives an upper intercept with concordia at 1271± 4 Ma (2d) using a free-fit regression and 1269 ± 5 Ma (2a) using a forced-zero regression (Table 3.2; Fig. 3.4d). If it is 107  assumed that each of the samples crystallized contemporaneously and disregard fractions where the grains have experienced minor Pb loss, then the best estimate for the crystallization age of the Muskox intrusion is 1269 ± 2 Ma based on four concordant analyses, which is within error of a previously reported U-Pb age of 1270 ± 4 Ma (baddeleyite and zircon) by LeCheminant & Heaman (1989) for a pyroxenite layer within the upper part of the layered series of the Muskox intrusion.  3.5.2 Trace element variations The stratigraphic variations in parent-daughter elemental concentrations and ratios for the SmNd and Lu-Hf systems from both the West Pyrrhotite Lake and Far West Margin sections are shown in Fig. 3.5. At West Pyrrhotite Lake the abundances of incompatible trace elements (Sm, Nd, Lu, Hf) are constant within peridotite and then progressively increase through the feldspathic peridotite and olivine gabbronorite units (Fig. 3.5). This trend is expected from the progressive increase in the amount of postcumulus phases (pyroxene and plagioclase) at the expense of olivine, because the partition coefficients for incompatible trace elements in pyroxene and plagioclase are much larger than those for olivine (e.g. McKenzie & O'Nions, 1991). At the Far West Margin, trace element abundances are relatively constant within both chromite-rich horizons and feldspathic peridotite, with the exception of a slight relative increase within the lowermost feldspathic peridotite sample (Fig. 3.5). The Sm/Nd values are relatively high and constant within the peridotites at both sections and then decrease within gabbronorite towards the values typical of the adjacent country rocks. This shift is consistent with the effects of crustal contamination. The Lu/Hf values are variable within peridotites at both locations. The reason for this is uncertain however. It may reflect the heterogeneous distribution of accessory phases (baddeleyite?) that crystallized from local pockets of extremely fractionated interstitial liquids. Alternatively, fluctuations in this ratio may be the result of slight mobility of Lu and Hf during post-crystallization alteration/metasomatism (i.e. high Lu/Hf in the stratigraphically lower serpentinized peridotite sample from West Pyrrhotite Lake section). Primitive mantle-normalized trace element patterns and chondrite-normalized rare earth element (REE) patterns for marginal rocks from West Pyrrhotite Lake and Far West Margin are shown in Fig. 3.6. A l l intrusive rocks at both sections are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE) relative to heavy rare earth 108  (a) West Pyrrhotite Lake Nd (ppm) •o  E ~ 120 U co 4-* C  S  80  E o  k_ 40 **-  Hf(ppm)  20  10  160  30  Nd • Sm O  2 •  2a  4  o  160  Hf • Lu O  2o I—I  D  120  Peridotite  •o  ST  sr  3 O CD  80  4 Feldspathic Peridotite  40  0>  ma  o c  6  EU  Ol Gbnr  0  - D -  •  -40 0  2  4  0.16  0.20  Sm(ppm)  0.24  0.0  0.1  SrrVNd  3  r-t-  ra  Qtz-feldbio Gneiss  O  3 o o  0.2  0.02  0.06  Lu (ppm)  0.10  a  -40 0.14  Lu/Hf  (b) Far West Margin Nd (ppm) 10  100 Chr-rich Peridotite  JL  80  §  60 Feldspathic  20  Hf(ppm)  Nd • Sm o  o •  2  30  4  100 Hf • Lu O  2a  2a 80  o sr  u  u I  • a  40 Chr-rich Peridotite  20  b  Gbnr Sulphidic Paragneiss  o»  •  3 O IB  40  =T o 3 o o  20  o  Peridotite  E  2  60  3  o  A 1 •  Eta  ft  -20 5  Sm (ppm)  0.16  0.20  0.24  SrrVNd  0.0  0.2  Lu (ppm)  0.04  0.08  0.12  —I-20 0.16  Lu/Hf  Fig. 3.5: Parent-daughter (Sm-Nd, Lu-Hf) elemental concentrations and ratios for the (a) West Pyrrhotite Lake and (b) Far West Margin sections of the Muskox intrusion. Elemental concentrations for Sm (open symbols) and Nd (closed symbols), and for Lu (open symbols) and Hf (closed symbols), are plotted within the same graph. Abbreviations: Chr-rich = chromite-rich; Ol Gbnr = olivine gabbronorite, Gbnr = gabbronorite, and Qtzfeld-bio = quartz-feldspar-biotite. Distance from contact = distance from contact in metres along the drill hole. Average analytical error (2a) is equal to, or less than, symbol size unless otherwise shown.  109  1000  CD  1  100  CD  E  CD > •I  a. ~cB  10  CL  E  CD  -•— Peridotite —•— Feldspathic Peridotite -±— Gabbronorite —•— Olivine Gabbronorite 0.1  -I  •  1  1  1  1  I  • Qtz-feld-bio Gneiss  -  —i  L_  1  1  Lower Copper Creek Fm. Mackenzie Dikes 1  1  1  1  1  1  i  Cs Rb Th U K Nb Ta La Ce Pr Sr Nd Zr Hf Sm Ti Eu Gd Tb Dy Ho Er Yb Y Lu 1000  -I  1  i  I  r-  i  (b) Far West Margin 0)  |  100  CD  >  E CO CO  Chromite-rich Peridotite Feldspathic Peridotite 0.1  I  1  1  1  1  I  Gabbronorite Hornfelsed paragneiss L-  _1  I  I  Lower Copper Creek Fm. - ; Mackenzie Dikes  L_  Cs Rb Th U K Nb Ta La Ce Pr Sr Nd Zr Hf Sm Ti Eu Gd Tb Dy Ho Er Yb Y Lu Fig. 3.6: Primitive mantle-normalized trace element patterns of all samples from the (a) West Pyrrhotite Lake and fb) Far West Margin sections of the Muskox intrusion. Chondrite-normalized rare earth element patterns are shown in the insets. Element incompatibility increases to the left in each diagram and normalizing values are from McDonough & Sun (1995). The shaded region represents the range observed in basalts from the Copper Creek Formation (Griselin et al., 1997) and the region between solid and dashed lines represents that of the Mackenzie dikes (Baragar et al., 1996). A l l samples from both sections, including the peridotites, are relatively enriched in LREE and LILE and have prominent Nb-Ta depletions. The Lower Copper Creek Formation and Mackenzie dikes have comparable enriched patterns and Nb-Ta depletions.  elements (HREE). The degree of enrichment within the Muskox intrusion rocks is lowest in peridotite, feldspathic peridotite, olivine gabbronorite, and chromite-rich peridotite (La/Yb(pm)= 2.5 to 4.5). The gabbronorites have more enriched patterns (La/Yb(pm) = 5.0 to 7.7) approaching those of the crustal rocks (La/Yb(pm) = 4.5 to 7.7). The increased degree of trace element enrichment within the gabbronoritic rocks at the margin is consistent with the addition of crustal material. The shapes of the trace element patterns observed for the intrusive rocks are broadly similar to those of the Mackenzie dikes (Baragar et al., 1996) and Coppermine River flood basalts (Griselin et al., 1997), especially when compared to the gabbronorites. All intrusive rocks and crustal rocks at both sections, with the exception of the chromite-rich horizons, are relatively depleted in Nb-Ta (Fig. 3.6). This signature is typical of crustal rocks and can be used as a proxy for crustal contamination within mantle-derived basaltic rocks (e.g. Rudnick & Fountain, 1995). The fact that Nb-Ta depletion is observed even within the peridotites may reflect contamination of the Muskox magmas prior to emplacement (see discussion). The chromite-rich peridotite horizons have relatively flat LREE patterns compared to the other peridotite samples, which likely is a consequence of the relatively high modal abundance of orthopyroxene in these samples (e.g. McKenzie & O'Nions, 1991).  3.5.3 Hf-Nd Isotopic Variations Age-corrected (1270 Ma) epsilon Hf-Nd values for samples from both the West Pyrrhotite Lake and Far West Margin section are plotted against the distance from the margin in Fig. 3.7. The peridotite and olivine gabbronorite samples from the West Pyrrhotite Lake section have a relatively restricted range in initial SHf (+2 to-4) and 8Nd (-1.0 to 0.5). These results overlap with previously published results for the overlying layered series for em (Stewart & DePaolo, 1996) and unpublished  results from Purves (2005). The gabbronorite samples within 10 m  of the margin however have more negative initial SHf (-2.5 to -5.0) and initial £Nd (-1.0 to -5.5) values. The crustal rocks are characterized by very negative 6Hf (-24 to -29) and  values (-  14 to -15) that are consistent with their relatively low Lu/Hf and Sm/Nd, and time-integrated enrichment of Hf relative to Lu and Nd relative to Sm since formation of these rocks (Fig. 3.5). The shift to more negative values within the gabbronorites coincides with the appearance of both granophyre and euhedral orthopyroxene. The feldspathic peridotite and the lower chromite-rich peridotite samples at the Far West Margin section have initial 6Hf (0 to -3.0) and ill  (a) West Pyrrhotite Lake 160  ^  •  120-j Peridotite  c 0 o E o i_ 0)  o c  •  2o H  •  2a h—1  •  •  •  •  • •  •  80 J  40 J  160  O  120 5T f*  80 Feldspathic Peridotite  3 V)  "cTGbnr" Gbnr  D  Feld-BioQtz Gneiss  JP • .  •  •  .  _ _• A  •  A  1•  •  P  •  -*  3 3  * _  :  0) 3 O (D  40  o o  3 0)  o  •  •  -40  -40 0  10  20  30  40  0  5  Th/Yb(pm)  10  -30  -20  -10  La/Yb(pm)  t  0 -20  -10  0  ENd(t)  m )  (b) Far West Margin 100  E. U ro c o  u  80  100 Chr-rich Peridotite  o  60 Feldspathic Peridotite  | 40 »*—  Q) u £  CO m  5  Chr-rich Peridotite 20  „ -20  2a M  o  •  •  •  • o  2a r—1  80  •  60  40  c o  o  20  o  3 o o  ST  a  A  A  Sulphidic Paragneiss  • •  0  Gbnr  o  0  LTD  - 5  20  5  o-  a  a  0  • a  I  -20 0  10  Th/Yb(pm)  10  -30  -20  La/Yb (pm)  -10  0 -20  c H(t)  -10  0  £ Nd(t)  Fig. 3.7: Stratigraphic variations in Th/Yb(pm), La/Yb(pm), 8Hf(t), and eNd( ) values for the (a) West Pyrrhotite Lake and (b) Far West Margin sections of the Muskox intrusion, where (pm) refers to the primitive-mantle normalized ratio and (t) equals 1.27 Ga. Symbols and abbreviations are the same as for Fig. 3.6. Uncertainty in trace element ratios is estimated from the average analytical uncertainty of all samples. The shaded region indicates the range in published initial (Stewart & DePaolo, 1996) and reported initial enf (Purves et al., 2005) for rocks of the overlying layered series for comparison. The shift towards lower Th/Yb(pm) and La/Yb(pm), and higher 8 ^ ) and £Nd(t> at the transition from peridotite to gabbronorite within -10 m from the contact is consistent with the affects of local crustal contamination. The Enf(t) and Em(t) values within the peridotites are relatively constant and are comparable to those of the layered series, with the exception of the upper chromite-rich peridotite at the Far West Margin section. The relatively low Th/Yb(pm) and La/Yb(pm), and high SHf(t) and e d ) values within the peridotites indicate that they formed from magmas that were not exposed to local crustal contamination. t  H  t  N  (t  112  initial  SN<J  (-2.0 to 2.8) values that are within error of the initial epsilon values reported for the  layered series (references noted above). The chromite-rich peridotite sample at the top of the section, however, has considerably more negative initial  £Hf  and  6N<J  values (-11 and -7,  respectively) than the other peridotites. As with the West Pyrrhotite Lake section, the gabbronorite samples within the Far West Margin section have low initial Enf (-14 to -15 ) arid initial  (-12 to -13) values and likely represent strongly contaminated marginal rocks.  3.5.4 Alteration/metasomatic effects? Although the HFSE and HREE (including Sm-Nd and Lu-Hf) are typically considered to be immobile during hydrothermal alteration, several studies of altered komatiitic and basaltic rocks (e.g. Lahaye et al., 1995; Polat et al., 2003) have demonstrated that this is not always the case and, importantly, perturbations in the values of Rb/Sr, Sm/Nd, and Lu/Hf correlate with anomalous isotopic compositions. Given the presence of secondary mica in the chromite-rich peridotite horizons, the anomalous isotopic and trace element compositions of sample 71064 need to be evaluated. Sample 71064 was collected from a chromite-rich peridotite horizon within the upper part of the Far West Margin section (Fig. 3.3). The sample has anomalously low initial e d (-6.9), initial e f (-11.2), and La/Yb(pm) (3.0), and high Th/Yb(pm) (2.6) values N  H  and positive K anomalies compared to those of all other peridotite samples (Fig. 3.6 & 3.7). The elevated Th/Yb and K values are a typical feature of both chromite-rich horizons, which suggests that K, and possibly other LILE, may have been added during or after serpentinization. However, given that the Sm/Nd and Lu/Hf ratios of the chromite-rich peridotite are comparable to those of the adjacent peridotites (Fig. 3.5), it is suggested that the relatively low initial epsilon values of the chromite-rich peridotite are reflective of the magma from which they crystallized and have not been affected by secondary alteration processes.  3.6 DISCUSSION Using the new U-Pb geochronologic, trace element, and Hf-Nd isotopic results obtained during this study, below we provide constraints on (1) the magnitude and spatial extent of crustal contamination along the basal margin of the Muskox intrusion, (2) the timing of emplacement of the Muskox intrusion and the genetic relationship between the Muskox intrusion and the other elements of the Mackenzie magmatic event, especially the overlying Coppermine River basalts, and (3) the composition of the mantle source for the Muskox magmas and potential influence of crustal contamination prior to emplacement within the Muskox chamber. Finally, we provide a brief synthesis of the evolution of the Mackenzie event based on the results of this study combined with previous investigations of the different Mackenzie components.  3.6.1 Spatial extent and degree of crustal contamination within marginal rocks of the Muskox intrusion Variations in initial gHf and 8N<I values and incompatible trace element ratios from the marginal zone of the Muskox intrusion provide important constraints on the extent and degree of crustal contamination that occurred along the basal contact of the intrusion, which has important implications for the emplacement history of the Muskox intrusion and the potential for magmatic sulphide mineralization. At both West Pyrrhotite Lake and Far West Margin, the gabbronoritic marginal rocks have more negative initial e f and ENd values and higher H  Th/Yb(pm) and La/Yb(pm) values than the directly overlying peridotites (Fig: 3.7). Thus, the chemical effects of crustal contamination are restricted to the orthopyroxene- and granophyrebearing rocks within 10 m from the outer contact. A similar thickness of contaminated gabbronorite was noted by Francis (1994) in his study of marginal zone rocks along the eastern margin of the intrusion. This limited extent of contamination recorded within the gabbronoritic marginal rocks is the result of local contamination of the magmas (potentially partially solidified) along the outer walls of the Muskox magma chamber. The addition of siliceous material led to a local increase in silica activity, which stabilized orthopyroxene over olivine (e.g. Irvine, 1970). Because of the heat loss to the surrounding rocks the contaminated magmas would have solidified rapidly (see Chapter 2) and would have prevented subsequent magma influxes from interacting with the surrounding crustal rocks. This explains the uncontaminated signatures within the peridotites at both sections and throughout the layered  series. An apparent exception to this is the anomalously low initial EHf and 8Nd values within the upper chromite-rich peridotite at the Far West Margin. This peridotite may represent a cumulate layer that accumulated from an influx of contaminated magma during construction of this part of the marginal zone, or potentially assimilation of overlying roof rocks. The approximate amount of crustal contamination within the gabbronoritic marginal rocks can be estimated using binary mixing relationships (Fig. 3.8). As a parental magma composition the isotopic composition of a relatively uncontaminated peridotite from the West Pyrrhotite Lake (initial £Hf= 1.3; initial ENd = 0.2) and Far West Margin sections (initial £ H T  =  -  3; initial E d = -2) and the trace element concentrations of a lower Copper Creek Formation N  basalt from the overlying Coppermine River basalts are used (Table 3.5). The contaminant, in terms of isotopic and trace element composition, is given by the average country rock composition at each section. The binary mixing calculations assume simple end-member mixing with no associated fractional crystallization and provide a first-order estimate of the different amounts of crustal material added to the Muskox magmas at the two studied locations. In Fig 3.8, the initial enf and ENd isotopic compositions of the marginal rocks from the Muskox intrusion and country rocks are plotted against two different incompatible element ratios (Th/Yb(pm), Sm/Ti(pm)) that have different sensitivities to contamination and that show the effects of assimilating host rocks of different compositions. In general, rocks from the thin gabbronoritic subzone plot along the mixing arrays, which is consistent with contamination by local assimilation of the adjacent crustal rocks. The calculated degree of contamination within the gabbronorite at West Pyrrhotite Lake is -20% with respect to the Sm-Nd isotopic system and -40% with respect to Lu-Hf. For the gabbronorite at Far West Margin, the degree of contamination is considerably higher at >80% for both the Sm-Nd and Lu-Hf systems. As documented in Chapter 2, the difference in amount of contamination at the two studied regions likely reflects the greater ability of the Muskox magmas to assimilate the paragneiss at the Far West Margin than the quartz-feldspar-biotite gneiss at West Pyrrhotite Lake. The actual composition of the contaminant could have been derived through bulk assimilation, partial melting, and/or diffusive exchange with the wall rocks during the formation of the Muskox magma chamber. Stewart & DePaolo (1992) showed that diffusive exchange between a lens of melted roof rock and underlying basaltic magma could explain the decoupling of Nd and Sr isotopic systematics; a consequence of the high relative diffusivity of Sr relative to Nd in silicate melts. Assuming that Hf diffusivity is comparable to that of Nd, diffusive exchange is  10  20  30  0.0  1.0  Th/Yb(pm) Far West Margin  West Pyrrhotite Lake  Chromite-rich peridotite  •  Peridotite  •  Feldspathic peridotite  •  Feldspathic Peridotite  A  Gabbronorite  A  Gabbronorite  •  Hornfelsed Paragneiss  •  Qtz-bio-feld Gneiss  Mixing (10% increments)  3.0  4.0  5.0  6.0  Sm/Ti(pm)  o  —  2.0  Coppermine River Basalts Lower Copper Creek Middle Copper Creek C_~)  Upper Copper Creek Husky Creek  ——- Mixing (10% increments)  Fig. 3.8: Initial eHf(t) and eNd(t) isotopic compositions vs. selected incompatible trace element ratios for marginal rocks from the Muskox intrusion showing the results of binary mixing calculations. Mixing lines are calculated for the parental magma to the marginal zone using the isotopic composition of a relatively uncontaminated peridotite from each respective locality and the trace element composition of a lower Copper Creek Formation basalt for the parental magma composition, and the isotopic composition and trace element abundances of the average wall rock composition at each locality. Tick marks along curves indicate the addition of crustal material at increments of 10%. Gabbronorite samples plot along the mixing lines between the assumed parental magma composition and the average wall rock sample at both the West Pyrrhotite Lake and Far West Margin sections.  