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Geologic setting of listwanite, Atlin, B.C. : implications for carbon dioxide sequestration and lode-gold… Hansen, Lyle D. 2005

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GEOLOGIC SETTING OF LISTWANITE, A T L I N , B.C.: IMPLICATIONS FOR C A R B O N DIOXIDE SEQUESTRATION A N D LODE-GOLD MINERALIZATION by L Y L E D. H A N S E N B . S c , The University of Alberta, 2000  A THESIS SUBMITTED IN P A R T I A L F U L F I L M E N T OF THE REQUIREMENTS FOR THE D E G R E E OF M A S T E R OF SCIENCE in THE F A C U L T Y OF G R A D U A T E STUDIES Geological Sciences  THE UNIVERSITY OF BRITISH C O L U M B I A M A Y 2005  © Lyle D. Hansen, 2005  ABSTRACT ABSTRACT Listwanite (carbonated-serpentinite), commonly associated with high-grade lodegold mineralization, binds large quantities of the greenhouse gas carbon dioxide  (CO2).  At Atlin, B . C . , listwanite distribution is controlled by a basal thrust fault and regional joint/fracture system with four steeply dipping sets.  Carbonation proceeded via three  sub-reactions fossilized as spatially distinct mineralogical zones.  The index minerals,  magnesite, talc and quartz, record three metamorphic isograds defining the magnesite-, talc- and quartz-zones.  This same overall mineralogical transformation  is under  consideration for industrial sequestration of CO2 in a process referred to as mineral carbonation. The carbonate-alteration reactions were isochemical in terms of major nonvolatile chemical species, except where quartz-carbonate veining and/or Cr-muscovite are present in areas of intense carbonation (indicating S i , M g a n d K metasomatism). The 2 +  2+  +  progressive destruction of magnetite during listwanite-alteration allowed for the use of a magnetic susceptibility meter in recording reaction progress and helped delineate subtle variations in reaction progress that might otherwise have gone unnoticed in the field. Although magnesite-zone alteration only accounts for about 5% - 15% of the total carbonation potential for serpentinite, it is widespread and may represent a significant portion of the total bound CO2. Moreover, the progression of the talc-zone appears to generate fracture permeability. The first two reactions combined can fix approximately half the total carbon sequestration potential for serpentinite with a small associated increase in the volume of solids. The quartz-zone is limited to highly carbonated areas and may be limited in extent due to a large associated gain in solid volume that may act to seal permeability. The first two reaction steps therefore hold the most promise for in situ mineral carbonation and could be preferentially driven by controlling the input fluid composition. Anomalously high gold values are associated with organic hydrocarbons in talcmagnesite rock and depleted § C (ca. -6%o) in carbonate. 13  This combined with 5 0 18  values of 7%o to 16%o for carbonate is consistent with hydrothermal fluids circulating through and scavenging gold from organic-bearing metasedirnentary rocks. Alteration is contemporaneous with the nearby Fourth of July Batholith (ca. 170 Ma), which may have  ABSTRACT provided a heat source for hydrocarbon maturation and large-scale hydrothermal convection.  iii  T A B L E OF CONTENTS T A B L E OF C O N T E N T S  ABSTRACT  ii  T A B L E OF CONTENTS  iv  LIST OF T A B L E S  vii  LIST OF FIGURES  viii  LIST OF A B B R E V I A T I O N S  xii  LIST OF S Y M B O L S  xiii  PREFACE  xvii  ACKNOWLEDGMENTS  xix  C H A P T E R I: OVERVIEW  1  1.1  OVERVIEW  1  1.2  REFERENCES  5  C H A P T E R II: GEOLOGIC SETTING OF LISTWANITE (CARBONATEDSERPENTINITE) AT ATLIN, BRITISH COLUMBIA: A GEOLOGIC A N A L O G U E TO CARBON DIOXIDE SEQUESTRATION  7  2.1  INTRODUCTION  7  2.2  REGIONAL GEOLOGY AND FIELD METHODS  8  2.3  ULTRAMAFIC ROCKS  12  2.4  LISTWANITE  15  2.5  LISTWANITE PETROGRAPHY, GEOCHEMISTRY A N D REACTION PATHS  20  2.6  IGNEOUS INTRUSIONS  22  2.7  MAGNETIC PROPERTIES...  22  2.8  IMPLICATIONS FOR C 0 SEQUESTRATION  23  2.8  IMPLICATIONS FOR LODE-GOLD MINERALIZATION  25  2.9  REFERENCES  27  2  C H A P T E R III: STRUCTURAL SETTING, TIMING A N D ISOTOPIC CHARACTER OF LISTWANITE (CARBONATED-SERPENTINITE), ATLIN, BRITISH COLUMBIA: IMPLICATIONS FOR LODE-GOLD MINERALIZATION  iv  33  T A B L E OF CONTENTS 3.1  INTRODUCTION  '.  3.2  REGIONAL GEOLOGY AND ROCK UNITS  3.3  STRUCTURAL ANALYSIS  33 . [  34 36  3.3.1  PRE- TO SYN-OBDUCTION STRUCTURAL ELEMENTS  36  3.3.2  POST-OBDUCTION STRUCTURAL ELEMENTS  41  3.4  IGNEOUS INTRUSIONS  44  3.5  TIMING AND SETTING OF LISTWANITE ALTERATION  50  3.6  ALTERATION ENVIRONMENT  54  3.7  STABLE ISOTOPES  56  3.8  H Y D R O T H E R M A L ORGANIC MATERIAL  60  3.9  SOURCE OF GOLD AND CARBON  60  3.10 CONCLUSIONS  64  3.11  65  REFERENCES  C H A P T E R IV: CARBONATED SERPENTINITE (LISTWANITE) ATLIN, BRITISH COLUMBIA: A GEOLOGIC A N A L O G U E TO C A R B O N DIOXIDE SEQUESTRATION  -.  :...70  4.1  INTRODUCTION  70  4.2  R E L E V A N C E TO INDUSTRIAL APPLICATIONS  71  4.3  GEOLOGIC SETTING  72  4.4  STRUCTURAL CONTROL  74  4.5  MINERALOGICAL ZONATION AND REACTION SEQUENCE  74  4.6  GEOCHEMICAL CHANGE DURING LISTWANITIZATION  81  4.7  MAGNETIC SUSCEPTIBILITY  84  4.8  V O L U M E STRAIN ACCOMPANYING REACTION  90  4.9  IMPLICATIONS FOR C 0 SEQUESTRATION  90  2  4.10 REFERENCES  96  C H A P T E R V: MASS B A L A N C E AND MODELING  102  5.1  INTRODUCTION  102  5.2  PROTOLITH AND ALTERATION ASSEMBLAGES  106  5.3  A N A L Y T I C A L METHODS  107  5.4  STANDARD ERROR AND WHOLE ROCK GEOCHEMISTRY  107  v  T A B L E OF CONTENTS 5.5  DIMENSIONAL ANALYSIS  110  5.6  MASS B A L A N C E  118  5.7  RESULTS  127  5.8  IMPLICATIONS  132  5.9  COMPARISON TO GRESEN'S ANALYSIS  133  5.10 CONCLUSIONS  133  5.11 REFERENCES  135  CHAPTER VI: CONCLUSIONS 6.1  CONCLUSIONS  6.2  REFERENCES  137 137 '.  139  APPENDIX A: MISCELLANEOUS TABLES FOR CHAPTER IV  140  APPENDIX B: MINERALOGY  147  APPENDIX C: GEOCHEMICAL, STABLE ISOTOPE A N A L Y S E S A N D GOLD A S S A Y DATA  153  APPENDIX D: GEOCHRONOLOGIC DATA  163  APPENDIX E: PROCEDURES AND MISCELLANEOUS INFORMATION  181  APPENDIX F: SAMPLE LOCATIONS  188  GEOLOGICAL MAP  insert  vi  LIST OF TABLES LIST O F T A B L E S  C H A P T E R II Table 2.1:  Mineralogy of carbonated serpentinite from Atlin, B . C  Table 2.2: Volume changes  18  24  C H A P T E R III Table 3.1:  Geochronologic data from Atlin area  51  Table 3.2:  Stable isotopic data from various listwanite systems  58  Mineralogy of carbonated serpentinite from Atlin, B . C  76  C H A P T E R IV Table 4.1:  Table 4.2: Volume changes  91  CHAPTER V Table 5.1:  Geochemical analyses of replicates  Table 5.2: B.C  Representative geochemical analyses of ultramafic rocks from Atlin,  Table 5.3:  Lowest rank from datasets using unweighted SVD  114  Table 5.4:  Lowest rank from datasets using weighted SVD  114  Table 5.5:  Lowest rank from datasets using iterative weighted SVD  117  Table 5.6:  Lowest rank of each group using each SVD technique at 3o  119  108  109  vii  LIST OF F I G U R E S  LIST OF FIGURES  CHAPTER I Figure 1.1: Location map o f A t l i n , B . C  2  CHAPTER II Figure 2.1: B e d r o c k map o f the A t l i n area  9  Figure 2.2: C o m p o s i t e image, detailed geologic, magnetic susceptibility, and calculated CO2 maps o f a 2 m by 2 m area containing fracture-controlled zones o f listwanite 10 Figure 2.3: A e r o m a g n e t i c map o f the A t l i n area  11  Figure 2.4: Outcrop and transmitted light images o f the harzburgite and serpentinite units 13  Figure 2.5: Equal area stereonet plots o f the harzburgite and bastite foliation and magnetite-serpentinite and quartz carbonate veins  14  Figure 2.6: a) Fracture-controlled listwanite. b) B a s a l decollement-controlled listwanite and post-alteration dikes 16 Figure 2.7: A r e a l v i e w and geological map s h o w i n g recessive-weathering lineaments  19  Figure 2.8: S i m p l i f i e d flow chart illustrating reaction path for listwanite  21  CHAPTER III Figure 3.1: B e d r o c k map o f the A t l i n area  35  Figure 3.2: Stereonet plots and imagery illustrating the orientations o f the So and S i structural fabrics  37  Figure 3.3: Stereonet plots and images illustrating the orientation o f the S2 structural fabric  38  Figure 3.4: A r e a l v i e w and geological map showing recessive-weathering lineaments  39  viii  LIST OF FIGURES Figure 3.5: Photomicrograph of sheared serpentinite showing reverse sense of shear 40 Figure 3.6: Stereonet plot and image showing four joint and fracture orientations controlling listwanite 42 Figure 3.7: Stereonets plots illustrating orientations of the regional joint and fracture system 43 Figure 3.8: Stereonet plot and images showing serpentine-magnesite veins....45 Figure 3.9: Stereonet plot and image showing quartz-carbonate veins  46  Figure 3.10: Image of bladed carbonate in listwanite  47  Figure 3.11: Map of 10 m by 10 m area and stereonet plot of quartz-carbonate veins contained within the same map area 48 Figure 3.12: Total alkali vs. S i 0 (TAS) plot of dike samples  49  Figure 3.13: Simplified flow chart illustrating the geological history of the Atlin area  52  2  Figure 3.14: Schematic block diagram illustrating the structural controls of listwanite and dikes 55 Figure 3.15: 5 0 - 8 C plot of isotopic data from carbonate in listwanite 18  13  57  Figure 3.16: Composite image and detailed geologic maps of a 2 m by 2 m area containing fracture-controlled zones of listwanite 59 Figure 3.17: Images of organic matter from Atlin and Nahlin fault localities..61 Figure 3.18: Plots of Au assay results, CO2 content, and 8 C 13  62  C H A P T E R IV  Figure 4.1: Simplified geological map of the Atlin area  73  Figure 4.2: Simplified flow chart illustrating reaction path for listwanite  77  Figure 4.3: Back-scattered scanning electron microscope images showing minerals formed during progressive listwanite alteration  78  ix  LIST OF FIGURES Ternary phase and fluid H2O - CO2 activity diagrams of the listwanite system 80  Figure 4.4:  Figure 4.5:  Wt% MgO - S i 0 circle diagrams 2  82  Ratio of residual error to standard error in whole rock geochemistry of carbonated samples 85 Figure 4.6:  Figure 4.7:  Plot of magnetic susceptibility and whole rock CO2 content  87  Composite image, detailed geologic, magnetic susceptibility, and calculated C 0 maps of a 2 m by 2 m area containing fracture-controlled zones of listwanite 88 Figure 4.8:  2  Figure 4.9:  Measured and calculated wt% C O 2 across transect A-B from Figure  2.2b  89  Relationship of fracture permeability in advance of a reaction undergoing a gain in the volume of solids  92  Figure 4.10:  fluid diagram at 250 bars and 60°C  95  Figure 5.1:  Simplified flow chart illustrating reaction path for listwanite  103  Figure 5.2:  Wt% MgO - S i 0 2 circle diagrams and ternary diagram of listwanite 104  Figure 4.11: H 0 - C 0 2  2  CHAPTER V  system  SVD solutions to a hypothetical two dimensional dataset using weighted and unweighted techniques 112  Figure 5.3:  SVD solutions to a hypothetical two dimensional dataset using weighted and weighted-iterative techniques 115 Figure 5.4:  Residual over analytical error calculated using an unconstrained system of equations and a MgO - S i 0 2 diagram of the protolith, altered rock data and model protoliths calculated using unconstrained system of equations .....121  Figure 5.5:  Residual over analytical error calculated using a constrained system of equations 124 Figure 5.6:  Mass factor vs. wt% C O 2 diagram and MgO - S i 0 2 diagram of the protolith, altered rock data and model protolith calculated using the constrained system of equations 125 Figure 5.7:  x  LIST OF FIGURES Figure 5.8: Mass factor vs. wt% CO2 diagram and MgO - S1O2 diagram of the protolith, altered rock data and model protolith calculated using the constrainedweighted system of equations 128 Figure 5.9: Residual over analytical error calculated using constrained and weighted system of equations 129 Figure 5.10: Residual over analytical error calculated using constrained and weighted system of equations for rank reduced datasets 131 Figure 5.11: Plots of a) mass factor and wt% C 0 and b) residual over analytical error calculated using Gresens' analysis and the model protoliths calculated using the constrained-weighted system of equation 134 2  xi  LIST OF ABBREVIATIONS LIST OF ABBREVIATIONS A A C - Atlin Accretionary Complex AOA - Atlin Ophiolitic Assemblage FOJB - Fourth of July Batholith GPS - Global positioning system PCIGR-Pacific Centre for Isotopic and Geochemical Research ppm - Parts per million ppb - Parts per billion SVD - Singular value decomposition TIMS - Thermal ionization mass spectrometry VPDB - Vienna Pee Dee Belemnite VSMOW - Vienna Standard Mean Ocean Water XRD - X-ray diffractometer XRF - X-ray fluorescence  xii  LIST OF SYMBOLS LIST OF SYMBOLS  Wt% - Weight percent oxide N A D 83 - North American Datum 83 50 - Compositional layering within the harzburgite unit 51 - Fabric defined by flattened arid stretched orthopyroxene crystals within harzburgite unit 5 - Fabric defined by sheared and stretched bastite (serpentinized orthopyroxene) within the serpentinite unit. 2  Ri, R2, R3 - Denotes reactions 1 to 3 (Chapter II and IV) R A , R B - Denotes reactions A to B (Chapter IV) A i , A2, A 3 , A 4 - Denotes mineral assemblages 1 to 4 (Chapters II and IV) L , Lb, L , La - Denotes the four main steeply-dipping listwanite zone trends a  c  M i , M2, M 3 - Denotes the generation of magnesite produced during each of the three listwanite carbonation reactions (Ri to R3 respectively) AVs* (rxn) - Change in volume of solid material of the reaction in question AVs (rock) - Change in volume of solid material of a rock a - One standard deviation d/1 - Detection limit proto - Protolith min - Minimum max - Maximum Ma - million years  xiii  LIST OF S Y M B O L S MINERALS  Atg - Antigorite Brc - Brucite Cal - Calcite Chi - Chlorite Chr - Chromite Dol - Dolomite Eri9o  - Orthopyroxene.(90% enstatite end member)  F090 - Olivine (90% forsterite end member) L i z - Lizardite Mgs - Magnesite M g t - Magnetite 01-Olivine Opx - Orthopyroxene Qtz - Quartz Srp - Serpentine Tic - Talc  S Y M B O L S USED IN C H A P T E R V  A, b , Aeq, beq ,C ,d - The constrained linear system of equations Alt - Altered Sample  xiv  LIST OF S Y M B O L S Alt ™'° -Alt weighted by the covariance matrix of the 46 samples of the protolith group. p  Co - Coefficient cov - Covariance matrix defined by replicate analyses err  cov -Covariance prolo  matrix defined by the protolith group of samples  e- Number of elements in the dataset E- Denotes an element / / - L o w e r limit of an element defined by the protolith group //"'' - Lower limit of an element defined by the protolith group weighted by the covariance matrix of the 46 samples of the protolith group m - Denotes an element mf - Mass factor M i - M o d e l Protolith 5  Mpp™'°- Model protolith weighted by the covariance matrix of the 46 samples of the protolith group. n - Denotes a sample P - Matrix of the basis vectors of the protolith group pprom_p  w e  ; g h t i by the covariance matrix of the 46 samples of the protolith group e c  pu - Upper limit placed on the protolith composition puff'"- Weighted upper limit placed on the protolith composition pi- Lower limit placed on the protolith composition PKT" ~ Weighted lower limit placed on the protolith composition R - Rank of a matrix s - N u m b e r of samples in a dataset XV  LIST OF SYMBOLS S - Matrix representing a dataset S*"- Matrix S weighted by cov  err  Sapprox- SVD approximation of S Sapprox"™ - SVD approximation of S ", e  Sapprox * - Approximation of a modified Sapprox or Sapprox^ matrix Serr- Vector containing the standard errors of the dataset ul - Upper limit of an element defined by the protolith group ul"' - Upper limit of an element defined by the protolith group weighted by the covariance matrix of the 46 samples of the protolith group 1  unwt - Matrix to unweighted data weighted by cov err  err  wt - Matrix to weight a dataset by cov err  wt  err  - Matrix to weight a dataset by cov  prolo  x- Contains the coefficients Co that when multiplied with P gives a 'best fit' to Alt z - Number of basis vectors in P <j '""- Covariance between two elements in the protolith group of samples pr  a - Covariance between the analyses of two elements err  xvi  PREFACE PREFACE This thesis is composed of four body chapters, two of which have been published and two of which are in preparation for publication. Chapter II is published as a Current Research paper through the Geological Survey of Canada and is entitled Geological Setting of Listwanite (Carbonated Serpentinite) at Atlin, British Columbia:Implications for CO2 Sequestration and Lode-gold Mineralization'.' This paper summarizes the geology including the geological units, an incomplete listing of structural elements and geophysical properties discovered or used during the first season of geological mapping and sampling. This paper was co-authored by Dr. Bob Anderson and Dr. Gregory Dipple who helped revise the manuscript and provided support and expertise in the field and K'oko Nakano who provided field and laborator y assistance. Chapter III is unpublished and elaborates on the first paper in describing the structural controls, timing and origin of altering fluids and discusses potential scenarios for the anomalous gold contents detected in the Atlin listwanite. The U-Pb (zircon) analysis, A r / A r analyses, and stable isotope 40  39  analyses for carbonate were performed by Richard Friedman, Thomas Ullrich and Janet Gabites respectively. Chapter IV is published in The Canadian Mineralogist and is entitled Carbonated Serpentinite (listwanite) at Atlin, British Columbia: A Geological Analogue to Carbon Dioxide Sequestration'.'  It describes the metamorphic reactions,  geochemistry and petrology of the alteration assemblages in detail. It was co-authored by Dr. Gregory Dipple who supervised and aided in revisions, Dr. Terry Gordon who provided the geochemical mass balance calculations and Dawn Mlett who, for her undergraduate Honours thesis at the University of British Columbia, examined mineral assemblages and magnetic susceptibility of alteration.  My subsequent analysis  substantially revised and refined the mineral assemblages.  Chapter V outlines a new  geochemical space-based mass balance technique. It is a simplified and altered version of Terry Gordon's geochemical mass balance technique and demonstrates that the listwanite alteration at Atlin was an isochemical process. The map in the insert is a published Geological Survey of Canada Open File map, which I produced and digitized with the help of Stephen Williams and Bob Anderson. The authorship, final or expected, is given at the beginning of each chapter, except for the Open File insert where the xvii  PREFACE authorship is given on the map. Dr. Greg Dipple and Dr. Bob Anderson secured the funding, and provided supervision, for this prqpct.  xviii  ACKNOWLEDGEMENTS ACNOWLEDGEMENTS This research was funded by a Natural Sciences and Engineering Council of Canada Discovery Grant, by the Oil, Gas and Energy Branch of Environment Canada, and by the Innovative Research Initiative for Greenhouse Gas Mitigation, a program under the Climate Change Action Plan 2000, and administered under Environment Canada and Natural Resources Canada, Earth Sciences Sector. It was conducted under the auspices of Activity Sa, CO 2 Storage by Mineral Carbonation Reactions: teetic and Mechanical Insights from Natural Analogues"under the Earth Sciences Sector Climate Change Program, Prqpct CC480, en titled Monitoring methods and assessment of carbon sequestration over Canadas landmass" I would like to thank Bill Reynen, Environment Canada, for encouraging the initiation of this prqpct and Mitch Miha lynuk, British Columbia Geological Survey Branch, for his help and expertise at Atlin, including logistics, data sharing, and aerial photography.  Carmel Lowe of the Pacific Geoscience Centre first suggested using  magnetic susceptibility to map alteration. K'oko Nakano provided invaluable field and laboratory assistance, and Sasha Wilson performed Raman analysis. Dawn Mlett is thanked for all her insightful ideas generated during her honours thesis studying the carbonated ultramafic bedrock at Atlin. I thank A. E. Williams-Jones, L. P. Baumgartner, D. Pattison and R. Martin for their insights and comments during the review process of Chapter IV.  Stephen Williams of the Geological Survey of Canada at Vancouver  provided expertise and help in digitizing my map. I have benefited greatly from Terry Gordon for his geochemical and mathematical expertise.  James Scoates provided  excellent feedback in the final review of my thesis. I would like to thank Bob Anderson of the Geological Survey of Canada at Vancouver for his invaluable contributions during the review process of much of this thesis and for his insight both at the office and in the field. Finally I would like to thank Greg Dipple for his insightful guidance over the last two and a half years and who took the chance at bring me to Vancouver and getting me involved in such an interesting prqpct.  xix  CHAPTER I CHAPTER I: INTRODUCTION 1.1 INTRODUCTION Listwanite (carbonated-serpentinite),  (e.g. Ash, 2001; Hansen et ah, 2004;  Chapter II) is commonly associated with high-grade lode-gold mineralization and binds large quantities of carbon dioxide, a greenhouse gas. It forms from the same overall mineral transformation proposed for mineral carbonation, an industrial form of C O 2 sequestration.  The Mother Lode gold district in California (Wittkopp, 1983) and the  Abitibi greenstone belt of the Superior Province of Canada (Schandl and Naldrett, 1992) are two of the most well known examples of mesothermal listwanite-associated lode-gold in North America. In general, the richest gold grades within these deposits are associated with, or in close proximity to carbonate-altered ultramafic rocks (e.g. Ash 2001). Significant debate exists over the role ultramafic rocks and their carbonate-altered equivalents play in lode-gold mineralization. Additionally, the artificial alteration of serpentine and olivine to carbonate, a process known as mineral carbonation, has the potential to fix vast quantities of anthropogenic carbon dioxide ( C O 2 ) , a greenhouse gas that has been implicated in global warming (Seifritz, 1990).  Globally, mineral  carbonation offers virtually unlimited capacity and the promise of safe, permanent storage of C O 2 , with little risk of accidental release (Guthrie et al., 2001). The objectives of this thesis are to document the mineral transformations, geochemical alteration, structural relationships, timing, environmental conditions and stable isotopic signatures for the listwanite alteration at Atlin, British Columbia (Fig. 1.1). Results of this study have resulted in a much better understanding of listwanitesystems in general and have spawned numerous ideas for optimizing in situ mineral carbonation systems where C O 2 is directly injected into an ultramafic body or aquifer. This study has also resulted in a better understanding of the development of the highgrade gold lodes associated with listwanite systems. Chapter II, a previously published paper with the Geological Survey of Canada, highlights the geologic setting, geological units, geophysical properties and structural controls of the listwanite deposits at Atlin. This setting is elaborated in Chapter III,  1  CHAPTER I  Figure 1.1: Location of Atlin and the Atlin map area (NTS 104N), northwestern British Columbia. Main rivers are shown in blue and main highways in black.  2  .  CHAPTER I  which presents a detailed structural analysis, detailed geological history, and stable isotopic study highlighting the possible fluid flow patterns and a discussion on the possible origins for the lode-gold mineralization. Chapters II and III have identified that in addition to the basal thrust fault (Ash, 1994) there exists a regional joint/fracture system with four steeply-dipping fracture sets that control the spatial distribution of listwanite. Gold is not only associated with zones of intense listwanite alteration (e.g. Ash, 2001), but also with organic material. Stable isotopic evidence and petrography have detected an organic signature of carbonate within the listwanite and indicate that the fluids have likely interacted with metasedimentary rock material. Gold may have been mobilized by hydrogen sulphide complexes, derived from organic material and redeposited in areas of intense carbonate alteration. Magnetite stability is strongly influenced by serpentinization (magnetite-producing) and listwanite alteration (magnetite-destroying).  This allowed for the employment of a magnetic  susceptibility metre as an aid to mapping serpentinized or carbonated fractures. Chapter IV, a previously published paper in Canadian Mineralogist, discusses the petrology, mineralogical transformations and geochemical alteration based on a limited dataset of 23 samples. Here it was described how listwanite alteration proceeded via three sub-reactions fossilized spatially into distinct mineralogical zones.  The first  appearance of the index minerals, magnesite, talc and quartz define three metamorphic isograds and the magnesite-, talc- and quartz-zones.  The three reactions were  carbonation- (de)hydration reactions, were isochemical with respect to non-volatile chemical species, and were controlled by the C 0 content of the infiltrating fluid. The 2  magnesite- and talc-zone reactions are likely the most suitable for the development of in situ  mineral carbonation injection systems because of their small associated gain in solid  volume and the potential development of permeability caused by fracturing as the talczone reaction progresses. Chapter V supplements Chapter IV in introducing a new geochemical mass balance technique, based on the work of Gordon (2003). This technique was applied to a larger dataset of 160 samples. The novelty of this approach is that it calculates a model protolith for each altered sample that is constrained within a defined chemical space. Results strongly suggest that, with the exception of intensely altered rocks, listwanite  »  3  .  CHAPTER I  alteration at A t l i n occurred without the modification o f the major non.-volatile component o f the rocks. carbonate  A handful o f samples that have undergone complete to near-complete  alteration contain extensive quartz-carbonate  present in hand sample and indicates limited S i , M g 2 +  4  2 +  v e i n i n g and Cr-muscovite is  and K  +  metasomatism.  CHAPTER I 1.2: REFERENCES Ash, C. H. (1994): Origin and Tectonic Setting of Ophiolitic Ultramafic and Related Rocks in the Atlin Area, British Columbia (NTS 104N); B.C. Ministry of Energy, Mines and Petroleum Resources, Bulletin 94, 48 p. Ash, C. H. (2001): Relationship Between Ophiolites and Gold-Quartz Veins in the North American Cordillera; British Columbia Department of Energy, Mines and Petroleum Resources, Bulletin 108, 140 p. Gordon, T.M. (2003): Algebraic Generalization of the Graphical Gresens and Pearce Methods for Identification of Geochemical Mass-Transfer Processes.  (abstract),  Vancouver 2003 Abstracts, CD-ROM, GAC-MAC-SEG, Vancouver 2003 Annual General Meeting, Vancouver, B.C., 28-146, ISSN 0701-8738, ISBN: 0-919216-86-2.  Guthrie, G. D., Carey, J. W., Bergfeld, D., Byer, D., Chipera, S., Ziock, H . and Lackner, K. S. (2001). Geochemical Aspects of the Carbonation of Magnesium Silicates in an Aqueous Medium.  Proceedings  of the First National Conference  on Carbon  Sequestration, May 14-17, 2001, Washington, DC, session 6C, 14 pages.  Hansen, L. D., Dipple, G. M . , Anderson, R. G. and Nakano, K. F. (2004): Geologic Setting of Carbonate Metasomatised Serpentinite (Listwanite) at Atlin, British Columbia: Implications for CO2 Sequestration and Lode-Gold Mineralization, in Current Research, Geological Survey of Canada, Paper 2004-A5, 12 pages.  Schandl, E. S. and Naldrett, A . J. (1992): C 0 Metasomatism of Serpentinites, South of 2  Timmins, Ontario; Canadian Mineralogist, v. 30, p. 93-108.  Seifritz, W. (1990): C 0 Disposal by Means of Silicates. Nature, 345, 486. 2  5  CHAPTER I Wittkopp, R. W. (1983): Hypothesis for the Localization of Gold in Quartz Veins, Allegheny District. California Geology, 36-6, 123-127.  \  6  CHAPTER II CHAPTER  II: GEOLOGICAL  SETTING  OF LISTWANITE  (CARBONATED  SERPENTINITE) AT ATLIN, BRITISH COLUMBIA: IMPLICATIONS FOR C 0 SEQUESTRATION AND LODE-GOLD MINERALIZATION  2  1  2.1 INTRODUCTION Listwanite forms from the reaction of ultramafic rocks with carbon dioxide (C0 )-bearing fluid.  It is also a natural analogue to the geologic sequestration of the  2  greenhouse gas C 0 by mineral carbonation. Mineral carbonation reactions bind C 0 2  within carbonate minerals by reaction with M g  2+  2  derived from serpentine and olivine.  Globally, mineral carbonation offers virtually unlimited capacity and the promise of safe, permanent storage of C 0 (Guthrie et al., 2001). In situ mineral carbonation, the direct 2  injection of C 0 into large subsurface ultramafic formations, allows for reaction times of 2  tens to hundreds of years (Guthrie et al., 2001). Historically, listwanite is also known for its spatial association with lode-gold mineralization (e.g. Wittkopp, 1983; Schandl and Naldrett, 1992; Ash, 2001). Our goal in studying listwanite is to document reaction environments, pathways, catalysts and reaction mechanics and uncover fluid flow patterns and evidence for gold mobility. This information will aid in the development of in situ mineral carbonation systems and refine listwanite lode-gold deposit models. Here we document the structural controls, mineral reactions, geochemical alteration, and permeability system that accompanied listwanite formation near Atlin, located in northwestern British Columbia. Evidence for carbonation, indicated by Mgcarbonate minerals, is present for metres to tens of metres into wallrock adjacent to controlling fractures.  Our field mapping and sampling show that listwanite occurs  primarily along the basal decollement of an allochthonous ultramafic body and a transecting joint- and fracture-system.  Listwanite-alteration and serpentinization both  affect magnetite stability. As a consequence, magnetic susceptibility was successfully tested as a tool to map the degree of serpentinization and carbonation reaction.  A version of this chapter has been published as: Hansen, L.D., Anderson, R.G., Dipple, G . M . and Nakano, K. (2004): Geological Setting of Listwanite (Carbonated Serpentinite) at Atlin, British Columbia: Implications for C 0 Sequestration and Lode-gold Mineralization, Geological Survey of Canada, Current Research, 2004-A5, 12 p. 1  2  7  CHAPTER II 2.2 REGIONAL GEOLOGY AND FIELD METHODS The Atlin Ultramafic Allochthon (Ash and Arksey, 1990a) was first mapped by Aitken (1959) as an ultramafic intrusion. Ash and Arksey (1990a) reinterpreted the rocks as the tectonically emplaced residual upper mantle section of oceanic lithosphere. The ultramafic rocks, combined with associated oceanic rocks, including metabasalt and pelagic sedimentary rocks and mafic to ultramafic cumulates, form an assemblage of fault-bounded and dismembered, but geologically related, sub-units. The Atlin Ophiolitic Assemblage (Ash and Arksey, 1990a) includes the ultramafic and mafic rocks, whereas the sedimentary accretionary rocks comprise the Atlin Accretionary Complex (Ash and Arksey, 1990a). Both were obducted onto the Stikine and Cache Creek terranes during Early to Middle-Jurassic amalgamation and accretion.  This study focuses on the  listwanite occurrences within the ultramafic section. Previous geological work around Atlin is described by Aitken (1959), Monger (1975, 1977a, b), Monger et al. (1978), Bloodgood et al. (1989), Mihalynuk et al. (1992), Ash and Arksey (1990a, b), Ash et al. (1991) and Ash (1994, 2001). Geochemical and other studies of the Atlin listwanite include: detailed petrography and geochemistry (Kellett, 2002; Hansen et al, 2003a, b, 2005; Chapter IV); mineralogical and geochemical studies of lode-gold prospects around the Atlin camp (Lueck, 1985; Newton, 1985); a fluid inclusion study (Andrew, 1985); mineral chemistry of the principal minerals in the harzburgite (Ash, 1994); and  40  A r - A r and K-Ar 39  geochronological ages of Cr-muscovite (Ash, 2001) interpreted as cooling ages related to Middle Jurassic batholiths. The map of Ash (1994) was the basis for choosing the study area and the foundation for the 1:6000 scale mapping of the listwanite within the Atlin Ultramafic Allochthon (Fig. 2.1). The nature and geometry of the structural zones were mapped at 1:20 scale from a well-preserved listwanite zone on the west flank of Monarch Mountain (Fig. 2.2). A l l mapping was aided by an aeromagnetic map (Fig. 2.3), a magnetic susceptibility meter and standard GPS techniques.  A l l locations are given as UTM  eastings and northings using the 1983 North American Datum (NAD 83).  8  CHAPTER II  Figure 2.1: Simplified geologic map of the study area showing the distribution of listwanite near Atlin area (this paper; Hansen et ai, 2003b; Ash, 1994). AOA and A A C are Atlin Ophiolitic Assemblage and Atlin Accretionary Complex, respectively, of Ash and Arksey (1990a). Sample locations are denoted 01 AT X X .  9  CHAPTER II  Figure 2.2: a) Composite image of a 2 by 2 metre pavement outcropping on the western slope of Monarch Mountain (E 575887, N 6602098, NAD 83). Dashed yellow lines are contacts in Figure 2.2b. b) Detailed geologic map of the listwanite zone mapped at 1:20 scale. Sample locations and section A-B correspond to those of Figure 3.7. c) Magnetic susceptibility map composed of ca. 1550 measurements, showing the correlation of magnetic susceptibility with map units in Figure 2.2b. d) Whole rock Wt% CO2 map calculated using Eqi following Hansen et al. (2005), Chapter IV.  10  CHAPTER II  Figure 2.3: Aeromagnetic map of the study area and contacts to the main geological units in Figure 2.1. Aeromagnetic lows correspond to known zones of listwanite. Aeromagnetic data acquired from the National Geophysical Data Base and is maintained by the Geological Survey of Canada. Image generated by C. Lowe (GSC-Pacific).  11  CHAPTER II 2.3 ULTRAMAFIC ROCKS The Atlin Ultramafic Allochthon, composed of serpentinized harzburgite, underlies an area of about 25 km (Fig. 2.1) and comprises variably serpentinized, 2  carbonitized and deformed harzburgite with minor dunite lenses and pyroxenite veins. It is a tectonic klippe, separated from the Atlin Accretionary Complex lithologies by a basal decollement termed the Monarch Mountain Thrust Fault (Ash and Arksey, 1990a). Serpentinization is most intensely developed near the basal decollement and adjacent to joints and fractures that crosscut the body (Fig. 2.1).  The serpentine minerals are  dominantly antigorite +/- minor chrysotile that occurs within fractures. The harzburgitic ultramafic rocks are divided into two units based on the degree of serpentinization. The harzburgite unit includes all weakly- to moderately-serpentinized harzburgite (Fig. 2.4a, b). The freshest harzburgite is located at the west-central section on the plateau of Monarch Mountain where serpentine is <30 volume percent (Fig. 2.4b). It is characteristically studded with 5-40 volume percent resistant red-brown orthopyroxene grains (2-10 mm in diameter), commonly pseudomorphed by serpentine, within a recessive dun-brown weathering, partially serpentinized olivine matrix. This unit forms rounded and jointed outcrops. Fresh surfaces are dark green with the orthopyroxene crystals distinguished by their vitreous luster and cleavage. Compositional layering (So) is defined by alternating 1 to 10 cm orthopyroxene-rich and -poor layers. Flattening of orthopyroxene grains defines a weakly to moderately developed planar Si tectonite fabric (Fig 2.5a) and parallels So where present together. The serpentinite unit is intensely to completely serpentinized harzburgite (Fig. 2.4c, d).  