Geology of the Indian River Area Southwestern British Columbia

GEOLOGY OF THE INDIAN RIVER AREA SOUTHWESTERN BRITISH COLUMBIA

DOUGLAS GERALD REDDY

B.Sc.(Honours), The University of British Columbia, 1986

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF

THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

THE FACULTY OF GRADUATE STUDIES

(Department of Geological Sciences)

We accept this thesis as conforming

to the required standard

THE UNIVERSITY OF BRITISH COLUMBIA

APRIL 1989

The University of British Columbia 2075 Wesbrook Place Vancouver, British Columbia Canada V6T 1W5

To whom it may concern: In presenting this thesis in partial fulfillment of the requirements for an advanced degree at The University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of the Department of Geological Sciences or by his or her representatives that include n supervisors, Drs. J.V. Ross and C.I. Godwin. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.

Douglas G. Keddy Department of Geological Sciences ii

ABSTRACT

The Britannia - Indian River pendant is a composite of volcanic and sedimentary units within the Coast Plutonic Complex, southwestern British Columbia. Geology of the Indian River valley consists of a rhyolitic to basaltic calc-alkaline suite of volcanic flows and tuffs interbedded with shallow marine sedimentary rocks. The pendant is within Wrangellia and has been assigned to the Gambier Group of Late Jurassic to Early Cretaceous age.

K-Ar analyses indicate three major thermal events took place in the Britannia - Indian River pendant: (1) a late Early Cretaceous contact metamorphism (108 — 4 Ma), (2) an early Late Cretaceous regional metamorphic reset associated with emplacement of granitoid plutons (96.1 — 3.0 Ma, 95.6 — 3.3 Ma), and (3) a Late Cretaceous (83.5 — 3.0 Ma, 84.2 — 2.9 Ma) metamorphic reset due to a deformational and/or intrusive event. A poorly defined whole rock Rb-Sr isochron from seven fresh- looking volcanic units indicates a 102 — 10 Ma age that also probably reflects metamorphic reset. An internal Rb-Sr isochron comprising partial mineral separates from one sample yielded 93 — 3 Ma, which supports the regional metamorphic reset.

Younger dykes and sills are dated as Early Oligocene (36.1 — 1.3 Ma). These Tertiary intrusives are the same age as dykes in the city of Vancouver and indicate a more widespread magmatic event than previously recognized.

The stratigraphic section in the Indian River and Stawamus River valleys consists of more than 2,850 metres, and comprises seven units that trend northwesterly and dip moderately south or southwest. A change in the overall strike from northwest in the Indian River valley to west in the Stawamus Valley suggests either: (1) an angular unconformity within unit 4a, (2) the existence of a major shear zone in the Stawamus River valley, or (3) warping of the strata due to emplacement of the plutonic bodies. The stratigraphy in the Indian River area forms the western limb of a broad northwesterly trending antiform, overturned to the northeast. Along the Indian River a smaller anticline has been disrupted by several faults. These northwest trending faults are the northern extension of the Indian River shear zone.

The stratigraphic units are mainly subaqueous felsic to intermediate pyroclastic rocks, felsic and intermediate to mafic flows, and sedimentary rocks including cherts, argillites and greywackes. Major and trace element chemistry of volcanic units indicates the calc-alkaline rocks are dominantly rhyolite and basaltic andesite. Mafic units on Sky Pilot Mountain have a "borderline" tholeiitic - calc-alkaline character.

Late Cretaceous lower greenschist facies metamorphism is related to emplacement of Coast Plutonic Intrusives. Intense cordierite-biotite contact metamorphism post-dates mineralization in the Slumach zone: a polymetallic quartz- chlorite vein with anomalous gold values. The War Eagle zone is a low grade volcanogenic system containing remobilized sulphides. Galena lead isotopic analyses of volcanogenic prospects in the Indian River valley are uniform and are less radiogenic than those of the Britannia volcanogenic ore bodies 10 kilometres to the west. The Indian River portion of the Britannia - Indian River pendant is proposed to be Late Jurassic in age while the Britannia area is Late Jurassic to Early Cretaceous. iv

TABLE OF CONTENTS Page ABSTRACT ii TABLE OF CONTENTS iv LIST OF FIGURES ix LIST OF TABLES jriii ACKNOWLEDGEMENTS xv

1.0 INTRODUCTION 1 1.1 INTRODUCTION AND LOCATION 1

1.2 PHYSIOGRAPHY 1 1.3 HISTORY 4

1.4 SCOPE OF THESIS 7

2.0 REGIONAL GEOLOGY 8 2.1 INTRODUCTION 8 2.1.1 TWIN ISLANDS GROUP 8 2.1.2 BOWEN ISLAND GROUP 9 2.1.3 GAMBIER GROUP 11 2.1.3.1 Nomenclature and Divisions 12 2.1.3.1.1 Goat Mountain Formation 14 2.1.3.1.2 Britannia Formation 15 2.1.3.2 Regional Setting 15 2.1.4 COAST PLUTONIC INTRUSIVES 17 2.1.5 LATE INTRUSIVES 17

3.0 REGIONAL DISCRIMINATION, USING GALENA LEAD ISOTOPE DATA, OF VOLCANOGENIC FROM PLUTONOGENIC DEPOSITS IN GAMBIER GROUP AND SPATIALLY RELATED STRATIGRAPHY 19 V

Page 3.1 INTRODUCTION 19 3.2 REGIONAL GEOLOGY AND MINERAL DEPOSITS 25

3.2.1 BOWEN ISLAND GROUP 26 3.2.2 HARRISON LAKE FORMATION 27 3.2.3 BROKENBACK HILL FORMATION 28

3.2.4 FIRE LAKE GROUP 29 3.2.5 GAMBIER GROUP 29 3.2.6 CHEAKAMUS GROUP 31 3.3 GALENA LEAD ISOTOPE ANALYSES 33 3.4 GALENA LEAD ISOTOPE DATA AND DISCUSSION 36 3.4.1 CLUSTERS A TO C: Volcanogenic Group V 39 3.4.2 CLUSTERS D AND E: Plutonogenic Group P 41 3.4.3 DEPOSITS WITH ISOTOPIC VALUES THAT PLOT IN TWO CLUSTERS 43 3.5 INCREASING RADIOGENIC SIGNATURES COINCIDENT WITH YOUNGING OF STRATIGRAPHY 43 3.6 CONCLUSIONS 45

4.0 LOCAL GEOLOGY 48 4.1 INTRODUCTION 48 4.1.1 LOWER GOAT MOUNTAIN FORMATION (unit LGM) 48 4.1.2 MIDDLE GOAT MOUNTAIN FORMATION 53 4.1.2.1 Lower Intermediate Volcanics (unit 1) 54 4.1.2.2 Felsic Volcanics and Sediments (unit 2) 55 4.1.2.3 Massive Intermediate to Mafic Volcanics (unit 3) 57 4.1.2.4 Felsic Tuffs and Sediments (unit 4a) and Intermediate to Mafic Volcanics (units 4b and 4c) 59 vi

Page 4.1.2.5 Intermediate Volcanics (unit 5a) and Felsic Sediments (unit 5b) 62 4.1.2.6 Sky Pilot Succession (unit 6).. 62

4.1.3 PLUTONIC INTRUSIONS 63

4.1.3.1 Stawamus Gabbro (unit A) 63

4.1.3.2 Granodiorite Intrusives (units B^, B2 and B3) 65 4.1.3.3 Porphyritic Rhyolite (unit C) 68 4.1.4 LATE INTRUSIVE DYKES (unit D) 71

4.1.4.1 Aplite Dykes 71

4.1.4.2 Andesite Dykes 71 4.1.4.3 Basalt Dykes 72

4.1.5 METAMORPHISM 74 4.1.5.1 Regional Metamorphism 74 4.1.5.2 Contact Metamorphism 75 4.2 STRUCTURE 78 4.2.1 STRUCTURAL DOMAINS 78 4.2.2 FAULTS AND SHEAR ZONES 83 4.2.3 SUMMARY OF STRESS 84 4.3 MAJOR AND TRACE ELEMENT CHEMISTRY 86 4.3.1 DUPLICATE SAMPLES AND PELLETS 87 4.3.2 MAJOR ELEMENT CHEMISTRY 88 4.3.2.1 Classification of Rock Types 91 4.3.2.2 Alteration 96 4.3.2.3 Classification and Trends of the Volcanic Suite 101 4.3.3 TRACE ELEMENT CHEMISTRY 107 4.3.3.1 Classification of Rock Types 107 4.3.3.2 Magmatic Differentiation Trends 110 vii

Page 4.3.3.3 Tectonic Setting 113 4.4 GEOCHRONOLOGY 115 4.4.1 POTASSIUM-ARGON 116 4.4.1.1 Late Early Cretaceous (108 Ma) 118 4.4.1.2 Early Late Cretaceous (101 - 89 Ma) 118

4.4.1.3 Late Cretaceous (84 - 79 Ma) 119 4.4.1.4 Mid-Tertiary (36 - 31 Ma) 119

4.4.2 RUBIDIUM-STRONTIUM 120

4.4.2.1 Middle Jurassic (168 - 166 Ma) 126 4.4.2.2 Early Cretaceous (119 -100 Ma) 126

4.4.2.3 Late Cretaceous (93 Ma) 127 4.4.2.4 Mid-Tertiary 127 4.4.3 GEOCHRONOLOGICAL SUMMARY 127 4.5 MINERALIZATION 131 4.5.1 DEPOSITS 131 4.5.2 SUMMARY 135

5.0 CONCLUSIONS 137

6.0 BIBLIOGRAPHY 143

APPENDIX A: STRUCTURAL DATA FOR UNITS IN THE INDIAN AND STAWAMUS RIVER VALLEYS 148 A. 1 STEREONET PLOTS OF STRUCTURAL DATA. 148 i APPENDIX B: MAJOR AND TRACE ELEMENT X-RAY FLUORESCENCE PREPARATION AND ANALYTICAL PROCEDURES 152 B. l SAMPLE PREPARATION AND ANALYSES 152 viii

Page B.1.1 MAJOR ELEMENTS 152 B. 1.2 TRACE ELEMENTS 158

APPENDIX C: POTASSIUM-ARGON AND RUBIDIUM-STRONTIUM PREPARATION AND ANALYTICAL PROCEDURES 160 C.l SAMPLE PREPARATION 160 C. 1.1 POTASSIUM-ARGON ANALYSES 160 C.1.2 RUBIDIUM-STRONTIUM ANALYSES 161

APPENDIX D: GALENA LEAD ISOTOPE FOR DEPOSITS IN THE HARRISON LAKE TO JERVIS INLET AREA 163 ix

LIST OF FIGURES Page 1.1 location and regional geology map for the Indian River project area, southwestern British Columbia 2 1.2 A view looking northwesterly from the north end of Maggie Ridge over the broad "U" shaped Stawamus River valley 5 2.1 Comparison of the Gambier Group type sections with the lithologic sections from the Britannia - Indian River pendant, southwestern British Columbia 13 3.1 Regional geology and locations of deposits sampled for galena lead isotope analyses. Tectonic assemblage map of British Columbia is inset 20 3.2 Plot of ^Pb/^Pb versus ^Pb/^Pb data for deposits sampled within the Harrison Lake to Jervis Inlet area 22 3.3 Plot of ^Pb/^Pb versus ^Pb/^Pb data for deposits sampled within the Harrison Lake to Jervis Inlet area 23 3.4 Plot of ^Pb/^Pb versus ^Pb/^Pb data for deposits sampled within the Harrison Lake to Jervis Inlet area 24 3.5 Average galena lead isotope analyses plotted on a

207pb/204pb versus ^Pb/^Pb diagram to compare with the shale, mantle and upper crust growth curves 38 4.1 Local geology map (1:10,000), cross sections and stratigraphic section for the Indian River area 4.2 Field Map #1 (1:2,500) Northwest Corner I 4.3 Field Map #2 (1:2,500) Northeast Corner / , 4.4 Field Map #3 (1:2,500) Southwest Corner * / Collect 4.5 Field Map #4 (1:2,500) Southeast Corner J 4.6 Pale green flowbanded rhyolite of the lower Goat Mountain formation (unit LGM) 49 4.7 Heterolithic fragmental tuff of the lower Goat Mountain formation (unit LGM)...49 4.8 Graded tuffaceous siltstone of the lower Goat Mountain formation (unit LGM) showing tops to west 51 4.9 Fossiliferous calcareous tuff of the lower Goat Mountain formation (unit LGM): (a) handspecimen, and (b) rubber casts from fossil molds of echinoderm spines that are visible in (a) 52 4.10 Sample, from a tuff in the middle portion of unit 2, consists of flattened, partly welded devitrified glass shards replaced by penninite 56 X

Page 4.11 Heterolithic fragmental tuff, from the upper portion of unit 2, exhibiting poor bedding 56 4.12 Massive basaltic andesite flows of unit 3 crop out along the crest of Maggie Ridge. Upper and lower contact outlines are indicated 58 4.13 Flow bottom of a basaltic andesite flow (unit 4b) is in contact with the top of recessive felsic tuffaceous sediments (unit 4a) 58 4.14 Massive pyroxene phyric mafic flows (unit 4c) crop out in the Stawamus River valley 61 4.15 Ash-rich mudstone (unit 5b) containing accretionary lapilli crops out on the west side of the Stawamus River valley 61 4.16 Coarse grained Stawamus gabbro (unit A) is characterized by labradorite megacrysts 64 4.17 Medium grained Indian River biotite granodiorite (unit B^) is characteristic of the Indian River Intrusives 64 4.18 Medium to fine grained Mountain Lake biotite hornblende granodiorite (unit B2) is characteristic of the Mountain Lake pluton 67 4.19 Pink, medium grained Squamish biotite granodiorite (unit B3) is characteristic of the Squamish pluton 67 4.20 Quartz and feldspar porphyritic rhyolite intrusives (unit C) occur along the east side of the Indian River valley 70 4.21 Weathered cordierite-biotite hornfels is observed in the Slumach zone 76 4.22 Porphyroblasts of cordierite within a cordierite-biotite hornfels occur near the Slumach zone 76 4.23 Domain 1 stereonet plots of structural data (unit LGM) 79 4.24 Domain 2 stereonet plots of structural data (units 1,2,3 and the lowermost portion of unit 4a) 80 4.25 Domain 3 stereonet plots of structural data (units 4a, 4b, 4c, 5a, 5b and 6) 81

4.26 FeOTOTAL/MgO versus SiC>2 for volcanic rocks from the Indian River and Stawamus River valleys 92 4.27 (a) Normative colour index versus normative plagioclase composition, and (b) AI9O3 versus normative plagioclase composition for volcanic rocks from the Indian River and Stawamus River valleys 93 4.28 Na^O + K^O versus SiC>2 for volcanic rocks from the Indian River and Stawamus River valleys 97 xi

Page 4.29 MgO versus CaO for volcanic rocks from the Indian River and Stawamus River valleys 97 4.30 MgO versus Si02 for volcanic rocks from the Indian River and Stawamus River valleys 98 4.31 CaO versus Si02 for volcanic rocks from the Indian River and Stawamus River valleys 98 4.32 Na^O versus Si02 for volcanic rocks from the Indian River and Stawamus River valleys 99 4.33 K7O versus Si02 for volcanic rocks from the Indian River and Stawamus River valleys 99 4.34 AFM ternary diagram for volcanic rocks from the Indian River and Stawamus River valleys 103 4.35 An-Ab'-Or ternary diagram for volcanic rocks from the Indian and Stawamus River valleys 103

4.36 MgO versus FeOTOTy4, for volcanic rocks from the Indian River and Stawamus River valleys 104 4.37 AI7O3 versus Si02 for volcanic rocks from the Indian River and Stawamus River valleys 104

4.38 FeOTOTAL versus SiCh for volcanic rocks from the Indian River and Stawamus River valleys 105

4.39 TiO? versus FeOTOTAL for basalts from the Indian River and Stawamus River vafleys 105 4.40 Si02 versus Zr/Ti02 for volcanic rocks from the Indian River and Stawamus River valleys Ill 4.41 Si02 versus Nb/Y for volcanic rocks from the Indian River and Stawamus River valleys Ill 4.42 Nb/Y versus Zr/Ti02 for volcanic rocks from the Indian River and Stawamus River valleys 112 4.43 Ti versus Zr for volcanic rocks from the Indian River and Stawamus River valleys 112 4.44 (a) Ti-Zr-Y and (b) Ti-Zr-Sr ternary diagrams for volcanic rocks from the Indian River and Stawamus River valleys 114 4.45 Rb-Sr internal isochrons for volcanic rocks from the Indian River and Stawamus River valleys, southwestern British Columbia 123 xii

Page 4.46 Rb-Sr isochrons based on whole rock analyses of volcanic rocks from the Britannia - Indian River pendant 124 4.47 Isotopic dates and correlated geologic events in the Britannia - Indian River pendant 129 A.1 Stereonet plots of structural data for (a) unit LGM, (b) unit 1, and (c) unit 2 149 A.2 Stereonet plots of structural data for (a) unit 3, (b) unit 4a of package II, and (c) unit 4 of package III 150 A.3 Stereonet plots of structural data for (a) unit 5, (b) unit 6, and (c} all minor fold axes, mineral lineations and slickensides (upper stereonet) and all faults (lower stereonet) measured in the project area 151 xiii

LIST OF TABLES Page 2.1 Table of Groups and Formations in the Howe Sound area, southwestern British Columbia 10 3.1 Capsule descriptions of deposits sampled for galena lead isotope analyses from Jurassic and Cretaceous pendants in the Harrison Lake to Jervis Inlet area, southwestern British Columbia 34

3.2 Averaged galena lead isotope analyses, and interpreted ages for clusters within groups, for deposits and showings from the Harrison Lake to Jervis Inlet area, southwestern British Columbia 35

4.1 Major element oxides of samples from volcanic units in the Indian and Stawamus River valleys 89 4.2 Major element oxides of samples from intrusive units in the Indian and Stawamus River valleys 90 4.3 Average weight percent oxides for rock types and packages of units sampled in the Indian and Stawamus River valleys 94 4.4 Trace element analyses of volcanic units from the Indian River and Stawamus River valleys 108 4.5 Trace element analyses of intrusive units from the Indian River and Stawamus River valleys 108 4.6 Potassium-argon analyses of volcanic rocks and mineral separates from the Britannia - Indian River pendant 117 4.7 Rubidium-strontium analyses of volcanic rocks from the Indian and Stawamus River valleys 121 4.8 Rubidium-strontium analyses of volcanic rocks Britannia Ridge and Sky Pilot Mountain 122 4.9 Calculated rubidium-strontium isochron dates for volcanic rock suites from the Britannia - Indian River pendant 125 B.l Major element oxides (prior to normalization) of rock samples from the Indian and Stawamus River valleys 154 B.2 The major element weight percent oxides, means and standard deviations for the BCR-1 monitor pellet 155 B.3 Cation and CIPW Norms were calculated from normalized major element weight percent oxides for volcanic and intrusive rocks from the Indian and Stawamus River valleys 156 B.4 Minor element concentrations, means and standard deviations for the monitor pellet (AGV-1) which was run to estimate the analytical precision 159 xiv

Page B.5 Standard errors for trace elements calculated in the program OBTRACE based on the scatter of the measurements from the calibration curve 159 D.l Galena lead isotope data for deposits from the Harrison Lake to Jervis Inlet area, southwestern British Columbia 164 XV

ACKNOWLEDGMENTS

I thank John Ross and Colin Godwin for their guidance. Funding for the thesis was from a British Columbia Ministry of Energy, Mines and Petroleum Resources and Canada/British Columbia Mineral Development Agreement grant to Ross and Godwin. Some field support was provided kindly by Minnova Inc. through the cooperation of Alex Davidson who was also a thesis committee member. Discussions with Harold Gibson (formerly with Minnova Inc.) and Colin Burge, Minnova Inc., contributed to an understanding of the geologic setting. Colin Burge helpfully reviewed the thesis.

I thank Tom Schroeter, British Columbia Geological Survey, for his suggestions while visiting the project area and for reviewing the thesis. Gary Sutton and Chris Hood were enthusiastic field assistants during the 1986 and 1987 field seasons respectively. I am grateful to the following people for providing samples for the lead isotope study: Dieter Schindelauer of Chahce Mining Co., Harold Hopkins, Nils von Fersen of Falconbridge Ltd. and Vic Guinet of Golden Eye Resources. Specific thanks are extended to James Laird for providing several samples and being a source of information on several otherwise little known deposits. R.L. Armstrong and Stanya Horsky helped in the organization of the X-ray fluorescence analyses and reviewed portions of the thesis. I am grateful to Janet Gabites, Dita Runkle, John Knight and Joe Harakal for their expertise in varying aspects of sample analyses. I also thank the department staff, technicians, and fellow graduate students. Special thanks are extended to my fiance, family and friends for their understanding and support. 1

1.0 INTRODUCTION

1.1 INTRODUCTION AND LOCATION

The Indian River project area includes the eastern half of the Britannia - Indian River pendant within the Coast Plutonic Complex in southwestern British Columbia (Fig. 1.1). The pendant is a variably metamorphosed assemblage of marine pyroclastics, flows and sedimentary units that host the major volcanogenic Britannia deposits as well as several small volcanogenic prospects along the Indian River valley.

The map area covers 15 square kilometres centred at latitude 49° 38' north and longitude 123° 02' west (NTS map sheet 92G/11E). Vancouver is 40 kilometres to the south and Britannia Mine is 10 kilometres west of the Indian River. Access is from Squamish by 10 kilometres of logging and power-line service roads that parallel the Stawamus and Indian River valleys and continue to Indian Arm. Several clear-cut areas and logging roads in poor condition provide access to both sides of the valleys.

1.2 PHYSIOGRAPHY

The project area straddles the pass, 800 metres in elevation, between the Indian and Stawamus Rivers. Indian River drains southeast to Indian Arm of Burrard Inlet, and the Stawamus River flows northwest towards Squamish. Rugged relief ranges in elevation from 750 to 1,900 metres within the project area but reaches 2,600 metres at Sky Pilot Mountain, immediately west of the area. Vegetation, typical of a temperate 2

Figure 1.1 Location and regional geology map for the Indian River project area, southwestern British Columbia. Geology is modified from Roddick (1965), Roddick et al. (1979) and Roddick and Woodsworth (1979).

Legend Cover Units Quaternary Alluvial, marine and glacial deposits.

Tertiary - Quaternary Garibaldi Group: basalt, andesite, dacite and rhyodacite flows. Upper Cretaceous - Tertiary Kitsilano and Burrard Formation: sandstone, shale, conglomerate; minor tuff and coal.

Coast Plutonic Complex Jurassic - Tertiary + Plutonic Rocks: quartz diorite, granodiorite, + + diorite, granite and minor gabbro. Age Unknown 23 Migmatitic complexes of amphibolite grade.

stratified Units Jurassic - Lower Cretaceous Gambier Group: andesite to rhyolite flows and pyroclastics, some mafic flows, greenstone, greywacke, argillite, agglomerate, minor conglomerate, limestone and schist. Middle Jurassic ? EE| Bowen Island Group: greenstone, tuff, minor tuffaceous chert and greywacke. Pennsyh'anion and Permian ? Twin Islands Group: granulite, gneiss, schist, amphibolite, conglomerate, hornfels, quartzite, meta-arkose and migmatite. 3

123"15'W 123°W + + + 1+ + + \t- +¥ +*S f + + + + + Squam + + +/«- + + + + + + +^

kilometres Figure 1.1 (continued) 4 rain forest, consists of thick underbrush and heavy timber growth that thins at higher elevations.

The best rock exposures are along bluffs, on steep slopes and in stream cuts. Glacial and alluvial accumulations in the valleys limit the amount of outcrop. The broad U-shape of Stawamus valley (Fig. 1.2) and rounded outcrops on ridges are due to Pleistocene glaciation. Remnant cirques can be found on the slopes of Sky Pilot Mountain (Figs. 1.1 and 4.1).

1.3 HISTORY

Previous studies have focused on the western half of the Britannia - Indian River pendant around Britannia Mine or on areas to the south (Schofield, 1908; James, 1929; Armstrong, 1953; Roddick, 1965). The earliest works describe shoreline geology near Howe Sound and Jervis Inlet (Bauerman, 1885; Le Roy, 1908).

Development of the Britannia ore bodies in the early 1900's led to intense prospecting in the Britannia and Indian River areas. In 1910 the ABC claim group was staked near the centre of the present project area (Lisle, 1981). Completion of the Squamish to Indian Arm trail in 1917 allowed examinations of several prospects by government geologists (Grant, 1917; Camsell, 1917; Brewer, 1918).

Numerous pendants exposed on Howe Sound and in Jervis Inlet were referred to as the Britannia Group by Le Roy (1908). Schofield (1918, 1926) divided the Britannia Group into the Goat Mountain Formation, and the overlying Britannia Formation that hosts the Britannia ore bodies. James (1929) extended mapping of these formations to Figure 1.2 A view looking northwesterly from the north end of Maggie Ridge over the broad "U" shaped Stawamus River valley. The northern half of the Indian River project area is in the foreground. 6 the Indian River valley, but indicated that the Britannia Formation was older than, and was thrust over, the Goat Mountain Formation. Subsequent studies have dealt mainly with plutonic rocks or other pendants in the region (Phemister, 1945; Armstrong, 1953; Roddick, 1965).

Gambier Group, named by Armstrong (1953), is based on a type section at Gambier Island. Several other pendants, such as the Britannia - Indian River pendant, have been assigned to the Gambier Group based on lithologic similarities to the type section, and to a second type section at Mount Brunswick introduced by Roddick (1965). Several theses have since been completed on pendants along Howe Sound and at Britannia Mine (Lee, 1958; McKillop, 1973; Caron, 1974; Heah, 1982; McCoU, 1987).

Stratigraphy of Sky Pilot Mountain and Goat Ridge, west of the project area, was mapped most recently by Heah (1982) as Gambier Group (Fig. 1.1). This area is adjacent to and west of the Indian River map area, and overlies the Indian River stratigraphy. Heah's mapping provides a link from this study to work by McColl (1987) on Britannia Ridge (Fig. 1.1). McColl's work supports a continuous south to southwest dipping succession over Britannia Ridge.

Recent mineral exploration in the project area has been conducted by: (1) New Jersey Zinc Exploration Co. and Croyden Mines Limited (1969-1970), (2) Anaconda (early 1970's), (3) International Maggie Mines Ltd. (1977-1987), and (4) Placer Development Incorporated who optioned the property from International Maggie Mines Ltd. (1978-1980). Minnova Inc. and Falconbridge Ltd. are currently exploring in the area, and Minnova Inc. has an option on the project area. 7

1.4 SCOPE OF THESIS

Although the area is close to Vancouver, little detailed geologic mapping has been done. This study examines the relative structural and stratigraphic position of the Indian River area with respect to the previously defined Gambier Group. It also attempts a stratigraphic comparison of the mineral prospects in the project area with the Britannia volcanogenic ore bodies, about 10 kilometres to the west.

The 1:2,500 field maps of the Indian River area (Figs. 4.2 to 4.5 in pocket) were made during the summers of 1986 and 1987. They show outcrop density, accurate sample locations and provide structural data. The geology has been generalized to 1:10,000 in Figure 4.1 (in pocket). 8

2.0 REGIONAL GEOLOGY

2.1 INTRODUCTION

The Coast Plutonic Complex extends from the Fraser lowlands to Alaska, and is over 1,700 kilometres long and 96 kilometres wide (Roddick el al., 1977). The southwestern portion of the Complex consists of plutonic bodies and amalgamated allochthonous terranes. Monger §1 ah (1982) believe they were part of a composite terrane of Alexander and Wrangellia that came together in Late Jurassic and accreted to North America in the Cretaceous and Early Tertiary. Plutonic activity migrated from Vancouver Island eastwards into the Coast Mountains from the Jurassic to Tertiary (Godwin, 1975; Woodsworth and Tipper, 1980). The Coast Plutonic Intrusives enclose portions of stratified rocks creating screens and/or pendants.

Pendants in the Howe Sound area are divided on the basis of relative age, from oldest to youngest, and lithology into: (1) Twin Islands Group, (2) Bowen Island Group, and (3) Gambier Group. These major groups, plutonic bodies and late intrusives are described in the following five sections.

2.1.1 TWIN ISLAND GROUP

Twin Islands Group pendants occur south of the project area, near Indian Arm and Horseshoe Bay (Fig. 1.1), and at the north end of Harrison Lake (Fig. 3.1). Roddick (1965) noted that most units in this group trend northwest, dip steeply and are isoclinally folded. Twin Islands Group rocks have experienced upper amphibolite fades 9 regional metamorphism (Roddick, 1965). Rock types include: granulite, gneiss, schist, amphibolite, micaceous quartzite, as well as minor conglomerate, hornfels, meta- arkose, and migmatite (Roddick, 1965; McKillop, 1973).

No fossils or radiometric dates have been obtained for this group but it is postulated to be Pennsylvanian to Permian (Roddick and Okulitch, 1973; Table 2.1). Ditson (1978) contended that the unit is a "catch-all" term for intensely metamorphosed pendants and therefore could include rock of various ages. Roddick (1965) noted that the presence of granitic pebbles indicates that the unit is not older than all of the granitic rocks and therefore the age is more appropriately defined as pre-Jurassic or Late Paleozoic.

Contacts with younger plutonic rocks are often gradational migmatites or faults (Bostock, 1963). The Twin Islands Group is unconformably overlain by the Gambier Group on Mount Seymour, 35 kilometres southeast of the project area (Bostock, 1963).

2.1.2 BO WEN ISLAND GROUP

The Bowen Island Group was named by Armstrong (1953) for rocks on Bowen Island and other exposures around Howe Sound. Armstrong (1953) divided the group into: (1) basaltic to andesitic volcanic rocks, and (2) tuffs and sedimentary rocks. Sedimentary rocks, sheared agglomerates and breccias are interbedded with the volcanic rocks. Locally the group has been metamorphosed to chloritic and biotitic schists, and migmatite (Armstrong, 1953; Lee, 1958). 10 Table 2.1 Table of Groups and Formations in the Howe Sound area, southwestern British Columbia. Modified from Roddick, 1965 and updated with information from McKillop, 1973; Roddick et al., 1979; and McColl, 1987.

Period Group/Formation Lithology Age(Ma)

Pleistocene Cover units Alluvial, marine and glacial deposits to Recent (up to 1,100 metres)

Garibaldi Group Andesite, basalt, dacite and rhyo- 0.04 to (up to 600 metres) dacite flows; minor pyroclastic rocks 1.3

Unconformable and nonconformable contacts (Cover units overlie older units)

Oligocene Dykes Andesite and basalt intrusives and flows 36.1^.3

Intrude and overlie older units

Cretaceous Kitsilano and Sandstone, shale and conglomerate; minor to Tertiary Burrard Formations tuff and coal. Intercalated and cross (> 2,700 metres) -cut with: basalt flows and/or sills, and dykes and minor pyroclastic rocks

Unconformably overlie older units

Jurassic, Coast Plutonic Medium to coarse grained quartz diorite, Cretaceous, Intrusives granodiorite, diorite, granite, to Tertiary -Indian River pluton minor gabbro and migmatite -Mountain Lake pluton -Squamish pluton 10^2

Intrude and surround pre-Cretaceous units

Jurassic Gambier Group Andesite to rhyolite flows and pyroclastics; to Lower (> 6,000 metres) some mafic flows, greenstone, greywacke, Cretaceous argillite and agglomerate; minor conglomerate, limestone and schist.

[Divisions, correlations and lithologies of James (1929), Armstrong (1953), Roddick (1965), Heah (1982), and McColl (1987) are presented in Fig. 2.1]

Angular unconformity between Bowen Island & Gambier Groups (Armstrong, 1953)

Thornbrough Intrusions cross-cut Bowen Island Group (McKillop, 1973) \S3rS

Middle Bowen Island Group Mainly altered andesite flows and tuff; minor Jurassic (> 1,525 metres) tuffaceous chert, greywacke, agglomerate and metamorphosed equivalents

Relationship uncertain—in part equivalent (Roddick, 1965)

Pre-Jurassic: Twin Islands Group Granulite, gneiss, schist, amphibolite, Pennsylvanian (thickness unknown) conglomerate, hornfels, quartzite, meta to Permian(?) -arkose, calc-silicate rocks and migmatite 11

Several thousand metres (cf. Roddick, 1965: several thousand feet) of section are present on Bowen Island, but no stratigraphic breakdown has been attempted. Other Bowen Island pendants occur at the southern end of Howe Sound. The group is characterized by west to northwest trending folds with steeply dipping limbs (Bostock, 1963).

A probable Middle Jurassic age has been suggested for the Bowen Island Group without firm fossil evidence (Roddick and Woodsworth, 1979). The Thornbrough Intrusions, dated as Late Jurassic by McKillop (1973) at 153 — 5 Ma (average of potassium-argon dates of biotite and hornblende separates), intrude the Bowen Island Group indicating that it must be Jurassic or older. The Bowen Island Group is not observed in contact with the Twin Islands Group, but is assumed to be younger because of the intense regional metamorphism of the Twin Islands Group. An angular unconformity separates the Bowen Island Group from the overlying Gambier Group (Armstrong, 1953).