116  Table 3.5: Composition of Muskox magmas and potential contaminants used in mixing calculations. Section Endmember Th (ppm) Yb Sm Ti  1  Hf(t) Nd(t)  E  e  West Pyrrhotite Lake Magma Contaminant 4.2 11.6 2.8 1.6 8.5 3.9 28100 4550 1.3 -27  Far West Margin Magma Contaminant 4.2 9.2 2.8 2.4 8.5 4.3 28100 3880 -2.1 -16  0.2  -3.2  -15  -24  Composition of Muskox magma estimated from the trace element abundances of a lower Copper Creek basalt (Griselin et al., 1997) and the isotopic composition of Muskox marginal zone rocks (this study); Composition of the contaminant is taken as the average country rock composition at each studied section.  unlikely to produce variations in the Nd and Hf isotopic compositions of the marginal rocks. Francis (1994) proposed that the contamination process within the marginal rocks of the Muskox intrusion may have been selective, because the estimated level of enrichment within the contaminated rocks depended on which trace element ratio was used. For example, when using LILE/HFSE the level of enrichment was considerably greater (30-50%) than using LREE/HFSE (10-30%). We observe a similar relationship and estimate variable degrees of contamination within the gabbronoritic marginal rocks with respect to Nd and Hf isotopic compositions and different trace element ratios. In plots of K/Yb vs. K/Ti the estimated degree of contamination is 50%, and using Sm/Ti vs. K/Ti it is approximately 30% (not shown). This feature is likely the combined result of the relative compatibilities between LILE vs. HREE during partial melting of the crustal rocks, and also the preferred diffusive exchange for the most incompatible elements as documented by Stewart & DePaolo (1992). The presence of granophyre globules within the gabbronorites at both sections indicates that the contaminated signature was in part derived directly through the addition of partial melts from the adjacent rocks that did not fully mix with the magmas along the outer wall of the Muskox chamber. The appearance of early-forming cumulus orthopyroxene indicates that contamination also involved some amount of complete mixing of crustal material with the Muskox magmas along the contact region.  3.6.2 Temporal relationships and isotopic compositions of the Muskox intrusion, Coppermine River basalts, and Mackenzie dikes The U-Pb geochronologic and Nd isotopic compositions from the marginal rocks of the Muskox intrusion determined in this study can be used to better constrain the genetic relationships between the different members of the Mackenzie magmatic event. U-Pb ages obtained in this study indicate that rocks within the marginal zone (including contaminated gabbronorite) crystallized within error of each other at -1269 Ma. They are also within error of a previous U-Pb age (baddeleyite and zircon) of 1270 ± 4 Ma reported by LeCheminant & Heaman (1989) for a feldspathic pyroxenite layer within the layered series, confirming that the entire Muskox intrusion crystallized within a few million years (Fig. 3.9). This is consistent with the estimated duration of emplacement for the Muskox intrusion of 50,000-100,000 years, as predicted by Stewart & DePaolo (1992) on the basis of the timescale for diffusive isotopic exchange between basaltic magma within the chamber and an overlying silicic magma derived 118  Mackenzie Magmatic Event  0  L  •  Muskox (this study)  •  Muskox pyroxenite  •  Mackenzie dike (composite)  •  Mackenzie dike (single)  A  Bear River dike 1 & 2  A  Bear River dike 3  J  this study it  Mackenize Components  Fig. 3.9: Compilation of precise U-Pb ages for Mackenzie magmatic event samples. The ages are concordia-intercept ages for the Muskox intrusion (this study; and LeCheminant & Heaman, 1989), Mackenzie dikes (LeCheminant & Heaman, 1989; 1991), and Bear River dikes (Schwab et al., 2004). Error bars are the reported 2a analytical uncertainties. The shaded region represents the weighted mean of 4 concordant fractions from the two studied sections and the associated 2a uncertainty as described in the text.  through melting of the overlying roof rocks. Precise U-Pb concordia-intercept ages for the emplacement of the Mackenzie dikes (1267 ± 2 Ma; LeCheminant & Heaman, 1989) and two dikes from the Bear River region of the Yukon Territory (1268 ± 2 Ma; Schwab et al., 2004) overlap with the crystallization age of the Muskox intrusion (1269 ± 2 Ma; this study) (Fig. 3.8). Field relations demonstrate that the Mackenzie dikes cross-cut and are cut by the Muskox intrusion, supporting their synchronous emplacement (Fig. 3.2) (Smith, 1962). The age of the Coppermine River basalts is not well constrained (1257 ± 45 Ma, Rb-Sr isochron; Wandless & Loveridge, 1972) however, their temporal relationship with Muskox intrusion comes from the observation that most of the Mackenzie dikes (emplaced synchronously with the Muskox intrusion) terminate within the lower Copper Creek Formation basalts (Baragar, 1969). A compilation of all available Nd isotopic compositions from the Muskox intrusion (this study & Stewart & DePaolo, 1996), Mackenzie dikes (unpublished; Dundas & Peterson, 1992), and Coppermine River flood basalts (Griselin et al., 1997) is shown with respect to relative stratigraphic position in Fig. 3.10. The initial 8Nd values of the layered series and the peridotite portion of the marginal zone of the Muskox intrusion overlap with those of basalts in the lowermost 1000 m of the Copper Creek Formation and some of the Mackenzie dikes, and they are distinctly more negative than those of the basalts at higher stratigraphic levels (Fig. 3.10). This observation indicates that only the lowermost flows of the Coppermine River basalts could be directly related to magmas that produced the Muskox intrusion. These basalts may represent residual magmas after the removal of olivine within the Muskox chamber given their relatively low MgO contents (5-10 wt %; Baragar, 1969) compared to the proposed picritic parental magmas to the Muskox intrusion (14 wt % MgO; Irvine, 1977). The overlying Husky Creek Formation basalts formed from magmas that apparently bypassed the Muskox chamber and erupted through a separate conduit system. Assuming that the lower Coppermine River basalts are directly related to the Muskox intrusion, this also suggests that the Muskox intrusion remained active for only the early stages of the Mackenzie event. The Mackenzie dikes have Nd isotopic compositions that span the range of compositions within the entire Coppermine River basalts, which supports the idea that the dikes represent the conduits for the basalts. Importantly, Ernst & Baragar (1992) have shown from the anisotropy of magnetic susceptibility measurements that the magma flow direction within the dikes records the vertical ascent of magmas within 500 km of the focus of the dike swarm and outward flow  -15 4000 3500 3000  -10  10  Coppermine River Basalts Husky Creek Fm.  o  CD  r*-r>  Copper Creek Fm.  CD  I •D  I •  I Mackenzie Dikes i • I—  1 km  LEGEND Coppermine River Basalts  Muskox Intrusion  Muskox Intrusion  Gabbro / Granophyre Olivine & pyroxene cumulates  ro CN  Olivine cumulates Olivine & orthopyroxene cumulates (marginal zone & feeder dike)  Country R o c k s Hornby Bay sandstone / Dismal Lake carbonates  CD  o  Pelitic metasediments / Granite and metavolcanic rocks  -15  -10  -5  0  10  ENd (1-27 Ga) Fig. 3.10: Compilation diagram showing the stratigraphic variations in initial E ^ J isotopic composition for the marginal zone (this study; solid squares; light blue = Far West Margin; dark blue = West Pyrrhotite Lake) and layered series (Stewart & DePaolo, 1996; open squares) of the Muskox intrusion, the Coppermine River flood basalts (Griselin et al., 1997; open triangles) and Mackenzie dikes (unpublished; Dudas & Peterson, 1992). The horizontal dashed lines separate the major divisions of the Muskox intrusion (Francis, 1994) and the Coppermine River basalts (Baragar, 1969). The grey field covers the range of values from the Muskox intrusion that were not affected by local crustal contamination. This range in E^d is projected onto the Coppennine River basalt stratigraphy as two vertical dotted lines. For comparison the initial ENd range for the depleted mantle at 1.27 Ga is shown by the vertical dashed line (determined from the ENJ range of mid-ocean ridge basalts (Vervoort & Blichert-Toft, 1999; Hofmann, 2005)).  121  at greater distances. This implies that the dikes exposed throughout most of the dike swarm likely represent the lateral extension of the conduit system through which the basalts were erupted. The similar Nd isotopic compositions of the Mackenzie dikes and Coppermine River basalts also suggest that distinct sets of the dikes could be related to compositionally (and stratigraphically) distinct members of the flood basalts. 3.6.3 Mantle source composition of the Muskox intrusion and other Mackenzie components The Hf and Nd isotopic composition and incompatible trace element concentrations and patterns of peridotites from this study, combined with available Nd isotopic compositions of layered,series rocks of the Muskox intrusion (Stewart & DePaolo, 1996) and Coppermine River basalts, allow the composition of the mantle source region from which the Muskox magmas were derived to be constrained (Fig. 3.6 & 3.10). The peridotites have low initial eNd (-2 to +1) and SHf (-5 to +3) values and are clearly enriched in LILE and LREE. These geochemical characteristics are consistent with the derivation of their parental magmas from a mantle source more enriched than depleted asthenospheric mantle. There is however evidence that indicates the Muskox magmas were contaminated by continental crust prior to emplacement within the Muskox chamber, which (as discussed below) may indicate that the Nd and Hf isotopic compositions of the primary Muskox magmas had more positive s-values (i.e. were more depleted). A l l rocks within the marginal zone of the Muskox intrusion, including the peridotites furthest from the margin, have prominent negative Nb-Ta anomalies in primitive mantlenormalized trace element patterns (Fig. 3.6). Similar anomalies were also noted by Francis (1994) in his study of marginal zone and layered series rocks within the Muskox intrusion. As noted previously, negative Nb-Ta anomalies are typical of continental crust (e.g. Rudnick & Fountain, 1995) and are not considered to represent variations in the degree or depth of melting in the mantle (e.g. Wooden et al., 1993; Amdt et al., 2003). Thus the appearance of these anomalies within intrusive and extrusive rocks must record some amount of interaction with continental material during magma ascent through the crust (Arndt et al., 1993). However,  UCHUR  Nd model ages of many marginal zone and layered series rocks are  comparable to the U-Pb crystallization age of 1269 Ma of the intrusion (Fig. 3.11), which suggests that the amount of contamination prior to emplacement within the Muskox chamber 122  tcHUR (Ga) Nd Model Age 7  *DM (Ga) Nd Model Age  Fig. 3.11: Histograms of Nd model ages (tcHUR d ^DM) for marginal z o n e peridotites (this study) and layered series rocks (Stewart & DePaolo, 1996) o f the Muskox intrusion, basalts from the Coppermine River and Husky Creek groups (Griselin et al., 1997), and contaminated gabbronorites and crustal rocks from the margin of the Muskox intrusion (this study). t c H U R model ages cannot be calculated for the Husky Creek Formation basalts because their present-day '43Nd/l44Nd values are more radiogenic than CHUR, and therefore these samples are only included in the tQM histogram. Many of the marginal zone and layered series rocks have t^HUR model ages that are comparable to the U-Pb crystallization age of the intrusion, which suggests that these rocks crystallized from a relatively uncontaminated m a g m a s that were derived from a near-chondritic mantle source. The contaminated gabbronoritic marginal rocks and granophyric roof zone rocks (GRZ) are displaced towards the older model ages of the crustal rocks. a n  was minimal, although sufficient enough to produce the negative Nb-Ta anomalies. The Husky Creek Formation basalts have positive initial em values (+4.5) and lack Nb-Ta depletion indicating that they represent an uncontaminated end-member composition of the mantle source during the Mackenzie event; this places a limit on the isotopic composition of the primary Muskox magmas. The range in Nd isotopic compositions of the Mackenzie components (e d = -2 to + 4.5) is consistent with those of many modern-day oceanic island and N  plateau basalts (e.g. Hoffman, 2005), suggesting that they formed from a similar enriched mantle source region that is distinct from that estimated for the depleted asthenospheric mantle at 1.27 Ga (e = +6 to +12 & e = +10 to +14; Vervoort & Blichert-Toft, 1999). Some of the Nd  w  variation in isotopic compositions within the Coppermine River basalts and Muskox intrusion may reflect heterogeneities within the mantle source region, rather than exclusively crustal contamination.  3.6.4 Evolution of the Mackenzie magmatic event The magmatic episode that led to the emplacement of the Muskox intrusion, Mackenzie dikes, and the eruption of the Coppermine River basalts is considered to reflect the impingement of a mantle plume at the base of the lithosphere (LeCheminant & Heaman, 1989; Baragar et al., 1996; Griselin et al., 1997). Domal uplift associated with plume emplacement is recorded by pre-flood basalt karst topography, which extends for >400 km from 100 km to the west of the Muskox intrusion to Bathurst Inlet towards the east, and the radial fracture system into which the Mackenzie dikes were emplaced (LeCheminant & Heaman, 1989; Baragar et al., 1996). As indicated above, the enriched trace element and isotopic compositions and Nb-depletions of the lowermost Coppermine River basalts are consistent with their being directly related to the Muskox intrusion. A large volume of fractionated magma would have been expelled from the Muskox chamber to account for the abundance of olivine (Irvine & Smith, 1967) and given that there is little evidence of a substantial erosional event within the overlying sediments (Kerans, 1983), it is likely that the lowermost Coppermine basalts resided within the Muskox chamber. Trace element characteristics of the Lower Copper Creek Formation basalts (e.g. high Gd/Yb and low Lu/Hf) indicate that they were derived by partial melting of the mantle within the garnet stability field (>100 km; Griselin et al., 1997). During ascent these magmas were contaminated by continental crust (possibly the lower crust), which resulted in a decrease in Nb/La and a shift towards more negative initial e d- Griselin et al. (1997) demonstrated N  124  that the subcontinental lithospheric mantle was unlikely the source of the chemical signatures observed in the Lower Copper Creek basalts, based on the distinct trace element characteristics of mantle peridotite xenoliths, and lithospheric mantle-derived volcanic rocks (e.g. lamprophyres). The magmas from which the Lower Copper Creek basalts were derived then resided within the Muskox chamber, prior to eruption on the surface. The Muskox intrusion itself formed through repeated picritic magma injections and likely represents a shallow-level staging chamber where magmas stagnated and fractionated during their ascent to the surface. Local crustal contamination within the Muskox intrusion along the walls and roof (Stewart & DePaolo, 1996) of the intrusion only affected a small amount of magma, which would explain the lack of significantly more enriched isotopic compositions within the Lower Copper Creek Formation basalts. At some point, the Muskox chamber became inactive and ascending magmas utilized alternate conduits systems. Several discrete gravity anomalies occur near the focus of the dike swarm to the north of the Muskox intrusion, which, as suggested by Baragar et al. (1996), could represent unexposed intrusions related to the Mackenzie event. The Husky Creek Formation basalts lack the chemical signature of residual garnet, which indicates that at later stages within the Mackenzie event mantle melting took place at shallower levels, perhaps as result of lithospheric thinning, or at higher degrees of melting (Griselin et al. 1997). The parental magmas to the Husky Creek basalts were not contaminated by continental crust during transit due to the combined effects of lithospheric thinning, plating of conduit walls by crystallization products of earlier magma pulses, and/or ascent through conduits where wall rocks had been previously melted and dehydrated.  3.7 CONCLUSIONS This detailed geochronologic and geochemical study of the marginal rocks of the Muskox intrusion, Nunavut, provides important constraints on the timing of emplacement of the Muskox intrusion, the spatial extent and degree of contamination along the basal margin of the intrusion, the relationship between the marginal zone and layered series of the Muskox intrusion, and the genetic relationship between the different components of the 1.27 Ga Mackenzie magmatic event. Precise U-Pb baddeleyite ages from uncontaminated peridotites and contaminated gabbronorites obtained in this study indicate that the marginal zone of the Muskox intrusion crystallized synchronously with the layered series and the Mackenzie dikes. Hf and Nd isotopic compositions and incompatible trace element ratios of marginal zone rocks indicate that crustal contamination by the adjacent crustal rocks is restricted to a thin (<10 m) zone of gabbronoritic rocks at the base of the Muskox intrusion. The degree of contamination varies at different locations along the margin of the intrusion, which likely relates to the different wall rock lithologies to the intrusion. The Nd isotopic compositions of the marginal zone peridotites and layered series rocks of the Muskox intrusion and the overlying Coppermine River basalts indicate that only the lower Copper Creek basalts can be directly related to the Muskox intrusion, perhaps as residual melts formed during fractionation within the Muskox chamber. Nb-Ta depletions within Muskox peridotites suggest that magmas which entered the chamber were previously contaminated, likely during ascent through the lower and middle crust, although the correlation between  ICHUR  model ages for the peridotites  and their U-Pb crystallization ages indicates that the degree of lower crustal contamination must have been minimal. The Nd isotopic compositions of the uncontaminated Husky Creek Formation basalts represent the least enriched component within the Mackenzie event and are comparable to those of modern-day oceanic island and plateau basalts. Thus, the voluminous magmas that fed the Muskox intrusion, the Mackenzie dikes, and the Coppermine River basalts at 1.27 Ga were ultimately derived from an enriched mantle source. The radial nature of the Mackenzie dikes and pre-flood basalt erosional features near the focus of the dike swarm, combined with the isotopic compositions strongly support a mantle plume origin for the Mackenzie magmatic event.  