The contact is gradational, commonly making it difficult to differentiate  serpentinite from harzburgite. The weathering colour of serpentinite is variable grey to near black, green, and blue. Lichen-free surfaces are spotted due to the presence of dark bastite after orthopyroxene. Commonly a well-developed S fabric, oriented 244° / 54° 2  NW (Figs. 2.4c, 2.5b), is developed and defined by flattened and sheared bastite spots (serpentinized orthopyroxene). Relict orthopyroxene is mantled by bastite. The best examples of serpentinite occur along the lower west flank of Monarch Mountain, where  12  CHAPTER II  Figure 2.4: a) Resistant orthopyroxene within recessive, partially serpentinized olivine matrix; typical of weakly serpentinized harzburgite. b) Photomicrograph of freshest harzburgite under cross-polars. c) Moderately foliated serpentinite defined by the flattening of bastite spots, d) Photomicrograph of typical serpentinite under cross-polars.  13  C H A P T E R II  Harzburgite Foliation  A )  1  C)  N  1  B)  Bastite Foliation  D)  Quartz-Carbonate Veins  N  (VI  Serpentine  N  = 182  N = 136  Figure 2.5: Structural data (poles to planes on equal area stereonets) of: a) Harzburgite foliation (Si) defined by flattening of orthopyroxene grains; b) Bastite foliation (S ) 2  defined by flattened and sheared bastite spots. Great circle represents the average foliation; c) Magnetite-serpentine veinlets; d) quartz-carbonate high-grade listwanite.  14  veins associated with  CHAPTER II the bastite foliation is common, and on the lake shore north of Atlin where well-polished rocks have a spotted green and dark blue texture. Dunite lenses and pyroxenite veins, commonly too small to show in Figure 2.1, make up a small proportion of the map area. The lenses within the Atlin Ultramafic Allochthon range from less than 1 m to about 100 m in length and form smooth 'dun' brown weathering outcrops. Dunite is commonly highly fractured forming rubble within outcrops of more resistant harzburgite. The long axes of the lenses occur within the planar Si fabric of the harzburgite. Pyroxenite veins are generally 1 to 5 cm thick and generally are concordant with the Si foliation fabric. However, they are often isoclinally folded and cut by later pyroxenite veins indicating they were emplaced pre- to postdeformation (Ash, 1994). The axial surfaces of the isoclinal folds parallel the tectonite fabric of the harzburgite. The orientation of the S2 fabric, mullion structures reported by Ash and Arksey (1990a) and southeasterly striking geological units to the south and to the east of the map area (Ash, 1994) suggest shortening along an northwest-southeast axis with "thrusting" to southeast (Ash and Arksey, 1990a). To the northwest, there is an area of geologic units striking northwest; listwanite controlling joints and fractures are dominantly oriented parallel to these two directions.  2.4 LISTWANITE Listwanite in Russian and Eastern European literature (e.g. Rose, 1837; Ploshko, 1963; Kashkai and Allakhverdiev, 1965; Halls and Zhao, 1995) is a term used to describe distinctive, rusty-red weathering quartz-carbonate-chromium muscovite rocks produced during the carbonate-alteration of ultramafic rocks.  Listwanite and other mineral  assemblages produced during the same carbonation process as listwanite are termed listwanite series assemblages and are akin to the rocks of this study (Fig. 2.6). In North America, listwanite is more broadly defined as; "a carbonitized and variably silicified serpentinite, occurring as dikes in ophiolite complexes" (Jackson, 1997). Unfortunately this definition is inappropriate for use at Atlin because it implies metasomatism which has been discounted at Atlin (Hansen et al, 2003a, b, 2005; Chapters IV, V). Furthermore, listwanite-alteration is a multi-step process (Hansen et al., 2005; Chapter 15  CHAPTER II  Figure 2.6: a) View to northwest of well-preserved, rusty-brown, talc-magnesite listwanite zone (Lb) which is about 50 cm thick. Scale = 5 cm. b) View to the north of a large area of distinctive rusty red listwanite associated with the basal decollement (below water) along eastern shore of Atlin Lake. The small peninsula in the centre of the image is underlain by a melanocratic basaltic dike. Evergreen tree just to the left of the centre of the photograph is approximately 8 metres tall.  16  CHAPTER II IV) and intermediate mineral assemblages do not contain quartz (Table 2.1). The other common North American term "silica carbonate alteration", used to describe these deposits, is also not suitable for the same reasons. Consequently, our usage of listwanite refers to any carbonate-altered serpentinite.  Halls and Zhao (1995) discuss listwanite  terminology in greater detail. At Atlin, listwanite occurs along the shallowly-dipping lower boundary of the Atlin Ultramafic Allochthon (Figs. 2.1 and 2.6b). Any brecciation appears to predate listwanite-alteration.  Listwanite is also common along steeply-dipping joints and  fractures dominantly trending about 140° (L trend) and 50° (Lb trend) (Figs. 2.1, 2.5d, a  2.6a).  Fracture-controlled listwanite is generally expressed as lineament depressions,  commonly vegetated and filled with overburden.  Rusty-red weathering side walls  confirm they are underlain by listwanite. The lineament and listwanite association is clearly seen at the head of the Monarch Mountain hiking trail on Warm Bay road (Fig. 2.7). Within the harzburgite unit, the margins of surface lineaments are commonly marked by chalky blue-green weathering serpentine alteration suggesting that they mark structural weaknesses that acted to focus fluids. The serpentinization along fractures is overprinted by listwanite. Small serpentine-magnetite veinlets, usually less than 1 cm thick, cut harzburgite, dunite and serpentinite. Structural measurements indicate that the dominant orientations of the veinlets are collinear with lineament and listwanite trends (Fig. 2.5c, d). Generally, L  a  listwanite zones are fewer but more extensive, pervasively  carbonated and contain more stockwork quartz-carbonate veins and Cr-muscovite than Lb zones. The highest concentration of L zones transects the map area, extending from a  about 700 m south of Atlin to the west side of Monarch Mountain, about 3 km southeast of town (Fig. 2.1). It may mark the locus of a broad fault or fracture zone. The Anna and Aitken gold prospects, the only showings in the map area clearly not associated with the basal decollement, are both associated with L -trending listwanite zones and Cra  muscovite. Subsequent mapping has defined two other trends and are described in detail in Chapter III.  17  CHAPTER II  Table 2.1: Mineralogy of carbonated serpentinite from Atlin, BC Chr Mgt Brc Ol Srp Mgs Tic Qtz Sample X X X 01AT-8-1 X X X 01AT-13-1 X X X X 01AT-3-1 X X X X X 01AT-10-1 X X 01 AT-10-2 X X X X X X X X X 01AT-2-2 X X X X X 01AT-9-1 X X X X X 01AT-11-1 X X X X 01AT-1-9 X X X X 01AT-6-3 X X X X 01AT-1-8 X X X X 01AT-13-2 X X X X 01AT-11-2 X X X X X 01AT-7-3 X X X X X 01AT-1-7 X X X X X 01AT-1-6 X X X X 01AT-9-2 X X X X 01AT-7-1 X X X X x 01AT-5-4 w X X x 01AT-1-5 X X X X X X X 01AT-4-1* X X 01AT-5-2 X X X X 01AT-6-1* only occurs in small veins occurs in small isolated patches armored relicts and late mantling of chromite and pyrite magnetite in late fractures and late mantling of chromite * sample contains Cr-muscovite Sample locations in Appendix F. V  y  z  v  w y  z  18  C0  A, Ai A, A, A, A, Ri Ri A A A A A R R R R R R R R A A  2 2  2  2  2  2  2  2  2  3 3  3  3  4  4  2  (wt%)  0.06 0.10 0.21 0.15 0.26 0.33 2.10 2.57 3.37 4.00 4.60 7.12 9.60 3.40 7.19 9.54 17.26 21.83 28.01 34.00 34.34 35.20 36.19  CHAPTER II  Figure 2.7: a) Aerial view to the northeast showing recessive weathering lineaments representing L and L orientations associated with listwanite at head of Monarch a  b  Mountain Hiking trail (photo by M . Mihalynuk, August 2003) (E 575900, N 6602100, N A D 83). b) Geologic map of the area in Figure 2.7a.  19  CHAPTER II 2.5 LISTWANITE PETROGRAPHY, GEOCHEMISTRY AND REACTION PATH Listwanite at Atlin is zoned mineralogically outward from the controlling fracture permeability network and tracks the migration of three sequential and isochemical carbonation-(de)hydration reactions (Hansen et al., 2005; Chapter IV). The most distal reaction (Ri) was detected geochemically and petrographically (Table 2.1) and involves the breakdown of olivine +/- brucite (assemblage A i , Fig. 2.8) to magnesite-antigorite (A ).  The magnesite-antigorite rocks commonly resemble serpentinite (Aj) but in  2  outcrop typically contain small carbonate veinlets. The low abundance of olivine in serpentinite (Ai) limits reaction R.. Antigorite-magnesite grades into talc-magnesite ( A 3 ) produced via reaction R . It is soft, has a waxy feel and commonly weathers to a 2  distinctive smooth but irregular dark-red surface. Quartz plus magnesite ( A 4 ) is present in completely carbonated areas that resulted from the carbonation of talc (R3).  The  quartz-magnesite zone weathers to a rough orange-red surface. Minor chromite present in serpentinite survives all three reactions. The reactions (R) are:  Mg48Si34 0 5(OH) + 20 M g C 0  34 M g S i 0 + 20 C 0 + 31 H 0 2  4  2  8  2  62  (Ri)  3  Olivine -> Antigorite + Magnesite  2 Mg48Si34 0 (OH) 2 + 45 C 0 -5» 45 M g C 0 + 17 Mg Si4O, (OH) + 45 H 0 85  6  2  3  3  0  2  2  (R ) 2  Antigorite -> Magnesite + Talc  Mg Si4Oi (OH) + 3 C 0 -S» 3 M g C 0 + 4 S i 0 + H 0 3  0  2  Talc  2  3  2  2  (R ) 3  Magnesite + Quartz  Olivine is not present with talc and quartz does not occur with serpentine indicating the three reactions have occurred in sequence.  The mineral zonation is  therefore amenable to the mapping of metamorphic .isograds: the magnesite, talc and quartz isograds indicate the first appearance of magnesite, talc and quartz, respectively. The highly altered cores of listwanite zones may contain stockwork quartz-carbonate veins,  bright-green  Cr-muscovite (mariposite,  20  fuchsite),  sulfide  (mainly pyrite)  CHAPTER II  Assemblage Ai  Talc + Magnesite  Serpentine +/- Olivine +/- Brucite  \ R i  Assemblage A4  Assemblage A3  R  3  Quartz + Magnesite  R 2 /  *Reaction R-| by-passed if no olivine or brucite present in the protolith (Assemblage Ai).  Assemblage A2 Serpentine + Magnesite  Figure 2.8: Simplified flow chart for the reaction path of the Atlin listwanite system during progressive carbonation of serpentinite. A detailed description of the reactions is provided in Hansen et al. (2005), Chapter IV.  21  CHAPTER II mineralization and anomalous Au values (e.g Ash, 2001). Cr-muscovite results from limited chromite destruction and the addition of K . Though C a +  2+  addition is common in  listwanite systems (e.g. Aydal, 1990), our studies have been unable to detect it at Atlin.  2.6 IGNEOUS INTRUSIONS At least three distinct phases of dikes are present in the map area. They include a melanocratic medium-grained hornblende diabase, a medium- to coarse-grained lightgrey porphyritic feldspar-, quartz-dacite and a grey-brown porphyritic plagioclase-, Kfeldspar-, biotite-, hornblende- and quartz- dacite. A l l contain sulfide minerals, mostly pyrite. Locally they are carbonated, but clearly cross-cut the listwanite. This crosscutting relation is clearly seen about 500 m south of Atlin near the Anaconda lode-gold prospect (Fig. 2.5b). Xenoliths of listwanite occur within the mafic dike phase at this location.  Dikes are commonly spatially associated with listwanite and surface  lineaments. Regional crustal weaknesses have likely provided the same guides to magma ascent as they did for fluids associated with earlier episodes of serpentinization and listwanite generation. A U-Pb geochronological analysis of the light-grey dacite and a fresh  40  A r - A r geochronological biotite sample from the grey-brown phase, both of 39  which crosscut listwanite, are reported in Chapter III. These two dates further constrain the age and duration of the listwanite genesis at Atlin and show a temporal correlation with the widespread Middle Jurassic plutonism in the area, potential sources of gold-rich fluid.  2.7 MAGNETIC PROPERTIES Magnetite forms during the serpentinization of olivine and is destroyed during carbonate-alteration. F090)  During serpentinization, iron contained in harzburgitic (roughly  olivine is preferentially excluded from serpentine resulting in the formation of  magnetite (Toft et al., 1990). Magnetite occurs as rim overgrowths on chromite and as disseminated grains aligned in foliation planes and in fractures. A l l increase the magnetic susceptibility of the serpentinite rocks. Magnetic susceptibility varies strongly between the harzburgite unit (2 to 50 (10" SI units)) and serpentinite unit (>50 to as high as 150 3  22  CHAPTER II (10~ SI units)). This observation is useful for differentiating between the two units in 3  lichen-covered areas where the degree of serpentinization is not easily discernable. Magnetite is progressively consumed during reaction R (Hansen et ah, 2005; 2  Chapter IV). The Fe derived from the breakdown of magnetite was accommodated in magnesite (Hansen et al. 2005; Chapter IV). Magnetic susceptibility is usually at the lower detection limit of a hand-held magnetic susceptibility meter (lxl0" SI units) in 5  rock containing >20 wt% C 0 , corresponding to complete progress of reaction R . A 2  2  magnetic susceptibility contour map, including ca. 1550 magnetic susceptibility measurements from the detailed mapping area of a Lb listwanite zone, illustrates the association of magnetic susceptibility with mineralogy (Fig. 2.2c). Following Hansen et al. (2005; Chapter IV), a C 0  2  content map was calculated from the magnetic  susceptibility map (Fig. 2.2d) and tracks whole rock C 0 content to within 5 wt%. 2  Airborne magnetic surveys are able to detect areas of vast carbonate-alteration (e.g. Ash, 1994; Lowe and Anderson, 2002). Areas of listwanite-alteration in Figure 2.1 correspond to aeromagnetic lows in Figure 2.3. The basal decollement, which traces from just north of Atlin to the Heart of Gold prospect then along the east to south slopes of Monarch Mountain, is easily distinguished on the aeromagnetic map (Figs. 2.1, 2.3). The aeromagnetic saddles in Fig. 2.3 through and just south of Atlin and through the Pictou prospect correspond to areas of known listwanite.  2.8 IMPLICATIONS FOR C 0 SEQUESTRATION 2  The overall mineral transformation in listwanite-alteration is the same as that proposed for sequestration of C 0 in minerals, but in nature proceeds through a series of 2  sub-reactions fossilized as spatially distinct zones. Direct carbonation of olivine +/brucite (Ri) was previously unrecognized at Atlin and records carbonation of intact bedrock many tens of metres from the primary fracture permeability system.  Initial  carbonation of olivine by reaction Ri is likely due to the higher reactivity of olivine (+/brucite) to that of serpentine in the presence of a C0 -bearing fluid (Lackner et al., 1995; 2  Guthrie et al., 2001) and the small solid volume increase associated with the carbonation of small amounts of relict olivine (Table 2.2). Though reaction R i only accounts for about 5-15 % the carbonation potential for the serpentinite at Atlin (Table 2.1), because it 23  CHAPTER II  Table 2.2: Volume Changes AVs* (rxn)  AVs (rock**)  R : Ol -» Srp + Mgs  55.1%  4.2%  R : Brc -> Mgs  13.8%  0.4%  Reaction 1a  1b  R : Srp -> Tic + Mgs  2.6%  2.3%  R : Tic -> Qtz + Mgs  28.5%  16.2%  2  3  * Calculated from Berman (1988) at 250°C and 500 bars (Chapter IV) Assuming 2.5% brucite and 7.5% relict olivine by volume.  24  CHAPTER II is widespread, it may have sequestered a significant portion of the total CO2 contained in the Atlin listwanite system. Each of the three carbonation reactions involves an increase in the volume of solids, therefore each has the potential to create or destroy permeability. Reaction R2 binds large quantities of CO2 with small associated loss of porosity and permeability (Tables 2.1, 2.2). Moreover, the progression of reaction R2 may create a permeability front in advance of it, promoting further carbonation. The development of carbonatefilled veins orthogonal to the R reaction front in Figures 2.2a and b may represent 2  fracture permeability generated in tension (Hansen et al., 2005; Chapter IV). The mechanical model of Jamtveit et al. (2000) predicts the development of high permeability zones downstream of an advancing reaction undergoing a solid volume increase. Indeed, the pattern of reaction and vein formation in Figures 2.2a and b resembles the model prediction. The distribution of tensile fractures approximately marks the outer extent of rust-weathering serpentinite suggesting they have enhanced percolation of reactive CO2bearing fluid into the wall rock. Complete carbonation to magnesite plus quartz (A4) is generally limited to the cores of the largest systems. The large solid volume gain associated with reaction R3 may seal the fluid percolation pathways and limit the usefulness of in situ mineral carbonation systems. For this reason, reactions Ri and R2, which combined account for about half of the carbonation potential for serpentinite (Table 2.2), may hold the most promise for in situ carbonation of minerals. The stability of the three reaction steps is controlled by the activity of C 0 in the fluid phase (Hansen et al, 2005; Chapter IV). 2  Therefore, industrial mineral carbonation systems could potentially be tailored to drive only those reactions that minimize porosity loss and maximize permeability generation in the subsurface. 2.9 IMPLICATIONS FOR LODE-GOLD MINERALIZATION A positive correlation of Au with K-altered quartz-carbonate listwanite has been noted in listwanite systems worldwide (e.g. Ploshko, 1963; Buisson and LeBlanc, 1987; Ash and Arksey, 1991). Ploshko (1963) also noted an association of K-alteration in listwanite systems with felsic igneous intrusions in the northern Caucasus. Similarly, 25  CHAPTER II Ash (2001) noted a general correlation in ophiolite-hosted Au occurrences with granitic intrusions in the Canadian Cordillera.  Granitic intrusions could promote listwanite  development by providing a heat source to drive fluid circulation, by serving as a fluid source, and possibly as a source for gold and other metals. Middle Jurassic plutonism is widespread to the south and immediately north of the listwanite occurrences. Southern plutons include the Mount McMaster and Llangorse Mountain batholiths (172 +/- 0.3 Ma and 171 +/- 0.3 Ma (U-Pb, zircon) respectively (Anderson et al, 2003)) 45-60 km south of Atlin. The south margin of the large, multiphase Middle Jurassic Fourth of July batholith (FOJB) occurs a few kilometres to the north of the Atlin Ultramafic Allochthon. The batholith's U-Pb zircon age range of 166174 Ma (Mihalynuk et al., 1992) overlaps the age range of Cr-muscovite in the listwanite (168-172 Ma ( Ar- Ar); Ash, 2001). 40  39  Streams that drain the FOJB contain stream  sediments with anomalous Au contents (Jackaman, 2000) suggesting that the intrusion was a possible source for Au and other metals. A small stock correlated with the FOJB crops out between Monarch Mountain and Union Mountain (Ash, 1994). New isotopic ages for dikes in the study area show a direct correlation to the FOJB (Chapter III). Magmatic-hydrothermal activity associated with the FOJB may have contributed to gold mineralization in the Atlin area. Lode-gold prospects near Atlin are spatially associated with the most intense Crmuscovite-bearing listwanite zones along the basal decollement and in the L orientation. a  L  a  listwanite zones therefore may be preferential targets for future exploration.  Listwanite-alteration destroys magnetite. Zones of listwanite appear as magnetic lows on aeromagnetic survey maps (Fig. 2.3). Ground surveying with a magnetic susceptibility meter could help identify subtle to cryptic carbonation which may aid in vectoring to potential lode-gold deposits.  26  CHAPTER II 2.10 REFERENCES Aitken, J. D. (1959): Atlin Map Area, British Columbia; Geological Survey of Canada, Memoir 307, 89 pages and accompanying map at 1:253 440 scale. Anderson, R. G., Lowe, C. and Villeneuve, M . E. (2003): Nature, Age, Setting, and Mineral Potential of Some Mesozoic Plutons in Central and Northwestern Atlin Map Area (NTS 104N), Northwestern B.C.; (abstract); Vancouver 2003 Abstracts, CD-ROM, GAC-MAC-SEG Vancouver 2003 Annual General Meeting, Vancouver, B.C., v. 28, abstract no. 600, ISSN 0701-8738, ISBN: 0-919216-86-2.  Andrew, K . (1985): Fluid Inclusion and Chemical Studies of Gold-Quartz Veins in the Atlin Camp, Northwestern British Columbia; unpublished B.Sc. thesis, Department of Geological Sciences, Vancouver, B.C., Canada, 116 p. Ash, C. H . (1994): Origin and Tectonic Setting of Ophiolitic Ultramafic and Related Rocks in the Atlin Area, British Columbia (NTS 104N); B.C.. Ministry of Energy, Mines and Petroleum Resources, Bulletin 94, 48 p.  Ash, C. H . (2001): Relationship Between Ophiolites and Gold-Quartz Veins in the North American Cordillera; British Columbia Department of Energy, Mines and Petroleum Resources, Bulletin 108, 140 p. Ash, C. H . and Arksey, R. L. (1990a): The Atlin Ultramafic Allochthon: Ophiolite Basement Within the Cache Creek Terrane; Tectonic and Metallogenic Significance (104N/12); Geological Fieldwork 1989, B.C. Department of Energy and Mines, Paper 1990-1, p. 365-374.  27  CHAPTER II Ash, C. H. and Arksey, R. L. (1990b): The Listwanite-Lode Gold Association in British Columbia; Geological Fieldwork 1989, B.C. Department of Energy and Mines, Paper 1990-1, p. 359-364.  Ash, C. H., Macdonald, R. W. J. and Arksey, R. L . (1991): Towards a Deposit Model for Ophiolite Related Mesothermal Gold in British Columbia; Geological Fieldwork 1991, BC Department of Energy and Mines, Paper 1992-1, p. 253-260. Aydal, D. (1990): Gold-Bearing Listwaenites in the Arag Massif, Kastamonu, Turkey; Terra Nova, v. 2, p. 43-52. Berman, R. G. (1988): Internally-Consistent Thermodynamic Data for Minerals in the System: NasO-KzO-CaO-FeO-AbOs-SiOz-TiOa-HaO-^; Journal of Petrology, v. 29, Part 2, p. 445-522. Bloodgood, M . A., Rees, C. J., and Lefebure, D. V. (1989): Geology and Mineralization of the Atlin Area, Northwestern British Columbia (104N/11W and 12E); Geological Fieldwork 1988, B.C. Department of Energy and Mines Paper 1989-1, p. 311-322.  Buisson, G. and LeBlanc, M . (1986): Gold-Bearing Listwaenites (Carbonitized Ultramafic Rocks) From Ophiolite Complexes; in Metallogeny of Basic and Ultrabasic Rocks, Gallagher, M . , Ixer, R., Neary, C. and Prichard,.H., Editors, The Institution of Mining and Metallurgy, pages 121-131.  Buisson, G. and LeBlanc, M . (1987): Gold in Mantle Peridotites from Upper Proterozoic Ophiolites in Arabia, Mali, and Morocco; Economic Geology, v. 82, p. 2091-2097.  28  CHAPTER II Guthrie, G. D., Carey, J. W., Bergfeld, D., Byer, D., Chipera, S., Ziock, H . and Lackner, K. S. (2001): Geochemical Aspects of the Carbonation of Magnesium Silicates in an Aqueous  Medium; Proceedings  of the  First National Conference  on Carbon  Sequestration, May 14-17, 2001, Washington, DC, session 6C, 14 pages. Halls, C. and Zhao, R. (1995): Listvenite and Related Rocks: Perspectives on Terminology and Mineralogy With Reference to an Occurrence at Cregganbaun, Co. Mayo, Republic of Ireland; Mineralium Deposita, v. 30, p. 303-313. Hansen, L . D., Dipple, G. M . , and Anderson, R. G. (2003a): Carbonate Altered Serpentinites of Atlin, B C : A Two Stepped Analoge to CO2 Sequestration; (abstract); Geological Society of America, 2003 annual meeting, Seattle, WA; Abstracts with Programs - Geological Society of America; Session 144-14. Hansen, L. D., Dipple, G. M . , and Gordon, T. M . (2003b):  Carbonate-Altered  Serpentinites, Atlin, BC: A Natural Analog to CO2 Sequestration; (abstract); Vancouver 2003 Abstracts, CD-ROM, GAC-MAC-SEG Vancouver 2003 Annual General Meeting, Vancouver, B.C., v. 28, abstract no. 494, ISSN 0701-8738, ISBN: 0-919216-86-2.  Hansen, L. D., Dipple, G. M . , Gordon, T. M . and Kellett, D. A . (2005): Carbonated Serpentinite (Listwanite) at Atlin, British Columbia: a Geological Analogue to Carbon Dioxide Sequestration, Canadian Mineralogist, v. 43, part 1, p. 675-689.  Jackaman, W. (2000): British Columbia Regional Geochemical Survey, NTS 104N/1 Atlin; British Columbia Ministry of Energy and Mines, BC RGS 51. Jackson, J. A . (1997): Glossary of Geology, Fourth Edition; American Geological Institute, Alexandria, Virginia, 769 p.  29  CHAPTER II Jamtveit, B., Austrheim, H., and Malthe-Sorenssen, A . (2000): Accelerated Hydration of the Earth's Deep Crust Induced by Stress Perturbations; Nature, v. 408, p. 75-87.  Kashkai, A . M . and Allakhverdiev, I. (1965): Listwanites: Their Origin and Classification; U . S. Geological Survey, Library, Reston, V A , United States, 146 p., Translated from the Russian, Listvenity, ikh genezis i klassifikatsiya, Akad. Nauk A Z SSR, Inst. Geol. Baku, 1965. Kellett, D. A . (2002): Geochemical and Geophysical Monitors of Reaction Progress During Carbonate Alteration of Serpentinite at Atlin, British Columbia; unpublished B.Sc. thesis, Department of Earth and Ocean Sciences, Vancouver, B.C., Canada, 48 p. Lackner, K . S., Wendt, C. H., Butt, D. P., Joyce, E. L . and Sharp, D. H . (1995): Carbon Dioxide Disposal in Carbonate Minerals; Energy, v. 20, 1153-1170. Lowe, C and Anderson, R G. (2002): Preliminary Interpretations of New Aeromagnetic Data For the Atlin Map Area, British Columbia; Geological Survey of Canada, Current Research, no. 2002-A17, 11 p. Lueck, B. A. (1985): Geology of Carbonitized Fault Zones on the Anna Claims and Their Relationship to Gold Deposits, Atlin, British Columbia; unpublished B.Sc. thesis, Department of Geological Sciences, Vancouver, B.C., Canada, 55 p.  Mihalynuk, M . G , Smith, M . , Gabites, J. E., Runkle, D. and Lefebure, D. (1992): Age of Emplacement and Basement Character of the Cache Creek Terrane as Constrained by New Isotopic and Geochemical Data; Canadian Journal of Earth Sciences, v. 29, p. 24632477. Monger, J. W. H . (1975): Upper Paleozoic Rocks of the Atlin Terrane; Geological Survey of Canada, Paper 74-47, 63 p. 30  CHAPTER II Monger, J. W. H . (1977a): Upper Paleozoic Rocks of Northwestern British Columbia; in Current Research, Part A, Geological Survey of Canada, Paper 77-1 A, p. 255-262.  Monger, J. W. H. (1977b): Upper Paleozoic Rocks of the Western Canadian Cordillera and Their Bearing on the Cordilleran Evolution; Canadian Journal of Earth Sciences, v. 14, p. 1832-1859. Monger, J.W.H., Richards, T.A. and Paterson, LA. (1978): The Hinterland Belt of the Canadian Cordillera: New Data From Northern and Central British Columbia; Canadian Journal of Earth Sciences, v. 15, p. 823-830. Newton, D. (1985): A Study of Carbonate Alteration of Serpentinites Around Au and Ag Bearing Quartz Veins in the Atlin Camp, British Columbia; unpublished B.Sc. thesis, Department of Geological Sciences, Vancouver, B.C., Canada, 85 p. Ploshko, V. V. (1963): Listwaenitization and Carbonitization at Terminal Stages of Urushten Igneous Complex, North Caucasus, International Geology Review, v. 7, p. 446463. Rose, G. (1837): Mineralogisch-Geognostistiche Reise Nach Dem Ural, dem Altai und dem Kaspischen Meere. v. 1: Reise nach dem nordlichen Ural und dem Altai. Berlin, C W . Eichoff (Verlag der Sanderschen Buchhandlung), xxx plus 641 p. and plates I-VII.  Schandl, E. S. and Naldrett, A . J . (1992): C 0 Metasomatism of Serpentinites, South of 2  Timmins, Ontario; Canadian Mineralogist, v. 30, p. 93-108. Toft, P. B., Arkani-Hamed, J. and Haggerty, S. E. (1990): The Effects of Serpentinization on Density and Magnetic Susceptibility: A Petrophysical Model; Physics of the Earth and Planetary Interiors, v. 65, p. 137-157.  31  CHAPTER II Wittkopp, R. W. (1983): Hypothesis for The Localization of Gold in Quartz Veins, Allegheny District; California Geology, p. 123-127.  32  CHAPTER III CHAPTER  III:  STRUCTURAL  SETTING  A N D TIMING  OF LISTWANITE  (CARBONATED SERPENTINITE), ATLIN, BRITISH COLUMBIA: IMPLICATIONS FOR LODE-GOLD MINERALIZATION.  3.1 INTRODUCTION Listwanite, a carbonate-altered ultramafic rock (e.g. Hansen et al, 2004; Chapter II;  Ash, 2001),  is commonly spatially associated  with  high-grade lode-gold  mineralization. The Mother Lode gold district in California (Wittkopp, 1983) and the Abitibi greenstone belt of the Superior Province of Canada (Schandl and Naldrett, 1992) are two of the best known examples of mesothermal listwanite-associated lode-gold in North America. In general, the richest gold grades within these deposits are associated with, or in close proximity to, carbonate-altered ultramafic rocks (e.g. Ash, 2001). Significant debate exists over the role ultramafic rocks and their carbonate-altered equivalents play in lode-gold mineralization. Buisson and LeBlanc (1987) suggest a model where by ultramafic rocks are stripped of gold by C02-bearing hydrothermal fluids during the initial stages of carbonation and redeposited in areas of intense carbonate alteration, quartz-carbonate veining and K metasomatism recorded by the development +  of Cr-muscovite. An alternative model poses that gold is stripped from tectonically thickened packages  of oceanic, volcanic and sedimentary rocks by large-scale  hydrothermal convection and redeposited within or near the alkaline environment of Kmetasomatized (Cr-muscovite bearing) zones of listwanite (e.g. Ash et al, 1991). The main difference between the two models is the source of gold. This chapter builds on Chapter II by elaborating upon the structural controls, mineral  reactions,  geochemical alteration,  tectonic  setting,  stable  isotope and  geochronologic evolution of the extensive listwanite-altered serpentinite rocks in the vicinity of Atlin, located in northwestern British Columbia. This information is used to assess the various scenarios for mesothermal listwanite-associated lode-gold deposition. Field mapping in the summers of 2003 and 2004 shows that listwanite is spatially distributed primarily along the basal decollement of an allochthonous ultramafic body and along a steeply-dipping late syn- to post-obduction regional joint and fracture system. 33  CHAPTER III Evidence for carbonation, indicated by the presence of Mg-carbonate minerals, is present for metres to tens of metres into wallrock adjacent to these fluid-controlling fractures. Stable isotope and gold assay data support a model where gold is scavenged from either nearby felsic batholiths or the structurally lower accretionary complex materials by hydrocarbon-bearing fluids. Geochronologic evidence indicates that the nearby Fourth of July Batholith (FOJB) is contemporaneous with the listwanite alteration and therefore has likely acted as the heat source for hydrocarbon maturation and hydrothermal convection. 3.2 REGIONAL GEOLOGY AND ROCK UNITS  &  The Atlin Ultramafic Allochthon (Ash and Arksey, 1990) underlies an area of about 25 km (Fig. 3.1, insert) and comprises variably serpentinized, carbonated and 2  deformed harzburgite along with minor dunite lenses and pyroxenite veins.  The  ultramafic body forms a tectonic klippe, separated from the Atlin Accretionary Complex lithologies by a basal decollement termed the Monarch Mountain Thrust Fault (Ash and Arksey, 1990). Serpentinization is most intensely developed near the basal decollement and adjacent to a penetrative joint and fracture system that cuts both the ultramafic and structurally lower lithologies. The serpentine minerals are dominantly antigorite +/minor lizardite and fracture-filling chrysotile. Harzburgitic ultramafic rocks are divided into the harzburgite and serpentinite units based on the degree of serpentinization and are discussed in Hansen et al. (2004) and Chapter II. Other rock types associated with the harzburgitic ultramafic body include metavolcanic rocks, limestone, chert and argillite, which occur structurally below the ultramafic rocks. They are not central to this study and are discussed in detail by Ash (1994). Listwanite is zoned mineralogically outward from fluid-controlling fractures (discussed below). The zonation tracks the migration of three isochemical carbonation(de)hydration reactions (Hansen et al, 2005; Chapter IV). The magnesite-, talc- and quartz-zones are separable by metamorphic isograds (reactions Ri to R 3 ; Hansen et al, 2005; Chapter IV) defined by the first appearance of magnesite, talc and quartz respectively. The three reactions occurred in sequence and are isochemical (Hansen et al., 2005; Chapter IV), except in the intensely altered cores where stockwork quartz34  CHAPTER III  Figure 3.1: Simplified geologic map of the study area showing the distribution of listwanite near Atlin area (this paper; Hansen et ai, 2003b; Ash, 1994). AOA and A A C are Atlin Ophiolitic Assemblage and Atlin Accretionary Complex, respectively, of Ash and Arksey (1990a).  35  CHAPTER III carbonate veins, bright-green Cr-muscovite (mariposite, fuchsite), sulfide (mainly pyrite) and anomalous Au values are common. 3.3 STRUCTURAL ANALYSIS There are a number of different structural elements that were identified within the map area. They are broadly divided into two groups: those which do not influence listwanite distribution (pre- and early syn-obduction) and those which do (syn- and postobduction). 3.3.1 PRE- TO SYN-OBDUCTION STRUCTURAL ELEMENTS Compositional layering (So) occurs within the harzburgite unit and is defined by alternating 1 to 10 cm orthopyroxene-rich and -poor layers (Figs. 3.2a, d). Flattening of orthopyroxene grains defines a weakly to moderately developed planar Si tectonite fabric (Figs. 3.2b, e). Where present together, So parallels Si. The orientation of these two fabrics changes from moderately to steeply dipping towards the northwest in the northwestern map area to moderately to steeply dipping towards the west in the southeast map area (Figs. .3.2d, e). This could be the result of kilometer-scale folding, faulting and/or rotation within the ultramafic unit. These two fabrics are interpreted to have formed prior to obduction during sea floor spreading-related processes (Ash, 1994). Commonly a well-developed S2 fabric, oriented 244° / 54° NW (Fig. 3.3a, c), occurs and is defined by flattened and sheared bastite spots in highly serpentinized zones. This fabric likely represents zones of shear which were active during obduction of the ultramafic body (Ash, 1994). These shear zones are cross-cut by later serpentine- and listwanite-filled lineaments (Fig. 3.4). The S2 fabric is most common on the lower west flank of Monarch Mountain.  Visual analysis of an oriented thin section within the  sheared bastite indicates northwest-southeast compression with top to the southeast movement (Fig. 3.5). This observation is constituent with reported mullion structures (Ash and Arksey, 1990), northeast-southwest striking geological units south and east of the map area (Ash, 1994) and with a narrow zone of faults oriented about 231° / 57° NW located about 1 km south of the ultramafic body's south contact.  36  CHAPTER III  Figure 3.2: Structural data (poles to planes on equal area stereonets) of: a) Photograph showing prominent compositional layering on Monarch Mountain, b) Photograph of harzburgite fabric (pen parallels fabric), c) Photomicrograph of freshest harzburgite under cross-polars.  d) Equal area stereonet plot (poles to planes) of compositional  banding within harzburgite. e) Equal area stereonet (poles to planes) of harzburgite fabric defined by the flattening of orthopyroxene crystals.  