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Geology and geochronology of porphyry copper and molybdenum deposits in west-central British Columbia Carter, Nicholas Charles 1974

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GEOLOGY AND GEOCHRONOLOGY OF PORPHYRY COPPER AND MOLYBDENUM DEPOSITS IN WEST-CENTRAL BRITISH COLUMBIA by NICHOLAS CHARLES CARTER B.Sc, University of New Brunswick, Fredericton, 1960 M.S., Michigan Technological University, Houghton, 1962 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of Geological Sciences We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1974 In presenting th i s thesis in par t i a l fu l f i lment of the requirements for an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree that the L ibrary shal l make it f ree ly ava i lab le for reference and study. I further agree that permission for extensive copying of this thesis for scholar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l icat ion of this thesis for f inanc ia l gain sha l l not be allowed without my written permission. Department of £fZotdd,u <^f^/€^d.^3 The Univers i ty of B r i t i s h Columbia Vancouver 8, Canada i i ABSTRACT Porphyry copper and molybdenum deposits i n west-central British Columbia are associated with plutons of Late Cretaceous and Tertiary age which intrude Mesozoic volcanic and sedimentary rocks of the Intermontane Tectonic Belt. The porphyry deposits are contained in an area bounded on the west by granitic rocks of the Coast Plutonic Complex, and on the east and southeast by a belt contain-ing Mesozoic granitic stocks and an extensive area of Tertiary volcanic rocks. The porphyry intrusions take the form of small stocks, plugs , dykes, and dyke swarms generally not exceeding 1 square mile i n surface area. The intrusions are commonly multiple and range in composition from quartz diorite to granite. Copper and molybdenum sulphides occur as fracture f i l l i n g s and as veinlet stockworks within and adjacent to the intrusive bodies. Sulphide and alteration minerals exhibit concentric zoning patterns. Volcanic and sedimentary rocks marginal to the intrusions are thermally metamorphosed to biotite hornfels. Results of potassium-argon dating indicate four crudely parallel north to northwest-trending belts of porphyry intrusions, each being distinctive i n age, rock composition, and contained metallic mineralization. From west to east these include: (1) Alice Arm intrusions - 50 m.y. molybdenum-bearing quartz monzonite and granite intrusions; (2) Bulkley intrusions - 70 to 84 m.y. copper-molybdenum and molybdenum-bearing porphyries of granodiorite to quartz monzonite composition; (3) Nanika intrusions - 50 m.y. copper-molybdenum and molybdenum-bearing intrusions of quartz monzonite composition; (4) Babine intrusions - 50 m.y. copper-bearing intrusions of quartz diorite and grano-diorite composition. i i i Potassium-argon analyses were carried out mainly on biotite separates from the mineralized porphyry phases within the deposits. Dating of inter-mineral and post-mineral porphyry phases, common at many of the deposits, yielded ages equivalent to, or 2 to 3 m.y. younger than, the mineralized phases, indicating that the age of mineralization i s essentially synchronous with the age of intrusion. Limits of analytical errors i n these potassium-argon analyses are within 3 per cent of the calculated ages. The distribution of potasslum-argon ages for porphyry deposits i n west-central British Columbia does not f i t the plate tectonic theories proposed for the origin of similar deposits elsehwere in the Cordillera of North and South America, i n which deposits are progressively younger i n a given direction. Here, four crudely parallel belts of porphyry intrusions display a reversal i n age from 50 m.y. to 70 - 84 m.y. to 50 m.y. in an eastward direction. This distribution of ages may have been caused by periodic movement from Late Jurassic to Tertiary time along a subduction zone beneath the Coast Plutonic Complex which forms the west border of the area containing the porphyry deposits. i v ACKNOWLEDGMENTS This study was initiated by the late Professor W. H. White of the Department of Geological Sciences. As original thesis supervisor, he provided valuable advice and encouragement. Dr. A. E. Soregaroli supervised the study i n i t s later stages and con-tributed greatly to the organization of the manuscript. Dr. W. H. Mathews offered useful suggestions for improvement of the manuscript. J. E. Harakal supervised a l l of the argon analyses and assisted i n the interpretation of the potassium-argon analytical data. Much of the financial support for this study was provided by the Mineralogical Branch, now the Geological Division, Mineral Resources Branch, of the British Columbia Department of Mines and Petroleum Resources. Dr. Stuart S. Holland, current Chief of the Geological Division, and Drs. M. S. Hedley and H. Sargent offered encouragement for the study. Several of the author's colleagues in the Geological Division helped with useful discussion and advice, especially Drs. A. Sutherland Brown, P. A. Christopher, and A. Panteleyev. Drs. H. W. Tipper, R. V. Kirkham, and T. Richards of the Geological Survey of Canada contributed information on the regional geology of the area. Finally, this study would not have been possible without the cooperation of mining and exploration company personnel active i n west-central B r i t i s h Columbia during the course of f i e l d work related to the study. Their assistance i s gratefully acknowledged. V CONTENTS Page 1. INTRODUCTION 1 1.1 SCOPE OF STUDY 1 1.2 LOCATION OF AREA 2 1.3 PORPHYRY MINERAL DEPOSITS STUDIED 5 1.4 SAMPLING METHODS FOR POTASSIUM-ARGON STUDIES 7 2. GENERAL GEOLOGY OF WEST-CENTRAL BRITISH COLUMBIA 10 2.1 PHYSIOGRAPHY 10 2.2 REGIONAL TECTONIC SETTING 13 2.3 GENERAL GEOLOGY 13 2.3.1 Sedimentary and Volcanic Rocks 14 2.3.2 Metamorphic Rocks 23 2.3.3 Intrusive Rocks 23 2.4 TECTONIC HISTORY 25 2.5 STRUCTURAL GEOLOGY 28 2.6 EVOLUTION AND SIGNIFICANCE OF THE SKEENA ARCH 29 3. AGE AND DISTRIBUTION OF GRANITIC ROCKS 35 3.1 UPPER TRIASSIC AND JURASSIC GRANITIC ROCKS 39 3.1.1 Topley Intrusions 39 3.1.2 Omineca Intrusions 40 3.1.3 Francois Lake Intrusions 41 3.1.4 Kitsault Intrusions 42 3.2 TERTIARY AND OLDER COAST PLUTONIC COMPLEX 43 v i Page 3. AGE AND DISTRIBUTION OF GRANITIC ROCKS (continued) 3.3 UPPER CRETACEOUS AND TERTIARY INTRUSIONS 44 3.3.1 Upper Cretaceous 46 3.3.2 T e r t i a r y (Eocene) Intrusions 46 Goosly Lake Intrusions 46 A l i c e Arm Intrusions 47 Nanika Intrusions 48 Babine Intrusions 48 3.4 CHEMISTRY OF UPPER CRETACEOUS AND TERTIARY INTRUSIONS 49 3.4.1 Major and Trace Element Analyses 49 3.4.2 Metal Content 52 4. GEOLOGICAL RELATIONSHIPS AND GEOCHRONOLOGY OF PORPHYRY COPPER AND MOLYBDENUM DEPOSITS 54 4.1 PORPHYRY MOLYBDENUM DEPOSITS ASSOCIATED WITH THE ALICE ARM INTRUSIONS 54 4.1.1 Geologic Setting 54 4.1.2 Geology and Style of M i n e r a l i z a t i o n 56 4.1.3 Potassium-Argon Dating of the A l i c e Arm Porphyry Molybdenum Deposits 62 4.1.4 Summary 66 4.2 PORPHYRY COPPER-MOLYBDENUM DEPOSITS ASSOCIATED WITH THE BULKLEY INTRUSIONS 67 4.2.1 Geologic Setting 69 4.2.2 Geology and Style of M i n e r a l i z a t i o n 69 4.2.3 Potassium-Argon Dating of the Bulkley Intrusions 73 4.2.4 Summary 76 v i i Page GEOLOGICAL RELATIONSHIPS AND GEOCHRONOLOGY OF PORPHYRY COPPER AND MOLYBDENUM DEPOSITS (continued) 4.3 PORPHYRY COPPER-MOLYBDENUM DEPOSITS ASSOCIATED WITH THE NANIKA INTRUSIONS 77 4.3.1 Geologic Setting 77 4.3.2 Geology and Style of Mineralization 79 4.3.3 Potassium-argon Dating of the Nanika Intrusions 83 4.3.4 Summary 86 4.4 PORPHYRY COPPER DEPOSITS ASSOCIATED WITH THE BABINE INTRUSIONS 86 4.4.1 Geologic Setting 87 4.4.2 Geology and Style of Mineralization 88 4.4.3 Potassium-argon Dating of the Babine Intrusions 95 4.4.4 Summary 98 COMPARISON OF PORPHYRY DEPOSITS POTASSIUM-ARGON AGES TO OTHER AREAS AND THEIR TECTONIC EVOLUTION 100 5.1 INTRODUCTION 100 5.2 POTASSIUM-ARGON AGES OF PORPHYRY DEPOSITS IN NORTH AMERICA 100 5.2.1 British Columbia 101 5.2.2 Washington State 103 5.2.3 Southern Alaska 103 5.2.4 Yukon 104 5.2.5 Southern Basin and Range Province, U.S.A. 104 5.3 EVOLUTION OF PORPHYRY DEPOSITS OF WEST-CENTRAL BRITISH COLUMBIA 105 CONCLUSIONS - i m v i i i Page REFERENCES 114 APPENDIX A. POTASSIUM-ARGON METHOD 122 A.1 PROCEDURE 122 A.2 PRECISION AND ACCURACY 122 A.3 APPLICATION OF INITIAL ARGON AND POTASSIUM-ARGON ISOCHRON DIAGRAMS 123 A. 4 GEOLOGICAL TIME SCALE 124 APPENDIX B. CHEMISTRY OF INTRUSIVE ROCKS 129 B. 1 CHEMICAL ANALYSES OF INTRUSIVE ROCKS 129 B. 2 MAJOR AND TRACE ELEMENT ANALYSES OF BIOTITES 129 APPENDIX C. PORPHYRY COPPER AND/OR MOLYBDENUM DEPOSIT DESCRIPTIONS (INCLUDING POTASSIUM-ARGON SAMPLE LOCATIONS AND DESCRIPTIONS) 134 C. 1 ALICE ARM INTRUSIONS AND ASSOCIATED MOLYBDENUM DEPOSITS 134 C.1.1 B r i t i s h Columbia Molybdenum 134 C.1.2 B e l l Molybdenum 140 C.1.3 Ajax 146 C.1.4 Roundy Creek 152 C.1.5 Molly Mack 156 C.1.6 Nass River Molybdenum Deposits 158 C.1.7 Coast Plutonic Complex 163 C.1.8 Lamprophyre Dykes 166 C.1.9 Basalt Lava Flows 167 ix Page APPENDIX C. PORPHYRY COPPER AND/OR MOLYBDENUM DEPOSIT DESCRIPTIONS (INCLUDING POTASSIUM-ARGON SAMPLE LOCATIONS AND DESCRIPTIONS) (continued) C.2 BULKLEY INTRUSIONS AND ASSOCIATED COPPER AND MOLYBDENUM DEPOSITS 168 C.2.1 Glacier Gulch 168 C.2.2 Huber 171 C.2.3 Sunsets Creek 174 C.2.4 Rocher Deboule 176 C.2.5 Bear 177 C.2.6 Huckleberry 180 C.2.7 Ox Lake 184 C.2.8 Coles Creek 187 NANIKA INTRUSIONS AND ASSOCIATED MOLYBDENUM DEPOSITS COPPER AND 188 C.3.1 Mount Thomlinson 188 C.3.2 Big Onion 190 C.3.3 Lucky Ship 192 C.3.4 Goosly 195 C.3.5 Berg 197 C.3.6 Red Bird 202 C.3.7 Nadina Mountain 204 C.3.8 Goosly 204 C.3.9 Morice Lake 205 BABINE INTRUSIONS AND ASSOCIATED COPPER DEPOSITS 205 C.4.1 Granisle 205 C.4.2 Newman (Bell Copper) 215 X Page APPENDIX C. PORPHYRY COPPER AND/OR MOLYBDENUM DEPOSIT DESCRIPTIONS (INCLUDING POTASSIUM-ARGON SAMPLE LOCATIONS AND DESCRIPTIONS) (continued) C.4 BABINE INTRUSIONS AND ASSOCIATED COPPER DEPOSITS (continued) C .4.3 Morrison 220 C.4.4 Old Fort 223 C.4.5 T r a i l Peak 227 C.4.6 Newman Peninsula 232 C.4.7 Lennac Lake 233 C.4.8 Tachek Creek 235 x i LIST OF TABLES Page I. Table of Formations 15 II. Subdivision of Granitic Rocks 36 III. Potassium-argon Ages of Alice Arm Intrusions 63 IV. Potassium-argon Ages of Bulkley Intrusions 74 V. Potassium-argon Ages of Nanika Intrusions 84 VI. Potassium-argon Ages of Babine Intrusions 96 A.1 Geological Time Scale 125 A. 2 Potassium-argon Analytical Data 126 B. 1 Chemical Analyses of Intrusive Rocks 130 B.2 Major and Trace Element Analyses of Biotites 132 x i i LIST OF FIGURES Page 1 Location of Area 3 2 Access 4 3 Porphyry Deposits, West-central B r i t i s h Columbia 6 4 Porphyry Deposits Studied, West-central B r i t i s h Columbia i n pocket 5 Ideal Porphyry Deposit f o r K-Ar Dating 8 6 Major Physiographic Subdivisions, West-central B r i t i s h Columbia 11 7 Generalized Tectonic Map 12 8 General Geology i n pocket 9 Major Tectonic Elements 26 10 J u r a s s i c Rocks, West-central B r i t i s h Columbia 31 11 Cretaceous Rocks, West-central B r i t i s h Columbia 32 12 Upper Cretaceous-Tertiary Intrusions 33 13 G r a n i t i c Rocks 37 14 Age and D i s t r i b u t i o n of G r a n i t i c Rocks dcn=poeteet L°>c 3 15 K-Ar Age Determinations, West-central B r i t i s h Columbia 38 16 Age and D i s t r i b u t i o n of Upper Cretaceous and T e r t i a r y Intrusions 45 17 a & b D i s t r i b u t i o n of Normative Quartz, P l a g i o c l a s e , and Orthoclase i n Chemically Analysed Samples 50 18 a & b Major and Trace Elements i n B i o t i t e s 51 19 A l i c e Arm-Nass River Area i n pocket 20 Molybdenum Deposits, A l i c e Arm 57 21 Molybdenum Deposits, Nass River Area 58 22 Bulkley Intrusions 68 x i i i LIST OF FIGURES (continued) Page 23 Bulkley Intrusions - Copper-molybdenum Deposits 71 24 Nanika Intrusions 78 25 Nanika Intrusions - Copper-molybdenum Deposits 80 26 Porphyry Copper Deposits, Babine Lake Area i n pocket 27 Babine Intrusions - Copper Deposits 90 28 Late Cretaceous-Early Tertiary Porphyry Deposits, British Columbia 102 C.1 British Columbia Molybdenum 135 C.2 Bell Molybdenum 141 C.3 Ajax 148 C.4 Roundy Creek 153 C.5 Nass River Molybdenum Deposits 159 C.6 Glacier Gulch 169 C.7 Huber 172 C.8 Sunsets Creek 175 C.9 Bear 178 C.10 Huckleberry 181 C.11 Ox Lake 185 C.12 Mount Thomlinson 189 C.13 Big Onion 191 C.14 Lucky Ship 193 C.15 Goosly 196 C.16 Berg and Red Bird 198 C.17 Granisle 207 x i v LIST OF FIGURES (continued) Page C.18 Newman 216 C.19 Morrison 222 C.20 Old Fort 224 C.21 T r a i l Peak 229 1. 1. INTRODUCTION 1.1 SCOPE OF STUDY This study of porphyry-type copper and molybdenum deposits i n west-central British Columbia was initiated i n 1967 to establish, by the potassium-argon method, the age of intrusion and mineralization. An integral part of the pro-ject i s a comparative geological study of these deposits plus an analysis of their regional distribution relative to the geological and tectonic framework of the area. The area was selected for several reasons. F i r s t , the author had obtained first-hand knowledge of both molybdenum deposits i n the Alice Arm area and the porphyry copper deposits of the Babine Lake area, while conducting geological studies for the British Columbia Department of Mines and Petroleum Resources. Second, other deposits with similar characteristics were known throughout west-central British Columbia, and the area appeared to comprise a metallogenic province. Further, the study i s a continuation of previous investigations into the age of mineral deposits of British Columbia initiated by the late Dr. W. H. White. Prior to the inception of this study, only one porphyry deposit i n the area had been dated by isotopic methods. Two samples from the British Columbia Molybdenum deposit at Alice Arm indicated an apparent Eocene age of intrusion and mineralization (Woodcock, et a l . , 1966). Elsewhere i n British Columbia, studies by White and others (White, et a l . , 1967; Sinclair and White, 1968) indicated a Late Triassic age for porphyry deposits, and thus i t was apparent that at least several deposits i n the central part of Br i t i s h Columbia represented a younger age. 2. Geological studies and sampling of porphyry deposits i n west-central British Columbia (Figure 1), which began i n the 1967 f i e l d season, were sponsored by the British Columbia Department of Mines and Petroleum Resources. Deposits sampled during that year included copper deposits i n the Babine Lake area, copper and molybdenum deposits i n the Hazelton-Smithers and Morice-Tahtsa Lake areas, and molybdenum deposits i n the Alice Arm-Nass River area. At deposits where the author had no first-hand knowledge, several days were spent studying geological relationships and style of mineralization before samples were collected. In addition to those collected by the author, a number of samples were provided by staff geologists of the British Columbia Department of Mines and Petroleum Resources and by mining exploration company personnel. Additional samples were collected i n 1968, 1969, and 1970. Samples were analysed at the geochronology laboratory operated jointly by the Department of Geological Sciences and Department of Geophysics, University of British Columbia. A total of 70 potassium-argon ages were obtained from samples collected at or near 27 porphyry deposits. 1.2 LOCATION OF AREA West-central British Columbia, for purposes of this study, i s situated between latitudes 53 degrees and 56 degrees north and longitudes 124 degrees and 130 degrees west, as indicated on Figure 1. The town of Smithers i s near the geographic centre of this area. Access within the area i s reasonbly good (Figure 2). Northern Trans-Provincial Highway 16 crosses the area i n an east-west direction and i s paralleled by the Canadian National Railway line linking Jasper, Alberta, and Prince Rupert. 5. Access to the north and south i s provided by numerous secondary roads. Heli-copter and/or fixed-wing aircraft transportation i s necessary to reach the more remote parts of the area. A new extension of the British Columbia Railway extends northwesterly from Fort St. James along the eastern shore of Takla Lake. 1.3 PORPHYRY MINERAL DEPOSITS STUDIED Most of the known porphyry-type copper and molybdenum deposits i n west-central British Columbia are indicated on Figure 3. Porphyry deposits i n the area exhibit features that conform to those outlined i n the definition of porphyry deposits by Lowell and Guilbert (1970) and Sutherland Brown, et a l . (1971). The deposits are intimately associated with small (1 kilometre diameter or less) porphyritic, f e l s i c to intermediate intrusions which cut Mesozoic volcanic and sedimentary rocks. Extrusive equivalents of the porphyry intrusions have been recognized i n several areas. Copper and molybdenum sulphides occur as fracture f i l l i n g s and i n veinlet stockworks both within and adjacent to the intrusive bodies. Sulphide and alteration minerals exhibit concentric zoning relative to the host intrusion at many of the deposits. Unaltered primary and secondary biotite and lesser amounts of hornblende are common constituents of most deposits, rendering these minerals particularly useful for potassium-argon studies. Porphyry deposits of this study are shown on Figure 4 (pocket). Only two of these deposits, both of which are at Babine Lake, are currently being mined. Granisle Copper Limited i s i n production at a daily milling rate of 14,000 tons and the Newman mine of Noranda Mines, Limited, Bell Copper Division, i s milling ftk-fi \ PRINCE ~ a WEST—CENTRAL BRITISH COLUMBIA FIG. 3 PORPHYRY DEPOSITS • Mo Deposits • C o - M o Deposits . © Cu Deposits 30 60 H MILES • • HAZELTON " © SMITHER*9\2. ON 7 . 10,000 tons per day. Both mines have reserves i n excess of 50 million tons of grades exceeding 0.5 per cent copper. Br i t i s h Columbia Molybdenum mine at Alice Arm suspended operations i n mid-1972 due i n part to depressed molybdenum markets. The mine produced for nearly five years at a daily rate of 7,000 tons of rock grading close to 0.20 per cent M 0 S 2 . Other deposits, shown on Figure 4 and considered as potential producers, include: the Morrison deposit at Babine Lake; and the Berg and Huckleberry deposits near Tahtsa Lake. 1.4 SAMPLING METHODS FOR POTASSIUM-ARGON STUDIES The primary objective of this study was to determine the age of intrusion and the age of mineralization i n each porphyry deposit by the potassium-argon method. Figure 5, a generalized sketch incorporating features common to many of the deposits, il l u s t r a t e s an ideal deposit for potassium-argon dating. In this ideal case, the following samples would be collected and analysed: (1) A sample of mineralized porphyry intrusion, usually containing both primary and secondary biotite, to establish the age of mineralization. (2) A sample of primary biotite from the intrusive rock outside the mineralized zone and away from the area of hydrothermal alteration, i f possible, to determine the age of intrusion. Failing this, a whole-rock sample of biotite hornfels, a product of thermal meta-E X T R U S I V E E Q U I V A L E N T O F P O R P H Y R Y O U T E R L I M I T O F B I O T I T E H O R N F E L S N Q T Z - S U L P H I D E B I O T I T E V E I N L A T E O R P O S T M I N E R A L P O R P H Y R Y I N T R U S I O N S ( D K ) K - A R S A M P L E S I T E S FIG. 5 1/2 M I L E S IDEAL PORPHYRY DEPOSIT FOR K-AR DATING 9. moronism related to the intrusion, would be collected to give the same result. (3) Samples of extrusive equivalents of porphyry intrusions to deter-mine the age of intrusion and/or extrusion. Such extrusive equivalents have been recognized i n the Babine Lake area. (4) Samples of biotite from quartz-sulphide veins, collected from a few deposits, to yield the age of mineralization. Such a sample can be used to corroborate results obtained by the f i r s t sample type. (5) Samples of inter- and post-mineral porphyry dykes and intrusive breccias; petrologically similar to the main mineralized porphyry phase, to more closely define an upper age limit for intrusive and hydrothermal activity. Other samples that might be collected include basic dykes which are common in the molybdenum deposits of the Alice Arm area. Analyses of mineral separates or whole-rock samples from the dykes date the last igneous event at these deposits. Samples of nearby non-mineralized intrusive bodies, which apparently are unrelated to mineralization, were collected wherever possible. 10. 2. GENERAL GEOLOGY OF WEST-CENTRAL BRITISH COLUMBIA 2.1 PHYSIOGRAPHY The major physiographic subdivisions of west-central B r i t i s h Columbia are shown on Figure 6. Most of the porphyry deposits included in this study are situated within the Interior Plateau, the Hazelton Mountains, and along the eastern flanks of the Coast Mountains. Much of the area on Figure 6 i s occupied by the Nechako Plateau, the northernmost subdivision of the Interior Plateau. This area i s one of low r e l i e f , dominated by flat or gently r o l l i n g topography (Holland, 1964). Glacial d r i f t obscures much of the bedrock and ubiquitous glacial features include glacial grooving and drumlin-like ridges, numerous lakes, eskers, and dry melt-water channels. The northern and western boundaries of the Nechako Plateau are f a i r l y sharply defined by mountainous areas, which include the Omineca, Skeena, and Hazelton Mountains. Omineca Mountains consist of both rounded and serrated peaks i n excess of 6 ,000 feet which are separated by broad, d r i f t - f i l l e d valleys. Skeena Mountains feature jagged peaks, products of alpine glaciation, and are divided into ranges by northwest-trending valleys. Hazelton Mountains comprise a number of mountain ranges separated by prominent river valleys. Nass Basin, situated north of the Hazelton Mountains, i s an area of low r e l i e f entirely encircled by mountains which r i s e abruptly from the basin floor dotted with numerous lakes of glacial origin. Coast Mountains are underlain predominantly by granitic rocks. Within the area shown on Figure 6 , they include the Boundary and Kitimat Ranges which are i 13. separated by the Nass River valley. The ranges comprise rounded granitic peaks and serrated peaks underlain by sedimentary and volcanic rocks. Prominent U-shaped and hanging valleys are common as are extensive icefields. Steep topography i s a dominant feature. 2.2 REGIONAL TECTONIC SETTING The major tectonic features of west-central British Columbia are shown on Figure 7 (modified after Sutherland Brown, et a l , 1971). Most porphyry copper and molybdenum deposits of this area l i e within the Intermontane Belt which i s bounded on the east by predominantly metamorphic rocks of the Omineca Belt and on the west by granitic and lesser metamorphic rocks of the Coast Crystalline Belt. The Intermontane Belt i s underlain principally by Mesozoic volcanic and sedimentary rocks. Skeena Arch, a prominent transverse structure during Early Mesozoic time, marks the approximate boundary between the Bowser successor basin to the north and a broad area to the southeast covered by a veneer of Early to Late Tertiary volcanic rocks. Granitic intrusions of Late Cretaceous and Early Tertiary age, with which the porphyry copper and molybdenum deposits are associated, intrude Mesozoic volcanic and sedimentary rocks throughout the Intermontane Belt. 2.3 GENERAL GEOLOGY The regional geology of west-central British Columbia i s illustrated on Figure 8 (pocket) and i s based mainly on compilation maps prepared by the British Columbia Department of Mines and Petroleum Resources (Carter and Kirkham, 1969; 14. Carter and Grove, 1972), and on work directly related to this study. Additional information was obtained from previous and current work by geologists of the Bri t i s h Columbia Department of Mines and Petroleum Resources and the Geological Survey of Canada, references to which are included i n the following outline and in the bibliography. The following outline follows the divisions as lis t e d on the legend for Figure 8 and i n the Table of Formations (Table 1). 