126  3.8 ACKNOWLEDGEMENTS The author is grateful for assistance from Gwen Williams and Diane Hanano with sample digestion and dilution procedures; Jane Barling, Bert Mueller, Wilma Pretorius, Rich Freidman, and Elisa Dietrich-Sainsaulieu for their help with HR-ICP-MS, TIMS, and M C ICP-MS analyses at the Pacific Centre for Isotopic and Geochemical Research, University of British Columbia, Vancouver; and Claude Maerschalk for assistance with column chemistry. R A M thanks Gary DeScuhtter (Senior Project Geologist, Anglo American Exploration Ltd. Canada), Nathan Rand, and Tansy O'Connor for their wonderful support in logistics and sample collection. R A M was supported by an NSERC Industrial Postgraduate Scholarship (IPS). Funding for this research was provided by Anglo American Exploration Ltd. (Canada), (AAEC) by a Collaborative Research Development (CRD) grant from NSERC and A A E C , and by an NSERC Discovery Grant to JSS.  3.9 REFERENCES Arndt, N.T., Czamanske, G.K., Wooden, J.L. & Fedorenko, V . A . (1993). Mantle and crustal contributions to continental flood volcanism. Tectonophysics 223, 39-52. Arndt, N.T., Czamanske, G.K., Walker, R.J., Chauvel, C. & Fedorenko, V . A . (2003). Geochemistry and origin of the intrusive hosts of the Noril'sk-Talnakh Cu-Ni-PGE sulfide deposits. Economic Geology 98, 495-515. Baragar, W.R. A. (1969). The Geochemistry of the Coppermine River basalts. Geological Survey of Canada Paper 69-44,43 pp. Baragar, W.R.A. & Donaldson, J.A. (1973). Coppermine and Dismal Lakes map areas. 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(2000) High-precision trace element data for the USGS reference materials BCR-1, BCR-2, BHVO-1, BHVO-2, AGV-1, AGV-2, DTS-1, DTS-2, GSP-1 and GSP-2 by ID-TIMS and MIC-SSMS. Geostandards Newsletter: The Journal of Geostandards and Geoanalysis 25, 77-86. Roach, T.A., Roeder, P.L. & Hulbert, L.J. (1998). Composition of chromite in the Upper Chromitite, Muskox layered intrusion, Northwest Territories. Canadian Mineralogist 36, 117-135. Robinson, P., Higgins, N.C. & Jenner G.A. (1986). Determination of rare-earth elements, yttrium and scandium in rocks by an ion exchange-X-ray fluorescence technique. Chemical Geology 55, 121-137. Roddick, J.C. (1987). Generalized numerical error analysis with application to geochronology and thermodynamics. Geochimica et Cosmochimica Acta 51, 2129-2135. Rudnick, R.L. & Fountain, D.M. (1995). Nature and composition of the continental crust: a lower crustal perspective. Reviews of Geophysics 33, 267-309. 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The Muskox intrusion, Northwest Territories, Canada. In: Basu, A. & Hart, S. (eds) Earth Processes: Reading the Isotopic Code. Washington, DC: American Geophysical Union, pp 277-292. Tharp, T.M., Loucks, R.R. & Sack, R.O. (1998). Modeling compaction of olivine cumulates in the Muskox intrusion. American Journal of Science 298, 758-790. Totland, M . , Jarvis, I. & Jarvis, K.E. (1992). An assessment of dissolution techniques for the analysis of geological samples by plasma spectrometry. Chemical Geology 95, 140-143. Vervoort, J.D. & Blichert-Toft, J. (1999). Evolution of the depleted mantle: H f isotope evidence from juvenile rocks through time. Geochimica et Cosmochimica Acta 63, 533-556. Wanless, R.K. & Loveridge, W.D. (1972). Rubidium-strontium isochron age studies, Geological Survey of Canada Paper 72-23. 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Earth and Planetary Science Letters 5, 320-324.  CHAPTER 4  Controls on the chalcophile element concentrations of sulphide within the marginal rocks of the Muskox intrusion, Nunavut  4.1 INTRODUCTION The 1.27 Ga Muskox intrusion, one of the world's largest layered intrusions, has been the site of numerous exploration programs for Ni-Cu-platinum group element mineralization since its discovery in 1956 by members of the Canadian Nickel Company (Smith & Kapp, 1963). The intrusion is considered to have formed through multiple injections of basaltic magma during the Mackenzie magmatic event, which is also recorded by the emplacement of the Mackenzie dike swarm and eruption of the Coppermine River flood basalts (Irvine & Smith, 1967; Irvine, 1970; 1980; Fahrig, 1987; LeCheminant & Heaman, 1989; Baragar et al., 1996; Griselin et al., 1997). Sulphide mineralization is sporadically distributed along the basal margins of the intrusion and typically occurs as disseminated to massive sulphide within noritic rocks at the base of the marginal zone and as thin sulphide veins within the matrix of brecciated and partially melted wall rocks (Fig. 4.1) (Smith, 1962; Chamberlain, 1967; Irvine, 1988; Francis, 1994). Marginal zone sulphides typically have low metal contents and rarely form zones greater than a few metres in thickess. However, the occurrence of metal-rich sulphides (>10 wt % Ni and 20 wt % Cu in 100% sulphide) indicates that significant metal enrichment occurred locally during emplacement and crystallization of the Muskox magmas. Sulphur isotopic compositions of marginal zone sulphides have a strong crustal component indicating the availability of crustal sulphur was likely a controlling factor in the formation of marginal zone sulphide (Sasaki, 1969; Barnes & Francis, 1995; Chapter 2). In this study we evaluate variations in the Ni, Cu, and Pd contents of sulphide from the marginal rocks of the Muskox intrusion to constrain the processes affecting the formation of metal-rich and metal-poor sulphides at different regions along the margins of the intrusion. This study utilizes compositional data from all known mineralized regions along the basal margin of the intrusion and provides unique insights into sulphide mineralization in the Muskox intrusion. It will be shown that the majority of sulphides are metal-poor (<2 wt% Ni; 4 wt% Cu in 100% sulphide), however both Ni- and Cu-rich sulphides are locally developed within the marginal zone. Numerical modeling of the potential compositional variations produced in the initial sulphide liquid in response to changes in R-factor (silicate magma/sulphide liquid mass ratio) indicate that most of the metal-poor sulphide can be explained by relatively low R-factors of ~ 100, while the compositions of most of the Cu- and Ni-rich sulphides require R-factors ranging from 500-1000. This indicates that local conditions along the margin of the intrusion provided environments where significant metal 135  Legend M u s k o x Intrusion Granophyric roof zone I. + I Granophyre & gabbro Layered series Gabbro I Olivine pyroxenite & pyroxenite | Olivine gabbro I Dunite and Peridotite  I  Marginal zone & Feeder I Peridotite, feldspathic peridotite, gabbronorite  I  C o p p e r m i n e River H o m o c l i n e f " 1 Coppermine River Group h~H Dismal Lake Group and sills k -;. I Hornby Bay Group Wopmay Orogen 1. j Recluse Group 1  I', i 'I Epworth Group I.V] Akaitcho Group LZ3 Hepburn Batholith \  ^  ^  Faults  It 1  Mackenzie Dikes  Sulphide Mineralization  Figure 4.1  Fig. 4.1: Geological map of the Muskox intrusion and surrounding crustal rocks showing the location of the sample regions (after Hulbert, 2005; mapping by Smith (1962); supplied by Anglo American Exploration (Canada) Ltd.). The Muskox intrusion and its underlying feeder dike (extends off the map to the south) are exposed for over 120 km within metasedimentary rocks of the Recluse and Epworth groups, metaplutonic rocks of the Hepburn Intrusive Suite, and metasedimentary and metavolcanic rocks of the Akaitcho Group in the Wopmay Orogen. The intrusion forms an elongate funnel-shaped body that plunges shallowly towards the north beneath the overlying Dismal Lake carbonates and Hornby Bay sandstones. Sporadically distributed sulphide mineralization occurs at the base of the marginal zone and within the adjacent host rocks (indicated with red stars). Locations referred to in the text along the marginal zone are indicated.  enrichment could occur. We argue that extremely Cu-rich sulphides likely formed by fractional crystallization of sulphide liquid, analogous to the mechanism described for Cu-rich ores in the Noril'sk region of Russia (Naldrett et al., 1997) and the footwall ore in the Sudbury Igneous Complex (Mungal, 2002; Naldrett et al., 1992; L i & Naldrett, 1994). Finally, we will show that many sulphides contain relatively low Pd contents and argue that this is the result of sulphide segregation from contaminated magmas with elevated Cu/Pd values, as proposed for the formation of sulphide mineralization within the Partridge River intrusion, Duluth Complex, Minnesota (Theriault et al., 1997; 2002).  4.2 DATASET AND RECALCULATION PROCEDURE The compositional data used in this study was obtained from a previously compiled proprietary dataset of over 4000 samples (property of Muskox Minerals Corporation (now Prize Mining Corporation)). The samples were collected through both diamond drilling and surface prospecting and the dataset was filtered to include only samples with >2 wt % S and that had also been analyzed for Ni, Cu, Pd, and S concentrations. The resultant dataset consisted of-300 samples, including mainly geochemical results from drill core collected by Prize Mining Corporation (2000-2003) and Equinox Resources Ltd. (late 1980s). The whole rock data was recalculated to 100% sulphide to remove the variations due to variable abundances of sulphide within different samples. The recalculation method is that described in Barnes & Francis (1995), in which the whole rock Ni contents were assigned to pentlandite, the Cu contents were assigned to chalcopyrite, and any remaining sulphur was assigned to pyrrhotite. The Pd contents in 100% sulphide were estimated by dividing the whole rock data by the weight fraction of sulphide. A correction was applied to remove any contribution of metals from non-sulphide phases (e.g. Ni in olivine; Cu in pyroxene) for samples that contained <10% sulphur and that are hosted within gabbronorite and olivine gabbronorite. The estimated metal content of the silicate fraction (500 ppm Ni and 200 ppm Cu) is considered to be a slight overestimate for sulphides within the noritic rocks, and an underestimate for any sulphides within olivine-bearing rocks. Only samples with >2 wt % S have been used because the non-sulphide metal content correction becomes very significant at low S contents (Kerr, 2001). The recalculated data used in this study is taken as an estimate of the bulk sulphide composition, and the combined analytical uncertainties for S and base metal analyses are likely on the order of 15-20% relative (Kerr, 2001). 138  4.3 SULPHIDE COMPOSITIONAL VARIATIONS The majority of the sulphides have metal contents below 2 wt % Niioo (51% of samples) and 4 wt % Cuioo (70% of samples) (Fig. 4.2). These relatively metal-poor sulphides typically occur along the northern and southern sections of the Far West Margin, and at the East Valley and Speers Lake regions (Fig. 4.1). The remaining sulphides have a wide range in metal contents (2 to 26 wt % Niioo; 4 to 30 wt % Cuioo) and typically occur in the middle section of the Far West Margin, and at the Keel, Pyrrhotite Lake, and Southeast McGregor regions (Fig. 4.1). The Pd contents in 100% sulphide show a large variation within an individual region (<0.2 ppm to >10 ppm). For comparison, komatiite-related ores in the Cape Smith Belt, Nuvilik (Katinniq & Donaldson deposits) range from 10-17 wt % Niioo and 2-9 wt % Cuioo, and tholeiitic basalt-related massive ores in the Noril'sk region of Russia (Oktyabrsky & Talnakh deposits) typically range from 2-5 wt % Ni and 3-5 wt % Cu, with Cu-rich massive ore containing up to 22 wt % Cu (compilation in Naldrett, 2004). Similar Cu-rich ores are also found in the footwall deposits of the Sudbury Igneous Complex, and these extremely Cu-rich compositions are considered to form through fractional crystallization of a sulphide liquid (Naldrett et al., 1992; 1997). The compositional variability in sulphides from the different contact regions of the Muskox intrusion can be observed in atomic ratio diagrams (Fig. 4.3; as in Beswick, 2002). All samples plot within a triangle defined by any three of the major sulphide minerals pyrrhotite, pentlandite, cubanite, chalcopyrite, and rarely bornite. This is consistent with the sulphide mineralogy described by Chamberlain (1967) and noted in drill logs throughout the intrusion and adjacent wall rocks. The metal-poor sulphides, as expected, plot near the pyrrhotite apex, while the metal-rich sulphides form two separate arrays that trend towards pentlandite, and cubanite and chalcopyrite. The Pyrrhotite Lake region contains both Ni-rich and Cu-rich sulphides, whereas the Southeast McGregor and Keel regions contain mainly Curich sulphides. These compositional variations, in particular the trend towards relatively Curich sulphides, are broadly consistent with the effects of sulphide liquid fractionation and will be quantitatively evaluated below.  139  180  Cuioo% F i g . 4.2: Histograms and cumulative percentages of N i and C u contents of sulphides (i.e. recalculated to 100% sulphide) from the marginal zone of the Muskox intrusion. Short dashed lines indicate the range in compositions that are characteristic of a given geographic region (ds = disseminated; msv = massive sulphide). The majority of the marginal zone sulphides contain relatively low metal contents (<2 wt % Nijoo; <4 wt % CUJOO)- Metal-rich sulphides occur at three locations: Pyrrhotite Lake (>15 wt % Niioo), Southeast McGregor (>20 wt % Cuioo), and Keel Region (10-14 wt % CUJOO).  0.6  Pn  Locations x • x +  0.5  A  0.4  •  •  Keel West o Po Lake Po Lake West A SE McGregor A SE Speers Western Margin  CO 0.3  0.2  A  E Valley Feeder dike FW Margin Keel East  A  0.1  £5*  Cpy -• 0.1  0.2  0.3  C  u  b  0 4  0.5  0.6  0.4  0.5  0.6  Cu/S 0.90  CO 0>  0.65  0.40  0.0  0.1  0.2  0.3  Cu/S F i g . 4.3: Atomic ratio diagrams showing the compositional variations in marginal zone sulphides at different locations in the Muskox intrusion. The compositions of end member sulphide minerals are shown for reference (Po = pyrrhotite, Cpy = Chalcopyrite, Cub = Cubanite; Pn = Pentlandite; B m = bomite). Linear arrays towards relatively high Cu/S values are consistent with the effects of sulphide liquid fractionation. Note the distinct Ni-rich and Cu-rich sulphides that are characteristic of the Pyrrhotite Lake (Po Lake) region. See text for discussion.  4.4 DISCUSSION Sulphide saturation of a basaltic magma will result in the formation of an irnrnscible sulphide liquid info which chalcophile elements (Ni, Cu, and PGE) partition (e.g. Ebel & Naldrett, 1997). In the case of the marginal rocks of the Muskox intrusion, the magmas along the outer contact with the country rocks undoubtedly became sulphide-saturated in response to the addition of both crustal sulphur and silica as discussed in Chapters 2 and 3. As described by Campbell and Naldrett (1979), the composition of the sulphide liquid that initially segregates from the basaltic magma depends on the composition of the magma, the effective silicate/sulfide mass ratio (R-factor), and the sulfide liquid/silicate liquid partition coefficients, as expressed below.  