2.1.3 GAMBIER GROUP

During the Late Jurassic, plutonism occurred and portions of the Coast Mountains were uplifted (Woodsworth and Tipper, 1980). Intense intermediate and felsic island arc volcanism and sedimentation took place into successor basins that flanked the uplifted portions (Roddick el al., 1977). The volcanic activity started at least as early as the Middle Jurassic and spanned Lower Cretaceous (Albian) during the last marine transgression (Woodsworth and Tipper, 1980). These rocks are now represented by the Gambier Group pendants that have a calc-alkaline volcanic affinity. 12

Further uplift of the Coast Mountains was associated with emplacement of Late Cretaceous plutons such as those surrounding the Britannia - Indian River pendant.

2.1.3.1 Nomenclature and Divisions

Gambier Group has been assigned to numerous Mesozoic marine volcanic and sedimentary pendants in a northwest trending distribution from Indian Arm to Toba Inlet, 130 kilometres northwest of Howe Sound (Roddick et al., 1979). Pendants of similar lithology are found as far up the west coast of British Columbia as Whitesail Lake map area (Woodsworth and Tipper, 1980: NTS 93E). Armstrong (1953) based the group on a type section at the northern end of Gambier Island. Roddick (1965) mapped a second section on the southern side of Mount Brunswick and divided the group into lower, middle and upper Gambier Group (Fig. 2.1 and Table 2.1). Facies changes and poor lateral continuity of strata (Roddick, 1965) make regional correlations difficult (Fig. 2.1).

Gambier Group comprises mainly marine felsic and intermediate pyroclastics and flows, mafic flows, interbedded sedimentary rocks, and local agglomerates or volcanic breccias. A basal conglomerate on Gambier Island contains boulders of plutonic and Bowen Island Group rocks (Bostock, 1963). Locally there are thick sections of slate, argillite, quartzite and arkose.

Schofield (1918,1926) divided the Britannia Group into the Britannia Formation around Britannia Mine, and the Goat Mountain Formation north of the mine. James (1929) suggested that the Britannia Formation was older and had been thrust on top of the Goat Mountain Formation. Such a structural complexity would make comparison of the Gambier Group type sections to the Britannia - Indian River 13

LEGEND GAMBIER GROUP LITHOLOGIC SECTIONS Britannia-Indian River Pendants conglomerate. McColl, 1987 Jam**, 1929 3,400 motrm argil lite, shale, slates. Britannia Formation Only

arkose, quartzite.

greywacke.

tuff, pyroclastic rocks,

breccia, agglomerates,

rhyolite flows, tuff,

andesite flows, tuff,

'basalt flows, tuff, agglomerate.

GAMBIER GROUP TYPE SECTIONS

GAMBIER ISLAND Armstrong, 1993 1,830 motro*

Roaay, 1989 2,8SO metro*

Jama*, 1929 6,000 matrai

Figure 2.1 Comparison of the Gambier Group type sections with the lithologic sections from the Britannia - Indian River pendant, southwestern British Columbia. 14 pendant difficult. The thick shale sequence of the Britannia Formation has been correlated to uppermost middle Gambier Group (Roddick, 1965), but several other argillite units, approximately 500 metres thick, are also present in the Britannia - Indian

River pendant (McColl, 1987).

Although the type sections are less than 1,850 metres thick, the total thickness of stratigraphy in the Britannia - Indian River pendant has been estimated to be greater than 6,000 metres (James, 1929). Due to differences in the lithologic sequence, the Gambier Group type sections of Armstrong (1953) or Roddick (1965) cannot confidently be applied either to the project area or to Goat Ridge, adjacent and to the west (Reddy el al-, 1987; Heah, 1982; McColl, 1987). Consequently, the Indian River stratigraphy is subdivided after James (1929) as Goat Mountain Formation and the Britannia Formation.

2.1.3.1.1 Goat Mountain Formation

Strata on Goat Ridge was named Goat Mountain Formation by Schofield (1926). The volcanic units consist of a bimodal * suite of felsic volcanics and basaltic flows interbedded with greywacke. Rocks in the Indian River valley were later defined as lower Goat Mountain formation and middle Goat Mountain formation (James, 1929).

Lower Goat Mountain formation included all rocks east and south of the "diorite dyke" across the Indian River valley (Figs. 1.1 and 4.1). This unit was further subdivided into greenstone, rhyolitic volcanic rocks, and metamorphosed rocks (James,

1 Bimodal refers to the dominantly felsic and intermediate-mafic nature of the volcanic rocks in the study area. A bimodal genetic connotation (e.g. Yellowstone) is not implied. 15

1929). The middle Goat Mountain formation extends from this "dyke" west to Goat Mountain. Upper Goat Mountain formation crops out in the Britannia Creek valley and is overlain by the Britannia Formation.

2.1.3.1.2 Britannia Formation

The Britannia Formation, which hosts all of the Britannia ore bodies, is the economically significant part of the Britannia - Indian River pendant. This formation is more than 1,750 metres thick and is composed of slates, argillaceous quartzite and felsic volcanic rocks (James, 1929). The top of the formation is not exposed. These rocks have been altered along the Britannia shear zone to chloritic or sericitic schists. The Britannia Formation does not extend into the Indian River area.

2.1.3.2 Regional Setting

Gambier Group in the Gambier Island pendant nonconformably overlies and is therefore younger than the Late Jurassic (153 — 5 Ma; McKillop, 1973) Thornbrough Intrusions. Basal conglomerate of the Gambier Group, according to Caron (1974), rests on and is therefore younger than the Early Cretaceous Newman Creek diorite, which has a potassium-argon date of 117 — 4 Ma. However, Lee (1958) considered the Gambier Group to be in fault contact with the Newman Creek diorite.

Few age-diagnostic fossils have been found in the Gambier Group. Ammonites Cleoniceras (Grycia?) perazianum of Early Cretaceous (middle Albian: 100 to 106 Ma) age were found by H.W. Tipper near Brunswick Point on the east side of Howe Sound (identified by J.A. Jeletzky in McKillop, 1973). An ammonite found by H.H. Bostock in middle Gambier Group on Gambier Island was dated broadly as Mesozoic by H. 16

Frebold (Roddick, 1965). At the head of Jervis Inlet near Skwim Lake, Early Jurassic ammonites (upper part of Lower Sinemurian substage) were found (H.W. Tipper, pers. comm., 1988). Thus the fossil ages for Gambier Group varies from Early Jurassic to Early Cretaceous.

Potassium-argon dates from this study (section 4.4.1) range from 108 — 4 Ma to 83.5 — 3.0 Ma for volcanic rocks, but all of these are probably reset. The Gambier Group was metamorphosed to greenschist grade in early Late Cretaceous time (Woodsworth and Tipper, 1980). Rb-Sr isochrons indicate Cretaceous dates (102 — 10, 93 — 3 Ma; section 4.4.2) for metamorphic reset of a suite of volcanic rocks from middle Goat Mountain formation. These dates correspond well with potassium-argon dates for the plutonic rocks that are interpreted to have caused the regional metamorphism.

Pendants that have been suggested as lateral equivalents to Gambier Group include: (1) the Lower Cretaceous Fire Lake Group, immediately northwest of Harrison Lake (Ditson, 1978), (2) part of the Lower Cretaceous Brokenback Hill Formation on Harrison Lake (Ray si al., 1985), and (3) the Lower Cretaceous Cheakamus Formation and Helm Formation, north of Garibaldi Lake (Roddick §! al., 1977; Roddick ej al., 1976; Fig. 3.1). Mathews (1958) correlated the upper part of the middle member of the Cheakamus Formation with the Goat Mountain Formation based on lithologic similarities. Cheakamus Formation near Garibaldi Lake contains Inoceramus specimens indicating an Early Cretaceous age (Hauterivian-Barremian; J.A. Jeletzky in H.W. Tipper, pers. comm., 1988). 17

Pendants on the Sechelt Peninsula that were previously defined as Gambier

Group recently have been reassigned to the Upper Triassic Karmutsen Formation

(Roddick el al., 1976; Roddick and Woodsworth, 1979; Fig. 3.1).

2.1.4 COAST PLUTONIC INTRUSIVES

About 70 percent of the Howe Sound region consists of Coast Plutonic Intrusive bodies. The oldest potassium-argon dates for Coast Intrusives in this region are the Upper Jurassic Thornbrough Intrusions on Gambier Island. The range in potassium- argon dates of plutonic rocks from the Howe Sound area is 153 — 5 Ma to 83 — 4 Ma. There is a 25 Ma gap between the main pulse of plutonism from the Lower Cretaceous (140 Ma) to the Upper Cretaceous (115 Ma; Roddick el al., 1977). Composition varies from mostly granodiorite, quartz-diorite and granite to quartz-jnonzonite, diorite and rare gabbro. Earlier phases exhibit a dominantly northwesterly trending foliation.

The map area is bounded by intrusive rocks (Figs. 1.1 and 4.1). North of the Britannia - Indian River pendant is the Squamish granodiorite pluton and an earlier, smaller gabbro body. On the east side is a foliated granodiorite that cuts diagonally across Indian River (referred to as the Indian River Intrusions by James, 1929). The Mountain Lake pluton forms the southern boundary. 18

2.1.5 LATE INTRUSIVES

Pleistocene Garibaldi Group eruptives are part of the calc-alkaline Cascade volcanism that extends from Meagher Mountain, in southern B.C. to Mount Lassen, in California. The flows cover large areas around Garibaldi Lake and the Mamquam valley immediately north of the project area. Numerous "fresh-looking" late stage basalt to andesite dykes and sills cut through exposures around Indian River. Originally most were considered to be part of the Garibaldi Group, but potassium-argon analyses of an extensive dyke indicated that at least some are Early Oligocene (36.1 — 1.3 Ma: section 4.4.1.4) and cannot be correlated to the Garibaldi Group. These Oligocene intrusives are prevalent in highly hornfelsed and fractured zones, such as the Slumach zone (Figs. 4.1 and 4.5). Dykes and flows of equivalent Early Oligocene age (34.3 — 1.2 Ma; unpublished UBC K-Ar dates run for E. Irving and J. Monger) occur in the city of Vancouver (e.g. Queen Elizabeth Park basalt on Little Mountain). 19

3.0 REGIONAL DISCRIMINATION, USING GALENA LEAD ISOTOPE DATA, OF VOLCANOGENIC FROM PLUTONOGENIC DEPOSITS IN GAMBIER GROUP AND SPATIALLY RELATED STRATIGRAPHY, HARRISON LAKE TO JERVIS INLET, SOUTHWESTERN BRITISH COLUMBIA

3.1 INTRODUCTION

Lead isotope analyses of galena from 31 deposits and prospects in southwestern British Columbia can be divided into two groups: (1) a relatively nonradiogenic group (Figs. 3.2 to 3.4: Group V) and (2) a relatively radiogenic group (Figs. 3.2 to 3.4: Group P). Each group can be subdivided into distinct clusters. The two groups distinguish volcanogenic deposits that are cogenetic with their host rock from plutonogenic deposits that are mainly epigenetic veins.

Classification of major deposits and related showings was attempted from evaluation of geological settings and descriptions in the literature. However, most showings cannot be classified accurately because the geology is poorly known and complicated by intrusions of the Coast Plutonic Complex. Furthermore many descriptions of these prospects predate knowledge of volcanogenic models. As a consequence, some showings described either as disseminated mineralization in shear zones or as replacement deposits are likely volcanogenic. The successful discrimination of deposit types with the help of galena lead isotopes therefore has an important exploration significance. This is demonstrated by analyses of galena lead isotope data from deposits and showings sampled in the Harrison Lake to Jervis Inlet area.

The lead isotopes of clusters within the volcanogenic group (Figs. 3.2 to 3.4: group V, clusters A to C) suggest that Middle Jurassic to Lower Cretaceous stratigraphic ages are reflected by variations in galena lead isotopes. Most 20

Figure 3.1 Regional geology and locations of deposits sampled for galena lead isotope analyses from the Harrison Lake to Jervis Inlet area, southwestern British Columbia. The tectonic assemblage map of British Columbia is inset. Regional geology and pendant ages are modified from Roddick (1965), Roddick §1 al. (1979) and Roddick and Woodsworth (1979). LEGEND PLUTONIC ROCKS (Jurassic - Tertiary) + COAST PLUTONIC COMPLEX + + PENDANT UNITS (Lower Cretaceous) 1KC CHEAKAMUS FORMATION 1KH HELM FORMATION

1KP PENINSULA FORMATION 1KBH BROKENBACK HILL FORMATION 1KFL | FIRE LAKE GROUP (Jurassic - Lower Cretaceous) KG GAMBIER GROUP (Upper Jurassic) uJBC BILLHOOK CREEK uJK KENT FORMATION FORMATION uJAP AGASSIZ PRAIRIE FORMATION (Middle Jurassic) mJMC MYSTERIOUS CREEK mJEI ECHO ISLAND FORMATION FORMATION mJHL J HARRISON LAKE FORMATION (Middle Jurassic ?) TBI BOWEN ISLAND GROUP (Upper Triassic) uTK KARMUTSEN FORMATION uTP PIONEER FORMATION

TC CAMP COVE FORMATION (Pennsylvanian to Permian) PPTI I TWIN ISLAND GROUP Figure 3.1 (Continued) AVERAGED ANALYSES 290 2S0Ma 15.70 H 4/0 MO S70Ma 51°

Uppar Crust Growth Curve _Q CL O C\J 15.60 \ _Q CL f\ O Group P (N Group V

15.50 ~ r g SI/£

15.40 1 ' 1 • ' 1 ' ' ' I ' ' i i i i i i i | i i r i i i i i i | i i i i i i—i i i 18.30 18.50 18.70 18.90 19.10 206Pb/204Pb

Figure 3.2 Plot of ^Pt/20^ versus ^Pb/^Pb data (Table 3.2) for deposits sampled within the Harrison Lake to Jervis Inlet area, southwestern British Columbia. 39.00

- AVERAGED ANALYSES

X) CL 38.50 H 41Qy\^^\/ uPPer Crust Growth Curve O CN ^^^^ c B ;° A Q_ 1 5/0^ S70Ma^J /$ 1 00 1 \$/ O 1 CNJ 38.00 Group P Group V

37.50 18.30 18.50 18.70 18.90 19.10 206Pb/204Pb

Figure 33 Plot of ^Pb/^b versus ^b/^b data (Table 3.2) for deposits sampled within the Harrison Lake to Jervis Inlet area, southwestern British Columbia. 2.030 ZtOMa

AVERAGED ANALYSES 2.040 H

Q_ CD 440 O 2.050 Upper Crust Growth Curve

CL g 2.060

2.070 H

Figure 3.4 Plot of 208Pb/206Pb vergus, 207Pb/206Pb data (Table 3.2) for deposits sampled within the Harrison Lake to Jervis Inlet area, southwestern British Columbia. to 25 of these deposits are within "Cretaceous" Gambier Group pendants or units that have been proposed as Gambier-equivalent based on similarities in lithology. Volcanogenic deposits in the Harrison Lake area allow Jurassic lead characterization. Some revisions to presently accepted pendant ages are implied.

The elongate lead isotope cluster for the plutonogenic group (Figs. 3.2 to 3.4: group P) represents a mixing line (cf. Andrew el. al., 1984). A similar mixing line, has recently been noted by Leitch et. al, (in press); such lines could be characteristic of deposits generated by Cretaceous to Tertiary plutons of the Coast Plutonic Complex. Upper crust and mantle sources adequately describe the end-members of this mixing line.

Galena samples were collected from a region bound on the west by Jervis Inlet, to the east by Harrison and Lilloet Lakes, on the north by Pemberton, and to the south by the Fraser Valley (Fig. 3.1). Only units that host deposits which were sampled are discussed here. Capsule descriptions of the deposits are in Table 3.1, and complete analytical data are in Table D.l (Appendix D). Averaged analyses for each deposit, arranged according to position in groups and clusters, are in Table 3.2.

3.2 REGIONAL GEOLOGY AND MINERAL DEPOSITS

The project area includes numerous pendants in the Coast Plutonic Complex that are considered part of Wrangellia (Monger et al., 1982). The Coast Plutonic Complex formed as a tectonic welt due to overlap or compressional thickening of crustal rocks resulting from the Mesozoic accretion of the composite terrane that included Wrangellia (Godwin, 1975; Monger et al., 1982). Plutonic activity migrated 26 eastward from Vancouver Island to the Coast Mountains during the Jurassic to

Cretaceous (Woodsworth and Tipper, 1980). Uplift of the southern Coast Mountains began in Late Jurassic and a volcanic island arc formed. Marine sediments and extensive felsic to intermediate volcanics accumulated from the Middle Jurassic to

Lower Cretaceous (Woodsworth and Tipper, 1980). Plutonic activity from the Early

Cretaceous to Tertiary further contributed to the uplift of the Coast Plutonic Complex.

Approximately 80 percent of the project region consists of plutonic bodies, dominantly granodioritic in composition. The remaining 20 percent of the area is composed of variably metamorphosed pendants of volcanic and sedimentary units that were mostly marine. Pendant lithologies, ages and hosted deposits are discussed below.

3.2.1 BOWEN ISLAND GROUP (Middle Jurassic ?)

Bowen Island Group (Fig. 3.1, unit JBI) was named by Armstrong (1953) for pendants on Bowen Island and some exposures in Howe Sound. Armstrong (1953) divided the group into: (1) basaltic to andesitic flows, and (2) interbedded tuffs and sedimentary rocks. Locally the group is metamorphosed to chloritic and biotitic schists, and migmatite (Armstrong, 1953).

A probable Middle Jurassic age, without firm fossil evidence, has been suggested for the Bowen Island Group (Roddick and Woodsworth, 1979). The Late Jurassic (153 — 5 Ma by K-Ar: McKillop, 1973) Thornbrough Intrusions intrude the Bowen Island Group on the west side of Gambier Island and define an upper age limit. An angular unconformity, separating the Bowen Island Group from the overlying Gambier Group, is marked by a coarse basal conglomerate on Gambier Island (Armstrong, 1953). 27

The Bonanza prospect, on the west side of Bowen Island, was worked around 1905 (Le Roy, 1908). Adits and open cuts follow for a few hundred metres the Au-Ag- Pb-Zn-Cu-As mineralization along a fracture zone that cross-cuts chert and chloritic schist (Le Roy, 1908). The prospect is not on current mineral inventories and is within a no-staking reserve.

3.2.2 HARRISON LAKE FORMATION (Lower - Middle Jurassic)

Harrison Lake Formation (Fig. 3.1, unit mJHL) occurs on the west side of Harrison Lake. It unconformably overlies the Middle Triassic Camp Cove Formation (Arthur, 1986). The lower member of the Harrison Lake Formation is an argillite unit. It is Lower Jurassic based on Early Toarcian ammonites in the argillite immediately above a basal conglomerate on the unconformity (Arthur, 1986). The argillite is overlain by a thick section of intermediate and felsic volcanic rocks with rare fossils interpreted as Middle Jurassic by Crickmay (1962).

The Con, Fairplay, Seneca, Weaver, Bigfoot and Brett volcanogenic deposits and prospects are hosted by volcanic rock of the Harrison Lake Formation (Fig. 3.1, Table 3.1). Minor production is recorded only for the Seneca deposit, where 260 tonnes of Cu-Au-Zn-Ag-Pb-Ba stratiform and stringer ore was produced in 1962 (Minfile, BCMEMPR, 1979). The other deposits are mainly showings of disseminated or stringer volcanogenic mineralization. 28

3.2.3 BROKENBACK HILL FORMATION (Lower Cretaceous)

Brokenback Hill Formation (Fig. 3.1, unit 1KBH) at the northwestern side of Harrison Lake, overlies several Middle Jurassic to Lower Cretaceous units (Fig. 3.1: Echo Island, Mysterious Creek, Billhook Creek, Kent and Peninsula Formations) that separate it from the Harrison Lake Formation. The Brokenback Hill Formation is composed of tuffs, volcanic conglomerate, volcanic flows, pyroclastics, argillite and sandstone. Numerous fossils indicate a Lower Cretaceous (Upper Valanginian to Lower Hauterivian) age (J.A. Jeletzky, pers. comm., 1986 and H.W. Tipper, pers. comm., 1985, in Arthur, 1986).

An increase in the proportion of sedimentary to volcanic rocks in units above the Harrison Lake Formation indicates a pause in volcanism during the Late Jurassic (Crickmay, 1925 in Arthur, 1986). Increasing amounts of volcanic rocks in the Brokenback Hill Formation marks renewed volcanic activity in the Lower Cretaceous (Arthur, 1986).

The Brokenback Hill Formation is underlain by the Peninsula Formation. At the base of the Peninsula Formation is a coarse basal conglomerate on an unconformity. This granitic conglomerate indicates exposed plutonic bodies and signifies a major Late Jurassic uplift around Late Oxfordian to Early Kimmeridigian time (Arthur, 1986).

The Providence Mine and Doctors Point vein deposits occur within the Brokenback Hill Formation. The Providence Mine was a small producer of Pb-Zn-

Ag—Au from brecciated quartz-carbonate veins hosted by massive andesite (Ray el al., 1985). The only recorded shipment of 91 tonnes in 1896 graded 51 grams Au per tonne, 29 but equivalent grades have not been reproduced recently (Ray et al., 1985). Precious metal bearing quartz-sulphide veins at Doctors Point are associated with several small Upper Oligocene diorite and quartz-diorite plutons (25.7 — 1.0 Ma: by K-Ar analysis of hornblende (Ray el al., 1985)). The veins fill cone-sheet fractures in plutons and peripheral metamorphic aureoles (Ray and Coombes, 1985).

3.2.4 FIRE LAKE GROUP (Upper Jurassic - Lower Cretaceous)

The Fire Lake Group (Fig. 3.1, unit 1KFL) is restricted mostly to a pendant on the west side of Lilloet River between Harrison and Lilloet Lakes. Lithology of the group is mainly greenstone, slate and schist (Roddick §! al., 1979).

The Mayflower deposit, at the northern end of the pendant, is a Au-Pb-Zn-Ag bearing quartz-carbonate vein within brecciated sedimentary rocks. The deposit, probably worked in the early 1900's, has no recorded production, but the remains of a two stamp mill are on the property (Minfile, BCMEMPR, 1979).

3.2.5 GAMBIER GROUP (Jurassic - Lower Cretaceous)

Numerous marine volcanic and sedimentary pendants from the Indian Arm of Burrard Inlet to Toba Inlet, 70 kilometres northwest of Figure 3.1, have been assigned to the Gambier Group (Fig. 3.1, unit KG; Roddick et al. 1979). Gambier Group consists mainly of marine felsic and intermediate pyroclastics and flows, interbedded sediments and some mafic flows. Rapid facies changes and poor lateral continuity of 30 strata make regional correlations tenuous. Fossils in Gambier Group pendants range in age from Lower Jurassic to Lower Cretaceous (H.W. Tipper, pers. comm., 1988).

Based on similarities in lithology and the suggested Lower Cretaceous ages, Gambier-equivalent units include: (1) Brokenback Hill Formation (Ray e_i al., 1985), (2) Fire Lake Group (Ditson, 1975), and (3) Cheakamus Group (Roddick ej al, 1979; Roddick el al., 1977).

The major Britannia Camp and other volcanogenic massive sulphide prospects in the Indian River valley (War Eagle, Slumach, McVicar, Belle and minor showings) are hosted in Gambier Group rocks within the Britannia - Indian River pendant. At Britannia, 50 million tonnes of Cu-Zn-Pb-Ag-Au-Ba ore was mined from several ore bodies from 1905 to 1974 (Payne et al. 1980). Galena samples were obtainable for seven different ore zones. The volcanogenic deposits along the Indian River valley are described elsewhere in this thesis and compared to Britannia-type deposits.

The Red Tusk volcanogenic deposit, 20 kilometres northwest of Britannia, and Silver Bay, Mendella, Skwim and Malibu prospects along the shores of Jervis Inlet are hosted by variously metamorphosed Gambier Group pendants. The Red Tusk deposit consists of several Cu-Pb-Zn-Ag-Au stratiform and stringer zones (Minfile, BCMEMPR, 1979). Disseminated and locally massive Zn-Pb-Cu mineralization at Silver Bay and Mendella is reported to occur along shears or horizons parallel to the prominent cleavage (Boyle, 1985a; 1985b). On the Skwim property the Iinda and Mount Diadem Cu-Zn-Ag-Pb veins occur in shear zones in greenstone (Price, 1988). Mineralization at Silver Bay, Mendella and Skwim, however, occurs very close to contacts of pendants with plutonic bodies. The Skwim pendant also contains ammonites identified as Lower Jurassic (Lower Sinemurian substage; H.W. Tipper, 31 pers comm., 1988). Malibu Ag-Au-Pb-Cu-Zn mineralization is partly within a pendant of Gambier Group and partly within diorite surrounding it (Price, 1988).

The Lynn Creek deposit, 20 kilometres southeast of the Britannia Camp, has been described as a skarn deposit (Armstrong, 1953). The dominantly Zn-Pb-Ag-Cu- Cd bearing mineralization consists of abundant sphalerite, pyrite, galena, pyrrhotite and some quartz in calcareous epidote-rich gangue. Mineralization occurs as irregular bodies along a contact between limestone and quartzite (Emmens in Mahoney, 1912). The deposit contains a dubiously estimated 305,000 tonnes averaging 20 percent Zn (Western Miner and Oil Review, November 1963, p. 32).

The Chalice veins, on the Sechelt Peninsula, are within a Cretaceous - Tertiary pluton that intrudes pendants recently reassigned from Gambier Group to the Triassic Karmutsen Formation (Roddick and Woodsworth, 1979). Several Au-Ag bearing quartz-marcasite veins fill northeast trending fractures within granodiorite (Tomlinson, 1969).

3.2.6 CHEAKAMUS GROUP (Lower Cretaceous or older)

The Cheakamus Group (Fig. 3.1, unit 1KC) forms the large volcanic - sedimentary pendants in the Whistler - Garibaldi area. It consists mainly of felsic volcanic and pyroclastic rocks interbedded with greywacke and argillite. The Lower Cretaceous or older age of this group is constrained only by Lower Cretaceous ammonites in the Helm Formation that unconformably overlies the Cheakamus Group (Mathews, 1958). Basal conglomerate along the Cheakamus Group - Helm Formation 32 unconformity contains granitic cobbles, and could be equivalent with the basal conglomerate of the Gambier Group on Gambier Island.

The Northair Mine and Van Silver deposit are hosted by Cheakamus Group rocks of the Callaghan Creek pendant. At Northair 492,770 tonnes of Au-Ag-Cu-Pb-Zn ore was mined from 1976 to 1982 (Minfile, BCMEMPR, 1979). Van Silver produced a negligible tonnage of Ag-Pb-Zn-Cu-W-Sb-Au ore in 1976 (Minfile, BCMEMPR, 1979).

The Northair Mine (Miller and Sinclair, 1977; 1978) is in the Callaghan Creek pendant, which is cut on the west by Cretaceous plutonic rocks and overlain on the east by Tertiary Garibaldi Group basaltic flows. The ore bodies at Northair and Van Silver occur as either: (1) veins and disseminated bodies with abundant quartz and/or calcite gangue, or (2) massive lenticular layered masses generally parallel to bedding. Miller and Sinclair (1977; 1978) proposed that the sulphide mineralization was remobilized from the massive and disseminated ore-bodies during metamorphism, and that syngenetic mineralization showed sulphide deformation whereas the veins were undeformed. Veins farther from the massive ore bodies are sulphide-free (Woodsworth et al., 1977, in Miller and Sinclair, 1977).

The Fitzsimmons Creek prospect is hosted by the Cheakamus Group in an unnamed pendant near the town of Whistler. The deposit has been described as a skarn with Cu-Zn-Pb mineralization in a sheared, epidote-rich limestone. 33

3.3 GALENA LEAD ISOTOPE ANALYSES

Galena lead isotopes, reported in Tables D.l and 3.2 were analyzed by J.E. Gabites of the Geochronology Department, Department of Geological Science, The

University of British Columbia, as follows (c£ Godwin £1 al., 1988). Hand-picked galena crystals (0.5 milligrams) were converted to pure lead chloride solution by dissolution of the galena in pure 2-normal hydrochloric acid and evaporation to dryness. Lead chloride crystals so formed were cleaned by washing several times in 4-normal hydrochloric acid, and the cleaned lead chloride crystals were dissolved in ultrapure water. One microgram of lead in the lead chloride solution was loaded with phosphoric acid and silica gel onto a cleaned, single rhenium filament (cf. Cameron et. al., 1969). Lead isotope ratios were then measured on a Vacuum Generators Isomass 54R solid source mass spectrometer linked to a Hewlett-Packard HP-85 computer. Within run precision, expressed as a percentage standard deviation, is better than 0.01 percent, and the variation observed in duplicate analyses is less than 0.1 percent. Isotope ratios are normalized to the values of Broken Hill Standard lead (BHS-UBC1) given in Richards el. al, (1981): 206Pb/204Pb = 16.004, 207Pb/204Pb = 15.390, and 208Pb/204Pb = 35.651. Analytical precision is monitored by repeated measurement of BHS-UBC1 and systematic duplicate analyses of samples.

Fractionation error and 204Pb error trends are shown on data plots so that trends in data can be assessed as being real or related to analytical problems. Multiple analyses of the same sample or analyses of several ore bodies from the same deposit have a small spread on 207Pb/204Pb versus 206Pb/204Pb, and 208Pb/204Pb versus

206Pb/204Pb plots of Figures 3.2 and 3.3, due in part, to 204Pb error. Therefore the

2 206 208pb/206Pb VersUs 07pb/ Pb diagram is also used (Fig. 3.4). 34

Table 3.1 Capsule descriptions of deposits sampled for galena lead isotope analyses (Table D.l) from Jurassic and Cretaceous pendants in the Harrison Lake to Jervis Inlet area, southwestern British Columbia.

Number Deposit Name Minfile Lat(N)Long(W) Host unit Deposit type, commodity and status

GROUP R CLUSTER E 984-001 Brunswick Pt. 092G:NW- ? 49.53 122.26 Gambier Group Vein?; Zn-Pb showing. 868-Avg2 Doctors Point 092H:NW-071 49.64 121.98 Brokenback Hill Fm. Vein; Au-Ag-As deposit. 111-001 Malibu 092J:SW-? 50.13 123.85 Gambier Group Vein?; Ag-Au-Pb-Cu-Zn prospect. 109-001 Silver Bay 092J:SW-032 50.10 123.77 Gambier Group Vein?; Zn-Pb-Cu-Cd-As prospect. 727-002 Van Silver 092J:SW-025 50.08 123.15 Cheakamus Fm. Vein; Zn-Cu-Ag deposit. 622-001 Mayflower 092G:NE-010 49.95 122.44 Fire Lake Group Vein; Au-Pb-Zn-Ag prospect (remains of old mill but no known production). 985-001 Hercules Creek 092G:NE-? 49.62 122.98 Gambier Group Vein?; Cu-Zn-Pb showing. 620-Avg2 Mount Diadem 092ICSE-084 50.01 124.09 Gambier Group Vein; Ag-Pb-Zn prospect. 620-Avg4 Linda 14 092ICSE-082 50.01 124.10 Gambier Group Vein; Cu-Zn-Ag-Pb prospect. 105-001 Mendella 092J:SW-? 50.02 123.98 Gambier Group Vein?; Zn-Pb-Cu prospect. CLUSTERD 608-Avg2 Providence 092H:NW-030 49.62 121.95 Brokenback Hill Fm. Vein; Pb-Zn-Ag-Au producer of 91 tonnes. 108-001 Chalice 092G:NW-050 49.75 123.99 Tertiary Intrusive Vein; Au-Ag producer of 120 tonnes. 724-Avg2 Lynn Creek 092G:SW-003 49.42 123.06 Gambier Group Vole? Skarn?; Zn-Pb-Ag-Cu-Cd —Au deposit. GROUP N CLUSTER C 987-001 Slide Creek 092&NE-? 49.63 122.99 Gambier Group Vein?; Pb showing. 104-001 Bonanza 092G:SW- ? 49.37 123.40 Bowen Island Gp. Volcanogenic; Au-Ag-Pb-Zn-Cu-As prospect. 722-Avg9 Britannia 092G:NW-036 49.61 123.14 Gambier Group Volcanogenic; Cu-Zn-Pb-Ag-Au-Ba producer of 47,884^58 tonnes. 721-001 Fitzsimmons Ck. 092J-.SE-013 50.12 122.93 Cheakamus Group Vole? Skam?; Cu-Zn-Pb prospect. 107-Avg2 Red Tusk 092G:NW-051 49.77 123.32 Gambier Group Volcanogenic; Cu-Pb-Zn-Ag-Au prospect. CLUSTER B 433-001 Brett 092H:SW-133 49.38 121.90 Harrison Lk. Fm. Volcanogenic; Cu-Pb-Zn-Ba prospect. 935-001 Belle (WQ 092G:NW-014 49.62 123.01 Gambier Group Volcanogenic; Au-Ag-Cu-Zn prospect. 729-001 Con 092H:SW- ? 49.35 121.83 Harrison Lk. Fm. Volcanogenic; Cu-Zn-Pb prospect. 606-003 Big Foot 092H:SW-094 49.43 121.85 Harrison Lk. Fm. Volcanogenic, Cu-Ag-Pb-Zn-Ba prospect. 988-001 East Side Ck. 092G:NW- ? 49.65 123.04 Gambier Group Volcanogenic; Cu-Zn-Pb showing. 986-001 Indian River 092G:NW- ? 49.63 123.00 Gambier Group Volcanogenic; Cu-Zn-Pb showing. 605-Avg3 War Eagle 092G:NW-042 49.64 123.04 Gambier Group Volcanogenic; Cu-Pb-Zn-Ag prospect. 727-Avg2 Van Silver O92J:SW-O01 50.08 123.15 Cheakamus Fm Volcanogenic; Ag-Pb-Zn-Cu-W-Sb-Au deposit 605-Avg2 Slumach 092G.NW-024 49.63 123.03 Gambier Group Volcanogenic; Au-Cu-Zn prospect. 725-Avg4 McVicar 092G:NW-006 49.66 123.02 Gambier Group Volcanogenic; Cu-Zn-Pb-Ag prospect. 726-Avg3 Northair 092J:SW-012 50.13 123.10 Cheakamus Fm Volcanogenic; Au-Ag-Cu-Pb-Zn producer of 492,770 tonnes. 489-001 Weaver 092H:SW-069 49.36 121.88 Harrison Lk. Fm. Volcanogenic; Cu-Zn prospect. CLUSTERA 730-007 Seneca 092H:SW-013 49.32 121.95 Harrison Lk. Fm. Volcanogenic; Cu-Au-Zn-Ag-Pb-Ba producer of 260 tonnes. 110-001 Fairplay 092H:SW-031 49.23 121.83 Harrison Lk. Fm. Volcanogenic; Cu-Pb-Zn prospect.