2.3.1 Sedimentary and Volcanic Rocks Sedimentary and volcanic rocks occupy much of the central and eastern parts of the area illustrated on Figure 8 and comprise units ranging i n age from Permian to Recent. Permian - Cache Creek Group Cache Creek Group rocks of Late Paleozoic (mainly Permian) age are con-fined to the eastern margins of the area shown on Figure 8. The group i s characterized by limestones and ribbon cherts with subordinate interbedded andesite flows and fragmental rocks (Armstrong, 1949). Rocks of the Cache Creek Group are tightly folded about northwest-trending axes, and are mainly i n fault contact with younger rocks. Triassic - Takla Group Takla Group rocks, predominantly of Late Triassic age, are most wide-spread near the east and west boundaries of the area. In the type area east of Takla Lake, andesitic and basaltic flows predominate and are accompanied by lesser amounts of clastic volcanic and sedimentary rocks (Armstrong, 1949). 15. TABLE 1 TABLE OF FORMATIONS SEDIMENTARY AND VOLCANIC ROCKS ERA PERIOD EPOCH FORMATION LITHOLOGY C e n o z o l c ! ; ^ P l e i s t o c e n e and ! Q u a t e r n a r y Recent B a s a l t f l o w s and c i n d e r c o n e s . T e r t i a r y Eocene and Miocene Endako C roup , Goo s l y Lake and Buck C reek v o l c a n i c r o c k s B a s a l t and a n d e s i t e f l ows and b r e c c i a s , some r h y o l i t e and d a c l t e . U n c o n f o r m i t y Me so i o Ic and C e n o z o l c C r e t a c e o u s j Upper C r e t a c e o u s and T e r t i a r y and Pa l eocene L .: Oot sa Lake C r o u p , T i p Top H i l l v o l c a n i c cocks Sua tu t Croup B a s a l t , a n d e s I t e , d a c l t e and r e l a t e d t u f f s and b r e c c i a s , some r h y o l i t e f l ows and b r e c c i a s . Sands tone, c o n g l o m e r a t e , s h a l e . U n c o n f o r m i t y i ' Lower C r e t a c e o u s _ _ C r e t a c e o u s Skeena C roup , B r i a n Boru and Red Rose format Ions S i I t s t o n e , s a n d s t o n e , ahaIc, p o r p h y r l c i c andes I te f l o w s , b r e c c i a s and t u f f s . U n c o n f o r m i t y J u r a s s i c and C r e t a c e o u s Upper J u r a s s i c and Lower C r e t a c e o u s L o c a l U n c o n f o r m i t y H a z e l t o n Croup ( i n p a r t ) S l l t s t o n e , g reywacke , s a n d s t o n e , c o n g l o m e r a t e , a r g l l l l t e , m inor l i m e s t o n e and c o a l . J u r a s s i c M i d d l e J u r a s s i c H a z e l t o n Croup A n d e s i t e , b a s a l t , d a c l t e t u f f s and b r e c c i a s , v o l c a n i c sandstone and c o n g l o m e r a t e , s l l t s t o n e , and greywacke. U n c o n f o r m i t y Lower J u r a s s i c H a z e l t o n Croup G r e e n , r e d , and p u r p l e a n d e s i t e and b a s a l t t u f f s and b r e c c i a s , v o l c a n i c s and s tone and c o n g l o m e r a t e , a r g l l l l t e and greywacke. 16. TABLE 1 ( C o n t ' d . ) ERA PERIOD EPOCH FORMATION LITHOLOGY Mesotolc L o c a l U n c o n f o r m i t y T r l a a s l c Upper T r l a a s l c T a k l a Croup ( I n p a r t ) U n c o n f o r m i t y P a l e o z o i c Permian and ol d e r ? Cache C r e e k C r o u p M a f i c v o l c a n i c r o c k s , v o l c a n i c s a n d s t o n e , a r g l l l l t e , l i m e s t o n e , c h e r t , some a c i d m e t a v o l c a n l c r o c k s , c h l o r i t e , s e r l c l t e , and b i o t l t e s c h i s t s . A n d e s l t e f l o w s and b r e c c i a s , c h e r t . 1imeatone, q u a r t z t t c , c h l o r i t e and hornblende s c h i s t s . METAMORPHIC ROCKS P a l e o z o i c Gneiss Complex-almandlne, a m p h l b o l l t e , f a d e s , g n e i s s e s , and r e l a t e d mlgmatite g n e i s s , greenstone, a m p h l b o l l t e , and s c h i s t . 17. TABLE 1 (Cont'd.) INTRUSIVE ROCKS ERA PERIOD EPOCH FORMATION LITHOLOCT O l i g o c e n e Lamprophyre dyke swarms. P o r t l a n d C a n a l dyke swarma G r a n i t i c r o c k s . G o o s l y Lake i n t r u s i o n s Cabbro s y e n o m o n z o n l t e . C e n o z o l c T e r t i a r y Eocene A l i c e Arm i n t r u s i o n s Nan ilea l n t rus ions Qua r t z monzon i t e and g r a n i t e p o r p h y r y . Qua r t z m o n z o n i t e , p o r p h y r y , f e l d s p a r po rphy ry and f e l s l t e . Bab ine i n t r u s i o n s Quar tz d i o r i t e and g r a n o d l o r l t e p o r p h y r y . C e n o z o l c and Mesozo i c (?) T e r t i a r y and o l d e r (?) | Coa s t P l u t o n i c j Complex C r a n l t l c r o c k s , q u a r t z d i o r i t e , g r a n o d l o r l t e , q u a r t z m o n z o n i t e , l o c a l l y f o l i a t e d a n d / o r g n e i s s l c . C r e t a c e o u s Upper . C r e t a c e o u s ; B u l k l e y I n t r u s i o n s P o r p h y r i t i c q u a r t z monzon i te and g r a n o d l o r l t e . J u r a s s i c and C r e t a c e o u s • t i t s a u l t * I n t r u s i o n s F e l d s p a r , p o r p h y r y , a u g l t e p o r p h y r y , h o r n b l e n d e , d i o r i t e . Mesozo i c ! ' Upper J u r a s s i c F r a n c o i s Lake l n t r u s I o n s P o r p h y r i t i c q u a r t z m o n z o n i t e ; g r a n o d l o r l t e , and q u a r t z d i o r i t e . J u r a s s i c i L o v e r and | M idd le J u r a s s i c ! Omineca j i n t r u s i o n s | G r a n o d l o r l t e , q u a r t z d i o r i t e , s y e n i t e , g abbro , -i m o n z o n i t e , and d i o r i t e . ' T r i a s s i c and J u r a s s i c . ,, Upper j T r i a s s i c - -Lower j J u r a s s i c T o p l e y } i n t r u s i o n s { Qua r t z m o n z o n i t e , j g r a n o d l o r l t e , and q u a r t z d i o r i t e , and p o r p h y r i t i c v a r i e t i e s . P a l e o z o i c INTRUSIVE CONTACT Permian T r e m b l e u r l n t r u s ions U l t r a m a f l c r o c k s . 18. Along the west shore of Babine Lake, rocks regarded as Takla age (Tipper, 1971) comprise a succession of maroon fragmental volcanic rocks and interbedded white to grey crystalline limestone and calcareous and graphitic black shales. Chlorite and sericite schists are also included i n this sequence (Carter, 1973), but these may be i n part Cache Creek Group equivalent. In the Terrace area, rocks designated as part of the Takla Group (Figure 8) include some older rocks, perhaps of Permian age. These are comprised of fair thicknesses of white crystalline limestone underlain by mafic volcanic rocks. Metavolcanic rocks, which occur on the north side of the Skeena River, are considered as part of the Takla Group. Takla Group rocks i n the eastern part of the area are in fault contact with older Cache Creek rocks. In the Babine Lake area they are overlain with angular unconformity by Jurassic age rocks. Jurassic - Hazelton Group Volcanic and sedimentary rocks of Jurassic age, comprising the Hazelton Group, underlie much of west-central Br i t i s h Columbia. Recent work by Tipper (1971), Richards (1973, 1974), and Grove (1971) defines the Hazelton Group as a nearly continuous sequence ranging i n age from Early to Late Jurassic. The Hazelton Group consists of volcanic flows and fragmental rocks as well as sedimentary rocks derived from older volcanic terranes and the reworking of contemporary volcanic material. Lower Jurassic Lower Jurassic rocks occur mainly in the central part of the map-area and consist principally of submarine and subaerial andesite and basalt flows and fragmental rocks with some intercalated clastic and sedimentary rocks. In the 19. Portland Canal area, Lower Jurassic rocks include epiclastic volcanic conglom-erates and sandstones plus andesite flows and pillow lavas. Products of dynamic metamorphism, cataclasites, are also included i n this unit. Lower Jurassic rocks overlie Triassic and older rocks disconformably to unconformably. Middle Jurassic Middle Jurassic rocks of the Hazelton Group are distributed throughout the map-area and comprise a mainly marine sequence of tuffs, volcanic breccias, shales, and greywackes. The rocks are notably fossiliferous i n a number of l o c a l i t i e s . The Middle Jurassic sequence exhibits both conformable and unconformable contact relationships with older rocks. In parts of the Smithers map-area, they have been thrust over Lower Jurassic rocks (Tipper, 1971). Upper Jurassic - Lower Cretaceous Upper Jurassic and Lower Cretaceous rocks comprise a marine to continental sedimentary sequence which i s restricted to the northern half of the map-area, mainly within the Bowser successor basin. The lower part of this succession includes the upper unit of the Hazelton Group which consists of well-bedded siltstone, greywacke, a r g i l l i t e , sandstone, conglomerate, and minor limestone and coal. The upper part of the sequence i s a dominantly continental sedi-mentary sequence. The Upper Jurassic - Lower Cretaceous succession features conformable contacts with Middle Jurassic rocks i n the western part of the area and rests with angular unconformity on older rocks i n the central part of the area. 20. Cretaceous Lower Cretaceous Lower Cretaceous rocks were f i r s t recognized i n west-central Br i t i s h Columbia during the course of mapping by Sutherland Brown (1960) i n the Hazelton area. These rocks include the Red Rose Formation, a marine sediment-ary sequence, which Is overlain conformably by the Brian Boru Formation, a volcanic unit consisting primarily of porphyritic andesite flows. Recent work i n the Smithers and Hazelton map-areas by Tipper (1971) and by Richards (1973) indicates that similar rocks, now known to be of Albian (Early to Middle Cretaceous) age, are more widespread than previously recognized. Further mapping probably w i l l show that these rocks occupy a larger area of the Bowser Basin than indicated on Figure 8. This sequence of Lower Cretaceous rocks, informally called the Skeena Group, consists of black marine shales overlain by, and i n part interbedded with, volcanic tuffs and breccias. North of Babine Lake, a slightly younger continental sequence of sedimentary rocks has been mapped by Richards (1973). Lower Cretaceous rocks overlie older rocks with angular discordance or are in fault contact with them. Cretaceous and Tertiary Upper Cretaceous - Paleocene Rocks of this age include continental sedimentary and volcanic rocks which are widespread i n the central part of the area shown on Figure 8. The Sustut Group, which consists of a continental cl a s t i c sequence of sandstone, conglomerate, shale, and mudstone, i s restricted to the central part 21. of the map-area, principally i n the Babine and Takla Lake areas. These rocks occur mainly i n northwest-trending fault-bounded basins. Sedimentary rocks of similar age were noted on Nadina Mountain by Lang (1940). The Ootsa Lake Group i s a dominantly volcanic sequence which occurs mainly in the eastern half of the map-area where i t covers extensive areas south of Francois and Ootsa Lakes (Tipper, 1963; Duffel, 1959). The group includes rhyolite, dacite, andesite, and basalt flows as well as fragmental rocks and some sedimentary rocks. Recent work by Church (1973) has disclosed the presence of these rocks in an area east of Morice Lake. Whole-rock potassium-argon ages indicate a Late Cretaceous age (76 m.y.) for both Tip Top H i l l volcanic rocks of andesite and dacite composition, and for rhyolite flows and related quartz porphyry intrusions i n the same area. Similar acid volcanic rocks and intrusive equivalents have been recognized i n the Babine Lake area (Carter, 1973; Richards, 1973). Rocks of the Ootsa Lake Group feature moderate dips and l i e with angular discordance on older Mesozoic rocks. Tertiary Eocene - Miocene Rocks of Early to Middle Tertiary age include extensive areas of f l a t -lying to gently dipping andesitic to basaltic flows and pyroclastic rocks i n the east-central part of the map-area. Armstrong (1949) referred to these rocks as the Endako Group, which he believed to be of Oligocene or younger age. Recent mapping and whole-rock 22. potassium-argon dating by Church (1973) in the Buck Creek area south of Houston has shown the bulk of these rocks to be of Eocene age, corroborating earlier work by Mathews (1964). A two-fold division of this unit, separated by an angular discordance, has been recognized by Tipper (1971) and Church (1973). Many of the rocks mapped as Ootsa Lake Group south of Francois Lake also could be of this age. Small, fl a t - l y i n g olivine basalt outliers of definite Miocene age have been identified by Church (1973) i n the Buck Creek area. Quaternary Pleistocene and Recent Basaltic rocks of Quaternary age have been noted only i n the northwest part of the map-area, i n the Nass River-Alice Arm area. Basalt outliers, ranging i n thickness from tens to hundreds of feet, are best known in the Alice Arm area, where two whole-rock samples collected by the author indicated an age range of 0.29 + 0.5 m.y. to 1.1 + 0.8 m.y. The basalt outliers exhibit an east-northeast distribution from south of Alice Arm to the big bend of the Nass River, reflecting one of the dominant structural trends of the area. Similar remnants of Pleistocene volcanic activity have been noted i n the Nass River area, but the dominant young volcanic feature of this area i s the Recent Aiyansh lava flow which erupted from a vent area some 14 miles south of the prominent lava plain bordering the Nass River. This flow and associated cinder cones represent one of the youngest volcanic features i n British Columbia, yielding a 1/*C age of 220 + 130 years (Sutherland Brown, 1969). 23. 2.3.2 Metamorphic Rocks Metamorphic rocks are restricted to the core and eastern flank of the Coast Plutonic Complex near the west boundary of the area. Paleozoic - Gneiss Complex Gneissic rocks, probably the oldest rocks i n the map-area, are within and marginal to the Coast Plutonic Complex near the western boundary of the area. In the Prince Rupert map-area, high-grade gneisses and migmatites are referred to by Hutchison (1967) as Late Paleozoic age or older. The gneiss complexes have indistinct boundaries and grade into homogeneous plutonic rocks. A tentative pre-Permian age has been assigned to these rocks by Hutchison (1967) because they apparently are older than relatively non-metamorphosed Permian rocks i n the Terrace area. Similar gneissic rocks to the southeast apparently underlie metamrophic rocks containing fossils of Permian age. 2.3.3 Intrusive Rocks Mesozoic volcanic and sedimentary rocks of west-central British Columbia have been intruded by plutonic and hypabyssal rocks of variable composition and age. A brief description of these rocks i s included here, but a more detailed description of the age and distribution of the granitic rocks, an integral part of this study, w i l l be contained i n the following chapter. Permian and/or Triassic Intrusions Trembleur ultramafic intrusions, the oldest intrusive rocks recognized in the map-area, are confined to the eastern part of the area where they cut Permian and older rocks of the Cache Creek Group. The intrusions take the 24. form of s i l l s , stocks, and small batholiths of peridotite, dunite, pyroxenite, and minor gabbro and their serpentinized equivalents. Triassic and Jurassic Intrusions Granitic rocks of Late Triassic to Late Jurassic age include the Topley, Omineca, and Francois Lake intrusions. These intrusions occur as stocks and batholiths in the central and eastern parts of the area (Figure 8) where they cut volcanic and sedimentary rocks of similar age. Kitsault intrusions, consisting of stocks and irregular intrusions of feldspar porphyry, augite porphyry, and hornblende diorite, occur north of Alice Arm and appear to represent volcanic centres of part of the Hazelton Group. Cretaceous Bulkley intrusions of Late Cretaceous age occur as a northerly trending belt of stocks and small batholiths extending through the central part of the map-area. Tertiary Intrusive rocks of Tertiary age include a wide variety of large and small intrusive bodies. The Coast Plutonic Complex, bordering the area on the west (Figure 8), constitutes the most extensive area of Tertiary plutonic rocks, although older granitic rocks are also included i n the complex. Numerous small plugs, stocks, and dykes of Eocene age occur along the eastern margin of the Coast Plutonic Complex and throughout the central part of the area. 25. The Portland Canal dyke swarm, situated northeast of the head of Portland Canal, includes an extensive area of hundreds of granitic s i l l s and dykes related to the Coast Plutonic Complex (Grove, 1971). Lamprophyre dyke swarms with northeast trends are prominent i n the Portland Canal and Alice Arm dis t r i c t s (Carter and Grove, 1972) and i n neigh-bouring southeast Alaska (Smith, 1973), where they commonly transect the numerous vein-type mineral deposits of these areas. Two samples collected for potassium-argon analysis i n the Alice Arm area yielded ages of 34.4 +1-5 m.y. and 36.5 + 1.2 m.y. 2.4 TECTONIC HISTORY The major tectonic elements of west-central British Columbia are shown on Figure 9 (modified after Wheeler, et a l . , 1972). The northwest trend of the area i s defined by troughs and basins of Mesozoic and younger layered rocks which are separated by geanticlinal areas of similar trend. The major part of the area i s occupied by the Nechako Trough and Bowser Basin which are bounded on the east by the Pinchi geanticline and on the west by the Coast geanticline. Significant thicknesses of carbonate rocks i n Permian strata indicate stable shelf conditions i n the eastern part of the map-area during that time. In the western part of the area, the Coast geanticline was i n part an uplifted area by Permian time, as indicated by the gneiss complexes in this area, which are believed to be products of regional metamorphism which occurred i n pre-Permian time. t o ON 27. Orogenic activity i n Mid-Triassic time culminated i n u p l i f t and estab-lished the main tectonic elements including the Coast and embryonic Pinchi geanticlines, the Nechako and Quesnel Troughs, and marked the beginning of an eugeosynclinal regime. Late Triassic and Early Jurassic was a time of wide-spread volcanism and related sedimentation i n numerous basins throughout the area. This period of tectonic activity also included the emplacement and unroofing of the Topley and Omlneca intrusions and the total emergence of the Pinchi geanticline. During Early and Mid-Jurassic time, u p l i f t along the northeast-trending Skeena Arch separated the Nechako Trough from the Bowser Basin, i n which a thick succession of marine c l a s t i c sedimentary and volcanic rocks accumulated from Mid-Jurassic to Early Cretaceous time. Intrusion of the Francois Lake granitic rocks also took place during this time. In the Early Cretaceous, upl i f t occurred along the Coast geanticline and continental clastic rocks accumulated i n marginal parts of the Bowser Basin i n Mid-Cretaceous time. Uplift, faulting, and intrusion occurred i n Late Cretaceous and Early Tertiary time, principally along the Coast geanticline and i n the central part of the area where high-level subvolcanic granitic plutons were emplaced and extensive sheets of rhyolitic to basaltic lavas were extruded. Continental clastic sedimentary rocks, represented by the Sustut Group, were deposited i n fault-bounded basins i n the central part of the area. Pleistocene and younger volcanic rocks were erupted along northerly and northeasterly trending fault zones which developed late i n Tertiary time i n the western part of the area. 28. 2.5 STRUCTURAL GEOLOGY Structural features i n west-central British Columbia are related to several recognizable episodes of tectonic activity. Within the western gneiss complexes, tight, overturned, and recumbent folds trend east-northeast and northwesterly. In Mesozoic rocks marginal to the Coast Plutonic Complex, folds (simple to complex) were developed by repeated u p l i f t and plutonism principally from Early Jurassic through Tertiary time. Broad, open folds predominate, except adjacent to the Coast intrusions and s a t e l l i t i c intrusive bodies, where overturned and i s o c l i n a l folds and thrust faulting occur i n sedimentary rocks. Faults i n the western part of the area trend northerly, northeasterly, and northwesterly. Many basic dykes follow northeast faults and fracture zones and are offset by later northwesterly faults. The trend of major fiords, Portland Canal and Observatory Inlet, probably owe their trend to basement structures. The structure i n the central part of the area displays only slight deformation of the Mesozoic rocks represented mainly by broad, open folds. Thrust faults and related folds are common along the west side of the Babine Range and north of Smithers where a Lower Jurassic sequence i s thrust over Middle Jurassic rocks (Figure 8). The most persistent structures of the area are closely spaced block faults. Although important northeast-striking block faults exist, the dominant trend i s northwest, as exemplified by major faults parallel to the Bulkley River and along the east side of the Babine Range. Northwest-trending horst and graben structures are prominent i n the Babine Lake area. In the eastern part of the area, Mesozoic volcanic and sedimentary rocks display northwest fold trends. Upper Paleozoic Cache Creek Group rocks are 29. closely folded i n a northwest direction. Two faults of regional magnitude dominate the structure of the area. The Pinchi fault zone extends northwesterly through the area, marking the contact between the Cache Creek Group and plutonic rocks of the Hogem batholith. Movement has involved older Cache Creek rocks moving up relative to those on , the east side of the fault, either by thrusting or reverse movement. Truncating the Pinchi fault north of the map-area i s the north-trending Takla fault along which rocks on the west side moved down relative to those on the east side. 2.6 EVOLUTION AND SIGNIFICANCE OF THE SKEENA ARCH The Skeena Arch i s a transverse tectonic feature which segmented the Intermontane Tectonic Belt i n west-central British Columbia during Mesozoic time (Figure 9). The Skeena Arch was f i r s t recognized (White, 1959) as a salient i n fold trends which parallel the northwest Cordilleran trend. This salient i s coincident with northeast-trending apophyses of granitic rock along the eastern margin of the Coast Crystalline Belt near Terrace. Lack of geologic mapping north of latitude 56 degrees i n 1959 also suggested a concentration of small stocks and batholiths i n a northeast zone between the Coast Plutonic Complex and the Pinchi geanticline. The greatest number of the smaller intrusions appeared to be contained i n the axial region of the salient or arch, and suggested that this zone effected some control over the emplacement of the plutons. Recent geological mapping of the Mesozoic volcanic and sedimentary rocks and potassium-argon dating of many of the intrusions i n west-central British 30. Columbia has further defined the position and relative tectonic importance of the Skeena Arch. As now defined, the axis of the Skeena Arch i s south of that originally proposed and corresponds with a curved line projected northeasterly from the Coast geanticline north of Morice Lake, through the central part of Babine Lake to the Pinchi geanticline (Figure 10). This line i s roughly coincident with the projection of a major magnetic discontinuity extending southeasterly from the Great Slave Lake fault (Morley, et a l . , 1967). Assuming that this part of the Intermontaine Belt i s underlain by Precambrian basement, reactivation of this ancient zone of weakness i n Early Mesozoic time may have played a role i n the development of the Skeena Arch. The Skeena Arch was a positive tectonic feature throughout Jurassic time. Shoreline facies have been recognized in intravolcanic sedimentary rocks of Middle Jurassic age which flank the arch on the north and south (Tipper, 1971,, personal communication). The Lower Jurassic rocks, which occupy much of the axial region of the arch, are mainly products of subaerial volcanism. Rocks of Late Triassic and older age and gneissic rocks east of Babine Lake along the projection of the arch lend further proof that this represents a zone of u p l i f t in which older rocks were preserved. A northeast-trending belt of Upper Triassic Lower Jurassic granitic plutons , probably the roots of Triassic and Jurassic volcanoes, also coincides with the axial region of the arch (Figure 10). The restriction of Upper Jurassic sedimentary rocks to the north side of the arch indicates that i t remained an uplifted area u n t i l at least the close of Jurassic time. In Early Cretaceous time, the Skeena Arch was cut by north-northeast-and northwest-trending block faults. Clastic sedimentary rocks of Early to Late Cretaceous age are preserved i n fault-bounded basins near the axial region of WEST-CENTRAL BRITISH COLUMBIA FIG. 10 JURASSIC ] Upper Jurassic Sed. Rocks ==] M i d d l e Jurassic Vol. & Sed. Rocks Lower Jurassic Vol. Rocks Upper Triassic & Older Rocks Upper Triassic — Lower Jurassic Granite 0 30 60 MILES <0 \ Euliuk Lake 34. the arch (Figure 11). Many of these faults localized the intrusion of numerous granitic plugs and stocks i n Late Cretaceous and Early Tertiary time (Figure 12). In summary, the Skeena Arch was a dominant tectonic feature in central British Columbia only during Jurassic time when, as a positive feature, i t governed the distribution of volcanic and sedimentary rocks and provided one of the controls for the emplacement of Upper Triassic and Lower Jurassic granitic plutons. Most smaller intrusions of Late Cretaceous and Tertiary age show no apparent relationship to the Skeena Arch as now defined. 