Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Geology, alteration and mineralization in the 21A zone, Eskay Creek, northwestern British Columbia Roth, Tina 1993

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata


831-ubc_1994-0058.pdf [ 11.99MB ]
JSON: 831-1.0052492.json
JSON-LD: 831-1.0052492-ld.json
RDF/XML (Pretty): 831-1.0052492-rdf.xml
RDF/JSON: 831-1.0052492-rdf.json
Turtle: 831-1.0052492-turtle.txt
N-Triples: 831-1.0052492-rdf-ntriples.txt
Original Record: 831-1.0052492-source.json
Full Text

Full Text

GEoLoGY, ALTERATION AND MINERALIzATIONIN THE 21A ZoNE, EsKAY CREEK,NORTIIwEsTERN BRITIsH CoLuMBIAbyTINA ROTHBSc (Hons.), The University of Waterloo, 1989A THESIS SUBMITTED iN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR TIlE DEGREE OFMASTER OF SCIENCEinTHE FACULTY OF GRADUATE STUDIES(Department of Geological Sciences)We accept this thesis as conformingto the required standard:THE UNIVERSITY OF BRITIsH COLUMI3JANovember 1993© Tina Roth, 1993In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Library shall make itfreely available for reference and study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. It is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission.(Signature)Department ofThe University of British ColumbiaVancouver, CanadaDate C’C.DE-6 (2/88)11ABsTRAcTThe Eskay Creek deposit is an unusual high-grade precious and base metal volcanogenic massive suiphideand suiphosalt deposit hosted in volcanic and sedimentary rocks of the Lower to Middle Jurassic Hazelton Group.This deposit consists of several zones distinguished by differing ore mineralogies and grades. Published geologicalreserves for the deposit are 4.3 million tonnes grading 28.8 grams per tonne gold and 1 027 grams per tonne silver.The 2 1A zone, the focus of this study, contains an estimated 0.97 million tonnes grading 9.6 grams per tonne goldand 127 grams per tonne silver.The lowermost stratigraphic units in the Eskay Creek 21A zone are marine sedimentary and volcanic rocks.Stockwork and disseminated mineralization occur in an overlying flow banded and brecciated rhyolite that formsthe footwall to probable stratiform sulphide mineralization hosted in contact argillite. The argillite is overlain by athick sequence of massive to pillowed and brecciated basalt, intercalated with argillite and turbidite. The unitsrelated directly to mineralization apparently were generated in an extensional rifled arc environment. Fromlithogeochemical analyses, the overlying basalts reflect a back-arc environment of formation.Alteration in the 2 IA zone, most intense in the footwall rhyolite, is characterized by varying mineralabundances in an assemblage of quartz - sericite - pyrite ± potassium feldspar ± chlorite. Alteration (determinedby petrography, X-ray diffraction, transmitted electron microscope and lithogeochemistry) progresses from earlydevitrification through silicification, potassic alteration and sericitization (dominantly illite) to pervasivereplacement of rhyolite by clinochiore. Increasing hydrothermal alteration is traced geochemically, mainly in themobility of silica, potassium and magnesium. The most intense alteration in the footwall rhyolite, is a chlonticpipe defined by a discontinuous stockwork that underlies apparently stratiform mineralization. The overlyingbasalt sequence is not markedly altered.Mineralization within the 21A zone consists of a small, semi-massive, probably stratiform, stibnite-realgarrich lens in a small defineable basin which is underlain by stockwork and disseminated suiphides in the rhyolitethat is described above. An overall vertical zonation was observed in sulphides and distribution of metals.Veinlets in the rhyolite contain mainly sphalerite - galena - pyrite - tetrahedrite ± chalcopyrite. Chalcopyriteoccurs mainly in the lower part of the rhyolite. Near the upper contact, intensely altered rhyolite containsdisseminated arsenopyrite and stibnite. Stratiform semi-massive mineralization in the contact argillite consistsdominantly of realgar, stibnite, arsenopyrite and cinnabar; few intervals contain base metal rich sulphides. Assaydistribution within the rhyolite also varies vertically. Gold and silver increases with proximity to the upper contactof the rhyolite. Highest gold grades are in the semi-massive sulphides. Highest silver grades are in the 50 metresimmediately below the top of the rhyolite.111TABLE OF CoNTENTsPAGEABsr1&crTable of Contents HiList of Tables vList of FiguresList of PlatesAcIowIEDGEMENT x1. INTRODUCTION 11.1 Purpose and approach 11.2 Exploration history 41.3 Regional geology 72. GEoLOGY OF THE 21A ZONE 152.1 Introduction 152.2 Geological framework 172.3 Lithology 222.3.1 Lower sedimentary unit 222.3.2 Lower volcanic unit: flows or sill, volcaniclastic and sedimentary rocks 222.3.3 Rhyolitic volcanic unit 25Macroscopic textures 26Microscopic textures 262.3.4 Contact argillite2.3.5 Basalt intercalated with argillite and turbidites 402.3.6 Intrusive rocks 43Majic dykes and sills 43Felsic intrusions 442.4 Geochemistry 442.4.1 Major and trace elements 502.4.2 Rare earth and large ion lithophile elements 652.4.3 Summary 752.5 Summary and discussion 783. ALTERATION IN THE 21A ZoNE 813.1 Sedimentary and volcaniclastic unit 813.2 Footwall volcanic unit 813.3 Rhyolite sequence 833.3.1 Stages of alteration 88Devitrification 88Progressive hydrothermal alteration 88Silicification 89Sericitization 89Chloritization 90Late Overprint 933.3.2 Mineralogy of the alteration assemblage 93Quartz 93Potassiu,n Feldspar 93ivPhyllosilicates 95illite 95Clinochlore 100Pyrite 100Carbonaceous material 1023.3.3 Element Mobility within the R1iyolite Package 102Techniques in identifying element mobility 104Immobile elements 105Pearce element ratios 107Mass loss, mass gain and mobility ofelements during alteration 1073.4 Contact unit 1173.5 Basalt 1173.6 Intrusive rock 1173.7 Summary and discussion 1184. MINEI.&iJzATIoN IN THE 21A ZONE 1234.1 Mineralogical and assay data 123Statistical analysis of the assay data 1324.2 Distribution and style of mineralization 1534.2.1 Sedimentary and volcaniclastic unit 1534.2.2 Footwall volcanic unit 1534.2.3 IThyolite sequence 1544.2.4 Contact argillite 157Textures in the semi-massive suiphide body 160Base metal sulphides in the contact unit 167Mineralization associated with barite 1674.2.5 Hanging wall basalt and argillite 1694.3 Sulphur isotopes 1694.4 Summary and discussion 1715. Discussior”i AND CONCLUSIONS 175REFERENCES 178APPENDIX A: Supplementary cross sections 185APPENDIx B: Preparation and analysis of the lithogeochemical samples 201APPENDIx C: X-ray diffraction analysis of clay minerals 217VLIST OF TABLESPage1.1 Exploration history of the Eskay Creek area. 51.2 Plutonic events in northwestern Stikinia. 142.1 Textures in rhyolite. 302.2 Stages of devitrification 322.3 Criteria to distinguish flows and sills in the basalt 412.4 Lithogeochemical data for footwall volcanic unit 512.5 Lithogeochemical data for rhyolite 522.6 Lithogeochemical data for basalt and basaltic dykes 582.7 Lithogeochemical data for argillite 592.8 Summary of lithogeochemical characteristics 733.1 Characteristics of the alteration stages 853.2 Basal spacing and peaks in typical clinochlore 1013.3 Types of alteration indeces 1043.4 Mass changes in elements in the 21A zone rhyolite 1114.1 Sulphides in the 21A zone 1244.2 Statistical summary of assays in the footwall volcanic and sedimentary units 1334.3 Statistical summary of assays in the footwall rhyolite 1344.4 Statistical summary of assays in the contact unit 1354.5 Statistical summary of assays in the hanging wall basalt and argillite 1364.6 Typical assay intervals in the footwall volcanic unit 1374.7 Typical assay intervals in the footwall rhyolite 1384.8 Typical assay intervals in the contact unit 1394.10 Pearson correlation matrix for metals in the footwall volcanic and sedimentary unit 1404.11 Pearson correlation matrix for metals in the footwall rhyolite 1414.12 Pearson correlation matrix for metals in the contact unit 1424.13 Pearson correlation matrix for metals in the hanging wall basalt and argillite 1434.14 Sulphur isotope values from the 21A zone 170Appendix AA.1 List of driliholes in the 21A zone 186Appendix BB. 1 Analytical methods used in lithogeochemical analyses 203B.2 Analytical standards: summary statistical data 204B.3 Normalization values: MORB and NASC 209Appendix CC.1 Estimates for percent illite in illite/smectite mixed layer clays 219C.2 Estimate of symmetry in chlorite 220C.3 Estimate of Fe in chlorite 220C.4 Classification of phyllosilicate minerals 221viLIST OF FIGURESPage1.1 Location map.1.2 Geology of the Canadian Cordillera.1.3 Regional geology and distribution of Jurassic lithologies, northwestern BritishColumbia1.4 Stratigraphic nomenclature of the Iskut River Area.1.5 Local geology of the Eskay Creek area.1.6 Stratigraphic relationships of Eskay Creek lithologies.Section 1+OON (1:500)Section 0+00 (1:500)Section 1+OOS (1:500)Drillhole location map for the 21A zoneSurface geology of the 21A zone map area, Eskay Creek (1:1000)Contour map of the top of the contact unitFoliation measurements in the 21 A zone areaSection 2+OOSContour unit isopach mapGeochemical sample location map.Geochemical sample locations: Section l+OONGeochemical sample locations: Section 0+00Geochemical sample locations: Section l+OOSAlkali-silica geochemical discrimination diagramTrace element geochemical discrimination diagramTi02 vs. Zr plot - fractionation and alteration trendsTectonic discrimination diagrams for basaltLILE-REE spiderdiagram: footwall volcanic unitLILE-REE spiderdiagram: rhyoliteLILE-REE spiderdiagram: massive chloriteLILE-REE spiderdiagram: rhyolite transitionL1LE-REE spiderdiagram: basalt and dykesLILE-REE spiderdiagram: argilliteLILE-REE spiderdiagram: average trends for all lithologiesLILE-REE spiderdiagram: comparison of argillite to NASC3.1 843.2 863.3 873.4 963.5 983.6 993.7 1013.8 1033.9 1063.10 1083.11 1093.12 1143.13 1153.14 1203.15 122Src\ Pock,(BackP9etBack7ocketBa Pocketack Pocket,Alteration assemblages in rhyoliteDistribution of massive chlorite in rhyoliteSchematic diagram of chlorite pipeDistribution of potassium feldspar stain in rhyoliteTypical XRD trace of illiteCompositional profile of illite (TEM)XRD profile of clinochloreAlkali alteration index in 2 IA zone rhyoliteScatter plots of immobile elements in the 2 1A zone rhyoliteTest for feldspar fractionation in the 2 1A zone rhyoliteStandard deviations in PER for the 21 A zone rhyoliteMass loss and gain in major elements in the 2 IA zone rhyoliteMass loss and gain in minor and trace elements in the 2 1A zone rhyoliteStability phase diagram for chlorite, kaolinite, sericite and K-sparK20 vs. MgO in 21A zone rhyolitevii4.1 Assay distribution of Au and Ag in Section 1+OON 1264.2 Assay distribution of Zn and Pb in Section l+OON 1264.3 Assay distribution of Cu and Sb in Section 1+OON 1274.4 Assay distribution of As and Hg in Section l+OON 1274.5 Assay distribution of Au and Ag in Section 0+00 1284.6 Assay distribution of Zn and Pb in Section 0+00 1284.7 Assay distribution of Cu and Sb in Section 0+00 1294.8 Assay distribution of As and Hg in Section 0+00 1294.9 Assay distribution of Au and Ag in Section 1+OOS 1304.10 Assay distribution of Zn and Pb in Section l+00S 1304.11 Assay distribution of Cu and Sb in Section 1+OOS 1314.12 Assay distribution of As and Hg in Section 1+OOS 1314.13 Scatter plots of As and Sb vs. Au and Ag in the footwall volcanic unit 1454.14 Scatter plots of Zn, Pb and Cu vs. Au and Ag in the footwall volcanic unit 1464.15 Scatter plots of As, Sb and Hg vs. Au and Ag in the footwall rhyolite 1474.16 Scatter plots of Zn, Pb and Cu vs. Au and Ag in the footwall rhyolite 1484.17 Scatter plots of As, Sb and Hg vs. Au and Ag in the contact unit 1494.18 Scatter plots of Zn, Pb and Cu vs. Au and Ag in the contact unit 1504.19 Vertical distribution of metals in the footwall rhyolite 1514.20 Electron dispersion profiles of suiphides in the 21A zone 1584.21 Distribution of semi-massive sulphide intersections 1594.22 Textural variations in the possibly stratiform suiphides: CA89-023 1614.23 Metal distribution associated with the possibly stratifonn sulphide lens 1684.24 Sulphur isotopes in the 21A zone 1704.25 Summary of mineralization styles observed in the 21A zone 172Appendix ASection 1+75S 189Section 1+50S 190Section 1+25S 191Section 0+75S 192Section 0+50S 193Section 0+25S 194Section 0+25N 195Section 0+50N 196Section 0+75N 197Section l+25N 198Section 1+50N 199Section 1+75N 200Appendix BSupplementary scatter plots 210Appendix CRepresentative X-ray diffraction patterns for clay minerals in the 2 1A zone 222viiiLIST OF PLA TESOverview of the 21 A zone area Frontispiece2.1 Amygdules in altered footwall volcanic rocks 162.2 Relict clasts in altered volcaniclastic rocks 162.3 Bedded pyroclastic and epliclastic rocks in the footwall volcanic unit 162.4 Stockwork altered flow or sill in footwall volcanic unit 162.5 Volcaniclastic rock in the footwall volcanic unit 242.6 Graded epiclastic rocks in the footwall volcanic unit 242.7 Photomicrograph of footwall volcaniclastic rock 242.8 “Transition zone” 242.9 Flow banding in rhyolite 272.10 Rhyolite breccia 282.11 Quartz phenocrysts in rhyolite 292.12 Zircon in rhyolite 292.13 Fiamme or hyaloclastite fragments in rhyolite 292.14 Photomicrograph of a typical rhyolite breccia 332.15 Spherulites in rhyolite 332.16 Perlitic cracks in rhyolite 332.17 Lithophysae in rhyolite 332.18 Unusual concentric features in rhyolite 352.19 Unusual, radiating to wormy textures in rhyolite 362.20 Photomicrograph of flow banded rhyolite 362.21 Contact unit 362.22 Basaltic pillow breccia 422.23 Basaltic debris flow 422.24 Photomicrograph of crystalline basalt 422.25 Porphyroblasts in hanging wall argillite 422.26 #3 Bluff 452.27 Felsic intrusive rock 453.1 Stockwork alteration in footwall volcanic unit 823.2 Development of false textures in rhyolite 823.3 Sericite - pyrite alteration envelopes in rhyolite 913.4 Sericitic fracture in rhyolite 913.5 Mottled rhyolite 913.6 Chlorite alteration in rhyolite 923.7 Late overprint stage alteration 943.8 Intense silica-carbon alteration in rhyolite 943.9 Albite in least altered rhyolite 944.1 Photomicrograph of stockwork mineralization in rhyolite 1554.2 Sulphide vein in rhyolite 1554.3 Sericitic vein in rhyolite with associated suiphide mineralization 1554.4 Arsenopyrite needles in rhyolite 1554.5 Massive stibnite 1564.6 Realgar - stibnite with argillite clasts 1564.7 Textural variations in the sulphide lens 1624.8 Framboidal and spheroidal pyrite in stibnite 1634.9 Photomicrograph of stibnite-realgar mineralization 1634.10 Gold in stibnite-realgar 1634.11 Realgar - calcite veinlets in contact argillite 1654.12 Realgar in quartz 1654.13 Barium-rich muscovite 1654.14 Photomicrograph of barite in realgar-stibnite rich mineralization 1654.15 Base metal suiphide mineralization in contact unit 1664.16 Massive and bladed barite 1664.17 Mineralization in “hanging wall” argillite 166ixxACKNOWLEDGMENTSI would like to thank the many people who contributed their time and thoughts to me during the course ofthis project. I am grateful to Dr. Cohn Godwin for his supervision, guidance and for editing and re-editing thetext. Thanks go also to Dr. John Thompson for his encouragement, patience and sharing of ideas, Roland Bartschfor many discussions on the Eskay Creek area, Dr. A. James Macdonald for his support, Dr. Art Etthinger forhelping me to get started, and International Corona Corporation (now Homestake Canada Ltd.), for allowing me toundertake this project. Discussions with Ken Rye, Carl Edmunds, Dave Kuran, James Stewart, Henry Marsden,Ron Britten, Rod Allen, Jerry Blackwell and Gerry MacArthur were very beneficial and are gratefullyacknowledged. I am also indebted to Dr. Katsumi Marumo for patiently teaching me about the world of clay, Dr.Tim Barrett for his assistance with lithogeochemistry, and Arne Toma for his help with sample preparation,photography and drafting.Financial support for this research was provided by the Mineral Deposit Research Unit (MDRU), as partof the Iskut River Project entitled Metallogenesis ofthe Jskut River Area. Funding was provided to MDRU bythirteen mimng and exploration companies, the Science Council of British Columbia, and a Natural Science andEngineering Research Council (NSERC) CRD grant. Personal financial support was provided to me by a NSERCPostgraduate Scholarship.MINEsoft Ltd. kindly provided the use of TECHBASE software to MDRU. I would like to thank TonyClarke for his help in accelerating the learning curve in this program.Finally, I would like to thank James Moors for his patience, moral support and sense of humour.á’v7445SSOflVJsWfllfllOU-ylJOUI7uzyooj VJ9USflJO3wd1S3ozy3JO]\‘JddJ3Vjfc3‘?UOZWt?ifl£SOflV‘a1GEOLOGY, ALTERATION AND MINERALIzATION IN THE 21A ZoNE,EsKAY CREEK, NoRTHwEsTERN B1UTIsH COLUMBIA1. INTRODUCTIONThe Eskay Creek property (NTS 104B/09W; 56° 38’N, 1300 27’W), in the Iskut River area ofnorthwestern British Columbia, is approximately 80 kilometres north of Stewart (Figure 1.1). The property is onthe eastern side of the Prout Plateau, east of Tom Mackay Lake, about 2 kilometres west of the Unuk River, and ishost to several discrete zones of gold and silver bearing mineralization in Lower to Middle Jurassic volcanic andsedimentary rocks of the Ha.zelton Group.Most of the mineralization on the property is contained in the #21 zone which consists of several subzones(mainly the 2 lÀ and 2 1B) that are distinguished by differing ore mineralogies and gold grades. Geologicalreserves for the #21 zone are 4.30 million tonnes grading 28.8 grams gold per tonne and 1 027 grams silver pertonne (Edmunds et a!., 1992). The bulk of the reserves are hosted in the 2 lB zone in tabular, synsedimentarysheets of graded and fragmental suiphides and suiphosalts, and in underlying vein stockwork and disseminations.The stratiform mineralization occurs in argillite at the contact between rhyolite and overlying basalt. Currentlydefined mineable reserves (diluted by about 27%) for the 2 lB zone deposit are 1.08 million tonnes (1.19 milliontons) grading 65.5 grams gold per tonne (1.91 ounces gold per ton), 2 931 grams silver per tonne (85.5 ouncessilver per ton), 5.7% zinc, 2.89% lead and 0.77% copper (Rye eta!., 1993; The Northern Miner, June 21, 1993).Feasibility studies for the 21B zone deposit are ongoing.This study focuses on the geology, mineralogy and alteration in the 2 1A zone at Eskay Creek.Mineralization in the 2 1A zone occurs as a massive to semi-massive stratabound lens of stibnite-realgar-cinnabararsenopyrite underlain by disseminations and veins of dominantly sphalerite-galena-tetrahedritepynte±chalcopyrite. The 2 1A zone contains an estimated 0.97 million tonnes grading 9.6 grams gold per tonneand 127 grams silver per tonne (A. Ransom, International Corona Corporation, personal communication to A.J.Macdonald, MDRU, December 1991).1.1 Purpose and approachThe purpose of this study is to describe the 2 IA zone, which is a unique body of suiphide mineralizationhosted in argillite at the same stratigraphic position as the main ore mineralization contained in the 21B zone.The two zones are separated by an approximately 150 metre gap in mineralization and differ significantly withrespect to dominant ore mineralogy. The 21B zone is dominated by sphalerite and tetrahedrite; the 21A zone isdominantly stibnite and realgar.2FIGURE 1.1: Location maps. Map (a) shows the Iskut Project area, which is located north of Stewart inNorthwestern British Columbia, in relation to morphogeological belts of the westernCanadian Cordillera. Map (b) shows the location of major mineral deposits within theIskut Project area.3In order to understand the geometry and stratigraphy within the 21A zone, three cross sections spaced at100 metre intervals were selected for detailed evaluation. Core from 24 driliholes on the three sections (1+OON,0+00 and 1+OOS; Figures 2.1 to 2.4) was relogged in detail, with an emphasis on the mineralized argillite horizonand the footwall rhyolite. The holes were drilled by Prime Exploration Ltd. and originally logged by Primegeologists in 1988, 1989 and 1990. Hanging wall basalt was relogged where the core was accessible. These datawere supplemented by relogging of selected mineralized intervals in an additional 15 holes in order to evaluatechanges between the sections. This information was compiled onto a TECHBASE (MiNEsoft, Ltd., 1991) databasein order to generate cross-sections and to model the distribution of mineralization and alteration within the 2 1Azone. Geological information from an additional 82 drillholes was re-coded from original drill logs and enteredinto the database. Detailed mapping at a 1:1000 scale was conducted in a restricted area extending about 1kilometre south of the 21A zone (Figure 1.5) to correlate observations and structures identified in driuicore withthose on surface.An assay database was assembled in TECHBASE for all 121 drillholes in the 2 1A zone using the datagenerated by Prime during the original drilling program. Assays were prepared and analyzed by Bondar CleggLtd. in Vancouver (early holes) and TSL Laboratories Ltd. in Saskatoon. Original computer files of the assay datawere obtained from the laboratories and compiled into one large, comprehensive database. The assay samples weregenerally collected systematically in ito 1.5 metre intervals and were all analyzed for Au and Ag. A smallersubset of samples was analyzed for combinations of Cu, Pb, Zn, As, Sb and Hg. In early drillholes, these elementswere analyzed in samples collected from the contact argillite and in a restricted portion of the underlying rhyolitesuch as mineralized intervals. However during later drilling such analyses were sporadic and were eventuallyabandoned. Therefore, information on the distribution of these elements is sparse.The mineralogy and textures associated with alteration and mineralization in the 21A zone werecharacterized from detailed microscopy. Many of the minerals are microcrystalline and difficult to identi1’ bypetrographic means. These minerals, particularly clay sized alteration minerals in the rhyolite footwall, wereidentified using X-ray diffraction (XRD). The scanning electron microscope (SEM) and electron dispersion system(EDS) was used to aid in the identification of sulphide minerals. Many of the common sulphide and sulphosaltminerals identified within the 2 1A zone are similar shades of grey to white in reflected light and are commonlyfine grained; this makes optical identification difficult.Lithogeochemical samples were collected within the 2 1A zone area as part of a much larger databasecompiled regionally by the Iskut River Project of the Mineral Deposit Research Unit. The data from the 21A zonewas evaluated to identify lithogeochemical classifications of the host strata and to assess alteration trends due tometasomatism by hydrothermal fluids. A small number of suiphide and sulphate (barite) samples were analyzedfor their sulphur isotopic composition.4This study is part of a larger project, undertaken by members of the Mineral Deposit Research Unit(MDRTJ) at The University of British Columbia (UBC), entitled Metallogenesis ofthe Iskut River Area. The ‘IskutProject’ is an integrated effort of regional and structural mapping, as well as detailed studies of several mineraldeposits within the Iskut Project area (Figure 1.1) by members of MDRU in collaboration with geologists from theexploration industry and government. Funding for the research was provided by sixteen exploration companies,the Science Council of British Columbia, and the National Science and Engineering Research Council. Thevolcanic stratigraphy of the Prout Plateau in the area surrounding the Eskay Creek deposit is the subject of anM.Sc. thesis by R.D. Bartsch (UBC, 1993); this research, as well as property geology defined by explorationgeologists at Eskay Creek (Idziszek et a!., 1990, Blackwell, 1990; Edmunds et a!., 1992; Rye et a!., 1993), hasadvanced the understanding of the depositional environment of the Eskay Creek ore body.1.2 Exploration HistoryThe history and exploration activity of the Eskay Creek area are documented in the Annual Reports of theBritish Columbia Minister of Mines (1907, 1932, 1933, 1934, 1935, 1939, 1953 and 1967), in Exploration inBritish Columbia (1970, 1975, 1976, 1985 and 1991), in British Columbia Assessment Reports (#5683, #6075,#11160, #14099, #18958 and #18959) and in Donnelly (1976), Britton eta!. (1990), Idziszek eta!. (1990), andRye (1992).The first recorded activity in the area was in the late 1800’s when placer gold was discovered in the UnukRiver and its tributaries. However, transportation and access up the Unuk River was difficult. A wagon road wasbuilt along the Unuk River in the early 1900’s to provide access as far as Sulphur Creek, but this soon fell intodisrepair and early claims were abandoned.The first mineral claims in the immediate Eskay Creek area were staked in 1932 by the MacKay Syndicatedirected by Tom S. MacKay. Access to the property was by air (landing on Tom MacKay Lake) and pack train.The prospectors were attracted to the area by a seven kilometre line of prominent gossanous bluffs near Eskay andCoulter Creeks. Over the next sixty years the properties were optioned by several companies, resulting insignificant exploration (Table 1.1) and the discovery of numerous gold and silver showings. The showings werenumbered sequentially by the Premier Gold Mining Company in the 1930’s, and these names (#5, #21, #22 zones,etc.) are still used. Prospecting was focused on the gossanous bluffs and stockwork mineralization in the rhyolite,primarily south of the #21 zone. Two main adits were driven in the area. Excavation in the MacKay adit began in1939 by the MacKay Syndicate, and in the Emma adit in 1963 by Western Resources Ltd. May-Ralph IndustriesLtd. removed significant ore from the #22 zone trenches in 1979.In November 1988, Calpine Resources Incorporated announced the discovery of stibnite-realgar gold-richmassive sulphides at the contact between the rhyolite and overlying basalt (initially termed andesite) at the north5TABLE 1.1: Exploration histoiy of the Eskay Creek area, northwestern British Columbia.YEAR OPERATING COMPANY ACTIVITIES1932 T.S. Mackay and Associates Thomas S. Mackay, A. H. Melville and W.A. Prout staked about 30claims in two blocks, the Unuk and Barbara groups. They covered theeast side of the Prout Plateau over a distance of 5 kilometres north-south.They discovered a large, siliceous, heavily pyritized zone carryingsphalerite, galena and some chalcopyrite with locally encouraging goldvalues.1933 Mackay Syndicate The Mackay Syndicate excavated six open cuts and reported significantgold values. A cabin (still existing) was constructed where the presentEskay Creek Camp stands.1934 Mackay Syndicate The Syndicate drilled 11 X-ray diamond drill holes, varying from 8.5 to35 metres, around the No. 1 cut. Some prospecting was done in the‘dioritic’ rock of Prout Dome (Unuk 13 claim); generally low to sporadicgold values were obtained. Several quartz stringers with pyrite,sphalerite and some galena were exposed in porphyritic lava at the northend of the property (Unuk 21 claim); the best assay was 4.8 grams goldper tonne (0.14 oz gold per ton) and 21.2 grams silver per tonne (0.62 ozsilver per ton) in a grab sample.1934 Unuk Valley Gold Syndicate The Unuk Valley Gold Syndicate staked 16 claims ( Verna D. claims ) atthe north end of the Unuk and Barbara claim groups.1935 to Premier Gold Mining Company, The properties were optioned from the Mackay Syndicate and the Unuk1938 Limited Valley Gold Syndicate. They discovered and named over 30 gold andsilver showings on the property through extensive trenching anddiamond drilling (38 holes totaling 1825 metres). The showings werenumbered, and these names are still in use today (e.g. the #21, #22, #5zones, etc.1). Exploration, initially focused on the south end of theproperty, gradually moved northward.1939 Mackay Gold Mines, Limited The Mackay adit was driven 84 metres (276 feet) on the “North Endand Selukwe Gold Mining Limited Workings”, 3 kilometres south of the #21 zone. A second adit wasdriven 18.3 metres at the #13 zone.1946 Canadian Exploration Limited The Mackay adit was extended to a total length of 110 metres. A 1.5 x2.1 metre cross-cut was driven. A raise was put through to surface at 46metres in the adit.1953 American Standard Mines Limited This group of companies held the “Mackay group” of 36 claims throughPioneer Gold Mines of B.C. option agreements. Near the Mackay adit, 13 closely spaced holes wereLimited and drilled that encountered some gold assays greater than 30 grams perNew York-Alaska Gold Dredging tonne in plagioclase phyric rock. The gold seemed to have an erraticCorporation distribution.Over 320 metres of trenches were excavated on the #21 zone. Minorveins filled with tetrahedrite and minor galena and sphalerite were notedin well fractured felsic rock. They were somewhat more abundant over a75 metre width in the middle of the trenches. Seven driltholesintersected narrow veins that assayed thousands of grams silver, but theywere not abundant.At the #22 zone, about 20 trenches totaling 250 metres and two diamonddrill holes encountered mineralization similar to that in the #21 zone.Six trenches over 90 metres exposed relatively massive sphalerite,galena and pyrite mineralization in the # 5 zone.1963 Western Resources Ltd. This company held the “Kay” group of 40 mineral claims located 5kilometres east of Tom Mackay Lake, on the headwaters of the UnukRiver. They drove a 111 metre crosscut adit (Emma) and constructed atractor road from the lake to the property.1964 Canex Aerial Exploration Ltd. Canex acquired an option on 36 claims of the Kay group from WesternResources Ltd. Six underground AXK diamond drill holes totaling224.6 metres were drilled in the Emma adit, and the drift walls weresampled. Au, Ag, Pb and Zn minerals were found to occur mainly involcanic breccia. Vein widths up to 4 metres were intersected.6Table 1.1 continued1965 Stikine Silver Ltd. 2 This company held 40 claims of the Kay group and conducted 5months of work that included extending the Emma adit to a total of179 metres. Eighteen trenches totaling 460 metres were blasted andbulldozed. Thirteen pits were blasted and dug. Three holes weredrilled totalling 16 metres.1967 Stikine Silver Ltd. 2, Stikine Silver completed geological and geophysical surveys over theMount Washington Copper Ltd. Kay group.1970 Granduc Mines, Limited Granduc optioned the claims from Stikine Silver Ltd. and conductedgeophysical and geochemical surveys.1971 Stikine Silver Ltd. 2 Stikine Silver extracted a 1.5 tonne sample from the #22 zonetrenches that yielded: 9.3 grams gold, 7 435 grams silver, 29kilograms lead and 42.7 kilograms zinc. (Overall grades are: 6.2 gAu / tonne, 4 957 g Ag / tonne, 1.9% Pb and 2.8% Zn.)1973 Kalco Valley Mines Ltd. This company drilled seven diamond drill holes totaling 300 metres.1975 Texasguif Canada Ltd. Texasgulfoptioned 46 claims: KAY 11-18, TOK 1-22 and SIB 1-16(Figure 1 .xx). They conducted surface mapping at 1:5 000 over thearea covering KAY 1 1-18, TOK 1 and TOK 8, as well as line-cutting,a shootback EM survey and a magnetometer survey. The mappingproject provided the basis for a BSc thesis by Donnelly (1976,University of British Columbia).1976 Texasgulf Canada Ltd. The company drilled seven BQ diamond drillholes totaling 380metres. Six of the holes were drilled just south of the #21 trenches,and one was just above the Emma adit (#6 zone).1979 May-Ralph Industries Ltd. This company mined the #22 zone trenches to produce: 1 263 gramsgold, 25 490 grams silver, 412 kilograms lead and 1 008 kilogramszinc (tonnage not reported).1983 Ryan Exploration Ltd. (a subsidiary Ryan conducted a geochemical survey and a shallow diamond drillingof U.S. Borax) program, near the Emma and Mackay adits, of 7 holes totaling 452.3metres.1985 Kerrisdale Resources Ltd. Kerrisdale conducted a rock and soil geochemistry survey and drilledfive BQ diamond drillholes, totaling 614.5 metres, above the #21trenches which identified a zone of spotty gold and silver values inaltered felsic volcanic rocks related to the 2lA zone.1987 Consolidated Stilcine Silver Ltd.2 Consolidated Stikine conducted further stream, soil and rockgeochemistry samples, and split and assayed all Kerrisdale core.1988 Calpine Resources Inc. - Calpine conducted soil sampling and geological mapping. Theydrilled 16 NQ diamond drillholes totaling 2 099 metres. Hole CA88-6 was the discovery hole that intersected stibnite-realgar richmineralization (21A zone).1989 to Calpine Resources Inc. - Calpine drilled 414 NQ diamond drillholes, totaling 87 888 metres,March delineating the 2lA zone and identif’ing and delineating the 21B1990 zone (called the South, Central and North zones at that time). Sevenholes drilled into the #22 zone totaled 1 321 metres. A survey gridwas established over the entire property; soil geochemistry, groundgeophysics, prospecting and geological mapping of selected areas,legal surveys of the TOK and KAY claims and initial environmentalstudies were also conducted.1990 Prime Resources Group Inc. Prime completed about 200 diamond drillholes around the #21 zone.Underground development began on the 21B zone.1991 and International Corona Corporation Corona conducted detailed stratigraphic and structural mapping,1992 UTEM, borehole EM, seismics and i’M imaging, and surface andunderground diamond drilling; selected drillholes were relogged.1993 Homestake Canada Ltd. Feasibility studies commenced.‘The main numbered zones are shown in Figure 1.5.2 Name changed in 1985 to Consolidated Stikine Silver Ltd., now Stikine Resources Ltd.3Merged into Prime Resources Group, April 1990.4Merged with Homestake Canada Ltd. in 1992.7end of the #21 trenches. This is now known as the 21A zone. Further drilling led to the discovery, in 1989, andsubsequent delineation of the remarkable sphalerite-tetrahedrite gold and silver-rich ore of the 2 lB zone, andrelated zones of mineralization. A decline was driven into the 2 lB zone. International Corona Corporation, nowHomestake Canada Ltd., carried out further exploration in 1991 and 1992. The Eskay Creek deposit is jointlyowned by Homestake Canada Ltd. (28% direct interest, 55% total interest; project manager), Prime ResourcesGroup (50%) and Placer Dome Inc. (22%) (The Northern Miner-June 21, 1993). Feasibility studies are inprogress.1.3 Regional GeologyEskay Creek deposit is located in the Iskut River area of the Canadian Cordillera. The cordillera issubdivided into five morphogeological belts (Figure 1.1) comprising a number of accreted terranes (Figure 1.2),which are described in detail by Monger (1989) and Gabrielse et aL (1992). The Iskut River area is within theStikine Terrane, comprised of mafic and felsic volcanic rocks and clastic rocks of magmatic arc affinity (Tipperand Richards, 1976), and is located on the western edge of the Bowser Basin overlap succession (Figure 1.3). TheStikine Terrane and the Bowser Basin form the western part of the Intermontane Belt. Evidence suggests that theterranes of the Intermontane belt were amalgamated by Jurassic or latest Triassic time and accreted to the NorthAmerican continental margin by the Middle Jurassic (Monger, 1989). Areas of uplift and overthrusting related toaccretion provided the main source of Middle to Upper Jurassic clastic rocks shed into the Bowser Basin.Within the Iskut River area of northwestern Stikinia, the exposed geology comprises fourtectonostratigraphic elements proposed by Anderson (1989): (i) Paleozoic Stikine Assemblage, (ii) Mesozoic(Tnassic to Jurassic) volcanic-plutonic complexes, (iii) Middle to Upper Jurassic Bowser Lake Group overlapassemblage, and (iv) Tertiary Coast Plutonic Complex. The Triassic to Jurassic volcano-sedimentaiy assemblageis of particular interest because it hosts several significant mineral deposits including: Eskay Creek, Snip, JohnnyMountain (Skyline), Stonehouse, Sulphurets, Brucejack Lake, Kerr and numerous other showings within the IskutRiver area. These Mesozoic rocks are generally subdivided into the Upper Triassic Stuhini Group and the Lowerto Middle Jurassic Hazelton Group.Geology in the Iskut River area has been mapped by several workers including Kerr (1948), Grove (1986),Alldrick (1989), Alldnck and Britton (1988), Alldrick eta!. (1989), Anderson (1989), Anderson and Thorkelson(1990), Britton and Alldrick (1988), Britton eta!. (1989, 1990), Britton (1991), Marsden and Thorkelson (1992),Bartsch (1992, 1993), Lewis (1992), and Lewis eta!. (1992). Interest and exploration in the Iskut River area wasvery active during the late 1980’s, and in 1990 and 1991, due to numerous significant and economic discoveries.However, activity has recently waned.Existing stratigraphic nomenclature within the Iskut River area is presented in Figure 1.4 (after Andersonand Thorkelson, 1990). The Hazelton Group, which hosts the Eskay Creek deposit, is subdivided into several8\00FIGURE 1.2: Distribution of terranes in the Canadian Cordillera (from Monger, 1989). The IskutProject area (Figure 1.1) is within Stikinia. Terrane abbreviations: AX=Alexander,BR=Bridge River, CA=Cassiar, CC=Cache Creek, CD=Cadwallader, CGChugach,CN=Chilliwack-Nooksack, CR=Crescent, HO=Hoh, WJuan de Fuca Oceanic Plate,KO=Kootenay, MO=’Monashee, MTMethow, OZOzette, PAPadilic Oceanic Plate,PR=Pacific Rim, QN=Quesnellia, SH=Shulcsan, SM=Slide Mountain, ST=Stildnia,WR=Wrangellia, YA=Yakutat, YT=Yukon-Tanana.1Iii/71500 KM9Jurassic IntrusionSBowser Lake Group(sedimentary rocks)Lower to Middle JurassicHazeiton Group (volcaniCrocks, dominantlY colc_otkoWe)126’W 124’W128’W______________--‘p134w132’W130W0- q.pRoJEct.0••. 21er0s________58’N56’ N54’Nkm200 3000-Modified from G.S.C. Map 1712A,Whe&er and McFeely, P., 1991.1?IGURE 1,3: DisthbutiOfl of Jurassic rocks in northwestern British Columbia. The Iskut Project area islocated in the Lower to Middle Jurassic 1-lazelton Group on the western margin of theBowser Basin.UpperJurassic—163±15-__________________basinal marinetonon-marinesedimentaryrocksMiddle________________________________________________________________Jurassic__________________fadesvariabilityrangesfromtuffaceousturbiditetopillowedandbrecciatedmaficlavas—187+34——intermediatetofelsicvolcanictuffbreccia orflowdominantlyvolcaniclasticsuccessionwithLowerIcrJiicrbeddedtufficndflqwsJurassiovolcanicbreccia, tuffpillowedandmassiveandesiticflows,voIcmiclasi’icrocks,sandstoneandconglomerates—208±18—pyroxenerichporphyritic flows andtuffs,Triaicturbidite, limestoneandconglomerate—245±20—!FIGURE1.4:Stratigraphicnomenclatureof theIskut RiverArea,northwesternBritishColumbia(afterAndersonandThorkelson,1990).Thisclassificationschemeisdifficulttoapplyregionallybecauseof disagreement onthedistinctivecharacteristics,natureofcontacts,ageandpositionsofgroupboundarieswithinthedefinedformations,Theseproblemsandare-evaluationof thestratigraphicschemeareaddressedbyLewis(1992).OxfordianCeilovisnowserLkeGroupajoctan(,) 0 N 0 (c) UiAaientwiTo,rcIanMhmanFormationPiicnaI’achian5incmurIanHzeftotiGroupHettanglariSalmoniiverFormationMountPilworthFormationt3ettyCreekFormationNorianUnukiverFormationStuhiri IGroupStikiriAssembIgecorallinelimestone, chert,majic tofelsicvolcanicand volcaniclasticrocksandderivedsedimentsC11formations. However, the described characteristics, contact relationships, ages and correlation of thesesubdivisions throughout the region is inconsistent among various authors. This reflects the inherent regionalvariability within volcanic rocks due to changes in facies and unit thickness, and overlapping material from morethan one volcanic center. Correlation is further complicated by complex structural controls. These problems arediscussed by Lewis eta!. (1992) and Bartsch (1993b).The area around the Eskay Creek Deposit has been deformed into a series of generally northwest trendinganticlinal and synclinal folds. Major fault structures within the Iskut River area include the north to northwesttrending Harrymel Creek Fault, which juxtaposes less deformed Triassic strata on the west side of the fault againstdeformed Jurassic rocks to the east (Alldrick et at., 1989; Britton et at., 1990; Lewis, 1992). Normal and lowangle thrust faults have also been defined which cause duplication in the lithostratigraphic sequence (Britton andAlldnck, 1988; Britton ci’ at., 1989, 1990; Bartsch, 1993b; Lewis, 1992; Lewis et at., 1992).The Eskay Creek deposit is located on the western limb of a northeasterly plunging anticlinal foldstructure cut by a series of axial planar faults (Figure 1.5, modified with permission from Bartsch, 1 993b). Thetiming of these faults is unclear; they may be related to the deformation, or they may be reactivated synsedimentary or syn-volcanic faults. Stratigraphy in the 2 1A zone comprises rocks of the Hazelton Group, shownschematically in Figure 1.6. Hazelton Group stratigraphy here consists of marine sediments overlain by andesitic,rhyolitic and basaltic submarine volcanic rocks and associated volcaniclastic and sedimentary rocks. The BowserLaice Group overlies the basaltic sequence and consists of a thick succession of marine to non-marine shale,sandstone, wacke and conglomerate. The Hazelton Group rocks are intruded by felsic and mafic dykes related torhyolitic and basaltic volcanism respectively. Bartsch (1 993b) has suggested that the subvolcanic felsic dykes arefeeders to a linear series of northeast trending rhyolite flow domes; this rhyolite package forms the footwafi to theEskay Creek 21 Zone deposits. Subsequent mafic dykes foLlow the same structures as the earlier felsic dykes andfeed the overlying basaltic volcanics. Basalt, which forms the hanging wall to the Eskay Creek 21 Zone, is thickestin the vicinity of the deposit (Bartsch, personal communication, 1993). In the area overlying the deposit, basaltcomprises massive flows, grading laterally through pillowed to brecciated facies towards the south.Age constraints are provided by geochronometiy and biostratigraphy. Four principal plutomc events havebeen identified in this area of northwestern Stikinia, three of which are suggested to have extrusive equivalents(Anderson and Bevier, 1990; Table 1.2). Geochronometric U-Pb and K-Ar isotope data for the area are presentedby Anderson (1989), Anderson and Bevier (1990), Anderson and Thorkelson (1990), Anderson et at. (1991),Bevier and Anderson (1991) and Macdonald eta!. (1993). The distribution of Jurassic intrusions, as well as rocksof the Hazelton and Bowser Lake Groups, is shown in Figure 1.3.12628021* ZONE vvv , f -MAP AREA-v S,v’), -- vv— gSZONE-PORPRY Z€* ESKAY PY- - f+6276/; J /- - - r - -- - - - - - - -- - J - - - ///‘ ///f.U4f///f. - —L - - -6274 /_1T’//? / I SIB LAKE ADITiç---Ø9 LEGEND- --f,’ 1J2\ 1 - --BOWSER LAKE GROUPTurbidHe and Argillite- - -HAZELTON GROUP‘ f F— - •if1_’ / i 7 I - - - Basalt and Intercalated ArgililteJ !1:’: J\ ‘ - Rhyole/_fI//f \_\ -I ,j / — I - - ‘_, Palymodal Volcanic and Sedimentary Rocks/ /4J_ _1j‘// - - - - - Mafic Dikes/— I / I + 1 - - — - --- -Felsic Porphyritic Intrusions‘\/ X/—-If - - -6270 .. ArgilliteAndesiteGEOLOGICAL BOUNDARIES & SYMBOLSGeological Contact0 1 2 KM Exlent of outcrop traversed-,-—-,— Thrust FaullNormal Fault: Major. MinorUTM COORDINATES X 1000_$_ Syncilne, AnticlineNAPPED BY R.D.BARTSCHDRAFTED BY A.TOI4AIINERAL DEPOSIT RESEARCH UNIT. SKI/F RIVER PROJECT. 1993FIGURE 1.5: Local structure and stratigraphy of the Eskay Creek area, northwestern British Columbia,mapped by R.D. Bartsch (modified with permission, 1993). Important mineralized zonesand adits are identified. The 21 zone is located between the rhyolite and overlying basaltwith intercalated argillite on the western limb, near the nose of the northwest plungingEskay Creek anticline. Sediments in the Bowser Lake Group are tightly folded into aseries of anticlinal and synclinal structures. The structural setting of the Iskut Project areais described by Lewis (1992). The 21A zone map area is detailed in Figure 2.5.13Figure 1.6: Schematic stratigraphic column for the 21A zone, Eskay Creek, northwestern BritishColumbia. Refer to Chapter 2 for details.vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv/‘\ ,7\ V V V/Th 7\ 7\vvV/\ /\7\ /\ v,-,‘---,—- v ‘.‘VVVVVVVVVVVVV\vVvvvvvvvvvVv’VvvVvvvvvvvvvv,VVVVVVVVVVVVVV\ iVVVVVVVVVVVVVvvvvvvvVvVvVvv.- vVVvVvvvvvvvvvvvvvVvvvvvvvv ,VvvvvvvvvvvvBasalt intercalated with argilliteand turbiditesmassive to pillowedflows, pillowbreccia, hyalodastite, debrisflows, sills, and intercalatedargillite and thin turbidite.vvvv vvvvvv vvvLi,0Contact argillitehost to stratabowid 21 zone mineralization.Rhyolitic volcanic unitmassive tojlow banded rhyolite,rhyolite autobreccia, hydrothermal breccia, intrusive contactbreccia and pyroclastic rocks.‘V&zsalticdykes:i: :.‘Felstc intrusions.••.•.:‘• •- •..• •...• :••:Footwall volcanic unitbanded to amygdak*lal intermediate tomafic sills and/orflows. dacitic pyroclastic andepiclastic rocks, and shale and sandstone.Lower Sedimentary Unitargillite to shale, siltstone,sandstone, and minor volcaniclastic rocks.14Table 1.2: Plutonic events in northwestern Stikinia (Anderson and Bevier, 1990).Plutonic Event Plutonic Suite Extrusive Equivalent55- 51 Coast Plutonic ComplexTertiary179 - 172 Ma Three Sisters Salmon River FormationMiddle Jurassic211 - 187 Ma Texas Creek Hazelton GroupLate Triassic to Early230 - 226 Ma Stikine Stuhini GroupLate TriassicPorphyritic intrusions have been identified in the Eskay Creek area. A sill-like body, called the Eskayporphyry, crops out approximately 1 kilometre east of the #22 zone (Figure 1.5). It has been described in detail byDonelly (1976), Macdonald (1992) and Bartsch (1993b). The Eskay porphyry comprises phenocrysts of potassiumfeldspar and plagioclase with lesser amphibole, biotite and quartz, and trace sphene, apatite and zircon in agroundmass of fine grained quartz and feldspar; it has been dated at 186 ± 2 Ma (U-Pb) and is probablyrepresentative of the regional Texas Creek plutonic suite (Macdonald et a!., 1993). Biochronologic ageconstraints, using radiolaria and ammonoids, have been determined by Nadaraju (1993). Ages range from UpperPliensbachian (193±28 Ma) in the lower sedimentary rocks of the Eskay Creek stratigraphy, to Upper Bathonian(169±15 Ma) in the sediments of the Bowser Basin here. Argillite intercalated with basaltic volcanic rockscontains Upper Aalenian radiolaria, therefore constraining the timing of rhyolitic to basaltic volcanism toToarcian-Aalenian time (193±28 to 183±34 Ma) which correlates with available U-Pb age dates (Nadaraju, 1993).Bartsch (personal communication, 1993) has shown that the Eskay porphyry may be related to the rhyolite,representing an earlier stage in magma fractionation, although the precise age relationships are uncertain.Another similar, small, intrusive porphyry is located four kilometres south-southwest of the Eskay Creek deposit(Figure 1.5).Regional metamorphic grade of the Prout Plateau area is lower greenschist fades (Britton et al., 1990).This is characterized by chioritized mafic minerals, saussuritized plagioclase and the formation of white mica fromclay constituents. Peak metamorphism occurred in mid-Cretaceous time, based on resetting of K-Ar ages in theStewart and Suiphurets areas (Alldrick et aL, 1987).Existing formation names (Figure 1.4) are not applied to the units mapped within the 21A zone in thisstudy. The stratigraphy is described on the basis of lithology and textural variations only, Thus, this work can becompared directly to facies variations described by Bartsch (1 993b) in the surrounding area.152. GEOLOGY OF THE 21A ZONE2.1 IntroductionGeology of the 21A zone has been evaluated by relogging core from 24 diamond drill holes on three crosssections spaced at 100 metre intervals (Figures 2.1, 2.2 and 2.3), relogging core from selected intervals throughoutthe zone, reviewing all available drill logs within the zone (Figure 2.4), and mapping surface outcrops at 1:1000scale on an orthophoto in the immediate area of the 2 1A zone (Figure 2.5). Descriptions of the Eskay Creekdeposit have been published previously by Idzisek et at. (1990), Blackwell (1990) and Britton et aL (1990).The stratigraphy of the 2 1A zone map area occurs entirely within the Early to Middle Jurassic HazeltonGroup. Rock descriptions are based on lithology, textural features and stratigraphic position relative to strataboundmineralization. The sequence is interpreted to have been deposited in a submarine volcanic enviromnent. Theoldest rocks in the 2 1A zone map area are sedimentaiy and volcaniclastic rocks. These are overlain by the lowervolcanic unit which comprises altered mafic to intermediate flows or sills, tuffs and lesser sedimentary rocks.These rocks are overlain by a package of rhyolitic pyroclastic rocks, breccias and flow domes. The upper part ofthe felsic volcanic package grades into argillite which hosts stratabound mineralization. This argillite is referred toas the contact unit or contact argillite and is in turn overlain by basaltic volcanic rocks. The termsfootwall andhanging wall are used to describe strata which underlie and overlie the contact argillite respectively. Basalt,intercalated with argillite and thin turbidite, forms the hanging wall and is the youngest sequence in the map area.A small lens of rhyolite occurs, apparently within the basalt, in the northwest corner of the map (Figure 2.5). Thestratigraphic position of this lens is discussed in section 2.2.The 21A zone map area is located on the western limb of a northward plunging anticline known as theEskay Creek anticline (Figure 1.5). Strata within the map area strike northeasterly and dip about 45 degrees to thenorthwest. Local variations in bedding attitudes are caused by minor folding and complex faulting. Large faults,extending several kilometres, are parallel to the fold axis of the Eskay Creek anticline. Small offsets in thecontacts between the lithological units are common, but must be interpreted with care because they could be due topaleotopographical variation, especially on top of the rhyolite sequence. Such rhyolitic volcanic rocks, whetherflow or domal in origin, usually have highly irregular surfaces (cf Cas and Wright, 1988). Thus, interpretation ofthe cause of minor offsets (around 5 metres) in the argillite-rhyolite contact is difficult. Displacement due tofaulting is clear only where stratigraphic offsets continue through the drilled stratigraphic sequence. Major faultsrecorded in the 21A map area are described in section 2.2.Interpretation and correlation of the rock units is complicated by intense alteration in the Pumphouse Lakevalley. The outcrops in and flanking the valley are dominantly rhyolite and the lower volcanic unit that underliesit; intense silicification and sericitization make the distinction between the two difficult. However, amygdulespresent in flows or sills of the lower volcanic unit are distinctive and provide a reasonable marker (Plate 2.1).Intensely silicified, heterolithic volcaniclastic rocks also can be identified locally by relict clasts (Plate 2.2). This16Plate 2.1: Quartz-filled amygdules in flows or sills in the frtal1Plate 2.2: Intensely altered volcarnelastic rock from the footwallvolcanic unit.volcanic unit. Relict clasts are visible locally.I *-••‘.JI• :-.._z._4..