1. Laboratory numbers are prefixed by the number "30". Suffixes such as "Avg2", "Avg3", etc. define the number of analyses used in the arithmetic average. Table 3.2 Averaged galena lead isotope analyses (Table D.l), and interpreted ages for clusters within groups, for deposits and showings from the Harrison Lake to Jervis Inlet area, southwestern British Columbia. Localities are defined in Table 3.1; data are plotted in Figures 3.2 to 3.5.

l c Bowen Gambier Cheakamus 1 Island Group Group Average isotopic ratios for each deposit. u Group and and Assigned s and Brokenback Fire Lake Age2 [averages for cluster] & (standard deviation) t Harrison Hill Group e Lake Formation r Formation ^b/^Pb^Pb/^Pb ^W^Pb ^Pb/20^ 208Pb/20,sPb GROUP P (Plutonogenic)

E Brunswick Pt. 18.903 15.635 38.635 0.8272 2.0439 Doctors Pt. Tertiary 18.795 15377 38.347 0.8288 2.0403 Malibu 18.765 15594 38.381 0.8311 2.0454 Silver Bay 18.715 15589 38.337 0.8330 2.0484 Van Silver3 18.712 15359 38.232 0.8316 2.0432 Mayflower 18.712 15361 38.249 0.8316 2.0442 Hercules Ck. 18.661 15363 38.202 0.8341 2.0472 Mt Diadem 18.654 15367 38.227 0.8345 2.0492 Linda 18.616 15351 38.172 0.8354 2.0505 Mendella 18.607 15365 38.154 0.8366 2.0505 [18.71] [1538] [38.29] [0.8324] [2.0463] (0.09) (0.02) (0.14) (0.0029) (0.0034)

D Providence Cret. - 18.582 15367 38.168 0.8378 2.0541 Chalice Tertiary 18361 15556 38.082 0.8382 2.0518 Lynn Ck. 18.557 15562 38.122 0.8387 2.0544 [1837] [1536] [38.12] [0.8383] [2.0534] (0.01) (0.01) (0.04) (0.0005) (0.0014) GROUP V (Volcanogenic)

C Slide Ck. Late 18327 15373 38.137 0.8406 2.0585 Bonanza Jurassic 18318 15562 38.097 0.8405 2.0574 Britannia - 18304 15358 38.078 0.8408 2.0579 Fitzsimmons Early 18302 15352 38.062 ' 0.8406 2.0572 Red Tusk Cret. 18.477 15342 38.016 0.8412 2.0574 [1831] [1536] [38.08] [0.8407] [2.0577] (0.02) (0.01) (0.04) (0.0003) (0.0005)

B Brett Middle - 18500 15569 38.158 0.8417 2.0626 Belle Late 18.488 15572 38.109 0.8422 2.0612 Con Jurassic 18.482 15363 38.043 0.8421 2.0584 Big Foot 18.476 15350 38.099 0.8417 2.0621 East Side Ck. 18.474 15347 38.035 0.8417 2.0589 Indian R. 18.466 15341 38.018 0.8417 2.0589 War Eagle 18.453 15343 38.024 0.8418 2.0592 Van Silver3 18.451 15349 38.033 0.8428 2.0614 Slumach 18.442 15327 37.987 0.8426 2.0599 McVicar 18.429 15343 37.990 0.8435 2.0615 Northair 18.426 15341 37.997 0.8435 2.0622 Weaver 18.423 15554 38.043 0.8444 2.0650 |18.46] [1535] [38.04] [0.8425] [2.0609] (0.03) (0.01) (0.05) (0.0009) (0.0020)

A Seneca Early - 18320 15344 37.919 0.8486 2.0699 Fairplay Middle 18.301 15302 37.788 0.8471 2.0649 Jurassic [18.31] [1532] [37.85] [0.8479] [2.0674] (0.01) (0.03) (0.09) (0.0010) (0.0036)

1. Symbols for clusters in Figures are: A = circles, B = squares, C = triangles, D = diamonds and E = stars. 2. Ages constrained where possible by fossil evidence; see text. 3. Van Silver has a dual signature. Millsite is relatively radiogenic compared to Tedi and Silver Tunnel. 4. Linda and Mt. Diadem mineralized zones, both on the Skwim property, have different isotopic signatures. 5. Chalice deposit is hosted by Cretaceous quartz diorite of the Coast Plutonic Complex. 36

3.4 GALENA LEAD ISOTOPE DATA AND DISCUSSION

Averaged galena lead isotope data from Table 3.2 (detailed in Appendix D: Table D.l) are plotted in Figures 3.2 to 3.4. Reference curves plotted with the data in Figure 3.5 are segments of the "shale" curve (Godwin and Sinclair, 1982), and the upper crust and mantle curves (Doe and Zartman, 1979). Only the upper crust curve is plotted in Figures 3.2 to 3.4.

Data from deposits that are demonstrably volcanogenic, based on field evidence, plot in Group V. On the other hand, deposits that are clearly plutonogenic, because the veins occur within or adjacent to intrusive granitic bodies, plot in Group P. There is a natural gap between volcanogenic and plutonogenic groups of deposits. It therefore seems compelling that the two groups can be divided into distinct genetic categories (Figs. 3.2 to 3.4).

The two groups-the relatively radiogenic Group P and the relatively

nonradiogenic Group V-are divided by the values: ^Pb/^CHpb _ jg 54 an(j 207Pb/206Pb = 0.840. Group V can be resolved further into clusters A, B and C. Group P has an elongate trend, but three deposits that plot close together at the least radiogenic end allow a two-fold division into clusters D and E.

Averaged values and standard deviations of data for each cluster of deposits are presented in Table 3.2. The averages of each cluster are statistically distinct by

2^Pb/2*)4pb data2. The distribution of isotopic signatures and differentiation into clusters generally remains distinct on all three lead isotopic plots (Figs. 3.2 to 3.4).

2 Means and standard deviations of the clusters were compared using Welch's approximate "t" test for populations of differing size and differing variances. 37

Notable exceptions are the data for Brett and Red Tusk that appear to overlap clusters

B and C (Figs. 3.2 and 3.3). This overlap might be caused by 2^Pb error (Fig. 3.4).

Group V isotopic data have an orogenic character (cf. Doe and Zartman, 1979) in 207Pb/204Pb versus 206Pb/204Pb, and208 Pb/204Pb versus 206Pb/204Pb plots. This is reflected by the thorogenically enriched environment suggested in the

208Pb/206Pb versus 207Pb/206Pb plot. The data plot on the low side of crustal leads and this indicates evolution of the lead in a lower U/Pb ratio environment than for average upper crust (Sinclair and Godwin, 1981). In an orogenic setting the continentally-derived material is mixed with mantle and lower crustal material along subduction zones. The uniformity in the data within each cluster in group V supports an origin for lead derived from hosting volcanics and sediments.

The elongate nature of Group P strengthens the separation from Group V, because the steep slope on a 2^8Pb/2^4Pb versus 2^Pb/2u4pb plot is that expected for a mixing line (cf. Andrew el. al., 1984) between crustal and mantle reservoirs (Fig. 3.3) during the Mesozoic to Cenozoic. Similar linear arrays in the galena lead isotopic data are found for mesothermal to epithermal veins for deposits from the Bralorne-Pioneer mines northward to the Blackdome mine (Leitch el. al., in press). Leitch el. al-, (in press) have interpreted this array as a mixing line related to generation of successively higher veins related to plutons of the Coast Plutonic Complex that young to the east. This therefore reinforces the interpretation that Group P is genetically related to Cretaceous-Tertiary plutons generated within the Coast Plutonic Complex.

Characteristics of deposits associated with each cluster, outlined in Tables 3.1 and 3.2, are detailed below. Clusters are described in order of apparent age from oldest 15.80

AVERAGED ANALYSES

Upper Crust Growth Curve _Q CL 15.60 O

_Q CL

O OJ 15.40 Mantle Growth Curve

15.20 i i i i i i i i i I i i i i i i i i i l i i i i i i i i i I i i i i i i i i i I i i i i i i i i i 17.50 18.00 18.50 19.00 19.50 20.00 206Pb/204Pb

Figure 3.5 Average galena lead isotope analyses plotted on a

207pb/204pb versus ^Pb/^Pb diagram to compare with the shale, mantle and crust growth curves. The dashed line between the mantle and upper crust curves shows a mixing line isochron for 0 Ma. 39 to youngest. Deposits with analyses that fall into two clusters are described further below.

3.4.1 CLUSTERS A TO C: Volcanogenic Group V

The volcanogenic deposits plot in three clusters in Figures 3.2 to 3.4. Relative ages based on lead isotope signatures are indicated in Table 3.2.

Cluster A is defined by the signature of two deposits, Seneca and Fairplay, at the least radiogenic end in Figures 3.2 to 3.4. These deposits are interpreted to be syngenetic within volcanic rocks of the Lower - Middle Jurassic Harrison Lake Formation. Previous lead isotope analyses from stratiform and stringer zones at Seneca showed that the lead was homogeneous throughout the deposit (Sinclair and Godwin, 1981).

Cluster B data are from volcanogenic deposits in the Harrison Lake, Whistler and Britannia areas. The deposits (Weaver, Bigfoot, Con and Brett) in the Harrison Lake Formation are Middle - Late Jurassic in age. These deposits may represent: (1) cross-cutting stringer mineralization that feeds Late Jurassic volcanogenic activity, or (2) Middle Jurassic volcanic stratigraphy in the Harrison Lake Formation. Age assignment in the Harrison Lake area is complicated by block faults and rapid fades changes.

Granodiorite plutons within the Harrison Lake Formation have been dated as 160 — 2 Ma by U-Pb methods (P. Van der Heyden, pers. comm., 1986 in Arthur, 1986).

These high level felsic bodies are coeval to the Upper Jurassic Billhook Creek Formation and may be related to the mineralization. 40

In the Whistler area, Northair and Van Silver have syngenetic isotopic signatures except for a dual character of the Millsite zone of the Van Silver deposit (see section 3.4.3). The very tight clusters of data for each mine and the close grouping with other volcanogenic deposits support the volcanogenic origin. This is compatible with the two stage theory of Miller and Sinclair (1977) that suggested disseminated and massive volcanogenic mineralization was later mobilized into structurally controlled zones. The signatures are similar to the Late Jurassic mineralization at Harrison Lake area and thus the same age is suggested for these deposits. The Lower Cretaceous fossils in the Cheakamus Formation occur stratigraphically higher, above an unconformity within the formation. Furthermore, these fossils occur in a pendant separate from the Callaghan pendant (Mathews, 1958).

Volcanogenic deposits (McVicar, War Eagle, Belle and Slumach) along the Indian River plot within cluster B. These deposits are the focus of recent exploration activity (Reddy si ai>, 1988). Small showings (East Side Creek and Indian River) are on strike with the War Eagle deposit and plot within cluster B. The similarity in signatures encourages exploration for volcanogenic type mineralization.

Cluster C data are from volcanogenic deposits that include the major Britannia Camp. The age of Britannia host rocks has been suggested to be Lower Cretaceous by equating the mine lithology to pendants on Howe Sound that contain Albian ammonites (Roddick et al, 1977). Poor Rb-Sr isochrons (McColl, 1987; and this study, section 4.5) suggest a possible Jurassic host rock age. Stringer and stratiform ore bodies at Britannia Mine have essentially the same galena lead isotope signature. 41

Isotope ratios from the Bonanza prospect plot within those from the Britannia Mine. This presents a problem. How does the Bowen Island Group, that hosts the Bonanza prospect, relate to this scheme? Is the pendant hosting the Bonanza mineralization classified correctly? Either the Bonanza prospect represents deep- seated cross-cutting stringer mineralization feeding a Lower Cretaceous system associated with the Britannia era of volcanogenic activity, or at least some stratigraphy on Bowen Island is equivalent to Lower Cretaceous Gambier units.

The isotopic signature of the Red Tusk prospect is very similar to the Britannia signature, although Red Tusk is slightly less radiogenic. Thus, volcanogenic events at both sites appear to be temporally related. The data for Red Tusk plots in Cluster C on the 208Pb/206Pb versus 207Pb/206Pb diagram (Fig. 3.4), but the analyses are within

Cluster B in Figures 3.2 and 3.3; this is probably due to 2^Pb error.

Fitzsimmons Creek prospect, in a pendant of Cheakamus Group in the Whistler area, has been described as a skarn. The isotopic signature supports a Cretaceous, syngenetic origin to the mineralization. Mineralization more likely developed as volcanogenic activity that involved the adjacent limestone.

3.4.2 CLUSTERS D AND E: Plutonogenic Group P

The plutonogenic deposits plot in two clusters in Figures 3.2 to 3.4. Relative ages suggested in Table 3.2 are based on lead isotope signatures.

Cluster D deposits and prospects are plutonogenic and post-date the formation of their host rocks. The Lynn Creek deposit has been classified as a skarn (Armstrong, 42

1953). The sulphide minerals probably formed from Cretaceous or Early Tertiary plutonic activity.

The Chalice prospect is related to plutonic activity that generated several northeast striking precious metal-rich veins with minor sulphides (Tomlinson, 1969). The lead isotope signatures suggest a Lower Cretaceous age of mineralization associated with emplacement of the plutonic host.

Providence Mine, five kilometres south of the Doctors Point pluton, has a plutonogenic signature that probably reflects Tertiary plutonic activity (Ray et al., 1985).

Cluster E is marked by an elongate scatter of plutonogenic deposits and prospects. The spread in the cluster is due to the heterogeneity of lead generated from the Coast Plutonic Complex. Mayflower and Doctors Point deposits plot within this cluster. Mineralization at Doctors Point is Tertiary in age, associated with the margin of a 25 Ma diorite that hosts several of the veins (Ray, el al., 1985). The Brokenback Hill Formation, which hosts this deposit, is Lower Cretaceous in age. The commodities of interest at Doctors Point are precious metals, whereas at Mayflower and Providence the commodities are base metals.

The Jervis Inlet deposits all have epigenetic characters and reflect plutonogenic mineralization. Mendella, Silver Bay, Skwim and Malibu prospects are hosted by Gambier Group pendants or are in plutonic bodies near contacts. Isotopic data reflect their origin from the plutons. At Skwim, the Linda and Mt. Diadem veins have galena lead isotopes of slightly different character. They may be associated with different plutonic phases. 43

The Brunswick Point showing consists of disseminated mineralization at Brunswick Point on the Squamish Highway. The host rocks are known to be Albian in age by fossil evidence (Roddick el al., 1977). The isotopic character of the showing is very radiogenic, possibly reflecting a late Tertiary plutonic origin.

3.4.3 DEPOSITS WITH ISOTOPIC VALUES THAT PLOT IN TWO CLUSTERS

Van Silver is the only deposit with a distinctly dual signature. Two of the three zones at Van Silver have volcanogenic isotope signatures in cluster B. The third zone is plutonogenic and reflects contamination with very radiogenic lead. A Tertiary event, as noted by Miller and Sinclair (1977), was probably responsible for the mobilization of sulphides into the veins.

The two Skwim deposits, Mt. Diadem and Linda, have different signatures that probably reflect an association with different plutonic phases.

3.5 INCREASING RADIOGENIC SIGNATURES COINCIDENT WITH YOUNGING OF STRATIGRAPHY

The three isotopic clusters within the volcanogenic group appear to give relative age signatures to the deposits. Since these are volcanogenic or related deposits the relative stratigraphic ages of the pendants involved in this study might be refined using galena lead isotope data. Galena lead isotope analyses from plutonogenic veins do not help in establishing relative ages for their host rocks. 44

The lower argillaceous portion of the Harrison Lake Formation is overlain by felsic to intermediate volcanics that host the Fairplay and Seneca deposits. The volcanics were interpreted as Middle Jurassic (Arthur, 1986, from Crickmay, 1962). Mineralization at Seneca occurs as stratiform and stringer ore. Thus it is suggested to be syngenetic and a Middle Jurassic age is assumed for both Seneca and Fairplay.

The other deposits within the Harrison Lake Formation have slightly more radiogenic signatures. Thus they are interpreted here either to be cross-cutting volcanogenic stringer veins, or to be in host .units that have been assigned too old an age. Each of the deposits (Weaver, Big Foot, Con and Brett) is described as disseminated or stringer type-mineralization (Minfile, BCMEMPR, 1979).

Classification of cluster B as Late Jurassic indicates that portions of pendants hosting the Northair, Van Silver, McVicar, Slumach and War Eagle deposits may also be Late Jurassic.

Late Jurassic - Early Cretaceous mineralization would include the Britannia ore bodies, and Bonanza, Red Tusk and Fitzsimmons Creek prospects. The position of deposits in the stratigraphy of the Britannia - Indian River pendant is consistent with the relative ages of volcanogenic mineralization presented here. The continuous south to southwest dipping sequence hosts McVicar near the bottom (therefore oldest), and Britannia near the top (therefore youngest). Other deposits and prospects within the stratigraphy are in the correct order in relative chronology (i.e. McVicar - War Eagle - Slumach - Belle - Britannia). War Eagle, Slumach and Belle are very close in stratigraphic position, and appear to represent one episode of volcanogenic mineralization. 45

The correlation of Late Jurassic and Early Cretaceous units as presented here suggests that the widespread uppermost Jurassic - lowermost Cretaceous unconformity might be regionally correlated. Units with possibly related basal conglomerates include: (1) the Gambier Group on Gambier Island (Armstrong, 1953), (2) the Helm Formation near Black Tusk (Mathews, 1958), and (3) the conglomerate at the base of the Peninsula Formation (Arthur, 1986) west of Harrison Lake. In each case Jurassic units are overlain by units that are known to be Lower Cretaceous by fossil evidence. Each of the conglomerates along the unconformities contain granitic cobbles.

Age specific growth curves (Fig. 3.5) do not fit this small data base which is limited to the Jurassic to Tertiary events. However, this scheme can be used as a method of assigning relative ages of mineralization without implying a specific numerical date. Furthermore the deposit type and genetic history for a deposit can be implied. Galena lead isotope data therefore can help in determining an exploration strategy.

3.6 CONCLUSIONS

The galena lead isotope signatures of deposits in the Harrison Lake to Jervis Inlet region can be used to:

(1) establish the volcanogenic versus plutonogenic character of deposits and prospects,

(2) help define the relative age of volcanogenic deposits and associated host rocks, and 46

(3) aid in unravelling complicated genetic histories of those deposits with dual galena lead isotope signatures.

An example of the deposit-type classification can be applied to deposits and prospects from the Indian River area. The McVicar, War Eagle, Belle and Slumach are all known volcanogenic-related prospects that are the focus of recent exploration activity. Several small showings in the Indian River area can be classified with respect to major deposits and prospect subdivisions thus indicating the potential of these showings. The Indian River and East Side showings are on strike with the volcanogenic War Eagle deposit and plot within the War Eagle group of analyses. The economic potential of these showings is therefore good and prospecting in the area has shown that these are part of sporadic mineralization along the Indian River. The Slide Creek showing consists of calcite - galena veins within shale. The field evidence negates the importance of this mineralization, but the lead isotopes are consistent with a syngenetic origin. The Hercules creek showing, a small vein along a fault zone, has galena lead isotopes that indicate it to be plutonogenic; it therefore has little potential. The Brunswick Point showing occurs in a Gambier Group pendant on the east side of Howe Sound. The disseminated mineralization of this showing, due to the very radiogenic isotopic signature, would have very low priority thus supporting the decision made from field evidence.

A major regional geological implication of galena lead isotopes is a possible correlation between the Upper Jurassic units in the Harrison Lake area with other pendants with Upper Jurassic isotopic signatures. These include the Indian River portion of the Britannia - Indian River pendant, and the Callaghan pendant of the Cheakamus Group. There also appears to be a widespread unconformity within the Gambier Group and the equivalent units. Lower Cretaceous Gambier Group above 47 the basal conglomerate on Gambier Island appears to be correlated with the Lower Cretaceous Helm Formation, the Peninsula Formation and the Britannia portion of the Britannia - Indian River pendant. Brokenback Hill Formation and Fire Lake Group overlie the Peninsula Formation and also correlate with the Jurassic - Cretaceous Gambier Group.

Galena lead isotopic signatures can be used as an effective exploration tool, not only for deposits with galena as a major constituent, but also for those deposits with only traces of associated galena. By considering isotopic signatures for a group of deposits the comparisons can meaningfully guide or backup decisions for further work on showings and prospects. 48

4.0 LOCAL GEOLOGY

4.1 INTRODUCTION

The eastern side of the Britannia - Indian River pendant consists of seven north to northwest trending strips of stratigraphy that dip west. Plutonic bodies encompass most of the map area and separate portions of stratified units from the main Britannia - Indian River pendant. The stratigraphic and intrusive units are described, from oldest to youngest, in the following sections. A brief description of metamorphism follows the local geology. Major and trace element compositions, structure, geochronology and mineralization are discussed in ensuing sections.

4.1.1 LOWER GOAT MOUNTAIN FORMATION (unit LGM)

The lower Goat Mountain formation, on the east side of the Indian River valley, is a series of felsic volcanic rocks interbedded with sediments and a layer of intermediate tuffs (Fig. 4.1). The unit is at least 350 metres thick within the map area. The bottom of the formation is not exposed in the map area, and the unit extends to the east and southeast.

Felsic flows and pyroclastic rocks are more abundant than interbedded sediments. The rhyolite flows are flowbanded and contain quartz and feldpsar phenocrysts in a pale green groundmass (Fig. 4.6). Phenocrysts average 2 millimetres across and constitute up to 20 percent of the rock. Plagioclase in the flows is mostly albite to oligoclase, whereas tuffs contain mostly andesine. Several flows have vesicles m

Figure 4.6 Pale green flowbanded rhyolite of the lower Goat Mountain formation (unit LGM; Fig. 4.1). Pencil is 14 centimetres long.

Figure 4.7 Heterolithic fragmental tuff of the lower Goat Mountain formation (unit LGM; Fig. 4.1). Hammer handle is 3.5 centimetres wide. 50 and entrained fragments up to 2 centimetres long.

Pyroclastic rocks are fragmental and range from tuff-breccias to ash-tuffs (classification after Fisher, 1966). Subaqueous deposition is indicated by numerous thin interbeds of well sorted and normally graded material. A few tuffaceous layers are incipiently welded: devitrified shards are flattened and bent around fragments. Beds of heterolithic fragmental tuff average 30 to 60 percent clasts. The clasts of chert, argillite and tuff are up to 6 centimetres across and are set in a tuffaceous matrix (Fig. 4.7). Many fragments are elongate due to deformation, and locally schistose zones have developed. Pyroclastic rocks grade into tuffaceous sediments.

Marine sediments such as argillite, siltstone and greywacke are well bedded. Graded tuffaceous siltstones provide excellent indicators of tops (Fig. 4.8). A calcareous tuff with recrystallized fossils and molds of belemnites, echinoderm spines and deformed bivalves (not age specific; Figs 4.9a and 4.9b) was found in the small pendant, surrounded by Indian River granodiorite (unit Bj), in the northeast corner of the map area (Fig. 4.1). Similar rocks with equivalent fossil molds were found five kilometres to the southeast near Clarion Lake (C. Burge, pers. comm., 1988). James (1929) mapped this latter area as lower Goat Mountain formation, thus the small pendant on the northern edge of the thesis map area is tentatively correlated with this unit.

A layer of intermediate tuffs and flows less than 40 metres thick is interbedded with the felsic volcanics east of the Indian River granodiorite apophysis (unit B^: Fig. 4.1). These tuffs have a phyllitic sheen on cleavage surfaces. Heterolithic lapilli and plagioclase crystal fragments constitute 30 to 40 percent of these tuffs. Penninite has 51

Figure 4.8 Graded tuffaceous siltstone of the lower Goat Mountain formation (unit LGM; Fig. 4.1) showing tops to west. Pencil points in the direction of tops. Pencil is 19 centimetres long. 52

Figure 4.9 Fossiliferous calcareous tuff of the lower Goat Mountain formation (unit LGM; Fig. 4.1): (a) hand specimen with 12 centimetres long pen, and (b) rubber casts from fossil molds of echinoderm spines that are visible in (a). 53 replaced devitrified glass shards, which are flattened parallel to the bedding. (The penninite has grown parallel to the cleavage fabric.) Similar exposures of heterolithic intermediate tuff-breccia and lapilli tuff occur along the Indian River, south of the plutonic apophysis.

The lower Goat Mountain formation dips steeply west and numerous tops indicators-graded bedding-show it is upright. Cleavage-bedding relations and minor folds indicate a fold vergence to the northeast, but there is no closure of an anticlinal structure in Figure 4.1. James (1929) discussed such a structure striking northwesterly along the ridge on the eastern edge of Figure 4.1.

Indian River Intrusions (unit Bj) cross-cut the lower Goat Mountain formation. James (1929) inappropriately used one such intrusion, the granodiorite apophysis already noted, to define the stratigraphic division between lower and middle Goat Mountain formations. There is an overall change from predominantly felsic flows with interbedded sediments on the east side of the intrusion to predominantly tuffs and sediments with a few felsic flows on the west side. This lithologic change, rather than the division by the apophysis, might more suitably reflect a distinction between lower and middle Goat Mountain formation. Strong alteration of the stratified unit, near the plutonic margin in the northeast corner of the map, hampers correlation of this strata with outcrops in the east central edge of Figure 4.1.

4.1.2 MIDDLE GOAT MOUNTAIN FORMATION

Six units form a continuous stratigraphic succession from the Indian River valley to the eastern slopes of Sky Pilot Mountain. The middle Goat Mountain formation, 54 which is at least 2.5 kilometres thick within the map area, continues to Goat Ridge to the west. It dips moderately south-southwest. The units are described below, from oldest to youngest (Figs. 4.1 to 4.5).

4.1.2.1 Lower Intermediate Volcanics (unit 1)

Dark green massive fine grained plagioclase porphyritic andesite tuffs and flows (unit 1) occur on the west side of the Indian River granodiorite, along the Indian River. The minimum thickness of this unit is 50 metres; the base is not exposed at this locality. Major element analyses of volcanic rocks indicate intermediate to mafic compositions; one sample might be felsic, although it is probably silicified (Table 4.1).

The tuffs vary from fine grained ash and crystal tuffs to lapilli tuffs with a few large fragments up to 15 centimetres across. Brecciated zones of fine grained andesite with red hematitic chert and coarse pyrite cubes could be part of a hyaloclastic breccia of a subaqueous intermediate flow (S. Juras, pers. comm., 1987).

The flows have a microlitic plagioclase groundmass that hosts small, less than 0.5 millimetres across, phenocrysts of plagioclase (AI^Q, oligoclase-andesine), quartz, magnetite, chlorite and pyrite. Modal amounts of phenocrysts are variable. All flows are marked by ubiquitous chlorite, sericite and epidote. Local contact metamorphism to hornfels by granitic intrusions (unit Bj) has destroyed many textures and makes the upper contact of this unit indistinct. Locally, hornfelsin g is characterized by secondary biotite, albite and quartz — cordierite porphyroblasts (see section 4.1.5.2) associated with minor disseminated pyrite and chalcopyrite. Such mineralization is part of the ABC zone (see section 4.5.1). 55

Unit 1, interpreted as stratigraphically above the lower Goat Mountain formation, crops out mainly within the core of a fault-disrupted anticline that parallels the main Indian River antiform. Intermediate volcanic rocks of unit 1, on the west side of the Indian River Intrusion in the central part of the map area, are probably stratigraphically and conformably below unit 2. Intense propylitic alteration obscures contact relationships.

4.1.2.2 Felsic Volcanics and Sediments (unit 2)

Felsic tuffs and flows with sedimentary interbeds of chert and argillite (unit 2) conformably overlie unit 1. Unit 2 is about 750 metres thick. Numerous cycles of explosive volcanism are represented by repeated layers of coarse tuff-breccia with fragments up to tens of centimetres across. Unit 2 is broadly divided into lower, middle and upper parts. (The latter divisions correspond to packages II, HI and IV of Reddy §1 al., 1987.)

The lower portion is mainly hornfelsed felsic volcanic rocks interbedded with shale and tuffaceous sediments. Some layers of tuff contain heterolithic fragments that average 2 centimetres, but are up to 8 centimetres across.

The middle of unit 2 consists of tuff, pyritic shale, greywacke, tuffaceous chert and siltstone. Bedding is well developed and consistently faces upwards. A dark grey siltstone bed has been bioturbated but no fossils were found. Individual beds are commonly 1 centimetre thick; massive cherty beds are up to 2 metres thick. Some tuffs contain abundant flattened glass shards that are replaced by penninite (Fig. 4.10). Plagioclase crystals in a crystal ash tuff are andesine (An33) in composition and average one millimetre in size. Pyritic shale contains up to 4 percent disseminated pyrite and 56

Figure 4.10 Sample, from a tuff in the middle portion of unit 2 (Fig. 4.1), consists of flattened, partly welded devitrified glass shards replaced by penninite. Width of field is 3.2 millimetres. Magnification is 40X.

Figure 4.11 Heterolithic fragmental tuff, from the upper portion of unit 2 (Fig. 4.1), exhibits poor bedding. Metal band on pencil is 1.4 centimetres long. 57 minor chalcopyrite in some thin horizons; this could represent distal equivalents to the low grade stratiform War Eagle volcanogenic mineralization hosted by unit 2. The breccia at the War Eagle adit (Fig. 4.1) occurs at the top of the middle part of unit 2 and probably represents the start of a new eruptive cycle. Angular volcanic fragments up to 38 centimetres in size are set in a dacitic, plagioclase phyric matrix. This breccia zone has been mineralized, faulted, foliated and hornfelsed. Mineralization associated with the breccia and hornfels in the War Eagle zone is discussed in section 4.5.1.

The upper part of unit 2 is dominantly felsic pyroclastics with tuffaceous chert and shale interbeds. Pyroclastic rocks range from crystal tuffs to tuff-breccias with heterolithic fragments 0.5 to 2.5 centimetres long (Fig. 4.11). The unit was deposited as a conformable, bedded subaqueous sequence. Fine grained pyroclastics and greywackes consist largely of crystal fragments of andesine plagioclase (AJI33) and quartz, within a very fine grained matrix of micas, quartz, plagioclase and opaques. Sediments are often "spotted" by hornfelsing. An intensely hornfelsed portion of the upper part of unit 2 hosts the Slumach gold zone. As the Slumach zone is approached the relatively intact felsic and intermediate volcanic rocks give way to: (1) increasing propylitic alteration, (2) albite-quartz hornfels, and (3) silicification and cordierite- quartz-biotite hornfels (see section 4.1.5.1). Lithologies that host the veins are probably felsic lapilli tuff as suggested by rocks on strike with the hornfelsed mineralized zone. At the upper contact of unit 2, shale beds are conformable with overlying mafic flows of unit 3.

4.1.2.3 Massive Intermediate to Mafic Volcanics (unit 3)

Intermediate tuffs and massive, mafic flows (unit 3) form resistant bluffs at the north end and along the east side of Maggie Ridge (Fig. 4.12). The dark green, fine 58

Figure 4.12 Massive basaltic andesite flows of unit 3 crop out along the crest of Maggie Ridge (Fig. 4.1). Upper and lower contact traces are indicated.

Figure 4.13 Flow bottom of a basaltic andesite flow (unit 4b) is in contact with the top of recessive, felsic tuffaceous sediments (unit 4a; Fig. 4.1). Note book is 18 centimetres long. 59 grained volcanic rocks total about 150 metres in thickness. Whole rock analyses show the flows to be dominantly mafic in composition (Table 4.1).

The unit contains layers of intermediate tuffs and some contacts that resemble flow bottoms thus it is inferred that the unit is composed of several volcanic flows and not one major sill. This is the first major mafic unit encountered in the stratigraphy within the map area.

