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.Sc , The University of Alberta, 2000 A THESIS SUBMITTED IN PARTIAL F U L F I L M E N T OF THE REQUIREMENTS FOR THE DEGREE OF MASTER 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 A B S T R A C T A B S T R A C T Listwanite (carbonated-serpentinite), commonly associated with high-grade lode-gold 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 non-volatile chemical species, except where quartz-carbonate veining and/or Cr-muscovite are present in areas of intense carbonation (indicating S i 2 + , M g 2 + a n d K + metasomatism). The 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 talc-magnesite rock and depleted § 1 3 C (ca. -6%o) in carbonate. This combined with 5 1 8 0 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 A B S T R A C T 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 CONTENTS A B S T R A C T ii T A B L E OF CONTENTS iv LIST OF T A B L E S vii LIST OF FIGURES viii LIST OF ABBREVIATIONS xii LIST OF S Y M B O L S xiii P R E F A C E xvii A C K N O W L E D G M E N T S 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 (CARBONATED-SERPENTINITE) AT ATLIN, BRITISH COLUMBIA: A GEOLOGIC ANALOGUE 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 AND REACTION PATHS 20 2.6 IGNEOUS INTRUSIONS 22 2.7 MAGNETIC PROPERTIES... 22 2.8 IMPLICATIONS FOR C 0 2 SEQUESTRATION 23 2.8 IMPLICATIONS FOR LODE-GOLD MINERALIZATION 25 2.9 REFERENCES 27 C H A P T E R III: STRUCTURAL SETTING, TIMING AND ISOTOPIC CHARACTER OF LISTWANITE (CARBONATED-SERPENTINITE), ATLIN, BRITISH COLUMBIA: IMPLICATIONS FOR LODE-GOLD MINERALIZATION 33 iv T A B L E OF CONTENTS 3.1 INTRODUCTION '. 33 3.2 REGIONAL GEOLOGY AND ROCK UNITS . 34 3.3 STRUCTURAL ANALYSIS [ 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 HYDROTHERMAL ORGANIC MATERIAL 60 3.9 SOURCE OF GOLD AND CARBON 60 3.10 CONCLUSIONS 64 3.11 REFERENCES 65 C H A P T E R IV: CARBONATED SERPENTINITE (LISTWANITE) ATLIN, BRITISH COLUMBIA: A GEOLOGIC ANALOGUE TO CARBON DIOXIDE SEQUESTRATION -. :...70 4.1 INTRODUCTION 70 4.2 RELEVANCE 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 2 SEQUESTRATION 90 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 TABLE 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 137 6.1 CONCLUSIONS 137 6.2 REFERENCES '. 139 APPENDIX A: MISCELLANEOUS TABLES FOR CHAPTER IV 140 APPENDIX B: MINERALOGY 147 APPENDIX C: GEOCHEMICAL, STABLE ISOTOPE ANALYSES AND GOLD ASSAY 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 L I S T 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 18 Table 2.2: Volume changes 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 C H A P T E R IV Table 4.1: Mineralogy of carbonated serpentinite from Atlin, B .C 76 Table 4.2: Volume changes 91 C H A P T E R V Table 5.1: Geochemical analyses of replicates 108 Table 5.2: Representative geochemical analyses of ultramafic rocks from Atlin, B.C 109 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 vii LIST OF FIGURES LIST OF FIGURES CHAPTER I Figure 1.1: Locat ion map o f A t l i n , B . C 2 CHAPTER II Figure 2.1: Bedrock map o f the A t l i n area 9 Figure 2.2: Composite 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: Aeromagnetic map o f the A t l i n area 11 Figure 2.4: Outcrop and transmitted light images o f the harzburgite and serpen-tinite 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) Basal decollement-controlled listwanite and post-alteration dikes 16 Figure 2.7: Area l v iew and geological map showing recessive-weathering lineaments 19 Figure 2.8: S impl i f ied f low chart illustrating reaction path for listwanite 21 CHAPTER III Figure 3.1: Bedrock 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: Area l v iew 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 orienta-tions 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 i0 2 (TAS) plot of dike samples 49 Figure 3.13: Simplified flow chart illustrating the geological history of the Atlin area 52 Figure 3.14: Schematic block diagram illustrating the structural controls of list-wanite and dikes 55 Figure 3.15: 5 1 8 0 - 8 1 3 C plot of isotopic data from carbonate in listwanite 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 1 3 C 62 CHAPTER 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 Figure 4.4: Ternary phase and fluid H2O - CO2 activity diagrams of the listw-anite system 80 Figure 4.5: Wt% MgO - S i 0 2 circle diagrams 82 Figure 4.6: Ratio of residual error to standard error in whole rock geochemistry of carbonated samples 85 Figure 4.7: Plot of magnetic susceptibility and whole rock CO2 content 87 Figure 4.8: Composite image, detailed geologic, magnetic susceptibility, and calculated C 0 2 maps of a 2 m by 2 m area containing fracture-controlled zones of listwanite 88 Figure 4.9: Measured and calculated wt% CO2 across transect A-B from Figure 2.2b 89 Figure 4.10: Relationship of fracture permeability in advance of a reaction undergoing a gain in the volume of solids 92 Figure 4.11: H 2 0 - C 0 2 fluid diagram at 250 bars and 60°C 95 CHAPTER V 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 system 104 Figure 5.3: SVD solutions to a hypothetical two dimensional dataset using wei-ghted and unweighted techniques 112 Figure 5.4: SVD solutions to a hypothetical two dimensional dataset using wei-ghted and weighted-iterative techniques 115 Figure 5.5: Residual over analytical error calculated using an unconstrained sy-stem of equations and a MgO - S i02 diagram of the protolith, altered rock data and model protoliths calculated using unconstrained system of equations .....121 Figure 5.6: Residual over analytical error calculated using a constrained system of equations 124 Figure 5.7: Mass factor vs. wt% CO2 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 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 constrained-weighted 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 2 and b) residual over analytical error calculated using Gresens' analysis and the model protoliths calculated using the constrained-weighted system of equation 134 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 NAD 83 - North American Datum 83 50 - Compositional layering within the harzburgite unit 51 - Fabric defined by flattened arid stretched orthopyroxene crystals within harzburgite unit 52 - Fabric defined by sheared and stretched bastite (serpentinized orthopyroxene) within the serpentinite unit. 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 a , Lb, L c , La - Denotes the four main steeply-dipping listwanite zone trends 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 M I N E R A L S 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 iz - Lizardite Mgs - Magnesite M g t - Magnetite 0 1 - O l i v i n e Opx - Orthopyroxene Qtz - Quartz Srp - Serpentine Tic - Talc S Y M B O L S U S E D 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 Altp™'° -Alt weighted by the covariance matrix of the 46 samples of the protolith group. Co - Coefficient coverr- Covariance matrix defined by replicate analyses covprolo-Covariance 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 5 - M o d e l Protolith 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 e c i by the covariance matrix of the 46 samples of the protolith group 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 -Number of samples in a dataset XV LIST OF SYMBOLS S - Matrix representing a dataset S*"- Matrix S weighted by coverr Sapprox- SVD approximation of S Sapprox"™ - SVD approximation of Se", 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"'1- Upper limit of an element defined by the protolith group weighted by the covariance matrix of the 46 samples of the protolith group unwterr - Matrix to unweighted data weighted by coverr wterr - Matrix to weight a dataset by coverr wt - Matrix to weight a dataset by covprolo x- Contains the coefficients Co that when multiplied with P gives a 'best fit' to Alt z - Number of basis vectors in P Antigorite + Magnesite 2 Mg48Si34 0 8 5(OH)62 + 45 C 0 2 -5» 45 MgC0 3 + 17 Mg 3Si4O, 0(OH) 2 + 45 H 2 0 (R2) Antigorite -> Magnesite + Talc Mg 3Si4Oi 0(OH) 2 + 3 C 0 2 -S» 3 M g C 0 3 + 4 S i0 2 + H 2 0 (R3) Talc 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, fuchsite), sulfide (mainly pyrite) 20 CHAPTER II Assemblage Ai Serpentine +/- Olivine +/- Brucite Assemblage A3 Talc + Magnesite \ R i R 2 / Assemblage A2 Serpentine + Magnesite R 3 Assemblage A4 Quartz + Magnesite *Reaction R-| by-passed if no olivine or brucite present in the protolith (Assemblage Ai). 