--.Plate 2.3: Bedded pyroclastic and epiclastic rocks fromthe footwall Plate 2.4: Altered flow or sill from the footwall volcanic unit.volcanic unit. These units are variably graded to unsorted.Stockwork veins consist mainly of pyrite and quartz. The rockshows a banded to wormy texture typical of massive footwallvolcanic rocks. (CA89-024: 178.5m, scale is centimetres.)17zone of intense alteration is associated spatially with the felsic intrusions exposed in the #3 and #4 Bluffs (Figure2.5). Alteration associated with felsic intrusions south of the #21 zone is documented by Bartsch (1993b);alteration intensity increases with proximity to the felsic dykes.2.2 Geological frameworkThe surface geology of the 2 1A zone map area is shown in Figure 2.5. Strata reflect relatively simplenorthwest facing layering offset by a number of minor, and few major, faults. The stratigraphy is gently deformedinto broad, undulose folds which are observed at small scale in outcrop and at larger scale in cross-sections(Figures 2.2, 2.3, 2.4 and Al to A12). Drill holes in the 21A zone map area are not oriented perpendicular to thelocal strike of the strata (Figure 2.4), therefore cross-sections along the direction of drilling show apparent dip ofstratigraphy (generally 100 shallower than true dip). As a result, the core-to-bedding angles plotted on the sectionare slightly steeper than the stratigraphic relationships indicated in this projection. The contour surface of the topof the contact argillite (picked at the base of the first non-intrusive basalt unit), shown in Figure 2.6, is consistentwith a 45° dip to the northwest. Slight fluctuations are due to small fault offsets which reflect a series of minorfaults and gentle folding. These minor fault offsets, ranging from 5 to 10 metres apparent vertical displacement,persist from section to section through the 2 lA zone (Appendix A) and are indicated on Figure 2.6. These smallfaults locally control the thickness of the contact argillite and may represent synvolcanic growth fault structures(refer to section 2.3.4 for further discussion).FaultsThe Pumphouse fault zone (Figure 2.5) is a major structure that trends about 030° azimuth and followsthe Pumphouse Lake valley. Offset on the fault appears to be dextral and its southeastern block is downthrown, asobserved on drill sections. A parallel structure or splay of the Pumphouse fault is interpreted along the margin ofthe 21A ridge. Other faults parallel to the Pumphouse fault may also occur, but evidence is sparse because fewholes were drilled to penetrate units below the rhyolite, particularly northwest of the 21A zone mineralization.Foliation and shearing parallel to the Pumphouse fault are prominent in outcrop within the valley (Figure 2.5).Foliation measurements throughout the 21A zone map area suggest that the dominant orientation is about 030°azimuth with variable, but generally steep, dip in either direction (Figure 2.7). This suggests a principal northweststress direction, which is consistent with regional observations by Lewis (1992). Lewis proposes an overallnorthwesterly verging fold and thrust system for the eastern Iskut River area.Another major structure is a north-trending fault near Skeet Lake. This fault causes an apparent offset of100 metres on the the rhyolite-basalt contact (Figure 2.5). This feature is coincident with a gully; truedisplacements along this structure are unknown. Minor zones of shearing and deep gullies occur throughout thearea and may reflect minor faults or splays off the larger fault structures. Alternatively, some gullies may beoccupied by recessively weathered units.15010050 -50—100-150-200—250-300Figure2.6:Contour mapof thetopof thecontactunit,EskayCreek2 1Azone,northwesternBritishColumbia.Contour intervalsare10metres.000o00U)NNNU)o000IIIo220000000000In0II)02II)oINCUN0019EIGENVECrORS:Vector Trend Plunge1 28.5 17.22 222.9 72.23 119.8 4.2Figure 2.7: Stereonet diagram of foliation measurements in the 21A zone map area, Eskay Creek, northwesternBritish Columbia. The poles form a moderately developed cluster. Measurements indicate a principlestress direction trending 1200.N =8020Rhyolite lensA lens of rhyolite occurs in the northwest corner of the map area, apparently within the basaltic volcanicpackage (Figure 2.5). A significant northeast trending lineanient, evident as a gully on surface and clearly visibleon an orthophoto image, traces the contact between the rhyolite lens and basalt in this area of the map. Thislineament may mark a fault or a recessive unit at the contact between the rhyolite and the basalt. However, outcropin and immediately adjacent to the gully is sparse. Two holes have been drilled into this rhyolite lens near 2+OOS(CA89-047 by Prime, and GNC92-27 by International Corona). Holes drilled to the southeast of the lens on thesame section indicate a stratigraphic sequence similar to that observed throughout the 21A zone (driliholes CA89-046, 030, 031, 032, 033 and 034). Section 2+OOS is plotted in Figure 2.8 from original drill log information.Drill holes CA89-046 and -047 are drilled in opposite directions from the same point within the gully, However,CA89-047 intersects the rhyolite at significantly higher elevation than CA89-046 and is drilled essentially downthe dip of the stratigraphy. Argillite is present between the basalt and rhyolite units in CA89-046 and -047, butwas not intersected in GNC92-27. Several thin mafic intervals, ranging from 40 centimetres to 2 metres thick,were intersected within the rhyolite in both CA89-047 and GNC92-27. These intervals are described as massive tobrecciated, tan, fine grained and locally pillowed. One 1.4 metre interval of heterolithic debris flow containingbasaltic pillow fragments and banded mudstone clasts was also described within the rhyolite sequence in GNC92-27.The presence of the rhyolite lens and the abrupt changes observed between holes CA89-046 and -047 maybe interpreted in several ways. It may represent (i) fault repetition of the rhyolite unit, or (ii) later felsic volcanismthat is concurrent with the basaltic volcanism (as proposed by Edmunds et al., 1992).The linear nature and extent of the lineament on surface supports the interpretation that it may represent asignificant fault zone. However, no mention of significant fault gouge was made in the original drill log of CA89-047. In this hole, rhyolite was intersected at 13.8 metres, and if present, the fault would have been intersectedabove the rhyolite. The upper 5.2 metres of the hole are casing. Rubbly and oxidized wacke and argillite comprisemost of the remaining 8.6 metres, separated by 1.3 metres of basalt breccia. The rubbly nature of the sedimentaryrocks may simply reflect weathering effects from surface, or possibly may be associated with fault disruption. Afault along this gully, downthrown to the southeast, is consistent with other fault patterns observed in the area.Alternatively, the rhyolite lens may represent a later event of felsic volcanism, concurrent with the basalticvolcanism. This is supported by the presence of a debris flow within the rhyolite containing mafic pillowfragments and mudstone clasts. The massive to brecciated mafic intervals may be intrusive into the rhyolite. Theintervals are sparse and very thin. Similar intersections in drill core from Section 1+OOS were interpreted to bechilled mafic dykes. Such dykes appear to be restricted to the southernmost drillholes within the 21A zone.Further indications for either contemporal felsic and mafic volcanism or a second felsic volcanic event have not21a)110010501000950900850800750700Figure 2.8: Two possible interpretations for Section 2+OOS through the rhyolite lens in the northwestportion of the Eskay Creek 2 1A zone map area, northwestern British Columbia.Interpretation (a) implies occurrence of a separate felsic repetition within the basalt andsuggests contemporaneous rhyolitic and basaltic volcanism. Section in (b) is consistent withfaulted displacement of rhyolite. Refer to the text for details.b)110022been observed by the author, and were not reported by Bartsch (1993). However, such evidence has been notedelsewhere by the Eskay Creek project geologists (F.C. Edmunds and D.L. Kuran, International Corona Corp.,personal communication, 1992).2.3 Lithology2.3.1 Lower Sedimentary UnitLower sedimentary unit comprises the lowermost sequence in the Eskay Creek 2 1A area. The unitcrops out in the southeastern portion of the map area, southeast of Eskay Creek (Figure 2.5), and isrepresented in the deepest driliholes in the 21A zone. These drill holes indicate a thickness greater than 60metres (e.g. CA89-045, Figure 2.1). The sedimentary rocks are dominantly interbedded marine shale,siltstone, wacke, rare conglomerate and minor volcaniclastic material.Shale in drillhole CA89-045 is black to dark grey, generally poorly bedded and locally containsfragments of belemnites and bivalves, which are commonly pyritized. Nadaradju (1993) collected andidentified Early Jurassic, Upper Pliensbachian ammonoids from stratigraphically equivalent shales about 200metres northeast of the Eskay Creek camp (Figure 1.5). Irregular pynte laminae and thin sandy beds aresparse within the shale.The coarser sediments are generally grey to greenish grey, poorly sorted and generally weakly beddedto cross-bedded. Locally, graded beds and load casts indicate the stratigraphy has not been overturned. Thesediments are medium to fine-grained with thin beds of heterolithic fragments up to 5 millimetres in diameter.Clast supported conglomerates comprise poorly sorted, rounded, heterolithic cobbles and pebbles.2.3.2 Lower Volcanic Unit: flows or sills, volcaniclastic and sedimentary rocksLower volcanic unit comprises tuffs, epiclastic rocks, aphanitic and banded to amygdaloidal flows orsills, and sedimentary rocks. This sequence has previously been termed thefootwall dacite unit (Blackwell,1990; Britton et at., 1990; Roth, 1991, 1992, 1993; Roth and Godwin, 1992; Rye et aL, 1993).The unit is up to 50 metres thick and is distinguished from the underlying unit by the dominance ofvolcanic rocks. The volcanic sequence is locally separated from overlying rhyolite by a shale horizon. Theirregular distribution of the shale and generally slightly steeper bedding than in the higher stratigraphy,indicate that the upper contact of this sequence may be unconformable, erosive or locally intrusive, asdiscussed in section surface, this unit occurs in the Pumphouse Lake valley (Figure 2.5), where it is usually intenselyquartz-sericite altered, often almost beyond recognition. It is distinguished by the distinctive amygdaloidalnature of the flows or sills (Plate 2.1), and by relict clasts in altered volcaniclastic rocks (Plate 2.2). Tuffs andsediments are generally poorly represented in surface exposures due to recessive weathering and the difficultyof recognizing these altered units. Poorly to well sorted, locally graded volcaniclastic rocks are exposed in onewell preserved outcrop (Plate 2.3) near the #3 Bluff Accretionary lapilli were recognized within thissequence. Shale, occurring between the footwall volcanic rocks and the rhyolite, crops out at only one locationnorth of the #3 Bluff:Massive to amygdaloidal flows or sills are characteristically pinkish beige and commonly have anunusual banded to wormy texture (Plate 2.4). Pyrite-sericite stockwork alteration is widespread. Amygdules,comprising up to 20% of the rock and up to 1 centimetre in diameter, usually are filled with quartz or locallywith pyrite and chlorite. This rock is aphanitic and has a brownish felted appearance in thin section; opticalidentification of the minerals is impossible. Staining indicates that this unit generally contains significantpervasive potassium feldspar. X-ray diffraction studies show that the rock is comprised of quartz, orthoclaseand chlorite. The relative intensities of the (001) chlorite peaks are consistent with nimite, a Ni-rich variety ofchlorite. Trace element geochemistry of two samples of the massive flows or sills indicate a sub-alkalinebasalt signature (Figure 2.15, section 2.4).Volcaniclastic intervals include ash and lapilli tuffs and flows, debris flows, and reworked epiclasticrocks. Outcrops of these rocks are most prominent along the northwest side of Eskay Creek and at the base ofthe #3 Bluff (Figure 2.5). In drilicore, these rocks are best represented in holes CA89-044 and 045 (Figure2.1).Heterolithic volcaniclastic rocks contain angular clasts of argillite and mafic to intermediate volcanicrocks supported in a fine grained, dark green, chiorite-sericite-pyrite matrix. These rocks also locally containpumice fragments, which are up to 10 centimetres across and usually flattened (Plate 2.5). Locally, thismaterial has been reworked into graded, epiclastic beds (Plate 2.6).The pyroclastic rocks in the footwall volcanic unit include pale grey, massive, fine grained ash tolapilli tuffs that locally contain fiamme and flattened pumice fragments. The fragments and matrix arepervasively chlorite and sericite altered (Plate 2.7). Fine grained tuff or epiclastic rock contains up to 55%crystals dominated by twinned oligoclase with variable orthoclase, rare quartz and minor muscovite. Thecrystals are generally 200 microns to rarely 1 millimetre across. The groundmass of very fine grained sericite-quartz ± chlorite contains up to 3% disseminated euhedral pyrite. Accessory minerals include apatite andsphene; broken rock fragments containing zoned plagioclase are rare. Feldspar is variably replaced by sericite;4..-•_..-•‘irI ..‘ -:--‘I..,i 4.. •Plate 2.6: Graded epiclastic rock from the footwall volcanic unit.Clasts include mafic, intermediate and felsic volcanic rocks andargillite in a fine-grinned chiontic matrix.24rPlate 2.5: Poorly sorted volcaniclastic rock from the footwall volcanicunit. Clasts include mafic, intermediate and felsic volcanic rocks,minor argilhite and locally, slightly flattened pumice clasts.F.+. ,,-t.Plate 2.7: Photomicrograph of intensely altered volcaniclastic rock inthe footwall volcanic unit. Groundmass is chioritic and fragmentsare mainly sericite. (CA89-043: 253.3m, cross meols, 4mmacross.)Plate 2.8: in-situ, hyaloclastic breccia near the upper rhyolite contact.This rock is commonly referred to in drill core as transi$ion zone.25locally the rock is pervasively sericitized (CA89-43: 253.3). The groundmass appears to be recrystallized andeuhedral pyrite grains are commonly rimmed by quartzose pressure shadows.Black shale to argillite occurring locally between the lower volcanic unit and the overlying rhyolite isgraphitic, variably indurated, and often brecciated or rubbly in drillcore. Locally pyritic laminae are welldeveloped; some intervals are interbedded with tufi thin sandy layers or thin debris flows.2.3.3 Rhyolitic Volcanic UnitThe rhyolitic volcanic unit unconformably overlies the lower volcanic and sedimentary rocks, andranges from 70 to about 200 metres in thickness. The sequence consists of massive to flow banded aphaniticrhyolite, breccia, lapilli and ash tuffs. Bartsch (1 993b) presents the regional facies variations associated withthe felsic volcanic rocks in the Eskay Creek area, and describes the sequence as a linear series of rhyolitedomes with associated pyroclastic and brecciated rocks.The rhyolite sequence forms prominent, resistant ridges and topographic highs in the map area (seefrontispiece). At surface, the rhyolite is generally massive, white to grey weathering and featureless; texturesare commonly obscured by lichen. Some primary features have been preserved despite extensive alteration anddevitrification; these are described below.The lower contact of the rhyolite is generally sharp. The upper contact of the rhyolite is variably sharpto gradational; however, intense alteration in the vicinity of mineralization locally obscures the contactrelationships. A gradational increase from light grey sericitic, possibly tuffaceous, rhyolitic material to a darkgrey to black argillite is common in these altered areas. Locally, competent rhyolite breccia is sharply andconformably overlain by black, carbonaceous to cherty argillite. Elsewhere, brecciated rhyolite fragments mayoccur in a black, siliceous matrix near the upper contact; this lithology was originally termed the fransitionzone, and was included as the lower subunit of the contact unit (section 2.3.4). Where recognized within the21A area, these breccias are generally matrix supported, with unsorted clasts ranging from 1 millimetre to 5centimetres across. Little movement is indicated and individual clasts commonly show in situ brecciation(Plates 2.8 and 2.10).In some areas, the contacts are sheared or faulted over narrow intervals. This may reflect the uptake ofstresses along these zones of weakness during regional deformation; these faults do not generally indicatesignificant displacement (Rye, 1992). The significance of the contact relationships and textures described hereis discussed in section 2.5.26Macroscopic texturesPrimary textures in the rhyolite sequence generally have been obliterated by devitrification andhydrothermal alteration (section 3.2.3), however certain relict macroscopic textures such as flow bands andautobreccias occur locally. On surface, flow banding and breccia textures may be subtle or obscured by lichenand weathering processes. The textures are enhanced and most clearly visible where trenched or brokensurfaces have weathered for a short time. Flow banded rhyolite is prominent near the #3 Bluff and along thewestern side of the Pumphouse Lake valley (Figure 2.5). Flow bands in the rhyolite are commonly folded onthe scale of centimetres to tens of metres (Plate 2.9).Autobreccias are common and are identified by blocky, monolithic flow banded fragments indicatingmovement relative to one another in the rhyolitic magma and local viscous deformation (Plate 2. lOb). Suchautobreccias often form through flow fragmentation in which congealed, viscous cmst is deformed, stretchedor broken into slabs or blocks due to continued flow inside the lava (cf Cas and Wright, 1988). Hydrothermalbreccias form by explosive activity, when the fluid pressure exceeds the confining pressure and tensile strengthof the rock. Clasts within hydrothermally brecciated zones are sharply angular to irregular, reflecting theirhigh energy origin. Explosive breccias are commonly heterolithic, but are not prevalent in the 21A zonerhyolite. However, locally rhyolite fragments of variable alteration intensity occur together. These mayrepresent hydrothermal breccias formed during active hydrothermal alteration. Secondary or“pseudobreccias”, formed by stockwork alteration, look similar to autobreccias and hydrothermal breccias, butno mechanical movement of fragments has occurred. This type of breccia is common in the 2 1A zone rhyolite(Plate 2.lld).Flow banding and breccia textures are preserved locally in drill core (Plates 2.9c and 2. lOc). Massiveto flow banded rhyolite occurs dominantly in the lower part of the rhyolite unit. Breccias are commonthroughout the rhyolite sequence.Pyroclastic rocks are difficult to identify confidently within the rhyolite unit. Textures produced by theprocesses of devitrification, perlitic fracturing and hydrothermal alteration can look deceptively likepyroclastic and volcaniclastic textures (Allen, 1988). Such false pyroclastic textures have been documented inthe Eskay Creek rhyolite by Macdonald (1991). These textures are described further in Section 3.3 (Plate 3.2).Locally, true pyroclastic textures have been preserved despite the alteration overprint. Small flattened shardsin a tuffaceous groundmass are probably fiamme, and are described petrographically below.Microscopic texturesFew distinctive petrographic features are preserved within the rhyolite, however some relict primary anddevitrification textures have survived (Table 2.1). In general, the rhyolite comprises variable proportions of.,2.9b)•Plate2.9:Flowbandinginrhyolite.(a)Large-scaleflow-foldingina15metrecliff-face.(b)Flowbandingexposedositheweatheredsurfaceof therhyolite.(c)Flowbandedrhyolite indrillcore.Pervasivepotassiumfeldsparisindicatedbythebrightyellowstainfromsodiumcobaltinitrite.Thinquartzveinletscrosscuttherock.(d)Flowbandingisenhancedbyalterationanddevitrification.Darkgreybands aredominantlysericiteandpyrite.Lightgreyandwhitebandsaredominantlyquartz.Spottingof therockisduetoformationof spherulites.DrillcoreisNQ.S.-..Plate 2.10: Rhyolite breccia. (a) “Black matrix breccia.” In-situ breccia commonly occurs near the top of the thyolite unit.(b)Viscous deformation is locally evident in autobrecciated rhyolite where slightly deformed, flow banded clasts are rotated withrespect to one another in the rhyolite. (c) Rotated, flow banded clasts are also visible in drill core. This sample suggestshydrothermal brecciation resulted in angular clasts in a siliceous matrix. Potassium feldspar is commonly restricted to the clastsin such breccias, and rarely occurs within the matrix. (d) Sharply bounded “clasts” typical ofpseudobrecciated rhyolite in the2 la zone. This texture forms as a result of alteration in the rhyolite along sharp alteration fronts..10 a), m‘nmZ —4r•%CA9O-42. 188 5rnStained for K-sparI, ‘29Plate 2.13: Possible fiamme or hyaloclastite fragments in rhyolite. (a) The rock consists of micrecrystalline sericite±chlorite andpyrite with discrete, pale angular to cuspate comprising entirely sericite and little orno pyrite. (CA88-014: 49.Xm; core is NQ)(b) Photomicrograph of these flamme like features. The mineralogy of the flamme is different from the host rock, consistingentirely of sericite and less pyrite than the host rock. (CAS9-035: 66.6m; cross nicols, field of view is 4mm)-Plate 2.11: Rare quartz phenocrysts in rhyolite. The Plate 2.12: Rare zircon in rhyolite. (CA89-043 152.Om;phenocrysts are typically small, ranging from 50 to 200 cross polarized light; field of view is 0.1 mm).microns across, and commonly square. The matrixconsists of fine-grained sericite, quartz and pyrite.(CA89-044: 1 16.Xm, cross nicols, 1.2 mm field of view.)30TABLE 2.1: Textures in the rhyolite unit, Eskay Creek 21A Zone, northwestern British Columbia.RELICT PRIMARY FEATURESFM TURE OCCURRENCE CHARA CTERISTICSFlow banding common . alternating quartz dominant to sericite dominant bands. generally 2 to 5 millimetres wide. veiy fine grained disseminated pyrite is generallyconcentrated in sericitic bandsBreccia common • clasts with rotated flow bandingFiamme? rare . irregular to wedge shaped patches, altered to sericite,or hyaloclastite which are compositionally distinct from the surroundingfragments? microcrystalline groundmassQuartz phenocrysts sparse • round to square, euhedral grains. distinguished by lack of micro-inclusions and largergrain size than groundmass• generally range from 50 to 200 microns. locally have narrow quartz overgrowthsZircons rare • euhedral to subhedral. up to 30 microns. locally weakly zonedPlagioclase phenocrysts very rare • observed only in least altered samples• grains are approximately 200 microns• albite twinning is present• associated with annealed quartzDEVITRIFICATION FEATURESFM TURE OCCURRENCE CHARA CTERISTICSRadiating spherulites sparse • round, radiating aggregates of quartz, quartz-alkalifeldspar-sericite or quartz-sericite in the groundmass• range up to 250 microns. patches of annealed quartz or quartz with sericite that arecoarser grained than the microcrystalline groundmassmay be relicts of spherulites or lithophysaePerlitic cracks sparse • relict curved, concentric cracks now defined by finegrained pyrite hosted in annealed quartz• margins to the cracks are usually sericite or chlorite31quartz, sencite, chlorite, pyrite and locally potassium feldspar. These minerals reflect the hydrothermalalteration assemblage in the footwall of the 2 1A zone (section 3.2.3). Plagioclase, rutile and zircon are rare.Quartz is ubiquitously annealed and strained. Microcrystalline quartz, sericite and chlorite are difficult todistinguish, although sericite has a much higher birefringence than chlorite or quartz. The presence andidentification of these microcrystalline minerals within the rhyolite sequence was confirmed by X-raydiffraction (section 3.2.3).Flow banding in rhyolite (Table 2.1) comprises alternating microcrystalline layers that are eitherquartz dominant or sericite dominant. Very fine grained disseminated pynte is concentrated in the sericiticlayers. Macroscopically, the bands are alternately white (quartz dominant) to grey (sericite-pyrite dominant)and are generally 2 to 5 millimetres thick. Such flow banding is characteristic of laminar flow in viscous,highly siliceous flows (cf Cas and Wright, 1988).Primary quartz phenociysts (Plate 2.11), averaging 0.2 millimetres across, are sparse and generallyrounded to locally euhedral or subhedral squares. They commonly are strained and locally are rimmed by latequartz overgrowths. In plane polarized light the quartz phenocrysts stand out because they are somewhatcoarser than the groundmass, and are usually free of micro-inclusions. Euhedral, square grains may reflect thecrystal form of the high temperature quartz polymorph, cristobalite.Euhedral to subhedral zircon crystals, up to 30 microns across, were observed rarely in flow bandedrhyolite (Plate 2.12). Minor rutile occurs as irregular to subhedral brown to reddish brown crystals, up to 20microns long, or as aggregates up to 50 microns across. Identification of rutile was confirmed using electrondispersion spectrography (EDS) on a scanning electron microscope (SEM). In general rutile occurs only in theless altered to moderately altered rhyolite. Where observed, it is generally concentrated locally in narrow bandsor along thin irregular quartz veinlets; however it also occurs disseminated throughout the rhyolite. Plagioclasephenocrysts (Plate 3.9) are rarely preserved within the rhyolite and were observed only in relatively unalteredsamples collected near the #3 Blufl about 700 metres south of 2 1A zone mineralization (Figure 2.10: TR-92-59, TR-92-60). These samples have undergone some alteration, as indicated by the amount of sericite in thegroundmass. In advanced stages of alteration, as represented in the core of hydrothermal alteration proximal tothe 21 zone mineralization, plagioclase is altered to sericite.Primary pyroclastic textures are rarely preserved in the Eskay Creek rhyolite. However, small flattenedto cuspate fragments (Plate 2.13), up to 1 centimetre long by 4 millimetres wide, occur locally. They havesharp boundaries and are generally paler in colour than the surrounding matrix. Petrographically thesefragments consist of sericite with higher birefringence than the surrounding material and lack fine grainedpynte, which is pervasively disseminated throughout the surrounding microcrystalline groundmass (Plate2. 13b). These features may be interpreted as flattened pumice fragments in a pyroclastic ash deposit.Alternatively, they may have originated as hyaloclastite fragments which have been subsequently altered and32flattened. The interpretation of the origin of these fragments leads to quite differing interpretations of theenviromnent of deposition of the rhyolite. A pyroclastic origin suggests the rhyolite must have erupted. ifthese are hyaloclastites, then an intrusive origin for the rhyolite is possible, although they may have formed byquench fragmentation in water (c.f Cas and Wright, 1988). Breccias generally cannot be distinguishedpetrographically. The different types of breccias are identified macroscopically as described above.Mineralogically, the fragments and matrix are very similar (mainly quartz and sericite), but the mineralproportions are different. In general, the fragments comprise mainly annealed quartz, which is coarser grainedthan the quartz in the matrix (Plate 2.14). The breccia matrix is usually sericite dominant and contains ahigher concentration of fine grained, disseminated pyrite than the fragments.Devitrification textures are recognized locally within the rhyolite and are best represented byspherulites and relict perlitic cracks (Table 2.1). These features have been described regionally in the EskayCreek rhyolite by Macdonald (1991) and Bartsch (1 993b). The presence of sphemlites, lithophysae, relictperlitic cracks, and a paucity of phenocrysts or crystallites indicate that the rhyolite was extruded attemperatures above or equal to the liquidus and quenched to a glass (R. Allen,. personal communication, 1992).Devitrification is the process of nucleation, growth of crystals, and hydration in a volcanic glass; rates andcharacteristics of the process have been described by Lofgren (1970, 1971) and are summarized by Cas andWright (1988, p. 418). Lofgren defined four stages of devitrification, summarized in Table 2.2.TABLE 2.2: Stages of devitrification defined by Lofgren (1971; summarized by Cas and Wright, 1988).STAGE CHARACTERISTICShydration stage • polygonal mosaic of fractures in glass enclosed by a sharpcurviplanar fracture, called the hydration frontglassy stage • felsitic texture and minor sphemlitesspherulitic stage • abundant sphemlitesgranophyric stage . fine-grained, roughly equidimensional, recrystallizedaggregates of quartz and feldspar (common in old devitrifiedglassy rocks)Perlitic cracks occur locally in the rhyolite unit and form distinct, concentric fracture patterns (Plate2.16). Recrystallization and alteration of the rhyolite has enhanced the fabric through concentration of finegrained (about 1 micron) pyrite along the arcuate fractures with envelopes of chlorite or sericite. Perliticcracking formed during cooling of glassy material, providing conduits for hydration of the glass during theearly stages of devitrification. They also provided natural pathways for later hydrothermal fluids.33e 2.14: Photoniicrograph of typical rhyolite breccia.Breccia clasts most commonly consist of annealed quartzwhich is coarser grained than the surrounding host rock.The matnx is typically richer in sericite and pyrite.(CA89-043: 160.1, cross nicols, 4mm field of view.)Plate 2.15: Rare, well-formed sphemlite in aphanitierhyolite. Spherulites comprise mainly quartz alkalifeldspar, hosted in fine-grained quartz-sericite-pyrite.(CAXX-014: 49.8m, cross nicols, field of view is 0.1 mm.)-.Plate 2.16: Photomicrograph of perlitic cracks in massive,aphanitic rhyolite. The relict texture is defmed by theconcentration of fine grained disseminated pyrite alongthe fracture with chioritic envelopes. (CA89-044:109. 9ni, plane light, 2 mm field of view.)Plate 2.17: Lithophysae in altered rhyolite. These round,siliceous features are up to 1 cm across and conunonlyhave a hollow core. The surrounding rhyolite in thissample has been strongly altered by sericite, pyrite andcarbonaceous material. (CA9O-466: 246.4; core is NQ)34Radiating spherulites, generally less than 200 microns in diameter, are sparse but locally well formed(Plate 2.15). The spherulites consist mainly of quartz, but locally comprise quartz and sericite. Spherulitesgenerally form as fibrous crystallites of quartz, usually cristobalite, and alkali feldspar (Cas and Wright, 1988),but in the 2 1A zone, feldspar has generally altered to sericite. Patches of annealed quartz are common in therhyolite. The quartz grains are slightly coarser grained than the microcrystalline host, and may represent thegranophyric stage of devitrification (Table 2.2), overprinted by later hydrothermal alteration (section 3.2.3).Lithophysae are rare, but occur locally as distinct, round balls formed around a vesicle which may behollow or filled with quartz or sericite (Plate 2.17). Lithophysae up to one centimetre in diameter wereobserved in clusters in drillhole CA9O-466.Other textures of unknown origin are observed locally in the rhyolite near the 2 1A zone. Thesetextures are unusual and rare. A cluster of several round to oval, concentric objects up to 1.5 centimetresacross, was observed in drillhole CA89-44 at 109.9 metres depth (Figure 2.1, Plate 2.18). Some of these objectsappear to have been plastically melded to each other. These features consist of a 1.5 centimetre core of coarsergrained (60 microns) annealed quartz, rimmed by a one millimetre wide zone of finer grained (20 microns)annealed quartz. The core and rim are distinctly and discretely perlitically cracked (Plate 2. 18b-d). Theperlitic cracks are neither continuous from core to rim, nor extend into the surrounding groundmass. Wherethese objects appear macroscopically to have melded, they are petrographically distinct and retain discrete rimsand cores. The host rock is microcrystalline with perlitic cracking textures preserved locally. Hairline quartzveinlets in the host rock stop abruptly at the margins of these features and continue on the opposite side. Thisdiscontinuity could indicate either a later origin for these features than the quartz veinlet or contrastingrheological properties. The origin of these concentric features is enigmatic, but several possibilities have beenconsidered. They may represent lithophysae or modified spherulites which formed very early in the coolinghistory of the rhyolite and were subsequently cracked due to internal stresses. Alternatively, they may representimmiscible blebs of slightly different composition within the molten rhyolite, or hot lapilli-like objects thatwere ejected and fell into the molten rhyolite as quenched glass. Another unusual texture, which was observedin drillhole CA89- 19, consists of a wormy texture containing discrete, round patches of a similar nature (Plate2.19). These patches are sharply bounded against intensely sericitized rhyolite. X-ray diffraction study of thisrock indicated that it is composed entirely of illite. The narrow anastomosing veinlets may represent relictperlitic cracks in the rhyolite glass. The discrete round features may have developed by processes similar to thefeatures in CA89-44. Hydrothermal fluids may have migrated along these cracks, pervasively altering theglass and enhancing the fracture pattern.35•4’v.1—-‘V-—•1a4 1•. ,- -:•:.‘..kafPlate 2.18: Unusual, round, concentric features in rhyolite (CA89-044: 109.9m; core is NQ). (a) The features are siliceous, upto 1 cm across, and are hosted in an aphanitic quartz-sericite-pyrite rock containing numerous small spherulites. Some ofthese features appear to be stuck together. In the core sample, the features look similar to lithophysae (Plate 2.17), however,in thin section, these features are perlitically cracked as shown in (b), (c) and (d). (b) Perlitic cracking in the quartzose coreof the features (plane light, field of view is 1.2 mm). (c) and (d) Perlitic cracking in the rim of the round features. Note thatannealed quartz in the rim is finer grained than in the core, and that the perlitic cracks are not continuous between core andrim. The features have a sharp margin against the microctystalline host rock. (Plane and cross polarized light, field of viewis 1.2mm.)r.36Plate 2.21: Sedimentary rocks in the contact unit. (a) Typical, unmmeralized laminated argilhite in the contact unit. Lighter bandsare commonly silty and pyritic. (CA9O-464: 115.5, dull core is NQ) (b) Wacke intersected in the contact unit in CAR9-022 onSection 0+00. Coarser sediments such as these were observed only in this drillhole within the 21A zone. (55.0 m)I_____________Plate 2.19: Unusual, womly, radiating texture inrhyoite, sharplybounded against dark grey, sericitic thyolite. Notice the rOund, Plate 2.20: Photomicrograph of flow banded rhyolite.sharply bounded feature in the centre of the core sample. The Bands are defined by alternating quartz rich and sericitesample consists entirely of illite. The dark grey colouring of the rich bands. (CA89-043: 132.ltn, cross nicols, 4 mrri fieldmatrix and sericitic rhyolite is due to very fme-grained disseminated of view.)pyrite. (CA89-019: 92.Om; this sample was provided by J.Blackwell).372.3.4 Contact ArgilliteContact argillite occurs between the rhyolite and the overlying basaltic volcanic rocks. This intervalhas been called the contact unit (Blackwell, 1990; Britton et at., 1990) because of its stratigraphic position. Ithosts the bulk of the stratabound and stratiform mineralization in the 2 1A and 2 lB zones. Originally, thecontact unit was subdivided into a lower “debris breccia” with rhyolite clasts in a black cherty matrix, andupper bedded to laminated mudstone and argillite. The lower unit was termed the transition zone and reflectsthe uncertain to variable nature of the upper contact of the rhyolite. As discussed in section 2.3.3 above, thenature of the upper contact of the rhyolite is not uniform throughout the 2 1A zone. For the sake of clarity, theterm contact argittite will be used here to indicate rocks of a clearly sedimentary nature that occur between therhyolite and the overlying basaltic sequence.The thickness of the contact unit is variable, between 0 and 20 metres, throughout the 2 1A area.Estimation of the true thickness of the unit is complicated by the gradational to indistict nature of its lowercontact with the rhyolite, intrusion of basaltic sills into the sediments, and locally by faults within the contactunit. Where gradational, the lower contact of the unit was chosen at the point where the rocks are clearlydominated by bedded sediments and pelagic material, The upper contact of the contact unit was chosen at thebase of the first interpreted basalt flow, using the criteria outlined in Table 2.3 and relying heavily ondescriptions and interpretations provided in the original drill logs. These guidelines have limitations because itis very difficult to unequivocally discriminate between flows and sills from drill core information. Thethickness of the contact unit was measured from interpreted cross sections of the plotted drill core information(Appendix A). Structural thickening may affect the contact unit locally. Where such thickening could beinterpreted on the cross-sections, an attempt was made to correct the thickening based on intersections in theadjacent holes. True differences in thickness of the contact unit are suggested by the magnitude of the changesbetween drillholes. The true thicknesses of the contact unit may vary from the estimates due to variations inthe apparent dip of the unit, but the relative thicknesses are probably accurate. Contours of the interpretedupper contact of the contact unit are shown in Figure 2.6, indicating a reasonably consistent dip of about 450 tothe north-northwest. This is interrupted by small localized fault offsets, which are observed in the crosssections, and result in small fluctuations in the contoured surface.An isopach map of the estimated thickness of the contact unit is plotted in Figure 2.9 and indicates anumber of localized areas of thicker sediment accumulation. One such area is located between approximately0+25S and 0+75N, along the northwest trending ridge which truncates and exposes the contact unit at surface.Section 0+00 (Figure 2.2) provides a cross-sectional view through this area, indicating progressive thickeningof the contact unit between drillholes CA89-096 and CA89-022. The sedimentary rocks in the thickest portionof the contact unit on this cross-section, in drillhole CA89-022, contain coarser grained sedimentary beds thatwere not encountered elsewhere within the 2 1A zone. These coarser intervals include siltstone and wacke(Plate 2.2 Ia). Core recovery within much of the contact unit in CA89-022 was very poor and the interval waso0000oUa00000CUCU—u-C,00IIIIC,LflCdCUC)200—15010050 0 —50—100-150-200—250-3000Figure2.9:Contourisopachmapoftheestimatedthicknessofthecontactunit,projectedtosurface,intheEskayCreek21Azone,northwesternBritishColumbia.Contourintervalsare2metres.200Go39rubbly, probably due to faulting and proximity to the surface. However, the presence of these coarser sedimentsmay suggest a more active sedimentary environment, and may be related to a fault extending along the ridge.if this fault was synvolcarnc, then it may have acted as a growth fault, resulting in the formation of a sub-basin.The present apparent throw of the fault is inconsistent with this interpretation, but may be the result ofreactivation during later deformation. Stratabound sulphide mineralization in the 2 1A zone occurs on thewestern flank of this sub-basin and is intersected in drillholes CA89-023 and -024 on Section 0+00. This sub-basin is separated from other areas of thick sediment accumulation to the north and west by thinner contact unitintervals. Overall, the contact unit appears to thin to the northwest.Surface exposures of this unit in the map area (Figure 2.5) are restricted to resistant, cherty intervalslocated south of the 2 1A zone near Skeet Lake. In drill core, the contact unit is variably calcareous, cherty andcarbonaceous to bituminous and friable. The argillite is black, fine grained and commonly contains silty totuffaceous layers ranging from 1 to 30 millimetres in thickness. The thin laminae are frequently pyritic (Plate2.21b). Fine-grained to silty black argillite beds are typically 10 to 50 centimetres thick and vary in carbonate,silica and graphite content, often alternating within the package. Bedding is locally disrupted by slumping,folding and brecciation. Cherty beds are characteristically cut by quartz-filled extension cracks. Locally, thinbeds of crystalline black limestone occur within the graphitic argillite sequence. In general, the morecalcareous intervals of argillite are more common in the upper portion of the contact unit, but their distributionis inconsistent.Ubiquitous opaque carbonaceous residue obscures most textures in thin section. Graphite occurslocally as stringers and blebs and is identified by its low reflectance in polished thin sections. Confirmation byXRD is not possible because the graphite peak directly overlaps with the dominant quartz peak; since bothminerals are present in abundance they cannot be descriminated by this method. Quartz, calcite and finegrained lithic fragments (probably rhyolite) are locally visible. Pyrite, ubiquitous as tiny framboids andspheroids, also occurs as small nodules and concentrations in laminations.Locally, particularly in the thickest portions of the contact unit, intervals of rhyolitic material occurwithin the contact argillite (e.g. CA89-023 and CA89-024, Figure 2.2). This rhyolitic material is sericitic,friable, and very similar to rhyolite which immediately underlies the contact unit. This material may representan accumulation of redeposited rhyolitic ash in the surface depression.In some drill holes, rhyolitic intervals within the contact unit are siliceous and brecciated (eg. CA89-018, Section 0+25S). In hole CA89-0 18, the rhyolitic material directly overlies a rubbly fault zone and mayhave been emplaced into the contact unit along a shallow thrust fault. However, textures observedpetrographically within this interval are different from those observed in the underlying rhyolite sequence. Thesiliceous material consists of 70 to 80% irregular, annealed quartz clouded with abundant inclusions, both fluid40filled and solid; these quartz grains commonly have unclouded quartz overgrowths. The interval locallycontains fragments of fine grained, recrystallized quartz which contain relict colloform bands (Plate 4.13).Evidence for the deposition of the argillite in a marine environment is provided by fossils found in coreand surface samples. These include radiolaria (Nadaradju, 1993), dinoflagellate cysts (G.E. Rouse, TheUniversity of British Columbia, personal communication, 1993), and rare belemnites and coral fragments.Plant-like impressions have been found locally in the argillite (D.L. Kuran, Homestake Canada Ltd., personalcommunication, 1991). These are likely algal and possibly represent kelp (G.E. Rouse, University of BritishColumbia, personal communication, 1993). Radiolaria in this unit are Early Jurassic, Upper Aalenian age, andlikely were deposited in an offshore environment (Nadaradju, 1993).A palynological study was conducted by Dr. G.E. Rouse at The University of British Columbia on twosamples of argillite collected by the author from the intervals immediately overlying the massive sulphidemineralization (CA89-23: 58.7m, CA89-24: 68.5m). These samples yielded Early Jurassic dinocysts and rareconifer pollen grains. Because the pollen grains are sparse, some distance from a plant-rich terrestrialenvironment is implied. The Early Jurassic was a period of flourishing coniferous flora, thus terrestrial andnearshore sediments generally contain abundant pollen. Sparse concentrations can be due to transporthundreds of kilometres offshore (G.E. Rouse, UBC, personal communication, 1993).2.3.5 Basalt Intercalated with Argillite and TurbiditesBasalt intercalated with argillite and turbidites constitute the uppermost unit in the Eskay Creek 21Azone stratigraphy (Figure 1.6). The unit crops out in the northern part of the map area (Figure 2.5) mainly onhillsides and ridge faces. The intercalated sediments weather recessively and are best represented on steepridge faces and dip slope surfaces. In drill section, the sequence is at least 125 metres thick (Figures 2.1, 2.2and 2.3). Generally the basalts overlying the 2 1A zone mineralization are dominated by massive to brecciated,crystalline to porphyritic, submarine flows and sills. The flows become dominantly pillowed and pillowbrecciated to the southwest, near Skeet Lake (Figure 2.5). Regional facies within the basaltic pile are describedby Bartsch (1993b).Massive basalt is dominant in the northeastern part of the 21 A zone map area and in drill core in thearea overlying 2 1A zone mineralization. It comprises dark green, fine to medium grained, crystalline basaltwhich is variably crackle brecciated, amygdaloidal and chilled. This basaltic pile may represent extrusive sheetflows and intrusive feeder dykes and sills. The thickness of individual flows or sills ranges from one to 15metres. Minor blocky breccia, debris flows, pillow flows, pillow breccias and hyaloclastite also occur withinthe massive sequence. Distinction between intrusive and extrusive members of the volcanic pile is difficultbecause contact relationships are often not exposed, or are equivocal in drillcore. Features observed in themassive basalt and some criteria used to distinguish flows from sills in the basalt pile are presented in Table412.3. These criteria are not always recognizeable in drill core, thus the recognition of the first extrusive basalticunit above the contact argillite is often subjective.Basaltic sills are recognized locally in the contact argillite (e.g. Figure 2.1: Section 1+OON) andwithin the pillowed and brecciated basalts. Sills can also be traced underground in the 2 lB zone (D.L. Kuranand F.C. Edmunds, Homestake Canada Ltd., personal communication, 1992).TABLE 2.3: Characteristics used to discriminate flows from sills in massive basalts in the 2 1A zone map area,Eskay Creek, northwestern British Columbia. These criteria are not completely diagnostic.Sheet Flows Sills. clast supported flow top breccia at upper • chilled upper and lower contact (coimnonlycontact chilled throughout)• chilled or brecciated lower contact • may be vesiculated, towards top of unit or• may be vesiculated, especially near flow top throughout. flow units average 6 to 10 metres thickness • variable thickness; 10 cm to several metres• may be associated with peperites in sedimentsabove and/or below• weakly developed columnar jointing isapparent in some surface outcropsBrecciated basalt becomes dominant above the massive basalt. This brecciated basalt is poorlyrepresented in the 2 1A zone map area (Figure 2.5), but is abundant northeast of the 2 1A zone area (Bartsch,1993b). The breccia matrix is commonly calcareous.Pillow breccia and minor pillowedflow basalts are dominant in the northwest portion of the 2 1A zonemap area (Figure 2.5; Plate 2.22). Where pillowed flows are exposed, the pillows are generally elongate, lessthan 1 metre across, and have chilled margins rimmed by small amygdules averaging about 1 millimetre indiameter. Fragments in pillow breccias, generally broken into 20 to 40 centimetre clasts, are variablyamygdaloidal but have well developed pillow rims. The inter-pillow and breccia matrix is dominantlycalcareous argillite and locally hyaloclastite.Irregularly shaped, small pillow-like features occur locally within intercalated shale intervals. Theseare apparently formed by the intrusion of lava into unconsolidated, wet sediments, and are loosely termedpeperites (cf Cas and Wright, 1988, pp.44ff). These textures are also recognized locally in drillcore.Debrisflows occur locally in the basalt pile and consist of dominantly basalt fragments and minorargillite and rhyolite clasts. Argillite fragments are rarely large, rectangular rip-up clasts that are up to 3 by 10centimetres (Plate 2.23). The fragments are usually in a hyaloclastitic matrix that makes up to 15% of the rock.The debris flows were observed near the top of the massive basalt pile (Figures 2.1 and 2.5), and in one outcropnear the base of the pillow breccias (Figure 2.5).42Plate 2.22: Pillow breccia in the hanging wall basalt Plate 2.23: Basaltic debris flow from the hanging wall basalt —sequence. sequence. Clasts are dominantly bleached basalt and laminatedargillite rip-up clasts, with.minor angular, siliceous rhyolite clasts.The darts are hosted in a fine, chiorinc, hyaloclusric matrix; fewdark green, cuspate shards are visible in this photograph.Plate 2.24: Photonucrograph of typical, ciystalline,hanging wall basalt. The texture is sub-ophitic andcomprises mainly augite and weakly sericitizedplagioclase with chlorite and palagonite. (CAS9-95:I l.4m; cross polarized light, field of view is 4 mm)L.