The flows are very fine grained and consist of sub-trachytic andesine plagioclase

(45%; ^43), interstitial hornblende (36%), magnetite (2%), locally sub-ophitic augite (up to 20%) that is partly to entirely replaced by actinolite, and minor apatite. The actinolite pseudomorphing augite and abundant actinolite in the groundmass is due to lower greenschist metamorphism. Other alteration minerals include chlorite, epidote and sericite. Locally there are up to 15 percent epidotized fragments, 3 to 6 centimetres in size. Layers of epidotized fragments are oriented suggesting flow parallel to bounding units.

4.1.2.4 Felsic Tuffs and Sediments (unit 4a) and Intermediate to Mafic Volcanics (units 4b and 4c)

Felsic tuffs and sediments (unit 4a) conformably overlie the massive volcanics of unit 3 and are interbedded with intermediate to mafic volcanics (units 4b and 4c). The total thickness varies widely from 150 metres minimum at the top of Maggie Ridge to over 650 metres in the Stawamus River valley (Fig. 4.1). Bedding orientations change within unit 4a, below the contact of unit 4a with unit 4b, from a northwesterly to westerly strike. 60

Felsic tuff of unit 4a consists generally of thin to massive beds of ash to lapilli tuff, and rarely tuff-breccia, interlayered with thin beds of shale or greywacke. Locally the tuffaceous beds are boudinaged into a string of fragments. This is probably due to soft sediment deformation or slumping of beds. Beds always face up. Outcrops of unit 4a along the Stawamus River contain layers of mudstone concretions. Several rhyolite flows, some exhibiting flowbanding and spherulites, are exposed near the top of unit 4a along the Stawamus River.

Massive dark green intermediate to mafic flows with some intermediate pyroclastic interbeds (units 4b and 4c) are conformable with unit 4a in the Stawamus River valley, but interfinger and pinch out with the tuffaceous sediments west of Maggie Ridge. Figure 4.13 shows the base of an intermediate flow on top of felsic tuffaceous sediments of unit 4a. Most of units 4b and 4c are pyroxene phyric mafic flows (Fig.

4.14). Dominant mineralogy is andesine plagioclase (57%; ^44), ophitic twinned augite (35%) that is usually partly replaced by secondary actinolite, magnetite (2%), primary hornblende (2%), and minor biotite and apatite. Alteration minerals include chlorite, epidote, sericite and quartz. The unit has numerous epidote-rich layers, quartz-epidote veining and epidotized fragments. Unit 4c is poorly stratified, in part due to poor bedding of the higher proportion of tuffaceous material, but resembles 4b in more massive parts of outcrop.

Thinning of unit 4, irregular contacts between unit 4a and 4b, and the change of strike reflect a possible angular unconformity developed during deposition of the lowermost portion of unit 4a. 61

Figure 4.14 Massive pyroxene phyric mafic flows (unit 4c; Fig. 4.1) crop out in the Stawamus River valley. Pencil is 14 centimetres long.

Figure 4.15 Ash-rich mudstone (unit 5b; Fig. 4.1) containing accretionary lapilli crops out on the west side of the Stawamus River valley. Pen is 14 centimetres long. 62

4.1.2.5 Intermediate Volcanics (unit 5a) and Felsic Sediments (unit 5b)

Massive intermediate volcanics (unit 5 a) that form a resistant set of bluffs rimming the west side of the Stawamus River valley are overlain by felsic tuffs and fine ash tuffs (unit 5b) characterized by accretionary lapilli. Several faults disrupt the outcrop patterns on the west side of the Stawamus River valley.

The intermediate volcanic rocks are dominated by dark green plagioclase and pyroxene phytic basaltic andesite flows. Andesine plagioclase (up to 35%; An^), ophitic augite (5-10%) and minor hornblende phenocrysts are set in a groundmass of microlitic plagioclase, biotite, and actinolite and other alteration minerals. The unit is weakly chloritized, locally silicified, and has quartz-epidote veining.

The fine grained felsic tuffs are laminated to thick bedded. Graded bedding and cross bedding indicate tops are up. Some layers contain abundant ovoid accretionary lapilli up to 4 centimetres across (Fig. 4.15).

4.1.2.6 Sky Pilot Succession (unit 6)

Felsic tuffs, sediments, intermediate flows and tuff-breccias (unit 6) conformably overlie unit 5. Unit 6 was not mapped in detail, but a continuous bimodal succession of felsic and intermediate to mafic rocks continues off the map area (Heah, 1982). The overall orientation is south-dipping, but several faults disrupt the unit and complicate the stratigraphy.

Heah (1982) referred to the outcrops on the eastern slope of Sky Pilot Mountain as the Shannon Creek member of the middle Goat Mountain formation (see unit "1K1" 63 in Heah £t.._al, 1986). This unit includes basalt flows, black argillites, dacite flows, mafic tuffs, tuff breccias and minor agglomerates (Heah, 1982). Heah (1982,1986) mapped five more members that conformably overlie the Shannon Creek member (unit 6) on Sky Pilot Mountain.

4.1.3 PLUTONIC INTRUSIONS

The stratified units are intruded by several phases of Coast Plutonic Intrusives and late dykes. The relative ages of these units are based on cross-cutting relations and degree of deformation. The three main plutonic phases are described in the following sections.

4.1.3.1 Stawamus Gabbro (unit A)

Stawamus gabbro (unit A; Fig. 4.16) forms a series of small bluffs on the south side of Ledge Creek in the northwestern corner of the map area (Fig. 4.1). This coarsely crystalline mafic unit is dark green on fresh surfaces and has a distinct green to white mottling on weathered surfaces. Fresh specimens are dominated by holocrystalline and hypidiomorphic labradorite (70%; An^X olivine (18%), augite (6%), actinolite (5%), magnetite (1%), and minor spinel and apatite. Feldspar grains are up to 3 centimetres long; olivine and pyroxene are mostly 1 to 3 millimetre grains.

The degree or intensity of greenschist metamorphism in the gabbro is directly related to proximity to the Squamish granodiorite (unit B3). The metamorphism is characterized by moderate to intense alteration of olivine and pyroxene to actinolite, Figure 4.16 Coarse grained Stawamus gabbro (unit A; Fig. 4.1) is characterized by labradorite megacrysts. Plastic ruler is 15.5 centimetres long.

Figure 4.17 Medium grained Indian River biotite granodiorite (unit Bj) is characteristic of the Indian River Intrusives (Fig. 4.1). 65 chlorite, sericite and spinel. Plagioclase is weakly altered to paragonite and\or sericite where olivine and pyroxene alteration is intense.

A foliation and superimposed metamorphism in the gabbro suggest a comparatively older age for the gabbro compared to the relatively unaltered and unfoliated Squamish granodiorite. The plutonic contact between these two bodies follows Ledge Creek.

Several small, less than 15 centimetre wide, amphibolite veins intrude the gabbro near the contact with the Squamish granodiorite (unit B3). Hornblende is concentrated in the hanging wall selvage of the veins whereas quartz and plagioclase dominate the footwall selvage.

4.1.3.2 Granodiorite Intrusives (units Bj, B2 and B3)

Three granodiorite plutonic phases of approximately the same age can be distinguished in the map area (Fig. 4.1): (1) Indian River Intrusives, unit Bj, (2)

Mountain Lake pluton, unit B2, and (3) Squamish pluton, unit B3. Units Bj and B2 are probably slightly older than unit B3 based on the relative degree of alteration and foliation in these plutonic rocks. The Squamish pluton has been dated as late Early Cretaceous (101 — 2 Ma) by U-Pb zircon analyses (R.L. Armstrong, 1989, unpublished data). The three plutonic phases are discussed below from relatively oldest to youngest.

Indian River biotite granodiorite (unit B^; Figs. 4.1 and 4.17) is an irregular linear body that separates the lower and middle Goat Mountain formation according to James (1929). The intrusion is in contact with the Squamish pluton on the northern end 66 of the project area and meets the Mountain Lake pluton along the southern edge of Figure 4.1.

Dominant minerals are plagioclase (30%; An-^, oligoclase), microcline (10 to 20%), quartz (35%), biotite (5%), chlorite and epidote (9%), pyrite (1%), and minor sphene, actinolite, epidote and apatite. Potassic feldspars are perthitic and usually sausseritized. The mineral percentages are not uniform and vary greatly as do grain sizes. Overall, the unit is coarse grained, altered and somewhat foliated. Whole rock chemical analyses (Table 4.2) define compositions from granite to granodiorite. A moderate to intense greenschist metamorphic overprint is typified by chlorite, epidote, sericite, and locally alteration includes limonitic, sideritic and silicified zones.

The unit has been locally sheared, which has developed a northwesterly trending foliation. Intensely sheared and strongly epidotized outcrops along the Indian River suggest that a fault zone follows the trace of the Indian River shear zone through the granodiorite. Quartz grains are strained, and show undulose extinction, deformation lamellae and sutured contacts. In more foliated and sericitized zones, near margins of the pluton, there is up to 8 percent pyrite and 1 percent chalcopyrite. Pyrite- molybdenite-chalcopyrite porphyry-type mineralization has developed on the east side of the Indian River, west of the granodiorite apophysis.

Mountain Lake biotite hornblende granodiorite pluton (unit Fig. 4.18), is on the central south portion of the project area and forms the surnmit of Maggie Ridge. The main body is to the southwest of the map area. The pale brown, medium to fine grained granodiorite is composed of andesine plagioclase (42%; An42), quartz (24%), microcline (16%), biotite (7%), hornblende (9%), magnetite (2%), and minor sericite, chlorite and apatite. The granodiorite is mainly equigranular and medium grained. 67

Figure 4.18 Medium to fine grained Mountain Lake biotite hornblende granodiorite

(unit B2) is characteristic of the Mountain Lake pluton (Fig. 4.1).

Figure 4.19 Pink, medium grained Squamish biotite granodiorite (unit B3) is characteristic of the Squamish pluton (Fig. 4.1). 68

Plagioclase compositions within the pluton are approximately andesine (A^Q), but grains exhibit continuous normal zoning. A sample from near the margin of the pluton contains oligoclase (A^Q). Plagioclase grains are often sausseritized especially in calcic cores.

A chilled margin, approximately 75 metres wide along the northern contact of the intrusion, has a distinct sugary texture. The chilled margin contains fragments of coarser grained granodiorite up to 25 centimetres long. Locally, unit B2 has a foliation striking northwest.

Squamish biotite granodiorite pluton (unit B3; Fig. 4.19) is pink, medium grained and composed of quartz (39%), microcline (16%), plagioclase (40%; oligoclase,

An 13), and biotite (5%). Minor amounts of alteration minerals (2%) include chlorite (penninite), epidote, sericite and magnetite. Normally zoned plagioclase feldpsars and perthitic feldspars are both somewhat sausseritized, more so in the cores of the plagioclase crystals. Biotite rims are chloritized.

The unit is uniform in composition and lacks prominent foliation or alteration. The size of subhedral quartz grains average 5 millimetres; anhedral alkali feldspars range up to 3 niiJJirnetres; euhedral plagioclase is 8 millimetres; and biotite is 3 rrijllimetres. A few irregularly shaped mafic xenoliths up to 0.3 metres occur near the plutonic contact with the gabbro (unit A).

4.1.3.3 Porphyritic Rhyolite (unit C)

Numerous quartz and feldspar porphyritic rhyolite bodies (unit C; Fig. 4.20) have intruded the east side of the Indian River valley (Fig. 4.1). These intrusives are 69 sporadically distributed for several kilometres southeast of the map area. The rhyolite bodies are either: (1) associated with the felsic tuffs and flows of the lower Goat Mountain formation, or (2) they are late phases of the Coast Plutonic Intrusives. The porphyritic bodies intrude the Indian River plutonics--in the northeastern part of the map area~and lower and middle Goat Mountain formation stratigraphy. Rare granitic inclusions support a young age.

The rhyolite consists of subhedral quartz (15%), euhedral plagioclase (6%), microcline (up to 5%) and pyrite phenocrysts (1%) in a glassy and microlitic groundmass (73%). Plagioclase phenocrysts (AJI32, andesine) range from 1 to 4 millimetres in size. Quartz "eyes" are irregular, rounded crystals that are often embayed. The quartz grains average 2 millimetres and range up to 1 centimetre across. Undulose extinction, overgrowths (up to 0.5 millimetres thick), and deformation lamellae on quartz grains result from strain associated with a shearing and deformational event. This suggests either: (1) some deformation was later than the Late Cretaceous K-Ax date (89.1 — 2.7 Ma) for this unit, (2) this deformation is associated with the metamorphic resetting of the age of the rhyolite intrusives, or (3) the intrusions are part of the lower Goat Mountain formation and the K-Ar date is reset.

The rhyolite has an unaltered appearance, but a fine sericitic network cuts the groundmass, rims some phenocrysts, and is concentrated in some strain shadows. Biotite-chalcopyrite-quartz veins and disseminated pyrite occurs peripherally to some rhyolite bodies. 70

Figure 4.20 Quartz and feldspar porphyritic rhyolite intrusives (unit C) occur along the east side of the Indian River valley (Fig. 4.1). 71

4.1.4 LATE INTRUSIVE DYKES (unit D)

Late dykes (unit D) intrude all units in the map area, but are more prevalent in hornfelsed zones and near the margins of the Indian River Intrusives. The dominant dyke compositions are andesite and basalt, but both have several varieties based on phenocryst assemblages. Rare aplite dykes exist near margins of plutons but are of limited extent. They are probably coeval with the granodioritic plutons and therefore are the oldest dykes. Aplite, andesite and basalt dykes are discussed in the following three sections.

4.1.4.1 Aplite Dykes

Felsic dykes are not common and are usually associated with plutonic bodies. The pink aplitic dykes are found along the margin of the Mountain Lake pluton (unit

B2) and probably represent a late phase.

The aplite dykes exhibit well developed granophyric intergrowths of quartz and plagioclase. Albite (Ang) characterizes the plagioclase composition in these dykes.

4.1.4.2 Andesite Dykes

Andesite dykes are found mainly along the Indian River, especially near unit Bj, and around the hornfelsing and mineralization observed in the Slumach zone. The andesite dykes, blue-green on fresh surfaces, weather pale greenish brown. The average dyke is 0.6 metres thick, but can be up to 3.8 metres thick. A few dykes exhibit crude columnar joints. Major element analyses support an andesite composition. The variation in appearances of these andesite dykes is due to variable phenocryst 72 assemblages. They are aphyric and porphyritic with plagioclase and minor hornblende phenocrysts.

The groundmass is dominantly microlitic plagioclase (usually andesine), often arranged in a sub-trachytic texture. Minor constituents are magnetite, chlorite and sericite, and trace hornblende, biotite and sphene. Normally zoned plagioclase phenocrysts (A1135; andesine) range from 5 to 23 percent in abundance, and average 3 millimetres in size. Grains are sausseritized, especially in cores of zoned crystals. Euhedral hornblende phenocrysts are 1 millimetre across and average 1 percent of the rock.

Andesite dykes are often cross-cut by chlorite-epidote veinlets and silicified zones, especially in hornfelsed areas. Veinlets of heulandite were also noted. Disseminated cubic pyrite, up to 4 percent, is a minor constituent in the silicified zones. Some dykes have vesicles and/or chloritic amygdules.

4.1.4.3 Basalt Dykes

A 2.5 metre thick hornblende porphyritic basalt dyke cross-cuts stratigraphy at a shallow angle and has a large outcrop extent near the centre of the project area. Other dykes preferentially follow faults, contacts and cleavage.

These basalt intrusions vary from aphyric to hornblende porphyritic to hornblende and plagioclase phyric. The basalt dykes average 1.5 metres thick and often display columnar joints. The dark brown to olive-brown dykes have a very fine grained to glassy microlitic groundmass with up to 15 percent fine grained disseminated magnetite. Microlitic andesine (75%) exhibits a poor trachytic texture. The 73 groundmass also contains some carbonate, fine grained hornblende, biotite, chlorite, sericite and minor sphene.

Hornblende porphyritic dykes contain up to 20 percent black, euhedral, acicular crystals that are up to 1 centimetre long, randomly oriented and rarely twinned.

Skeletal hornblende, noted in some thin sections, has partially re-equilibrated with the groundmass.

Euhedral plagioclase phenocrysts (A^Q; andesine) average two millimetres and constitute up to 5 percent of some dykes. Several dykes contain continuously normally zoned plagioclase phenocrysts. Cores of zoned plagioclase phenocrysts are often sausseritized. Alteration minerals include carbonate, chlorite, epidote and illite.

Most dykes are vesicular and some have amygdules of calcite or zeolite. Vesicles average 2 millimetres in diameter and constitute up to 10 percent of some dykes. The zeolites are chabazite crystals in radiating groups of acicular rhombs that partly fill exceptionally large voids ranging up to 4 centimetres across. A 75 centimetre thick dyke in the Stawamus valley has a layer of small agate amygdules that are less than 5 centimetres in diameter.

Whole rock and hornblende separate K-Ar analyses from a basalt dyke were Early Oligocene (35.9 -±-1.3 Ma, 36.2 -±-1.3 Ma; section 4.4.1.4). 74

4.1.5 METAMORPHISM

The Britannia - Indian River pendant exhibits a lower greenschist facies regional metamorphism and zones of earlier biotite and cordierite-biotite contact metamorphism. Low pressure greenschist metamorphic belts of island arc volcanics are typically accompanied by abundant granitic bodies in geosynclinal settings (Miyashiro, 1973). Therefore regional metamorphism within the project area is interpreted to be directly related to the emplacement of the plutonic bodies that surround the pendant. High temperature contact metamorphic aureoles may have formed around these intrusives. Descriptions of the regional and contact metamorphism follow.

4.1.5.1 Regional Metamorphism

The lower greenschist facies metamorphism occurred in a low pressure, moderate temperature orogenic setting. The high temperature gradient was developed during emplacement and cooling of the plutonic bodies.

The metamorphic mineral assemblage observed in the project area includes: actinolite, chlorite, epidote, muscovite, — biotite, — albite and sericite. Intermediate and mafic units usually exhibit several of the metamorphic minerals and are often rendered massive texturally and become difficult to discern as tuffs or flows. The greenschist metamorphism has little effect on the felsic units; only a few of the metamorphic minerals are commonly present.

Some K-Ar and Rb-Sr dates (section 4.4) obtained from volcanic units in the project area are reset from 99 to 95 Ma. This metamorphic reset, in the Britannia - Indian River pendant, probably correlates with emplacement of the Squamish pluton 75

(101 — 2 Ma by U-Pb zircon analyses: R.L. Armstrong, 1989, unpublished data). Amphibolite dykes within volcanics on Sky Pilot Mountain and the gabbro (unit A) were dated as Late Cretaceous (101 — 4 Ma and 95.1 — 3.3 Ma respectively by Heah, 1982). This date was interpreted to be synmetamorphic (Heah, 1982).

4.1.5.2 CONTACT METAMORPHISM

Contact metamorphic zones occur along the Indian River and the west side of the valley. The metamorphism, characterized by pervasive purplish-brown secondary biotite, is prevalent in mineralized areas (Slumach, War Eagle, ABC and Belle). The biotitization is accompanied by silicification, chloritization and cordierite porphyroblasts in more intensely metamorphosed zones. Only the contact metamorphic zone along the Indian River, associated with the Indian River granodiorite, is in direct contact with an igneous body. Other zones are probably also related to this pluton. A K-Ar date on the biotite in the Slumach zone indicates an Early Cretaceous metamorphic date (108 — 4 Ma).

The cordierite-biotite hornfels is easily distinguished in hand specimen by pale brown, ovoid, 5 to 10 millimetre porphyroblasts of cordierite or retrograde minerals after cordierite (Figs. 4.21 and 4.22). The ovoid patches are randomly oriented and constitute up to 20 percent of the hornfels (Fig. 4.21). Minerals in the retrograde patches are quartz, sericite, muscovite and other minor secondary minerals. Cordierite porphyroblasts are best developed above the Slumach zone within totally biotitized rock (Figs. 4.21 and 4.22). Some of the specimens have a poorly developed S^ fabric that is probably due to the later regional deformation. 76

Figure 4.21 Weathered cordierite-biotite hornfels is observed in the Slumach zone (Fig. 4.1; see Fig. 4.22). Note the criss-crossing quartz veinlets and resistant cordierite porphyroblasts. Pencil is 14 centimetres long.

Figure 4.22 Porphyroblasts of cordierite within a cordierite-biotite hornfels occur near the Slumach zone (Fig. 4.1; see Fig. 4.21). Width of field is 0.53 centimetres. Magnification is 24X; crossed polarizers. 77

The typical zonation of contact metamorphism approaching the Slumach zone is: (1) increasing propylitic alteration and minor spotting in sediments, (2) increase of biotite, sericite and locally pronounced spotting (quartz-albite-biotite hornfels), and (3) intense silicification, development of patches of cordierite-quartz-biotite-this zone is around the brecciated quartz-sulphide vein (section 4.5)~or patches of retrograde minerals after cordierite. The hornfels in the Slumach zone is later than the volcanogenic mineralization, thus overprinting any original volcanogenic alteration pattern. The later hornfelsing also could have mobilized some of the sulphide mineralization in the veins. 78

4.2 STRUCTURE

The project area has three main structural domains: (1) east of the Indian River and the Indian River granodiorite apophysis, (2) between the Indian River granodiorite and Maggie Ridge (including the lowermost part of unit 4a), and (3) the Stawamus

River valley (Fig. 4.1). Structural domains are described in the following section. A discussion of faults and the overall style of deformation follows the descriptions of the domains. Structural style for each domain is presented in stereonets and contoured plots of bedding, cleavage, and extension joints in Figures 4.23 to 4.25 Stereonets of structural data for each unit are in Appendix A (Figs. A.1 to A.3).

4.2.1 STRUCTURAL DOMAINS

Domain 1 occurs in the part of the map area east of the Indian River (Fig. 4.1). Bedding, SQ, strikes north and dips steeply west or east (Fig. 4.23). The sequence faces consistently west and therefore it is locally overturned. Foliation, S^, is predominantly north-northwest striking with nearly vertical east and westerly dips. James (1929) and Roddick (1965) recognized this as the western limb of a major antiform that has a northeast vergence. Closure of the antiform would be to the southeast of the map area (James, 1929). The structural style within this series of felsic flows and interbedded sediments is distinct from that in felsic units to the west.

Domain 2 occurs between the Indian River and the lowermost part of unit 4a on Maggie Ridge (Figs. 4.1). Beds generally strike northwest and dip moderately to the southwest (Fig. 4.24). Excellent tops indicate that this sequence is upright. The change in strike of SQ from domain 1 to domain 2 is attributed to the plutonic intrusion DOMAIN 1 Structural data (unit LGM).

Figure 4.23 Domain 1 stereonet plots of structural data (unit LGM). The upper row of stereonets depict (from left to right) poles to bedding, poles to cleavage and poles to extension joints. The lower row are contoured nets of the corresponding data. DOMAIN 2 Structural data (units 1, 2, 3, & lowermost 4a).

Figure 4.24 Domain 2 stereonet plots of structural data (units 1,2,3 and the lowermost portion of unit 4a). The upper row of stereonets depict (from o left to right) poles to bedding, poles to cleavage and poles to extension joints. The lower row are contoured nets of the corresponding data. DOMAIN 3 Structural data (units 4a, 4b, 4c, 5a, 5b, & 6).

Figure 4.25 Domain 3 stereonet plots of structural data (units 4a, 4b, 4c, 5a, 5b and 6). The upper row of stereonets depict (from left to right) poles to bedding, poles to cleavage and poles to extension joints. The lower row are contoured nets of the corresponding data. 82 between the two sides of the valley. in domain 2 also has a northwest strike but nearly vertical dips. The changes in strike of SQ and S^ are consistent between domains 1 and 2, therefore the deformation (D-^) that developed S^ was earlier or cogenetic with the plutonic emplacement and disruption of the pendants.

An anticlinal structure, whose axial trace parallels the Indian River, is indicated by predominantly northwest striking, nearly vertical axial planar cleavage, S^ (Fig.

4.24). Extension (A-C) joints are consistently perpendicular to S^. Fold vergence, indicated by SQ - S^ relations, is to the northeast. The gradual change in bedding orientation from moderately southwest dipping beds near the Slumach zone, through shallow dips east of the Slumach zone, to vertical beds northeast of the War Eagle zone indicates a small asymmetrical anticline that might be overturned to the northeast. The eastern limb has been faulted off near the War Eagle zone but both east and west limbs exist to the northwest near the contact of unit 2 with B ^ and to the southeast at the contact of unit 1 with B^ (Fig. 4.1). The fold axis plunges northwest north of the pass, and moderately southeast to the south of the pass. Previous drilling results support the limited outcrop evidence for this interpretation northwest of the War Eagle zone (Drummond and Howard, 1985). East of the faulted-off anticline the units are southwest dipping and are on the west limb of the larger antiform mentioned earlier. The smaller fold is interpreted to be parasitic to the major antiform, or possibly a drag fold that resulted from reverse dip-slip movement on the Indian River shear. (Latest movement in the Indian River shear zone, indicated by slickensides, is dominantly right lateral.)

East of Maggie Ridge a second, locally developed cleavage (S2), strikes north

and dips steeply to the west. S2 is axial planar to some minor folds with steep 83 northwesterly plunging axes. This cleavage also parallels faults and shear zones in the area.

Domain 3 follows the Stawamus River valley (Fig. 4.1). Beds strike easterly and dip moderately to the south (Fig. 4.25). Tops are consistently to the south. Poorly defined S^ has a northwest strike and moderate dips. The change in bedding orientation and the rapid thinning of intermediate volcanic interbeds of units 4b and 4c are indicative of an angular unconformity (possibly with an irregular paleotopography) in the lower portion of unit 4a. This unconformity separates domain 2 from domain 3. Higher up, in the Sky Pilot volcanic sequence, thick-bedded units dip shallowly to the south or southwest (Heah et al, 1986).

Other possible reasons for the change in strike between domain 2 and 3 are (1) a rotational or a combination of normal and strike-slip movement on the fault that crosscuts the lower part of unit 4a, or (2) a fold or warping caused by plutonic intrusions. The latter possibilities, however, do not account for the drastic thinning of units 4b and 4c.

4.2.2 FAULTS AND SHEAR ZONES

Two dominant fault types have been noted within the map area: (1) north to northwest trending strike-slip faults, and (2) northeast striking faults with variable movements. The north to northwest striking faults are sub-parallel to the Sj cleavage in all three domains. The northeast striking faults are prominent near the Slumach zone and parallel most creeks east of the Indian River. These latter faults are second order to the northwest trending Indian River shear zone in the centre of the map area. 84

The northwest trending Indian River shear zone narrows from 12 metres southeast of the map area (James, 1929), to highly faulted and locally sheared zones up to 5 metres wide within and along the Indian River. The shear zone through the War Eagle zone and along the Indian River is assumed to be part of the Indian River shear. Mylonitized conglomerate and tuff breccias along Indian River attest to the presence of this steeply west dipping shear zone (Fig. 4.1). The latest movement is right lateral, as indicated by slickensides. This shear is sub-parallel to the Britannia shear (McColl, 1987; Payne et al., 1980), but has a steeper dip.

Numerous deeply incised northeasterly striking faults on the west side of the Stawamus River valley have disrupted contacts of several units by mostly strike-slip movements. The outcrop patterns in this area are the simplest version of an undoubtedly more complex pattern.

4.2.3 SUMMARY OF STRESS

Deformation in the Indian River valley was caused by a northeasterly horizontal compressional stress. Both noted deformations are consistent with a single ongoing stress.

During Dj, S^ and the major antiform developed perpendicular to the compressive stress. The deformation probably accompanied the first metamorphic reset (section 4.4). 85

Volcanogenic ore in the Indian River valley and at Britannia was deposited before deformation. Deformation of sulphides is prevalent at Britannia (Beatty, 1974). Partial remobilization of sulphides in the Slumach, War Eagle and Belle zones is apparent. The higher grade stringer veins may have been concentrated by this deformation.

Some deformation (D2) post-dates the emplacement of the plutonic bodies. The late rhyolite plutons exhibit several deformational features in thin section (see section 4.1.3.3) that suggest a major event occured during or after the 89.1 — 2.7 Ma date obtained for this unit. Samples of sericitic schist from the Britannia shear zone date the last major event on the Britannia and Indian River shear zones as Late Cretaceous (84 to 80 Ma; McColl, 1987).

Overall, the Britannia - Indian River pendant is the southern limb of an antiform with a northeast vergence. At least one angular unconformity occurs within the thick stratigraphic succession. A major northeast compressional stress that is probably cogenetic with plutonism, regional metamorphism, and the reset of K-Ar dates, created the main S^ cleavage and extension joints. Plutonic intrusions disrupted the pendant as shown by separation of domain 1 from 2. A deformational event associated with a second metamorphic reset (see section 4.4.1) that could be a continuation of the same deformational event initiated the Indian River shear. The faulted-off anticline along the Indian River probably formed as a drag fold due to reverse movement along the Indian River shear. 86

4.3 MAJOR AND TRACE ELEMENT CHEMISTRY

Samples were collected from major volcanic and intrusive units in the Indian and Stawamus River valleys. Thirty-one samples and ten duplicates were analyzed for major and trace elements to: (1) classify the samples on a chemical basis, (2) characterize alteration and the elements affected, and (3) compare the volcanic suite to established trends and classifications. The rock chip samples were prepared and analyzed as described in Appendix B. Mean values and standard deviations for major and trace elements were calculated from monitor pellets run as unknowns (Tables B.2, B.4 and B.5 in Appendix B).

The Indian - Stawamus River suite of volcanic units is divided into three informal packages (Fig. 4.1): (I) lower Goat Mountain formation (unit LGM), (II) middle Goat Mountain formation-Indian River valley (units 1,2 and 3), and (IJI) middle Goat Mountain formation-Stawamus River valley (units 4, 5 and 6). The packages I, II and LTI correspond to the structural domains 1,2 and 3 respectively (Fig. 4.1). The division between package II and III in the middle Goat Mountain formation marks a change from dominantly felsic volcanism, with minor intermediate interbeds of package U, to dominantly intermediate to mafic flows and sediments of package LTI. The latter division coincides with the change in strike from northwest in the Indian River valley (structural domain 2) to west in the Stawamus River valley (structural domain 3; section 4.2).

Major and trace element data for volcanic units are presented in Tables 4.1 and 4.4 respectively; data for intrusive units are in Tables 4.2 and 4.5. Samples are ordered in the tables from oldest to youngest. Discussions of duplicate analyses, major element and trace element results are in the following three sections. 87

4.3.1 DUPLICATE SAMPLES AND PELLETS

Duplicate samples and pellets were used to monitor the reliability of major and trace element analyses. Five duplicate sample pairs were pulverized in two shatterboxes of different composition: (1) a tungsten-carbide shatterbox, and (2) a chrome-steel one (denoted with "d" in Tables 4.1,4.2,4.4 and 4.5). A further five samples had duplicate pellets made from powders prepared in the tungsten-carbide shatterbox (denoted with "a" and "b" in Tables 4.1,4.2,4.4 and 4.5).

Samples prepared in a tungsten-carbide shatterbox can show contamination by Co, Nb and W~Co and W are not of interest here-whereas samples prepared in a chrome-steel shatterbox can be contaminated by Fe, Cr and Mn (Hickson and Juras, 1986). Specifically, duplicates prepared in the chrome-steel shatterbox in this study were dramatically higher in Cr (averaging 90 ppm higher), and marginally higher in Fe and V, than samples prepared in the tungsten-carbide shatterbox. Variations in Mn were not consistent between the two preparation methods. The validity of the V contamination could not be confirmed because of the poor reproducibility of concentrations of this element between analyses. No significant differences in Nb values were noted between the two preparation methods.

Machine drift between measurements of the sample pairs (both duplicate samples and duplicate pellets) is shown by small but consistent increases in Na (1.52% average increase) and almost consistently lower Mg values (0.66% average decrease except for 87IRD-81a and b). The drift may be due to gradual changes in "d" spacing of the detection crystal, as the crystals warms up, between analyzing the first pellet (start of run) and second pellet of a pair (end of run). Systematic machine drift was not noted for other element measurements. 88

The duplicate pellets showed no consistent variations in any of the major or trace elements. Only Ba and V had relatively poor repeatability. Results for the two pellets were averaged and are denoted "a" on Figures 4.26 to 4.44.

The trace element data were averaged from two separate sets of analyses made by the Department of Oceanography, The University of British Columbia, on an automated Philips PW 1400 X-ray fluorescence unit (XRF). Nb, Rb, Sr, Y and Zr were in excellent agreement between the two runs, whereas Ba, Cr and Ni were only fair, and V was poor in reproducibility.

The results from the duplicate samples, pellets and repeat analyses indicate that the tungsten-carbide method is suitable for the results obtained in this study. There is no significant difference in Nb concentrations due to use of the tungsten-carbide shatterbox. The reproducibility of most major and trace elements is excellent (Tables 4.1 to 4.5).