37  CHAPTER III  Figure 3.3: a) Photograph of foliated serpentinite defined by the flattening of bastite spots, b) Photomicrograph of typical serpentinite under cross-polars. c) Structural data (poles to planes on equal area stereonet) of bastite foliation defined by flattened and sheared bastite spots.  38  CHAPTER III  Figure 3.4: a) Aerial view to the northeast showing recessive weathering lineaments representing L and L orientations associated with listwanite at head of Monarch a  b  Mountain Hiking trail (photo by M . Mihalynuk, August 2003) (E 575900, N 6602100, N A D 83). b) Geologic map of the area in Fig. 3.4a.  39  CHAPTER III  Figure 3.5: Plane polarized light photograph of oriented thin section showing sheared serpentinite and kinematic indicators that suggest apparent top to the right movement (i.e. reverse movement). Horizontal is roughly in line with the direction labels. Sample location is E 575660, N 6602200, N A D 83.  40  CHAPTER III 3.3.2 L A T E S Y N - TO POST-OBDUCTION STRUCTURAL ELEMENTS In addition to the basal decollement, it is clear that a regional fracture/joint system provided high-permeability guides for C02-bearing fluids, and thus the controls on the spatial distribution of listwanite (Fig. 3.1).  As illustrated in Figures 3.1 and 3.6,  listwanite zones, unrelated to the basal decollement, are oriented in four steeply-dipping planar directions spanning 360° and have about a 45° spacing. These four orientations are referred to as L (140° trend), Lb (50° trend), L (N-trending) and L<j (E-trending). a  c  Fracture-controlled, planar zones of listwanite are generally expressed as lineament depressions, which are commonly vegetated and filled with overburden. Rusty-red weathering side walls suggest they are underlain by listwanite. Additionally, the margins of surface lineaments are commonly marked by chalky blue-green weathering serpentine-alteration suggesting that they mark structural weaknesses that acted to focus fluids. This association highlights the focusing of C02-bearing fluid along planar structural weaknesses, and permits extrapolation of listwanite zones into areas of vegetation and overburden.  The L and Lb trends tend to be the most commonly a  identified listwanite zones in the field. Generally, L zones are the most extensive and a  contain the most stockwork quartz-carbonate veins and Cr-muscovite. A consistent cross-cutting relationship between each trend was not identified. Thus, if multiple generations of listwanite exist, they are not reflected by the various orientations. Four sets of joints and fractures in the Atlin Ultramafic Allochthon are orientated parallel with those of the listwanite zones and lineaments (Figs. 3.7a). The spacing of the four steeply-dipping joints and fractures are 45° apart. Intensely serpentinized outcrops commonly have closer spaced fractures than fresher harzburgitic rocks, but the orientations of the fractures and joints in both geologic units are similar.  Likewise,  fractures and joints from the structurally lower metabasalts and Atlin Accretionary Complex lithologies are concordant with those in the Atlin Ultramafic Allochthon (Fig. 3.7b). Furthermore, the joint and fracture network cross-cuts the S2 fabric (Fig. 3.4b). Small serpentine-magnetite veinlets cut the harzburgite, dunite and serpentinite units and are typically less than 1 cm thick, but may be as much as 10 cm thick. The dominant orientations of the veinlets are broadly coincident with the listwanite zone  41  CHAPTER III  Figure 3.6: a) View to northwest of a well-preserved, rusty-brown, talc-magnesite listwanite zone (Lb) which is about 50 cm thick. Scale = 5cm. b) Equal area stereonet (poles to planes) of planar listwanite zones similar to those in Figure 3.6a.  42  CHAPTER III  Harzburgite Rocks  Serpentinite Rocks  Map Area  Map Area  Figure 3.7: a) Equal area stereonet plot (poles to planes) of fractures and joints within the ultramafic rock units (Atlin Ultramafic Allochthon). b) Equal area stereonet plot (poles to planes) of fractures and joints within the underlying Atlin Accretionary Complex lithologies (metabasalt, argillite, chert).  43  CHAPTER III orientations and joint/fracture system (Figs. 3.7 and 3.8). This supports at least one late serpentinization event which may or may not be related to the listwanite alteration. Intense areas of listwanite-alteration commonly contain densely-spaced stock work quartz-carbonate veins (Fig. 3.9).  As with other late syn- to post-obduction  structures, most veins are vertical to sub-vertical and strike in the same orientations as the listwanite zones, lineaments, fracture sets and serpentine-magnetite veinlets. The veins commonly display evidence for open fracture-filling including sugary and vuggy quartz and bladed carbonates (Fig. 3.10). Figure 3.11 illustrates that the orientations of the quartz-carbonate veins mapped both regionally and on an outcrop scale are sub-parallel to the other regional structures.  3.4 IGNEOUS INTRUSIONS Geochemical and petrographic analyses and isotopic ages confirm that at least three distinct phases of dikes are present in the map area depicted in Figure 3.1. The bulk chemical composition of the dike phases are plotted in Figure 3.12. All three phases are locally carbonate-altered where they intrude listwanite, but most are unaltered and appear to cross-cut the listwanite. Additionally, all dike phases are either spatially associated with listwanite-altered areas or surface lineaments parallel to the regional fracture and joint system. Much, if not all of the carbonate alteration within dikes could have resulted from the intrusion of dikes into the carbonate-rich material (i.e. listwanite).  The  association of dikes with listwanite and lineaments suggests that the fracture/joint system responsible for controlling the post-obduction listwanite and serpentinization also provided structural guides for magma ascent. The most abundant, widespread and generally least carbonate-altered phase is melanocratic, medium- to coarse-grained diabase dikes that contain plagioclase, clinopyroxene, orthopyroxene, hornblende and sulfide. The alteration mineralogy of this unit includes chlorite, actinolite and carbonate.  Xenoliths of intensely-carbonated  listwanite occur within the relatively unaltered diabase which has intruded intensely carbonate-altered rock.  Where diabase cuts zones of intense listwanite alteration it  remains relatively unaltered. These observations suggest that the diabase dikes postdate carbonate alteration. 44  CHAPTER III  Figure 3.8: a) Photograph of serpentine-magnetite veins in harzburgite. b) Photograph of serpentine-magnetite veins in serpentinite. c) Equal area stereonet (poles to planes) of serpentine-magnetite veins.  45  C H A P T E R III  Figure 3.9: a) Photograph o f stockwork quartz-carbonate veins w i t h i n zones o f intense listwanite alteration.  Pen tip is pointed approximately to the north,  b) Equal area  stereonet (poles to planes) o f quartz-carbonate veins within listwanite unit. Approximate orientations o f listwanite zones are given by symbols L - Ld. a  46  C H A P T E R III  4^  Strikeand dip direction of quartz carbonate veins  \  Strikeand dip direction of quartz fractures  Weakly carbonated serperttinUe  Quartz and/or carbonate veins Covered areas  N = 70 , P o l e st o p l a n e so f Q u a r t za n d / o rc a r b o n a t e veins  Poles to planes of fractures  Figure 3.11: a) 10 m by 10 m geologic map of a talc-magnesite to quartz-magnesite listwanite zone. Structural measurements of quartz-carbonate veins have been plotted on the map. b) Equal area stereonet (poles to planes) of quartz-carbonate veins obtained from the area depicted in Figure 3.1 la. The general orientations of the listwanite zones are given by the symbols L - L_. a  o  -x > -a  CHAPTER III  )l  35  I I  l l I i i i I 1I 40  45  I  ii I 50  I I I I  I  I  l l lIl  55  60  Wt% Si0 (Dry)  I  ll I l l 65  I I  I l l l l Il 70  75  2  Figure 3.12: Total alkali vs. S i 0 (TAS) plot (LeBas et al., 1986) of dike samples 2  collected within the map area depicted in Figure 3.1. The two exceptions are AT04-7B and AT04-8B, which were collected from dikes within the Fourth of July Batholith on the road cut near Como Lake. A l l analyses have been renormalized to 100 wt% excluding volatile chemical species.  49  CHAPTER III A light grey, felsic porphyritic dacite is the next most abundant intrusive phase and was always found associated with listwanite. Phenocrysts include plagioclase, Kfeldspar and quartz (as "quartz-eyes"). This unit is commonly highly carbonated and sericitized creating a ground-mass of carbonate, quartz and an interlocking mesh of sericite. Pyrite and chalcopyrite are common and locally account for a few modal percent of the rock. The timing of emplacement of this unit with respect to the carbonate alteration is uncertain, but the dacite dikes appear to cut through listwanite and no listwanite-associated quartz-carbonate veins were found which crosscut it. More precise evidence for the timing derives from the geochronologic evidence (discussed below) that indicates that these dikes are younger than the age range determined for the carbonate alteration. The third and least abundant igneous phase is a grey-brown medium- to coarsegrained porphyritic dacite dike that contains, in order of decreasing abundance, plagioclase, K-feldspar, biotite, quartz and hornblende phenocrysts. This unit appears to be restricted to the north-central part of the study area just off Highway 7 (Fig. 3.1). A l l phenocrysts are subhedral to euhedral and display clear evidence for resorption. This unit, as with the diabase, is relatively unaltered in areas of intense listwanite alteration, suggesting it postdates carbonation.  These relationships are also corroborated by  geochronologic evidence (discussed below) indicating that the unit is younger than the most intense carbonate alteration. 3.5 TIMING A N D SETTING OF LISTWANITE ALTERATION Two Cr-muscovite samples extracted from listwanite and one fresh euhedral biotite book taken from the grey-brown dacite dike yielded reliable A r - A r dates. In 40  39  addition, a U-Pb zircon date was determined from the light-grey dacite phase. Unfortunately, datable separates of the melanocratic diabase dikes could not be attained. Table 3.1 summarizes age data obtained for this, and all other studies obtained within and immediately adjacent to the map area. history of the area.  40  Figure 3.13 outlines the simplified geologic  A r - A r and U-Pb data are presented in Appendix F. A l l 39  geochronologic analyses were performed at the Pacific Centre for Isotopic and  50  Table 3.1 :Geochronologic Analyses from Atlin Area Sample/Location  Mineral  Rock Type  Source  4 0  Ar-  3 9  Ar  K-Ar  U-Pb  Interpretation  /  /  Carbonate-Alteration  /  /  Carbonate-Alteration  01AT-1-2  Cr- Muscovite  Listwanite  This Study  128.0+/-.1.9  02AT-8-1 (Goldstar)  Cr- Muscovite  Listwanite  This Study  172.7+/-2.0  AT03-44-7 (Anna)  Cr- Muscovite  Listwanite  This Study  174.4+/-1.4  /  /  Carbonate-Alteration  165 +/-.4  121 +/-4*  /  Carbonate-Alteration  +  Pictou  Cr- Muscovite  Listwanite  Ash (2001)  Yellowjacket  Cr- Muscovite  Listwanite  Ash (2001)  171 +/-3  /  /  Carbonate-Alteration  Surprise  Cr- Muscovite  Listwanite  Ash (2001)  168+/-3  171 +/- 6  /  Carbonate-Alteration  Goldstar  Cr- Muscovite  Listwanite  Ash (2001)  167+/- 3 '  156 +/- 5*  /  Carbonate-Alteration  Anna  Cr- Muscovite  Listwanite  Ash (2001)  169 +/- 6*  /  Carbonate-Alteration  84.0+/-0.6"  /  Cooling 280 °C  /  /  / 150.7+/-0.6  Crystallization age  /  170.4 +/-5  Crystallization age  AT03-28  Biotite  Dacite  This Study  AT03-5  Zircon  Dacite  This Study  FOJB  Zircon  Granitiod  /  /  Mihalynuket al. (1992)  171.5+/-3.3 Crystallization age / / Granitiod Mihalynuk et al. (1992) Zircon FOJB Cooling 500 °C / 172.7 +/-1.7 / Granitiod Harris et al. (2003) Hornblende FOJB Cooling 280 °C / / Harris et al. (2003) 165.1 +/-1.6 Granitiod Biotite FOJB Cooling 280 °C / 161.8 +/-1.6 Harris et al. (2003) Lamprophyre / Biotite FOJB / Cooling 280 °C 165.3+/-1.6 Lamprophyre Harris et al. (2003) / Biotite FOJB Crystallization age 83.8+/-5 / Granitiod Mihalynuket al. (1992) / Zircon SLB Crystallization age 172 +/-0.3 / Anderson et al. (2003) / Zircon Granitiod MMB Crystallization age 171 +/-0.3 / / Granitiod Anderson et al. (2003) Zircon LMB Cooling 280 °C / 167 +/3 / Hunt& Roddick (1988) Granitiod Biotite M/U Stock * Considered whole rock ages. All others are ages determined from separates. denotes integrated age (all other Ar-Ar ages are plateau ages) FOJB = Fourth of July Batholith, SLB = Surprise Lake Batholith, M/U Stock = unnamed stock between Monarch & Union mountains, MMB = Mount McMaster Batholith, LMB = Llangorse Mountain Batholith. Suspect ages are shaded grey. +  CHAPTER III  ALTERATION  DIKING  PLUTONISM  b^.+.+.-H  , &Vzr^ l  bi  LT)  Surprise Lake Batholith  o LU  u <  I— LU CC  U  Bowser Basin  zr mu  bi  e  y  1/1 <  —zrr x p l x  ;zrc  mp* m p  K-..V-..V:—V  v  vr  F o u r t h of July B a t h o l i t h  CE 3  V  V]  <  Kutcho ^ Formation 1  CC LU CL  CQ  or <  Northern Cache Creek  u  Figure 3.13: Simplified flow chart illustrating the geological history of the Atlin area. The symbols bi, mu, and mp represent A r / A r dates acquired from biotite, muscovite, 40  39  and Cr-muscovite (mariposite) respectively while zr denotes U-Pb zircon dates. * denotes analyses acquired from this study. Chart modified from Ash (2001).  52  CHAPTER III Geochemical Research (PCIGR) at the University of British Columbia. A l l supporting data is located in Appendix D. The reliable A r / A r Cr-muscovite dates of this study and Ash (2001) (Table 40  39  3.1, Fig. 3.13) suggest a primary listwanite alteration event at about 170 Ma, but possibly spanned a few million years (174 - 167 Ma). These ages are in excellent agreement with the U-Pb zircon age of 172 +/- 3 Ma for the FOJB (Mihalynuk et al, 1992), and 167 +/- 3 Ma for a K-Ar biotite (cooling 280°C) from a small stock between Monarch and Union mountains. The overlapping age range of the plutonism and joint- and fracture-controlled listwanite suggests that unloading (erosion) had commenced prior to that time and that the plutonism was the local energy source responsible for mobilizing listwanite-forming hydrothermal fluids. Aalenian (ca. 178 - 174 Ma, Okulitch, 2001, and references therein) sediments of Cache Creek affinity recorded within the Bowser Basin to the southeast are interpreted to record the initial erosion as thrusts of the Cache Creek terrane were loaded onto Stikinia (Ricketts et al, 1992). Two samples of Cr-muscovite have A r - A r plateau ages different from the 40  39  others. Sample AT03-44-7 produced a plateau age of 188 +/- 1.8 Ma which is older than the expected age of obduction at ca. 170 Ma. There are numerous reasons for the anomalously high plateau age. One possibility is recoil where K atoms are converted to 3 9  39  A r atoms of sufficient energy to eject the atoms from the mineral phase that is being  irradiated (Esser et al, 2004). Another is excess Ar (T.D. Ulrich, 2005 pers. comm.). However an integrated age of 174.4 +/- 1.4 Ma is in agreement with other Cr-muscovite ages and is likely the true age of this sample. Sample 01AT1-2 produced a plateau age of 128 Ma which, though younger than expected, could represent a thermally reset age (T.D. Ulrich, 2005 pers. comm.). The timing of listwanite alteration is constrained to have occurred synchronously or immediately after the collision of Stikinia with the northern Cache Creek terrane as determined by structural relationships and geochronologic analysis. As discussed earlier, the listwanite alteration is structurally controlled by four steeply-dipping sets of postobduction joints and fractures with approximately 45° spacing. This pattern is consistent with a vertical maximum principle stress (CM). The joints and fractures are present within the ultramafic rocks, the underlying accretionary lithologies and also cross-cut the syn53  CHAPTER III obduction S2 fabric.  Thus, the development of the fracture/joint system, and later  listwanite alteration, is likely associated with unloading of the Atlin Ultramafic Allochthon after and/or in the very late stages of the collision of Cache Creek with Stikinia. Localized carbonate-flooded and altered breccia in the vicinity of the basal decollement and along a two km-long ridge on the southwest portion of Monarch Mountain suggests that carbonation postdates the main phase of tectonism. Zircons extracted from the light-grey dacite phase yielded a date of 150.7 +/- 0.4 Ma (U-Pb, zircon) which is interpreted the age of crystalization. This age is unusual as there is very little known igneous activity in the area at this time (Mihalynuk, 1999). However, this places an upper limit on listwanite alteration at 150 Ma, and confirms that this phase is not associated with the FOJB. The fresh euhedral biotite book extracted from the grey-brown dacite yielded an A r - A r plateau age of 84.0 +/- 0.6 Ma which is 40  39  contemporaneous with and likely related to the Surprise Lake Batholith (83.8 +/- 5 Ma, U-Pb zircon date, Table 3.1) which outcrops about 18 km east of Atlin. Unfortunately, an age could not be determined for the diabase phase. The cross-cutting relationships, geochronologic and structural analyses clearly demonstrate the setting of listwanite alteration. Figure 3.14 shows schematically that the carbonate-alteration is controlled by a post-obduction fracture-joint system and that the igneous intrusions post-date both. A similar association of carbonate alteration with a basal thrust and along steeply dipping joints and fractures is documented within the Voltri ophiolite at Liguria, Italy (Buisson and Leblanc, 1986).  3.6 ALTERATION ENVIRONMENT The temperature of alteration is constrained by fluid inclusion analysis of quartzcarbonate veins to be in the range of 210°C to 280°C. Vapour to liquid homogenization temperatures (ThL-v(L)) of 210°C to 240°C were measured from low salinity (<5wt% equivalent NaCl) fluid inclusions that show no evidence for phase separation (Andrew 1985). This is consistent with other listwanite systems including the Bridge River area of B.C. at 240°C (Madu et al, 1990); the Timmins area of Ontario at ca. 250°C (Schandl and Wicks, 1991); and a listwanite occurrence in Morocco at 150°C to 300°C (Buisson and Lablanc, 1985). Pressure estimates for the Atlin listwanite alteration are poorly 54  CHAPTER III  Harzburgite  Serpentinite  Figure 3.14: Schematic block diagram illustrating that post-obduction fractures and joints controlled the distribution of later listwanite alteration and dike emplacement. Dikes post-date the listwanite-alteration.  55  CHAPTER III constrained. Al-in-hornblende geobarometry by Harris et al. (2003) suggests a depth of about 6 - 8 km (ca. 1.5 - 2.2 kbar lithostatic) for the southern section of the FOJB which outcrops less than 2 km north of the Atlin Ultramafic Allochthon.  Given that the  batholith and listwanite alteration are contemporaneous, listwanite was likely formed at the same depth or slightly shallower than this part of the FOJB.  The joint/fracture  controls, open space-filling nature and bladed carbonate within quartz and/or carbonate veins (Fig. 3.10) are consistent with a relatively shallow and sub-lithostatic to hydrostatic (ca. 600 - 800 bars at 6 - 8 km depth assuming a hydrostatic gradient of 100 bars/km depth) hydrothermal environment.  3.7 STABLE ISOTOPES The stable isotope compositions of O and C in carbonate minerals from weakly to completely carbonate-altered samples were measured at the PCIGR in an attempt to decipher the origin of the carbon and altering fluid.  Three different episodes of  magnesite generation (M] to M 3 ) were produced during the three listwanite reactions (Ri to R 3 ) .  In addition, stable isotopic data was acquired from one sample of hard black 13  organic material (5 C = -27.16%o) taken from the listwanite occurrence proximal to the northwest trending Nahlin fault located approximately 60 km to the south-southeast of Atlin. Figure 3.15 illustrates the results from Atlin and Table 3.2 shows a generalized comparison with other listwanite systems. In general, results from this study and from other listwanite systems are broadly similar and likely indicate a similar hydrothermal environment and origin for C02-bearing fluids. The results are discussed below. The boxes in Figure 3.15 enclose the stable isotopic results from the approximately 10 cm-thick transect A-B through the listwanite zone (depicted in Figure 3.16) and show the outcrop-scale change in isotopic composition during carbonate alteration. Regionally, magnesite-, talc- and quartz-zone carbonate all span a range of 5 C from -1 to -7%o VPDB and 5 0 from 6 to 16%o VSMOW. Within outcrop AT0313  I8  20, however, there is a clear difference in the stable isotope composition of the talc- and magnesite-zones.  The talc-zone is depleted in  13  C and enriched in  1 8  0 relative to  magnesite-zone samples. About 20% carbonate in the talc-zone has formed prior to the first appearance of talc (Mi magnesite, estimated from data in Appendix C). Thus, the 56  C H A P T E R III  Talc-Zone (AT03-20) Magnesite-Zone (AT03-20)  A  A  AA A  •A  ' A A A K  x  i X  x •  X  • Dikes • Magnesite-Zone A Magnesite-Zone (AT03-20) x Carbonate-Veins (AT03-20) x Quartz-Zone + Talc-Zone • Talc-Zone (AT03-20) -7  -4  -3  -2  -1  o C (VPDB) 13  Figure 3.15: Stable isotope compositions from carbonate within the listwanite in the Atlin area. The closed boxes enclose samples taken from within and near the 2 by 2 metre area shown in Figure 3.16.  57  Table 3.2: Stable isotopic compositions from various listwanite systems Notes  Reference  5.7 (3.8 to 7.7)  Silicate (Ai)  This Study  -3.5 (-2.3 to -6.4)  12.9 (6.3 to 15.4)  Mgs & Dol (Ri-A )  This Study  9  -4.8 (-0.3 to -6.2)  12.1 (10.2 to 17.3)  Carbonate (R2-A3)  This Study  14  -4.4 (-2.2 to -6.1)  10.5 (8.3 to 14.0)  Carbonate (R3-A4)  This Study This Study  Location  n  6 C (VPDB) %0  Atlin  5  -  Atlin  28  Atlin Atlin  1 3  6 0 18  (VSMOW)%0  5D(VSMOW)%O  2  Atlin  14  -4.6 (-1.3 to -5.6)  13.9 (12.9 to 15.1)  Carbonate (R2-A )  Atlin  3  -5.3 (-3.8 to -6.0)  14.8(14.0 to 15.7)  Mgs-Dol Vein from R2  This Study This Study  x  3  Atlin  1  -3.3  8.3  Carbonated Diabase  Atlin  1  -3.8  8.2  Carbonated Dacite  This Study  Nahlin Fault  1  -27.2  -  Pyrobitumen  This Study  Morocco  N/A  ca: -4  ca. 18  Mgs in Listwanite  Buison and Leblanc (1985)  Bridge River, B . C .  N/A  (-8.6 to -10.7)  13.2 +/-1.5*  -136 to -142  Fluid Inclusions  Madu et al. (1990) Madu et al. (1990) S c h a n d l a n d Wicks (1991)  Bridge River, B.C.  N/A  (-5.1 to-6.7)  (24 to 25)  Carbonate in Listwanite  Timmins, Ont.  N/A  (-7.5 to -7.9)  (11.7 to 16.5)  Mgs in Mgs-TIc rock  'Calculated from quartz-h^O equilibrium and fractionation factor of 3.7 denotes samples containing black organic material Compositions are given as an average and/or range given within parenthesis  x  O > H  m  70  Figure 3.16: a) Composite image of a 2 by 2 metre pavement outcropping on the western slope of Monarch Mountain (E 575887, N 6602098, N A D 83). Dashed yellow lines are contacts in Figure 3.16b. b) Detailed geologic map of the listwanite zone mapped at 1:20 scale.  CHAPTER III actual composition of M2 cou Id plot at about 5 C = -6%o and 5 0 = 15.5%o. The talcI3  ,8  zone samples also contain inclusions of black organic carbon.  3.8 HYDROTHERMAL ORGANIC MATERIAL Carbon isotope data and the presence of hydrothermally mobilized organic material within listwanite (Fig. 3.17) implicate hydrothermal circulation through metasedimentary material. The 8 C of around -6%o for carbonate approaches an organic 13  signature. Furthermore, the 5 C of -27%o for organic material sampled from the Nahlin 13  fault (Fig. 3.17a) is the expected value of petroleum derived from vegetation (Campbell and Larson, 1998, and references therein) and is similar to that acquired from hydrothermal petroleum by Rasmussen and Buick (2000) and Simoneit (2002). Similarlooking material was found within listwanite at Atlin (Figure 3.17b) and in carbon-rich veins material at the Erickson mine near Cassiar, B.C. (Sketchley and Sinclair, 1987). All three B.C. localities are associated with ultramafic material sutured to the edge of the northern Cache Creek Terrane. Fluid inclusion analyses reported by Madu et al. (1990); Buisson and Leblanc (1987) and Schandl and Wicks (1991) indicate CH4 within the altering fluid of their respective field studies. The only obvious nearby source for organic material is the Atlin Accretionary Complex (AAC).  3.9 SOURCE FOR GOLD AND CARBON Potential sources for gold include: the ultramafic rocks, underlying accretionary complex lithologies, and the Middle Jurassic igneous batholiths (particularly the nearby FOJB). In addition to the stable isotopic study, 40 samples were submitted for gold assaying with the results shown in Figure 3.18. Gold assay results were acquired by fire assay and IPCES at A L S Chemex laboratories in North Vancouver, British Columbia. Ten samples from each reaction zone (i.e. protolith samples, magnesite-, talc- and quartzzone samples) were analyzed. In order to assess the potential nugget effect of gold in these samples, replicates and a standard were submitted. Unfortunately, the masses of rock powder from magnesite- and talc-zone samples were inadequate to submit replicate samples. For these two zones, five samples from each group were taken from a 70 by 10 cm area within the grid-mapped outcrop depicted in Figure 3.16. 60  CHAPTER III  Figure 3.17: Reflected light photomicrographs of: a) organic material within veins in quartz-zone listwanite sampled from the Nahlin fault to the southeast of Atlin. b) organic material occupying a vein within talc-zone of the listwanite zone depicted in Figure 3.16. Note that the bright specs are sulfide and they are associated with the dark organic material.  61  • Contain black organic matter  a)  * Contain black organic matter  b)  • Lack black organic matter  3" 20  a. a  -QuartzZone -  4 replicates  Talc Zone -  Detection Limit I CO  20  C0 (wt%)  25  2  Figure 3.18: Gold content of samples verses a) whole rock C O 2 .  b) 8 C in carbonate minerals 13  • Lack black organic matter  CHAPTER III Buisson and Leblanc (1987) suggest that gold, concentrated within oxides (i.e. magnetite), is released and mobilized during the talc-generating reaction that destroys magnetite. The amount released from the ultramafic rocks during this step was suggested to be about 2.7 ppb. If 2.7 ppb was released during talc-zone alteration, the amount of gold released from the Atlin Ultramafic Allochthon would amount to about 141,000 oz gold. This number is based on a 25 km ultramafic body with a 50 m-thick listwanite zone at its base, 50% of which is talc-zone. Although this number is significant, no leaching of Au in the talc-zone was detected at Atlin (Fig. 3.18). In fact the assay results indicate that talc-zone samples are either similar to, or elevated in, Au relative to that of serpentinite. Thus, leaching of Au has likely not occurred within the talc-zone at Atlin. Ash et al. (1992) consider an alternate model that involves the leaching of gold from a tectonically thickened package of oceanic crustal rocks which have undergone partial melting at deeper levels of the crust that in turn drove large-scale hydrothermal convection. There are many lines of evidence that suggest gold was either derived from fluid exsolved from Middle Jurassic batholiths and/or leached from accretionary wedge lithologies during hydrothermal circulation driven by the large-scale igneous activity. Firstly, the U-Pb zircon age range of the FOJB completely overlaps the age range of Crmuscovite in the listwanite (Table 3.1). Streams that drain the FOJB contain stream sediments with anomalous Au contents (Jackaman, 2000). Ash et al, (1992) noted that most listwanite-associated lode-gold camps in B.C. are associated with syn- to postaccretionary felsic magmatism. The large range in 8 0 suggests that there was interaction of listwanite-altering 18  hydrothermal fluids with the heterolithic sedimentary and carbonate material of the AAC. Listwanite samples elevated in gold contain organic material and are depleted in 5 C I3  (Fig. 3.18). These observations suggest the gold was exsolved from the FOJB and/or scavenged from the ACC, possibly as bisulfide complexes, considered the most important group of ligands in transporting gold in hydrothermal fluids (Mikucki, 1998, and references therein). The correlation of organic material and gold suggests a possible role for organic material in the transportation and/or deposition of gold and sulfide.  63  CHAPTER III 3.10 CONCLUSION The listwanite alteration within the Atlin Ultramafic Allochthon at Atlin, B.C., is spatially controlled by a basal thrust fault (e.g. Ash, 1994; Hansen et al, 2004; Chapter II) and regional joint/fracture system with four steeply-dipping fracture sets spaced about 45°  apart (Hansen et al. 2004, Chapters II and III). The U-Pb (zircon) and A r - A r (Cr40  39  muscovite) isotopic ages of the nearby FOJB and the listwanite alteration respectively (Ash, 2001; Mihalynuk et al, 1992; This Study) indicate that the two events were contemporaneous and likely related and occurred at about 170 Ma. The most depleted 5 C within magnesite is around -6%o which is consistent with an organic signature and is 13  supported by the presence of organic material within listwanite-altered rocks. The large range in 8 0 of between 6.3%o and 17.3%o suggests interaction of the altering fluids with 18  the pelagic sedimentary rocks of the Atlin Accretionary Complex (AAC).  The only  obvious nearby source of organic material is the pelagic units of the A A C . These results suggest large-scale hydrothermal circulation of fluids, driven by the FOJB, through the metasedimentary, metavolcanic and carbonate rocks of the A A C . These fluids acted to mobilized and incorporated organic material which then infiltrated and carbonate altered the ultramafic rock material of the Atlin Ultramafic Allochthon. Anomalous gold values are associated with organic material and low 8 C values. 13  The gold content of the three listwanite zones are at or above that for the parental serpentinite.  These observations and analyses are consistent with gold having been  scavenged from the underlying accretionary complex lithologies or derived from the contemporaneous and nearby FOJB rather than being scavenged from the ultramafic rocks.  64  CHAPTER III 3.11 REFERENCES Andrew, K . (1985): Fluid Inclusion and Chemical Studies of Gold-Quartz Veins in the Atlin Camp, Northwestern British Columbia; Unpublished B.Sc. thesis, Department of Geological Sciences, Vancouver, B.C., Canada, 116 p. Anderson, R. G., Lowe, C. and Villeneuve, M . E. (2003): Nature, Age, Setting, and Mineral Potential of Some Mesozoic Plutons in Central and Northwestern Atlin Map Area (NTS 104N), Northwestern B.C.; (abstract); Vancouver 2003 Abstracts, CD-ROM, GAC-MAC-SEG Vancouver 2003 Annual General Meeting, Vancouver, B.C., v. 28, abstract no. 600, ISSN 0701-8738, ISBN: 0-919216-86-2. Ash, C. H . (1994): Origin and Tectonic Setting of Ophiolitic Ultramafic and Related Rocks in the Atlin Area, British Columbia (NTS 104N); B.C. Ministry of Energy, Mines and Petroleum Resources, Bulletin 94, 48 p. Ash, C. H. (2001): Relationship Between Ophiolites and Gold-Quartz Veins in the North American Cordillera; British Columbia Department of Energy, Mines and Petroleum Resources, Bulletin 108, 140 p. Ash, C. H . and Arksey, R. L . (1990): The Atlin Ultramafic Allochthon: Ophiolite Basement Within the Cache Creek Terrane; Tectonic and Metallogenic Significance (104N/12); Geological Fieldwork 1989, B.C. Department of Energy and Mines, Paper 1990-1, p. 365-374. Ash, C. H., Macdonald, R. W. J. and Arksey, R. L . (1991): Towards a Deposit Model for Ophiolite Related Mesothermal Gold in British Columbia; Geological Fieldwork 1991, BC Department of Energy and Mines, Paper 1992-1, p. 253-260.  65  CHAPTER III Buisson, G. and' LeBlanc, M . (1986): Gold-Bearing Listwaenites (Carbonitized Ultramafic Rocks) from Ophiolite Complexes; in Metallogeny of Basic and Ultrabasic Rocks, Gallagher, M . , Ixer, R., Neary, C. and Prichard, H., Editors, The Institution of Mining and Metallurgy, pages 121-131. Campbell, A.R. and Larsen, P. (1998): Introduction to Stable Isotope Applications in Hydrothermal Systems. In: Techniques in Hydrothermal Ore Deposit Geology. Editors: J. Richardson and P. Larsen. Reviews in Economic Geology, 10, 173-193. Buisson, G. and LeBlanc, M . (1987): Gold in Mantle Peridotites from Upper Proterozoic Ophiolites in Arabia, Mali, and Morocco; Economic Geology, v. 82, p. 2091-2097. Buisson, G. and Leblanc, M . (1985): Gold in Carbonatized Ultramafic Rocks from Ophiolite Complexes; Economic Geology, 80, 2028-2029. Esser, R. P., Mcintosh, W. C. and Mack, G. H. (2003): A r / A r Geochronology Results 40  39  from Clasts from Late from Late Cretaceous/Early Tertiary Units of the Caballo Mountains, New Mexico; New Mexico Bureau of Geology and Mineral Resources, Memoir 49, 22 pages. Hansen, L.D., Dipple, G. M . , Kellett, D. A . And Gordon, T. M . (2005): CarbonateAltered Serpentinite: A Geologic Analogue to Carbon Dioxide Sequestration, Canadian Mineralogist, v. 43, part 1, p. 225-239. Hansen, L . D., Dipple, G. M . , Anderson, R. G. and Nakano, K. F. (2004): Geologic Setting of Carbonate Metasomatised Serpentinite (Listwanite) at Atlin, British Columbia: implications for CO2 sequestration and lode-gold mineralization. In Current Research, Geological Survey of Canada, Paper 2004-A5, 12 pages.  66  CHAPTER III Harris, M . J., Symons, D. T., Blackburn, W. H., Hart, C. J., Villenueve, M . (2003): Travels of the Cache Creek Terrane: a Paleomagnetic, Geobarometric and  40  Ar/ Ar 39  Study of the Jurassic Fourth of July Batholith, Canadian Cordillera; Tectonophysics, 362, 137-159. Hunt, P.A. and Roddick, J.C. (1988): A Compilation of K-Ar Ages, Report 18; In Radiogenic Age and Isotopic Studies, Report 2, Geological Survey of Canada, Paper 882, 127-153. Jackaman, W. (2000): British Columbia Regional Geochemical Survey, NTS 104N/1 Atlin; British Columbia Ministry of Energy and Mines, BC RGS 51. Madu, B. E., Nesbitt, B. E. and Muehlenbachs, K. (1990): A Mesothermal Gold-StibniteQuartz Vein Occurrence in the Canadian Cordillera. Economic Geology, 85, 1260-1268. Matsuhisa, Y., Goldsmith, J. R. and Clayton, R. N . (1979): Oxygen Isotope Fractionation in the System Quartz-Albite-Anorthite-Water, Geochimica et Cosmochimica Acta, 43, 1131-1140.  Mihalynuk, M.G. (1999): Geology and Mineral Resources of the Tagish Lake Area (NTS 104M/8, 9, 10E, 15 and 140N/12W), Northwestern British Columbia; British Columbia Department of Energy, Mines and Petroleum Resources, Bulletin 105, 217 p.  Mihalynuk, M . G., Smith, M . , Gabites, J. E., Runkle, D. and Lefebure, D. (1992): Age of Emplacement and Basement Character of the Cache Creek Terrane as Constrained by New Isotopic and Geochemical Data; Canadian Journal of Earth Sciences, 29, p. 24632477.  Mikucki, E. J.(1998): Hydrothermal Transport and Deposition Processes in Archean Lode-Gold Systems: a Review; Ore Geology Reviews, 13, 307-321. 67  CHAPTER III Okulitch, A . V . (2001): Geological Time Scale, 2001. Geological Survey of Canada, Open File 3040 (National Earth Science Series, Geological Atlas) - REVISION  Rasmussen, B. and Buick, R. (2000): Oily Old Ores: Evidence for Hydrothermal Petroleum Generation in an Archean Volcanogenic Massive Sulfide Deposit; Geology, 28,731-734. Ricketts, D.B., Evenchick, C.A., Anderson, R.G. and Murphy, D.C. (1992): Bowser Basin, Northern British Columbia: Constraints on the Timing of Initial Subsidence and Stikinia - North America Terrane Interactions; Geology, 20, 1119-1122. Rytuba, J. J. (1993): Epithermal Precious-Metal and Mercury Deposits in the Sonoma and Clear Lake Volcanic Fields, California, In Rytuba, J. J., ed., Active geothermal systems and gold-mercury deposits in the Sonoma-Clear Lake volcanic fields: Soc. Econ. Geol. Guidebook Series, 16, 38-51. Schandl, E. S. and Wicks, F. J. (1991): Two Stages of CO2 Metasomatism at the Munro mine, Munro Township, Ontario: Evidence from Fluid-Inclusion, Stable-Isotope, and Mineralogical Studies. Canadian Journal of Earth Sciences, 28, 721-728.  