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 Ca 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 light-grey porphyritic feldspar-, quartz-dacite and a grey-brown porphyritic plagioclase-, K-feldspar-, biotite-, hornblende- and quartz- dacite. Al l contain sulfide minerals, mostly pyrite. Locally they are carbonated, but clearly cross-cut the listwanite. This cross-cutting 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 4 0 A r - 3 9 A r geochronological biotite sample from the grey-brown phase, both of 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. During serpentinization, iron contained in harzburgitic (roughly F090) 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"3 SI units)) and serpentinite unit (>50 to as high as 150 22 CHAPTER II (10~3 SI units)). This observation is useful for differentiating between the two units in lichen-covered areas where the degree of serpentinization is not easily discernable. Magnetite is progressively consumed during reaction R 2 (Hansen et ah, 2005; 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" 5 SI units) in rock containing >20 wt% C 0 2 , corresponding to complete progress of reaction R 2. A 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 2 content to within 5 wt%. 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 2 SEQUESTRATION The overall mineral transformation in listwanite-alteration is the same as that proposed for sequestration of C 0 2 in minerals, but in nature proceeds through a series of 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 C02-bearing fluid (Lackner et al., 1995; 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 Ri 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 Reaction AVs* (rxn) AVs (rock**) R 1 a: Ol -» Srp + Mgs 55.1% 4.2% R 1 b : Brc -> Mgs 13.8% 0.4% R 2: Srp -> Tic + Mgs 2.6% 2.3% R3: Tic -> Qtz + Mgs 28.5% 16.2% * 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 carbonate-filled veins orthogonal to the R 2 reaction front in Figures 2.2a and b may represent 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 CO2-bearing 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 2 in the fluid phase (Hansen et al, 2005; Chapter IV). 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, multi-phase 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 166-174 Ma (Mihalynuk et al., 1992) overlaps the age range of Cr-muscovite in the listwanite (168-172 Ma ( 4 0 Ar- 3 9 Ar); Ash, 2001). 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 Cr-muscovite-bearing listwanite zones along the basal decollement and in the L a orientation. 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, BC: 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, VA, United States, 146 p., Translated from the Russian, Listvenity, ikh genezis i klassifikatsiya, Akad. Nauk AZ 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. 2463-2477. 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. 446-463. 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 2 Metasomatism of Serpentinites, South of 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 AND 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 K-metasomatized (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 2 (Fig. 3.1, insert) and comprises variably serpentinized, carbonated and 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 quartz-34 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 post-obduction). 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 a and L b orientations associated with listwanite at head of Monarch Mountain Hiking trail (photo by M . Mihalynuk, August 2003) (E 575900, N 6602100, NAD 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, NAD 83. 40 CHAPTER III 3.3.2 LATE SYN- 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 a (140° trend), Lb (50° trend), L c (N-trending) and L -a CHAPTER III )l I I l l I i i i I 1 I I i i I I I I I I I l l l I l I l l I l l I I I l l l l I l 35 40 45 50 55 60 65 70 75 Wt% Si0 2 (Dry) Figure 3.12: Total alkali vs. S i0 2 (TAS) plot (LeBas et al., 1986) of dike samples 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. Al 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, K-feldspar 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 coarse-grained 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). Al 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 AND 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 4 0 A r - 3 9 A r dates. In 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. Figure 3.13 outlines the simplified geologic history of the area. 4 0 A r - 3 9 A r and U-Pb data are presented in Appendix F. Al l 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 A r - 3 9 A r K-Ar U-Pb Interpretation 01AT-1-2 Cr- Muscovite Listwanite This Study 128.0+/-.1.9 / / Carbonate-Alteration 02AT-8-1 (Goldstar) Cr- Muscovite Listwanite This Study 172.7+/-2.0 / / Carbonate-Alteration AT03-44-7 (Anna) Cr- Muscovite Listwanite This Study 174.4+/-1.4+ / / Carbonate-Alteration Pictou Cr- Muscovite Listwanite Ash (2001) 165 +/-.4 121 +/-4* / Carbonate-Alteration 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 AT03-28 Biotite Dacite This Study 84.0+/-0.6" / / Cooling 280 °C AT03-5 Zircon Dacite This Study / / 150.7+/-0.6 Crystallization age FOJB Zircon Granitiod Mihalynuket al. (1992) / / 170.4 +/-5 Crystallization age FOJB Zircon Granitiod Mihalynuk et al. (1992) / / 171.5+/-3.3 Crystallization age FOJB Hornblende Granitiod Harris et al. (2003) 172.7 +/-1.7 / / Cooling 500 °C FOJB Biotite Granitiod Harris et al. (2003) 165.1 +/-1.6 / / Cooling 280 °C FOJB Biotite Lamprophyre Harris et al. (2003) 161.8 +/-1.6 / / Cooling 280 °C FOJB Biotite Lamprophyre Harris et al. (2003) 165.3+/-1.6 / / Cooling 280 °C SLB Zircon Granitiod Mihalynuket al. (1992) / / 83.8+/-5 Crystallization age MMB Zircon Granitiod Anderson et al. (2003) / / 172 +/-0.3 Crystallization age LMB Zircon Granitiod Anderson et al. (2003) / / 171 +/-0.3 Crystallization age M/U Stock Biotite Granitiod Hunt& Roddick (1988) / 167 +/- 3 / Cooling 280 °C * 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 A L T E R A T I O N D I K I N G P L U T O N I S M LT) o LU u < I— LU CC U y 1/1 < CE 3 < CC LU CL CQ or < u m u e mp* mp b i zr b .^+.+.