4.3.2 MAJOR ELEMENT CHEMISTRY

Relatively fresh samples, based on hand and thin sections, were analyzed by XRF for ten major elements (Table B.l in Appendix B). The results were recalculated and normalized volatile free with total iron as FeO (Tables 4.1 and 4.2). CD?W (Cross, Iddings, Pirsson and Washington) norms and cation norms were calculated (using OBCATNORM program written by R.L. Armstrong) and are presented in Table B.2 of Appendix B. 89

Table 4.1 Major element oxides of samples from volcanic units in the Indian and Stawamus River valleys, southwestern British Columbia (Figs. 4.1 to 4.5). The data are recalculated from XRF analysis of pressed glass powders. Normalized data are plotted in Figures 4.26 to 4.44. Samples with "d"1 are duplicates prepared in a chrome-steel shatterbox (see Appendix B). Samples denoted "a" and "b"2 are duplicate pellets.

Sample Weight percent oxides

4 Number Unit Si02 TiC>2 A1203 FeO* MnO MgO CaO Na20 I^O P20,

I Lower Goat Mountain Formation-Indian River valley

Rhyolite 86IRD-161 1-1 75.75 0.09 14.75 0.75 0.01 0.40 0.48 0.44 7.30 0.02 Rhyolite 87IRD-122 1-1 78.75 0.08 13.31 0.86 0.00 0.43 0.41 0.92 5.21 0.02

II Middle Goat Mountain Formation-Indian River valley

Basalt 86IRD-1876 II-l 52.97 1.00 17.80 8.70 0.26 8.08 6.08 4.10 0.73 0.29 Rhyolite 86IRD-189 II-l 72.83 0.39 14.86 2.33 0.07 0.80 1.33 4.41 2.90 0.10 Andesite 86IRD-193a II-l 59.73 0.94 17.76 7.31 0.12 2.45 7.28 3.07 1.05 0.30 86IRD-193b II-l 59.69 0.94 17.72 7.39 0.12 2.40 7.30 3.09 1.06 0.30 Rhyolite 86IRD-121 II-2 75.60 0.08 14.30 1.09 0.04 0.64 0.92 3.56 3.76 0.02 86IRD-121d n-2 75.50 0.07 14.25 1.16 0.04 0.63 0.92 3.61 3.79 0.02

Andesite 87IRD-151a6 II-3 55.23 0.94 19.30 8.21 0.18 3.70 3.47 5.62 3.11 0.25

87IRD-151b6 II-3 55.04 0.94 19.44 8.30 0.17 3.68 3.44 5.63 3.08 0.25

Basalt 87IRD-1796 II-3 51.38 1.00 17.03 930 0.26 7.43 9.30 2.83 0.81 0.46

Basalt 87IRD-1856 II-3 52.75 1.11 17.90 8.45 0.16 5.70 7.90 3.81 1.75 0.46

III Middle Goat Mountain Formation-Stawamus River valley

Rhyolite 87IRD-97 IIMa 76.73 0.28 13.26 1.86 0.02 0.44 0.96 5.84 035 0.06

Basalt 87IRD-606 11Mb 52.03 1.02 1737 831 0.16 6.84 937 3.16 0.82 0.31 Basalt 87IRD-88 IIMb 50.77 1.06 17.85 9.47 0.17 6.76 9.94 231 1.11 0.34

Andesite 87IRD-64a6 IIWc 56.14 0.86 16.36 7.78 0.14 5.65 837 3.19 1.08 0.24

87IRD-64b6 IIMc 56.26 0.85 16.40 7.66 0.13 5.69 830 3.15 1.10 0.24

87IRD-64b5,6 rrwc 56.17 0.84 16.41 7.64 0.14 5.74 8.48 3.22 1.09 0.26 Basalt 87IRD-1336 III^c 52.59 t.10 16.25 9.97 0.20 7.40 7.06 4.05 0.94 0.44

Basalt 87IRD-726 III-5a 5235 0.93 16.79 8.76 0.19 7.39 9.32 3.05 0.67 0.33

87IRD-72d6 III-5a 52.67 0.93 16.73 8.72 0.19 7.24 9.36 3.18 0.66 0.33

Basalt 87IRD-766 III-5a 51.76 1.02 1736 8.69 0.14 7.72 6.37 338 2.87 0.31 Basalt 87IRD-79 III-5a 4932 0.94 15.99 10.67 0.21 8.03 11.83 1.39 1.03 0.39 Andesite 87IRD-192 III-5a 56.90 1.07 16.69 7.72 0.18 4.93 7.88 3.38 0.93 0.31 87IRD-192d IIl-5a 56.95 1.08 1635 7.72 0.19 4.92 7.85 331 0.92 0.31

1. Duplicate samples denoted "d" were not used in data plots. 2. Normalized data for duplicate pellets were averaged for use in data plots. 3. Weight percent oxides are normalized to 100% volatile free. Totals are not meaningful. 4. FeO* = 0.8998 x Fe^. 5. Sample was a repeat analysis of the same pellet #871RD-64b. 6. These samples are considered to be altered according to CaO-MgO plots (Fig. 4.29). 90

Table 4.2 Major element oxides of samples from intrusive units in the Indian and Stawamus River valleys, southwestern British Columbia (Figs. 4.1 to 4.5). The data are recalculated from XRF analyses of pressed glass powders. Normalized data for the dykes are plotted in Figures 4.26 to 4.44. Samples with "d"1 are duplicates prepared in a chrome-steel shatterbox (see Appendix B). Samples denoted "a" and "b"2 are duplicate pellets.

Sample Weight percent oxides3

1 Number Unit sio2 Ti02 A12Q3 FeO" MnO MgO CaO Na20 P2°5

A Stawamus Gabbro Pluton

Gabbro 87IRD-67 A 46.03 0.35 24.29 735 0.14 7.03 13.44 0.92 0.18 0.08 Gabbro 87IRD-125 A 42.21 0.44 15.14 15.85 0.25 14.9 10.52 0.48 0.11 0.09

B Squamish Granodiorite Pluton

Granodiorite 86IRG-18 Bl 77.81 0.18 1338 1.04 0.01 0.00 0.66 2.96 3.73 0.01 Diorite 87IRD-190 B2 61.17 0.84 16.93 7.14 0.16 2.65 5.96 336 1.37 0.23 87IRD-190d B2 60.61 0.85 17.04 736 0.16 2.68 5.88 3.59 1.39 0.23 Granodiorite 87IRD-81a B3 75.47 0.22 13.94 1.72 0.04 0.06 2.00 3.74 2.76 0.05 87IRD-81b B3 7533 0.21 14.00 1.65 0.04 0.01 2.00 3.71 2.79 0.05

C Quartz Feldspar Porphyritic Rhyolite Intrusives

Rhyolite 86IRD-50 C 78.11 0.08 12.67 0.90 0.02 0.00 0.69 237 4.94 0.02 Rhyolite 87IRD-166 C 77.45 0.07 12.32 0.81 0.00 0.00 0.43 1.18 7.74 0.02 Rhyolite 87IRD-169 C 71.71 0.41 14.85 2.81 0.10 1.49 0.96 4.80 2.77 0.09

Dykes Late Intrusives

Basalt 86IRD-53a5 D 51.63 1.13 17.75 9.02 0.17 6.86 831 2.32 2.29 0.32 86IRD-53b5 D 51.33 1.13 17.75 9.22 0.17 6.82 836 2.40 2.30 0.32 Dacite 86IRD-63 D 6733 0.35 16.79 5.69 0.11 031 138 536 1.68 0.18 Andesite 86IRD-1455 D 54.82 •1.21 16.91 7.49 0.16 7.08 8.32 2.82 1.00 0.21 SeiRD-MSd5 D 54.91 1.21 16.87 738 0.16 6.96 8.27 2.84 1.01 0.21 Andesite 87IRD-75 D 5334 137 17.77 8.46 0.16 5.03 8.64 3.23 1.30 0.28 Dacite 87IRD-161 D 6532 0.68 16.91 4.43 0.12 1.16 5.15 332 2.20 0.33

1. Duplicate samples denoted "d" were not used in data plots. 2. Normalized data for duplicate pellets were averaged for use in data plots. 3. Weight percent oxides are normalized to 100% volatile free. Totals are not meaningful. 4. FeO* = 0.8998 x Fe^. ° 5. These samples are considered to be altered according to CaO-MgO plots (Fig. 4.29). 91

4.3.2.1 Classification of Rock Types

Twenty-three samples from volcanic units and dykes representing the lower and middle Goat Mountain formation of both the Indian and Stawamus River suites have been plotted on chemical variation diagrams. The rock type classification is based on

an FeOtotai/MgO versus Si02 variation diagram (Fig. 4.26) with the weight percent SiC»2 fields defined by Gill (1981), and the tholeiite - calc-alkaline boundary from Miyashiro (1974). The suite has a bimodal distribution with clusters in the rhyolite and andesite - basalt fields. Bimodal distributions of chemical data for volcanic units higher in the Gambier Group stratigraphy were noted by McColl (1987) and Heah (1982) in the Britannia - Indian River pendant. Most samples are classified on Figure 4.26 as calc-alkaline, except for some andesite-basalts and most dyke rocks, which are tholeiitic.

The analyses have a more distinctly bimodal character on a normative colour index versus normative plagioclase composition diagram (Fig. 4.27a; Irvine and Baragar, 1971). Samples that are classified as andesites, based on Si02, plot as basalts when classification is based on normative plagioclase.

Package I samples of the lower Goat Mountain formation (plotted as triangles in Figs. 4.26 to 4.43) are from two felsic flows that plot as calc-alkaline rhyolite in Figure 4.26. These analyses are representative of the volcanic component of the lower Goat Mountain formation (Table 4.3). The predominance of felsic pyroclastics and flows is suggestive of felsic island arc volcanism.

Package II samples of the middle Goat Mountain formation in the Indian River valley (plotted as squares in Figs. 4.26 to 4.43) are from units 1,2 and 3. The 12.00 Legend Package I (unit LGM) Package II (units 1,2,3) o Package III (units 4,5,6) 0 Dykes o

D -4—» O O

i—i—i—|—i—r 50.00 60.00 70.00 80.00 Si02 (wt.s)

Figure 4.26 FeOjo^^/MgO versus SiO^ for volcanic rocks from the Indian River and Stawamus River valleys. Tholeiitic - calc-alkaline boundary defined by FeO~OTAr/MgO = 0.1562 x Si02 - 6.685 (Gill, 1981 from Miyashiro, 1974). Rock composition boundaries are based on weight percent SiC<2 (Gill, 1981). Solid symbols indicate "unaltered" samples as defined in Figure 4.29. 93

0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 Normative Plagioclase Composition

Symbols are defined in Figure 4.26.

Calc -alkaline

18.00 - 7 5 185*187 # 5Jq,«M 76 ° 80 ° 63 ,79 • 461 f 192* "° 25*^^ -t—> 79 •

161^-.— . 189 ^—-i e 193o . 121

O 122 Tholeiitic CNJ 97 • <

10.00 0.00 10.00 20.00 30.00 40.00 50.00 Normative Plagioclase Composition Figure 4.27 (a) Normative colour index versus normative plagioclase composition, and (b) A^O-j versus normative plagioclase composition for volcanic rocks from the Indian River and Stawamus River valleys. Tholeiitic - calc-alkaline and compositional boundaries are from Irvine and Baragar (1971) for common volcanic rocks. Solid symbols indicate "unaltered" samples as defined in Figure 4.29. 94

Table 4.3 Average weight percent oxides for rock types and packages of units sampled in the Indian and Stawamus River valleys, southwestern British Columbia.

Package I n n in Average Average Rhyolite1 Rhyolite" Andesite- Andesite- of Rhyolite of Andesite- Basalt3 Basalt4 Cluster5 Basalt Cluster6 mean st.dev. mean st.dev. mean st.dev. mean st.dev. mean st.dev. mean st.dev.

Oxide

Si02 77.25 2.12 74.22 1.96 54.40 3.27 52.79 2.53 75.93 2.14 52.96 2.04 Ti02 0.09 0.01 0.24 0.22 1.00 0.07 1.00 0.08 0.18 0.14 1.06 0.17 A1203 14.03 1.02 14.58 0.40 17.97 0.86 16.89 0.69 14.10 0.77 1731 0.86 FeO* 0.81 0.08 1.71 0.88 8.45 0.78 8.94 1.04 1.38 0.69 8.77 0.87 MnO 0.01 0.01 0.06 0.02 0.20 0.06 0.17 0.03 0.03 0.03 0.18 0.04 MgO 0.42 0.02 0.72 0.11 5.46 2.41 6.84 1.06 034 0.17 6.57 1.29 CaO 0.45 0.05 1.13 0.29 6.81 2.20 8.81 1.74 0.82 038 8.18 1.94 Na20 0.68 0.34 3.99 0.60 3.89 1.10 3.04 0.80 3.03 230 3.27 0.95 K20 6.26 1.48 333 0.61 1.49 0.98 1.18 0.70 3.94 233 136 0.78 P205 0.02 0.00 0.06 0.06 035 0.10 033 0.06 0.04 0.04 033 0.08

2. N = 2: samples : 87LRD-121 and 189. 3. N = 5: samples : 87LRD-179,185,187,193a and 151a. 4. N = 8: samples : 87IRD-79, 88,76,60, 72,133,64a and 192. 5. N = 5: samples : 87IRD-161,122,189,121 and 97. 6. N = 15: samples : 87LRD-187,185,133,79, 88,179,53a, 76,60, 72,75,145, 64a, 151a and 192. 95 compositions of the three analyses from unit 1 are rhyolite, andesite and basalt (Fig. 4.26). Although outcrops of unit 1 are dominantly basaltic andesite there are a few felsic interlayers. The andesite sample (86IRD-193a) plots within the tholeiitic field; it could be a late dyke within the unit.

The rhyolite of unit 2 is one of several felsic flows within the sediments and pyroclastics. Rhyolite volcanic rocks make up at least 20 percent of Package II.

Two basalt and one andesite analysis from unit 3 are part of the first distinct andesite-basalt flow in the stratigraphy. Intermediate volcanic rocks constitute less than 15 percent of Package II. Unit 3 samples are within or marginal to the tholeiitic field (Fig. 4.26).

Package III samples of the middle Goat Mountain formation in the Stawamus River valley (plotted as circles in Figs. 4.21 to 4.43) are from units 4a, 4b, 4c and 5a. The proportion of andesite-basalt volcanics increases in units 4 and 5 to 49 percent of the map area (Fig. 4.1). The rhyolite flow of unit 4a is within felsic pyroclastics and tuffaceous sediments. Of the four analyses from units 4b and 4c, three are basalts and one is andesite. Two basalt analyses plot in the tholeiitic field of Figure 4.26.

The transitional tholeiitic - calc-alkaline chemical character of the andesite- basalts was noted by McColl (1987) at East Britannia Ridge, and by Heah (1982) in the Sky Pilot volcanic rocks. The latter volcanic rocks are immediately below McColl's package 1 and above package III of this study. The combined thickness of this borderline tholeiitic - calc-alkaline, dominantly mafic section is in the order of 3,000 metres. 96

Dyke samples (plotted as diamonds in Figs. 4.26 to 4.43) are from late intrusions of unit D (Figs. 4.1 to 4.5). Compositions of four of the five dyke samples are basalt to dacite and plot on the boundary of or within the tholeiitic field (Fig. 4.26). The other sample is from an Early Oligocene hornblende porphyritic dyke (86IRD-145) that plots as calc-alkaline andesite. Abundant hornblende phenocrysts cause an abnormally high MgO content, making the sample appear calc-alkaline although it is more likely tholeiitic.

4.3.2.2 Alteration

All rocks in the project area are altered by regional, contact and/or hydrothermal metamorphism associated with volcanogenic activity. Alteration assemblages consist of some or all of: quartz, chlorite (and penninite), sericite, calcite, epidote (and clinozoisite), actinolite and rarely zeolites. Localized hornfelsic alteration includes: quartz, albite, biotite, sericite and cordierite.

Gains and losses of Si02, K20, Na20, MgO, CaO and FeO due to hydrothermal metamorphism has been noted in this study and by Payne et al. (1980) and McColl (1987) for other portions of the Britannia - Indian River pendant. The mobility of these oxides invalidates most standard classification schemes as only unaltered samples can be used. "Unaltered" or "least-altered" samples can be identified by a method developed by de Rosen-Spence (1976) for normal subalkaline rocks in a study of the Archean Noranda volcanic sequence. The method was also applied by McColl (1987) to samples from East Britannia Ridge (cf. de Rosen-Spence and Sinclair, 1987).

Identifying the least altered samples using variation diagrams (Figs. 4.28 to 4.33) allows the samples to be applied to standard classification schemes. Gains and losses of 97

Figure 4.28 Na^O + K^O versus SiO^ for volcanic rocks from the Indian River and Stawamus River valleys. Dashed line is the alkaline - subalkahne boundary from Irvine and Baragar (1971). Solid lines are from de Rosen-Spence (1976, after Kuno, 1966). Solid symbols indicate "unaltered" samples as defined in Figure 4.29. 10.00 Symbols are defined in Figure 4.26.

8.00 -

Altered Domain (MqO added and 6.00 /or CaO lost)

O 4.00 CD

CaO Added 2.00 -

0.00 I ( I I I I I I I | I I I I I IT I I | I I I I I I I I I | I I I I I I I I l | I l I I I I l I I | I I l I I I I I I | II l I l I I I I | 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 CaO (wt.s) Figure 4.29 MgO versus CaO for volcanic rocks from the Indian River and Stawamus River valleys. Boundaries are from de Rosen-Spence (1967). Solid symbols indicate "unaltered" samples as defined in this Figure. 98

10.00

40.00 50.00 60.00 70.00 80.00 Si02 (wt.s) Figure 4.30 MgO versus SiC^ for volcanic rocks from the Indian River and Stawamus River valleys. Boundaries are from de Rosen-Spence (1967). Solid symbols indicate "unaltered" samples as defmed in Figure 4.29.

Figure 4.31 CaO versus Si02 for volcanic rocks from the Indian River and Stawamus River valleys. Boundaries are from de Rosen-Spence (1967). Solid symbols indicate "unaltered" samples as defmed in Figure 4.29. 8.00 Symbols art defined in Figure 4.26.

6.00

Na Added

4.00 - O Normal D Subalkaline Domain 2.00 -

Na Lost

0.00 r—i—r—1—i i i i i—|—i—i—i—i—i—i—i—i—i—|—i i i—i—IIII—i | i i—i I i—i—i—r~ 40.00 50.00 60.00 70.00 80.00 Si02 (wt.

Figure 4.32 Na20 versus SiC^ for volcanic rocks from the Indian River and Stawamus River valleys. Boundaries are from de Rosen-Spence (1967). Solid symbols indicate "unaltered" samples as defined Figure 4.29.

8.00 Symbols ore defined in Figure 4.26. fit

6.00 - Very High K m

'4.00 - High K .in O rt

| „ - " i" Medium K 2.00 ' c •3 -^1 w - ' •" • Jg _ I. - - "" 17»0 0 1 Low K •" — ~~ " 1 40.00 50.00 60.00 70.00 80.00 Si02 (wt.S8) Figure 4.33 F^O versus Si02 for volcanic rocks from the Indian River and Stawamus River valleys. Dashed boundaries are from de Rosen-Spence (1967). Solid boundaries are from Gill (1981). Solid symbols indicate "unaltered" samples as defined in Figure 4.29. 100

K20, Na20, MgO and CaO have been identified, but changes in Si02 and FeO are difficult to monitor with these diagrams.

The samples are first plotted on a Si02 versus alkalies variation diagram to establish that the volcanic samples in this study are mostly normal subalkaline rocks (Fig. 4.28; Kuno, 1966). The five samples that plot outside the subalkaline domain are enriched in alkalies and may be altered due to sea-water Na-enrichment or spilitization. Samples from package 1 of McColl (1987) also plot in this alkaline mafic field.

Twelve "unaltered" samples that have not had distinct Mg metasomatism or Ca loss (solid symbols) can be identified using the MgO versus CaO variation diagram (Fig.

4.29). On MgO versus S1O2, CaO versus Si02, Na20 versus Si02 and K2O versus Si02 variation diagrams four of these samples are shown to be "altered" with Mg, Na or K gains and/or Ca, Na or K losses (Figs. 4.30 to 4.33). Abundant hornblende phenocrysts in 86IRD-145 give it an abnormally high MgO content, thus it appears to be

altered on the MgO versus Si02 diagram although it is fresh and post-dates all major metamorphic events.

The main elemental changes are: (1) Mg metasomatism with Ca loss (— Na loss), and (2) K metasomatism with Na loss (— Ca loss). The former alteration pattern is indicative of chloritization associated with hydrothermal activity of regional metamorphism, and is particularly prevalent in the mafic samples in Stawamus River valley. The second style of alteration is typical of serialization. It is most noticeable in felsic samples near the contact metamorphism along the Indian River shear zone and plutonic contacts in the Indian River valley. Sericitization could be associated with regional metamorphism or the volcanogenic activity accompanying the deposition of the Indian River stratigraphy. 101

4.3.2.3 Classification and Trends of the Volcanic Suite

The "least-altered" volcanic samples are compared with established trends on variation diagrams to help classify this suite. As already noted, the analyses have a bimodal distribution and are mostly calc-alkaline, although some are tholeiitic (Figs. 4.26, 4.27a and b).

The two clusters of compositions, andesite-basalt and rhyolite, may indicate an extensional environment where volcanics of two compositions are deposited (cf. Heah, 1982). Basalts in the Indian and Stawamus River valleys are not as distinctly tholeiitic as at Sky Pilot Mountain (Heah, 1982). There is a change from calc-alkaline island arc volcanism in Indian River valley (packages I and II), to the more arc tholeiitic character of volcanism at Sky Pilot Mountain (package III, unit IK1 of Heah (1982) and package 1 of McColl (1987)), to calc-alkaline volcanism on Britannia Ridge (packages 2 and 3 of McColl (1987)). Irvine and Baragar (1971) have noted other suites with similar variations; a tholeiitic series can end with rhyolite (ejg. Thingmuli) or can be associated with calc-alkaline rocks (e_,g. Yellowknife volcanic suite). Alternatively, the Gambier Group could represent an island arc with an adjacent short-lived back arc rift. Felsic island arc volcanism was interrupted and interspersed with intermediate to mafic arc tholeiitic volcanics.

The dual tholeiitic and calc-alkaline nature of the Britannia - Indian River volcanic suite was noted by McColl (1987), and is similar to that of the Northeast Japan arc (see Miyashiro, 1974). The partly extensional tectonic setting, bimodal volcanics and volcanogenic mineralization in the Britannia and Indian River areas are similar to the Japan Basin that hosts the Kuroko deposits (McColl, 1987; Ohmoto, 1983). 102

On the alkalies versus Si02 diagram (Fig. 4.28) the original magmatic trend of "unaltered" samples overlaps the calcic (arc tholeiite) and calc-alkaline fields as defined by de Rosen-Spence (1976 after Kuno, 1966). Britannia Ridge samples plot between

arc tholeiite and calc-alkaline series on a K20 versus Si02 variation diagram (McColl, 1987). In this study the samples plot close to the calc-alkaline field (fields from Jakes and Gill, 1970, are not shown in Fig. 4.33), and define a medium-K trend from basalts to rhyolites.

Almost all of the samples plot in the calc-alkaline fields defined in Irvine and Baragar (1971) whether using an AFM (best for andesites or dacites), AI2O3 versus normative plagioclase (best for basalts) or anorthite-albite-orthoclase (An-Ab-Or) diagram (Figs. 4.27b, 4.34 and 4.35). The suite shows a gradual enrichment in iron on the AFM diagram, which is typical of calc-alkaline suites (Fig. 4.34; Irvine and Baragar, 1971). The Indian - Stawamus River suite can be further defined on the An-Ab-Or diagram as "average rocks" with no consistent enrichment trend (Fig. 4.35).

The Britannia Ridge volcanic suite has been classed as a 'Type I" arc tholeiite by de Rosen-Spence and Sinclair (1987) based on the Peacock indices of "unaltered" samples analyzed by McColl (1987). The majority of unaltered samples were dykes from the mine area and are not representative of the rest of the volcanic pile. A Peacock index from Figures 4.32 and 4.33, of this study, indicates a borderline calcic - calc-alkaline suite that is within the Type I domain (defined by Gill, 1980; Spence, 1985). This suite is similar to medium-K Mount Shasta and Kuroko suites (de Rosen- Spence and Sinclair, 1987). 103

Figure 4.34 AFM ternary diagram for volcanic rocks from the Indian River and Stawamus River valleys. Tholeiitic - calc-alkaline boundary is from Irvine and Baragar (1971). Volcanic and dyke samples are plotted as + 's.

Figure 435 An-Ab'-Or ternary diagram for volcanic rocks from the Indian and Stawamus River valleys. Boundary lines are from Irvine and Baragar (1971). Volcanic and dyke samples are plotted as +'s. 104

10.00 Symbols or« defined in Figure 4.26.

» Bock ore basalt* (Stem, 1980) 8.00 -

6.00 -

O 4.00 -

2.00

0.00 0.00 6.00 8.00 10.00 12.00 FeOtotal (wt.s)

vo caa c Fe or Figure 4.36 MgO versus OTOTAL ^ ^ ^ rocks from the Indian River and Stawamus River valleys. Cascades (calc-alkaline) trend is from Jakes and Gill (1970). Back arc basalts are from Stern (1980). Solid symbols indicate "unaltered" samples as defined in Figure 4.29.

20.00

18.00 -

16.00

O CN < 14.00 -

12.00 Si02 (wt.s)

Figure 4.37 ALjO^ versus Si02 for volcanic rocks from the Indian River and Stawamus River valleys. Cascades trend is from de Rosen-Spence (1967). Solid symbols indicate "unaltered" samples as defined in Figure 4.29. 105

16.00 Symbols art defined in Figure 4.26. ' \

/ \ 12.00 H / \ • V \ -<-> ° ^\ N •° \, \ 0 \, \ \ N 8.00 N. \ "o X. \ v -I-' N^./v Fe—rich o Fe-poor -t—' o - \. \ SAX U. 4.00 • • 0.00 40.00 45.00 50.00 55.00 60.00 65.00 70.00 75.00 80.00 Si02 (wt.s) Figure 4.38 FeOTOTAL, versus SiC^ for volcanic rocks from the Indian River and Stawamus River valleys. Boundary lines and trend lines are from de Rosen -Spence (1967). Solid symbols indicate "unaltered" samples as defined in Figure 4.29.

3.00

Symbola are dtflned in Figure 4.26. • Sky Pilot Basalt* (Heah. 1082). * East Britannia Ridg* (McColl. 1987). ** /

2.00 -

CM O 1.00 - •° • * * •

Basalts: 48* < Si02< 53*

0.00 7.00 9.00 11.00 13.00 15.00 FeO total (wt.s)

Figure 4.39 TiC^ versus FeOTOTAL f°r basalts from the Indian River and Stawamus River valleys. Boundary lines are from de Rosen-Spence (1967). Solid symbols indicate "unaltered" samples as defined in Figure 4.29. Basalt data from Sky Pilot Mountain (Heah, 1982) and Britannia Ridge (McColl, 1987) has also been plotted. 106

The Indian-Stawamus River volcanic suite resembles the Cascade (calc-alkaline)

trend on an MgO versus FeOtotal plot (Fig. 4.36; Jakes and Gill, 1970). Heah (1982) also compared the Sky Pilot volcanics with other basalts and demonstrated a similarity to back-arc basin basalts.

Data from Britannia Ridge (in McColl, 1987) and the Indian and Stawamus River valleys follows but is slightly offset from the Cascade trend on the AI2O3 versus

SiC»2 variation diagram (Fig. 4.37; de Rosen-Spence, 1976). On an FeOtotaj versus SiC*2 diagram the suite follows the boundary between intermediate and poor-Fe depletion fields, slightly above the Cascade trend (Fig. 4.38; de Rosen-Spence, 1976).

The tectonic setting of the basalts can be inferred using the TiC^ versus

FeOtotai variation diagram (de Rosen-Spence, 1976). Basalts from the Indian and Stawamus River suite plot in Figure 4.39 on the ocean ridge - island arc boundary as do basalts from Heah (1982) and McColl (1987). The shallow marine setting and abundant pyroclastic material in the Britannia -Indian River pendant supports an island arc origin.

In summary, the Indian-Stawamus River suite has two dominant compositions, andesite-basalt and rhyolite. The suite has a dual compositional character, the felsic samples are of calc-alkaline island arc origin (package I and II), whereas mafic samples are partly arc tholeiitic, some possibly originating in a back arc environment (package III). The tectonic setting is interpreted to be an island arc that rifted so that basalts of borderline tholeiitic - calc-alkaline affinity were extruded. The suite follows several Cascade trends and has a medium-K composition and an Fe-poor depletion trend. 107

4.3.3 TRACE ELEMENT CHEMISTRY

The Indian and Stawamus River suite of volcanic and intrusive samples were analyzed by XRF for nine trace elements. The counts per second were recalculated to account for mass absorption coefficients and elemental interferences. Concentrations, in parts per million, are in Tables 4.4 and 4.5.

Some trace elements are relatively immobile (Y, Nb, Zr and Ti; Floyd and Winchester, 1978), so that the original concentrations of these elements have not been affected by metamorphism. Consequently, they are used: (1) to classify rock types using SiC»2 based and immobile element based schemes, and to compare these schemes, (2) to compare magmatic differentiation trends based on trace elements, and (3) to clarify the tectonic setting of the volcanic suite. Analyses of plutonic rocks have been plotted in several diagrams for comparative, but not classification purposes.

4.3.3.1 Classification of Rock Types

SiC*2 versus Zr/TiC»2 and SiC>2 versus Nb/Y rock type classifications are based on SiC*2 weight percent, as in Figure 4.29, but groups are defined using trace element ratios as the independent variable (Figs. 4.40 and 4.41; Floyd and Winchester, 1977 and 1978). The only samples that are not classified as common rock types are 87IRD-63 and 87IRD-161. Both samples are from dykes that plot in the alkaline fields of comendite/pantellerite and trachyte, respectively (Fig. 4.41). These dykes may be a final differentiation product of a tholeiitic parent (Williams e_l a!., 1982). Samples 87IRD-67 and 87IRD-125 are from the Stawamus Gabbro and are exceptionally low in

Si02 and Zr. 108

Table 4.4 Trace element analyses of volcanic units from the Indian River and Stawamus River valleys, southwestern British Columbia (Figs. 4.1 to 4.5). XRF counts were recalculated for the mass absorption coefficients based on major element concentrations. Data are plotted in Figures 4.40 to 4.44. The data have been averaged from two separate sets of analyses. Samples with "d"1 are duplicates prepared in a chrome-steel shatterbox (see Appendix B). Samples denoted "a" and "b"2 are duplicate pellets.

Sample Unit Ba Cr Nb Ni Rb Sr V Y Zr Number (parts per million)

I Lower Goat Mountain Formation-Indian River valley

Rhyolite 86IRD-161 1-1 1797 1 10 5 150 63 20 24 89 Rhyolite 87IRD-122 1-1 846 3 10 2 112 47 9 19 79

II Middle Goat Mountain Formation-Indian River valley

Basalt 86IRD-1873 II-l 252 146 7 79 11 397 206 28 95 Rhyolite 86IRD-189 II-l 1616 2 8 4 32 127 33 23 147 Andesite 86IRD-193a III 255 4 11 7 13 366 106 24 152 86IRD-193b II-l 259 4 12 7 14 379 102 26 157 Rhyolite 86IRD-121 II-2 1323 1 10 1 66 143 16 18 77 86IRD-121d II-2 1328 146 10 0 66 141 13 18 76

Andesite 87IRD-151a3 11-3 1150 6 7 13 61 267 219 20 88

87IRD-151b3 II-3 1116 7 7 15 62 270 226 21 88

Basalt 87IRD-1793 II-3 321 172 8 95 13 511 220 32 116

Basalt 87IRD-18S3 11-3 627 66 12 35 24 541 231 31 145

III Middle Goat Mountain Formation-Stawamus River valley

Rhyolite 87IRD-97 IIMa 140 7 11 7 7 85 13 28 195

Basalt 87IRD-603 IIMb 422 105 7 64 10 550 215 26 95 Basalt 87IRD-88 III-4b 216 119 7 70 19 557 235 28 96

Andesite 87IRD-64a3 HI-4c 165 111 6 61 19 429 178 25 107

87IRD-64b3 III-4c 153. 111 6 58 19 423 183 25 106

Basalt 87IRD-1333 III-4c 309 162 8 81 14 462 228 32 120

Basalt 87IRD-723 III-5a 216 136 8 67 13 527 224 26 109

87IRD-72d3 III-5a 199 181 8 65 13 518 224 26 107

Basalt 87IRD-763 III-5a 670 137 7 74 40 340 222 27 108 Basalt 87IRD-79 III-5a 246 211 8 97 14 530 268 27 114 Andesite 87IRD-192 III-5a 509 76 8 49 11 690 210 30 135 87IRD-192d III-5a 508 136 8 47 11 687 214 30 133

1. Duplicate samples denoted "d" were not used in plots. 2. Duplicate pellets denoted "a" and "b" were averaged for use in plots. 3. Samples are considered to be altered according to MgO versus CaO variation diagrams (Fig. 4.29). 109

Table 4.5 Trace element analyses of intrusive units from the Indian River and Stawamus River valleys, southwestern British Columbia (Figs. 4.1 to 4.5). XRF counts were recalculated for the mass absorption coefficients based on major element concentrations. Data are plotted in Figures 4.40 to 4.44. The data have been averaged from two separate sets of analyses. Samples with "d"1 are duplicates prepared in a chrome-steel shatterbox (see Appendix B). Samples denoted "a" and "b"2 are duplicate pellets.