sul/sll  D  +  R  where C i is the final concentration a element in the sulphide melt, D |/ n is the partition su  su  S  coefficient expressing the partitioning of the element in the sulphide liquid relative to silicate magma at equilibrium, R is the ratio of the mass of silicate magma to the mass of sulphide liquid, and C° n refers to the original concentration of the metal in the silicate magma. The Rs  factor is a measure of the amount of silicate liquid that a sulphide liquid equilibrates with, and is considered to reflect the physical environment in which the sulphides formed. Many major magmatic Ni-Cu sulphide deposits occur within channels or conduit systems through which a significant volume of magma has flowed (high R-factors) (Naldrett, 1997). An additional control on the composition of sulphide liquids is the initial crystallization of an Fe-rich monosulphide solid solution (mss), such that, the composition of the residual sulphide liquid during crystallization reflects the partitioning of chalcophile elements between mss and the sulphide liquid (Barnes et al., 1997a; Ebel & Naldrett, 1997). The crystallization of mss is, in some cases, followed by the crystallization of an intermediate solid solution (iss) from highly evolved sulphide liquids. Experimental and empirical studies have shown that Ir, Rh, and Ru partition into mss, while Cu, Pd, Pt, and Au partition into the sulphide liquid (e.g. Fleet et al., 1991; L i et al., 1996; Naldrett et al., 1997; Barnes et al., 1997a; Ballhaus et al., 2001; Mungall et al., 2005). The behaviour of Ni is more complicated, as described by Ballhaus et al. (2001), and appears to be incompatible in mss at high temperatures and high metal/sulphur ratios, while at low temperatures and metal/sulphur ratios Ni is compatible in mss. Barnes et al. (1997b) documented empirically that Ni partitions into the Fe-rich portion 142  of ores in tholeiitic systems, whereas in komatiitic systems Ni partitions, along with Pd and Pt, into the Cu-rich portion. The occurrence of Ni- and Cu-rich sulphides within the marginal zone is consistent with the effects of fractional crystallization of sulphide liquid. In the atomic ratio diagrams (Fig. 4.3), as discussed by Beswick (2002), the fractionation of any particular phase or combination of phases from a parental liquid will result in a linear trend of derivative liquid compositions projecting away from that of the fractionated solid. Considering that mss (approximated by pyrrhotite) was likely the first phase to crystallize, the trend extending from pyrrhotite to cubanite and chalcopyrite observed for the Southeast McGregor and Keel sulphides undoubtedly reflects one of these linear arrays. Several samples from each of these regions plot off this trend and are relatively Ni-rich. Assuming that the sulphides from each region originated from a common parental sulphide liquid, this can be explained by (1) fractionation of pyrrhotite (Fei. S), which results in progressive enrichment of the residual x  liquid in Cu and Ni, and (2) fractionation of Ni-bearing pyrrhotite (i.e. a composition along the pyrrhotite-pentlandite join), which results in further enrichment in Cu. The latter process may reflect a change in compatibility of Ni in mss from incompatible to compatible. Depending on the initial sulphide liquid composition, the point at which Ni becomes compatible in mss, and the effectiveness of physically separating solids from liquids, numerous paths could be followed. The metal-poor sulphides that are common throughout the intrusion likely do not represent fractionated mss cumulates, but instead reflect metal-poor parental sulphide liquids. The sulphides at Pyrrhotite Lake are anomalously enriched in both Cu and Ni, which suggests that they may represent a fractionated component of a metal-rich sulphide liquid where both Ni and Cu remained incompatible in mss. As described above, the variation in the metal content of sulphides is controlled by the exchange of metals between silicate and sulphide melts, and may also record subsequent fractional crystallization of mss from residual sulphide liquid. The compositional variation in the initial segregated sulphide liquid produced by changes in R-factors has been calculated based on the method outlined by L i and Naldrett (1994) and Mungall (2002), using a parental magma composition of an uncontaminated norite from Muskox feeder dike (Francis, 1994) and appropriate partition coefficients between silicate/sulphide melt (Fig. 4.4 & 4.5). The composition of the parental magma and calculated sulphide liquid composition and partition coefficients used in the calculation are shown in Table 4.1. The compositional effects during 143  (a) R = 200  o.o  5  15  10  Cuioo% 30  (b) R = 1000 A  25  20  r  •  Po Lake  •  •  S E McGregor  D  +  Keel E  - « — EC liquid - ° — FC liquid  r  - • — E C mss  -o—FC mss •-  15  R 50-10000  10  •  10  15  20  residual sulphide liquid  25  30  Cuioo% Fig. 4.4: Ni and Cu contents of sulphides (recalculated to 100% sulphide) for the Southeast McGregor, Keel East, and Pyrrhotite Lake regions (shown at two scales) showing the modeling results with constant DNj( / i). Model curves represent the compositional variation in equilibrium sulphide liquid with changing R-factor (light grey line with horizontal ticks; R=50-10000), and compositional variations produced during equilibrium crystallization (EC; solid curves with solid circles) and fractional crystallization (FC; solid curves with open circles) of monosulphide solid solution (mss) at R = 200 (a) and R = 1000 (b). The mss/sulphide liquid partition coefficient for Ni is assumed to be constant at 1.5. The fraction of liquid remaining is indicated for each curve at increments of 0.05 (circles). Mixtures of mss and liquid span the region between the two sets of curves. The parental magma composition and partition coefficients are shown in Table 1. See text for discussion. mss  su  144  (a) R = 200  ++ +  +  +  o o  + A + +  +  +  +  +  + 0.1  residual +  sulphide liquid  Cuioo%  10  15  30  (b) R = 1000 25  •  •  Po Lake  •  S E McGregor  +  Keel E  - • — E C liquid 20  - « — F C liquid - * — E C mss -°—FCmss  =  15  —  R 50-10000  Fig. 4.5: Ni and Cu contents of sulphides (recalculated to 100% sulphide) for the Southeast McGregor, Keel East, and Pyrrhotite Lake regions (shown at two scales) showing the modeling results with variable DNj( / i). Model parameters as indicated in Figure 4.4. Calculated model curves assume R-factors of 200 (a) and 1000 (b). DNj( / |) varies from 0.6 to 1.2 during crystallization. The fraction of liquid remaining is indicated for each curve at increments of 0.05 (circles). See text for discussion. mss  su  mss  su  145  Table 4.1: R-factor and sulphide liquid fractionation model parameters R = 1000 Element Cu (ppm) Ni (ppm) Pd (ppb)  Parental Magma 120 200 4  Sulphide liquid 40040 46200 3875  Depleted magma 80 154 0.13  Parental Magma 120 200 4  Sulphide liquid 17229 24120 799  Depleted magma 34 80 0.03  Dsul/si!  Dmss/sul  500 300 30000  0.18 0.6-1.5 0.1  Dsul/sil  ^mss/sul  500 300 30000  0.18 0.6-1.5 0.1  R = 200 Element Cu (ppm) Ni (ppm) Pd (ppb)  "Parental magma" is the estimated composition of the inital Muskox magma prior to sulphide segregation, from the uncontaminated chilled margin of the Muskox feeder dike (from Francis, 1994); "Sulphide liquid" is the calculated composition of the sulphide that equilibrated with the parental magma at the stated R-factor; "Depleted magma" is the calculated composition of the Muskox magma after sulphide segregation. D(sul/sil) and D (mss/sul) are partition coefficients for sulphide liquid/silicate liquid and mss/sulphide liquid, respectively. Partition coefficients are estimated from experimental results of Peach et al. (1990), Bezmen et al. (1994), Peach et al. (1994), Li et al. (1996), Crocket et al. (1997), Ballhaus et al. (2001), Mungal et al. (2005), Barnes et al. (1997a), and Gaetani & Grove (1997).  subsequent sulphide liquid fractionation can be modeled at a given R-factor using experimentally determined partition coefficients between mss and sulphide liquid under both equilibrium and fractional crystallization conditions (Table 1). The partitioning of Cu and Pd between mss and sulphide liquid has been determined experimentally and is treated as constant at D equals 0.2 and 0.1, respectively (Li et al., 1996; Barnes et al. 1997a). As discussed above, the partitioning of nickel is not as well constrained and therefore model curves have been calculated for both the compatible and incompatible behaviour of Ni in mss. In Figure 4.4, a partition coefficient of 1.5 is used throughout crystallization to simulate the compositional variation produced during equilibrium and fractional crystallization assuming Ni is compatible in mss. In Figure 4.5, the partition coefficient is adjusted from 0.6 to 1.2 progressively from 50-100% crystallized to simulate the change in the compatibility of Ni during cooling. The corresponding equilibrium and fractional crystallization curves show an inflection at the point where the assigned partition coefficient equals one. The modeling results indicate that samples with <1.5% Niioo and <5 % Cuioo, which represent the majority of sulphides within the marginal zone, can be explained by R-factors of ~100, regardless of the behaviour of Ni during fractionation (Fig. 4.4 & 4.5). As suggested in Chapter 2, this likely reflects local sulphide saturation of magmas along the outer wall of the magma chamber. Rapid cooling and solidification of this magma likely prevented segregated sulphide droplets from interacting with large volumes of basaltic magma. Using the variable D N J model, sulphides with 20 wt % Cuioo (Southeast McGregor and Keel regions) require Rfactors of at least 500, and sulphides with 5 wt % Niioo (Pyrrhotite Lake region) require Rfactors of 1000. The constant D N J model shows more consistent results for samples with relatively high N i |  0 0  (6-7 wt %) and Cuioo (15-25 wt %) contents at R-factors of 800-1000.  These high R-factors may reflect an increased circulation of sulphide droplets due to flow of magma over irregularities in the chamber wall (Irvine, 1988). Neither set of calculations however adequately explains the extremely Ni-rich sulphides (~25 wt % Niioo) at Pyrrhotite Lake. To generate sulphides with these Ni contents, the parental magma would have to contain 700 ppm N i , which is inconsistent with the proposed picritic parental magma to the Muskox intrusion (<300 ppm Ni). For similar Ni- and Cu-rich sulphides in the footwall of the McCreedy West region of the Sudbury Igneous Complex, Naldrett et al. (1997) suggested that they may represent the product of fractionation of pentlandite from Cu-rich residual sulphide  147  liquid. Ballhaus et al. (2001) also noted that in a metal-rich sulphide liquid, Ni may remain incompatible in mss and become progressively enriched in the residual liquid. Finally, given the large difference in the partition coefficients of Cu and Pd during sulphide segregation from a basaltic magma  (Dpd( i/sii) Su  = 30000; Dc (sui/sii) 500), the Cu/Pd =  U  value is sensitive to changes in R-factor, and can also be used to examine the potential effects of previous sulphide segregation events and addition of crustal material (e.g. Theriault et al., 1997; Barnes & Maier, 1999; Theriault et al., 2000). As described by Theriault et al. (2000), the extraction of a small amount of sulphide results in high Cu/Pd ratios in the later-forming sulphides. Similarly, the mixing of a basaltic magma with crustal material results in an increase in Cu/Pd within the hybrid magma as well as the equilibrium sulphide liquid. Many of the mineralized Muskox samples have extremely high Cu/Pd, which, given that the sulphides occur within mainly noritic marginal rocks and adjacent country rocks, this likely reflects the formation of sulphide liquid from hybrid magmas as proposed in Chapter 2 (Fig. 4.6).  148  1000000 c  100000  TTT  Crust  1—I I I I II I  M L  .-tar'  T3 ^  1  10000  o  + • 1000  Keel East Po Lake  10% 20% 50% 100%  -  SE McGregor R = 300  + sulphide liquid fractionation  R=1000 R = 5000 100  _i i * i 10  100  1000  10000  1 I I 11111,  100000  Pd (ppb)  Fig. 4.6: Plot of Cu/Pd vs. Pd (not recalculated) for mineralized samples from the Southeast McGregor, Keel East, and Pyrrhotite Lake regions of the Muskox intrusion. Model curves represent mixing lines between the assumed parental magma composition (Table 1) and its equilibrium sulphide liquid at a given R-factor. Points along the mixing line indicate the composition of rocks that would contain 1,10, 20, 50, and 100% sulphide. Many of the samples can be modeled at various R-factors (<300 to 5000); however samples with high Cu/Pd values (>20000) require a parental magma with significantly higher Cu/Pd than that of the assumed parent. This may reflect the formation of a hybrid magma derived through assimilation of crust and would shift the model curves towards higher Cu/Pd values. Residual sulphide liquids formed during fractional crystallization would trend towards high Pd contents (Dpj = 0.1; D c 0.2), which would explain why massive sulphide samples from Pyrrhotite Lake and Southeast McGregor plot at higher Pd contents than the modeled trends at 100% sulphide. =  u  149  4.5 CONCLUSIONS This study of the metal contents of sulphides within the marginal zone of the Muskox intrusion allows the processes affecting the formation sulphide mineralization at different locations along the basal contact of the intrusion to be constrained. The majority of the marginal zone sulphide in the Muskox intrusion formed at low R-factors. As described in Chapter 2, this is considered to reflect rapid cooling of sulphide-saturated magma along the outer wall of the chamber, which likely prevented the segregated sulphide droplets from interacting with large amounts of silicate magma. The extreme compositional variability of sulphides within, and between, geographic regions along the basal margin of the Muskox intrusion likely reflects the formation of isolated pockets of sulphide liquid, each of which evolved under local conditions. The occurrence of sporadically distributed metal-rich sulphides may record regions of enhanced circulation of sulphide droplets in a larger volume of basaltic magma in response to irregularities in the wall of the chamber, however it is uncertain if this mechanism could generate significant quantities of sulphide. Cu-rich sulphides at the Southeast McGregor and Keel regions appear to have formed from a fractionated sulphide liquid. The mss component of these liquids would contain 2-4 wt % Ni, however it is not clear based on the present sample suite that this component has been found. This is an important observation as the liquid component would be volumetrically small compared to the mss portion, indicating that these regions should be targeted in future exploration programs. The Keel region, and its northward extension, is of particular interest given that this position in the intrusion represents the site where multiple magmas entered the chamber, as evidenced by the occurrence of magmatic breccia horizons (Francis, 1994). Ni- and Cu-rich sulphides at Pyrrhotite Lake require a unique mechanism of formation, perhaps involving crystallization of sulphide liquid at relatively high temperatures and/or the fractionation of pentlandite from a fractionated Cu-rich sulphide liquid. The few Pyrrhotite Lake samples with >20 wt % Cu may represent a mixture of pentlandite and Cu-rich sulphide at this location. The Pd-depleted signature of many of the sulphides is consistent with other geochemical and isotopic evidence (Chapter 2 & 3) and suggests that they formed from a sulphide liquid that segregated from a hybrid silicate magma along the outer wall ,of the magma chamber.  150  4.6 ACKNOWLEDGEMENTS Prize Mining Corporation (formerly Muskox Minerals Corp.), in cooperation with Larry Hulbert (National Resources Canada; Geological Survey of Canada) and Anglo American Exploration (Canada) Ltd. (AAEC), supplied the geochemical and corresponding spatial data from all historic drilling on the Muskox intrusion, and for that the author is grateful. Dave Peck (AAEC) is thanked for his helpful reviews of this work and for ongoing discussions on the processes involved in the formation of magmatic sulphide deposits. The author would also like to acknowledge the contribution of all previous exploration and research projects on the Muskox intrusion over the past 50 years.  4.7 REFERENCES Ballhaus, C , Tredoux, M . & Spath, A. (2001). Phase relations in the Fe-Ni-Cu-PGE-S system at magmatic temperature and application to massive sulphide ores of the Sudbury Igneous Complex. Journal of Petrology 42, 1911-1926. Baragar, W.R.A., Ernst, R.E., Hulbert, L. & Peterson, T. (1996). Longitudinal petrochemical variation in the Mackenzie dike swarm, Northwestern Canadian Shield. Journal of Petrology 37-2, 317-359. Barnes, S.J. & Francis, D. (1995). The distribution of platinum-group elements, nickel, copper, and gold in the Muskox Layered Intrusion, Northwest Territories, Canada. Economic Geology 90, 135-154. Barnes, S.J., Makovicky, E., Makovicky, M . , Rose-Hansen, J. & Karup-Moller, S. (1997a). Partitioning coefficients for Ni, Cu, Pd, Pt, Rh, and Ir between monosulfide solid solution and sulfide liquid and the formation of compositionally zoned Ni-Cu sulfide bodies by fractional crystallization. Canadian Journal of Earth Sciences 34, 366-374. Barnes, S.J., Zientek, M X . & Severson, M.J. (1997b). Ni, Cu, Au, and platinum-group element contents of sulphides associated with intraplate magmatism: a synthesis. Canadian Journal of Earth Sciences 34, 337-351. Barnes, S.J. & Maier, W.D. (1999). The fractionation of Ni, Cu, and the noble metals in silicate and sulphide liquids. In: Keays, R.R., Lesher, C M . , Lightfoot, P . C & Farrow, C E . G . (eds.) Dynamic Processes in Magmatic Ore Deposits and Their Application to Mineral Exploration, Geological Association of Canada, Short Course 13, pp 69-106. Beswick, A.E. (2002). An analysis of compositional variations and spatial relationships within Fe-Ni-Cu sulfide deposits on the North Range of the Sudbury Igneous Complex. Economic Geology 97, 1487-1508. Bezmen, N.I., Asif, M . , Brugmann, G.E., Romanenko, I.M. & Naldrett, A.J. (1994). Distribution of Pd, Rh, Ru, Ir, Os, and Au between sulfide and silicate metals. Geochimica et Cosmochimica Acta 58, 1251-1260. Campbell, I.H. & Naldrett, A.J. (1979). The influence of silicate:sulfide ratios on the geochemistry of magmatic sulphides. Economic Geology 74, 1503-1506. Chamberlain, J.A. (1967). Sulfides in the Muskox intrusion. Canadian Journal of Earth Sciences 4, 105-153.  