35. 3. AGE AND DISTRIBUTION OF GRANITIC ROCKS The granitic rocks of west-central British Columbia, shown on Figure 13, range in age from Early Mesozoic to Tertiary and occur i n a number of forms. The Coast Plutonic Complex constitutes the western border of the area. Batho-l i t h s and large stocks of Late Triassic and Jurassic age occupy the central and eastern parts of the area, while small plugs and stocks of Late Cretaceous and Tertiary age occur i n the central part of the area. Potassium-argon age determinations were obtained for many of these plutons during the course of this study and these determinations, coupled with those obtained by previous and current workers i n the area, have enabled a new definition of the granitic rocks i n this part of British Columbia. These potassium-argon ages are listed in Appendix A and are shown on Figure 14 (pocket) and Figure 15. Age and distribution of the granitic rocks are presented i n two parts. The Late Triassic and Jurassic stocks and batholiths and the Tertiary and older Coast Plutonic Complex are described f i r s t . Although the granitic rocks of the Coast Plutonic Complex are generally of a much younger age, they are i n -cluded i n the f i r s t section because they form the western boundary of the area containing the Upper Cretaceous and Tertiary intrusions, the principal subject of this study. The second part includes a more detailed description of the Upper Cretaceous and Tertiary intrusions which are host to porphyry copper and molybdenum deposits. The subdivision and nomenclature of granitic rocks used i n this study i s li s t e d i n Table II. TABLE II. SUBDIVISION OF GRANITIC ROCKS TERTIARY INTRUSIONS TERTIARY Middle Eocene Goosly Lake intrusions (49 m.y.) Alice Arm intrusions (48 - 54 m.y.) Nanika intrusions (47 - 54 m.y.) Babine intrusions (49- 55 m.y.) TERTIARY AND OLDER INTRUSIONS Coast Plutonic Complex (43 - 140 m.y.) MESOZOIC INTRUSIONS CRETACEOUS Upper Cretaceous Bulkley intrusions (70 - 84 m.y.) JURASSIC AND CRETACEOUS Kitsault intrusions JURASSIC Upper Jurassic Francois Lake intrusions (133 - 155 m.y.) Lower and Middle Jurassic Omineca intrusions (121 - 189 m.y.) TRIASSIC AND JURASSIC Upper Triassic - Lower Jurassic Topley intrusions (173 - 206 m.y.) WEST-CENTRAL BRITISH COLUMBIA F/G.-13 GRANITIC ROCKS Upper Cretaceous-Tertiary Intrusions L. . J C o o s f P 'ufomc Comp/ex § | | § | | | Ear/y Mesozo ic P/ufonic Rocks 0_ 30_ 60 9 Maes ALICE ARM INTRUSIONS BULKLEY INTRUSIONS 2 5 | 2 0 1 I I ul U J I— U J Q U J 5 1 CC U J I 2 25 NANIKA INTRUSIONS BABINE INTRUSIONS | § i GOOStV INTRUSIONS COAST PLUTONIC COMPLEX X L 1 0 0 X L l l 1 2 5 XL 1 5 0 iiiiiiiii FRANCOIS LAKE INTRUSIONS l*.IIJLlm.t | | OMINECA INTRUSIONS H H TOPLEY INTRUSIONS 175 AGE IN m.y. Fig-15 K-Ar AGE DETERMINATIONS-WEST CENTRAL BRITISH COLUMBIA X L 200 39. 3.1 UPPER TRIASSIC AND JURASSIC GRANITIC ROCKS Granitic rocks of Late Triassic to Late Jurassic age occur as small stocks and batholiths in the central and eastern part of the area (Figure 13). From oldest to youngest, they include the Topley, Omineca, Francois Lake, and Kitsault intrusions. 3.1.1 Topley Intrusions Topley intrusions of Late Triassic to Early Jurassic age (173 - 206 m.y.) are here defined as a northeast-trending belt of stocks and small batholiths extending from the margins of the Coast Plutonic Complex near Morice Lake to Babine Lake (Figure 14). These rocks range i n composition from quartz diorite to quartz monzonite and occupy the core of the Skeena Arch. They probably represent centres of eruption of Lower Jurassic volcanic rocks. In recent years, the term Topley intrusions has been used to refer to a northwest-trending belt of stocks and batholiths extending from south of Vanderhoof to the central part of Babine Lake (Armstrong, 1949; White, et a l . , 1969). However, previous work (White, et a l . , 1970) coupled with results from this study demonstrates that the bulk of granitic intrusions previously included with the Topley intrusions are of a different age and character. These rocks are called the Francois Lake intrusions and are discussed i n a subsequent section. The term Topley intrusions i s retained for the granitic intrusions in the Skeena Arch area because i t was originally used by Hanson and Phemister (1928) to describe the granitic rocks north of Topley which are known to be definitely part of the newly defined Topley intrusions. The significance of this northeast-trending belt of Upper Triassic-Lower Jurassic was not realized prior to age determinations made on granitic 40. rocks at Morice Lake and south of Babine Lake during the course of this study (Figure 14). Subsequent potassium-argon dating along this belt by the Geological Survey of Canada yielded ages ranging from 173 to 206 m.y. (Tipper, personal communication) corroborating the earlier dates. The Topley intrusions of the Skeena Arch area are not known to contain significant economic mineral deposits. South of the central part of Babine Lake, low-grade copper and molybdenum mineralization i s associated with 176 m.y. hornblende-biotite-quartz-feldspar porphyry dykes which cut somewhat older (ca. 205 m.y.) granitic rocks (Carter, 1969). 3.1.2 Omineca Intrusions Omineca intrusions, originally described by Armstrong (1949), are chiefly of Early Jurassic age and occur i n the northeast part of the area (Figure 14). The largest intrusive mass, the Hogem batholith, i s a complex, composite intrusion in which diorites and quartz monzonites are cut by syenites of Early Jurassic age and by later, possibly Early Cretaceous, granitic rocks (Garnett, 1971, 1973). Potassium-argon ages obtained from the Hogem batholith by Garnett (1973) range in age from 189 to 121 m.y. Smaller batholiths and stocks included with the Omineca intrusions consist of quartz diorites, quartz monzonites, granodiorites, diorites, and some monzonite and syenite. Northeast of Babine Lake, stocks and s i l l s of diorite and monzonite are included with the Omineca intrusions, although they may i n part be of a younger, possibly Cretaceous age. Porphyry-type copper mineralization i s associated with syenitic phases of the Omineca intrusions in the central and southern parts of the Hogem 41. batholith. Copper and molybdenum mineralization also occurs i n fractured granitic rocks of Early Cretaceous age near the west margin.of the Hogem batholith. 3.1.3 Francois Lake Intrusions Francois Lake intrusions refers to a number of granitic intrusions of batholithic size, which extend i n a southeasterly direction from the south end of Babine Lake for approximately 100 miles (Figure 14). They were originally grouped by Armstrong (1949) with the Topley intrusions and this terminology has continued to the present. Potassium-argon age determination studies, however, indicate a Middle to Late Jurassic age for these intrusions , i n contrast to the Late Triassic-Early Jurassic age for the Topley intrusions. Potassium-argon dating of the granitic rocks i n the Endako area by White , et a l . (1970) indicate a Middle Jurassic age (133 - 155 m.y.) for the bulk of the intrusive phases. Because of the proximity of this batholith to Francois Lake , a prominent geographic feature of this area, these intrusions are here called the Francois Lake intrusions. Similar rocks east of the south end of Babine Lake yielded one age determination of 178 m.y. (Tipper, 1962), but this has since been recalculated to 144 m.y. (Tipper, personal communication) which i s consistent with potassium-argon ages obtained by White, et a l . (1970). Further evidence supporting a division between Topley intrusions and Francois Lake intrusions i s a gravity survey conducted by the Earth Physics Branch of the Department of Energy, Mines, and Resources. This study indicates the northwest boundary of the Francois Lake intrusions as being near the south end of Babine Lake as shown on Figure 14 (Stacey, personal communication). 42. Porphyritic quartz monzonite i s the dominant rock type of the Francois Lake intrusions i n the Endako area, but lesser amounts of diorite, granite, and alaskite are present. The quartz monzonites in the Endako area are sub-divided by Carr (1965) and Dawson and Kimura (1972) into numerous mappable phases. Francois Lake intrusions are host to numerous molybdenum prospects and one major molybdenum mine, the Endako mine, the largest molybdenum producer in Canada. This deposit i s an elongate stockwork of quartz-molybdenum veins developed i n porphyritic quartz monzonite and i n dyke swarms of fine-grained f e l s i c porphyries (Dawson, 1972). 3.1.4 Kitsault Intrusions Quartz diorites, augite porphyries, and feldspar porphyries of the Kitsault intrusions have been recognized only i n the northwest part of the area (Figure 14) and are so named because of their distribution near the Kitsault River which flows into the head of Alice Arm (Carter and Grove, 1972). Because of the highly altered nature of these intrusions, samples suitable for potassium-argon determinations were not collected. Geological relationships, however, indicate that they probably represent volcanic centres of Middle Jurassic and younger fragmental volcanic rocks of the Hazelton Group i n this area. The Kitsault intrusions are host to numerous copper deposits of limited or unknown potential i n the Alice Arm area (Carter, 1970). 43. 3.2 TERTIARY AND OLDER COAST PLUTONIC COMPLEX Granitic rocks of the Coast Plutonic Complex l i e along the west boundary of the area (Figure 13) and are part of a continuous granitic terrane, 1,100 miles long and 80 to 100 miles wide, which extends along the coast of British Columbia and Alaska. Originally referred to as the Coast intrusions (Rice, 1947; Duffell and Souther, 1964), the term Coast Plutonic Complex more accurately describes the varied nature of this belt of granitic rocks. Coast Plutonic Complex comprises a number of coalescing, northwesterly elongate granitic plutons and narrow belts of metamorphic rocks. The complex consists of three zones which are younger and more potassic eastward (Wheeler and Gabrielse, 1973). These are: (1) a western zone of quartz diorite and diorite with potassium-argon ages of 84 to 140 m.y. i n the western part and 64 to 79 m.y. ages in the eastern part; (2) a central core zone of migmatitic gneiss, quartz diorite, and granodiorite, yielding potassium-argon ages averaging 45 m.y.; and (3) an eastern zone of post-tectonic quartz diorite and quartz monzonite (43 - 51 m.y.) intrusive into Mesozoic rocks. The western and central zones of the Coast Plutonic Complex are to the west of the area (Figure 14) studied. The oldest potassium-argon age (140 m.y.) was obtained from an island south of Douglas Channel (Hutchison, 1970), 80 miles west of Eutsuk Lake. The eastern zone forms the western boundary of the area shown on Figure 14. Several large, easterly trending apophyses extend from the main mass in the Terrace area and numerous small s a t e l l i t i c stocks are present along the eastern flank of the complex throughout the map-area. Quartz diorite, granodiorite, and quartz monzonite are the dominant rock types found i n the eastern zone although a wider diversity of granitic 44. rocks are present i n the apophyses i n the Terrace area (Duffell and Souther, 1964). In general, the rocks are equigranular and foliated only near contacts with older rocks. Contacts between the granitic rocks and Mesozoic layered rocks generally are sharp. Evidence of forceful emplacement i s common, especially adjacent to small s a t e l l i t i c stocks. Hutchison (1970) describes the granitic rocks of the eastern zone as being marginal to and generated from a central migmatitic gneiss complex. Potassium-argon dates obtained by both the Geological Survey of Canada and this study indicate a Middle Eocene (43 - 51 m.y.) age for the emplacement of the granitic rocks of the eastern zone (Figure 14). 3.3 UPPER CRETACEOUS AND TERTIARY INTRUSIONS Granitic rocks of Late Cretaceous and Tertiary age occur i n an area bounded on the west by the Coast Plutonic Complex and on the east by a belt of Mesozoic stocks and batholiths (Figures 13 and 14). A five-fold division of these intrusions i s proposed, based on areal distribution, age, whole-rock chemistry, major and trace elements i n b i o t i t e , and on associated metal content. The distribution of these intrusions (Figure 16) can be described i n a general way as consisting of a central north to northwest-trending belt of stocks and small batholiths of Late Cretaceous age, flanked on the east and west by small intrusions of Tertiary (Eocene) age. The intrusive rocks are discussed i n order, from oldest to youngest. P E L Q V $ ^ ; - # ' : t 7 ARM 4 « ;?PR/NCf j :\HUPERH K y_...| ( / A S • M S/ERRA | W E S T - C E N T R A / . 8R/7/SH C O L U M 6 / A 1 8u/k/ey /nfrusions -^ -<4/ice Arm Intrusions • Mo Deposits •^Goosly Lake Intrusions ®Cu-Mo Deposifs I "^"Nanika Intrusions ACU Depos/fs Upper Crefaceous— Tertiary Intrusions 9 30 60 i° T HOUSTON M o r i c e # ® « * > .if ... v- -Fig.-16 AGE AND D/STR/BUT/ON OF UPPER CRETACEOUS AND TERTIARY INTRUSIONS-WEST CENTRAL B.C. 46. 3.3.1 Upper Cretaceous Bulkley Intrusions The term Bulkley intrusions was f i r s t proposed by Kindle (1954) to describe the granitic rocks i n the Hazelton area. The name has been retained for intrusive rocks of similar age and composition which occur i n the central part of the Intermontane Belt, extending from north of Hazelton to the south boundary of the area shown on Figure 14. Bulkley intrusions occur as stocks and small batholiths of porphyritic granodiorite and quartz monzonite. Potassium-argon ages obtained from a number of intrusions (Figure 14) yielded ages ranging from 70 to 84 m.y. A number of intrusions which were not sampled for potassium-argon dating are grouped with the Bulkley intrusions on the basis of their description, associated metallic mineralization, and their tectonic setting. These in -clude granite plutons north of Hazelton in the Sicintine and Atna Ranges and the Quanchus intrusions in the Whitesail Lake area (Duffell, 1959). The Bulkley intrusions are host to important copper-molybdenum and molybdenum-tungsten deposits. 3.3.2 Tertiary (Eocene) Intrusions Goosly Lake Intrusions The Goosly Lake intrusions, named by Church (1970), refer to a number of small plugs of porphyritic gabbro and syenomonzonite south of Houston. They occur i n a northeast-trending belt of apparent limited extent (Figure 14), and are regarded by Church (1970) as centres of Eocene volcanism. 47. Intrusive rocks of similar composition and texture have been recognized only i n a few other l o c a l i t i e s , including the Grouse Mountain area north of Houston (Church, 1972) and i n an area south of Francois Lake as shown on Figure 14. Two potassium-argon samples, both biotite separates, analysed at the University of British Columbia, yielded identical ages of 49 m.y. A replicate sample analysed at Geochron Laboratories, Ltd. returned a potassium-argon age of 53 m.y. This analysis was carried out on a mafic (biotite + hornblende) concentrate, which may in part explain the disparity i n age obtained by the two laboratories. The relationship between the Goosly Lake intrusions and sulphide mineralization i s not clear. Church (1970) considers the intrusions as the source of the copper and s i l v e r mineralization at the Sam Goosly deposit, while Ney, et a l . (1972) believe the deposit to be of the volcanogenic type, contemporaneous with the enclosing Hazelton volcanic rocks. The syenomonzonite stock and related dykes are regarded as post-mineral age , perhaps causing some remobilization of pre-existing sulphide mineralization. Alice Arm Intrusions The Alice Arm intrusions are so named because of their distribution along the east margin of the Coast Plutonic Complex north and south of the village of Alice Arm (Figure 14). The intrusions take the form of small stocks of one-half mile in diameter or less. Quartz monzonite porphyry i s the dominant rock type. Potassium-argon ages from a number of these intrusions range from 48 to 54 m.y. Plutons grouped with the Alice Arm intrusions extend from the Terrace area to Stewart. Molybdenite i s the major economic mineral associated with the Alice Arm intrusions. 48. Nanika Intrusions Nanika intrusions are here named to include a number of small plutons of quartz monzonite to granite composition which are distributed within and marginal to the central belt containing the Bulkley intrusions (Figures 14 and 15). The name Nanika intrusions i s used because of the proximity of two important porphyry deposits, Lucky Ship and Berg, to Nanika Lake. Plutons of this group extend from Mount Thomlinson, north of Hazelton, to the Red Bird molybdenum deposit, west of Eutsuk Lake. Potassium-argon ages of these intrusions range from 47 to 56 m.y. Several of the Nanika intrusions contain major deposits of copper and molybdenum. Many, however, are apparently barren of economic mineralization. Examples of barren plutons are the small stocks i n the Babine Range east of Smithers, and a stock that forms the core of Nadina Mountain. Babine Intrusions Babine intrusions include a number of small plugs , dykes, and dyke swarms of fine-grained biotite feldspar porphyry of granodiorite and quartz diorite composition which occur near Babine Lake. Potassium-argon ages range from 49 to 55 m.y. for this unique suite of intrusions which have been recognized only in the Babine area. The intrusions are regarded as volcanic centres and extrusive equivalents are preserved i n several l o c a l i t i e s . The Babine biotite feldspar porphyries invariably contain chalcopyrite mineralization and several intrusions host major deposits. 49. 3.4 CHEMISTRY OF UPPER CRETACEOUS AND TERTIARY INTRUSIONS Chemical analyses of samples from a number of Upper Cretaceous and Te r t i a r y i n t r u s i o n s were made by the A n a l y t i c a l Branch of the B r i t i s h Columbia Department of Mines and Petroleum Resources (see Appendix B). CIPW (water free) weight per cent norms were ca l c u l a t e d and ternary q u a r t z - a l k a l i feldspar-p l a g i o c l a s e normative diagrams (Figures 17a and 17b) were p l o t t e d to i l l u s t r a t e the range i n composition of the f i v e i n t r u s i v e d i v i s i o n s . The c l a s s i f i c a t i o n scheme on Figure 17a w i l l be used throughout t h i s t h e s i s . Figure 17b i s f o r comparative purposes, being the c l a s s i f i c a t i o n and nomenclature recommended i n 1973 by the I.U.G.S. Subcommission on the Systematics of Igneous Rocks. Bulkley i n t r u s i o n s , with the exception of one pluton, are predominantly within the granodiorite f i e l d as i l l u s t r a t e d on Figure 17a. Several samples f a l l j u s t within the quartz monzonite f i e l d . Babine i n t r u s i o n s of Early T e r t i a r y age are clustered i n the granodiorite f i e l d . Other T e r t i a r y i n t r u s i o n s , the A l i c e Arm and Nanika i n t r u s i o n s , are predominantly of quartz monzonite or granite composition. The basic Goosly Lake intr u s i o n s are w e l l within the monzodiorite f i e l d according to the c l a s s i f i c a t i o n on Figure 17a. 3.4.1 Major and Trace Element Analyses Major and trace element contents were dtermined on 39 b i o t i t e separates from a number of in t r u s i o n s i n west-central B r i t i s h Columbia. Analyses were conducted by Cominco Research, T r a i l , under the supervision of M. Osatenko. Detailed r e s u l t s of these analyses are contained i n Appendix B. 50. 1. B.C.Moly 2. Roundy CJc. 3. Nass River 4. Bel/ Moly SAjox 60'd for* 7 Granls/e 8. Morrison 9 Newman 10 Red Bird 11 Berg I 12. Nadina Mtn 13 Goosly Granite 14 Berg 15 Goosly Gobbro 16 Parrot Lake 17 Sunsets Oo. 18 Huckleberry 19 Bergerte 20 Ox Lake 21. Laura 22 Rocber De Boole 23. Hudsons Bay Mtn. 24. tennac Lake 25. Nadina Microdiorite 26 Jan TERTIARY {EOCENE) 0 Alice Arm Intrusions A Babine Intrusions • Nanika Intrusions X. Goosly Lake Intrusions UPPER CRETACEOUS O Bulkley Intrusions QUARTZ DIORITE DIORITE FIG. 17a DISTRIBUTION OF NORMATIVE QUARTZ (Q), PLAGIOCLASE{Ab + An)&ORTHOCLASE{K) IN CHEMICALLY ANALYZED SAMPLES(Rock Classification After Hutchison 1970). ARITHMETIC MEAN "^JS^l? y / SAMPLES CaO — 1 0°) • ••»|»M» (7) N o 2 0 H -«+• K20 MgO ! . | l _ Fe ' Ti02 • 1 1 1 1 1 0 2 4 6 8 . 