Sample Unit Ba Cr Mb Ni Rb Sr V Y Zr Number (parts per million)

A Stawamus Gabbro Pluton

Gabbro 87IRD-67 A 32 89 2 18 3 655 132 7 8 Gabbro 87IRD-12S A 0 218 2 90 2 412 213 8 7

B Squamish Granodiorite Pluton

Granodiorite 86IRG-18 Bl 1242 3 9 0 56 70 27 13 107 Diorite 87IRD-190 B2 531 11 7 17 30 364 131 39 159 87IRD-190d B2 538 171 7 18 31 368 133 39 160 Granodiorite 87IRD-81a B3 982 2 7 4 57 273 22 21 112 87IRD-81b B3 987 3 7 3 57 272 24 19 112

C Quartz Feldspar Porphyritic Rhyolite Intrusives

Rhyolite 86IRD-50 C 2343 0 8 2 68 no 19 17 68 Rhyolite 87IRD-166 C 3286 1 9 0 86 117 36 14 77 Rhyolite 87IRD-169 C 862 3 8 3 36 125 55 18 120

Dykes Late Intrusives

Basalt 86IRD-53a3 D 942 68 7 56 40 502 268 28 101

86IRD-53b3 D 969 69 7 56 39 499 262 28 100 Dacite 86IRD-63 D 489 3 30 9 24 440 12 32 349

Andesite 86IRD-1453 D 418, 94 8 65 10 607 205 20 88

86IRD-145d3 D 405 140 7 70 10 615 206 19 87 Andesite 87IRD-75 D 330 34 14 40 18 552 207 24 130 Dacite 87IRD-161 D 877 6 22 6 32 607 65 21 188

The Nb/Y versus Zr/TiO^ diagram is a classification of rock types based solely on immobile elements (Fig. 4.42; Floyd and Winchester, 1977 and 1978). The suite retains a bimodal distribution; and the field names are fairly consistent with the SiC»2 based schemes. Rhyolitic samples are rhyodacite on a trace element basis; other samples also reflect a shift to more mafic classification. The immobile element plots show that metamorphism has not greatly changed the rock compositions indicated in Figure 4.29, and that the SiC>2 based classification is acceptable.

4.3.3.2 Magmatic Differentiation Trends

Floyd and Winchester (1977) used immobile elements to establish magmatic differentiation trends for several suites of volcanic rocks. As noted earlier, the plutonic samples in this study have a very similar trend to the volcanic rocks. Thus, they may have evolved from the same parent magma.

On the Si02 versus Zr/Ti02 diagram (Fig. 4.40), the Indian-Stawamus River trend (dot-dash line) most closely resembles the calc-alkaline trend of Mt. Misery (St. Kitts; dashed line on Fig. 4.40). On the Si02 versus Nb/Y diagram (Fig. 4.41) the suite is most similar to the Mt. Ararat, Turkey, calc-alkaline suite. The slope of the Indian- Stawamus River trend of increasing trace element ratios with increasing Si02 is much less pronounced than comparative calc-alkaline suites in Floyd and Winchester (1977).

The Indian-Stawamus River magmatic trend on the Zr/Ti02 versus Nb/Y diagram (Fig. 4.42) is the most distinctive of the plots examined so far. The volcanic samples define a trend that either has an abrupt change within the magmatic series

(dot-dash line), or has two short trends. The dykes seem to have evolved on a Ill

Figure 4.40 SiC^ versus Zr/TiCK for volcanic rocks from the Indian River and Stawamus River valleys. Solid lines are field divisions, and dashed lines are trends from Floyd and Winchester (1977). Dot-dash line is the approximate trend of the Indian -Stawamus River trend. Solid symbols indicate "unaltered" samples as defined in Figure 4.29.

80.00 X A • • ^ Symbols ant dofinod in Figure 4.26. RHYOLITE • ^ m f • Plutonic tampios from Indian and _/ 4 x Stawamus Rivtr voitoyt. / * '' COMENOITE 70.00 PANTELLERITE RHYODACITE j 1 DACITE • , \ 1 / • i. / \— 1/t '60.00 - A • ! TRACHYTE CM y • ANDESITE O y 1 * * Ho —' to f\' SUB-ALKALINE / TRACHYANDESITALKALI-BASALT E 50.00 J» BASALT / • •

* 40.00 10"' 10 Nb/Y

Figure 4.41 SiO^ versus Nb/Y for volcanic rocks from the Indian River and Stawamus River valleys. Solid lines are field divisions, and dashed lines are trends from Floyd and Winchester (1977). Dot -dash line is the approximate trend of the Indian - Stawamus River trend. Solid symbols indicate "unaltered" samples as defined in Figure 4.29. 112

104

Symbols an) dcfinod in Figurs 4.26. • Plutonic samples from tho Indian COMENOITE and Stawomus Rhrsr vallsys.

SUB-ALKALWE BASALT

10 -I 1 1 I—I—I—I I I -I 1 1 1—i—i—i—r 10 - 1 10 Nb/Y

Figure 4.42 Nb/Y versus Zr/TiCK for volcanic rocks from the Indian River and Stawamus River valleys. Solid lines are field divisions, and dashed lines are trends from Floyd and Winchester (1977). Dot-dash line is the approximate trend of the Indian - Stawamus River trend. Solid symbols indicate "unaltered" samples as defined in Figure 4.29.

15000

Symbols or * dsflned in Figurs 4.26.

10000- OFB / E CL CL .* . / OFB 6 o a } / CAB 0 • I 5000- / LKT A CAB I

/ LKT

Basalts: 48*

0 50 100 150 200 Zr (ppm) Figure 4.43 Ti versus Zr for basalts from the Indian River and Stawamus River valleys. Solid lines and field divisions are from Pearce and Cann (1973). OFB = ocean floor basalts; LKT = low K tholeiitic basalts; CAB = calc-alkaline basalts. Solid symbols indicate "unaltered" samples as defined in Figure 4.29. 113 separate path (dashed lines), but the data is too limited to establish these as diverging evolutionary trends.

4.3.3.3 Tectonic Setting

The original tectonic setting of basalts can be discerned using Ti, Zr, Y and Sr concentrations (Pearce and Cann, 1973). The Indian - Stawamus River tectonic setting is known to be a convergent plate margin that has had a period of extensional volcanism. Comparison of the Indian-Stawamus River volcanic rocks to other suites in Pearce and Cann (1973) indicates this island arc suite may contain low-K tholeiite or calc-alkaline basalt. On a Ti versus Zr, and ternary Ti-Zr-Y and Ti-Zr-Sr diagrams the basaltic samples plot in the calc-alkaline fields (Figs. 4.43 and 4.44a and 4.44b; Pearce and Cann, 1973). Sky Pilot volcanics plot closer to and within low-K tholeiite fields; Heah (1982) described them as tholeiitic basalts. 114

Figure 4.44 (a) Ti-Zr-Y ternary diagram for volcanic rocks from the Indian River and Stawamus River valleys; (b) Ti-Zr-Sr ternary diagram for volcanic rocks from the Indian River and Stawamus River valleys. Solid lines and field divisions are from Pearce and Cann (1973). OFB = ocean floor basalts; LKT = low K tholeiitic basalts; CAB = calc-alkaline basalts; WPB = within plate basalts. Solid symbols indicate "unaltered" samples as defined in Figure 4.29. 115

4.4 GEOCHRONOLOGY

Potassium-argon (K-Ar) and rubidium-strontium (Rb-Sr) analyses were made to help establish stratigraphic and metamorphic ages in the Indian River valley. Rock samples collected from the project area and analyzed by K-Ar methods indicate: (1) a late Early Cretaceous contact metamorphism (108 — 4 Ma), (2) an early Late Cretaceous regional metamorphism (96.1 — 3.0 Ma, 95.6 — 3.3 Ma), (3) a possible Late Cretaceous (84.2 — 2.9 Ma, 83.5 — 3.0 Ma) metamorphic and/or structural event, and (4) Early Oligocene dykes (36.1 — 1.3 Ma).

Rb-Sr isochrons of volcanic rocks also reflect metamorphism and possibly an original rock age. A seven point whole rock isochron for the Indian and Stawamus River suite is late Early Cretaceous (102 — 10 Ma). An internal isochron based on analyses of several fractions from one sample (86IRD-161) yielded a Late Cretaceous date (93 — 3 Ma) which corresponds closely to the regional metamorphic event indicated by K-Ar analyses. Although interpretations by McColl (1987) and those expressed in this paper vary in detail, both conclude that the depositional age of the Britannia - Indian River pendant may be as old as Jurassic. An internal isochron (86IRD-121) with a large uncertainty yielded an early Early Cretaceous age (131 — 77 Ma). Whole rock isochrons for some samples give a Middle Jurassic date (167 — 9 Ma, 168 — 13 Ma); this is older than expected for the rock suite.

Several other analyses in the Howe Sound region are in the range of 101 to 93 Ma

(Roddick ejt al, 1977; 1979). Some are reset, others date the emplacement and cooling of plutonic bodies such as the Squamish and Furry plutons around 101 Ma (R.L. Armstrong, unpublished U-Pb data). 116

Sample preparation and analytical procedures (for K-Ar and Rb-Sr analyses) are described in Appendix C. The results for both methods, and a geochronological summary follow.

4.4.1 POTASSIUM-ARGON

Major volcanic and intrusive units in the Indian River and Stawamus River valleys were sampled for K-Ar analyses (Fig. 4.1). Sample 86IRD-121 is from a grey-green flowbanded rhyolite (unit 2) in the Indian River valley. Sample 87IRD-179 is from a blue- grey massive basaltic andesite flow (unit 3) that crops out along Maggie Ridge. Massive pyroxene porphyritic basalt flows (87IRD-76) of unit 5b are in the Stawamus valley. Sample 86IRD-50 is from a late quartz and feldspar porphyritic rhyolite intrusive (unit C), which is similar to several other small irregularly shaped intrusive bodies along the east side of the Indian River valley. Analyses of a late hornblende porphyritic andesite dyke, located on the northeast side of the Indian River, were done on a whole rock sample (86IRD-145) and a hornblende separate (86IRD-145Hb). Major and trace element analyses for the whole rock samples (Tables 4.1 to 4.5) show samples 86IRD-121 and 87IRD-179 to be "unaltered" using the CaO versus MgO variation diagram (see section 4.3.2.2; Fig. 4.29). Sample 86IRD-145 is also unaltered but appears anomalously MgO rich because of abundant hornblende phenocrysts.

Biotite alteration associated with mineralization provided biotite separates from: (1) biotitic hornfels (86IRD-74Bi) in the contact metamorphic zone associated with the Slumach mineralized zone, and (2) chalcopyrite-biotite veinlets (87IRD-128Bi) that occur on the periphery of the rhyolite intrusive (sampled, above, as 86IRD-50). 117 Table 4.6 Potassium-argon analyses of volcanic rocks and mineral separates from the Britannia - Indian River pendant, southwestern British Columbia. Samples from this project are located in Figures 4.1 to 4.5. Argon analyses were by J. Harakal and potassium analyses were by D. Runkle; all analyses were done at the Geochronology Laboratory, The University of British Columbia. Potassium analyses for McColl (1987) and Heah (1982) were by K. Scott.

Sample Sample Description Northing Latitude K Radiogenic 40Ar Radiogenic 40Ar Date (Ma)2 Number1 Type Rock Type (Unit) Easting Longitude (wt%) Ar total (106 cm3g"' ) Time3

1. Late Early Cretaceous (108 Ma) 86IRD-74 Bi Biotitic hornfels 5497745 49°38'03"N 0.521 0.887 22.485 108 ± 4 (Slumach Zone) 497990 123°01'39"W ±0.000 Early Cretaceous

2. Late Early - Early Late Cretaceous (101 - 89 Ma) TH-19A,B Hb Hornblende from 49°38'57"N 0.605 0.772 2.436 101 ±4 gabbro6 123°05'43"W ±0.006 Early Cretaceous 86IRD-128 Bi Chalcopyrite and 5498448 49°38'26-N 5.02 0.914 19.256 96.1 ± 3.0 Biotite veins (C) 498246 123°01'28"W ±0.06 Late Cretaceous 87IRD-76 WR Basalt flow5 5497080 49°3741"N 1.47 0.891 5.609 95.6 ±3.3 (5) 496338 123O03'21"W ±0.01 Late Cretaceous TH-Hb Hb Hornblendite vein 49°38'11"N 0.143 0.412 0.5428 95.1 ± 3.3 123°04'35"W Late Cretaceous MC83-633 WR Basalt, altered4 5495850 0.255 0.652 0.920 90.5 — 3.2 (1-7) 490460 ±0.001 Late Cretaceous 86IRD-50 WR Rhyolite pluton 5498448 49°38'26"N 4.09 0.932 14.518 89.1 — 2.7 (Q 498213 123°01'29"W ±0.01 Late Cretaceous

3. Late Cretaceous (84 - 79 Ma) 87IRD-179 WR Basalt flow 5498813 49°38'37"N 0.635 0.798 2.127 84.2 ± 2.9 (3) 496696 123°02'44"W ±0.003 Late Cretaceous 86IRD-121 WR Rhyolite flow 5498583 49°38'31"N 3.15 0.924 10.466 83.5 - 3.0 (2) 497963 123°01'41"W ±0.01 Late Cretaceous MC83-657 WR Quartz-sericite 5494980 3.26 0.961 10.768 83.1 - 3.0 schist4 (2-11) 489740 ±0.03 Late Cretaceous MC83-625 WR Crystal lithic 5494630 1.12 0.691 3.634 81.6 — 3.0 tuff (3-13) 490480 ±0.03 Late Cretaceous MC83-640 WR Crystal lithic 5494170 1.72 0.723 5.557 813 - 2.9 tuff (2-10) 490090 ±0.02 Late Cretaceous MC83-619 WR Dacite, slightly 5494640 49°36'00"N 2.27 0.879 7.166 79 J — 2.9 altered4 (2-9) 491180 123°0T12"W ±0.03 Late Cretaceous

4. Mid-Tertiary (36-31 Ma) 86IRD-145 Hb Andesite 5498511 49°38,28"N 0.203 0.649 0.289 36.2 ±1.3 (Late dyke) 497980 123°01'40"W ±0.001 Early Oligocene 86IRD-145 WR 5498511 49°38'28"N 0.750 0.721 1.058 35.9 ±1.3 497980 123°0r4O"W ±0.001 Early Oligocene Prospect Point Basalt dyke 49°18,48'N 1.22 0.489 1.507 31.5 ±1.1 Unpublished data7 123°08'30"W Early Oligocene Dyke on west wall of Stawamus Chief 49°40,55"N 1.37 0.711 32.9 — 2.4 Wanless et al., 1978 123°09'00"W Early Oligocene Queen Elizabeth Park Basalt 49°14'36-N 0.819 0.692 1.103 343-1.2 Unpublished data7 123°06'36"W Early Oligocene 6th Avenue dyke whole rock 49°15'57"N 0.361 0.567 0.490 34.6 ±1.2 Unpublished data 123°05'U"W Early Oligocene

1. Samples prefixed by; "86IRD" or "87IRD" = Reddy, this thesis, "MC* = McColl (1987) and TH" = Heah (1982). Sample locations are from these references. 2. Decay constants are from Steiger and Jager (1977): lambda = O^SlxlO"10^"1; lambda = 4.962xl0"10yr"1; 40 -4 e B K/K = 1.167x10 . Errors are one standard deviation. 3. Time intervals used are from Decade of North American Geology (Palmer, 1983). 4. Alteration designation is from McColl (1987) based on MgO versus CaO variation diagrams. 5. Sample is altered according to MgO versus CaO variation diagrams (Fig. 4.29). 6. The gabbro in Heah (1982) is equivalent to unit A of this study (Fig. 4.1). 7. Unpublished UBC K-Ar dates run for E. Irving and J. Monger. 118

The five whole rock and three mineral separate samples were analyzed for K-Ar in the Geochronology Laboratory, The University of British Columbia (Table 4.6). Argon analyses were by J. Harakal and potassium analyses were by D. Runkle.

All K-Ar dates of volcanic units in the Britannia - Indian River pendant of the Gambier Group are reset. The oldest K-Ar date obtained is late Early Cretaceous (108 — 4 Ma) from secondary biotite of the cordierite-biotite hornfels associated with the Slumach mineralized zone. Therefore this and all younger dates do not represent the original stratigraphic rock age, but reflect, from oldest to youngest, the events described in the following sections.

4.4.1.1 Late Early Cretaceous (108 Ma)

Late Early Cretaceous (108 — 4 Ma on biotite in hornfels, above the Slumach zone: Figs. 4.1 and 4.5, Table 4.6) contact metamorphism of the Slumach zone by the Indian River or Mountain Lake plutons.

4.4.1.2 Early Late Cretaceous (101 - 89 Ma)

Early Late Cretaceous (96.1± 3.0 Ma, 95.6 ± 3.3 Ma: Figs. 4.1,4.3 and 4.4, Table 4.6) K-Ar dates reflect the lower greenschist facies metamorphism noted throughout the Britannia - Indian River pendant. Hornblende from the gabbro (unit A) yielded a date at 101 — 4 Ma, and is interpreted to be reset by metamorphism associated with the Squamish granodiorite (Heah, 1982). A hornblendite vein cutting volcanic rocks on Sky Pilot mountain was dated as 95.1 — 3.3 Ma, and interpreted to be "synmetamorphic" by Heah (1982). 119

Rhyolite intrusives (unit C) in the Indian River valley were dated as Late Cretaceous (89.1 -±- 2.7 Ma; sample 86IRD-50: Figs. 4.1 and 4.3). This K-Ar analysis for the rhyolite intrusive is a minimum date for the age of the unit. The small pluton dated appears to be equivalent to other rhyolite plutons that locally crosscut the Indian River Intrusions (unit Bj); therefore the date appears to be consistent with field evidence. Numerous deformational features noted in thin sections (see section 4.3) indicate that a deformational event followed or occurred at the same time as emplacement of these bodies. The latter deformation may or may not have reset the rhyolite intrusions.

4.4.1.3 Late Cretaceous (84 - 79 Ma)

Two Late Cretaceous (84.2 -±- 2.9 Ma, 83.5 ^ 3.0 Ma; Figs. 4.1 to 4.3) dates in the Indian River area may indicate a second metamorphic event. At Britannia Ridge, several analyses around this same age (83.1 — 3.0 Ma, 81.6 — 3.0 Ma, 81.3 — 2.9 Ma and 79.5 ± 2.9 Ma: Table 4.7) were interpreted as metamorphism related to a deformational or intrusive event (McColl, 1987).

4.4.1.4 Mid-Tertiary (36-31 Ma)

The late hornblende porphyritic andesite intrusive unit was dated by a hornblende separate and by whole rock analyses as mid-Tertiary at 36.2 — 1.3 Ma and 35.9 — 1.3 Ma respectively. The fresh appearance of the rock and close agreement between the two dates indicates an accurate age for the dyke. These intrusives do not correlate with Garibaldi Group or any other igneous or volcanic event within the Britannia - Indian River pendant. However, andesite and basalt intrusions of a very similar age have been dated on the west face of the Stawamus Chief, near Squamish (32.9 — 2.4 Ma; Wanless et al, 1978) and in the city of Vancouver at Prospect Point in 120

Stanley Park (31.5 — 1.1 Ma), Sixth Avenue on Fairview Slopes (34.6 — 1.2 Ma) and Queen Elizabeth Park on Little Mountain (34.3 — 1.2 Ma; unpublished UBC K-Ar dates run for E. Irving and J. Monger). The analyses all indicate an Early Oligocene magmatic episode of wide extent but small volume.

4.4.2 RUBIDIUM-STRONTIUM

Six volcanic flows and two intrusive units in the Indian River and Stawamus River valleys were sampled for whole rock Rb-Sr analyses. All of the samples except for 87IRD-60 and 86IRD-161 were analyzed for K-Ar and described above. Sample 87IRD-60 is from a basalt flow (unit 4b) in the Stawamus valley, and sample 86IRD-161 is from a rhyolite flow (unit LGM) on the east side of the Indian River valley.

Rb and Sr analyses were made by D. Runkle, Geochronology Laboratory, The University of British Columbia. Major and trace element chemistry for the whole rock samples is shown in Tables 4.1 to 4.5. Samples 87IRD-60, 87IRD-76 and 87IRD-179 are "altered" based on the CaO versus MgO variation diagram (Fig. 4.29).

Most of the data have a low *^Rb/^Sr ratio, comparable with analyses by Heah (1982) and McColl (1987; Fig. 4.45). In an attempt to define internal isochrons (Fig. 4.45), six partial separates (density fractions) were made for three samples (86IRD-50,

86IRD-161 and 86IRD-121) that had relatively higher 87Rb/86Sr ratios. The internal isochrons indicate three possible events with increasing uncertainties coincident with increasing ages. 121

Table 4.7 Rubidium-strontium analyses of volcanic rocks from the Indian and Stawamus River valleys, southwestern British Columbia. Sample locations are on Figures 4.1 to 4.5. Data are plotted in Figures 4.45 and 4.46. Calculated isochron dates are in Table 4.10.

Sample Sample Description Northing Latitude SiO Sr Rb Rb/Sr Vsr 2 Number Rock Type (Unit) Easting Longitude (ppm) (ppm) (^0.0001) (wt%)

86IRD-503 Rhyolite 5498448 49°38'26"N 78.11 108 67.5 0.626 1.811 0.7066 CO 498213 123°01'29"W 86IRD-50-2 Heaviest - 114 102 0.895 2.592 0.7078 separate (C)

86IRD-50-63 Lightest - 201 160 0.796 2.305 0.7077 separate (C)

87IRD-60 Basalt flow4 5498181 49°38*18"N 52.03 534 9.7 0.018 0.052 0.7033 (4b) 496379 123°02'59"W

87IRD-763 Basalt flow4 5497080 49°3741"N 51.76 326 39.3 0.121 0.350 0.7042 (5) 496338 123°03'21"W

87IRD-97 Rhyolite flow 5497428 49°37'53"N 76.73 77.4 6.5 0.083 0.240 0.7046 (4a) 496296 123°03'04"W

86IRD-1213 Rhyolite flow 5498583 49°38'31"N 75.60 133 62.2 0.467 1.351 0.7064 497963 123°01'41"W 86IRD-121-6 Lightest - 110 59.4 0541 1566 0.7068 separate (2)

86IRD-161 Rhyolite flow 5498160 49°38'16"N 75.75 58.6 145 2.47 7.15 0.7135 (LGMF) 498750 123°01'03"W 86IRD-161-5 Heaviest - 78.0 112 1.44 4.16 0.7098 separate (LGMF) 86IRD-161-3 Middle - 30.4 182 5.99 17.4 0.7276 separate (LGMF) 86IRD-161-1 Lightest - 21.2 227 10.7 31.1 0.7461 separate (LGMF)

87IRD-1793 Basalt flow4 5498813 49°38'3rN 51.38 480 11.7 0.024 0.069 0.7035 (3) 496696 123°02'44"W

86IRD-1453 Andesite4 5498511 49°38'28"N 54.82 572 10.3 0.018 0.052 0.7031 497980 123°01'40"W

1. Rubidium and strontium analyses by D. Runkle; all analyses were done at the Geochronology Laboratory, The University of British Columbia.

2. The decay constant for 87Rb = l^lO"11^"1. 3. The whole rock potassium-argon analyses is reported in Table 4.6. 4. Sample is altered according to MgO versus CaO variation diagrams (Fig. 4.29). 5. ^Rb/^Sr error is —2% for samples with greater than 50 ppm Rb or Sr. Error for less than 50 ppm Rb or Sr is — {(Rb/Sr)/(ppm Rb or Sr whichever is lowest)} 122

Table 4.8 Rubidium-strontium analyses ' of volcanic rocks from Britannia Ridge (MC) and Sky Pilot Mountain (TH), southwestern British Columbia. Data are plotted in Figures 4.45 and 4.46. Isochron dates calculated by McColl (1987) and Heah (1982) are in Table 4.10.

W Sample Sample Description Northing Latitude s;o2 Sr Rb Rb/Sr ^RbAi Sr/«Sr Number^ Rock Type (Unit) Easting Longitude (wt%) (ppm) (ppm) (±0.0001) 4 MC83-608 5494940 50.04 415 13.1 0.076 0.091 0.7044 Basalt, altered 491300 (1-7) MC83-609 Rhyodacite (3-14) 5495076 71.69 311 30.2 0.097 0.282 0.7040 489800 MC83-610 Rhyodacite, 5494990 65.33 406 32.4 0.080 0.229 0.7038 altered (3-14) 489740

MC83-6193 Dacite, Victoria 5494640 66.15 233 40.9 0.176 0.506 0.7051 Dome (2-9) 491180 MC83-620 Dacite, Victoria 5494750 68.69 316 31.0 0.098 0.283 0.7043 Dome (2-9) 491380 MC83-626 Andesite-Basalt 5496230 55.08 458 4.5 0.010 0.029 0.7036 (1-2) 491540 MC83-631 Basalt (1-7) 5495840 48.80 458 2.1 0.005 0.013 0.7040 490580

MC83-633-1 Basalt (1-7) 5495850 47.46 543 10.1 0.019 0.054 0.7044 490460 MC83-634 Dacite, Pit Dome 5495500 57.90 399 9.9 0.025 0.071 0.7041 (2-9) 490430 MC83-644 Chert/Exhalite 5495060 93.17 12 14.1 1.18 3.504 0.7117 (2-11) 490230 MC83-654 Dacite Dyke, Mine 5494990 72.06 236 33.5 0.142 0.409 0.7047 Dyke (?-18) 489900

Heah-5A Dacite 49°3748" 73.01 269 21.3 0.079 0.229 0.7036

123O05'27" Heah-6A Basalt 49°3T44" 50.72 512 6.6 0.013 0.037 0.7033 123°05'15" Heah-17 Quartz Basalt 49°39'02" 61.18 477 4.5 0.009 0.027 0.7036 123°05'52" Heah-26A Dacite 49°38'11" 65.22 442 2.4 0.006 0.016 0.7035 123°04'05"

1. Rubidium and strontium analyses by K. Scott; all analyses were done at the Geochronology Laboratory, The University of British Columbia. 87 11 1 2. The decay constant for Rb = 1.42x10 yr. 3. The whole rock potassium-argon analyses is reported in Table 4.7. 4. Alteration designation is from McColl (1987) based on MgO versus CaO variation diagrams. 5. Samples prefixed by;"MC" = McColl (1987); "Heah" = Heah (1982). Sample locations are from these references. 6. ^Rb/^Sr error is —2% for samples with greater than 50 ppm Rb or Sr. Errors for samples with less than 50 ppm Rb or Sr is — {(Rb/Sr)/(ppm Rb or Sr whichever is lowest)}. 0.000 0.500 1.000 1.500 2.000 2.500 87Rb/86Sr Figure 4.45 Rb-Sr internal isochrons for volcanic rocks from the Indian River and Stawamus River valleys, southwestern British Columbia. The internal isochron and data points for sample 86IRD-161 is inset. The dashed line is a seven point whole rock isochron that yielded a late Early Cretaceous (102.5 — 10 Ma) date. 0.7110 -

0.7090 d

Ul CD 00 0.7070 1

CO 0.7050 -

0.7030 - • =lndian River Data, x =Sky Pilot Data. A =Bntannia Ridge Data, o =Tertiary Intrusive.

0.7010 i i i i I i i i i i I I I I I I I I I—I I I I I I I I i i i i i I i i 0.000 1.000 2.000 3.000 4.000 87Rb/86Sr Figure 4.46 Rb-Sr isochrons based on whole rock analyses of volcanic rocks from the Britannia - Indian River pendant, southwestern British Columbia. The solid lines represent upper and lower ages from isochrons based on data in this study. The coarse dashed line is the maximum rock age suggested by McColl (1987) for volcanic rocks from Britannia Ridge. The fine dashed line is an isochron for the Squamish pluton based on two volcanic rocks from Sky Pilot Mountain by Heah (1982). 125

Table 4.9 Calculated rubidium-strontium isochrons dates for volcanic rock suites from the Britannia - Indian River pendant. Significant isochrons are plotted in Figures 4.45 and 4.46. Data for calculations are from Tables 4.7 and 4.8.

Isochron Number Sample MSWD Initial Age Time Number of Points Numbers Ratios (Ma)

Indian River data 1 All whole rock 7 50,60,76, 16 0.7037^0.0002 1025 — 10 Ma Early Cretaceous samples. 97,121,161,179

2 Upper boundary 2 121,97 0.7042±O.0O01 114 —15 Ma Early Cretaceous on data.

3 Upper boundary 2 121,60 0.7032±0.0001 168 —13 Ma Middle Jurassic on data.

4 Lower boundary 2 161,60 0.7032±0.0001 101 - 25 Ma late Early Cretaceous on data. 5 86IRD-50(3). 3 50,50-2, 4.7 o^ose^.oon 119 — 36 Ma Early Cretaceous internal isochron 50-6 Large uncertainty 6 86IRD-121 (2). 2 121,121-6 0.7057^0.0010 131 — 77 Ma Early Cretaceous internal isochron Large uncertainty 7 86IRD-161 (4). 4 161,161-1, 0.7 0.7042^0.0003 93.4 — 3 Ma early Late Cretaceous internal isochron 161-3,161-5

Sky Pilot data 8 Heah's 2 Heah 5A, 6A O.TOSS-^O.OOOl 114-^40 Ma Early Cretaceous isochron. Britannia Ridge data 9 McColl's 6 MC-634,620,644 0.7036^0.0002 167-^37 Ma Middle Jurassic isochron, 619,609,610 including chert. 126

. 4.4.2.1 Middle Jurassic (168 - 166 Ma)

An internal isochron (whole rock and partial fractions of sample 86IRD-121) from a rhyolite flow (unit 2) yielded an Early Cretaceous age (131 — 77 Ma) but with a very large uncertainty (Fig. 4.45). Regressions through this sample to other analyses with low 87Sr/86Sr ratios (87IRD-60, 87IRD-179) gives Jurassic ages (168 ± 13 Ma, 159 — 13 Ma respectively; Table 4.10). The Middle Jurassic date may be an approximation of the original rock age, but is unreliable because it is based two points; one is 86IRD-121 with a relatively high 87Sr/86Sr and the other with a low 87Sr/86Sr ratio.

A Jurassic date (167 — 37 Ma) was also obtained for volcanic units on Britannia Ridge (McColl, 1987), but the associated errors were high and the interpretation is doubtful (Fig. 4.45).

4.4.2.2 Early Cretaceous (119 -100 Ma)

Whole rock isochrons for the seven samples analyzed yields a late Early Cretaceous isochron (102 — 10 Ma). Similar isochron ages can be obtained from samples 86IRD-161 and 87IRD-60 that have relatively low 87Sr/86Sr ratios (101 ± 2.5 Ma). An isochron for the latter samples is the lower boundary of the data (Fig. 4.46). The isochron for the samples that form the upper boundary on the data (86IRD-121 and 87LRD-97) yields an Early Cretaceous date (114 -±- 15 Ma).

The rhyolite intrusive bodies (86IRD-50) were postulated to be late plutonic rocks or they were reset. K-Ar dating indicates they are 89.1 — 2.7 Ma. The rock has a glassy groundmass that is essentially the same specific gravity as the phenocrysts 127 separates give an internal isochron of late Early Cretaceous age (119 — 36 Ma) with a large error (Table 4.9, Fig. 4.45).

4.4.2.3 Late Cretaceous (93 Ma)

One rhyolite flow (86IRD-161) is distinctly higher in Rb/Sr than other rocks analyzed (Figure 4.45, inset). The sample is known to have a fine sericitic alteration therefore an internal isochron for this sample is used to define a metamorphic reset. Three partial separates and the whole rock analysis yield a 93 — 3 Ma isochron (initial ratio 0.7042 — 0.0003) which corresponds to the early Late Cretaceous regional metamorphic reset noted earlier (section 4.4.1.2). Samples 87IRD-76, 87IRD-97, 86IRD-50 and other Rb-Sr analyses by McColl (1987) lie close to or on this isochron.

4.4.2.4 Mid-Tertiary

Sample 86IRD-145 is from an Early Oligocene (36.1± 1.3 Ma by K-Ar methods) dyke and thus has no similar analyses with which to construct an isochron. The initial ratio is 0.7031 -±- 0.0001 Ma.

4.4.3 GEOCHRONOLOGICAL SUMMARY

The geochronological picture is more complete when data from previous and on• going studies are considered together (Heah, 1982; McColl, 1987; Figure 4.46; R.L. Armstrong, 1989, unpublished data). Stratigraphy that hosts the volcanogenic deposits in the Indian River portion of the Britannia - Indian River pendant may be as old as Late Jurassic whereas the Britannia area is more likely Late Jurassic to Early 128

Cretaceous based on the lead isotope study (see section 3.0) and fossils (see section 2.0; McKillop, 1973).

Several Coast Plutonic bodies were intruded from about 119 to 112 Ma (R.L.

Armstrong, 1989, unpublished data) in the Howe Sound area. Stawamus gabbro (unit

A), Indian River granodiorite (Bj) and Mountain Lake (B2) plutonic bodies may have been emplaced at this time. Volcanic and sedimentary deposition of the Gambier

Group continued through the Lower Cretaceous as indicated by Albian ammonites

(Roddick eiaj., 1977).