___Plate 2.25: Porphyroblasts in hanging wall argillite. Theseradiating features occur mainly within the hanging walloverlying the 21A zone, and are sparse in the contact unitin this area. (CA89-95: 64.2m; scale is in centimetres)43An ophitic to subophitic texture is preserved in thin section in the crystalline flows and sills with weakto moderate chlorite alteration (section 3.5). The dominant minerals are pyroxene, plagioclase laths andchlorite (Plate 2.24). Basaltic glass has altered completely to palagonite and chlorite. Pyrite or pyrrhotitedisseminations or nodules are minor. Calcite occurs locally in amygdules and veinlets.Intercalated turbidite units form discontinuous lenses within the basalt pile (Figures 2.1, 2.2 and 2.3).The discontinuous nature of the sediments is likely due to disruption by sills and dykes, as well as localdepressions on the paleosurface of the flows. The turbidites are laminated to thinly bedded with silty totuffaceous layers that normally contain framboidal pyrite or pyrrhotite. Thin sandy beds are sparse. Gradingand load casts, visible in drill core samples, consistently indicate that tops are up.The interfiow sediments are dominantly black, variably calcareous, indurated argillite laminated withpynte-rich silt or sand turbidite flows. Thin chert beds are marked locally by quartz-filled tension cracksoriented perpendicular to bedding. Black crystalline limestone occurs rarely as thin beds within the sediments.Textures in thin section are masked by pervasive carbonaceous material. Pyrite is commonlyframboidal and disseminated throughout. Pyrite nodules are concentrated in silty to sandy laminae. Radiatingporphyroblasts are common and consist of prehnite, calcite or a mixture of quartz-sericite-pyrobitumen(Eftlinger, 1991). The porphyroblasts are up to 5 millimetres across, and are generally concentrated in distinctbeds within the argillite (Plate 2.25). Those composed of prehnite are variably altered to sericite.Porphyroblasts now consisting of quartz-sericite-pyrobitumen may pseudomorph earlier barite or anhydrite(Ettlinger, 1991).Belemnites and radiolaria in argillite indicate that the hanging wall sequence was also deposited in amarine environment. Nadaradju (1993) has identified radiolaria of Upper Aalenian (Early Jurassic) age withinargillite and calcareous concretions of this sequence.The sediments within the basaltic sequence likely represent D,E-turbidites described by Walker (1984).These probably reflect a distal facies.2.3.6 Intrusive rocksMafic dykes and sillsMafic dykes and sills occur locally throughout the 2 1A zone. The presence of sills in the basalt pile isdiscussed in section 2.2.5, above. At surface, mafic dykes intruding the footwall stratigraphy are exposed in thePumphouse Lake valley, on the shore of Pumphouse Lake and near the base of the #3 Bluff (Figure 2.5). Ingeneral, they follow the dominant north-northeast structural trend, and regionally intrude structures occupiedby earlier felsic dykes (Bartsch, 1993). Few dykes were encountered in driuiholes under the 21A zone. Thin44(10 to 50 centimetre) intervals occur in southermnost drill sections (e.g. Section 1+OOS, Figure 2.3) and in thewesternmost driliholes in the area.The dykes are dark grey to dark green, locally amygdaloidal and relatively unaltered to weakly altered.Round amygdules, filled mainly with chlorite and rarely with calcite, range from 1 to 5 millimetres in diameterand generally are not distributed uniformly.Mineralogy and textures observed in thin section are similar to the basalts. Ophitic to sub-ophiticplagioclase and pyroxene are fresh to weakly altered, mainly by chlorite after pyroxene and locally by sericiteafter plagioclase. Geochemically, the mafic dykes are the same as the hanging wall basalts (section 2.4). Thusthey are probably feeders to the volcanic sequence.Felsic IntrusionsFelsic intrusions can be traced discontinuously for at least seven kilometres south of the Eskay Creek21A zone and often occur as prominent bluffs. They cut stratigraphy at a low angle (Edmunds eta!., 1992;Bartsch, 1993a; Rye et at., 1993). Within the 21A zone map area (Figure 2.5), these intrusions are expressedby two prominent, gossanous bluffs, the #3 Bluff (Plate 2.26) and the #4 Bluff These intrusive rocks aregeochemically equivalent to the rhyolite unit (section 2.4 and Rye, 1992) and reach their highest stratigraphiclevel directly beneath the 21 zone deposits (Rye et a!., 1993). Bartsch (1993 a) proposed that these intrusionsare the feeders to rhyolite flow domes in the Eskay Creek area.The felsic intrusions are aphanitic, remarkably textureless and pervasively altered to quartz-sericitepyrite (Plate 2.27). Thin veinlets of quartz form a fine network locally. Primary textures are not evident. Finegrained quartz is annealed and recrystallized. Sericite is microcrystalline and is associated with 1 to 10%disseminated pyrite. Minor sphalerite, galena and pyrite are locally associated with quartz veinlets. Furthersouth, on the SIB property (Figure 1.5), the intrusions are less altered and comprise predominantlymicrocrystalline quartz, sericite and potassium feldspar; feldspar phenocrysts are commonly discernible asghosts after alteration (Bartsch, 1993b).2.4 GeochemistryMajor, trace and rare earth element (REE) analyses were carried out on 60 representative samples of: (i)flows or sills of the lower volcanic unit, (ii) rhyoLite, including massive to flow banded rhyolite that has undergonevariable stages of alteration, intensely chloritized rhyolite (often massive chlorite), and material from the rhyolite“transition” zone which is generally black and sericitic, (iii) rhyolitic intrusions are represented in the #3 and #4bluffs (TR-92-72 and 73, respectively, and also TR-92-68) and in drilicore (CA9O-477: 100.6, 123.0 and 149.0),(iv) basalt flows or sills, (v) basaltic dykes, and (vi) argillite in the contact zone and from intercalations with the45Plate 2.26: Surface expression of the felsic intrusive rocksin the #3 Bluff These bright,. gossanous bluffs,extending seven kilometres to the south of the EskayCreek deposit, initially attracted prospectors to the area.Plate 2.27: Aphanitic, siliceous, featureless felsic intrusiverock. (Drill core is NQ.)46/R-9219’>, o0/ / / / / /• o o/°%°%°°°o%CoI:ontds.:°°co%%o°o%o / .—‘_:7oo%%o o0 ° Loe. pnd, VcstcL fhlsge Lc/ / / / / .A°0o°00Qr k sop(s_______/ ,4o•::•:• facFigure 2.10: Sample location map for surface lithogeochemical samples, Eskay Creek 21A zone,northwestern British Columbia. Location of Section 1+OON, Section 0+00 and Section1+OOS are also shown.0501050Figure2.11:Locationof samplescollectedfromdrilicoreonSection1+OON.Samplesaremarkedbytheir ‘samplecode’,referencedinTables2.4to2.7.Blackunitsareargillite.Shadedunitindicatessedimentaryrocks.000 9509008508007507006506001000950850750700—300€—050€—000€—150€—lOVE—50€0€50€lOVE150€008€050€300€350€400€650600—50OE50EIOOEISOE200EOSOC300C350400EFigure2.12:Locationof samplescollectedfromdrilicoreonSection0+00.Samplesaremarkedbytheir‘samplecode’,referencedinTables2.4to2.7.Blackunitsareargillite.Crosses indicatelocationof thefelsicintrusion.—300—50E-000—150—100E05000095085080075070065010501000.950900850800750700650600600—300—50E—200—150-LOGE—50EGE50ELODE150E00E250E300E350E400E00—3000—2500—2000—1500—1000—500DE5001000150020002500300E3500400060011001100l0501000 95090085080075070065010501000950900850800750700650600—300E—2500—2000—1500—1000—500CESCE10001500200025003000350E400EFigure2.13:Locationof samplescollectedfromdrilicoreonSection1+OOS.Samplesaremarkedbytheir ‘samplecode’,referencedinTables2.4to2.7.Blackunitsareargillite.50hanging wall basalt. Sample locations are plotted in Figures 2.10 to 2.13. Twenty-five of these samples werecollected from two driliholes (CA89-63 and CA89-89) in 1990 by A.D. Ettlinger (A.E.) of MDRU and wereanalyzed for 61 elements by X-Ray Assay Laboratories (XRAL), Toronto. The other 35 samples were collectedfrom surface and drillcore by the author (T.R.) during 1991 and 1992. Sixteen drillcore samples, collected in1991, were analyzed for 43 elements by Bondar Clegg, Vancouver, courtesy of International Corona Corporation(ICC). The remaining 19 samples were analyzed for 59 elements by XRAL, Toronto. The analytical data andinformation regarding source and processing of the samples are presented in Tables 2.4 to 2.7. Analyticalmethods, detection limits, standard sample data and estimates of analytical error are presented in Appendix B.Barium and yttrium analyses measured by induced coupled plasma spectrometry (ICP) were discarded dueto incomplete acid digestion; these values are consistently lower than those measured by X-ray fluorescence(XRF). Data from two samples (CA89-63: 263.5 and CA89-89: 42.1) were discarded as unrepresentative becausethey contain significant amygdules. One sample of basaltic debris flow material (CA89-63: 35.0) was notconsidered because it contains clasts of different lithologies.2.4.1 Major and trace elementsMajor, trace and rare earth element analyses for 59 whole rock samples are in Tables 2.4 to 2.7. Majorelements have been significantly affected by alteration, causing scatter inNa2O+K0vs. SiO2 discriminationdiagrams (Figure 2.14: after LeMaitre, 1989). However, the hanging wall basalt and basaltic dyke samples arealtered weakly, and plot within the basalt field. Alteration of the rocks is discussed in detail in chapter 3.Some trace elements are much less mobile than the major elements during alteration and provideconstraints for classi1’ing the rocks. A Zr/Ti02vs. Nb/Y discrimination plot (Figure 2. 15a: after Winchesterand Floyd, 1977) distinguishes three clusters of volcanic rocks within the 2 1A zone. Two discrete clusterswithin the subalkaline basalt field reflect the composition of the hanging wall basalts and two samples from thefootwall volcanic unit flows or sills respectively. Additional samples from the footwall volcanic unit aredocumented by Rye (1992). These samples, including pyroclastic and volcaniclastic rocks, have a scattereddistribution which plot in subalkaline basalt, andesite/basalt, andesite, and rhyodacite/dacite fields (Figure2. 15b). Basaltic dykes, which cut the footwall lithologies, plot close to the hanging wall basalts. Samplescollected from the footwall rhyolite, the rhyolite lens, the intrusive rhyolitic bluffs and the rhyolite ‘transitionzone’ plot mainly within the rhyolite field. Scatter probably is due to minor trace element mobility duringalteration. Massive chlorite samples, representing end member alteration of the rhyolite, plot in the comenditepantellente field and reflect mobility of Nb and Y at this intense stage of alteration. Two rhyolite samples thatplot in the comendite-pantellente field are brecciated and altered and probably also affected by changes in Nbor Y due to these processes. Analyses of argillite samples are generally scattered, but locally reflecting theinfluence of volcanic rocks spatially associated with the sediments. Thus, argillite samples collected from units51Table 2.4: Major, trace and rare earth element data for samples from the footwall volcanic unit, EskayCreek 21A zone, northwestern British Columbia.DrHlholeJ Outcrop!, CA89-24 CAX9-36 CAS9-63 CAS9-63 CAS9-63Depth (m) 179.5 286.2 263.5 272.0 286.1Lab Code! CA89-24-1 79.5 CA9O-36-206.2 CAO9-63-263.5 CA89-63272.O CAS9-83 286.1Sample Code!: VI V2 V3 V4 VSRock Type FWVoIc FWVoIC FWVoIc FWVoIG FWVoIcLab XRAL XRAL XRAL XRAL XRA.LBatch! 3 3 1 1 1Sampled-by T.R T.R AE. AE. AE.Easting 411464 411486 411545 411545 411545Northing! 6278799 6278752 6278864 6278864 6278864.ILJh W17 3O.hU O.’5J IV.3UT102 wt%! 1.38 1.51 0.83 1.20 0.98A1203 wt%! 14.50 15.10 10.40 13.40 15.00Fe203 wt % 7.07 9.82 5.66 9.09 9.34MoO wt% 0.20 0.28 0.02 <0.01 0.21MgO wt%1 3.62 5.75 0.95 0.41 6.22CaO 0.84 0.75 0.80 0.53 2.50Na20 wt%: 0.07 0.92 0.15 0.21 0.13K20 wt%! 7.78 3.98 5.18 9.56 3.25P205 wt% 0.41 0.42 0.18 0.31 0.131120+ % 2.3 4.1 1.5 0.7 4.9C02 % 0.30 0.15 0.62 0.02 1.85LOT % 4.85 4.43 4.77 5.54 5.39StIM %! 97.70 99.55 99.62 100.37 98.74Cr ppm 54 14 100 72 45NI ppm!. <I <1 3 3 7Co ppm! Ii 23 25 42 31V ppm! 222 345 203 326 191Cu ppm 14.1 4.5 17.6 83.9 5.3Pb ppm! 386 12 7 18 57Zn ppm. 117.0 134,0 14.5 109.0 141.0Ge ppm 14 <10 <10 <10 18BI ppm!: <1 <1 <I <1 <1Cd ppm! <0.2 <0.2 <C2 <0.2 <0.2W ppm! 9 5 9 9 1Mo ppm! <1 3 3 <1 <1S ‘ppm! 31100 I0770 >5000 >5000 4350As ppm! 92.0 125.0 270.0 860.0 24.0Sc ppia 23.50 28.30 18.70 19.80 26.80Se ppm <0.5 <33.5 <33.5 0.7 0.5Sb ppmS 15.0 41.5 61.0 64.0 4.4Te ppm <0.02 <0.02 0.04 <0.02 <0.02Au ppb! 75 15 280 3200 5Ag ppm! 2.1 2.0 3.6 26.8 0.5Pt ppb! na no 10 <10 <10Pd ppb! na no 2 2 4Hg “ppb 637 130 >1000 >1000 50Rb ppm! 129 74 115 125 98Cs ppm 2 4 4 2 6Ba ppm 6500 1745 1530 3590 816Sr ppm! 279 62 58 81 22TI ppm! 3.3 1.5 3.4 5.0 1.0INb ppm! 10 11 14 15 13Zr ppm. 113 131 96 97 118V ppm!. 21 22 45 46 17Th ppm! 3.0 3.1 2.4 2.9 2.8U ppm!! 1.8 1.8 1.2 1.9 1.2B ppm IS 31 28 II 15Cl ppm! <100 <100 <100 <100 <100La ppm! 13.3 17.3 10.8 6.3 I 1.1Ce ppm! 29.2 37,9 19.7 16.0 23.1Pr ppm! 3.2 4.1 2.7 2.6 2.8Nd ppm 14.7 18.2 13.3 15.0 14.1Sm ppm!. 4.1 4.8 3.1 3.5 3.5Eu ppm 1.84 1.23 0.55 0.73 1.01Gd ppm 4.5 5.1 2.9 3.9 3.8Tb ppm! 0.6 0.7 0.4 0.6 0.6Dy ppm 3.4 4.0 2.3 3.5 3.2Ho ppm! 0.61 0.74 0.44 0.68 0.62Er ppm 1.6 2.0 1.3 1.7 1.9Tm ppm! 0.3 0.3 0.1 0.2 0.2Yb ppm 1.7 2.0 0.9 1.2 1.5Lu ppm! 0.25 0.27 0.13 0.20 0.23* valuesfrom batches 3 and 4 are convertedfrom %: na = not analyzed52Table 2.5: Major, trace and rare earth element data for samples from the rhyolite sequence in the EskayCreek 2 Ia zone, northwestern British Columbia.DiilIholeI0uterop CA89-63 CAS9-63 CA89-3 CAS9-63 CAS9-63 CAS9-63 CAS9-89Depth (rn) 102.2 152.S 173.1 234.5 245.7 95.3 123.7CABSSample Code ROl R02 R03 R04 R05 R06 R09Rock Type! RHYL RHYL RHYL RHYL RHYL RHYL RHYLLab XRAL XRAL XRAL XRAL XRAL XRAL XRALBatch: I I I 1 1 1 2Sampled by. AE. A.E. kE. kB AE. AE. AE.Easting! 411545 411545 411545 411545 411545 411545 411648Northlng 6278864 6278864 6278864 6278864 6278864 6278864 6278715Si02 wt/e 7180 82.40 79.00 77.30 76.80 74.00 70.20Ti02 wt% 0.10 0.08 0.08 0.10 0.07 0.09 008A1203 wt% 13.20 9.30 10.70 11.90 11.00 13.10 15.70Fe203 wt % 1.75 0.81 1.30 1.40 0.73 1.71 1.56MoO wt %! 0.03 0.01 0.03 0.02 0.03 0.02 0.04MgO wt % 2.93 0.84 2.82 1.44 1.77 1.50 2.88CaO wt%! 0.75 0.17 <0.01 0.11 0.67 0.94 0.16Na20 M % 0.30 0.29 0.09 0.08 0.16 1.16 0.17K20 wt% 4.08 3.25 3.12 4.20 5.75 4.20 4.21P205 wt%, 0.02 0.01 0.01 0.02 0.02 0.02 0.031{20+ %! 2.5 1.3 2.2 1.9 1.3 1.8 1.7C02 % 0.94 0.13 <0.01 0.24 0.97 0.81 0.02LOl % 3.47 2.16 3.08 3.62 2.31 2.54 3.77SUM % 98.91 99.61 100.34 100.27 99.55 99.94 99.05Cr ppm 78 130 100 98 100 97 75Ni ppm 2 2 2 <I 2 12 <1Co ppm 2 <1 1 <I <I 2 1V ppm 2 3 <2 <2 5 8 7Cu ppm 5.0 4.5 1.1 7.2 4.0 7.4 78.5Pb ppm! 8 8 <2 5 <2 8 534Zn ppm 139.0 20.6 69.2 44.8 25.7 164.0 3280.0Ge ppm <10 16 <10 <10 22 25 <10Bi ppm! <1 <1 <1 <I <1 <1 <1Cd ppm <0.2 <O2 <0.2 <0.2 <0.2 <0.2 <0.2W ppm! 2 5 4 6 2 1 4Mo ppm!, 8 2 3 3 2 17 3S ppm! 4870 3130 1830 >5000 2510 >5000 9570As ppm! 480.0 59.0 15.0 100,0 19.0 160.0 150.0Sc ppm! 1.25 0.91 0.90 1.19 0.58 1.00 1.25Se ppm! 0.5 <0.5 115 <0.5 0.5 <0.5 <0.5Sb ppm! 20.0 11,0 5.9 16.0 15.0 27.0 96.0Te ppm 0.06 <0.02 0.11 <0.02 0.02 , 0.06 <0.02Au ppb 36 93 10 290 160 59 200Ag ppm! 0.6 <0.1 <0.1 0.6 <0.1 0.7 14.0Pt ppb! 10 20 10 10 10 20 <10Pd ppb! 2 1 3 3 2 3 1hg “ppb! >1000 270 170 110 170 >1000 170000Rb ppm! 140 129 142 177 132 131 157Cs ppm! 6 2 2 3 2 3 2Ba ppm! 4110 2440 823 613 1910 5730 1980Sr ppm 21 28 16 18 179 79 16TI ppm’ 28.4 3.3 2.3 2.1 1.9 21.5 14.0Nb ppm! 51 37 37 38 44 39 58Zr ppm! 175 131 139 179 149 139 197Y ppm! 143 86 69 100 53 119 88Th ppm! 18.0 10.0 12.0 14.0 15.0 14.0 16.0U ppm! 25.4 ‘ 7.3 7.3 8.2 9.6 12.2 11.3B ppm; 30 26 26 31 42 37 30CI ppm! <100 <100 <100 <100 <100 <100 <100La ppm! 47.2 35.5 37.7 46.2 17.5 22.4 22.8Ce ppm! 106.0 59.8 65.9 89.7 37.2 48.7 55.4Pr ppm! 14.2 7.3 7.8 11.0 5.0 6.9 7.5Nd ppm! 62.7 32.4 34.0 48.3 22.2 32.0 34.0Sm ppm! 15.6 7.9 7.8 10.9 5.7 8.5 9.1Eu ppm! 1105 <0.05 0.07 0.12 0.07 <0.05 0.08Gd ppm! 15.7 8.4 8.9 10.6 5.6 9.2 10.1Tb ppm! 2.7 1.6 1.6 2.0 0.9 1.7 1.8Dy ppm! 17.0 10.8 10.8 13.6 5.8 11.5 14.3Ho ppm! 3,49 2.16 2.16 2.62 1.10 2.30 2.98Er ppm! 10.7 6.3 5.9 7.3 2.9 7.1 9.4Tm ppm! 1.7 1.0 0.9 1.1 0.4 1.0 1.3Yb ppm! 10.5 5.7 5.1 6.6 2.7 7.0 7.9Lu ppm! 1.51 0.81 0.75 0.97 0.35 1.01 1.13valuesfrom batches 3 and 4 are conve fledfrom % ** values >1000 ppb in batch 2 are convertedfrom ppm; na = not analyzed53Table 2.5: . . .continuedDrilllioIe/Outcrop CAX9-89 CAS9-42 CAS9-466 CA89-466 CA89-46 CA8844 CA89-24Depth(m) 149.2 125.7 173.8 201.6 225.6 48.3 116.5LabCoJe cAe9e9.i 49.2 O4 TH-05 TR-06 - TR-O TR-08SampleCode RIO RH R12 R13 R14 R15 R16Rock Type RHYL RHYL RHYL RHYL RHYL RHYL RHYLLb XRAL BC BC BC BC BC BCBatch 2 4 4 4 4 4 4Sampled by A.E. T.R T.R T.R. T.R T.R. T.REasting 411658 411481 411593 411587 411579 411539 411610Northing 6278699 6278763 6278967 6278966 6278965 6278663 6278733SiOZ t/. 74.00 72.47 59.97 73.10 19.31 67.44 78.73Ti02 wt %! 0.09 0.09 0.13 0.07 0.06 0.09 0.05A1203 wt’/. 13.10 12.16 14.18 12.33 10.23 15.16 9.50Fe203 wt% 1.15 2.26 3.21 1.27 0.99 2.76 0.72MnO wt% 0.09 0.03 0.04 <0.01 <1)01 0.02 0.02MgO wt% 4.96 4.84 9.99 1.60 0.31 2.43 4.20CaO wt%! 0.08 0.42 1.40 0.11 0.21 0.80 0.03Na20 wt%! 0.05 0.07 0.07 0.05 0.11 0.08 0.041(20 wt% 2.92 2.93 2.84 4.11 6.57 4.94 2.17P205 wt%i 0.02 0.04 0.03 0.02 0.07 0.06 0.041120+ % 2.9 na na no no na naC02 % 0.03 no na no na no naLOl % 3.54 4.61 7.57 3.38 1.67 546 3.42SUM % 100.10 99.92 99.43 98.04 99.53 99.24 98.92Cr - - ppm 94 77 9 121- 176 42 130Ni ppm! 6 <1 20 1 3 2 <1Co ppm <I <I 1 <1 <I <1 <1V ppm 7 2 8 <I 2 <I <1Cu ppm 2.1 24.0 16.0 7.0 18.0 9.0 17.0Pb ppm! <2 24 64 30 16 35 84Zn ppm 69.8 21.0 59.0 160.0 53.0 160.0 39.0Ge ppm! <10 no no na na na naBi ppm <I <5 <5 <5 <5 <5 <5Cd ppm! <0.2 <I <I <1 <I <1 <1W ppm 5 <.20 <20 <20 <20 <20 <20Mo ppm 3 4 20 3 5 7 1S ppm! 2470 9900 17200 6500 3500 16400 3200As ppm! 63.0 195.0 540.0 156.0 28.0 446.0 31.0Sc ppm 1.16 1.30 2.00 1.10 0.90 1.40 0.60Se ppm <0.5 na na no no no noSb ppm! 18.0 24.0 77.0 11.0 17.0 35.0 13.0Te ppm! <0.02 <10 <10 <10 <10 <10 <10Au ppb! 39 no no no no no noAg ppm <0.1 2.3 3.6 1.6 5.3 <0.2 0.5Pt ppb! <10 na na na na na naPd ppb! <I na na no no no naHg ppb 770 na na no no na naRb ppm! 97 na na no no no noCs ppm! 2 na no no no no noBa ppm! 652 262 79 178 181 85 73Sr ppm 16 32 28 10 13 23 7TI ppm 4.1 no no no no no noNb ppm! 57 51 43 56 43 57 37Zr ppm! 183 219 257 207 187 230 163Y ppm! 117 106 79 94 156 112 64Tb ppm 13.0 20.0 19.0 20.0 17.0 24.0 14.0U ppm! 8.5 10.0 17.0 10.0 10.0 14.0 6.0H ppm! 29 no no no no no noCI ppm <100 no no no no no noLa ppm 20.9 30.0 42.0 28.0 26.0 44,0 22.0Ce ppm! 52.3 69.0 82.0 56.0 58.0 87.0 44.0Pr ppm! 7.2 no no no no no noNd ppm 34.6 39.0 40.0 35.0 40.0 49.0 25.0Sm ppm 9.9 10.3 10.0 10.0 12.3 14.4 8.0Eu ppm! 0.09 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5Gd ppm! 9.7 no no no no no noTb ppm 1.7 2.0 2.0 2.0 3.0 3.0 2.0Dy ppm 13.4 no no no no no noHo ppm! 2.73 no no no no no noEr ppm! 8.6 no no no no no noTm ppm 1.2 <2 <2 <2 3.0 <2 <2Yb ppm 7.3 10.0 7.0 9.0 14.0 11.0 6.0Lu ppm 1.65 1.80 1.20 1.40 2.40 1.90 1.00* valuesfrom batches 3 and 4 are convertedfrom %; •5vajues >1000 ppb in botch 2 ore converledfrom ppm: no = not analyzed- 54Table 2.5: ...continuedDrfflholel Outcrop CA89-35 CA89-36 88-14 CA89-95 TR-92-59 TR-92-60 TR-92-64Depth (m) 67.4 92.5 70.0 106.6LaTCoJe3 TR-12 IR.13 IWi .........Sample Code RI? R18 R19 R20 R21 P.22 P.23Rock Type RI-IYL RHYL RHYL RHYL R}JYL RISYL RHYLLab BC BC BC BC XRAL XRAL XRALBatch 4 4 4 4 3 3 3Sampled by, T.R T.R T.R T.R T.R T.R T.R.Easting 411519 411505 411543 411597 411285 411285 411509Northing 6278694 6278717 6278655 6278763 6278112 6278112 6278548SiOZ wt% 66.05 71.65 87.64 64.52 80.80 82.44) 79.44)T102 wt % 0.12 0.08 0.03 0.07 0.08 0.10 0.09A1203 wt% 17.40 11.82 5.29 11.44 10.50 8.89 10.90Fe203 wt ‘ 2.73 1.58 1.20 1.47 0.47 0.46 0.79MnO wt•/. 0.01 0.02 cOol 0.02 0.01 0.01 0.02MgO wt% 1.68 4.99 0.65 9.86 0.11 0.21 1.02CaO wt% 0.14 0.09 0.02 0.06 0.20 0.29 0.09Na20 wt% 0.10 0.05 0.03 0.04 3.16 1.87 0.01K20 wt% 5.90 2.83 1.54- 1.39 4.35 4.01 3.09P205 wt% 0.04 0.07 0.02 0.05 0.03 0.05 0.021*20+ na na na na 0.3 0.4 1.8C02 % na na na ha <0.01 0.11 <0.01LOT % 4.55 4.37 1.83 5.93 0.45 0.70 2.75SliM •/. 98.72 97.55 98.25 98.85 100.30 99.10 98.30Cr ppm. 90 74 237 60 150 200 100Ni ppm <I 1 2 3 3 2 <1Co ppm <1 <1 <I <I <I 2 <1V ppm <1 <1 1 3 2 3 3Cu ppm 11.0 7.0 14.0 5.0 2.9 3.8 7.9Pb ppm: 36 14 67 20 <2 3 48Zn ppm- 165.0 22.0 1.0 92.0 13.1 15.2 146.0Ge ppm no na no no 12 <10 <10Bi ppm <5 <5 <5 <5 <I <1 <ICd ppm <I <I <1 <I <0.2 <0.2 0.2W ppm <20 <20 <20 <20 3 2 4Mo ppm 4 2 1 ‘ 7 <1 <1 2S *ppn 11600 6300 5900 94(X) 2210 291) 3950Aa ppm 361.0 79.0 51.0 661.0 10.0 13.0 100.0Sc ppm 1.80 1.10 0.50 1.10 0.43 0.42 0.67Se ppm- na ha no na <0.5 <0.5 <0.5Sb ppm 43.0 18.0 11.0 66.0 27.0 43.0 67.0Te ppm <10 <10 <10 <10 <0.02 <0.02 <0.02Au ppb no na na ha 17 11 444)Ag ppm. 5.7 0.7 1.1 1.3 <0.1 0.7 6.7Pt ppb na no na na na na naPd ppb na na na na na na noHg **ppb na na na na 242 149 2110Kb ppm4 na na na na 73 80 122Cs ppm na no na na <I 1 2Ba ppm 67 186 61 219 675 997 1020Sr ppm 13 19 6 9 53 117 <10Ti ppm na na na na 1.5 1.7 4.5Nb ppm 61 47 19 29 28 25 25Zr ppm 301 221 99 194 143 127 122Y ppm 86 131 41 51 77 63 48Th ppm 27.0 18.0 7.2 16.0 13.0 10.0 10.0U ppm. 11.0 14.0 3.0 8.0 7.7 7.9 7.0B ppm na na na na 49 56 53CI ppm na na na na <100 <100 <100La ppm 30.0 42.0 21.0 31.0 19.9 20.9 5.2Ce ppm 62.0 78.0 37.0 57.0 43.3 44.4 14.1Pr ppm na na no na 4.9 4.9 2.1Nd ppm 44.1.0 42.0 17.0 28.0 20.8 20.6 11.3Sm ppm 11.6 11.2 4.0 7.4 6.1 5.7 4.5Eu ppm <0.5 <0.5 <0.5 <0.5 0.18 0.21 0.21Gd ppm no ha na na 6.0 5.6 5.0Tb ppm. 2.0 2.0 <1 1.0 1.0 0.8 0.8Dy ppm no no na na 6.6 5.9 5.7Ho ppm na na na na 1.38 1.13 1.18Er ppm na na na na 3.8 3.3 3.4Tm ppm 2.0 2.0 <2 <2 0.6 0.5 0.5Yb ppm 13.0 10.0 4.0 5.0 5.1 3.6 3.6Lu ppm 2.10 1.60 0.70 0.90 0.62 0.45 0.43* valuesfrom batches 3 and 4 are convertedfrom % *avalues >1000 ppb in batch 2 are convertedfrom ppm; na = not analyzed• outcrop duplicae ofTR-92-59Table 2.5: ...continued55Dr111ho1eIOutcrop TR-92-78 TR-92-19 9227 — CA89-89 CA89-89 CA89-89 CA9O—465Dept1i(ni) •• 60.0 137.4 138.5 140.5 190.0Cole- TR.92?8 TR-92-19 CA8-89-137.4Sample Code R24 RL RL2 Cl C2 C3 C4Rock Type RHYL R}{YL RHYL CLOR CLOR CLOR CLORLab XRAL XRAL BC XRAL XRAL XRAL XRALBatch 3 3 5 3 2 2 3Sampled by T.R. T.R. ICC T.R. A.E. A.E. T.REasting 411509 411330 411654 411654 411657 411649Northing 6278548 6278894 6278707 6278706 6278702 6278867ipz wt /. 1.40 76.10 74.03 30.70 33.30 30.90 33.70Ti02 wt% 0.07 0.16 0.10 0.14 0.14 0.12 0.17A1203 wt % 9.78 12.40 13.06 22.40 24.30 22.50 19.80Fe203 wt % 0.98 1.28 2.10 1.38 1.38 2.16 2.35MnO wt% 0.01 0.03 0.03 0.47 0.42 0.55 0.18MgO wt% 0.74 0.25 0.33 31.90 27.70 28.10 24.10CaO wt % 0.25 0.60 1.69 0.17 0.09 0.10 0.20Na20 wt% <0.01 4.96 0.44 <1101 0.07 0.19 0.24K20 wt% 2.85 2.64 6.12 0.16 1.35 0.68 1.63P205 0.02 0.03 <0.03 0.03 0.03 0.04 0.041120+ % 1.4 0.6 na 11.5 9.6 10.7 8.9C02 % <0.01 <0.01 na 0.03 0.03 0.01 <0.01LOT % 2.35 1.50 2.94 13.10 11.40 11.60 11.20SUM % 98.60 100.00 na 100.50 100.24 96.99 93.70Cr ppm1 120 76 137 8 19 15 <100Ni ppm. 2 1 no <1 46 62 <1Co ppm <1 1 no 2 3 2 1V ppm 4 7 no 8 9 6 10Cu ppm 7.5 4.8 na 3.3 2.8 4.8 5120.0Pb ppm 48 <2 na 444 <2 5690 5470Zn ppm 176.0 30.5 no 125.0 114.0 8030.0 14700.0(e ppm <10 <10 na <10 10 13 <10Bi ppm <I <I no <I <1 <I <1Cd ppm 0.7 <0.2 na <0.2 <0.2 12.4 75.3W ppm 4 1 na 2 2 2 <IMo ppm 1 2 na 2 4 2 6S * ppm 4410 90 no 3490 1300 4440 17200As ppm 130.0 0.4 no 44.0 51.0 86.0 370.0Sc ppm; 0.68 0.74 no 0.74 0.81 0.99 2.22Se ppm. <0.5 <0.5 no <0.5 <0.5 0.5 <0.5Sb ppin. 68.0 2.7 no 2.4 7.8 9.6 4100.0Te ppni. <0.02 <0.02 no <0.02 <0.02 <0.02 <0.02Au ppb 430 3 no 90 74 52 140Ag ppm 5.8 0.9 na 1.5 0.3 4.6 96.6Pt ppb na no no na <10 <10 noPd ppb. na no na na <1 <I noHg **ppb: 2720 137 no 2400 1080 68900 65200Rb ppm. 107 77 no 5 44 25 60Cs ppm 2 1 no 3 3 3 8Ba ppm. 963 238 188 166 323 319 566Sr ppm. <10 49 na 11 16 26 38TI ppm 4.0 1.1 no 0.2 1.6 1.1 2.8Nb ppm. 23 19 46 75 116 124 56Zr ppm 107 157 258 331 332 308 356Y ppm 35 32 145 61 94 60 67Tb ppm 9.3 9.6 na 33.0 33.0 29.0 30.0U ppm. 7.0 . 6.0 na 22.8 20.1 16.6 <10B ppm 41 30 na 16 26 18 57CI ppm <100 <100 no <100 <100 <100 <100La ppm 6.1 17.6 no 61.1 49.2 122.0 7a.6Ce ppm 14.5 36.7 no 127.0 92.5 197.0 165.0Pr ppm 1.9 3.9 na 13.5 10.9 19.4 17.0Nd ppm 9.3 16.3 na 53.2 46.1 78.3 65.6Sm ppm 3.4 4.5 no 14.0 11.9 17.8 14.2Eu ppm 0.19 0.15 no 0.11 0.10 0.20 0.19Gd ppm 3.7 5.3 na 11.4 8.1 11.9 13.1Tb ppm. 0.6 0.8 no 1.7 1.4 1.8 1.9Dy ppm 4.7 5.7 no 10.3 11.1 14.9 12.6Ho ppm. 0.96 1.14 na 1.79 2.16 2.77 2.45Er ppm. 2.9 3.2 no 5.2 6.5 8.3 7.8Tm ppm 0.4 0.5 na 0.8 1.0 1.3 1.3Yb ppm 3.1 3.3 no 6.0 6.5 8.1 9.7Lu ppm 0.37 0.47 no 0.86 0.92 1.14 1.27* valuesfrom batches 3 and 4 are convertedfrom %; values >1 000 ppb in batch 2 are converiedfrom ppm: no = not analyzed56Table 2.5: ...continuedDrilUioIe/Outcrop CA89-89 CAS9-89 CA9O-477 CA89-477 CA89-477 TR-92-68 TR-92-72Depth(m) 114.4 115.8 149.0 100.6 123.0YdC6.1144 CA89-89-1158°771490 jj.7Sample Code R07 R08 Fl F2 F3 F4 F5Rock Type CA.CLOR CA.CLOR SILC SILC SILC SILC #3 BLUFFLab XR.AL XRA.L XRAL BC BC XRAL XRALBatch 2 2 3 4 4 3 3Sampled by A..E A.E. T.R T.R T.R T.R T.REastkag 411644 411645 411720 411707 411712 411697 411329Northing 6278721 6278720 6278547 6278561 6278553 6278378 6278027Si02 wtI.i 35.70 12.50 73.80 77.97 76.69 75.70 77.20TiOZ wt% 0.04 0.05 0.09 0.05 0.05 0.07 0.07A1203 wt% 4.67 9.15 11.80 8.90 7.92 10,90 9.08Fe203 wt’/. 1.01 0.88 2.79 1.81 5.15 0.77 3.06MoO wt/. 0.45 0.19 0.02 0.03 <0.01 <3101 <0.01MgO wt% 11.00 12.80 1.90 2.97 0.45 0.24 0.20CaO wt% 21.30 32.50 0.24 0.03 0.07 0.12 0.14Na20 wt % 0.02 0.02 <0.01 0.04 0.10 <0.01 <0.011(20 wt% <0.01 <0.01 4.92 2.70 4.94 7.63 6.21P205 wt % 0.02 0.02 0.02 0.06 0.01 0.03 0.021120+ % 3.3 4.8 1.6 na na 0.5 0.6C02 %i 16.50 25.70 0.01 na na <0.01 <0.01LOl % 18.20 27.60 3.35 3.13 3.00 1.10 2.35“‘7:6 :°Cr ppm 58 <10 79 139 165 140 160Ni ppm 15 16 <I 2 1 2 1Co ppm <1 1 I I <I 1 2V ppm <2 8 5 3 <I 3 4Cu ppm 17.5 13.7 5.3 4.0 7.0 1.6 6.6Pb ppm 42 <2 6 58 162 <2 383Zn ppm 50.2 17.5 26.1 77.0 14.0 26.5 860.0Ge ppm 2.5 26 <10 na no <10 13Bi ppmi <1 <1 <1 <5 <5 <1 <1Cd ppm 1.2 <0.2 <0.2 <1 <I <0.2 4.8W ppm I 1 2 <20 <20 1 8Mo ppm I 2 <I 4 <1 <I 4S ppm 34200 18700 10100 32100 220 23100As ppm 38.0 100.0 74.0 68.0 139.0 55.0 93.0Sc ppm: 0.45 0.84 0.72 1.50 0.50 0.40 0.22Se ppm <0.5 <0.5 <0.5 no no <0.5 <0.5Sb ppm 24.0 16.0 15.0 12.0 34.0 9.7 52.0Te ppm <0.02 <0.02 <0.02 <10 <10 <3102 <0.02Au ppb 46 94 63 na no 72 110Ag ppm 19.9 2.7 0.8 0.3 1.1 0.3 1.5Pt ppb <10 <10 no na no no noPd ppb I <1 na na na no noHg *ppb 4950 10100 274 na no 1680 2690Rb ppm 4 3 100 na na 158 116Cs ppm 1 1 4 na na IBa ppm 2340 1930 2680 137 34 4780 5440Sr ppm 400 714 97 14 8 213 88TI ppm. 0.1 1.4 3.6 na na 3.5 4.5Nb ppm IS 22 30 37 24 26 29Zr ppm 71 115 150 164 120 122 117Y ppm 27 28 87 83 65 95 38Th ppm 6.0 10.0 15.0 15.0 13.0 12.0 9.6U ppm 3.3 5.1 9.0 9.0 8.0 7.8 10.1B ppm 14 11 41 na na 46 39Cl ppm <100 <100 <100 na no <100 <100La ppm 15.0 16.3 10.2 15.0 6.0 22.9 7.2Ce ppm 31.0 35.1 27.3 31.0 13.0 55.9 18.7Pr ppm 3.6 4.3 3.4 na no 6.6 2.4Nd ppm 16.6 18.6 15.7 22.0 12.0 28.3 10.9Sm ppm 3.7 5.3 5.5 7.2 3.6 6.6 4.1Eu ppm 0.05 0.20 0.56 <0.5 <0.5 0.93 1.01Gd ppm 3.6 5.1 5.9 na no 5.0 4.8Tb ppm 0.5 0.9 0.9 2.0 1.0 0.7 0.8Dy ppm 4.4 6.1 6.6 no no 3.9 5.9Ho ppm 0.94 1.14 1.26 no no 0.73 1.18Er ppm 3.1 3.5 3.8 no na 2.3 3.5Tm ppm 0.4 0.5 0.6 2.0 <2 0.4 0.5Yb ppm. 2.7 3.0 4.8 8.0 7.0 3.2 4.2Lu ppm. 0.40 0.49 0.66 1.40 1.20 0.46 0.53* value3from ba1che. 3 and 4 are convertedfrom %; value. >1000 ppb in batch 2 are convertedfrom ppm; no = not analyzed57Table 2.5: ...continuedDriflholel Outcrop TR-92-73 CA89-89 CA89-42 CA89-42 CA89-35 CA89-36Depth (m) 98.3 113.1 102.0 62.3 66.4tibSample Code F6 TI T2 T3 T4 T5Rock Type #4 BLUFF TRANS TRANS TRANS TRANS TRANSLab XRAL Xi.L BC BC BC BCBatch 3 2 4 4 4 4Sampled by T.R. A.E. T.R T.R T.R T.REastIng 411694 411638 411484 411487 411520 411510Northing 6278287 6278730 6278758 6278753 6278693 6278705SiOZ wt %i 79.80 84.00 74.94 78.56 62.73 64.15TI02 wt% 0.08 0.06 0.07 0.09 0.12 0.14A1203 wt •/. 9.27 8.37 9.88 8.08 14.55 14.40Fe203 wt % 0.85 1.06 2.13 2.88 4.01 3.76Mn0 wt % <0.01 0.01 0.01 0.02 0.02 0.03MgO wt /. 0.07 0.61 2.62 2.35 4.82 6.04CaO wt /. 0.12 0.10 0.26 0.78 0.46 0.38Na20 wt/. <0.01 0.10 0.06 1.81 0.23 0.24)C20 wt /. 6.89 2.13 2.95 1.18 4.19 3.52P205 wt %i 0.02 0.02 0.07 0.02 0.06 0.09H20+ 0.2 1.5 na no no naC02 %i <0.01 <0.01 na no na noLOl % 0.80 2.23 4.33 2.86 6.45 5.85SUM •/.i 98.30 98.88 97.32 98.63 97.64 98.60Cr ppm 200 130 104 131 57 61Ni ppm 2 99 11 58 80 139Co ppm 2 <1 <1 2 2 3V ppm 5 <2 <1 9 5 6Cu ppm 2.3 9.5 8.0 45.0 12.0 9.0Pb ppm 58 16 30 20 27 25Zn ppm 22.4 101.0 82.0 118.0 205.0 175.0Ge ppm <10 <10 no na na naEl ppm <1 <1 <5 <5 <5 <5Cd ppm <0.2 3.6 <1 <1 <1 <1W ppm 2 <50 <20 <20 <20 <20Mo ppm <1 <1 17 28 17 15S ppm 4720 12800 12500 10900 20100 11400As ppm 52.0 >5000 1132.0 407.0 925.0 462.0Sc ppm 0.37 0.74 1.10 1.90 3.00 2.80Se ppm <0.5 0.5 no no no naSb ppm 14.0 6400.0 110.0 89.0 114.0 108.0Te ppm <0.02 <0.02 <10 <10 <10 <10Au ppb 120 490 na no na naAg ppm 0.7 3.9 0.2 0.3 <0.2 <0.2Pt ppb na <10 no no na naPd ppb. na 3 no no na na* ppb 484 34300 no no no naRb ppm 111 68 no no na noCs ppm <1 <10 no no na naBa ppm 2950 1550 123 149 71 163Sr ppm 245 19 21 17 18 22TI ppm 4.3 24.4 na no na noNb ppm 26 31 38 28 42 32Zr ppm 113 120 49 113 213 232Y ppm 67 59 36 66 123 106Tb ppm 10.0 <10 16.0 11.0 20.0 19.0U ppm 7.0 <10 7.0 8.0 15.0 11.0B ppm 25 26 no no no naCI ppm <100 <100 na no no noLa ppm 16.2 24.0 20.0 22.0 33.0 32.0Ce ppm 38.1 49.6 41.0 42.0 65.0 63.0Pr ppm 4.4 6.0 no no na naNd ppm 19.2 26.5 22.0 25.0 44.0 40.0Sm ppm 5.6 6.4 5.9 6.7 11.7 10.0Eu ppm 0.56 0.09 <0.5 <0.5 <0.5 <0.5Gd ppm 5.2 4.7 no no na naTb ppm 0.8 0.8 <1 1.0 2.0 2.0Dy ppm 4.8 6.0 na no na noHo ppin 0.90 1.21 no no no noEr ppm 2.7 3.8 no no no naTm ppm 0.4 0.6 <2 <2 <2 <2Yb ppm 3.0 3.3 6.0 6.0 10.0 9.0Lu ppm 0.38 0.52 1.10 0.90 1.60 1.60* volues from botches 3 and 4 ore convertedfrom %; values >1000 ppb in batch 2 are com’ertedfrom ppm; no = not analyzed58Table 2.6: Major, trace and rare earth element data for basalts (BASL) and basaltic dykes(MDYK) in the Eskay Creek 21 A zone, northwestern British Columbia.Drillhole I Outcrop CA8949 CA89-89 CA89-95 CA89-96 CA9O-465 TR-92-38 TR-92-51Depth (m) 34.3 42.1 11.4 100.4 53.1Lab Code CA29-80-34.3 CAOO-OO.42.1 CAO9-96-1l.4 CAOO-96-100.4 CA5O-465-531 TR-92-38 TR.92.51Sample Code BI B2 B3 B4 B5 1)1 D2Rock Type BASL BASL BASL BASL BASL MDYK MDYKLab XRAL XRAL XRAL XRAL XR.AL XRAL XRALBatch 2 2 3 3 3 3 3Saapled by A.E A.E T.R T.R T.R T.R T.R.EasUng 411612 411615 411575 411589 411607 411497 411751North 62 769 6278765 27 6278772 62789 6278 6278725102 wt% 47.20 39.90 47.80 46.20 46.30 48.40 48.20T102 wt% 1.52 0,93 1.67 1.33 1.59 1.44 1.47A1203 wt% 15.50 9.90 14.80 13.10 14.90 15.40 15.60Fe203 wt% 12.30 8.71 13.00 13.30 13.30 10.60 12.40MnO wt% 0.21 0.24 0.20 0.22 0.19 0.21 0.20MgO wt% 5.65 3.75 6.73 11.90 7.93 7.99 6.12CaO wt% 9.37 19.60 8.35 7.80 9.49 6.69 10.90Na20 wt% 3.68 2.38 3.61 1.00 1.64 3.70 2.29X20 wt% 0.43 0.02 0.35 0.16 0.39 0.83 0.32P205 wt% 0.17 0.14 0.23 0.14 0.21 0.15 0.16H20+ % 3.4 2.0 3.2 4.9 3.5 3.7 2.5C02 % 1.19 13.10 0.17 0.12 0.23 0.03 0.61LOl hL. . 2.70 12.50 2.85 4.80 3.25 3.70 2.30SliM % 98.79 98.07 99.70 100.00 99.20 99.30 100.00Cr ppm 230 170 280 370 260 250 240Ni ppm 67 44 62 124 77 53 53Co ppm 53 37 43 54 43 36 38V ppm 389 234 338 302 344 271 316Cu ppm 38.5 36.6 24.6 34.5 34.0 38.6 39.1Pb ppm <2 <2 <2 <2 <2 <2 <2Za ppm 113.0 74.8 102.0 94.4 99.8 80.2 89.6Ge ppm <10 28 15 18 <10 <10 10Bi ppm <1 <1 <I <I <1 <1 <1Cd ppni 4.8 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2W ppm 3 <1 <1 <1 <I <1 <1Mo ppm <1 <1 <1 <1 <I <1 <1S ppm 627 5290 200 1510 570 180 210As ppm. 15.0 31.0 <0.1 6.0 0.9 2.9 0.5Sc ppa 42.40 26.40 42.80 36.40 39.60 39.40 40.90So ppm <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5Sb ppm 2.9 8.1 1.5 3.1 4.9 4.8 1.3To ppm <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02Au ppb, II 3 <4 5 4 <1 4Ag ppm 0.3 0.3 0.2 0.3 0.7 0.2 0.3Pt ppb 10 <10 na na no na naPd ppb. <1 <1 no na no no naHg 1b: 230 240 41 192 59 41 153Rb ppm 10 2 6 5 10 10 8Cs ppin <1 <1 I 3 2 1 <1Ba ppm. 459 <10 213 152 153 1030 249Sr ppm 258 141 403 101 161 463 238TI ppm 0.6 0.1 0.2 0.4 0.2 0.3 0.3Nb ppm. 31 15 5 4 5 5 6Zr ppm 76 52 83 63 78 73 78Y ppm. 32 21 31 23 29 25 28Th ppm <0.5 . <0.5 <0.5 <0.5 <0.5 <0.5 <0.5U ppm 0.1 1.0 0.2 <0.1 0.2 <0.1 0.1B ppm 25 13 25 39 33 13 20CI ppm <100 <100 <100 <100 <100 <100 <100La ppm 4.1 2.8 4.6 3.6 4.3 4.2 4.1Ce ppm 11.2 7.1 13.0 9.7 12.0 11.3 11.5Pr ppm 1.7 1.1 1.8 1.3 1.7 1.6 1.6Nd ppm 9.7 6.3 10.0 7.2 9,3 8.6 8.7Sm ppm 2.9 1.9 3.9 2.6 3.4 3.3 3.2Eu ppm 1.31 0.77 1.32 0.97 1.35 1.34 1.19Gd ppm: 4.2 2.6 5.1 3.6 4.6 4.2 4.5Tb ppm 0.7 0.5 0.8 0.5 0.7 0.6 0.7Dy ppm 5.2 3.2 5.6 4.0 5.1 4.6 5.0Ho ppm. 1.10 0.72 1.08 0.77 1.02 0.89 1.00Er ppm 3.4 2.3 3.0 2.3 2.9 2.5 2.9Tm ppm 0.5 0.3 0.5 0.3 0.4 0.4 0.4Yb ppm’ 3.2 1.9 3.4 2.5 3.4 2.8 3.2Lu ppm. 0.52 0.33 0.47 0.36 0.45 0.37 0.47valuesfrom batches 3 and 4 are convertedfrom 86; no not analed59Table 2.7: Major, trace and rare earth element data for contact argillite and argillite intercalatedwith hangingwall basalt in the Eskay Creek 21A zone, northwestern British Columbia.Drillhole! 0utcrop CA89-63 CAS9-63 CAS9-89 CAS9..89 CA8949 CAS9-89 CA89-89Depth (m) 108.8 41.6 10.3 10.5 74.7 83.6 89.0Lab Code CAO9.83-lO8.8 CABO-63.41.6 CA89-89-lO.3 CA89-80-1O.5 CA89-89-74.7 CA8O-69.83.6 CAO9-69-89.OSample Code Sl-cz S2.hw S3-hw S4.hw S5-cz S6-cz S7-czRock Type SHAL SHAL SHAL SHAL SHAL SHAL SHALLab XRAL XRAL XRAL XRAL XRAL XRAL XRA.LBatch I I 2 2 2 2 2Sampled by AE. AE. A.E AE AS. AK AS,East1ng 411545 411545 411601 411602 411628 411632 411634Northing 6278864 6278864 6278784 6278784 6278745 6278739 6278736Si02 wt%! 77.00 61.00 58.40 48,20 58.10 49.90 67.50Ti02 wt% 0.09 0.43 0.33 1.54 0.57 0.16 0.14A1203 wt% 6.87 10.80 13.90 15.10 11.60 17.10 13.10Fe203 wt% 1.90 3.94 6.52 11.40 5.95 2.71 2.56MnO wt% 0.07 0.02 0.07 0.17 0.04 0.03 0.03MgO wt%: 7.43 0.67 3.44 6.57 2.29 7.90 7.43LaO wt% 0.59 8.24 12.20 6.59 3.82 0.55 0.12Na20 wt% 0.12 0.37 0.02 3.18 1.90 0.26 0.12520 wt% 0.75 4.65 0.05 0.57 2.06 2.69 1.41P205 wt%! 0.02 0.09 0.16 0.28 0.36 0.04 0.031120+ % 3.0 1.5 2.6 3.8 2.9 5.2 4.6£02 % 0.78 6.11 0.33 2.65 2.16 0.34 coOlLOl % 3.85 7.47 4.62 4.93 11.20 8.93 6.23SliM % 98.77 97.77 99.72 98.57 98.76 90.79 98.91Cr ppm 110 65 100 200 48 <150 26Ni ppm 16 80 39 52 356 64 30Co ppm 2 10 3 43 15 <1 <IV ppm! 16 336 216 337 575 35 26Cu ppm! 6.8 54.8 41.6 23.8 102.0 112.0 27.4Pb ppm! 2260 6 <2 <2 <2 34 9Zn ppm! 210.0 1110.0 421.0 124.0 1030.0 1420.0 273.0Ge ppm: 14 20 20 <10 <10 <10 <10Bi ppm <I <1 <I <I <1 <1 <1Cd ppm: 0.3 17.1 <0.2 1.6 <112 <0.2 10.6W ppm! 3 I <I <I 5 <100 5Mo ppm!. 13 28 <1 <1 132 14 22S ppm! >5000 >5000 5750 1920 56800 49200 21400As ppm 640.0 64.0 2.6 25.0 1800.0 >5000 2700.0Sc ppm 0.91 15.20 10.50 37.50 20.30 2.49 2.21Se ppm 3.0 4.2 1.6 <0.5 7.0 1.7 <115Sb ppm 32.0 56.0 6.9 4.5 100.0 32000.0 330.0Te ppm 0.08 <0.02 <0.02 <0.02 0.08 <0.02 <1102Au ppb! 120 15 5 7 120 >10000 >10000Ag ppm!: 2.2 1.7 0.2 0.3 1.2 65.4 12.3Pt ppb! 10 10 <10 10 10 10 10Pd ppb 4 4 1 <1 4 8 5{g **ppb! 690 820 1020 300 150000 690000 160000Rh ppm! 28 92 5 9 74 95 52Cs ppm! 2 2 <I I 5 <20 5Ba ppm! 709 777 30 326 2360 4470 2130Sr ppm! 12 44 13 106 118 27 16TI ppm! 3.1 5.) 0.3 0.7 50.7 103.0 108.0Nb ppm: 30 8 20 22 14 47 43Zr ppm! 115 68 92 74 104 232 209V ppm! 21 19 23 31 49 92 52Th ppm! 7.8 1.7 4.9 <0.5 2.6 <20 12.0U ppm! 10.7 6.6 4.0 0.5 12.3 <20 14.9It ppm 17 34 <10 25 37 30 33CI ppm!. <100 <100 <100 <100 <100 <100 <100La ppm- 25.3 9.2 15.1 5.4 12.2 33.8 28.9Ce ppm! 49.4 14.8 25.1 12.7 20.5 68.6 61.6Pr ppm 6.2 2.5 3.3 1.9 3.7 8.3 7.2Nd ppm 25.0 11.3 14.7 11.0 18.0 37.7 31.3Sm ppm. 4.9 2.9 2.8 3.2 4.1 9.1 7.0Eu ppm cOOS 0.76 0.95 1.23 1.07 0.33 0.19Gd ppm!. 3.8 3.4 2.9 4.0 3.9 8.0 6.1Tb ppm! 0.6 0.5 0.4 0.7 0.6 1.4 1.0Dy ppm! 4.1 3.2 3.5 5.) 4.5 10.4 8.4Ho ppm! 0.90 0.68 0.73 1.12 0.93 2.02 1.70Er ppm 2.9 2.1 2.2 3.5 2.8 6.5 5.4Tm ppm!. 0.6 0.3 0.3 0.5 0.4 0.9 0.8Yb ppm 3.7 2.2 2.2 3.1 3.0 5.7 4.7Lu ppm! 0.56 0.37 0.36 0.47 0.56 0.89 0.71values >l000ppb in batch 2 are convertedfrom ppm; na = not analyzed60LegendP%crobasaltBasalt01 Basaltic Andesite02 Andesite03 DaciteSi Trachybasalt52 Basaltic trachyandesite53 TrachyandesiteT Trachyte - Tracyda citerh Tephriter12 PhonotephritetL3 Tephriphonolite!1Y Phonolite1 FoiditeQ RhyoliteNa20+K vs. Si02 classification diagram for rocks within the Eskay Creek 2 1A zone,northwestern British Columbia. Alteration has caused significant changes in the amount ofalkali and silica, resulting in significant spread across the diagram. However, hanging wallbasalt and basalt dyke samples are altered only weakly, and consequently, plot appropriatelywithin the basalt field. Data are from Tables 2.4 to 2.7.15100C”+0C.”z035 45 55 65 75After Le Maitre (1989: Fig. B. 14)o Basalt• Basalt dykeso Footwall volcanic rocks+ Hangingwall argilliteContact argilliteS102(wt %)RhyoliteRhyolite lensRhyolite transition zoneSiliceous, altered rhyoliteRhyolitic intrusions(#3 and #4 bluffs)FIGURE 2.14:61LegendBasaltBasalt dykesRhyoliteRhyolite lensSiliceous altered rhyoliteRhyolite transition zoneRhyolitic intrusions(#3 and #4 bluffs)v Massive chloriteFootwall volcanic rocks+ Hangingwall argillitex Contact argilliteFIGURE 2.15: ZrITiO2vs. Nb/Y discrimination plot for volcanic rocks in the Eskay Creek 21A zone,northwestern British Columbia. (a) The hanging wall basalt and footwall volcanic unit formtwo distinct clusters within the subalkaline basalt field. Basalt dykes are related to thehanging wall basalts. Rhyolitic volcanic rocks plot mainly in the rhyolite field, but arescattered due to alteration. The most intensely altered samples (massive chlorite) plot in theadjacent comendite-pantellerite field. One sample in the trachyandesite field is from theupper contact of the rhyolite ‘transition zone’ and may contain material from the overlyingargillite. Argillite analyses are scattered, but plot relatively closest to spatially associatedvolcanic rocks. Data are from Tables 2.4 to 2.7. (b) Lithogeochemical samples from thefootwafi volcanic unit indicate that these rocks have a variable composition. These samplesinclude pyroclastic and massive volcanic rocks. Data are from Rye, 1992.,101=rJb)0Nb/YAfter Winchester and Floyd (1977: Fig. 6)Samples from the footwallvolcanic unit (Rye, 19921Nb/Y62intercalated with the hanging wall basalt plot relatively closer to the mafic to intermediate fields. By contrast,samples from the contact argillite plot within the felsic fields with the exception of one sample (CA89-89:74.7), collected close to the upper contact with overlying basalt, which plotted in the andesite field.A plot ofTi02 vs. Zr (Figure 2.16) reflects trends in primary igneous fractionation and the extent ofalteration in volcanic rocks (after Maclean, 1988, 1990; Barrett et al., 1991, 1992). The fractionation trend fora specific series of rocks may only be plotted on the diagram if the rocks are cogenetic and the unalteredcomposition of each stage is known. Ideal fractionation trends follow a curve through the unalteredcompositions of progressively evolving magma, as the relative Ti02 content decreases and Zr increases.Because Ti and Zr are relatively immobile during hydrothermal alteration, the Ti to Zr ratio remains constantas other elements are added and removed. Therefore rocks altered from a single precursor composition plotalong a straight line through the precursor composition and the origin. The position of a sample along this linereflects the degree of alteration of the rock and the net mass loss or mass gain relative to its precursorcomposition (Figure 2.16; after Barrett et a!., 1991, 1992). The geochemistry of alteration in the rhyolite isdiscussed further in section 3.3. Volcanic rock samples from the 2 1A zone plot in three distinct groups onFigure 2.16, reflecting the units as mapped. The footwall volcanic unit is intermediate to the basalts andrhyolite in terms of overall degree of igneous fractionation. However, this does not imply that they arecogenetically related.The Ti02 vs. Zr plot indicates that all the rhyolite, ‘transition’, intensely chloritized, and bluff sampleslie along a single rhyolite alteration line. All of the massive chlorite samples plot at the far right end of theline, reflecting the end member of alteration and extreme mass loss. Argillite from the contact unit plot withthe rhyolite samples (with the same exception of CA89-89: 74.7). Argillite intercalated with the hanging wallbasalt are scattered, but generally have lower zirconium values and higher titianium values relative to the shalespatially associated with the rhyolite assemblage.Trace elements are also useful for characterizing mafic volcanics with respect to their tectonicenvironment of formation. Discrimination plots for basalt are shown in Figure 2.17. The diagrams indicatethat the basalts have both ocean floor basalt (Figures 2. 17a to f) and volcanic arc characteristics (Figures 2. 17b,c and d). They plot in overlapping areas in Figures 2. 17b and c. On a plot of Zr-Ti-Sr (Figure 2. 17d) thesamples plot in a straight line through the ocean floor basalt and island arc basalt fields, and the Sr/2 vertex.This may indicate some Sr exchange with seawater during calcareous alteration of the basalt, since the Srcation commonly enters the Ca site in calcite. The plot of V vs. TiIl000 (Figure 2. 17e) indicates that the rocksare more characteristic of ocean floor basalt than arc type basalt, but plot close to the line of discrimination. Lavs. Nb (Figure 2.171) indicates that the rocks are enriched relative to normal MORB. Such enrichment, and theindication of arc type affinity of the 2 1A zone basalts, indicate that these rocks were probably formed during thetransition between rifting of an island arc and the formation of oceanic basalt in a back-arc environment.632.0 i i ‘ i i ‘4if “,‘4/ ,1.5‘‘ /i/ //_o/ o\1.0 /\/c.’J0x0.5+A v0 0Ala!-*j4 A AAA AI0 50 100 150 200 250 300 350 400 450Zr (ppm)Legendo Basalt A Rhyolite General alteration trends• Basalt dykes Rhyolite lens issgath.° Footwall volcanic rocks v Siliceous altered rhyolite\+ Hangingwall argillite Rhyolite transition zone-Fractionation trendContact argillite Rhyolitic intrusions(#3 and #4 bluffs)v Massive chloritealtered rhyolite Least alteredrhyolite withinthe2lAzoneFIGURE 2.16: Ti02 vs. Zr plot for rocks within the Eskay Creek 21A zone, northwestern British Columbia.Values are recalculated to anhydrous composition. Idealized primary fractionation trendsfrom tholeiitic to transitional rocks is shown; however, the position of the fractionation pathon the diagram is unknown because each magma is unique. Such a trend also assumes thatthe magmas are cogenetic. Therefore, more than one fractionation trend is implied if thevolcanic series are not cogenetic. Alteration causes shifts towards (mass gain) or away from(mass loss) the origin with respect to the composition of an unaltered precursor (Maclean,1990). The volcanic rocks at Eskay Creek form three discrete groups which have undergonevarying degrees of alteration. Argillite spatially associated with rhyolite generally hascomparable Ti02:Zr ratios; argillite spatially associated with basalt has relatively higherTi02 and low Zr values. Data are from Tables 2.4 to 2.7.25 50 75 100 125 150 175 200 225 251) 10Zr (ppm)Aft,, Pearce & Carat (1973; FIg. 2)lAO 1000Zr (ppm)Airer Pearce & Worn’ (1979; FIg. 3)FIGURE 2.17: Tectonic discrimination plots of analyses from the hanging wall basalt (open circles) and basaltdikes (solid circles) inthe Eskay Creek 2 1A zone, northwestern British Columbia. (a) Ti vs. Zrplot indicates the rocks are ocean floor basalt. (b) Zr/Y vs. Zr plot indicates the rocks havecharacteristics of both island arc tholeiites and MORB. (c) Zr-Nb-Y diagram supports MORB andarc affinities. (d) Zr-Ti-Sr diagram indicates a linear trend through ocean floor basalt, island arcbasalt and the Sr/2 vertex. This shift may reflect a change of Sr from seawater. (e) V vs. TiJ 1000plot indicates the rocks have a more ocean floor basalt than an arc affinity. (f) La vs. Nb plotindicates the rocks are characteristic of enriched MORB. Data are from Table 2.6.a1200064Ocean Floor BaseS: 0. BL Potassium Tholerite: A. BCalc-AJk&ine Basalt A. CE0,1=900020In>-F’,’0bA: W,hin plate basalt,B: Island atc basalt,C: Mid-ocean ridge basa?tsBCC Nb’ 2 W,tl’,ln Plate ASaline Basalts: Al, AllWIth, Plate Tholeutes: All. CP MOFIB: BN MOFIB: 0Vofrenki An, Basalt,: C, C)d Ti/lOUAfte, Pea,ce & Cans (1973)f10 151111000 (ppm)AfterShervais (1982: Fig 21‘Nb (ppm)After Gill (1981: FIg. A 16 ci65The basalts collected from the hanging wall and basaltic dykes that cut the footwall lithologies aregeochemically indistinguishable on these diagrams. Thus, the chemistry supports the hypothesis that the dykesare feeders to the hanging wall basalt.2.4.2 Rare earth and large ion lithophile elementsBulk rare earth element (PEE) and large ion lithophile element (LILE) analyses are listed in Tables2.4 to 2.7. Data are nonnalized to average mid-ocean ridge basalt (MORB) and plotted on Figures 2.18 to2.24. Values of MORB used in normalization are listed in Table B.3.Enrichment of PEE relative to primordial mantle or chondnte reflect the degree of differentiation thathas taken place during the formation of the rock and is reflected in the value of total REE. Higher values oftotal PEE indicate a greater degree of fractionation; thus felsic lavas typically have higher total REEconcentrations than mafic lavas (Henderson, 1984). Total PEE concentrations of the volcanics in the 2 1A zonestratigraphy indicate that the basalt and mafic dykes are least fractionated with respect to a primitive source,and that the rhyolite is most fractionated (Table 2.8). Footwall volcanic rocks have an intermediate degree offractionation relative to basalt and rhyolite. The total PEE values for rhyolite range between 48 and 460 ppm.This large range may reflect the degree of alteration in the rhyolite. Although the REE are generally immobile,primary REE concentrations can be modified by mass loss or mass gain of mobile elements. In addition, lightREE may become preferentially mobile under certain alteration conditions (MacLean, 1988).Rare earth elements (La to Lu) behave as incompatible trivalent ions, except for Eu which acts as atrivalent or divalent ion depending on oxygen fugacity and temperature in the system (Henderson, 1984).Divalent Eu is taken up in feldspars and generates an Eu depletion anomaly when feldspar is removed byfractionation. Felsic lavas typically are more enriched in light REE relative to mafic lavas, and have a distinctnegative Eu anomaly due to plagioclase fractionation. The normalized La/Lu ratio reflects the overall slope(LaN/LuN = 1 is a flat line) of the normalized pattern on the spiderdiagram; high ratios and a steep negativeslope reflect a high degree of fractionation relative to MORB. Similarly LaN/SmN and DyN/LUN reflect thedegree of fractionation within light PEE and heavy REE portions of the pattern respectively. These ratios andthe spiderdiagrams are useful for general comparisons of rocks, and aid in the discrimination of rock formingenvironments. The normalized La/Lu ratio for basalt and basaltic dykes is close to 1 with a weak negativeslope in the light REE. The normalized La/Lu ratios for footwall volcanic rocks and rhyolite are variable andrange from 1.5 to 15.1. However, the LaN/SmN ratios in rhyolite are generally higher than in the footwallvolcanic unit.Large ion lithophile elements (including K, Rb, Sr, Ba, Zr, U, Th and light PEE) are those that areincompatible with respect to normal mantle minerals, and therefore are concentrated preferentially in residualliquids during the fractionation process. LILE concentrations plotted on spiderdiagrams are usefuldiscriminants in distinguishing unaltered basalts erupted in different tectonic settings (Wilson, 1989).66100010010C)00.10.01FIGURE 2.18: Large ion lithophile (LILE) and rare earth element (REE) spiderdiagram for footwall volcanicrocks in the Eskay Creek 21A zone, northwestern British Columbia. Most samples have anegative Sr anomaly relative to Ce and Nd. The rocks are enriched in LILE and have a gentlenegative slope in the REE pattern. Data are from Table 2.4.