70 12 14 16 18 WEIGHT PERCENT Figure 18c- MAJOR ELEMENTS IN BIOTITES • ADITUA>CT / r A/CAKI NUMBER OF ARITHMETIC MEAN ^ SAMPLES Cu — ( 9 K ^ -(11) —1 (10) •••1 (7) 1 Mn | _ J Zn • v | • • Rb +-1 r 1 1 1 1 0 7000 2000 3000 4000 5000 6000 PARTS PER MILLION . TRACE ELEMENTS IN BIOTITES Figure 18b BABINE INTRUSIONS ALICE ARM INTRUSIONS NANIKA INTRUSIONS 52. A tabular summary of some of these analyses are presented on Figures 18a and 18b. The various intrusive types are indistinguishable on the basis of their CaO, Na^O, and K 20 contents i n bibtites (Figure 18a). MgO results occupy a wider range with biotites from the Babine intrusions having a higher MgO content, possibly because of the presence of abundant secondary biotite in these samples. Iron and titanium contents are roughly similar for the various intrusive types. Copper content i n biotites varies for different intrusive types. As might be expected, copper values are very low i n Alice Arm intrusions which are predominantly molybdenum-bearing plutons. The copper-bearing Babine intrusions contain the highest trace copper values, whereas copper-bearing and molybdenum-bearing Nanika and Bulkley intrusions f a l l i n the middle range. An interesting feature of the Babine intrusions i s that copper contents i n biotites of late or post-mineral porphyry phases are two to three times higher than the copper contents i n biotites of mineralized porphyry phases. Manganese values are highest for the Alice Arm intrusions. Trace zinc contents are roughly similar for the four intrusive types, while rubidium exhibits the highest range in the biotites from the Bulkley intrusions. 3.4.2 Metal Content Figure 16 shows the five-fold subdivision of Upper Cretaceous and Tertiary intrusions and their type of associated metallic mineralization. In a general way, there i s a crude metal zonation from west to east consisting of the following: molybdenum-bearing Alice Arm intrusions of Eocene age; copper-bearing and molybdenum-bearing Upper Cretaceous Bulkley intrusions and Eocene Nanika intrusions; and copper-bearing Babine intrusions. Notable 53. exceptions to this westward pattern of copper, copper-molybdenum, and molybdenum mineralization are found i n the central belt where several deposits related to the Bulkley intrusions contain only molybdenum. An example i s the Hudson Bay Mountain molybdenum-tungsten deposit at Smithers. 54. 4. GEOLOGICAL RELATIONSHIPS AND GEOCHRONOLOGY OF PORPHYRY COPPER AND MOLYBDENUM DEPOSITS The majority of known porphyry copper and molybdenum deposits in west-central B r i t i s h Columbia are spatially and genetically associated with Upper Cretaceous and Tertiary intrusions. From west to east, these include the Alice Arm intrusions, the Bulkley intrusions, the Nanika intrusions, and the Babine intrusions. Each group i s discussed as a unit. Each section includes a description of the geological setting of the porphyry deposits, detailed geology and style of mineralization s potassium-argon results, and a discussion of the results. 4.1 PORPHYRY MOLYBDENUM DEPOSITS ASSOCIATED WITH THE ALICE ARM INTRUSIONS A number of molybdenum deposits are related to the Alice Arm intrusions in the area between Stewart and Terrace (Figure 19, i n pocket). These deposits exhibit features typical of porphyry deposits although they have been referred to by some writers as stockwork molybdenum deposits (Clark, 1972) because the bulk of molybdenum mineralization i s contained i n a stockwork of quartz veinlets. 4.1.1 Geologic Setting Most of the known molybdenum-bearing stocks occur near the western edge of the Bowser successor basin, marginal to the Coast Plutonic Complex (Figure 19). The intrusions occur i n the form of small stocks, generally not exceed-ing one-half mile in diameter. Porphyritic quartz monzonite i s the dominant rock type, and this distinguishes the molybdenum-bearing stocks from the 55. equigranular, s a t e l l i t i c stocks related to the Coast Plutonic Complex. Molybdenum-bearing stocks generally intrude argillaceous siltstones, greywackes, and shales of Late Jurassic and Early Cretaceous age, although some occur within the Coast Plutonic Complex. Evidence for both forceful and passive emplacement of the intrusions i s well documented. In the Alice Arm area, sedimentary rocks have been arched and domed around the stocks. Elsewhere, l i t t l e disturbance of the country rock i s seen and the elongate nature of some of the intrusions indicates that they probably were emplaced along major fault zones. South of Alice Arm, several molybdenum-bearing stocks are clustered near remnants of fla t - l y i n g Quaternary basalt which probably overlie their feeders. In the Nass River area, small stocks occur south and west of the Recent lava flow (Figure 19). These features suggest that the extrusion of lava may have been related, i n part, to deep-seated structures that previously controlled the intrusion of the granitic stocks. Many of the stocks apparently have been localized at or near inter-sections of east-northeast and north-northwest faults. The east-northeast trend i s reflected by the elongation of several of the stocks (Bell Molybdenum, Roundy Creek, Kay) in the Alice Arm-Nass River areas which may also represent some control of the attitude of the sedimentary rocks. Also a crude east-northeast distribution of the stocks i s evident i n the cluster south of Alice Arm and south of the Nass River (Figure 19). Some stock contacts are r e c t i -linear i n plan, again reflecting the dominant fault and fracture patterns. A good example of this i s seen at the Ajax molybdenum deposit northeast of Alice Arm (Figure 20). 56. 4.1.2 Geology and Style of Mineralization Molybdenum deposits are associated with the Alice Arm intrusions, which occur as small oval or elongate stocks. Some intrusions, most notably the Roundy Creek intrusion south of Alice Arm, are sheet- or s i l l - l i k e i n form and are related to small feeder pipes. Intrusions at Alder Creek, near Lava Lake (Figure 19) and Molybdenum Creek, north of Terrace, are northwest-striking dyke swarms intruding sedimentary rocks. Quartz monzonite porphyry i s the most common host rock at most deposits. Phenocrysts range in size from 2 millimetres to 1 centimetre and include, i n decreasing order of abundance, euhedral plagioclase, K-feldspar, and both euhedral and anhedral quartz eyes. Quartz monzonite porphyry i s character-i s t i c a l l y mesocratic with both biotite and hornblende as primary mafic minerals. Leucocratic quartz feldspar porphyry phases of quartz monzonite to granite composition also are prominent at most of the deposits and at some they con-stitute the bulk of the intrusive rocks. Muscovite i s the mica mineral of this phase. Some intrusions are zoned, most notably the intrusion that i s host to the British Columbia Molybdenum deposit. Here, a core of quartz monzonite porphyry i s bordered by more basic granodiorite and quartz diorite which possibly formed by contamination from the argillaceous siltstone and greywacke country rocks. Most molybdenum-bearing stocks exhibit several stages of intrusion. The f i r s t stage i s represented by quartz monzonite and/or quartz feldspar porphyry and constitutes the bulk of the stock. This main phase may be intruded by fine-grained, equigranular alaskite that consists essentially of quartz, K-feldspar, 57. F/G-20 MOLYBDENUM DEPOSITS QUATERNARY | ALICE ARM BASALT TERTIARY—OLIGOCENE [771 LAMPROPHYRE DYKES INTRUSIVE ROCKS-EOCENE COAST COMPLEX—GRANODIORITE ] ALASKITE, LEUCOCRATIC QUARTZ FELDSPAR PORPHYRY I5SS3 QUARTZ DIORITE rrrrnQUARTZ MONZONITE— GRANODIORITE PORPHYRY JURASSIC- CRETACEOUS I I BIOTITE HORNFELS LATE QUARTZ MONZONITE PORPHYRY LIMIT OF BIOTITE HORNFELS INTRUSIVE BRECCIA Ag-Pb-Zn Showing Q fEET 3000 K-Ar Sample 129*15' 59. and myrmekite. Alaskites, which are very common at the British Columbia Molybdenum and Roundy Creek properties (Figure 20), occur as dykes and irregular masses and are host to better grades of disseminated and replacement molybdenite mineralization. Other inter-mineral intrusions include dykes and irregular lenses of intrusive breccia, best developed along the northern stock contact at the British Columbia Molybdenum deposit (Figure 20). Angular fragments 1 to 2 centimetres i n size, of both intrusive and country rock, are contained i n a granulated matrix of quartz, plagioclase, and K-feldspar. Several deposits feature intrusive phases that are very late i n the intrusive-mineralization sequence. These also are quartz monzonite in composition. Examples include an unexposed plug at the British Columbia Molybdenum deposit, the southwest portion of the Bell Molybdenum stock (Figure 20), and post-mineral dykes at some of the Nass River deposits (Figure 21). Post-mineral lamprophyre and basalt dykes cut v i r t u a l l y a l l of the molybdenum-bearing stocks. These usually strike northeasterly, dip vertically, and truncate a l l pre-existing rocks and structures, including mineralized fractures. Northwest-striking, post-intrusive, and post-lamprophyre dyke faults are found at the Bell Molybdenum, Roundy Creek, and Nass River deposits (Figures 20 and 21). Sedimentary rocks adjacent to the Alice Arm intrusions have been thermally metamorphosed to biotite hornfels i n an aureole which may extend outward from the stock contact for several hundred feet (see property descriptions, Appendix C). Biotite hornfels i s a brown, indurated, fine-grained rock with a grano-blastic texture that consists of quartz, minor feldspar, and abundant felted, brown biotite. Some cordierite and andalusite are developed i n the hornfels adjacent to intrusive contacts. 60. Alteration patterns within and marginal to the molybdenum-bearing stocks are typical of porphyry deposits. At many of the deposits, a central zone of potassic alteration i s coincident with molybdenite mineralization. At the Brit i s h Columbia Molybdenum deposit, the most intense potassic alteration i s contained within an annular ore zone (Figure 20). Rock within this core of intense alteration i s laced with barren quartz veinlets rimmed by secondary K-feldspar, such that the original quartz monzonite porphyry has been con-verted to a rock consisting mainly of quartz and K-feldspar. Within the annular zone of mineralization, secondary K-feldspar i s restricted to the margins of quartz-molybdenite veinlets. Other deposits also feature secondary K-feldspar but not to the same degree as at Bri t i s h Columbia Molybdenum. Secondary b i o t i t e , an alteration of primary hornblende, i s present to a limited degree i n several of the deposits. At Roundy Creek, quartz-muscovite veins constitute the potassic alteration zone. The potassic zone at most deposits i s gradational outward to a phyllic (quartz-sericite-pyrite) zone which i s marginal to the plutons and involves an overprinting on the effects of thermal metamorphism. The phyllic zone i s represented at many deposits by a bleaching of the biotite hornfels to a cream or ligh t green colour marginal to fractures and quartz veinlets and i s due to the development of very fine-grained quartz, se r i c i t e , albite, and epidote. This type of alteration may be weakly developed, as at many of the deposits, or so intense that the original biotite hornfels has been largely transformed to a buff or light green-coloured rock within a zone a few hundred feet outward from the stock contact as at the British Columbia Molybdenum and Ajax deposits. Pyrite i s a common constituent i n this alteration zone, occurring both i n quartz veinlets and as disseminations. The intensity of pyritization may be 61. related i n part to thermal metamorphism, which involves a concentration of syngenetic pyrite and pyrrhotite i n the sedimentary country rocks. Better grades of molybdenite mineralization i n the Alice Arm intrusions are dependent on structural and lithologic controls. Fracturing and attendant quartz-molybdenite veining are best developed near stock contacts. Later alaskite intrusive phases contain disseminated to near-massive molybdenite. An example i s the ore zone at British Columbia Molybdenum which i s annular or ring-shaped i n plan, occurring near the contacts of the northern half of the stock (Figure 20) with molybdenite occurring as selvages i n a network of east-northeast and west-northwest quartz veinelts. A similar style of mineraliz-ation occurs at most of the other deposits. Disseminated rosettes of molybdenite occur i n leucocratic quartz-feldspar porphyry phases at the Tidewater and Kay properties. Disseminated molybdenite i s contained i n the alaskite intrusive phase at the British Columbia Molybdenum deposit. At Roundy Creek, the alaskite contains near-massive lenses, pods, and parallel bands of molybdenite. At least three stages of quartz-molybdenite veining are present i n the Br i t i s h Columbia Molybdenum deposit. Virtually a l l of the Alice Arm molybdenite deposits feature late-stage quartz-carbonate veins which contain pyrite, galena, sphalerite, tetrahedrite, chalcopyrite, minor molybdenite, and at Br i t i s h Columbia Molybdenum, a silver-lead-bismuth sulphosalt, neyite (Drummond, et a l . , 1969). These silver-lead-zinc veins which are best developed peripheral to the stocks were explored many years before the molybdenite mineralization attained economic significance. 62. A pyrite halo may extend outward from the molybdenite zone for several hundred to a thousand feet. Where exposed, the pyrite zone i s weathered to a prominent gossan, particularly at the Ajax and Snafu properties. Other molybdenite deposits studied i n the Alice Arm area include the Molly Mack prospect near Anyox and the Penny Creek showing south of Alice Arm (Figure 19). At the Molly Mack property, coarse-grained molybdenite i s abundantly disseminated in a small zone of biotite granite contained within a stock-like body of leucocratic quartz monzonite porphyry which i s similar i n appearance to some phases of the Alice Arm intrusions. The Penny Creek occur-rence consists of rosettes of molybdenite i n a biotite quartz monzonite, a late phase of the Coast Plutonic Complex. Numerous showings of molybdenite occur near the eastern margin of the Coast Plutonic Complex and in the s a t e l l i t e stocks related to the complex. 4.1.3 Potassium-argon Dating of the Alice Arm Porphyry Molybdenum Deposits Potassium-argon ages obtained from samples collected i n the Alice Arm-Nass River area are shown on Figures 19, 20, and 21. Analytical data, sample descriptions, and precise locations are contained i n Appendices A and C. Most samples were collected to date the age of intrusion and mineral-ization. Several, however, were collected to date other geologic units and to assess their relationship to the molybdenum deposits. These include samples collected from the Coast Plutonic Complex and from the basalt outliers south of Alice Arm. Potassium-argon results for a l l samples collected are l i s t e d i n Table III. Unless otherwise indicated, a l l analyses were carried out on biotite separates. 63. TABLE III. POTASSIUM-ARGON AGES OF ALICE ARM INTRUSIONS Sample Age No. Location Rock Unit (m.y.) NC-67-38 British Columbia Molybdenum Quartz monzonite porphyry 53.2 ± 3 NC-69- 2 British Columbia Molybdenum Intrusive breccia 53.7 + 1.7 NC-70- 1 British Columbia Molybdenum Lamprophyre dyke (W.R.) 36.5 + 1 .2 NC-70- 2 British Columbia Molybdenum Quartz diorite 51.4 + 1.5 NC-70- 3 British Columbia Molybdenum 'Late' quartz monzonite 48.3 + 1.6 porphyry NC-67-30 Bell Molybdenum Quartz monzonite porphyry 52.9 + 2 NC-67-31 Bell Molybdenum Biotite hornfels (W.R.) 48.7 + 1.5 NC-68- 2 Bell Molybdenum Quartz diorite - border 51.7 + 2.2 phase NC-67-33 Ajax Granodiorite 53.5 + 3 NC-67-35 Roundy Creek Quartz monzonite porphyry 52.5 ± 2* NC-67-25 Ridge 'Late' porphyry 49.0 ± 2 NC-67-26 Valley Quartz monzonite porphyry 52.0 ± 3 NC-67-27 Kay Quartz feldspar porphyry 53.2 + 2.3 NC-67-45 Penny Creek Biotite quartz monzonite 36.1 ± 1 .6 NC-68-11 Molly Mack Biotite granite 48.3 ± 1 .9 NC-67-24 Mount Priestly Coast Plutonic Complex 48.4 ± 1.5* NC-67-28 Nass River Coast Plutonic Complex 49.1 ± 2 NC-67-29 Alice Arm Coast Plutonic Complex 50.5 + 3 NC-69- 3 Lava Lake Coast Plutonic Complex 50.7 ± 2.1 NC-68- 3 Bonanza Creek - Anyox Biotite schist 33.3 + 1.4 NC-68- 4 Illiance River Lamprophyre dyke 34.4 + 1 .5 NC-67-32 Alice Arm Basalt 0.62 + 0.6* NC-70- 4 Alice Arm Basalt 1 .6 + 0.8 *Average of two or more analyses. (W.R.) - Whole Rock Sample. Note: Calculation of analytical error i s outlined i n Appendix A.2. 64. Molybdenum-bearing Stocks Samples for dating were collected from molybdenum-bearing quartz monzonite porphyries and related intrusive phases at six of the deposits. Potassium-argon results from the main mineralized phase at these deposits f a l l within the range of 52.0 + 3 m.y. to 53.3 + 3 m.y. (Table III and Figures 20 and 21). Quartz diorite border phases at British Columbia Molybdenum and Bell Molybdenum are 51.4 ±1.5 m.y. and 51.7 + 2.2 m.y. respectively, within the limits of analytical error of the main phase. Late intrusive phases, which exhibit definite crosscutting relationships with the f i r s t phase, were sampled at British Columbia Molybdenum. A dyke of intrusive breccia near the northern contact of the stock has an age of 53.7 + 1.7 m.y., almost identical to the age obtained from the geologically older quartz monzonite porphyry phase (53.2 + 3 m.y.). An age of 48.3 +1.6 m.y. was obtained for a sample of a later, nearly barren phase of quartz monzonite occurring at a depth some 1,000 feet vert i c a l l y below the northeast section of the stock. This age determination corroborates the geological evidence that this i s a younger porphyry phase which post-dates the main period of molybdenite mineralization and provides an upper limit for the age of mineralization. A similar post-mineral porphyry dyke that cuts the quartz monzonite porphyry host rock at one of the Nass River deposits (Figure 21) yields a potassium-argon age of 49.0 ± 2 m.y. A whole-rock sample of biotite hornfels from outside the mineralized zone at Bell Molybdenum was dated at 48.7 + 1.5 m.y. Although such a sample should reflect the age of intrusion, the somewhat younger age could be explained by par t i a l argon loss inherent i n a whole-rock sample. 65. Two molybdenum deposits returned somewhat anomalous ages. The 48.3 + 1.9 m.y. age determined for the Molly Mack occurrence south of Anyox might be explained by partial resetting of a slightly older age by the emplacement of the adjacent Coast Plutonic Complex granitic rocks. The 36.1 +1.6 m.y. age for the Penny Creek occurrence southwest of Alice Arm (Figure 19) possibly could be due to a complete resetting of the original age by a younger lamprophyre dyke not seen during f i e l d examination. However, i t should be noted that similar Oligocene ages for granitic rocks have been reported i n the Prince William Sound area of southern Alaska by Lanphere (1966) and on Vancouver Island by Carson (1969). Coast Plutonic Complex Potassium-argon ages for four samples collected from granitic rocks of the Coast Plutonic Complex between Alice Arm and Lava Lake (Figure 19) range from 48.8 ±1.5 to 50.7 + 2.1 m.y. These are i n agreement with ages obtained by the Geological Survey of Canada i n the same area and are somewhat younger than the mean age of 53 m.y. determined for the molybdenum-bearing porphyry stocks. Although with the limits of analytical error, these consistently younger ages found along the eastern margin of the Coast Plutonic Complex over a relatively large geographic area (Figure 19) suggest that the molybdenum-bearing stocks were intruded a measurable amount of time prior to the emplace-ment of the Coast granitic rocks. Basalt Outliers Prior to this study, the f l a t - l y i n g basalts south of Alice Arm were regarded as being of Early to Mid-Tertiary age. A sample collected from north 66. of the Bell Molybdenum stock has an age of 0.62 +0.6 m.y. which i s an average of three determinations. A similar sample from a basalt remnant east of British Columbia Molybdenum has an age of 1.6 + 0.8 m.y. This apparent disparity i n age can be attributed to a lower level of accuracy i n the conventional potassium-argon method in this young age range. Potassium-argon Results from Other Studies Potassium-argon results obtained from previous and contemporary studies in the Alice Arm area are i n good agreement with those determined i n this investigation. Woodcock, et a l . (1966) reported a potassium-argon age of 53.3 m.y. for a sample collected near the south contact of the Br i t i s h Columbia Molybdenum stock. Later work on the same deposit i n 1971 by D. L. Giles (personal communication), formerly of Kennecott Research, indicated ages of 53.7 m.y. for secondary biotite from the alaskite phase and 63.2 m.y. for a biotite from fresh intrusive rock in a d r i l l hole at a depth of 2,400 feet below the open p i t . The latter date i s at variance with the ages obtained from this study and could be due to accumulation of excess argon i n this sample. Giles also obtained a date of 52.4 m.y. for a secondary sericite sample from the Roundy Creek deposit, in good agreement with the result obtained from this study. 4.1.4 Summary The following conclusions can be drawn based on potassium-argon results obtained i n the Alice Arm-Nass River area: (1) Age of intrusion of the molybdenite-bearing quartz-monzonite porphyry 67. stocks i s i n the range of 50 to 54 m.y., based on results of samples from the main intrusive phase and biotite hornfels from outside the zone of mineralization. (2) The age of mineralization i s synchronous, or nearly so, with the age of intrusion. This i s borne out by the 48 and 49 m.y. ages obtained from later, nearly post-mineral porphyry phases which provide an upper limit for the age of mineralization. (3) Molybdenite-bearing Alice Arm intrusions were emplaced an average of 3 million years prior to the granitic rocks i n the east margin of the Coast Plutonic Complex. (4) Lamprophyre dykes, prominent i n this area, were intruded i n Oligocene time (33.3 - 36.5 m.y.). (5) The youngest igneous events of the region are represented by the Quaternary basalt outliers south of Alice Arm and the Recent lava flow south of the Nass River. 4.2 PORPHYRY COPPER AND MOLYBDENUM DEPOSITS ASSOCIATED WITH THE BULKLEY INTRUSIONS Bulkley intrusions of Late Cretaceous age, which occur i n the central part of the area (Figure 22), extend from north of Hazelton to Eutsuk Lake. A number of intrusive bodies are grouped with the Bulkley intrusions on the basis of their geologic setting and their geological descriptions. These include granitic stocks in the Atna and Sicintine Ranges north of Hazelton and the Quanchus intrusions north of Eutsuk Lake. Bulkley intrusions host a number of important copper-molybdenum deposits, principally i n the southern part of the area (Figure 22). One important 69. molybdenum-tungsten deposit, Glacier Gulch, i s also related to an intrusion of this age. 4.2.1 Geologic Setting Bulkley intrusions cut sedimentary and volcanic rocks ranging i n age from Early Jurassic to Early Cretaceous. They occur as oval and elongate stocks which range from one-half to more than 2 miles i n diameter. The largest known of these intrusions i s the Rocher Deboule stock south of Hazelton which occupies an area of 27 square miles (Sutherland Brown, 1960). The more important copper-molybdenum deposits are associated with stocks of less than 1 square mile surface area or with offshoot dykes related to them. Most available evidence favours forceful emplacement of the Bulkley intrusions. Country rocks are domed around the relatively large Sunsets Creek pluton and around the buried stock related to the Glacier Gulch molybdenum deposit (Kirkham, 1966). Passive emplacement i s postulated for the Rocher Deboule stock (Sutherland Brown, 1960). The Bulkley intrusions have been localized, at least i n part, by north to northwest-striking faults. 