152  Crocket, J.H., Fleet, M.E. & Stone, W.E. (1997). Implications of composition for experimental partitioning of platinum-group elements and gold between sulfide liquid and basalt melt: the significance of nickel content. Geochimica et Cosmochimica Acta 61, 4139-4149. Ebel, D.S. & Naldrett, A.J. (1997). Crystallization of sulfide liquids and the interpretation of ore composition. Canadian Journal of Earth Sciences 34, 352-365. Fahrig, W.F. (1987). The tectonic settings of continental mafic dyke swarms: Failed arm and early passive margins. Geological Association of Canada Special Paper 34, 331-348. Fleet, M.E., Stone, W.E. & Crocket, J.H. (1991). Partitioning of palladium, iridium, and platinum between sulfide liquid and basalt melt: Effects of melt composition, concentration, and oxygen fugacity. Geochimica et Cosmochimica Acta 55, 2545-2554. Francis, D. (1994). Chemical interaction between picritic magmas and upper crust along the margins of the Muskox intrusion, Northwest Territories. Geological Survey of Canada Paper 92-12, 94 pp. Gaetani, G.A. & Grove, T.L. (1997) Partitioning of moderately siderophile elements among olivine, silicate melt, and sulfide melt: Constraints on core formation in the Earth and Mars. Geochimica et Cosmochimica Acta 61, 1829-1846. Griselin, M . , Arndt, N . & Baragar, W.R.A. (1997). Plume-lithosphere interaction and crustal contamination during formation of Coppermine River basalts, Northwest Territories, Canada. Canadian Journal of Earth Sciences 34, 958-975. Hulbert, L. (2005). Geology of the Muskox intrusion and associated N i and Cu occurrences. Geological Survey of Canada, Open File 4881, CD-ROM. Kerr, A. (2001). The calculation and use of sulfide metal contents in the study of magmatic ore deposits: a methodological analysis. Exploration and Mining Geology 10, 289-301. L i , C. & Naldrett, A.J. (1994). A numerical model for the compositional variations of Sudbury sulfide ores and its application to exploration. Economic Geology 89, 1599-1607. L i , C , Barnes, S.J., Makovicky, E., Rose-Hansen, J. & Makovicky, M . (1996). Partitioning of nickel, copper, iridium, rhenium, platinum, and palladium between monosulfide solid solution and sulfide liquid: effects of composition and temperature. Geochimica et Cosmochimica Acta 60, 1231-1238. Irvine, T.N. (1970). Crystallization sequences in the Muskox intrusion and other layered intrusions - 1 . Olivine-pyroxene-plagioclase relations. In: Visser, D.J.L. & Von  153  Gruenewaldt, G. (eds) Symposium on the Bushveld Igneous Complex and Other Layered Intrusions. Geological Society of South Africa, Special Publication 1, 441-476. Irvine, T.N. (1980). Magmatic infiltration metasomatism, double-diffusive fractional crystallization, and adcumulus growth in the Muskox intrusion and other layered intrusions. In: Hargraves, R.B. (ed.) Physics of Magmatic Processes. Princeton: Princeton University Press, pp. 325-383. Irvine, T.N. (1988). Muskox intrusion, Northwest Territories. In: Hulbert, L.J. et al. (eds.) Geological Environments of the Platinum Group Elements. Geological Survey of Canada, Open File 1440, 25-39. Irvine, T.N. & Smith, C.H. (1967). The ultramafic rocks of the Muskox intrusion, Northwest Territories, Canada. In: Wyllie, P.J. (ed.) Ultramafic and Related Rocks. New York: John Wiley & Sons, Inc., pp. 38-49. LeCheminant, A.N. & Heaman, L . M . (1989). Mackenzie igneous events, Canada: Middle Proterozoic hotspot magmatism associated with ocean opening. Earth and Planetary Science Letters 96, 38-48. Mungall, J.E. (2002). Late-stage sulfide liquid mobility in the main mass of the Sudbury Igneous Complex: examples from the Victor Deep, McCreedy East, and Trillabelle Deposits. Economic Geology 97, 1563-1576. Mungall, J.E., Andrews, D.R.A., Cabri, L.J., Sylvester, P.J. & Tubrett, M . (2005). Partitioning of Cu, Ni, Au, and platinum-group elements between monosulfide solid solution and sulfide melt under controlled oxygen and sulfur fugacities. Geochimica et Cosmochimica Acta 69, 4349^1360. Naldrett, A.J. (1997). Key factors in the genesis of Noril'sk, Sudbury, Jinchuan, Voisey's Bay and other world-class Ni-Cu-PGE deposits: implications for exploration. Australian Journal of Earth Sciences 44,283-315. Naldrett, A.J. (2004). Magmatic Sulfide Deposits. Geology, Geochemistry and Exploration. Spinger-Verlag Berlin Heidelberg, 727 pp. Naldrett, A.J., Coats, C.J.A. & Johannessen, P. (1992). Platinum, palladium, gold, and copperrich stringers at the Strathcona Mine, Sudbury: their enrichment by fractionation of a sulphide liquid. Economic Geology 87, 1584-1598.  154  Naldrett, A.J., Ebel, D.S., Asif, M . , Morrison, G. & Moore, C M . (1997). Fractional crystallization of sulfide melts as illustrated at Noril'sk and Sudbury. European Journal of Mineralogy 9, 629-635. Peach, C.L., Mathez, E.A. & Keays, R.R. (1990). Sulfide melt-silicate melt distribution coefficients for noble metals and other chalcophile elements as deduced from MORB: implications for partial melting. Geochimica et Cosmochimica Acta 54, 3379-3389. Peach, C.L., Mathez, E.A., Keays, R.R. & Reeves, S.J. (1994). Experimentally determined sulfide melt-silicate melt partition coefficients for iridium and palladium. Chemical Geology 117, 361-377. Sasaki, A. (1969). Sulphur isotope study of the Muskox intrusion, District of Mackenzie (86 J/13, 0/3). Geological Survey of Canada Paper 68-46, 68 pp. Smith, C H . (1962). Notes on the Muskox Intrusion, Coppermine River area, District of Mackenzie. Geological Survey of Canada Paper 61-25, 16 pp. Smith, C H . & Kapp, H.E. (1963). The Muskox intrusion, a recently discovered layered intrusion in the Coppermine River area, Northwest Territories, Canada. Mineralogical Society of America, Special Paper 1, 30-35. Theriault, R.D., Barnes, S.J. & Severson, M.J. (1997). The influence of country-rock assimilation and silicate-sulfide ratios (R factor) on the genesis of the Dunka Road Cu-Niplatinum group element deposit, Duluth Complex, Minnesota. Canadian Journal of Earth Sciences 34, 375-389. Theriault, R.D., Barnes, S.J. & Severson, M.J. (2000). Origin of Cu-Ni-PGE sulphide mineralization in the Partridge River Intrusion, Duluth Complex, Minnesota. Economic Geology 95, 929-943.  CHAPTER 5  Summary and Conclusions  5.1 SUMMARY AND CONCLUSIONS This detailed study of the marginal rocks at two locations (West Pyrrhotite Lake and Far West Margin) along base of the Muskox intrusion includes petrography, major and trace element geochemistry, olivine chemistry, and Hf-Nd-S isotope geochemistry, combined with the metal contents of sulphides throughout the intrusion to evaluate the processes by which the marginal zone and associated sulphide mineralization formed. In addition, new U-Pb geochronology of marginal zone rocks of the Muskox intrusion and available Nd isotopic compositions of the Muskox intrusion, Mackenzie dikes, and Coppermine River basalts provide important constraints on the petrogenetic relationship between each of the main components of the 1.27 Ga Mackenzie magmatic event in northern Canada. The marginal zone of the Muskox intrusion, based on the observations made in this study, consists of a lower gabbronorite subzone and an upper peridotite subzone. The gabbronoritic rocks within the outer 10 m of the marginal zone are characterized by the early crystallization of orthopyroxene and by the appearance of granophyre globules. These petrographic observations correlate with shifts in whole rock Hf and Nd isotopic compositions and incompatible trace element ratios towards those of the surrounding country rocks, indicating that the gabbronoritic marginal rocks represent a hybrid zone. Incompatible trace element ratios of the gabbronorites (this study) and sulphur isotopic compositions of sulphides (this study and Sasaki, 1969) indicate that the addition of silicate material and sulphur occurred in situ and that the contaminant was derived directlyfromthe adjacent wall rocks. The gabbronorite at the Far West Margin is significantly more contaminated than that at West Pyrrhotite Lake, which may reflect an enhanced ability of the magma to incorporate the biotite- and sulphide-rich paragneiss at this location. Early solidification of this contaminated zone appears to have prevented overlying magmas from interacting with the adjacent crustal rocks, and resulted in uncontaminated incompatible trace element and Nd and Hf isotopic signatures within the overlying peridotites. The peridotite subzone of the marginal zone of the Muskox intrusion is characterized by an overall progression to more evolved compositions towards the base (decreasing whole rock MgO and increasing A I 2 O 3 and other elements incompatible in olivine) and a corresponding increase in the proportion of postcumulus material. This variation is consistent with the effects produced by the crystallization of varying amounts of intercumulus liquid relative to cumulus olivine grains during compaction of the cumulate pile and cooling through 157  the base or outer walls of the magma chamber. The overall mineralogical and chemical variations observed can be successfully modeled using IPJDIUM and the results indicate that this simple temperature-driven compaction model is a viable mechanism to explain the inverted character of the marginal zone in the Muskox intrusion. The compositional variation of cumulus olivine within the marginal zone is consistent with the re-equilibration of olivine with varying amounts of intercumulus liquid during solidification (i.e. lower forsterite contents of olivine correlate with increased abundances of postcumulus material). The distinct mineralogical and geochemical variations observed within the Far West Margin peridotites (e.g. abundant chromite and coarse-grained olivine) appear to correspond to changes within the layered series at a comparable stratigraphic height. This indicates that the marginal zone of the Muskox intrusion may have formed throughout the evolution (growth) of the Muskox chamber, rather than representing a single initial magma injection. Thus, it can be expected that the compositional and mineralogical variations within the marginal zone of the Muskox intrusion reflect both the minerals initially accumulated at different stages in the evolution of the chamber (Irvine & Smith, 1967) and superimposed effects of compaction and cooling through the base of the chamber. Sulphide mineralization within the Muskox intrusion typically occurs within the gabbronorite at the base of the marginal zone and as veins within brecciated wall rocks (Chamberlain, 1967). Based on the associations observed at the West Pyrrhotite Lake and Far West Margin sections, these basal sulphide accumulations reflect sulphide saturation of magma(s) along the outer wall of the chamber in response to the local addition of both sulphur and silica. The large variation in the metal contents of the sulphides within, and between, geographic regions likely reflects the formation of isolated pockets of sulphide liquid, each of which evolved under local conditions. The majority of the marginal zone sulphide in the Muskox intrusion appears to have formed in a relatively non-dynamic environment (low Rfactors), which is considered to reflect the. early solidification of the contaminated zone along the margin of the intrusion. The occurrence of metal-rich sulphide at specific regions along the outer contact of the intrusion (Southeast McGregor and Pyrrhotite Lake regions) may be the result of increased circulation of sulphide droplets owing to irregularities in the outer contact of the intrusion (Irvine, 1988), however it is uncertain whether this environment could produce significant quantities of sulphide. The Cu-rich character of the sulphides at the Southeast McGregor and Keel regions is consistent with their formation from a fractionated 158  sulphide liquid. The evidence for multiple magma injections at the Keel region (magmatic breccia horizons; Francis, 1994) indicates that this position holds the highest potential for the formation of significant quantities of metal-rich sulphide mineralization. U-Pb baddeleyite ages from uncontaminated peridotites and contaminated gabbronorites obtained in this study indicate that the marginal zone (1269 ±2 Ma; weighted mean of 4 concordant analyses) of the Muskox intrusion crystallized synchronously with the layered series and the Mackenzie dikes (1269 Ma; LeCheminant & Heaman, 1989), confirming the relatively short duration of the Mackenzie magmatic event (<4 million years). The Nd isotopic compositions of the marginal zone peridotites (this study) and layered series rocks (Stewart & DePaolo, 1996) of the Muskox intrusion and the overlying Coppermine River basalts (Griselin et al., 1997) indicate that only the lower Copper Creek basalts can be directly related to the Muskox intrusion. Given the relatively low MgO content of these basalts (<10 wt %), they likely represent the fractionated residual liquids that were expelled from the Muskox chamber. The presence of negative Nb-Ta anomalies in marginal zone peridotites that were unaffected by in situ contamination indicates that magmas which entered the chamber had experienced some amount of contamination prior to emplacement within the Muskox magma chamber. The Nd isotopic compositions of the uncontaminated Husky Creek Formation basalts (initial e d = +4.5; Griselin et al., 1997) represent the least enriched N  component within the Mackenzie event, however they are distinct from that estimated for the depleted mantle at 1.27 Ga (e = +6 to +12 & e f = +10 to +14; Vervoort & Blichert-Toft, Nd  H  1999). This indicates that the voluminous magmas generated during the Mackenize magmatic event were derived from an enriched mantle source. These geochemical constraints, combined with the evidence for domal uplift prior to the eruption of the Coppermine River basalts (Baragar et al., 1996), are consistent with a mantle plume origin for the Mackenzie magmas.  REFERENCES Baragar, W.R.A., Ernst, R.E., Hulbert, L. & Peterson, T. (1996). Longitudinal petrochemical variation in the Mackenzie dike swarm, Northwestern Canadian Shield. Journal of Petrology 37-2, 317-359. Chamberlain, J.A. (1967). Sulfides in the Muskox intrusion. Canadian Journal of Earth Sciences 4, 105-153. Francis, D. (1994). Chemical interaction between picritic magmas and upper crust along the margins of the Muskox intrusion, Northwest Territories. Geological Survey of Canada Paper 92-12, 94 pp. Griselin, M . , Arndt, N . & Baragar, W.R.A. (1997). Plume-lithosphere interaction and crustal contamination during formation of Coppermine River basalts, Northwest Territories, Canada. Canadian Journal of Earth Sciences 34, 958-975. Irvine, T.N. (1988). Muskox intrusion, Northwest Territories. In: Hulbert, L.J. et al. (eds) Geological Environments of the Platinum Group Elements. Geological Survey of Canada, Open File 1440, 25-39. Irvine, T.N. & Smith, C H . (1967). The ultramafic rocks of the Muskox intrusion, Northwest Territories, Canada. In: Wyllie, P.J. (ed.) Ultramafic and Related Rocks. New York: John Wiley & Sons, Inc., 38-49. LeCheminant, A.N. & Heaman, L . M . (1989). Mackenzie igneous events, Canada: Middle Proterozoic hotspot magmatism associated with ocean opening. Earth and Planetary Science Letters 96, 38-48. Sasaki, A. (1969). Sulphur isotope study of the Muskox intrusion, District of Mackenzie (86 J/13, 0/3). Geological Survey of Canada Paper 68-46, 68 pp. Stewart, B.W. & DePaolo, D.J. (1996). Isotopic studies of processes in mafic magma chambers: III. The Muskox intrusion, Northwest Territories, Canada. In: Basu, A. & Hart, S. (eds) Earth Processes: Reading the Isotopic Code. Washington, DC: American Geophysical Union, pp 277-292. Vervoort, J.D. & Blichert-Toft, J. (1999). Evolution of the depleted mantle: Hf isotope evidence from juvenile rocks through time. Geochimica et Cosmochimica Acta 63, 533556.  APPENDICES  161  A p p e n d i x I: A C M E A n a l y t i c a l Laboratory w h o l e - r o c k a n a l y s e s Package Sample wt (g)  4AWR 0.2  4BVVR 0.2  Digestion  LiB02 fusion  LiB02 fusion  Acid  5% HN03 5% HN03 2:2:2  18:10:3:6  -  Instrument Oxide/Element  ICP-ES Si0  ICP-MS Cs  ICP-MS Mo  ICP-ES Ni  LOI  Al 0  Ga  Cu  Hf  Pb  2  2  3  Fe 0 2  3  MgO  Nb  Zn  CaO Na 0  Rb Sn  Ag Ni*  KO  Sr  Co  Ti0  Ta  Mn  Th  As  U V  Au Cd  W  Sb  2  z  2  P 0 2  5  MnO Cr 0 2  Ba  2  1FMS 30 Aqua Regia HN03-HCLH20  3  Zr  Bi  Y  Cr  La  B*  Ce  TI  Pr Nd  Hg Se  Sm  Te  Eu  Ge  Gd  Sc*  Tb  In  Dy  Re  Ho  Be  Er  Li*  Tm'  Pd  Yb Lu  Pt  7TDA 0.5  4AL0  1  4ALC 10  2  H20-HfHCL04-HN03 -  Loss on ignition (LOI) determined by weight difference after ignition at 1000°C. Total carbon and sulphur determined by Leco analyses.  TOT/C TOT/S  Appendix II: Duplicate analyses of major and trace elements from ACME Analytical Laboratories . 1  Sample No. Batch No.  71068 A303993  71069 A303993  avg  a  %RSD  71008 A303994  71009 A303994  avg  0  %RSD  71128 A304116  71129 A304116  avg  0  %R  Cr 0 LOI TOT/C TOT/S SUM  38.13 0.42 4.13 11.15 0.13 32.2 2.73 0.13 0.28 0.08 0.316 10.2 0.03 0.37 100.19  38.33 0.41 4.15 11.06 0.13 32.3 2.79 0.09 0.30 0.08 0.300 10.0 0.04 0.35 100.25  38.23 0.42 4.14 11.11 0.13 32.3 2.76 0.11 0.29 0.08 0.308 10.1 0.04 0.36 100.22  0.14 0.01 0.01 0.06 0.00 0.08 0.04 0.03 0.01 0.00 0.011 0.1 0.01 0.01 0.04  0.37 1.7 0.34 0.57 0.00 0.26 1.54 25.71 4.88 0.00 3.673 1.4 20.2 3.93 0.04  50.21 0.61 7.38 12.93 0.15 18.5 6.23 0.88 0.52 0.04 0.261 2.0 0.02 1.37 99.90  50.31 0.61 7.42 12.93 0.15 18.6 6.32 0.87 0.51 0.04 0.265 1.7 0.05 1.32 99.90  50.26 0.61 7.40 12.93 0.15 18.5 6.28 0.88 0.52 0.04 0.263 1.9 0.04 1.35 99.90  0.07 0.00 0.03 0.00 0.00 0.06 0.06 0.01 0.01 0.00 0.003 0.2 0.02 0.04 0.00  0.1 0.0 0.4 0.0 0.0 0.3 1.0 0.8 1.4 0.0 1.1 11 61 2.6 0.0  40.78 0.72 5.85 14.78 0.17 25.2 4.08 0.52 0.37 0.09 0.335 6.7 0.04 0.02 99.80  41.02 0.74 5.83 14.86 0.17 25.4 3.96 0.48 0.37 0.10 0.338 6.8 0.02 0.01 100.20  40.90 0.73 5.84 14.82 0.17 25.30 4.02 0.50 0.37 0.10 0.337 6.8 0.03 0.02 100.00  0.17 0.01 0.01 0.06 0.00 0.08 0.08 0.03 0.00 0.01 0.002 0.1 0.01 0.01 0.28  0.4 1.9 0.2 0.4 0.0 0.3 2.1 5.7 0.0 7.4 0.6 1.0 47 47 0.3  Chalcophile elements (ppm) Co Ni Ni* Cu Pd(ppb) Pt(ppb) Au (ppb)  115 2086 1726 265 14 2 2.3  113 2098 1728 262 27 3 1.7  114 2092 1727 264 21 3 2  1 8 2 2 9 1 0.4  1.3 0.4 0.1 0.6 45 28. 21  80 1613 1150 1252 118 30 10.1  82 1603 1199 1262 120 32 9.1  81 1608 1175 1257 119 31 9.6  1 7 35 7 1 1 0.7  1.7 0.4 2.9 0.6 1.2 4.6 7.4  90 1200 960 95 20 9 1.2  87 1231 957 91 22 8 1.0  89 1216 959 93 21 9 1.1  2 22 3 2 1 1 0.1  2.5 1.8 0.3 2.5 6.7 8.3 13  Trace elements (ppm) Li* Be B* Sc* V Cr Mn Zn Ga Ge As Se Rb Sr  35.4 0.4 191 6 107 400 1141 88 5 0.3 0.5 0.6 9.4 64  34.6 0.2 187 6 108 399 1132 88 6 0.2 0.6 0.7 9.5 66  35.0 0.3 189 6 108 400 1137 88 6 0.3 0.6 0.7 9.5 65  0.6 0.1 3 0 1 0 6 0 1 0.1 0.1 0.1 0.1 1  1.6 47.1 1 2 1 0 1 0 13 28 13 10.9 0.7 2  7.7 0.2 8 2 187 216 104 15 10 <.1 1.5 2 13.1 108  7.7 <.1 10 2 193 223 103 20 10 0.1 1.6 2 13.9 112  7.7 0.2 9 2 190 220 104 17 10 0.1 1.6 2 13.5 110  0.0  0.0  1 0 4 5 1 3 0  16 0 2 2 1 20 4  0.1 0.0 0.6 3  4.6 0.0 4.2 3  15.7 0.2 24 4 165 239 1127 56 8 0.2 1.6 0.2 11.4 117  15.7 0.2 25 4 154 245 1113 54 10 0.2 1.5 0.2 10.6 111  15.7 0.2 25 4 160 242 1120 55 9 0.2 1.6 0.2 11 114  0.0 0.0 1 0 8 4 10 1 1 0.0 0.1 0.00 0.6 4  0.0 0.0 3 3 5 2 1 3 10 0.0 4.6 0.0 5.1 4  Major elements (wt %) Si0 Ti0 Al 0 Fe 0 MnO MgO CaO Na 0 K 0 2  2  2  3  2  2  3  2  2  P2O5 2  3  Appendix II (continued) Sample No. Batch No. Y Zr Nb Mo Cd In Sn Sb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Ag (ppb) Tl Pb Th U 1  2  71068 A303993 5.9 21.4 1.4 0.23 0.28 0.03 1 <.02 0.8 126 3.4 6.1 0.7 3 0.9 0.37 0.90 0.16 1.01 0.17 0.52 0.09 0.42 0.08 0.7 0.1 0.2 287 0.26 46 0.6 0.2  71069 A303993 5.3 20.7 1.9 0.25 0.30 0.02 1 0.02 0.9 127 3.4 6.7 0.8 3.5 1 0.41 0.76 0.18 1.08 0.19 0.55 0.08 0.58 0.08 0.7 0.1 0.2 283 0.25 41 0.6 0.2  avg  a  %RSD  5.6 21.1 1.65 0.24 0.29 0.03 1 0.02 0.9 127 3.4 6.4 0.7 3.25 0.95 0.39 0.83 0.17 1.05 0.18 0.54 0.09 0.50 0.08 0.7 0.1 0.2 285 0.255 43 0.6 0.2  0.4 0.5 0.35 0.01 0.01 0.01  7.6 2.4 21 5.9 4.9 28  0.1 1 0.0 0.4 0.1 0.35 0.07 0.03 0.10 0.01 0.05 0.01 0.02 0.01 0.11 0.0 0.0 0.0 0.0 3 0.01 3 0.00 0.00  8.3 1 0.0 6.6 8.8 11 7.4 7.3 11.9 8.3 4.7 7.9 4.0 8.3 23 0.0 0.0  Duplicate analyses are multiple digestions of a single crushed sample. AIIFeasFe 0 . 2  3  * Partial digestion only. LOI = loss on ignition TOT/C = total carbon; TOT/S = total sulphur by leuco  0.0 1 2.8 7 0.00 0.00  71008 A303994 10.8 37.3 2.5 0.34 0.33 <.02 <1 0.02 0.4 209 4.9 11.3 1.4 6.8 1.6 0.55 1.62 0.28 1.61 0.36 1.10 0.13 0.91 0.14 1.2 <.1 0.1 641 0.18 17 0.5 0.2  71009 A303994 10.4 39.2 2 0.31 0.36 0.02 1 0.02 0.4 209 5.0 11.1  i.5  6.1 1.6. 