-H , l & V z r ^ Surprise Lake Bathol i th ;zrc — z r r bi x p l x K-..V-..V:—V v vr B o w s e r B a s i n Fourth of July Bathol i th V V ] K u t c h o 1 ^ F o r m a t i o n N o r t h e r n C a c h e C r e e k Figure 3.13: Simplified flow chart illustrating the geological history of the Atlin area. The symbols bi, mu, and mp represent 4 0 A r / 3 9 A r dates acquired from biotite, muscovite, 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. Al l supporting data is located in Appendix D. The reliable 4 0 A r / 3 9 A r Cr-muscovite dates of this study and Ash (2001) (Table 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 4 0 A r - 3 9 A r plateau ages different from the 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 3 9 K atoms are converted to 3 9 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 post-obduction 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 syn-53 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 4 0 A r - 3 9 A r plateau age of 84.0 +/- 0.6 Ma which is 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 quartz-carbonate 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 1 3C from -1 to -7%o VPDB and 5 I 8 0 from 6 to 16%o VSMOW. Within outcrop AT03-20, however, there is a clear difference in the stable isotope composition of the talc- and magnesite-zones. The talc-zone is depleted in 1 3 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 AA ' A K A A • A A A i x 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) -2 -7 -4 -3 o 1 3 C (VPDB) -1 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 Location n 6 1 3 C (VPDB) %0 6 1 80 (VSMOW)%0 5D(VSMOW)%O Notes Reference Atlin 5 - 5.7 (3.8 to 7.7) Silicate (Ai) This Study Atlin 28 -3.5 (-2.3 to -6.4) 12.9 (6.3 to 15.4) Mgs & Dol (Ri-A 2) This Study Atlin 9 -4.8 (-0.3 to -6.2) 12.1 (10.2 to 17.3) Carbonate (R2-A3) This Study Atlin 14 -4.4 (-2.2 to -6.1) 10.5 (8.3 to 14.0) Carbonate (R3-A4) This Study Atlin 14 -4.6 (-1.3 to -5.6) 13.9 (12.9 to 15.1) Carbonate (R2-A3)x This Study Atlin 3 -5.3 (-3.8 to -6.0) 14.8(14.0 to 15.7) Mgs-Dol Vein from R2 This Study Atlin 1 -3.3 8.3 Carbonated Diabase This Study 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) Bridge River, B.C. N/A (-5.1 to-6.7) (24 to 25) Carbonate in Listwanite Madu et al. (1990) Timmins, Ont. N/A (-7.5 to -7.9) (11.7 to 16.5) Mgs in Mgs-TIc rock Schandland Wicks (1991) 'Calculated from quartz-h^O equilibrium and fractionation factor of 3.7 x denotes samples containing black organic material Compositions are given as an average and/or range given within parenthesis 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, NAD 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 I 3 C = -6%o and 5 , 8 0 = 15.5%o. The talc-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 1 3C of around -6%o for carbonate approaches an organic signature. Furthermore, the 5 1 3C of -27%o for organic material sampled from the Nahlin 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). Similar-looking 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). Al l 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 C H 4 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 quartz-zone 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 a) I CO • Contain black organic matter • Lack black organic matter Talc Zone -Detection Limit -QuartzZone -4 replicates 3" 20 a. a b) 20 25 C02(wt%) Figure 3.18: Gold content of samples verses a) whole rock C O 2 . b) 8 1 3 C in carbonate minerals * Contain black organic matter • 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 Cr-muscovite 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 post-accretionary felsic magmatism. The large range in 8 1 8 0 suggests that there was interaction of listwanite-altering 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 I 3 C (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 4 0 A r - 3 9 A r (Cr-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 1 3 C within magnesite is around -6%o which is consistent with an organic signature and is supported by the presence of organic material within listwanite-altered rocks. The large range in 8 1 8 0 of between 6.3%o and 17.3%o suggests interaction 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 . 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 1 3 C values. 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): 4 0 A r / 3 9 A r Geochronology Results 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): Carbonate-Altered 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 4 0 A r / 3 9 A r 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 88-2, 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-Stibnite-Quartz 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. 2463-2477. 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 1987-1, 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 ANALOGUE TO CARBON 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 is chemically bound within a carbonate mineral structure by reaction with M g 2 + or Ca 2 + 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 1 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. 70 CHAPTER IV major chemical species except H 2 0 and C 0 2 , and the overall mineralogical 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 2 sequestration potential and impact on porosity and permeability. Mg3Si 20 5(OH)4 + 3 C 0 2 -> 3 M g C 0 3 + 2 S i0 2 + 2 H 2 0 (RA) (Serpentine -> Magnesite + Quartz) Mg2Si04 + 2 C 0 2 - » 2 M g C O _ + S i 0 2 (RB) (Olivine -> Magnesite + Quartz) 4.2 RELEVANCE 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 2 from a point source such as a coal-fired power plant, and 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 2 injection into serpentine reservoirs (at 250 bars and 60°C) 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 R A a n d B 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 4 0 A r - 3 9 A r age determination of chromium-muscovite to be in the 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 quartz-carbonate veins to be in the range of 210 - 280°C. Homogenization temperatures (TIIL-v ( 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). Fracture-72 C H A P T E R IV 6 6 0 6 0 0 0 Basaltic dikes Porphyritic dikes | Listwanite i Carbonate-altered 1 fault breccia Accretionary complex sedimentary rocks Meta basalt 6 4 3 Serpentinite Dunite Harzburgite Fault Basal Decollement Road Drainages NAD 83 Grid 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 XRD 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 a to antigorite and magnesite (Fig. 4.3a, assemblage A 2 of Fig. 4.2): 34 Mg 2 Si0 4 + 20 C 0 2 + 31 H 2 0 -» Mg 48Si34 0 85(OH) 6 2 + 20 M g C 0 3 (Ru) 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 ! a . Lacking evidence to the contrary, 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) 2 + C 0 2 -> M g C 0 3 + H 2 0 (R,b) Brucite -> Magnesite 75 CHAPTER IV Table 4.1: Mineralogy of carbonated serpentinite from Atlin, BC Sample Chr Mgt Brc Ol Srp Mgs Tic Qtz C 0 2 (wt%) 01AT-8-1 X X x A, 0.06 01AT-13-1 X X X A , 0.10 01AT-3-1 X X X X A i 0.21 01AT-10-1 X X X X X A , 0.15 01 AT-10-2 X X X X X x v A , 0.26 01AT-2-2 X X X X X A, 0.33 01AT-9-1 X X X X X Ri 2.10 01AT-11-1 X X X X X Ri 2.57 01AT-1-9 X X X X A 2 3.37 01AT-6-3 X X X X A 2 4.00 01AT-1-8 X X X X A 2 4.60 01AT-13-2 X X X X A 2 7.12 01AT-11-2 X X X X A 2 9.60 01AT-7-3 X X X X X R 2 3.40 01AT-1-7 X X X X X R 2 7.19 01AT-1-6 X X X X X R 2 9.54 01AT-9-2 X X X X R 2 17.26 01AT-7-1 X X X X R 3 21.83 01AT-5-4 X x y X X X R 3 28.01 01AT-1-5 X . x z x w X X X R 3 34.00 01AT-4-1* X X X X R 3 34.34 01AT-5-2 X X X A 4 35.20 01AT-6-1* X X X A 4 36.19 v only occurs in small veins w occurs in small isolated patches y armored relicts and late mantling ; of chromite and pyrite z magnetite in late fractures and late mantling of chromite * sample contains Cr-muscovite Sample locations in Appendix F. 76 CHAPTER IV Assemblage A i Serpentine +/- Olivine +/- Brucite Assemblage A3 Talc + Magnesite \ R i R 2 / Assemblage A2 Serpentine + Magnesite Rs Assemblage A 4 Quartz + Magnesite *React ion R 1 by-passed if no ol ivine or brucite present in the protolith (Assemblage A i ) . 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 2 : antigorite to magnesite (M 2) + talc, c): Reaction R 3 : magnesite (M3) + quartz assemblage, d): Close-up of (c). M i , M 2 and M 3 are interpreted to represent magnesite generated during reactions Ri , R 2 and R3 respectively. Note that magnesite M 2 rims Mi and that M 3 rims M 2 and forms euhedral boundaries with quartz. 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 a and Rib will be considered together as reaction 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 2 0 (Fig. 4.4b). 