Schandl, E. S. and Naldrett, A . J. (1992): CO2 Metasomatism of Serpentinites, South.of Timmins, Ontario; Canadian Mineralogist, v. 30, p. 93-108.  Simoneit, B. (2002): Carbon Isotope Systematics of Individual Hydrocarbons in Hydrothermal Petroleum from Middle Valley, Northeastern Pacific Ocean; Applied Geochemistry, 17, 1429-1433. Sketchley, D. A . and Sinclair, A, J. (1987): Multi-Element Lithogeochemistry of Alteration Associated with Gold-Quartz Veins of the Erickson Mine, Cassiar District (104P/4); Geological Fieldwork 1991, BC Department of Energy and Mines, Paper 19871, p. 57-63. 68  CHAPTER III Wittkopp, R. W. (1983): Hypothesis for the Localization of Gold in Quartz Veins, Allegheny District; California Geology, p. 123-127.  69  CHAPTER IV CHAPTER IV: CARBONATED SERPENTINITE  (LISTWANITE)  AT ATLIN,  BRITISH COLUMBIA: A GEOLOGICAL A N A L O G U E TO C A R B O N DIOXIDE SEQUESTRATION.  1  4.1 INTRODUCTION The presence of low-temperature carbonated ultramafic rocks in nature suggests that conditions favourable for mineral carbonation exist at shallow levels of the crust. In mineral  carbonation,  CO2  structure by reaction with M g  is chemically bound 2 +  or C a  2+  within  a carbonate mineral  derived from silicate minerals. Fossil analogues  to mineral carbonation systems are common in ultramafic terranes throughout the world and produce a suite of metamorphic rocks composed of serpentine, magnesite, talc and quartz-bearing mineral assemblages. These rocks are known as listwanite (Kashkai and Allakhverdiev, 1965) or silica-carbonate alteration (Sherlock et al., 1993). Listwanite has historically been studied because it is common spatial association with lode-gold mineralization (e.g. Ash, 2001; Schandl and Naldrett, 1992; Wittkopp, 1983). Liswanite metamorphism has generally been considered a highly metasomatic process that leads to wholesale changes in bulk rock composition (Schandl and Naldrett, 1992, Sherlock et al, 1993). Here we document  the  mineral reactions,  geochemical alteration,  and  permeability system accompanying listwanite formation near Atlin, British Columbia. Listwanite distribution is controlled structurally by a pre-existing joint and fracture network, which served as high-permeability pathways for percolation of C02-bearing fluid. Evidence for carbonation, indicated by Mg-carbonate minerals, is present for tens of metres into wallrock adjacent to controlling fractures. The permeability structure of these systems is therefore similar to that of proposed industrial-scale in situ mineral carbonation systems, which would utilize joints and fractures as a permeability network. Pervasive listwanite formation adjacent to the fracture systems was isochemical in all A version of this chapter has been published as: Hansen, L.D., Dipple, G.M., Gordon, T.M. and Kellett, D.A. (2005): Carbonated Serpentinite (listwanite) at Atlin, British Columbia: A Geological Analogue to Carbon Dioxide Sequestration, Canadian Mineralogist, Vol. 43, pp. 225-239. 1  70  CHAPTER IV major  chemical species  except H 0 and C 0 , and the overall mineralogical 2  2  transformation is the same as R A and B (see reactions below). These deposits therefore serve as a geological analogue to mineral carbonation. The carbonation process is recorded as mineralogical zonation separated by reaction fronts, which permits each reaction to be examined in isolation. Reactions can therefore be examined individually for their C 0 sequestration potential and impact on porosity and permeability. 2  Mg3Si 0 (OH)4 + 3 C 0 -> 3 M g C 0 + 2 S i 0 + 2 H 0 2  5  2  3  2  2  (R ) A  (Serpentine -> Magnesite + Quartz)  Mg2Si04 + 2 C 0 - » 2 M g C O _ + S i 0 2 2  (RB)  (Olivine -> Magnesite + Quartz)  4.2 R E L E V A N C E TO INDUSTRIAL APPLICATIONS The carbonation of serpentine and forsterite (Mg-olivine), to stable Mg-carbonate minerals is of environmental interest because of its ability to fix anthropogenic carbon dioxide (CO2) (Seifritz, 1990). Globally, mineral carbonation offers virtually unlimited capacity and the promise of safe, permanent storage of CO2, with little risk of accidental release (Guthrie et ah, 2001). Proposed industrial implementation of mineral carbonation includes the capture of C 0 from a point source such as a coal-fired power plant, and 2  transport by pipeline to a reaction facility for storage. Reaction could occur within an industrial chemical reactor by carbonation of ultramafic rock mined from a quarry. However, this process demands highly efficient and rapid mineral transformation (O'Connor et al., 2001).  Alternatively, direct injection of CO2 into large subsurface  ultramafic formations allows for reaction times of tens to hundreds of years (Guthrie et ah, 2001), in a process known as in situ mineral carbonation. Numerous magnesium silicate carbonation schemes have been tested in the laboratory (Goff and Lackner, 1998; Goldberg et al, 2001; O'Connor et al, 2001; Wu et 71  CHAPTER IV al. 2001; Zevenhoven and Kohlmann, 2001), and all involve chemical reactions such as R A and R B . T O date, the rate of reaction in the laboratory has been reported to be up to about 80% conversion of serpentine to silica and magnesite in 30 minutes at 155°C and 185 bar (O'Connor et al., 2001). However this is still too sluggish and the process too costly to accommodate industrial CO2 output within industrial reactors. In situ mineral carbonation could proceed at a more leisurely pace; however there are no reliable mineral carbonation experiments in CO2 injection systems (Matter et al., 2002). Reaction path modelling predicts that C 0 injection into serpentine reservoirs (at 250 bars and 60°C) 2  would result in substantial CO2 sequestration in a few 10's of years (Cipolli et al., 2004). Moreover, the large increase in the volume of solids (21% for serpentine and 80% for olivine) associated with  RAandB  may reduce the sequestration capacity of the reservoir by  destroying permeability at the injection site.  4.3 GEOLOGICAL SETTING The ultramafic rocks at Atlin represent a tectonically emplaced upper mantle section of oceanic lithosphere (Ash and Arksey, 1990a) composed predominantly of harzburgite and minor dunite, now mostly transformed to serpentinite and listwanite. Aitken (1959), Ash and Arksey (1990a), Hansen et al. (2004) and Chapters II and III documented the structural controls of listwanite distribution (Fig. 4.1, insert). Listwanite overprints serpentinite foliation formed during ophiolite obduction, indicating that listwanite formation postdates the emplacement of ophiolitic material onto the Stikine and Cache Creek terranes (Ash 1994). The timing of listwanite genesis in the Atlin area is also constrained by A r - A r age determination of chromium-muscovite to be in the 40  39  range of ca. 168 - 172 Ma (Ash, 2001). Further details on the regional geology near Atlin are provided in Monger (1975, 1977a, b), Monger et al. (1978), Bloodgood et al. (1989), Ash and Arksey (1990b), Ash et a\. (1991), Mihalynuk et al. (1992) and Ash (1994). The temperature of formation is constrained by fluid inclusion analysis of quartzcarbonate veins to be in the range of 210 - 280°C. Homogenization temperatures (TIILv ( L ) ) of 210 to 240°C were measured from low salinity (< 5wf% equivalent NaCI) fluid inclusions that show no evidence for phase separation (Andrew, 1985). 72  Fracture-  C H A P T E R IV  6 6 0 6 0 0 0  Basaltic dikes Porphyritic dikes | Listwanite  6  4 3  i Carbonate-altered 1 fault breccia Accretionary complex sedimentary rocks Meta basalt Serpentinite Dunite  Fault Basal Decollement Road Drainages NAD 83 Grid  Harzburgite  Figure 4.1: Simplified geologic map of the Atlin, B.C. area, illustrating the distribution of listwanite along the basal decollement and a fault/fracture permeability network (modified from Ash 1994, Chapter II and Hansen et al. 2003b).  73  CHAPTER IV controlled listwanite likely formed under sub-lithostatic fluid pressure which is assumed to be approximately 500 bars. Listwanite is very common in ultramafic bodies; two other well known occurrences include the Timmins area of Ontario.(e.g. Schandl and Naldrett, 1992) and the Mother Lode camp in California (e.g. Wittkopp, 1983). Madu et al. (1990) and Schandl and Wicks (1991) report similar temperatures of formation from other listwanite occurrences.  4.4 STRUCTURAL CONTROL Our field mapping confirms structural control of listwanite distribution along the basal decollement and along a transecting network of steeply-dipping joint and fractures sets (e.g. Hansen et al. 2004; Chapter II; Chapter III; Fig. 4.1). Although the joint and fracture systems served as the primary conduit for infiltration of C02-bearing fluid, pervasive carbonate alteration extends from a few centimetres to many tens of metres outward from the primary structural controls into intact bedrock.  The most distal  carbonation persists heterogeneously throughout the map area and cannot be accurately represented at the scale of Figure 4.1 where only the more focused and intense carbonation is mapped as listwanite. The reaction halos thus extend beyond the area mapped as listwanite, but the spatial distribution of more intensely carbonated rocks serves to illustrate the structural control of fluid infiltration.  Mineralogical zonation  within the halos is a record of the pathway of the carbonation reaction.  4.5 MINERALIGICAL ZONATION AND REACTION SEQUENCE The Atlin ultramafic rocks are depleted mantle harzburgitic material formed during adiabatic melt extraction beneath a mid-ocean ridge (Ash and Arksey, 1990a). The melt extraction process and serpentinization event(s) have left the residual harzburgite chemically heterogeneous prior to listwanite metamorphism. The variation in modal orthopyroxene (opx) is a record of the original harzburgite heterogeneity. Serpentinization reactions consumed olivine + orthopyroxene to form serpentine + magnetite. The extent of serpentization generally exceeds 70% by volume. Serpentine pseudomorphs of opx are common.  74  CHAPTER IV The mineral content of serpentinite and listwanite was determined by X-ray diffraction (XRD) and optical and scanning electron microscopy (Table 4.1). Serpentine within uncarbonated samples was confirmed as antigorite by X R D and Raman spectroscopy (Rinaudo and Gastaldi, 2003). Uncarbonated antigorite +/- relict olivine, brucite and orthopyroxene assemblages were transformed to assemblages containing antigorite, magnesite, talc and quartz. The mineral assemblages track the migration of three carbonation reactions summarized in Figure 4.2. In sum, these reactions result in the overall transformations recorded in reactions RA and B- The physical separation of the reaction fronts allows each reaction to be examined in isolation.  The boundaries  separating each mineral assemblage are reaction isograds in the sense of Carmichael (1970). The most distal carbonation reactions are volumetrically minor and involve the breakdown of relict olivine via reaction R i to antigorite and magnesite (Fig. 4.3a, a  assemblage A of Fig. 4.2): 2  34 M g S i 0 + 20 C 0 + 31 H 0 -» 2  4  2  2  Mg 8Si34 0 8 5(OH) 6 2 4  + 20 M g C 0  3  (R ) u  Olivine -> Antigorite + Magnesite  O'Hanley and Wicks (1995) documented reaction of olivine to lizardite and subsequent transformation to antigorite at Cassiar, B.C. We have been unable to confirm the presence of lizardite in samples recording reaction R . Lacking evidence to the contrary, !a  we therefore consider all serpentine to be antigorite. Trace amounts of brucite are present in some A\ assemblages but are not found in samples containing magnesite.  Carbonation of olivine-bearing samples may therefore  also have included the reaction:  Mg(OH) + C 0 -> M g C 0 + H 0 2  2  3  Brucite -> Magnesite 75  2  (R, ) b  CHAPTER IV  Table 4.1: Mineralogy of carbonated serpentinite from Atlin, BC Chr Mgt Brc Ol Srp Mgs Tic Qtz Sample x X X 01AT-8-1 X X X 01AT-13-1 X X X X 01AT-3-1 X X X X X 01AT-10-1 x X X X X X 01 AT-10-2 X X X X 01AT-2-2 X X X X X X 01AT-9-1 X X X X X 01AT-11-1 X X X X 01AT-1-9 X X X X 01AT-6-3 X X X X 01AT-1-8 X X X 01AT-13-2 X X X X 01AT-11-2 X X X X X X 01AT-7-3 X X X X X 01AT-1-7 X X X X X 01AT-1-6 X X X 01AT-9-2 X X X X X 01AT-7-1 X X X X x 01AT-5-4 X x X X X . x 01AT-1-5 X X X 01AT-4-1* X X X 01AT-5-2 X X X X 01AT-6-1* only occurs in small veins occurs in small isolated patches armored relicts and late mantling; of chromite and pyrite magnetite in late fractures and late mantling of chromite * sample contains Cr-muscovite Sample locations in Appendix F. v  y  w  z  v  w y z  76  C0  A, A, Ai A, A, A, Ri Ri A A A A A R R R R R R R R A A  2  2 2  2  2  2  2  2  2  3 3  3  3  4  4  (wt%) 0.06 0.10 0.21 0.15 0.26 0.33 2.10 2.57 3.37 4.00 4.60 7.12 9.60 3.40 7.19 9.54 17.26 21.83 28.01 34.00 34.34 35.20 36.19 2  CHAPTER IV  Assemblage A i  Talc + Magnesite  Serpentine +/- Olivine +/- Brucite  \Ri  Assemblage A 4  Assemblage A3  Rs  Quartz + Magnesite  R2/  *Reaction R by-passed if no olivine or brucite present in the protolith (Assemblage A i ) .  Assemblage A2  1  Serpentine + Magnesite  Figure 4.2: Simplified flow chart for the reaction path of the Atlin listwanite system during progressive carbonation of serpentinite.  77  C H A P T E R IV  Figure 4.3: Backscattered scanning electron images showing progressive carbonation during listwanite genesis, a): Reaction Ru,: olivine to serpentine and magnesite (Mi) + magnetite,  b): Reaction R : antigorite to magnesite (M ) + talc, 2  2  c): Reaction R 3 :  magnesite (M3) + quartz assemblage, d): Close-up of (c). M i , M and M 3 are interpreted 2  to represent magnesite generated during reactions R i , R and R3 respectively. Note that 2  magnesite M rims M i and that M 3 rims M and forms euhedral boundaries with quartz. 2  2  Light grey magnesite has a higher mean atomic mass and higher Fe content than dark grey magnesite.  78  CHAPTER IV Coexisting products and reactants of R ^ have not been observed in any samples collected from Atlin. For simplicity, reactions R i and Rib will be considered together as reaction a  Ri. Reaction R\ generally accommodates less than ca. 5 wt % CO2 (Table 4.1) and is limited in progress by olivine (+/- brucite) abundance prior to carbonation. Formation of magnesite at the expense of olivine (+/- brucite) can be driven by a modest increase in the activity of CO2 in the fluid phase with negligible decrease in activity of H 0 (Fig. 4.4b). 2  Early, distal carbonation of brucite and olivine is consistent with the observed higher reactivity of olivine and brucite relative to serpentine in mineral carbonation experiments (Guthrie et al, 2001; Lackner et al., 1995). The formation of magnesite plus talc (Assemblage A 3 ) and destruction of antigorite (Fig. 4.3b) marks a major carbonation front and occurs throughout most of the area mapped as listwanite in Figure 4.1. Carbonation proceeded via the reaction:  2 Mg  48  S i 3 4 0 85(OH)62  + 45 C 0 -> 45 M g C 0 + 17 Mg Si40,o(OH) + 45 H 0 2  3  3  2  2  (R ) 2  Antigorite -> Magnesite + Talc  which combined with reaction R|, accounts for about half of the overall carbonation potential for the serpentinite rocks at Atlin (up to about 20 wt %, Table 4.1, Fig. 4.4a). It also marks a further increase in the C 0 content of the fluid phase (Fig. 4.4b). The cores 2  of large listwanite systems consist of magnesite plus quartz (Assemblage A 4 , Fig. 4.2), which formed by the reaction R3 at the highest activity of C 0 in the fluid phase (Fig. 2  4.4b).  Mg Si Oio(OH)2 + 3 C 0 -> 3 M g C 0 + 4 S i 0 + H 0 3  4  2  3  Talc -> Magnesite + Quartz  79  2  2  (R) 3  Figure 4.4: a) Ternary phase diagram comparing the observed mineral content and whole rock composition in a MgO+FeOS i 0 - C 0 ternary diagram projected from H 0 . b) Mineral stability in the system M g O - S i 0 - C 0 - H 0 as a function of 2  2  2  2  2  2  activity of H 0 and C 0 in the fluid phase calculated using PTAX and the mineral database of Berman (1988). The dashed 2  2  line is the metastable extension of reaction R i . The arrowed dashed line is the path of Pfl a  fluid, calculated with the CORK equation of state (Holland and Powell 1991).  uid  = 500 bars for a binary H 0 - C 0 2  2  CHAPTER IV Thus, the overall mineral transformation of serpentine and olivine to quartz and magnesite is the same as that recorded in reactions RA and B- Total carbonation of serpentinite leads to CO2 contents in excess of 36 wt% on a whole-rock basis (Table 4.1). Reactions Ri, R2 and R3 record an increase in activity of CO2 in an H20-rich fluid (Fig. 4.4b). Reactions Ri to R 3 produce magnesite of different compositions that are discernible with back-scattered electron imaging because of differences in mean atomic mass. Energy-dispersive spectroscopy confirms that increasing mean atomic mass is due primarily to an increase in Fe content of magnesite. Magnesite M | formed during Ri exhibits euhedral faces with serpentine and is overgrown by M2 magnesite with a higher Fe content associated with talc (Fig. 4.4b). The dark cores to magnesite in Figures 4.3c, d are likewise interpreted to record M i magnesite growth overprinted by magnesite formed by reaction R2. Dark rims of M 3 magnesite in Figure 4.3d contain less Fe than M2 magnesite and forms euhedral contacts with quartz. 4.6 GEOCHEMICAL CHANGE DURING LISTWANITIZATION The mineralogical transformations in reactions Ri to R3 can be achieved through (de)hydration-carbonation reactions and no modification of the major oxide chemical composition of serpentinite. Previous studies of listwanite, however, have argued for pervasive chemical change accompanying carbonation (Schandl and Naldrett, 1992; Sherlock et al., 1993; Buisson and LeBlanc, 1985). Indeed the term silica-carbonate alteration that is commonly applied to these systems implies metasomatism.  If the  mineral reactions at Atlin involve substantial mobility of major non-volatile species, then this system may not serve as a useful analogue for mineral carbonation processes. Whole-rock chemical compositions from Atlin (data in Appendix A) are consistent with the hypothesis that carbonation was not accompanied by chemical changes of major non-volatile chemical species. Decreases in wt% MgO and Si02, which combined make up about 90% of the non-volatile component of the Atlin rocks, correlate with an increase in CO2 content at a constant MgO:Si02 ratio (Fig. 4.5). This trend is consistent with the immobility and passive depletion of Si and M g during mass increase (CO2 addition). Serpentinite and listwanite overlap completely in composition if 81  CHAPTER IV  C0  2  55  Content  C0  50  2  Content )35wt% •  35wt% 45  30 wt% 25  G-35 O CD  ^  _g>30  2 5  20  wt%  20 wt%  . o o o  15  15wt% 10wt% 5 wt% 0 wt%  N, < f \  A t  /  9*  '/  D u n i t e  /  N.  y  Harzburgite  10 5 0  10  0  15  20  25  Wt% S i 0  30  35  40  a  b 0  5  10  15  2  20  25  30  35  wt% S i 0 (Dry)  40  45  50  55  2  Figure 4.5: a) Weight percent MgO plotted vs. Si02. Circle size is proportional to CO2 content. Data is in Appendix A . The observed trend is consistent with the passive dilution of MgO and Si02 by increase in CO2 content. Dashed lines represent the chemical range defined by the protolith samples and passive dilution, b) MgO and Si02 whole rock compositions renormalized to 100% (excluding H2O and CO2). Carbonated and uncarbonated samples plot on calculated dunite and harzburgite compositions (using F090  and  En9o  compositions for olivine and orthopyroxene, respectively). Note that the  MgO and Si02 contents of serpentinite and listwanite are indistinguishable. *Denotes an antigorite-rich rock which contains 7 wt% magnetite (estimated from the data in Appendix A) created during the complete serpentinization of  82  Fo9o/Enc>o  rich rocks.  CHAPTER IV major oxide compositions are renormalized to 100% excluding H 0 and C 0 (Fig. 4.5b). 2  2  The variation of Si0 :MgO ratio within the suite of rocks may be a function of the degree 2  of initial serpentinization, or the amount of initial orthopyroxene (Fig 4.5b). Whole-rock geochemical compositions were tested against model sequestration reactions R i , Rib, R2 and R 3 using the method of Gordon (2003), a new geochemical a  mass balance technique that quantitatively accounts for protolith heterogeneity. The six samples with assemblage A] (Table 4.1) and the lowest C 0 content (<0.5 wt%; 2  Appendix A) were chosen to define the protolith. The protolith for each carbonated rock was modeled as a linear combination of these six so that compositional heterogeneities in the protolith did not propagate into the assessment of the carbonation. The remaining samples were divided into three groups.  Seven samples without talc or quartz were  considered to have experienced only reactions R i and Rib, four samples with talc but no a  quartz were considered to have experienced reactions R i , Rib and R , and the remaining a  2  six quartz-bearing samples were considered to have experienced the full suite of reactions. Reaction R i requires the model mass-transfer vector for the seven low-C0 a  2  samples be zero for all species except C and H. For these samples, the model ratio of C added to H added is 20:62. Model reactions Rib, R and R3 have the ratios of C added to 2  H added of l:-2, l:-2 and 3:-2 respectively. A linear algebraic basis (Strang, 1993) for the vector space orthogonal to the model mass-transfer vectors (invariant space) can be obtained by simple manipulations using linear algebra.  The basis contains linear  combinations of elements unaffected by the proposed mass-transfer reactions. Because more than one reaction is involved in each group of samples, the possibility of various extents of reaction of R i , Rib, R2 and R3 means that this method does not constrain the a  C/H ratio of the mass-transfer vector. Given the composition of a carbonated rock, the mass-transfer vector must have an origin that can be described by a linear combination of the vectors in protolith space and be orthogonal to vectors in invariant space. This approach provides a vector equation, the least-squares solution of which provides a "best fit" protolith composition and "best fit" mass-transfer vector for each carbonated rock.  83  CHAPTER IV The success of the model sequestration reactions in predicting the observed composition of a modified rock can be judged by comparing the residuals of the leastsquares solution with the errors permitted by analytical uncertainties determined from replicate analyses. These results are shown in Figure 4.6. Positive residuals indicate that the altered rock contains more of that element than permitted by the hypothesis. In general, the isochemical reaction model provides a good fit to the data. Residuals for Si, Ti, Fe, Mg, Na, K, P, and V return a good to excellent fit, generally within 3 standard errors (see Appendix A). The variation in the composition of these elements in listwanite can be fully explained by the variability of the protolith rocks and the dilution effect of mass addition. The model protolith subspace and simple sequestration reactions do not adequately describe the variation in A l , Mn, Ca, Cr, Ni and Zn, which all show large residuals.  The failure of the model to explain the compositional variation in these  elements is most likely due to inadequate geochemical characterization of protolith variability due to the small number of protolith samples. The residuals are generally both positive and negative and show no systematic variation with degree of carbonation. Moreover, A l , Cr, N i and Zn are relatively immobile compared to many other major elements such as Mg and Fe in hydrothermal systems. There is no convincing evidence for chemical mobility beyond the volatile species. A more extensive database and geochemical mass balance calculation in Chapter V provides for a more thorough examination of the protolith and alteration.  4.7 MAGNETIC SUSCEPTIBILITY Ri carbonation occurs many tens of metres from major fracture systems but is generally not evident in the field.  We have been unable to map the distribution of  magnesite formed after olivine breakdown, for example, because this reaction is commonly not discernable in hand sample. The magnetic susceptibility of serpentinite is relatively high because of the formation of magnetite during serpentinization of harzburgite and dunite (e.g., Toft et al., 1990). There is also evidence for magnetite generation during reaction Ri (Fig. 4.3a). Generally magnetite forms rim overgrowths on chromite and as disseminated grains aligned in foliation planes and in fractures.  84  C H A P T E R IV  3o >  >-3o  <-3o  > 3o  Figure 4.6: Ratio of residual error to standard error in whole rock chemical composition of carbonated samples. Residual error is the difference between compositions predicted by reactions R 1 - R 3 and measured compositions. Values of the ratio that exceed three standard errors (positive/negative) indicate an excess/deficiency of the species which cannot be accounted for by the model sequestration reactions of all residuals is included in the appendix.  85  (Ri &b, R 2 a  and  R3).  Table  CHAPTER IV Magnetite was subsequently destroyed during carbonation (Table 4.1) and is completely consumed by the final stages of reaction R . 2  Mass balance calculations indicate that Fe is conserved during carbonation of serpentinite.  Fe liberated by magnetite destruction must therefore be hosted within  another mineral. The increase in Fe content of magnesite in M is consistent with 2  conservation of Fe during magnetite destruction. There is a corresponding decrease in whole rock magnetic susceptibility in samples recording reaction R (Fig. 4.7). 2  We have exploited the correlation of whole-rock C 0 content and magnetic 2  susceptibility (Fig. 4.7) to develop a semi-quantitative measure of reaction progress that can be employed in the field. Magnetic susceptibility of outcrops and hand specimens were measured with an Exploranium KT-9 Kappameter. Although fully carbonated rocks contain > 35 wt% C 0 , virtually all magnetic susceptibility appears to have been 2  destroyed by about 20 wt% C 0 , which corresponds to the completion of reaction R . 2  2  Magnetic susceptibility of serpentinite is heterogeneous and reflects the degree of initial serpentinization. A least squares fit to the data yields a semi-quantitative relationship between magnetic susceptibility and C 0 , and thus reaction progress: 2  Magnetic Susceptibility (10" S.I. units) = 61.003 - 3.0544(wt% C 0 )  (4.1)  3  2  To test the utility of this relationship in mapping reaction progress, a 2 by 2 metre pavement of variably carbonated serpentinite was mapped and analyzed in the field for magnetic susceptibility (approx. 1550 analyses, Fig. 4.8). Fracture-controlled talc + magnesite + minor serpentine (R ) transects the pavements in two discrete reaction zones 2  that are flanked by distal antigorite + magnesite assemblages (A ). The mineralogical 2  zonation at this locale corresponds to discrete changes in magnetic susceptibility. The distinction between serpentinite and rusty serpentinite in the field is very subtle, yet this alteration is prominent in magnetic susceptibility. Measured whole rock C 0 content for 2  samples along transect A - B is within 5% of C 0 content calculated from magnetic 2  susceptibility and (Equation 4.1, Fig. 4.9). Calculated C 0 content increases continuously 2  within the zone of rust-weathering serpentinite, implying a gradation in reaction progress across this zone. However, whole rock geochemistry through the section indicates an 86  CHAPTER IV  120Magnetic Susceptibility = -3.0544(CO ) + 61.003 2  f 35  40  wt% CO2 Figure 4.7: Magnetic susceptibility vs. whole rock wt% C O 2 . Linear fit was constrained to intersect zero magnetic susceptibility at 20 wt% C O 2 , which approximately marks the maximum C O 2 content of rocks that record complete progress of reaction R 2 .  87  CHAPTER IV  bli  WML •  Srp + Mgs (Rust Stained) Srp + Mgs Carbonate filled veins front permeabiirty|  —. V i J  PU<  '•.'Si £2'  j  ]  x = s a m p l e location  90  2  'c  80  3  a »  1 60  1*1  | SO  u  30  #1  it  12  •  Magnetic Susceptibility (measured)  CO Content (calculated)  Figure 4.8: a) Composite image of a 2 by 2 metre pavement outcropping on the western slope of Monarch Mountain (E 575887, N 6602098, N A D 83). Dashed yellow lines are contacts in Figure 2.2b. b) Detailed geologic map of the listwanite zone mapped at 1:20 scale. Sample locations and section A-B correspond to those of Figure 3.7. c) Magnetic susceptibility map composed of ca. 1550 measurements, showing the correlation of magnetic susceptibility with map units in Figure 2.2b. d) Whole rock Wt% CO2 map calculated using Eqi following Hansen et al. (2005), Chapter IV.  88  CHAPTER IV  25  • Calculated from magnetic susceptibility <§> Measured  t20 \  I  CM  °  15  sc  o £10  o £  5  &  <§>  .<^....  0  70 cm  A  B  Figure 4.9: Measured and calculated wt% C 0 across A-B from Figure 2.2b. Wt% C 0 2  2  calculated using E q i and magnetic susceptibility data of Figure 2.2c.  The range in  calculated C 0  susceptibility  2  content reflects  the full  measurements at each location.  89  range of four magnetic  CHAPTER IV abrupt change in C 0 content (Fig. 4.9). The gradation in magnetic susceptibility at the 2  reaction front could either reflect the resolution of the magnetic susceptibility metre or the progressive destruction of magnetite not directly linked to progress of carbonation reaction. Regardless, magnetic susceptibility maps provide semi-quantitative estimates of reaction progress in the field and are invaluable in discerning the geometry of reaction fronts associated with reaction R . 2  4.8 V O L U M E STRAIN ACCOMPANYING REACTION The carbonation reactions involve an increase in the volume of solids (Table 4.2); each reaction therefore has the potential to create or destroy porosity and permeability. The development of carbonate veins orthogonal to the outer limit of talc plus magnesite reaction in Figures 4.8a, b likely developed in tension.  The mechanical model of  Jamtveit et al. (2000) predicts the development of high-permeability zones downstream of reactions that produce a net solid volume increase (Fig. 4.10). Indeed, the pattern of carbonation and vein formation in Figures 4.8a, b resembles the patterns produced by the Jamtveit et al. model. If vein formation outboard of the talc-magnesite reaction front records tension and mechanical coupling of swelling during reaction R , then the volume 2  strain of the two processes should balance, at least approximately. Volume strain was calculated by measuring vein thickness (7.6 +/- 3.8 mm) and density in the rusty serpentinite zone of Figure 4.8.  The calculated volume increase of 3.6 +/- 1.8%  compares well with the solid volume change of reaction R (2.3 % in a serpentinite rock 2  with 7.5% relict olivine). The distribution of carbonate-filled tension gashes appears to control the outer extent of formation of rusty serpentinite alteration and thus likely has enhanced percolation of reactive fluid into intact wallrock.  4.9 IMPLICATIONS FOR C 0 SEQUESTRATION 2  Direct carbonation of olivine (+/- brucite) was previously unrecognized at Atlin and records infiltration and carbonation of intact bedrock many tens to hundreds of metres from the primary fracture-controlled permeability system. The relative ease by which fluid infiltrated intact bedrock may be due to the inherently high reactivity of olivine and brucite and by the small solid volume increase associated with carbonation of 90  CHAPTER IV  Table 4.2: V o l u m e C h a n g e s  AVs* (rxn)  AVs ( r o c k * * )  R : O l -» S r p + M g s  55.1%  4.2%  R : B r c -> M g s  13.8%  0.4%  Reaction 1 a  1 b  R : S r p -» T i c + M g s  2.6%  2.3%  R : T i c -» Q t z + M g s  28.5%  16.2%  2  3  * C a l c u l a t e d from B e r m a n (1988) at 250°C and 500 bars (Chapter IV) A s s u m i n g 2 . 5 % brucite a n d 7 . 5 % relict olivine by v o l u m e .  91  CHAPTER IV  Fluid Conduit  Un reacted Rock  \ 1 /  Reaction Front  Figure 4.10: Distribution of fracture permeability in advance of a reaction, predicted by the mechanical model of Jamtveit et al. (2000).  In the model, tension fracture  permeability results from an overall increase in solid volume during reaction. Modified from Jamtveit et al. (2000).  92  CHAPTER IV  ;  small amounts of brucite and relict olivine. The extent of reaction Ri indicates that the primary permeability of serpentinite at Atlin was sufficient for fluid infiltration and progress of R\.  However, the large increase in solid volume of R\ may limit its  usefulness for fluid infdtration in olivine-rich bedrock.  From Table 4.1, the direct  carbonation of brucite and olivine to magnesite plus serpentine only accounts for about 5 - 15 % of the carbonation potential for the serpentinite at Atlin.  However, because  products of reaction Ri are widespread, it may have sequestered a significant portion of the total CO2 content of the Atlin listwanite system. The listwanite is best developed along a regional joint and fracture system as well as a basal thrust fault (Chapter III), hence the Altin Ultramafic Allochthon had good potential for carbonation due to the structural preparation.  This suggests that the  potential of an ultramafic body for CO2 sequestration is directly linked to its original fracture permeability because without it, the carbonation potential is limited regardless of the efficiency of the various COrsequestering reactions. The carbonation of antigorite to magnesite and talc binds large quantities of CO2 with small associated gain in the volume of solid material. Moreover, within intact bedrock, the progress of this reaction may create a permeability front in advance of the reaction front, promoting further fluid infiltration and reaction. Reactions R\ and R2, which combined account for about half of the carbonation potential for serpentinite (Table 4.1), may hold the most promise for industrial-scale in situ carbonation of minerals. Complete carbonation of serpentinite to magnesite plus quartz is generally limited to the fractured cores of the largest listwanite systems. Products of reaction R3 generally are not developed far into intact bedrock, which may have been incapable of accommodating the large increase in solid volume associated with this reaction. This indicates that carbonation to magnesite plus quartz may limit the sequestration capacity of in situ mineral-carbonation systems by destroying porosity and permeability in the vicinity of injection sites. The reaction path models of Cipolli et al. (2004) predict significant conversion of serpentine within in situ mineral carbonation systems to carbonate and chalcedony (microcrystalline quartz) within a few 10's of years. Their model assumes direct transformation of serpentine to chalcedony and magnesite at 250 bars and 60°C based on the conditions of the Gruppo di Voltri serpentinite aquifer at 93  CHAPTER IV Genova, Italy. Our investigations at Atlin and Figure 4.11 suggest that carbonation within the subsurface under these conditions would more likely proceed via a series of reactions (Ri to R 3 ) .  