—0——-— CA89-24: 179.5—°-——— CA89-36: 236.2—&-—— CA89-63: 272.0—X— CA89-63: 286.1£2 (U £: D S D (U C) -0 :5R-0 >.>.-(3DabAhyolitelens—Of—-—TR-92-19Flowbandedrhyolite—°--—TR-92-59—---—TR-92.60Ahyolitefromthe21Atrenches—-——Th-92-54—sf---—TR-92-78—t-----CABS-14:48,3—0———CABS-1470.0—D——-•CA89-24.116.5——5935674——CAB9-36925—k——-—CA8S-42.125.7—e---——CAS9-95106.6—h--—CAB9-466173.8CA8O-466201.6—n-’-——CAB9-4662256EuvaluesarebelowdetectionFIGURE2.19:LILEandREEspiderdiagramsforrhyolitefromtheEskayCreek21Azone,northwesternBritishColumbia.(a)Rhyolitecollectedfromsurfaceoutcropsof flowbandedrhyolite,the2 1Atrenchesandtherhyolitelens.(b)Rhyolitesamplesfromdrillcore(analyzedcourtesyof InternationalCoronaCorporation).(c)Siliceousrhyoliteandrhyoliticintrusions.(d)Rhyolitesamplesfromdrillcore(collected byA.D.Ettlinger, MineralDepositsResearchUnit,Universityof BritishColumbia,1990).DataarefromTable2.5.1000 100 10 01 0.011000 100 10 0.10010C0D‘8f;.)-1000 100 10 0.1 0.0110000 C d C 0 C100 10—h--’-—CA9O-477:100.6—°—----CA9O-477123.0——0---——CA9O-477,1490—X——TR-92-68—W---—TR-92-72#3Bluff—c——--Tfl973#4Bluff3D-331=3->-01ICAB9-6395.3—ô--——-CA89-63’1022—0-—-—CA89-631528—0--—CA89-631731—X—CA89-63:2345——CAB9-632457—a---—CAS9-891237—k------CAB9-89149.20018D-80‘3->-0-680C)01000100100.10.01FIGURE 2.20:-— CA89- 89: 114.4—°—— CA89-89: 115.8—°- CA89- 89: 137.4-X— CA89- 89: 138.5-— CA89- 89: 140.5I CA9O-465: 190.4LILE and REE spiderdiagrams for massive chlorite samples in the Eskay Creek 21A zone,northwestern British Columbia. The patterns are similar to those for rhyolite (Figure 2.19)which indicates that these samples are pervasively chiontized rhyolite. However, thesesamples are notably depleted in potassium relative to less altered rhyolite. All samples have anegative Sr anomaly relative to MORB, Ce and Nd, except for CA89-89: 114.4 and 115.8which have Sr added from flooding by calcite. Data are from Table 2.6.Cl) U- D ø CD Cl) -o 0 >- >- - Z’Z-UZ (DD W>j69100010010U0a:0.10.01FIGURE 2.21: LILE and PEE spiderdiagrams for samples collected from drillcore near the upper contact ofrhyolite, in the ‘transition zone’, Eskay Creek 21A zone, northwestern British Columbia. Thesamples are dark grey to black and may contain some pelagic or sedimentary material. Theyclearly have the same patterns as rhyolite (Figure 2.19). Data are from Table 2.6.CA89- 89: 98.3CA89-42: 102.0° CA89-42: 113.1CA89- 35: 62.3CA89- 36: 66.40 .D .C D - CU CU E >- >- - ZUH z-U (/)W (Z)O W>J700U01000100—— CA89- 89: 34.3-— CA89- 95: 11 .410° CA89- 96: 100.4—X CA9O-465: 53.11-— TR-92-38: Dyke0.1-— TR-92-51: Dyke0.01* Th values are below detectionFIGURE 2.22: LILE and REE spiderdiagrams for basalt and basalt dykes from the Eskay Creek 21A zone,northwestern British Columbia. Both light and heavy REE mimic MOPE. Most samples havea positive Sr anomaly relative to MORB. Enrichment in LLE is characteristic of island arcto back-arc basalts. Data are from Table 2.6.CO0 D .D 03 1) c DZ13 )->- ‘-D Docrin’— Z-JUw LU>._j710C)010001001010.10.01FIGURE 2.23: LILE and REE spiderdiagrain for argillite samples in the Eskay Creek 21A zone,northwestern British Columbia. Filled symbols are samples from the contact argillite. Opensymbols are samples from argillite intercalated th the hanging wall basalt. Data are fromTable 2.7. Note that the patterns in the hanging wall samples are similar to the basalts(Figure 2.22); LILE and REE concentrations are lower than in the contact argillite, with theexception of Eu and Ti which are generally higher. The contact argillite samples havenegative Eu and Ti anomalies similar to the rhyolite (Figure 2.19), with the exception ofCA89-89: 74.7 which is near the upper contact of the argillite to the hanging wall basalt. Srcontent in the contact argillite and argillite in the hanging wall basalt is indistinguishable.CA89-63: 41.6- CA89-63: 108.8—0-—- CA89-89: 10.3- CA89-89: 10.5a CA89-89: 74.7CA89-89: 83.6O .0 .0 D -zCA89-89: 89.01000 100 100 0________0 cc10.1 0.01FIGURE2.24:L1LEandREEspiderdiagramforaveraged:(i)footwallvolcanicrocks,(ii)rhyolite(not includingmassivechlorite),(iii)contactargillite(withCA89-89:74.7removed),(iv)basalt andbasaltdykes,and(v)argillitewithinthehangingwall basalt intheEskayCreek21Azone,northwesternBritishColumbia.AllrocksareenrichedinLILErelativetoMORB.RhyoliteisenrichedinREErelativetoMORB.Argillitefromthecontactunithas aLILEandREEtrendsimilar torhyolite.Argilliteintercalatedwithhangingwallbasalt issimilar tothe basalt.Footwall volcanicrocksaregenerallyintennediatetorhyoliteandbasalt.-—Averagefootwall volcanicrockAveragerhyolite°AveragecontactargilliteAveragebasaltandbasaltdykesAveragehangingwall argillite0D-DS-CDCD-jZU>->-£)DUI—Z-JC.)ZWQW>.-JTable2.8:Summaryof geochemicalclassfficationandcharacteristicsformajorlithologiesintheEskayCreek21Azone,northwesternBritishColumbia.Thissummaryisbasedonmajor,traceandrareearthelements(Tables2.4to2.7,andFigures2.14to2.24).AverageLILEandREEpatternsaresummarizedinFigure2.24.Allsamplesfromthe21Azoneareincludedinthistable.Rangesareprobablyduelargelytoalterationeffects.FOOTWALLRHYOLITEBASALTARGILLITEVOLCANICRhyoliteI#3&#4BluffsIMassivechlorite&DYKESincontactzoneintercalatedClassificationsubailcalinebasaltrhyoliterhyolitecorn/pantsubalkalinebasaltscattered-closertoscattered-closerto(Figure2.15)(alterationshift)rhyolitebasaltsREEpatternsnegativeslope,stronglynegativeEuandTianomaliesflat,similartosimilartorhyolitesimilar tobasaltrelativetoweaklyenrichedMORBMORErelativetoMORBLILEstronglyenrichedstronglyenrichedrelativetoMORBenrichedrelativetostronglyenrichedstronglyenrichedenrichmentrelativetoMORBMORBrelativetoMORBrelativetoMORBTotalREE52to93ppm48to287ppm61and96ppm233to460ppm37to50ppm71to154ppm50to70ppmLarçfLu4.5toll.7l.5to7.ll.9and6.07.6to15.ll.ltol.43.lto6.4l.6to5.9LaN/SmN1.6to3.3l.lto4.8l.6and2.6S.lto6.3l.ltol.33.4to4.7l.5to4.9(light REE)DyNILUNL3to1.70.7tol.6l.OandL20.9tol.20.9tol.00.7tol.l0.Stol.1(heavyREE)74The main characteristics of the LILE and PEE chemistry of volcanic rocks in the 2 1A zone(summarized in Table 2.8) are as follows:1. The lower footwall volcanic rocks are enriched in LILE and light REE relative to MORE and have agentle negative overall slope in PEE (Figure 2.18). Light REE are more fractionated than heavy REE(Table 2.8).2. Rhyolite in the 21A zone is generally enriched in all LILE and REE relative to MORB, although somesamples are the same as MORB with respect to heavy PEE (Figure 2. 19a-d). Light REE are morefractionated than heavy REE (Table 2.8).3. All of the rhyolite samples, including samples from the transition zone, exhibit a characteristic, strongnegative Eu anomaly (Figures 2. 19a to d).4. Most of the rhyolite samples also have strong negative Sr anomalies relative to MORE, probably due tobreakdown of the feldspar minerals during alteration. The least altered samples in the suite (TR-92-59and 60: Figure 2. 19a) and the rocks associated with the felsic intrusions (TR-92-68, 72 and 73, andCA9O-477: 149.0: Figure 2. 19c) show a weak to absent negative Sr anomaly.5. Intensely chloritized rhyolite samples (Figure 2.20) have LILE and REE patterns similar to less alteredrhyolite (Figure 2.19). The massive chlorite samples also have strongly negative Sr anomalies withthe exception of two samples. These two samples (CA89-89: 114.4 and 115.8) contain significantcalcite that may hold Sr in the Ca site. Another distinctive feature of the chlorite pattern is a strongnegative K anomaly due to potassium loss during alteration (Chapter 4). Total PEE values in massivechlorite are up to twice as high as in less altered rhyolite due to mass loss of mobile elements.LaN/SmN ratios are significantly greater than Dy/Lu (Table 2.8) suggesting addition of light PEErelative to heavy REE.6. Samples from the ‘transition zone’ that were collected near the upper contact of the rhyolite have thesame REE pattern as the rhyolite (Figure 2.21); thus they are clearly part of the rhyolite package.7. Basalt and mafic dyke samples are enriched in LILE relative to MORE, but have flat PEE patternswhich are similar to MORE (Figure 2.22). (Rock/MORE ranges from 0.73 to 0.98.)8. Most of the basalts and mafic dykes have a positive Sr anomaly (Figure 2.22) perhaps suggestingenrichment from seawater reflected by weak calcite alteration.9. Argillite generally has LILE and REE patterns similar to the stratigraphically closest volcanic rocks(Figure 2.23). Most of the contact argillite samples have strong negative Sr, Eu and Ti anomalieswhich are similar to the rhyolite (except for CA89-89: 74.7 from the top of the contact unit). These75argillites are also generally enriched relative to MORB in all LILE and REE. Argillite samplescollected from intercalated units within the hanging wall basalt have a generally flat REE pattern thatis similar to MORB.2.4.3 SummaryThe geochemical classification and characteristics of the major lithologies in the Eskay Creek 2 1Azone are summarized in Table 2.8. Three volcanic units are clearly distinguished on the basis of trace and rareearth element patterns (Figures 2.15, 16 and 24).The hanging wall basalts and two samples of flows or sills from the footwall volcanic unit plot asdistinct clusters within the subalkaline basalt field of Figure 2.15. The volcanic rocks are also distinguished bydiffering REE signatures (Figure 2.24). Other samples from the footwall volcanic unit, documented by Rye(1992), indicate scattered compositions including subalkaline basalt, basaltic andesite, andesite, rhyodacite anddacite. Locally, these rocks are difficult to differentiate visually from rhyolite due to intense alteration.However, the massive flows or sills from the footwall volcanic unit are clearly discriminated from the othervolcanic rocks in the 2 1A zone by their geochemical signature, microcrystalline felted appearance in thinsection, and prominence of quartz or chlorite filled amygdules.Rhyolite and the rhyolitic intrusions are geochemically indistinguishable and plot mainly in therhyolite field of Figure 2.15. The rhyolitic intrusions may represent feeders to the rhyolite in the 2 1A zone, assuggested by Bartsch (1993a). Samples collected from the rhyolite lens (Figure 2.10: TR-92-19 and 9227-60.0)are also geochemically similar to the rhyolite in the footwall of the 2 1A zone. Scatter in the trace elementdistribution is due to variable degrees of alteration, but all of the felsic samples plot along on a single alterationtie line on a Ti02 vs. Zr diagram (Figure 2.16). Massive chlorite represents an extreme end member ofalteration and plots in the area of maximum mass loss.Hanging wall basalt and basaltic dykes are also geochemically indistinguishable. They plot along asingle alteration tie line on a TiO2 vs. Zr diagram (Figure 2.16). Their similar Ti02/Zr ratio suggests that thedykes are feeders to the overlying basalt package. Tectonic discrimination diagrams may be useful in thecharacterization of the tectonic environment of the basaltic pile. The hanging wall basalts mainly plot inoverlapping ocean basin to island arc fields (Figures 2. 17a-d) or close to arc fields (Figure 2. 17e). The rocksappear to be weakly enriched in Sr relative to MORB (Figure 2.22), possibly due to alteration by seawater,suggesting that the samples have shifted out of the ocean floor basalt field in Figure 2. 17d. Specifically, thebasalt is enriched in LILE relative to MORB (Figures 2. 17f and 2.22). The geochemical signature of thesebasalts is transitional between ocean floor and island arc and is consistent with formation in a back-arc setting(cf Wilson, 1989). In such an environment, the basalts may become enriched by the influence of subduction76related fluids, particularly in the large, low-valency cations. However, enrichment may also be due to alterationprocesses.Average LILE and REF patterns for each of the volcanic units, and the contact and hanging wallargillites, are presented in Figure 2.24. The footwall volcanic rocks, rhyolite and basalt each have distinctivepatterns reflecting the relative degree of fractionation that these rocks have undergone. The footwall volcanicrocks are intermediate with respect to overall degree of fractionation, lying between the rhyolite and basaltpatterns. This distinction is also clear on a Ti02 vs. Zr diagram (Figure 2.16) and is reflected by an increase intotal REE in rhyolite relative to basalt (Table 2.8). The rocks from the footwall volcanic unit have a negativeslope relative to MORB and (LaN/SmN ratios are greater than Dy/Lu; Table 2.8) and an REE patternintermediate to the basalts and the rhyolite. The strong negative Eu anomaly in the rhyolite REE patternreflects fractionation of plagioclase during the evolution of this rock. IN/SmN ratios are greater thanDYNI’LuN for the rhyoLite as well.ArgiLlites in the 2 IA zone generally reflect the geochemical characteristics of their underlyinglithology. Trace and rare earth element concentrations in the lower contact argillite reflect patterns of theunderlying rhyolite. These argillites have distinct negative Sr, Eu and Ti anomalies of similar magnitude tothat of the rhyolite. Total REE values are in a range similar to the rhyolites. Argillites intercalated with thehanging wall basalt, however, have relatively flat REE patterns, similar to the basalts. Total REE values in thehanging wall argillite are slightly higher than those in the basalts, but lower than in the contact argillite. LILEconcentrations in the hanging wall argillite are higher than those in the basalt, but generally lower than thosein the rhyolite or footwall volcanic unit. Therefore, the volcanic rocks appear to contribute significantly to thechemistry of associated sediments.Argillite samples were also compared to the North American Shale Composite (NASC) which is anestimate of the REF composition of the upper crust (Haskin et aL, 1968: Table B.3). Relative to MORB,NASC is enriched in light REE, and is about the same in middle to heavy REF (Figure 2.25a). The averageREE values from the contact argillite (not including the anomalous sample CA89-89: 74.7), normalized toNASC, plot close to the upper crustal average (Figure 2.25b). The contact argillite samples have a strong,negative Eu anomaly relative to NASC, which again reflects input from the rhyolite. In the hanging wallargillites, light REE elements are more depleted than the heavy REE, reflecting a signature more similar toMORB.Analysis of genetic relationships among the three volcanic units within the study area is hampered byintense hydrothermal alteration in the rhyolite, which has resulted in mobilization of most of the elements analyzed(discussed in section 3.3). The footwall volcanic rocks are also altered. Studies of unaltered to weakly alteredvolcanic rocks found regionally in the Eskay Creek stratigraphy were conducted by Bartsch (1993b) and indicatepossible cogenetic relationships among the volcanic units.77a 1000 -:100 -.5 10 -.zCI001 I I I I5 D 0 0 * 5* Average values forLii MORS not availableb1000——Average hangingwall argillite100Average contact argilliteC) 10(1)z0< upper cnista! signature —0.01 I I I I I I I I I I I3 3FIGURE 2.25: REE spiderdiagrams for average argillite samples in the Eskay Creek 2 1A zone, northwesternBritish Columbia, normalized to NASC. (a) Comparison of REE in North American ShaleComposite (NASC) and average Mid-Ocean Ridge Basalt (MORB). NASC is etmched inlight REE relative to MORB. Middle to heavy REE are similar in MORB and NASC. (b)Averaged argillite samples from the Eskay Creek 21A zone, northwestern British Columbia,normalized to NASC. Contact argillite samples have a more upper crustal signature (i.e. thesame as, or higher than, NASC) than argillite intercalated with hanging wall basalt, whichare more similar to MORB.782.5 Summary and DiscussionThe stratigraphy in the Eskay Creek 2 1A zone comprises sedimentary and volcanic rocks. The lowermostunit consists mainly of marine sediments including shale, siltstone and wacke. The presence of numerous bivalveslocally in this unit suggests that it may have been deposited in a relatively shallow water environment. Thissedimentary unit grades upwards into the footwall volcanic unit, in which rocks of volcanic origin becomedominant over sedimentary rocks. The chemistry of these volcanic rocks is variable, ranging from subalkalinebasalt to dacite. Pyroclastic deposits containing large, slightly flattened pumice fragments occur within thissequence, but this does not neccessarily imply that these units were deposited in a subaerial environment; pumiceclasts are common in some subaqueous pyroclastic deposits (Moreton, 1992). Recent studies in the Lau Basin nearTonga and in the Okinawa Trough south of Japan indicate that pumiceous material has been erupted in submergedarcs and in associated back-arc basins at depths of over 1400 metres (Halbach et a!., 1989; Cashman and Fiske,1991). However, it is suggested by Cas (1992) that in situ pyroclastic deposits are only likely to occur in relativelyshallow water (< 500 metres).The footwall volcanic unit is overlain by the rhyolite sequence. Locally, massive flows and sills in thelower volcanic unit have been pervasively silicified and are difficult to distinguish from the rhyolite. However, theintermediate to matic petrochemical signature, microcrystalline felted appearance in thin section, and quartz andchlorite filled amygdules are distinctive of the footwall volcanic unit flows or sills. The trace element chemistrysuggests that both the hanging wall basalt and the footwall volcanic flows or sills are similar. However, the basaltseqence and basaltic dykes form a discrete cluster from the footwall volcanic rocks with respect to Zr/Ti02vs.Nb/Y (Figure 2.15) and Ti02 vs. Zr (Figure 2.16). The two rock types also have differing REE patterns (Figure2.24); the footwall volcanic unit has a distinct negative slope relative to MORB, whereas the basaltic rocks have aflat signature. Bedding relationships suggest an angular unconformity between the footwall volcanic unit and therhyolite, since the core to bedding angles within the footwall volcanic unit are generally steeper than in theoverlying strata; however this is not clear in all cross-sections. Such an unconformable contact is not unexpectedin an active volcanic environment.Although many textures are obscured by hydrothermal alteration within the rhyolite, some significanttextural variations occur. In general, much of the rhyolite is brecciated by either autoclastic processes or byhydrothermal brecciation. Massive siliceous to flow banded rhyolite is more prevalent near the base of thesequence. Locally, the upper contact of the rhyolite sequence consists of in situ rhyolite breccia with a black,siliceous matrix. Elsewhere, small white, angular rhyolite fragments are supported in a black argillite to blacksiliceous matrix, referred to as the transition zone. These rhyolite fragments commonly have cuspate shapes andrepresent hyaloclastites and/or peperites (R. Allen, personal communication, 1993). Such textures have also beenintersected locally at the base of the rhyolite unit, to the north of the 21 A area, in contact with underlying argillite.These contact relationships suggest that the rhyolite may be partially intrusive into existing argillite. However,79such features are not observed in all driliholes, and pyroclastic deposits are evident locally within the rhyolitesequence. Tuff and lapilli tuff intervals are poorly preserved in the 2 lÀ zone, but are locally well developed andpreserved in drill core from the 2 lB zone. Intensely sericitized rhyolite near the upper contact of the sequence inthe 2 1A zone (Figures 2.1 and 2.2) may also be tuffaceous. Increased permeabilty in these pyroclasticaccumulations may have allowed increased hydrothermal fluid flow and therefore increased alteration of theseintervals. Geochemically, the pyroclastic rhyolite deposits are indistinguishable from the rhyolite flows (Rye,1992).The presence of all of these features suggests that the rhyolite may have been both intrusive and extrusive.The flow banded to massive base and core of the rhyolite sequence, and abundance of flow banded autobrecciasuggests the growth of a rhyolite flow or flow dome. Bartsch (1993a) has described the rhyolite sequence as part ofa linear series of at least three flow domes, extending south from the Eskay Creek deposit. Pyroclastic rhyolites areobserved near the base, top, and locally within the rhyolite sequence. This may indicate intrusion of the rhyoliteflow into its own ejecta. There is no clear evidence to indicate whether the flows or flow domes were extrusive.The tuffaceous intervals within the rhyolite package may reflect a break between two separate flows, or may be ascreen within the rhyolite. It is unlikely that a thick accumulation of argillite existed into which the rhyoliteintruded, as this would require a significant hiatus between the deposition of explosive pyroclastic material and theintrusion of cogenetic massive rhyolite.The contact unit comprises shale and argillite which is variably calcareous, cherty and graphitic.Although the unit contains marine fossils, the depth of deposition is poorly constrained. The thin pyrite laminaeand fine grained argillite suggest deposition in a quiescent environment, certainly below wave base. The lack ofbivalves and other relatively shallow water fauna suggests that deposition of the contact unit may at least be deeperthan the fossiliferous sediments in the lower footwall. This is supported by the presence of increased numbers ofradiolaria associated with deeper water (Nadaradju, 1993) although depths are poorly constrained by theassemblages and range from 35 to 3000 metres.The hanging wall basalt package comprises mainly massive, crystalline flows and sills in the vicinity ofstratabound mineralization in the 2 1A zone; this sequence of massive basalt pinches out laterally into pillow andbreccia facies. This accumulation of massive basalt may indicate proximity to the vent (cf Cas and Wright, 1988),pooling in a depression, or local inflation of the sequence by sills. A depression may have formed as a faultcontrolled basin or graben as depicted by Bartsch (1993b). A unit of basaltic debris flow occurs near the top of thesequence of massive basalt, and near the base of the pillow basalt breccia to the southwest. This debris flow mayrepresent a marker horizon separating the environment of massive basalt and blocky, brecciated to pillowed andpillow brecciated basalts which overlie it.80Field evidence does not support the presence of the basalts prior to the emplacement of the rhyolite. Maficdykes which feed the hanging wall basalt cut the rhyolite and are only weakly altered or unaltered. Evidencesuggesting these events occurred over a relatively short interval includes: (i) the partially intrusive contacts in therhyolite, (ii) weak alteration in some of the hanging wall basalts, and (iii) indications that rhyolite activity mayextend into the basaltic package.The chemistry of the basalt is consistent with enriched ocean floor basalt. It has been suggested that theHazelton Group volcanic sequence represents an arc environment (Tipper and Richards, 1976; Anderson, 1989;Anderson and Thorkelson, 1990; Marsden and Thorkelson, 1992). The basalt may be related to riffing, subsequentto arc activity, in the formation of a back-arc. A back-arc basinal enviromnent for the sedimentary to pillowed lavasequence (Salmon River Formation) of the Eskay Creek area has been suggested by Anderson and Thorkelson(1990).813. ALTERATION IN THE 21A ZONEAlteration and mineralization in the 21 A zone are most significant in the rhyolite and the contactargillite. A diffuse pipe-like stockwork of intense alteration and mineralization extends in rhyolite below massiveto semi-massive sulphides in the contact argillite. The footwall volcanic unit is variably altered, and the basalticdykes and hanging wall basalt are relatively unaltered or weakly altered. Strong to intense quartz-sericite-pyritealteration is expressed in the felsic intrusions and is reflected in the bright gossanous nature of the #3 and #4 Bluffs(Plate 2.26). Alteration and mineralization in the 21A zone have been described by Idziszek et at. (1990),Blackwell (199) and Britton et at. (1990).Rocks in the Eskay Creek 2 1A zone have dominantly been altered by silica, potassium and magnesiumrich hydrothermal fluids. The presence or absence of potassium feldspar was determined by staining samples withsodium cobaltinitrite.Alteration at the surface is intense near the Pumphouse fault and marginal to the bluffs. In these areas theprotoliths are rarely identifiable because they are intensely silicified, sericitized and pyritized.. The alteration ismainly pervasive, but quartz veinlets (less than 5 millimetres wide) with sericitic envelopes are common.3.1 Sedimentary and volcaniclastic unitSedimentary and volcaniclastic rocks in the lower footwall of the 21A zone are weakly altered tounaltered. Fine grained, disseminated pyrite is ubiquitous.3.2 Footwall Volcanic UnitThe footwall volcanic unit, underlying the rhyolite, is pervasively but variably altered. The rocks arelocally strongly to intensely silicified. This type of alteration, prominent in the Pumphouse Lake valley (Figure2.5), makes this unit difficult to distinguish from the rhyolite in the field. Geochemically, the rock types aredistinctive, though the composition of rocks in the footwall volcanic unit is variable (as described in section 2.4).Quartz and chlorite filled amygdules are characteristic markers of flows or sills within the unit. Relict fragmentsmay be preserved in silicified volcaniclastic intervals.The volcanic flows or sills commonly have a characteristic beige to pinkish-beige hue due to pervasivepotassium feldspar alteration, identified by staining and X-ray diffraction. These rocks have locally beenoverprinted by stockwork alteration consisting of quartz - pyrite veinlets with grey, sericitic envelopes (Plate 3.1).Tuffaceous rocks in the footwall volcanic unit contain plagioclase weakly altered to sericite. Maficminerals in volcaniclastic rocks are weakly chloritized imparting an overall green colour to the rocks in drill core.82Plate 3.2: Progressive alteration of rhyolite to produce false textures. (a) Development of hairline fracture stockwork inaphanitic rhyolite. (b) Strong sericite - pyrite envelopes developed around fractures to produce apseudobrecck#edtexture. (c) Advanced stage of (b) Some relict patches have cuspate edges and continued alteration may result inerroneous interpretation of the “fragments” as fiamme, (Core is NQ.)Plate 3.1: Stockwork alteration in flows and s s in the footwallvolcanic unit. The relict rocks are characteristically beige to pinkishin colour. The stockwork veins are quartz with envelopes of pyriteand sericite. Locally the veins are dominantly pyrite with lesserquartz gangue. (CAS9: 43: 235.5m, scale is in centimetres.)833.3 Rliyolite SequenceRhyolitic rocks in the 21 A zone are strongly to intensely altered. Primary volcanic textures are largelydestroyed through the replacement of primary glass and minerals, particularly feldspars, with quartz + sericite +pyrite ± chlorite. Many of the rocks have a mottled overall appearance. Regional geochemical and petrographicalstudies indicate that all samples collected within the 21 A zone are strongly altered (Bartsch, 1 993b). The mobilityof various elements are discussed in section 3.3.3.The rocks in the rhyolite sequence have undergone progressive alteration ranging from devitrification tointense hydrothermal alteration, culminating in pervasive replacement by chlorite, and local subsequentoverprinting by quartz and sericite. Progressive hydrothermal alteration in the rhyolite has been subdivided intofour stages:(i) devitrification stage (D),(ii) progressive hydrothermal alteration stage (A),(iii) chlontization stage (C), and(iv) late overprint stage (LO).The progressive hydrothermal alteration stage is subdivided into two processes: silicification and sericitization.These stages, and the alteration intensity, are defined by the relative proportions of the alteration minerals in therhyolite (Figure 3.1). The characteristics of each stage are summarized in Table 3.1.Paragenetic relationships between the minerals are often difficult to distinguish because the hydrothermalfluids are evolving and crosscutting relationships are variable. Hydrothermal alteration has obliterated many of thetextures associated with earlier devitrification. Relationships among different alteration assemblages are furthercomplicated or obscured by faulting, folding and regional metamorphism.Despite these complications, alteration in the 21A zone is generally centered about a diffuse, chloritestockwork “pipe” that is directly overlain by massive sulphides within the contact argillite. It is defined by therestricted, though sparse, distribution of massive chlorite in a zone extending below the massive sulphides,generally northward towards the 2 lB zone (Figure 3.2). Massive chlorite represents the most advanced stage ofalteration in the wallrock immediately adjacent to the fractures, The chlorite envelopes around fractures generallygrade outward to a dominantly sericite + chlorite, then sericite + quartz, and finally a quartz dominant alterationassemblage. A similar zonation is observed, in a broader sense, around the diffuse pipe. However relicts of lessaltered or siliceous rhyolite also occur within the pipe zone where alteration envelopes around the main fractureshave not merged (Figure 3.3).84Pro,qres.cive at1eration100 -Glass\ Silicification Chioritizati\ Sericitization I Quartz‘ ; — — — Alkali Feldspars\— —- Sericite:, \ ‘ I — — Chlorite:i \ /_i_—Accessory Minerals0_______rrrrriCD A C LOAlteration StageFigure 3.1: Schematic diagram of the relative proportions of minerals in rhyolite with progressivealteration in the Eskay Creek 21A zone, northwestern British Columbia. The alterationstages are described in Table 3.2. G = glass stage; D = devitrification stage; A = progressivehydrothermal alteration stage; C = pervasive chlorite alteration stage; LO= later overprint.Table3.1:Maincharacteristicsofthealterationstagesaffectingtherhyoliteinthe21Azone,EskayCreek,NorthwesternBritishColumbia.Seetextfordetailsoflossesandgainswithinthestages.Onlyelementsshowingprogressivetrends areshown.ALTERATIONSTAGETEXTURESPLATESMINERALOGYCHEMISTRYVariableNo:GainsLosseschangechangeGlass&PrimaiyTexturesGflowbanding.quartzphenocrysts,glassisglnot,-vednotpreservedDevitrification&HydrationDper1iticcracks,spherulites,lithophysae2.15,2.16,2.17quartz-alkalifeldspars,pyriteProgressiveHydrothermalAlterationASi,...:Fe,Mg,Sr,SilicificationSIveinletstopervasivesericite,B,Ba,Cr,NaK,Ca, BC02,Rb,SSericitizationSEalongfractures,inveinenvelopes,and3.4,3.5:sericite>quartz>chloritepyriteH20,Rb,NaK,CaMn,P,Ti,pervas1ve;quartzislocallycorrodedCr,SiAl,Th,SrChioritizationalongfractures,inveinenvelopes,and36chlorite>>sericite, pyrite>>>Mg,Mn,.NSKBP,Ti,Al,pervasive;relictquartziscorrodedquartzFe,H20bCr’Sr,Th,Sstockworkveinlets andenvelopescrosscuttingpervasivechloritealteration.LateOverprintLO.....3.7quartz-sericite>chloriteresultingmrelictgreenchloritepatchesmquartz-sericite0O ‘-‘Io a a a aa U-, a u- 0 0in oi c — -I I I Io o 0 0o u, 0 5-)in C’)I Ia a a aa a 1 a fl0 5) — — C’) C’)200N1100 —AlOON WON—lODE —50€ lIE 50N SOC ON lODE-50N -lOONlODE 200EA—1 50Nzso10O150N1050su/phidesApPr0x1 _Massive chloriteintersected in drill coreprojected onto section86E Z. +* E—100 —100...:N . ....—150. “Ø . —150—200 —200::: I L z:0U-)a a a a 0a )c) )fl— Sorfoo p jostion ofrnosoivo thlontoSrfoce projeotion01 strotoboond ,olphid,so 0o U-)C’) C’)1000950250N900—100E850800750300N— loftt.cvn’105010009501009900WOE850800750509700Projected section A — A’Section dips 70 degreesto the east300NOE 250N 50E 200N lODE 150N 150€ 10011200€ 500E 300EFigure 3.2: Distribution of massive chlorite in rhyolite in the 21A zone, Eskay Creek, northwesternBritish Columbia. (a) Plan view showing the surface projection of massive chloriteintersections and stratabound suiphides. The southern extent of the 21B zone strataboundmineralization is located about 50 metres off the top of the diagram (to the northeast). (b)Distribution of all massive chlorite intersections, projected onto Section A-A’. The plane ofthe section dips 70° east, therefore the view in (b) is eastward, but upward at 200.Figure3.3:Schematicdiagramof thechloritealterationpipeintherhyolitebelowthestrataboundsulphidesinthe21Azone,EskayCreek,northwesternBritishColumbia.Relativelylessalteredrhyoliteoccurswithinthepipewherealterationenvelopeshavenotmerged.\Nt.,..—,•.,..,,,,•.:•\stratiformsulphidesquartz-sericite±K-feldspar/‘massivechloritesericjte-quartzchlorite-quartz\/relict lessalteredrhyoliteN/ /RHY0LITE’quartz-sericite±K-feldspar00883.3.1 Stages of AlterationAlteration processes change the textures and chemistry of the rocks. Processes that commonly occurcontemporaneously with the emplacement of volcanic rocks include: vapour phase ciystallization, devitrification,hydration and hydraulic fracturing. Subsequently, the processes of diagenesis, recrystallization, hydrothermalalteration, metamorphism and deformation may overprint and obliterate original textures and modify the rockchemistry further (cf Cas and Wright, 1988). All of these mechanisms have likely played a role in the history ofthe rhyolite at Eskay Creek.The resultant chemistry of the rock is also affected by the duration of the processes acting on the rock, andthe physical conditions of the rock. Hydrothermal alteration is influenced by the permeability of the rock and thechemistry, temperature and flow rates of the hydrothermal fluids. Devitrification and fracturing increasepermeability and therefore, increase access to hydrothermal fluids. Because these processes are progressive andmay overlap in time, it is often difficult to discriminate between hydrothermal alteration and devitrilication effects,particularly where earlier textures have not been preserved. Hydrothermal alteration along fractures may producetextures that look like relict fragments, resulting in erroneous interpretation of the rocks as pyroclastic deposits(Allen, 1988; Ettlinger, 1991; Plate 3.2).DevitrficationThe Eskay Creek rhyolite, as discussed in sections 2.3.3 and 2.5, was probably partially extruded intoa marine environment as a glassy body with few phenocrysts or crystallites. Primary glass is not preservedwithin the 2 1A zone. Devitrification and hydration would have commenced rapidly (cf Lofgren (1971; Table2.2). Textures associated with devitrification, and recognized in the 21A zone, are described in section 2.3.3and include relict perlitic cracks, spherulites and lithophysae. These devitrification features have subsequentlybeen overprinted by the effects of hydrothermal alteration throughout the 2 1A zone area. Perlitic crackingtextures are now defined by the concentration of fine grained disseminated pyrite along relict curved fractures.These pyrite filled cracks have envelopes of chlorite or sericite. Nucleation of crystallites within the glassduring devithfication usually results in the formation of quartz and alkali feldspars as spherulites (Lofgren,1971). Spherulites observed within the 21 A zone commonly consist entirely of quartz, or of quartz andsericite, indicating subsequent replacement of the alkali feldspars during hydrothermal alteration.Progressive Hydrothermal AlterationProgressive hydrothermal alteration has affected all of the rocks within the 2 1A map area. Theobservations recorded within the 2 1A zone rhyolite package, and described below, are probably part of a muchlarger alteration zone that also hosts the 2 lB zone. The mineralogy of the rhyolite is essentially entirely90the intensity of alteration. In less altered rhyolite, sericite dominates the microcrystalline groundmass tolarger quartz phenocrysts and patches of annealed quartz.In the presence of causative veins or fractures, the proportion of sericite increases within the envelopeto the veinlet, and decreases beyond the envelope. However, this sericitic envelope may be subtle and is oftennot bounded by a sharp alteration front. Sericitic envelopes are visible macroscopically where the proportionof disseminated pyrite within the envelope is significantly greater than within the host rock. For examplePlate 3.3 shows a moderately altered rhyolite cut by hairline pyritic microveins. Dark grey sericitic envelopeswith sharp alteration fronts extend up to one centimetre on either side of the microvein. However,petrographically, the causative fracture is not clearly discernible and is generally delineated by a discontinuousline of fine grained disseminated pyrite. The mineralogy of the alteration envelope is sericite, quartz andpyrite. The quartz grains are weakly corroded due to leaching of silica and are partly replaced by sericite. Thesharp alteration front is barely visible petrographically and is defined by a slightly greater concentration of finedisseminated pyrite than in the envelope itself. On the other side of the alteration front, the rhyolite consistsdominantly of quartz, with less sericite and disseminated pyrite than within the alteration envelope.Therefore, differences in mineralogy between the alteration envelope and the wallrock are slight. Suchsubtleties within the rhyolite package make it difficult to clearly define the stage of alteration whencrosscutting vein relationships are not present.Sericite is concentrated locally along narrow microveins, commonly with disseminated pyrite and/orcarbonaceous material, which anastomose through the fine-grained quartz-sencite host (Plate 3.4).Development of these sericitic microveins commonly gives an overall mottled appearance to the rock (Plate3.5).ChioritizationChlorite is present mainly within the core of the alteration pipe. The most intense stage of alterationis represented by pervasive replacement of the rhyolite by chlorite and is usually associated with disseminatedpyrite (Plate 3.6). These pervasively replaced rocks are dark green, waxy, and consist entirely of chlorite,pyrite and commonly other mineralizing sulphides. Locally the massive chlorite also contains unusual blebs ofcalcite (Plate 3 .6c). A mixture of pervasive chlorite and sericite ± quartz generally occurs adjacent to themassive chlorite. This mixed chlorite-sericite zone reflects an intermediate stage in the progression fromsericitic alteration to the more intense, pervasive chlorite replacement.Locally, chlorite occurs in the envelopes of thin, hairline veinlets that commonly crosscut earliersericitic microveins in moderately to strongly altered rhyolite. Both chlorite and sericite are microcrystalline,but the minerals are distinguished by differences in colour and birefringence. In plane polarized light thedifferences are subtle; the chlorite has a faint pale greenish cast against colourless sericite. The birefringenceof chloritePlate3.3:Sericite-pyriteenvelopesin rhyolite.(a)Hairlinefractures withsericite-pyritealterationenvelopescuttingflowbandedquartz.(b)Photomicrographof(a).Thepyriticmicroveinandsurroundingenvelopearesubtle.(Planelight, 3.5mmfieldof view).I—i’11.Plate3.4:Sericiticfracturecuttingfine-grainedsericite.-quartz-pyriterhyolJOpaquemineralsarepyriteandcarbonaceousmaterial.(CA9O-465:185.1;crosspolarizedlight,3.5mmfieldofview)Plate33:Mottledrhyolite comprisingquartz-sericite-pyrite.Minorsphalerite,galena,tetrahedriteandpyriteoccurindiffuseveinlets.Lackof stainingindicatesnopotassiumfeldspariscontainedinthisrock. (CoreisNQ.)Plate3.6:Chlorite alterationinrhyolite.(a)Mottledquartz-sericitealteredrhyolite cutbychlorinealterationmarginal toahairlinefracture.Notetherelativelysharpalterationfrontbetween thechlorite replacement andsiliceousrhyolite.(CA9O-477:18.Sm) (b)Pervasivelychloritealteredrhyolite withassociatedpyrne andminorsphalente,galena andtetrahecirite.(c)Calciteblebs in pervasivelychlorite altered rhyolite.All drill coreisNQ.CA89-23‘.093is anomalous blue-grey, whereas the sericite generally has higher, pale yellow overall birefringence. Locally,patches of sericite are replaced by chlorite, leaving local relict sericite patches within the chlorite.Late OverprintLocally the crosscutting relationships of alteration minerals in the rhyolite within the 2 1A zone donot reflect the expected paragenetic sequence. For example, massive chlorite stage alteration is cut by a lateoverprinting stockwork of sericite and quartz (Plate 3.7) in the area 100 metres south of the 21A zonemineralization (Section 1+OOS, Figure 2.3) and locally within the pipe (Section 1+OON, Figure 2.1). This mayreflect retrograde variations and fluctuations in chemistry and temperature of the hydrothermal fluids affectingthe 2 1A zone. Alternatively, it could be related to superimposition of the hydrothermal system associated withthe 21B zone and mineralization to the south. Timing relationships between the 21A, 21B and other relatedmineralization have not been definitively constrained, though they probably reflect a single evolving system.Later quartz or quartz-calcite veins crosscut all stages of mineralization in the 21A zone. These aredeveloped locally and are related to extension during regional deformation at Eskay Creek.3.3.2 Mineralogy of the Alteration AssemblageQuartzQuartz occurs ubiquitously throughout the rhyolite sequence, at all stages of the alteration process andas a gangue mineral in sulphide mineralized veinlets. It occurs as a primary mineral in the rhyolite asphenociysts; its square habit suggests it may have originally formed as crystobalite; a higher temperature formof quartz: . During devitrification, quartz forms in spherulites nucleating from glass. Silicification of therhyolite is expressed in crosscutting microveinlets of quartz through the aphanitic rock.In zones of more intense sericitization, the quartz content decreases significantly suggesting that thesilica is leached from the rock by the hydrothermal fluids. Excess silica is produced in the reaction of feldsparaltering to sericite. This silica may be removed in solution or precipitate as quartz. The quartz content withinmassive chlorite is minor and occurs as small, irregular grains.Late quartz veins up to three centimetres wide cut all textures in the rhyolite and represent quartzfilled tension cracks related to deformation. The dominant orientation of these quartz veins is northwest andsteep, approximately perpendicular to the orientation of foliation and the direction of minimum regional stress.Potassium FeldsparSome potassium feldspar is present locally, but it is completely absent from the most strongly alteredrocks immediately underlying massive sulphide mineralization in the 2 1A zone. None of the rhyolites from94Plate 3.7: Late overprint stage alteration. (a) Massive chlorite alteration is crosscut by later quartz-sericite veins.(CAX9-36: 72.5m). (b) Advanced stage of late overprint alteration in rhyolite. Relict chlorite patches overprinted byquartz-sericite and quartz-sericite pyrite. (CA9O-464: 165. im and CAS9-35: 188.9m)Plate 3.8: Intense silica-carbon alteration in rhyolite Plate 3.9: Photomicrograph of albite in least altered flow(RHPB). The black staining appears to selectively replace banded rhyolite (TR-92-59, cross nicols, 1 mm across.)certain bands and clasts within the rhyolite (CASX- 14:67.9m, scale is in centimetres)95the driliholes that intersected the contact mineralization (CA89-23 and 24) stained positively for potassiumfeldspar. However, marginal to the most intense alteration, and in clasts in autobreccias away from the core ofmineralization, signfficant potassium feldspar occurs sporadically (Figure 3.4).Staining of the rhyolite suggests that potassium feldspar is pervasively distributed and, at least locally,predates hydrothermal brecciation (cf Plate 2.10). The microcrystalline nature of the rhyolite makespetrographic identification of the potassium feldspar difficult; thus, mineral relationships could not bedetermined. Phenocrysts of potassium feldspar were not observed. It is unclear whether any potassiumfeldspar was primary or formed during devitrification, or if it all reflects potassic hydrothermal alteration.Variable addition ofK20 in siliceous rhyolite suggests at least some potassic alteration through hydrothermalactivity whether expressed by sericite or potassium feldspar. Regional studies have shown that potassiumcontent in the rhyolite increases with proximity to the felsic intrusions (Bartsch, 1993b). Rhyolite withinabout 75 metres of the felsic intrusions appear to contain more potassium than least altered rhyolite andinternal flow dome facies rhyolite.PhyllosilicatesMicrocrystalline sericite and chlorite minerals in the 2 1A zone rhyolite have been identified mainlyusing X-ray diffraction (XRD). They consist of illite and clinochlore, respectively. These phyllosilicates aremainly in the clay size fraction (less than 2 microns), but are chemically and structurally similar to layersilicates that are greater than two microns across (Moore and Reynolds, 1989). Samples were selected fromthe intensely chlorite and sericite altered zone immediately underlying massive suiphide 21A zonemineralization in the contact argillite, as well as from the moderately to strongly quartz-sericite alteredrhyolite. Techniques used in sample preparation are outlined in Appendix C.The classification of clay minerals is complex and has evolved as analytical techniques haveimproved and new varieties have been identified. As a result, clay nomenclature also has evolved anddefinitions associated with various terms have changed. This has resulted in some confusion anddisagreement with respect to general usage of the terms. Clays have a phyllosilicate structure consisting oflayered tetrahedral and octahedral sheets which may be classified into groups by layer types, chemistry andgeometry of the octahedral layers (Moore and Reynolds, 1989; Appendix C). Details follow.IlliteThe term illite was introduced by Grim et al. (1937) to describe clay sized minerals in the micagroup. However, since then a number of varieties of micaceous clays have been identified. Several termshave been applied synonymously with the term i/tile (including: bravaisite, degraded mica, hydromica,hydromuscovite, hydrous illite, hydrous mica, K-mica, micaceous clay and sericite), resulting in some0—50—150-200Figure3.4:Estimateofpotassiumfeldsparcontentofrhyoliteinthe21Azone,EskayCreek,northwesternBritishColumbia,basedonstainingwithsodiumcobahinitrite.Thedistributionofpotassiumfeldsparisirregular,butabsentfromtheareaproximaltoandunderlyingstrataboundmineralization.aU)0U)aII)CU(U——LI)NU-)LI)CU200150100 50IL)CUC I”ofK—sparstainIntensity 0 0 0strong,pervasiveI Imoderate,pervasiveweak,pervasive0veryweak,nostainpatchyID0—100\\0\-50-2500 0 0JILLcJILlI))I°cI_<-00—200—25097confusion in describing such minerals (Moore and Reynolds, 1989). Srodon and Eberl (1984) describe thestructure and identification of illite by XRD in detail and have defined it as: “...a nonexpanding,dioctahedral, aluminous, potassium mica-like mineral which occurs in the clay-size fraction.” Thisdefinition distinguishes illite from similar species such as mixed-layer illite/smectite, trioctahedral illite,glaucomte, celadonite, branimallite, ammonium illite, coarse muscovite that is not clay-size, and muscovitethat has been ground to clay size during sample preparation. However, the definition is general enough thatknowledge of polytype and potassium content is not required. Moore and Reynolds (1989) point out thatthere is little general agreement on the nature of illite as a specific mineral and that the term remainssomewhat ambiguous. They classi1’ illite as an end-member species with more Si, Mg andH20, and lesstetrahedral Al and interlayer K than muscovite. The generalized, ideal composition of illite is:075Al2(Si32535507)O1OH)(Deer et al., 1966). The average composition of illite as definedby Moore and Reynolds (1989) is:(Ca005Na 03K6i) (Al153Fe3022203Mgg)(Si34A106)010.