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 4 8 Si34 0 85(OH)62 + 45 C 0 2 -> 45 MgC0 3 + 17 Mg 3Si40,o(OH) 2 + 45 H 2 0 (R2) 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 2 content of the fluid phase (Fig. 4.4b). The cores 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 2 in the fluid phase (Fig. 4.4b). Mg3Si4Oio(OH)2 + 3 C 0 2 -> 3 M g C 0 3 + 4 S i0 2 + H 2 0 (R3) Talc -> Magnesite + Quartz 79 Figure 4.4: a) Ternary phase diagram comparing the observed mineral content and whole rock composition in a MgO+FeO-S i 0 2 - C 0 2 ternary diagram projected from H 2 0 . b) Mineral stability in the system MgO-Si0 2 -C0 2 -H 2 0 as a function of activity of H 2 0 and C 0 2 in the fluid phase calculated using PTAX and the mineral database of Berman (1988). The dashed line is the metastable extension of reaction R i a . The arrowed dashed line is the path of Pfl u i d = 500 bars for a binary H 2 0 - C 0 2 fluid, calculated with the CORK equation of state (Holland and Powell 1991). 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 R3 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 Mi 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 Mg during mass increase (CO2 addition). Serpentinite and listwanite overlap completely in composition if 81 CHAPTER IV C D 2 5 ^ 20 15 10 5 0 C 0 2 Content 35wt% a 0 10 15 20 25 30 35 40 Wt% S i 0 2 55 50 45 G-35 O _g>30 C 0 2 Content )35wt% • 30 wt% 25 wt% N , < f \ A t 9 * ' / 20 wt% / 15wt% D u n i t e . o 10wt% / N. y o 5 wt% Harzburgite o 0 wt% b 0 5 10 15 20 25 30 35 40 45 50 55 wt% S i 0 2 (Dry) 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 E n 9 o 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 Fo9o/Enc>o rich rocks. 82 CHAPTER IV major oxide compositions are renormalized to 100% excluding H 2 0 and C 0 2 (Fig. 4.5b). The variation of Si0 2:MgO ratio within the suite of rocks may be a function of the degree of initial serpentinization, or the amount of initial orthopyroxene (Fig 4.5b). Whole-rock geochemical compositions were tested against model sequestration reactions R i a , Rib, R2 and R3 using the method of Gordon (2003), a new geochemical mass balance technique that quantitatively accounts for protolith heterogeneity. The six samples with assemblage A] (Table 4.1) and the lowest C 0 2 content (<0.5 wt%; 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 a and Rib, four samples with talc but no quartz were considered to have experienced reactions R i a , Rib and R 2 , and the remaining six quartz-bearing samples were considered to have experienced the full suite of reactions. Reaction R i a requires the model mass-transfer vector for the seven low-C0 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 2 and R 3 have the ratios of C added to 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 a , Rib, R2 and R3 means that this method does not constrain the 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 least-squares 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, Ni 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 ( R i a & b , R 2 and R 3 ) . Table of all residuals is included in the appendix. 85 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 2 is consistent with conservation of Fe during magnetite destruction. There is a corresponding decrease in whole rock magnetic susceptibility in samples recording reaction R 2 (Fig. 4.7). We have exploited the correlation of whole-rock C 0 2 content and magnetic 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 2 , virtually all magnetic susceptibility appears to have been destroyed by about 20 wt% C 0 2 , which corresponds to the completion of reaction R 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 2 , and thus reaction progress: Magnetic Susceptibility (10"3 S.I. units) = 61.003 - 3.0544(wt% C0 2 ) (4.1) 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 (R2) transects the pavements in two discrete reaction zones that are flanked by distal antigorite + magnesite assemblages (A 2). The mineralogical 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 2 content for samples along transect A-B is within 5% of C 0 2 content calculated from magnetic susceptibility and (Equation 4.1, Fig. 4.9). Calculated C 0 2 content increases continuously 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 120-Magnetic Susceptibility = -3.0544(CO2) + 61.003 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 b l i WML • Srp + Mgs (Rust Stained) Srp + Mgs Carbonate filled veins front permeabiirty| 1*1 u 30 • — . V i J PU< j '•.'Si £2' ] x = sample location 90 2 80 'c 3 a » 1 60 | SO # 1 it Magnetic Susceptibility (measured) CO Content (calculated) 12 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, 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. 88 CHAPTER IV 25 t20 C M ° 15 sc o £ 1 0 o £ 5 0 • Calculated from magnetic susceptibility <§> Measured I \ & <§> .< .^... 70 cm A B Figure 4.9: Measured and calculated wt% C 0 2 across A-B from Figure 2.2b. Wt% C 0 2 calculated using E q i and magnetic susceptibility data of Figure 2.2c. The range in calculated C 0 2 content reflects the full range of four magnetic susceptibility measurements at each location. 89 CHAPTER IV abrupt change in C 0 2 content (Fig. 4.9). The gradation in magnetic susceptibility at the 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 VOLUME 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 2, then the volume 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 (2.3 % in a serpentinite rock 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 2 SEQUESTRATION 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 Tab le 4.2: Vo lume C h a n g e s R e a c t i o n AVs* (rxn) AVs ( rock**) R 1 a : O l -» Srp + M g s 5 5 . 1 % 4 . 2 % R 1 b : Brc -> M g s 13.8% 0.4% R 2 : Srp -» T ic + M g s 2.6% 2 . 3 % R 3 : T ic -» Qtz + M g s 28 .5% 16 .2% * Calcu la ted from Berman (1988) at 250°C and 500 bars (Chapter IV) Assuming 2 .5% brucite and 7 .5% relict olivine by volume. 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 R 3 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 2 is a C02-rich 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 1 -1 -0.75 -0.5 -0.25 0 Log a(H20) Figure 4.11: Mineral stability in the system MgO- Si02-C02-H20 as a function of activity of H2O and C 0 2 in the fluid phase calculated at the Gruppo di Voltri serpentinite 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. 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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, 753-773. 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 2 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, 30, 93-108. Seifritz, W. (1990): C 0 2 Disposal by Means of Silicates. Nature, 345, 486. 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). Al 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 non-volatile 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 Serpentine +/- Olivine +/- Brucite Hz Assemblage A3 Talc + Magnesite \ R i Ryi Assemblage A2 Serpentine + Magnesite Assemblage A4 Quartz + Magnesite *React ion R 1 by-passed if no ol ivine or brucite present in the protolith (Assemblage A i ) . 