4.2.2 Geology and Style of Mineralization Bulkley intrusions are of granodiorite and quartz monzonite composition. The hypabyssal rocks invariably are porphyritic with phenocrysts of plagio-clase and quartz ranging i n size from 2 millimetres to 1 centimetre. Most intrusions contain both biotite and hornblende, which in many intrusions occur as phenocrysts. 70. Multiple intrusion i s a feature of several porphyry deposits associated with the Bulkley intrusions. Perhaps the best example i s the Glacier Gulch molybdenum deposit at Smithers. Here a sheet of intensely altered granodiorite is intruded by a small (1,100 feet i n diameter) quartz porphyry plug which was emplaced i n three pulses (Kirkham, 1966; Jonson, et a l . , 1968). The bulk of the molybdenum mineralization in the older granodiorite sheet i s related to the f i r s t pulse, and a lesser amount i s related to inter-mineral quartz porphyry breccias and dykes. The quartz porphyry plug i s truncated by a large (at least 2 miles i n diameter) weakly mineralized quartz monzonite porphyry stock , indicating that i t occurred.very late i n the mineralization-intrusive sequence. Other examples of multiple intrusion which have been documented are the Coles Creek deposit (Maclntyre, 1974) and the Huber molybdenum prospect (Sutherland Brown, 1965). At the latter deposit (Figure 23), the sequence has been fine-grained alaskite, porphyritic quartz monzonite, and a post-mineral monzonite dyke. At the Ox Lake property (Figure 23), mineralized granodiorite porphyry i s preceded by the intrusion of porphyritic quartz monzonite and related feldspar porphyry dykes. Late post-mineral diabase and lamprophyre dykes are a common feature of most of the deposits. Mesozoic volcanic and sedimentary rocks adjacent to the Bulkley intrusions have been thermally metamorphosed to biotite hornfels. The metamorphic aureole may extend outward from the stock contacts for 15 hundred to several thousand feet. Locally, higher grade metamorphic minerals, such as garnet, epidote, and actinolite , are noted i n the innermost contact zones. Fairly well-developed alteration zones are present at most of the better mineralized deposits. At the Glacier Gulch deposit, an inner zone of s i l i c i f i -cation overlies the quartz porphyry plug and a K-feldspar-sericite-carbonate a 70 HUBER N HUCKLEBERRY OX LAKE BULKLEY INTRUSIONS-COPPER,MOLYBDENUM DEPOSITS CRETACEOUS (UPPER CRETACEOUS) r : : : : : : : : : : 3Mor )Zon i " t e L ...1 Granodiorite Porphyry i I Alaskite Porphyritic Ouartz Monzonite, Feldspar Porphyry MESOZOIC [JURASSIC) I I Sedimentary & Volcanic Rocks & Hornfelsed Equivalent S K~Ar Age(m.y.) 1600 32,00 SCALE IN FEET FIG-23 72. alteration i s spatially related to the zone of molybdenite mineralization (Jonson, et a l , 1968). This zone i s partly expressed by bleaching of the hornfelsed volcanic and sedimentary rocks , principally marginal to quartz veinlets. Similar bleaching of biotite hornfels adjacent to quartz veinlets has been noted at Huckleberry (Carter, 1970) and at Ox Lake (Sutherland Brown, 1969; Richards, 1974). Most deposits exhibit an outer phyllic (quartz-sericite-pyrite) zone of alteration. Copper and molybdenum mineralization i s contained i n a stockwork of quartz veinlets and fractures best developed near stock contacts i n both the intrusive and country rocks. Good examples of this style of mineralization are the Huckleberry and Ox Lake deposits where better grades of mineralization occur around one end of the stock. At Huckleberry, most mineralization i s restricted to homfelsed country rocks and extends for hundreds of feet from the northeast stock contact. Where both chalcopyrite and molybdenite occur, molybdenum grades are better in that part of the ore zone which i s within the stock. At Glacier Gulch, molybdenite and scheelite-powellite are contained i n a stockwork of veins best developed i n the granodiorite sheet between the quartz porphyry plug and the quartz monzonite porphyry stock. At least two periods of molybdenite mineralization are recognized (Kirkham, 1966; Jonson, et a l . , 1968). Molybdenite mineralization at the Huber property i s best developed i n veinlets i n the alaskite tongue and i n adjacent hornfelsed rocks. At the Bear property, four stages of fracturing, veining, and attendant molybdenite-chalcopyrite mineralization are recognized, with better grades occurring near the periphery of the stock. 73. Pyrite haloes, often weathered to prominent gossans, envelop most deposits related to the Bulkley intrusions. This pyrite zone most often i s restricted to the hornfelsed zone. Vein deposits of silver-lead-zinc, peripheral to the main zone of copper-molybdenum mineralization, are known at Glacier Gulch, Huber, Sunsets Creek, Coles Creek, and Ox Lake properties. 4.2.3 Potassium-argon Dating of the Bulkley Intrusions Potassium-argon ages from the Bulkley intrusions are shown on Figures 22 and 23. Results obtained from this study are l i s t e d i n Table IV. Analytical data i s presented i n Appendix A, with sample locations i n Appendix C. Only one sample was collected at most deposits because only one intrusive phase was recognized or deemed suitable for dating. Two samples from the Glacier Gulch deposit were analysed. Copper-molybdenum-bearing Stocks Most samples collected and analysed for the Bulkley intrusions are from the mineralized intrusive phase. Potassium-argon results from these samples range i n age from 70+3 m.y. to 83.8 + 2.8 m.y. (Table IV). Results from this study, coupled with those obtained from other sources, suggest that the Bulkley intrusions were emplaced over a span of 13 to 14 million years, i n three main pulses. These are: 70, 76, and 82 million years. A biotite sample from a quartz-biotite-molybdenite vein at Glacier Gulch yields a potassium-argon age of 69.5 + 3 m.y., which i s interpreted as the age of mineralization. A sample from the buried quartz monzonite porphyry stock, interpreted by Jonson, et a l . (1968) and Kirkham (1966) as being late in the intrusive-mineralization sequence, gave a potassium-argon age of 74. TABLE IV. POTASSIUM-ARGON AGES OF BULKLEY INTRUSIONS Sample No. Location Rock Unit Age (m.y.) NC-67-16 Huber Biotite hornfels (W.R.) 69.5 ± 2 NC-67-41 Glacier Gulch Quartz-biotite-sulphide vein 69.5 ± 3* NC-68- 6 Glacier Gulch Quartz monzonite porphyry 73.3 ± 3.4 NC-67-39 Sunsets Creek Granodiorite 70.0 ± 3 NC-67-46 Rocher Deboule Granodiorite 71.9 ± 3.1 NC-68-12 Bear Quartz monzonite porphyry 82.4 ± 3.1 NC-67-44 Huckleberry Granodiorite porphyry 82.0 ± 3 NC-69- 5 Ox Lake Granodiorite porphyry 83.4 ± 3.2 MC-9 Coles Creek Quartz monzonite porphyry 83.8 ± 2.8 *Average of two analyses. (W.R.) - Whole Rock sample. Note: Calculation of analytical error i s outlined i n Appendix A.2. 75. 73.3 + 3.4 m.y. , somewhat older than the geological relationships suggest, but s t i l l within the limits of analytical error. A number of samples from Glacier Gulch were collected by Kirkham (1969) and analysed at the geochemistry laboratories of the Geological Survey of Canada. Biotite from a quartz l a t i t e porphyry dyke, interpreted by Kirkham as post-dating the molybdenite mineralization, yielded an age of 60 + 5 m.y. A sample of quartz-biotite-molybdenite vein, the duplicate of which was analysed during this study (NC-67-41), gave an age of 63 + 4 m.y., and a hornblende sample, also from a quartz vein, was analysed as being 65+6 m.y. Biotite from the buried quartz monzonite porphyry stock returned an age of 67 + 5 m.y. Four Bulkley intrusions are illustrated on Figure 23. Biotite samples from the main mineralized phase at three of these (Bear, Huckleberry, and Ox Lake) yielded potassium-argon ages in the narrow range of 82.0 to 83.4 m.y. Lack of suitable biotite i n the intrusive rocks at the Huber property necessitated analysis of a whole-rock biotite hornfels sample which gave a potassium-argon age of 69.5 + 2.0 m.y. Other ages obtained from mineralized Bulkley intrusions include 70+3 m.y. for the Sunsets Creek pluton and 83.8 + 2.8 m.y. for part of the Coles Creek intrusion (Figure 22). A sample of porphyritic granodiorite from the Rocher Deboule stock in the vi c i n i t y of Rocher Deboule mine, which contains veins of chalcopyrite with lesser molybdenite, arsenopyrite, and pyrrhotite (Sutherland Brown, 1960) gave a potassium-argon age of 71.9 ±3.1 m.y. 76. Potassium-argon Results from Other Studies Three samples from Bulkley intrusions were analysed during geological studies i n the Owen Lake-Tahtsa Lake area by Church (1971, 1972). The results are shown on Figure 22. The Nadina microdiorite s i l l yielded an age of 74 + 2 m.y. This unit i s cut by vein deposits of the Bradina mine which are related to a younger intrusive event. The Duck Lake granitic stock to the southwest, apparently devoid of mineralization, gives a potassium-argon age of 76 ± 2 m.y. The Bergette sample (76.7 ±2.5 m.y.) is from a feldspar porphyry phase of the Sibola stock which i s host to copper and molybdenum mineralization. The Troitsa Lake copper-molybdenum-bearing intrusion was dated by Cawthorne (1973) as being 76 ± 2 m.y. and the Jan porphyry was dated by Kirkham as 72 ± 3 m.y. (Wanless, et a l . , 1974). A l l of these ages f a l l within the time interval determined for the Bulkley intrusions. 4.2.4 Summary (1) The Bulkley copper-molybdenum-bearing intrusions were emplaced over a span of ages between 70 and 84 m.y., with the major pulses of intrusion occurring i n the three time periods of 70 m.y., 76 m.y., and 83 m.y. (2) Potassium-argon results from the Glacier Gulch deposit suggest that the age of mineralization, within the limits of analytical error, i s synchronous with the age of intrusion of the Bulkley intrusions. Ages obtained from other Bulkley intrusions also suggest this, 77. 4.3 PORPHYRY COPPER-MOLYBDENUM DEPOSITS ASSOCIATED WITH THE NANIKA INTRUSIONS The Nanika int r u s i o n s of Early T e r t i a r y age occur i n the c e n t r a l part of west-central B r i t i s h Columbia. Their d i s t r i b u t i o n ranges from north of Hazelton to the south boundary of the area shown on Figure 24. They apparently occur i n four d i s c r e t e areas with the same geographic s e t t i n g as the previously described Bulkley i n t r u s i o n s . The Nanika int r u s i o n s are so named because of the proximity to Nanika Lake of several important copper-molybdenum deposits associated with i n t r u s i o n s of t h i s age. 4.3.1 Geologic Setting Nanika int r u s i o n s cut Mesozoic v o l c a n i c and sedimentary rocks as small stocks and plugs. Many intr u s i o n s have n o r t h e a s t - s t r i k i n g dykes p r o j e c t i n g from them and a few, such as the Red B i r d deposit, are bordered by p a r t i a l r i n g dykes. Many Nanika int r u s i o n s were emplaced f o r c e f u l l y causing doming and arching of surrounding sedimentary rocks such as at Mount Thomlinson and Nadina Mountain r (Figure 24). Some examples of passive emplacement, wherein the intrusions have occupied p r e - e x i s t i n g fractures and f a u l t zones, are seen at the Lucky Ship, Berg, and Big Onion properties. S t r u c t u r a l controls f o r emplacement of the Nanika i n t r u s i o n s include i n t e r -sections of regional northeast and northwest-striking f a u l t s and the cores of a n t i c l i n a l structures. Northeast-striking dykes p r o j e c t i n g from many of the plutons i n d i c a t e t h i s d i r e c t i o n as a dominant s t r u c t u r a l trend. WEST-CENTRAL BRITISH COLUMBIA f/G-24 NANIKA INTRUSIONS COPPER-MOLYBDENUM DEPOSITS 2? INTRUSIONS X56 K-Ar AGE(m.y) 0 b 30 60 T!H MILES 79. 4.3.2 Geology and Style of Mineralization Nanika intrusions occur i n a variety of forms. They may be oval or circular as at the Berg and Red Bird deposits (Figure 25), elongate as at Big Onion and Lucky Ship, or as dyke swarms as at Serb Creek. Oval stocks or plugs generally do not, exceed 0.5 mile in diameter, but elongate intrusions may extend for thousands of feet i n their long direction. Some non-mineralized Nanika intrusions , most notably that at Nadina Mountain, may be several square miles in area. The major rock type of Nanika intrusions i s quartz monzonite porphyry i n which 2- to 4-millimetre phenocrysts of quartz, plagioclase, and K-feldspar are set in a fine-grained matrix. Biotite occurs as prominent phenocrysts and books in many of these intrusions. The main intrusive phase at some deposits, including Lucky Ship and Big Onion, i s represented by fine-grained quartz feldspar porphyry of rhyolitic composition. Examples of multiple intrusion are evident at most deposits related to the Nanika intrusions. One of the better examples of this i s the Berg deposit, where the mineralized quartz monzonite porphyry stock i s intruded by a number of younger, post-mineral quartz l a t i t e porphyry dykes, similar i n texture and composition to the main phase (Figure 25). A breccia pipe occurs south of the quartz monzonite porphyry stock and i s believed to be intermediate i n age between the quartz monzonite porphyry and the post-mineral dykes (Sutherland Brown, 1966). A similar situation exists at Red Bird, where small post-mineral monzonite porphyry dykes cut mineralized quartz monzonite porphyry. At Lucky Ship, a circular breccia pipe containing some molybdenite represents an i n i t i a l intrusive phase (Figure 25). This i s intruded by the 80. NANIKA INTRUSIONS—COPPER—MOLYBDENUM DEPOSITS Tertiary (Eocene) E5§gg§ QUARTZ LATITE PORPHYRY I" " ' '1 RHYOLITE PORPHYRY Ijjjfjfl BRECCIA PIPE L 1 INTRUSIVE BRECCIA [ | QUARTZ MONZONITE PORPHYRY ]] QUARTZ DIORITE Mesozoic (Jurassic) 1 [ SEDIMENTARY & VOLCANIC ROCKS &HORNFELSED EQUIVALENTS B K-Ar DATE 1400 3200 FEET FIG.-25 81 . elongate 'wipeout' rhyolite porphyry phase which i t s e l f i s essentially non-mineralized and obliterates some pre-existing mineralization i n the breccia pipe. This in turn i s intruded by a small granitic plug containing molybdenite. At Big Onion, the i n i t i a l quartz porphyry phase i s intruded by a quartz diorite and f i n a l l y by a post-mineral, fine-grained quartz monzonite dyke. Basic dykes of post-mineral age and principally of andesitic composition transect several of the Nanika intrusions. Sedimentary and volcanic rocks adjacent to the Nanika intrusions are thermally metamorphosed to biotite hornfels. Hydrothermal alteration patterns include a central potassic alteration zone which grades outward to a quartz-sericite-pyrite (phyllic) zone. This latter zone may or may not be well developed. Potassic zone alteration generally occurs as secondary K-feldspar within and marginal to quartz veinlets and as replacement of original plagio-clase in the rock matrix. Development of secondary muscovite i s a feature of some potassic alteration zones. At some deposits such as Lucky Ship, the central alteration zone i s extensively s i l i c i f i e d . The phyllic zone i s represented by an addition of quartz, s e r i c i t e , and pyrite i n hornfelsed country rocks marginal to the plutons. Better grades of copper and molybdenum are restricted to contacts of the Nanika intrusions. Chalcopyrite and molybdenite occur in stockworks of quartz veinlets , with molybdenum mineralization occupying an inner zone almost entirely within the intrusion and copper mineralization best developed i n hornfelsed rocks marginal to the stock contacts. An example of this i s the Berg deposit (Sutherland Brown, 1966). At Red Bird, molybdenite occurs i n a stockwork of quartz veinlets within a crescent-shaped zone developed around 82. the north h a l f of the stock contact area. Several stages of quartz v e l n i n g and attendant m i n e r a l i z a t i o n are recognized at both deposits. At Lucky Ship, best grades of molybdenite m i n e r a l i z a t i o n are contained i n an annular zone around the l a t e r stage quartz monzonite porphyry plug (Figure 25), coincident with a zone of intense s i l i c i f i c a t i o n and quartz v e i n -ing. Molybdenite mineralization at Mount Thomlinson i s confined to a stockwork of quartz v e i n l e t s within the i n t r u s i o n near the northwest contact. At the Big Onion property, chalcopyrite and molybdenite occur near the contacts between the quartz d i o r i t e and quartz feldspar porphyry, with chalcopyrite p r i n c i p a l l y within the quartz d i o r i t e and molybdenite i n the quartz feldspar porphyry. P y r i t e haloes envelope deposits associated with the Nanika in t r u s i o n s extending outward from them a distance of several hundred to thousands of feet. Extensive gossans are v i s i b l e at the Berg and Red B i r d deposits where they are not obscured by vegetation. Mineralized zones at Red B i r d , Berg, and Mount Thomlinson have been subjected to intense oxidation and leaching, which may extend 200 feet below the surface and which i s accompanied by the development of limonite and f e r r i -molybdite. At Berg an enriched zone i n which secondary ch a l c o c i t e appears as coatings on disseminated p y r i t e i s developed beneath a leached zone. The enriched zone may be up to 400 feet thick (Sutherland Brown, 1966). Vein deposits of s i l v e r - l e a d - z i n c occur i n the outer part of the p y r i t e halo surrounding the Berg deposit. •3 83. 4.3.3 Potassium-argon Dating of the Nanika Intrusions Potassium-argon ages obtained from samples collected from the Nanika intrusions are shown on Figures 24 and 25, and li s t e d on Table V. Analytical data and sample descriptions and locations are contained in Appendices A and C. Where possible, more than one sample was collected from each deposit studied to establish the ages of both intrusion and mineralization. One sample was collected from a stock at Morice Lake to determine i t s possible relationship to the Lucky Ship deposit immediately to the north. A sample also was collected from an apparently barren granitic stock at Nadina Mountain. Potassium-argon results for a l l samples are li s t e d i n Table V. Most analyses were made on biotite separates although a few whole-rock samples were analysed. Copper-molybdenum-bearing Intrusions The bulk of samples for dating were collected from mineralized intrusive phases at the various deposits. Potassium-argon results from these samples range in age from 49.5 + 3 m.y. to 56.2 + 2.3 m.y. Later intrusive phases were dated at three of the deposits. At Red Bird, a geologically younger, post-mineral monzonite porphyry was dated at 49.0+2 m.y., slightly younger than the 49.5 + 3 m.y. age obtained for the mineralized quartz monzonite porphyry. Two samples from nearly barren quartz l a t i t e porphyry at Berg gave an average age of 47.5 + 3 m.y., or 4 million years younger than the mineralized quartz monzonite porphyry phase. A post-mineral quartz monzonite 84. TABLE V. POTASSIUM-ARGON AGES OF NANIKA INTRUSIONS Sample No. Location Rock Unit Age (m, •y.) NC-68-13 Mount Thomlinson Quartz monzonite porphyry 53.8 + 2.2 NC-67- 7 Big Onion Quartz monzonite 48.7 + 1.9 NC-67-42 Lucky Ship Biotite hornfels (W.R.) 49.9 + 2.3 NC-69- 6 Goosly Quartz monzonite porphyry 56.2 + 2.3 NC-68- 7 Nadina Mountain Quartz monzonite 52.9 + 2.2 NC-67- 8 Berg Quartz diorite 46.8 + 1 .5 NC-67- 9 Berg Quartz l a t i t e porphyry 48.0 + 3 NC-67-10 Berg Quartz l a t i t e porphyry 47.0 + 3 NC-67-11 Berg Quartz monzonite porphyry 52.0 + 2 NC-67-12 Berg Biotite hornfels (W.R.) 52.0 + 3 NC-67-13 Berg Metamorphosed quartz diorite 49.9 + 2.1 NC-67-17 Red Bird Biotite hornfels (W.R.) 50.0 + 1.7 NC-67-19 Red Bird Quartz monzonite porphyry 49.5 + 3* NC-67-20 Red Bird Quartz monzonite porphyry 49.0 ± 2 *Average of two analyses. (W.R.) - Whole Rock Sample. Note: Calculation of analytical error outlined i n Appendix A.2. 85. dyke at Big Onion was dated at 48.7 +1.9 m.y. A l l of these ages provide an upper limit for the age of mineralizaton of these deposits. Biotite Hornfels Whole-rock biotite hornfels samples from the Berg and Red Bird deposits and the results (52 + 3 and 50.0 ±1.7 m.y. respectively) are i n good agree-ment with those obtained for the i n i t i a l porphyry phases (Table V and Figure 25). Comparing these results with that obtained from a biotite hornfels sample at the Lucky Ship deposit, the age of intrusion of the Lucky Ship pluton may be inferred as being 49.9 ± 2.3 m.y. Similarly, a sample of quartz diorite from within the metamorphic aureole at Berg, which contains secondary biotite after hornblende, yields an age of 49.9 ± 2.1 m.y., very close to the age determined for the main quartz monzonite porphyry intrusion. Other Intrusions Three samples were collected from intrusive bodies apparently barren of copper or molybdenum mineralization, but spatially related to mineralized Nanika intrusions. The quartz monzonite stock at Nadina Mountain has a potassium-argon age of 52.9 ± 2.2 m.y. , similar to ages obtained for copper-molybdenum-bearing Nanika intrusions , although i t apparently i s lacking i n sulphide mineralization. The large elongate quartz diorite pluton bordering the Berg deposit on the east (Figure 25) i s believed to be a stock s a t e l l i t i c to the Coast Plutonic 86. Complex or a pluton related to the Bulkley intrusions. The 46.8 +1.5 m.y. age i s anomalously young compared to the metamorphosed sample dated at 49.9 + 2.1 m.y., and may be explained by the chloritized nature of the biotite sample. The low potassium content of 2.64 per cent signifies probable argon loss. The quartz monzonite stock at Morice Lake yielded a potassium-argon age of 178+8 m.y. indicating that i t i s unrelated to the molybdenum-bearing Lucky Ship pluton. Instead, i t i s part of the much older Topley intrusions. 4.3.4 Summary (1) The age of intrusion of the copper-molybdenum-bearing Nanika intrusions i s in the range of 49.5 to 56 million years, based on results obtained from samples of the i n i t i a l intrusive phase and of biotite hornfels samples peripheral to several of the intrusions. (2) The age of mineralization i s congruent or slightly younger than the age of intrusion as indicated by the slightly younger ages obtained from post-mineral porphyry phases which are petrologically similar to the i n i t i a l porphyry phases at the Berg and Red Bird deposits. (3) Where suitable biotite cannot be collected from plutons (e.g. , Lucky Ship) the age of intrusion and/or mineralization can be obtained by analysing whole-rock samples of biotite hornfels. 4.4 PORPHYRY COPPER DEPOSITS ASSOCIATED WITH THE BABINE INTRUSIONS Babine intrusions occur i n a northwest-trending belt, not more than 25 miles wide, near the east boundary of the area shown on Figures 14 and 16. 87. They extend from the northern part of Babine Lake northward almost to latitude 56 degrees. Babine intrusions comprise a number of small stocks, plugs, and dyke swarms of equigranular quartz diorite and quartz monzonite and a dis-tinctive biotite feldspar porphyry which i s host to important porphyry copper deposits. 