0.552.08 0.32 1:51 0.37 1.03 0.13 0.94 0.15 1.1 <.1 0.1 697 6.18 21 1.5 0.2  avg  a  %RSD  10.6 38.3 2.25 0.33 0.35 0.02 1 0.02 0.4 209 5.0 11.2 1.4 6.45 1.6 0.55 1.85 0.30 1.56 0.37 1.07 0.13 0.93 0.15 1.2  0.3 1.3 0.35 0.02 0.02  2.7 3.5 16 6.5 6.1  0.00 0.0 0 0.1 0.1 0.0 0.49 0.00 0.00 0.33 0.03 0.07 0.01 0.05 0.00 0.02 0.01 0.1  0.0 0.0 0.0 1.4 1.3 2.4 7.7 0.0 0.0 18 9.4 4.5 1.9 4.6 0.0 2.3 4.9 6.1  0.1 669 0.18 19 1 0.2  0.0 40 0.00 3 0.71 0.00  0.0 5.9 0.0 15 71 0.0  71128 A304116 10.5 47.8 3.5 0.28 0.02 0.02 <1 <.02 1.3 107 6.4 13.9 1.8 8.5 2.1 0.56 1.92 0.33 2.10 0.34 1.03 0.13 1.03 0.13 1.3 0.3 0.2 54 0.04 3 1 0.3  71129 A304116 10.3 47.4 3.7 0.23 0.02 0.02 <1 <.02 1.4 109 6.1 13.9 1.7 7.4 2 0.54 1.96 0.31 1.85 0.34 0.97 0.12 0.94 0.12 1.3 0.2 0.1 53 0.03 3 1.3 0.3  avg  a  %RS  10.4 47.6 3.6 0.26 0.02 0.02  0.1 0.3 0.14 0.04 0.00 0.00  1.4 0.6 3.9 13.9 0.0 0.0  1.4 108 6.3 13.9 1.8 7.95 2.05 0.55 1.94 0.32 1.98 0.34 1.00 0.13 0.99 0.13 1.3 0.3 0.2 54 0.035 3 1.15 0.3  0.1 1 0.2 0.0 0.1 0.78 0.07 0.01 0.03 0.01 0.18 0.00 0.04 0.01 0.06 0.01 0.0 0.1 0.1 1 0.01 0 0.21 0.00  5.2 1.3 3.4 0.0 4.0 9.8 3.4 2.6 1.5 4.4 9.0 0.0 4.2 5.7 6.5 5.7 0.0 28 47 1.3 20 0.5 18 0.0  Appendix II (continued): Duplicate analyses of major and trace elements from ACME Analytical Laboratories . 1  Sample No. Batch No.  71188 A304221  71189 A304221  avg  a  %RSD  71228 A304331  71229 A304331  avg  o  %RSD  Averag %RSD  37.7 0.37 2.72 13.05 0.12 32.69 0.42 0.05 0.14 0.01 0.550 12.0 0.03 0.08 100.06  37.27 0.38 2.64 12.96 0.12 32.76 0.42 0.06 0.12 0.01 0.560 12.5 0.05 0.09 100.03  37.485 0.375 2.68 13.005 0.12 32.725 0.42 0.055 0.13 0.01 0.555 12.3 0.04 0.085 100.045  0.30 0.01 0.06 0.06 0.00 0.05 0.00 0.01 0.01 0.00 0.007 0.4 0.01 0.01 0.02  0.81 1.89 2.11 0.49 0.00 0.15 0.00 12.86 10.88 0.00 1.274 2.9 35.36 8.32 0.02  34.49 0.19 2.01 15.59 0.17 33.62 0.42 <.01 0.07 <.01 0.527 12.4 0.05 0.01 99.7  34.99 0.19 2.03 15.86 0.17 33.17 0.36 <.01 0.07 <.01 0.540 12.2 0.07 0.02 99.8  34.74 0.19 2.02 15.725 0.17 33.395 0.39  0.35 0.00 0.01 0.19 0.00 0.32 0.04  1.02 0.00 0.70 1.21 0.00 0.95 10.88  0.07  0.00  0.00  0.009 0.1 0.01 0.01 0.07  1.723 1.1 23.57 47.14 0.07  0.55 1.11 0.76 0.53 0.00 0.41 3.11 11.26 3.43 1.86 1.68 3.59 37.38 21.83 0.08  1800 1487 1.19 13 6 0.8  86 1810 1544 1.21 <10 7 0.3  87 1805 1515 1.2 13 6.5 0.6  1 7 40 0  0.8 0.4 2.7 1.2  1 0.4  11 64  109 1671 1428 5 19 5 1.2  100 . • 1713. 1374 4 10 . 3 0.7  104 1692 1401 5 15 4 0.95  6 30 39 1 6 1 0.4  5.8 1.8 2.8 17 44 35 37  2.41 0.96 1.75 4.4 24 17 29  19.6 0.3 202 10.8 119 591.7 1052 13.1 5.8 0.1 0.3 0.3 6.8 13  19.5 0.2 207 10.6 115 614.9 1062 14.8 4.4 0.1 0.4 0.2 6.1 16  19.55 0.25 204.5 10.7 117 603.3 1057 13.95 5.1 0.1 0.35 0.25 6.45 15  0.07 0.07 3.54 0.14 2.83 16.40 7.07 1.20 0.99 0.00 0.07 0.07 0.49 2  0.36 28.28 1.73 1.32 2.42 2.72 0.67 8.62 19.41 0.00 20.20 28.28 7.67 14  18.6 <.1 25 9.2 106 549.3 1502 27 3.1 0.2 <.1 0.4 2.6 5  14.8 <.1 24 8.9 114 535.9 1435 24.3 3.7 0.2 0.1 0.4 4.1 5  16.7  2.69  16.09  3.61  0.71 0.21 5.66 9.48 47.38 1.91 0.42 . 0.00  2.89 2.34 5.14 1.75 3.23 7.44 12.48 0.00  4.94 1.86 3.07 1.66 1.20 7.70 11.57 7.07  0.00 1.06 0  0.00 31.66 5  7.83 9.88 6  Major elements (wt %) Si02 Ti02 AI203 Fe203 MnO MgO CaO Na20 K20 P205 Cr203 LOI TOT/C TOT/S SUM  Chalcophile elements (ppm) 87 Co Ni Ni* Cu Pd (ppb) Pt(ppb) Au (ppb)  " 0.534 12.3 0.06 0.015 99.75  -  Trace elements (ppm) Li* Be B* Sc* V Cr Mn Zn Ga Ge As Se Rb Sr  24.5 9.05 110 542.6 1468.5 25.65 3.4 0.2 0.1 0.4 3.35 5  Appendix II (continued) Sample No. Batch No. Y Zr Nb Mo Cd In Sn Sb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Ag (ppb) Tl Pb Th U  71188 A304221 6.5 25.9 19 0.12 0.01 0.02 • <1 . <.02 0.5 28 4.5 9.4 1.3 4.8 1.2 0.61 1.44 0.20 1.09 0.23 0.64 0.07 0.48 0.06 0.6 0.1 <.1 61 0.11 2 0.2 0.2  .  71189 A304221 6.4 24.7 2.2 0.12 0.01 0.02 <1 <.02 0.2 31 4.8 9.3 1.2 5.3 1.4 0.72 1.32 0.21 1.07 0.20 0.52 0.06 0.45 • 0.06 0.8 <.1 0.1 52 0.11 2 0.2 0.2  avg  a  %RSD  6.5 25.3 2.05 0.12 0.01 0.02  0.1 0.8 0.21 0.00 0.00 0.00  1.1 3.4 10 0.0 0.0 0.0  0.35 30 4.7 9.4 1.2 5.05 1.3 0.67 1.38 0.21 1.08 0.22 0.58 0.07 0.47 0.06 0.7 0.1 0.1 57 0.11 2 0.2 0.2  0.21 2 0.2 0.1 0.0 0.35 0.14 0.08 0.08 0.01 0.01 0.02 0.08 0.01 0.02 0.00 0.1  61 7.2 4.6 0.8 3.4 7.0 11 12 6.1 3.4 1.3 9.9 15 11 4.6 0.0 20 0.0  6 0.00 0 0.00 0.00  11.3 0.0 2.1 0.0 0.0  Duplicate analyses are multiple digestions of a single crushed sample. All Fe as F e 0 . * Partial digestion only. LOI = loss on ignition  2  2  3  TOT/C = total carbon; TOT/S = total sulphur by leuco  71228 A304331 3.0 9.3 0.7 0.09 <.01 0.02 <1 <.02 0.2 17 1.5 3.7 0.5 2.5 0.5 0.19 0.63 0.11 0.47 0.12 0.23 0.05 0.34 0.04 <.5 <.1 0.1 24 <02 2 0.6 <.1  71229 A304331 2.9 10.0 0.6 0.07 0.01 <,02 <1 <.02 0.3 24 1.5 3.5 0.4 2.3 0.7 0.19 0.76 0.08 0.54 0.10 0.28 <.05 0.32 0.04 <.5 <.1 <.1 26 <.02 1 <.1 0.1  avg  a  %RSD  3.0 9.7 0.65 0.08 0.01 0.02  0.1 0.5 0.07 0.01  2.4 5.1 11 18  %RSD avg 3.0 3.0 12 8.8  0.25 21 1.5 3.6 0.4 2.4 0.6 0.19 0.70 0.10 0.51 0.11 0.26 0.05 0.33 0.04  0.07 5 0.0 0.1 0.0 0.14 0.14 0.00 0.09 0.02 0.05 0.01 0.04  28 24 0.0 3.9 4.9 5.9 24 0.0 13 22 9.8 13 14  20 6.6 1.9 2.5 4.7 8.2 9.1 4.3 10 9.6 5.9 6.5 8.3  0.01 0.00  4.3 0.0  8.0 2.1 6.6 14  1  5.7  5.0  0  5.0 0.0 0.0  6.0 18 0.0  0.1 25 2 0.6 0.1  Appendix III: All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock Thin Section Geochem ID Probe point Drilled depth (m) Area Grain Site  West Pyrrhotite Lake / MX03-002 Peridotite Peridotite Peridotite RMX02-3A RMX02-3A RMX02-3A  Peridotite RMX02-3A  71112 2_3a_10  71112 2_3a_13  53 01 1 core  71112  71112  2_3a_11 53 01 1  2_3a_12 53 01 1  mid  rim  53 01 2 core  Peridotite RMX02-3A 71112 2_3a_14  Peridotite RMX02-3A 71112  53 01 2  2_3a_15 53 01 2  mid  rim  Peridotite RMX02-3A 71112 2_3a_16  Peridotite RMX02-3A 71112 2_3a_17  53 01 3 core  53 01 3  39.01 0.03 17.37 0.23 . 42.86 0.07-  39.15 0.01 17.69  mid  Peridotite RMX02-3A 71112  Peridotite RMX02-3A 71112  Peridotite RMX02-3A 71112  2_3a_18 53 01 3 rim  2_3a_1 53 02 1  2_3a_2 53 02  core  39.13 0.02  39.23 0.02  17.31 0.27  1 mid  Oxide wt % Si02 Ti02 FeO MnO MgO CaO  39.35 0.03 17.45 0.23 42.97  39.17 0.04  39.47  39.27  39.00  39.28  0.00 17.63 0.23 42.84 0.05  0.02 17.65 0.20  0.05 17.78  0.04 0.00  0.06 17.75 0.24 42.87 0.06 0.07  39.43 0.05 17.21 0.19 42.74 0.07  0.06 0.04  17.48 0.26 42.83 0.05 0.06  0.06  43.00 0.05 0.03  0.10  0.20 42.96 0.04 0.00  1  0.31  0.31  0.30  0.29  0.31  0.30 .  0.30  0.29  0.30  0.30  0.31  2  0.34  0.33 100.2  0.33 100.6  0.33 100.5  0.27 100.4  0.25 100.6  0.26 99.98  0.36 100.3  0.26 100.2  0.30 100.4  0.30 100.0  0.996 0.001  0.994  0.998 0.000  0.994  0.991 0.001  0.994 0.001  0.992  0.994  0.001  0.000  0.993 0.000  0.996  0.001  1.001 0.001  0.369 0.005 1.622  0.371  0.373  0.374  0.005 1.615  0.004 1.623  0.378 0.005 1.627  0.375  0.006 1.621 0.001  0.369 0.005 1.625  0.375 0.004  0.367 0.006  0.365 0.004  0.001 0.003  0.001 0.001  1.626 0.001  1.633 0.001  0.375 0.006 1.619 0.002  0.000 0.006  0.000 0.006  3.003  0.006 3.004  0.000 0.006  0.000  0.006 3.001  3.006  3.006  3.004  0.006 2.998  81.4 18.6  81.2 18.8  81.3 18.7  81.2 18.8  81.6 18.4  81.2 18.8  81.6 18.4  Cr203 NiO NiO  total  100.4  0.25 42.97  t  43.15 0.04 0.00  17.65 0.30 42.80 0.07 0.00  0.00  Cation (p.f.u.) Si Ti Fe * 2  Mn Mg Ca Cr Ni Sum  0.002 0.002 0.006 3.002  0.003 0.006  0.000  0.001  0.005 1.617 0.002  0.000 0.006  0.003 0.006  3.008  3.003  0.006 3.005  81.2 18.8  81.2 18.8  81.5 18.5  0.002 0.005  0.000  1.618 0.002  Endmembers % Fo Fa  81.4 18.6  ' Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition. 2  Data collected using the standard 20 nA beam current and 20 second counting time.  Appendix III (continued): All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock Thin Section Geochem ID  Peridotite RMX02-3A 71112  Peridotite RMX02-3A 71112  Peridotite RMX02-3A 71112  Peridotite RMX02-3A 71112  Peridotite RMX02-3A 71112  Peridotite RMX02-3A 71112  Probe point Depth (m) Area Grain  2_3a_3 53 02 1  2_3a_4 53 02 2  2_3a_5 53 02 2  2_3a_6 53 02 3  2_3a_7 53 02  Site  rim  mid  rim  mid  3 rim  2_3a_8 53 02 4  39.22 0.07  39.25 0.02  39.11  39.37  39.10 "  17.29 0.22 42.80 0.06 0.08  0.01 16.95 0.27  MgO CaO Cr203  17.75 0.19 42.76 0.02 0.02  39.36 0.03 17.57  0.03 17.00 0.26 42.90 0.06 0.00  NiO  1  0.30  NiO  2  mid  Peridotite RMX02-3A  Peridotite RMX02-4  Peridotite RMX02-4  Peridotite RMX02-4  Peridotite RMX02-4  71112 2_3a_9  71115 2_4_1 71  71115 2_4_2 71  71115 2_4_3 71  71115 2_4_4 71  4 rim  01 1 core  01 1 mid  01 1 rim  01 2 core  39.37 0.04  39.35 0.04  17.44 0.28 43.07 0.03  17.89 0.22 42.96 0.07  38.91 0.02 17.58 0.18 42.93 0.06  39.20 0.02 17.60 0.22 42.92 0.04  53 02  Oxide wt % Si02 Ti02 FeO MnO  total  0.04 0.02  43.10 0.08 0.11  0.00 17.26 0.26 43.17 0.04 0.02  0.01  0.01  0.13  39.33 0.01 17.78 0.25 42.96 0.07 0.02  0.30  0.30  0.31  0.30  0.31  0.29  0.31  0.31  0.32  0.30  0.31 100.3  0.32 100.0  0.30 100.5  0.37 99.93  0.29 100.4  0.25  0.31  0.27  99.66  100.5  100.9  0.28 100.1  0.35 100.7  0.29 100.4  0.995 0.001  0.997  0.996 0.001  0.993 0.000  0.996 0.000  0.997 0.001  0.996 0.001  0.994 0.001  0.989 0.000  0.995 0.000  0.994 0.000  0.377 0.004  0.367  0.372 0.005  0.360 0.006  0.365 0.006  0.362 0.006  0.369 0.006  0.378 0.005  0.374 0.004  0.376 0.005  0.002 0.004  1.620 0.001 0.001  1.631 0.002 0.005  1.628 0.001 0.001  1.630 0.002  1.624 0.001  1.618 0.002  1.627 0.002  1.619 0.002  0.373 0.005 1.622 0.001  0.006 3.003  0.006 3.001  0.006 3.003  0.006 3.004  0.006 3.003  0.000 0.006 3.003  0.000 0.006  0.000 0.006  0.006 0.006  0.001 0.006  3.003  3.005  3.008  3.005  0.002 0.006 3.004  81.1 18.9  81.5 18.5  81.3 18.7  81.9 18.1  81.7 18.3  81.8 18.2  81.5 18.5  81.1 18.9  81.3 18.7  81.2 18.8  81.3 18.7  0.25 '42.94  0.05  Cation (p.f.u.) Si Ti Fe * 2  Mn Mg Ca Cr Ni Sum  1.618 0.001 0.001  0.000 0.005 1.620  Endmembers % Fo Fa 1  Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition.  2  Data collected using the standard 20 nA beam current and 20 second counting time.  Appendix III (continued): All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock Thin Section Geochem ID Probe point Depth (m) Area Grain Site  Peridotite RMX02-4  Peridotite RMX02-4  Peridotite RMX02-4  71115 2_4_5 71  71115 2_4_6 71  71115 2_4_7  01 2 mid  01 2 rim  39.08 0.03 18.01 0.27 43.15  39.12 0.04 17.39  71 01 3 mid  Peridotite RMX02-4 71115 2_4_8 71 Ol 3 rim  Peridotite RMX02-4 71115  Peridotite RMX02-4 71115  Peridotite RMX02-4  Peridotite RMX02-4  Peridotite RMX02-4  Peridotite RMX02-4  Peridotite RMX02-4  2_4_9 71 02 1  2_4_10 71 02 1  71115 2_4_11 71 02 1  71115 2_4_12 71 02 2  71115 2_4_13 71 02  71115 2_4_14 71 02  71115 2_4_15 71  mid  rim  core  2 mid  2 rim  02 3 core  core  39.25 0.06  39.38 0.02  39.36 0.04  39.28 0.04  17.56 0.21 43.17  17.42 0.26 43.27 0.04 0.00  39.33 0.02 17.41 0.18 43.13  0.03 17.85 0.23 43.32  Oxide wt % Si02 Ti02 FeO MnO MgO CaO Cr203 NiO  0.05 0.00  1  NiO  2  total  39.36 0.04 17.97 0.21 43.12  39.18 0.00 17.69 0.22 43.21 0.04  39.57 ;  39.29  0.03 17.70 0:20 43.14 0.05  17.55 0.27 43.24 0.06  0.00  0.01  0.03 0.02  0.05 0.00  0.00  0.05 0.02  17.61 0.21 43.19 0.05 0.00  0.31  0.32  0.31  0.33  0.33  0:32  0.33  0.33  0.32  0.32 101.1  0.34  0.30 100.6  0.35 100.8  0.34 100.7  0.32 101.0  0.36 100.8  0.28 100.4  0.26 101.1  0.993 0.001  0.992  0.993 0.001  0.994  0.997 0.001  0.992 0.001  0.991  0.000  0.994 0.001  0.995  0.000  0.000  0.001  0.379  0.374  0.371  0.368  0.371  0.004 1.621  0.005  0.004  0.373 0.004  0.368 0.004  0.001 0.001  1.630 0.001 0.000  1.628 0.001 0.001  0.376 0.005 1.628  0.006 3.005  0.006 3.006  0.006 3.008  0.006 3.006  81.5 18.5  81.1 18.9  81.3 18.7  81.4 18.6  0.23 43.01 0.04 0.10  0.05 0.02  0.31  0.30  0.31 100.9  0.31 100.2  0.989  0.992  0.001  0.001  0.381 0.006 1.627  0.369 0.005 1.626  0.001 0.000 0.006  0.001 0.005  3.011  81.0 19.0  100.7  Cation (p.f.u.) Si Ti Fe * 2  Mn Mg Ca Cr Ni Sum  0.372 0.004 1.626 0.001  0.006 1.629 0.001  0.000 0.007  0.000 0.007  0.000 0.006  3.005  3.005  3.003  0.000 0.007 3.007  81.4 18.6  81.6 18.4  81.3 18.7  81.5 18.5  1.620 0.001  0.006 1!628 0.002  1.627 0.001 0.001 0.007  0.001 0.000  3.004  0.006 3.009  81.5 18.5  81.2 18.8  Endmembers % Fo Fa  Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition. 2  Data collected using the standard 20 nA beam current and 20 second counting time.  Appendix III (continued): All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock Thin Section Geochem ID Probe point Depth (m) Area Grain Site  Peridotite RMX02-4 71115 2_4_16 71 02 3 mid  Peridotite RMX02-4 71115 2_4_17 71 02 3 rim  F. Peridotite F. Peridotite F. Peridotite RMX02-5 RMX02-5 RMX02-5 71123 71123 71123 2_5_1 2_5_2 2_5_3 118 118 118 01 01 01 1 1 1 core mid rim  F. Peridotite RMX02-5 71123 2_5_4 118 01 2 core  F. Peridotite F. Peridotite RMX02-5 RMX02-5 71123 71123 2_5_5 2_5_6 118 118 01 01 2 2 mid  rim  38.97 0.03 18.29  39.00 0.08  F. Peridotite RMX02-5 71123 2_5_7 118 01 3 core  F. Peridotite RMX02-5 71123 2_5_8 118 01 3 mid  F. Peridotite RMX02-5 71123 2_5_9 118 01 3 rim  Oxide wt % Si02 Ti02 FeO MnO MgO CaO  39.42 0.03 17.57 0.22 43.37 0.04  Cr203 NiO 1  NiO  2  total  39.29 0.00 17.57 0.21 43.34  39.27 0.04 . 18.97'  38.82  39.16 0.03 18.64 0.24 42.17  39.13 0.04  0.03  0.04 0.00  0.27 42.20 0.05 0.12  0.05 , 18.44 0.29 42.17 0.05 . 0.00  0.32  0.31  0.30"  0.28  0.30  0.29  0.36 101.0  0.36 100.8  0.31 101.2  0.34  0.29  100:1  100.7  0.28 100.7  0.993 0.001  0.993  0.993 0.001  0.992 0.001  0.994  0.994  0.992  0.001  0.001  0.001  0.370 0.005 1.629  0.371  0.401 0.006  0.394  0.395 0.005 1.595  0.389 0.006 1.612  0.001 0.001  0.001 0.000  o.ooi  0.006 1.607 0.001  0.396 0.005 1.602  0.006 3.006  0.006 3.007  0.006 0.006' 3.004  0.000 0.006 3.007  0.001 0.001  81.5 18.5  81.5 18.5  79.9 20.1 "  80.3 19.7  39.04 0.04 18.87 0.27  39.02  39.00 0.06 18.24 0.32 42,43 0.05 0.00  18.33 0.25 42.62 0.06 0.03  42.57 0.05 0.00  0.03 18.61 0.24 42.32 0.04 0.07  0.29  0.29  0.30  0.30  0.29  0.39 100.4  0.27 100.7  0.34  0.34  101.2  100.6  0.27 100.4  0.990 0.002  0.989 0.001  0.991 0.001  0.993  0.389 0.005  0.400 0.006  0.395  0.388 0.007  0.001 0.000  1.613 0.002 0.001  1.608 0.001  3.003  0.006 3.005  0.006 3.007  0.006 3.008  0.000 0.006 3.010  80.1 19.9  80.2 19.8  80.6 19.4  80.6 19.4  80.1 19.9  0.03 0.12 .  18.63 0.24 42.31 0.04 0.03  0.30 42.49 0.04 0.00  Cation (p.f.u.) Si Ti Fe  2 t  Mn Mg Ca Cr Ni Sum  0.000 0.004 1.632  1.590  0.001 0.006 0.006  0.005 1.603  0.001  1.610  0.001 0.003 0.006  0.001 0.000 0.006  3.006  3.006  80.2 19.8  80.6 19.4  Endmembers % Fo Fa 1  Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition.  2  Data collected using the standard 20 nA beam current and 20 second counting time.  Appendix III (continued): All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock Thin Section Geochem ID Probe point Depth (m) Area Grain Site  F. Peridotite  F. Peridotite  RMX02-5 71123  RMX02-5 71123  F. Peridotite RMX02-5 71123  2_5_10 118 02 1  2_5_11 118 02 1  2_5_12 118 02 1  core  mid  rim  38.70 0.02  38.82 0.01 18.66  38.62  0.28 41.94 0.11 0.02  0.30 42.18 0.05 0.02  F. Peridotite F. Peridotite RMX02-5 RMX02-5 71123 71123 2_5_13 2_5_14 118 118 02 02  F. Peridotite F. Peridotite F. Peridotite F. Peridotite RMX02-5 RMX02-5 RMX02-6 71123 71123 71127 2_5_17 2_5_16 2_6_1 118 118 118 141 02 02 02 02 2 3 1 3 rim core mid core  F. Peridotite F. Peridotite RMX02-6 RMX02-6 71127 71127 2_6_2 2_6_3 141 141 02 02 1 2 mid  core  38.21 0.04  38.61 0.04  38.48 0.04  20.09 0.25 40.88 0.05 0.09  20.31 0.26 40.75 0.07 0.08  19.43 0.28 41.39 0.08 0.08  RMX02-5 71123 2_5_15  2 core  2 mid  38.73 0.04 18.70 0.29 42.46 0.05  0.03 18.58 0.25 42.47 0.07  38.99 0.01 18.78 0.29 42.07 0.04  Oxide wt % Si02 Ti02 FeO MnO MgO CaO  18.39 0.29 42.20 0.09 0.02  0.05 18.74  38.74  38.59 "0.05 18.77 0.29  38.94 0.05 18.87 0.29 41.96 0.07 0.00  0.00  0.13  0.03  42.01 0.05 0.03  1  0.28  0.28  0.28  0.28  0.28  0.28  0.29  0.28  0.28  0.29  0.29  2  0.21 100.1  0.27 100.2  0.30 100.5  0.29 100.5  0.31 100.5  0.29 100.1  0.32 100.5  0.32 99.88  0.31 100.4  0.24  total  0.30 99.99  Car/on (p.f.u.) Si Ti  0.990 0.000  0.993 0.000  0.987  0.987 0.001  0.985 0.001  0.993 0.000  0.988 0.001  0.993 0.001  0.986 0.001  0.991 0.001  0.988 0.001  0.393 0.006  0.399 0.006  0.401 0.006  0.398  0.436 0.006  1.608 0.001  0.402 0.006 1.604  0.434 0.005  1.599 0.003  0.400 0.006 1.598  0.402 0.006  1.610 0.002 0.001  0.395 0.005 1.610 0.002  0.417  0.006 1.613 0.001 0.000 0.006  0.006  0.006  0.006  0.006  3.011  3.012  0.006 3.006  0.005 0.006  0.006 1.585 0.002 0.004  0.006 3.011  0.000 0.006  1.560 0.002 0.004  0.006 3.009  0.001 0.006  0.001 0.001  1.573 0.001  0.001 0.006 3,007  0.001 0.001  1.595 0.002  3.010  3.006  3.011  3.006  3.009  80.4 19.6  80.0 20.0  80.1 19.9  80.2 19.8  80.3 19.7  80.0 20.0  80.0 20.0  79.9 20.1  78.4 21.6  78.2 21.8  79.2 20.8  Cr203 NiO NiO  Fe * 2  Mn Mg Ca Cr Ni Sum  0.001  100.1  Endmembers % Fo Fa 1  Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition.  2  Data collected using the standard 20 nA beam current and 20 second counting time.  Appendix III (continued): All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock Thin Section  F. Peridotite RMX02-6 71127  F. Peridotite RMX02-6 71127  F. Peridotite RMX02-6 71127  F. Peridotite F. Peridotite F. Peridotite F. Peridotite F. Peridotite F. Peridotite RMX02-6 RMX02-6 RMX02-6 RMX02-6 RMX02-6 RMX02-6 71127 71127 71127 71127 71127 71127  Ol-Gbnr  2_6_4 141 02  2_6_5 141 02  2_6_6 141 02  2_6_7 141  2 rim  3 core  3 rim  2_8_1 162 01 1  38.67  38.85  38.73  FeO MnO MgO CaO Cr203  0.02 19.52 0.27 41.48 0.05 0.12  0.06 19.62  0.00 19.43 0.24 40.96 0.08 0.02  0.28 41.41 0.06 0.00  NiO  1  0.28  0.28  0.28  NiO  2  0.28 100.4  0.36 100.3  0.33 99.75  0.989 0.000  0.996 0.001  0.417 0.006  Geochem ID Probe point Depth (m) Area Grain Site  03 1  2_6_8 141 03 1  2_6_9 141 03 2  2_6_10 141 03 2  core  rim  core  mid  38.81 0.02 19.27  38.74  38.42 0.04  38.48 0.04 19.12  2_6_11 141 03  2_6_12 141 03  3 core  3 mid  38.51 0.02  38.82  RMX02-8 71133  Ol-Gbnr RMX02-8 71133 2_8_2 162 01 1  core  mid  38.13 0.01  38.32 0.04  21.99 0.28 39.14  22.01 0.27  Oxide wt % Si02 Ti02  total  41.30 0.08 0.03  19.19 0.28 41.33 0.06 0.04  0.27 41.52 0.02 0.04'  19.28 0.25 41.49 0.06 . 