(OH)2Illite forms the same polytypes as muscovite (lMd, 1M, 3T, and 2M), which may reflect pressure andtemperature conditions.Samples containing sericite consistently produced mica XRD peaks that indicate illite, as definedby Srodon and Eberl (1984). Most of the diffraction patterns of illite indicated a small, second peak or aspreading of the d-spacing to the left of the {00 1) mica peak (Figure 3.5). On heating, this collapsed to asharp mica peak. This spread and collapse in the (001) peak suggests that the clay may contain some mixedlayers of a collapsible clay, such as smectite or kaolinite.Two samples of intensely altered rhyolite (CA89-024:74.5m, CA89-043: 102.2m) were selected fordetailed evaluation of clay composition. These samples are both highly friable and incompetent. At thetime of drilling they had been competent enough to cut with a saw, but through sitting in adverse conditions(though sheltered) for two years, they completely fell apart and absorbed enough water to double in size.The clay fractions were separated using the method described by K. Marumo (Geological Survey of Japan,personal communication, 1992; Appendix C) and then sent to Japan to be studied on a transmitted electronmicroscope (TEM) by Dr. Marumo. The TEM studies indicated that these clays are “crystalline, platy,probable 2M ± 1M hydromicas that are potassium-rich and magnesium-poor” (K. Marumo, GeologicalSurvey of Japan, written communication; Figure.3.6). Spacing between the clay layers is about 10angstroms, typical of the mica group. Random powder XRD samples were prepared to confirm the polytypeof these micas; diagnostic peaks for the 2M polytype are present (Figure 3.5).The presence of expanding clay, such as smectite, within the illite was tested by preparations oforiented samples of the clay separates. These produced results similar to the random powder samples,although problems with the XRD equipment generated low counts. The untreated sample produced two98b)C,.4.,CCI UNTHEATE.A \DE000\DATA\23—76 .RAH 23—76 (CT: 0.Bs, SE :5 .020d9 , WL: 1 .S4OSAc)A \D60210\DATA\23—76H .66W 23—TEH (CT: .E, c , ND: ,5-l’79Ac)a)2—Theta— ScaleC I I I I I I ICCASS—23: 76NHEATEDFigure 3.5: Typical XRD traces of illite in rhyolite from the 21A zone, Eskay Creek, northwesternBritish Columbia. (a) Oriented sample showing the (001), (002) and (003) peaks. In theuntreated sample, the (001) peak is broad. On heating, this peak is sharper suggesting theclay is interlayered with a small component of collapsible clay or water. (b) Random powdermount of clay separate. The numerous small peaks flanking the (003) peak are typical of a2M polytype.9919—JAN—93 IRATE CCFS= 2391/A CA 89—43:1: 05: 18PS239 :1.1 0 2 . I —SUPERTI MEPRST—QUANT100 LS E CIOOLSECFigure 3.6: Electron dispersion spectrometty patterns in clay separates from the 21A zone, Eskay Creek,northwestern British Columbia. Analyses provided by Dr. K. Marumo, Geological Survey ofJapan. The patterns show that the mica are dioctahedral and poor in Mg (K. Marumo, writtencommunication, 1993).2.0074CNT 6. 4OKEV8.00i.OeV/ch A EDAX19—JAN—93 14:39:10 SUPER QUANT.RATE 5772CPS TIME 34LSECFS 2744/ 2744 PRST IOOLSECA =CA89—24—73 . Sm—i49CNTFE4.00 6.2. S4KEV8.00aOeV/ch AFEEDAX100strong peaks near the illite (001) peak which merged into one sharp peak upon heating. The percentage ofillite in the structure was tested using the method of Srodon (1980) as defined in Moore and Reynolds(1989). The value of 29 is defined as the degrees 20 between the (003) and (002) peaks in the glycolatedsample. The A20 value in CA89-024: 73.5 was determined to be 8.99°. The percentage of illite, relative tosmectite, in the structure was estimated to be greater than 90% illite from a table of values derived fromemperical studies of known compositions (Appendix C; values of A20 greater than 8.3 8° contain greaterthan 90% illite). Since the XRD patterns of the other sericite samples are similar to the patterns of thesesamples, and all measured values of A20 are greater than 8.90°, all of the sericite probably reflects a similartype of illite.ClinochloreSamples of massive chlorite from the alteration pipe, also analyzed by powder XRD, producedpeaks consistent with cLinochlore (Figure 3.7), the magnesium end-member of the chlorite group, whencompared to accepted standards (JCPDS, 1980). Basal spacing and relative intensities of the 001 peaks formassive chlorite from Eskay Creek are listed in Table 3.2. The relative intensities of the 001 chlorite peaksprovide an estimate of the iron content and distribution in the chlorite using equations and tables developedby Brindley and Brown (1980; Appendix C). Clinochiore within the chlorite pipe in the 21A zone containseffectively no Fe. This is also indicated by the geochemistry of the massive chlorite samples (Table 2.5).Iron in these samples is very low and is mainly in disseminated pyrite.PyritePynte is ubiquitous throughout the 21A zone rhyolite. It is disseminated throughout massive siliceousrhyolite and rhyolite clasts, and concentrated along perlitic cracks and in sericite-rich flow bands. Finegrained pyrite is concentrated in the matrix of rhyolite breccia, imparting a darker colour to the matrix againstthe paler clasts. Pyrite also occurs in veins and veinlets, including along selvages and in alteration envelopes.Pyrite appears particularly to be associated with the sericitic to chioritic stages of alteration. In sericitizedrhyolite, disseminated pyrite is ubiquitous and in greater concentrations than within siliceous samples.Pyrite may be subdivided into two main groups: spheroidal and euhedral to subhedral. Spheroidal pyriteis generally very fine grained (commonly less than 10 microns) and evenly disseminated, particularly inassociation with sericite. This very fine pyrite also occurs in the clay fraction (<2 microns) of the rhyolite andwas identified by K. Marumo (personal communication, 1993) in the two clay separates described above. Thepyrite remained suspended in the clay fraction even after a minimum of 5 hours settling time. Euhedral tosubhedral pyrite grains are usually slightly coarser grained than the spheroidal pyrite (greater than 20microns). This type of pyrite commonly occurs concentrated along hairline fractures, often associated with1014)000-S 1 15 20 25 30 35 40 45A:\fl5a55\DTA\cA59_137BA CB9—137 (CT: O.Bs, SS:O.CZSdg, I.JL: 1.S4a60)55Figure 3.7: XRD profile of a random powder mount of massive chlorite in the Eskav Creek 2 1A zone,northwestern British Columbia (CA89-089: 137.4). Major peaks are listed in Table 3.2.Table 3.2: Measured d-spacings and intensities in two XRD samples of massive clinochiore.The samples were prepared as random powder mounts. The iron content of thechlorite is estimated using the method of Brown and Brindley (1980) and wasfound to be zero (see Appendix C for calculations and tables).2 thetaCAS9-023: 83.7md I 2 thetaCA89-089: 137.4md I(001) 6.219 14.2028 61.27 6.395 13.8100 37.45(002) 12.451 7.1048 78.31 12.646 6.9942 74.70(003) 18.738 4.7327 100.00 18.936 4.6828 76.35(004) 25.115 3.5437 81.48 25.279 3.5203 100.00(005) 31.551 2.8339 23.34 31.699 2.8205 22.07Calculations after Brown and Brindley (1980):(1(003)/1(005)) 4.28 3.46estimated symmetry (D): -0.04 0.051(003)’ 76.24 76.49[1(002) + I(004)]I1(003 2.10 2.28Est. of Fe mY site: 0.00 0.00C89—EE: 13?mdLJicJPeak102black carbonaceous material, described below. Coarser grained euhedral pyrite is also typical in massivechlorite stage alteration of the rhyolite.Carbonaceous MaterialA diffuse black or brown staining is present locally within the rhyolite (Plate 3.8). This alteration orstaining was observed in intensely silicified rhyolite in two driliholes on Section 1+005 (CA88-014 and -015,Figure 2.3) and on surface at the north end of the #21 trenches (Figure 2.5). The black material isconcentrated in zones parallel to the fabric within the rhyolite and thus enhances variations and bandingwithin the rock. The alteration fronts defining these black patches are gradational to wispy. In thin section,the dark patches are diffuse, amorphous and commonly interstitial to quartz and sericite grains. Reflectancelevels of this material are too low for pyrobitumen (Ettlinger, UBC, personal communication, 1992). Analysisof similar material from the 2 lB zone by International Corona Corporation indicated that this black substanceis an amorphous, probably mature, hydrocarbon (Rye, 1992).Black carbonaceous material is also prevalent along sericitic hairline fractures throughout the rhyolite.The fractures appear opaque in thin section, but the material is non-reflective. Euhedral pyrite is commonlyconcentrated along these fractures.3.3.3 Element Mobility Within the Rhyolite PackageGeochemical analyses from 40 rhyolite samples (Table 2.5) within the 2 1A zone were examined toevaluate element mobility within the rhyolite alteration zone. All of the rhyolite samples plot along a singlealteration line on a Ti02 vs. Zr diagram (Figure 2.16), indicating that the rocks have been modified from aprecursor of uniform composition.Several alteration indexes have been developed and are used to describe changes in elements thatreflect the alteration assemblage in the area of interest (Table 3.3). The alkali alteration index, (Saeki andDate, 1980) [CaO+Na20]I [CaO+Na20+K],is used to monitor the behaviour of the alkali elements duringalteration. In the 21A zone, smaller index values generally plot close to the stratabound sulphidemineralization and indicate attendant depletion of Na and/or Ca and/or increase in K content (Figure 3.8).Such element mobility would be expected during typical sericitization. However, within the 21A area, veiylow index values also occur further away from the mineralization, particularly in association with the stronglyaltered intrusive rocks where potassium content is increased due to K-feldspar alteration. On the scale of thissmall area, the alkali alteration index does not provide a reliable vector towards the mineralization. Thesealteration indices cannot discriminate which elements are mobile in the system and they are affected by theeffects of closure, as described below.(CoO + Na20)(CoO + Na20 + K20)Alkali alteration indexvalues for samples inrhyoliteFigure 3.8: Bubble plot showing the distribution of the alkali alteration index applied to rhyolite samplesin the 2 1A zone, Eskay Creek, northwestern British Columbia. The alteration index iscalculated as:(CaO + Na20) / (CaO + Na20+ K20).103/1—0 10 20 3040 50// &/_ ‘(after Saek ond Date, 1980)104Table 3.3: Alteration indeces commonly used in lithogeochemical exploration. Summarized by Stanley(1993).NameIshikawa / DateFormula Reference(MgO + K20)I Ishikawa et a!. (1976),(MgO + K20+ CaO + Na20) Date et aL (1983)Chlorite (Fe203+ MgO)I Saeki and Date (1980)(Fe203+ MgO + CaO + Na20)Alkali (CaO + Na20)/ Saeki and Date (1980)(CaO + Na20÷ K20)Hashiguchi(Fe203)/ Hashiguchi and Usui (1975),(Fe203+ MgO) Hashiguchi et aL (1983)Sericite (K20)I Saeki and Date (1980)(Na20+ K20)Techniques in identifying element mobilityThe bulk (weight %) concentration of any element in the analysis is affected by the relativeproportions of the other elements. Therefore, comparisons made using the bulk analytical data cannotdiscriminate between true addition of an element to the system and the relative increase in concentration ofthat element due to the loss of other elements (i.e. an overall decrease in the size of the system). This effect iscalled closure and has been described in detail by Nicholls (1988) and Stanley (1993). However, real changesin the composition of the rock through metasomatism can be traced using immobile elements. Since theabsolute concentration, or number of moles, of an immobile element will remain unchanged throughout thealteration history of the rock, its relative concentration in the bulk analysis is a reflection of the mass changesthat an individual sample has undergone. In other words, it reflects dilution or concentration due to additionor loss, respectively, of mobile elements.Several approaches have been developed using immobile elements to describe changes in thechemical composition of rocks. Relative mass gains and losses with respect to each element in the analyticalsuite may be calculated using the method described by MacLean and Kranidiotis (1987), and Barrett et al.(1991, 1992). In this technique, the immobile element is used to trace the relative net mass changes in the sizeof the system by calculation of a correction factor. This assumes that all samples in the sample suite arederived by alteration of a single, homogeneous, lithogeochemical unit and requires the estimation of thisprecursor composition. The absolute amount of an immobile element (Z) in the system is, by definition,constant. Therefore the ratio of Zprecursoi.IZaltered sample defines the correction factor and reflects netchanges in the size or mass of the system. For example, if the concentration of Z in the precursor is twice as105much as that in the altered sample, then the correction factor will be 2 and therefore the system size of thealtered sample must have doubled in order for the concentration of the immobile element to be halved. Thiscorrection factor is then applied to each element in each sample to produce the reconstituted composition. Thedifference between the concentration of each element in the precursor to the concentration in the reconstitutedcompositon indicates the behaviour of the element during alteration.Another means of circumventing the effect of closure is to calculate the ratios of the molecularproportions of each element against the immobile and incompatible element; these ratios are called PearceElement Ratios (PER). If two other elements are also immobile, then their PER values remain unchangedthrough the processes of fractionation and metasomatism and will form a cluster when plotted against oneanother. However, elements that are added to, or removed from, the system will reflect increased or decreasedPERs respectively. If the change in concentration of the element is systematic, as in fractionation, the PERwill plot along a line which reflects a rate of change proportional to the stoichiometric composition of themineral or minerals involved. PER techniques have been applied to model changes in the chemicalcomposition of magmatic systems during fractionation (Pearce, 1968, 1990; Nicholls and Russell, 1990) and todiscriminate the effects of alteration (Fowler, 1990; Stanley and Madeisky, 1993).Immobile elements.As described above, the rhyolite within the 2 IA zone has undergone progressive hydrothermalalteration from quartz-sericite-pynte to complete replacement by chlorite-pyrite. Elements which are typicallyimmobile during alteration include high field strength elements (Ti, Al, Zr, Nb, Y and P), heavy rare earthelements, and certain transition metals (including Ni, Cr and V). Two immobile elements plotted against oneanother will produce a straight line through the origin and the precursor composition within analytical error(cf MacLean and Kranidiotis, 1987).Zr is identified as the most immobile element in the 21A zone rhyolite. The possible immobileelements, plotted against Zr (Figure 3.9), are more scattered about lines of best fit than variance due toanalytical error alone would allow. Scatter away from the line of conservation may be due to mobility of eitherof the two elements. However, a plot of Th vs. Zr (Figure 3.91) produces a straight line with little scatter aboutthe line of conservation. Independent evaluations by Rye (1992) and Bartsch (1 993b), of samples collectedthroughout the Eskay Creek rhyolite sequence, both identified Zr as the most immobile element in the rhyolite.The local presence of pristine, euhedral zircons (Plate 2.12) may also support the immobility of Zr duringhydrothermal alteration.0c..l00 50 100 150 200 250 300 350 400Zr (ppm>Figure 3.9: Scatter diagrams of six elements in rhyolite plotted against Zr to test for immobility. Twoimmobile elements form a straight line, within analytical error indicated by the error bars,which passes through the origin. Thorium and zirconium in (f) appear to be the mostimmobile elements within the rhyolite in the 21A zone, Eskay Creek, northwestern BritishColumbia. Data are from Table 2.5.106Zr (ppm) Zr (ppm)a)2520151050c)10075E0.50.0250e).1 --0 50b). 1000>- 7550250f)353025201510500 50 100 150 200 250 300 350 400Zr (ppm)100 150 200 250 300 350 400Zr (ppm)0 50 100 150 200 250 300 350 400Zr (ppm)107Pearce Element RatiosAs described above, Pearce element ratios (PER), may be used to describe systematic changes in thecomposition of a cogenetic volcanic sequence through fractionation and alteration. Samples from the rhyolitewithin the 21A zone were plotted on PER diagrams to test for fractionation of feldspars (Figure 3.10).However no systematic changes in the concentration of alkali elements were observed. Scatter below theexpected fractionation trend reflects relative losses of the alkali elements due to metasomatic processes. Thelack of feldspar phenocrysts within rhyolite would also suggest that feldspar fractionation was not activewithin the 21A zone. Relative mobility of the elements due to metasomatism cannot be distinguished on thesediagrams because there is no related fractionation trend developed with which to compare it.Mass loss, mass gain and mobility ofelements during alterationThe 21 A zone rhyolite suite has undergone significant changes in mass and composition duringalteration, as indicated on the plot of Ti02 vs. Zr (Figure 2.16), Because Zr is immobile within the rhyolitesuite, changes in the ratios of the molar proportions of each element against Zr (the PER) provide anindication of the relative variation of that element, and therefore, its relative mobility and involvement in thealteration process. Variation for each element is reflected in the standard deviation of the PER in the samplesuite. Standard deviations for each element against Zr are presented graphically in Figure 3.11. Silica is thedominant mobile major element during alteration of the rhyolite. Weaker variations, in decreasing order, aredemonstrated by: Mg, K, Na, Al and Fe. Not surprisingly, sulphur and the metals associated withmineralization in the 21A zone footwall also indicate significant variability (Figure 3.1 ib), with relativechanges as follows: S >> Zn> Sb> As> Cu> Pb> Cr> Au >> Ni, Ag and Hg. However these variations aremainly the result of a few anomalous samples in the data set. Variations in LILE and REE are close to zero,with the exception of Ba, Sr, B and Rb. Small variations occur in Nb, Y, Ge and the light REE (La, Ce andNd) which are also evident in scatter plots against Zr (Figure 3.9 and Appendix B).More rigorous evaluation of the mobility of these elements may be determined by calculation of massgains and losses relative to a less altered or unaltered precursor, as described by MacLean (1990) andsummarized above. The least altered sample in the 2 1A zone rhyolite suite is TR-92-59. a flow bandedrhyolite containing minor albite (Plate 3.9) with quartz, potassium feldspar, sericite and pyrite collected fromsurface near the #3 bluff (Figure 2.10). This sample has likely undergone some hydrothermal alteration anddoes not represent pristine rhyolite glass composition. The sample plots towards the left end of the rhyolitealteration line on a Ti02 vs. Zr diagram (Figure 2.16), and contains only 129 ppm Zr. Also, the bulk 5i02and K20 contents of this sample are 80.8 and 4.35 weight % respectively. Fresh rhyolites typically contain Zrconcentrations greater than 150 ppm, less than 78 weight % Si02 and commonly less than 4 weight % K20 insimilar environments (T.J. Barrett, Mineral Deposits Research Unit, UBC, personal communication, 1993).1080.250.200.15+ 0.10U‘— 3.10: Test for feldspar fractionation in the Eskay Creek 2 1A zone rhyolite, northwestern BritishColumbia, using Pearce Element Ratios. Points lying along a slope of 1 indicate elementmobility proportional to the removal of feldspar in the melt by fractionation. However, themajority of points from rhyolite within the 2 IA zone lie well below the line, suggesting lossof alkali elements due to metasomatism. Scatter in aluminum is due to fractionationprocesses rather than metasomatism because Al is relatively immobile, as discussed in them=1..Al/Zr0.05 0.10 0.15 0.20 0.25(R07 & R08 are not plotted)text.1090CIDa) —-, -LID [- . 4 U Zb)0.0020.q0.001cri0Figure 3.11:. r.3 d 8 c3Standard deviation in the molar ratios of elements in the Eskay Creek 2 1A zone rhyolite,northwestern British Columbia. (a) Major element mobility. Silica is the dominant mobileelement involved in hydrothermal alteration. (b) Trace element mobility. Barium, copper,sulphur, antimony and zinc are mobile, but results are strongly influenced by a few isolated,anomalous samples representing low grade mineralization.110Thus, the low Zr and high Si02 ± K20values indicate that TR-92-59 has probably undergone some massgain, or dilution, as a result of silicification and possibly potassium feldspar alteration. As discussed above,the rhyolite was likely devitrified from glass during early stages of alteration. The processes of vapour phasecrystallization, devitrification and hydration result in mobility of some elements (Lofgren, 1971; cf Cas andWright, 1988) and would affect the bulk composition of the rhyolite prior to effects of progressivehydrothermal alteration. Thus, TR-92-59 may approximate the bulk compositon of the rhyolite subsequent tothe actions of early diagenetic processes and the earliest stages of hydrothermal alteration. If this is the case,calculated net gains and losses of the elements in the rhyolite represent only the mobility of elements as aresult of subsequent hydrothermal fluid processes.Net changes were calculated for each element in the rhyolite suite assuming TR-92-59 isrepresentative of the precursor composition (Table 3.4). The percent gain or loss of each element, relative tothe precursor, is plotted against Zr (Figures 3.12 and 3.13). The Zr concentration directly reflects the changein mass of the overall rock because it is assumed to be immobile and has a linear relationship to the effects ofdilution and concentration in the rock. Massive chlorite samples have the highest Zr content due to the degreeof concentration, due to mass loss, that they have undergone. Two outlying samples, marked as filled stars inthe plots in Figures 3.12 and 3.13, represent chlorite flooded by calcite as in Plate 3.6c. These rocks containrelatively lower concentrations than the massive chlorite because they have experienced mass loss to formchlorite and subsequent mass gain as calcite was added, which then diluted the Zr value. The mobility of theelements in the rhyolite is summarized below:1) Silica shows the most dramatic changes in progressive alteration. Addition and leaching of silica is thedominant control of mass changes within the rhyolite sequence. Twelve samples show mass gain insilica, ranging from 0.5 to 45.9 weight %. This addition of Si is reflected in thin quartz veinlets andpervasive dominance of quartz throughout the samples. Massive chlorite samples indicate up to 67.6weight % loss of silica. The remaining samples plot along a smooth curve against Zr (Figure 3. 12a),which indicates progressive leaching of silica as progressive alteration moves towards the massivechlorite end member.2) Potassium shows a general trend indicating progressive depletion towards the chlorite end member(Figure 3. 12b), culminating in a maximum mass loss of 4.3 weight % K20 in the massive chlorite. Thistrend also suggests that potassium is depleted during the sericitization stage of alteration; this point isdiscussed further below.3) Sodium is depleted in all but one sample, indicating a maximum loss of 3.1 weight % mass loss in Na20(Figure 3. 12c). The single anomalous sample is from the rhyolite lens and indicates a mass gain of 1.4weight % Na20.Table3.4:f&ecursorCalculatedlossesandgainsinrhyolite.Samplesarefromthe21Azone,EskayCreek,northwesternBritishColumbia.Sample NumberRef.No.RockTypeZrfactorSi02Ti02A1203Fe203MnOMgOCoONa20K20P205H20+C02AgAsAuBBaCdCewt%wt%wt%wt%wt%wt%wt%%%ppmwt %wt%wt %ppmppmppbppmpppmCA88-14-70.0RIORIIYL1.445.86-0.04.2861.270.83-0.17-3.12-,,80-,0TR-92-68F4SILC1.17.940.002.280.430.17-0.064.600.010.290.3SOS67.54.94935.222.3CA89-43-173.1R03RHYL1.00,470,000.510,870.022.80-3.07-1.14-0.021.9754-6.7-22.3171,924.5CA8O-63-95.3RO6RHYL1.0-4,600,012,981.290.011,440.77-1.97-,417.2-611.9-4.7CA89-477.l00.6F2SILC0.8-12.83-0.04-2.741.,01-0.990.690.011.94-0.11-3.10-1.00-’YL0.7-20.18-0.04-2.680.290.13-0.04-3.080.680.024.011.4-537.41.1CAR9-63-102.2ROtRHYL0.8-,960,012290.41.2.92-1.02.0,011,750.776.5392,812,4-24.52687.543.4.29CA89-89-149.2RioRI4YL0.8-23,91-0,01-0.260,430.963.77-0.14-3,13-2,07.0.011,970,0239.313.5-26.4-165.8-2.4CA89-466-201.6R13RHYL0.7-28.96-0.03-1.990,411.00-0,12-3.13-1.51-,900.660.021.98-0.08-3.94-1.30-0.010.940.0110.199.9128.4-27.3763.4-3.1CAS9-95:106.6R20RH’’L0.7-30,34-0,,17-0,16.5.14-3.330.010,9477.9-514.3-1.3CA89-42-12.5.7RuR0fl1_0.6.33.53-0.02-2.961,010.013,050.07-3.12-2.440,001.5117.5-304.71.8CA89-36-92.5RIORHYL0.6-34.49-0.03-2.860.550.003.12-0.14-3.13-2.520.02OA41.2-555.57.2CAS9-35-62.3T4TRANS0.6.38,740.00-0.732.,03-,5.39,83-0,03-3.279,690,010.070.74-2.92-0.96.371.7CA89-36—66.4T5TRANS0.6-41.320.01-1.631.850,013.620.03-3.02-2.180.03275.2.575.4-4.5CA89-466-173.8R12RI4YL0.5-47.50-0.01-2.611.320.015.460,58-3.13-2.77-0,012.0290.9-632.02.3CA89-35-67.4R17RJ4YL0.4-49.50-0.02-2.240.83-0.010.69-6.13-3.12-1.55-0.012.7161.7-644.1-13.9CAS9.89-140.5C3Cl_OR0.4-66.55-0.02-0.050.530.2512.96-0.15-3.08-4.04-0.014.670.,75.748.2CA89-89-138.5C2Cl_OR0.4-66,56.0.02-0.030,120.1711.84-0.16-3.13-3.77-0.023.840.,470.069.58-0.12-,8280.7-26.1-448.336.223.04CA89-89-137.4CiCl_OR0.4-67.64-0.02-0.820,130,1913.69-,570.9022.0842.76-,35-0.020.880.630.2315.8340.27-3.14-0.015.6832.003.3114.5100.0-35.41727.50.3*Zrfactor=Zrinprecornoc/ Zr insample.Missingvaluesacebelowthedetectionlimit,orwerenotanalyzed.RefertoTable2.6far details.RI4YL=rhyohte;SILC=siliceousrode. feisicintnsaivr;TRANStransitionrhyotite;Cl_ORmassivechlorite;CA-Cl_ORcalcite-floodedchlorite.Ref.No.RockType-DyErEuGdGeHg---NbNdNiPbPdPrppmppmppmppmppmppb.ppmppmppmppmppbppmHoLaLuMooomppmppm£!!L10.46.41.1-,40.50.6371.,90.22.8- 55.7 2.7192.7 8.1Tablo3.4:continuei..SampleNumberCoCrCsCuoomoumtCA8S-14-70.0RIORHYL192.617.3TR.92-78R24RHYL10.42.37.1-2.4TR-92-73F6#4BLUFF2.2103.30.00.7CA89-89-98.3TiTRANS4.!TR.92-72F503BLUFF2.,45TR.92-60022RHYL1.975.30.814-0.70.6CA89-477-123.0F3SILC46.75.4-1.8CA8O-63-152.8R02RHYL-8.!1,92.05.23.!3.2-!3.2-,10.417.,2CA89-63-245.7R05RHYL-!-0.31.614.20.5-1.11,9-0.1CA9O-477-149.0FlSILC0.6-!-1.7TR-92-i9RIR3{YL-Icns0.6-,4-0.90.0-,350.0CA89-63-234.5034R3{YL.,22.12.417.83.32,43.9CA89-466-225.6R14R5{YL.15,410.,3-{S’L.76.71.2-,8-3.60,’L.99.912.8-,!.!36.8-0.10.629.615.625.22645.14.1CASO-89-138.5C2GLOB1.0-142.01.0-!-5.55.62199.91.9:CA89-89-137.4ClCLOR0.5-146.81.9-,2191.40.9.CA89-29-114.4R07CA-CLOR-33.21.732.42.32,4-0.11.338.49742.30.510.,384.12.02.4CA8O-89-115.8R08CA.CLOR0.90.914.21,çle.MissitvaIuesarebelowthedetcelionlimit.orwercnolinalyzod.RcfcrtoThbIc2.6fordctails.RHYL=rhyolitc;SILCsiliceousrock. folsicitOnisive, TRANStraroftionrftyolile;CLOR=tenssivcchlorite;CA-CLORcalcite-floodedchlorite.Table3.4:continued..tCAS8-14-70.0TR-92-78TR-92-73CAS9-89-95.5CAS9-42-102.0TR-92.72TR.92.64TR.02-60CAS9-477.123.0CAS9.63-152.0TR-92-68CAR9-63.173.IrecursorCAS9-63-95.3CAS9-63-245.7CAOO-477-149.0TR-92-19CAO9-24-116.5CAS9-477.100.6CAS9-63-234.5CA89-466-225.6:CAS9-63-102.2CAS9-89.149.2CA89-466-201.6CAS9-89-123.7CAS9-95:1066CAS9-42.125.7CAS9-36.925CAS9-35-62.3CASS.14-48.39227-60,0CAS9-36-66.4CAS9-466-173.8CAS9-35.67.4R19R}IYLR24RHYLF604BLUFFTITRANST3TRANSF503BLTJFFamamRWF3SILCR02RHYLF4SILCR03RHYLR06RHYLR05RHYLFlSILCRLRHYL-lenaRIORIft’TF2SJLCR04RHYLR14RHYLROlRHYLRIORHYLR13RJ4YLR09RHYLamRHYLRhRHYLRIORJ4YLT4TRANSR15RHYLRL2pJ{O’T_.IensT5TRANSR12RJ4YLR17RHYLCICLORC2CLORC4CLORClCLORR07CA-CLORR08CA-CLOR0.6-,251.617.1- 0.80.0-12.61.6-12.7-0.2-24.60.1-15.60.7-16.68,,00.542.70.521.70.4-,539.60.715.90,6-6.6-61.50.0-22.6-54.1.0,2-23.7-49.00,51622.3-70.9-0,1-26,0-65.06.721.4-69.40.9-7.1SmSr‘lbppmppmppm-0,3-44.4-,41.5-,,50.71.6197.0-0,21.9-,939.5-0.1-10-8.4-0.30.9-,70.63.3-,6-,40.5-41.40.5-0.6-46.4-050,6-3220.31.1-40.80.31,8-,1-0.6-,0-46.2-0.4-0,4-37.8-0,2-0.1-48,3-0.31.4753.80.00.5836.10.1‘IcTh‘11Tmppmppmppm.2.6-,34.0-1,33.8-,01.40,31.31.9-4.3-0.5-0.70.1- 0.I-1.4 0,4 1.90.5-!!Lppmppmppmppm-3.4-0.6-17.80.7-—0.57.8-1.315.3-6.7-1.2107.,,,20.44.96,2-,,50.813.1-0.4-1.439.915100.60.3-,5-0.8-,4548-1.2-0.7-,41.786.50.00.0-2.1-49.2-1.33720.,70.388.1-1.48.0-1.8-42.2-1.48.7SampleNumberRefNo,RockTypePtRbSSbScSe‘—,——.—.‘ppbppm%ppmppmppm20.661.99.653.822,4-2.90,3 0.5 0.0 0,5 2.0-0.2 0.4 0.0 0.5 0.6 0.1 0.3 0.2 0.1 0,9 0.5 0.3 0.6 0,50.3 0,5 0.4 0,4 0.3 1.60.4 1.30.7 0.4 0.0-0.1 0.5-0-I0.5 0.6CAS9-89-140.5CAS9-89-138.5C-CA9O-465-190.4CAS9-89-137.4CAO9-89-114.4CAS9-89-115.83.4-1.3-0,91.7-11.70.494. SILCeiiicnoosrock, felsicmtniaive;TRANS=triaitionrhyolite,CLOR=mocoivechlorite;CA-CLOR=calcite-floodedchlorite.C..0ccccc-Cw0Ua.— —2c-CFigure 3.12: Gains and losses in major elements within the 21A zone rhyolite relative to a least alteredprecursor, Eskay Creek, northwestern British Columbia. Refer to text for explanation anddiscussion.1146400b I0Oa%0*%00D00 0*•4 *100 200 300 400 500Zr (ppm)0HF000009I 0L 00 00000o 0I- *100 200 300 400 500Zr (ppm)500—50-10020C.z-jCUC0—2c-C—3— 0 00 0 ** *‘ I100 200 300 400 500Zr (ppm)100****000 0.:0 0100 200 300 400 500Zr (ppm)0—4-60300ccCUccCci—1065I00CCccCCci440 *0I I0e0 00*0 0 00000 0 0 0000*000 * *00100 200 300 400 500Zr (ppm)0.0 100.0 200.0 300.0 400.0 500.0Zr (ppm)0— 40000 0C. C.C. C.—10 3000-20 2000CO_3o ioooFigure 3.13: Gains and losses in minor and trace elements within the 2 1A zone rhyolite relative to a leastaltered precursor, Eskay Creek, northwestern British Columbia. Refer to text forexplanation and discussion.-115*0000 *Zr (ppm)1500100I50- 00000**—1000 100 200 300 400 500S0000* 000**r0 1013 200 300 400 500Zr (ppm)2010Zr (ppm)1000500CVCV.C 0L0 100 200 300 400 500000000000o% o *0 100 200 300 400 500Zr (ppm)600050000-1000—40—so20 00Vç) 0oe0000oI 0 *00 100 200 300 400 500Zr (pp&8r6-**I ***z *CoC 000V0 0—2 I I0 100 200 300 400 500Zr (ppm)1164) Progressive alteration in the rhyolite is indicated by weak mass gain in magnesium, culminating in again of 13.7 weight % MgO in massive chlorite (Figure 3. 12d). The two outlying samples of massivechlorite, flooded with calcite, indicate a gain of 15.8 and 22.1 weight % MgO respectively.5) Manganese indicates little change, except in the massive chlorite samples in which gains ranging from0.06 to 0.9 weight % are registered (Figure 3. 12e).6) All samples exhibit small mass gains in iron, up to 5.7 weight % Fe203(Figure 3. 12f). Notably, themassive chlorite samples contain little iron and indicate the lowest gains of up to only 0.5 weight % FeO.One of the calcite-flooded chlorite samples gained 1.6 weight % Fe203.7) Rubidium and boron indicate trends very similar to potassium. Rb is added mainly in siliceous and somesericitized samples, with gains up to 112 ppm. Depletion up to 71 ppm Rb is calculated in massivechlorite samples (Figure 3.13a). Up to 14 ppm B are added to silicified samples and 42 ppm B areremoved from massive chlorite (Figure 3. l3c).8) Strontium and barium mobility are similar to one another and to CaO (3. 13b, d and e). Sr and Baregister gains up to 257 and 5983 ppm respectively, mainly in silicified rocks. Mass losses up to 48 ppmSr and 644 ppm Ba are distributed throughout all samples. Sr is significantly added with addition ofcalcite in the calcite-flooded chlorite samples (up to 836 ppm Sr and 40 weight % CaO). CaO indicateslittle addition or depletion during alteration, however the overall CaO content of the rocks is low.9) 1-120 is added in all samples, but the most is gained in massive chlorite alteration (up to 6.3 weight %).This reflects the hydrous nature of the chlorite mineral relative to minerals in the other samples.10) Small flucniations in aluminum, ±3 weight % (Table 3.4), are indicated but do not suggest a trendrelated to progressive alteration to chlorite. Aluminum is relatively immobile within most hydrothermalsystems.11) Mass gains and losses in Ti02 andP205 are relatively small and reflect the relative immobility of theseelements.12) Gains and losses in metals (Table 3.4) are generally low; however a few samples plot as outliers andindicate large gains in elements such as Au, Ag, Cu, Pb, Zn, As, Sb and Hg, as well as S. Thesesporadic additions reflect localized low grade mineralization.13) LILE and light PEE are variably mobile (Table 3.4), but generally do not follow any clear trends withprogressive alteration towards the massive chlorite end member. Yttrium shows progressive depletion,up to 42 ppm loss, as alteration approaches massive chlorite end members. Heavy PEE indicate small,scattered gains and losses of± 5 ppm.1173.4. Contact unitThe contact unit has been affected by the processes of diagenesis and locally by hydrothermal alteration.In the vicinity of stratabound mineralization, black carbonaceous mudstone is locally cut by thin sericitic fracturesand the rock is veiy soft. Away from mineralization, the lower contact unit is commonly siliceous and crosscut bythin quartz veinlets. This may be due to silicification effects from the underlying rhyolite. The chemical changesassociated with alteration have not been quantified because the unit has a mixed clastic origin.3.5. BasaltAlteration within the basaltic sequence is weak. Most of the minerals in the basalt are relatively pristine.Basaltic glass matrix has altered entirely to palagonite and chlorite. Augite is locally weakly altered to chlorite.Plagioclase is locally weakly altered to sericite. Calcite veinlets, locally with up to 20% black bitumen, arecommon and appear to be extensional. Calcite is locally pervasive and commonly fills amgydules in the basalt.The geochemical database for basaltic rocks is insufficient to quantify chemical changes associated withfractionation and alteration. The alteration mineral assemblage in the basalts is consistent with greenshist faciesmetamorphism, which is observed regionally (Britton et al,, 1990).3.6 Intrusive rocksFelsic intrusive rocksThe felsic intrusive rocks exposed in the #3 and #4 bluffs are intensely and pervasively altered to quartz,potassium feldspar, sericite and pyrite. Thin quartz veinlets occur throughout these rocks. Bartsch (1993b) notedthat regionally, alteration in the surrounding rocks increases with proximity to felsic intrusions extendingsouthward from the Eskay Creek deposit.Basaltic dykesThe basaltic dykes in the footwall of the 2 1A zone are weakly altered. In places, these mafic rocks arerelatively fresh and exhibit minor alteration of mafic minerals to chlorite. As in the hanging wall basalt, weakalteration is expressed in the alteration of augite to chlorite and plagioclase to sericite.1183.7 Summary and DiscussionHydrothermal alteration is concentrated in the footwall to the apparently stratiform mineralization in theEskay Creek 2 1A zone. Basalts in the hanging wall and basaltic dykes that cut the footwall are weakly altered andhave not clearly been subjected to significant hydrothermal activity. Varying degrees of alteration in the rhyolitesequence define some of the conditions for the evolution of the hydrothermal system.Intensity of alteration is controlled by the relative permeability of the original rock. Breccias andpyroclastic rocks have relatively higher permeability than the massive rhyolite flow, and therefore, are moresusceptible to hydrothermal alteration. Thus, the distribution of alteration in the rhyolite sequence is controlled toa large extent by the permeability of the original rock and by development of fracture systems.Identification of zones that may reflect primary permeability is difficult because alteration has obliteratedmany of the primary textures that could have distinguished eruptive pyroclastic units from autobreccias andhydrothermal eruption breccias. High fluid flow through such permeable zones has resulted in replacement oforiginal clasts and matrix with a quartz-sericite-pyrite-chlorite alteration assemblage, which often completelyobscures original fragments. Locally, ghosts of breccia fragments are visible in pervasively sericitized rock. Themargins of primary clasts may become corroded by advancing alteration as fluids pass through a permeable matrix.This results in ragged patches that look like less altered islands related to stockwork fracturing in a massive body.Conversely, the development of alteration envelopes along a network of fractures in massive rocks may result inrelict islands of unaltered or less altered rocks that look like primary clastic features (Plate 3.2). The developmentof such “false” textures has been described in Australian volcanic hosted massive sulphide deposits by Allen (1988)and in the Eskay Creek rhyolite by Ettlinger (1992). Where alteration has not completely obscured early textures,true breccias are identified by clear indication of movement and rotation of the clasts that comprise them. Flowbands provide an excellent marker for distinguishing rotation of primary breccia clasts.Increased permeability through the development of perlitic cracks during devitrification provided accessfor hydrothermal fluids that resulted in pervasive alteration of the original glass and devitrified rhyolite. Locallythe relict perlitic cracks are preserved by concentration of pyrite along the fractures; this process was probablymore common than relict textures in the rhyolite now indicate.Narrow, sericitic gouge and fault zones are common in the drillcore throughout the rhyolite and may alsohave provided conduits for the fluids. The fractures are usually difficult to correlate and often are not associatedclearly with zones of major faulting. These narrow, altered gouge zones may represent, at least in part, theformation of a network of hydraulic fractures. Hydraulic fracturing, that forms when fluid pressures exceed theconfining strength of the rock, is common in volcanic environments.119The chlorite pipe probably represents the main network of fracture conduits for hydrothermal fluidsfeeding the 2 1A zone. Progressive alteration of the wall rock in the 2 1A zone may have been controlled by thefollowing reactions:6(K,Na)AJSi3O8+ 4H(aq) K115A14[Si76 Al115020J(OH)4+ 8-lOSiO2+ 4.5.5(K,Naj(a&alkali feldspar sericite (illite) quartzandK06Al2(Si35)01OH)+ 4.5SiO2+ 15Mg2(+ 24H0—i 2.5Mg6(Si3AI)010OH) + O.6K(a& + 3OH(a&illite quartz clinochloreThe stability fields for these mineral phases, in a temperature range from 100 to 250°C, are shown in Figure 3.14(from Riverin and Hodgson, 1980). The chlorite stability field increases with increasing temperature, suggestingthat the chlorite core reflects higher temperatures in the hydrothermal system. Changes in temperature may beaffected by thermal gradients, and possibly by boiling.Reactions (D and © are consistent with petrographic observations and the mass loss and gain calculationsdiscussed above (section 3.3.3). The excess silica in reaction cD may form quartz or be carried away in thehydrothermal fluids to be redeposited elsewhere. Progressive mass loss in silica suggests that the quartz wasprobably leached from the rhyolite as sericite formed from feldspars. The solubility of silica increases withincreasing pH and temperature, and amorphous silica is more soluble than quartz (Brownlow, 1979). Thus,amorphous silica in the rhyolite glass may also have been leached by the hydrothermal fluids. The formation ofclinochlore from illite may be controlled by reaction © in which quartz is consumed and potassium is carried out ofthe system in the hydrothermal fluids.Reaction D also results in excess K+ and/or Na+ during the formation of sericite (illite). This is reflectedgeochemically in the depletion of these elements (Figures 3.12 b and c) with progressive alteration towards thechlorite end member. In some volcanogenic massive sulphide deposits, the potassium content increases withprogressive sericitization (cf Barrett, 1991), reflecting addition of Kto form sericite. In the 21A zone, fewsamples indicate addition of potassium (Figure 3. 12b). The greatest addition ofK20 is in the felsic intrusive rocks(#3 and #4 Bluffs, TR-92-68 and CA9O-477: 123.0) and in siliceous rhyolite samples that contain pervasivepotassium feldspar as indicated by staining. This suggests that either the fresh Eskay Creek rhyolite containedsignificant potassium, or K was added during a stage of potassium feldspar alteration. A stage of K-feldsparalteration is suggested regionally by Bartsch (1 993b), increasing with proximity to the felsic intrusions. Asdiscussed in section 3.3.3, the precursor composition used for the gain/loss calculations, may have been affected by120Stability diagram for chlorite, sericite, kaolinite and potassium feldspar (from Riverin andHodgson, 1980). All phases are in equilibrium with quartz. The shaded area outlines theapproximate limits of the composition of a solution which will react with sericite to formchlorite at 250°C. Point B is sea water at 250°C. A fluid of composition A will react toform chlorite at 250°C, however on cooling of the system it enters the sericite stability field.12+ILOG OKkH*Figure 3.14:121some alteration. This has the effect of changing the position of the ‘zero change’ lines in Figures 3.12 and 3.13.However, the relative trends remain the same.A diagram of the changes in K20 vs. MgO (Figure 3.15) in the 2 1A zone rhyolite indicates that MgOincreases substantially only when K20 is depleted by 1 to 2 weight %. This suggests exclusivity between thepotassic and magnesian alteration events. Thus, the potassium content in the rock may be affected by eitherfractionation processes (Figure 3.10) or earlier potassic alteration.Clinochlore forms at the expense of quartz and sericite in the presence of an Mg+2 rich fluid withattendant loss of K+, as suggested in reaction ®. This process is supported by the strong increase of MgO withdecreasing K20 as the trend approaches the massive chlorite end member (Figure 3.15). The abundant Mg2required to pervasively alter rhyolite, which has a very low primary magnesium content, to pervasive clinochlorehas probably been added by seawater. Hydrothermal fluids emanating from modern seafloor vents are consideredlobe modified seawater (Franklin, 1990).A seawater component to the hydrothermal fluids is supported by the low iron content in the hydrothermalsystem. Seawater contains an average of 1 290 ppm Mg and 0.0034 ppm Fe (Turekian, 1968). If the source of themagnesium in the fluids had been derived mainly from destruction of ferromagnesian minerals in the circulatingsystem, then the iron concentration in the fluid would also increase. However, chlorite in the 2 1A rhyolite containsno iron. Mass changes calculated for Fe203 (Table 3.4, Appendix B) suggest that total gains in Fe relative to theleast altered rock are low; iron that is added forms pyrite associated with sericite and chlorite.Changes in the chemistry of the hydrothermal fluid through complex evolution and interaction with thewalirock, and probably progressive cooling during the late stages of the system, has locally resulted in retrogradealteration of chlorite to sericite and overprinting of chlorite by quartz and sericite. Specifically, cooling of the fluidcauses the stability field of chlorite in Figure 3.14 to shrink, driving a fluid of composition A into the sencitestability field. Decreasing pH, perhaps at least in part due to the formation of chlorite, may have a similar effect bydriving the fluid composition towards the lower left of the diagram, through the sericite stability field.0Ca)U)CCU-cC-)-5.00 0.00 5.00 10.00 15.00 20.00 25.00Change in MgO (wt%)Figure 3.15: Changes in K20vs. MgO relative to a least altered precursor from the 2 1A zone rhyolite,Eskay Creek, northwestern British Columbia. MgO increases as 1(20 is depleted,suggesting reaction © may be active in the core of the hydrothermal system. See text fordiscussion.122543210—1-2-3-4-5:1*4.• Rhyolite• Transition Rhyolite• Siliceous and intrusiverocksA Massive chlorite1234. MINER&LIz&TIoN IN THE 21A ZONEMineralization in the 2 1A zone is most significant in the contact argillite and the underlying rhyolite.High grade, massive to semi-massive, stibnite - realgar dominant, apparently stratiform mineralization occurs atthe base of the contact argillite. Within the rhyolite, mineralization occurs in veinlets and disseminated in zones ofintense chlorite and sericite alteration. Sulphides are dominantly sphalerite, galena and tetrahedrite.Arsenopyrite and stibnite become prevalent in mineralized zones near the upper contact of the rhyolite. Minormineralization dominated by pyrite + sphalerite + galena ± chalcopyrite occurs in stockwork veins in the footwallvolcanic unit. The hanging wall basalt sequence is unmineralized except for minor mineralization in argillite nearthe base of the basaltic package on the northwest end of Section 1+OON. This argillite may be part of the contactunit, separated by intrusion of a basaltic sill. The character, habit and distribution of the suiphides in the 2 1A zoneare summarized in Table 4.1. Mineralization in the 21A zone has been described by Idziszek eta!. (1990),Blackwell (1990) and Britton et al. (1990). Petrographic and microprobe studies of mineralization in the EskayCreek deposits have been conducted by Barnett (1989) and Harris (GSC, written communication, 1992).4.1 Mineralogical and assay dataThe variations in mineralization throughout the 21 A zone were recorded during relogging of drillcore,and close examination of intervals with anomalously high assay values. An assay database for 121 driliholeswithin the 2 1A zone was compiled from original assay data generated by Prime Exploration during the originaldrilling program. The assay samples were generally collected systematically in 1 to 1.5 metre intervals along thelength of the hole. In later holes, samples were not collected from the hanging wall basalt, but sampling of theintercalated argillite was continued. All samples were analyzed for gold and silver; a smaller subset was analyzedfor combinations of copper, lead, zinc, arsenic, antimony and mercuiy. During the early drilling, these additionalelements were routinely analyzed in the contact unit and in mineralized intervals in the rhyolite. However duringlater drilling in 1990, these analyses were abandoned. Therefore, in general, analyses of these additional elementscomes mainly from intervals containing sulphide mineralization or anomalous concentrations of precious metals.Computer files, provided by the assay laboratories (Bondar Clegg Ltd. in Vancouver and TSLLaboratories in Saskatoon), were merged into a TECHBASE database (MINEsoft Ltd., 1991). The assays werecoded to drillhole information based on detailed relogging as well as the original drill logs. The database contains16 510 assays of gold and silver ranging up to 3.028 ounces gold per ton (103.8 grams gold per tonne) and 170ounces silver per ton (5828.6 grams silver per tonne). The database also includes: 1 238 assays of lead and zinc, 1135 of copper, 1134 of antimony, 744 of mercury and 320 of arsenic.The distribution of visible sulphides on Sections 1+OOS, 0+00 and 1+OON is presented in Figures 2.1, 2.2and 2.3; the associated assay values are shown in Figures 4.1 to 4.12. The percentage of sulphides indicated in thecross-sections reflect the estimated average of visible sulphides over the logged geological intervals.Unfortunately, this distribution does not include disseminated sulphides of microscopic to submicroscopic size,124Table 4.1: Sulphide mineralogy of the 2 1A zone, Eskay Creek, Northwestern British Columbia.MineralogyStibniteSb3STRealgarAsSRECinnabarHgSCICharacteristics• fme-grained (averaging 20microns)• anhedral, annealed• rare needles are up to 2mmlong• strong birefringence (whitegrey) and anisotropism (greyto brown or dark blue)• bright orange in transmittedlight, grey in reflected lightwith strong orange internalreflections• anhedral grains generallyappear to be crackled• deep red in transmitted light,white in reflected light withstrong red internal reflectionsOccurrence• massive• as clasts in realgar matrix• in massive veins• disseminated in sericiticrhyolite• rarely as needles in quartz-calcite veinlets• as matrix to stibnite andargillite clasts• interstitial to stibnite grains inmassive stibnite• in veinlets, commonly with acalcite selvage• rarely as inclusions in quartz-rich siliceous intervals withinthe contact unit• rarely in quartz veinlets• mainly infilling late fracturesin the massive sulphides• with realgar and calcite inveinletsStratigraphic location• near the base of the contactunit• in sericitic rhyoliteimmediately underlying thecontact unit at the top of therhyolite sequence• near the base of the contactunit• rarely in trace amounts inquartz-calcite veinlets at thetop of the rhyolite.