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 9 0 /En 9 0 rich rocks, c) Ternary phase diagram comparing the observed mineral content 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 2 + - M g 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. Al 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 2 , it is very likely that the chemical range in CaO (and all other chemical species) 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 2 ) , talc (R2, A 3 ) and quartz ( R 3 , A 4 ) . For simplicity, the five groups are labelled protolith, serpentinite zone, magnesite zone, talc zone, and quartz zone. Al l 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 ANALYTICAL 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. The results are included in Appendix C. The samples were analyzed for major, minor and trace elements, C 0 2 content by induction furnace, and total volatile content by loss on ignition (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 S i 0 2 T i 0 2 A l 2 0 3 F e 2 0 3 M n O M g O C a O N a 2 0 K 2 0 P 2 0 5 C r 2 0 3 Ni V Zn L O I C O . Total AT03-pc2' 38.71 0.013 0.75 8.03 0.108 40.22 0.85 - 6 c Weighted and Unweighted SVD Fits o Matrix S Approximation of Matrix S (Unweighted) * Approximation of Matrix 5 (Weighted) 4 5 6 Element X 10 b) 25 .20 QJ •15 c 01 10 SVD Fit in Weighted Space o Matrix S (Weighted) * Approximation of Matrix S (Weighted) 10 15 20 Element X (Weighted) 30 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 (E\,E2) ,err .err (E\,Ee) COV, (E2,E\) ,err (E2,Ee) (5.4) err ( V c o v - ) ' (5.5,6) w/w/e ) r = yjcov^, S = unwterr • Sew", Sapprox = unwterr • Sapprox™ (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 Proto Srp-zone Mgs-zone Tic-zone Qtz-zone 1a 16 - 16 16 16 2a 15 - 16 16 16 3a 15 - 16 15 15* 4a 15 - 16 15 15* 5a 15 - 16 14 15* 6a 14 - 15 14 15* n 46 9 42 44 19 * contains one or more negative va lues within the approximation of the dataset. S V D not done on Srp-zone because of the smal l number of ana lyses. Table 5.4: Lowest rank of each group using weighted SVD Proto Srp-zone Mgs-zone Tic-zone Qtz-zone 1a 16 - 16 16 15* 2a 14* - 15 14* 14* 3a 10 - 14 12 13* 4a 10 - 14 11 13* 5a 9 - 14 11 13* 6a 9 - 11 11 11* n 46 9 42 44 . 19 * contains one or more negative va lues within the approximation of the dataset. S V D not done on Srp-zone because of the smal l number of ana lyses. 114 CHAPTER V Weighted Iterative SVD fits without covariance in X and Y 1 2 3 4 5 6 7 Element X (Moles/Kg) 2 3 4 5 6 7 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 2 0 removal. Dolomite veins, common in weakly 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 P r o t o S r p - z o n e M g s - z o n e T i c - z o n e Q t z - z o n e 1 a 16 16 16 15 2 a 13 13 12 13 3 a 11 12 11 13 4 a 10 11 11 12 5 a 9 11 11 11 6 a 9 11 10 11 n 46 9 42 44 19 S V D not done on Srp -zone because of the smal l number of ana lyses . 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 (5.11) P = The subscript z represents the number of basis vectors in P. The composition of each altered sample (n) is designated Alt(n), a 1 by e vector listing moles element per Kg rock. Thus, x{n)=Alt(n)\P (5.12) where the 'V symbol gives the least squares solution to P-X(„j = Alt(n), and provides the vector X(n), containing the coefficients Co that when multiplied with P gives a 'best fit' to 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(n)=MPin)*Altw ' (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 Proto Srp-zone Mgs-zone Tic-zone Qtz-zone Full Rank 16 - 16 16 16 Unweighted 15 - 16 15 15* Weighted 10 - 14 12 13* Weighted iterative 11 - 12 11 13 n 46 9 42 44 19 * 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 2 content. The vertical dimension corresponds to the elements. 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 3a 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 Al Fe Mn Mg Cn N a K P Cr N i V Zn b) 3a > >-3a <. -3a o Protolith Samples + Altered Samples o Model Protolith Data 3 4 5 Si (Moles/Kg) Figure 5 .5 illustrating of MP. : a) Residual over standard error calculated using Matlab left division on data reduced in rank to 3a. b) M g vs. Si plot that MP mimics the actual data of the altered samples because there are no constraints placed on the chemical make-up o > —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 } UE\ pl= and pu = Jhe J , thus pi < MP < pu for all e (5.14) 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 | | > -3cj ] > 3a | < -3a Figure 5.6: 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 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 1.4 O 1.3 rc 1.2 1.1 0.9 | Calculated Range in mf from Geochemistry 0 Model Calculated mf o o 10 15 20 25 C 0 2 (Wt%) 30 35 40 45 • Protolith Samples + Altered Samples o Model Protolith Data Si (Moles/Kg) Figure 5.7: a) G a i n in mass vs. CO2 content. Circles represent model calculated mfs wh ich are in good agreement wi th the range calculated from the total dry renormalized geochemistry assuming the passive di lut ion hypothesis, b) M g vs. S i diagram showing the altered samples, protolith samples and calculated MPs. 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. cov proto ( n p m ' " \ nP"»" V° (£ l ) j °(/•!,/• 2) -pr"'" ( r : P n " " \ 2 uH>-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 of the species 5 that cannot be accounted for by the given protolith range in composition and the passive dilution hypothesis, b) Same as a) except H pa it shows the more significant residuals that exceed 10 standard errors. 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 rock-forming 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 clino-pyroxene); 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 BI , 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 C H A P T E R V calculated by data reduced in rank by unweighted svd calculated by data reduced in rank by weighted iterative svd Si I Ti AI Fe Mn Mg Ca Na K I' Cr N i V Zn -3o | | a 3g b) si I Ti Al Fe 1 Mn Mg Ca Na K P Cr Ni v Zn d) calculated by data reduced in rank by weighted svd -3o [ ] ; !a o unweighted svd « weighted svd o weighted iterative svd 15 20 25 30 35 « C 0 2 (wt % oxide) 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 well-behaved 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) S i T i Al Fe M n M g Ca N a K P Cr Ni V Z n 15 20 25 30 3a > gg > -3a • > 3a | < -3a C 0 2 (wt % Oxide) 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 sub-reactions fossilized as spatially distinct zones. The index minerals of magnesite, talc and quartz represent three metamorphic isograds defining the magnesite-, talc- and quartz-zones (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 2 + - M g 2 + metasomatism) and limited K + (Cr-muscovite) and possibly Ca 2 + 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 1 3 C within magnesite is around -6%o which is consistent with an organic signature and is supported by the presence of organic material within listwanite altered rocks. The large range in 5 l s O of between 6.3%o and 17.3%o suggests interaction 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 1 3C values (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 magnesite-and 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): Carbonate-Altered 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. 2463-2477. 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 Sample S i 0 2 TI0 2 A l 2 0 3 F e 2 0 3 MnO MgO C a O N a 2 0 K 2 0 P 2 0 5 C r 2 0 3 Ni V Zn LOI Total co2 01AT-8-1 41.50 0.012 0.140 7.990 0.098 38.61 0.02 0.03 0.01 0.012 3617 2191 23 25 11.65 100.66 0.06 01AT-13-1 40.64 0.014 1.190 6.930 0.088 39.12 0.15 <0 a 3 s ^ o o ? O) © S ID I ^ * 3 CO »-U5 rol - 9 9 m if) CD XI CO T3 C ro CD c o 9 9 9 9 9 CO •g to " 9 9 -CO CO CO t o T- 00 o o ro a: CN < CO OT H < i i S S CD C _C) CO B v « i ; = s C 142 APPENDIX A Tab le A 3 : Hypothet ical data supporting Figures 5.2 and 5.3 Figure 5.2 1 2 3 4 Covariance Matrix X 2.0 7.0 8.0 - 0.09 0.00 Y 3.0 4.3 8.0 - 0.00 0.80 Figure 5.3a 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 Figure 5.3b X 1.0 4.0 7.0 8.5 0.09 -0.23 Y 2.0 3.0 2.9 8.1 -0.23 0.80 143 APPENDIX A Table A4 : Residual (moles/Kg) from mass balance using full rank data Ti Al Fe Mn Mg Ca Na K Cr Ni Zn 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 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 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 . 