0.02  0.05 19.06 0.22 41.23 0.07 0.03  0.30  0.31  0.33  0.32  0.31  0.34 100.2  0.32 100.1  0.35 99.70  0.25 99.82  0.32 99.95  0.997 0.000  0.995 0.000  0.994  0.990 0.001  0.990 0.001  0.990 0.000  0.420 0.006  0.418 0.005  0.413 0.006  0.413 0.006  0.411 0.006  0.414  1.582 0.001  1.572 0.002  1.572 0.002  1.583 0.002  0.415 0.006 1.579  0.006 0.006 3.008  0.000 0.006 3.003  0.001 0.006 3.002  0.000 0.006 3.005  0.006 3.005  1.588 0.002 0.002 0.007  79.1 20.9  78.9 21.1  79.0 21.0  79.3 20.7  79.2 20.8  0.27 41.15 0.07 0.00  0.03 19.37 0.27  0.02 0.00  39.06 0.06 0.00  0.31  0.25  0.25  0.31  0.26 99.82  0.27 100.0  0.997 0.001  0.994  0.996 0.001  0.409 0.005  0.479  0.005  1.592 0.001 0.002  1.590 0.002 0.001  1.579 0.002 0.001  0.007  0.006  3.008  3.009  3.009  0.006 3.001  79.3 20.7  79.5 20.5  79.3 20.7  79.4 20.6  99.78  Cation (p.f.u.) Si Ti Fe * 2  Mn Mg Ca Cr Ni Sum  0.001  0.002 0.001  0.000 0.006 1.521 0.001  0.479 0.006 1.514 0.002  0.000 0.005  0.000 0.005  3.006  3.003  76.0 24.0  76.0 24.0  Endmembers % Fo Fa 1  Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition.  2  Data collected using the standard 20 nA beam current and 20 second counting time.  Appendix III (continued): All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock Thin Section Geochem ID Probe point Depth (m) Area Grain Site  Ol-Gbnr  Ol-Gbnr  Ol-Gbnr  Ol-Gbnr  Ol-Gbnr  Ol-Gbnr  Ol-Gbnr  Ol-Gbnr.  RMX02-8  RMX02-8  RMX02-8  71133 2_8_4  71133 2_8_5 162  RMX02-8 71133 2_8_7  RMX02-8 71133  RMX02-8 71133  RMX02-8  71133 2_8_3 162 01 1  RMX02-8 71133 2_8_6 162  2_8_8 162 01 3  2_8_9 162 01  rim  core  38.14 0.03 22.54  38.11 0.01  162 01 2  01 2 mid  01 2 rim  162 01 3 core  mid  3 rim  38.36 0.02  38.41 0.04  20.89 0.28 39.79  Ol-Gbnr RMX02-8  71133 2_8_10 162 02 1  71133 2_8_11 162 . 02 1  core  mid  Ol-Gbnr  Ol-Gbnr  RMX02-8 71133 2_8_12 162  RMX02-8 71133 2_8_13  02 1 rim  162 02 2 core  Oxide wt % Si02 Ti02 FeO MnO MgO CaO Cr203  38.32  38.24 0.04 22.04 0.27 38.87  0.05 0.00  38.94 0.05 0.02  0.02 22.78 0.32 39.07 0.07 0.00  0.28 39.37  22.03 0.34  0.06 0.01  38.51 0.02 21.03 0.28 40.09 0.07 0.03  38.38  38.29 0.02 21.97 0.33 39.64  0.06 0.03  21.46 0.26 39.95 0.07 0.00  0.03 21.48 0.29 39.53 0.03 0.05  NiO  1  0.25  0.24  0.26  0.25  0.25  0.25  0.25  0.26  NiO  2  0.26 100.7  0.23 99.73  0.25  0.18 99.78  0.25 100.3  0.28 99.69  0.28 100.4  0.30 100.1  0.988 0.001  0.994 0.000  0.992  0.997 0.001  0.994 0.000  0.996 0.000  0.992 0.001  0.995 0.001  0.488 0.006  0.481  0.493 0.007  0.453 0.006  0.463 0.006  0.465  1.539 0.002 0.002  1.538 0.002  total  100.8  0.06 0.00 • 0.26 0.27 100.6  38.18 0.00 21.64 0.30 39.66 0.04  38.57 0.04 21.30 0.29 40.07  0.02  0.09 0.01  0.27  0.26  0.29 100.1  0.25 100.6  0.991 0.000  0.993 0.001  0.470 0.007 1.534  0.459 0.006  Cation (p.f.u.) Si Ti Fe  2 +  Mn Mg Ca Cr Ni Sum  1.521 0.001  0.008 1.515 0.001  0.000  0.480 0.006 1.511  0.454  0.000  0.002 0.001  0.002 0.002  0.005 3.002  0.005 3.005  0.005  75.9 24.1  77.3 22.7  1.508 0.002  0.000 0.005 3.011  0.001 0.005 3.005  0.005 3.008  75.7 24.3  75.9 24.1  75.4 24.6  0.006 1.542  0.006 1.527 0.001  0.991 0.000  u  •  0.475 0.007 :  1.529 0.002 0.000  0.001 0.001  1.538 0.002 0.000  0.003 0.006  3.003  0.000 0.005 3.007  3.003  0.005 3.009  0.006 3.009  0.005 3.006  77.3 22.7  76.8 23.2  76.6 23.4  76.3 23.7  76.6 23.4  77.0 23.0  Endmembers % Fo Fa 1  Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition.  2  Data collected using the standard 20 nA beam current and 20 second counting time.  Appendix III (continued): All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock  Far West Margin / MX03-001 Ol-Gbnr  Ol-Gbnr  Ol-Gbnr  Ol-Gbnr  RMX02-8 71133 2_8_15 162  RMX02-8 71133  RMX02-8 71133 2_8_17  Area Grain  RMX02-8 71133 2_8_14 162 02 2  Site  rim  core  FeO MnO MgO CaO Cr203  38.51 0.03 21.16 0.31 40.11 0.08 0.02  38.58 0.00 21.50 0.26 40.04  NiO  1  NiO  2  Thin Section Geochem ID Probe point Depth (m)  02 3  2_8_16 162 02 3 rim  Ol-Gbnr RMX02-8  Ol-Gbnr RMX02-8  162 02 4  71133 2_8_18 162 02 4  71133 2_8_19 162 02 4  core  mid  rim  38.61 0.00  38.61 0.02  38.50 0.04  21.08 0.26 40.29 0.08 0.02  21.01 0.31 40.21 0.03 0.04  21.00 0.28 40.22  Cr. Peridotite Cr. Peridotite Cr. Peridotite Cr. Peridotite Cr. Peridotite RMX01-1 71061  RMX01-1 71061  RMX01-1 71061  1_1_1 10 01 1 core  1_1_2 10 01 1  1_1_3 10 01 1 rim  39.97  40.02 0.01 12.78 0.18 46.87  mid  RMX01-1  RMX01-1  71061  71061  1_1_4 10 01 2  1_1_5 10 01 2  core  mid  39.28  40.40  0.01 18.54 0.14  0.00 12.36 0.19 47.11  40.26 0.04  Oxide wt % Si02 Ti02  total  •  38.22 0.02 21.20 0.27  0.05 0.00  40.18 0.09 0.00  0.27  0.26  0.27  0.26  0.27  0.27  0.26 100.5  0.31 100.7  0.21 100.2  0.25 100.6  0.27 100.5  0.29 100.4  0.993 0.001  0.994 0.000  0.989 0.000  0.993 0.000  0.994 0.000  0.456 0.007  0.463 0.006 1.537  0.459 0.006 1.549  0.453 0.006  0.452 0.007  0.001 0.000  0.002  1.545 0.002 0.001  1.543 0.001 0.002  0.005 3.006  0.006 3.005  77.3 22.7  77.3 22.7  0.02 12.95 0.23 46.80 0.07  0.07 0.15  12.86 0.13 47.19 0.09 0.04  0.17  0.28  0.29  0.14 100.6  0.28  0.31  100.6  100.9  0.996 0.000  0.996 0.000  0.993 0.001  0.393 0.003  0.255 0.004  0.265  1.731 0.002 0.007  0.05 0.09  42.33 0.01 0.13  0.28  0.29  0.29 100.5  0.24  0.993  0.990  0.992  0.001  0.000  0.000  0.453  0.268 0.005 1.728 0.002  0.265 0.004 1.733  0.06 0.00  0.16  100.3  Cation (p.f.u.) Si Ti Fe  2 t  Mn Mg Ca Cr Ni Sum  1.541 0.002 0.001 0.005 3.006  0.005 3.006  0.000 0.006 3.011  77.2 22.8  76.9 23.1  77.2 22.8  0.006 1.546 0.002  0.003 1.734 0.002  0.008  0.001 0.004  1.599 0.000 0.006  0.006 3.005  0.003 3.001  0.006  0.002 0.006  3.006  0.006 3.006  3.000  3.006  77.3 22.7  86.6 13.4  86.7 13.3  80.3 19.7  87.2 12.8  86.7 13.3  0.000 0.006  Endmembers % Fo Fa 1  Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition.  2  Data collected using the standard 20 nA beam current and 20 second counting time.  Appendix III (continued): All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock  Cr. Peridotite Cr. Peridotite RMX01-1 RMX01-1 71061 71061 1_1_7 1_1_6 10 10 01 01 2 3 rim core  Cr. Peridotite Cr. Peridotite RMX01-1 RMX01-1 71061 71061 1_1_8 1_1_9 10 10 01 01 3 mid  3 rim  core  mid  rim  Si02 Ti02 FeO  40.08 0.04 12.77  40.07  40.73  40.34  MnO MgO CaO Cr203  0.25 47.04  0.03 13.00 0.22 47.03 0.07 0.06  0.01 11.99 0.13 47.13 0.07 0.02  40.33 0.01 12.13 0.13 47.13 0.06  40.18 0.03 12.26 0.15 47.14  0.04 0.11  12.89 0.20 47.04 0.07 0.06  0.01 12.72 0.21 47.10 0.08 0.16  NiO  1  0.29  0.29  0.30  0.28  0.30  NiO  2  0.27  0.31  100.6  0.33 100.7  100.6  0.35 101.4  0.34 99.97  0.991 0.001  0.992 0.000  0.990 0.000  0.999 0.001  0.264 0.005  0.266 0.004  0.263 0.004  1.733 0.001  1.732 0.002  0.005 0.006  Thin Section Geochem ID Probe point Depth (m) Area Grain Site  Cr. Peridotite Cr. Peridotite Cr. Peridotite RMX01-1 RMX01-1 RMX01-1 71061 71061 71061 1_1_10 1_1_11 1_1_12 10 10 10 02 02 02 1 1 1  Cr. Peridotite Cr. Peridotite Cr. Peridotite Cr. Peridotite RMX01-1 71061 1_1_13  RMX01-1 71061 1_1_14  10 02 2 core  10 02 2 rim  40.54 0.03 12.11 0.18 47.71  40.38 0.02 12.10 0.16 47.83  0.06 0.07  0.08 0.00  0.30  0.29  0.29 100.1  0.29 100.2  0.999 0.000  0.999 0.000  0.266  0.248  1.734 0.002  0.005 1.719 0.002  0.003 1.741 0.002  0.003 0.006  0.008 0.006  0.003 0.006  0.001  3.006  3.006  3.006  2.999  0.006 3.000  86.8 13.2  86.7 13.3  86.8 13.2  86.6 13.4  87.5 12.5  RMX01-1 71061 1_1_15 10 02 3 core  RMX01-1 71061 1_1_16 10 02 3 mid  Oxide wt %  total  40.18 0.02  40.76 0.01 12.05 0.17  40.59 0.01 11.69  0.05 0.10  47.86 0.06 0.07  0.18 47.85 0.05 0.04  0.26  0.28  0.28  0.30  0.29 100.9  0.21 100.9  0.25 101.3  0.28 100.7  0.995 0.001  0.996 0.001  0.991 0.000  0.997  0.997 0.000  0.251  0.254  0.249  0.003 1.740 0.002  0.003 1.740  0.004 1.747  0.248 0.003  0.246 0.004 1.744  0.000  0.002 0.003  0.002 0.000  0.006 3.001  0.006 3.003  0.005 3.004  0.005 0.005 3.006  0.003 0.006 3.002  87.4 12.6  87.3 12.7  87.5 12.5  87.6 12.4  87.6 12.4  0.01  Cation (p.f.u.) Si Ti Fe ' 2  Mn Mg Ca Cr Ni Sum  1.751 0.001  0.000  0.002  0.240 0.004 1.752 0.001 0.002 0.006 3.002  Endmembers % Fo Fa 1  Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition.  2  Data collected using the standard 20 nA beam current and 20 second counting time.  87.9 12.1  Appendix III (continued): All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock Thin Section Geochem ID Probe point Depth (m) Area Grain Site  Cr. Peridotite Cr. Peridotite Cr. Peridotite RMX01-1 RMX01-3 RMX01-3 71061 71063 •71063 1_1_17 1_3_2 1_3_1 10 23 23 02 02 02 3 rim  1 core  1  Cr. Peridotite Cr. Peridotite Cr. Peridotite RMX01-3 RMX01-3 RMX01-3 71063 71063 71063 1_3_3 1_3_4 1_3_5 23 23 23 02 02 02 1 2 2  mid  rim  core  mid  40.22  40.35 0.05 12.95 0.18  40.10 0.02 13.07 0.19  40.45  46.66 0.08  40.01 0.03 13.04 0.17 46.20 0.11  40.14 0.03 12.88 0.26 46.59  0.05  46.75 0.08 0.05  0.01 12.70 0.19 46.51 0.07 0.08  Cr. Peridotite Cr. Peridotite Cr. Peridotite Cr. Peridotite Cr. Peridotite RMX01-3 71063 1_3_6 23 02 2 rim  RMX01-3 71063 1_3_7 23 01 1 core  RMX01-3 71063 1_3_8 23 01 1 mid  RMX01-3 71063  RMX01-3 71063  1_3_9 23 01 2  1_3_10 23 01 2  core  mid  40.18 0.00 12.27  40.34 0.02  Oxide wt % Si02 Ti02 FeO MnO MgO CaO Cr203 NiO  0.00 13.46 0.17 47.04 0.01 0.00  0.05  0.10 0.00  39.89  40.18 0.05 12.59 0.19 46.57  40.37  0.00  0.09 0.00  0.08 13.06 0.22 46.92 0.09  0.02 12.79 0.17 46.71 0.06 0.10  0.18 47.01 0.03 0.03  12.73 0.20 47.04 0.08 0.03  1  0.21  0.15  0.15  0.14  0.16  0.16  0.14  0.14  0.15  0.14  0.15  2  0.21 101.1  0.13 100.5  0.14 100.4  0.09 100.2  0.15 99.76  0.12 100.2  0.19 100.4  0.12 99.80  0.14  0.16 99.84  0.16  0.992 0.000  0.998 0.001  0.994  1.002 0.000  0.998 0.001  0.997  0.990 0.001  1.000  0.999  0.001  0.001  0.000  0.998 0.000  0.996 0.000  0.278 0.004  0.268 0.004  0.271  0.263 0.004  0.272 0.004  0.268 0.005  0.271 0.005  0.262 0.004  0.265 0.004  0.255 0.004  0.263 0.004  Mg Ca Cr Ni  1.730 0.000  1.721 0.002  1.718  1.726 0.003 0.000  1.727 0.002  1.722 0.002  1.740 0.001  1.732 0.002  0.002  0.003 2.996  3.000  3.008  . 2.999  0.003 2.999  0.001 0.003 3.002  0.001 0.003  3.008  0.003 3.002  0.000 0.003  Sum  0.003 3.004  0.000 0.003  0.005  0.003 3.000  0.003 0.002 0.003  1.736 0.002  0.000 0.004  0.002 0.002  86.2 13.8  86.5 13.5  86.4 13.6  86.7 13.3  86.3 13.7  86.6 13.4  86.7 13.3  87.2 12.8  86.8 13.2  NiO  total  100.4  100.6  Cation (p.f.u.) Si Ti Fe  2 t  Mn  0.000 0.004 1.728  1.718 0.002 0.004  3.002  Endmembers % Fo Fa 1  Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition.  2  Data collected using the standard 20 nA beam current and 20 second counting time.  86.5 13.5  86.8 13.2  Appendix III (continued): All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock Thin Section Geochem ID Probe point Depth (m) Area Grain Site  Cr. Peridotite Cr. Peridotite RMX01-3 RMX01-3 71063 71063 1_3_12 1_3_11  Cr. Peridotite Cr. Peridotite RMX01-3 RMX01-3 71063 71063 1_3_14 1_3_13  Cr. Peridotite Cr. Peridotite RMX01-3 RMX01-3 71063 71063 1_3_15 1_3_16 23 23 01 01 4 4  23 01 2 rim  23 01  23 01  23 01  3 core  3 mid  3 rim  40.24 0.00 12.17 0.17  40.21 0.03 12.87  40.22 0.04 12.97  47.22 0.04 0.05  0.21 46.55 0.10 0.03  Cr. Peridotite Peridotite RMX01-3 RMX01-4 71072 71063 1_3_17 1_4_1  Peridotite RMX01-4 71072  Peridotite RMX01-4 71072  56 01 1  1_4_2 56 01 1  1_4_3 56  23 01 4  01 1  core  mid  rim  core  mid  rim  40.22  40.18  40.24  40.08  39.85  0.03 12.90 0.17  0.03 12.47 0.19 46.98 0.05 0.13  0.06 14.32 0.21 45.35 0.07 0.02  39.86 0.02 14.88 0.16 45.37 0.10  Ti02 FeO MnO MgO CaO Cr203  0.23 46.31 0.08 0.00  0.01 13.11 0.18 46.86 0.05 0.03  0.00 12.56 0.16 46.78 0.09 0.07  46.82 0.05 0.02  71072 1_4_4 56 01 2 core  •  Oxide wt % Si02  Peridotite RMX01-4  39.95  39.69  0.05 14.27  0.02 14.35 0.20 45.42 0.11  0.09  0.17 45.18 0.06 0.04  NiO  1  0.15  0.15  0.13  0.14  0.15  0.14  0.14  0.33  0.33  0.34  0.34  NiO  2  0.19  0.09 99.99  0.17  0.13 100.4  0.35 100.2  0.27 100.8  0.35 100.1  0.29  100.6  0.16 100.0  0.11  100.0  0.12 100.2  0.997 0.000  0.998 0.001  1.001 0.001  0.995 0.000  0.997 0.000  0.997 0.001  0.994 0.001  0.997  0.993 0.000  1.000 0.001  0.994  0.252 0.004  0.267  0.271 0.004  0.261  0.267 0.004  0.258 0.004  0.299 0.004  0.310  0.004  0.270 0.005  0.299 0.004  0.301 0.004  1.744 0.001 0.002  1.723 0.003  1.718 0.002  1.728 0.001  1.729 0.001  1.736 0.001  1.691 0.002  0.003  0.001 0.003  0.000 0.003  0.003 0.003  0.001 0.003  0.006 0.003  3.002  3.000  2.999  0.001 0.003 3.004  3.001  3.002  87.4 12.6  86.6 13.4  86.4 13.6  86.4 13.6  86.9 13.1  86.6 13.4  total  100.1  0.00  100.1  Cation (p.f.u.) Si Ti Fe ' 2  Mn Mg Ca Cr Ni Sum  0.003 1.731 0.002  0.001  0.003 . 1.685  0.000  1.685  1.696  0.001 0.007  0.003 0.004 0.007  0.002 0.002 0.007  0.003 0.000 0.007  3.003  3.002  3.005  2.998  3.005  87.0 13.0  85.0 15.0  84.5 15.5  85.0 15.0  84.9 15.1  Endmembers % Fo Fa 1  Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition.  2  Data collected using the standard 20 nA beam current and 20 second counting time.  Appendix III (continued): All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock Thin Section Geochem ID Probe point Depth (m) Area Grain Site  Peridotite RMX01-4  Peridotite RMX01-4  Peridotite RMX01-4  71072 1_4_5  71072 1_4_6  71072 1_4_7  56 01 2 mid  56 01 2 rim  56 01 3  39.69 0.04 14.45 0.29 45.71 0.04  39.97 0.02 14.68 0.25  39.83 0.06 14.45 0.21 45.24  14.28 0.20 45.34  0.06 0.07  0.06: 0.00  39.85 0.05 14.54 0.19 45.47 0.07" 0.00  core  Peridotite RMX01-4 71072 1_4_8 56 01 3 mid  Peridotite RMX01-4  Peridotite RMX01-4  71072 1_4_9  71072 1_4_10  56  56 02 1 core  01 3 rim  Peridotite  Peridotite RMX01-4 71072  Peridotite RMX01-4 71072  Peridotite RMX01-4 71072  1_4_11 56 02 1 mid  1_4_12 56 02 1  1_4_13 56 02  1_4_14 56 02  2 core  2 rim  39.66 0.01 14.53 0.24 45.14  39.85  0.05 14.76 0.17 45.30 0.10 0.02  RMX01-4 71072  rim  Peridotite RMX01-4 71072 1_4_15 56 02 3 core  Oxide wt % Si02 Ti02 FeO MnO MgO CaO Cr203  0.00  45.68 0.05 0.01  39.64 0.04  39.87  39.50 0.04  0.11 0.10  0.05 14.85 0.21 45.44 0.05 0.04  14.26 0.22 45.19 0.07 0.00  39.74  39.62  0.01 14.39 0.15 45.26 0.05  0.01 14.62 0.20 44.98  0.00  0.13 0.07  NiO  1  0.33  0.33  0.33  0.33  0.33  0.34  0.34  0.33  0.35  0.34  0.34  NiO  2  0.34  0.36 100.2  0.32 99.88  0.36 100.5  0.34 100.6  0.35 100.1  0.34  0.37  100.5  0.28 101.0  100.8  99.63  0.42 99.94  0.31 99.97  0.991  0.994  0.995 0.001  0.995  0.994  0.001  0.001  0.000  0.993 0.001  0.994 0.001  0.997  0.000  0.996 0.001  0.995  0.001  0.000  0.995 0.000  0.302  0.305 0.005 1.693  0.302 0.004  0.300 0.004 1.697  0.304 0.004  0.308 0.004  0.304  0.309 0.004  0.300  0.302  0.307  1.685  0.004 1.684  0.003 0.001 0.007  1.688 0.001  0.000 0.007 3.004  1.686 0.003 0.005 0.007  0.003 1.693  0.002  1.692 0.002  0.005 1.696 0.002  0.002 0.007  0.000 0.007  0.001 0.000 0.007  0.003 0.003 0.007  3.003  3.004  3.005  3.005  3.003  3.003  84.8 15.2  84.5 15.5  84.7 15.3  84.5 15.5  85.0 15.0  84.9 15.1  84.6 15.4  total  Cation (p.f.u.) Si Ti Fe  2 t  Mn Mg Ca Cr Ni Sum  0.006 1.701 0.001  1.686 0.002 0.003  0.000 0.007  0.001 0.000 0.007  3.008  3.006  3.001  0.000 0.007 3.004  84.9 15.1  84.7 15.3  84.8 15.2  85.0 15.0  0.007  0.005  Endmembers % Fo Fa 1  Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition.  2  Data collected using the standard 20 nA beam current and 20 second counting time.  Appendix III (continued): All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock Thin Section  Peridotite  Peridotite  RMX01-4 71072 1_4_17  RMX01-4 71072  Peridotite RMX01-4 71072  1_4_18 56 02 4  1_4_19 56 02 4  mid  rim  39.84 0.09 14.55 0.17  40.00  45.30 0.07 0.00  39.63 0.02 16:08 0.20 43.71 0.17  0.00  45.21 0.07 0.10  40.01 0.02 14.80 0.21 45.41 0.08 0.04  1  0.32  0.33  0.35  2  ' 0.30 100.4  0.33 100.4  0.995 0.001 0.307  Geochem ID Probe point Depth (m) Area Grain Site  Peridotite RMX01-4 71072 1_4_16 56 02 3 mid  56 02 3 rim  F. Peridotite F. Peridotite F. Peridotite RMX01-5 RMX01-5 RMX01-5 71075 71075 71075 1_5_2 1_5_1 1_5_3 76 76 76 01 01 01 1 1 1 core mid rim  F. Peridotite RMX01-5  76 01 2  F. Peridotite F. Peridotite F. Peridotite RMX01-5 RMX01-5 RMX01-5 71075 71075 71075 1_5_5 1_5_6 1_5_7 76 76 76 01 01 01 2 2 3  core  mid  71075 1_5_4  rim  core  39.59 0.03 15.66 0.23 44.03 0.11  Oxide wt % Si02 Ti02 FeO MnO MgO CaO Cr203 NiO NiO  total  39.76 0.04 14.69 0.20 45.24 0.11  39.65 0.00 16.76 0.25 43.85  39.27 0.01 16.32 0.24 43.67  0.11  0.11 0.00  0.07 0.00  0.33  0.25  0.24  0.27  0.34 100.7  0.32  0.24 100.2  0.22 100.9  0.17 99.85  0.24  100.9  0.995 0.002  0.997  0.996 0.000  0.998 0.000  0.996 0.000  0.995 0.000  0.306 0.005 1.684  0.308 0.004  0.339  0.352  0.004 1.642  0.005 1.642  0.346 0.005  0.005 0.005  0.003 0.000  3.003  0.005 2.998  84.5 15.5  82.9 17.1  0.06 14.67 0.24  •  39.75 0.04 16.21  39.48  39.62  0.01 15.92 0.22 43.90 0.09 0.08  0.05 15.81 0.22 43.99 0.04 0.14  0.25  0.26  0.25  0.28 .99.95  0.21  100.3  100.1  0.22 99.92  0.999 0.001  0.997 0.000  0.997 0.001  0.999 0.001  0.341  0.336  0.006 1.644 0.003  0.005 1.652 0.002 0.004  0.333 0.005 1.650  0.331 0.005 1.657  0.001 0.007  0.003 0.000  0.27 43.88 0.10 0.04  0.00  Cation (p.f.u.) Si Ti Fe  0.001  Mn  0.004  0.304 0.004  Mg Ca Cr Ni  1.688 0.003 0.000  1.683 0.002 0.005  0.006 3.004  0.007 3.001  0.007 3.002  84.6 15.4  84.7  84.6 15.4  2 t  Sum  0.002 0.000  1.684 0.002 0.002 0.007  1.650 0.002  0.005 3.004  0.000 0.006 3.004  0.002 0.005 2.999  3.001  0.005 2.999  0.005 3.000  82.3 17.7  82.7 17.3  82.8 17.2  83.1 16.9  83.2 16.8  83.4 . 16.6  0.005  Endmembers % Fo Fa  15.3  1  Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition.  2  Data collected using the standard 20 nA beam current and 20 second counting time.  Appendix III (continued): All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock Thin Section Geochem ID Probe point Depth (m) Area Grain Site  F. Peridotite RMX01-5 71075 1_5_8 76 01 3 mid  F. Peridotite F. Peridotite RMX01-5 RMX01-5 71075 71075 1_5_9 1_5_10 76 76 01 02 3 1 rim core  F. Peridotite  F. Peridotite F. Peridotite F. Peridotite  F. Peridotite  RMX01-5 71075 1_5_11  RMX01-5 71075 1_5_12  RMX01-5 71075  76 02 1  76 02 1  1_5_13 76 02 2  mid  rim  39.63  39.60 0.03 16.35 0.27 43.61 0.08 0.06  F. Peridotite RMX01-5  F. Peridotite RMX01-5  71075 1_5_16 76 02 3  71075 1_5_17  76 02 2  1_5_15 76 02 2  core  mid  rim  core  39.51 0.02 17.01 0.24 43.81  39.75 0.04 16.34 0.21 44.14  39.50 0.04  39.56 0.00 16.72  0.08 0.03  0.08 0.00  39.42 0.03 16.44 0.22 44.22 0.07  RMX01-5 71075  RMX01-5 71075 1_5_14  F. Peridotite RMX01-5 71075  76 02  1_5_18 76 02  3 mid  3 rim  39.50 0.04  39.81 0.03 16.83 0.23 43.57 0.07  Oxide wt % Si02 Ti02 FeO  39.72 0.01 15.54  .  39.74 0.04 15.79 0.17  MnO MgO CaO Cr203 NiO  0.26 43.96 0.13 0.07  44.23 0.07 0.06  0.00 16.85 0.25 43.85 0.12 0.13  1  0.26  0.24  0.25  0.27  0.25  NiO  2  0.19 99.94  0.21 100.3  0.29  0.25 100.3  0.24  1.001 0.000  0.998 0.001  0.993 0.000  0.327 0.006  0.332 0.004  0.353 0.005  1.651 0.004 0.003  1.656 0.002 0.003  1.638 0.003  0.005 2.997  83.5 16.5  total  16.19 0.26 44.24  16.40 0.20 43.56 0.06 0.00  0.00  0.06 0.03  0.19 43.72 0.06 0.09 .  