• mainly within the massivesulphides near the base of thecontact unitrare specks in quartz-calciteveinlets near the top of therhyoliteNative ArsenicAs• irregular, anhedral grains upto 200 microns across• rare, as isolated grains alongthe margins of realgar veinsand in massive stibniterealgar• in siliceous interval within thecontact unit in CA89-018,associated with a realgar vein• in massive stibnite-realgarnear the base of the contactunit, closely associated withgold grainsGoldAu• irregular grains • rare• associated with realgar,stibnite and native arsenic• in massive suiphidemineralization near the baseof the contact unitArsenopyriteFeAsSAP• randomly oriented needles upto 3 mm long and locally aseuhedral rhoinbs• locally aligned parallel tofoliation in massive stibnite• mainly disseminated • in contact argillite abovestratabound sulphidesin massive stibnite near thebase of the contact unit• in intensely sericitizedrhyolite immediatelyunderlying the massivesulphides• spheroidal to framboidal• euhedral - cubes tododecahedrons• disseminated and in laminae• disseminated and in veinlets• disseminated and instockwork veins• contact unit argillite• throughout rhyolite• in footwall volcanic unitPyriteFeS2PY125Table 4.1: . . .continuedGalenaPbSGLChalcopyriteCuFeS2cPgreenish grey in reflectedlight• disseminated grains areanhedral and commonly lessthan 10 microns• usually occurs in associationwith SL, GL and PY• contains Ag (indicated byEDS)in hanging wallmineralization it is reddish-brown• dull grey in reflected light• anhedral to rounded grainscommon, ranging up to 3 mmacross• larger rounded grains may berecrystallized porphyroblasts• annealed grains• commonly in association withSL, TT, PY• brassy yellow• anhedral blebs in sphaleriteless than 10 microns across• anhedral, irregular grains upto 50 microns across wheredisseminated• disseminated and in veinlets• locally disseminated andsmeared along shear surfaceswithin massive chlorite• occurs mainly as blebs withinsphalerite• rare disseminated grains inassociation with sphalerite,galena and tetrahedritemineralization• rarely in significantconcentrations in vuggy quartzveins• occurs mainly within therhyolite package; appears tobe more abundant towards thetop of the sequence• in footwall volcanic unitmineralization• in hanging wall debrismineralization• in intensely sericitizedrhyolite underlying the contactunit• occurs mainly in the lowerportions of the rhyolite and inmineralized intervals of thefootwall volcanic unit• becomes increasingly commonwith depthMineralogy Characteristics Occurrence Stratigraphic locationTetrahedrite(Cu-Fe)12Sb43TISphaleriteZnSSL• mainly honey-yellow incolour, becomes increasinglyreddish to brown with depth;• mainly in rhyolite, insericitically and chloriticallyaltered zones and in veinlets• disseminated and in veinlets• common in veins anddisseminated• occurs mainly in rhyolite andfootwall volcanic unitmineralizationFigure 4.2: Distribution of lead and zinc assays on Section 1+OON. Details of the geology are found in Figure2.1.12610501000950900950800750700£5060010501008950900850800750700£50600Figure 4.1: Distribution of gold and silver assays on Section 1+OON. Details of the geology are found inFigure 2.1.00500008950980050800750700650600127Figure 4.3: Distribution of copper and antimony on Section 1+OON. Details of the geology are found inFigure 2.1.1008950980850800750780650600Figure 4.4: Distribution of mercuiy and arsenic on Section 1+OON. Details of the geology are found in Figure2.1.Figure 4.6: Distribution of lead and zinc assays on Section 0+00. Details of the geology are found in Figure2.2.128050Ixo9509008508007507000x0950900050800750700ZSOE 300 350 0000Figure 4.5: Distribution of gold and silver assays on Section 0+00. Details of the geology are found in Figure2.2.-3000: —2500: -2000: -0500: -100€ —00€005012905010009509008508007507001000950900850800750700Figure 4.7: Distribution of copper and antimony on Section 0+00. Details of the geology are found in Figure2.2.10501500 2800 2500 3000 3500Figure 4.8: Distribution of mercury and arsenic on Section 0+00. Details of the geology are found in Figure2.2.Figure 4.9: Distribution of gold and silver assays on Section 1+OOS. Details of the geology are found inFigure 2.3.130Figure 4.10:-10.10 0,,1”! [‘VC4h,-,Pb10jJJ JJ10‘2 Section 1+OOS00 Eskay Creek 21A Zone/7._,,.,—,.c it it toot tot toot tootDistribution of lead and zinc assays on Section 1+OOS. Details of the geology are found inFigure 2.3.Figure 4.11: Distribution of copper and antimony on Section 1+OOS. Details of the geology are found inFigure 2.3.€3K 43K - 3K K 3K lOX lOX lOX 23KNW SE131/ / / I “4 / // 4 / /‘\/ A /‘ fl- /- I -- >‘, /______________________1%h /\\//Hg As r’ \ /,J—Jj)_______________________‘7V /04o1.d SlO K * t*a ,OaU... Roll 5020.r Section 1+OOSEskay Creek 2 IA Zone-lOX 15X -lOll-OX K 3K lOll 3K 2020 0000”°Figure 4.12: Distribution of mercury and arsenic on Section 1+OOS. Details of the geology are found inFigure 2.3.‘50‘SO‘SO132which are conunon within the rhyolite. Sphalerite, galena, tetrahedrite and chalcopyrite occur mainly within therhyolite and in the footwall volcanic unit. On Section 1+OON these minerals occur within the contact unit and inhanging wall argillite on the northwest, or downdip, extension of the unit. They do not occur stratigraphicallyabove the rhyolite on Sections 0+00 and 1+00 S. Notably, the chalcopyrite concentration is generally lower thanthe other sulphides and sporadically distributed. Most occurrences of chalcopyrite are found on Section 1+OON andare generally lower in the rhyolite sequence. Some chalcopyrite is also associated with sphalerite, galena andtetrahedrite within the contact and hanging wall units on this section. Stibnite and arsenopyrite are localized inthe upper portions of the rhyolite and within the contact unit. Realgar and cinnabar are rare near the top of theargillite and are restricted mainly to mineralization hosted in the contact argillite.StatisticalAnalysis ofthe Assay DataThe assay database was subdivided by lithological unit to determine the distribution of metals within the21A zone. Statistical summaries for each unit are found in Tables 4,2 to 4.5; typical anomalous assay intervals arepresented in Tables 4.6 to 4.8. Each lithological unit was subdivided to reflect characteristics of the rocks. Assaysin the footwall volcanic unit were subdivided into sedimentary and volcanic rocks, tuffs, and flows or sills (Table4.2). The rhyolite was subdivided to reflect the dominant character of the rock, whether massive, brecciated orintensely altered to sericite or chlorite (Table 4.3). The contact unit is subdivided into massive and laminatedargillite, rhyolitic intervals, barite bearing intervals, stratabound sulphides, and transition type subunits (Table4.4). The hanging wall was subdivided into volcanic and sedimentary subunits (Table 4.5).Most of the precious and base metal concentrations are in the contact unit and rhyolite sequence. Zinc,lead and copper are highest within the rhyolite, and generally low within the contact unit, with a few anomalousexceptions. Arsenic, antimony and mercury values are highest in the stratabound sulphides and associated argillitein the contact unit. However, significant values of these elements are also contained locally within the rhyolite.Anomalous to significant gold mineralization occurs in the volcanic rocks of the footwall volcanic unit. Thehanging wall basalts are barren of anomalous mineralization. Significant values within the hanging wall argilliteare restricted to intervals located above massive basalt on the northwestern side of Section 1+OON.In order to estimate relationships between these elements, Pearson correlation matrices were calculated foreach lithology and subunit (Tables 4.9 to 4.12). These correlation values provide an estimate of the linearrelationship between two variables; a value of 1 indicates a perfect positive correlation, -1 indicates perfectnegative relationship, and values close to zero suggest no strong linear relationship. However, these values may beseverely affected by single high outliers, more than one population within the data set and transformations. Inorder to rigorously test the statistical significance of the correlations, the data must approximate a normaldistribution (Howarth and Sinding-Larsen, 1983), however the correlation estimate may be evaluated qualitativelyTable4.2:Statisticalsummaryofassays inthefootwall volcanicunitandsedimentaryunit.BMMSDACTFWARFWLTFWUSEDSVOLCundividednmmmaxmeanmedian80.0280.1900.0890.07710090.0000.5610.0120.0069250.0000.1180.0060.0037470.0001.1400.0110.00510770.0000.4770.0080.004780.0000.0290.0040.003690.0000.0420.0070.00539130.0001.1400.0090.004160.010.810.100.0410. 280.000.810.070.02iimmmaxmeanmedian80.261.500.620.5210090.004.560.180.099250. 0 0 0 0BMMSmassivesuiphides,DACT’flowsorsills,FWAR=footwallargillite,FWLTlapillituffs, FWTIJ=footwalltuffs, SEDS=sedimentasyrocks,VOLC=volcaniclastic rocksTable4.3:Statisticalsummaiyofassaysintherhyoliteunit,21azone,EskayCreek,northwesternBritishColumbia.RockTvoenmmmaxmeanmedianRIIYL720.,00577‘‘0.000.520.010.00RockTypeAu(oz/ton)nmmmaxmeanmedianRHYLRHPBRHBXRHATCLORundivided38770.0001.6890.0130.00319140.0001.7800.0240.00490.0110.0350.0230.02425360.0001.5500.2300.0043590.0001.3750.0960.025490.0000,8250.0580.00587440.0001.7800.0220.003Cu(¼)Pb(¼)nmmmaxmeanmediannmmmaxmeanmedianZn(%)RHYL3030.000.880.020.003030.,010.0090.¼)Sb(%)Hg(¼)TypenmmmaxmeanmediannmmmaxmeanmedianamiiimaxmeanmedianRHYL=maasivetomottledrhyolite,RHTTJrityoliteLuffRJIPB’.rhyolitewithaliceandcarbonalterion.RMBXrhyolitebrecciRHAT=elyaeaicitized,poaat’blytuffaceous rhyolite,CLOR=masalvechloritealteredrhyoliteTable4.4:Statistical summaiyofassays inthecontact unit.Au(oz/ton)ommmaxmeanmedian10.0650.0650.0650.0652440.0002.4450.0690.00650.0090.0660.0330.0351680.0000.4920.0270.005130.0000.2250.0360.00040.0320.7670,2480.0961640.0002.1810.1120.007490.0000.4580.0490.011150.0582.7421.4381.262Cu(%)nmmmaxmeanmedian210.0013.251.970.8580.004.831.410.9840.000.850.420.4220.040.460.250.25180.105.481.140.4330.070.470.210.10120.3836.4513.047.36560.0013.25‘1.360.66Ag(oz/ton)ommmaxmeanmedian10.300.300.300.302440.0010.040.230.0550.2337.5016.196.661680.0024.500.450.06130.010.480.080.0140.000.500.260.261640.0028.600.580.06490.0056.831.540.14150.0670.6012.504.526480.0056.830.600.06740.,000.420.150.02220.001.340.230,04130.000.890.120.05140.0251.7317.2010.691390.002.04‘0.140.03610.001.500.040.01220.•thesevaluesdonotincludedataftomsuiphideintervalsCLOR=chioriticrockCZAR=argillite; CZBAbantebedsinergilliteandmassivebstite;CZLM=IwsinatedargilliteCZRH=siliceousorrhyoliticiatervslwithinthecontactunit;CZTUtufthceoustoseiiciticintervalwithinthecontaceunit;TRANS=transitionzoneatthebaseofthecontactunit;TRTUtuffaceosoblacktransitionzonematerial:StJLPHSmassivetosemi-massivesslphideamainlystibnite-resigarRockTypeCLORCZARCZBACZLMCZRHCZTUTRANSTRTUSUI2HSundividedaRockType6480.0002.4450.0680.007nPb(%)mmmaxmeanmedian-Zn(%)nmm-max--meanmedianCZAR740.*1390.000.330.010.001460. summaryofassays inthehangingwallbasaltandargillitepackage,21Azone,.EskayCreek,northwesternBritishColumbia.’,137Table 4.6: Typical assay values from the footwall volcanic unit; Eskay Creek 21A zone, northwesternBritish Columbia.Drillhole From To Width Au (opt) Ag (opt) Pb (%) Cu (34) Zn (34) As (34) Sb (34) Hg (34) Rock ‘peCA8S-Oll 142.5 144.0 1.5 0.046 2.28 11.92 0.10 9.80 0.03 FWVolcaaicCA88-Oll 148.5 151.5 3.0 0.059 0.67 3.01 0.11 2.84 0.02 FWVolcanic-tuffCA8S-01l 165.0 169.5 4.5 0.095 0.25 0.10 0.05 0.29 0.03 fWVolcanjc-tuffCA89-017 171.0 175.5 4.5 0.049 0.16 ArgilltteCA8O-0l7 180.0 183.0 3.0 0.095 0.49 0.42 0.01 0.75 0.08 0.01 FWVolcanic-tuffCA89-018 199.5 200.4 0.9 0.142 0.22 0.05 0.00 0.02 0.04 0.01 FWVolcanic-tuffCA89-023 160.5 166.5 6.0 0.169 0.17 0.14 0.02 026 0.05 0.02 FWVolcamc-brccciaCA89-031 236.0 259.0 3.0 0.077 1.84 FwVolcanicCA89-031 263.5 268.0 4.5 0.091 0.36 FWVolcanicCA89-031 286.0 287.5 1.5 0.063 1.02 FW VolcanicCA89-035 234.5 236.0 1.5 0.118 0.96 ArgilliteCA89-036 291.0 292.5 1.5 0.077 0.66 FWVolcanicCA89-044 179.5 181.0 1.5 0.050 0.20 FWVokanicCA89-044 190.0 191.5 1.5 0.028 0.45 0.51 021 3.55 0.13 0.01 FWVolcanicCA89-045 208.1 209.6 2.8 0.074 0.34 FW Volcanic - oiffCA89-045 364.1 366.7 2.6 0.131 0.03 FW Volcanic - luffCA89-052 230.5 241.7 11.2 0.109 0.72 etaisulphidesCA89-052 252.0 254.4 2.4 0.062 0.13 FW Volcanic - luffCA89-053 250.4 251.9 1.5 0.477 0.29 FWVolcanic-tuffCA89-054 222.0 223.5 1.5 0.065 0.67 FW VolcanCA89-056 267.0 268.0 1.0 0.187 1.69 0.04 0.01 0.24 0.81 0.03 FWVolcanicCA89-056 268.0 269.0 1.0 0.065 1.05 FWVolcanicCAR9-062 238.0 239.0 1.0 0.055 0.36 FW Volcanic- luffCA89-063 270.0 274.0 4.0 0.069 0.67 FW VolcanicCA89-064 246.0 247.0 1.0 0.060 1.67 FW Volcanic- luffCA89-064 253.0 254.0 1.0 0.063 029 FW Volcanic- luffCA89-065 234.0 235.0 1.0 0.561 1.11 0.02 0.01 0.14 0.28 0.02 FWVolcanicCA9O-416 198.0 200.0 2.0 0.574 0.21 FWVolcanic-tuffCAO0-417 77.0 79.0 2.0 0.079 0.05 FWVolcanic-tuffCAOO-417 85.0 86.0 1.0 0.080 0.07 FW Volcanic - luffCAOO-417 184.0 185.0 1.0 0.054 0.14 MudstoneCA9O-426 282.0 284.0 2.0 0.094 0.86 FW VolcanicCA9O-426 316.0 317.0 1.0 1.140 4.22 FWVolcanic-tziffCA9O-432 66.0 70.0 4.0 0.071 0.45 FW Volcanic- brecciaCA9O-432 91.0 92.0 1.0 0.031 2.48 FWVolcanic-tuffCAOO-433 100.0 101.0 1.0 0.050 0.27 FWVolcanicCA9O-441 182.0 183.0 1.0 0.042 3.66 FWVolcanic5asticCA9O-446 57.0 61.0 4.0 0.051 1.97 ArgilliteCA9O-454 108.0 109.0 1.0 0.009 8.04 FW Volcanic - luffCA9O-468 111.0 112.0 1.0 0.066 0.80 FWVolcanicCA9O-469 109.0 110.0 1.0 0.167 0.71 FWVokanic-tuffCA9O-478 69.0 70.0 1.0 0.057 0.59 FW Volcanic - luffCA9O-478 87.0 88.0 1.0 0.017 7.80 FWVolcanic-tiffCA9O-496 24.0 25.0 1.0 0.022 4.56 FWVolcanicCAOO-502 131.0 132.0 1.0 0.057 1.18 FWVolcanicCA9O-502 139.0 140.0 1.0 0.052 0.11 FWVolcanicCA9O-503 143.0 144.0 1.0 0.081 0.46 ArgllliteCA9O-503 185.0 186.0 1.0 0.06! 0.14 FWVolcanic-luffCA9O-531 193.0 194.0 1.0 0.052 0.15 MudstoneCA9O-552 196.0 197.0 1.0 0.063 0.06 FWVolcanic-tuff138CA88-009 141.9 144.9CA88-012 117.5 122.0CA88-013 87.6 90.6CA88-014 49.5 51.0CA89-017 117.0 120.0CA89-019 58.5 61.5CA89-021 71.6 73.1CA89-023 75.0 76.5CAS9-024 74.1 77.1CA89-025 171.6 173.1CA89-027 63.3 64.5CA89-028 67.7 71.8CA89-037 91.5 93.0CA89-043 104.5 106.0CA89-044 117.0 118.5CA89-050 177.0 179.5CA89-054 111.0 112.5CA89-054 117.0 118.5CA89-064 160.0 161.0CA89-064 169.0 171.0CA89-066 107.5 108.5CA89O77 104.0 106.0CA89-080 110.0 119.0CAS9-081 110.0 112.0CA89-082 99.0 100.0CA89-082 111.0 113.0CA89-090 113.0 116.0CAS9-091 1440 146.0CA89-094 48.0 49.0CA89-094 55.0 56.0CA89-097 105.0 106.0CA89-099 107.0 108.0CA89.100 78.0 79.0CA89-100 99.0 100.0CA9O-426 172.0 175.0CA9O-429 162.0 164.0CA9O-465 179.0 189.0CA9O-465 190.0 191.0CA9O-465 196.0 197.0CA9O.552 58.0 59.03.0 0.484 1.014.5 1.143 11.563.0 0.516 11.401.5 0.423 1.583.0 0.713 0.873.0 0.628 5.341.5 0.765 0.981.5 0.561 1.213.0 0.555 0.021.5 0.640 0.331.2 1.019 5.134.1 1.042 0.301.5 0.657 0.991.5 0.618 0.261.5 0.498 0.302.5 0.614 5.361.5 0.428 2.311.5 0.473 0.821.0 0.506 4.822.0 1.130 25.451.0 0.503 0.082.0 0.520 5.909.0 0.355 4.912.0 0.998 46.551.0 0.830 0.062.0 0.463 1.003.0 0.961 1.192.0 0.559 2.291.0 0.520 0.891.0 0.428 18.291.0 0.542 0.011.0 0.468 2.751.0 0.430 5.841.0 0.569 0.403.0 0.564 0.582.0 0.7 18 0.3410.0 0.665 11.721.0 0.458 170.001.0 0.825 23.501.0 0.421 11.500.00 RHYL0.01 RHTU0.00 RHBX0.00 RHTU0.04 0.01 RHBX0.57 0.02 RHAT0.17 0.02 RHYL0.05 0.01 RHAT0.27 0.02 RHAT0.07 0.00 RHYL0.30 0.01 RHAT11.57 0.00 RHAT2.01 0.01 RHYL0.10 0.01 RHATRHAT0.03 0.01 RHTU0.04 0.00 RHTU0.02 0.00 RHTU0.00 RHTU0.01 RHYL3.60 0.00 RHYL0.07 0.01 RHBXRHATRHATRHATRHTURHBXRHBXRHYLRHYLRHBXRHYLRHATRHYLR1-IBXRHTURHBXCLORCLORRHBXTable 4.7: Representative anomalous assays in rhyolite, Eskay Creek 21 A zone, NorthwesternBritish Columbia. RHYL = undifferentiated; RHAT = intensely sericitized; RHTU =tuffaceous; RHBX = breccia.Drillhole From To Width Au Ag Zn Pb(m) (m) (in) (oz/ton) (ozfton) (%) (%)Cu Sb As Hg Rock(%) (%) (%) (%) TypeCA88-006 101.8 119.2 7.4 0.466 0.42 0.09 0.00 0.00 2.85 0.82 0.16 RHAT0.03 0.04 0.00 0.010.17 0.09 0.02 0.130.18 0.12 0.02 0.180.00 0.01 0.00 0.030.04 0.02 0.00 1.080.10 0.07 0.03 0.280.04 0.01 0.00 0.340.02 0.02 0.00 0.300.02 0.00 0.00 0.050.76 0.01 0.16 0.010.28 0.03 0.01 3.770.02 0.02 0.00 0.710.05 0.01 0.00 0.660.06 0.00 0.00 0.270.09 0.02 0.03 0.000.09 0.03 0.01 0.030.04 0.02 0.00 0.010.05 0.08 0.04 0.050.71 0.32 0.06 0.090.04 0.00 0.00 0.020.16 0.03 0.04 0.02139Table 4.8: Typical, anomalous assay values from the contact unit, Eskay Creek 21A zone, northwesternBritish Columbia.Drillhole From To Width Au A Cu Pb Zn As Sb Hg Rock Type(m) (m) (rn) (oz!ton) (ozfton) (%) (%) (%) (%) (%) (%)CA88-006 95.8 101.8 6.0 1.990 4.34 0.02 0.07 0.49 22.67 12.87 0.71 SulphidesCA88-007 109.2 112.2 3.0 1.125 1.85 0.01 0.02 0.08 0.46 ArgilhiteCA88-009 74.9 76.4 1.5 0.858 21.65 0.03 0.18 0.41 7.60 0.33 SulphidesCA88-012 87.7 89.2 1.5 0.250 56.83 0.33 1.00 1.66 0.89 0.08 TransitionCA89-018 54.0 55.5 1.5 0.749 1.18 0.00 0.02 0.04 0.79 0.19 0.03 ArgihliteCAS9-018 55.5 57.0 1.5 2.567 9.92 0.32 0.04 0.33 1.56 12.73 0.74 SulphidesCA89-021 59.6 65.6 6.0 1.321 33.07 0.04 0.19 0.69 1.81 38.83 0.16 SulphidesCA89-023 54.0 58.5 4.5 0.821 0.09 0.00 0.00 0.02 0.79 0.12 0.02 ArgilliteCA89-023 60.0 63.0 3.0 1.499 3.06 0.01 0.02 0.18 21.43 7.48 1.97 SulphidesCA89-024 66.6 68.1 1.5 0.236 0.08 0.01 0.00 0.08 2.79 0.04 0.03 Laminated ArgihhiteCA89-024 68.1 69.6 1.5 1.961 2.06 0.01 0.01 0.15 36.45 11.43 1.10 SulphidesCA89-024 71.1 74.1 3.0 0.665 1.36 0.01 0.02 0.07 1.07 1.23 0.05 ArgilliteCA89-028 64.8 67.7 2.9 2.267 0.19 0.00 0.01 0.04 5.61 0.17 0.01 TransitionCA89-037 91.5 93.0 1.5 0.657 0.99 0.00 0.01 0.05 2.01 0.66 0.01 TransitionCA89-042 106.5 109.5 3.0 0.521 2.86 0.00 0.00 0.07 0.17 0.15 0.01 TransitionCA89-043 100.0 101.5 1.5 2.445 7.80 0.03 0.02 0.20 13.25 1.10 1.50 ArgilliteCA89-043 101.5 103.0 1.5 1.200 2.91 0.01 0.00 0.28 1.92 1.34 1.60 TransitionCA89-045 118.3 119.7 1.4 0.276 1.01 0.01 0.01 0.13 0.13 0.01 0.01 LaminatedArgihliteCA89-063 105.0 106.0 1.0 0.429 0.15 0.00 0.02 0.02 0.03 0.00 ArgilliteCA89-066 107.5 112.5 5.0 0.217 0.27 0.01 0.06 0.14 3.19 0.08 0.00 ArgihhiteCA89-077 87.0 88.0 1.0 1.083 28.60 0.09 0.12 0.46 3.98 1.34 0.20 TransitionCA89-082 97.0 98.0 1.0 0.342 1.41 ArgilliteCA89-089 81.0 84.0 3.0 1.009 1.09 TransitionCA89-089 84.0 85.0 1.0 1.680 2.19 SulphidesCA89-089 86.0 88.0 2.0 1.077 5.81 TransitionCA89-090 95.0 96.0 1.0 0.294 0.19 ArgilliteCA89-096 108.0 109.0 1.0 0.873 11.82 TransitionCA89-099 89.0 93.0 4.0 0.253 0.82 Transition3914 53 53 53 28 53 00318 53 53 53 28 53 00.137 0.211 53 53 28 53 00.003 0.210 0.374 53 28 53 00.051 0.269 0.916 0.572 28 53 00.470 0.934 0.103 -0.076 0.105 28 00A74 0.587 0.235 0.341 0.221 0.522 - 0Massive - mainlypyrit sphaLesit4 akna chalcopyrileAu Ag Cu Pb Zn As Sb HgAuAgCuPbZnAsSbHgFlows or nIleAu Ag Cu Pb Zn Ag Sb HgAuAgCuPbZnAsSbHg— 1009 25 25 25 16 25 00.32— 25 25 25 16 25 00.085 0.156 25 0-0.043 0.097 058325 25 160.428 0.949.8280.07725 0-0.033 0.154 0.942 07020.524 0.604 0.157 0.182 0.094 0.584AiAlCsPbZnAsSbHgAu Ag Cu Pb Zn Ag • Sb Hg925 3 3 3 I 3 00.613—.. 3 3 3 I 3 0-0.803 -0.655 -..... 3 3 1 3 00.522 0.694 0.089 —..... 3 1 3 00.115 0.327 0.500 0.907 I 3 0- - - - - I 00.115 0.327 0.500 0.907 1.00 - 0Foofwall- lapilli osAn Ag Cu Pb Zn Ag Sb HgAuAgCuPbZnAsSbHg—. 747 18 18 18 5 18 0II 18 10 5 18 00.944 0.925 —_.... 18 18 5 II 00.663 0.823 0.706 18 5 II0.832 0.949 0.889 5 II 00.997 0.880 0.980 0.572 0.872---.. 5 00.446 0.487 0.443 0.549 0.533Volcanielastic rocks - heterolithicAu Ag Cu Pb Zn Ag Sb HgAuAgCuPbZnAgSbHg140Table 4.9: Pearson correlation matrices for the footwall volcanic unit and footwall sedimentary unit, in the 21a zone,Eskay Creek, northwestern British Columbia. The correlation coefficient for each pair is listed in thelower left haif of each matrix. The number of pairs available for the calculation are indicated in the upperright halfof each matrix. Correlation values significantly different than zero at the 999% confidence level arehighlighted in bold letters.UndividedAu Ag Cu Pb Zn As SbAuAgCuPbZnAgSbHgFootwail argillhteAuAgCuPbZnAgSbHgFooiwaU_tuffsAuAgCuPbZnAsSbHgAu Ar Cu Pb Zn As Sb Hr1077 6 6 6 6 6 00.255 6 6 6 6 6 0-0.018 0.267 6 6 6 6 0-0.291 0.223 0.220 6 6 6 0-0.126 0.523 0.888 0.245 6 6 00.466 0.573 -0.245 -0.230 0.098 6 00.176 0.621 0.775 0.364 0.780 0.000 - 0Sedimentary rocks1tJLITable 4.10: Pearson correlation mairices for the rhyolite unit; 21A zone, Eskay Creek, northwestern British Columbia.The correlation coefficient for each pair is listed inthe lower left half of each matrix. The number of pairsavailable for the calculation are indicated in the upper right half of each matrix. Correlation valuessignificantly different than zero at the 99.9% confidence level are highlighted in bold.undwrdAu Ag Cii Pb Z.. As Sb HgAu —..... 8744 8o 866 866 209 864 377Ag 0.308 —. 865 866 866 209 864 577Cu 0.062 0.597 865 865 209 864 573Pb 0.003 0.170 0.270 866 209 864 573Zn 0.042 0.367 0.499 0.886 209 864 573As 0.450 -0.041 -0.036 0.036 -0.041 209 197Sb 0.358 0.120 0.052 0.006 0.041 0.081 573Hg 0.213 0.280 0.201 0.204 0.240 0.053 0.692141Massive ChloriteAgCuPbZnAsSbHgAu Ag Cu Pb Zn As Sb Hg49 21 21 21 0 21 210. 21 21 21 0 21 210.532 0.9 21 21 0 21 210.486 0.853 0.93 21 0 21 210.416 0.877 0.946 0.9 0 21 21- . -- 0 00.608 0.977 0.973 0.910 0.869 - 21.0067 0.413 0.484 0.410 0.662 - 0.280Iiite?y iericitiedi*y.iiteA. Ag Cu Pb Zn As Sb HgAuAgCuPbZnAsSbHgAiA4CiPbZnSbH1A4CuPbZnSbH4Au Ag Cu Pb Zn As Sb Hg2536 277 277 277 35 277 1740.286 277 277 277 35 277 1740.110 0.827 277 277 35 277 170-0.006 0.144 0.275 277 35 277 1700.026 0.352 0.447 0.958 35 277 170-0.019 -0.014 -0.083 -0.096 -0.143 35 300.454 0.229 0.165 0.022 0.061 0.164 1700.186 0.788 0.627 0.576 0.708 -0.023 0.266Rky.uite -with zilira aiedcw6asi altutiAu Ag C. Pb Zn As Sb HgA.—. 9 9 9 9 0 9 3Ag 0.239 9 9 9 0 9 3Cu0.207 0.953 9 9 0 9 3Pb 0.218 0.161 0.135 9 0 9 3Zn 0.264 0.655 0.727 0.0.44 0 9 3Sb 0.066 0.973 0.969 0.169 0.582Rky.&e- ni,’e S. j..UiedAu Ag Cu Pb Zn As Sb HgAuAgCuPbZnAsSbHg3877 .w3 .suj 303 Ii 303 1930.413 303 303 303 72 303 1630.064 0.074 303 303 72 303 1630.139 0.291 0.339 303 72 303 1630.119 0.181 0.515 0.888 72 303 1630.618 -0.074 -0.038 -0.052 -0.048 72 660.147 0.168 -0.008 0.016 0.004 0.055 1630.017 0.220 -0.049 0.082 0.074 -0.092 0.316339 139 138 138 60 138 1220.360 138 138 138 60 138 1220.008 0.582 138 138 60 138 122-0.016 0.416 L688 138 60 138 220.026 0.395 0.623 8360 60 138 1220.535 -0.071 .0.083 -0.059 -0.079 60 590.564 0.035 -0.004 -0.021 0.073 0.055 1220.399 0.334 0.340 0215 0.244 0.023 0.795Rl.yolite brecriaRhyolite luffAu Ag Cu Pb Zn As Sb Hg116 94.1914 ; : : 116 940.055 0.2-0.060 .60117 117 42 116 94116 94-0.033 0.098 0.610 0.9 42 116 940.149 0.189 .0.O239:O12O.005 940.009 0.006 -0.077 0006 -0092 42 420.213 0.196 0.093 0.001 0.162 0.129142Table 4.11: Pearson correlation matrices for the contact unit; 21A zone, Eskay Creek, northwestern British Columbia.The correlation coefficient for each pair is listed inthe lower left half of each matrix. The number of pairsavailable for the calculation are indicated in the upper rigl-it half of each matrix. Correlation valuessignificantly different than zero at the 99.9% confidence level are highlighted in bold.undivided— not including abound ss4ohidesAu Ag Cu Pb Zn As Sb Hg648 139 146 146 56 139 1200.206 —. 139 146 146 56 139 1200.105 0.942 139 139 56 139 1190.026 0.645 0.775 —. 146 56 139 1190.105 0.758 0.862 0.953 56 139 1190.669 0.427 0347 0.148 0.309 56 550.513 0.429 0.320 0.185 0.298 0.463—..... 1190.579 0.169 0.101 0.006 0.146 0.579 0,479Au Ag Cu Pb Zn As Sb Hg— 244 74 75 75 21 74 610.541 ---..... 74 75 75 21 74 610.280 0.354 74 74 21 74 60-0.009 0.041 0.643 75 21 74 600.073 0.175 0.777 0.958 21 74 600.720 0.807 0.385 0.060 0.241 21 200.545 0.739 0.391 0.056 0.154 0.525 600.793 0.678 0.328 -0.022 0.091 0.895 0.4.64 .._..Barile-rich argillite andmas,ive bw-iie700000QArgillite - laminatedAu Ag Cu Pb Zn As Sb HgAu 168 23 23 23 8 23 22Ag 0.081 23 23 23 8 23 22Cu 0.061 0.094 23 23 8 23 22Pb 0.265 0846 0.243 23 8 23 22Zn -0.254 0.210 0.511 0.360 8 23 22As -0.166 -0.367 0.018 -0.308 0.168 8 8Sb 0.630 0.421 -0.193 -0.060 -0.100 0.278 22Hg 0.330 -0.122 0416 -8.096 0.284 0.332 -0.078Tuffaceous, rhyolitic intervals within the contact unitAu Ag Cu Pb Zn As Sb HgAuAgCuPbZnAsSbHgSiliceous or rhyolitic intervals within the contact unitAu Ag C. Pb Zn As Sb HgAuAgCuPbZnAsSbHg13 4 9 9 4 4 40.266-_. 4 9 9 4 4 4-0.547 0.990 4 4 4 4 40.276 0.947 0.870—. 9 4 4 40.069 0.989 0.989 0.899 4 4 40978 -0.668 -0.563 -0.897 -0.664 4 40.832 -0.457 -0.415 -0.650 -0.434 0.700 4-0.983 0.680 0.577 0.905 0.675 -1.000 .0.719‘Transition zone’- at the base ofthe contact unitAu Ag Cu Pb Zn As Sb Hg164 22 23 23 18 22 210.483 22 23 23 18 22 210.322 0.991 22 22 18 22 210.373 0.974 0.980 23 18 22 210.414 0.877 0.882 0.813—.... 18 22 2!0.897 0.458 0.486 0.555 0.456. 18 180 491 0.657 0.663 0.602 0.801 0.394 210.359 0.154 0.188 0.052 0.546 0.181 0.669Tuffaceous intervals In the ‘Transition zone’Au Ag Cu Pb Zn As Sb HgAuAgCuPbZnAsSbHgAu Ag Cu Pb Zn As Sb Hg15 14 14 14 12 14 14-0.264 14 14 14 12 14 140.401 0.059 14 14 12 14 14-0.298 0.964 0.002 14 12 14 14-0.104 0833 0.031 0888 12 14 140.408 -0.484 -0.300 -0.429 -0.396 12 120.079 0.774 0.024 0.669 0.722 -0.413 140.304 -0.306 0.004 -0.322 -0.251 0.599 -0.262AuAgCuPbZnAsSbHgArgillite - massiveAuAgCuPbZnAsSbHgAuAgCuPbSbHg—.-..-.---. 4 3 3 3 2 3 33 3 3 2 3 3-0.049 0.556 3 3 2 3 30.008 0.897 0.866 3 2 3 3-0.420 0.623 0.997 0.904 2 3 31.000 -1.000 -1.000 -1.000 -1.000 2 20.999 0.403 .0.536 -0.042 -0.465 1.000 31.000 0.441 -0.500 0.000 -0.427 1.000 0.999AuAgCuPbZnAsSbHgStrataboundsulphides49 13 13 13 3 13 90.345 13 13 13 3 13 90.249 1000 13 13 3 13 90.251 1.000 1.000 13 3 13 90.249 0989 1.000 1.000 3 13 90.122 -0.858 - - 0.898 3 30.404 0,972 0.972 0,972 0.972 -0.704 90.475 0.990 0,989 0.989 0.989 0.998 0.972AuAgCuPbZnAsSbHg143Table 4.12: Pearson correlation matrices for the hanging wall, 21A zone, Eskay Creek, northwestern British Columbia.The correlation coefficient for each pair is listed inthe lower left half of each matrix. The number of pairsavailable for the calculation are indicated in the upper right half of each matrix. Correlation valuessignificantly different than zero at the 99.9% confidence level are highlighted in bold.undividedAu Ag Cu Pb Zn Ai Sb HgAu 3062 40 135 135 4 41) IlAg 0.424 40 135 135 4 40 11Cu0.45 0.54 40 40 4 40 8Pb 0449 0.138 0.320 135 4 40 8Zn 0084 0.243 0.582 0.070 4 40 8As -0.270 -0.075 0.647 -0.245 0.974 4 3Sb 0.268 0.213 0.251 0.080 0.225 0,647 8Hg -0.288 -0.262 0.046- 043 0.911 -0.068Basak ArgiWieAu Ag Cu Pb Zn As Sb Hg Au Ag Cu Pb Zn As Sb HgAu 2039 32 107 107 1 32 9 Au 1023 8 28 28 3 8 2Ag 0.430 32 107 107 1 32 9 Ag 0420 8 28 28 3 8 2Cu 0.849 0725 32 32 1 32 6 Cu 0.329 0.017 8 8 3 8 2Pb * ‘ 107 1 32 6 Pb 0.987 0.275 0.378 28 3 8 2Zn 0,253 0.312 G604 • 1 32 6 Zn -0.133 -0.056 0.556 -0.118 3 8 2As -- - -- I I As -0.554 -0.342 0.530 -0.469 0.999 3 20344: - 6 SbO.0220.4010.3780.1430.2100.530 - 2.11 b.e, for Pb wor, 0.00144by the use of scatter plots. Data from the 2 1A zone are strongly skewed, but scatter plots of all elements againstgold and silver for each unit are shown in Figures 4.13 to 4.18.The correlation results in the rhyolite and contact units suggest that gold has a better correlation witharsenic, antimony and mercury than with lead, zinc or copper (Tables 4.10 and 4.11, Figures 4.15 and 4.17).Silver suggests a better correlation with lead, zinc and copper than with the other elements (Tables 4.10 and 4.11,Figures 4.16 and 4.18). This trend is not clear in the footwall volcanic unit where silver correlates well witharsenic and antimony, although the concentration of these elements is low. Lead and zinc, and zinc and copperindicate strong correlation in all mineralized units.The vertical distribution of the elements within the rhyolite is shown in Figure 4.19. The depth of themidpoint of each assay interval within the rhyolite was calculated trigonometrically from the angle of the drillholeand the estimated average dip of the upper rhyolite surface (45°). Values of gold, silver, arsenic, antimony andmercury increase with proximity to the upper contact. In particular, anomalous values of antimony and mercuryare concentrated in the upper 50 metres of the rhyolite; arsenic is highest in the upper 25 metres. High values ofzinc, lead and copper are more erratically distributed, but are mainly concentrated in the upper 100 metres of therhyolite, though few samples were analyzed below 110 metres. The highest values of gold and silver within therhyolite occur in the upper 50 metres. However along the upper contact, high gold values are maintained, butsilver values decrease.The highest gold grades are associated with the stratabound suiphides on Section 0+00 and in theinunediately underlying rhyolite. High gold concentrations are also found in association with realgar veinletswithin the contact unit of CA89-043 (Section 1+OON). One zone of anomalous to high gold grades is locatedwithin the rhyolite on Section 1+OON, and is directly associated with massive chlorite to intense sencite alteredintervals. Section 0+00 and Section 1+OOS host very little gold-rich mineralization in the footwall units.A statistical summary of assays in the contact unit is presented in Table 4.4. These data are subdividedinto subunits reflecting massive, laminated, baritic, tuffaceous and chioritic argillite, as well as rhyolitic intervalswithin the contact unit and ‘transition’ argillite from the base of the contact unit. The highest values in Au, Ag,As, Sb, Hg and Cu within the contact unit are contained in the stratabound suiphides. Significant Au, Ag, Zn, Pband Cu are contained within the transition subunits, mainly reflecting the mineralized intervals on the northwestend of Section 1+OON.The distribution of silver in the 21A zone is similar to gold because the values generally increasestratigraphically upwards; but it does not follow gold exactly. Silver is associated with tetrahedrite (section 4.2.3),and is commonly disseminated in massive chlorite or in veinlets in the rhyolite. High concentrations of silveroccur locally in the contact unit in association with massive to bedded bante intervals on the northwest end ofSection 1+OON (Figure 2.1).1.0- 0.5 10 1.5Au (ez/ton)-.0.20.00 —0.00 0.50 1.00 1.50Au (oz/tofi)2.00 4.00 6.00 8.00 10.00Ag oz/1on)Figure 4.13: Scatter plots of arsenic and antimony vs. gold and silver in the footwall volcanic unit, EskayCreek 21A zone, northwestern British Columbia. Mercuiy data was unavailable. Circles areassays in volcanic rocks, rhombs are assays in sedimentaiy rocks. Assay values of theseelements are lower in this unit than in the overlying rhyolite and contact units. A significantpositive correlation occurs between Ag and As. Correlation is weak between Ag and Sb. (n= number of samples; r = correlation coefficient)145n 26r= 0.4701.00.80.60ao? a0.40.04.0 6.0Ag (oz/ton)0.06-0.040.02 00n 53r= 0474001 = 53r=0.5870.060.040 00.02 00.00—0.00146Ag (oz/ton) —‘-—-—--——J-—-050 1.00 [50 0.00Au (oz/ton)Ag (01/ton)Figure 4.14: Scatter plots of zinc, lead and copper vs. gold and silver in the footwall volcanic unit, EskayCreek 21A zone, northwestern British Columbia. Circles are assays in volcanic rocks,rhombs are assays in sedimentaiy rocks. Assay values of these elements are lower in thisunit than in the overlying rhyolite and contact units. Correlation among these elements ispoor. (n = number of samples; r = correlation coefficient)0 n=53r.0510lb’k, I0.5 1.0 15Au (oz/ton)o no53= 0.2690toDo0. 4.0 6.0 80Ag (oz/ton)øo0.4020.000c)n=53r=0.00300‘O—9e- 0 00 0.5 1.0 15Au (oz/ton)——-——,o 0 02.0 4.0 6.0 8.0 10.00=53r= 0.137 0=53r=0.2110c)0O 00.000.00100 4.00 6.00 8.00 10.0025. -0.0 0.5 1.0 15 2.0Au (oz/ton> 100.0 150.0 200.0Ag (az/ton)14710.0—,—— = 864r = 0.3580.00.0 50.0 100.0 150.0 200.0Ag (oz/ton)Figure 4.15: Scatter plots of arsenic, antimony and mercury vs. gold and silver in the rhyolite sequence,Eskay Creek 21A zone, northwestern British Columbia. Note that gold correlates slightlybetter with As and Sb than silver does. These appears to be a poor relationship withmercuiy. (n = number of samples; r = correlation coefficient)n209r=0A50ILI—.4 . 1*n = 209= -0.0410.0A I8. r0.0 —0.0 0.5 7.0 15 2.0A (az/tool Ag (az/ton)1 = 577=0.2130.0 ft5 1.0 1.5 2.0Au (az/ton>n = 577r=0.2800.60.50.403010.00.0 0515.0 r—’Figure 4.16: Scatter plots of zinc, lead and copper vs. gold and silver in the rhyolite sequence, EskayCreek 21A zone, northwestern British Columbia. Note that silver correlates better with theseelements than gold does. (n = number of samples; r = correlation coefficient)1480.00.0Io.0{. 1 ‘- 10.0ri = 866r=0.0428.08.06.0 6.00N4.0 402.0 2.0,0.0 L. . I0.0 0.5 1.0 1.5 2.0Au (oz/ton)1-5.0 I10,05.00.0—.-.- -, i-p0.0 0.5 1.0 1.5 2.050.0 100.0Ag (az/ton)150.0 200.0n = 866t=Q.0030N.0C, (az/ton)n 865T0.062n 8660,17010.0 r-I0.00.0 50.0 100.0 150.0 200.0Ag (az/ton)n = 865r=0.5970.60A0.20.0 50.0 100.0 150.0 200.0Ag (az/ton)001.0 IS 2.0An (oz/ton)14940.0 40.0n = 66r=O636 n=68r0.0.3030.0 30.0I820.0 20.010.0. 10.0 •0.0 • • 0.0: , •0.0 1.0 2.0 3.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0Au (oz/tou> Ag (oz/ton)60.0 60.0 In=153 n15350.0 r0.485 50.0• rO.67140.0 F 40.030.0 30.020.0 20.0I I10.0 • I • leo *: :0.0 I0.0 1.0 2.0 3.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0An (oz/ton) Ag loz/ton)3.0 3.0 i I In=134 n=134r=0.632 r=O.1542.0 • 2.08IS1.0 1.0SI* ISa0.0—-- I 0.00.0 1.0 2.0 3.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0Au (oz/ton) Ag (oz/ton)Figure 4.17: Scatter piots of arsenic, antimony and mercury vs. gold and silver in the contact unit, EskayCreek 21A zone, northwestern British Columbia. Solid dots are assays in the strataboundsuiphides. Open triangles are assays in the contact argillite. Gold shows a better correlationwith arsenic and mercury than silver does. Silver indicates a better correlation withantimony than gold does. (n = number of samples; r = correlation coefficient)150Nn = 160r = 0 7912.0151.0n= 160= 02971.5a1.0aa0.5 aa aa20a3.0Au (oz/to)CN0.50.00.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.01.5n = 160r=00761.0 aOSa—a0.0 ,. a0.0 1.0 2.0 3.0Au (oz/ton)0.4Ag (oz/ton)r=0.620*0.0 a0.0 10.0 20.0 30.0 400 50.0 60.0 70.0 80.0Ag (oi/ton)0.4n = 153r= 0.5a0.30.200.1aa.L a S0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0Ag (oz/ton) = 153= 0334Sa •aaa aaa —aa a1.0 2.0 3.0 80.0Au (oz/ton)Figure 4.18: Scatter plots of zinc, lead and copper vs. gold and silver in the contact unit, Eskay Creek21A zone, northwestern British Columbia. Solid dots are assays in the strataboundsuiphides. Open triangles are assays in the contact argillite. Silver has better correlationwith these elements than gold does. (n = number of samples; r = correlation coefficient)1510.0 50.0 100.0 150.0 200.0 0.0 2.0 4.0 6.0 80 10.0I- 0.00.0 r AA A AA AA A50.050.0A100.0 A 100.0 AA A0.0A150.0AOA.0200.0200.0.250.0I 250.0 I0.0 50.0 100.0 150.0 200.0 0.0 2.0 4.0 6.0 8.0 10.0Ag (oz/ton). Zn (%)0.0 5.0 [0.0 15.0 0.0 0.2 0.4 0.6 0.8 1.00.0 I I 0.0 I I —A AV 50.0 AA A 50.0 A AAr4-100.0A AA100.0 AA0.C150.0 150.0,0V200.0 200.0250.0 I I 250.0-____________________________________________0.0 5.0 10.0 15.0 0.0 0.2 0.4 0.6 0.8 1.0Pb (%) Cu (%)Figure 4.19 a): Vertical distribution of silver, zinc, lead and copper in the rhyolite sequence, EskayCreek 2 1A zone, northwestern British Columbia.UCIC00UUUFigure 4.19 b): Vertical disthbution of gold, arsenic, antimony and mercury in the rhyolite sequence,Eskay Creek 21A zone, northwestern British Columbia.15260 80 10.0-IEU0000U.0U0UUA1.0 1.5 2.0 0.0 2.0 4.0—I-.----- I I 0.0 FA AA50.0100.0150.0200.0250.01.0Au (oz/ton)1.5 2.0AAAAAA100.0A150.0200.0250.0- I0.0‘.50.0100.0150.0200.0250.0 I0.0 5.0 10.0 15.0As (%)5.0 10.0 15.0 20.0 25.00.0 2.0 4.0 6.0 8.0 10.0Sb (%)0.0 2 0.3 0.4 0;5 6100.0150.0200.0250.0-— f.0.0 0.1 0.2 0.3 0.4 0.5 0.6Hg (%)20.0 25.0153A statistical summaiy of assay data collected from the hanging wall unit is shown in Table 4.5. Thesedata mainly reflect the lack of significant mineralization within the basaltic package. Mean and median values forall elements are typically lower than in the other lithological units in the 21A zone. Elevated values are containedentirely within a few mineralized argillite intervals on Section 1+OON.The mineral assemblage, mode of occurrence and grade in mineralization varies both vertically andlaterally in the 2 1A zone. The styles of mineralization observed within each lithological unit, and the variationswithin this part of the Eskay Creek deposit, are described below.4.2 Distribution and style of mineralization4.2.1 Sedimentary and volcaniclastic unitNo significant gold, silver nor base metal mineralization has been identified in this unit in the 21A area.The sedimentary and volcanic rocks locally contain concentrations or laminae of fine grained pyrite.4.2.2 Footwall volcanic unitA stockwork of quartz - pyrite ± sphalerite ± galena ± chalcopyrite veins with dark grey, sericiticenvelopes is observed locally in drilicore (Plate 2.4) and on surface. This type of mineralization is sporadicallydistributed and not well represented in the driliholes selected for this study. Pyrite is commonly the most dominantsuiphide in these sulphide veins. One 11 metre core intersection of semi-massive sulphides occurs where pyriteveins are densely concentrated in the volcanic rock (CA89-052). More commonly, intersections of pyrite-rich corerange up to 4 metres. The best intersection of this style of mineralization (CA9O-426: 3 16.Om) is 1.5 metresgrading 39.1 grams gold per tonne (1.14 ounces per ton) and 144.7 grams silver per tonne (4.22 ounces per ton).More typical values are lower (Table 4.6). On surface, this style of mineralization is best exposed in the #5trenches and in the cliff face northeast of the #3 Bluff (Figure 2.5). Distribution of this style of mineralization inthe drillholes is discontinuous laterally.The highest assays are contained in semi-massive volcaniclastic and massive volcanic units within thefootwall volcanic unit; sedimentary and heterolithic volcaniclastic units contain generally low values (Table 4.2).Zinc reaches concentrations of 3.5% locally. The highest lead and copper values are 0.84% and 0.2 1%respectively. One anomalous arsenic value of 0.81% was encountered, but most values are less than 0.3%. Allantimony values are below 0.03%.The silver assays in the footwall are generally low, but correlate well with available arsenic analyses(Figure 4.14). A general correlation with low values of antimony is also indicated. Correlations between gold andsilver and the other elements are generally scattered to exclusive (Figures 4.13 and 4.14).1544.2.3 Rhyolite sequenceWithin the rhyolite sequence, gold and silver bearing mineralization occurs locally in a diffuse stockworkof veins and veinlets and with disseminated sulphides and sulphosalts. Grades generally increase towards the topof the rhyolite (Figure 4.19). Elevated grades are commonly associated with thin veinlets, zones of increasedsericitic and chioritic hydrothermal alteration, or zones of increased permeability such as breccias. Locallyhowever, significant precious metal values are associated with microscopic to submicroscopic disseminatedsulphides in silicified rhyolite with no macroscopically visible indication of mineralization.The sulphide assemblage within the rhyolite is dominated by sphalerite, galena, pyrite ± chalcopyrite inthe lower portions of the sequence. Arsenopyrite, stibnite, pyrite, tetrahedrite and lesser sphalerite areconcentrated towards the upper contact of the sequence. Chalcopyrite is rare, but where present, it occurs mainlyin the lower parts of the rhyolite in association with sphalerite and galena. The minerals are intimately intergrown(Plate 4.1) suggesting an equilibrium assemblage.The concentration of suiphide veinlets in the rhyolite is generally sparse, particularly in the lower portionsof the rhyolite. Veinlets range from hairline up to 3 centimetres wide (Plate 4.2). The larger veins are commonlyquartz-rich and locally vuggy. Within more intensely altered rhyolite, the sulphide veinlets locally become diffuseand poorly defined. Concentrations of disseminated suiphides anastomose through the rock generally inassociation with strong to intense sericitic to chloritic alteration (Plate 4.3). Elsewhere, the sulphides are evenlydisseminated to patchy throughout the altered rocks.Sphalerite is typically honey-yellow, but becomes reddish brown towards the base of the rhyolite. Thissuggests that the iron content in the sphalerite increases with depth. Sphalerite grains are commonly coarsergrained than associated galena and tetrahedrite (locally up to 3 millimetres across) and often have a rounded habit.Sphalerite occurs throughout the rhyolite sequence. Microprobe analyses of sphalerite by Barnett (1989) and D.L.Harris (Geological Survey of Canada, written communication, 1992) indicate up to 29 weight percent Hg insphalerite, commonly increasing in concentration from core to rim. The highest values of mercury in sphaleritewithin the 2 1A zone occur in the uppermost levels of the rhyolite, and in the contact unit.Arsenopyrite within the rhyolite occurs as euhedral, disseminated needles up to 3 millimetres long, inintensely sericitized rhyolite that is immediately underlies the contact unit (Figures 2.1 to 2.3, Plate 4.4). This iscommonly associated with fine grained disseminated stibnite.Veins and veinlets of massive fine grained stibnite occur locally at the top of the rhyolite, proximal to theapparently stratiform sulphides within the contact unit. The stibnite is hosted in intensely sericitized rhyoliteoccurring immediately underneath argillite of the contact unit. Generally, stibnite is disseminated witharsenopyrite in this area, but massive stibnite in this position occurs in CA89-02 1 (Figure 2.4, Plate 4.5). In thisJIcm-..-r,._:-.Plate4.1:Photomicrographof asuiphideveininrhyolite (CA-88-015:73.8,reflectedlight, 0.25mmfieldofview).Abbreviations:gigalena,si=sphalerite,it=tetrahedrite, cp=chalcopyrite, py=pyrite.Plate4.2:Sulphideveininrhyolite.Sphalente,galena,pyrite andminorchalcopyritebearingveininflowbandedtomottledsiliceousrhyolite(CA9O-466:260.4m).(Coreis4.5cmwide.)Plate4.3:otomicrographof sericite‘-suiphidemineralization.Theopaquemineralsarepyrite,tetrahedrite,galena,andsphalerite.(CAS8-015:73.8m,crossnicols,4mmfieldofview.)VPlate4.4:Randomlyorientedarsenopyrite needlesinintenselysericitizedrhyolite (CA89-28: 68.6m)--________—-0’-_-________,F___-,___-Plate4.6:Semi-massivesuiphidesnearthebaseofthestrataboundlensinthe21Azone.(a)Angularargilliteclastsinamatrixofrealgarandstibnite.Stibnite(grey)ispatchy.Cinnabar(darkred)occursmainlyinhairline veinletscuttingthesample.(CAS9-024:70.2m, coreis4.5cmwide.)(b)Photomicrographof samplein (a).Thematrixisdominatedbyrealgar.The darkpatchontheleftis asharplybounded stibniteclastcontaininginterstitial realgar,quartzand calcite.Thedarkpatchontherightisshale, cutbyaveinletofmuscovite.Theshaleclastisangularandsharplybounded.Theirregularblackpatchesmarginaltotheclastarestibnite.(Planelight,4mmfIeldofview.)157interval the stibnite is generally foliated and contains about 10% disseminated quartz and a few entrained andflattened clasts of argillite. Arsenopyrite occurs as needles and rhombs, up to 0.2 millimetres long, whichoverprint the stibmte (Plate 4.4). The needles are weakly aligned with foliation.Overall, the suiphides have a vertical zonation through the rhyolite sequence. Sphalerite, galena andtetrahedrite are more common lower in the sequence. In particular, chalcopyrite is rare and occurs mainly inveinlets near the base of the rhyolite. Towards the top of the rhyolite the dominant mineralogy changes toarsenopyrite and stibnite. Realgar and cinnabar are rare, and occur only locally as trace specks within quartz-calcite veinlets. This vertical variation in mineralogy is reflected in the distribution of assays, shown in Figure4.19. As described above, high concentrations of Ag, Zn, Pb and Cu occur to greater depth in the rhyolite than Au,As, Sb and Hg. The former metals occur within the upper 100 metres of the rhyolite. As, Sb and Hg are mainly inthe upper 50 to 25 metres of rhyolite.Metal correlations within the rhyolite (Table 4.10, Figures 4.15 and 4.16) suggest Au is better correlatedwith As and Sb than with Cu, Pb and Zn. Ag shows better correlation with Cu and Zn than with As and Sb.However, the plot of Sb vs. Ag is split into two trends. The vertical trend suggests no correlation between elevatedSb and Ag, however the lower trend has a shallow positive slope. These split trends may reflect the variablemineralogy within the rhyolite. The vertical trend probably reflects the presence of stibnite as the dominant Sbbearing suiphide. The lower, positive trend reflects silver carried in tetrahednte; this corroborated by thecorrelation of Cu and Ag. Silver in tetrahedrite was confirmed using electron dispersion spectrometiy (EDS) onthe SEM (Figure 4.20). This observation also is supported by microprobe analyses by Barnett (1989) that indicate4 to 36 percent silver content in tetrahednte; the average Ag content is approximately 13 percent. Barnett’sanalyses also indicate that the tetrahedrite is rich in Sb and has generally a low As content.4.2.4 Contact argilliteThe contact argillite unit in the 21A zone area hosts high grade, probable stratiform, sulphidemineralization in the same stratigraphic position as the 2 lB zone clastic sulphide-sulphosalt ore. However, themineralogy and textures of the 2 1A zone deposit differ significantly to the 2 lB ore. The bulk of the high gradegold within the contact shale in the 21A zone is associated with massive to semi-massive, fine grained stibnite -realgar ± cinnabar ± arsenopyrite ± pyrite ± native gold. This apparently stratiform lens of sulphides is spatiallyrestricted to an area 30 metres wide by 40 metres long on the eastern flank of a small sub-basin defined in section2.3.4. Massive sulphide mineralization was intersected in only seven drill holes in the 2 1A zone area; thedistribution of these drillholes is shown in Figure 4.21. The average thickness of the sulphide lens is about 6metres. Two of these holes were relogged in detail on Section 0+00 (CA89-023 and CA89-024; Figures 2.2).Other intersections in the apparently stratiform lens occur in CA88-006 (the discovery hole), CA88-009 andCA89-089. In CA89-018 and CA89-021 massive stibnite occurs in intensely sericitized rhyolite immediately158CA9O-465: 191.8m $CA9O-465: 191 .8m KPR’ S iI4 S 59SEC 6 HITUe4 K—I13KEU 1H AO—113KV Ut 14 ti1I(EU iiH AOuL6KEV 1KTETRAHEDRITE SPHALERITEZnS‘CuAg5Fe Cu S Fe Cu__kk.