4.4.1 Geologic Setting The porphyry copper deposits of the Babine Lake area are associated with small intrusions of Tertiary (Eocene) age which intrude Mesozoic volcanic and sedimentary rocks. The Mesozoic rocks range in age from Late Triassic to Late Cretaceous or Early Tertiary age. Upper Triassic limestones, siltstones, and volcanic rocks are confined to a relatively small area west of Babine Lake. The most wide-spread rocks of the area are the clastic volcanic and sedimentary rocks of the Jurassic Hazelton Group (Figure 8, pocket). Sedimentary and volcanic rocks of Early to Mid-Cretaceous age are widespread north of Babine Lake, and younger cl a s t i c sedimentary rocks, part of the Sustut Group, are found as small outliers adjacent to northwest-trending faults of regional magnitude. Small remnants of young (post-Eocene ?) basaltic and andesitic volcanic rocks occur through-out the area shown on Figure 26 (pocket). Plutonic rocks of various ages intrude the Mesozoic rocks of the Babine Lake area (Figure 26). The oldest of these include Lower Jurassic porphyritic quartz monzonites and granodiorites of the Topley intrusions and small stocks of diorite, monzonite, and quartz diorite of Cretaceous age, possibly a part of the Omineca intrusions. Upper Cretaceous intrusions include rhyolite 88. porphyry stocks and dykes and granodiorite porphyries of similar age to the Bulkley intrusions. Babine intrusions of Eocene age are widespread and include equigranular quartz diorite, quartz monzonite, and related biotite feldspar porphyries. These occur as small stocks, dykes, dyke swarms, and plugs. Extrusive equiva-lents of these subvolcanic intrusions occur as flat - l y i n g sheets which exhibit columnar jointing near the south end of Newman Peninsula and west of Babine Lake (Figure 26). Although these rocks are similar i n appearance to the intrusive biotite feldspar porphyries, they differ by having hornblende as the chief mafic mineral. The hornblende imparts a flow texture to these rocks. Extrusive equivalents also include crystal tuffs and flow breccias. The major structural trend of the area i s northwest, as reflected by the trend of numerous parallel block faults. Important northeast faults are also known, most notably that which separates older bedded rocks and the Topley intrusions on the south from younger rocks to the north (Figure 8, pocket). The Tertiary Babine intrusions and related porphyry copper deposits have been localized at or near intersections of northeast and northwest faults (Carter, 1972). The bulk of porphyry copper deposits are contained i n three parallel northwest-trending graben structures which include, from west to east: (1) Granisle-Newman (Bell Copper) - Old Fort; (2) Morrison-Hearne H i l l ; (3) Dorothy-Nak Lake-Trail Peak (Figure 26). 4.4.2 Geology and Style of Mineralization Porphyry copper deposits are associated with the Babine intrusions which occur as irregular dykes, dyke swarms, and plugs of one-half to 1 square mile 89. in surface area. Copper mineralization invariably i s related to the biotite feldspar porphyry phase of the Babine intrusions. This distinctive rock type i s a crowded porphyry i n which 2-millimetre to 3-millimetre phenocrysts of euhedral plagioclase and biotite are set i n a fine-grained matrix of plagioclase, quartz, biotite, and minor K-feldspar. The rocks range i n composition from quartz diorite to granodiorite. Multiple intrusion i s evident at most copper mines and prospects associated with the Babine intrusions. At the Granisle and Old Fort properties (Figure 26), the f i r s t intrusive phase i s represented by oval plugs of fine-grained, equigranular quartz diorite and/or quartz monzonite. These quartz diorites are intruded by somewhat younger biotite feldspar porphyries. At Granisle, the small, e l l i p t i c a l quartz diorite plug i s invaded by a large northeast-striking dyke of biotite feldspar porphyry i n which several pre-and intermineral phases are recognized (Kirkham, 1971; Carter, 1972). These are grossly similar i n appearance and composition, but can be distinguished by slight differences i n the colour of the matrix resulting mainly from variations in grain size, by crosscutting relationships, and by the presence of inclusions of earlier phases contained i n later ones. The later phases are progressively less well fractured and mineralized. Within the ore zone, a narrow zone con-sisting of dykes and stringers of intrusive breccia occurs along the contact between biotite feldspar porphyry and the quartz diorite. These breccias commonly contain 1-centimetre to 2-centimetre rounded fragments of both the quartz diorite and biotite feldspar porphyry in a fine-grained, light to dark grey granulated matrix of strained and fractured quartz, broken plagioclase grains, and locally abundant, very fine-grained biotite. The quartz diorite and biotite feldspar porphyry fragments commonly contain quartz-filled 90. Fig. 27 BABINE INTRUSIONS • TERTIARY Biotite Feldspar Porphyry. ffiZ Extrusive Equivalents tHjijIjIjl 11111111. t Quartz Diorite CRETACEOUS-TERTIARY K«j|g§§9 Sustut Group •• Greyvvocke saaZzZ&is Sandstone • 49 K-Ar Age(m.y.) C^P Ore Bodies COPPER DEPOSITS CRETACEOUS Quartz Diorite, Monzonite, mm Quartz Monzonite JURASSIC Argillaceous Siltstones, Hornfelsed Equivalents Andesite Tuffs & Breccias Miles 91. fractures mineralized with chalcopyrite. Breccias are obviously intermineral i n t r u s i o n s inasmuch as they contain disseminated chalcopyrite i n the matrix. The l a t e s t porphyry phase at Granisle contains only sparse chalcopyrite and i s interpreted as being nearly of post-mineral age. This phase occurs as small dykes of dark grey b i o t i t e feldspar porphyry which intrude quartz d i o r i t e near the eastern edge of the ore zone. Mult i p l e i n t r u s i o n , i n the form of intermineral dykes and s t r i n g e r s of porphyry and i n t r u s i v e b r e c c i a , i s also a feature of the Morrison, Nak Lake, and Dorothy properties. At B e l l Copper, a northerly s t r i k i n g dyke of l a t e , possibly post-mineral, b i o t i t e feldspar porphyry, up to 400 feet wide, truncates the eastern part of the ore zone. Stringers of i n t r u s i v e b r e c c i a occur near the contact between t h i s i n t r u s i v e phase and the mineralized phase. A c h a r a c t e r i s t i c of the Babine int r u s i o n s as contrasted with others i n west-central B r i t i s h Columbia i s the r e l a t i v e lack of post-mineral basic dykes. One basic dyke was noted i n diamond-drill core at the Morrison deposit. Horn-f e l s i n g of sedimentary and v o l c a n i c rocks adjacent to the Babine i n t r u s i o n s i s not a prominent feature, due to the composition of the country rocks. Well-developed b i o t i t e hornfels aureoles were noted only at the Old Fort, Morrison, and T r a i l Peak properties. Hydrothermal a l t e r a t i o n at porphyry copper deposits r e l a t e d to Babine in t r u s i o n s has been w e l l documented i n a recent paper by Carson and Jambor (1974). E s s e n t i a l l y , hydrothermal a l t e r a t i o n zones consist of a c e n t r a l potassic zone, represented by abundant secondary b i o t i t e , gradational outward to a q u a r t z - s e r i c i t e - p y r i t e zone which i n turn i s enveloped by a p r o p y l i t i c zone. 92. At Granisle, the potassic zone i s roughly coincident with the zone of copper mineralization. Within this zone, the intrusive rocks appear relatively fresh i n hand specimen and plagioclase phenocrysts are essentially unaltered. The main alteration product i s secondary biotite which occurs as very fine-grained, dark brown aggregates which retain original amphibole outlines i n both the porphyries and quartz diorites. Fine-grained secondary biotite also i s uniformly distributed i n the matrix of the intrusive rocks. Minor secondary K-feldspar also occurs i n the potassic zone, usually as fine grains i n the intrusive rock matrix and i n thin envelopes enclosing quartz veinlets and fractures i n the deeper sections of the ore zone. At the Newman deposit (Bell Copper), the potassic zone also coincides with the zone of copper mineralization, but i s d i f f i c u l t to recognize i n the upper parts of the ore zone because supergene alteration has destroyed the biotite. The biotite or potassic zone at the Morrison deposit extends some-what beyond the copper zone and consists of sugary textured, brown hydrothermal biotite that has replaced hornblende phenocrysts and locally has flooded the matrix of the host biotite feldspar porphyry. Carson and Jambor (1974) indicate that dark brown, coarse-grained, sugary textured hydrothermal biotites are associated with relatively strong copper mineralization , whereas greenish and/or fine-grained hydrothermal biotites are indicative of weak copper mineralization. The latter point would appear to apply to such deposits as Old Fort, Nak Lake, Dorothy, and T r a i l Peak where secondary biotite alteration i s only weakly developed and copper mineralization i s of low grade and/or sporadic distribution. However, i t should be pointed out that late or post-mineral biotite feldspar porphyry dykes, which occur within the biotite zones at Granisle and 93. Newman, contain l i t t l e , i f any, secondary biotite. This would indicate that alteration i s an integral part of an earlier intrusive-mineralization time period. The quartz-sericite-pyrite alteration zone also i s best developed at the better mineralized properties. Intrusive and adjacent volcanic and sedimentary rocks within this zone are weathered to a uniform buff colour. Abundant fine-grained quartz and pyrite have been introduced, mafic minerals have been altered to a mixture of sericite and carbonate, and plagioclase i s clouded by sericite. Enveloping this zone i s the propylitic zone which i s represented by chlorite, carbonate, and epidote alteration of volcanic and sedimentary rocks. Chalcopyrite i s the dominant ore mineral at a l l Babine porphyry copper deposits. It occurs primarily i n northeast and northwest-striking, vertically dipping, quartz-filled fractures which vary i n width from 1 to 5 millimetres. Chalcopyrite also i s disseminated i n the fine-grained quartz diorite and intrusive breccia at Granisle. Also at Granisle, bornite occurs with chalco-pyrite i n the central part of the ore zone. Irregular veins up to 1 foot wide, which consist of coarse-grained chalcopyrite, bornite, quartz, b i o t i t e , and apatite have been uncovered in the southern half of the ore zone at Granisle. The Granisle orebody i s localized along the contact between biotite feldspar porphyry and quartz diorite (Figure 27). Most other deposits, most notably Newman (Bell Copper), also exhibit better grades of copper mineralization at or near contacts between the porphyries and marginal sedimentary and volcanic rocks. 94. The Newman orebody i s unique i n that i t i s one of the few porphyry deposits i n B r i t i s h Columbia with a s u b s t a n t i a l zone of supergene mi n e r a l i z -a t i o n . This zone extends to depths of as much as 400 feet and consists of chal c o c i t e coating p y r i t e and chalcopyrite i n fractures and quartz v e i n l e t s i n porphyry and adjacent s i l t s t o n e s . The best-developed zone of supergene m i n e r a l i z a t i o n i s centred over best grades of primary chalcopyrite m i n e r a l i z -a t i o n which are contained i n a v e r t i c a l p i p e - l i k e zone approximately 400 feet i n diameter and extending to a depth of at l e a s t 2,500 feet . Within t h i s zone, fine-grained chalcopyrite occurs i n a stockwork of quartz v e i n l e t s and i n i r r e g u l a r s i l i c i f i e d areas i n the porphyry and bordering s i l t s t o n e s . Lower grade, primary and secondary copper min e r a l i z a t i o n i s p e r i p h e r a l to a higher grade zone on i t s eastern side. Better grades of copper min e r a l i z a t i o n at the Morrison deposit consist of chalcopyrite and minor bornite i n q u a r t z - f i l l e d fractures, and are best developed i n , and marginal to, northerly trending dyke swarms of b i o t i t e feldspar porphyry which occur west and east of a small pluton of s i m i l a r composition. P y r i t e haloes are well developed around the Granisle, Newman, and Morrison deposits and these may extend outward at l e a s t 1,000 feet from the copper orebodies. Carson and Jambor (1974) suggest that large p y r i t e haloes, containing 5 to 10 per cent p y r i t e , are developed only around economic copper deposits i n the Babine Lake area. Both the Granisle and Newman deposits have peripheral quartz-carbonate vein deposits which contain varying amounts of p y r i t e , galena, s p h a l e r i t e , and chalcopyrite. These were explored 40 years before the copper deposits attained economic s i g n i f i c a n c e . 95. 4.4.3 Potassium-argon Dating of the Babine Porphyry Copper Deposits Potassium-argon ages obtained from samples collected i n the Babine Lake area are shown on Figures 26 and 27. Analytical data, deposit and sample descriptions, and precise locations are contained i n Appendices A and C. Most samples were collected at or near porphyry deposits related to the Babine intrusions. Several samples were collected from other intrusive and extrusive bodies to determine their geologic sigificance. Potassium-argon results for a l l samples collected are l i s t e d i n Table VI. Analyses were made on biotite separates from a l l but one sample. Copper-bearing Intrusions Samples from the mineralized biotite feldspar porphyry phase were collected from five deposits (Table VI) and potassium-argon ages obtained from these samples range from 49.0 + 2 to 55.0 + 3 m.y. Because these samples contain hydrothermal biotite i n addition to primary biotite phenocrysts , these results can be interpreted as reflecting the apparent age of mineralization at these deposits. The age of mineralization at Granisle i s indicated by the 50.2 +2.1 m.y. age obtained from a coarse-grained quartz-biotite-apatite-chalcopyrite-bornite vein. Late , nearly post-mineral, biotite feldspar porphyry phases at Granisle and Newman give ages of 51.0 + 2 and 48.9 + 2.1 m.y. respectively. While within the limits of analytical error, these are younger than the ages obtained for the mineralized porphyry phases at these deposits and provide an upper limit for the age of mineralization. 96. TABLE VI. POTASSIUM-ARGON AGES OF BABINE INTRUSIONS Sample No. Location Rock Unit Age (m.y.) NC-67- 1 Old Fort NC-67- 2 Old Fort Biotite feldspar porphyry Biotite quartz monzonite 49.0 + 2 52.0 + 2 NC-67- 4 NC-67- 5 NC-68- 1 NC-69- 8 Granisle Granisle Granisle Granisle Biotite feldspar porphyry Biotite feldspar porphyry Biotite feldspar porphyry Quartz-biotite-sulphide vein 55.0 + 3 51.0 + 2 51.0 + 2 50.2 + 2.1 NC-67-22 Newman NC-67-23 Newman Biotite feldspar porphyry Biotite feldspar porphyry 49.8 + 2.1 51.0 + 3 NC-67-40 Morrison B i o t i t e feldspar porphyry 52.1 + 2.1 NC-68-10 T r a i l Peak NC-69- 1 T r a i l Peak Biotite feldspar porphyry Quartz diorite 48.9 + 1 .5 104 + 4 NC-67-43 Newman Peninsula Hornblende feldspar porphyry 51.5+1.9 NC-69- 4 Tachek Creek Hornblende-biotite-quartz porphyry 176+7 NC-72- 1 Lennac Lake Quartz-hornblende-biotite feldspar 77.0 + 2.5 porphyry 97. The age of intrusion of the Babine porphyries i s congruent, or nearly so, with the age of mineralization as indicated by three of the samples analysed. An age of 52.0 + 2 m.y. was obtained for a biotite sample collected from a non-mineralized biotite-quartz-monzonite s i l l south of the Old Fort property (Figure 26). Biotite from a biotite feldspar porphyry dyke south of the Granisle deposit (Figure 27), and devoid of secondary biotite and sulphide minerals, yielded an age of 51.0 +2 m.y. A hornblende sample (NC-67-43) from a hornblende feldspar porphyry extrusive on the south end of Newman Peninsula (Figure 26) returned an age of 51.5 +1.9 m.y. Because this porphyry i s an extrusive equivalent of biotite feldspar porphyry, the age obtained can be interpreted as being that of extrusion and intrusion. Other Intrusions Stocks of medium-grained to coarse-grained equigranular di o r i t e , quartz diorite, and monzonite occur throughout the northern Babine Lake area (Figure 26). These are believed to be related to the Omineca intrusions and are non-mineralized i n this area. Several of these stocks, including those at Hearne H i l l and T r a i l Peak (Figures 26 and 27) are cut by dykes and irregular bodies of biotite feldspar porphyry which contain some copper mineralization. A sample from the quartz diorite stock at T r a i l Peak yielded a potassium-argon age of 104 + 4 m.y., somewhat younger than the Early Cretaceous ages obtained for some phases of the Omineca intrusions i n the Hogem batholith to the northeast (Garnett, 1972). This younger age would be due to partial 98. radiogenic argon loss in the biotites of the quartz diorite due to the intrusion of younger biotite feldspar porphyry dykes. Porphyry-type copper and molybdenum mineralization i n Tachek Creek south of Topley Landing (Figure 26) i s associated with hornblende-biotite-quartz-feldspar porphyry dykes which cut porphyritic quartz monzonite of the Topley intrusions. A sample from one of these dykes (NC-69-4) returned a potassium-argon age of 176 + 7 m.y., indicating that these dykes represent a late phase of the Topley intrusions of Late Triassic-Early Jurassic age. A relatively coarse-grained quartz-hornblende-biotite feldspar porphyry from the Lennac Lake porphyry copper prospect (Figure 26), similar i n appear-ance to some of the typical Babine porphyries, was analysed as 77.0 + 2.5 m.y. Similar intrusions with associated copper-molybdenum mineralization are known in the French Peak-Mount Thoen area to the northwest and these constitute a third age of mineralization i n the Babine Lake area. 4.4.4 Summary (1) Babine intrusions were emplaced at about 52.0 m.y. as indicated by results from samples collected away from mineralized and hydrothermally altered zones. (2) The age of mineralization in Babine intrusions i s synchronous, or nearly so, with the age of intrusion. This i s borne out by a number of potassium-argon ages obtained from (a) mineralized porphyry phases containing abundant hydrothermal biotite; (b) from late porphyry phases which provide an upper limit for the age of mineralization; and (c) from a quartz-biotite-sulphide vein. 99. At least four ages of intrusive activity are known in the northern Babine Lake area including: 176 to 200 m.y. (Topley intrusions); 104 m.y. (Omineca intrusions); 77 m.y. (Bulkley intrusions); and 50 m.y. (Babine intrusions). Three ages of porphyry copper mineralization have been defined i n the Babine area. Babine intrusions of Middle Eocene (50 m.y.) age are known to be the most significant. The other two ages include copper-molybdenum mineralization related to a late porphyry phase of the Topley intrusions and porphyry stocks of Late Cretaceous age, equivalent to the Bulkley intrusions and hosting copper-molybdenum mineralization. 100. 5. COMPARISON OF PORPHYRY DEPOSIT POTASSIUM-ARGON AGES TO OTHER AREAS AND THEIR TECTONIC EVOLUTION 5.1 INTRODUCTION Two metallogenic epochs have been defined i n this study. These include the 50 m.y. ages obtained for copper and molybdenum deposits related to the Alice Arm, Nanika, and Babine intrusions and the 70 to 84 m.y. ages for the copper-molybdenum deposits associated with the Bulkley intrusions. A l l of these deposits are situated within or marginal to the Intermontane Tectonic Belt. Similar ages for porphyry deposits have been reported in the Intermontane, Coast Crystalline, and Insular Tectonic Belts of British Columbia, Yukon, southern Alaska, and Washington State. The classic porphyry copper province of southwest Arizona and northern Mexico i s of similar age being i n the 50 to 70 m.y. range. 5.2 POTASSIUM-ARGON AGES OF PORPHYRY DEPOSITS IN NORTH AMERICA Most porphyry copper and molybdenum deposits i n western North America are of Cretaceous or Tertiary age. The major exceptions are the important porphyry copper deposits in British Columbia, principally those i n the Princeton, Highland Valley, Cariboo, Omineca, and Stikine areas, which are of Late Triassic and Jurassic age. Porphyry deposits of Late Cretaceous and Tertiary age , outside the study area, are brie f l y described on the following pages. 101. 5.2.1 British Columbia Late Cretaceous and Tertiary ages for many porphyry deposits outside the study area are shown on Figure 28. In northern British Columbia, the Eocene (50 m.y.) and Late Cretaceous (70 m.y.) metallogenic epochs have been documented by Christopher (1972, 1973). Ages ranging from 48.7 ±1.9 to 50.5 ±1.5 m.y. were obtained for samples from the Mount Haskin and Mount Reed molybdenum properties east of Cassiar (Figure 28). The Cassiar molybdenum property south of Cassiar i s of Late Cretaceous or Early Tertiary age (68 to 72 m.y,) and the Adanac molybdenum property east of A t l i n i s of similar (62 m.y.) age. Late Cretaceous and Early Tertiary ages have also been reported for porphyry deposits i n south-central British Columbia. The Maggie porphyry copper-molybdenum deposit 10 miles north of Cache Creek has a potassium-argon age of 61.2 + 2 m.y. (McMillan, 1970). An age of 67 m.y. was obtained for the Rey Lake porphyry copper prospect east of the Guichon batholith (McMillan, personal communication). Several other porphyry prospects situated i n the Intermontane Tectonic Belt of southwestern British Columbia are believed to be of Late Cretaceous or Early Tertiary age although no radiometric ages have as yet been determined for them. These include the Fish Lake copper-gold porphyry deposit east of Taseko Lakes, the Poison Mountain copper-molybdenum deposit northwest of L i l l o o e t , and the Whipsaw Creek and Ashnola River porphyry prospects south of Princeton. The Red Mountain molybdenum deposit at Rossland i s believed to be related to an igneous event dated at 48 m.y. (Fyles, et a l . , 1973). 103. Granitic rocks of the Chilliwack batholith range i n age from 16 to 32 m.y., with the majority of ages being about 20 m.y. (Richards and White, 1970). Minor copper occurrences have been reported i n these rocks. Two discrete age groups of Tertiary porphyry-type mineralization are known on Vancouver Island (Carson, 1969). These include 48 and 50 m.y. ages for the Catface copper and Tofino molybdenum properties on the west coast of the Island, and the 30 to 39 m.y. ages for the Mount Washington, Faith copper, and Gem Lake deposits west of Courtenay, and the Corrigan Creek prospect south of Alberni (Figure 28). In summary, the Late Cretaceous and Tertiary mineralizing epochs can be extended north and south of the study area, although definition of these awaits further study. 5.2.2 Washington State Numerous copper deposits of vein and porphyry type i n the Cascade Range of Washington are temporally and spatially related to high-level calc-alkaline intrusive rocks ranging i n age from Oligocene to Miocene (15 to 30 m.y.) (Grant, 1969). These ages correspond to those obtained for the Chilliwack batholith immediately to the north in British Columbia (Richards and White , 1970) . 5.2.3 Southern Alaska Most known mineral deposits and areas of hydrothermal alteration i n southern Alaska are associated with hypabyssal intrusions of Late Cretaceous and Tertiary age, ranging from 58 to 75 m.y. (Reed and Lanphere, 1969; 104. Hollister, et a l . , 1974). These ages are i n good agreement with those obtained in west-central British Columbia. 5.2.4 Yukon Potassium-argon ages have been determined for two porphyry deposits i n the Yukon. The Casino copper-molybdenum deposit at Canadian Creek has a mean age of 70 + 3 m.y. (Phillips and Godwin, 1970), in good agreement with ages obtained for similar deposits in central British Columbia. The Burwash Creek copper-molybdenum deposit west of Kluane Lake has a mean age of 26.0 + 0.3 m.y. (Christopher, 1972), much younger than the 50 m.y. epoch i n central B r i t i s h Columbia but similar to ages of deposits i n the Cascade Range of Washington. 