The next plutonic event was intrusion of the Squamish granodiorite (unit B3; 101 — 2 Ma by U-Pb zircon analyses; 100 — 10 Ma by Rb-Sr isochron; R.L. Armstrong, 1989, unpublished data) and Furry pluton (100 — 2 Ma by U-Pb zircon analyses; R.L. Armstrong, 1989, unpublished data). Regional metamorphism associated with this plutonic activity has reset numerous potassium-argon dates to the 101 to 89 Ma range.

A later metamorphic reset between 84 and 80 Ma records a deformational event within the Britannia - Indian River pendant (McColl, 1987). Perhaps this is coincident with the major uplift and shearing of the pendant.

Mid-Tertiary basalt and andesite dykes crosscut pluton and pendant rocks in the Indian River area and Late Cretaceous to Tertiary sediment around Vancouver. Quaternary Garibaldi Group activity occurred mostly to the north around Garibaldi Lake, but some dykes in the Britannia - Indian River pendant are probably related. These Tertiary volcanics were generated by subduction that continues to the present. ISOTOPIC AGES IN THE K-Ar EARLY OLIGOCENE INTRUSIVES BRITANNIA-INDIAN RIVER PENDANT & Associated Intrusives Wanless et.aL,1978 Unpublished | Reddy.1989

75 50 25 Plutonic Possibly related to million years Events the Indian River or Squamish Plutonic Event? Mountain Lake Plutons Pluton Deformational Event? Metamorphic Contact Regional Lower Events Metamorphism Greenschist Metamorphism Reset Average 108 101 95 83

U - Pb UNPUBLISHED UBC DATA Squamish Granodiorite I

REDOY, Rb-Sr i9a» SquamishGranodiorite 161(4) UNPUBLISHED UBC DATA ±10Ma I 6S7 I ,626' MeCOLL, 1987 I I- 633 640 H I- REODY, 1989 60 179. K-Ar 74BI 128BI 121 I- HEAH, 1982 TH-Hb TH-19A.B I

ISOTOPIC AGE IN no I05 I00 95 90 85 60 MILLION YEARS

Figure 4.47 Isotopic dates and correlated geologic events in the Britannia - Indian River pendant, southwestern British Columbia. 130

As more analyses become available, the complex history of this portion of the Coast Plutonic Complex will be deciphered. More U-Pb zircon analyses are needed in this portion of the Coast Plutonic Complex to accurately date plutons and pendant units. 131

4.5 MINERALIZATION

Within the project area the five main mineral prospects, some examined since the 1900's, are: (1) Christina, (2) ABC, (3) War Eagle, (4) Belle, and (5) Slumach (Figs. 4.1 to 4.5). Immediately north of the map area and the Christina prospect, is the McVicar volcanogenic deposit. Southeast of the project area, along the Indian River valley, other properties include the Bulliondale, London and Roy.

4.5.1 DEPOSITS

The Christina prospect (MINFILE: 092G/NW-041), in the northeastern corner of the map area (Fig. 4.3), crops out as a scattered series of showings~in the lower Goat Mountain formation~of pyrite, chalcopyrite, sphalerite and minor galena in sheared felsic volcanic rocks (Seraphim, 1977). Mineralization probably represents the southern extension of the volcanogenic mineralization on the McVicar claims on Mount Baldwin, two kilometres to the north.

The McVicar deposit (MINFILE: 092G/NW-006), immediately north of the map area, occurs in tuffs or agglomerates of the lower Goat Mountain formation, which strike northwest or north and dip steeply west (Bacon, 1953). Showings consist of irregular masses and stringers (anastomosing veinlets) of pyrite, chalcopyrite, sphalerite and galena within silicified and schistose zones of greenstone (Bacon, 1953).

The ABC prospect (MINFILE: 092G/NW-028; Brewer, 1918) occurs on the east bank of the Indian River where its most northern tributary joins the river. The mineralization is associated with hornfelsed volcanic rocks of the middle Goat 132

Mountain formation apparently related to the Indian River granodiorite where it cuts across the Indian River shear zone. Old reported workings probably lie within the area of disseminated pyrite, chalcopyrite and sphalerite (up to 4 % sulphides) in the zone of intensely hornfelsed and silicified volcanic rock. Numerous faults and a pervasive cleavage characterize the area. An adit driven 9.1 metres into the bank of the river, early in the century, has since caved (H. Hopkins, pers. comm., 1986).

The War Eagle prospect (MINFILE: 092G/NW-042), just north of the centre of the map area, was the focus of exploration before 1982 when the Slumach zone was discovered. Altered felsic volcanics of unit 2 of the middle Goat Mountain formation host disseminated and stringer mineralization. The close proximity to the breccia (Fig. 4.1) and a narrow rhyolite breccia "vent zone" (Clendenan and Pentland, 1979) suggests a volcanogenic type of deposit. An adit has been driven along quartz-sulphide "stringer" mineralization in a sheared zone (Archibald, 1981), which is about two metres wide and contains up to 15 percent sulphides. Minor amounts of disseminated and patchy sulphides occur in a wider, biotitized, silicified and locally sericitic zone around the stringer mineralization (Drummond and Howard, 1985). Two flat-lying volcaniclastic horizons, encountered by drilling at approximately 40 metres and 130 metres depth, host subeconomic mineralization (Archibald, 1981). Although high grade zones of anastomosing veins occur locally within the adit, sampling in 1979 returned an average grade of 0.50 percent copper, 0.35 percent zinc and 0.20 percent lead (Clendenan and Pentland, 1979). The portal is now buried, but mineralization in dump material is dominantly pyrite, chalcopyrite, sphalerite and pyrrhotite with minor galena in a silicified, brecciated, biotitic hornfelsed gangue.

The Belle prospect (Irish Molly or W.C.; MTNFTLE: 092G/NW-014) occurs near

the centre of the southern edge of the map area (Fig. 4.1). Mineralization is localized 133 along a dyke within schistose volcanics of the middle Goat Mountain formation (Brewer, 1918). Abundant mineralized float was found in the area, but the bedrock prospects were not located. Pyrite and chalcopyrite occur in a 3.1 metre wide zone of "schistose gangue" trending northwest, dipping about 65° to the southwest (Brewer, 1918; Camsell, 1917). Samples supplied by H. Hopkins (pers. comm., 1987), are silicified and biotitized, brecciated volcanics with up to 20 percent massive and disseminated sulphides as irregular pods. Sulphides include sphalerite, chalcopyrite, pyrrhotite, galena and pyrite with minor covellite. Sphalerite contains up to 20 percent intergrowths and exsolution of crystallographically controlled chalcopyrite blebs up to 1 millimetre diameter ("chalcopyrite disease"). Brewer (1918) sampled a 7.6 metre wide (25 foot) zone that assayed trace gold, 68.6 grams per tonne silver, and 5.3 percent copper. Three other possibly related mineralized exposures, noted upslope of the latter zone, are probably on strike with the Belle prospect. A 31 metre adit (not relocated) was driven prior to 1917 to intersect the lower zone, but reportedly did not reach it (Brewer, 1918).

The Slumach zone (MINFILE: 092G/NW-024), just south of the centre of the project area, has been extensively explored since its discovery in 1982 (Fig. 4.1). The wallrocks are intensely hornfelsed felsic tuffaceous sediments of unit 2 of the middle Goat Mountain formation.

Mineralization consists of two quartz-sulphide veins, the Main and East, that trend northwest and dip steeply northeast. The sulphide content of the veins is variable (up to 15 percent) and is primarily sphalerite, lesser chalcopyrite, pyrite and traces of galena in a brecciated and silicified wallrock gangue. The sulphides in the veins occur as irregular disseminations and massive selvages that appear to have been re-brecciated and cemented by quartz. Sphalerite has up to 15 percent chalcopyrite intergrowths and 134 exsolution. Fragments of wall rock within the vein are biotitized and/or chloritized and have rims of cockscomb quartz. Both veins have high grades of precious metals (gold > silver) over widths of approximately one metre; lower grades of precious metals occur in adjacent altered hanging wall and footwall rocks (Drummond and Howard, 1985).

The biotite-cordierite hornfels is due to contact metamorphism of the Slumach zone. Similar alteration pipes have been described for some of the Noranda ore bodies, Quebec. For example, Millenbach (Noranda) exhibits a contact metamorphic assemblage around the Lake Dufault granodiorite body (Franklin et al., 1981 from Kelly, 1975; de Rosen-Spence, 1969) that has similarities to the biotite and cordierite also noted in the hornfelsed Slumach zone. The following excerpt from Franklin, el al. (1981) describes the spotting and contact metamorphism noted in the Millenbach pipe:

The most intensely chloritized zones have been converted to anthophyllite. Outside these anthophyllite zones a spotted hornfels texture has developed which is locally called dalmatianite. The intensity and size of spots in the dalmatianite reflects the amount of chlorite in the pipe, with giant spots (Riverin, 1977) in a very chlorite-rich zone, probably reflecting the development of cordierite during prograde contact metamorphism. Smaller spots occur in the sericite plus chlorite zones.

The Slumach hornfelsed zone is not intensely chloritized but has abundant secondary biotite; this probably reflects less retrograde metamorphism. An Early Cretaceous date (108 — 4 Ma by K-Ar methods) for the secondary biotite in the hornfels reflects post- mineralization contact metamorphism (section 4.4.1.1). This likely remobilized some of the sulphides in the Main and East veins.

The Main vein varies from 30 to 70 centimetres wide over its 70 metres known length, and averages 68.5 grams per tonne (1.91 ounces per ton) gold over a 31- centimetre width (Drummond and Howard, 1985: based on nine channel samples from the Slumach adit subdrift~the range is 19.7 to 109.4 grams per tonne). Free gold has 135 been reported and an association of gold within pyrite has been determined (Blundell, 1984). The East vein, nine metres east of the Main vein, is at least 20 metres long and varies from 30 to 200 centimetres in width (Drummond and Howard, 1985).

4.5.2 SUMMARY

All deposits discussed are polymetallic and are hosted by altered felsic volcanics. War Eagle, McVicar and Christina have many similarities to typical volcanogenic deposits such as the Kuroko-type deposits in the Green Tuff belt of Japan that include:

(1) a bimodal calc-alkaline island arc environment, (2) felsic pyroclastic host units formed probably in a submarine environment, (3) an intensely altered pipe with classical zoning from a sericite-quartz core, to a chloritic outer zone that possibly formed around discharge sites focused by faults or fractures, (4) clusters of polymetallic, locally precious metal bearing stratiform and/or vein and disseminated (stringer) deposits.

The similar relative stratigraphic position, sulphide mineralogy and galena lead isotope signatures (see section 3.0) of the Slumach, War Eagle and Belle supports them as being part of the same period of volcanogenic activity. While the War Eagle has both stratiform and stringer zones, Belle and Slumach i|i.n i/-sulphide mineralization is vein-like and probably represents remobilized mineralizauon in a feeder pipe. 136

Indian River deposits are stratigraphically lower than Britannia ore bodies, eight kilometres to the southwest, and have correspondingly less radiogenic lead isotopic signatures. Indian River mineralization is probably uppermost Jurassic whereas Britannia is probably lowermost Cretaceous (section 3.0). The lack of major domes related to mineralization (ejj. the Victoria dacite dome) noted by McColl (1987) distinguishes the Indian River area from the Britannia area. 137

5.0 CONCLUSIONS

The Britannia - Indian River pendant is one of the larger Gambier Group pendants. Because it contains the Britannia volcanogenic camp, it has been the most productive. Detailed mapping and interpretations in the eastern half of the Britannia - Indian River pendant, presented here, help to unravel the complex geologic history of the Gambier Group. Conclusions from this thesis are drawn regarding: (1) the regional distribution of Jurassic and Cretaceous pendants, (2) the local geology of the Indian River portion of the Britannia - Indian River pendant, and (3) mineralization within the Indian River valley. These conclusions are based on geology from field mapping, petrography from thin and polished sections, metallogeny from galena lead isotopes, petrochemistry from major element and trace element analyses, and geochronometry from K-Ar and Rb-Sr analyses.

The regional geology is characterized by mostly Jurassic and Cretaceous pendants of Wrangellia within the Coast Plutonic Complex. Conclusions regarding the regional distribution of the Gambier Group include:

(1) The Britannia - Indian River pendant stratigraphy cannot be correlated to any specific part of Gambier Group type sections. The type sections are limited in applicability due to the rapid fades changes and/or large differences in thickness of units witMn the Group. (2) Fossils in various pendants indicate that some Gambier Group pendants are Lower

Jurassic to Cretaceous in age.

Conclusions based on the regional galena lead isotope study (section 3.0) are: 138

(1) There is a possible correlation of Upper Jurassic units in the Harrison Lake area with other pendants containing deposits with Upper Jurassic lead isotopic signatures including: the Indian River portion of the Britannia - Indian River pendant, and the Callaghan pendant of the Cheakamus Group. (2) There is a possible correlation of Lower Cretaceous Gambier Group on Gambier Island with the Helm Formation, the Peninsula Formation, and the Britannia portion of the Britannia - Indian River pendant. The Brokenback Hill Formation and Fire Lake Group could also be equivalent to Lower Cretaceous Gambier Group.

Further general conclusions from the lead isotope study include:

(1) Mineralization in the region is both volcanogenic and plutonogenic, and lead isotopic signatures can be used to distinguish between these two deposit types. (2) Indian River deposits are less radiogenic than Britannia deposits, possibly corresponding to a relatively older stratigraphy. (3) The main mineralizing events are represented by Middle Jurassic to Lower Cretaceous volcanogenic deposits, and Cretaceous to Tertiary plutonogenic deposits.

The local geology of the project area is divided into seven units of the lower and middle Goat Mountain formation of the Gambier Group. The lower Goat Mountain formation, on the east side of the Indian River valley, is mostly felsic flows and pyroclastics with sedimentary interbeds. Beds generally strike north and dip steeply; tops are to the west. The division between lower and middle Goat Mountain formation is a granodiorite apophysis along the Indian River. 139

The middle Goat Mountain formation is dominantly felsic tuff and volcaniclastics interbedded with marine sediments in the Indian River valley, and tuffaceous sediments with intermediate to mafic pyroxene phyric flows in the Stawamus River valley. The bedding strikes northwest in the Indian River valley and west in the Stawamus River valley; tops are consistently up. The change in strike may be due to an angular unconformity within the middle Goat Mountain formation.

The main features of the local geology, based on field observations, thin sections and geochemistry are:

(1) Sedimentary and volcanic rocks were deposited in a shallow marine environment.

(2) Volcanic rocks in the east half of the project area are dominantly felsic and calc- alkaline, and are of island arc affinity. (3) The more tholeiitic mafic rocks in the Stawamus River valley and on Sky Pilot Mountain may indicate a short-lived back arc rift with extensional volcanism. (4) An angular unconformity is interpreted to exist within the lowermost part of unit 4a in the middle Goat Mountain formation. (5) The stratigraphy is on the western limb of a northwestern trending antiform with northeast vergence; this fold does not exhibit closure within the mapped area. (6) A smaller faulted-off anticline along the Indian River is probably a drag fold caused by reverse movement on the Indian River shear. A similar structural setting exists at Britannia Ridge where a broad monocline contains a smaller anticline- syncline pair that has been disrupted by the Britannia shear zone. (7) A single, horizontal northeast trending compressive stress could have developed

both the main Sj and the local S2 cleavage and other deformational features. 140

(8) The combined detailed sections of Heah (1982), McColl (1987) and this thesis

suggest a total thickness of 7,250 metres of stratigraphy in the Britannia - Indian River pendant.

Major and trace element analyses of rocks in the Indian River area support a bimodal (dual composition) calc-alkaline character and a modern island arc affinity for the volcanic suite. Further conclusions from these analyses are:

(1) Late dykes have a tholeiitic character by most classifications.

(2) The intermediate to mafic volcanic rocks in the western half of the project area are of borderline tholeiitic - calc-alkaline affinity by some classifications. (3) Alteration is typically spilitization, chloritization or sericitization; this is indicated by Na, K and Mg gains and/or Ca, Na and K losses noted on chemical variation diagrams. (4) The trend of major and trace elements for the volcanic suite follows the Cascade calc-alkaline trend, and has a medium-K composition and Fe-poor depletion trend. (5) Basalts are clearly classified as calc-alkaline by trace element data, although some basalts from Sky Pilot Mountain have been classified as tholeiitic (Heah, 1982).

Whole rock and mineral separate K-Ar analyses and Rb-Sr isochrons date some of the major events noted in the Britannia - Indian River pendant as follows:

(1) A poor Rb-Sr isochron indicates a possible late Middle Jurassic (date = 168 — 13 Ma) maximum age for Gambier Group volcanics. (2) A rhyolite flow yielded an Early Cretaceous (131 — 77 Ma) internal Rb-Sr isochron

with a large uncertainty. 141

(3) A local Early Cretaceous (108 + 4 Ma by K-Ar on biotite) contact metamorphism of volcanic units was probably caused by the Mountain Lake or Indian River granodiorite plutons. (4) Late Cretaceous (101 to 89 Ma by whole rock K-Ar analyses; 119 to 100 Ma by Rb- Sr isoshrons; 93 Ma by an Rb-Sr internal isochron) regional greenschist metamorphism followed the plutonic emplacement of the Squamish granodiorite.

(5) A Late Cretaceous (84 to 80 Ma by whole rock K-Ar analyses) deformational event reset dates along the Britannia and Indian River shear zones-this may be the period of major movement in the shear zones. (6) Early Oligocene dykes (36.1 + 1.3 Ma average of hornblende and whole rock K-Ar analyses) intrude the stratigraphic and plutonic units.

Comparisons of rriineralization within the Indian River valley are based on sulphide mineralogy, lead isotopes and host rock units. The polymetallic group of prospects occur within a northwest trending belt of felsic volcanic rocks of lower and middle Goat Mountain formations. Conclusions are:

(1) War Eagle, McVicar and Christina have similarities to Kuroko-type volcanogenic deposits. (2) Intense cordierite-biotite hornfelsed zones have been created peripheral to the Slumach, War Eagle and ABC deposits. The remobilization of some mineralization may have been associated with contact metamorphism, but it was the earlier volcanogenic activity that initiated the ground preparation.

(3) The galena lead isotope signatures of Indian River prospects are very uniform and are similar to deposits within known Jurassic units in the Harrison Lake 142

volcanics (section 3.0). The signatures are less radiogenic than Britannia ore bodies.

(4) Indian River prospects are slightly older than Britannia deposits, but have similar

host units and volcanogenic potential.

The complexity of pendant lithologies requires detailed geological interpretations. This study provides mapping and interpretations of an area with high exploration potential as well as regional geological significance. The stratigraphic setting and position of the prospects in the Indian River valley are shown. Knowledge of the tectonic and depositional environment are valuable when piecing together the geologic history of the Gambier Group.

Combined with other recent studies by McColl (1987) and Heah (1982), most of the Britannia - Indian River pendant has been mapped in detail and an almost complete stratigraphic section has been compiled. Two main problems need to be resolved in this pendant: (1) What stratigraphic juxtaposition has occurred along the major thrusts/shear zones? and (2) What is the original age of units within the Britannia - Indian River pendant? 143

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APPENDIX A. STRUCTURAL DATA FOR UNITS IN THE INDIAN AND STAWAMUS RIVER VALLEYS Al STEREONET PLOTS OF STRUCTURAL DATA Structural data for the seven major stratigraphic units are plotted in Figures Al to A.3 as follows: (1) poles to bedding, cleavage and extensional joints in the upper stereonets, and (2) poles to other joints, faults, and dykes in the lower stereonets. The third upper stereonet of Figure A3 features all minor fold axes, mineral lineations, and slickensides noted in the project area. The third lower stereonet of Figure A3 features all poles to faults noted in the project area. Figure A.l Stereonet plots of structural data for (a) unit LGM, (b) unit 1, and (c) unit 2. The upper stereonets depict poles to bedding (circles), poles to cleavage (triangles), and poles to extensional joints (+'s). The lower stereonets depict poles to other joints (x"s), poles to faults (boxes), and poles to dykes (diamonds). Figure A.2 Stereonet plots of structural data for (a) unit 3, (b) unit 4a of package II, and (c) unit 4 of package III. The upper stereonets depict poles to bedding (circles), poles to cleavage (triangles), and poles to extensional joints (+'s). The lower stereonets depict poles to other joints (x's), poles to faults (boxes), and poles to dykes (diamonds). Figure A3 StereoneFpTots of structural data for (a) unit 5, (b) unit 6, and (c) all minor fold axes, mineral lineations and slickensides (upper stereonet) and all faults (lower stereonet) measured in the project area. The upper stereonets for (a) and (b) depict poles to bedding (circles), poles to cleavage (triangles), and poles to extensional joints (+'s). The lower stereonets for (a) and (b) depict poles to other joints (x's), poles to faults (boxes), and poles to dykes (diamonds). 152

APPENDIX B.

MAJOR AND TRACE ELEMENT X-RAY FLUORESCENCE SAMPLE PREPARATION AND ANALYTICAL PROCEDURES B.l SAMPLE PREPARATION AND ANALYSES

Each major volcanic and intrusive unit was sampled for analyses of the major and trace element compositions. The 31 fresh-looking samples were: (V) cleaned of weathered material, (2) crushed to less than 0.5 centimetres in a jaw crusher, (3) split by cone and quartering method to 0.5 kilogram, and (4) pulverized to -200 mesh in a tungsten-carbide shatterbox.

Five samples were prepared in duplicate using separate 0.5 kilogram splits. The duplicates were crushed in a chrome-steel shatterbox to determine if there was any contamination of major or trace elements for the samples prepared in the tungsten- carbide shatterbox. These samples are designated as duphcates by the "d" suffix to sample numbers in Tables 4.1,4.2,4.4 and 4.5. The differences between these two preparation methods are discussed in section 4.2.1. The duplicates were not used in the major or trace element plots in section 4.2.2.

B.l.l MAJOR ELEMENTS A total of 31 rock powders and 5 duplicate powders were prepared for major element analysis as fused pellets. Duplicate pellets were made for five of the rock powders denoted "a" and V in Tables 4.1 and 4.2. The variation of results between the pellets are discussed in section 4.2.1. The averages of the two analyses were used in the major element plots in section 4.2.2. The pellet preparation procedure, below, is modified from the laboratory instruction sheets. Fnsed pellet (1) Weigh 1.000 gram rock powder and 2.000 gram lithium tetraborate (flux). Mix together and place in a graphite crucible. (2) Place crucible in muffle furnace (preheated to 1,000°C) for 10 minutes. Remove the crucible and allow it to cool. (3) Shatter the "rock buttons" and crush them in a set of six small tungsten-carbide shatterboxes. (4) The crushed fused powder is then used to make a pellet using a polyvinyl alcohol (PVA) two percent water solution as a binding agent, and boric acid as backing. (5) The finished pellets are air-dried before using them in the XRF machine. Loss on ignition (6) Accurately weigh out 1.0000 gram rock powder and a ceramic crucible. 153

(7) Place in the muffle furnace for 60 minutes at 1,000°C, remove and cool in a dessicator. (8) Re-weigh the crucible and contents to determine the weight lost on ignition. The pellets were then analyzed using the Philips PW 1410 with a Mo tube (for Mn) and a Cr tube (for Fe, Ti, Ca, K, Si, Al, P, Mg, and Na) in the Department of Geological Sciences, The University of British Columbia. The data were reduced using the TurboPascal program "XRF3" (written by J.K. Russell and U. Thirugnanam, 1988) for use on a personal computer. Standards excluded from the calibration curve for

Si02 were PCC-1, NIM-G, and NIM-S; those excluded for Fe203 were PCC-1 and NIM-D. The data are presented as normalized weight percent oxides in Tables 4.1 and 4.2. Raw percentages and losses on ignition are reported in Table B.l.

A reference sample (BCR-1) was run as an unknown during the major element analyses to estimate the error by calculating the standard deviation. The analytical data, mean and standard deviations for each major elemental oxide of the standard is in Table B.2. Cation normative and CIPW normative values have been calculated using OBCATNORM (written by R.L. Armstrong) and are in Table B.3. Normative results for all samples have been calculated except for one sample (87IRD-151) that gave null results due to low amounts of certain element oxides. 154 Table B.l Major eleient oxides of rock saiples froi the Indian and Stawaius River valleys, southwestern British Coluibia (Figures 4.1 to 4.S). The data are froi XRF analyses of pressed fused pellets. Norialized data are plotted in figures 4.9 to 4.18. Saiples with "d" are duplicates prepared in a chroie-steel shatterbox (see Appendix B). Saiples denoted 'a' and 'b'* are duplicate pellets.

Saiple Height percent oxides Sub LOI Oxygen

3 8 4 Nuiber Unit SiO, TiO, A1,0, FeO HnO MgO CaO Na,0 K,0 P,0S Total I ,* gain Total

SUvaius 6abbro Pluton 87IRD-67 A 45.32 0.34 23.92 7.43 0.14 6. 92 13.23 0.91 0.18 0.08 98.46 2.64 9.25 0.83 99.29 87IRD-12S A 41.86 0.44 15.01 15.72 0.25 14. 78 10.43 0.48 0.11 0.09 99.17 1.84 17.47 1.75 100.92 Squaiish Granodiorite Pluton 861RG-18 77.44 0.18 13.52 1.04 00 0.66 2.95 3.71 0.01 99.53 0.89 1.16 0.12 99.65 87IRD-190 59.76 0.82 16.54 6.98 59 5.82 3.48 1.34 0.22 97.70 1.34 7.75 0.78 98.48 87lRD-190d 59.22 0.83 16.65 7.39 62 5.74 3.51 1.36 0.22 97.70 1.09 8.21 0.82 98.53 87IRD-8U 75.12 0.22 t3.87 1.71 06 1.99 3.72 2.75 0.05 99.53 0.74 1.90 0.19 99.72 87IR0-81b 73.89 0.21 13.70 1.61 01 1.96 3.63 2.73 0.05 97.83 0.74 1.79 0.18 98.01 C Quartz Feldspar Porphyritic Rhyodacite Intrusives 86IRD-50 C 75.97 0.08 12.32 0.88 0.02 00 0.67 2.50 4.80 0.02 97.26 0.80 0.97 0.10 97.36 87IRD-I66 c 75.76 0.07 12.05 0.79 0.00 00 0.42 1.15 7.57 0.02 97.82 0.35 0.87 0.09 97.91 87IRD-169 c 69.33 0.40 14.36 2.72 0.10 44 0.93 4.64 2.68 0.09 96.68 1.42 3.03 0.30 96.99 Dykes Late Stage Intrusives 86IRD-53a 0 50.65 1.11 17.41 8.85 0.17 73 8.35 2.28 2.25 0.31 98.10 0.80 9.83 0.99 99.09 86IRD-53b 0 50.20 1.11 17.36 9.02 0.17 67 8.37 2.35 2.25 0.31 97.80 0.80 10.02 1.00 98.81 86IRD-63 D 65.19 0.34 16.21 5.49 0.11 49 1.53 5.37 1.62 0.17 96.53 2.89 6.11 0.61 97.15 86IRD-145 0 54.39 1.20 16.78 7.43 0.16 02 8.25 2.80 0.99 0.21 99.21 3.85 8.26 0.83 100.04 86IR0-I45d D 54.59 1.20 16.77 7.54 0.16 92 8.22 2.82 1.00 0.21 99.41 3.77 8.38 0.84 100.25 87IRD-75 D 53.40 1.57 17.72 8.44 0.16 02 8.62 3.22 1.30 0.28 99.73 4.42 9.38 0.94 100.67 87IRD-I61 D 64.41 0.67 16.62 4.35 0.12 14 5.06 3.46 2.16 0.32 98.30 1.01 4.83 0.48 98.79 I Lover 6oat Mountain Formation 86IRD-161 1-1 75.02 09 14.61 0.74 0.01 40 0.44 7.23 0.02 99.03 2.34 0.82 0.08 99.12 87IRD-122 1-1 78.91 08 13.34 0.86 0.00 43 0.92 5.22 0.02 100.20 1.64 0.96 0.10 100.30 II Middle 6oat Mountain Foreation - Indian River valley 86IRD-187 2-1 51.50 0 97 17.31 8.46 0.25 86 5.91 3.99 0.71 0.28 97, 1.96 9.40 0.94 98.16 86IRD-189 2-1 71.93 0.39 14.68 2.30 ,07 79 I. 31 4.36 2.86 0.10 98. 0.82 2.56 0.26 99.03 86IR0-193a 2-t 59.80 0.94 17.78 7.32 12 45 7.29 3.07 1.05 0.30 100. 6.67 8.13 0.81 100.93 86IRD-193b 2-1 59.81 0.94 17.76 7.40 12 40 7.31 3.10 1.06 0.30 100. 6.67 8.23 0.82 101.02 86IRD-121 2-2 74.25 0.08 14.04 1.07 04 63 0.90 3.50 3.69 ,02 1.27 1.19 0.12 98.33 86IRD-121d 2-2 73.91 0.07 13.95 1.14 ,04 62 0.90 3.53 3.71 ,02 0.80 I. 27 0.13 98.02 87IR0-15U 2-3 S3.21 0.91 18.59 7.91 17 56 3.34 5.41 3.00 ,24 0.94 8.79 0.88 97.22 87IRD-151b 2-3 53.53 0.91 18.91 8.07 0.17 58 3.35 5.48 3.00 ,24 0.94 8.97 0.90 98.15 87IRD-179 2-3 50.49 0.98 16.74 9.34 0.26 30 9.14 2.78 0.80 ,45 1.59 10.38 1.04 99.31 87IRD-185 2-3 51.21 1.08 17.38 8.20 0.16 53 7.67 3.70 1.70 0.45 0.92 9.12 0.91 97.99 HI Middle Goat Mountain Formation - Stawaius River valley 87IRD-97 3-4a 75.30 0.27 13.01 1.83 0.02 0 43 0.94 5.73 0.06 98.13 0.94 2.04 0.20 98.34 87IRD-60 3-4b 50.54 0.99 17.07 8.27 0.16 64 9.30 3.07 0.30 97.14 1.12 9.20 0.92 98.06 87IRD-88 3-4b 49.64 1.04 17.45 9.26 0.17 ,61 9.72 2.45 0.33 97.77 1.34 10.29 1.03 98.80 87IRD-64a 3-4t 55.12 0.84 16.06 7.64 0.14 55 8.41 3.13 0.24 98.19 0.52 8.49 0.83 99.04 87IRD-64b 3-4c 55.15 0.83 16.08 7.51 0.13 ,58 8.33 3.09 0.24 98.03 0.52 8.3S 0.84 98.87 87IR0-64b' 3-4c 54.93 0.82 16.05 7.47 0.14 ,61 8.30 3.15 0.25 97.82 0.52 8.31 0.83 98.63 87IRD-133 3-4c 51.47 1.08 15.90 9.76 0.20 ,24 6.91 3.96 0.43 97.87 1.73 10.85 1.09 98.95 87IRD-72 3-5a 51.47 0.91 16.45 8.58 0.19 ,24 9.13 2.99 0.32 97.95 0.74 9.54 0.96 98.91 87lRD-72d 3-5a 51.73 0.91 16.43 8.56 0.19 ,11 9.19 3.12 0.32 98.21 0.92 9.SI 0.93 99.17 87IRD-76 3-5a 50.38 0.99 17.09 8.46 0.14 .51 6.20 3.48 0.30 97.33 1.57 9.41 0.94 98.27 87IR0-79 3-5a 48.25 0.92 15.58 10.40 0.20 .82 II. 53 1.35 0.38 97.44 1.00 II. 55 1.16 98.60 87IRD-192 3-5a 55.60 1.05 16.31 7.54 0.18 ,82 7.70 3.30 0.30 97.72 0.36 8.38 0.84 98.56 87lRD-192d 3-5a 55.94 1.06 16.26 7.58 0.19 .83 7.71 3.45 0.30 98.22 0.47 8.42 0.84 99.06 1. Duplicate saiples denoted 'd' were not used in data plots. 2. Duplicate pellets denoted 'a' and V were averaged for use in data plots. 3. Subtotal is the norialized total of eletental oxides (assuiing all iron is ferrous). 4. Total iron oxidt assuiing all iron is ferric. 5. Oxygen correction for ferrous-ferric gain of one oxygen. 6. Total with LOI and oxygen gain included. 7. Saipli was a repeat analysis of the urn pellet !87IRD-64b. 155

Table B.2 The lajor eleient weight percent oxides, aean and standard deviation for the BCR-1 tonitor run as an unknown to estiiate the analytical precision.

MONITOR BCR-1

TOTAL 98.77 98.8 98.72 98.89 98.83 98.66 98.54 98.84 98.71 98.73 98.89 99.01 98.89 98.68 156

Table B.3 Cation and CIPU Hons (in weight percent) based on normalized totals (Tables 3.1 and 3.3).