Moreover, as indicated above, reactions Ri and R2 involve a  relatively small increase in the volume of solids limiting porosity destruction yet still sequester half the CO2 as complete carbonation to quartz plus magnesite. The stability of carbonation reactions are controlled by the activity of CO2 in the fluid phase and Figure 4.11 indicates that the fluid chemistry favorable for driving Ri and R is a C02-rich 2  aqueous fluid. Industrial mineral carbonation processes could therefore be engineered to control the input gas composition so as to preferentially drive carbonation reactions that minimize porosity loss and maximize permeability generation in the subsurface.  94  CHAPTER IV  _5  H  1  1  -0.5  -0.75  -1  1  -0.25  0  Log a(H 0) 2  Figure 4.11: Mineral stability in the system MgO- Si02-C02-H20 as a function of activity of H2O and C 0 in the fluid phase calculated at the Gruppo di Voltri serpentinite 2  aquifer at Genova, Italy (P = 250 bars, T = 60°C, Cipolli et al. 2004). Calculated using PTAX and the mineral database of Berman (1988).  95  CHAPTER IV 4.10 REFERENCES Aitken, J. D. (1959): Atlin Map Area, British Columbia. Geological Survey of Canada, Memoir 307: 89 pages. Andrew, K. (1985): Fluid Inclusion and Chemical Studies of Gold-Quartz Veins in the Atlin Camp, Northwestern British Columbia. B.Sc. Thesis, Department of Geological Sciences, University of British Columbia, Vancouver, B.C., Canada, 116 pages. Ash, C. H . (1994): Origin and Tectonic Setting of Ophiolitic Ultramafic and Related Rocks in the Atlin Area, British Columbia (NTS 104N). B.C. Ministry of Energy, Mines and Petroleum Resources, Bulletin 94, 48 Pages. Ash, C. H. (2001): Relationship Between Ophiolites and Gold-Quartz Veins in the North American Cordillera. Department of Energy, Mines and Petroleum Resources, Bulletin 108, 140 pages. Ash, C. H . and Arksey, R. L. (1990a): The Atlin Ultramafic Allochthon: Ophiolite Basement Within the Cache Creek Terrane; Tectonic and Metallogenic Significance (104N/12).  Geological Fieldwork 1989, B.C. Department of Energy and Mines, Paper  1990-1,365-374. Ash, C. H. and Arksey, R. L. (1990b): The Listwanite-Lode Gold Association in British Columbia. Geological Fieldwork 1989, B.C. Department of Energy and Mines, Paper 1990-1,359-364. Ash, C. H., MacDonald, R. W. and Arksey, R. L. (1991): Towards a Deposit Model for Ophiolite Related Mesothermal Gold in British Columbia. Geological Fieldwork 1991, B.C. Department of Energy and Mines, Paper 1992-1, 253-260.  96  CHAPTER IV Berman, R. G. (1988): Internally-Consistent Thermodynamic Data for Minerals i n the System: N a 2 b - K 0 - C a O - F e O - A l 2 0 3 - S i 0 2 - T i 0 2 - H 2 0 - C 0 2 . 2  Journal of Petrology, 29-2,  445-522. Bloodgood, M . A., Rees, C. J. and Lefebure, D. V. (1989): Geology and Mineralization of the Atlin Area, Northwestern British Columbia (104N/11W and 12E). Geological Fieldwork 1988, B.C. Department of Energy and Mines, Paper 1989-1, 311-322.  Buission, G. and LeBlanc, M . (1985): Gold in Carbonatized Ultramafic Rocks from Ophiolite Complexes. Economic Geology, 80, 2028-2029. Carmichael, D.M., (1970): Intersecting Isograds i n the Whetstone Lake area, Ontario. Journal of Petrology, 11, 147-181. Cipolli, G., Gambardella, B., Marini, L., Ottonello, G. and Zuccolini, M . V. (2004): Geochemistry of High-pH Waters from Serpentinites of the Gruppo di Voltri (Genova, Italy) and Reaction Path Modeling of CO2 Sequestration i n Serpentinite Aquifers. Applied Geochemistry, 19, 787-802.  Goff, F. and Lackner, K . S. (1998): Carbon Dioxide Sequestering Using Ultramafic Rocks. Environmental Geosciences, 5-3, 89-101. Goldberg, P., Chen, Z. Y., O'Connor, W. K., Walters, R. P. and Ziock, H . (2001): C 0  2  Mineral Sequestration Studies in US. Proceedings of the First National Conference o n Carbon Sequestration, May 14-17, 2001, Washington, DC, session 6C, 10 pages.  Gordon, T . M . (2003): Algebraic Generalization of the Graphical Gresen and Pearce Methods for Identification of Geochemical Mass-Transfer Processes.  (abstract),  Vancouver 2003 Abstracts, CD-ROM, GAC-MAC-SEG, Vancouver 2003 Annual General Meeting, Vancouver, B.C., 28-146, ISSN 0701-8738, ISBN: 0-919216-86-2.  97  CHAPTER IV Guthrie, G. D., Carey, J. W., Bergfeld, D., Byer, D., Chipera, S., Ziock, H . and Lackner, K. S. (2001). Geochemical Aspects of the Carbonation of Magnesium Silicates in an Aqueous Medium.  Proceedings of the First National Conference on Carbon  Sequestration, May 14-17, 2001, Washington, DC, session 6C, 14 pages. Hansen, L . D., Dipple, G. M . , Anderson, R. G. and Nakano, K . F. (2004): Geologic Setting of Carbonate Metasomatised Serpentinite (Listwanite) at Atlin, British Columbia: Implications for CO2 Sequestration and Lode-Gold Mineralization. In Current Research, Geological Survey of Canada, Paper 2004-A5, 12 pages. Hansen, L. D., Dipple, G. M . and Anderson, R. G. (2003b): Carbonate Altered Serpentinites of Atlin, BC: A Two Stepped Analogue to CO2 Sequestration, (abstract), Programs with Abstracts, GSA Annual Meeting & Exposition, Seattle, WA, 133-14, 329.  Holland, T and Powell, R. (1991): A Compensated-Redlich-Kwong (CORK) Equation For Volumes and Fugacities of CO2 and H2O in the Range 1 bar to 50 kbar and 100-1600 C. Contributions to Mineralogy and Petrology, 109, 265-273. Jamtveit, B., Austrheim, H. and Malthe-Sorenssen, A . (2000): Accelerated Hydration of the Earth's Deep Crust Induced by Stress Perturbations. Nature, 408, 75-78. Kashkai, A. M . and Allakhverdiev, I. (1965): Listwanites: Their Origin and Classification. U. S. Geol. Surv., Libr., Reston, V A , United States, 146 pages, Translated from the Russian, Listvenity, ikh genezis i klassifikatsiya, Akad. Nauk A Z SSR, Inst. Geol. Baku, 1965 Lackner, K. S., Wendt, C. H., Butt, D. P., Joyce, E. L . and Sharp, D. H . (1995): Carbon Dioxide Disposal in Carbonate Minerals. Energy, 20, 1153-1170.  98  CHAPTER IV Madu, B. E., Nesbitt, B. E. and Muehlenbachs, K. (1990): A Mesothermal Gold-StibniteQuartz Vein Occurrence in the Canadian Cordillera. Economic Geology, 85, 1260-1268.  Matter, J. M . , Takahashi, T., Goldberg, D., Morin, R. H . and Stute, M . (2002): Secure, Long-Term Geological Carbon Sequestration in Mafic Rocks: Results from Field and Laboratory Experiments, (abstract), Programs with Abstracts, GSA Annual Meeting & Exposition, Denver, CO, 135-5. Mihalynuk, M . G., Smith, M . , Gabites, J. E., Runkle, D. and Lefebure, D. (1992): Age of Emplacement and Basement Character of the Cache Creek Terrane as Constrained by New Isotopic and Geochemical Data. Canadian Journal of Earth Sciences, 29, 24632477. Monger, J. W. H. (1975): Upper Paleozoic Rocks of the Atlin Terrane. Geological Survey of Canada, Paper 74-47, 63 pages. Monger, J. W. H. (1977a): Upper Paleozoic Rocks of Northwestern British Columbia. In Current Research, Part A, Geological Survey of Canada, Paper 77-1 A, 255-262. Monger, J. W. H. (1977b): Upper Paleozoic Rocks of the Western Canadian Cordillera and Their Bearing on the Cordilleran Evolution. Canadian Journal of Earth Sciences, 14, 1832-1859. Monger, J. W. H., Richards, T. A. and Paterson, I. A . (1978): The Hinterland Belt of the Canadian Cordillera: New Data from Northern and Central British Columbia. Canadian Journal of Earth Sciences, 15, 823-830. O'Connor, W. K., Dahlin, D. C , Nilsen, D. N , Rush, G. E., Walterd, R. P. and Turner, P. C. (2001): Carbon Dioxide Sequestration by Direct Mineral Carbonation: Results From Studies and Current Status. Proceedings of the First National Conference on Carbon Sequestration, May 14-17, 2001, Washington, DC, session 6C, 10 pages. 99  CHAPTER IV O'Hanley, D. S. and Wicks, F. J. (1995): Conditions of Formation of Lizardite, Chrysotile and Antigorite, Cassiar, British Columbia. Canadian Mineralogist, 33, 753773. Rinaudo, C. and Gastaldi, D. (2003): Characterization of Chrysotile, Antigorite and Lizardite by FT-Raman Spectroscopy. Canadian Mineralogist, 41, 883-890. Schandl, E. S. and Wicks, F. J. (1991): Two Stages of C 0 Metasomatism at the Munro 2  Mine, Munro Township, Ontario: Evidence from Fluid-Inclusion, Stable-Isotope, and Mineralogical Studies. Canadian Journal of Earth Sciences, 28, 721-728. Schandl, E. S and Naldrett, A . J. (1992): CO2 Metasomatism of Serpentinites, South of Timmins, Ontario. Canadian Mineralogist, 30, 93-108. Seifritz, W. (1990): C 0 Disposal by Means of Silicates. Nature, 345, 486. 2  Sherlock, R. L., Logan, M . A . V., and Jowett, E. C. (1993): Silica Carbonate Alteration of Serpentinite, Implications for the Association of Precious Metal and Mercury Mineralization in the Coast Ranges. Society of Economic Geologists Guidebook Series, 16, 90-116. Strang, G. (1993): Introduction to Linear Algebra. Wellesley-Cambridge Press.  Todt, P. B., Arkani-Hamed, J. and Haggerty,  S. E. (1990): The Effects of  Serpentinization on Density and Magnetic Susceptibility: A Petrophysical Model. Physics of the Earth and Planetary Interiors, 65, 137-157.  Wittkopp, R. W. (1983): Hypothesis for the Localization of Gold in Quartz Veins, Allegheny District. California Geology, 36-6, 123-127.  100  CHAPTER IV Wu, J., Sheen, J., Chen, S. and Fan, Y . (2001): Feasibility of CO2 Fixation Via Artificial Rock Weathering. Industrial and Engineering Chemical Research, 40, 3902-3905.  Zeverhoven, R. and Kohlmann, J. (2001): CO2 Sequestration by Magnesium Silicate Mineral Carbonation in Finland. Second Nordic Minisymposium on Carbon Dioxide Capture and Storage, Gotenborg (October 26, 2001): http://www.entek.chalmers.se/~anly/svmp/sviTip200l .html.  101  CHAPTER V CHAPTER V : GEOCHEMICAL MASS B A L A N C E USING A PROTOLITH SPACE  5.1 INTRODUCTION There are a number of methods currently available for assessing the geochemical mass balance between altered samples and unaltered protolith material. The most widely employed methods are the system of linear equations of Gresens (1967), the graphical method of Grant (1987) and the bootstrap method of Ague and Van Haren (1996). A l l of the aforementioned methods require that a chemically heterogeneous protolith be represented by a single composition and at best assess the impact of protolith heterogeneity through propagation of the variance of the protolith composition (e.g. Ague and Van Haren, 1996). Furthermore, at least one chemical species must be assumed to be immobile when assessing the alteration. Here I outline an alternate method, following Gordon (2003), in which a model protolith (MP) is calculated for each altered sample and is allowed to span a defined geochemical space. Any difference between the altered sample and the MP thus is considered alteration. This mass balance approach is applied to chemical alteration of carbonate altered serpentinite, also known as listwanite alteration (e.g. Hansen et al, 2004; Chapter II), at Atlin, British Columbia. In Hansen et al. (2005) and Chapter IV it was demonstrated using a data set of 23 samples that the formation of listwanite at Atlin occurred in three sequential reaction steps (Fig. 5.1), and that the alteration was isochemical. MgO vs. Si02 and ternary diagrams (Fig. 5.2), as well as a mass balance technique similar to that outlined below, were used to determine that the most significant process that affected the major nonvolatile chemical species alteration was passive dilution caused by mass gain as CO2 content increased. Misfits in A l , Mn, Ca, Cr, Ni and Zn between model protoliths and observed compositions were considered to have resulted from the incomplete geochemical characterization of the protolith. Here a much larger data set of 160 samples, including 45 samples of protolith material, are used to rigorously test a geochemical space-based mass balance technique. This method indicates that the major non-volatile chemical constituents remained unaltered except in extremely carbonated  102  CHAPTER V  Assemblage A i  Assemblage A3  Assemblage A4  Talc + Magnesite  Quartz + Magnesite  Hz  Serpentine +/- Olivine +/- Brucite  \ R i  Ryi *Reaction R by-passed if no olivine or brucite present in the protolith (Assemblage A i ) .  Assemblage A2  1  Serpentine + Magnesite  Figure 5.1: Simplified flow chart for the reaction path of the Atlin listwanite system during progressive carbonation of serpentinite. The detailed description of the reactions and mineral assemblages is given in Chapter IV.  103  CHAPTER V  104  CHAPTER V Figure 5.2: a) Wt% MgO plotted vs. Si02. Circle size is proportional to CO2 content. Data is in Appendix C. The observed trend is consistent with the passive dilution of MgO and Si02 by increase in CO2 content except for seven outliers (dashed circles) which are near-completely to completely carbonate-altered.  Dashed lined represent the  chemical range defined by the protolith material and passive dilution, b) MgO and Si02 whole rock compositions renormalized to 100% (excluding H2O and CO2). Carbonated and uncarbonated samples plot on calculated dunite and harzburgite compositions (using F090  and Engo compositions for olivine and orthopyroxene respectively). Note that the  MgO and Si02 contents of serpentinite and listwanite are indistinguishable. *Denotes an antigorite rich rock which contains 7 wt% magnetite (estimated from the whole rock geochemical data in Appendix C) created during the complete serpentinization of Fo /En rich rocks, c) Ternary phase diagram comparing the observed mineral content 90  90  and whole rock composition in a MgO+FeO+CaO-Si02-C02 ternary diagram projected from H2O.  105  CHAPTER V areas where extensive quartz-carbonate veining ( S i - M g 2+  2+  metasomatism) and limited  K (Cr-muscovite) and possibly Ca metasomatism occurred.  5.2 PROTOLITH & ALTERATION ASSEMBLAGES The geochemical dataset was collected from the Atlin Ultramafic Complex which contains depleted mantle harzburgite formed during adiabatic melt extraction beneath a mid-ocean ridge (Ash and Arksey, 1990). The melt extraction process and subsequent serpentinization event(s) have left the residual harzburgite chemically heterogeneous prior to listwanite metamorphism. The variation in modal orthopyroxene (opx) is a likely record of the original harzburgite heterogeneity (Fig. 5.2b). Samples are divided, on the basis of mineral content, into five groups including protolith  serpentinized harzburgite and four  mineralogically  distinct alteration  assemblages (Fig. 5.2) of Hansen et al. (2005; Chapter IV). The data from Chapter IV is augmented by additional geochemical and mineralogical data on all 160 samples (Appendixes B and C). The serpentinized harzburgitic to dunitic protolith material is chemically variable. A l l samples contain measurable CO2, even the freshest harzburgite samples. Thus, serpentinite samples without magnesite (Ai) and that.contain less than 1 wt% CO2 are considered protolith samples while those with greater than 1 wt% are considered altered samples. The most likely chemical species to be affected during a small amount of CO2 addition is Ca in dolomite with or without calcite veins. If all CO2 addition is attributed to carbonate addition, 1 wt% CO2 would require the addition of about 1.2 wt% CaO if all the carbonate is calcite or 0.6 wt% if it is all dolomite. Given that the maximum amount of CaO in the 46 protolith samplesis 1.96 wt% with only 0.59 wt% C 0 , it is very likely that the chemical range in CaO (and all other chemical species) 2  reflects to some degree protolith heterogeneities (e.g. clinopyroxene content with respect to CaO). Group A i samples do not contain magnesite and therefore have not undergone any of the three listwanite alteration reactions of Hansen et al. (2005). However they do contain up to 3.17 wt% CO2. High CO2 contents correlate with dolomite and/or calcite veining which is prevalent within serpentinite away from obvious carbonate alteration. These samples are excluded from the assessment of protolith heterogeneity. The altered 106  CHAPTER V suite that I assessed includes samples without magnesite (Ai), and three groups separated by the metamorphic isograds defined by the first appearance of magnesite (Ri, A ), talc 2  (R2, A 3 ) and quartz (R3, A 4 ) .  For simplicity, the five groups are labelled protolith,  serpentinite zone, magnesite zone, talc zone, and quartz zone. All geochemical data is converted from wt% oxide to moles/Kg of rock for each element. Fe is likely present in variable oxidation states because it is hosted in olivine, pyroxene, serpentine, magnetite and magnesite.  Total whole rock Fe is represented as Fe  3+  total.  The generalized  mineralogy for each zone is illustrated in Figure 5.1 (see Appendix B for complete mineralogy). 5.3 A N A L Y T I C A L METHODS Bulk geochemical samples were crushed and powdered in a tungsten carbide shatterbox. Powders were sent to the Geochemical Laboratories at McGill University, Montreal, PQ for bulk geochemical analysis by X-ray fluorescence. included in Appendix C.  The results are  The samples were analyzed for major, minor and trace  elements, C 0 content by induction furnace, and total volatile content by loss on ignition 2  (L.O.L). The semi-quantitative mineralogy was determined from rock powders using a Siemens Diffraktometer D5000 X-Ray Diffractometer (XRD) at The University of British Columbia. Powders were further reduced in grain size using an aluminum oxide mortar and pestle in ethanol and uniformly smeared onto glass slides for analysis. Where possible, XRD-determined mineralogy was cross-checked with standard transmission light petrography, back scattered electron imagery and energy dispersive spectrography.  5.4 ERROR & WHOLE ROCK GEOCHEMISTRY The error on the geochemical analyses was determined from four sets of blind replicates totalling 13 analyses on a single sample over a period of about 14 months. The error O" is reported as one standard deviation for each chemical species as determined from replicates (Table 5.1).  Where the detection limit is greater than the variance  determined from the replicate analyses for a particular element, the detection limit is substituted for 0".  Table 5.2 illustrates representative analyses from each of the 107  CHAPTER V  Table 5.1: Geochemical Analyses of Replicates Sample  Si0  2  Ti0  2  Al 0 2  3  Fe 0 2  3  MnO  MgO  CaO Na 0 K 0 2  2  P 0 2  5  Cr 0 2  3  Ni  V  Zn LOI  CO.  Total  AT03-pc2'  38.71 0.013  0.75  8.03  0.108 40.22 0.85  <d/l  0.02  0.007  3827  2277 34 13 11.12 0.41 100.45  AT03-pc2'  38.81 0.012  0.77  8.10  0.107 40.45 0.84  <d/l  0.01  0.006  3902  2289 34 13 11.12 0.41 100.85  AT03-pc2'  38.59 0.013  0.78  8.00  0.109 40.12 0.83  0.01  0.01  0.007  4100  2282 35 13 11.14 0.45 100.25  AT03-pc2"  38.78 0.013  0.78  8.06  0.108 40.35 0.85  0.06  0.01  0.008  3844  2288 33 13 11.22 0.51 100.86  AT03-pc2"  38.57 0.013  0.76  8.04  0.107 40.25 0.82  0.06  0.01  0.007  3857  2286 38 16 11.21 0.52 100.47  3969  2280 34 13 11.23 0.52 100.69  AT03-pc2"  38.68 0.012  0.77  8.10  0.109 40.23 0.84  0.07 0.01  0.007  AT03-pc2  38.61  0.013  0.77  8.06  0.107 40.19 0.83  0.07 0.01  0.008  3878  2283 34 13 11.24 0.53 100.53  38.61 0.014  0.77  8.08  0.106 40.28 0.85  0.04  0.01  0.007  4173  2265 38 14 11.19 0.58 100.61  0.01  0.008  3935  2274 37  ii  AT03-pc2'"  14 11.22 0.57 100.36  AT03-pc2'"  38.68 0.012  0.77  8.03  0.107 40.02 0.83  0.05  AT03-pc2"'  38.68 0.013  0.77  8.04  0.108 40.15 0.85  0.05  0.01  0.007  3779  2271  AT03-pc2  il  38.81  0.013  0.77  8.01  0.109 40.21 0.84  0.08  0.02  0.007  3918  2283 39 13 11.24 0.59 100.73  AT03-pc2  iv  38.75 0.012  0.77  8.08  0.111 40.24 0.83  0.06  0.01  0.008  3932  2274 38 14 11.21 0.61 100.71  38.69 0.015  0.79  8.02  0.110 40.20 0.86  0.09 0.01  0.007  3846  2268 39 13 11.25 0.57 100.66  AT03-pc2" Z d/1  0.0808 9E-04 0.01  35 12 11.22 0.56 100.51  0.033 0.001 0.104 0.012 0.028 0.004 0.0006 109.93 7.655 2.2  0.006 0.004 0.012 0.003 0.003 0.01  0.002 0.008 0.003 0.0035  15  3  10  1 0.045 0.07 2  0.01  0.01  0.0808 0.004 0.012 0.033 0.003 0.104 0.012 0.028 0.004 0.0035 109.93 7.655 10 2 0.045 0.07 a All chemical species are reported as wt% except C r 0 , Ni, V , Zn which are in ppm. i, ii, iii and iv 2  3  denote replicates from four different times over a 14 month period. Z = standard deviation.d/l = detection limit, o = error.  108  CHAPTER V  Table 5.2: Representative Geochemical Analyses of Ultramafic Rocks Ti0  Sample  SiO;  01AT-8-1  41.50 0.012 34.98 0.010 37.29 0.010 36.05 0.012 39.91 0.014 38.67 0.012 38.33 0.012 38.21 0.013 40.40 0.014 38.65 0.015 37.96 0.013 37.30 0.013 34.74 0.009 39.35 0.014 37.02 0.011 30.14 0.009 38.23 0.012 33.30 0.010 34.58 0.013 33.86 0.012 28.84 0.009 28.65 0.009 34.34 0.009 31.84 0.008 27.87 0.008  01AT-10-1 01AT-10-2 AT04-6B AT03-44-23 AT03-21-PCb AT03-21-Ma AT03-21-PFc AT03-44-14 AT03-20-PEla AT03-20-PDla AT03-44-36 AT03-44-5 AT03-44-15 AT03-44-37 AT04-20F AT03-20-ij2b AT03-44-1 AT03-20-CD2d AT03-20-ij3c 01AT-6-1 01AT-5-2 AT03-44-9 01AT-5-4 01AT-4-1  2  Al 0 2  3  FejOj  MRO C a O  MnO  0.14 7.99 0.098 0.09 8.08 0.105 0.40 7.96 0.113 0.12 7.67 0.093 0.84 8.04 0.056 0.73 8.13 0.112 0.68 8.05 0.106 0.69 7.96 0.104 0.95 8.03 0.099 0.87 8.22 0.115 0.96 7.67 0.105 0.55 7.81 0.091 0.08 7.29 0.088 1.06 8.41 0.115 0.10 7.06 0.090 0.05 6.64 0.086 0.89 7.32 0.066 0.18 7.46 0.105 0.89 6.92 0.107 0.87 6.82 0.115 0.24 4.80 0.071 0.07 5.69 0.065 0.32 6.48 0.111 0.07 5.76 0.066 0.14 6.78 0.113  38.61 0.02 43.25 0.06 40.39 0.37 41.93 0.02 38.87 0.26 40.57 0.80 40.48 0.80 40.01 0.63 37.18 1.18 40.27 0.74 38.57 0.90 39.41 0.37 39.04 0.03 39.22 0.81 42.51 0.04 36.73 0.05 37.50 0.54 38.72 0.07 35.20 0.88 34.55 0.77 28.88 30.03 33.94 33.61 30.33  2.05 0.18 0.12 0.10 0.24  Na 0 2  K 0 P 0, Cr 0 2  2  2  3  Ni  V  Zn  LOI  :  Total  0.03 0.01 0.012 3617 2191 23 25 11.65 0.06 100.66 Proto Proto <d/l 0.01 0.010 4274 2637 19 31 13.50 0.15 100.77 Proto <d/l 0.01 0.009 4540 2315 31 33 13.14 0.26 100.38 0.10 0.01 0.008 4757 2529 26 6 13.99 0.38 100.73 Proto 0.08 0.01 0.008 4086 2344 36 14 12.13 0.49 100.87 Proto 0.05 0.01 0.008 3938' 230231 13 11.04 0.58 100.76 Srp-zone 0.06 0.01 0.007 3204 2320 33 8 11.63 0.68 100.72 Srp-zone 0.04 0.01 0.007 3283 2250 33 5 12.54 0.82 100.77 Srp-zone 0:06 0.01 0.008 3866 2208 38 11 12.24 0.89 100.78 Srp-zone 0.06 0.01 0.008 3789 2361 42 14 11.06 1.31 100.64 Srp-zone 0.06 0.01 0.008 3693 2144 40 10 13.95 2.29 100.79 Mgs-Zone 0.07 0.01 0.008 3815 2396 26 17 14.59 3.95 100.85 Mgs-Zone 0.04 0.01 0.007 3441 2240 14 16 18.90 9.91 100.81 Mgs-Zone 0.05 0.01 0.007 3793 2238 44 16 11.12 2.22 100.78 Mgs-Zone 0.05 0.01 0.007 4362 2602 12 9 13.09 3.7 100.69 Mgs-Zone 0.06 0.01 0.008 2254 2355 <d/l <d/l 26.42 24.72 100.66 Tic-Zone 0.02 0.01 0.008 3733 2201 35 12 15.05 4.67 100.24 Tic-Zone 0.05 0.01 0.007 3875 2130 21 22 20.34 11.9 100.86 Tic-Zone 0.06 0.01 0.007 3653 1960 33 16 21.18 15.88 100.41 Tic-Zone 0.02 0.01 0.007 3646 1944 39 13 22.53 18.65 100.13 Tic-Zone 0.03 0.03 0.006 3206 1793 14 28 34.63 35.17 100.09 Qtz-Zone 0.02 0.01 0.008 3359 1502 <d/l 17 34.99 35.20 100.21 Qtz-Zone 0.07 0.01 0.007 3232 1377 24 35 24.57 22.45 100.44 Qtz-Zone <d/l 0.01 0.011 3110 1760 <d/l 23 28.41 28.01 100.38 Qtz-Zone <d/l 0.01 0.008 3926 1956 15 21 34.09 34.34 100.18 Qtz-Zone  All data given in wt% oxide except C r 0 , N i , V and Zn which are reported in ppm. 2  CO  3  109  CHAPTER V aforementioned groups defined above.  The full table of analyses can be found in  Appendix C. Many analyses contain concentrations for certain elements that are reported as being below the detection limit reported by the laboratory. The mass balance calculations require a species abundance. Any element reported as below the detection limit defined by the laboratory is replaced with half the detection limit reported for that element. Furthermore, H2O was not directly measured.  It was determined by the difference  between L.O.I, and CO2. The variance in H2O is reported as the variance in L.O.I, defined by the 13 replicate analyses.  The accuracy of Na20, L.O.I, and CO2 differ  significantly between batches in the replicate analyses.  Because the suite of 160  geochemical analyses was collected over two years, the variance produced from all replicates is used in determining the standard error. 5.5 DIMENSIONAL ANALYSIS The geochemical data are represented in matrix form. The dimensionality of a geochemical matrix is a measure of the number of linearly independent processes, in geochemical space, that formed each group.  For example, the protolith group was  formed by melt extraction and serpentinization of peridotite then subsequently carbonated to form listwanite and likely metasomatized in the most extremely carbonated cases. Thus, one would expect.the dimensionality of the listwanite-altered samples to exceed that of the protolith group, and the quartz-zone group, with extensive quartz-carbonate veining, to be the highest. The rank (dimensionality) of a matrix is the minimum number of columns (or rows) that when combined in linear combinations can reproduce all other columns and rows in the matrix (e.g. Strang, 1993). These columns span the compositional space defined by the matrix and, if taken in vector form, define a basis for that matrix. Each of the five groups of samples is represented by matrix S of dimension e (rows) by s (columns), where e is equal to the number of elements E in the dataset and s is equal to the number of samples in each group.  110  CHAPTER V E  (E  fa  \ ,  S =  \  Serr -  F  The standard errors of the analysed elements in the dataset define an e by 1 vector Serr. Because uncertainty exists in the analyses of each chemical constituent, there is the possibility that one or more approximations of S exist that has a lower dimensionality and falls within standard error of the original matrix S. Three techniques useful in reducing a matrix within standard error constraints are outlined below. Sapprox matrixes are found using singular value decomposition (svd) (e.g. Strang, 1993) where the smallest singular values are changed to O's while satisfying:  J5  (e s)  -Sapprox  {e  | < Serr  j}  for all e and s  (e)  (5.3)  As illustrated in Figure 5.3a, this 'unweighted' technique is limited in its ability to find a Sapprox that satisfies (5.3) when attempting the reduction of a hypothetical two dimensional system to a rank of one.  The unweighted svd solution only considers  variations in S that are perpendicular to the model line. In the unweighted solution, Approx falls outside the error ellipses (crosses in Fig. 5.3a) for one sample, even though the error ellipse intersects the solution space (indicated by the thick black line connecting the crosses in Fig. 5.3a). This can be rectified by using a weighted svd technique where S is weighted by the inverse of the square root of the covariance matrix cov , defined by the 13 blind err  replicate analyses (5.4). The diagonals of cov  err  contain the square of the variance for  each element. In the Atlin geochemical datasets the standard error is the greater of the variance and detection limit for each element (Table 5.1), therefore the diagonal values of the cov must be replaced with square of the standard error. en  Ill  b)  a) 10  Weighted and Unweighted SVD Fits  25  o Matrix S Approximation of Matrix S (Unweighted) * Approximation of Matrix 5 (Weighted)  .20  SVD Fit in Weighted Space  o Matrix S (Weighted) * Approximation of Matrix S (Weighted)  QJ >- 6 c  •15 c  01  10  4  5  Element X  6  10  10  15  20  30  Element X (Weighted)  Figure 5.3: a) Actual SVD solutions to a hypothetical two dimensional dataset using both weighted and unweighted SVD where the data is weighted by the inverse of the standard errors, b) Illustrated weighted SVD in weighted space.  CHAPTER V .err (E\,Ee)  ,err (E\,E2)  COV,  e)r  = yjcov^,  (5.4)  err  (V w/w/  ,err (E2,Ee)  (E2,E\)  c o v  -) '  (5.5,6)  S = unwt • S ", e  err  w  Sapprox = unwt • Sapprox™ err  (5.7,8,9)  The weighted svd technique finds a Sapprox that is one dimensional and falls within the error ellipses of all three samples (stars in Fig. 5.3a). Rank reduction with weighted and unweighted svd on the geochemical data from Atlin is summarized in Tables 5.3 and 5.4.  The original rank of the matrix is 16,  reflecting the number of rows (number of chemical species analysed).' The degree of rank reduction depends on the size of the error ellipses represented in Tables 5.3 and 5.4 as the number of standard errors. Tables 5.3 and 5.4 show the lowest rank each group could be reduced to within multiples of the O" values using unweighted and weighted data. The rank of S may be further reduced if iterative techniques are used to fully explore the chemical space enclosed within the error ellipses. Figure 5.4a (iteration 1) illustrates another two dimensional hypothetical data set where the weighted svd technique fails to produce an Sapprox that is within the defined error. However Sapprox matrices do exist that satisfy (5.3). To find a solution within error, the original values from S are substituted back into Sapprox for all entries that fail criterion (5.3). The modified Sapprox is denoted Sapprox*. Performing weighted svd on Sapprox* produces a new Sapprox which is an approximation of Sapprox*. This iteration effectively 'pulls' Sapprox towards the sample(s) which did not satisfy (5.3) in the previous iteration. After four iterations on this hypothetical two dimensional dataset, the solution in Figure 5.4a (solid black line) is acquired.  113  CHAPTER V  Table 5.3: Lowest rank of each group using unweighted SVD 1a  Proto  Srp-zone  Mgs-zone  Tic-zone  Qtz-zone  16  -  16  16  16  16  16  16  16  15  15*  16  15  15*  16  14  15*  15  14  15*  2a  15  3a  15  4a  15  5a  15  6a  14  19 44 42 9 46 n * contains o n e or more negative v a l u e s within the approximation of the dataset. S V D not done on S r p - z o n e b e c a u s e of the s m a l l number of a n a l y s e s .  Table 5.4: Lowest rank of each group using weighted SVD Tic-zone  Qtz-zone  16  16  15*  15  14*  14*  14  12  13*  14  11  13*  14  11  13*  11  11  11*  Proto  Srp-zone  Mgs-zone  1a  16  2a  14*  -  3a  10  4a  10  5a  9  6a  9  44 . 19 42 9 46 n * contains o n e or more negative v a l u e s within the approximation of the dataset. S V D not done on S r p - z o n e b e c a u s e of the s m a l l number of a n a l y s e s .  114  CHAPTER V  Weighted Iterative SVD fits without covariance in X and Y  1  2  3  4  5  6  2  7  3  4  5  6  7  Element X (Moles/Kg)  Element X (Moles/Kg)  Figure 5.4: SVD solutions to a hypothetical two dimensional dataset using an iterative technique with data weighted by the inverse of the standard error. Two cases are shown, a) shows a situation where there is no covariance between the errors of X and Y . b) shows a situation where covariance does exist in the errors of X and Y . Acceptable solution is found after three iterations. The sample data is in Appendix A.  115  CHAPTER V This procedure was scaled up to the real 16 dimensional datasets defined from Atlin. The iterative technique applies the additional constraint that all values of Sapprox be>0.  Sapprox^ ^>0 for all e and s  (5.10)  Each dataset is initially reduced to a rank of R = 1 using the weighted data. If Sapprox fails inequality (5.3) for any element(s) in a sample then the original data from S are substituted back into Sapprox to create Sapprox*. The iterative process is repeated until an Sapprox matrix is found that satisfies (5.3), or a specified number of iterations have been completed. It was found, by trial and error, that 250 iterations was adequate for this study as no difference in rank was produced between this number and 1000 iterations. If no satisfactory Sapprox matrix is found, then R is increased by 1 and the process is continued. R is increased in this manner until an Sapprox is found that satisfies (5.3) or R=e in which case the dataset could not be reduced in rank. Table 5.5 shows the lowest rank found for each of the four metamorphic zones and their protolith using this technique for various multiples of O". In general, the results of the two weighted rank reduction techniques are consistent with the hypothesis that additional processes have affected listwanite-altered samples in addition to those responsible for the development of the heterogeneous protolith. The compositional space required by the protolith sample suite has a lower dimension than that required by the altered rocks. The quartz-zone altered samples have the largest dimensionality. In the magnesite and talc zones, the additional processes most likely include CO2 addition and H 0 removal. Dolomite veins, common in weakly 2  carbonated samples and often difficult to remove prior to powdering of samples, result in Ca addition and thus is also a possible process. The-quartz zone group of samples is the highest.in rank despite the fact that it contains the smallest number of samples. They display significant evidence for metasomatism which includes quartz-carbonate veining (Mg, Si +/- Ca addition/removal) and Cr-muscovite formation (K addition).  This  apparent chemical mobility is assessed with mass balance calculations on the unmodified  116  CHAPTER V  Table 5.5: Lowest rank of each group using iterative weighted SVD Proto  Srp-zone  Mgs-zone  Tic-zone  Qtz-zone  1a  16  16  16  15  2a  13  13  12  13  3a  11  12  11  13  4a  10  11  11  12  5a  9  11  11  11  6a  9  11  10  11  n  46  42  44  19  9  S V D not d o n e o n S r p - z o n e b e c a u s e of the small number of a n a l y s e s .  117  CHAPTER V full rank datasets and on the 3a approximation results for unweighted, weighted and weighted iterative svd (Table 5.6).  5.6 MASS B A L A N C E The chemical differences, or alteration, between the protolith group and each altered sample can be assessed using least squared linear algebraic manipulations. A least squares change of basis (Strang, 1993) is the heart of the mass balance calculation and is outlined as follows.  The change of basis calculation uses a system of linear  equations. The column basis for the protolith group is represented as the matrix P.  , \ '(1,0  i  P =  (5.11)  The subscript z represents the number of basis vectors in P. The composition of each altered sample (n) is designated Alt , a 1 by e vector listing moles element per Kg rock. (n)  Thus,  x =Alt \P {n)  (5.12)  (n)  where the 'V symbol gives the least squares solution to  = Alt ,  P-X(„j  (n)  and provides the  vector X( ), containing the coefficients Co that when multiplied with P gives a 'best fit' to n  Alt „). (  This 'best fit' is the model protolith MP that is made up of a linear combination of  the basis vectors of P. In other words  P-x =MP *Alt (n)  in)  w  '  (5.13)  One advantage of this approach is that it identifies a unique protolith composition for each altered sample. The protolith is chosen from the chemical space defined by the basis vectors to all protolith samples and is chosen so as to minimise the misfit between  118  CHAPTER V  Table 5.6: Lowest rank of each group using each SVD technique at 3o Full Rank Unweighted Weighted Weighted iterative  Proto  Srp-zone  16 15 10 11 46  -  Mgs-zone Tic-zone  16 16 14 12 42  16 15 12 11 44  Qtz-zone  16 15* 13* 13 19  9 n * contains one or more negative values within the approximation of the dataset  119  CHAPTER V the protolith and altered sample. This approach therefore minimises the amount of alteration. Differences between MP(„) and Alt(„) indicate that the altered sample falls outside the chemical space defined by P. The mineralogical changes during alteration require significant mobility in elements H and C. These two elements were therefore removed from the mass balance calculation to eliminate their influence on the linear least-squares fit. This allows for a more reliable test of the passive dilution hypothesis in that it is now easier to detect changes of non-volatile elements with respect to each other. Thus, e = 14 and z < 14. Data was rank reduced to within 3a. Model protoliths for altered samples are compared to altered rock compositions in Figure 5.5a. Each altered sample is represented as a column of boxes, and samples from each group are arranged from left to right on the basis of increasing C 0 content. The vertical dimension corresponds to the elements. 