5.2.5 Southern Basin and Range Province, U.S.A. No comparison of potassium-argon ages obtained during this study would be complete without relating them to potassium-argon ages for the extremely important porphyry copper deposits of Arizona, New Mexico, and Sonora state of Mexico. The deposits of this area are regarded as the typical porphyry copper. The porphyry deposits of west-central British Columbia have many features i n common with them, including size, form, composition of host intrusive, style of mineralization, and hydrothermal alteration. A similarity of potassium-argon ages i s also apparent. Potassium-argon ages for 27 porphyry deposits i n the southern Basin and Range province range in age from 52 m.y. to 72 m.y., referred to as Laramide age (Livingston, 1973). 105. The greater number of deposits have an age of about 65 m.y. Where determined, the age of mineralization i s indistinguishable from the age of the host pluton (Livingston, et a l . , 1968), again in agreement with results obtained from this study. The potassium-argon ages i n the southern Basin and Range province have a trend from oldest to youngest i n a southeast direction from northwestern Arizona to Sonora state i n Mexico (Livingston, 1973). 5.3 EVOLUTION OF PORPHYRY DEPOSITS OF WEST-CENTRAL BRITISH COLUMBIA Several authors have attempted to relate the distribution of porphyry copper deposits i n North and South America to the plate tectonic theory (Farrar, et a l . , 1970; Hodder and Hollister , 1972; S i l l i t o e , 1972; Livingston, 1973). This theory postulates that calc-alkaline igneous rocks and related porphyry mineral deposits are generated by part i a l melting of oceanic crustal rocks in subduction zones beneath the continental margins. These subduction zones are believed to have migrated with time. Farrar, et a l . (1970) and S i l l i t o e (1972) give good evidence for migration of subduction zones resulting i n varying ages of intrusive activity. An example of this i s shown by the potassium-argon ages obtained i n Peru and northern Chile (Farrar, et a l . , 1970). Magmatism began in Permian time as represented by intrusion of this age near the present coastline, and was followed by four major intrusive episodes i n the Lower Jurassic, Middle Cretaceous, Lower Paleocene, and Upper Eocene. Intrusive rocks of these ages 106. are arranged in linear belts crudely parallel to the present coastline, and these belts decrease in age eastward. Clark and Z e n t i l l i (1972) indicate that porphyry copper deposits i n northern Chile and northwestern Argentina are related to f e l s i c stocks of Upper Jurassic, Middle Cretaceous, Lower Paleocene, Upper Eocene, Oligocene-Miocene , and Miocene-Pliocene age. They postulate that from Triassic-Jurassic time to Middle Tertiary, the l o c i of epizonal magmatism has migrated in an east-southeast direction to form a series of discrete longitudinal metaliogenie sub-provinces. The trend i n ages of porphyry copper deposits i n the southern Basin and Range province, from 70 m.y. i n Arizona to 50 m.y. i n northern Mexico, i s explained by Livingston (1973) as being due to the migration of the North American plate in a northwesterly direction over a mantle hot spot. The potassium-argon ages for porphyry deposits in west-central British Columbia show no simple trend as i n South America or the southern Basin and Range province. Four crudely parallel belts are evident, including from west to east: 50 m.y. Alice Arm molybdenum deposits; 70 to 84 m.y. Bulkley copper-molybdenum deposits; 50 m.y. Nanika copper-molybdenum deposits; and the 50 m.y. Babine copper deposits. Thus, there i s no simple eastward migration of intrusive centres, rather there appears to be a reversal from 50 m.y. to 70-84 m.y., and back to 50 m.y. This more complicated pattern of intrusive ages may be a reflection of the complex tectonic history of the northwestern Cordillera of North America. The study area i s bordered on the west by the Coast Plutonic Complex, a tectonic belt unique i n the Cordillera of North and South America. It i s 107. possible that the numerous copper and molybdenum-bearing intrusions i n west-central B r i t i s h Columbia were related to the evolution of the Coast Plutonic Complex. Wheeler, et a l . , (1972) postulate that the Coast Plutonic Complex evolved independently of the rest of the Cordillera until Mid-Mesozoic time. After this time, i t i s impinged on the remainder of the Cordillera and a subduction zone beneath the Complex affected the tectonic evolution of the entire Cordilleran region. Potassium-argon ages obtained from granitic rocks of the Coast Plutonic Complex indicate three parallel belts which are younger and more potassic in an eastward direction. These belts include a western zone , predominantly of quartz diorite composition (84 - 140 m.y. on the west and 79 - 64 m.y. on the east part of the zone), a central core zone of migmatitic gneiss, quartz d i o r i t e , and granodiorite (45 m.y.), and an eastern zone of granodiorite and quartz monzonite (40 - 50 m.y.) which i s intrusive into Mesozoic layered rocks. This trend in ages i s i n agreement with the concept of an eastward migrating subduction zone beneath the Coast Plutonic Complex from Late Jurassic to Early Tertiary time. The Bulkley copper and molybdenum-bearing intrusions (70 - 84 m.y.) correspond in age and composition to the quartz diorites and granodiorites of the eastern part of the west zone of the Coast Plutonic Complex (64 - 79 m.y.). Although situated a f a i r distance to the east, the Bulkley intrusions may have been generated by the same period of underthrusting along the subduction zone that resulted i n the emplacement of the east part of the western zone of the Coast Plutonic Complex. The hypabyssal nature of the Bulkley intrusions, i n 108. contrast to the plutonic nature of the granitic rocks of the Coast Complex, and their localization at or near fault intersections, reflects their greater ve r t i c a l distance above the east-dipping subduction zone. Renewed underthrusting of the oceanic plate beneath the continental crust i n Eocene time (40 - 50 m.y.) culminated i n the emplacement of the core and eastern zones of the Coast Plutonic Complex. Related to this igneous event are the Alice Arm molybdenum-bearing intrusions (50 m.y.) which occur along the eastern flank of the Coast Complex. These are of quartz monzonite or granite composition and were intruded a measureable amount of time (2 - 5 m.y.) prior to the emplacement of the eastern zone of the Coast Plutonic Complex. The Nanika and Babine intrusions, also of 50 m.y. age, may be related to this period of movement along the subduction zone. Most Nanika intrusions are similar i n chemical composition to the Alice Arm intrusions and similarly several of them are not far removed from the east flank of the Coast Plutonic Complex. Those Nanika intrusions further to the east appear to have been localized by the same fault systems governing the emplacement of the Bulkley intrusions i n Late Cretaceous time. The Babine intrusions are also of 50 m.y. age but are markedly different from the Alice Arm and Nanika intrusions in form and composition. They are of granodiorite and quartz diorite composition and exhibit features typical of subvolcanic intrusions, occurring as dykes, dyke swarms, necks, and plugs. Volcanic features include the presence of intrusive breccias and extrusive sheets and flows preserved nearby several of the intrusive centres. They, l i k e the Bulkley intrusions of earlier age, occur a f a i r distance to the east of the youngest zone of the Coast Plutonic Complex and were localized at inter-sections of major faults. The volcanic nature of the Babine intrusions may 109. be a reflection of their emplacement a great vertical distance above an active subduction zone. The crude zonation of contained metallic mineralization i n the porphyry deposits of west-central British Columbia include from west to east: Alice Arm molybdenum deposits, Bulkley and Nanika copper-molybdenum deposits, and Babine copper deposits. Notable exceptions to this pattern include the several deposits associated with the Nanika and Bulkley intrusions which contain only molybdenum. As might be expected, molybdenum-bearing plutons such as the Alice Arm intrusions are more acidic than those containing copper-molybdenum or copper. Alice Arm molybdenum-bearing plutons also intrude a sedimentary sequence while the copper-molybdenum and copper-bearing Bulkley, Nanika, and Babine intrusions occur i n predominantly volcanic sequences. 110. 6. CONCLUSIONS Porphyry copper and molybdenum deposits i n west-central British Columbia are associated with the Alice Arm, Bulkley, Nanika, and Babine intrusions which occur i n four subparallel belts and are distinguished on the basis of age, chemical composition, and contained metal content. These i n -trusions cut Mesozoic volcanic and sedimentary rocks of the Intermontane Tectonic Belt. Copper and molybdenum sulphides occur as fracture f i l l i n g s and i n veinlet stockworks within and adjacent to the intrusive bodies. Sulphide and alteration minerals exhibit concentric zoning relative to the host intrusions. (a) The 50 m.y. Alice Arm molybdenum-bearing intrusions make up the westernmost belt, occurring as small stocks which intrude Mesozoic sedimentary rocks along the east flank of the Coast Plutonic Complex. Multiple intrusion i s a common feature of the deposits and potassium-argon dating of two or more inter-mineral and post-mineral intrusive phases indicates that the age of mineralization i s synchronous with the age of intrusion. Coast Plutonic Complex granitic rocks nearby the Alice Arm intrusions were emplaced a few million years later than the molybdenum-bearing stocks. (b) Bulkley intrusions of 70 - 84 m.y. age occur i n the central part of the area studied and are i n the form of stocks of granodiorite composition which contain copper and molybdenum mineralization. Mesozoic sedimentary and volcanic rocks adjacent to the intrusions are hornfelsed and whole-rock potassium-argon dating of these rocks were found to give reliable ages of intrusion of stocks 111. which contained no suitable mafic minerals. Multiple intrusion i s a common feature and potassium-argon dating of various intrusive phases indicates congruent ages for mineralization and intrusion. (c) Nanika intrusions have the same geographic setting as the Bulkley intrusions but are of 50 m.y. age. They also host copper and molybdenum mineralization and occur as small stocks or plugs of quartz monzonite porphyry. Sedimentary rocks marginal to the intrusions are converted to biotite hornfels and in some instances whole-rock samples of hornfels were used to date the age of intrusion. Potassium-argon dating of mineralized and inter-mineral porphyry phases indicates congruent ages for intrusion and mineralization. (d) Babine intrusions and associated copper deposits occur i n the eastern part of the area studied and are of 50 m.y. age. They dif f e r i n form, composition, and texture from the other plutons of similar age. They are subvolcanic intrusions and occur as dykes, dyke swarms, necks , and plugs emplaced into Mesozoic porphyries of quartz diorite-granodiorite composition and extrusive equivalents of these are present i n the area. Multiple intrusion i s a common feature and potassium-argon dating of two or more phases at several deposits demonstrates congruent ages for mineralization and intrusion. This study proposes a new subdivision of granitic rocks i n central British Columbia. These range in age from Early Mesozoic to Tertiary. Mesozoic granitic intrusions occur as batholiths and stocks and include the Upper Triassic-Lower Jurassic Topley intrusions (176 - 206 m.y.), the Lower to Upper Jurassic Omineca intrusions (121 - 177 m.y.), and 112. the Upper Jurassic Francois Lake intrusions (133 - 155 m.y.). The Kitsault intrusions of Jurassic and Cretaceous age occur as stocks i n the northwest part of the area. Granitic rocks of the Coast Plutonic Complex border the area on the west and range in age from 43 to 140 m.y. The great number of Late Cretaceous and Tertiary intrusions in the central part of the area include the Bulkley intrusions (70 - 84 m.y.), Babine intrusions (49 - 55 m.y.), Nanika intrusions (47 - 54 m.y.), Alice Arm intrusions (48 - 54 m.y.), and Goosly Lake intrusions (49 m.y.). Porphyry deposits of Late Cretaceous and Early Tertiary age, similar to those i n west-central British Columbia, are known throughout the North American Cordillera. These include the porphyry deposits of the southern Basin and Range province, U.S.A., southern and northern British Columbia, Yukon , and southeast Alaska. The distribution of potassium-argon ages of porphyry deposits i n west-central British Columbia does not f i t the relatively simple plate tectonic theory advanced for deposits of similar type and age i n the Andes of South America and the southern Basin and Range province , where deposits become progressively younger in a given direction. Here instead two widely separated belts of plutons, the Alice Arm and Babine intrusions, of the same 50 m.y. age but of different character, are separated by a belt of older (70 - 84 m.y.) Bulkley intrusions. Also occurring within this central belt are the Nanika intrusions, of similar 50 m.y. age to the Alice Arm and Babine intrusions. These intrusions may have been related to periodic movement along a subduction zone from which the granitic rocks of the Coast Plutonic Complex evolved i n three distinct episodes. Potassium-argon ages in 113. the Coast Plutonic Complex range from 140 to 40 m.y. and are contained in three parallel belts which are progressively younger in an eastward direction. The hypabyssal Bulkley intrusions of 70 to 84 m.y. age range may have been related to a period of underthrusting along the subduction zone that gave r i s e to part of the western zone of the Coast Plutonic Complex which ranges i n age from 64 to 79 m.y. Repeated movement along the subduction zone i n Eocene (50 m.y.) time culminated i n the emplace-ment of the eastern zone of the Coast Plutonic Complex, and from west to east, the Alice Arm, Nanika, and Babine intrusions. These intrusions become more volcanic i n nature i n an eastward direction, reflecting increased depth of generation along the subduction zone. 114. 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Geol., Vol. 63, pp. 612-621. Morley, L. W., MacLaren, A. S., and Charbonnaeu, B. W. (1967): Magnetic Anomaly Map of Canada, Geol. Surv. , Canada, Map 1255A. Ney, C. S. (1972): Berg Prospect, XXIV International Geological Congress, Guidebook, F i e l d Excursion A09-C09, Copper and Molybdenum Deposits of the Western C o r d i l l e r a (C. S. Ney and A. Sutherland Brown, Eds.), pp. 26, 27. Ney, C. S., Anderson, John M., and Panteleyev, Andre (1972): Discovery, Geologic Setting, and Style of M i n e r a l i z a t i o n , Sam Goosly Deposit, B.C., C.I.M., B u l l , V o l. 65, pp. 53-64. Northcote, K. E. (1969): Geology and Geochronology of the Guichon Creek B a t h o l i t h , B.C. Dept. of Mines & Pet. Res., B u l l . 56. P h i l l i p s , M. P. and Godwin, C. I. (1970): Geology and Rotary D r i l l i n g at the Casino S i l v e r Mines Property, Western Miner, V o l . 43, No. 10, pp. 43-49. Reed, B. L. and Lanphere, M. A. 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Dept. of Mines & Pet. Res., B u l l . 43. (1965a): Lucky Ship, Minister of Mines, B.C., Ann. Rept., 1965, pp. 84-87. (1965b): Huber, Minister of Mines, B.C., Ann. Rept., 1965, pp. 75, 76. (1966a): Big Onion, Minister of Mines, B.C., Ann. Rept., 1966, pp. 83-86. (1966b): Berg, Minister of Mines, B.C., Ann. Rept., 1966, pp. 105-111. (1966c): Red B i r d (CAFB), Minister of Mines, B.C., Ann. Rept., 1966, pp. 112-116. (1967): Fog, F l y , M i n i s t e r of Mines, B.C., Ann. Rept., 1967, pp. 97-100. (1968): Bear (Laura), Minister of Mines, B.C., Ann. Rept., 1968, pp. 113-116. (1969a): M i n e r a l i z a t i o n i n B r i t i s h Columbia and the Copper and Molybdenum Deposits, C.I.M., B u l l . , Vol. 62, No. 681, pp. 26-40. (1969b): Ox (Ox Lake Property), B.C. Dept. of Mines & Pet. Res., GEM, 1969, pp. 93-97. (1972): Red B i r d Prospect, XXIV International Geological Congress, Guidebook, F i e l d Excursion A09-C09, Copper and Molybdenum Deposits of the Western C o r d i l l e r a (C. S. Ney and A. Sutherland Brown, Eds.), pp. 25, 26. Sutherland Brown, A., Cathro, R. J . , Panteleyev, A., and Ney, C. S. (1971): Metallogeny of the Canadian C o r d i l l e r a , C.I.M., B u l l . , Vol. 64, pp. 37-61. Tipper, H. W. (1963): Nechkao River Map-area, B r i t i s h Columbia, Geol. Surv., Canada, Mem. 324. 121. (1971): Smithers Map-area, British Columbia, Geol. Surv., Canada, Report of Act i v i t i e s , Paper 71-1, Pt. A, pp. 34-37. Wanless, R. K., Stevens, R. D., Lachance, G. R., and Delabio, R. N. (1970): Age Determinations and Geological Studies, K-Ar Isotopic Ages, Geol. Surv., Canada, Report 9, Paper 69-2A, pp. 21-23. (1974): Age Determinations and Geological Studies, K-Ar Isotopic Age Determinations and Geological Studies, K-Ar Isotopic Ages, Geol. Surv., Canada, Report 11, Paper 73-2, pp. 22-23. Wheeler, J. 0., Aitken, J. D., Berry, M. J., Gabrielse, H., Hutchinson, W. W., Jacoby, W. R., Monger, J.W.H., Niblett, E. R., Norris, D. K., Price, R. A., and Stacey, R. A. (1972): The Cordillera Structural Province, Geol. Assoc. Canada, Special Paper No. 11, Variations in Tectonic Styles i n Canada (R. A. Price and R.J.W. Douglas, Eds.), pp. 1-82. White, W. H. (1959): Cordilleran Tectonics i n British Columbia, Amer. Assoc. Pet. Geol., Bull., Vol. 43, No. 1. (1966): Summary of Tectonic History of B.C., C.I.M., Special Vol. No. 8, Tectonic History and Mineral Deposits of the Western Cordillera, pp. 185-189. White, W. H., Erickson, G. P., Northcote, K. E., and Harakal, J. E. (1967): Isotopic Dating of the Guichon Batholith, B.C., Cdn. Jour. Earth Sci., Vol. 4, pp. 677-690. White, W. H., Harakal, J. E., and Carter, N. C. (1968): Potassium-argon Ages of Some Ore Deposits i n British Columbia, C.I.M., Bull., Vol. 61, pp. 1326-1334. White, W. H., Sinclair, A. J., Harakal, J. E., and Dawson , K. M. (1970): Potassium-argon Ages of Topley Intrusions near Endako, British Columbia, Cdn. Jour. Earth Sci., Vol. 7, No. 4, pp. 1172-1178. Woodcock, J. R., Bradshaw, B. A., and Ney, C. S. (1966): Molybdenum Deposits at Alice Arm, British Columbia, C.I.M., Special Vol. No. 8, Tectonic History and Mineral Deposits of the Western Cordillera, pp. 335-339. York, D. (1966): Least Squares Fitting of a Straight Line, Cdn. Jour. Physics, Vol. 44, p. 1079. (1970): Recent Developments in Potassium-argon Dating, Comments, Earth Sci. - Geophysics, Vol. 1, No. 2, pp. 47-54. 122. APPENDIX A. POTASSIUM-ARGON METHOD A.1 PROCEDURE Biotite , whole rock, and hornblende potassium-argon ages were determined in laboratories of the Department of Geology, University of Bri t i s h Columbia, using procedures and equipment previously described (White, et a l . , 1967; Northcote , 1969). The potassium analyses were performed on quadruplicate splits and the solutions atomized i n Baird-Atomic KY and KY-3 series flame photometers. The argon data was recorded with an AEI MS-10 mass spectrometer modified to permit rapid, static isotopic ratio measurements on a small quantity of gas, approximately 5 per cent by volume. Argon analyses carried out after late 1970 also involved the baking out of the fusion system and sample at 130 degrees centigrade for approximately 18 hours to eliminate or reduce atmospheric argon contamination. Analytical data and potassium-argon isotopic ages are given i n Table A.2. A.2 PRECISION AND ACCURACY The precision and accuracy of the potassium-argon age determination must be continually monitored to determine r e l i a b i l i t y of potassium-argon model ages. Interlaboratory standard mineral and rock samples are analysed i n the University of British Columbia potassium-argon laboratory to establish the accuracy of the equipment and replicate analyses of minerals are used to deter-mine the precision of the equipment (see White, et a l . , 1967; Northcote, 1969). 123. J. E. Harakal rims periodic checks on the Ar* t u/Ar J O ratio of atmospheric argon and on the argon isotope ratios in the spike system as measured on the Unversity of British Columbia MS-10 mass spectrometer. For samples containing less than 50 per cent atmospheric argon contamination, University of British Columbia results are internally consistent within 1 per cent and a li m i t of error i n an age determination (accuracy) i s within 3 per cent of the calculated age (J. E. Harakal, personal communication). A.3 APPLICATION OF INITIAL ARGON AND POTASSIUM-ARGON ISOCHRON DIAGRAMS I n i t i a l argon and potassium-argon isochron diagrams provide a graphical means for checking values of i n i t i a l argon and i n i t i a l A r ^ / A r ^ ratios. Investigation of argon content of biotite ( G i l e t t i , 1971) and hornblende 40 (Roddick and Farrar, 1971) shows that excess i n i t i a l Ar can occur i n most datable minerals. Samples should be treated i n a manner that does not assume that i n i t i a l argon has the present atmospheric ratio ( A r ^ / A r ^ = 295.5). The potassium-argon isochron method (Roddick and Farrar, 1971; Hayatsu and Carmichael, 1970) provides a method of determining the i n i t i a l argon ratio. The data necessary for determining isochron ages i s the same as the data required for the conventional potassium-argon calculation. The isochron method requires that for each rock unit dated, preferably three analyses are available from phases of minerals differing by at least 50 per cent i n potassium content. In addition, the entire fusion system must be baked at 130 degrees centigrade for about 18 hours to remove loosely held atmospheric argon. . 40.. 36 ,,40.. 36 , . 40 , ,. . N J # Ar /Ar versus K /Ar and Ar (radiogenic) versus %K diagrams can be plotted and the method least squares (York, 1966) i s used to f i t the best 124. straight line to the points. The lines produced are called isochrons and the slope of the line i s used to calculate an isochron age. The baking-out procedure of the sample and fusion system was applied to only 12 samples analysed during this study. Since no more than two of these analyses were from the same intrusive body, the plotting of A r ^ / A r ^ versus K ^ / A r ^ diagrams was not attempted. Potassium-argon data for each of the intrusive types (Alice Arm, Bulkley, 40 Nanika, and Babine intrusions) was evaluated using Ar (radiogenic) versus %K diagrams. These isochron plots supported the conventional age determinations. For the four intrusive types the mean age of conventional determinations was consistent with the isochron age. For a l l types, the i n i t i a l argon ratio i s essentially the same as the present-day value ( A r ^ / A r ^ = 295.5). A.4 GEOLOGICAL TIME SCALE The geological time scale used throughout this study i s that proposed by Holmes (1959). Divisions of the Mesozoic and Cenozoic eras are shown on Table A.1. TABLE A.1. GEOLOGICAL TIME SCALE (Holmes, 1959) ERA PERIOD Quaternary Tertiary Cenozoic Cretaceous Juras sic Mesozoic Triassic EPOCH Pleistocene Pliocene Miocene Oligocene Eocene Paleocene APPROXIMATE TIME (m.y.) 1 11 25 40 60 70 Upper Lower 136 Upper Middle Lower 180 Upper Middle Lower 225 126. TABLE A.2 POTASSIUM-ARGON ANALYTICAL DATA ALICE ARM INTRUSIONS Specimen No. L o c a t i o n Rock Type M i n e r a l I K+S* or C o n c e n t r a t e » A*°r a d . * V A«°rad. ,40 t o t a l ( 1 0 " 5 c c STP/g) K 4 0 NC-67-38 NC-69-2 NC-70-1 NC-70-2 NC-70-3 NC-67-35 Run 1 NC-67-35 Run 2 B r i t i s h Columbia Molybdenum B r i t i s h Columbia Molybdenum B r i t i s h Columbia Molybdenum B r i t i s h Columbia Molybdenum B r i t i s h Columbia Molybdenum . Roundy Creek Roundy Creek NC-67-30 B e l l Molybdenum NC-67-31 NC-6B-2 NC-67-33 B e l l Molybdenum B e l l Molybdenum AJax NC-67-25 Rldge-Nass R i v e r SC-67-26 NC-67-27 V a l l e y - N a s s R i v e r Kay-Noas R i v e r Quartz monzonite porphyry I n t r u s i v e b r e c c i a Lamprophyre dyke Quartz d i o r i t e Quartz monzonite porphyry "Late phase" Quartz monzonite porphyry Quartz monzonite porphyry Quartz monzonite porphyry B i o t i t e h o r n f e l s Quartz d i o r i t e Quartz monzonite porphyry Quartz monzonite porphyry "Late phase" Quartz monzonite porphyry Quartz f e l d s p a r porphyry B i o t i t e 7.59+.02 0.77 B i o t i t e 6.62+.03 0.23 Whole Rock 2.30+.01 0.66 B i o t i t e 6.47+.01 0.90 B i o t i t e 4.4O+.03 0.85 B i o t i t e 6.09+.06 0.60 B i o t i t e 6.09+.06 0.65 B i o t i t e 5.72+.05 0.33 Whole Rock 1.66+.01 0.19 B i o t i t e 4.75+.04 0.58 B i o t i t e 6.47+.04 0.67 B i o t i t e 5.13+.03 0.75 B i o t i t e 7.08+.08 0.56 B i o t i t e 6.07+.04 0.71 1.623 1.429 3 . 