__________——XE 1.4IJ’CA89-023:61.2m TCA89-023:61.2mPI S 7$SEC 13 HIT PR S 295EC 13 HITV1134 KEU 11H AQj8I(EtJ U14 H—tKEV 1:1K AQ—113KEU INSTIBNITE CINNABARHSSSbJ pIi24UCA89-023:603m E CA89-018:51.Om !13! MES 65SEC 13 HIT 2OSEC 0 HITJt134 IIII3KEU 1’IN •tkEU IN Vf4 NkfV 11H AQ!13(EV INNATIVE ARSENICREALGAR AsAs sFigure 4.20: Electron dispersion spectra for typical sulphides in the Eskay Creek 21A zone, northwesternBritish Columbia. Note the significant silver peak in the tetrahedrite pattern and the lack ofan As peak. Sphalerite shows significant copper and iron peaks reflecting minutechalcopyrite inclusions.IrnIJ)CAB9—018narrow Intervalof moooiv. ofibnita CA89—021of lop of thyolfie ,,,ao,lv. otiboll. attop of rhyolito-250[-OOE —150E —lOGE—50ESOONScale I :3500159GE 50E I 50ECAS9—089150NlOON50NON—50N—lOON-150N—200N200N150NlOON50NON—50N—lOON—150N—200N—250E-200E —150E—WOE —50E GE 50E lOGE 150EFigure 4.21: Distribution of massive suiphide intersections in the 2 1A zone, Eskay Creek northwestern BritishColumbia. Massive suiphide intersections are projected to surface.160below the contact unit and contains minor entrained argillite. Precious metal mineralization also occurs inassociation with sulphide veinlets, fine grained disseminated sulphides and barite rich beds.Textures in the massive to semi-massive suiphide bodyThe massive to semi-massive, apparently stratiform stibnite-realgar mineralization in holes CA88-006,CA88-009, CA89-023 and CA89-024 is projected on Section 0+00 (Figure 2.4), and occurs on the western flank ofthe sub-basin, which is located along the ridge described in section 2.3.4 (Figure 2.9). The contact argillite thinsmarkedly to the west of the stibnite-realgar body and is generally unmineralized. To the southeast on Section 0+00(drill hole CA89-022), the stratigraphic equivalent of the contact unit contains argillite and intervals of coarsesedimentaiy rocks, including siltstone and wacke. Core recovery in the contact unit of CA89-022 was poor andrubbly, possibly due to influence from surface weathering; no significantly mineralized intervals were intersected.Textures within the stibnite-realgar body vary vertically (Figure 4.22, Plate 4.7). In general, realgar isdominant near the base of the sulphide lens and stibnite becomes dominant towards the top. Unfortunately, contactrelationships between these styles of mineralization were not observed due to the condition of the drill core andsampling by previous workers. Near the base, clasts of argillite are suspended in a realgar dominant matrix (Plates4.6 and 4.7). The argillite clasts are mainly angular to subangular and locally contain up to 2% framboidal tospheroidal pyrite, but do not contain other suiphide minerals. Microveins of realgar locally cut the argillite clasts.Stibnite occurs with the realgar as irregular interstitial fillings, and locally as sharply bounded patches(Plate 4.6b). These patches contain interstitial realgar and other gangue minerals including quartz, calcite,muscovite and barite and may themselves be reworked clasts. The concentration and size of argillite clastsgenerally decreases upward, with an associated increase in stibnite-nch patches (Plate 4.7). Locally, massivestibnite occurs in veins cross-cutting argillite and the argillite clast bearing mineralization (Plate 4.6b). In thinsection, the sulphides are fine grained (generally less than 50 microns across), intricately intergrown and annealed.In some samples (Plate 4.9), stibnite grains occur as rounded to irregular shapes in a realgar matrix. The texture isreminiscent of elastic deposition of stibnite grains cemented by realgar. However, this texture is not ubiquitous.Realgar is generally irregular and has a finely crackled appearance throughout in transmitted light. Thinrealgar veinlets are common. Where these veinlets cut stibnite, they are rimmed by a dark grey mineral. Electrondispersion spectrometry (EDS) and wave dispersion spectroscopy (WDS) indicate that this mineral consists mainlyof As and little S.Cinnabar is generally minor within semi-massive stibnite-realgar mineralization filling small intersticesand as blebs within stibnite. It occurs in the core of one stibnite vein cutting across the stratabound lens (Plate4.6b). It is more common along cross-cutting microveins and locally in minor amounts within realgar veinlets.These microveins also commonly contain opaque, non-reflective material, which is probably carbonaceous. Traceto 1% arsenopyrite is locally disseminated through the suiphides. The arsenopyrite occurs as well formed rhombsor elongate needles up to one millimetre in length. These grains are usually randomly distributed and overgrow161:4:• . . • . .• • S S S U •I * S • S S •I• •• S S S •• . S S S S SFigure 4.22: Detailed section through the apparently strntifonn suiphidelens in CA89-023, Eskay Creek21A zone, northwestern British Columbia. Realgar generally decreases upwards as stibniteincreases. The abundance of argillite clasts decreases towards the top of the lens.CA89-0231)01)) -0V57 I SHALE- friable- contains 5% calcite veinlets with stibnite, realgarand cinnabar. -CHERTY ARGILLTE- thin, irregular pyrite laminae- minor porphyroblasts- minor calcite veining with realgar- cinnabar- very fine grained disseminated stibnite - arsenopyrite605859 ——6261MASSIVE STIBNITE - REALGAR (see Plate 4.7d)- foliated at 80 degrees to core axis- about 5 - 10% entrained, flattened argillite clasts- 1-3% disseminated arsenopyrite needles- minor cinnabarEi-lALE - massive, realgar veinlets, dissem. stibnitne, cinnabarSEMI-MASSIVE REALGAR-STIBNITE- Argillite clasts in a realgar and stibnite-rich matrix.- Cut by thin stibnite veinlets.Mottled rhyolitic interval cut by irregular veinlets of realgar,cinnabar, minor stibnite and black, carbonaceousmaterial. (see Plate 4.7c)SEMI-MASSIVE REALGAR-STIBNITEArgillite clasts in a realgar-stibnite rich matrix. Clasts arevariably deformed and flattened. Stibnite occurs as apparentclasts and in cross-cutting veins, locally cored by cinnabar (seePlate 4.7b).SHALE - tuffaceous?, medium grey, quartz-realgar/cinnabar veinletsSEMI-MASSIVE REALGAR-STIBNITE- (see Plate 4.7a)INTENSELY SERICITIZED RHYOLITE- cut by quartz veinlets containing carbonaceous materialand minor cinnabar, realgar and stibnite.- up to 10% very fine grained, disseminated stibnite-arsenopyrite(as in Plate 4.4)63646566INTENSELY SERICITIZED RHYOLITE- progressively decreasing disseminated arsenopyrite- stibnitedownhole.Plate 4.7: Vertical variations in the stratabound lens, Eskay Creek 21A zone, represented in CAS9-023. (a) Angular tosubrounded argillite clasts in a realgar and stibnite rich matrix. (64.4 m) (b) Similar to (a). Cut by stibnite vein whichis cored by cinnabar. (63.0 m) (c) Thin interval of intensely altered rhyolitic rock cut by anastomosing realgar andcinnabar veinlets. Realgar is disseminated throughout. (61.4 m) (d) Banded stibnite and realgar with minor patchesof argillite. Banding is probably due to foliation. (58.9m) (Cores are NQ.)162LLaLL—:_12CA89-23163Plate 4.10: Gold in apparently stratiform sulphides. (a) Rare visible gold in patchy stibnite - realgar (CAS9-024:69.2m, core is NQ). (b) Photomicrograph of gold in stibnite with associated realgar. Dark grey gangue ismuscovite with framboidal pyrite. (CA89-024: 70.2m, reflected light, 0.25 mm field of view.) au = gold; at =stibnite; re = realgar.te4.8:j—----r---—--pynte (pale yellow) in stibnite (grey) near a shale clast(black). (CAS9.023: 59.9m, reflected light, 0.25 mm fieldof view.)Plate 4.9: Photomicrograph of stibnite (light grey) in arealgar matrix (grey) with minor calcite (daiic grey).(CA89-023: 70.2m, reflected light, 1.2mm field of view.)164the surrounding suiphides. In foliated sulphides, arsenopyrite needles are aligned parallel to the fabric. Tracesphalerite occurs locally as tiny (less than 25 microns), irregular, embayed patches within massive stibmte. EDSstudy of this sphalerite indicates a significant mercury peak. This is supported by microprobe studies conducted byBarnett (1989) that indicated between 25 and 35% Hg in the sphalerite within these mineralized intervals.Framboidal and spheroidal pynte is common within the argillite clasts, and is locally disseminated instibmte-realgar proximal to the clasts (Plate 4.8). Euhedral pyrite disseminated in stibmte occurs locally.Rare specks of visible gold have been observed in these stibnite-realgar rich intervals (CA89-024: 69.2m;Plate 4.10). The gold occurs as irregular grains up to 300 microns across in close association with both stibmteand realgar (Plate 4. lOb). The gold does not occur in association with a specific mineral. It was observed instibnite, realgar and muscovite. Wave dispersion spectrometiy indicates that the gold contains some silver andtrace mercury. Barnett (1989) detected 9.55 wt% Ag and 5% Hg from a similar grain in CA88-009.The stibnite-realgar mineralization contains 5 to 25% disseminated gangue minerals. Within massivestibnite, quartz is common. The quartz occurs as isolated, irregular grains, up to 250 microns across, disseminatedthroughout the stibnite. Within realgar-stibnite mineralization, the gangue minerals commonly include quartz,calcite, barite, muscovite and minor potassium feldspar. The sulphides commonly form inclusions within thegangue minerals or intricate intergrowths. The gangue minerals occur as isolated grains, clustered together withinthe sulphides. Calcite is commonly euhedral and may contain inclusions of realgar. Barite occurs as bundles ofradiating blades, commonly associated with quartz and calcite (Plate 4.14). Muscovite is common and occurs asdistinctive, highly birefringent, radiating sheaths within realgar and associated with other gangue minerals (Plate4.13). Electron dispersion spectra indicate a small Ba peak associated with this muscovite. Barnett (1989)conducted microprobe studies on this mineral and determined that it locally has a remarkably high barium contentranging between 0.02 and 2.91 weight % BaO. He noted that the barium content of the muscovite was correlativewith the gold content corresponding to the assay intervals from which they were collected. Potassium feldspar israre, and occurs locally in association with the barium-rich muscovite.Argillite overlying massive to semi-massive suiphide mineralization contains up to 10% very fine graineddisseminated stibnite and arsenopyrite; the sulphide content gradually diminishes over 3 to 8 metres above thesulphides. The sulphide rich interval, and the argillite immediately overlying the semi-massive sulphides, is crosscut locally by veinlets of realgar-cinnabar-calcite. These veinlets have locally been stretched and deformed.Arsenic and antimony rich mineralization occurs locally within the contact argillite away from the areaimmediately surrounding the semi-massive mineralization. In the eastern-most hole on Section 1+OON (drill holeCA89-43; Figure 2.1), veinlets containing realgar and cinnabar with calcite selvages cut the contact shale and areassociated with significant grades (Plate 4.11). Assays in this one metre interval reach 2.45 oz Au/ton, 7.8 ozAu/ton Ag, 13.25% As, 1.10% Sb, 1.5% Hg, 0.2 % Zn, 0,03% Cu and 0.02% Pb. In Section 1+OOS, arsenopyrite165Plate 4.13: Gangue minerals in realgar. stibnite mineralization:radiating barium-rich muscovite sheaths in potassium tldspar.(CA89-023: 60.3m; cross nicols, 0.5 mm field of view.)4.11CA8943: .L_____-----—Plate 4.11: Realgar - calcite - cinnabar veins in laminated to chertycontact argillite. (CA89-043: 100. Im; sample is 3 cm wide.)Plate 4.12: Realgar in quartz. Quartz is annealed but contains relictcolloform textures, commonly defmed by realgar inclusions. Thesetextures are observed in rhyolitic intervals within the contact unit.(CA89-018: 51.5m; plane light, 0.5 mm field of view.)Plate 4.14: Gangue minerals in realgar-stibnite mineralization:bladed barite. (CA89-023: 61.2m; cross nicols, 4 mm field ofview.)Plate 4.15: Base metal rich mineralization in the contact unitSphalerite - galena - pyrite chalcopyrite occur locally in brecciatedargillite matrix or as veins in silicified argillite. (CA89-066: 1 16.7m(left) and 1 14.7ni (right); scale is in centimetres.)Plate 4.16: Barite mineralization in the contact unit. On the left(CA9O-464: 135.lm) massive barite, with minor calcite, is cut byanastomosing pyritic veinlets. On the right (CA9O-465: 148.7m):beds of recrystallized, bladed barite. (Scale is in centimetres.)Plate 4.17: Mineralization in hanging wall argillite. (a) Weakly bedded sphalerite, galena and pyrite in argillite. Thisbed locally contains angular clasts of basalt. (b) Photomicrograph of (a). Round sphalerite grains are rimmed byquartz with interstitial galena and pyrite (plane light, 4mm field of view).167needles occur in sericitic rhyolite tuff that occurs within the contact shale sequence in hole CA89-037. Thisarsenopyrite is associated with minor sphalerite and elevated gold values.Thin, siliceous to sericitic rhyolitic intervals occur locally within this mineralization (e.g. CA89-023:61.4m, (Plate 4.7c) and CA89-018: 51.5m (Plate 4.12)). These intervals consist mainly of annealed quartz withminor calcite, barite and potassium feldspar. Thin, irregular veinlets of realgar-calcite-cinnabar and minorassociated arsenopyrite anastomose through the rock. Native arsenic occurs locally adjacent to the realgar veinlets.Fine grained disseminated realgar and lesser cinnabar are also disseminated interstitially between quartz, bariteand calcite grains, as well as entrained as solid inclusions within them. This imparts an overall orange to purplishhue to the rock. Solid inclusions within the gangue minerals are commonly aligned in straight lines that mayreflect annealing along secondary microfractures. Locally relict colloform textures are observed in the annealedquartz (Plate 4.12). Locally these textures are defined by inclusions of realgar.The distribution of assay values in the apparently stratiform suiphides of CA89-023 and -024 and theimmediately surrounding rocks are shown in Figure 4.23. The highest Au, As, Sb and Hg values occur within thestratiform sulphide lens. Gold values reach 2.72 ounces per ton. As concentration reaches 36.5%, and Sb as muchas 51.7%; these values are equivalent to 25% realgar and 37% stibnite respectively. Au and As progressively dropoff in the argillite overlying the semi-massive suiphides reflecting decreasing concentration of disseminatedarsenopyrite. Gold values also decrease progressively and are associated in the intensely altered rhyolite below thesemi-massive sulphides with disseminated arsenopyrite and stibnite. Silver is elevated within the semi-massivesulphides, and reaches 70 ounces per ton in the stibnite-rich portions of CA89-023. Silver is higher in theintensely altered rhyolite underlying the massive sulphides where it is associated with zinc, lead and copper richmineralization in the form of microscopic sphalerite, galena and tetrahedrite.Base metal suiphides in the contact unitSphalerite, galena, chalcopyrite and tetrahedrite rich suiphide intervals occur locally in the contact unit.This type of mineralization was intersected in holes on Section 1+OON (Figure 2.1) and in hole CA89-066 onSection 0+50N (Appendix A). The sulphides occur as veins in and as the matrix to brecciated argillite (Plate4.15).Mineralization associated with bariteA small zone of barite rich beds and massive barite intervals occurs in the northernmost corner of the 21Amap area on Section 1+OON (Figure 2.1; Plate 4.16). This type of mineralization is restricted to four driliholes:CA9O-428, -429, -464 and -465. The baritic intervals include massive barite consisting of radiating blades ofrecrystallized barite with minor calcite and quartz. Approximately 1% fine grained pyrite and tetraliedrite aredisseminated throughout and locally are concentrated along hairline microveins. These massive barite beds are upto 50 centimetres thick and are hosted in bedded contact argillite. Surrounding the massive barite intervals, theC89—O23bsoatogiUiteIsericftictff7_______________________________crgfttvteL LFStrotsLphdesnSSivEchoriter1iyoute,cor3petent0IZ0IXr-10,,AgPbZnAsoot00.5X01XIIX030Pr—r—,r---—-,zSbHg____________________________X010XCA89—024opt9.10,,intenselysericitizedrhyoUte±00.5Z30X30X010ZIbasoitIorgitt;teL_____________=p::::::::.________.:....:::Strcot,st.lphIdes1ntenselysericitizedrhyoliterhyolitebreccioI3IIIFigure4.23:Assaydistributionaroundapparentlystratiformsulphidesinthe21Azone,EskayCreek,northwesternBritishColumbia.Goldvaluesarehighestinthesemi-massivesuiphidesinbothholes.Valuesdecreaseoneithersideof thelenswithdecreasingarsenic(arsenopyrite)andantimony(stibnite).SilverishigherinCA89-023andismainlyconcentratednearthetopofthesuiphidelensandinintenselysericitizedrhyolitebelowthelens..169argillite locally contains up to 50% randomly oriented barite laths up to 15 millimetres long, in beds up to 20centimetres thick.Stratigraphically the baritic interval is located in the upper half of the contact unit. This barite rich zoneis silver rich with low associated gold content. Silver assays range up to 37.5 oz/ton over one metre, with less than0.066 oz Au/ton. The maximum thickness of the zone is approximately 3 metres.4.2.5 Hanging wall basalt and argilliteThe hanging wall basalt and argillite package is umnineralized, with the exception of three intersectionson Section 1+OON (Figure 2.1). These intervals are separated from the contact unit by a crystalline, locallyamygdaloidal basaltic sill or flow that is 10 metres thick. Mineralization within the hanging wall argillite isassociated with sphalerite, pyrite, galena, chalcopyrite and tetraliedrite.Weakly bedded, mineralization in hole CA9O-466 (Plate 4.17) is within argillite that grades uphole into aheterolithic debris flow of argillite and basaltic fragments. This mineralized interval is about 50 centimetres thick.Reddish brown sphalerite is the dominant sulphide, reaching 40% of the rock locally. The sphalerite grains tend tobe rounded, average about 3 millimetres across, and are commonly rimmed by white quartz, or less commonly, bypyrite or galena. Thin beds 10 to 20 centimetres above the mineralization contain up to 20%, medium grainedbladed barite. In the adjacent hole (CA9O-429) sulphides are finely disseminated in thin beds over 20 centimetres,within argillite at the same stratigraphic interval. The mineralogy of these sulphides includes pyrite, sphaleriteand minor disseminated arsenopyrite. The mineralized interval in hole CA9O-464 is associated with brecciatedshale and basalt containing disseminated pyrite and minor sphalerite in the matrix.4.3 Sulphur isotopesSulphur isotopes were measured in ten sulphide and two barite samples collected from mineralization onSection 1+OON in the 21A zone, The sulphide samples include realgar, stibnite, cinnabar, galena, sphalerite andpyrite from the contact unit, pyrite and sphalerite from massive chlorite, pyrite from the footwall volcanic unit andstibnite from a quartz veinlet near the top of the rhyolite unit. Sample descriptions and results are listed in Table4.13 and plotted in Figure 4.24. The sulphides were separated by hand picking.The 834S values in the base metal sulphides are close to zero. The lightest 634S value measured is-l.44%o in pyrite from the top of the footwall volcanic unit. Sphalerite and pyrite sampled from a massive chloriteinterval (CA89-023: 81 .7m) measured -0.67%o and -0.83%o respectively. Pyrite preferentially fractionates scompared to sphalerite (Bachinski, 1969), thus the pyrite is not in equilibrium because it is lighter than sphalerite.Similarly, sphalerite and galena collected at the base of the contact argillite on Section 1+OON (CA9O-465:145. im) have 834S values of -0.04%o and 0.85%o respectively. Under equilibrium conditions, sphalerite170Table 4.13: Sulphur isotopes measured in the Eskay Creek 21A zone. Analyses wererun by Dr. R. Krause at the University of Calgary.Mineral Host DDH Depth (m) del 34S DescriptionBarite Contact argillite CA9O-465 148.7 23.68 Bladed barite in shale.Bante Contact arilhte CA9O-465 1351 2270 MassivebariteCinnabar Contact argillite CA89-023 60.3 6.77 Dark red to black colour.1.96 Samplemixedwith 10-20%ye 4•37Irealar.Realgar Contact argillite CA89-023 60.3 6.75 From massive suiphide with minorfragmentsCinnabar Contact argillite CA89-043 101.1 12.23 From vein in sericitic rhyolite.I 1.38 Contains about 25% realgar.Avera 1.80Stibmte Contact argillite CA89-023 59.9- 1.39 Massive stibnite in strataboundStibnite Quartz vein CA89-024 102.3 l.46 From quartz vein in rhyolite. Needlesto blebs.Galena Contact argillite CA9O-465 145.1 0.85 From an irregular sulphide vein inSphalerite Contact argillite CA89-465 145.1 -0.04 From an irregular sulphide vein in4•ç4tePyrite Massive chlorite CA89-23 81.7 -0.83! Disseminated in massive, waxychloriteSphalerite Massive chlorite CA89-23 81.7 -0.67 Disseminated in massive, waxy! chloritePyrite Footwall volcanic unit CA89-44 174.5 : -1.44 From semi-massive pyrite at the top ofj the footwall volcanic unitBarite25.Cinnabar &20realgar Sphalerite -1 5 Stibnite galena pair Sphalerite; Pyrite in(7) pyrite pair (.) footwallci) 10UC)01--.-....I_._-•.- I-5 .1.a in 0 0 0 N C) in in ——j< ‘)< (DW 100 Q_ j)_. ..J _l .J a)>- r’>-m — - ‘-(1) Cl) ‘-0 U) (I) Q —0L) L c’ in in CoCO CD N N N N CO CD N NMineralsFigure 4.24: Sulphur isotope values in the Eskay Creek 21A zone. Data are from Table 4.13. Pyrite,sphalerite, galena and stibnite are close to O%o, but cinnabar and realgar are notably heavier.171preferentially fractionates 34S and would be heavier than galena. Without an equilibrium pair, estimates oftemperature cannot be made. Stibnite was sampled from a quartz vein near the top of the rhyolite and frommassive suiphides in the apparently stratiform lens (Table 4.13). Their 34S values are similar: 1.46%o and1.3 9%o respectively.The sulphur isotope data are inconclusive. Based on fractionation curves summarized by Field andFifarek (1985), 34S values in H2S around 0%o are consistent with fractionation by reduction from sea watersulphate between 200 and 300°C. Sea water sulphate in the Jurassic typically fluctuated around 17%o (Faure,1986). However, sulphur from magmatic sources is also typically around O%o.The 634Svalues in realgar and cinnabar are interesting because they are slightly heavier than the othersuiphides. Normally, cinnabar, fonned from H2S, has a negative fractionation coefficient resulting in sulphide thatis lighter than the source (Field and Fifarek, 1985); sphalerite and pyrite have positive coefficients, and stibmteand galena are similar to cinnabar (data for realgar are not available). Therefore the heavy isotopic signature inthe cinnabar (and possibly the associated realgar) suggests that cinnabar formed from a more isotopicafly heaviersource than the other sulphides.4.4 Summary and discussionThe important features of the mineralization in the 21A zone are summarized below and in Figure 4.25.Individual features and the relationships among them must be accounted for in any model for the 21A zone.A vertical metal zonation was observed in the 21A zone: pyrite and base metal rich suiphides aredominant near the base of the rhyolite and zone upward to antimony - arsenic - mercury sulphides in the top of therhyolite and in the contact unit. Pyrite - sphalerite - galena ± chalcopyrite occur in the footwall volcanic unit. Inthe overlying rhyolite, the mineral assemblage is dominated by sphalerite - galena - pyrite- tetrahedrite ± minorchalcopyrite near the base of the felsic sequence. The prevalence of these minerals generally decreases towards thetop of the rhyolite sequence where mineralization is dominated by arsenopyrite - stibnite - tetrahednte - pyrite ±sphalerite ± galena. In the semi-massive sulphides at the base of the contact unit, the mineral assemblage isdominated by realgar and stibmte with lesser cinnabar and arsenopyrite. Upward zoning sequences, from Fe to Fe-Cu to Cu-Pb-Zn to Pb-Zn-Ba, are recognized in most volcanic hosted massive sulphide (VHMS) deposits(summarized by Large, 1992). Zoning in the 2 1A zone is mineralogically more typical of epithermal stylemineralization.Sphalerite- galena - pyrite ± tetrahedrite ± chalcopyrite occur locally in the contact unit, in veins or asmatrix to argillite breccia. Such intersections were observed in holes CA89-050 and CA9O-427 on Section 1+OONand in CA89-066 on Section 0+50N. The mineralogy and location of these intersections,-(D(DOw...000IIit’<(ft173near the north end of the 21A zone, suggest that this base metal rich mineralization in the contact argillite may berelated to the 21B zone. Barite rich beds were also intersected on Section 1+OON, mainly in the upper part of thecontact unit.The semi-massive suiphide lens is deposited on the western flank of a sub-basin, described in section2.3.4. The stratigraphic position of the lens near the base of the contact argillite on Section 0+00 suggests it maybe stratiform, However the detailed mechanism of deposition of the stratabound suiphides in the 2 1A zone remainsenigmatic. The presence of angular argillite clasts and subangular patches of stibnite supported in a matrix ofrealgar-stibnite near the base of the sulphide lens may be explained by two possible mechanisms: (i) the argillitefragments may have been clastically deposited in a basin, or (ii) fragmentation may have resulted from localizedhydrothermal brecciation and precipitation of realgar and stibmte in the matrix. Textural evidence for bothmechanical deposition and brecciation with matrix replacement are present.One possible model to explain both these textural features is as follows.(1) Sediments accumulated into a small sub-basin, possibly controlled by a growth fault, on top ofrhyolite.(2) Fluids, migrating up fracture conduits in the rhyolite, discharged on the margin of this sub-basin.(3) Massive stibnite ± realgar precipitated at the discharge site.(4) Sphalerite, galena, tetrahedrite and pyrite precipitated in the stockwork in the rhyolite footwall.(5) As precipitation of the suiphides progressed, the fluid conduits became constricted and eventuallysealed.(6) Hydrothermal fluid pressure increased and eventually exceeded the confining pressure of the seal,causing the sulphides and sediments to shatter and brecciate, perhaps explosively.(7) On the steepened flank of a basin, the brecciated material was reworked by slumping. Thisprocess may have been repeated, resulting in a small clastic mound on the sea floor.(8) Fluids continued to percolate through the mound, causing further deposition of realgar, cinnabarand stibnite, possibly some replacement, and perhaps subsequently, cross-cutting veinlets of theseminerals.(9) Disseminated sulphides were deposited in the overlying sediments from metalliferoushydrothermal fluids that continued to discharge simultaneously with sediment accumulation inthe basin.Arsenic-antimony minerals, such as those in the 21A zone, are not normally major components insyngenetic massive sulphide deposits. Although these minerals are largely restricted to the contact argillite,textural characteristics are ambiguous. Massive stibnite replaces other sulphides in parts of the Eskay Creekdeposits, thus formation of the massive stibnite - realgar lens by replacement cannot be ruled out in the 21A zone.Arsenopyrite appears to overprint the sulphide assemblage and may have formed later, perhaps during the waningstages of the hydrothermal system, or during metamorphism. Gold-bearing realgar - calcite veinlets cross-cut the174suiphides and extend into the surrounding argillite. Locally the veinlets follow tension cracks (Plate 4.11) thatmay be related to deformation. These veinlets would suggest at least some late remobilization of arsenic, mercuryand gold.In spite of textural complications, there is reasonable evidence to suggest that the stibnite - realgar -cinnabar formed, at least in part, as a primary assemblage on or close to the sea floor. Absence of thermodynamicdata for arsenic and antimony complexes precludes detailed investigation of the conditions necessary to precipitatethese sulphides (Henley and Brown, 1985; Ballantyne and Moore, 1988). However, observations in moderngeothermal systems such as Broadlands, suggests that precipitation of As and Sb suiphides may be pH controlled(Henley and Brown, 1985). Solubility of orpiment decreases abruptly below a pH of 4 (Ballantyne and Moore,1988). Limited fluid inclusion data in the 21A zone, place temperatures in quartz from the apparently stratiformsuiphides at about 200°C (Baldwin, 1993). The mineralogy, and the implied low temperature of depostion, suggestthat the system may have formed in relatively shallow water, In shallow water, boiling and hydrothermalbrecciation are likely to occur as previously suggested based on textural evidence.1755. DISCUSSION AND CONCLUSIONSThe Eskay Creek 21A zone is an unusual deposit with respect to its mineralogy and texturalcharacteristics. The stratigraphy of the deposit, from oldest to youngest, consists of:(1) lower sedimentary unit,(2) footwall volcanic unit,(3) rhyolite sequence,(4) contact argillite unit, and(5) basalt and intercalated argillite and turbidites.These rocks were deposited in a marine environment. The rhyolite package is part of a linear series of domes,apparently generated in an extensional rift environment (Bartsch, 1993). The geochemistry of the overlyingbasaltic volcanic package has an enriched MORB signature that is consistent with development in a back-arc riftenvironment. The depth at which these units were deposited is not well constrained. The footwall sedimentaryrocks appear to have fonned in a relatively shallow environment, as suggested by the presence of abundant silt andwacke and relatively shallow water fossils such as bivalves. The contact argillite unit appears to have formed in adeeper or more quiescent environment than the lower sedimentary rocks. The contact unit contains mainlyradiolaria, dinocysts, belemnites and ammonites. Preliminary comparisons of radiolaria in the contact unit withthose in the footwall sediments suggests that the contact sediments contain species of deeper origin (Nadaradju,1993).Contact relationships and internal textures in the rhyolite under the 2 1A zone indicate both intrusive andextrusive characteristics. The lack of phenocrysts and abundant devitrification textures suggest that the rhyolitewas probably emplaced as a glassy unit. The rhyolite has been pervasively affected by devitrification andprogressive hydrothermal alteration.Lack of significant hydrothermal alteration in the hanging wall basalt package suggests it was not presentat the time of peak hydrothermal activity in the footwall rhyolite. However, fossil evidence (Nadaradju, 1993) andpossible intercalation of felsic and mafic volcanism suggest that basaltic volcanism closely followed felsicvolcanism and may have overlapped locally in time and space.The rhyolite is cut by a diffuse, stockworked chiontic pipe which directly underlies semi-massive,probable stratiform mineralization within the contact unit. The pipe consists of Mg-chlorite in the core of thealteration, grading outward to sericite + quartz and subsequently quartz + sericite ± potassium feldspar.Progressive alteration and the associated reactions are discussed in section 3.5. This zonational alteration patternis common in numerous volcanic hosted massive sulphide (VHMS) deposits (e.g. Noranda, Quebec; Hellyer,Teutonic Bore, Mount Morgan and Balcooma, Australia; Franklin, 1990; Large, 1992). The sericite in the 2 1A176zone apparently consists entirely of illite without significant interstratified expandible clays. This homogenaeitymay reflect the small sampling area of the 2 1A zone, as most VBMS deposits contain a zonation of clays thatgrade to lower temperature kaolinite in the outermost shell of the alteration (cf Kuroko-type deposits, Large,1992). The determination of a zonal distribution to the clay minerals can provide a good exploration parameter toestimate proximity to the core of the system.Mineralization in the 2 1A zone consists of a small, semi-massive, probably stratiform, stibmte-realgarrich lens in a small sub-basin underlain by stockwork and disseminated sulphides related to the chlorite pipe.Textures within the semi-massive suiphide lens remain enigmatic. Veinlets dominated by realgar or stibnitemineral assemblages cut one another, presumably reflecting variations in the local conditions of deposition.Angular to subrounded fragments of argillite supported in a matrix of realgar, particularly near the base of thelens, suggest a clastic depositional mechanism. This is locally supported by the presence of sharply bounded toangular patches, or clasts, of stibnite with entrained gangue minerals and interstitial realgar. These textures mayhave formed as the result of single or multiple explosive brecciation events, which resulted in a broken mound onthe sea floor, that was perhaps partially reworked (see section 4.4).The Eskay Creek 21A zone has several features that are typical of syngenetic VHMS deposits. Theseinclude: (i) association with rhyolite domes, (ii) relationship to synvolcanic faults, (iii) deposition in basins, (iv)overlying mafic volcanics, (v) chlorite - sericite alteration in the footwall to the ore. However, the precious metalgrade and mineralogy are unusual for a typical VHMS environment. There are two modem analogues, in differingenvironments, whose characteristics overlap with those of the 21A zone: the modern geothermal systems of thevolcano Osorezan, Japan, (Izawa and Aoki, 1991; Aoki, 1991), and the Jade hydrothermal field in the OkinawaTrough back-arc basin (Halbach eta!., 1989; Sakai et a!.,1990; Urabe and Marumo, 1991).Osorezan is a hydrothermal system discharging in a subaerial caldera lake of a composite volcano in thenorthern Honshu arc, Japan. It is unusual among hot springs because of its surprisingly high metal concentration,its polymetallic nature, and its zonation in mineral precipitation over short time intervals. The hot spring fluidssampled at Osorezan are markedly enriched in gold and mercury relative to waters from other hydrothermaldistricts. Concentrations in precipitates from the geothermal waters range up to 6 510 ppm Au, 5 520 ppm Hg,0.37% As and 0.10% Sb (Izawa and Aoki, 1991). Precipitation of minerals changed progressively with time asfollows: (i) Pb and Zn sulphides, (ii) Au and Hg tellurides, Pb-Sb and Pb-As sulphides, (iii) As-suiphide (orpimentand realgar), (iv) Hg-sulphide, and (v) sulphur. This progression is reflected in a concentric zonation marked byperipheral Pb-Zn and a central, overprinting As-sulphide zone formed in hydrothermal eruption craters less than100 metres across (Izawa and Aoki, 1991). The system is partially subaqueous although dominated by meteroricwater rather than seawater. Magmatic fluids may represent an important component in the system.The Jade hydrothermal field occurs on the slope of a caldera-like cauldron within an active back-arcbasin, in the Okinawa Trough (Halbach eta!., 1989). Unlike most submarine hydrothermal systems that have been177described, Jade is associated with dacitic volcanism and the formation of domes. Active and inactive suiphidesulphate chiiimeys and mounds occur at a depth of 1 300 to 1 550 m below sea level (Sakai et al., 1990). Mineralsin massive suiphides from the outer portion of chimney stacks include barite, realgar, orpiment, amorphous silica,thin coatings of hydrous iron- manganese nxides, sphalerite, Ag-bearing galena and pyrite. Within thehydrothermally altered rhyolite hosting the mounds, thin stockwork fracture fillings of sphalerite, Ag- and Sb-bearing tennantite, galena, enargite, and lesser pyrite and chalcopyrite are found (Flalbach et a!., 1989).The mineralogy of the 2 1A zone at Eskay Creek shows distinct similarities to the Osorezan and Jadesystems. Both systems have precipitated realgar, but in entirely different environments and water depths. Verticalprogression from sphalerite, galena and tetrahedrite in the footwall rhyolite to realgar mineralization within theargillite of the contact unit shows similarities to the mineral distribution at Jade. Vertical metal distribution atOsorezan is untested, but lateral changes are similar to the sulphide distribution between the 2 1A and 2 lB zones.Eskay Creek, Jade and Osorezan are all associated with subaqueous sedimentation. Osorezan isassociated with lacustrine deposits within a shallow crater lake, but Jade is submarine within the Okinawa Trough,a rifled arc. Eskay Creek argillites contain fossils such as belemnites and radiolaria indicating a marineenvironment. The occurrence of realgar in the sulphide mounds at 1 300 m depth at Jade indicates that this type ofmineralization is not necessarily restricted to very shallow water environments.The Eskay Creek 21A zone formed in a submarine environment. The presence of Mg-rich chlorite in thealteration assemblage may suggest a sea water component to the mineralizing fluids, as proposed for similaralteration zones in VHMS deposits (cf Franklin, 1990). A component of other fluids may also have been present.Bartsch (1993) documented high temperature alteration in the rhyolite and suggested that magmatic fluids mayhave contributed to the mineralizing system. Magmatic fluids have also been inferred at Osorezan (Isawa andAoki, 1991) and Jade (Urabe and Marumo, 1991).Interpretation of the depositional environment for the Eskay Creek ore body must incorporate observationsfrom the entire area. This study was focused on only a very small part of the Eskay Creek deposit. The bulk of themetal resources are contained in the 2 lB zone, just 100 metres north of the 2 1A map area, that consist of sheets ofclastic suiphides and sulphosalts. Future research to determine the origin and depositional processes of thesesulphide clasts will further the understanding of the overall depositional environment. Chemical modelling of theore mineralogy, using thermodynamic modelling programs such as CHILLER and PCPA TH, will help to constrainthe nature of the mineralizing fluids. Further work of this kind will provide insight into this unusual deposit and amodel to assist in the discovery of others of its kind.178REFERENCESAlidrick, D.J. (1989): Volcanic Centres in the Stewart Complex; in Geological Fieldwork 1988, British ColumbiaMinistry ofEnergy, Mines and Petroleum Resources, pp. 23 3-240.Alldrick, D.J, and Britton, J.M. (1988): Geology and Mineral Deposits of the Sulphurets Area; British ColumbiaMinistry ofEnergy, Mines and Petroleum Resources, Open File 1988-4.Alidrick, D.J., Gabites, J.E. and Godwin, C.I. (1987): Lead Isotope Data from the Stewart Mining Camp (104B);in Geological Fieldwork 1986, British Columbia Ministry of Energy, Mines and Petroleum Resources, Paper1987-1, pp. 93-102.Alidrick, D.J., Britton, J.M., Webster, I.C.L. and Russell, C.W.P. (1989): Geology and Mineral Deposits of theUnuk Area (104B/7E, 8W, 9W, bE); British Columbia Ministry ofEnergy, Mines and Resources, Open File1989-10.Alien, R. (1988): False Pyroclastic Textures in Altered Silicic Lavas, with Implications for Volcanic-AssociatedMineralization; Economic Geology, Vol. 83, pp. 1424-1446.Anderson, R.G. (1989): A Stratigraphic, Plutonic and Structural Framework for the Iskut River Map Area (NTS104B), Northwestern British Columbia; in Current Research, Part B, Geological Survey ofCanada, Paper 89-1E, pp. 145-154.Anderson, R.G. and Bevier, M.L., (1990), A Note on Mezozoic and Tertiary K-Ar Geochronometry of PlutonicSuites, Iskut River Map Area, Northwestern British Columbia; in Current Research, Part E, Geological SurveyofCanada, Paper 90-1E, pp.141-147.Anderson, R.G. and Thorkelson, D.J. (1990): Mesozoic Stratigraphy and Setting for some Mineral Deposits in theIskut River Map Area, Northwestern British Columbia; in Current Research, Part E, Geological Survey ofCanada, Paper 90-1E, pp. 13 1-139.Aoki, M. (1991): Gold and Base Metal Mineralization in an Evolving Hydrothermal System and Osorezan,Northern Honshu, Japan; Geological Survey ofJapan Report, No. 277, pp.67-70.Bachinski, (1969): Bond strength and sulphur isotopic fractionation in coexisting suffides; Economic Geology,Vol. 64, pp. 56-65.Baldwin, R. (1993): A preliminary study of fluid inclusions in orpiment, realgar and associated quartz from theEskay Creek deposit, British Columbia, unpublished B.Sc. thesis, The University of British Columbia, 33pages.Ballantyne, J.M. and Moore, J.N. (1988): Arsenic geochemistry in geothermal systems; Geochemica etCosmochemicaActa, V. 52, pp.475483Barnett, R.L. (1989) Petrography and Mineral Chemistry of Selected Samples from the Eskay Creek GoldProspect, Stewart, British Columbia; confidential reportfor Prime Explorations Ltd. (July 4, 1989).Barrett, T.J., Cattalani, S., Chartrand, F., and Jones, P. (1991a): Massive suffide dposits of the Noranda area,Quebec. II. the Aldermac Mine, Canadian Journal ofEarth Sciences, Vol. 28, pp. 1301-1327.Barrett, T.J., MacLean, W.H., Cattalani, S., Hoy, L., and Riverin, G. (199 ib): Massive suffide deposits of theNoranda Area, Quebec. III. The Ansi! Mine, Canadian Journal ofEarth Sciences, Vol. 28, pp. 1699-1730.179Barrett, T.J., Cattalani, S., Hoy, L., Riopel, 3., and Lafleur, P.-J. (1992): Massive suffide deposits of the Norandaarea, Quebec. IV. The Mobrun Mine, Candadian Journal ofEarth Sciences, Vol. 29, pp. 1349-1374.Bartsch, R.D. (1 992a): Eskay Creek Area, Stratigraphy Update; in Geological Fieldwork 1991, Grant, B. andNewell, J.M., Editors, British Columbia Ministry ofEnergy, Mines and Petroleum Resources, Paper 1992-1,pp. 5 17-520.Bartsch, R.D. (1 992b): Lithostratigraphy of the Prout Plateau; in MDRU Metallogenesis of the Iskut River Area,Northwestern British Columbia, MDRU Library, Department ofGeological Sciences, The Univeristy ofBritishColumbia, Annual Technical Report - Year 2.Bartsch, R.D. (1993a): Rhyolite Flow Domes in the Upper Hazelton Group, Eskay Creek Area; in GeologicalFieldwork 1992, Grant, B. and Newell, 3M., Editors, British Columbia Ministry ofEnergy, Mines andPetroleum Resources, Paper 1993-1, pp. 33 1-334.Bartsch, R.D. (1993b): Volcanic Stratigraphy and Lithogeochemistry of the Lower Jurassic Hazelton Group, Hostto the Eskay Creek Precious and Base Metal Volcanogemc Deposit; unpublished MSc Thesis, The University ofBritish Columbia, 179 pages.Bevier, M.L. and Anderson, R.G. (1991): Jurassic Geochronometry in Northwestern Stikima (56-57°), BritishColumbia; Abstracts with Programs, Geological Society ofAmerica, Annual Meeting, October 1991, SanDiego California, Vol. 23, No. 5, p. A-191.Blackwell, J.D. (1990): Geology of the Eskay Creek 21 Deposits; in The Gangue, No. 31, Mineral DepositsDivision, GeologicalAssociation ofCanada, April 1990, pp. 1-4.Brown, G. and Brindley, (3.W. (1980): X-ray diffraction procedures for clay mineral identification; in CrystalStructures of Caly Minerals and Their X-ray Identification, edited by G.W. Brindley and G. Brown,Mineralogical Society ofLondon, Monograph 5, pp. 305-359.British Columbia Minister of Mines Annual Reports: 1932 p.A6 1, 1933 p.A6 1, 1934 p.B30-B3 3, 1935 p. B7-B9,1939 p.A65, 1946 p.85, 1953 p.87-89, 1963 p.10, 1964 p.20, 1965 p.44, 1967 p.30.Geology, Exploration andMining in British Columbia, (1970) p.64-65, (1971) p.63.Exploration in British Columbia, (1975) p.E182-E183, (1976) p.E182, (1985) p.C380, (1991) p.3 1,Britton, J.M. (1991): Stratigraphic Notes from the Iskut-Sulphurets Area; in Geological Fieldwork 1990, BritishColumbia Ministry ofEnergy, Mines and Petroleum Resources Paper 1991-1, pp. 131-137.Britton, J.M. and Alldrick, D.J. (1988): Sulphurets Map Area; in Geological Fieldwork 1987, British ColumbiaMinistry ofEnergy, Mines and Petroleum Resources, pp. 199-209.Bntton, J.M., Webster, I.C.L., and Alidrick, D.J. (1989): Unuk Map Area (104B/7E, 8W, 9W, bE); inGeological Fieldwork 1988, British Columbia Ministry ofEnergy, Mines and Petroleum Resources, Paper1989-1, pp.24150.Britton, J.M., Blackwell, J.D. and Schroeter, T.G. (1990a): #21 Zone Deposits, Eskay Creek, Northwestern BritishColumbia; in Exploration in British Columbia 1989, British Columbia Ministry ofEnergy, Mines andPetroleum Resources, pp. 197-223.Browniow, A.H. (1979): Geochemistry; Prentice-Hall Inc., Englewood Cliffs, Calif, 498 pages.180Cas, R.A.F. (1992): Submarine Volcanism: Eruption Styles, Products, and Relevance to Understanding the Host-Rock Successions to Volcanic-Hosted Massive Suiphide Deposits, Economic Geology, Vol 87, pp. 511-541.Cas, R.A.F. and Wright, J.V. (1988): Volcanic Successions: Modern andAncient, published by Unwin HymanLtd., London, 528 pages.Cashman, K.V. and Fiske, R.S. (1991): Fallout of Pyroclastic Debris from Submarine Volcanic Eruptions;Science, Vo. 253, pp. 275-280.Date, 3., Watanabe, Y. and Saeki, Y. (1983): Zonal Alteration Around the Fukazawa Kuroko Deposits, AkitaPrefecture, Northern Japan; in The Kuroko and Related Volcanogenic Massive Sulfide Deposits, edited by H.Ohmoto and B.J. Skinner, Economic Geology, Monograph 5, pp.365-86.Donnelly, D.A. (1976): A Study of the Volcanic Stratigraphy and Volcanogemc Mineralization on the Kay ClaimGroup, Northwestern British Columbia, unpublished B.Sc. Thesis, The University ofBritish Columbia, 61pages.Edmunds, F.C., Kuran, D.L. and Rye, K.A. (1992): The Geology of the Eskay Creek Property and the #21 ZoneDeposits; Abstracts of Technical Presentations; Geological Society of the Canadian Institute ofMining andMetallurgy, Second Annual Field Conference, Kamloops, British Columbia, September 28,29, 1992.Ettlinger, A.D. (1991): Eskay Creek - 21 Zone; in MDRU Metallogenesis of the Iskut River Area, NorthwesternBritish Columbia, MDR U Library, Department ofGeological Sciences, The University ofBritish Columbia,Annual Technical Report - Year 1.Ettlinger, A.D. (1992): Hydrothermal Alteration and Brecciation Underlying the Eskay Creek PolymetallicMassive Sulphide Deposit (104B/9W); in Geological Fieldwork 1991, Paper 1992-1, British Columbia MinistryofEnergy, Mines and Petroleum Resources, pp.135-541.Faure, G. (1986): Principles ofisotope Geology, 2nd Edition, John Wiley and Sons, New York, p.532.Field, C.W. and Fifarek, R.H. (1985): Light Stable-Isotope Systematics in the Epithermal Environment, inGeology and Geochemistry of Epithermal Systems, edited by B.R. Berger and P.M. Bethke, Society ofEconomic Geologists, Reviews in Economic Geology, Vol. 2, pp. 99-128.Fowler, A.D. (1990): Rock alteration: A further application of Pearce diagrams and related techniques, in Theoryand Application of Pearce Element Ratios to Geochemical Data Analysis, edited by J.K. Russell and C.R.Stanley, Geological Association ofCanada, Short Course Vol. 8, pp. 235-242.Franklin, J.M. (1990): Volcanic-Associated Massive Suiphide Deposits; in Gold and Base Metal Mineralization inthe Abitibi Subprovince, Canada, University of Western Ausfralia, Publication No. 24, pp. 211-243.Gabrielse, H., Monger, J.W.H., Wheeler, J.O., and Yorath, C.J. (1992): Morphogeological belts, tectonicassemblages and terranes; in, Geology of the Cordilleran Orogen in Candada, edited by H. Gabrielse and C.J.Yorath, Geological Survey ofCanada, No. 4, pp. 15-28.Grim, R.E., Bray, R.H. and Bradley, W.F. (1937): The mica in argillaceous sediments. American Mineralogist,Vol. 22, pp.813-29Grove, E.W. (1986): Geology and Mineral Deposits of the Unuk River - Salmon River - Anyox Area; BritishColumbia Ministry ofEnergy, Mines and Pefroleum Resouces, Bulletin 63, 152 pages.181Halbach, P., Nakamura, K., Wahsner, M., Lange, J., Sakai, H., Kaselitz, L., Hansen, R.D,, Yamano, Post, J.,Prause, B., Seifert, R., Michaelis, W., Teichamnn, F., Kinoshita, M., Marten, A., Ishibashi, J., Czerwinski, S.,and Blum, N. (1989): Probable modem analogue of Kuroko-type massive sulphide deposits in the OkinawaTrough back-arc basin; Nature, Vol. 338, No. 6, pp. 496-498.Hashiguchi, H., Yamada, R. and Inoue, T, (1983): Practical application of low Na20anaomalies in footwall acidlava for delimiting promising areas around the Kosaka and Fukazawa Kuroko deposits, Akita Prefecture,Japan; in The Kuroko and Related Volcanogenic Massive Sulfide Deposits, edited by H. Ohmoto and B.J.Skinner, Economic Geology, Monograph 5, pp.387-394.Hashiguchi, H. and Usui, H. (1975): An Approach to Delimiting Targets for Prospecting of the Kuroko OreDeposits: On the Sulphur and Magnetic Susceptibitlity Haloes; Mining Geology, Vol. 25, pp.283-301.Haskin, L.A., Wildeman, T.R. and Haskin, M.A. (1968): An accurate procedure for the determination of the rareearths by neutron activation; Journal ofRadioanalytical Chemistry, Vol. 1, pp. 337-348.Henderson, P. (1984): General geochemical properties and abundances of the rare earth elements; in Rare EarthElement Geochemistry, British Museum ofNatural History, Elsevier Science Publishing Co., London, pp. 1-32.Henley, R.W. and Brown, K.L. (1985): A Practical Guide to the Thermodynamics of Geothermal Fluids andHydrothermal Ore Deposits, in Geology and Geochemistry of Epithermal Systems, edited by B.R. Berger andP.M. Bethke, Society ofEconomic Geologists, Reviews in Economic Geology, Vol. 2, pp. 25-44.Howarth, R.J. and Sinding-Larsen, R. (1983): Multivariate analysis; Chapter 6 in Statistical and Data Analysis inGeochemical Prospecting, Handbook ofExploration Geochemistry, Vol. 2, Elsevier, New York, pp. 207-292.Idziszek, C., Blackwell, J., Fenlon, R., MacArthur, G. and Mallo,D. (1990): The Eskay Creek Discovery; MiningMagazine, March 1990, pp.172-3Ishikawa, Y., Sawaguchi, T., Iwaya, S. and Horiuchi, M. (1976): Delineation of Prospecting Targets for KurokoDeposits Based on Modes of Volcanism of Underlying Dacite and Alteration Halos; Mining Geology, Volume26, Pp. 105-1 17.Izawa, E., and Aoki, M. (1991): Geothermal activity and epithermal gold mineralization in Japan; Episodes, Vol.14, No. 3, pp. 269-273.JCPDS (1980): Selected Powder Diffraction Data for Minerals; Joint Committee on Powder D[fractionStandards, International Cenfre for Research Data, Swarthmore, Pa..Kerr, F.A. (1948): Lower Stikine and Western Iskut River Areas, British Columbia; Geological Survey ofCanada, Memoir 246, Pub. 2482, 94 pages.Le Maitre, R.W.L. (1989): Some problems of the Projection of Chemical Data into Mineralogical Classifications;Contributions to Mineralogy and Petrology, Vol. 56, pp. 18 1-189.Lewis, P.D. (1992): Structural Geology of the Prout Plateau Region, Iskut River Map Area, British Columbia; inGeological Fieldwork 1991, Grant, B. and Newell, 3M., Editors, British Columbia Ministry ofEnergy, Minesand Petroleum Resources, Paper 1992-1, pp. 52 1-527.Lewis, P.D., Macdonald, A.J. and Bartsch, R.D. (1992): Hazelton Group / Bowser Lake Group Stratigraphy in theIskut River Area: Progress and Problems; in MDRU Metallogenesis of the Iskut River Area, NorthwesternBritish Columbia, MDRU Library, Department ofGeological Sciences, The University ofBritish Columbia,Annual Technical Report- Year 2.182Large, R.R. (1992): Australian Volcanic-Hosted Massive Sulphide Deposits: Features, Styles and GeneticDeposits; Economic Geology, Vol. 87, pp. 471-5 10.Lofgren, G. (1970): Experimental Devitrification Rate of Rhyolite Glass, Geological Society ofAmerica Bulletin,V. 81, pp. 553-560.Lofgren, G. (1971): Experimentally produced devitrification textures in natural rhyolite glass: Geological SocietyofAmerica Bulletin, V. 82, pp. 111-124.Macdonald, A.J. (1991): Lithostratigraphic Reconnaissance - Eskay Creek Area; in IvIDRU Metallogenesis of theIskut River Area, Northwestern British Columbia, MDR U Library, Department ofGeological Sciences, TheUniversity ofBritish Columbia, Annual Technical Report - Year 1.Macdonald, A.J. (1992): Eskay Porphyiy; in MDRU Metallogenesis of the Iskut River Area, Northwestern BritishColumbia, MDRULibrary, Department ofGeological Science, The University ofBritish Columbia, AnnualTechnical Report - Year 2.Macdonald, A.J., van der Heyden, P., Lefebure, D.V., and Alldrick, D.J. (1992): Geochronometry of the IskutRiver Area - An Update; in Geological Fieldwork 1991, Paper 1992-1, British Columbia Ministry ofEnergy,Mines and Petroleum Resources, pp. 495-50 1.MacLean, W.H. (1988): Rare earth element mobility at constant inter-REE ratios in the alteration zone at thePhelps Dodge massive sulphide deposit, Matagami, Quebec, Mineralia Deposita, Vol. 23, pp. 231-238.MacLean, W.H. (1990): Mass change calculations in altered rock series, Mineralia Deposita, Vol. 25, pp. 44-49.MacLean, W.H. and Kramdiotis, P. (1987): Immobile Elements as Monitors of Mass Transfer in HydrothermalAlteration: Phelps Dodge Massive Sulfide Deposit, Matagami, Quebec, Economic Geology, Vol. 82, pp. 951-962.Marsden, H. and Thorkelson, D.J. (1992): Geology of the Hazelton Volcanic Belt in British Columbia:Implications for the Early to Middle Jurassic Evolution of Stikina, Tectonics, Vol. 11, No. 6, pp. 1266-1287,Monger, J.W.H. (1989): Overview of Cordilleran Geology; in Western Canada Sedimentary Basin - A CaseHistory, edited by B.D. Ricketts, Canadian Society ofPetroleum Geologists, pp. 9-32.Moore, D.M and Reynolds Jr., R.C. (1989): X-Ray Diffraction and the Identification and Analysis of ClayMinerals; Oxford University Press, New York,Moreton, R.L. (1992): Introduction to Hydrovolcamsm; in Volcanogemc Massive Sulphide Deposits:Enviromnents of Deposition and Preservation, Mineral Deposit Research Unit Short Course Notes: SC-9, April7-10, 1992.Nadaraju, G.D. (1993): Triassic-Jurassic Biochronology of the Eastern Iskut River Map Area, NorthwesternBritish Columbia; unpublished M.Sc. thesis, The University ofBritish Columbia.Nicholls, J. (1988): The statistics of Pearce element diagrams and the Chayes closure problem; Contributions toMineralogy and Petrology, Vol. 99, pp. 11-24.Nicholls, J. and Russell, J.K. (1990): Pearce Element Ratios - An Overview, Example and Bibliography; in Theoryand Application of Pearce Element Ratios to Geochemical Data Analysis, edited by J.K. Russell and C.R.Stanley, Geological Association of Canada, Short Course Vol. #8, pp.11-21.183Pearce, T.H. (1968): A contribution to theory of variation diagrams, Contributions to Mineralogy and Petrology,Vo. 19, PP. 142-157.Pearce. T.H. (1990): Getting the most from your data: Applications of Pearce element ratio analysis, inTheory andApplication of Pearce Element Ratios to Geochemical Data Analysis, edited by J.K. Russell and C.R. Stanley,GeologicalAssociation ofCanada, Short Course Vol. 8, pp. 99-130.Riverin, G. and Hodgson, C.J. (1980): Wall-Rock alteration at the Millenback Cu-Zn Mine, Noranda, Quebec;Economic Geology, Vol. 75, pp. 424-444.Roth, T. (1991): Eskay Creek 2 1A Zone; in MDRU Metallogenesis of the Iskut River Area, Northwestern BritishColumbia, MDRU Library, Department of Geological Science, The University ofBritish Columbia, AnnualTechnical Report, Year 1.Roth, T. (1992): Geology of the 2 1A Zone - An Update; in MDRU Metallogenesis of the Iskut River Area,Northwestern British Columbia, MDRU Library, Department ofGeological Sciences, The University ofBritishColumbia, Annual Technical Report - Year 2.Roth, T. (1993): Surface Geology of the 2 IA Zone, Eskay Creek, British Columbia; in Geological Fieldwork 1992,British Columbia Ministry ofEnergy, Mines and Petroleum Resources, Paper 1993-1, PP.32530.Roth, T. and Godwin, C.I. (1992): Preliminary Geology of the 2 1A zone, Eskay Creek, British Columbia; inGeological Fieldwork 1991, Grant, B. and Newell, J.M., Editors, British Columbia Ministry ofEnergy, Minesand Petroleum Resources, Paper 1992-1, pages 529-533.Rye, K.A. (1992): Geological and Geochemical Report on the 1991 Eskay Creek Diamond Drill Relog Program;internal report for International Corona Corporation.Rye, K.A., Edmunds, F.C. and Kuran, D.L. (1993): Geology of the Eskay Creek 21 Zone Deposits; Abstract,presented at Cordilleran Roundup, January 1993, Vancouver, British Columbia.Saeki, Y. and Date, J. (1980): Computer Application of the Alteration Data for the Footwall Dacite Lava at theEzuri Kuroko Deposits, Akita Prefecture; Mining Geology, Vol. 30, pp. 241-250.Sakai, H., Gamo, T., Kim, E-S., Tsutsumi, M., Tanaka, T., Ishibashi, J., Wakita, H., Yamano, M., and Oomori, T.