CATION NORMS (volcanic rocks) Ninerals/Saaples 87IRD 87IR0 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IR0 87IRD 87IRD 87IRD 87IR0 -161 "122 -187 -189 -193a -121 -I51al -179 -185 -97 -60 -88 -64a -133 -72 -76 -79 -192 quartz 41.21 49.23 0.0 29.01 15.28 34.58 - 0.0 0.0 34.52 0.0 0.0 5.94 0.0 0.49 0.0 0.16 7.86 anorthite 2.31 1.96 27.72 5.98 32.08 4.47 - 31.53 26.54 4.38 31.37 34.44 27.41 23.34 30.20 23.15 34.93 27.85 orthoclase 44.32 31.75 4.27 17.22 6.35 22.41 - 4.81 10.33 3.26 4.85 6.61 6.48 5.54 3.96 16.79 6.19 5.54 albite 4.06 8.52 36.43 39.81 28.19 32.25 - 25.53 34.17 52.55 28.40 22.72 28.62 36.29 27.43 3l.45 12.69 30.6O •agnetite 0.11 0.13 1.20 0.33 1.05 0.16 - 1.33 1.18 0.26 1.19 1.33 1.09 1.39 1.23 1.20 1.52 1.09 iltenite 0.13 0.11 1.38 0.55 1.33 0.11 - 1.40 1.54 0.39 1.42 1.49 1.20 1.53 1.30 1.41 1.33 1.50 corundui 5.95 6.15 0.0 2.51 0.0 3.03 - 0.0 0.0 1.59 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 apatite 0.04 0.04 0.60 0.21 0.64 0.04 - 0.97 0.96 0.13 0.65 0.72 0.50 0.92 0.69 0.64- 0.83 0.65 pyroxene, 1.88 2.11 21.47 4.38 15.08 2.95 - 33.13 18.36 2.93 30.17 30.78 28.77 23.07 34.70 4.92 42.35 24.91 <*'side 0.20 2.24 9.45 7.68 11.30 10.43 10.89 7.00 11.17 4.92 17.73 7.62 hypers. 1.88 2.it 21.27 4.38 12.84 2.95 23.68 10.68 2.93 18.87 20.35 17.89 16.07 23.53 24.62 17.29 olivine, 0.0 0.0 6.92 0.0 0.0 0.0 - 1.30 6.91 0.0 1.95 1.91 0.0 7.92 0.0 20.21 0.0 0.0 fors*- 4.99 0.89 4.58 1.36 1.28 5.36 14.51 fay*>it* 1.93 0.41 2.33 0.59 0.63 2.56 5.70

CIPU N0RNS (volcanic rocks) Ninerals/Saaples 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IR0 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IR0 87IRD 87IRD 87IR0 "161 -122 -187 -189 -193a -121 -151al -179 -185 -97 -60 -88 -64a -133 -72 -76 -79 -192 quartz 43.33 51.57 0.0 31.22 16.29 37.04 - 0.0 0.0 37.25 0.0 0.0 6.42 0.0 0.53 0.0 0.17 8.47 anorthite 2.25 1.90 28.24 5.96 31.68 4.44 - 31.66 26.79 4.38 31.59 34.47 27.44 23.61 30.40 23.56 34.70 27.82 orthxlase 43.17 30.81 4.35 17.17 6.28 22.24 - 4.83 10.42 3.26 4.88 6.62 6.49 5.61 3.99 17.10 6.15 5.54 albite 3.73 7.79 34.97 37.39 26.24 30.15 - 24.16 32.50 49.50 26.96 21.43 27.02 34.60 26.03 30.17 11.88 28.81 tagnetite 0.15 0.17 t.70 0.46 1.44 0.21 - 1.86 1.65 0.36 1.67 1.85 1.51 1.95 1.71 1.70 2.09 1.51 iltenite 0.17 0.15 1.91 0.74 1.80 0.15 - 1.92 2.13 0.53 1.95 2.03 1.64 2.11 1.78 1.95 1.80 2.05 nepheline 0.0 0.0 0.0 0.0 0.0 0.0 - 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.20 0.0 0.0 corundui 5.30 5.46 0.0 2.29 0.0 2.75 - 0.0 0.0 1.46 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 apatite 0.05 0.05 0.68 0.23 0.70 0.05 - 1.08 1.07 0.14 0.72 0.80 0.56 1.03 0.77 0.72 0.91 0.72 pyroxene, 1.86 2.09 21.46 4.55 15.58 2.97 - 33.24 18.67 3.12 30.34 30.94 28.92 23.36 34.78 5.07 42.28 25.07 diopside 0.21 2.31 9.66 7.92 11.57 10.65 11.11 7.21 11.42 5.07 17.95 7.78 hypers. 1.86 2.09 21.25 4.55 13.27 2.97 23.58 10.75 3.12 18.77 20.29 17.81 16.15 23.37 24.33 17.29 olivine, 0.0 0.0 6.68 0.0 0.0 0.0 - 1.26 6.77 0.0 1.89 1.85 0.0 7.74 0.0 19.53 0.0 0.0 4.29 0.75 3.89 1.16 1.08 4.57 12.45 fayalite 2.40 0.50 2.88 0.73 0.77 3.16 7.09 nor• C.I. 2.17 2.41 31.76 5.75 18.82 3.34 - 38.27 29.21 4.02 35.84 36.67 32.07 35.16 38.28 28.26 46.18 28.63

1. Very low normalized values (or this satple caused dubious results in normative programs. 157

Table B.3 CONTINUED.

CATION NORMS (intrusive rocks) Hinerals/Saiples 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD -67 -125 -18 -190 -81a -50 -166 -169 -53a -63 -145 -75 -161 quartz 0.0 0.0 41.92 14.84 35.83 39.98 37.65 25.68 0.0 20.37 4.77 2.72 21.17 anorthite 61.Bl 39.20 3.27 26.56 9.74 3.36 2.05 4.18 31.26 6.69 30.59 30.42 23.71 orthoclase 1.07 0.66 22.45 8.21 16.63 29.77 46.89 16.38 13.64 9.97 5.92 7.75 13.17 albite 8.29 4.35 27.08 32.43 33.93 23.54 10.8643.1 3 21.32 50.16 25.36 29.26 32.03 •agnetite 1.06 2.22 0.15 1.02 0.25 0.13 0.12 0.40 1.29 0.80 1.05 1.19 0.63 ilienite 0.49 0.62 0.26 1.19 0.31 0.11 0.10 0.57 1.58 0.49 1.69 2.21 0.96 corundui 0.0 0.0 3.89 0.0 1.47 2.10 1.42 2.65 0.0 3.71 0.0 0.0 0.18 apatite 0.17 0.19 0.02 0.49 0.11 0.04 0.04 0.19 0.67 0.38 0.44 0.59 0.70 pyroxene* 20.32 19.14 0.97 15.26 1.76 0.97 0.87 6.82 26.48 7.42 30.19 25.86 7.45 diopside 3.64 10.31 1.54 7.40 7.51 8.79 hypers. 16.68 8.83 0.97 13.72 1.76 0.97 0.87 6.82 19.08 7.42 22.67 17.08 7.45 olivine* 6.80 33.62 0.0 0.0 0.0 0.0 0.0 0.0 3.77 0.0 0.0 0.0 0.0 forst. 4.80 23.74 2.57 fayalite 1.99 9.88 1.20

CIPU NORMS (intrusive rocks) Ninerals/Saiples 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD 87IRD B7IRD 87IRD 87IRD 87IRD 87IRD 87IR0 -67 -125 -18 -190 -Bla -50 -166 -169 -53a -63 -145 -75 -161 quartz 0.0 0.0 44.47 15.90 38.20 42.35 39.66 27.78 0.0 22.01 5.17 2.94 22.64 anorthite 62.04 39.46 3.21 26.34 9.61 3.29 2.00 4.19 31.33 6.70 30.74 30.40 23.48 orthoclase 1.07 0.66 22.06 8.15 16.44 29.21 45.75 16.41 13.68 9.98 5.95 7.74 13.05 albite 7.84 4.13 25.07 30.32 31.57 21.76 9.99 40.72 20.15 47.30 24.02 27.55 29.90 •agnetite 1.48 3.10 0.20 1.40 0.33 0.18 0.16 0.55 1.79 1.11 1.47 1.66 0.87 ilienite 0.67 0.85 0.34 1.61 0.41 0.15 0.13 0.78 2.16 0.67 2.31 3.01 1.30 corundui 0.0 0.0 3.50 0.0 1.33 1.89 1.27 2.43 0.0 3.40 0.0 0.0 0.17 apatite 0.19 0.21 0.02 0.54 0.12 0.05 0.05 0.21 0.75 0.42 0.49 0.65 0.77 pyroxene* 20.21 19.29 1.12 15.75 2.03 1.12 0.99 6.93 26.51 8.40 29.85 26.05 7.83 diopside 3.71 10.53 1.59 7.55 7.62 8.97 hypers. 16. SO 8.76 1.12 14.16 2.03 1.12 0.99 6.93 18.97 8.40 22.23 17.07 7.83 olivine* 6.51 32.28 0.0 0.0 0.0 0.0 0.0 0.0 3.64 0.0 0.0 0.0 0.0 forst. 4.06 20.14 2.17 fayalite 2.44 12.14 1.47 nori C.I. 28.86 55.52 1.66 18.75 2.77 1.44 1.29 8.26 34.10 10.18 33.63 30.71 10.00 158

B.1.2 TRACE ELEMENTS Samples for trace element analyses were prepared as pressed powder pellets. Duplicate pellets were made for five of the rock powders denoted "a" and "b" in Table 4.4 and 4.5. The variations in results between the pellets are discussed in section 4.2.1. The averages of the two analyses were used in the trace element plots in section 4.2.3. Polyvinyl alcohol (PVA) was used as a binding agent and boric acid as backing for the three grams of rock powder used in each pellet. Pellets were air-dried before being used in the automated Philips PW 1400 X-Ray Fluorescence unit with a rhodium tube at the Department of Oceanography, University of British Columbia. The counts per second were corrected for mass absorption coefficients based on the major element concentrations using the programs OBMAC and OBTELA (R.L. Armstrong, 1985). Data are presented as parts per million in Tables 4.4 and 4.5. A standard sample was run as an unknown to estimate the error by calculating the standard deviation of the trace element data (Table B.4). Standard error, calculated in the program OBTELA, is based on the scatter of measurements from the calibration curves used within the program (Table B.5). 159

Table B.4 Minor element mean and standard deviations for repeat analyses of a standard run as unknown.

MONITOR AGV-1

Ba 1220ppm 1218 1242 1 203 1221 16. 1 Cr 8ppm 10 9 10 9 1.0 Nb 15ppm 15 14 15 15 0.5 Ni 18ppm 20 14 16 17 2.6 Rb 65ppm 67 64 66 66 1.3 Sr 662ppm 673 647 663 661 10.7 V 135ppm 137 137 124 133 6.2 Y 21ppm 21 21 21 21 0.0 Zr 251ppm 255 244 256 252 5.5

Table B.5 Standard errors calculated in the program 0BTRACE based on the scatter of the measurements from the calibration curve. These are the larger standard errors for each element from either of the two runs.

STANDARD ERRORS

Ba 16ppm Ni 4ppm V 7ppm Cr 6 Rb 1 Y 2 Nb 0 Sr 2 Zr 8 160

APPENDIX C.

POTASSIUM-ARGON AND RUBIDIUM-STRONTIUM PREPARATION AND ANALYTICAL PROCEDURES C.1 SAMPLE PREPARATION Eleven samples were prepared for potassium-argon or rubidium-strontium dating methods. The initial steps are described in the following steps; specific treatments follow under respective sub-headings. The samples were:

1) cleaned of weathered material, 2) crushed to less than 0.5 centimetres in a jaw crusher (a split of the sample is removed for major and trace element analysis; see Appendix B), 3) ground in a disc mill, and 4) sieved to -28 mesh to retain the -28 mesh fraction. (Steps 3 and 4 were repeated with the +28 mesh fraction until the entire sample passed -28 mesh.)

C.1.1 POTASSnjM-ARGON ANALYSES Eight potassium-argon analyses were made from five whole rock and three mineral separate samples. Biotite mineral separates were made from a biotitic hornfels and from biotite within a vein of sulphide mineralization. A hornblende mineral separate was made from a hornblende porphyritic basalt dyke. The latter dyke was also analyzed as a whole rock. The various sample preparations follow:

All samples (1) Each sample was sieved in a set of nested sieves (-65 mesh on top of -80 mesh) m a Ro-Tap for 15 minutes. Whole rock samples (2) Whole rock samples were crushed and sieved to -65 + 80 mesh for further analysis. (The -28 +65 mesh, and -80 mesh fractions were saved for back• up.) Hornblende separates (3) Samples selected for hornblende separates were crushed and sieved to -65 +80 mesh. This fraction was retained for further separation of the hornblende. (The -28 +65 mesh, and -80 mesh fractions were saved for back-up.) (4) The fraction in (3) was passed through a magneticseparator several times at different amperages to separate the strongest from the least magnetic grains. (5) Heavy liquids (methylene iodide) were used on the separate from (4) to further concentrate the hornblende grains. 161

Biotite separate (6) Samples sellected for biotite separates were crushed and sieved to -28 + 65 mesh. This fraction was retained for further separation of the biotite. (The -65 + 80 mesh, and -80 mesh fractions were saved for back-up.) (7) The fraction in (6) was passed over a tilted vibrating table that separates flat or platy grains from rounded grains. (8) Heavy liquids (bromoform) were used on the separate from (7) to further concentrate the biotite. Potassium and argon analyses (9) Chemical procedures for potassium analyses are described in detail in the unpublished laboratory instructions in the Geochronology Laboratory, The University of British Columbia. Potassium is determined in duplicate by atomic absorption using a Techtron AA4 spectrophotometer on dilute sulphate solutions buffered by Na and Li nitrates. (10) Argon is determined by isotope dilution using an AEI MS-10 mass spectrometer with Carey Model 10 vibrating reed electrometer, high purity38Ar spike and conventional gas extraction and purification procedures as described by White el al- (1967). The precision of the resulting dates are the estimated analytical uncertainties at one standard deviation. Decay constants are those recommended by the IUGS Subcommision on Geochronology C^K decay to 40Ar and to ^Ca are O.SSlxlO"10^"1 and 4.962xl0"10yr"1 respectively, Steiger and Jager, 1977). The data are presented in Table 4.6.

C.1.2 RUBIDIUM-STRONTIUM ANALYSES Eight samples were prepared and analyzed for rubidium and strontium as briefly described in the following steps. Eight analyses were of whole rock samples and six more were partial mineral separates made from three of the samples. Whole rock samples (1) Approximately 50 grams of -28 mesh material was ground to a fine powder m an automated agate mortar for 15 minutes. (2) A four gram pressed powder pellet was made using a PVA binding agent and a boric acid backing. (3) Replicate analyses were made for Rb, Sr and mass absorption coefficients (on Mo K-alpha Compton scattering measurements) using the Philips PW 1410 XRF unit with a Mo tube in the Department of Geological Sciences, The University of British Columbia. (U.S. Geological Survey standards were used for calibration.) (4) Strontium chemical preparation for mass spectrometer analyses utilized ion exchange techniques described in detail in the unpublished laboratory instructions in the Geochronology Laboratory, The University of British Columbia.

Partial mineral separates (1) Samples selected for partial mineral separates were crushed and sieved (-65 on top of -150 mesh) in a Ro-tap for 15 minutes. 2) The -65 +150 mesh fraction was retained for preparation. 3) Magnetic grains were removed with a hand magnet. 162

(4) Heavy liquids (bromoform) were used on the separate from (2) to attempt to concentrate the plagioclase. (5) The initial fractions had the highest specific gravity and are dominantly micas and glass. 6} The final fractions were dominantly feldspar and quartz grains. 7) The heaviest and lightest fractions were then treated in the same manner as described above for a whole rock sample.

Rb/Sr ratios have a precision of two per cent (one standard deviation) where both concentrations exceed 50 ppm. If either concentration is below 50 ppm the ratio uncertainty is based on an uncertainty in the concentration measurement of one part per million. Concentrations have a precision of five per cent or one part per million, whichever is greater. Sr isotopic composition was measured on unspiked samples prepared using standard ion exchange techniques. Sr isotopic measurements were made on a Vacuum-Generators Isomass 54R mass spectrometer automated with a Hewlett-Packard HP-85 computer. Measured ratios have been normalized to a ^Sr/^Sr ratio of 0.1194 and adjusted so that the National Bureau of Standards standard

SrC03 (SRM967) gives a "Sr/^Sr ratio of 0.71019 -±- 0.00002 and the Eimer and Armand Sr standard a ratio of 0.70800 ± 0.00002. The precision of a single "Sr/^Sr ratio is normally less than or equal to 0.0001 (one standard deviation). Any exceptions are noted. Rb-Sr dates are based on a Rb decay constant of 1.42xlO"11yr1 (Steiger and Jager, 1977). The regressions are calculated according to the technique of York (1967). Errors reported are one standard deviation or the standard error of the mean, unless otherwise noted. The resulting data are listed in Table 4.8, dates from different regressions are in Table 4.9. 163

APPENDIX D.

GALENA LEAD ISOTOPE DATA The eight samples of galena collected from the thesis area are used as part of an evaluation of galena lead-isotope signatures in the Gambier Group and laterally equivalent groups. Sample preparation and analytical techniques are described in detail in "Leadtable: A galena lead isotope data base for the Canadian Cordillera" by Godwin si gj. (1988).

Table D.l contains all of the analyses used to calculate the averaged values of the deposits presented in Table 3.2. 164

Table D.l Lead isotope data lor deposits between Harrison Lake and Jervis Inlet, southwestern British Col tub i a (Fig. 3.1). Deposits are ordered by saiple nuiber. Analyses with an V after the saiple nuiber are old saiples analyzed prior to 1986 the analyses are used because taterial for a rerun was not available.

Saiple Deposit NTS « Nin.Inv. Host Host Deposit Quality »«/»«Pb *"/»«Pb loa/iotpi, zoT/Mcpt, aoa/XMpt, Nuiber' Lat.N Long. II Unit Age Type TeipW (terror) (terror) (terror) (terror) (terror)

104- 001 Bonanza Nine 092/6/06/U:SU- ? Boven JM Vole. Good 18.518 15.562 3B.097 0.84050 2.05737 49.37 123.40 Island Gp (0.00) (0.00) (0.00) (0.00) (0.00) 105- 001 Mendel la 092/J/04/U:SU- ? Gaibier J-K Plut. Fair 18.607 15.565 38.154 0.83661 2.05050 50.02 123.98 6roup (0.00) (0.00) (0.00) (0.00) (0.01) 107-001 Red Tusk 092/G/13/U:NU-O51 6aibier J-K Vole. Good 18.477 15.544 38.032 0.84134 2.05833 Havis Zone 49.77 123.32 Group (0.00) (0.00) (0.00) (0.01) (0.00) 107- 003 Red Tusk 092/6/13/W:NU-O51 Gaibier J-K Vole. Good 18.477 15.540 37.999 0.84111 2.05654 North Zone 49.77 123.32 Group (0.00) (0.00) (0.00) (0.01) (0.01) 108- 001 Chalice 092/8/12/U:NU-OS0 Cret.-Tert KE Vein Good 18.561 15.556 3B.082 0.83817 2.05176 49.75 123.99 Intrusives (0.00) (0.00) (0.00) (0.00) (0.00) 092/J/04/U:SU-032 109- 001 Silver Bay 6aibier J-K Vein Good 18.715 15.589 3B.337 0.833O4 2.04844 50.10 123.77 Group (0.00) (0.00) (0.00) (0.00) (0.00) 110- 001 Fairplay 092/H/04/H:SU-031 Harrison JH Vole. Fair 18.301 15.502 37.78B 0.84714 2.06485 Hell's Angel 49.23 121.83 Lake Fitn (0.00) (0.00) (0.00) (0.01) (0.02) 092/J/04/U:SH- ? 111- 001 Nalibu Gaibier J-K Plut. Good 18.765 15.594 38.381 0.83109 2.04537 50.13 123.85 6roup (0.00) (0.00) (0.00) (0.00) (0.00) 092/H/05/U:SU-133 433-001 Cloud 1 Harrison JH Vole. Fair 18.500 15.569 38.158 0.84166 2.06258 Brett 49.38 121.90 Lake Fitn (0.00) (0.00) (0.00) (0.00) (0.01) 489-001 Heaver 092/H/05/U:SH-069 Harrison JH Vole. Good 18.423 15.554 38.043 0.84436 2.06495 49.36 121.8B Lake Fitn (0.00) (0.00) (0.00) (0.00) (0.00) (05-001 Haggie 092/6/U/E:NU-042 Gaibier J-K Vole. Fair 18.459 15.542 38.026 0.84198 2.06005 -Uar Eagle 49.64 123.04 6roup 1150 (0.02) (0.01) (0.04) (0.0 ) (0.0 ) 605-001R Haggie 092/8/ll/E:NH-042 Gaibier J-K Vole. Good 18.450 15.532 37.975 0.84186 2.03830 -Uar Eagle 49.64 123.04 Group 1150 (0.02) (0.02) (0.02) (0.0 ) (0.0 ) 605-OO1R Haggie 092/6/11/E.-NH-042 Gaibier J-K Vole. Poor 18.441 15.527 37.992 0.84196 2.06017 -War Eagle 49.64 123.04 Group 1200 (0.06) (0.03) (0.08) (0.0 ) (0.0 ) 605-002 Haggie -Sluiach, 092/6/U/E:NU-024 Gaibier J-K Vole. Fair 18.429 15.524 37.949 0.84235 2.05919 Barite zone 49.63 123.03 Group 1200 (0.01) (0.00) (0.01) (0.01) (0.01) 605-002D Maggie -Sluiach, 092/G/ll/E:NU-O24 Gaibier J-K Vole. Fair 18.454 15.550 3B.024 0.84274 2.06054 Barite Zone 49.63 123.03 Group (0.00) (0.00) (0.00) (0.01) (0.01) 605-003 Haggie -Uar Eagle 092/6/ll/E:NU-042 Gaibier J-K Vole. Good 18.470 15.549 38.027 0.84186 2.03889 Collar of Adit 49.64 123.04 Group 1220 (0.00) (0.03) (0.01) (0.01) (0.02) 605-003D Maggie -Uar Eagle 092/6/ll/E:MH>42 Gaibier J-K Vole. Good 18.466 15.542 38.020 0.84175 2.05901 Collar of Adit 49.64 123.04 Group (0.00) (0.00) (0.00) (0.00) (0.00) 605- 004 Haggie -Uar Eagle 092/6/ll/E:NU-042 Gaibier J-K Vole. Good 18.464 15.540 38.014 0.84173 2.03882 Inside Adit 49.64 123.04 Group (0.00) (0.00) (0.00) (0.00) (0.00) 606- 003 Big Foot 092/H/05/HISU-O94 Harrison JN Vole. Good 18.476 15.550 38.099 ' 0.84168 2.06213 49.43 121.85 Lake Fitn 1150 (0.01) (0.01) (0.02) 608-00IR Providence Nine 092/H/12/H:NlM>30 Brokenback KE Vein? 6ood 18.576 15.564 38.155 0.83784 2.03401 49.62 121.95 Hill Fitn 1150 (0.01) (0.01) (0.01) 608-001D Providence Mine 092/H/12/U:NU-O30 Brokenback KE Vein? Fair 1B.587 15.570 38.180 0.83781 2.05417 49.62 121.95 Hill Fitn (0.00) (0.00) (0.00) (0.01) (0.00) 620-002 Skwii Lake 092/K/01/E:SE-OB2! 6aabier JE Vein 6ood 18.609 15.542 38.151 0.83521 2.03016 Linda 14 50.01 124.10 Group 1150 (0.02) (0.02) (0.02) 620-O02R Skwii Lake 092/K/01/E:SE-082 Gaibier JE Vein Good 18.622 15.560 38.192 0.B3537 2.03088 Linda 14 50.01 124.10 Group 1150 (0.01) (0.01) (0.01) 165

Table D.l Continued.

Satpie Deposit NTS t Nin.lnv. Host Host Deposit Quality «V»«f>b *«/»«Pb *«/»«Pb »'/»«f»b »»/"*f>b Nuiber1 Lat.N L0n9.ll Unit Age Type Tetp(*C) (Zerror) (Zerror) (Zerror) (Zerror) (Zerror)

620-004 Skyn Lake 092/K/01/E:SE-084 Gaibier JE Vein 6ood 18.654 15.569 38.232 0.83461 2.04951 Nt Diadei 50.01 124.09 Group 1150 (0.03) (0.02) (0.04) 620-004R Skvii Lake 092/K/01/E:SE-084 Gaibier JE Vein Good 18.653 15.564 38.218 0.83442 2.04892 Nt Diadei 50.01 124.09 Group 1150 (0.00) (0.00) (0.00) 620-004D Skuii Lake 092/K/01/E:SE-084 Gaibier JE Vein 6ood 18.656 15.567 38.231 0.83443 2.04925 Nt Diadei 50.01 124.09 Group 1150 (0.01) (0.01) (0.02) 622-001 Hayflower 092/G/16/U:NE-O10 Fire Lake KE Vein Good 18.712 15.561 38.249 0.83163 2.04417 (Jo, Dandy) 49.95 122.44 Group 1150 (0.02) (0.01) (0.02) 721-001 Fitisutons Creek 092/J/02/U:SE-OI3 Cheak- KE Skarn Fair 18.502 15.552 38.062 0.84064 2.05717 50.12 122.93 aius Fitn (0.00) (0.00) (0.00) (0.00) (0.00) 722-001O Britannia 092/6/U/EiNU-036 Gaibier J-K Vole. Fair 18.531 15.573 38.097 0.84038 2.05585 East Bluff 49.61 123.14 Sroup (0.10) (0.18) (0.10) 722-002O Britannia 092/6/U/E:NU-003 6aibier J-K Vole. Fair 1B.459 15.556 37.952 0.84273 2.05602 Victoria Pit 49.60 123.13 6roup (0.09) (0.17) (0.22) 722-003O Britannia 092/6/U/E:NtM>03 6aibier J-K Vole. Fair 18.524 15.579 38.221 0.84102 2.06332 Victoria Pit 49.60 123.13 Group (0.05) (0.11) (0.11) 722-004O Britannia 092/6/lt/E:NH-036 Gaibier J-K Vole. Fair 18.502 15.548 38.054 0.84034 2.05675 Jane Pit 49.61 123.14 Sroup (0.07) (0.10) (0.18) 722-005 Britannia 092/6/U/E:NU-036 Gaibier J-K Vole. Poor 18.526 15.584 38.221 0.84131 2.06316 Bluff Orebody 49.61 123.14 Group 1310 (0.01) (0.00) (0.02) (0.02) (0.05) 722-006 Britannia 092/G/11/E:NH-003 Gaibier J-K Vole. Good 18.497 15.546 38.041 0.84034 2.05661 No. 5 orebody 49.60 123.13 Group 1150 (0.00) (0.00) (0.00) (0.00) (0.00) 722-007 Britannia 092/G/ll/E:NIH>36 Gaibier J-K Vole. Good 18.491 15.545 38.036 0.84072 2.05694 No. 8 orebody 49.61 123.14 Group (0.00) (0.00) (0.00) (0.00) (0.00) 722-008 Britannia 092/G/ll/E:NIH)36 Gaibier J-K Vole. Good 1S.506 15.550 38.059 0.84038 2.05665 Fairviev 49.61 123.14 Group (0.00) (0.00) (0.00) (0.01) (0.01) 722-014 Britannia 092/6/11/E:KIH>36 Gaabiir J-K Vole. Good 18.499 15.541 38.024 0.84018 2.05544 Bluff 1400'level 49.61 123.14 Group (0.00) (0.00) (0.00) 724-001 Lynn Creek 092/6/06/E:SU-003 Gaibier KE Skarn Poor 18.554 15.565 3B.129 0.83900 2.05502 49.42 123.06 Sroup 1130 (0.01) (0.00) (0.01) (0.01) (0.02) 724-010 Lynn Creek 092/6/06/EISU-003 Gaibier KE Skarn Good 18.559 15.559 3B.115 0.83848 2.05376 49.42 123.06 Group (0.00) (0.00) (0.00) (0.00) (0.00) 725-003 Ik Vicar -Ruth 092/6/1l/E>NN-006 Gaibier J-K Vole. Good 18.417 15.536 37.964 0.84366 .2.06142 49.66 123.02 Group (0.00) (0.00) (0.00) (0.01) (0.00) 725-004 NcVicar -Nhistler 092/6/U/ElNlH>06 Gaibier J-K Vole. 6ood 18.425 15.540 37.980 0.84350 2.06131 49.66 123.02 Group (0.00) (0.00) (0.00) (0.00) (0.00) 725-005 NcVicar -Lead 092/G/ll/E:NU-O06 Saibier J-K Vole. Fair 18.434 15.545 38.002 0.84337 2.06153 49.66 123.02 Group (0.00) (0.00) (0.00) (0.00) (0.00) 725-006 NcVicar -Rainstori 092/6/ll/E:NIMK>6 Gaibier J-K Vole. Good 18.438 15.550 38.014 0.84348 2.06177 49.66 123.02 Group (0.00) (0.00) (0.00) (0.00) (0.00) 726-001 Northair 092/J/03/EISN-O12 Cheak- KE Vole. Good 18.427 15.543 38.003 0.84359 2.06234 Manifold 50.13 123.10 ams Fitn (0.00) (0.00) (0.00) (0.00) (0.01) 726-002 Northair 092/J/03/EiSU-O12 Cheak- KE Vole. 6ood 18.420 15.534 37.981 0.84343 2.06193 Discovery 50.13 123.10 aius Fitn (0.00) (0.00) (0.00) (0.00) (0.00) 726-004 Northair -Marian 092/J/03/E:SH>12 Cheak- KE Vole. 6ood 18.430 15.546 38.007 0.84339 2.06224 50.13 123.10 aaus Fitn (0.00) (0.00) (0.00) (0.01) (0.00) 727-001 Van Silver 092/J/03/E1SU-001 Cheak- KE Vole. Good 18.451 15.551 38.038 0.84291 2.06156 Tedi Pit 50.08 123.13 aws Fitn 1100 (0.00) (0.00) (0.00) (0.00) (0.00) 166

Table D.l Continued.

Saiple Deposit NTS I Kin.Inv. Host Host Deposit Quality *«V»»«Pb »7/*°*Pb 10*/»°*Pb M»/*»1>b *—/*»*n Nuiber' Lat.N Long.M Unit Age Type TetpCC) (lerror) (lerror) (Zerror) (Zerror) (Zerror) 727-002 Van Silver 092/J/03/E:SN-025 Cheak- KE Vein Fair 18.712 15.559 3B.232 0.83159 2.04323 Hillsite 50.06 123.13 aws Fitn (0.00) (0.00) (0.00) (0.00) (0.00) 727-006 Van Silver 092/J/03/E:SU-O03 Cheak- KE Vole. Fair 18.450 15.547 38.028 0.84273 2.06116 Silver Tunnel 50.07 123.15 ams Fitn (0.00) (0.00) (0.00) (0.00) (0.01) 729-001o Con 092/H/05/H:SU- ? Harrison JH Vole. Fair 1B.4B2 15.563 38.043 0.84206 2.05838 49.35 121.83 Lake Fitn (0.07) (0.14) (0.17) 730-007 Seneca Nine 092/H/05/W:S«-013 Harrison JN Vole. Fair 18.320 15.544 37.919 0.84857 2.06991 49.32 121.95 Lake Fitn (0.00) (0.00) (0.00) (0.02) (0.01) 868-101 Doctors Point 092/H/12/M:NN-O71 Brokenback KE Vein Good 18.785 15.570 38.313 0.82886 2.03953 49.64 121.98 Hill Fitn 1150 (0.04) (0.03) (0.05) 868-101D Doctors Point 092/H/12/MiNIM>71 Brokenback KE Vein 6ood 18.805 15.585 38.380 0.82881 2.04099 49.64 121.93 Hill Fitn 1150 (0.01) (0.01) (0.01) 935-001 Belle U-C Adit 092/6/ll/E:NH-O14 Gubier J-K Vole. Fair 18.488 15.572 38.109 0.84223 2.06122 (Irish Nolly) 49.62 123.01 6roup 1200 (0.01) (0.00) (0.01) (0.01) (0.02) 984-001 Showing 092/6/ll/U:NU- ? Saibier J-K Plut. 6ood 18.903 15.635 38.635 0.82718 2.04386 Brunswick Point 49.53 122.26 Sroup (0.00) (0.00) (0.00) (0.00) (0.01) 985-001 Shoving 092/6/10/E:NE- ? 6aibier J-K Plut. Good 18.661 15.563 38.202 0.83406 2.04716 Hercules Creek 49.62 122.98 Group (0.00) (0.00) (0.00) (0.00) (0.00) 986-001 Shoving 092/6/1l/E:Ny- ? Saibier J-K Vole. Fair 18.466 15.541 38.018 0.84171 2.05885 (0.00) Indian River 49.63 123.00 Sroup (0.00) (0.00) (0.00) (0.00) 987-001 Shoving 15.573 092/6/10/H:NE- ? Saibier J-K Vole? 6ood 18.527 38.137 O.B4064 2.05845 (0.00) Slide Creek 49.63 122.99 6roup (0.00) (0.00) (0.01) (0.01) 988-001 Shoving 15.547 092/6/11/EsNH- ? 6aibier J-K Vole. Fair 18.474 38.035 0.84169 2.05889 (0.00) East Side Creek 49.65 123.04 Sroup (0.00) (0.00) (0.00) (0.01) 1. Saiple nuiber sulfites i ndicate the follovingi aR* = repeat analysis; '0* = duplicate analysis; V = old analysis (prior to 1986).