0.25  0.24  0.24  0.26  0.26  0.25  0.23 100.6  0.29 100.6  0.23 100.6  0.28 100.0  0.24  100.9  0.24 100.8  0.999  0.993  0.997  0.992  0.001  0.000  0.001  0.001  0.993 0.001  0.995 0.000  0.999 0.001  1.001 0.001  0.345  0.357 0.005 1.641 0.002  0.343 0.004  0.346 0.005  0.340 0.006  0.352 0.004  0.347 0.004  0.354  0.006 1.639 0.002  1.650  0.001  0.002 0.000  1.640 0.002 0.004  0.005 3.000  0.003 0.005  1.658 0.002 0.001  1.642 0.002  0.006 0.005 3.004  1.658 0.002 0.000  0.005 3.002  0.005 3.008  0.005  2.999  0.005 3.006  0.005 3^002  83.3 16.7  82.3 17.7  82.6 17.4  82.1 17.9  82.8 17.2  82.7 17.3  83.0  101.1  0.00  100.8  Cation (p.f.u.) Si Ti Fe * 2  Mn Mg Ca Cr Ni Sum  3.006  0.000 0.005  0.005 1.632 0.002  3.000  0.000 0.005 2.999  82.6 17.4  82.2 17.8  Endmembers % Fo Fa 1  Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition.  2  Data collected using the standard 20 nA beam current and 20 second counting time.  17.0  82.3 17.7  Appendix III (continued): All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock  Cr. Peridotite Cr. Peridotite Cr. Peridotite RMX01-6 RMX01-6 RMX01-6 71078 71078 71078 1_6_1 1_6_2 1_6_3 93 93 93 01 01 01 1 1 1  93 01 2  93 01 2  1_6_6 93 01 2  core  mid  rim  core  mid  rim  3 core  Si02  39.92  40.07  Ti02 FeO MnO MgO  0.02 14.40 0.24 45.56 0.07  0.03 14.19 0.17 45.54 0.07  40.10 0.06 14.14  39.86 0.06 14.79 0.14  39.54 0.05 14.40 0.18  39.67 0.02  39.70 0.02  39.95 0.02  0.00  0.00  0.05 0.17  45.89 0.07 0.03  45.56 0.08 0.06  14.45 0.22 45.90 0.07 0.01  14.10 0.21 45.66 0.08 0.14  14.48 0.18 45.43 0.11 0.00  Thin Section Geochem ID Probe point Depth (m) Area Grain Site  Cr. Peridotite Cr. Peridotite RMX01-6 RMX01-6 71078 71078 1_6_4 1_6_5  Cr. Peridotite Cr. Peridotite Cr. Peridotite Cr. Peridotite Cr. Peridotite Cr. Peridotite RMX01-6 71078  RMX01-6 71078 1_6_7 93 01  RMX01-6 71078 1_6_8 93 01 3 mid  RMX01-6 71078 1_6_9 93 01  RMX01-6 71078 1_6_10 93 02 1  RMX01-6 71078 1_,6_11 93 . 02  3 rim  core  1'. mid  39.67  40.01  39.67  0.01 13.89 0.25 45.80 0.06  0.03 14.41  0.03 14.53 0.21 45.25 0.13 0.00  Oxide wt %  0.05  0.21 45.62 0.12 0.07  NiO  1  0.25  0.26  0.24  0.26  0.26  0.26  0.25  0.25  0.24  0.24  0.23  NiO  2  0.19 100.5  0.21  0.28 100.6  0.29 101.1  0.23 100.1  0.23 100.6  0.16 100.2  0.22 100.4  0.22 99.97  0.23 100.7  0.29  0.996  0.999 0.001  0.996 0.001  0.990 0.001  0.990 0.001  0.989 0.000  0.992 0.000  0.997  0.000  0.993 0.000  0.995 0.001  0.001  0.300 0.005 1.695  0.296 0.004 1.693  0.294  0.307 0.003  0.302 0.004  0.294 0.004  0.302 0.004  0.300 0.004  0.305 0.004  0.002 0.000  0.002 0.000  0.001 0.008  1.699 0.002 0.001  0.301 0.005 1.707  0.291  0.005 1.690  1.700 0.002 0.007  1.691 0.003  0.005 3.004  0.005 3.000  0.005 2.999  0.005 3.008  84.9 15.1  85.1 14.9  85.2 14.8  84.7  CaO Cr203  total  100.3  0.23 45.64  100.1  Cation (p.f.u.) Si Ti Fe * 2  Mn Mg Ca Cr Ni Sum  1.701 0.002  0.002  0.003 0.005 3.007  0.000 0.005 3.010  84.9 15.1  85.0 15.0  0.000  0.005 1.708 0.002  0.995  '1.692  1.692  0.003 0.003  0.003 0.000  0.002 0.005  3.005  0.000 0.005 3.002  3.006  0.005 3.003  0.005 3.004  85.2 14.8  84.8 15.2  85.5 14.5  85.0 15.0  84.7 15.3  0.005  Endmembers % Fo Fa  15.3  1  Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition.  2  Data collected using the standard 20 nA beam current and 20 second counting time.  Appendix III (continued): All olivine core, middle, and rim compositions by EPMA Region / Drillhole Rock Thin Section Geochem ID Probe point Depth (m) Area Grain Site  Cr. Peridotite Cr. Peridotite Cr. Peridotite Cr. Peridotite Cr. Peridotite Cr. Peridotite Cr. Peridotite Cr. Peridotite Cr. Peridotite Cr. Peridotite RMX01-6 71078 1_6_12  RMX01-6 71078  RMX01-6 71078  RMX01-6 71078  RMX01-6 71078  1_6_13 93 02 2  1_6_14 93 02 2  1_6_16 93 02  core  mid  1_6_15 93 02 2 rim  3 core  39.98 0.02 14.66 0.24  40.27 0.04 13.74 0.14  39.75 0.04 14.70 0.22  39.74 0.05 14^17  39.73 0.04 14.47  CaO Cr203  45.60 0.06 0.00  44.96 0.09 0.09  45.50 0.06 0.00  0.23 45.37  NiO  1  0.24  0.26  NiO  2  0.21 100.8  0.22 99.59  0.995 0.000 0.305 0.005 1.692  93 02 1 rim  RMX01-6 71078 1_6_17 93 02 3 mid  RMX01-6 71078 1_6_18 93 02 3 rim  RMX01-6  RMX01-6 71078  71078 1_6_19 93 02 4  1_6_20 93 02 4  core  mid  RMX01-6 71078 1_6_21 93 02 4 rim  Oxide wt % Si02 Ti02 FeO MnO MgO  total  39.67  39.86 0.04  0.07 0.07  0.20 45.50 0.07 0.00  0.01 14.26 0.19 45.56 0.03 0.09  14.39 0.21 45.46 0.04 0.07  0.25  0.25  0.24  0.25  0.16 100.5  0.25 99.95  0.28 100.27  0.26 100.1  1.008 0.001  0.993 0.001  0.995 0.001  0.994  0.288 0.003  0.307 0.005 1.694  0.297 0.005 1.694  0.303 0.004 1.697  0.002 0.000  0.002 0.003  0.002 0.000  1.700 0.001 0.004  39.59 0.04 13.77  39.91  39.87 0.04  0.22 45.39 0.13 0.00  0.03 14.30 0.23 45.58 0.07 0.00  14.45 0.18 45.93 0.08 0.03  0.25  0.22  0.22  0.22  0.25 100.3  0.24 99.35  0.26 100.3  0.24 100.8  0.993 0.000  0.995 0.001  0.996 0.001  0.996 0.001  0.992 0.001  0.298 0.004  0.300 0.004 1.692  0.290 0.005  0.299 0.005  0.300 0.004  1.703 0.004  1.696 0.002  1.703 0.002  0.000 0.004  0.000 0.004  3.003  3.003  0.001 0.004 3.007  85.5 14.5  85.0 15.0  85.0 15.0  Cation (p.f.u.) Si Ti Fe  2 t  Mn Mg Ca Cr Ni Sum  0.001  0.002 0.000  1.678 0.002 0.004  0.005 3.004  0.005 2.989  0.005 3.006  0.005 3.002  0.005  0.005  3.005  3.005  0.005 3.002  84.7 15.3  85.4 14.6  84.7 15.3  85.1 14.9  84.9 15.1  85.1 14.9  84.9 15.1  0.001 0.003  Endmembers % Fo Fa 1  Data collected using 100 nA beam current, 100 second counting time, and a fixed matrix composition.  2  Data collected using the standard 20 nA beam current and 20 second counting time.  Far West Margin  West Pyrrhotite Lake 140  120  120  t>  re  — 100  100  o 2  8  o o E o  80  E o * 60 re o  re u  I°  c re  4  80 60  40  r  (0 Q  a  20 h  20 h  500  1500  2500  3500  500  Ni (ppm)  1500  2500  3500  Ni (ppm) •  Standard Method  •  High Precision Method  Appendix IV: Comparison of the Ni abundance (ppm) of olivine by different EPMA methods. The standard method used a 20 nA beam current and 20 second counting time, and resulted in analytical uncertainties of 10-20% relative. The high precision method used a 100 nA beam current and 100 second counting time. This resulted in signficantly lower uncertainties (%RSD 2-5) and greatly reduced the range of measured Ni concentrations.  183  Appendix V: Duplicate analyses of trace element abundances by HR-ICP-MS  1  Sample No.  71072 (Feldspathic Peridotite; 36 wt% MgO)  71078 (Feldspathic Peridotite; 32 wt% MgO)  71128 (Feldspathic Peridotite; 27.5 wt% MgO)  Analysis  a  b  avg  a  % RSD  a  b  avg  o  % RSD  a  b  avg  o  % RSD  La  2.69  2.73  2.71  0.03  1.3  1.76  1.95  1.86  0.13  6.9  5.45  5.49  5.47  0.03  0.5  Ce  6.05  6.10  6.07  0.04  0.6  5.94  5.71  5.83  0.17  2.8  13.79  13.71  13.75  0.06  0.4  Pr  0.79  0.79  0.79  0.00  0.1  0.90  0.84  0.87  0.04  4.2  1.79  1.81  1.80  0.02  1.0  Nd  3.45  3.44  3.45  0.01  0.2  4.29  4.07  4.18  0.16  3.7  7.88  7.98  7.93  0.07  0.8  Sr  41.5  41.2  41.4  0.2  0.6  45.9  42.7  44.3  2.3  5.2  109.1  108.2  108.6  0.6  0.6  Sm  0.89  0.89  0.89  0.00  0.2  1.13  1.10  1.12  0.02  2.1  1.94  1.87 .  1.90  0.05  2.7  Eu  0.41  0.41  0.41  0.00  0.1  0.21  0.25  0.23  0.03  11  0.63  0.62  0.62  0.01  1.2  Gd  1.01  1.00  1.01  0.01  0.7  1.17  1.16  0.02  1.4  1.80  1.94  1.87  0.10  5.5  Tb  0.18  0.18  0.18  0.00  0.3  1.15 0.22  0.21  0.21  0.00  0.32  0.32  0.00  0.4  1.00  1.00  1.00  0.00  0.1  1.23  1.18  1.21  1.8 2.9  0.32  Dy  1.93  1.98  1.96  0.03  1.5  Ho  0.22  0.22  0.22  0.00  0.2  0.26  0.26  0.26  0.2  0.38  0.38  0.38  0.00  0.9  5.6  1.07  1.05  1.06  0.02  1.8  0.1  0.97  0.93  0.95  0.03  3.0  .  0.04  Er  0.58  0.58  0.58  0.00  0.6  0.74  0.68  0.71  0.00 0.04  Yb  0.53  0.53  0.53  0.00  0.7  0.61  0.61  0.61  0.00  Lu  0.09  0.09  0.09  0.00  0.3  0.08  0.10  0.09  0.01  10  0.13  0.14 .  0.13  0.00  3.1  U  0.15  0.15  0.15  0.00  0.6  0.23  0.21  0.22  0.01  5.4  0.26  0.26  0.26  0.01  2.1  Pb  3.5  4.1  3.8  0.4  11  43.9  40.8  42.4  2.2  5.2  2.6  2.6  2.6  0.00  0.0  Li  27.1  25.1  26.1  5.5  50.9  39.8  45.3  7.8  17  22.0  21.3  21.7  0.5  2.3  Sc  12.17  10.79  11.48  1.4 0.97  4.30  9.02  6.66  3.34  50  17.17  16.45  16.81  0.51  3.0  V  80.8  85.1  83.0  3.1  8.5 3.7  130.5  120.7  125.6  6.9  5.5  167.8  164.0  165.9  2.7  1.6  Co  79.6  79.1  79.3  0.3  0.4  125.4  99.8  112.6  18.1  16  109.7  109.0  109.3  0.5  0.4  Cu  15.5  15.6  15.6  0.1  0.7  149.4  127.9  138.6  15.2  11  96.0  94.3  95.1  1.2  1.3  Zn  57  55  56  1.4  2.4  130.6  105.2  117.9  17.9  15  82.2  79.0  80.6  2.3  2.8  Ga  4.41  4.28  4.34  0.09  2.0  6.10  5.37  5.73  0.52  9.0  8.39  7.79  8.09  0.42  5.2  Rb  6.7  6.7  6.7  0.0  0.1  30.1  29.7  29.9  0.3  0.9  10.9  10.7  10.8  0.2  1.4  Sr  41.5  41.2  41.4  0.2  0.6  45.9  42.7  44.3  2.3  5.2  109.1  108.2  0.6  0.6  Y  4.49  4.57  4.53  0.05  1.2  5.15  5.46  5.30  0.22  4.1  8.64  8.49  108.6 8.57  0.11  1.2  Zr  21.0  20.5  20.8  0.36  1.7  19.4  23.2  21.3  2.63  12  52.67 .  50.28  51.47  1.69  3.3  2.90  0.05  1.9  0.07  0.04  60  Nb  1.39  1.40  1.39  0.01  0.7  1.13  1.79  1.46  0.47  32  2.94  2.86 ,  Cd  0.07  0.07  0.07  0.00  0.2  0.14  0.21  0.17  0.05  28  <lod  <lod  Sn  0.91  0.14  0.53  0.54  103  0.12  0.08  0.10  0.03  29  0.10  0.04  Sb  0.05  0.07  0.06  0.01  19  0.01  0.10  0.05  0.06  107  <lod  <lod  Cs  0.55  0.56  0.55  0.00  0.7  1.67  1.57  1.62  0.07  4.4  1.30  1:28  1.29  0.02  1.2  Hf  0.60  0.59  0.60  0.01  1.2  0.65  0.68  0.66  0.02  2.4  1.49  1.46  1.47  0.03  1.9  Ta  0.09  0.09  0.09  0.00  1.6  0.07  0.12  0.09  0.03  33  0.18  0.18  0.18  0.00  1.5  W  0.15  0.11  0.13  0.03  21  0.07  0.10  0.09  0.02  20  0.24  0.27  0.26  0.02  8.3  Bi  0.03  0.03  0.03  0.00  1.0  0.16  0.41  0.29  0.18  64  <lod  <lod  Th  0.5  0.5  0.5  0.0  5.4  0.2  0.7  0.4  0.3  71  1.0 104  1.0 102  0.0  99 .  0.8 3.4  Ba  148  1  Duplicate analyses are multiple digestions of a single powdered sample.  2  Average %RSD of samples 71072, 71078, & 71128.  3  Analysis a from 100 mg and b from 150 mg.  <lod = Below detection limit  1.0  3  Appendix V (continued): Duplicate analyses of trace element abundances by HR-ICP-MS  1  Sample No.  G-2 Granite (USGS referenc material; 0.75 wt% MgO)  DTS-2 Dunite (USGS reference material; 49.4 wt% MgO)  Analysis La Ce Pr Nd Sr Sm Eu Gd Tb Dy Ho Er Yb Lu U Pb Li Sc V Co Cu Zn Ga Rb Sr Y Zr Nb Cd Sn Sb Cs Hf Ta W Bi Th Ba  a 82.07 149.80 15.69 50.77 439.5 6.70 1.21 3.62 0.41 2.01 0.33 0.82 0.70 0.10 1.57 23.5 12.6 1.69 15.9 2.0 3.6 37.5 10.01 77.1 217.9 4.03 129.0 4.38 0.13 0.07 0.01 0.62 3.44 0.31 0.08 0.01 11.5  a 0.009 0.028 <lod 0.01 0.7 0.005 <lod 0.005 <lod 0.005 <lod 0.005 0.009 <lod <lod 3.0 1.63 3.11 21.1 134.2 2.6 49.1 0.71 0.91 0.71 0.01 0.11 0.08 <lod 0.15 0.54 0.06 0.11 0.004 0.07 <lod <lod 11  b 77.96 136.66 14.79 47.81 455.9 6.06 1.19 3.45 0.40 2.02 0.32 0.78 0.71 0.10 2.06 23.8 14.3 1.77 16.3 2.2 6.9 40.6 10.05 76.7 227.8 4.23 129.9 5.02 0.14 0.09 0.01 0.64 3.55 0.35 0.10 0.01 9.7 .  avg 80.02 143.23 15.24 49.29 447.7 6.38 1.20 3.54 0.41 2.02 0.33 . 0.80 0.70 0.10 1.81 23.6 13.4 1.73 16.1 2.1 5.3 39.1 10.03 76.9 222.9 4.13 129.5 4.70 0.14 0.08 0.01 0.63 3.49 0.33 0.09 0.01 10.6  a 2.91 9.29 0.64 2.10 11.6 0.45 0.01 0.12 0.00 0.01 0.00 0.03 0.00 0.00 0.35 0.2 1.2 0.05 0.2 0.1 2.4 2.2 0.03 0.3 7.0 0.14 0.7 0.45 0.01 0.01 0.00 0.01 0.08 0.02 0.01 0.00 1.3  % RSD 3.6 6.5 4.2 4.3 2.6 7.1 1.0 3.3 0.8 0.3 1.5 3.8 0.5 2.2 19 0.7 8.9 3.2 1.4 4.4 45 5.6 0.3 0.4 3.1 3.4 0.5 9.6 6.3 14 53 2.3 2.2 6.9 14 5.1 12  1  Duplicate analyses are multiple digestions of a single powdered sample.  2  Average %RSD of samples 71072, 71078, & 71128.  Analysis a from 100 mg and b from 150 mg. <lod = Below detection limit  3  3  b 0.012 0.024 0.003 0.01 0.4 0.003 0.002 0.021 0.001 0.004 0.002 0.004 0.009 0.002 0.002 2.7 1.31 2.82 22.1 101.7 1.9 38.1 0.84 <lod 0.42 0.03 0.12 0.04 0.019 0.37 0.50 <lod 0.00 <lod 0.00 <lod <lod  avg 0.011 0.026 0.003 0.01 0.6 0.004 0.002 0.013 0.001 0.004 0.002 0.004 0.009 0.002 0.002 2.8 1.47 2.96 21.6 117.9 2.2 43.6 0.78 0.91 0.56 0.02 0.12 0.06 0.019 0.26 0.52 0.06 0.05 0.004 0.04  11  e 0.002 0.003  % RSD 21 10  0.002 0.2 0.001  17 37 28  0.012  91  0.001  14  0.000 0.000  11 3.9  0.193 0.23 0.20 0.7 22.9 0.5 7.7 0.09  6.8 16 6.8 3.3 19 23 18 11  0.21 0.01 0.01 0.03  37 51 8.0 57  0.15 0.03  59 5.9  0.07  132  0.05  133  %RSD average 2.9 1.3 1.8 1.6 2.1 1.7 4.1 2.5 0.8 1.5 0.5 2.7 1.2 4.6 2.7 5.3 8.3 21 3.6 5.6 4.3 6.8 5.4 0.8 2.1 2.2 5.8 • 11 14 64 63 2.1 1.8 12 16 32 26 3.4  2  Appendix VI: Trace element a b u n d a n c e s for U S G S reference materials (G-2 and D T S - 2 ) Material Source  Method Sampe N o .  G-2 (Granite) PCIGR this study  PCIGR Pretorius (in press)  HR-ICP-MS  ICP-MS  ICP-MS  2  3  HP4500  ICP-MS 2 a (n=34) 5  24.4  3.3  24.9  0.78 11.9 89.6 164 16.7 54.9  0.10 2.1  0.89 11.2 87.1  1.26 156  0.03 5.7  1.3 1.8  1.36 201  19 2.1 0.69 10 78 137  19 1.8 0.67 10 80 143  9.0 0.52 0.063 1.4 4.3  23.7  27  24.7  23  14.8 4.7 7.0 2.7 4.6  0.63 11.6 91  0.88 12  11  15 48 24  15 50 24 437 263  100  100  1.25 156  1.26 159  Th  23  U Ta Nb La Ce Pr Nd  1.6 0.63 9 82 150 16 51 24  14 1.7  C s (ppm) Rb  XRF  1  1.28 153  100  2  INAA %RSD  RM25  Liang et al. (2000)  Totland et Meisel et al. (1992) al. (2001)  2o  RM06r  Weight (mg)  Robinson etal. (1986)  average  RM06  1  Govindaraju (1994)  Do D a  Pb Sr Zr Hf Sm Eu Gd Tb Dy Ho Er  439 260 6.9 6.7 1.21 3.6 0.41  0.68 10 81 144 16 51 25 414 268 7.1 6.8 1.23 3.7 0.41  2.0 0.33 0.82  2.1 0.34  Yb  0.70  Y Lu  8.1 0.096  0.73 8.4 0.094  0.85  456 260 7.1 6.1 1.19 3.5 0.40 2.0  7.0 6.5 1.21 3.6 0.41 2.1  0.32 0.78 0.71  0.33 0.82 0.71  8.5 0.099  8.3 0.096  1  "r" denotes a replicate analysis from one digestion.  2  Weight of sample powder in milligrams.  13.1 1.1  165 17 54  89 160 18 55  3.5 1.5 41.7 9.1  3.6 3.5 3.1 4.8 1.7  0.19 0.78 0.04  1.3 6.0 1.7  8.5 7.3 1.4  0.25 0.01 0.12  3.5 1.2 2.8  3.8 0.46 2.2  4.3 0.48 2.4  0.021 0.073  3.1 4.5  0.37 0.93  0.4 0.92  0.033 0.36 0.004  2.3 2.1 2.3  0.76 9.2 0.11  0.8 11 0.11  365  86 165.5 15.2 52.4  309 7.9 7.2 1.4  91.3 166 15.6 53.7  313  300 8.1  7.54  6.32  1.63 4.13  1.43 4.23  0.55 2.15  0.55 2.07  7.48 1.48 4 0.49  0.38 1 0.81 10.8 0.15  8.9  6.1 12.1 1.3 4.3  155 17.1 52.6  51.6 1.5 0.6  262 6.95 7.22  0.1 0.3 0.0  1.46 4.13 0.45  2.32 0.38  0.2 0.0  0.97 0.74  0.1 0.1  2.29 0.31 0.87  10 0.108  0.8 0.0  0.72 10.2 0.1  Appendix VI (continued): Trace element abundances for USGS reference materials (G-2 and DTS-2) Material Source  DTS-2 (Dunite) P C I G R - this study  Method Sampe N o .  1  Weight (mg) C s (ppm) Rb Ba Th U  2  Raczek et al. Raczek et al. 2000 2000  HR-ICP-MS  HR-ICP-MS  HR-ICP-MS  RM01  RM16  RM16r  100  150  150  0.06 0.9 10.99 <lod  <lod <lod  0.00 0.0  0.0032  0.0033 0.0016 <lod 0.03  Ta Nb La Ce Pr Nd  <lod 0.0045 0.08 0.009 0.028 <lod 0.014  Pb Sr  3.0 0.7  Zr Hf Sm  0.11 0.11  0.0016 <lod 0.04 0.012 0.024 0.0032 0.011 2.7 0.4 0.12  0.013 0.025 0.0031 0.011 2.7 0.4 0.12  2o  %RSD  0.0304  0.0838  0.46 10.99 0.0032 0.0016 0.0045 0.05  1.3  138 138  0.0002 0.0001  3 2  0.056  55 17  0.00284  61 2  0.0010 0.0001  12 2  0.00436  0.00401  0.0008 0.0006  9 4  0.00471  0.00458 0.0093  0.018 0.0001  36 2  Ho Er Yb  <lod 0.0047  0.0016  0.0016  0.0016  0.0040 0.0088 0.03 0.0024  0.0048 0.0087  0.0045 0.0089 0.02 0.0024  Weight of sample powder in milligrams.  0.0032 0.00092 0.00313  0.019 0.00002 •  0.0008 0.004  2  0.0122  0.02 0.0008 0.004  <lod 0.005  "r" denotes a replicate analysis from one digestion.  0.014  0.0018  Tb Dy  1  0.0117 0.0232  0.004  0.02 0.0008 0.004  0.03 0.0023  0.0136 0.0275  31 6 157 25  Eu Gd  Y Lu  DTS-2 (2)  0.33 0.015 0.12  0.00 0.003 <lod 0.02  0.0039 0.0042 0.0001 0.004 0.31  DTS-2 (1)  0.011 0.026 0.0032 0.012 2.8 0.5 0.12 0.04  0.005 <lod 0.00  0.0093 0.01 <lod  0.00 0.003 <lod  average  8 2 15 5  0.00996  0.00081 0.00294  0.002  200  200  Cesium (ppm)  Rubidium (ppm)  y = 0.99x + 0.13 R2= 0.99  y = 1.06x + 1.25  150  Barium (ppm) y = 1.12X-7.30 F?= 0.98  UJ  o  o <  <  100 50  100  150  0  200  50  100  PCIGR 16 r  UJ  oS <  0  ' 4 UJ  £  o <  8 •  Uranium (ppm) y = 1 . 1 9 x + 0.02 R2= 0.99  0  /  1.0 •  9/0  „  UJ  3  0.8 •  Tantalum (ppm) y = 1.00x + 0.05 R2= 0.96  o  y  S  O 0.6 • <  2  6 -  200  1.2 r-  5  14 • Thorium (ppm) y = 1.25x-0.22 12 • R2= 0.99 10 •  150  PCIGR  0.4 •  4 • 0.2 •  2 • 0 S 0  2  4  6  8  10 12 14 16  2.0  PCIGR  4.0  0.0 0.0  5.0  0.2  PCIGR  15  50  y = 1.07x + 0.47 R2= 0.99  UJ  1  o <  40  0.4  0.6  0.8  1.0  1.2  PCIGR 100  60 Niobium (ppm)  10  3.0  Lanthanum (ppm) y = 1.19x-0.20 R^O.99  Cerium (ppm)  0  80  y = 1.24X-1.38  R2= 0.99  60  30 40 20 0  5  15  10  20  PCIGR  30  40  50  40  60  uj  8  <  6  S  100  250  12  10  60  PCIGR  PCIGR  Lead (ppm)  N e o d y m i u m (ppm) y = l.14x + 0.13 R*= 0.99  Praseodymium (ppm) y = 122x - 0.20 0.99  200 £  o <  10  12  10  20 PCIGR  30  40  y = 1.06x+ 1.69 R^O.98  o,  150 100  50  100  150  200  250  PCIGR  Appendix VII: Comparison of trace element results from PCIGR (HR-ICP-MS) and A C M E Analytical Laboratories, Vancouver (ICP-MS and ICP-ES). A C M E analytical methods summarized in Appendix I. All samples are included in Table 3.3 (PCIGR) and Table 2.1 (ACME). R2 values are >0.98 with the exception of Tantalum.  188  6  300 Dysprosium (ppm) y = 1.06x-0.01 F#= 0.99  5 4  10 Hafnium (ppm)  Zirconium (ppm) y = 1.05x + 0.73 F?= 0.99  200  8 £ o <  LU  5»  o <  6 4  100  2  2  1  0 1  0  2  3  4  100  PCIGR  200  300  PCIGR 1.0  g |_ Samarium (ppm) y = 1.18x - 0 . 0 3 F?= 0.98 o. S 4 U  300 Strontium (ppm)  Terbium (ppm)  jjj  111  <  y = t 1 5 x + 0.02 P r = 0.99  0.8 \y = 1.34X-0.06 R2=0.97 0.6  200  0.4  100  y = 1.18x-1.14 J 1^=0.98 'W  /  3  o  3  <  r  2 0.2  1 0  1 2  3  0.00.0  4  0.2  0.4  PCIGR  uj S  4  S  0.8  0  1.0  100  Gadolinium (ppm) y = 1.24x - 0 . 2 5 R^O.95 o  25 UJ  Yttrium (ppm)  Europium (ppm)  y = 1.19x + 0.55 Fr = 0.99  y = 1.17X-0.07 R*= 0.98  1.0  8 20 <  2  300  1.5  30  3  200 PCIGR  35  6 5  0.6  PCIGR  f  o <  15  0.5  10  1  5  0 1  2  3  0  4  PCIGR  0  5  10  15 20  UJ 0.8 •  35  0.0 0.0  0.5  1.0  1.5  PCIGR 0.6  o  Holmium (ppm) y = 1.19x-0.06 R^O.98  Ytterbium (ppm)  A  UJ  S o 0.6 <  S  y2  0.4 •  y = 1.03x + 0.02 R*= 0.99  0.5 uj 0.4  Lutetium (ppm) y = 1.22X-0.03 R?= 0.99  0 /  o 0.3 < 0.2 0.1  0.2 • 0.0 • 0.0  30  PCIGR  1.2 , 1.0 •  25  0.2  0.4  0.6  PCIGR  0.8  1.0  1.2  0.0 0.0  0.2  0.4 PCIGR  Appendix VII (continued): Comparision of trace element results from PCIGR and A C M E Analytical Laboratories, Vancouver. R2 values are >0.98 with the exception of gadolinium and terbium.  0.6  

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