0 0 9 3 0.0000 0 . 0 3 1 3 0.0000 0.0000 0.0000 0.0000 0 . 0 0 2 7 0.0000 - 0 . 0 0 0 2 9 0.0000 0.0000 - 0 . 0 0 0 7 0.0000 - 0 . 0 1 1 9 0.0000 0 . 0 4 9 0 0.0000 0.0000 0.0000 - 0 . 0 0 1 9 - 0 . 0 0 0 5 0.0000 - 0 . 0 0 0 2 10 0.0000 0.0000 0 . 0 1 0 6 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 - 0 . 0 0 1 8 0.0000 - 0 . 0 0 0 1 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 . 0 0 0 4 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 . 0 0 1 2 0.0000 - 0 . 0 0 0 1 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 . 0 0 0 1 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 . 0 0 0 5 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 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 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 . 0 0 0 1 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 . 0 0 0 3 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 . 0 0 0 1 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 . 0 0 0 2 33 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0 . 0 0 6 3 0.0000 0 . 0 0 0 3 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 . 0 0 0 1 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 . 0 0 1 4 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 . 0 1 0 2 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0 . 0 0 2 3 0.0000 - 0 . 0 0 0 1 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 . 0 0 0 2 45 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0 . 0 0 4 9 0.0000 0.0000 - 0 . 0 0 0 4 0.0000 0 . 0 0 0 2 144 APPENDIX A Table A4: (cont.) A l Fe M n M g C a Na K P C r Ni V Z n 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 -0.1407 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0019 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 0.0002 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0002 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0013 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 0.0000 0.0000 0.0014 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0017 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 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 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 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 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 0.0015 0.0000 0.0002 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 0.0000 -0.0006 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 0.0029 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 0.0000 0.0000 0.0014 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 0.0000 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 0.0000 0.0000 0.0000 -0.0008 0.0000 0.0000 0.0000 0.0000 0.0000 -0.0094 -0.0095 0.0000 0.0002 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 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 0.0008 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 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 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 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 0.0006 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 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 -0.0002 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 S i T i 46 0.0000 0.0000 47 0.0000 0.0000 48 0.0000 0.0000 49 0.0000 0.0000 50 0.0000 0.0000 51 0.0000 0.0000 52 0.0000 0.0000 53 0.0000 0.0000 54 0.0000 0.0000 55 0.0000 0.0000 56 0.0000 0.0000 57 0.0000 0.0000 58 0.0000 0.0000 59 0.0000 0.0000 60 0.0000 0.0000 61 0.0000 0.0000 62 0.0000 0.0000 63 0.0000 0.0000 64 0.0000 0.0000 65 0.0000 0.0000 66 0.0000 0.0000 67 0.0000 0.0000 68 0.0000 0.0000 69 0.0000 0.0000 70 0.0000 0.0000 71 0.0000 0.0000 72 0.0000 0.0000 73 0.0000 0.0000 74 0.0000 0.0000 75 0.0000 0.0000 76 0.0000 0.0000 77 0.0000 0.0000 78 0.0000 0.0000 79 0.0000 0.0000 80 0.0000 0.0000 81 0.0000 0.0000 82 0.0000 0.0000 83 0.0000 0.0000 84 0.0000 0.0000 85 0.0000 0.0000 86 0.0000 0.0000 87 0.0000 0.0000 88 0.0000 0.0000 89 0.0000 0.0000 145 APPENDIX A Table A4: (cont.) Si Ti Al Fe Mn Mg Ca Na K P Cr Ni V Zn 9 0 0 . 0 0 0 0 0 . 0 0 0 0 -0.0036 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0.0002 91 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0.0007 9 2 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 -0.0069 0.0039 0 . 0 0 0 0 0 . 0 0 0 0 9 3 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0.0024 0 . 0 0 0 0 0 . 0 0 0 0 9 4 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 -0.0085 0 . 0 0 0 0 0.0005 9 5 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 9 6 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0.0110 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 -0.0075 0 . 0 0 0 0 0 . 0 0 0 0 9 7 0 . 0 0 0 0 0 . 0 0 0 0 -0.0006 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0.0008 0 . 0 0 0 0 0 . 0 0 0 0 9 8 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 9 9 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 . 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0.0013 0 . 0 0 0 0 0 . 0 0 0 0 1 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 -0.0019 0 . 0 0 0 0 0.0003 101 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 1 0 2 1.1134 0 . 0 0 0 0 0 . 0 0 0 0 -0.1992 0.0210 -1.2388 1.1090 0 . 0 0 0 0 0.0520 0 . 0 0 0 0 -0.0006 -0.0076 0 . 0 0 0 0 0.0006 1 0 3 -0.4236 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0.2169 0 . 0 0 0 0 . 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 104 0.4140 0 . 0 0 0 0 0.0123 -0.1373 0.0069 -0.3504 0.7551 0 . 0 0 0 0 0:0730 0 . 0 0 0 0 0 . 0 0 0 0 -0.0066 0 . 0 0 0 0 0.0006 1 0 5 0 . 0 0 0 0 0 . 0 0 0 0 0.0618 0.0593 -0.0051 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0.0102 0 . 0 0 0 0 -0.0016 0.0008 0 . 0 0 0 0 0.0001 1 0 6 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0.0022 0 . 0 0 0 0 0 . 0 0 0 0 1 0 7 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 -0.0007 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0.0053 0 . 0 0 0 0 0 . 0 0 0 0 0.0037 0 . 0 0 0 0 0 . 0 0 0 0 1 0 8 0.9357 0 . 0 0 0 0 0 . 0 0 0 0 -0.0093 0 . 0 0 0 0 -0.7992 0 . 0 0 0 0 0 . 0 0 0 0 0.0312 0 . 0 0 0 0 0 . 0 0 0 0 -0.0078 0 . 0 0 0 0 -0.0001 1 0 9 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 -0.0037 0 . 0 0 0 0 0.0001 1 1 0 0 . 0 0 0 0 0 . 0 0 0 0 -0.0126 0.1559 -0.0084 0 . 0 0 0 0 0.0165 0 . 0 0 0 0 0.0102 0 . 0 0 0 0 0 . 0 0 0 0 0.0031 0 . 0 0 0 0 0 . 0 0 0 0 111 0 . 0 0 0 0 0 . 0 0 0 0 -0.0144 -0.0139 -0.0066 0 . 0 0 0 0 0.1659 0 0 0 0 0 0.0053 0 0 0 0 0 -0.0006 0.0064 0 . 0 0 0 0 0.0004 1 1 2 -0.2459 0 . 0 0 0 0 0.1012 0.1454 0 . 0 0 0 0 0.1187 0.0733 0 . 0 0 0 0 0.0451 0 . 0 0 0 0 0.0127 0 . 0 0 0 0 0 . 0 0 0 0 0.0006 1 1 3 -1.2349 0.0016 0.0161 0 . 0 0 0 0 -0.0053 0.4924 0 . 0 0 0 0 0 . 0 0 0 0 0.0046 0.0030 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0.0001 114 -1.6169 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0.5806 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 0 . 0 0 0 0 -0.0049 -0.0011 0 . 