2  Grey-filled boxes indicate that the elemental abundance in the model protolith and altered sample differ by less than 3a. White boxes denote elements for which the abundance in the altered sample abundance exceeds that of the model protolith by more than 3a. Black boxes denote those elements where a deficiency of more than 3 a in the altered rock relative to the model protolith exists. Geochemical (Fig. 5.2) and petrographical evidence exists for the metasomatism in the most extreme carbonated samples. These include, high density quartz-carbonate veining (Si and Mg metasomatism) and the presence of Cr-muscovite (K metasomatism). However, the change of basis calculation did not detect these elemental alterations (Fig. 5.5). Rather, the most abundant rock-forming elements, such as Mg and Si, display an excellent fit throughout the entire suite of altered samples even though outliers, shown as dashed circles in Figure 5.2, exist. The misfit was forced into the least abundant elements such as Zn and V . This indicates that the geochemical space approach to this point can only detect if altered samples fall outside the sub-space defined by P. Two reasons exist for this. One is because to this point there have been no constraints placed on the protolith aside from forcing it to be contained within the sub-space defined by P. The second reason is because the most abundant elements have the most control on the fit of MP to Alt. Figure 5.5b shows an Mg vs. Si plot for the calculated model protolith MP. It  120  b)  Al Fe Mn Mg  Cn N  a  K  P Cr  o Protolith Samples + Altered Samples o Model Protolith Data  N i  V  Zn 3 3a >  Figure 5.5 : a)  >-3a  <. -3a  4 5 Si (Moles/Kg)  Residual over standard error calculated using Matlab left division on data reduced in rank to 3a. b) M g vs. Si plot  o  illustrating that MP mimics the actual data of the altered samples because there are no constraints placed on the chemical make-up  >  of MP.  —i <  CHAPTER V illustrates that these two elements almost perfectly mimic the original data of all altered samples. To limit the model protoliths to lie within the bounds of the protolith variations, the system of equations were solved with additional linear constraints. Each element in MP was constrained to fall within a set chemical range defined by the 46 protolith samples. The upper and lower limits (ul and // respectively) of each element define two 1 by e vectors termed pu and pi, respectively.  (11 } E\  U  pl=  Jhe  , thus pi < MP < pu for all e  and pu =  (5.14)  J  Here the minima and maxima of each element within the 46 protolith samples were chosen to define pi and pu, respectively, rather than a mean +/- one standard deviation. Sampling bias, caused by sampling a significant portion of protolith samples from a relatively small area of the project area, skews the averages of each element. A range defined by minima and maxima avoids this problem by allowing MP to be constrained within a protolith geochemical range known to exist. The new system of equations with the additional linear constraints was solved using the medium scale optimisation option of the Matlab function lsqlin (Coleman et al, 1999). This function employs an active set method similar to that described in Gill et al. (1981). The system of equations  A-x = b  (5.15)  is solved in a least squares sense forcing the optional inequality  Cx<d  and optional equality  122  (5.1.6)  CHAPTER V (5.17)  Aeq • x = beq  (5.14) and (5.15) are setup in the following way (modified and simplified from Gordon (2003).  l  (n)  2  Co„  ^  r  f -p  C  p  ,  (5.18, 19)  o)  b = (0  A = (-P\Alt ),  d = (-Pi) [pu J  (n)  (5.20,21,22)  X  V  Co  m  K fn  J  m  Note that (5.15) set up with (5.18) and (5.19) is simply a rearranged form of (5.8) with the addition of the mass factor term mf in X(„). If (5.23) is satisfied, mf represents the calculated gain in mass of the altered sample. (5.23)  C o , + Co + • • • + Co = 1 2  z  Equation (5.23) forces the protolith or starting martial to add up to 1 (i.e. 1 Kg of starting material), and is satisfied by equality (5.17) where:  Aeq = 1 and beq - (l,  ••• l  z  0)  (5.24)  Thus, one Kg of protolith material forms m/Kg of rock following alteration. Figure 5.6 shows where the residual between MP and Alt exceeds 3a, following the calculations (5.15) to (5.24) on the original, full rank data (results for the rank reduced data are shown below). Generally the data fit the model well. In addition, the resultant mf for each sample is in agreement with the range of mass factors calculated from whole rock data assuming a passive dilution hypothesis (Fig. 5.7a). The range in mass factors for an altered sample is the minimum and maximum of the sum of the non123  CHAPTER V  Si Ti Al  Fe Mn Mg Ca Na K  P Cr Ni V  Zn agnesite-Zone  Talc-Zone  T  3a > | | > -3cj  ] > 3a  Quartz-Zone  | < -3a  Figure 5.6: Ratio of residual error to standard error in whole rock chemical composition of carbonated samples. compositions  predicted  Residual error is the difference between model protolith by  reactions  equations  (5.15)  to  (5.24)  and  measured  compositions of altered samples. Values of the ratio that exceed three standard errors (positive/negative) indicate an excess/deficiency of the species that cannot be accounted for by the given protolith range in composition and the passive dilution hypothesis.  124  1.6  | Calculated Range in mf from Geochemistry 0 Model Calculated mf  1.4  O  1.3  rc 1.2  1.1 o  0.9  10  o  15  • Protolith Samples + Altered Samples o Model Protolith Data  20 25 C 0 (Wt%)  30  35  40  2  45  Si (Moles/Kg)  Figure 5.7: a) G a i n in mass vs. CO2 content. C i r c l e s represent model calculated mfs w h i c h are in good agreement w i t h the range calculated from the total dry renormalized geochemistry assuming the passive d i l u t i o n hypothesis, the altered samples, protolith samples and calculated  MPs.  b) M g vs. S i diagram s h o w i n g  CHAPTER V volatile component, in wt%, of the 45 protolith samples divided by the same in the altered sample. Problems become evident when one element from MP is plotted verses another (Fig. 5.7b). The model protolith compositions span the rectangular bounds defined by (5.14) and are not restricted to ellipses defined by covariances between elements in the protolith group. This covariance is shown as the ellipse centred on the median of the two elements in Figure 5.7b. This can be partially rectified by adding an additional constraint to inequality (5.16). The addition is similar to (5.20) and (5.21) but instead uses data weighted by the inverse of the square root of the covariance matrix cov defined by the protolith group of samples proto.  (n  p  m  '" \  V°(£l)  -pr"'" <E2,El)  u  covproto  proto  nP"»"  j  °(/•!,/• 2) (r:P ""\ \ (E2) ) n  (E\,Ee) proto  2  '(E2.Ee)  U  (5.25,26)  ™tpro,o=(^ov y prolo  \  "(Ee,E\)  «r)  °(/Te,£2)  2  (5.26, 27)  , thus pl jr < MP:;'"" < pu T" for all e p  &P<"'" =  pi :r = p  p  w  (5.28)  uF'  IF'  Equations (5.16) and (5.20) become  -P C  P p proto  -pi d=  pu  (5.31, 32)  jproto  ~*wt p  proto  proto  pu,wt  126  J  CHAPTER V and constrain elements within MP to simultaneously plot within the error boxes defined by the unweighted data, and within rhombohedra which roughly mimic the shapes of covariance ellipses. A, b, Aeq, beq and x remain unchanged.  5.7 RESULTS The results of the mass balance calculation using unmodified full-rank data sets and with the weighted constraints in place are shown in Figure 5.8 and 5.9. Figure 5.8a shows the model calculated mf as a function of the degree of carbonation (CO2 content) superimposed over the range in mass factors calculated from whole rock data. In general, there is a very good correlation between the two. Figure 5.8b shows the Mg/Si makeup of the protolith samples (boxes), altered samples (crosses) and model protoliths (circles). The model protoliths fall within the rectangular bounds defined by (5.14) and within the rhombohedra defined by (5.28). Figure 5.9 shows a) the residuals (model protoliths subtracted from the altered samples) that fall outside +/- 3a from the altered rocks and b) residuals that fall outside +/- 10a highlighting the more extensive alteration. A table of residuals is included in Appendix F. Positive and negative residuals (white and black boxes, respectively) indicate that the altered rock contains more (or less) of that element than permitted by the hypothesis. In general, the isochemical reaction model provides a very good fit to the data. Excluding the seven almost to completely-carbonated outliers, identified as samples with dashed circles in Figure 5.2, the 12 elements Si, Ti, A l , Fe, Mn, Mg, Ca, Na, K, P, Cr and V return a good to excellent fit, generally within +/- 3a (Fig. 5.9). Thus, the variation in the composition of these elements can almost exclusively be explained by the variability of the protolith rocks and the dilution effect during mass addition. Where deviation from a perfect fit is displayed, mainly in Zn and Ni, it is both positive and negative throughout the whole suite of alteration and produces no trends. Therefore it is most likely that these two elements were also immobile during the carbonate-alteration. The poor fit in these two elements could be due to inadequate characterization of the protolith. Another possibility is that the calculation forces more of the misfit into the least abundant elements which have the least control on the fit. This could explain the misfit in Zn.  127  1.6  T  r  Calculated Range in mffrom Geochemistry 1.5  0 Model Calculated mf  1.4  c r  O 1.3  u ra rc  1.2  •  • Protolith Samples + Altered Samples o Model Protolith Data 0.9  10  15  20  C 0  2  25  35  (Wt%)  40  45  3  4  5  Si (Moles/Kg)  Figure 5.8: a) Gain in mass vs. C O 2 content. Circles represent model calculated mfs which are in good agreement with the range calculated from the total dry renormalized geochemistry assuming the passive dilution hypothesis, b) M g vs. Si diagram showing the altered data, protolith data and calculated MPs.  ^ a^  ^ ^ ^ ^ ^ ^ ^ ^  9  3a>H>-3o  •  i 3a  •  •: -3a  10c>H>-10a  •  > 10a  |  s -10a  Figure 5.9: Ratio of residual error to standard error in whole rock chemical composition of carbonated samples. Residual error is the difference between model protolith compositions predicted by equations (5.15) to (5.32) and measured compositions of altered samples, a) Values of the ratio that exceed three standard errors (positive/negative) indicate an excess/deficiency o f the species that cannot be accounted for by the given protolith range in composition and the passive dilution hypothesis, b) Same as a) except it shows the more significant residuals that exceed 10 standard errors.  5 H pa  CHAPTER V Seven samples from the quartz-zone display widespread elemental mobility. High density veins are evident in hand sample and were difficult to remove prior to crushing of the sample for geochemical analysis. In terms of the most abundant rockforming elements, Figure 5.2 illustrates that only samples that are near completely- to completely-carbonated deviate from the passive dilution trend. The sporadic positive residuals in Ca can be attributed to a number of different reasons including: the inadequate removal of vein material prior to powdering of samples; inadequate characterization of the protolith (i.e. the abundance of clinopyroxene); and Ca addition during carbonation in the most highly carbonated samples. Though significant Ca addition has not convincingly been detected in this study, documented cases (e.g. Aydal, 1990) have clearly shown that Ca addition is important in some listwanite systems. Large positive residuals in K displayed in highly carbonated samples likewise are consistent with mineralogical observations. Bright green Cr-muscovite, a K-bearing mineral, is common in samples that have undergone extreme carbonate alteration and quartz-carbonate veining (Table B I , appendix B). Though K addition occurred during the most intense alteration, it was absent during most of the listwanite alteration. Figure 5.10 shows the results of the mass balance using the rank reduced datasets where the approximations of the original data was allowed to differ by as much as 3a from the original unmodified data. The results are almost identical to those acquired from the calculations on the unmodified data. One would except that the smaller amount of basis vectors in the rank reduced datasets would result in a poorer fit. However this is not the case. Likely the dimensionality removed during the rank reduction was negligible indicating that the true dimensionality is indeed less than 16. The use of data that is reduced in rank is of limited use in this approach of mass balance. Figure 5.5a illustrates that the dimensionality throughout most of the alteration is about the same. Quartz-carbonate veining and Cr-muscovite correspond well with the sudden increase in the misfit in the most extreme carbonate altered samples. Although numerical extraction of the differences in dimensionality between the groups is not yet possible, future mass balance techniques may be able to incorporate this information.  130  CHAPTER V b)  calculated by data reduced in rank by unweighted svd  si  I  calculated by data reduced in rank by weighted svd  Ti  Al  Fe  1  Mn Mg Ca Na K P Cr Ni v Zn -3o  calculated by data reduced in rank by weighted iterative svd Si  [];  !a  d)  I  o unweighted svd « weighted svd o weighted iterative svd  Ti AI Fe Mn Mg Ca Na K I'  Cr Ni  V Zn 15 -3o  |  20  25  30  35  «  C 0 (wt % oxide)  | a 3g  2  Figure 5.10: Ratio of residual error to standard error in whole rock chemical composition of carbonated samples.  Residual error is the difference between model protolith  compositions predicted by equations (5.15) to (5.32) and measured compositions of altered samples. Values of the ratio that exceed three standard errors (positive/negative) indicate an excess/deficiency of the species which cannot be accounted for by the given protolith range in composition and the passive dilution hypothesis,  a), b and c)  correspond to residuals calculated using data reduced in rank to 3a using the unweighted, weighted and weighted-iterative svd techniques,  d) shows the model calculated mass  factor as a function of C O 2 content of the rock superimposed over the range in mass factors calculated from the dry chemistry of the rocks. 131  CHAPTER V 5.8 IMPLICATIONS This geochemical mass balance approach has many advantages over other popular mass balance techniques. Possibly the most attractive is this technique calculates a model protolith, constrained to fall within a defined geochemical space, for each altered sample rather than assigning the same average protolith for all altered samples. Any difference between the altered rock and its calculated model protolith, assuming the protolith is chemically characterized adequately, is thus considered to represents alteration. The calculation is still based on a least-squares best fit.  For this reason,  significant alteration in major elements tends to cause misfit in those that are wellbehaved because the least squares calculation finds the solution that best fits all elements in the altered sample.  In other words, misfits in mobile elements are balanced by  introducing misfit in immobile elements. For this reason, this geochemical assessment procedure, as outlined beforehand, is best suited to test systems hypothesized to have involved little mobility in non-volatile chemical species, such as the listwanite rocks of this study. Ideally this technique should also constrain the ratio of each pair of elements (i.e. all possible pairs) in the model protolith to fall within the minimum and maximum ratios for the same pair in the protolith group of samples. This would confine model protoliths to fall within the two lines in Figure 5.7b which define the minimum and maximum ratio of Mg to Si in the protolith group. In theory this constraint is easy to comprehend and define mathematically (5.33); however it is very difficult to impossible using Isqlin.  for each element m. (5.33)  132  CHAPTER V 5.9 COMPARISON TO GRESENS' ANALYSIS In this section, the geochemical mass balance technique is compared to that of Gresens (1967), probably the most widely applied geochemical mass balance technique. However, instead of using a average protolith for all altered samples, the Gresens (1967) technique as applied here uses the model calculated protoliths on each altered sample calculated from the previous section (using the unaltered datasets). For all but the seven identified outlier samples, represented as dashed circles in Figure 5.2, Si and Mg are assumed to be immobile during the listwanite alteration. The elements used as baseline immobile elements for the seven outliers were chosen on a sample-by-sample basis. Here the two or three most abundant elements which show no residual in Figure 5.9a were used. Results, including the calculated mass factors, are shown in Figure 5.11 and are comparable to the results produced from the constrained weighted mass balance technique from the previous section. 5.10 CONCLUSION This chapter clearly illustrates, using a new and powerful geochemical space based approach to mass balance, that the listwanite alteration at Atlin primarily involved non-metasomatic (de)hydration/carbonation reactions.  The limited cases of clear  metasomatism, primarily Si, Mg and K, are backed up with hand sample evidence that includes extensive quartz-carbonate veining and Cr-muscovite generation or can be accounted for by the incomplete characterization of the protolith. One of the major advantages this technique has over other popular mass balance options is that it allows for a protolith, given an allowable geochemical space in which to reside, for each altered sample. Dimensional analysis by the reduction of the datasets in rank is consistent with the hypothesis that additional processes have affected listwanite altered samples in addition to those responsible for the development of the heterogeneous protolith. That is, protolith group has the lowest dimensionality while the quartz-zone has the highest.  133  a) Si Ti  Al Fe Mn Mg  Ca Na  K P  Cr Ni  V Zn 15  3a > gg > -3a  •  > 3a  | < -3a  20  25  30  C 0 (wt % Oxide) 2  Figure 5.11: a) Ratio of residual error to standard error in whole rock chemical composition of carbonated samples. Residual error is the that calculated using the method of Gresens (1967) assuming Si and Mg are immobile, for all but the identified outliers, and using the model calculated protolith for each altered sample. The most abundant elements, which do not show residuals in Figure 5.9a, are assumed immobile for the seven outliers, b) Gresens' analysis calculated mass factors superimposed on the range in mass factors calculated from the total dry geochemistry assuming the passive dilution hypothesis.  n  S  > H W  <  CHAPTER V 5.10 REFERENCES Ague, J. J. and Van Haren, J. L. M . , 1996, Assessing Metasomatic Mass and Volume Changes Using the Bootstrap, With Application to Deep-Crustal Hydrothermal Alteration of Marble: Economic Geology, v. 91, p. 1169-1182. Ash, C. H. and Arksey, R. L. (1990a): The Atlin Ultramafic Allochthon: Ophiolite Basement Within the Cache Creek Terrane; Tectonic and Metallogenic Significance (104N/12); Geological Fieldwork 1989, B.C. Department of Energy and Mines, Paper 1990-1, p. 365-374. Aydal, D. (1990): Gold-Bearing Listwaenites in the Arag Massif, Kastamonu, Turkey; Terra Nova, v. 2, p. 43-52. Gill, P.E., W. Murray, and M . H . Wright, Practical Optimization, Academic Press, London, UK, 1981. Coleman, T., Branch, M . and Grace, A . (1999): Optimization Toolbox: for Use with Matlab, Version 2. Gordon, T . M . (2003): Algebraic Generalization of the Graphical Gresen and Pearce Methods for Identification  of Geochemical Mass-Transfer Processes.  (abstract),  Vancouver 2003 Abstracts, CD-ROM, GAC-MAC-SEG, Vancouver 2003 Annual General Meeting, Vancouver, B.C., 28-146, ISSN 0701-8738, ISBN: 0-919216-86-2.  Grant, J. A . 1986: The Isocon Diagram - A Simple Solution to Gresens Equation for Metasomatic Alteration; Economic Geology, v. 81, p. 1976-1982.  Gresens, R. L. (1967): Composition-Volume Relationships of Metasomatism. Chemical Geology, 2, 47-65.  135  CHAPTER V Hansen, L.D., Dipple, G. M . , Kellett, D. A. and Gordon, T. M . (2005): Carbonate-Altered Serpentinite:  A Geologic Analog to Carbon Dioxide  Sequestration,  Canadian  Mineralogist, v. 43, part 1, p. 225-239. Hansen, L. D., Dipple, G. M . , Anderson, R. G. and Nakano, K . F. (2004): Geologic Setting of Carbonate Metasomatised Serpentinite (Listwanite) at Atlin, British Columbia: Implications for CO2 Sequestration and Lode-Gold Mineralization. In Current Research, Geological Survey of Canada, Paper 2004-A5, 12 pages.  Strang, G. (1993): Introduction to Linear Algebra. Wellesley-Cambridge Press.  136  CHAPTER VI CHAPTER VI: CONCLUSION  6.1: CONCLUSION The listwanite alteration within the Atlin Ultramafic Allochthon at Atlin B.C. is spatially controlled by a basal thrust fault (e.g. Ash, 1994; Hansen et al., 2004) and regional joint/fracture system with four steeply-dipping fracture sets spaced about 45° apart (Hansen et ah, 2004, Chapters II and III). The alteration proceeded via three subreactions fossilized as spatially distinct zones. The index minerals of magnesite, talc and quartz represent three metamorphic isograds defining the magnesite-, talc- and quartzzones (Hansen et al., 2005; Chapter IV). The major non-volatile chemical constituents remained unaltered during all but the most extreme cases of carbonate alteration where extensive quartz-carbonate veining (Si muscovite) and possibly C a  2+  2+  - Mg  2 +  metasomatism) and limited K (Cr+  metasomatism occurred (Chapter V). Each carbonation  reaction is controlled by the CO2 content within a CO2-H2O fluid. The isotopic ages of the nearby Fourth of July Batholith (FOJB) and the listwanite alteration are coeval (Ash, 2001; Mihalynuk et ah, 1992; Chapter IV) and likely related. The most depleted 8 C within magnesite is around -6%o which is consistent with an 13  organic signature and is supported by the presence of organic material within listwanite altered rocks. The large range in 5 O of between 6.3%o and 17.3%o suggests interaction ls  of the altering fluids with the pelagic sedimentary rocks of the Atlin Accretionary Complex (AAC). The only obvious nearby source of organic material is the pelagic units of the A A C . These results suggest large-scale hydrothermal circulation of fluids, driven by the FOJB, through the metasedimentary, metavolcanic and carbonate rocks of the A A C which mobilized and thermally matured organic material and scavenged carbonate which then infiltrated and altered the ultramafic rocks of the Atlin Ultramafic Allochthon. Anomalous gold values are associated with organic material and low 5 C values 13  (Chapter IV). The gold content of the three listwanite zones are at or above that for the parental serpentinite. These observations and analyses are consistent with gold having been scavenged from the underlying accretionary complex lithologies or derived from the contemporaneous and nearby FOJB rather than being scavenged from the ultramafic  137  CHAPTER VI rocks. Gold is associated with organic material which may have acted as a transporting agent. Although magnesite-zone alteration, the first reaction, only accounts for about 5 15 % of the total carbonation potential of serpentinite, it is spatially heterogeneously widespread and therefore may have sequestered a significant portion of the total bound CO2 within the Atlin listwanite system. Moreover, within intact bedrock, the progression of the talc-zone reaction generates fracture permeability, and appears to have locally enhanced reaction by generating a permeability wave in advance of it. The magnesiteand talc-zones combined, represent approximately half the carbonation potential for typical serpentinite rock and were produced with a small associated increase in the volume of solids. The quartz-zone, on the other hand, is limited to only the most highly carbonated areas and may be limited in extent due to the large associated gain in solid volume. The first two reaction steps therefore hold the most promise for in situ mineral carbonation as they limit porosity loss and potentially can generate permeability. Because the three carbonation reactions are controlled by the CO2 content of the fluid, industrial injection systems could be tailored to preferentially only drive the first two carbonation reactions. The listwanite is best developed along a regional joint and fracture system as well as a basal thrust fault (Chapter III), hence the Altin Ultramafic Allochthon had good potential for carbonation due to the structural preparation.  This suggests that the  potential of any ultramafic body for CO2 sequestration is directly linked to its original fracture permeability because without it the carbonation potential is limited regardless of the efficiency of the various CdVsequestering reactions. The next logical step in terms of advancing the in situ industrial mineral carbonation injection systems is to use the information gained in this study and incorporating it into a model. Cipolli et al. (2004) have modeled a serpentinite aquifer in Italy. Although their results are promising, they assume that serpentinite material is transformed directly to a chalcedony (a form of silica) and magnesite. This study clearly shows that the reaction of serpentinite is more likely to follow a sequence of reactions. The modification of the Cipolli et al. (2004) model to incorporate this information could potentially accelerate the carbonation rates high enough to an economically feasible. 138  CHAPTER VI 6.2 REFERENCES Ash, C. H . (1994): Origin and Tectonic Setting of Ophiolitic Ultramafic and Related Rocks in the Atlin Area, British Columbia (NTS 104N); B.C. Ministry of Energy, Mines and Petroleum Resources, Bulletin 94, 48 p. Ash, C. H . (2001): Relationship Between Ophiolites and Gold-Quartz Veins in the North American Cordillera; British Columbia Department of Energy, Mines and Petroleum Resources, Bulletin 108, 140 p. Cipolli, G., Gambardella, B., Marini, L., Ottonello, G. and Zuccolini, M . V. (2004): Geochemistry of High-pH Waters from Serpentinites of the Gruppo di Voltri (Genova, Italy) and Reaction Path Modeling of CO2 Sequestration in Serpentinite Aquifers. Applied Geochemistry, 19, 787-802. Hansen, L.D., Dipple, G. M . , Kellett, D. A . And Gordon, T. M . (2005): CarbonateAltered Serpentinite: A Geologic Analogue to Carbon Dioxide Sequestration, Canadian Mineralogist, v. 43, part 1, p. 225-239. Hansen, L . D., Dipple, G. M . , Anderson, R. G. and Nakano, K . F. (2004): Geologic Setting of Carbonate Metasomatised Serpentinite (Listwanite) at Atlin, British Columbia: Implications for CO2 Sequestration and Lode-Gold Mineralization. In Current Research, Geological Survey of Canada, Paper 2004-A5, 12 pages.  Mihalynuk, M . G , Smith, M . , Gabites, J. E., Runkle, D. and Lefebure, D. (1992): Age of Emplacement and Basement Character of the Cache Creek Terrane as Constrained by New Isotopic and Geochemical Data; Canadian Journal of Earth Sciences, 29, p. 24632477.  139  APPENDIX A  Appendix A : Miscellaneous Tables for Chapter IV and V  140  APPENDIX A Bulk geochemical samples were crushed using a jaw crusher and powdered in a tungsten carbide shatterbox.  Powders were sent to the Geochemical Laboratories at  McGill University, Montreal, PQ, for bulk geochemical analysis by X-ray fluorescence. The results are included in Table A l below. Samples were analyzed for major, minor and trace elements, C O 2 content by induction furnace, and total volatile content by loss on ignition (LOI).  The Standard errors used in any calculations in Chapter IV were  determined from 7 blind replicate analyses of sample AT03-20-PC2.  Table A1: Whole Rock Geochemical Data Ni  V  Zn  LOI  Total  co  2191 2196 2637  23 46  25  11.65 11.90  100.66 100.57  0.06  100.77 100.83  0.15  2315  31  31 28 33  13.50  2393  19 23  100.38  0.26  4648  2452  20  13.16  100.57  0.33  0.010  4012  2299  36  28 39  13.50  100.44  2.10  0.01  0.012  3778  50  36  12.10  100.78  2.57  0.01 0.02  0.02  0.012  17  36  2175  33  28  <d/l 0.02  0.01  0.010 0.011  14.10 14.04  18 12  25 7  14.53  100.60 100.02 100.34  3.37  0.01  4206 3412  2220 2789  39  15.35  100.47 100.72  4.60  32  12  100.69 100.81  7.19  31 38  16.70 17.64 17.84  100.59  9.60 17.26 21.83  MnO  MgO  CaO  Na 0  K 0  P 0  0.098 0.088  38.61 39.12  0.02  0.01  0.15  0.03 <d/l  0.012 0.010  3617 3154  0.105  43.25  0.06  «m  0.01  0.010  4274  8.230  0.090  0.01  7.960  0.113  0.02 0.37  0.01  0.400  40.78 40.39  <d/l  0.01  0.010 0.009  3254 4540  0.160  7.900  0.37  <d/l  0.01  0.010  1.080  6.800  0.099 0.085  41.95  39.32  0.010 0.012  38.81  0.11  0.06  0.01  01AT-11-1  37.38  0.013  1.110  9.150  0.167  39.78  0.44  0.01  01AT-1-9  38.62  0.082  39.62  0.03  38.80  0.270 0.910  7.120  01AT-7-3  0.011 0.017  7.210  01AT-6-3  38.01  0.012  0.340  7.030  0.140 0.074  36.69 39.77  1.61 0.06  01AT-1-8  38.05 35.79  0.011  0.140 0.920  6.580 8.580  0.070  40.01  0.139  39.10  0.06 0.04  0.150 1.050  0.083 0.110  38.88 36.01  0.09 0.97  01AT-11-2  35.58  0.011 0.014 0.011  8.100  01AT-1-6  35.88 36.62  0.220  7.450  38.29  0.46  01AT-9-2  0.009 0.022  0.070  0.23  01AT-5-4  31.84  0.008  1.090 0.070  7.110 6.800  37.90  01AT-7-1  30.63 33.85  0.121 0.095  01AT-1-5  25.86 27.87  0.010  0.860  0.008  01AT-6-1*  28.65 29.07  0.009 0.009  0  0.0939  0.0005  Sample  Si0  2  01AT-8-1  41.50  01AT-13-1 01AT-10-1  40.64 34.98  01AT-3-1  36.93  01AT-10-2  TI0  Al 0  2  2  3  0.012 0.014  0.140 1.190  0.010 0.010  0.090 0.230  37.29  0.010  01AT-2-2  36.21  01AT-9-1  01AT-13-2 01AT-1-7  01AT-4-1* 01AT-5-2  0.013  Fe 0 2  3  7.990 6.930 8.080  7.780  2  2  0.01  2  5  Cr 0 2  3  2522  21  13.94 13.14  0.10 0.21  3.40  0.01 0.01  0.010  0.03  0.010  2861 5138  2388 2389 2194  0.11 0.02 <d/l  0.02 0.02 0.01  0.009 0.009  4111 3375  2427 2214  20 37  0.009  3969  2004  29  <d/l 0.04  0.01 0.01  0.009  3216  23.80  3119  17 41  27  0.009  2250 2088  25  22.91  100.40 100.09  <d/l  0.01  0.011  1760  23  28.41  100.38  28.01  1938  <d/l 34  28  33.66  100.67  34.00  1956  15  34.09  100.18  34.34  <d/l 11  21 17  100.21  35.20  41  34.99 34.63  100.18  36.19  2  1  0.0537  0.103  33.85  5.760 7.210  0.066  33.61  0.88 0.10  0.088  31.46  0.90  0.05  0.05  0.008  3110 3185  0.140 0.070  6.780  0.113  0.24  <d/l  0.01  5.690  0.18  0.02  0.01  0.008 0.008  3926 3359  0.240  4.790  0.065 0.072  30.33 30.03 28.78  2.06  <d/l  0.03  0.007  3177  1502 1794  0.0107  0.0364  0.0009  0.109  0.0111  0.0438  0.0038  0.0007  95  4  14.98  Units in wt% except Cr 0 , Ni, V and Zn which are reported in ppm. *denotes samples which contain Cr-muscovite 2  2  3  0= standard deviation  141  4.00 7.12 9.54  0.0538  APPENDIX A  CN  CO  rj>  <0  o O)  o? ©  S  ID  m  if)  a 3 s ^ I ^ * 3 CO  U5  -  »-  9 9  rol  <D  CTJ  3 CO  T3 C  g  ro >  CD XI CO  T3 C  ro CD  9  9 9  9 9  c o  " 9 9 -  CO  •g to  CO  CO  CO  to  T-  00  o o ro  a: CN <  CO  CD C _C) CO B OT H < i i S S  142  v  «  i; =  s  C  APPENDIX A  T a b l e A 3 : Hypothetical data supporting F i g u r e s 5.2 a n d 5.3 1  2  3  4  X  Figure 5.2  2.0  7.0  8.0  -  Covariance Matrix 0.09  0.00  Y  3.0  4.3  8.0  -  0.00  0.80  X  1.0  4.0  7.0  9.2  0.09  0.00  Y  2.0  3.0  2.7  7.5  0.00  0.80  X  1.0  4.0  7.0  8.5  0.09  -0.23  Y  2.0  3.0  2.9  8.1  -0.23  0.80  Figure 5.3a  Figure 5.3b  143  APPENDIX A Table A 4 : Residual (moles/Kg) from mass balance using full rank data Ti  Al  Fe  Mn  Mg  Ca  Na  Cr  K  Zn  Ni  1 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  2  0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000 0.0000  0.0000  3  0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  4 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  5  0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  6  0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  7  0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  8 0.0000 0.0000  0.0000  0.0000  -0.0093  0.0000  0.0313  0.0000 0.0000 0.0000  0.0000  0.0027  0.0000  -0.0002  9 0.0000 0.0000  -0.0007  0.0000  -0.0119  0.0000  0.0490  0.0000 0.0000 0.0000  -0.0019  -0.0005  0.0000  -0.0002  10 0.0000 0.0000  0.0106  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  -0.0018  0.0000  -0.0001  11 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  12 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0004  0.0000  0.0000  13 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  14 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0012  0.0000  -0.0001  15 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  16 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  17 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0001  18 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000 0.0000  19 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0005  20 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  21 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000  22 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  23 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000 0.0000  24 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0001  25 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  26 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  27 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000 0.0000  28 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  -0.0003  29 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  30 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  -0.0001  31 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  32 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  -0.0002  33 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0063  0.0000  0.0003  34 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  35 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  36 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  -0.0001  37 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  38 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  39 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  -0.0014  0.0000  0.0000  0.0000  40 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  41 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000  42 0.0000 0.0000  0.0000  -0.0102  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0023  0.0000  -0.0001  43 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000 0.0000  44 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000 0.0000 0.0000  0.0000  0.0000  0.0000  -0.0002  45 0.0000 0.0000  0.0000  0.0000  0.0000  0.0000 0.0000 0.0000  0.0000  -0.0004  0.0000  0.0002  144  0.0049  0.0000  APPENDIX A Table A4: (cont.) Si  Ti  Al  Fe  Mn  Mg  Ca  Na  K  P  Cr  Ni  V  Zn  46  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0003  47  0.0000  0.0000  0.0000  -0.1407  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0019  0.0000  0.0000  48  0.0000  0.0000  0.0000  0.0000  0.0000  0:0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0001  49  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0002  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0002  50  0.0000  0.0000  51  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0013  0.0000  0.0000  52  0.0000  0.0000  0.0000  -0.0329  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0008  0.0000  0.0000  53  0.0000  0.0000  0.0000  0.0000  0.0014  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0017  0.0000  0.0000  54  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  55  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  56  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  57  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  58  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0003  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  59  0.0000  0.0000  0.0000  60  0.0000  0.0000  0.0000  -0.2178 -0.0021  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0051  0.0000  0.0000  61  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0001  62  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0015  0.0000  0.0002  63  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  -0.0014  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  -0.0006  0.0000  0.0000 0.0000  64  0.0000  0.0000  0.0000  65  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  66  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0029  0.0000  0.0000  67  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0075  0.0000  0.0000  0.0000  68  0.0000  0.0000  0.0000  0.0000  0.0014  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0014  0.0000  0.0000  69  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  -0.0002  70  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  71  0.0000  0.0000  0.0000  0.0000  -0.0008  0.0000  0.0000  0.0000  0.0000  0.0000  -0.0094 -0.0095  0.0000  0.0002  72  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  73  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  74  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  75  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0008  0.0000  0.0000  76  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  77  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  78  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  79  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  80  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  81  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  82  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  -0.0002  83  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0006  0.0000  0.0000  84  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  85  0.0000  0.0000  0.0000  86  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  87  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  -0.0002  88  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000. 