(1990): Venting of carbon Dioxide-Rich Fluid and Hydrate Formation in Mid-Okinawa Trough Backarc Basin;Science, Vol. 248, pp.1094-1096.Srodon, J. (1980): Precise identification of illite/smectite interstratifications by X-ray powder diffraction; Claysand Clay Minerals, Vol. 28, pp. 401-411.Srodon, J. and Eberl, D.D. (1984): Illite; in Micas, edited by S.W. Bailey, University of Wisconsin at Madison,Reviews in Mineralogy, Vol. 13, pp. 495-544.Stanley, C.R. (1992): The Mathematical Basis for Material Balance Equartions and Their Application inQuanti1ring the Effects of Metasomatism; in New Developments in Lithogeochemistry, MDRU Short CourseNotes SC-8, Mineral Deposit Research Unit Library, The University ofBritish Columbia, Department ofGeological Sciences.Stanley, C.R and Madeisky, H.E. (1993): Pearce Element Ratio Analysis: Applications in LithogeochemicalExploration; in MDRU Short Course Notes SC-13, Mineral Deposit Research Unit Library, The University ofBritish Columbia, Department ofGeological Sciences, in association with associationfo ExplorationGeochemists, Special Volume #14.184Taylor, S.R. and McLennan, S.M. (1985): ‘The Continental Crust: Its Composition and Evolution”, Blackwell,Oxford, 312 pp.Tipper, H.W, and Richards, T.A. (1976): Jurassic stratigraphy and histoiy of North-central British Columbia;Geological Survey ofCanada, Bulletin No. 270, 73 pages.Turekian, K.K. (1968): Oceans, Prentice-Hall Inc., Englewood Cliffs, N.J., p. 92.Urabe, T., and Marumo, K. (1991): A new model for Kuroko-type deposits of Japan; Episodes, Vol. 14, No. 3, pp.247-251.Walker, R.G. (1984): Turbidites and Associated Coarse Clastic Deposits; in Facies Models, edited by RG. Walker,Geoscience Canada, Reprint Series 1, pp. 171-188.Wheeler, 3.0. and McFeely, P. (1991): Tectonic Assemblage Map of the Canadian Cordillera and Adjacent Partsof the United States of America; Geological Survey ofCanada, Map 17 12A, scale 1:2 000 000.Wilson, M. (1989): “Igneous Petrogenesis, A Global Tectonic Approach”, Unwin Hyman, London, 466 pages.Winchester, J.A. and Floyd, P.A. (1977): Geochemical discrimination of different magma series and theirdifferentiation products using immobile elements, Chemical Geology, Vol. 20, pp. 325-343.185APPENDIX AThe 2 1A zone is defined by the area southwest of line 2+OON. Driliholes collared in this area arelisted in Table A. 1 and plotted on Figure 2.4. Three cross sections, spaced 100 metres apart, wereevaluated in detail: Section 1+00N, Section 0+00, and Section 1+OOS (Figures 2.1 to 2.3). Cross sectionsplotted at 25 metre intervals between these three sections are shown in Figures A. 1 to A. 12 at 1: 4000scale. Only the major lithological contacts are shown. The drillhole information is projected from 12.5metres on either side of the grid line. The interpretations are based on original drill logs and reloggedintervals from this study, as indicated in Table A. 1. The drill holes in each figure are projected into the25 metre wide plan view at the top of each cross section.186Table A.1: Drillholes in the 21A zone. Surface projections are shown in Figure 2.4. Cross sections areplotted on Figures 2.1 to 2.3 and A. 1 to A. 12. All grid locations are in metres from the baseline.Drillhole Length Orientation Collar Location Relogged SectionNumber (m) Azimuth Dip Easting Northing Elevation From (m) To (m)CA88-003 93.0 90 -45.0 15.86 -114.15 1046.60CA88-005 108.0 0 -90.0 51.18 -149.30 1055.60 H-SOSCA88-006 119.2 95 -45.0 0.16 -58.80 1041.80 83.9 EOHCA88-007 191.4 90 -47.5 0.16 -58.80 1041.80CA88-008 311.8 90 -72.5 0.16 -58.80 1041.80CA88-009 200.3 90 -50.0 23.66 -25.79 1032.50 46.8 109.5CA88-010 130.1 150 -45.0 30.09 26.32 1026.80 0.0 EOH 0+25NCA88-011 215.5 150 -75.0 30.09 26.32 1026.80 0+25NCA88-012 139.3 150 -45.0 0.16 -58.80 1041.80 0+50SCA88-013 261.5 150 -70.0 0.16 -58.80 1041.80 0+50SCA88-014 200.3 150 -45.0 27.44 -93.75 1039.40 0.0 EOH 1+00SCA88-015 151.5 150 -70.0 27.44 -93.75 1039.40 46.8 EOH 1+OOSCA88-016 297.8 150 -45.0 2.11 51.75 1031.70 0+SONCA89-017 261.8 150 -80.0 2.11 51.75 1031.70 0+50NCA89-018 200.4 150 -45.0 22.46 -28.12 1032.50 38.4 97.9 0+25SCA89-019 188.7 150 -67.0 22.46 -28.12 1032.50 44.5 100.5 0+25SCA89-020 223.7 330 -85.0 22.46 -28.12 1032.50 69.9 87.2 0+25SCA89-021 149.0 150 -48.0 32.32 -44.33 1032.20 44.2 100.0 0+50SCA89-022 163.7 150 -45.0 28.52 3.80 1030.00 39.2 EOH 0+00CA89-023 169.8 150 -67.0 28.52 3.80 1030.00 0.0 EOH 0+00CA89-024 197.8 150 -86.0 28.52 3.80 1030.00 0.0 EOH 0+00CA89-025 236.8 150 -45.0 -64.68 -137.30 1052.70 1+25SCA89-026 350.3 150 -54.0 -271.84 -33.53 973.40 0+25SCA89-027 215.6 150 -70.0 -64.68 -137.30 1052.70 56.8 68.2 1+25SCA89-028 214.3 330 -85.0 -64.68 -137.30 1052.70 59.1 82.1 1+25SCA89-029 307.5 150 -75.0 -271.84 -33.53 973.40 0+25SCA89-030 233.8 150 -45.0 -69.62 -193.30 1029.50 2+OOSCA89-031 304.8 150 -70.0 -69.62 -193.30 1029.50 2+OOSCA89-032 307.5 330 -75.0 -271.84 -33.53 973.40 0+25SCA89-033 145.3 330 -88.0 -69.62 -193.30 1029.50 2+OOSCA89-034 122.2 330 -45.0 -69.62 -193.30 1029.50 2+OOSCA89-035 244.4 0 -88.0 26.97 -95.71 1038.70 52.2 EOH 1+008CA89-036 319.7 330 -75.0 26.97 -95.71 1038.70 47.3 EOH l+OOSCA89-037 277.9 330 -55.0 26.97 -95.71 1038.70 80.9 EOH 1+OOSCA89-042 217.9 330 -45.0 26.97 -95.71 1038.70 98.2 EOH 1+OOSCA89-043 269.7 150 -45.0 -18.70 95.48 1031.90 0.0 EOH 1+OONCA89-044 240.2 150 -68.0 -19.59 95.60 1031.80 0.0 EOH 1+OONCA89-045 418.6 330 -88.0 -20.04 95.65 1031.60 0.0 EOH 1+OONCA89-046 193.5 150 -60.0 -176.15 -193.07 999.30 2+OOSCA89-047 203.3 330 -60.0 -178.18 -194.85 999.20 2+OOSCA89-048 264.3 150 -45.0 -160.39 -133.13 1000.40 1+25SCA89-049 154.5 150 -85.0 -161.61 -133.15 1000.20 1+25SCA89-050 233.8 330 -72.0 -21.82 90.47 1031.90 123.1 EOH 1+OONCA89-051 114.8 150 -45.0 -43.16 154.28 1035.80 1+SONCA89-052 270.3 150 -71.0 -44.08 154.17 1035.90 1+50NCA89-053 307.1 0 -90.0 -44.52 154.23 1035.70 1+50NCA89-054 252.1 150 -48.0 -81.45 -49.01 1015.60 O+50SCA89-055 255.1 150 -72.0 -82.31 -49.03 1015.60 0-i-SOSCA89-056 303.3 0 -90.0 -82.76 -48.98 1015.50 0+50S187Drillhole Length Orientation Collar Location Relogged SectionNumber (m) Azimuth Dip Lusting Nortking Elevation From (m) To (m)CA89-060 268.3 150 -47.0 -49.34 154.92 1035.70 1+50NCA89-061 238.7 150 -45.0 -108.79 14.12 1020.50 133.4 156.0 0+25NCA89-062 274.9 150 -62.0 -109.29 14.45 1020.50 O+25NCA89-063 291.7 150 -87.0 -109.79 14.43 1020.40 0+25NCA89-064 258.2 150 -47.0 -141.31 50.76 1010.20 132.4 198.0 0+50NCA89-065 270.4 150 -70.0 -142.09 50.68 1010.20 0+50NCA89-066 249.6 0 -90.0 -142.67 50.71 1009.80 98.1 128.0 0+50NCA89-070 239.9 330 -70.0 -144.53 53.51 1010.10 0+50NCA89-077 159.1 150 -45.0 -21.03 126.38 1029.10 75.0 121.1 1+25NCA89-078 154.5 150 -60.0 -21.45 126.30 1029.00 85.2 120.0 1+25NCA89-079 150.0 150 -75.0 -22.03 126.33 1029.30 92.8 115.2 1+25NCA89-080 146.9 150 -60.0 -16.32 98.70 1031.70 Bulk sampled 1+OONCA89-081 154.8 150 -75.0 -1668 98.70 1031.50 Bulk sampled 1+OONCA89-082 154.5 150 -45.0 -14.57 73.24 1031.00 91.5 126.5 0+75NCA89-083 153.0 150 -62.0 -15.12 73.12 1031.00 0-I-75NCA89-088 153.0 150 -62.0 -0.11 53.47 1031.50 0+50NCA89-089 151.2 150 -45.0 -9.93 23.83 1033.70 74.0 110.3 0+25NCA89-090 148.4 150 -73.0 -10.88 23.86 1033.70 90.7 118.0 0+25NCA89-091 156.4 150 -89.0 -11.29 23.78 1033.70 0+25NCA89-094 191.2 150 -45.0 44.27 -150.81 1054.00 1+50SCA89-095 154.5 150 -60.0 -37.33 6.42 1036.30 0.0 EOH 0+00CA89-096 159.1 150 -70.0 -37.33 6.42 1036.30 0.0 EOH 0+00CA89-097 152.7 150 -77.0 -26.01 -25.07 1033.60 93.1 117.0 0+25SCA89-098 167.3 150 -45.0 -20.79 -64.77 1036.10 0+50SCA89-099 151.2 150 -75.0 -21.56 -64.85 1036.50 0+50SCA89-100 161.5 150 -45.0 16.02 -61.70 1040.90 56.3 103.0 0+SOSCA89-107 162.2 150 -45.0 0.39 -161.78 1060.30 1+50SCA89-108 162.8 150 -72.0 -0.06 -161.72 1060.30 H-SOSCA89-115 210.6 150 -56.0 -78.88 54.39 1036.10 0+50NCA89-116 180.1 150 -67.0 -79.32 54.44 1036.30 0+50NCA89-117 156.3 150 -87.0 -79.88 54.33 1036.80 0+50NCA89-119 203.3 150 -45.0 -87.85 69.04 1042.70 0+75NCA89-130 173.1 150 -45.0 17.48 -127.02 1045.60 1+25SCA89-131 167.0 150 -75.0 17.34 -127.04 1045.60 1+25SCA89-135 194.5 150 -70.0 -83.37 77.00 1042.60 0+75NCA9O-399 207.0 150 -45.0 -170.99 153.22 1018.10 1+50NCA9O-400 259.4 150 -74.0 -170.99 153.22 1018.10 1+50NCA9O-416 203.3 150 -45.0 154.87 178.67 963.40 1+75NCA9O-417 197.2 150 -70.0 154.87 178.67 963.40 1+75NCA9O-426 340.8 0 -90.0 -170.99 153.22 1018.10 1+50NCA9O-427 212.4 150 -45.0 -165.30 105.04 1012.20 146.0 EOH 1+OONCA9O-428 214.3 150 -67.0 -165.30 105.04 1012.20 132.4 EOH 1+OONCA9O-429 215.8 150 -86.0 -165.27 104.90 1012.10 133.2 EOH 1+OONCA9O-432 185.0 150 -45.0 185.11 110.36 959.40 1-t-OONCA9O-433 189.9 150 -70.0 185.11 110.36 959.40 1+OONCA9O-440 194.2 150 -45.0 227.48 53.18 961.70 0+50NCA9O-441 200.3 150 -70.0 227.48 53.18 961.70 0+50NCA9O-445 188.1 150 -45.0 241.94 -12.49 983.90 0+00CA9O-446 178.9 150 -70.0 241.94 -12.49 983.90 0+00CA9O-453 185.6 150 -45.0 235.98 -73.61 971.60 0+75SCA9O-454 185.0 150 -70.0 235.98 -73.61 971.60 0+75SCA9O-464 220.6 150 -75.0 -165.27 104.90 1012.10 0.0 EOH 1+OON188Drillhole Length Orientation Collar Location Relogged SectionNumber (m) Azimuth Dip Easting Northiiig Elevation From (m) To (m)CA9O-465 209.4 150 -55.0 -165.27 104.90 1012.10 0.0 EOH 1+OONCA9O-466 266.9 330 -78.0 -165.27 104.90 1012.10 0.0 EOH H-OONCA9O-467 150.0 150 -50.0 147.59 -72.51 982.10 0+75SCA9O-468 172.8 150 -70.0 147.59 -72.51 982.10 0+75SCA9O-469 166.1 330 -88.0 147.59 -72.51 982.10 0+75SCA9O-477 194.8 150 -50.0 170.20 -6.09 962.60 0.0 EOH 0+00CA9O-478 182.0 150 -80.0 170.20 -6.09 962.60 0-1-00CA9O-495 119.5 150 -45.0 318.19 -171.60 998.80 1+75SCA9O-496 154.2 150 -70.0 318.19 -171.60 998.80 1+75SCA9O-502 169.2 150 -50.0 138.54 56.32 961.50 0+50NCA9O-503 190.8 330 -88.0 138.54 56.32 961.50 0+50NCA9O-511 132.3 150 -46.0 117.58 120.00 957.80 1+25NCA9O-512 166.7- 330 -88.0 117.58 120.00 957.80 1+25NCA90-530 201.8 150 -60.0 165.58 -134.33 1002.60 1+25SCA9O-531 202.4 0 -90.0 165.58 -134.33 1002.60 1+25SCA9O-551 215.8 150 -60.0 134.32 -182.36 1022.40 1+75SCA9O-552 242.9 0 -90.0 134.32 -182.36 1022.40 1+75SCA9O-619 233.2 150 -52.0 -320.82 98.91 943.27 0.0 EOH 1+OONCA9O-620 105.5 115 -45.0 -320.82 98.91 943.30 1+OONGNC9227* 227.0 150 -64.0 -316.50 -193.07 954.38 2+OOS* location is approximatePlanView—350E—300E—25O—200E—150E—100E—50EOE50E100E150E200E250E300E350E400E11001100105010501000100095095090090085085080080075075070070050650600600OE50EIOOE150200250E300E350400450E450E—350E—300—250E—200E—150E—lOGE—50E00P/anView III110010501000 950900850800750700650600—350E—300E—250E-200E—150E—100E—50EOE50E100E150E200E250E300E350E400450E110010501000950900850800750700650600OE50EIOOE150E200E250E300E350E400450E—350E—300E—250E—200E—150E—100—50EF________110010501000 950900850800750700650600—350E—300E—250E—200E—150E—lOGE—50EGE50ElOGE150E200E250E300E350E400E450E110010501000950900850800750700650-350E—300E—250E—200E—150E—lOGE—50E600GE50ElOGE150E200E250E300E350E400E450E‘0PlanView[.--—I(S—=---110010501000 950900850800750700650110010501000950900850800750700650600400E450E—350E—300E—250E—200E—150—bCE—50EOE50E100E150E200E250E300E350E400E450E600—350E—300E—250E—200E—150E—100E—50EOE50EIOOE150E200E250E300350EP/onViewF—----——H-L(3(3110010501000 950900850800750700650600—350E—300E—250E—200E—150E—lOGE—50EGE50ElOGE150E200E250E300E350E400E110010501000950900850800750700650600450E450E—350E—300E—250E—200E—150E—IOOE—50EOE50ElODE150E200E250300E350E400EP/or,View110010501000 950900850800750700650600I--350E—300E—250E-200E—150E—lODE—50EDE50EWOE•1200E250E300E350E400EPlanviewF—350E—300E—250—2OO—15O—100E—50E110010501000 950900850800750700650600—350E—300—250—200—150-100E-50E050950900850800750700650SectionO+25NI600100150E200E250E300E350E400E450ENWOE50E100150200250300350E400E450 1100SE10501000/C,, ‘a 0’ w C)P/anViewF -H-------H=-10501000 950900850800750700650—350E—300E—250E—200E—150E—100E—50EOE50EWOE150E200E250E300E350E400E450E110010501000950900850800750700650600450E1100 600OE50E100E150E200E250E300E350E400E—350E—300E-250E—200E—150E—100E—50EPlanViewFH—350E—300—250E-200E—150E—100E—50ENWSE110010501000 950900850800750700650600PC1nphoseFuVtZonelUte t1tco1.tceC.,——C)OE50EIOOE150E200250300E350400E4501100105010009509008508007507006507777tl’cooC)60050E100E150E200E250E300E350E400E450ESectionO+75N—350E—300E—250E—200E—150E—100E—50EOEP/onView-------HV1100SE10501000950900850800(U C750C)700650Section1 +25NII60050E100E150E200E250E300E350E400E450E—350E—300—250E—200E—150E—IOOE—50ENWOE50E100E150E200E250E300E350400E450E5alt3tgt110010501000 950900850800750700650600C)uf1tC)—350E—300E—250E—200E—150E—lODE—50EOE00wP/onViewLI—350E—300—250—200E—150E—100E—50EOE50E100E150200E250E300E350E400E450E1100III1100NWSE10501050100010009509509009008500 ON8000800750750700700650650600600OE50IDOE150E200E250E300E350400E450Ein c 0in ON LIFootWvolcanicunitSection1+50N—350E—300E-250E-200E-150E—IOOE—50EPlanView__H-350E—300E-250E—200E-150E-100E—50E110010501000 950900850800750700650600-350—300E-250E—200E—150E—lODE—50EOEOE50ElODE150[200E250E300E350E400E450EII1100SE1050P.wphouse1000950900850coOtctt?800UIU750700650Sectioini1+75N60050E100E150E200E250E300E350E400E450ENWFo1tZone1eI3 C C201APPENDIX BP1utPTIoN ANI) ANALYSIS OF THE LITHOGEOCHEMICAL SAMPLESThis section describes the sample preparation, analysis and standards for the lithogeochemical samplesdescribed in section 2.4 and listed in Tables 2.4 to 2.7. The samples were collected by Art Ettlinger (ADE) in 1990and the author in 199 1-1992. Most of the samples were analyzed by X-Ray Assay Laboratories using their MER,research grade package. Some samples (Batches 4 and 5) were analyzed by Bondar Clegg using their researchquality package. These were early samples collected by ADE, and 16 samples that were analyzed courtesy ofInternational Corona Corporation. The rocks were prepared by the method outlined below, with the exception ofthe 16 samples which were crushed, using standard procedures, by Bondar Clegg.Sample SizeApproximately 20 to 30 centimetres of split NQ drill core was collected from core samples. At least 1kilogram was collected for samples from surface. The rocks are generally aphanitic, except in the more crystallinebasaltic rocks. To ensure a representative sample, approximately 50 centimetres of unsplit NQ core was collectedfrom these basalt intervals.MethodThese procedures were established by Arne Toma and Art Ettlinger of MDRU to achieve uniform,uncontaminated -200 mesh powder for analysis at X-Ray Assay Laboratories, Toronto, Ontario. Adequategrinding times were determined by running a sieve test a minimum of every 10 samples during the early stages ofprocedure design.1. Thoroughly clean surface of sample to remove soil, dirt and as much weathered material as possible.2. Retain a representative sample for thin section analysis.3. Thoroughly clean jaw crusher with stiff wire brush and compressed air before processing a newsample.4. Crush sample in jaw crusher set at closest setting between jaws. If the original sample is too coarse,crush at a wider jaw setting and repeat until closest jaw setting is obtained.5. Thoroughly clean chrome ring mill with water and compressed air before processing a new sample.6. Place crushed rock in a chrome steel ring mill (shatter box) and mill sample for 40 seconds.2027. Clean the sample splitter and sample trays thoroughly with a soft brush and compressed air.8. When the entire sample is ground, obtain about 60 grams of the milled rock by repetitive splitting.9. Submit 60 gram sample for analysis.10. Archive remainder.Analytical methodsThe analytical methods for each batch of samples are listed in Table B. 1. The abbreviations are asfollows:AA Atomic absorption spectrophotometiyCOIJLOM Coulometty SpectrometryCVAA Cold vapour AADCP Direct coupled plasma spectrometiyFADCP Fire assay DCPGFAA Graphite furnace AAGRAV Gravimetric analysisICP Inductively coupled plasma spectrometiyICP-MS ICP Mass spectrometiyLECO Leco analyzerNA Neutron activation analysisWET Wet chemistryXRF X-ray fluorescence spectrometlyDet. Lim. Lower detection limit quoted by the laboratoryUpper lim. Upper detection limit quoted by the laboratoryQuality controlA minimum of 10% internal standards were sent with each sample batch. The standards used were IJBCMDRU internal rock standards: P-i (Porteau Cove dacite), WP-1 (Watts Point dacite), QGRM 100, QGRM 101,ALB 1 and MBX 1. A statistical summaly of these analyses is presented in Table B.2. This sununaiy includes themaximum, minimum, mean, standard deviation and coefficients of variance for each of the rock standards. Aminimum of 5% duplicate samples were included with each sample batch. This data has been tabulated by A.Toma (MDRU).203TABLE B. 1: Analytical methods for samples collected in the Eskay Creek 21 A zone, NW British Columbia.Batehi Batcbi Batcb3 Batches4andsUppaElement Method Units Det tim Urn Method Units Det Urn Urn Method Units Oct Lint: Method Units Pet Lint5i02: XRF ¼ 0.01 : XRF ¼ 0.01 XRF % 0.01: DCP ¼ 0.01Ti02! XRF V. 0.01 XRF ¼ 0.01 XRF ¼ o.oi: DCP ¼ 0.01M2O3 XRF ¼ 0.01 XRF ¼ 0.01 XRF ¼ 0.01 DCP ¼ 0.01Fe203! XRF ¼ 0.01 XRF ¼ 0.01 XRF ¼ 0.01 DCP ¼ 0.01MnO XRF ¼ 0.01 XRF ¼ 0.01 XRF ¼ 0.01; DCP ¼ 0.01MgO! )F ¼ 0.01 XRF ¼ 0.01 XRF ¼ 0.01; 0(21’ ¼ 0.01CaO XRF ¼ 0.01 XRF ¼ 0.01 XRF ¼ 0.01; DCP ¼ 0.01Na20! XRF ¼ 0.01 XRF ¼ 0.01 XRF ¼ 0.01 OCP ¼ 0.01K2O XRF ¼ 0.01 XRF ¼ 0.01 XRF ¼ 0.01 DCP ¼ 0.01P205! XRF ¼ 0.01 XRF ¼ 0.01 XRF ¼ 0.01; 0(21’ ¼ 0.01H20+! Wet % 01 Wet ¼ 01 Wet ¼ 0.1 noC02! Wet ¼ 0.01 C0ULOM ¼ 0.01 COULOM ¼ 0.01 noCr! NA ppm 2 NA ppm 2 NA ppm 2 ; ICP ppm INi! ICI’ ppm I ICP ppm” I-ICP ppm 1 ICP ppm ICo! ICP ppm I ICP ppm 1 3 1(21’ ppm I ICP ppm IV! DCI’ ppm 2 DCP ppm 2 DCP ppm 2 ; ICP ppm ICu 1(21’ ppm 0.5 : ICP ppm 0.5 : ICP ppm 0.5: ICP ppm IPb! ICP ppm 2 ; ICP ppm 2 ICP ppm 2 ; ICP ppm 2Zn! ICP ppm 0.5 : ICP ppm 0.5 t ICP ppm 0.5: 1(21’ ppm IGe! DCP ppm 10 ! DCP ppm 10 DCP ppm 10 noHi; ICP-MS ppm I ICP-M5 ppm I ICP-Ms ppm I ICP ppm 5Cd! AA ppm 0.2 AA ppm 0.2 AA ppm 0.2; 1(21’ ppm 1.0W NA ppm I NA ppm I NA ppm I ICP ppm 20Mo! ICP ppm I ICP ppm I : ICP ppm ICP ppm Is; XRF ppm SO 5000 XRF ppm 50 LECO ¼ 0.005 LECO ¼ 0.02As! NA ppm 0.1 5000 NA ppm 0.1 NA ppm 0.1 ICP ppm 55c ICP ppm 0.05 1(21’ ppm 0.05 ICP ppm 0.OSInstNA ppm 01Se! GFAA ppm 0.5 : GFAA ppm 0.5 GFAA ppm 0.5 : nosb NA ppm 01 NA ppm 01 NA ppm 01 ICP ppm 5Te! GFAA ppm 0.02 : GFAA ppm 0.02 GFAA ppm 0.02 : ICP ppm 10AuFA-DCP ppb I iFADCP ppb I toooo: NA ppb I noAg! ICP ppm 0.1 ; ICP ppm 0.1 . ICP ppm 0.1 ; 1(21’ ppm 0.2Pt; FA-DCP ppb 10 FA-DCP ppb 10 no noPd! FA-PCP pph I FA-DCP pph I no ; noHg Wet pph S Wet ppb 5 1000: Wet ppb 5 : noHg! Wet ppm 0.01Rb; XRF ppm 2 XRF ppm 2 XRF ppm 2 noCs! NA ppm I NA ppm I NA ppm I noBa! XRF ppm I XRF ppm I XRF ppm 1 *eICP ppm 2Sr! XRF ppm I XRF ppm I XRF ppm I ICP ppm ITI; ICP-MS ppm 0.1 ICP-MS ppm 0.1 ICP-Ms ppm 0.1 noppm2 XRF ppm 2 XRF ppm 2 XP.F ppm IZr: XRF ppm I:XRF ppm I XRF ppm I.XRF ppm IY! XRF ppm I : XRF ppm I : XRF ppm I : XRF ppm I‘(“: ICP ppm I ICP ppm I ICP ppm ITh! NA ppm 0.5 : NA ppm 0.5 NA ppm 0.5 : Inst.NA ppm 0.5U; NA ppm 01 NA ppm 01 NA ppm 01 InatNA ppm I8! 0(21’ ppm 10 1 DCP ppm 10 0(21’ ppm 10; noC1 XRF ppm 100 : XRF ppm 100 XRF ppm 100: noLa! ICP-MS ppm 0.1 ; ICP-MS ppm 0.1 ; ICP-MS ppm 0.1 ; Inst. NA ppm 1Ce ICP-MS ppm 0.1 : ICP-MS ppm 0.1 ICP-MS ppm 0.1 : tmt.NA ppm 2Pt! ICP-MS ppm 0.1 ; ICP-Ms ppm 0.1 ; ICP-MS ppm 0.1 ; noNd; ICP-MS ppm 0,1 ICP-M5 ppm 0.1 : ICE-MS ppm 0.1 that. NA ppm 10Sm! ICP-MS ppm 0.1 ICP-M5 ppm 0.1 ICP-MS ppm 0.1 Inst. NA ppm 0.1Eu ICE-MS ppm 0.05 ICP-MS ppm 0.05 ICP-MS ppm 0.05 Inst NA ppm 0.5Gd; ICE-MS ppm 01 ICE-MS ppm 01 ICP-MS ppm 0,1: noTb; ICE-MS ppm 0.1 ICP-MS ppm 0.1 ICP-MS ppm 0.1 lnstNA ppm IDy! ICP-MS ppm 0.1 ICP-Ms ppm 0.1 ICE-MS ppm 0.1 noHo; ICE-MS ppm 0.05 ICP-MS ppm 0.05 ICE-MS ppm 0.05 noEr! ICE-MS ppm 0,1 : ICP-MS ppm 0,1 i ICE-MS ppm 0.1 : noTm3 ICE-MS ppm 0.1 ICP-MS ppm 0,1 ICE-MS ppm 0.1 Inst NA ppm 2rb; ICE-MS ppm 0.1 : ICE-MS ppm 0.1 ICE-MS ppm 0.1 : Inst NA ppm ILu; ICE-MS ppm 0.05 ICP-MS ppm 0.05 3 ICE-MS ppm 0.05 Inst NA ppm 0.2= nói i’nilyzed• voices over detection limit ofother methodsvoices are low—discarded in favour ofvalues measured byXRFTableB.2:Analyticalstandards:summarystatisticaldata.SampleNo.ofSi02T102M203Fe203MnOMgOCaON.20K20P205LOTSUMH20+Samples%%%%%%%%%%%%%QGRM100QGRM101ALB1MBX1wP1P1 MeansStandardDeviationsQGRM100QGRM101ALBIMBXIwP1P1 CoefficientsofJ’ariancsQGRM100QGRM101ALBIMBXIwPIP181.9415.2014,400.5114.803.690.6018.701.580.4817.303.890.5116.404.340.3914.203.740.,000,,830. 8.7010.1012.2517.98 7.25MaximumvaluesQGRM100QGRM101ALB1MBX1;p1P1 Minimumvalues2.0115.6015.200.5115.003.900.6219.001.650.5117.704.080.5316.604.480.4114.503.860.195.768.532.830.‘0.090.62100.4048.8067.2055.4058.6064.7070.4048.4066.2054.2056.9063.3069.7048.5866.6854.8557.8064.1170.040.500.601.501.100.300.50QGRM100QGRM101ALB1MBX1wP1P14 4 4 5 7 8 4 4 4 5 7 8 4 4 4 5 7 8 4 4 4 5 7 8 4 4 4 5 70.190.0098.400.151.2099.000.292.9598.200.253.2597.910.180.0899.000.090.3199.791.9815.4314.900.5114.853.800.6118.881.620.5017.563.980.5216.504.400.4014.393.800.195.618.432.800.050,982.,420.751.800.002.551.341.305.170.7127.500.6813.63TableB.2:...continuedSampleNo.ofSamples%ppmppmppmppmppmppmppmppmppmppmppmppmMaxStandardDeviationsC02CrNiCoVCuPbGeBICdWMoQGRM10040.4484.0045.0043.00216.00143.001.00125.0018.000.500.102.001.00QGRM10140.66250.006.005.0039.0051.701.0037.305.000.500.105.002.00ALB141.6034.0045.0010.00186.001650.001.0013.3010.000.500.100.501.00MBX152.8544.007.007.00177.00467.001.0030.4014.000.500.105.004.00Wp170.0375.0043.0015.0095.0018.301.0062.0019.000.500.102.001.00P180.71140.004.0010.0072.0011.301.0045.2013.000.500.105.002.00Mm QGRM10040.3877.0039.0040.00200.00129.001.00100.005.000.500.100.500.50QGRM10140.61230.003.002.0028.0048.901.0032.305.000.500.100.500.50ALB141.5627.0038.005.00147.001570.001.0010.405.000.500.100.500.50MBX152.7835.005.003.00136.00418.001.0027.305.000.500.102.003.00WP1700160.0037.007.0072.0014.301.0052.305.000.500.100.500.50P180.01120.000.504.0054.007.001.0040.705.000.500.100.500.50MeansQGRM10040.4180.7541.5041.75206.00134.501.00113.008.250.500.100.880.63QGRM10140.63242.504.503.7532.2549.981.0034.285.000.500.101.751.13ALB141.5930.2542.507.25169.251612.501.0012.356.250.500.100.500.63MBXI52.8240.205.604.60160.60434.801.0029.067.800.500.103.803,40Wi’170.0266.2939.579.8682.1415.561.0057.019.570.500.100.710.57P180.11128.572.315.8861.888.941.0042.987.500.500.101.930.75QGRM10041.267.356.030.0010.426.500.000.000.750.25QGRM10141.504.721.’172.799.751.310. ofVarianceQGRM10044.676.383.013.574.480.009.2378.790.000.0085.7140.00QGR.M10143.9528.6940.0014.632.470. 1.090.9850TableB,2:...continuedSampleNo.ofSAsScSeSbTeAuAgPtPdHgRbCsSamplesppmppmppmppmppmppmppbppmppbppbppbppmppmMax3.3028. 1.000.750.750.502.600.64 1.00StandardDeviationsQGRM100QGRM101ALB1MI3XIWPIP1 CoefficientsofVarianceQGRM100QGRM101ALB1MBX1wPP14 4 4 5 7 8 4 4 4 5 7 8AverageCoefficientofVariance102.9690.00231.9585.8326.4633.526.137.7911.153.91330743.460.750.080.750.250.210.351.070.270.330.100.350.4834.483.9785.718.8312.912.675.001.5134.443.8864.074.7117.5939.444. MmQGRM100QGRM101ALB1MBX1WP1P1 MeansQGRM100QGRM101ALB1MBX1wPIP14 4 4 5 7 8 4 4 4 5 7 8 4 4 4 5 7 81800.001200.002400.002300.00110.00140.001550.001020.001890.002090.0050.0050.001680.001155.002080.002195.0080.0077. Miii QGRN100QGRM101ALB1MBX1wpiP1 MeansStandardDeviationsAverageCoefficientofVariance14.215.0677.8441.169.1737.067.1514.4633.1216.124.804.329.44TableB.2:...continuedSampleNo.ofBaSrTiNbZrYTbUBClLaCePrSamplesppmppmppmppmppmppmppmppmppmppmppmppmppmMax4249.00245.001.508.00160.0031.002.201.0028.00347.0013.3031.904.8041150.00580.000.8015.00448.0071.0010.001.8035.00415.0091.80183.0021.004307.001020.000.507.0094.0041.001.301.1064.00241.008.2018.702.805880.00640.000.6019.00112.0025.003.000.8053.00178.0016.9030.103.607707.00905.000.2013.00144.0026.002.101.0039.00280.0014.9031.304.208903.00288.001.5012.00147.0029.004.301.6036.00127.0014.1028.603.404167.00230.000.204.00137.0021.001.800.8011.00311.0012.2029.803.8041010.00521.000.3010.00384.0033.0010.001.405.00381.0080.10164.0016.604127.00932.000.052.0063.0015.000.900.9043.00186.007.4017.302.205658.00585.000.206.0093.008.002.400.4027.00131.0014.5026.402.707560.00726.000.051.00119.0011.001.800.4013.00142.0013.4027.303.308757.00228.000.202.00115.0015.003.901.3015.0050.0012.7025.102.90QGRM1004210.00236.250.656.50147.2527.251.980.9019.50334.5012.7530.484.35QGRM10141087.50552.750.5313.25409.0049.7510.001.6022.50394.7585.50172.5019.68ALB14242.50976.500.205.2577.0025.751.101.0051.50220.507.7018.032.50MBX15781.20613.400.4812.2099.2012.602.660.6442.40156.4015.4027.903.22WP17658.71850.290.097.00128.0015.001.910.8026.14227.0014.1329.543.69P18863.00267.290.465.86125.5719.884.031.5126.2578.7113.4926.313.11QGRM100444.617.090.591.7310.054.350.170.086.9516.340.470.960.44QGRM101468.5025.320.262.2227.3617.910.000.1813.5015.974.827.852.08ALB1479.2744.910.262.3613.2912.530.160.089.1124.280.350.680.24MBX1587.6923.840.184.977.767.230.240.1711.0117.541.121.540.36WP1750.7258.990.064.329.435.770.120.198.6744.580.631.360.37P1852.5819.670.433.2911.395. VarianceQGRM100421.243.0091.0226.656.8215.968.659.0735.654.883.653.1610.19QGRM10146.304.5850.0916.736.6936.010.0011.4160.014.045.644.5510.58ALE1432.694.60129.9045.0117.2648.6514.858.1617.6911.014.503.779.80MBX1511.223.8937.2740.747.8257.409.0526.1525.9811.227.265.5411.28WP177.706.9464.9161.727.3738.496.3523.9433.1619.644.434.6010.08P186.097.3693.8556.139.0725,863.988.0226.2245.943.304.314.68C -‘ITableB.2:...continuedSampleNo.ofNdSmEuGdTbDyHoErTmYbLuSamplesppmppmppmppmppmppmppmppmppmppmppmMaxQGRM100424.606.401.955.901.206.801.384.400.604.200.62QGRM101486.3015.702.3415.101.9010.601.815.900.904.900.74ALB1415.204.001.414.200.704.200.782.700.402.800.39MBX1514.303.101.062.600.402.100.511.,30MBX1513.262.800.892.360.341.880.371.,8910.7714.247.209.10AverageCoefficientofVariance12.6912.1512.8211.5718.9711.6813.1717.8217.9511.6416.0800209TABLE B.3: Values for mid-ocean ridge basalt and North American shale compositeused to normalize data from the 21A zone.Element Units Average MORB 1 NASC2K ppm 955Rb ppm 1.12Cs ppm 0.013Ba ppm 14.3Sr ppm 122Ti ppm 9000Nb ppm 3.58Zr ppm 90Y ppm 34.2Th ppm 0.185U ppm 0.075La ppm 3.96 32Ce ppm 11.97 73Pr ppm 7.9Nd ppm 10.96 33Sm ppm 3.62 5.7Eu ppm 1.31 1.24Gd ppm 4.78 5.2Th ppm 0.85Dy ppm 5.98Ho ppm 1.04Er ppm 3.99 3.4Yb ppm 3.73 3.1Lu ppm 0.56 0.48PEE Tot for MOPE 50.9PEE Tot for NASC 166.9MOPE Mid-Ocean Ridge BasaltNASC North American Shale Composite1 Taylor and McLennan, 19852 Haskin et. al., 1968210SuPPLEMENTuy ScATrER PLOTS8760(.420211100 . I I • IA_7 F—I ‘A50A,‘V250• I I I0 50 100 150 200 250 300 350 400Zr (ppm). I • I • I •VI=1:•aa•A.aA g aI I • I • I0 50 100 150 200 250 300 350 400Zr (ppm).5(.40C’)0C0co2U0.10I I • I • IVI-- VA aa•A VA AAZ • a AAA,a.,. I I0 50 103 150 200 250 300 350 400Zr (ppm)I I • I I IV.I-..—-I VVA VI IAf1’ Au ,0 50 100 150 200 250 300 350 400Zr (ppm)I I I • IIIILa— A I I0 50 100 150 200 250 300 350 400Zr (ppm)650(.4LL0353025201510S054—.30z03025201501050II----I i af IV •VI I IVIV V At•AV•A Va VVI I . I I Vo 50 100 150 200 250 30) 350 400Zr (ppm)I I I IVAA Al*I •IIA• I I I0 50 100 150 200 250 30) 350 400Zr (ppm)0 50 100 150 200 250Zr (ppm)300 350 4002520Ea..15010502120. I • I • IIIa A AI AAIA1V .11 I0 50 100 150 200 250 300 350 400Zr (ppm)I—- I • • IT A VA A A VA ALS S A• LA AI I • I I I50 100 150 200 250 300 350 400Zr (ppm)I I I I I II-IVA Aa:I250200E 1500.010050001000070E6o0.50Q40302010075E0.50C250150100E0.0.z501080.0.>4200600500400E0..9’300.0a-2001000108E60.0.20I • I I I •aa.aIV AALA AA4AA‘A • A 4• A AVI I I I I V50 100 150 200 250 300 350 400Zr (ppm), I I I I IaAA A AaAAj.A A AA, ,5,IV’1•IV0 50 100 150 200 250 300 350 400Zr (ppm)I I I I I+AVA IVA.I I I0 50 100 150 200 250 300 350 403Zr (ppm)0 50 103 150 200 250 303 350 400Zr (ppm)I I I IALA AA AVALI I0I I I I IAAA•V A A VALA AA A V V•* jA•0 40350 100 150 200 250 300 350 400Zr (ppm) 50 100 150 203 250 300 350Zr (ppm)Ea0C,,E0a213I I I •+VAV4aAaaa V•a a.aI II I I •IIIaAaaata tAavavtI a..a I I I r0 50 100 150 200 250 300 350 400Zr (ppm)I I I I II=1aa aa AVa aa‘aI IA I I I V I50 100 150 200 250 300 350 400Zr (ppm)43EaC-,C,)0700600500E400300200100000 50 100 150 200 250 300 350 400Zr (ppm)‘ I I I I I IV•AAV•aatI I I I01000900800700E 600a50040Q30020010001501005002520S 15aa< 1050302520Sa15D1050050 100 150 200 250 300350Zr (ppm)400I I I I I II=1A aVAa. VI I?1% I I I V50 100 150 200 250 300 350 400Zr (ppm)200010000IIII -• I IVI IIVAa.aS A tA4,.As LA06000500)4000Saa,2000100000 50 100 150 200 250 300 350 4(1)Zr (ppm)I I_aV“I’k I I Io 50 100 150 200 250 300 350 400Zr (ppm)50 100 150 200 250 300 350 400Zr (ppm)E0.0.I—200150E0..9’ ioo.0a:502140I• I • III, AAA..VAVVVA IA I I I I0 50 100 150 200 250 300 350 400Zr (ppm)I I I I IAAA AAA.j.I • I • I8007006000..9’ 4002001000605040E0..9’3020100I I • I I I±VI ,A V ,0 50 100 150 200 250 300 350 400Zr (ppm)I I I IA VVA 4A,AAA VVI I I30201000 50 100 150 200 250 300 350 400Zr (ppm)0 50 100 150 200 250 30) 350Zr (ppm)400E- 10>E0a20z2a-a22I-201521543. I • I • I •+VA’A%.V. I I I I0 50 10) 150 200 250 30) 350 400Zr (ppm)I I I I • I+V—A’ •‘AVI I I I0 50 100 150 200 250 30) 350 400Zr (ppm)043, I I I I IAV‘A Va.:.AVI I . I I I I0 50 100 150 200 250 300 350 400Zr (ppm)I I I I I I IAV a aAv V‘a VVI I I I I I0 50 100 150 200 250 300 350 400Zr (ppm)5012S40151050200UI20a.032I I I IaA AV oVA AA VAaAI I I I2a-a-JI I IAV aaA.• aI I I00 50 1(0) 150 2(X) 250 300 350 400Zr (ppm)0 50 100 150 200 250 300 350Zr (ppm)400E 75ci.216125 . i I • 1v100¼25•A4 a• .LA,VA’0• I0 50 100 150 200 250 300 350 400Zr (ppm). I • I • IV II— VVA VAAv A•A. aAa..I I I . I .0 50 100 150 200 250 300 350 400Zr (ppm)2015E0.- 1002001751501250.- 100C..)50250807060.500- 40z302010021.5E0.Dw.50020I I I I I I, IV.ataaI I I I0 50 100 150 200 250 300 350 400Zr (ppm)I I • I I I IF-f-Si‘S +? A gC I I0 50 100 150 200 250 300 350 400Zr (ppm)015F0.10F(/)I I I I I IVA A Aa A.I I I I I50 100 150 200 250 300 350 400Zr (ppm)I I I I I I+••SA • VA VI I ‘1 I2015F0.100(3501 IIIISiS.I I0 50 100 150 200 250 300 350 400Zr (ppm)4 i • i+3 A AS0.Na aaa a S.0 a A VI—VI ‘‘0 ‘ I I I0 50 100 150 200 250 300 350 400Zr (ppm)0 50 100 150 200 250 300 350Zr (ppm)400217APPENDIX CX-RAY DIFFRACTION ANALYSES OF CLAY MINERALsX-ray diffraction samples for the identification of clay minerals were prepared according to standardmethods outlined in the Clay Identification Manual, compiled by Dr. L.A. Groat, Dr. W.C. Barnes and Mrs. S.Horsky. A summary of the procedure is outlined below:Procedure for XRD analysis of clay minerals (oriented samples):Preparation(1) A small sample was ground to a fine powder using a mortar and pestle(2) The powder was dispersed in a small beaker of tap water, allowing a few moments of settling time.(3) Three slides were prepared by transferring the suspended solution to glass slides using a pipette.(4) The slides were left to air-dry, undisturbed, overnight.AnalysisSpectra were collected from 0 to 30 degrees 29, stepping 0.02° every 0.8 seconds.(1) An XRD spectrum was collected from one untreated slide.(2) A second slide was heated to 5 50°C for 1 to 2 hours, and an XP.D spectrum was coliected aftercooling.(3) The third sample was glycol treated by suspending the slide in a dessicator over ethylene glycol forat least 12 hours before collecting an X-ray spectrum.Representative X-ray patterns from the Eskay Creek 21A zone are shown in the appended figures.Procedure for the separation of the clay fraction for detailed XRD and TEM analysesThe purpose of this procedure is to get a clean separate of the clay fraction of a sample for detailedstudy. The procedure was outlined by Dr. Katsumi Marumo (Geological Survey of Japan, personalconununication, 1992).Materials required• 1 L glass beaker • distilled water• 500 ml glass beaker • long stirring rod• 4 to 8 plastic centrifuge tubes • (sodium metaphosphate)• centrifuge • (small beaker)218Method1. Gently crush or crumble the sample and place in the 1 litre beaker. Ensure that the sample is not groundtoo finely, as coarser minerals might be crushed into the clay size fraction and will not separate.2. Add approximately 100 ml distilled water to the beaker to create a sluny and then progressively fill thebeaker to about 1 litre with distilled water.3. Let the sample settle for 10 to 15 minutes and observe:(a) If most of the clay material is still suspended, proceed to Step 5 below.(b) lithe clay has flocculated and settled to the bottom, proceed with Step 4.4. Proceed with this step only if necessaiy, to minimize potential contamination and exchange of Na with theclays.(a) Prepare a small amount of dilute sodium metaphosphate solution by dissolving about ¼teaspoon of sodium metaphosphate in about 200 ml distilled water.(b) Add about 5 to 10 ml of the solution to your clay solution and stir.(c) Allow the sample to settle again for 10 to 15 minutes and observe as in Step 3.(d) lithe clays continue to flocculate, repeat (b) and (c). Repeat this process until the clays remainrelatively suspended after 15 minutes; then proceed to Step 5.5. Let the clay solution settle for 3 hours.6. Carefully pour off the top 1/3 of the settled solution into the clean 500 ml beaker. This fraction shouldcontain only suspended clays.7. Refill the 1 L beaker with distilled water, stir and allow the sample to settle again for the next nm.8. Measure about 30 ml of the solution from the 500 ml beaker into each of the centrifuge tubes. Ensure thatthe centrifuge is precisely balanced. (Each tube should be weighed to ensure equal weight distribution inthe centrifuge.)9. Centrifuge the sample for about 15 minutes at Thigh’ setting (about 1 800 rpm) to draw the clays to thebottom of the tubes.10. Carefully pour off the excess fluid and examine the settled clay in the tube. If it appears that mineralsother than clays are being separated (i.e. pyrite will leave a thin black layer in the clay extract), then thesettling time must be increased.11. Repeat Steps 8 to 10 until all the solution from the 500 ml beaker has been centrifuged.21912. Repeat Steps 5 to 11 until enough material has collected in the centrifuge tubes for XRD analysis.Depending on the amount of clay extracted during each centrifuge session, this may take up to a week ormore.13. Day the sample by scooping the wet, pasty clay out of the centrifuge and allowing it to air-dry in a cleanglass dish or on weighing paper.Method for the estimation of the percent of illite in mixed layered illite/smectiteThe percent composition of illite in possible illite/smectite mixed layer clays may be estimated bycomparing the diffraction patterns from air dried and ethylene glycol-solvated sample preparations. Thequantity A29 is obtained by calculating the difference, in degrees 29, between the (002) and (003) peaks in theethylene glycol solvated sample. An estimate of the illite content of the sample can then be made using thedata presented in Table C.1.Table C.1: Estimates of percent illite in illite/smectite based on empirical observations by Srodon (1980).% Ulite °A2910 5.4920 5.6830 5.9440 6.1650 6.5260 7.0170 7.3880 7.8890 8.38Estimates of iron content in chloriteThe iron content in chlorite can be estimated using the X-ray diffraction pattern of a randomlyoriented powder sample preparation. The method of Brindley and Brown (1980) is described by Moore andReynolds (1989). This method assumes that the only heavy metal present in the chlorite is Fe, and thereforethat the chlorite does not contain significant abundances of Ni, Co, Cr or Mn. Magnesium and aluminum arethe light metals which occupy the chlorite octahedral sites; the differences in scattering power of Mg and Alare negligible for these calculations. Mg is assumed to be occupying the site.The calculations are based on a chlorite formula represented by (Mg,Al)6yFey(Si,Al)4010OH)g.The distribution of Fe with respect to Mg is referred to as the symmetry of the chlorite (D) and is defined as the220number of Fe atoms in the octahedral site of the silicate layer, minus the number of Fe atoms in the hydroxidelayer. Equal portions of Fe and Mg in the two chlorite layers gives a syinmetiy value of zero. The total Fecontent of the chlorite is defined as Y, and ranges between 0 and 6.The value of D is estimated from the ratio of intensities of the (003) and (005) reflections. Estimatesof D can be read from Table C.2.Table C.2: Estimates of symmetry in chlorite (from Brindley and Brown, 1980)D 1(003)11(005)3.0 0.2422.5 0.430.681.5 1.091.0 1.670.5 2.540.0 3.83-0.5 5.76-1.0 8.74-1.5 13.3-2.0 21.2-2.5 34.1-3.0 54.1Using the estimated value of D, a corrected value of 1(003) must be calculated from:I(003)’= I(003)(1 14)2(114— 12.1D)The measure of Y can then be obtained using the values in Table C.3.Table C.3: Estimate of the number of Fe atoms in the six octahedral sites (Y)Y [I(002)+I(004)1 / 1(003)’0 2.381 3.542 5.03 6.74 8.65 10.86 13.4221TABLE C.4: Classification of phyllosilicate minerals--mainly clays (from Moore and Reynolds, 1989).Layer Type Group Subgroup Geometry Species1:1 Serpentine-kaolin Serpentines Tr Cluysotile, antigorite,lizardite, berthierineKaolins Di Kaolinite, dickite, nacrite,halloysiteTaic-pyrophyllite Talc TrpteDiSmectite Smectites Ti Saponite, hectoriteDi Montmorillonite,beideffite, nontroniteVenniculite Vermiculites TrDi2:1 Illite Illite DiMica Micas Tr Biotite, phlogopite,lepidoliteDi Muscovite, paragonite...tlnu Btt1eimcas Di eChlorite Chiorites Tr,Tr Clinochiore (Mg-rich),chamosite (Fe-rich),nimite (Ni-rich),penantite (Mn-rich)Di,Di DonbassiteDi,Tr SudoiteTr,DiTr = trioctahedrat, Di = dioctahedral222The figures on the following pages are representative X-ray diffraction patterns for clay minerals in theEskay Creek 21A Zone. The samples were collected mainly from drillhole CA89-023 to evaluate the downholevariation in composition. All of the samples contained variable proportions of illite, chlorite and quartz with theexception of the lowermost sample at 142 metres, which contained no chlorite. Intensely altered samplescomprising only illite from CA89-019, CA89-043 and CA9O-466 are also shown. CA89-019 is a randomlyoriented powder sample.Both untreated and heated samples were analyzed. Glycol treated samples were run for a small subset ofsamples. The following is a summary of the characteristics of the minerals detected in these samples:C = chloriteOn heating, the (001) peak increases in intensity, while the (002), (003) and (004) peaks essentially disappear.Glycolation has no effect on chlorite.I = illiteOn heating, the (001) peak generally sharpens, suggesting some collapsible component within the illite structure.This may be smectite or possibly interlayer water which is driven off during the heating process. Glycolation hasno effect on the iffite. lithe illite contains expandible clay, such as smectite, as a mixed interlayer, then the peakswill shift after glycolation in relative proportion to the smectite content. However, using the method described bySrodon (1980) and outlined by Moore and Reynolds (1989), the Eskay Creek illite contains less than 10%interlayer smectite.Q = quartzSome quartz was locally suspended during sample preparation and forms distinct peaks on the X-ray diffractionpatterns. Quartz is unaffected by heat and glycol treatments.2232—Theta— ScaleI I I I I‘:C’—23 CD HETEt.•UNTDEATELA1\DsSSe\oATA\23—secRAl1 23—SSC (CT S.S, SS:S.D2Dd, IlL: 1B4S9Fio)A :\D5OSO\DATA\23—BgH FlAW 23—SSH (CT 0 .8s SS :0 D2Dq IlL: 1 .E’4ODjo)2—Theta— ScaleI I-HETEtI‘-III JIlT IJiil II IA:\DS0SS\DATA\23—67CJAW 23-6?C (CT: BS0.0Z0d9 WL: 1.S409Aø)A :\D5000\DATA\23—S7H IRAN 23—67H (CT C S, LCD .D205 IlL 1 E-DLAQ)2242—Theta— ScaleI I I I I I I I I I ICAE:S—23: 72NA HEATED -U: TREATSAfl’.DSOOS’sDPTA\23—72CRAW 23—720 (CT: Ø.Ss, SS:ØS2edg, WL: 1.S4SSAo)A :\D5Og3\DTA\2T—72H RAW 23—72H (CT: S Bs, 55:0 O2Ddg WL 1 E4DSAo2—Theta— ScaleI I I I I ICADS—ES: ESHEATEDC) C! )A:’DS000\DATc\23—83CRAW 23—830 (CT: 0.Ss, SS:O.8205g, HL 1.S4SSAc)A \DECS5\DA\25—B3H SAW 23—83W (CT: 8 As, 8S8 .82839 WL: 1 T-45I5A:m I2252—Theta— Scalec-I I I00,m-I,C0000C. irj-..-ri .W”Y”l i”’f’9”P”V”. 14 £ 6 13 12 14 16 16 23 22 24 26 26A:\DS000\DATA\23—IO7JRAI-4 23—107 (CT: OSs, SSOO2Odg, HL: 1.S4OSAc)A :\DB000\DATA\23—1670 RAU 23—1070 (CT: S Ss, BB:O S2Odg DL: 1 .B4OSAo)A :\DB330\DATA\23—107H BAL-J 23—107H (CT: 0 Bs, SB 0 020d9, HL: 1 E409Ac)&00-I4 6 S 10 12 14 16 16 23A :\DB505\DATA\23—1574C .RAH 23—1074C (CT: 0 Os, SS:0 520d9,A:\DB000\DATA\23—1074H.RAL-J 23—1074H (CT: O.S, SS:0J32Sd9I I I I I I I I I ICAOS—23: 107rnGLYCOLHEATEDb4 aba$ 1MvaUHTPEATEDC C ILL, d.. MA.1 .s..J AI.AØ4fbk,kM4Ji tiItIJskJAaj k.aLlikl,h.2—Theta— Scale0 I I I I I I I I I IC-IUI CAO3—23: 107.4rAHEATED00IQUIITREATECCIIJJA A’ iL. uiSi WU) ‘L.1a22 24DL: IS4OSAc)DL: 1.EAD9Ao)is 62262—Theta — Scale___________0 I I I I I I I I I0CASC—zs: 1@7Sm HEATEDJHTREHTEDCA:\DSØSS\DATA\23—1S79CRAl-J 23—IMT9C (CT: DOs, BS:0.O2Ddg, [4L: 1.S409Ac)A:\DS000\DATA\23—10791-LRAN 23—1074H (CT: 0Ss, 98:0 .020d9 • WL: 1 5409Ao)2—Theta — Scale0 I I I I I I0CAB9—23: 11?-1-1EATEt’UNTIREATEC C Q! q4idáA:\DS000\DATA\23—117C.EAN 23—117C (CT: 0.Es, ES:0.O2Edg, WL: 1.SADSAc)A:\DE000\DATA\23—117H RAW 23—117W (CT: 0.Bs, 9E:0820d ND: 1E409Ao)2272—Theta — ScaleC I I I I I I I I IC‘V CAB9—23: 129mHEATEDI-.UNTFEATEDA:\DE2SO\DATA\23—129C.PAL.1 23—1290 (CT: O.Bs, SS:O.020dg, 146: 1S4Ø9Ac)A:\DEDHO\DATA\23—129H RAN 23—129H (CT: O.Ss, S60.02@dg, WL: 164O9Ao)2—Theta — ScaleC I I I I I I I I&CABS—CS: 139 HEATEDm1UA-urITR:—:EcA :\D9BOØ\DATA\23—ISSC .RAN 23—1350 (CT: 0 9s, 99:0 .020d9 14L: I .S4OSAc)A:\DSOOB\DATAN23—I3EHRAL1 23—136H (CT: BBs, 9900203g WL 154B3Ac,)2—Theta— Scale228I I I I I I ICAB9—22: l42rn—EATEt,ffiYS1Mfl9It.Ø.il4SJ[’.r•’ r’.4 6 S 18 12 14 16 18 28 22 24 26 25A:\DS000\DATA\23—142C.RAW 23—1420 (CT: 0.Ss, S5:5.520d9 WL: 1.S409Ao)A:\0S000\DATA\23—142H.RAW 22—142H (CT: 0.8s, SS:0.020d9, WL: 1.S409AoJh—Theta — ca1e0 I I I I I I I ICCC iH:—19. I’DmrIV.4.1CCS 10 1’S 20 25 20 35 40 45A:\DS000\DATA\19-92 RAW 19—92 CT: BBs, SS:0.020d31 WL: i.S4BSAc)— —9j I h H:r )H1.fl’M1 11 HC Ill it IT Ii F HF IiL 1 JRBAn j00CN.4.1CCa0CCI’QUNTREATEDki ,Il.iLL ...... u 1k .na,Ii..I . . ...k II,lLI /tIL IUIIIkA I1kJs2292—Theta— ScaleI I I I I I INmCA89—43: 1030A:\D500S\D4T\43—1O3oALJ 43—103 (CT: 0.8, SS:3.020d9 (-IL: 1.E4OSAc)2—Theta — ScaleI I I ILCOLE iTEC:\DB000\DATA\T043—104.BAI-J TJ43—104 (CT 08, SS:0.022dg, L-JL: 1E406)C 1\DS000\DATA\GT043—10 .RAW GTR43—104 :CT C SB :C .Ccq (-IL: 1 S4CBAcC:\DB000\DATA\HTFI43—1O.RAI HTFI43—104 (CT: 0.S, BB:0BCdg, (-IL: 1.5406Aü)2302—Theta — Scale(T3 I I I I IICA9O—466: 179CU,GLYCOLiaaa)g HEATEDI Ji+thAJS 4AkJi4WA? LL4&MA;C :\DSSSe\DATA\BG465—17 LAW EG4SS—179 (CT: 6.Ss, 69:0 .020d9, WL: 1 .S4OSAo)C:\D6000\DATA\GTR4GS—1.RAW GTR4BS—179 (CT: 0.Bs, s90.Q2IZa9, L1L: 1.S4OSAo)C:\D9000\DATA\HTR4GS—1LAW HTR4SS—179 (tT:, 9S0.020d9, L-JL: 1.S4OGAo)


Citation Scheme:


Citations by CSL (citeproc-js)

Usage Statistics



Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            async >
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:


Related Items