0 0 0 0 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 C 0 2 01AT-8-1 X X X X x A, 0.06 01AT-13-1 X X X X A , 0.10 01AT-10-1 X X X X X X A, 0.15 AT03-44-25 X X X X X X A, 0.16 01AT-3-1 X X X X X x A , 0.21 AT03-42 X X X X X X X A , 0.22 AT03-44-17 X X X X X A, 0.22 01AT-10-2 X X X X X X x * v X A, 0.26 AT03-44-24 X X X X X A , 0.27 AT03-51C X X X X X X A , 0.27 AT04-21b X X X X X A , 0.30 AT03-44-30 X X X X X X X A, 0.32 AT04-3 X X X X X X A, 0.32 01AT-2-2 X X X X X X X A , 0.33 AT04-9 X X X X X A, 0.34 AT04-6B X X X X A, 0.38 AT04-11 X X X X A , 0.39 AT03-20-PC2 X X X X X X x A , 0.41 AT03-44-26 X X X X X X X A , 0.44 AT03-44-34 X X X X X A, 0.44 AT03-20-PC3a X X X X X X A , 0.48 AT03-44-23 X X X X X X A , 0.49 AT03-20-PC1a X X X X X X A , 0.53 AT03-21-PCb X X X X X X X A, 0.58 AT04-13 X X X X X A , 0.59 AT04-16 X X X X X X X A , 0.61 AT03-20-PA1a X X X X X X A , 0.64 AT03-21-PGb X X X X X X A, 0.64 AT04-10 X X X X X X X X A, 0.66 AT03-21-Ma X X X X X X X A, 0.68 AT03-21-PCa X X X X X X X X A , 0.69 AT03-44-35 X X X X X X A , 0.71 AT03-20-PE3b X X X X X X X X A, 0.74 AT03-21-PKb X X X X X X X A, 0.74 AT04-23 X X X X X X A , 0.76 AT03-21-PFb X X X X X X A , 0.77 AT03-21-PGa X X X X X X A , 0.80 AT03-44-20 X X X X X X A, 0.80 AT03-21-PFC X X X X X X X A, 0.82 AT03-51E X X X X A , 0.83 148 APPENDIX B Table B1 (continued): Mineralogy of carbonated se rpentinite from Atlin, BC Sample Chr Mgt Opx Brc Ol Atg Liz Mgs Tic Qtz Dol Cal Chi C 0 2 AT03-21-PFa X X X X X X X A, 0.86 AT03-20-PE3A X X X X X X X A, 0.87 AT03-21-PKa X X X X X X A, 0.88 AT03-44-14 X X X X A, 0.89 AT03-20-PD2a X X X X X X A, 0.95 AT03-20-PA2b X X X X X X X A i 0.96 AT04-4 X X X X A, 1.11 AT03-44-21 X X X X X X A, 1.20 AT03-20-PE1a X X X X X A, 1.31 AT03-21-PHb X X X X X X X A, 1.31 AT03-20-PB3b X 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 X X X A, 3.17 AT03-44-22 X X X X A, 3.17 AT03-44-13 X X X X X X X Ri 0.40 AT03-20-PB2b X X X X X X X •Ri 1.91 AT03-44-15 X X X X X X X X Ri 2.22 01AT-11-1 X X X X X X X Ri 2.57 AT03-20-CD4d X X X X X X X X Ri 3.21 AT03-44-3 X X X X X X X Ri 3.42 AT03-20-CD4C X X X X X X X X Ri 3.55 AT03-44-37 X X X X X X Ri 3.70 01 AT-13-2 X X X X X X R, 7.12 AT03-51F X X X X A 2 1.25 AT03-44-18 X X X X X X X A 2 1.44 AT03-44-19 X X X X X X X A 2 2.06 01AT-9-1 X X X X X X A 2 2.10 AT03-20-PD1a X X X X X X A 2 2.29 AT03-21-EF1a X X X X X X X A 2 2.33 AT03-51D X X X X X A 2 2.40 AT03-20-CD2a X X X X X X A 2 2.49 AT03-20-PD3a X X X X X A 2 2.67 AT03-20-PD2b X X X X X X X A 2 2.72 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 X A 2 3.06 AT03-20-CD1a X X X X X X A 2 3.17 AT03-20-IJ2e X X X X X X X A 2 3.20 01AT-1-9 X X X X X A 2 3.37 149 APPENDIX B Table B1 (continued): Mineralogy of carbonated serpentinite from Atlin, BC Sample Chr Mgt Opx Brc Ol Atg Liz Mgs Tic Qtz Dol Cal Chi co2 AT03-20-CD2b X X X X X X A 2 3.57 AT03-20-IJ2d X X X X X X X A 2 3.72 AT03-20-IJ2C X X X X X A 2 3.92 AT03-44-36 X X X X X X A 2 3.95 AT03-20-CD1C X X X X X X A 2 3.98 01AT-6-3 X X X X X A 2 4.00 AT03-20-CD1b X X X X X X A 2 4.05 AT03-20-IJ4d X X X X X X X A 2 4.11 AT03-44-29 X X X X A 2 4.37 01AT-1-8 X X X X X A 2 4.60 AT03-51A X X X X X X A 2 6.11 AT03-44-4 X X X X X A 2 6.54 AT03-44-38 X X X X X A 2 6.60 AT03-51b X X X X X A 2 6.74 AT03-44-2 X X X X X A 2 9.86 AT03-44-5 X X X X A 2 9.91 AT03-44-39 X X X X A 2 10.94 AT03-21-EF1c X X X X X X X R 2 1.97 01AT-7-3 X X X X X X X X R 2 3.40 AT03-20-IJ4C X X X X X X X R 2 3.91 AT03-20-IJ4b X X X X X X X X R 2 4.11 AT03-20-IJ2b X X X X X X X X R 2 4.67 AT03-20-CD4b X X X X X X R 2 5.21 AT03-20-CD2C X X X X X X R 2 5.91 AT03-44-28 X X X X X R 2 6.34 AT03-44-33 X X X X X X R 2 6.45 01AT-1-7 X X X X X X R 2 7.19 01AT-1-6 X X X X X X X X X R 2 9.54 01AT-11-2 X X X X X X X R 2 9.60 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 X X R 2 15.20 AT03-20-IJ2a X X X X X X X R 2 15.60 AT03-20-CD2d X X ? X X X R 2 15.88 AT03-21-EF2b X X X X X X R 2 15.89 AT03-20-CD3b X X ? X X X R 2 17.11 AT03-20-CD4a X X X X X R 2 17.19 01AT-9-2 X X ? X X X R 2 17.26 150 APPENDIX B Table B1 (continued): Mineralogy of carbonated serpentinite from Atlin, BC Sample Chr Mgt Opx Brc Ol Atg Liz Mgs Tic Qtz Dol Cal Chi c o 2 AT04-20C X X X X X X X R 2 17.27 AT03-21-EF1d X X X X X R 2 17.77 AT03-20-CD3a X X ? X X X R 2 17.78 AT03-44-10 X X X X R 2 17.86 AT03-20-IJ3a X X X X X X R 2 18.08 AT03-21-EF1e X X X X X R 2 18.10 AT03-20-IJ3C X X X X X R 2 18.65 AT03-20-IJ3b X X X X X X R 2 18.70 AT03-21-EF2e X X ? X X X R 2 18.73 AT03-21-EF1f X X ? X X X R 2 19.05 AT03-20-CD3C X X ? X X X R 2 19.22 AT03-21-EF2c X X ? X X X R 2 19.40 AT03-20-IJ4a X X X X X X R 2 19.43 AT03-20-CD3d X X ? X X X R 2 19.69 AT03-21-EF2d X X X X X R 2 19.85 AT03-44-6 X X X X X R 2 21.60 AT03-44-40 X X X X X R 2 24.49 AT04-20F X X . X A 3 24.72 01AT-7-1 X X X X X X R 3 21.83 AT03-44-9 X X ? X X X R 3 22.45 AT04-20J X X X X . R 3 23.80 AT03-44-12 X X X X R 3 25.86 AT04-20N X X X X X R 3 26.16 AT04-20L X X X X R 3 26.77 AT04-20I X X X X R 3 27.17 01AT-5-4 X xy X X X R 3 28.01 AT04-20E X X X X R 3 29.71 AT03-44-8* X X X X X R 3 30.79 AT04-20M X X X X R 3 32.04 AT04-2* X X X X X R 3 32.95 01AT-1-5 X x z xw X X X X X R 3 34.00 01AT-4-1* X X X X X R 3 34.34 AT04-20A X X X X R 3 36.82 01AT-1-2* X X X A) 31.42 01AT-5-2 X X X A 4 35.20 AT04-20B X X X A4 35.50 01AT-6-1* X X X X A4 36.19 AT04-20K* X X X X A 4 37.07 AT04-20H X X X X A4 40.40 01AT-5-3* X X X A4 41.73 151 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 phases * sample contains Cr-muscovite C 0 2 reported in wt% 152 APPENDIX C Appendix C : Geochemical, Stable Isotope Analyses and Gold Assay Data 153 c n fe Table C1: Geochemical Analyses of Ultramafic Rocks Sample S i0 2 Ti0 2 A l 2 0 3 Fe 2 0 3 MnO MgO CaO Na 20 K 2 0 p2o5 Cr 2 O s Ni V LOI co2 Total 01AT-10-1 34.98 0.010 0.09 8.08 0.105 43.25 0.06 tn O X O APPENDIX C Table C4: Gold Assay Results SAMPLE Au(ppm) Zone C 0 2 (wt%) AT03-20-PC2a <0.001 Proto 0.41 AT03-42 <0.001 Proto 0.22 AT03-44-22 <0.001 Proto 3.17 AT03-21Ma <0.001 Proto 0.68 AT03-20-PC2b 0.014 Proto 0.41 AT03-20-PC2C 0.003 Proto 0.41 AT03-44-23 0.002 Proto 0.76 AT03-20-PE3a 0.001 Proto 0.87 AT03-20-PC2d <0.001 Proto 0.41 AT03-20-PC2e <0.001 Proto 0.41 AT03-51A 0.003 Mgs 6.11 AT03-44-15 <0.001 Mgs 2.22 AT03-44-37 0.001 Mgs 3.70 AT03-20-CD1b 0.001 Mgs 4.05 AT03-20-CD1c 0.001 Mgs 3.98 AT03-21-EF1b 0.002 Mgs 3.04 AT03-44-19 0.001 Mgs 2.06 AT03-51D <0.001 Mgs 2.40 AT03-20-IJ2d <0.001 Mgs 3.72 AT03-20-IJ1C 0.001 Mgs 3.06 AT03-21-EF2d 0.005 Talc 19.85 AT03-20-CD3b 0.033 Talc 17.11 Table C4: Gold Assay Results (cont.) SAMPLE Au(ppm) Zone C Q 2 (wt%) AT03-20-IJ2a 0.002 Talc 15.60 AT03-20-IJ3a 0.030 Talc 18.08 AT03-44^0 0.001 Talc 24.49 AT03-20-IJ3b 0.027 Talc 18.70 AT03^4-27 <0.001 Talc 15.20 AT03-21-EF1d 0.001 Talc 17.77 AT03-20-CD3C 0.016 Talc 19.22 AT03-21-EF1e <0.001 Talc 18.10 AT04-20Na <0.001 Qtz 26.16 01AT7-1 0.003 Qtz 21.83 01AT4-1 0.005 Qtz 34.34 AT04-20i 0.002 Qtz 27.17 AT04-20BC 0.004 Qtz 35.50 01AT5-2 0.005 Qtz 35.20 AT03-44-12 0.002 Qtz 25.86 AT04-20Bd <0.001 Qtz 35.50 AT04-20Bb <0.001 Qtz 35.50 AT04-20Ba 0.008 Qtz 35.50 GS2-B 0.180 GS na GS1-A 0.182 GS na GS3-C 0.230 GS na GS = gold standard (230 ppb) 161 Table C5: Stable I CD ro Table C5: Stable Isotope Analyses (cont.) Number ( V P D B ) " " " ( V S M O W ) C 0 2 (wt%) Zone Number ^ ( V P D B ) , J ( V S M O W ) C0 2 (wt%) Zone 01 AT 1-5 -4.43 9.44 34.00 Qtz AT03-20-CD4D -4.31 12.80 3.21 Srp 01 AT 4-1 -4.63 10.13 34.34 Qtz AT03-20-DH1 -6.04 15.70 n/a Mgs Vein 01 AT 5-2 -4.07 10.57 35.20 Qtz AT03-20-DH2 -5.97 14.80 n/a Mgs Vein 01AT-11-1 -2.30 11.78 2.57 Mgs AT03-20-DH3 -3.75 13.96 n/a Mgs Vein 01AT-11-2 -5.44 10.70 9.60 Tic AT03-20-IJ1A -3.02 12.98 2.80 Mgs 01AT-1-2 -4.06 10.42 31.42 Qtz AT03-20-IJ1B -2.30 13.42 2.97 Mgs 01AT-13-2 -5.08 11.37 7.12 Tic AT03-20-IJ1C -2.64 14.41 3.06 Mgs 01AT-1-5 -4.58 9.69 34.00 Qtz AT03-20-IJ2A -3.13 12.87 15.60 Tic 01AT-1-6 -5.97 10.94 9.54 Tic AT03-20-IJ2B -2.78 12.99 4.67 Mgs 01AT-1-7 -6.20 10.22 7.19 Tic AT03-20-IJ2C -2.30 13.40 3.92 Mgs 01AT-1-8 -4.47 13.21 4.60 Mgs AT03-20-IJ2D -4.28 12.90 3.72 Mgs 01AT-1-9 -5.50 14.19 3.37 Mgs AT03-20-IJ2D -3.67 12.72 3.72 Mgs 01AT-4-1 -4.97 10.07 34.34 Qtz AT03-20-IJ2E -4.18 12.78 3.20 Mgs 01AT-5-2 -4.13 9.15 35.20 Qtz AT03-20-IJ2E -2.80 13.62 3.20 Mgs 01AT-5-3 -2.24 8.15 41.73 Qtz AT03-20-IJ3A -5.39 14.18 18.08 Tic 01AT-5-4 -5.08 11.16 28.01 Qtz AT03-20-IJ3B -4.88 14.49 18.70 Tic 01AT-6-1 -4.32 13.97 36.19 Qtz AT03-20-IJ3C -5.55 15.08 18.65 Tic 01AT-6-3 -6.40 6.27 4.00 Mgs AT03-20-IJ4A -5.19 14.87 19.43 Tic 01AT-7-1 -4.39 17.25 21.83 Tic AT03-20-IJ4B -4.08 13.26 4.11 Mgs 01AT-7-3 -5.20 12.31 3.40 Mgs AT03-20-IJ4C -3.40 13.32 3.91 Mgs 01AT-9-2 ^.79 15.26 17.26 Tic AT03-20-IJ4D -3.32 13.32 4.11 Mgs