0.0000  -0.0001  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  89  0.0000  145  0.0000  APPENDIX A  Table A4: (cont.) K  P  Cr  Ni  V  Si  Ti  Al  Fe  Mn  Mg  Ca  Na  90  0.0000  0.0000  -0.0036  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0002  Zn  91  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0007  92  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  -0.0069  0.0039  0.0000  0.0000  93  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0024  0.0000  0.0000  94  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  -0.0085  0.0000  0.0005  95  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  96  0.0000  0.0000  0.0000  0.0000  0.0110  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  -0.0075  0.0000  0.0000  97  0.0000  0.0000  -0.0006  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0008  0.0000  0.0000  98  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  99  0.0000  0.0000  0.0000  0.0000  0.0000 . 0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0013  0.0000  0.0000  100  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  -0.0019  0.0000  0.0003  101  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  102  1.1134  0.0000  0.0000  -0.1992  0.0210  -1.2388  1.1090  0.0000  0.0520  0.0000  -0.0006  -0.0076  0.0000  0.0006  103  -0.4236  0.0000  0.0000  0.0000  0.0000  0.2169  0.0000.  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  104  0.4140  0.0000  0.0123  -0.1373  0.0069  -0.3504  0.7551  0.0000  0:0730  0.0000  0.0000  -0.0066  0.0000  0.0006  105  0.0000  0.0000  0.0618  0.0593  -0.0051  0.0000  0.0000  0.0000  0.0102  0.0000  -0.0016  0.0008  0.0000  0.0001  106  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0022  0.0000  0.0000  107  0.0000  0.0000  0.0000  0.0000  -0.0007  0.0000  0.0000  0.0000  0.0053  0.0000  0.0000  0.0037  0.0000  0.0000  108  0.9357  0.0000  0.0000  -0.0093  0.0000  -0.7992  0.0000  0.0000  0.0312  0.0000  0.0000  -0.0078  0.0000  -0.0001  109  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  0.0000  -0.0037  0.0000  0.0001  110  0.0000  0.0000  -0.0126  0.1559  -0.0084  0.0000  0.0165  0.0000  0.0102  0.0000  0.0000  0.0031  0.0000  0.0000  111  0.0000  0.0000  -0.0144  -0.0139  -0.0066  0.0000  0.1659  00000  0.0053  00000  -0.0006  0.0064  0.0000  0.0004  112  -0.2459  0.0000  0.1012  0.1454  0.0000  0.1187  0.0733  0.0000  0.0451  0.0000  0.0127  0.0000  0.0000  0.0006  113  -1.2349  0.0016  0.0161  0.0000  -0.0053  0.4924  0.0000  0.0000  0.0046  0.0030  0.0000  0.0000  0.0000  0.0001  114  -1.6169  0.0000  0.0000  0.0000  0.0000  0.5806  0.0000  0.0000  0.0000  0.0000  -0.0049  -0.0011  0.0000  0.0001  146  APPENDIX B  Appendix B : Mineralogy  147  APPENDIX B  Table B1: Qualitative mineralogy of carbonated serpentinite from Atlin, BC Sample  Chr  Mgt  Opx  Brc  Ol  Atg  Liz  Mgs  Tic  Qtz  Dol  Cal  Chi x  C0  0.06 0.10 0.15  01AT-8-1  X  X  X  X  01AT-13-1  X  X  X  X  A,  X  X  X  A,  X  X  X  X  X  01AT-10-1 AT03-44-25 01AT-3-1 AT03-42  X  X  X  X  X  X  X  X  AT03-44-17  X  X  X  X  X  X  X  X  01AT-10-2 AT03-44-24 AT03-51C  X X X X  X  X  X X  AT04-21b AT03-44-30  X  X  X  X  AT04-3 01AT-2-2  X  X  X  X  X  AT04-9  X  X  X  AT04-6B AT04-11  X  X  X  X  AT03-20-PC2 AT03-44-26  X  X  X  X  AT03-44-34 AT03-20-PC3a  X  X  X  X  AT03-44-23  X  X  AT03-20-PC1a  X  X  AT03-21-PCb  X  X  AT04-13  X  X  AT04-16  X  X  AT03-20-PA1a AT03-21-PGb  X  X  X  X  X  X  X  X  X  x  X  X  X  A,  X  X  X  A,  X  X  A,  X  X  A,  X  X  X  A,  X  X  A,  X  X  X  X X X  A,  0.27 0.30 0.32 0.32 0.33 0.34 0.38 0.39 0.41  X  X  X  X  X  X  X  X  X  X  X  A,  X  X  X  A,  0.48 0.49  A,  x X  A, A,  0.44 0.44  X  X  A,  X  X  X  X  A,  0.53  X  X  X  X  X  A,  0.58  X  X  X  A,  0.59  X  X  X  X  A, A,  0.61 0.64  A,  0.64  A,  0.66  A,  0.68  A,  0.69  A,  X  X  X  X  X  X  X  X  X X  AT03-21-Ma AT03-21-PCa  X  X  X  X  X  X  X  X  X  X  X  X  X  AT03-44-35  X  X  X  AT03-20-PE3b AT03-21-PKb  X  X  X  X  X  AT04-23 AT03-21-PFb AT03-21-PGa  X  X  X  X  X X X X  X  X  X  X  X  X  X  X  A,  0.71 0.74  X  X  X  X  X  A,  0.74  A,  0.76 0.77 0.80  A,  0.80  A,  0.82  A,  0.83  X  X  A,  X  X  X  A,  X X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  A,  X  X  X  X  X  X  X  X  X  X  X  v  X  X  AT03-51E  *  X  X  AT03-21-PFC  0.26 0.27  X  X  X  0.22  A,  X  AT04-10  AT03-44-20  A,  A,  X  X X  A,  0.16 0.21 0.22  A,  x  2  A,  X  X  148  X X X X  APPENDIX B  Table B1 (continued): Mineralogy of carbonated se rpentinite from Atlin, BC Chr Mgt Opx Brc Ol Atg Liz Mgs Tic Qtz Dol Sample AT03-21-PFa  X  X  AT03-20-PE3A  X  X  AT03-21-PKa  X  X  AT03-44-14  X  X  X  X  X  X  X  X  X  X  X X  X  X  X  X  X  X  X  X  X  Cal  Chi  X  C0  2  A,  0.86  A,  0.87  A,  0.88  X  A,  0.89  X  X  A,  0.95  X  X  Ai  0.96  X  A,  1.11  A,  1.20  A,  1.31  AT03-20-PD2a  X  AT03-20-PA2b  X  X  AT04-4  X  X  AT03-44-21  X  X  X  X  X  AT03-20-PE1a  X  X  X  X  X  AT03-21-PHb  X  X  X  X  X  A,  1.31  AT03-20-PB3b  X  X  X  X  X  X  A,  1.77  AT03-20-PD1b  X  X  X  X  X  X  A,  1.85  AT03-44-16  X  X  X  X  AT03-44-22  X  X  AT03-44-13  X  X  AT03-20-PB2b  X  X  AT03-44-15  X  X  01AT-11-1  X  X  AT03-20-CD4d  X  X  AT03-44-3  X  X  AT03-20-CD4C  X  X  AT03-44-37  X  X  01 AT-13-2  X  X  AT03-51F  X  X  AT03-44-18  X  X  AT03-44-19  X  X  01AT-9-1  X  X  AT03-20-PD1a  X  X  AT03-21-EF1a  X  X  AT03-51D  X  X  X  X  X X  X  X  X X  X  A,  3.17  X  A,  3.17  X  X  X  X  X  Ri  0.40  X  X  •Ri  1.91  X  Ri  2.22  X  X  X  X  X  X  X  X  X  X  X  Ri  2.57  X  X  X  X  X  Ri  3.21  X  X  X  X  X  Ri  3.42  X  X  X  X  X  Ri  3.55  X  X  X  Ri  3.70  X  X  X  X  R, A  7.12  2  1.25  A  2  1.44  A  2  2.06  A  2  2.10  A  2  2.29  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  X  A  2  2.33  X  X  X  A  2  2.40  X  X  X  A  2  2.49  X  X  A  2  2.67  X  X  X  X  A  2  2.72  AT03-20-CD2a  X  X  AT03-20-PD3a  X  X  AT03-20-PD2b  X  X  AT03-20-IJ1a  X  X  X  X  X  X  X  A  2  2.80  AT03-20-IJ1b  X  X  X  X  X  X  X  A  2  2.97  AT03-21-EF1b  X  X  X  X  X  X  A  2  3.04  AT03-20-IJ1C  X  X  X  X  X  X  A  2  3.06  AT03-20-CD1a  X  X  X  X  X  X  A  2  3.17  X  X  X  X  X  A  2  3.20  A  2  3.37  AT03-20-IJ2e 01AT-1-9  X X  X  X X X  X  149  X  X  X  X  APPENDIX B Table B1 (continued): Mineralogy of carbonated serpentinite from Atlin, BC Chr Mgt Opx Brc Ol Atg Liz Mgs Tic Qtz Dol Sample  3.57  A  2  3.72  X  A  2  3.92 3.95  X  X  X  X  X  AT03-20-IJ2d  X  X  X  X  X  X  AT03-44-36 AT03-20-CD1C  X  2  2  X  X  co  Chi A  AT03-20-CD2b AT03-20-IJ2C  Cal  X  X  X  X  X  X  X  X  X  A  2  X  X  X  X  X  X  A  2  3.98  X  A  2  4.00  A  2  4.05  01AT-6-3  X  X  X  AT03-20-CD1b  X  X  X  X  X  AT03-20-IJ4d  X  X  X  X  X  AT03-44-29  X  X  X  01AT-1-8  X  X  X  X  AT03-51A  X  X  X  X  AT03-44-4  X  X  X  X X  A  2  4.11  X  A  2  4.37  X  A  2  4.60  X  A  2  6.11  X  A  2  6.54  A  2  6.60  X  X X  X  AT03-44-38  X  X  X  X  X  AT03-51b  X  X  X  X  X  A  2  6.74  AT03-44-2  X  X  X  X  X  A  2  9.86  X  X  X  A  2  9.91  X  A  2  10.94  AT03-44-5  X  AT03-44-39  X  X  X  AT03-21-EF1c  X  X  X  X  X  X  X  01AT-7-3  X  X  X  X  X  X  X  AT03-20-IJ4C  X  X  X  X  X  X  X  AT03-20-IJ4b  X  X  X  X  X  X  X  AT03-20-IJ2b  X  X  X  X  X  X  X  X  X  X  X  X  X  X  AT03-20-CD4b  X  AT03-20-CD2C  X  AT03-44-28  X  X  X  AT03-44-33  X  X  X  X  X  01AT-1-7  X  X  X  X  X  01AT-1-6  X  X  X  X  01AT-11-2  X  X  X  X  X  X X  R  2  1.97  R  2  3.40  R  2  3.91  X  R  2  4.11  X  R  2  4.67  R  2  5.21  R  2  5.91  R  2  6.34  R  2  6.45  R  2  7.19  R  2  9.54  R  2  9.60  X  X X  X X X  X  X  X  X  X  X  X  AT03-44-1  X  X  X  X  X  R  2  11.89  AT04-20D  X  X  X  X  X  R  2  12.54  AT03-21-EF2a  X  X  X  X  X  X  R  2  14.58  AT03-21-EF2f  X  X  X  X  X  R  2  14.83  AT03-44-27  X  X  X  R  2  15.20  AT03-20-IJ2a  X  X  R  2  15.60  AT03-20-CD2d  X  AT03-21-EF2b  X  X  X X  X  X  AT03-20-CD4a  X  X  X  X  150  X X  ?  ?  X  X  X X  X  X X  ?  X  X X  X  AT03-20-CD3b  01AT-9-2  ?  X X X  X  X  R  2  15.88  X  R  2  15.89  X  R  2  17.11  X  R  2  X  R  2  17.19 17.26  APPENDIX B Table B1 (continued): Mineralogy of carbonated serpentinite from Atlin, BC Chr Mgt Opx Brc Ol Atg Liz Mgs Tic Qtz Dol Sample AT04-20C  X  AT03-21-EF1d  X  X  AT03-20-CD3a  X  X  X  X  X  ?  Cal  co  Chi  2  R  2  17.27  X  X  X  X  X  X  R  2  17.77  X  X  X  R  2  17.78  R  2  17.86  AT03-44-10  X  X  X  X  AT03-20-IJ3a  X  X  X  X  X  R  2  18.08  AT03-21-EF1e  X  X  X  X  X  R  2  18.10  X  X  X  R  2  18.65  X  AT03-20-IJ3C  X  X  AT03-20-IJ3b  X  X  X  X  X  R  2  18.70  AT03-21-EF2e  X  X  ?  X  X  X  R  2  18.73  X  ?  X  X  X  R  2  19.05  X  X  X  R  2  19.22  X  X  X  R  2  19.40  X  X  X  R  2  19.43  2  19.69  AT03-21-EF1f  X  AT03-20-CD3C  X  X  ?  AT03-21-EF2c  X  X  ?  AT03-20-IJ4a  X  X  ?  X  X  AT03-20-CD3d  X  X  X  X  X  R  AT03-21-EF2d  X  X  X  X  X  R  2  19.85  X  X  X  R  2  21.60  X  X  X  R  2  24.49  A  AT03-44-6  X  X  AT03-44-40  X  X  AT04-20F  X  X  . X  01AT-7-1  X  X  X  X  X  X  ?  24.72  3  21.83  R  3  X  R  3  22.45 23.80  X  X  AT03-44-9  X  AT04-20J  X  X  X  X.  R  3  AT03-44-12  X  X  X  X  R  3  AT04-20N  X  X  X  X  R  3  AT04-20L  X  X  X  X  R  3  AT04-20I  X  X  X  X  R  3  X  X  X  R  3  R  3  R  3  30.79  R  3  32.04  R  3  R  3  R  3  3  X  X  x  y  01AT-5-4  X  AT04-20E  X  X  X  X  AT03-44-8*  X  X  X  X  AT04-20M  X  X  X  X  AT04-2*  X  X  X  X  X  01AT-1-5  X  X  X  X  X X  x  z  x  w  X  X  25.86 26.16 26.77 27.17 28.01 29.71  32.95 34.00 34.34  01AT-4-1*  X  X  X  X  AT04-20A  X  X  X  X  R  01AT-1-2*  X  X  X  A)  31.42  A  4  35.20  01AT-5-2  X  X  X  AT04-20B  X  X  X  01AT-6-1*  X  X  X  AT04-20K*  X  AT04-20H  X  01AT-5-3*  X  X  151  36.82  A4  35.50  X  A4  36.19  X  A  37.07  X  X  X  X  A4  40.40  X  X  A4  41.73  4  APPENDIX B Table B1 (continued): Mineralogy of carbonated serpentinite from Atlin, B C v  only occurs in small veins  w  occurs in small isolated patches  y  armored relicts & late mantling of chromite and pyrite  z  magnetite in late fractures & late mantling of chromite  ?  Masked in X R D by other p h a s e s  * sample contains Cr-muscovite C0  2  reported in wt%  152  APPENDIX C  Appendix C : Geochemical, Stable Isotope Analyses and Gold Assay Data  153  Table C1: Geochemical Analyses of Ultramafic Rocks Ti0 Al 0 Fe 0 Si0 Sample 2  01AT-10-1 01AT-10-2  01AT-11-1 01AT-11-2 01AT-1-2 01AT-13-1  01AT-13-2 01AT-1-5  01AT-1-6  01AT-1-7 01AT-1-8 01AT-1-9 01AT-2-2  01AT-3-1  01AT-4-1  01AT-5-2 cn fe  01AT-5-3 01AT-5-4 01AT-6-1  01AT-6-3 01AT-7-1  01AT-7-3 01AT-8-1 01AT-9-1 01AT-9-2 AT03-20-CD1A AT03-20-CD1B AT03-20-CD1C AT03-20-CD2A AT03-20-CD2B AT03-20-CD2C AT03-20-CD2D AT03-20-CD3A AT03-20-CD3B AT03-20-CD3C  34.98 37.29 37.38 35.58 36.75 40.64 35.79 25.86 36.62 35.88 38.05 38.62 36.21 36.93 27.87 28.65 18.33 31.84 28.84 38.01 33.85 38.80 4.1.50 39.13 30.58 38.34 37.28 38.17 39.43 38.72 37.32 34.58 34.23 34.85 33.59  2  0.010 0.010 0.013 0.011 0.010 0.014 0.013 0.010 0.014 0.011 0.011 0.011 0.010 0.010 0.008 0.009 0.007 0.008 0.009 0.012 0.022 0.017 0.012 0.013 0.009 0.013 0.012 0.013 0.012 0.013 0.011 0.013 0.011 0.012 0.012  2  3  0.09 0.40 1.11 0.22 0.68 1.19 0.92 0.86 1.05 0.15 0.14 0.27 0.16 0.23 0.14 0.07 0.14 0.07 0.24 0.34 1.09 0.91 0.14 1.06 0.05 0.55 0.63 0.73 0.91 0.95 0.92 0.89 0.91 0.86 0.80  2  3  8.08 7.96 9.15 7.45 5.27 6.93 8.58 7.21 7.78 8.10 6.58 7.12 7.90 8.23 6.78 5.69 5.63 5.76 4.80 7.03 6.80 7.21 7.99 6.79 7.06 7.76 7.69 7.61 7.33 7.36 7.82 6.92 6.83 6.78 6.76  MnO  MgO  CaO  0.105 0.113 0.167 0.121 0.072 0.088 0.139 0.088 0.110 0.083 0.070 0.082 0.099 0.090 0.113 0.065 0.084 0.066 0.071 0.074 0.103 0.140 0.098 0.085 0.097 0.091 0.099 0.093 0.074 0.074 0.068 0.107 0.111 0.106 0.116  43.25 40.39 39.78 38.29 26.24 39.12 39.10 31.46 36.01 38.88 40.01 39.62 41.95 40.78 30.33 30.03 35.10 33.61 28.88 39.77 33.85 36.69 38.61 38.57 37.77 39.23 38.51 38.67 37.74 37.68 36.88 35.20 34.53 34.51 34.48  0.06 0.37 0.44 0.46 0.28 0.15 0.04 0.90 0.97 0.09 0.06 0.03 0.37 0.02 0.24 0.18 0.18 0.10 2.05 0.06 0.88 1.61 0.02 0.11 0.23 0.50 0.76 0.75 0.91 1.01 0.66 0.88 1.10 1.09 1.42  Na 0 <d/l <d/l 2  0.01 <d/l <d/l <d/l  0.03 0.05 0.02 0.11 0.02 0.01 <d/l  0.01 <d/l  0.02 <d/l <d/l  0.03 <d/l  0.04 0.02 0.03 0.04 <d/l  0.05 0.07 0.04 0.09 0.04 0.09 0.06 0.08 0.06 0.08  K 0 2  0.01 0.01 0.01 0.01 0.13 0.01 0.01 0.05 0.02 0.02 0.01 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.03 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01  po 2  5  0.010 0.009 0.012 0.009 0.008 0.010 0.010 0.008 0.009 0.009 0.010 0.012 0.010 0.010 0.008 0.008 0.010 0.011 0.006 0.011 0.009 0.010 0.012 0.008 0.007 0.008 0.008 0.008 0.008 0.007 0.008 0.007 0.006 0.007 0.007  Cr O 2  s  4274 4540 3778 3969 2267 3154 5138 3185 3375 4111 2861 4206 4648 3254 3926 3359 2177 3110 3206 2522 3119 3412 3617 4071 3165 4115 3419 3657 3809 3838 3818 3653 3693 3372 3139  Ni  V  2637 2315 2220 2004 1294 2196 2194 1938 2214 2427 2389 2789 2452 2393 1956 1502 1807 1760 1793 2388 2088 2175 2191 2298 2237 2228 2175 2156 2120 2086 2078 1960 1919 1947 1908  19 31 50 29 23 46 32 34 37 20 12 17 20 23 15 <d/l  13 <d/l  14 18 41 33 23 36 16 31 39 39 34 41 41 33 42 35 36  LOI  31 33 36 38 14 21 39 28 31 12 7 36 28 28 21 17 16 23 28 25 25 28 25 20 9 9 11 12 13 16 21 16 14 10 8  13.50 13.14 12.10 17.84 30.72 11.90 15.35 33.66 17.64 16.70 14.98 14.10 13.16 13.94 34.09 34.99 40.48 28.41 34.63 14.53 22.91 14.04 11.65 13.67 23.95 13.68 14.63 14.25 13.42 14.12 15.87 21.18 21.93 21.45 22.83  co  2  0.15 0.26 2.57 9.60 31.42 0.10 7.12 34.00 9.54 7.19 4.60 3.37 0.33 0.21 34.34 35.20 41.73 28.01 35.17 4.00 21.83 3.40 0.06 1.73 16.44 3.17 4.05 3.98 2.49 3.57 5.91 15.88 17.78 17.11 19.22  Total  100.77 100.38 100.78 100.59 100.52 100.57 100.72 100.67 100.81 100.69 100.47 100.60 100.57 100.83 100.18 100.21 100.35 100.38 100.09 100.34 100.09 100.02 100.66 100.13 100.29 100.87 100.26 100.93 100.53 100.58 100.25 100.41 100.31 100.27 100.61  Table C1: Geochemical Analyses of Ultramafic Rocks (continued) MnO Fe 0 MgO Ti0 Al 0 Sample Si0 35.04 0.76 6.88 0.121 0.010 AT03-20-CD3D 33.19 7.77 0.112 35.74 0.012 0.78 31.93 AT03-20-CD4A 0.85 7.47 0.068 37.80 38.21 0.012 AT03-20-CD4B 0.88 7.84 0.092 38.55 37.84 0.012 AT03-20-CD4C 7.81 0.091 39.11 0.93 38.27 0.012 AT03-20-CD4D 0.84 7.82 0.094 38.73 38.15 0.012 AT03-20-ij1a 0.78 7.81 0.100 38.54 38.29 0.015 AT03-20-ij1b 0.107 38.64 0.72 7.68 38.20 0.013 AT03-20-ij1c 0.109 35.56 0.85 7.40 33.86 0.013 AT03-20-ij2a 7.32 0.066 37.50 0.012 0.89 AT03-20-ij2b 38.23 7.74 0.082 38.31 37.91 0.015 0.90 AT03-20-ij2c 0.095 38.37 0.012 0.89 7.68 37.75 AT03-20-ij2d 7.75 0.101 38.39 0.015 0.90 AT03-20-ij2e 37.98 0.87 6.85 0.112 34.92 34.06 0.013 AT03-20-ij3a 6.89 0.116 34.80 33.58 0.011 0.82 AT03-20-ij3b 0.87 6.82 0.115 34.55 33.86 0.012 AT03-20-ij3c 0.119 34.95 0.72 6.91 33.10 0.011 AT03-20-ij4a 7.10 0.056 37.67 0.012 0.97 39.09 AT03-20-ij4b 7.62 0.083 37.95 37.94 0.013 0.88 AT03-20-ij4c 0.012 0.97 7.78 0.091 38.00 37.07 AT03-20-ij4d 0.014 0.82 8.04 0.110 39.49 AT03-20-PA-1A .39.33 7.77 0.012 0.87 0.108 38.82 AT03-20-PA-2B 39.23 0.94 0.102 39.47 0.012 7.86 AT03-20-PB-2B 38.68 0.104 39.39 0.014 0.88 8.09 AT03-20-PB-3B , 38.85 0.71 8.09 0.109 40.23 AT03-20-PC-1A 38.52 0.012 8.16 0.109 40.42 0.012 0.73 AT03-20-PC-3A 38.51 0.105 38.57 0.013 0.96 7.67 AT03-20-PD-1A 37.96 0.97 7.65 0.100 38.69 38.22 0.016 AT03-20-PD-1B 0.108 38.48 0.84 7.72 39.21 0.013 AT03-20-PD-2A 0.113 38.66 0.90 7.61 37.89 0.012 AT03-20-PD-2B 0.93 7.28 0.112 38.48 37.96 0.013 AT03-20-PD-3A 0.87 8.22 0.115 40.27 AT03-20-PE-1A 0.015 38.65 8.02 0.116 39.89 1.02 AT03-20-PE-3A 39.33 0.015 0.121 39.38 1.18 7.85 AT03-20-PE-3B 40.03 0.015 0.60 7.81 0.098 39.59 AT03-21-EF1-A 37.90 0.011 2  cn  2  2  3  2  3  CaO 0.66 0.99 0.30 0.92 0.82 0.83 0.73 0.75 0.68 0.54 1.04 1.11 0.96 0.76 0.91 0.77 0.86 0.25 0.89 1.10 0.77 1.31 0.84 0.87 0.63 0.67 0.90 0.94 1.24 0.89 0.92 0.74 1.10 1.51 0.44  Na 0 0.05 0.08 0.05 0.06 0.07 0.03 <d/l 0.02 0.01 0.02 0.01 0.03 <d/l 0.03 <d/l 0.02 <d/l <d/l <d/l <d/l 0.03 0.05 0.04 0.09 0.08 0.08 0.06 0.06 0.06 0.07 0.06 0.06 0.05 0.06 0.04 2  K 0 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.01 0.02 0.01 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 2  po 2  5  0.007 0.007 0.007 0.008 0.008 0.008 0.008 0.008 0.006 0.008 0.008 0.008 0.008 0.007 0.007 0.007 0.006 0.008 0.008 0.008 0.007 0.008 0.008 0.008 0.008 0.007 0.008 0.008 0.007 0.008 0.009 0.008 0.008 0.008 0.007  Cr 0 2957 3191 3454 3656 3756 3374 3509 3552 3692 3733 3858 3544 3729 3403 3331 3646 3574 3934 3469 4363 3633 3968 4138 3637 3629 3512 3693 3735 3918 3829 3582 3789 4131 4307 3941 2  3  Ni 1965 1986 2162 2208 2186 2238 2197 2172 2006 2201 2198 2141 2168 1975 1986 1944 2023 2151 2148 2152 2252 2179 2210 2212 2271 2289 2144 2187 2142 2159 2123 2361 2280 2197 2247  V 32 34 36 40 38 35 39 34 36 35 35 40 38 34 33 39 31 38 39 40 39 41 41 43 35 32 40 36 40 31 34 42 43 52 28  Zn 7 13 15 12 12 6 10 9 13 12 15 12 14 10 10 13 15 15 11 18 7 13 15 9 11 10 10 13 11 15 12 14 15 15 12  LOI 23.09 22.74 15.25 13.22 13.02 13.56 13.60 13.83 21.21 15.05 14.21 14.15 13.81 22.22 22.64 22.53 23.51 14.73 14.50 14.45 11.58 12.10 11.98 11.84 11.86 11.57 13.95 13.52 12.47 13.97 14.20 11.06 10.58 10.04 13.68  co  2  19.69 17.19 5.21 3.55 3.21 2.80 2.97 3.06 15.60 4.67 3.92 3.72 3.20 18.08 18.70 18.65 19.43 4.11 3.91 4.11 0.64 0.96 1.91 1.77 0.53 0.48 2.29 1.85 0.95 2.72 2.67 1.31 0.87 0.74 2.33  Total 100.31 100.69 100.59 100.02 100.75 100.65 100.46 100.55 100.28 100.24 100.85 100.68 100.51 100.39 100.33 100.13 100.77 100.51 100.45 100.14 100.79 100.91 100.58 100.74 100.85 100.86 100.79 100.78 100.77 100.74 100.55 100.64 100.79 100.86 100.81  Table C1: Geochemical Analyses of Ultramafic Rocks (continued) Sample AT03-21-EF1-B  AT03-21-EF1-C AT03-21-EF1-D AT03-21-EF1-E AT03-21-EF1-F AT03-21-EF2-A  AT03-21-EF2-B AT03-21-EF2-C AT03-21-EF2-D AT03-21-EF2-E AT03-21-EF2-F  AT03-21-Ma AT03-21-PC-A AT03-21-PC-B  AT03-21-PF-A AT03-21-PF-B AT03-21-PF-C AT03-21-PG-A  AT03-21-PG-B AT03-21-PH-B AT03-21-PK-A AT03-21-PK-B AT03-42  AT03-44-1 AT03-44-10 AT03-44-12 AT03-44-13 AT03-44-14  AT03-44-15 AT03-44-16 AT03-44-17 AT03-44-18  AT03-44-19 AT03-44-2 AT03-44-20  Si0  2  37.81 40.97 32.81 33.68 32.96 36.06 30.59 33.31 32.89 33.56 35.73 38.33 38.61 38.67 38.13 37.98 38.21 38.57 38.10 37.99 37.85 37.71 41.49 33.30 36.07 31.28 39.68 40.40 39.35 37.84 39.03 38.67 39.36 34.54 39.28  Ti0  2  0.012 0.012 0.011 0.011 0.009 0.011 0.008 0.011 0.013 0.011 0.011 0.012 0.014 0.012 0.012 0.014 0.013 0.012 0.014 0.012 0.014 0.011 0.017 0.010 0.016 0.008 0.017 0.014 0.014 0.012 0.016 0.013 0.015 0.009 0.013  Al 0 2  3  0.59 0.68 0.54 0.48 0.47 0.47 0.48 0.53 0.52 0.53 0.70 0.68 0.72 0.73 0.71 0.69 0.69 0.77 0.71 0.69 0.72 0.76 1.12 0.18 0.81 0.11 1.28 0.95 1.06 0.88 1.11 0.98 1.13 0.10 1.16  Fe 0 2  3  7.75 6.48 7.12  6.89 6.97 6.73 7.67 6.82 6.82 6.80 6.69 8.05 7.92 8.13 7.75 7.72 7.96 7.81 8.15 7.54 8.17 8.26 8.54 7.46 6.90 7.06 8.26 8.03 8.41 7.70 8.86 8.57 8.28 7.20 8.72  MnO  0.102 0.057 0.120 0.112 0.104 0.094 0.095 0.101 0.104 0.101 0.091 0.106 0.106 0.112 0.109 0.104 0.104 0.103 0.110 0.098 0.108 0.103 0.122 0.105 0.054 0.193 0.142 0.099 0.115 0.079 0.107 0.085 0.115 0.092 0.165  MgO  39.49 37.58 35.95 35.55 35.88 35.63 37.53 35.64 35.62 35.70 35.33 40.48 40.58 40.57 39.76 39.81 40.01 39.80 40.27 39.50 39.46 39.72 41.89 38.72 34.38 34.26 38.80 37.18 39.22 37.63 38.75 37.98 39.13 38.50 40.27  CaO  0.55 0.64 0.45 0.52 0.38 0.42 0.92 0.36 0.41 0.53 0.58 0.80 0.69 0.80 0.57 0.44 0.63 0.76 0.53 0.83 0.60 0.52 1.24 0.07 0.09 0.16 1.09 1.18 0.81 1.98 0.16 1.08 0.88 0.10 0.60  Na 0 2  0.07 0.06 0.09 0.07 0.09 0.08 0.05 0.07 0.07 0.05 0.08 0.06 0.05 0.05 0.03 0.07 0.04 0.09 0.06 0.10 0.07 0.06 0.10 0.05 0.06 0.04 0.07 0.06 0.05 0.03 0.08 0.06 0.09 0.05 0.09  K 0 2  0.01 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.01 0.01 0.01 0.01 0.01  po 2  5  0.008 0.008 0.007 0.006 0.007 0.007 0.007 0.007 0.006 0.007 0.007 0.007 0.008 0.008 0.008 0.008 0.007 0.008 0.007 0.008 0.008 0.007 0.009 0.007 0.007 0.007 0.008 0.008 0.007 0.008 0.008 0.007 0.007 0.007 0.008  Cr 0 2  3  3749 3980 3549 3102 3109 3261 2303 4057 3389 3606 4963 3204 4589 3938 3124 3175 3283 3944 3426 3249 3851 4926 3449 3875 3185 3240 4312 3866 3793 3905 3921 3403 4011 3918 4052  Ni  V  Zn  LOI  2235 2306 1965 2028 2071 2265 1645 2101 2057 2169 2130 2320 2339 2302 2205 2240 2250 2222 2300 2227 2203 2263 2351 2130 2107 1528 2072 2208 2238 2324 2187 2253 2218 2365 2238  29 32 25 25 22 27 21 27 22 29 38 33 37 31 31 30 33 35 33 30 34 37 41 21 32 17 47 38 44 35 45 40 48 18 50  11 6 10 6 7 9 13 14 8 9 19 8 15 13 12 13 5 14 13 9 14 20 11 22 8 12 19 11 16 12 12 7 16 27 24  13.84 13.50 23.04 22.56 23.22 20.37 23.02 23.03 23.46 22.76 20.49 11.63 11.38 11.04 13.20 13.20 12.54 12.19 12.26 13.27 13.22 12.73 5.50 20.34 21.50 26.74 10.79 12.24 11.12 13.91 12.21 12.87 11.17 18.81 10.00  co  2  3.04 1.97 17.77 18.1 19.05 14.58 15.89 19.4 19.85 18.73 14.83 0.68 0.69 0.58 0.86 0.77 0.82 0.8 0.64 1.31 0.88 0.74 0.22 11.89 17.86 25.86 0.4 0.89 2.22 3.17 0.22 1.44 2.06 9.86 0.8  Total  100.83 100.64 100.70 100.41 100.62 100.44 100.78 100.51 100.47 100.64 100.43 100.72 100.79 100.76 100.83 100.59 100.77 100.74 100.80 100.60 100.84 100.62 100.62 100.86 100.43 100.35 100.79 100.78 100.78 100.72 100.96 100.90 100.82 100.05 100.95  Table C1: Geochemical Analyses of Ultramafic Rocks (continued) MgO Fe 0 MnO SiO Ti0 Al 0 Sample 1.05 8.99 0.138 39.03 AT03-44-21 38.98 0.015 1.00 7.50 0.068 37.56 37.88 0.014 AT03-44-22 0.84 8.04 0.056 38.87 AT03-44-23 39.91 0.014 9.29 0.105 39.10 0.98 AT03-44-24 39.33 0.014 9.64 0.105 39.29 1.06 AT03-44-25 39.35 0.014 8.49 0.138 40.10 AT03-44-26 39.96 0.016 1.11 33.79 0.010 0.29 7.53 0.144 36.59 AT03-44-27 7.04 0.110 38.48 37.54 0.009 0.33 AT03-44-28 0.32 6.39 0.087 39.83 AT03-44-29 38.40 0.011 7.34 . 0.099 40.92 0.12 38.33 0.011 AT03-44-3 8.12 0.120 39.29 0.90 AT03-44-30 40.20 0.013 4.80 0.070 40.73 37.51 0.009 0.06 AT03-44-33 1.06 9,14 0.139 40.02 39.15 0.016 AT03-44-34 8.4.1 0.132 39.70 1.06 AT03-44-35 39.32 0.015 0.55 7.81 0.091 39.41 AT03-44-36 37.30 0.013 0.10 7.06 0.090 42.51 AT03-44-37 37.02 0.011 6.80 0.086 38.98 37.48 0.011 0.40 AT03-44-38 6.45 0.102 40.54 33.11 0.009 0.07 AT03-44-39 0.32 7.73 0.068 37.72 AT03-44-4 36.77 0.011 29.41 0.08 6.10 0.060 37.03 AT03-44-40 0.009 7.29 0.088 39.04 34.74 0.009 - 0.08 AT03-44-5 30.04 0.008 0.03 6.38 0.111 37.29 AT03-44-6 3.80 0.177 23.11 34.94 0.012 0.76 AT03-44-8 0.32 6.48 0.1,11 33.94 AT03-44-9 34.34 0.009 35.13 0.008 0.09 8.16 0.099 39.77 AT03-51-A 5.34 0.115 40.99 35.45 0.009 0.10 AT03-51-B 0.10 8.34 0.118 44.04 37.02 0.010 AT03-51-C 0.42 7.86 0.102 40.06 AT03-51-D 37.39 0.010 7.55 0.103 38.97 39.26 0.013 1.03 AT03-51-E 0.77 7.32 0.090 39.25 39.23 0.013 AT03-51-F 0.013 0.75 8.03 0.108 40.22 38.71 AT03-PC2 8.24 0.111 39.62 0.92 38.73 0.012 AT04-10 38.80 0.013 0.69 7.89 0.082 39.34 AT04-11 40.97 0.018 0.98 8.66 0.132 38.43 AT04-13 38.42 0.017 0.96 7.86 0.105 39.61 AT04-16 z  2  2  3  2  3  CaO 0.60 2.12 0.26 0.05 0.03 1.13 0.30 0.17 0.07 0.30 0.99 0.03 0.20 1.48 0.37 0.04 0.03 0.04 0.29 0.07 0.03 0.09 5.93 0.12 0.18 0.03 0.03 0.11 0.40 0.05 0.85 1.10 0.09 1.96 0.73  Na 0 K O 0.06 0.01 0.01 0.06 0.08 0.01 0.06 0.01 0.01 0.05 0.05 0.01 0.06 0.01 0.06 0.01 0.04 0.01 0.07 0.01 0.10 0.01 0.07 0.01 0.02 0.06 0.01 0.07 0.07 0.01 0.05 0.01 0.01 0.06 0.01 0.04 0.04 0.08 0.06 0.01 0.04 0.01 0.05 0.01 0.07 0.19 0.07 , 0.01 0.02 0.01 0.01 0.08 0.01 0.05 0.09 0.01 0.01 0.07 0.06 0.01 <d/l 0.02 0.01 0.06 0.01 0.08 0.09 0.01 0.02 0.06 2  z  p o 0.009 0.008 0.008 0.008 0.008 0.007 0.007 0.008 0.008 0.008 0.007 0.008 0.008 0.007 0.008 0.007 0.008 0.007 0.008 0.007 0.007 0.006 0.006 0.007 0.009 0.008 0.007 0.008 0.008 0.009 0.007 0.008 0.009 0.008 0.008 2  5  Cr O 4112 3549 4086 3946 3815 4060 3432 3399 3553 3153 4019 3610 3848 3814 3815 4362 3668 3640 3480 3551 3441 3692 2497 3232 3565 4269 4275 3768 3779 4618 3827 3446 3337 3929 3754 2  s  Ni 2290 1981 2344 2378 2328 2246 2242 2272 2502 2509 2237 2713 2276 2237 2396 2602 2258 2496 2170 2186 2240 2176 1215 1377 2396 2543 2520 2281 2189 2324 2277 2177 2246 2226 2234  Total V Zn LOI co 48 16 11.20 1.2 100.73 41 8 '14.07 3.17 100.85 36 14 12.13 0.49 100.87 41 19 11.31 0.27 100.90 45 17 10.77 0.16 100.95 44 23 9.17 0.44 100.82 26 25 21.21 15.2 100.51 26 13 16.37 6.34 100.70 21 3 14.80 4.37 100.57 18 3 13.03 3.42 100.81 39 12 10.41 0.32 100.79 11 5 16.61 6.45 100.54 41 23 10.51 0.44 100.94 49 17 10.07 0.71 100.89 26 17 14.59 3.95 100.85 12 9 13.09 3.7 100.69 34 42 16.30 6.6 100.77 13 6 19.62 10.94 100.61 30 21 16.51 6.54 100.12 13 41 27.04 24.49 100.46 14 16 18.90 9.91 100.81 13 27 25.56 21.60 100.17 25 35 30.38 30.79 99.75 24 35 24.57 22.45 100.44 19 <d/l 16.68 6.11 100.75 20 13 17.55 6.74 100.37 15 7 10.41 0.27 100.82 29 11 14.14 2.4 100.81 39 12 12.76 0.83 100.78 30 20 13.20 1.25 100.70 34 13 11.12 0.41 100.41 38 16 11.32 0.66 100.70 39 29 12.97 0.39 100.54 8.93 0.59 100.81 45 9 34 13 12.42 0.61 100.81 2  Table C1: Geochemical Analyses of Ultramafic Rocks (continued) Sample AT04-2 AT04-20A AT04-20B AT04-20C AT04-20D AT04-20E AT04-20F AT04-20H AT04-20I AT04-20J AT04-20K AT04-20L AT04-20M AT04-20N AT04-21B AT04-23 AT04-4 AT04-6B AT04-9 AT04-3 d/l (ppm)  Si0  2  Ti0  2  Al 0 2  3  Fe 0 2  3  MnO  MgO  CaO  Na 0 2  K 0  p 0  2  2  5  Cr 0 2  3  Ni  V  Zn  LOI  co  2  Total  4.12 0.109 25.47 4.45 0.05 0.26 0.006 3037 1242 35 42 32.38 32.95 99.80 0.90 31.60 0.015 0.23 6.66 0.073 32.08 0.15 0.05 0.03 0.007 3530 2114 22 7 35.79 36.82 100.66 25.01 0.008 0.34 7.88 0.067 30.52 0.20 0.05 0.05 0.008 3785 1999 27 17 34.68 35.50 100.75 26.36 0.011 6.46 0.070 35.82 0.17 0.08 0.02 0.006 3553 2194 23 9 22.22 17.27 100.64 0.010 0.33 34.88 0.007 3789 2250 27 19 19,36 12.54 100.88 0.38 6.81 0.073 38.30 0.08 0.06 0.01 35.18 0.012 0.006 3586 2078 15 <d/l 30.47 29.71 100.66 0.14 6.29 0.118 34.78 0.09 0.08 0.01 28.10 0.009 0.008 2254 2355 <d/l <d/l 26.42 24.72 100.66 6.64 0.086 36.73 0.05 0.06 0.01 30.14 0.009 0.05 0.07 0.03 0.021 3489 1961 19 9 39.30 40.40 100.56 6.04 0.067 34.16 0.21 0.43 19.66 0.022 0.007 4342 2180 24 2 28.15 27.17 100.52 6.30 0.064 34.01 0.07 0.05 0.01 31.04 0.008 0.16 0.007 3828 2162 15 <d/l 25.67 23.80 100.44 0.09 6.95 0.077 34.83 0.04 0.07 0.01 32.09 0.010 7.22 0.117 31.02 0.92 0.06 0.16 0.008 4081 1851 38 41 36.88 37.07 100.36 0.79 22.57 0.009 0.006 3887 2066 12 3 28.36 26.77 100.55 6.74 0.091 34.97 0.10 0.06 0.01 0.10 29.51 0.008 0.007 4043 2088 12 5 32.77 32.04 100.60 0.09 5.91 0.079 35.96 0.06 0.03 0.01 25.06 0.008 0.007 3347 2157 12 2 27.46 26.16 100.48 0.04 7.34 0.084 34.25 0.05 0.05 0.01 30.63 0.008 0.008 4010 2226 36 18 12.71 0.30 100.48 7.96 0.110 39.72 0.02 0.05 0.01 0.74 38.51 0.013 0.007 3725 2283 27 11 14.27 0.76 100.80 0.36 7.93 0.107 39.85 0.34 0.05 0.01 37.26 0.011 0.009 3776 2254 51 12 12.35 1.11 100.82 1.05 8.51 0.108 38.26 0.73 0.09 0.01 39.08 0.014 0.008 4757 2529 26 6 13.99 0.38 100.73 7.67 0.093 41.93 0.02 0.10 0.01 0.12 36.05 0.012 0.008 4118 2610 18 8 14.83 0.34 100.80 0.10 7.45 0.095 43.10 0.03 0.04 0.01 34.45 0.011 0.007 4959 2695 16 14 12.09 0.32 100.81 0.12 7.59 0.091 44.56 0.09 0.04 0.01 35.43 0.013 0.01 0.01 3 10 2 15 0.006 0.004 0.012 0.003 0.003 0.0095 0.0015 0.0075 0.0025 0.0035 All geochemistry and the reported detection limits (d/l) are expressed in wt % oxide except Cr 0 , Ni, V, Zn which are reported in parts per million 2  3  Table C2: Geochemical Analyses of Replicates Sample  Si0  2  Ti0  2  Al 0 2  3  Fe 0 2  3  38.71 0.013 0.75 8.03 0.108 AT03-PC2 38.81 0.012 0.77 8.10 0.107 AT03-pc2 38.59 0.013 0.78 8.00 0.109 AT03-pc2" 38.78 0.013 0.78 8.06 0.108 38.57 0.013 0.76 8.04 0.107 AT03-pc2 AT03-pc2 38.68 0.012 0.77 8.10 0.109 AT03-pc2" 38.61 0.013 0.77 8.06 0.107 AT03-pc2 38.61 0.014 0.77 8.08 0.106 AT03-pc2 38.68 0.012. 0.77 8.03 0.107 AT03-pc2 38.68 0.013 0.77 8.04 0.108 AT03-pc2 38.81 0.013 0.77 8.01 0.109 AT03-pc2 38.75 0.012 0.77 8.08 0.111 AT03-pc2 38.69 0.015 0.79 8.02 0.110 0.0808 9E-04 0.01 0.033 0.001 d/l 0.006 0.004 0.012 0.003 0.003 0.0808 0.004 0.012 0.033 0.003 Std Error All chemical species are reported as wt% except Cr 0 AT03-pc2'  1  !  n  M  iM  iM  iH  lv  iv  iv  2  over a 14 month period.  Ni V Zn LOI co2 Total P O Cr 0 0.007 3827 2277 34 13 11.12 0.41 100.45 0.02 40.22 0.85 <d/l <d/l 0.01 0.006 3902 2289 34 13 11.12 0.41 100.85 40.45 0.84 0.83 0.01 0.01 0.007 4100 2282 35 13 11.14 0.45 100.25 40.12 0.06 0.01 0.008 3844 2288 33 13 11.22 0.51 100.86 40.35 0.85 0.007 3857 2286 38 16 11.21 0.52 100.47 0.01 40.25 0.82 0.06 0.07 0.007 3969 2280 34 13 11.23 0.52 100.69 0.01 40.23 0.84 0.07 0.01 0.008 3878 2283 34 13 11.24 0.53 100.53 40.19 0.83 0.04 0.01 0.007 4173 2265 38 14 11.19 0.58 100.61 40.28 0.85 0.05 0.01 0.008 3935 2274 37 14 11.22 0.57 100.36 40.02 0.83 0.007 3779 2271 35 12 11.22 0.56 100.51 0.05 0.01 40.15 0.85 0.02 0.007 3918 2283 39 13 11.24 0.59 100.73 40.21 0.84 0.08 0.008 3932 2274 38 14 11.21 0.61 100.71 40.24 0.83 0.06 0.01 0.09 0.01 0.007 3846 2268 39 13 11.25 0.57 100.66 40.20 0.86 0.1044 0.012 0.028 0.004 0.0006 109.93 7.655 2.2 1 0.045 0.07 0.01 0.01 3 10 2 15 0.0095 0.0015 0.0075 0.0025 0.0035 0.07 10 2 0.045 0.004 0.0035 109.93 7.655 0.1044 0.012 0.028 , Ni, V, Zn which are in ppm. i, ii, iii and iv denote replicates from four different times MgO  MnO  3  CaO  Na 0 2  K0 2  2  5  2  3  Talbe C3: Geochemical Analyses of Igneous Intrusions  Sample  AT03-04-A AT03-49 AT03-50 AT04-12 AT04-14 AT03-24 AT04-5 AT04-8B AT04-7B AT03-05-A AT04-25 AT03-28 d/l  Si0 49.47 49.78 43.79 49.19 50.83 52.82 51.22 38.39 49.65 62.57 61.16 66.23 0.006 2  Ti0 1.596 1.637 1.048 1.974 1.729 1.628 1.944 1.508 1.085 0.429 0.411 0.453 0.004 2  Al 0 2  3  14.33 14.44 10.63 13.71 14.48 14.83 13.92 10.79 13.01 15.39 15.09 14.96 0.012  Fe 0 2  3  12.50 12.88 7.75 14.31 13.24 12.44 13.91 9.35 7.83 3.35 3.16 3.82 0.003  K 0 P 0 MnO MgO CaO Na 0 0.24 0.164 8.34 4.52 0.200 6.56 0.16 0.144 0.195 6.20 10.44 3.20 8.49 2.84 0.450 0.132 11.14 0.93 0.179 9.71 3.81 0.53 0.231 6.19 0.160 5.22 4:05 0.59 0.220 7.81 8.39 4.84 0.26 0.172 0.195 4.11 0.17 0.171 5.22 8.42 4.10 0.236 13.61 2.16 2.43 1.307 0.149 9.51 2.92 2.54 0.432 0.138 7.72 8.92 1.87 0.291 0.063 2.50 3.75 4.61 2.34 0.289 0.062 2.79 3.66 3.87 0.187 4.11 3.20 3.10 0.081 1.65 0.003 0.0095 0.0015 0.0075 0.0025 0.0035 2  2  2  5  Cr 0 2  195 138 845 57 32 <d/l <d/l  518 446 53 57 42 15  3  Ni 45 36 138 23 9 <d/l  10 71 58 50 48 7 3  V 300 358 178 381 355 340 387 239 177 62 58 68 10  Zn 40 35 28 57 61 37 68 7 28 10 18 16 2  LOI 2.54 1.24 12.32 0.97 2.06 0.61 0.92 10.13 5.14 5.06 7.11 1.94 0.01  co  2  0.65 0.17 9.21 0.09 0.64 0.19 0.37 8.14 3.21 2.28 4.73 0.62 0.01  Total 100.52 100.37 99.64 100.86 100.43 100.33 100.28 99.42 99.46 99.90 99.96 99.74  Type A A A A A A A A B C C D  All chemical species are reported as wt% except C r 0 , Ni, V , Z n which are in ppm. 2  3  A = Diabase Dyke, B = Lamprophyre, C = Light-Grey Dacite and D = Grey-Brown Dacite  > tn O X O  APPENDIX C  Table C4: Gold Assay Results (cont.)  Table C4: Gold Assay Results SAMPLE  Au(ppm)  Zone  C0  2  (wt%)  <0.001 <0.001 <0.001 <0.001 0.014 0.003 0.002 0.001 <0.001 <0.001 0.003 <0.001  Proto  0.41  Proto Proto Proto Proto Proto Proto Proto Proto Proto Mgs Mgs  0.22 3.17 0.68 0.41 0.41 0.76 0.87 0.41 0.41  0.001 0.001 0.001  Mgs Mgs Mgs  AT03-44-19 AT03-51D AT03-20-IJ2d AT03-20-IJ1C  0.002 0.001 <0.001 <0.001 0.001  Mgs Mgs Mgs  AT03-21-EF2d AT03-20-CD3b  0.005 0.033  Talc  AT03-20-PC2a AT03-42 AT03-44-22 AT03-21Ma AT03-20-PC2b AT03-20-PC2C AT03-44-23 AT03-20-PE3a AT03-20-PC2d AT03-20-PC2e AT03-51A AT03-44-15 AT03-44-37 AT03-20-CD1b AT03-20-CD1c AT03-21-EF1b  Mgs Mgs Talc  SAMPLE  Au(ppm)  Zone  C Q (wt%)  AT03-20-IJ2a  Talc Talc  15.60  AT03-20-IJ3a AT03-44^0 AT03-20-IJ3b AT03^4-27 AT03-21-EF1d AT03-20-CD3C AT03-21-EF1e  0.002 0.030 0.001 0.027 <0.001 0.001 0.016 <0.001 <0.001 0.003 0.005 0.002 0.004 0.005  Talc Talc Talc Talc  0.002 <0.001  Qtz Qtz  35.50 35.20 25.86 35.50  AT04-20Ba GS2-B GS1-A  <0.001 0.008 0.180 0.182  Qtz Qtz GS GS  35.50 35.50 na na  GS3-C  0.230  GS  na  AT04-20Na 01AT7-1 01AT4-1 AT04-20i AT04-20BC 01AT5-2 AT03-44-12 AT04-20Bd AT04-20Bb  6.11 2.22 3.70 4.05 3.98 3.04 2.06 2.40 3.72 3.06 19.85 17.11  G S = gold standard (230 ppb)  161  Talc Talc Qtz Qtz Qtz Qtz Qtz Qtz  2  18.08 24.49 18.70 15.20 17.77 19.22 18.10 26.16 21.83 34.34 27.17  Table C5: Stable Isotope Analyses (cont.)  