Geology of the Indian River Area Southwestern British Columbia
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GEOLOGY OF THE INDIAN RIVER AREA SOUTHWESTERN BRITISH COLUMBIA by 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 in 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 © Douglas Gerald Reddy, 1989 COPY AND REFERENCE PERMISSION 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