AT03-20-CD1A -2.51 13.07 3.17 Mgs AT03-21-EF1B -1.26 12.06 3.04 Mgs AT03-20-CD1B -2.26 13.45 4.05 Mgs AT03-21-EF1D -4.69 12.04 17.77 Tic AT03-20-CD1C -2.66 , 13.20 3.98 , Mgs AT03-21-EF1E -4.68 , 12.40 18.10 Tic AT03-20-CD2A -3.64 12.26 2.49 Mgs AT03-21-EF2D -4.64 13.07 19.85 Tic AT03-20-CD2B -3.88 12.97 3.57 Mgs AT03-44-12 -6.05 13.01 25.86 Qtz AT03-20-CD2C -3.68 13.35 5.91 Mgs AT03-44-27 -5.43 11.26 15.20 Tic AT03-20-CD2D -1.31 13.94 15.88 Tic AT03-44-40 -5.18 10.64 24.49 Tic AT03-20-CD3A -5.20 14.27 17.78 Tic AT03-44-6 -0.34 11.07 21.60 Tic AT03-20-CD3B -4.93 14.23 17.11 Tic AT03-51A -4.16 15.40 6.11 Mgs AT03-20-CD3C -5.12 14.46 19.22 Tic AT04-20B -2.99 8.29 35.50 Qtz AT03-20-CD3D -5.05 14.66 19.69 Tic AT04-20I -5.36 11.15 27.27 Qtz AT03-20-CD4A -4.81 14.63 17.19 Tic AT04-20N -4.84 •11.21 26.16 Qtz AT03-20-CD4B -4.27 12.91 5.21 Mgs AT04-25 -3.79 8.20 4.73 dyke AT03-20-CD4C -3.63 13.47 3.55 Srp AT03-50 -3.31 8.30 9.21 dyke APPENDIX D Appendix D: Geochronologic Results 163 APPENDIX D TABLE D1: Geochronology Sample E U T M ( N A D 83) N U T M (NAD 83) S y s t e m A g e A n a l y s t Other AT03-5B 573283 6603671 U-Pb zircon 150.7 +/-0.4 Ma Richard Friedman Population B AT03-28 573556 6605367 4 0 A r / 3 9 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 4 0 Ar/ 3 9 Ar (Cr-Muscovite) 172.7 +/-2.0 Ma Thomas Ulrich Plateau Age P l a t e a u s t e p s a r e f i l l e d , r e j e c t e d s t e p s a r e o p e n 280 240 200 160 120 80 40 box heights are 2a 02AT-8-1 Muscovite Plateau age = 172 .7±2 .0 Ma (2100 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 1 8 0/d 1 6 0 ratios have been corrected for fractionation between phosphoric 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 BN 13, B N 83-2, H6M, which are calibrated against two international standards, NBS 18 and NBS 19. The final results 813C(VPDB) and 5180(VSMOW) are corrected to VPBD and VSMOW 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 S13C(VPDB) and 5180(VSMOW)-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 Eastings Northings Geochemistry 4 0 Ar/ 3 9 Ar U-Pb 1 3 C 1 8 0 Au Assay 01AT-10-1 577844 6601933 X 01AT-10-2 577844 6601933 X 01AT-11-1 577860 6601820 X X X 01AT-11-2 577860 6601820 X X X 01AT-1-2 574013 6603080 X X X X 01AT-13-1 577782 6602226 X 01AT-13-2 577782 6602226 X X X 01AT-1-5 574013 6603080 X X X 01AT-1-6 574013 6603080 X X X 01AT-1-7 574013 6603080 X X X OiAT-1-8 574013 6603080 X X X 01AT-1-9 574013 6603080 X X X 01AT-2-2 573954 6603058 X 01AT-3-1 573866 6603293 X 01AT-4-1 573552 6603542 X X X X 01AT-5-2 573278 6603742 X X X X 01AT-5-3 573278 6603742 X X 01AT-5-4 573278 6603742 X X X 01AT-6-1 575352 6604258 X X X 01AT-6-3 575352 6604258 X X X 01AT-7-1 574956 6604734 X X X X 01AT-7-3 574956 6604734 X X X 01AT-8-1 575800 6602042 X 01AT-9-1 575856 6602056 X 01AT-9-2 575856 6602056 X X X 02AT-8-1 575800 6602042 X AT03 - 28 573556 6605367 X AT03-20-CD1A 575884 6602100 X X X AT03-20-CD1B 575884 6602100 X X X X AT03-20-CD1C 575884 6602100 X X X X AT03-20-CD2A 575884 6602100 X X X AT03-20-CD2B 575884 6602100 X X X AT03-20-CD2C 575884 6602100 X X X AT03-20-CD2D 575884 6602100 X X X AT03-20-CD3A 575884 6602100 X X X AT03-20-CD3B 575884 6602100 X X X X AT03-20-CD3C 575884 6602100 X X X X AT03-20-CD3D 575884 6602100 X X X AT03-20-CD4A 575884 6602100 X X X AT03-20-CD4B 575884 6602100 X X X AT03-20-CD4C 575884 6602100 X X X AT03-20-CD4D 575884 6602100 X X X AT03-20-DH1 575884 6602100 X X AT03-20-DH2 575884 6602100 X X AT03-20-DH3 575884 6602100 X X AT03-20-ij1a 575884 6602100 X X X AT03-20-ij1b 575884 6602100 X X X AT03-20-ij1c 575884 6602100 X X X X AT03-20-ij2a 575884 6602100 X X X X 189 APPENDIX F Table F l : Sample locations (NAD 83) Sample Eastings Northings Geochemistry 4°Ar/ 3 9Ar U-Pb 1 3 c 1 8 0 Au Assay AT03-20-ij2b 575884 6602100 x X X AT03-20-ij2c 575884 6602100 X X X AT03-20-ij2d 575884 6602100 X X X X AT03-20-ij2e 575884 6602100 X X X AT03-20-ij3a 575884 6602100 X X X X AT03-20-ij3b 575884 6602100 X X X X AT03-20-ij3c 575884 6602100 X X X AT03-20-IJ4a 575884 6602100 X X X AT03-20-IJ4b 575884 6602100 X X X AT03-20-ij4c 575884 6602100 X X X AT03-20-ij4d 575884 6602100 X X X AT03-20-PA-1A 575884 6602100 X AT03-20-PA-2B 575884 6602100 X AT03-20-PB-2B 575884 6602100 X AT03-20-PB-3B 575884 6602100 X AT03-20-PC-1A 575884 6602100 X AT03-20-PC2 575884 6602100 X X AT03-20-PC-3A 575884 6602100 X AT03-20-PD-1A 575884 6602100 X AT03-20-PD-1B 575884 6602100 X AT03-20-PD-2A 575884 6602100 X AT03-20-PD-2B 575884 6602100 X AT03-20-PD-3A 575884 6602100 X AT03-20-PE-1A 575884 6602100 X AT03-20-PE-3A 575884 6602100 X X AT03-20-PE-3B 575884 6602100 X AT03-21-EF1-A 575742 6602243 X AT03-21-EF1-B 575742 6602243 X X X X AT03-21-EF1-C 575742 6602243 X AT03-21-EF1-D 575742 6602243 X X X X AT03-21-EF1-E 575742 6602243 X X X X AT03-21-EF1-F 575742 6602243 X AT03-21-EF2-A 575742 6602243 X AT03-21-EF2-B 575742 6602243 X AT03-21-EF2-C 575742 6602243 X AT03-21-EF2-D 575742 6602243 X X X X AT03-21-EF2-E 575742 6602243 X AT03-21-EF2-F 575742 6602243 X AT03-21-Ma 575742 6602243 X X AT03-21-PC-A 575742 6602243 X AT03-21-PC-B 575742 6602243 X AT03-21-PF-A 575742 6602243 X AT03-21-PF-B 575742 6602243 X AT03-21-PF-C 575742 6602243 X AT03-21-PG-A 575742 6602243 X AT03-21-PG-B 575742 6602243 X AT03-21-PH-B 575742 6602243 X AT03-21-PK-A 575742 6602243 X AT03-21-PK-B 575742 6602243 X 190 APPENDIX F Table F l : Sample locations (NAD 83) 1 J C "O Au Assay Sample Eastings Northings Geocher AT03-24 577613 6602505 X AT03-28 573556 6605367 AT03-42 577758 6601257 X AT03-44-1 577809 6601758 X AT03-44-10 577809 6601758 X AT03-44-11 577809 6601758 AT03-44-12 577809 6601758 X AT03-44-13 577809 6601758 X AT03-44-14 577809 6601758 X AT03-44-15 577809 6601758 X AT03-44-16 577809 6601758 X AT03-44-17 577809 6601758 X AT03-44-18 577809 6601758 X AT03-44-19 577809 6601758 X AT03-44-2 577809 6601758 X AT03-44-20 577809 6601758 X AT03-44-21 577809 6601758 X AT03-44-22 577809 6601758 X AT03-44-23 577809 6601758 X AT03-44-24 577809 6601758 X AT03-44-25 577809 6601758 X AT03-44-26 577809 6601758 X AT03-44-27 577809 6601758 X AT03-44-28 577809 6601758 X AT03-44-29 577809 6601758 X AT03-44-3 577809 6601758 X AT03-44-30 577809 6601758 X AT03-44-31 577809 6601758 AT03-44-32 577809 6601758 AT03-44-33 577809 6601758 X AT03-44-34 577809 6601758 X AT03-44-35 577809 6601758 X AT03-44-36 577809 6601758 X AT03-44-37 577809 6601758 X AT03-44-38 577809 6601758 X AT03-44-39 577809 6601758 X AT03-44-4 577809 6601758 X AT03-44-40 577809 6601758 X AT03-44-5 577809 .6601758 X AT03-44-6 577809 6601758 X AT03-44-7 577809 6601758 X AT03-44-8 577809 6601758 X AT03-44-9 577809 6601758 X AT03-49 576020 6601915 X AT03-4a-b 573293 6603629 X AT03-50 576219 6602005 X AT03-51-A 575925 6602101 X AT03-51-B 575925 6602101 X AT03-51-C 575906 6602113 X 191 APPENDIX F Table F l : Sample locations (NAD 83) I J C '°Q Au Assay" Sample Eastings Northings Geoche AT03-51-D 575906 6602113 X AT03-51-E 575891 6602083 X AT03-51-F 575891 6602083 X AT03-5a-b 573283 6603671 X AT04-10 576330 6604222 X AT04-11 575516 6603708 X AT04-12 577894 6601135 AT04-13 578966 6601258 X AT04-14 577809 6601758 AT04-16 574004 6603443 X AT04- 2 577809 6601758 X AT04 - 20 - A 573459 6603577 X AT04 - 20 - B 573459 6603577 X AT04 - 20 - C 573459 6603577 X AT04 - 20 - D 573459 6603577 X AT04 - 20 - E 573459 6603577 X AT04 - 20 - F 573459 6603577 X AT04 - 20 - H 573459 6603577 X AT04- 20 -1 573459 6603577 X AT04 - 20 - J 573459 6603577 X AT04 - 20 - K 573459 6603577 X AT04 - 20 - L 573459 6603577 X AT04 - 20 - M 573459 6603577 X AT04 - 20 - N 573459 6603577 X AT04 - 21 - B 575660 6602200 X AT04- 23 575422 6603169 X AT04- 25 574050 6603084 X AT04- 3 577700 6601269 X AT04- 4 577817 6601847 X AT04- 5 577572 6602483 X AT04- 6 - B 576671 6602340 X AT04- 7 - B 574838 6608489 X AT04- 8 - B 574884 6608579 X AT04- 9 574310 6604486 X X X X X X X X X X X 192