Table C5: Stable I  CD  ro  Number 01 AT 1-5 01 AT 4-1 01 AT 5-2 01AT-11-1 01AT-11-2 01AT-1-2 01AT-13-2 01AT-1-5 01AT-1-6 01AT-1-7 01AT-1-8 01AT-1-9 01AT-4-1 01AT-5-2 01AT-5-3 01AT-5-4 01AT-6-1 01AT-6-3 01AT-7-1 01AT-7-3 01AT-9-2 AT03-20-CD1A AT03-20-CD1B AT03-20-CD1C AT03-20-CD2A AT03-20-CD2B AT03-20-CD2C AT03-20-CD2D AT03-20-CD3A AT03-20-CD3B AT03-20-CD3C AT03-20-CD3D AT03-20-CD4A AT03-20-CD4B AT03-20-CD4C  """(VSMOW)  (VPDB)  C0  2  (wt%)  Zone  -4.43  9.44  34.00  Qtz  -4.63  10.13  34.34  Qtz  -4.07  10.57  35.20  Qtz  -2.30  11.78  2.57  Mgs  -5.44  10.70  9.60  Tic  -4.06  10.42  31.42  Qtz  -5.08  11.37  7.12  Tic  -4.58  9.69  34.00  Qtz  -5.97  10.94  9.54  Tic  -6.20  10.22  7.19  Tic  -4.47  13.21  4.60  Mgs  -5.50  14.19  3.37  Mgs  -4.97  10.07  34.34  Qtz  -4.13  9.15  35.20  Qtz  -2.24  8.15  41.73  Qtz  -5.08  11.16  28.01  Qtz  -4.32  13.97  36.19  Qtz  -6.40  6.27  4.00  Mgs  -4.39  17.25  21.83  Tic  -5.20  12.31  3.40  Mgs  ^.79  15.26  17.26  Tic  -2.51  13.07  3.17  Mgs  -2.26  13.45  4.05  Mgs  13.20  3.98  , Mgs  -3.64  12.26  2.49  Mgs  -3.88  12.97  3.57  Mgs  -3.68  13.35  5.91  Mgs  -1.31  13.94  15.88  Tic  -5.20  14.27  17.78  Tic  -4.93  14.23  17.11  Tic  -5.12  14.46  19.22  Tic  -5.05  14.66  19.69  Tic  -4.81  14.63  17.19  Tic  -4.27  12.91  5.21  Mgs  -3.63  13.47  3.55  Srp  -2.66  ,  Number AT03-20-CD4D AT03-20-DH1 AT03-20-DH2 AT03-20-DH3 AT03-20-IJ1A AT03-20-IJ1B AT03-20-IJ1C AT03-20-IJ2A AT03-20-IJ2B AT03-20-IJ2C AT03-20-IJ2D AT03-20-IJ2D AT03-20-IJ2E AT03-20-IJ2E AT03-20-IJ3A AT03-20-IJ3B AT03-20-IJ3C AT03-20-IJ4A AT03-20-IJ4B AT03-20-IJ4C AT03-20-IJ4D AT03-21-EF1B AT03-21-EF1D AT03-21-EF1E AT03-21-EF2D AT03-44-12 AT03-44-27 AT03-44-40 AT03-44-6 AT03-51A AT04-20B AT04-20I AT04-20N AT04-25 AT03-50  ^  (VPDB)  ,  J  (VSMOW)  C0  2  (wt%)  Zone  -4.31  12.80  3.21  Srp  -6.04  15.70  n/a  Mgs Vein  -5.97  14.80  n/a  Mgs Vein  -3.75  13.96  n/a  Mgs Vein  -3.02  12.98  2.80  Mgs  -2.30  13.42  2.97  Mgs  -2.64  14.41  3.06  Mgs  -3.13  12.87  15.60  Tic  -2.78  12.99  4.67  Mgs  -2.30  13.40  3.92  Mgs  -4.28  12.90  3.72  Mgs  -3.67  12.72  3.72  Mgs  -4.18  12.78  3.20  Mgs  -2.80  13.62  3.20  Mgs  -5.39  14.18  18.08  Tic  -4.88  14.49  18.70  Tic  -5.55  15.08  18.65  Tic  -5.19  14.87  19.43  Tic  -4.08  13.26  4.11  Mgs  -3.40  13.32  3.91  Mgs  -3.32  13.32  4.11  Mgs  -1.26  12.06  3.04  Mgs  -4.69  12.04  17.77  Tic  -4.68  , 12.40  18.10  Tic  -4.64  13.07  19.85  Tic  -6.05  13.01  25.86  Qtz  -5.43  11.26  15.20  Tic  -5.18  10.64  24.49  Tic  -0.34  11.07  21.60  Tic  -4.16  15.40  6.11  Mgs  -2.99  8.29  35.50  Qtz  -5.36  11.15  27.27  Qtz  -4.84  •11.21  26.16  Qtz  -3.79  8.20  4.73  dyke  -3.31  8.30  9.21  dyke  APPENDIX D  Appendix D : Geochronologic Results  163  APPENDIX D TABLE D1: Geochronology Sample E U T M (NAD 83) 573283 AT03-5B  System U-Pb zircon  N U T M (NAD 83) 6603671  Age 150.7 +/-0.4 Ma  Analyst Richard Friedman  Other Population B  AT03-28  573556  6605367  A r / A r (Biotite)  84.0 +/- 0.6 Ma  Thomas Ulrich  Plateau Age  AT03-44-7  577809  6601758  ""Ar/^Ar (Cr-Muscovite)  174.4 +/-1.4 Ma  Thomas Ulrich  Integrated Age  01AT-1-2  574013  6603080  ""Ar/^Ar (Cr-Muscovite)  128.0+/-1.9 Ma  Thomas Ulrich  Plateau Age  02AT-8-1  575800  6602042  40  A r / A r (Cr-Muscovite)  172.7 +/-2.0 Ma  Thomas Ulrich  Plateau Age  Plateau  steps  a r efilled,  40  rejected  39  39  steps  box heights are 2a  a r e o p e n  02AT-8-1 M u s c o v i t e  280  240  200  160  120 Plateau age = 1 7 2 . 7 ± 2 . 0 M a (2<T, including J-error of .5%) M S W D = 2.0, probability=0.13 Includes 84.7% of the A r  80  3 9  40  0 l 0  •  ' 20  •  ' 40  •  • 60  •  • 80  •  ' 100  39  Cumulative Isoplot Step-Heat Data  A r Percent  Isoplot Inverse Isochron Data  Cum39Ar  Age  error  %39Ar  39/40  err  36/40  err  rho  0.26  65.83  93.27  0.26  0.010722  0.00068  0.00319  0.000281  0.253  2.97  127.91  20.5  2.71  0.029449  0.000404  0.002332  0.000174  0.022  8.38  113.3  6.81  5.41  0.055011  0.001006  0.00165  9.90E-05  0.097  31.17  170.3  3.13  22.79  0.051852  0.000532  0.000888  3.80E-05  0.107  87.29  174.24  2.45  56.12  0.065155  0.00093  0.000171  1.00E-05  0.016  93.06  171.76  6.84  5.77  0.052027  0.000739  0.000857  9.70E-05  0.053  98.52  156.29  6.77  5.46  0.056624  0.000689  0.000892  0.000108  0.008  100.01  92.38  21.74  1.49  0.037094  0.000632  0.002436  0.000228  0.027  164  APPENDIX D A g e = 172.7±2.0 M a (2s, including J-error of .5%) M S W D = 2.0, probability = 0.13 84.7% of the 39Ar, steps 4 through 6  in  O g  < o  Model 1 Solution (±95%-conf.) on 3 points A g e = 174.9±3.0 M a 40/36 intercept: 273±22 M S W D = 0.13, Probability = 0.71 (at J=.006959±.5% 2s)  U  It  u  Fraction  39Ar  data-point error ellipses are 2 a  0.0012 02AT-8-1 Muscovite 0.0010  A g e = 174.9±3.0 M a  0.0008 36 40  Ar  M S W D = 0.13  0.0006  Ar  Two-point isochron: unreliable.  0.0004  0.0002  0.0000 0.048  0.052  0.056  0.060  ^Ar^Ar 165  0.064  0.068  APPENDIX D  02AT-8-1  Muscovite  Laser  Isotope Ratios  Power(%)  40Ar/39Ar  2  100.643±0.058 0.142±0.282  2.3  34.890 0.014  2.5  Ca/K  Cl/K  %40Ar f 39Ar atm  40Ar739ArK  Age  0.794*0.090 0.306±0.088  1.095  0.011  94.24 0.26  5.340±7.705  65.83±93.27  0.063 0.141  0.079 0.080 0.082 0.073  0.101  0.007  68.85 2.71  10.558 1.753  127.91 20.50  18.690 0.018  0.028 0.173  0.056 0.061 0.031 0.059  0.147  0.002  48.68 5.41  9.314 0.578  113.30 6.81  2.8  19.377 0.010  0.020 0.060  0.051 0.049 0.018 0.041  0.259  0.001  26.2  22.79  14.225 0.274  170.30 3.13  3.1  15.378 0.014  0.012 0.063  0.009 0.076 0.003 0.055  0.038  -0.001  5.05  56.12  14.571 0.215  174.24 2.45  19.694 0.014  0.016 0.167  0.038 0.076 0.017 0.106  0.054  0  25.28 5.77  14.354 0.599  171.76 6.84  3.3  38Ar/39Ar  37Ar/39Ar  36Ar/39Ar  3.6  18.170 0.012  0.015 0.158  0.040 0.087 0.017 0.113  0.055  -0.001  26.32 5.46  13.004 0.588  156.29 6.77  4  28.800 0.017  0.042 0.144  0.146 0.074 0.069 0.089  0.195  0.002  71.91 1.49  7.550 1.823  92.38 21.74  Total/Average  17.658±0.004  0.017±0.020  0.056±0.008 0.013±0.013  0.003  100  14.463±0.078  166.26±0.95  0.006959±0.000030  Volume 39ArK=  125.43  Integrated Date =  166.26±1.91  Volumes are 1E-13 cm3 NPT  166  APPENDIX D  280  Plateau  steps  a r e filled, r e j e c t e d  AT03-44-7  steps  a r e  box heights are 2a  o p e n  Muscovite  240  200  160  120  Plateau age = 188.0±1.8 M a (2or, i n c l u d i n g J - e r r o r o f .5%) M S W D = 0.51, probability=0.60 I n c l u d e s 62.7% of t h e A r 3 9  80  40  20  60  40  100  80  39  Cumulative  Isoplot Step-Heat Data um39Ar 4.65  A r Percent  Isoplot Inverse Isochron Data  Age  error  %39Ar  39/40  err  36/40  err  rho  148.29  4.49  4.65  0.041054  0.000473  0.001674  4.60E-05  0.204  2.10E-05  0.01  35  154.76  1.43  30.35  0.05902  0.000282  0.000814  60.01  187.6  2.16  25.01  0.054068  0.00054  0.000504  1.90E-05  0.008  91.89  189.36  3.15  31.88  0.057298  0.000948  0.000301  1.20E-05  0.132  97.71  187.42  3.23  5.82  0.054538  0.000794  0.000482  2.50E-05  0.141  98.73  111.82  9.85  1.02  0.042612  0.000719  0.002059  0.000115  0.102  99.11  95.25  54.62  0.38  0.027616  0.000786  0.002656  0.000427  0.055  99.98  80.96  17.65  0.87  0.023503  0.000384  0.00286  0.000116  0.154  167  APPENDIX D  A g e = 188.0±1.8 M a (2s, including J-error of .5%) M S W D = 0.51, probability = 0.60 62.7% of the 39Ar, steps 3 through  Model 1 Solution (±95%-conf.) on 3 points A g e = 191.8±7.6Ma 40/36 intercept: 255±79 M S W D = 0.048, Probability = 0.83 (at J=.006961 ± . 5 % 2s)  Model 1 Solution (±95%-conf.) on 3 points Age = 191.77 +7.25 -7.31 (MonteCarlo) 40/36 intercept: 255 +58.8 -109 M S W D = 0.048, Probability = 0.83 (atJ=.006961±.5%2s) Fraction  168  39Ar  APPENDIX D  AT03-44-7 Laser  Muscovite Isotope Ratios  Power(%)  40Ar/39Ar  38Ar/39Ar  37Ar/39Ar  36Ar/39Ar  Ca/K  Cl/K  %40Ar atm  2  24.521+0.011  0.039±0.090  0.040±0.044  0.042±0.027  0.158  0.004  49.41  4.65  12.307±0.388  148.29± 4.49  0.484  0.001  24.01  30.35  12.868 0.124  154.76 1.43  f 39Ar 40Ar*/39ArK  Age  2.2  16.947 0.005  0.020 0.027  0.084 0.023  0.014 0.025  2.3  18.495 0.010  0.014 0.073  0.202 0.019  0.010 0.038  1.184  -0.001  14.86  25.01  15.743 0.191  187.60 2.16  2.4  17.455 0.016  0.012 0.086  0.024 0.049  0.005 0.040  0.128  -0.001  8.89  31.88  15.898 0.279  189.36 3.15  -0.001  14.21  5.82  15.727 0.285  187.42 3.23  2.5  18.481 0.014  0.013 0.153  0.017 0.072  0.009 0.050  0.04  2.7  24.410 0.016  0.036 0.143  0.091 0.061  0.050 0.054  0.195  0.002  60.78  1.02  9.186 0.834  111.82 9.85  3  38.606 0.027  0.057 0.282  0.208 0.091  0.101 0.153  0.329  0.004  78.43  0.38  7.789 4.585  95.25 54.62  0.87  6.594 1.470  80.96 17.65  100  15.820±0.056  174.41±0.72  4  43.505 0.016  0.061 0.076  0.146 0.117  0.124 0.040  Total/Average  18.310±0.003  0.017±0.015  0.274±0.003  0.013±0.008  0.00696UO.O00O 28  Volume 39ArK = Integrated Date =  Volumes are 1E-13 cm3 NPT  169  0.462  0.005  0.002  84.44  APPENDIX D  Plateau  a r e filled,  rejected  steps  a r e  box heights are 2a  o p e n  0 1 A T - 1 - 2 Muscovite  240  200  s t e p s  h  160  120  80 Plateau age = 1 2 8 . 0 + 1 . 9 M a  (2cr, including J-error of .5%) M S W D = 1.05, probability=0.38 Includes 6 3 . 9 % of the A r  40  3 9  20  Cumulative  Isoplot Step-Heat Data  80  60  40 3 9  Ar  100  Percent  Isoplot Inverse Isochron Data %39Ar  39/40  err  36/40  err  rho  0  0.000576  0.013724  0.004574  0.005487  0.975  3712.78  0.01  0.00185  0.002464  0.00329  0.00135  0.298  684.21  1349.74  0.03  0.003468  0.002897  0.002606  0.001268  0.528  99.54  46.94  0.72  0.020385  0.000752  0.002822  0.00027  0.104  0.058432  0.000426  0.001343  6.30E-05  0.021  Cum39Ar  Age  error  0  ERR  ERR  0.01  179.49  0.04 0.76  step ignored  13.23  125.13  3.87  12.47  42.21  129.43  3.27  28.98  0.069483  0.001162  0.00087  4.00E-05  0.283  63.89  128.51  2.66  21.68  0.064922  0.000735  0.001052  3.80E-05  0.158  117  4.83  16.01  0.04971  0.000525  0.001764  6.40E-05  0.139  87.47  111.9  6.02  7.57  0.034311  0.000376  0.002316  5.70E-05  0.185  93.83  90.11  8.94  6.36  0.042402  0.000609  0.002328  0.000106  0.066  99.99  58.68  12.86  6.16  0.045527  0.001682  0.002652  0.000146  0.55  79.9  170  APPENDIX D  Age = 128.0±1.9Ma (2s, including J-error of .5%) MSWD = 1.05, probability = 0.38 63.9% of the 39Ar, steps 1 through 6 Model 1 Solution (±95%-conf.) on 6 points Age= 132.2±4.8 Ma 40/36 intercept: 274+23 MSWD = 0.68, Probability = 0.61 (at J=.006959±.5% 2s)  in  o fl o  H U  Model 1 Solution (±95%-conf.) on 6 points Age = 132.15 +4.66-5.19 (MonteCarlo) 40/36 intercept: 274.4 +22.4-24.1 MSWD = 0.68, Probability = 0.61 (at J=.006959±.5% 2s)  U  Fraction  39Ar  H a t a - p n i n t grrnr Pllipspg a r p ? r r  0.005  01AT-1-2 Muscovite Age = 1 3 2 . 2 ± 4 . 8 Ma Initial A r / A r = 2 7 4 ± 2 3 MSWD = 0.68 40  36  0.004  3 6 ^ 40  r  0.003  Ar 0.002  0.001  0.000 0.00  0.02  0.06  0.04 3 9  171  Ar/ Ar 4 0  0.08  APPENDIX D  01AT-1-2  Muscovite  Laser  Isotope Ratios  Power(%)  40Ar/39Ar  38Ar/39Ar  1.8  609.568±0.638  1.263±0.824  %40Ar 37Ar/39Ar  36Ar/39Ar  Ca/K  1 4 . 1 8 8 ± 0 . 6 4 6 2 . 1 5 9 ± 0 . 6 6 6 73.185 1.147 0.616 19.716  Cl/K  atm  0.383 135.14  f 39Ar  40Ar*/39ArK  0  -610.328±1039.634  Age —t  —  2  415.394 0.540  1.139 0.716  8.678 0.541  0.271  97.21  0.01  15.039 326.806  179.49 3712.78  2.2  2 8 4 . 9 1 7 0.632  0.251 1.393  3.925 0.540 0.690 0.562  7.413  -0.003  77  0.03  66.301  684.21 1349.74  2.6  51.591 0.036  0.085 0.127  0.228 0.091 0.143 0.094  0.327  0.009  83.32  0.72  8.155  3  17.263 0.007  0.042 0.059  0.018 0.061  0.024 0.046  0.046  0.005  39.6  12.47  10.325  3.3  14.450 0.017  0.026 0.050  0.015 0.053 0.013 0.043  0.062  0.002  25.65 28.98  0.5  15.482 0.011  0 . 0 2 2 0.130  0.046 0.035 0.017 0.035  0.242  0.001  31.03 21.68  128.51  2.66  3.7  20.207 0.010  0.025 0.218  0.193 0.033 0.036 0.036  1.11  0.001  52.04  16.01  9.632  0.410  117.00  4.83  4  29.321 0.011  0.0430.064  0.520 0.027 0.069 0.024  3.017  0.003  68.37  7.57  9.199  0.510  111.90  6.02  4.4  23.851 0.014  0.044 0.134  0.432 0.031  0.056 0.045  2.469  0.004  68.69  6.36  7.363  0.749  90.11  8.94  1.032  0.002  78.26  6.16  4.753  1.059  58.68  12.86  100  10.593±  5  22.265 0.036  0.036 0.077  0.193 0.043 0.060 0.045  Total/Average  18.499±0.003  0.030±0.021  0.389±0.003 0.030±0.007  0.006956±0.00 J = Volume  0032 39ArK 167.42  Integrated Date=  118.44±2.02  V o l u m e s are 1E-13cm3  172  0.062  10.692 10.614  157.159 3.953 0.331 0.280 0.227  0.083  99.54  46.94  125.13  3.87  129.43  3.27  118.44±  1.01  APPENDIX D  100  Plateau steps are filled, rejected steps are open  h n x  h e i g h t s  a n  AT03-28 Biotite 90 80  =F  70 60  Plateau age = 83.97±0.60 M a (2a, including J-error of .5%) M S W D = 0.97, probability=0.44 Includes 78.3% of the A r  50  3 9  40 30 20 10  80  60  40  20  100  Cumulative A r Percent 3 9  Isoplot Step-Heat Data  Isoplot Inverse Isochron Data  Cum39Ar  Age  error  %39Ar  39/40  err  36/40  err  rho  0.69  80.24  9.32  0.69  0.06407  0.000901  0.001968  0.000167  0.008 0.108  4.69  77.44  1.48  4  0.114311  0.001412  0.000949  3.30E-05  13.15  81.61  1.38  8.46  0.13712  0.001916  0.000302  2.90E-05  0.05  22 31  83.3  0.97  9.16  0.140378  0.001313  0.000162  2.20E-05  0.028 0.053  34.46  83.97  1.33  12.15  0.140803  0.002149  0.000125  1.50E-05  45.21  83.68  1.53  10.75  0.140464  0.002462  0.000144  1.70E-05  0.06  54.31  83.46  1.26  9 1  0.140562  0.001917  0.000151  2.10E-05  0.044  71.55  84.29  0.95  17.24  0.141515  0.001591  9.60E-05  4.00E-06  0.17  0.001325  9.80E-05  9.00E-06  0.061  91.42  84.5  0.82  19.87  0.141087  98.72  81.46  0.98  7.3  0.142616  0.001659  0.000184  6.00E-06  0.24  100.01  78.66  3.52  1.29  0.123648  0.001942  0.000707  0.000113  0.045  173  APPENDIX D  Age = 83.97±0.60 Ma (2s, including J-error of .5%) MSWD = 0.97, probability = 0.44 78.3% of the 39Ar, steps 4 through 9  to  o  I< o  Model 2 Solution (±95%-conf.) on 11 points Age = 83.0±1.6 Ma 40/36 intercept: 276±24 MSWD = 4.9, Probability = 0.000 (at J=.006963±.5% 2s)  Ui .-I  U  Ui  rt o Fraction  39Ar  data-point error ellipses are 2a 0.0024  AT03-28 Biotite  Age = 8 3 . 0 ± 1 . 6 Ma 0.0020  Initial  4 0  Ar/ Ar =276±24 3 6  M S W D = 4.9 0.0016  36  Ar  40  Ar  0.0012  0.0008  0.0004  0.0000 0.04  0.06  0.08  0.12  0.10 3 9  174  Ar/ Ar 4 0  0.14  0.16  APPENDIX D  AT03-28  Biotite  Laser  Isotope Ratios  Power(%)  40Ar/39Ar  38Af/39Ar  37Ar/39Ar  36Ar/39Ar  Ca/K  Cl/K  %40Ar atm  f 39Ar  40Ar"/39ArK  Age  2  16.227±0.014  0.083±0.091  0.081±0.110  0.031±0.085  0.424  0.014  58^04  0.69  6.532±0.776  80.24i9.32  2.2  8.859 0.012  0.090 0.031  0.009 0.105  0.008 0.035  0.041  0.017  27.9  4  6.299 0.123  77.44 1.48  0.017  6.84  8.46  6.646 0.115  81.61 1.38  2.4  7.350 0.014  0.090 0.081  0.003 0.101  0.002 0.095  0.014  2.6  7.178 0.009  0.093 0.040  0.002 0.181  0.001 0.138  0.01  0.018  4.72  9.16  6.786 0.081  83.30 0.97  2.8  7.144 0.015  0.085 0.077  0.003 0.108  0.001 0.118  0.013  0.016  3.64  12.15  6.842 0.111  83.97 1.33  3  7.166 0.017  0.085 0.059  0.005 0.092  0.001 0.120  0.025  0.016  4.21  10.75  6.819 0.128  83.68 1.53  3.2  7.169 0.014  0.092 0.032  0.008 0.066  0.001 0.140  0.046  0.018  4.4  9.1  6.800 0.105  83.46 1.26  3.5  7.098 0.011  0.091 0.052  0.014 0.043  0.001 0.042  2.78  17.24  6.869 0.080  84.29 0.95  7.116 0.009  0.095 0.064  0.013 0.040  0.001 0.089  0.019  2.83  19.87  6.886 0.069  84.50 0.82  0.016  5.37  7.3  6.633 0.082  81.46 0.98  20.79  1.29  6.400 0.293  38  7.078 0.012  0.085 0.081  0.012 0.059  0.001 0.031  8.433 0.015  0.091 0.028  0.014 0.143  0.006 0.159  Total/Average  0.090±0.011  J=  0.006963*0.000026  Volume 39ArK =  1089.19  Integrated Date = Volumes are 1E13 cm3 NPT  83.25±0.50  175  0.076 0.066  1  78.66 3.52  APPENDIX D 4U  A r / A r DATING METHOD PROCEDURES 39  Each sample was crushed.  Mineral separates were hand-picked, wrapped in  aluminum foil and stacked in an irradiation capsule with similar-aged samples and neutron flux monitors (Fish Canyon Tuff sanidine, 28.02 Ma (Renne et al., 1998)). The samples were irradiated on May 27 and 28, 2004 at the McMaster Nuclear Reactor in Hamilton, Ontario, for 56 MWH, with a neutron flux of approximately 3xl0  16  neutrons/cm . Analyses (n=54) of 18 neutron flux monitor positions produced errors of 2  <0.5% in the I value. The samples were analyzed on July 27 and 28, 2004, at the Noble Gas Laboratory, Pacific Centre for Isotopic and Geochemical Research, University of British Columbia, Vancouver, BC, Canada. The separates were step-heated at incrementally higher powers in the defocused beam of a 10W CO2 laser (New Wave Research MIR 10) until fused. The gas evolved from each step was analyzed by a VG5400 mass spectrometer equipped with an ion-counting electron multiplier. A l l measurements were corrected for total system blank, mass spectrometer sensitivity, mass discrimination, radioactive decay during and subsequent to irradiation, as well as interfering Ar from atmospheric contamination and the irradiation of Ca, CI and K (Isotope production ratios: ( Ar/ Ar)K = 0.0302, ( Ar/ Ar)Ca = 1416.4306, ( Ar/ Ar)Ca - 0.3952, Ca/K = 40  39  37  39  36  39  1.83( ArCa/ ArK).). The plateau and correlation ages were calculated using Isoplot 37  39  ver.3.09 (Ludwig, 2003). Errors are quoted at the 2-sigma (95% confidence) level and are propagated from all sources except mass spectrometer sensitivity and age of the flux monitor.  REFERENCES Ludwig, K.R 2003. Isoplot 3.00 A Geochronological Toolkit for Microsoft Excel. Berkeley Geochronology Center, Special Publication No. 4 Renne, P.R., C.Swisher, C C , III, Deino, A.L., Karner, D.B., Owens, T. and DePaolo, D.J., 1998. Intercalibration of standards, absolute ages and uncertainties in A r / A r 40  dating. Chemical Geology, 145(1-2): 117-152. 176  39  APPENDIX D  Sample AT03-05B, a quartz-K-feldspar porphyritic dacite, was dated using the U-Pb TIMS-ID technique in the Pacific Centre for Isotopic and Geochemistry Research at the University of British Columbia. Four abraded multi-grain zircon fractions were analyzed and all yielded statistically concordant results. As there is no evidence for inheritance, fraction B, which gives the oldest result of 150.7 ± 0.4 Ma ( P b / U date, 2a errors) is 206  238  considered to be the best estimate for the age of the rock. Younger results from the other fractions are likely due to minor Pb loss.  177  U-Pb ID-TIMS analytical data for sample AT03-05B Fraction  1  Wt  U  2  Pb*  3  206  Pb  4  204™.  Pb  5  ,  Th/U*  „  (mg) (ppm) (ppm) Pb (pg) Interpreted age of 150.7 ± 0.4 Ma, based on oldestfractionB 298 54 0.23 0.018 585 13 A2 0.022 11 991 16 0.27 B4 469 3241 4 0.26 0.017 523 12 C6 4580 6 0.31 0.029 596 14 D20  Isotopic ratios (±lo,%) 206 , ,238 n  207,,, ,235  TT  rI  Pb/ U 0.02274 0.02366 0.02336 0.02324  Pb/ U  (0.25) (0.13) (0.13) (0.14)  0.1537 (1.5) 0.1601 (0.32) 0.1579 (0.26) 0.1570 (0.22)  Apparent ages (±2o,Ma)  7  207 , ,206™  206 , ,238  n  D  Pb/ Pb 0.04903 (1.4) 0.04910(0.24) 0.04900 (0.20) 0.04901 (0.14)  TI  7  207 , ,235 D  TT  Pb/ U  Pb/ U  144.9 (0.7) 150.7(0.4) 148.9 (0.4) 148.1 (0.4)  145.2(4.1) 150.8 (0.9) 148.9 (0.7) 148.1 (0.6)  'Fraction identifier: single letter. Fraction ID is followed by number or approximate number of grains or fragments analysed. All analysed zircon grains were air abraded prior to dissolution and all were clear, pale pink prisms with aspect ratios of-2-4. U blank correction of 1 pg ± 20%; U fractionation corrections were measured for each run with a double  2  233  U-  235  U spike.  Radiogenic Pb  3  Measured ratio corrected for spike and Pb fractionation of 0.0037/amu ± 20% (Daly collector) which was determined by repeated analysis  4  NBS Pb 981 standard throughout the course of this study. Xotal common Pb in analysis based on blank isotopic composition.  5  Radiogenic Pb  6  Blank and common Pb corrected; Pb blank corrections were 2-20 pg; U was 1 pg. Common Pb isotopic compositions are based on Stacey  7  '  Kramers (1975) model Pb at the interpreted age of the rock or the  207  206  Pb/ Pb age of the fraction.  APPENDIX D U-Pb Geochronology: Analytical Techniques Zircon was separated from rock samples using conventional crushing, grinding, and Wilfley table techniques, followed by final concentration using heavy liquids and magnetic separations.  Mineral fractions for analysis were selected based on grain  morphology, quality, size and magnetic susceptibility. All zircon fractions were abraded prior to dissolution to minimize the effects of post-crystallization Pb-loss, using the technique of Krogh (1982). All mineral separations, geochemical separations and mass spectrometry were done in the Pacific Centre for Isotopic and Geochemical Research in the Department of Earth and Ocean Sciences, University of British Columbia. Samples were dissolved in concentrated HF and H N O 3 in the presence of a mixed  " U - Pb  tracer. Separation and purification of Pb and U employed ion exchange column techniques modified slightly from those described by Parrish et al. (1987). Pb and U were eluted separately and loaded together on a single Re filament using a phosphoric acid-silica gel emitter. Isotopic ratios were measured using a modified single collector VG-54R thermal ionization'mass spectrometer equipped with a Daly photomultiplier. Measurements were done in peak-switching mode on the Daly detector. U and Pb total procedural blanks were in the range of 1 pg and 3-5 pg, respectively, during the course of this study. U fractionation was determined directly on individual runs using the  2 3 3  "  2 3 5  TJ  tracer, and Pb isotopic ratios were corrected for a fractionation of 0.37%/amu for Faraday and Daly runs, respectively, based on replicate analyses of the NBS-981 Pb standard and the values recommended by Todt et al. (2000). A l l analytical errors were numerically propagated through the entire age calculation using the technique of Roddick (1987). Concordia intercept ages and associated errors were calculated using a modified version the the York-II regression model (wherein the York-II errors are multiplied by the MSWD) and the algorithm of Ludwig (1980). All errors are quoted at the 2o level.  179  APPENDIX D REFERENCES Krogh, T.E, (1982): Improved accuracy of U-Pb zircon ages by the creation of more concordant systems using an air abrasion technique. Geochimica et Cosmochimica Acta, 46, p.637-649. Ludwig, K.R., (1980): Calculation of uncertainties of U-Pb isotopic data. Earth and Planetary Science Letters, 46, p. 212-220. Parrish, R., Roddick, J.C, Loveridge, W.D., and Sullivan, R.W. (1987): Uranium-lead analytical techniques at the geochronology laboratory, Geological Survey of Canada. In Radiogenic Age and Isotopic Studies, Report 1, Geological Survey of Canada, Paper 87-2, p. 3-7. Roddick, J.C (1987): Generalized numerical error analysis with application to geochronology and thermodynamics. Geochimica et Cosmochimica Acta, 51, p. 2129-2135. Stacey, J.S. and Kramers, J.D. (1975): Approximation of terrestrial lead isotope evolution by a two-stage model: Earth and Planetary Science Letters, v. 26, p. 207-221.  180  APPENDIX E  Appendix E : Miscellaneous Calculations and Procedures  181  APPENDIX E E. 1: GEOCHEMICAL POWDER PREPARATION Accurate and precise geochemical analysis of the suite of rocks is very important for determining chemical alteration. For this reason, contamination during sample preparation must be kept to a minimum. The procedures followed for preparation of powders submitted for geochemical analysis are outlined below. 1. A l l weathered surfaces were cut off with a diamond rock saw generally resulting in a cubic shape. 2. The cut samples were then polished with 240 mesh-sized  AI2O3  to remove any  metal that was abraded from the rock saw during step 1. 3. Samples were then washed with distilled water in a sonic bath for 3-5 minutes to remove any A I 2 O 3 and other microscopic contaminants from step 2. 4. The samples were then crushed in a rock jaw crusher. To minimize contamination during this step, the crusher was first cleaned with water and a wire brush to remove any rock, or other material (e.g. coal) from previous uses. Blank samples of the same rock type as the samples to be crushed were then sent through the machine in order to decrease the chance of contamination from other lithological types and to reduce the tendency for the metal jaws of the crusher to abrade onto the sample during crushing. The crusher and tray used to catch the sample was then blown out with compressed air before the next sample was sent through. Samples of similar type (degree of alteration) were crushed together again to reduce contamination. When samples of different alteration or type needed to be crushed, the jaws of the crusher were cleaned dry with a wire brush. 5. Before powdering the samples, the ring mill was cleaned with clean rinsing organic soap, rinsed with tap water then acetone, and finally dried with compressed air. This method of washing was also done between all samples. As with the jaw crushing step, a blank sample of similar composition as the samples powdered was powdered to minimize contamination from other lithologies during previous powdering sessions.  182  APPENDIX E 6. The crushed samples were placed on a blank piece of white paper and manually picked through as to obtain pieces which fit in the ring mill and contain no vein material which commonly remain in cut and polished samples. Generally the largest pieces were used. If the sample was coarse grained enough to warrant, more than one crushing step was done to increase the representativeness of the sample. During this step the crushed samples were also visually inspected to remove any pieces with abraded metal from the crusher. Metal usually abraded only the smooth cut and polished sides vs. the jagged sides produced during crushing. Abraded metal was easily identifiable. 7. The ring mill, with enclosed sample, was then placed in the shatter box and ran for 1.5 to 3 minutes until adequately powdered. This usually was when a persistent and distinctive vibrating sound was produced from the ring mill with in the shatter box. 8. The powdered sample was then homogenized using a quartering method for 3 to 5 minutes before submission to the geochemical laboratory. Bulk geochemical samples were crushed and powdered in a tungsten carbide shatterbox. Powders were sent to the Geochemical Laboratories at McGill University, Montreal, PQ for bulk geochemical analysis by X-ray fluorescence. Results are included in the table. Samples were analyzed for major, minor and trace elements, C O 2 content by induction furnace, and total volatile content by loss on ignition (L.O.I.). Standard errors used in calculations were determined from 13 blind replicate analysis of one sample (AT03-20-PC2, Appendix C).  E.2: ERROR DETERMINATION Knowledge of the uncertainty for each chemical species was determined by sending blind replicates of AT03-PC2 for analysis. In all, 13 blind analyses were completed (Table C-2, Appendix C); these were submitted 3 to 4 at one time accompanying other samples. The reproducibility during the same session is related to the ability of the laboratory to reproduce the same result from the same sample and the ability to adequately homogenize the sample before submitting replicates. The reproducibility 183  APPENDIX E over time is a test of the ability of the laboratory to reproduce the same result for the same sample over time. Of notable difference between the two groups are the L.O.I, and CO2 analyses. Group 1 is consistently about 0.1 wt% L.O.I, and CO2 below those of group 2. This is likely due to slight differences in the procedure to drive-off moisture between the two groups. Group 1 had 0.1 wt% more loosely bound CO2 driven off than group 2. For example, 0.1 wt% less CO2 will result in 0.1 wt% less L.O.I, as L.O.I, contains CO2. Since both L.O.I, and CO2 determinations are independently measured and because both L.O.I and CO2 are consistently about 0.1 wt% lower in group 1 than in group 2, the difference must be because some CO2 was lost in group 1 that was not lost in group 2. The other major detectible difference is in the Na20 analyses between the two groups. Clearly there is a difference; however it is not currently known what the difference is attributed to. The standard error for Na20 was determined only with those measurements which are above detection.  E.3: MAGNETIC SUSCEPTIBILITY MEASUREMENTS OF HAND SAMPLES VS OUTCROP MEASUREMENTS Magnetic susceptibility measurements of hand samples were compared to the measurements made in the field at the location of each sample (Fig. E . l ) . The KT-9 Kappameter magnetic susceptibility meter allows for the storage and averaging of 10 measurements. The reported magnetic susceptibility for all samples and for most field locations is the average of 10 measurements made from the sample or taken over the outcrop. The highest and lowest measurements were also reported. Often only the range of magnetic susceptibility was recorded for field locations. In this case the median, generally a good approximation, was used as the magnetic susceptibility. A comparison of hand sample and field measurements, shown in Figure B2, indicates that hand sample measurements appear to be systematically lower than the field measurements for the sample. This brings into question the validity of applying algorithms relating hand sample magnetic susceptibility to alteration vs. field measurements. Up to five different KT-9 Kappameter magnetic susceptibility meters have been used throughout this study. Though unlikely, the systematic differences in magnetic susceptibility may be due to 184  APPENDIX E machine calibration used between the instruments. A more likely explanation is the field measurements were not made on the exact rocks collected for hand sample measurement. Alteration in outcrop can be highly variable with a very large spread in measured magnetic susceptibility. When taking magnetic susceptibility measurements in the field, one looks for the smoothest and least weathered surfaces to take the measurements. Unfortunately these samples are near impossible to sample without a cement saw. Also, the more serpentinized an outcrop of harzburgite is, and therefore the higher the magnetic susceptibility, the harder the rock is to sample due increased fractures and alteration. Geochemical analysis can only be performed on the collected hand samples. For this reason the measurements reported from the hand samples are used as the magnetic susceptibility for any analysis involving the hand sample.  185  APPENDIX E  120  5>100  Figure E . l : Magnetic susceptibility of hand samples vs. the outcrops the hand samples were acquired from.  186  APPENDIX E STABLE ISOTOPE A N A L Y T I C A L TECHNIQUES Carbonate samples are analyzed using the Gas Bench and a Finnigan Delta Pus X L mass spectrometer. CO2 is extracted using continuous flow from the Gas Bench as follows. Between 150 and 300p.g of crushed sample is placed in the bottom of a clean exetainer, which is sealed with a piercable septum. The exetainers flushed with Helium for 5 minutes to displace air, then 7 drops of 99% phosphoric acid are introduced using a syringe through the septum. The acid and sample are left to equilibrate at 72°C for an hour, then the CO2 gas produced is sampled by a sampling needle attached to the gas bench.  The sample run consists of 5 aliquots of reference CO2 gas of known  composition, 10 aliquots of sample gas, and one final aliquot of reference gas. In-house rock standards are distributed throughout the samples in the gas bench after every eight samples. Raw d 0 / d 0 ratios have been corrected for fractionation between phosphoric 18  16  acid and calcite (from Das Sharma et al, 2002) then samples that are not calcite are corrected for the appropriate acid-mineral fractionation. The raw ratios are adjusted for machine fractionation using a factor calculated from repeated analyses of internal UBC standards B N 13, B N 83-2, H6M, which are calibrated against two international standards, NBS 18 and NBS 19. The final results 8 C(VPDB) and 5 0(VSMOW) are corrected to VPBD and VSMOW 13  18  based on an average of multiple analyses of NBS 18 and 19. The standard deviation on the average analyses of NBS 18 and 19 is > 0.1 per mil at the 2 sigma level for both S C(VPDB) and 5 0(VSMOW)13  18  REFERENCES  Das Sharma, S., Patil, D.J. and Gopalan, K. (2002): Temperature dependence of oxygen isotope fractionation of CO2 from magnesite-phosphoric acid reaction. Geochimica et Cosmochimica Acta, v. 66, n. 4, pp. 589-593.  187  APPENDIX F  Appendix F : Sample Locations  188  APPENDIX F  Table F l : Sample locations (NAD 83) Sample 01AT-10-1 01AT-10-2 01AT-11-1 01AT-11-2 01AT-1-2 01AT-13-1 01AT-13-2 01AT-1-5 01AT-1-6 01AT-1-7 OiAT-1-8 01AT-1-9 01AT-2-2 01AT-3-1 01AT-4-1 01AT-5-2 01AT-5-3 01AT-5-4 01AT-6-1 01AT-6-3 01AT-7-1 01AT-7-3 01AT-8-1 01AT-9-1 01AT-9-2 02AT-8-1 AT03 - 28 AT03-20-CD1A AT03-20-CD1B AT03-20-CD1C AT03-20-CD2A AT03-20-CD2B AT03-20-CD2C AT03-20-CD2D AT03-20-CD3A AT03-20-CD3B AT03-20-CD3C AT03-20-CD3D AT03-20-CD4A AT03-20-CD4B AT03-20-CD4C AT03-20-CD4D AT03-20-DH1 AT03-20-DH2 AT03-20-DH3 AT03-20-ij1a AT03-20-ij1b AT03-20-ij1c AT03-20-ij2a  Eastings 577844 577844 577860 577860 574013 577782 577782 574013 574013 574013 574013 574013 573954 573866 573552 573278 573278 573278 575352 575352 574956 574956 575800 575856 575856 575800 573556 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884  Northings 6601933 6601933 6601820 6601820 6603080 6602226 6602226 6603080 6603080 6603080 6603080 6603080 6603058 6603293 6603542 6603742 6603742 6603742 6604258 6604258 6604734 6604734 6602042 6602056 6602056 6602042 6605367 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100  Geochemistry  40  Ar/ Ar 39  U-Pb  1 3  C  18  0  Au Assay  X X X X X  X X X  X X X X X X  X X X X X X  X X X X X X X X  X X X X X X X X  X  X  X X X X  X X X X  X X X X  X  X X X X X X X  X X X X  X X X X X  X X X X X X  X  X X X X X X X X X X X X X X X X  X X  X  X X X X X X  X X X  X  X X X X X X X  X X X  X X X  189  X X X  X X  X X  X X X X X X X X X  X  X  X  APPENDIX F  Table F l : Sample locations ( N A D 83) Sample AT03-20-ij2b AT03-20-ij2c AT03-20-ij2d AT03-20-ij2e AT03-20-ij3a AT03-20-ij3b AT03-20-ij3c AT03-20-IJ4a AT03-20-IJ4b AT03-20-ij4c AT03-20-ij4d AT03-20-PA-1A AT03-20-PA-2B AT03-20-PB-2B AT03-20-PB-3B AT03-20-PC-1A AT03-20-PC2 AT03-20-PC-3A AT03-20-PD-1A AT03-20-PD-1B AT03-20-PD-2A AT03-20-PD-2B AT03-20-PD-3A AT03-20-PE-1A AT03-20-PE-3A AT03-20-PE-3B AT03-21-EF1-A AT03-21-EF1-B AT03-21-EF1-C AT03-21-EF1-D AT03-21-EF1-E AT03-21-EF1-F AT03-21-EF2-A AT03-21-EF2-B AT03-21-EF2-C AT03-21-EF2-D AT03-21-EF2-E AT03-21-EF2-F AT03-21-Ma AT03-21-PC-A AT03-21-PC-B AT03-21-PF-A AT03-21-PF-B AT03-21-PF-C AT03-21-PG-A AT03-21-PG-B AT03-21-PH-B AT03-21-PK-A AT03-21-PK-B  Eastings  Northings  575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575884 575742 575742 575742 575742 575742 575742 575742 575742 575742 575742 575742 575742 575742 575742 575742 575742 575742 575742 575742 575742 575742 575742 575742  6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602100 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243 6602243  Geochemistry °Ar/ Ar 4  x X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X  190  39  U-Pb  13  c  18  0  X X X X  X X X X  X X X X  X X X X X X X  X X X  Au Assay  X X X  X  X  X  X  X  X X  X X  X X  X  X  X  X  APPENDIX F  Table F l : Sample locations (NAD 83) Sample AT03-24 AT03-28 AT03-42 AT03-44-1 AT03-44-10 AT03-44-11 AT03-44-12 AT03-44-13 AT03-44-14 AT03-44-15 AT03-44-16 AT03-44-17 AT03-44-18 AT03-44-19 AT03-44-2 AT03-44-20 AT03-44-21 AT03-44-22 AT03-44-23 AT03-44-24 AT03-44-25 AT03-44-26 AT03-44-27 AT03-44-28 AT03-44-29 AT03-44-3 AT03-44-30 AT03-44-31 AT03-44-32 AT03-44-33 AT03-44-34 AT03-44-35 AT03-44-36 AT03-44-37 AT03-44-38 AT03-44-39 AT03-44-4 AT03-44-40 AT03-44-5 AT03-44-6 AT03-44-7 AT03-44-8 AT03-44-9 AT03-49 AT03-4a-b AT03-50 AT03-51-A AT03-51-B AT03-51-C  Eastings 577613 573556 577758 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 577809 576020 573293 576219 575925 575925 575906  Northings 6602505 6605367 6601257 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 6601758 .6601758 6601758 6601758 6601758 6601758 6601915 6603629 6602005 6602101 6602101 6602113  Geocher X X X X X X X X X X X X X X X X X X X X X X X X X  X X X X X X X X X X X X X X X X X X X X  191  1J  C  "O  Au Assay  APPENDIX F  Table F l : Sample locations (NAD 83) Sample AT03-51-D AT03-51-E AT03-51-F AT03-5a-b AT04-10 AT04-11 AT04-12 AT04-13 AT04-14 AT04-16 AT04- 2 AT04 - 20 - A AT04 - 20 - B AT04 - 20 - C AT04 - 20 - D AT04 - 20 - E AT04 - 20 - F AT04 - 20 - H AT04- 20 -1 AT04 - 20 - J AT04 - 20 - K AT04 - 20 - L AT04 - 20 - M  Eastings 575906 575891 575891 573283 576330 575516 577894 578966 577809 574004 577809 573459 573459 573459 573459 573459 573459 573459 573459 573459 573459 573459  AT04 - 20 - N AT04 - 21 - B AT04- 23 AT04- 25  573459 573459 575660 575422 574050  AT04- 3 AT04- 4 AT04- 5  577700 577817 577572  AT04- 6 - B AT04- 7 - B AT04- 8 - B AT04- 9  576671 574838 574884 574310  Northings 6602113 6602083 6602083 6603671 6604222 6603708 6601135 6601258 6601758 6603443 6601758 6603577 6603577 6603577 6603577  Geoche  I J  C  '°Q  Au Assay"  X X X X X X X X X X X  X  X  X X  6603577 6603577 6603577 6603577 6603577 6603577 6603577 6603577 6603577 6602200 6603169 6603084  X  6601269 6601847 6602483 6602340 6608489 6608579 6604486  X  X X X  X  X  X  X  X  X  X X X X X X X X X X X X X X  192  X  X  

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