3 5 3 x l O - 1 1.334 8.530X10" 1 1.280 1.289 1.217 3.2 4 1 x l O _ 1 9.857X10"1 1.390 1.U10 1.478 1.297 3.159 3.189 2.154 3.046 2.864 3.106 3.126 3.143 2.884 3.066 3.175 2.909 3.085 3.158 53.0+3 53.7+1.7 36.5+1.2 51.4+1.5 48.3+1.6 52! 0+3 53.0+2 53.0+2 48.7+1.5 51.7+2.2 54.0+3 49.0+2 52.0+3 53.2+2.3 ALICE ARM - NASS R1VKR AREA NC-67-32. A l i c e Arm Run 1 NC-67-32 A l i c e Arm Run 2 NC-67-32 A l i c e Arm Run 3 NC-70-4 A l i c e Arm NC-67-45 Penny .Creek NC-68-11 NC-68-3 NC-68-4 NC-67-24 Run 1 NC-67-24 Run 2 NC-67-29 NC-69-3 Molly Mack Bonanza Creek Anyox I l l i a n c e R i v e r A l i c e Arm Mt. P r i e s t l y Coast P l u t o n i c Complex Mt. P r i e s t l y Coast P l u t o n i c Complex A l i c e Arm Coast P l u t o n i c Complex Lava Lake Coast P l u t o n i c Complex Ba s a l t B a s a l t B a s a l t B a s a l t Whole Rock Whole.Rock Whole Rock Whole Rock B i o t i t e B i o t i t e q u a r t z monzonite B i o t i t e q r a n i t e . B i o t i t e Quartz b i o t i t e s c h i s t B i o t i t e B i o t i t e lamprophyre B i o t i t e Quartz monzonite B i o t i t e 1 .'.'') +.015 1.99 +10.1.5 1.99+.015 • s 1.30+.01 6.11+.05 6.54+.02 5.73+-04 6.55+.06 4.91+.02 Quartz monzonite B i o t i t e 4.91+.02 NC-67-28 Nass R i v e r Quartz monzonite B i o t i t e 7.30+.05 Quartz d i n r l re R i o t i to 6.95+.02 0.01, 0.04 0.04 * 0. 11 0.25 0.68 0.20 0.73 0.45 0.82 Quartz monzonite B i o t i t e 6.68+.05 0.55 0.85 , 8.,MBxlO"') , 6.-'.34xl0;2 '2.255X10" 3 1.724x10"* 3.468x!0" 3 2.651x10" 2 8. 362x10"-> 8.S05X3.0"1 1.266 7.621xl0" L 9.013x10" 9.114X10"1 1.011 1.355 1.485 1.369 9.503x10" 2.129 2.1160 1.965 2.033 2.742 3.043 2.997 3.006 2.91 1 1.1+0.8 0.293*0.5 0.453+0.5 1.6+0.8 36.1+1.6 48.3+1.9 33.3+1.4 34.4+1.5 46.3+1.4 51.3+1.6. 50.7+2.1 49.0+2.0 127. TABLE A.2 (ccmt.) BULKLEY INTRUSIONS Specimen No. Rock Type M i n e r a l o r Concencrate X K+s* A A 0 r a d . « -3 A t o t a l ( 1 0 " 5 c c STP/g) Apparent Age (m.y.) NC-68-12 Bear Quartz monzonite porphyry B i o t i t e 6. 23+. 01 0.81 2.078 4.929 82. 4+3. 1 NC-67-46 Rocher de Boule G r a n o d i o r i t e B i o t i t e 6. 64+.05 0.86 1.936 4.289 71. 9+3. 1 NC-67-41 Run 1 G l a c i e r Gulch Q u a r t z - b l o t i t e -s u l f i d e v e i n B i o t i t e 7. 27+.02 0.65 2.024 4.113 69. 0+3 NC-67-41 Run 2 G l a c i e r Gulch Q u a r t z - b i o t i t e -s u l f i d e v e i n B i o t i t e 7. 27+. 02 0.68 2.064 4.195 70. 0+3 NC-68-6 G l a c i e r Gulch Quartz monzonite porphyry B i o t i t e 5. 78+.06 0.79 1.711 4.373 73. 3+3. 4 NC-67-16 Huber B i o t i t e h o r n f e l s Whole Rock 1. 07+: 002 0.82 3.001x10" 1 4.144 69. 5+2. 0 NC-67-39 Sunsets Creek G r a n o d i o r i t e B i o t i t e 6. 92+.06 0.80 1.956 4.175 70. 0+3 NC-67-44 Huckleberry G r a n o d i o r i t e porphyry B i o t i t e 6. 29+. 05 0;89 2.079 4.884 82. 0+3 NC-69-5 Ox Lake G r a n o d l o r l t e porphyry B i o t i t e 4. 25+.01 0.78 1.435 4.987 83. 4+3. 2 MC-9 C o l e s Creek Quartz monzonite porphyry B i o t i t e 6. 89+.04 0.89 2.337 5.012 83. 8+2. 8 NANIKA INTRUSIONS : ; NC-68-13 Mt. Thomlinson Quartz monzonite porphyry B i o t i t e 7. 50+. 03 0.77 1.620 3.191 53. 8+2. 2 NC-67-7 Bi g Onion Quartz monzonite " L a t e phase" B i o t i t e 4. 50+. 01 0.77 8.782x10" 1 2.883 48.7+1. 9 NC-69-6 Goosly Quartz monzonite. porphyry B i o t i t e 7. 09+.04 0.77 1.601 3.336 56. ,2+2.3 NC-68-7 Nadlnn Mountain Quartz monzonite B i o t i t e 6. .55+.03 0.63 1.392 3.139 52. 9+2. 2 NC-67-42 Lucky Ship B i o t i t e h o r n f e l s Whole Hock 1 • 5i>f.05 0.29 3.131x10" •1 2.959 49. .9+2. 3 NC-67-8 Berg Quart2 d i o r i t e ICoast P l u t o n i c Complex) B i o t i t e 2. .64+.01 0.23 4.955x10" 2.773 46.8+1. .5 NC-b7-9 Berg Quartz l a t i t e porphyry ' "l-ate phase" Blot i t e 6 .69+.05 0.42 1.283 . , i , • • j 2.834 48. .0+3 NC-67-10 Berg Quartz l a t i t e porphyry . "La t e phase" Bl o t i t e 6 .56+.U6 0.38 1.249 2.813 47 .0+3 NC-67-11 Berg Quartz monzonite porphyry -B l o t i t e 6 .76+.05 0.34 ' i ' 1.413 . . . 3.088 52 .0+2 NC-67-12 Berg B i o t i t e h o r n f e l s Whole Rock 2 .92+.05 0.29 6.175x10' -1 3.124 52. .0+3 NC-67-13 Berg Quartz d i o r i t e .(Metamorphosed) ' B i o t i t e 6 .97+.05 C.75 1. J96 2.960 49 .9+2 .1 NC-67-17 Red B i r d B i o t i t e h o r n f e l s Whole Rock 4 .09+.03 0.23 8.201x10: -1 2.962 50 .0+1 .7 NC-67-19 Run 1 Red B i r d Quartz monzonite porphyry B i o t i t e 7 .94+.07 0.65 1.572 2.925 49 .0+3 NC-67-19 Run 2 Red B i r d Quartz monzonite porphyry B i o t i t e 7 .94+.07 0.59 1.603 2.982 50 .0+2 NC-67-20 Red B i r d Quartz monzonite porphyry "Late phase" B i o t i t e 7 .24+.03 0.74 1.433 2.924 49 .0+2 NC-67-15 Morlc e Lake Quartz monzonite (Topley I n t r u s i o n s ) B i o t i t e 6 .50+.07 0.70 4.821 10.957 178+8 NC-69-7 Goosly Syenomonzon i t e B i o t i t e 7 .53+.02 0.69 1.473 2.891 48 .8+1 .9 (Goosly Lake I n t r u s i o n s ) 128. TABLE A.2 (cont.) BABINE INTRUSIONS Specimen No. Location Rock Type Mineral Z K+S* or Concentrate A 4 0rad.«« A 4 0 t o t a l A 4 0rad. 40 -3 A , . r a d - " 1 0 Apparent Age (m.y. (10" 3cc STP/g) K NC-67-1 Old Fort NC-67-2 Old Fort NC-67-4 Granisle NC-67-5 Granisle NC-68-1 Granisle NC-69-8 Cranlsle NC-67-22 Newman-Bell Copper NC-67-23 Newman-Bell Copper HC-67-40 Morrison NC-68-10 T r a i l Peak NC-69-1 T r a i l Peak NC-67-43 Newman Peninsula NC-69-4 Tachek Creek NC-72-1 Lennac Lake Biotite feldspar Biotite porphyry Biotite quartz Biotite monzonite Biotite feldspar Biotite porphyry Biotite feldspar Biotite porphyry Biotite feldspar Biotite porphyry "Late phase" Quartz-biotlte- Biotite sulfide vein Biotite feldspar . Biotite porphyry "Late phase" Biotite feldspar porphyry "Late phase" Biotite feldspar porphyry Biotite feldspar porphyry Quartz diorite (Omineca Intrusions) Hornblende feldspar porphyry (Extrusive equivalent) Hornblende-!'lot i t e -qtiartz porphyry (Topley Intrusions) Quartz-hornhlende-biotite feldspar porphyry (Bulkley Intrusions). 7.59+.06 5.89+.04 7.63+.03 7. 06+.03 6.67+.01 4.42+.02 6.45+.04 Biotite 6.90+.02 Biotite Biotite Biotite Hornblende 6.66+.04 6.61+.01 6.80+.03 .072+.002 Ulotlte 6.54+.03 Biotite 6.71+.03 0.53 0.76 0.67 0.87 0.54 0.69 0.63 0.73 0.57 0.71 0.92 0.62 0.93 0.95 1.497 1.232 1.682 1.436 1.354 8.894X10"1 1.288 1.402 1.393 1.297 2.871 1.390x10"' 4.763 2.088 2.914 3.089 3.256 3.005 2.999 2.973 2.951 3.002 3.091 2.900 6.238 3.056 10.760 4.597 49.0+2 52.0+2 55.0+3 51.0+2 51.0+2 50.2+2.1 49.8+2.1 51.0+3 52.1+2.1 48.9+1.5 104+4 51.5+1.9 176+7 77.0+2.5 * Potassium analyses by V. Bobik and N. C. Carter, using KY and KY-3 flame photometers; S-standard deviation oi quadruplicate analyses **Argon analyses bv J. E. Harakal and N. C. Carter, using MS-10 mass spectometer. Constants used in model age calculations A e - 0.585 x 10" 1 0 y-1 * B - 4.72 x 10" 1 0 y-1 4 0K/K - 1.181 x 10"4 129. APPENDIX B. CHEMISTRY OF INTRUSIVE ROCKS B.1 CHEMICAL ANALYSES OF INTRUSIVE ROCKS Twenty-three samples collected for potassium-argon dating were submitted to the Analytical Laboratory of the Department of Mines and Petroleum Resource, for chemical analysis. These were analysed by S. Metcalfe using classical wet chemical techniques. Analyses are presented i n Table B.1. B.2 MAJOR AND TRACE ELEMENT ANALYSES OF BIOTITES Most of the biotite separates used for potassium-argon dating were analysed for major and trace elements. Analyses were carried out at the Cominco Research Laboratories, T r a i l , under the supervision of M. Osatenko. Major and minor elements were analysed by atomic absorption methods with the exception of Ti02 which was determined by colorimetric methods. Results were calibrated against known U.S.G.S. rock standards. Analyses of biotites are given i n Table B.2. 130. TABLE B.1: CHEMICAL ANALYSES OF INTRUSIVE ROCKS A L I C E A R M I N T R U S I O N S NC-67-38 NC-67-30 NC-67-33 NC-67-35 NC-67-26 B.C. HOLY BELL MOLY AJAX ROUNDY CREEK VALLEY sio2 71.38 66.98 65.78 71.16 68.92 . A1 20 3 12.01 14.64 13.56 14.23 15.20 * F«2°J FeO 0.99 0.62 0.69 2.02 1.29 2.22 0.36 1.86 1.02 0.87 P2°5 0.19 0.20 0.38 0.15 0.38 CaO 1.90 3.08 3.53 1.40 2.23 MgO 0.78 • 1.00 . 1-32 0.29 0.64 T10 2 0. 33 0.54 0.52 0.31 0.57 SO, 1.87 0.75 1.50 0.72 1.84 3 MnO 0.03 0.04 0.03 0.04 . 0.01 Na 0 2 V HjO belov 105°C 1.07 3.76 3.97 3.22 3.32 6.72 4.65 4.25 4.58 4.43 0.08 0.14 . 0.01 0.02 0.01 HjO above 105°C CO, 1.42 1.04 1.26 1.37 0.22 0.09 0.06 0.01 0.01 0.01 BaO 0.26 0.28 0.25 0.13 0.30 CuO - - - - 0.01 MoO, 0.11 - - 0.02 3 PbO 0.01 - - 0.01 0.01 B U L K L E Y I N T R U S I O N S NC-67-39 NC-68-6 NC-67-44 NC-68-12 NC-69-5 JAN ROCIIKR DE BOl't.E NA11ISA SUNSETS CREEK CLACIER GULCH HUCKLEBERRY BEAR OX LAKE (average) . Mlcroil lorlt S10, 65.44 70.98 66^98 63.'.2 64.22 60.86 64.58 57.92 4 A1,0, 16.39 13.58 • 15.37 15.74 16.36 17.53 15.74 17.74 2 3 2.11 1.06 1.93 1.50 2.02 1.99 1.67 3.10 2 3 FeO 2.11 1.43 .2.19 2.70 2.66 2.60 2.43 2.84 P2°5 0.35 0.20 0.33 6.26 0.19 0.19 0.20 0.22 CaO 3.59 1.87 2.12 3.15 2.53 4.72 4.48 — MgO 1.31 0.43 1.53 1.66 1.97 1.86 i:97 6.13 T10, 0.60 0.32 0.49 0.53 0.58 0.47 0.57 1.40 L SO 0.07 0.16 0.30 3.35 0.02 0.01 - 0.74 3 MnO 0.04 0.04 0.03 0.04 0.07 0.06 0.06 0.07 Na,0 •'. 3.32 5.55 3.48 3.51 3.75 5.80 3.73 0.18 2 K 0 3.53 4.08 3.30 ; 1.98 2.45 2.44 2.81 3.61 2 H,0 below 105°C , 0.01 0.03 0.12 . 0.04 0.27 0.28 0.10 3.25 4 H,0 above 105°C 0.85 0.20 1.36 2.15 2.78 0.65 1.49 0.11 2 CO 0.01 0.01 0.01 0.01 0.01 0.46 - 2.28 2 BaO 0.16 0.09 0.16 - . - - 0.10 0.11 CuO - - 0.16 - - - 0.18 TABLE B.f (cont.) 131 N A N I K A I N T R U S I O N S NC-67-10 NC-67-11 NC-67-14 NC-68-7 NC-69-6 BERG BERG RED BIRO NADINA MOUNTAIN CCOSLT SlOj 67.34 62.50 73.42 66.70 65.02 A1 20 3 15.62 15.12 13.25 15.46 15.76 F. 20 3 1.16 1.64 0.29 ,1.74 2.12 FeO 0.76 0.85 0.32 1.71 1.54 P2°5 0.30 0.18 0.17 0.21 0.28 CaO 1.02 2.39 1.14 1.96 -MgO 1.04 1.49 0.35 1.14 3.21 T10 2 0.51 0.51 0.36 0.62 1.27 SO 3 1.92 4.53 0.08 0.01 0.65 KnO 0.02 0.06 0.01 0.09 o.oi 2.76 3.13 2.97 3.69 0.04 V 5.06 4.55 6.02 *;ss 4.21 H^ O below 105°C 0.31 0.95 0.09 0.21 3.59 H20 above 105°C 1.32 2.18 1.18 2.10 0.21 CO, 0.02 0.01 0.01 0.02 1.69 BaO 0.12 - 0.13 - 0.08 CuO 0.38 - 0.03 - 0.18 MoOj - - 0.04 PbO - - 0.01 B A B I N E I N T R U S I 0 N S C O O S L Y I N T R U S I O N S NC-67-1 NC-67-4 NC-67-23 NC-67-40 NC-69-7 PARROT LAKE OLD FORT CKANISLE NEWMAN MORRISON GOOSLY sio2 63.90 64 34 59 76 63.18 . 52.80 50.80 A l . 0 15.22 15. 14 15 16 15.40 16. 95 16.25 2 3 5.00 F e2°3 2.60 2. 43 2 23 1.97 3. 97 FeO 1.97 2 74 2 60 3.02 3. 63 ' 2.28 P2°5 0.30 0. 34 0 36 0.27 0. 91 0.59 CaO 3.44 2 97 5 36 2.45 . - 7.32 MgO U49 1 51 2 54 2.17 6. 03 3.63 T10 2 0.54 0 61 0 56 0.66 3.85 ' 1.42 SO 0.82 0 35 3 13 1.78 1. 82 1-55 MnO 0.03 0 02 0 01 0.04 0. 01 0.10 Na20 4.32 4 59 4 88 3.91 0. 14 4.79 3.20 2 66 2 66 1.39 4. 10 2.64 H20 below 105°C 0.29 0 06 0 66 0.26 3. 30 0.89 B^ O above 105°C 0.99 1 35 1 32 . 2.39 0. 18 1.10 co2 0.02 0 01 0 08 0.01 1. 90 1.15 BaO 0.28 0 18 0 18 1.08 ' 0. 02 0.28 CuO 0.23 0 29 0 39 '• - 0. 27 0.12 Mo03 0.23 -PbO 0.01 o 02 — 132. TABLE B.2 MAJOR AND TRACE ELEMENT ANALYSES OF BIOTITES ALICE ARM INTRUSIONS SPECIMEN NUMBER LOCATION MAJOR CaO Na ELEMENTS 2° K 2 ° (wt. per MgO. ce n t ) Fe TIO, TRACE ELEMENTS Cu Ma Zn (PP") Rb NC-67-38 B r i t i s h Columbia Molybdenum 9 .5 9.2 14 7 12 .8 3.7 60 2800 900 1350 NC-69-2 B r i t i s h Columbia Molybdenum .8 .5 8.1 15 4 12 .6 3.5 50 1450 540 1200 HC-67-33 AJax 1. 5 .6 8.0 12 1 15 .2 3.9 60 2400 800 1000 NC-67-35 Roundy Creek 1. 1 .5 7.1 6 1 19 .0 3.2 10 5100 940 1200 NC-67-30 B e l l Molybdenum 1. 1 .5 7.0 12 3 15.3 3.5 20 2800 920 1000 NC-68-2 B e l l Molybdenum 3. 0 .6 5.2 12 7 14 .6 3.5 30 2900 750 500 NC-67-4S Penny Creek 1. 0 .7 7.4 8.4 17 .0 3.5 55 4600 930 1500 NC-67-25 Ridge-Nasa R i v e r ' • 9 .6 6.0 13 4 14 .8 3.9 40 2190 700 700 NC-67-26 V a l l e y - N a s s R i v e r 1. 2 .5 8.1 16 0 12 .3 2.7 140 4100 1080 1500 NC-67-27 Kay-Naas R i v e r 1. 8 .7 7.5 10 1 13 .8 3.9 80 3450 1050 1200 COAST PLUTONIC COMPLEX NC-67-24 Mt. P r i e s t l y 4. 3 .9 5.7 11 5 13 .6 3.3 30 1930 620 850 NC-67-28 NaBS R i v e r 1. 1 .6 8.3 10 2 15 .6 3.5 80 2160 690 950 NC-67-29 A l i c e Arm 1. 2 . .5 8.3 12 2 14 .3 3.7 100 2950 750 1550 NC-69-3 Lava Lake 8 .5 8.6 12 4 15 .4 3.9 10 2640 700 1300 BULKLEY INTRUSIONS SPECIMEN NUMBER MAJOR ELEMENTS (wt . per c e n t ) CaO N « 2 0 KjO MgO Fe T l O j TRACE ELEMENTS (ppm) Cu Hn Zn Rb KC-68-12 Laura 1 3 •> 7.6 13 6 13 2 4.0 650 1375 220 1250 XC-67-46 Rocher Deboule 1 4 • 5 7.9 9 4 18 0 3.8 35 1730 680 1900 NC-67-41 C l a c l c r G u l c h 4 . • 5 8.7 18 8 11 2 1.4 60 4650 460 6000 NC-68-6 C l a c l e r C u l c h 1 6 • 5 6.9 13 8 13 4 4.0 70 3100 540 1950 NC-67-39 Sunsets Creek 1 2 V 8.0 13 3 13 6 4.5 100 2750 600 1650 NC-67-44 Hu c k l e b e r r y 6 .6 7.2 IS 4 12 3 4.0 975 1450 4 30 1150 NC-69-5 Ox Lake 2 1 .5 4.8 15 6 13 6 4.6 900 2080 400 650 NANIKA INTRUSIONS SPECIMEN NUMBER LOCATION MAJOR ELEMENTS (wt. per c e n t ) CaO Na^o K 20* MgO Fe T 1 0 2 TRACE ELEMENTS Cu Mn • Zn (ppm) Rb KC-67-8 NC-67-9 Berg Berg 3.8 ~76"~ 2.8 16.0 13.5 3.9 90 3020 580 7.9 14.1 12.6 3.9 850 1000 610 NC-67-10 Berg .7 8.2 16.8 8. 3.9 1410 610 450 NC-67-13 NC-67-7 NC-67-19 NC-67-20 NC-68-13 NC-68-7 NC-69-6 Berg Berg B i g Onion Red B i r d MC. Thomlinson Nadlna Mountain. C o o s l y C o o s l y 1.0 8.4 17.0 8.9 1.4 8.5 16.8 9.8 4.0 3.3 1.1 4.9 13.6 11.3 5.0 9.5 17.4 9.6 3.2 8.6 12.3 14.6 3.2 8.6 11.5 12.8 3.2 7.5 14.3 13.1 4.3 B.3 14.4 12.8 4.5 .7 8.9 19.6 9.1 425 550 250 1000 590 450 300 900 1680 500 320 890 500 480 1900 600 90 3000 450 25 3100 680 10 1200 400 25 1000 400 950 400 1550 750 1650 1350 1300 1950 133. TABLE B.2 (coot.) . BABINE INTRUSIONS •' — : SPECIMEN LOCATION MAJOR ELEMENTS (wc . per cent.) TRACE ELEMENTS (ppm) NUMBER CaO NaO 2 K20* MgO Fe T10 2 Cu Mn Zn Rb NC-67-4 Granisle .5 .7 8.9 16.0 11. 9 4.0 300 550 375 800 NC-67r5 Craniale .9 .8 8.4 12.9 14.0 3.8 200 1060 735 700 NC-68-1 Cranlsle 1.2 .7 7.5 13.4 13. 7 3.8 680 440 450 700 NC-69-8 Craniale .9 .5 5.1 20.3 10. 6 1.6 1860 590 590 600 NC-67-22 Newman .9 .8 8.1 16.2 .10. 8 4.0 370 1080 560 850 NC-67-23 Newman 1.2 .8 8.4 16.6 10. 7 4.0 1630 640 530 900 NC-67-40 Morrison .9 .8 7.5 15.1 13. 6 3.6 1300 730 430 1000 NC-67-1 Old Fore Mouncain 1.1 .8 9.1 15.0 12. 2 3.9 600 920 . 465 950 NC-67-2 Old Fore Mountain 2.4 1.6 7.4 12.6 13. 9 3.8 300 3000 580 700 * Analyses carried out under the supervision of M. Osatenko, Cotninco Research, T r a i l . 134. APPENDIX C. PORPHYRY COPPER AND/OR MOLYBDENUM DEPOSIT DESCRIPTIONS (INCLUDING POTASSIUM-ARGON SAMPLE LOCATIONS AND DESCRIPTIONS) C.1 ALICE ARM INTRUSIONS AND ASSOCIATED MOLYBDENUM DEPOSITS C.1.1 British Columbia Molybdenum (after Carter, 1964) This property i s situated on the southeast fork of Lime Creek, approxi-mately 5 miles south of Alice Arm. Molybdenum mineralization was f i r s t identified in 1911 and several adits were driven i n molybdenum mineralization and i n marginal quartz veins containing lead, zinc, and silver prior to 1916. In 1959, the property was acquired by Kennco Explorations, (Western) Limited who conducted some 45 ,000 feet of diamond d r i l l i n g . Decision to equip the property for production was made in late 1964. Mining and milling began in late 1967. When the operation was suspended in mid-1972, some 10 million tons of material grading 0.15 to 0.20 per cent MoS^ had been mined. Molybdenite mineralization i s associated with a small e l l i p t i c a l stock of quartz monzonite-quartz diorite composition which intrudes siltstones and greywackes of Late Jurassic-Early Cretaceous age (Fig. C.1). An appendage or extension i s connected to the main stock on the eastern side. The main stock i s composed of granitoid rocks of several types and ages , with a central zone of quartz monzonite porphyry grading to a quartz diorite on the western and southeastern sides. These rocks appear to have formed contemporaneously and are cut by later inter-mineral and post-mineral dykes and irregular bodies. At least three types of quartz monzonite porphyry can be distinguished i n the central part of the stock on the basis of degree of alteration. The 136. rock i s essentially a medium-grained leucocratic rock with euhedral to sub-hedral 4-millimetre phenocrysts of normally zoned plagioclase (An^^,^) and p o i k i l i t i c K-feldspar making up the major portion of the rock volume. Hornblende and biotite are the chief mafic minerals. The quartz monzonite grades through granodiorite to quartz diorite on the western and eastern sides of the stock. These are medium-grained white to grey massive rocks with only sparse phenocrysts of plagioclase. Abundant secondary biotite i s a feature of these rocks. Intrusive into both the quartz monzonite porphyries and quartz diorites and apparently confined to the northern half of the stock are irregular lenses and dykes of finer grained quartz monzonite and granodiorite porphyries and intrusive breccias. These are of inter-mineral age and commonly contain angular fragments of biotite hornfels, quartz monzonite porphyry, and quartz diorite in a fine-grained granulated matrix. Fine-grained, white to pink equigranular alaskites are intrusive into a l l of the above-mentioned rock types. They consist essentially of anhedral quartz and K-feldspar and occur most commonly as dykes and irregular masses near the contact areas of the stock. The latest granitic intrusive phase i s represented i n a nearly post-mineral quartz feldspar porphyry situated beneath the northern half of the stock. This rock type was intersected only in d r i l l i n g several hundred feet below the original surface level, and i t apparently terminates the ore-grade mineralization of the northeastern part of the ore zone. Lamprophyre dykes which vary i n width from 2 to 30 feet cut a l l rocks i n the stock. These include both biotite and pyroxene varieties and have sharp, 137. chilled contacts. The lamprophyre dykes occur in northeasterly trending swarms near the eastern contact. Siltstones and greywackes adjacent to the stock have been thermally metamorphosed to biotite hornfels in a roughly circular zone 200 to 500 feet in width. The inner part of the hornfels aureole features a quartz-sericite bleaching of the biotite hornfels adjacent to quartz veinlets. Minor amounts of secondary contact metamorphic biotite are present within the sedimentary rocks i n a zone 1,000 to 4,000 feet outward from the stock. Alteration of granitic rocks includes secondary K-feldspar which rims mineralized quartz veinlets and occurs as 5-millimetre grains replacing plagioclase i n the rock matrix. Secondary K-feldspar alteration in the central barren zone of the northern half of the stock has been so intense as to obliterate a l l traces of the original rock, converting i t to an equigranular rock composed of quartz and pink orthoclase. A r g i l l i c and s e r i c i t i c alteration of plagioclase feldspar i s common in and adjacent to northeast-striking faults and shear zones. The zone of molybdenum mineralization i s a ring structure , e l l i p t i c a l in outline and elongated in an east-west direction (Figure C.1). The annular mineralized zone conforms roughly to the north, east, and west contacts of the stock, while the southern part of the zone cuts across the stock at i t s mid-point. Molybdenite content fades out toward the centre of the zone, with a central barren core containing l i t t l e or no molybdenite. Molybdenum mineralization occurs along the boundaries of one-eighth to one-quarter-inch quartz veinlets, and in hairline fractures. Disseminated molybdenite i s found only in the alaskites. Quartz veinlets are closely 138. spaced and appear randomly oriented i n a stockwork pattern, but as a general rule, the majority of the veins are vertical and strike north-northeast. A second stage of molybdenite-bearing quartz veinlets strikes west-northwest. The quartz-molybdenite veinlets are cut by drusy, white quartz veins ranging up to 3 feet wide and containing pyrite, galena, sphalerite, neyite, scheelite, chalcopyrite, tetrahedrite, and pyrrhotite. Some fluorite and gypsum were also noted i n these veins. Higher grades of molybdenum mineralization occur i n areas of intense fracturing and faulting particularly in the northeast contact area of the stock where the intensity of fracturing has also provided channelways for the later lamprophyre dyke swarms. Fractures and faults trend predominantly northeasterly with a subsidiary northwest fracture set. Disseminated pyrite i s widespread i n quartz veins and rock matrices particularly marginal to the annular zone of molybdenum mineralization. Locations of potassium-argon samples collected from the British Columbia Molybdenum deposit are shown on Figure C.1 and include the following: NC-67-38 - Quartz Monzonite Porphyry Sample i s from the northeast part of the orebody. The sample i s a leucocratic, medium-grained porphyritic rock cut by numerous quartz veinlets containing molybdenite and some pyrite. Making up 15 per cent of the rock are 1 to 2-millimetre phenocrysts or porphyroblasts of K-feldspar which occur marginal to quartz veinlets and replace plagioclase. The matrix contains abundant secondary quartz. 139. Biotite constitutes 7 per cent of the rock and occurs both as primary 0.5 to 1.0-millimetre plates and as finer grained aggregates on fractures which may be secondary. The biotite exhibits 10 to 15 per cent alteration to chlorite, principally along cleavage planes. NC-69-2 - Quartz Monzonite Porphyry Intrusive Breccia Sample i s from a dyke cutting quartz monzonite porphyry i n the northern part of the ore zone. The rock i s leucocratic and contains 1-inch angular fragments of biotite hornfels i n a porphyritic matrix. One to 2-millimetre subhedral phenocrysts of sericitized plagioclase (An^^) and K-feldspar make up 25 per cent of the rock. In thin section, these were seen to be broken crystals set in a very fine-grained granulated matrix of abundant quartz and subsidiary feldspar and biotite. Accessory minerals include epidote, apatite, sphene, and carbonate. Biotite equals 5 per cent of the rock and occurs as 0.5 to 1.0-millimetre broken plates with up to 20 per cent chlorite alteration, and as very fine-grained aggregates which may be up to 50 per cent chloritized. NC-70-2 - Quartz Diorite Sample i s from the west part of the ore zone. The quartz diorite i s medium grey, equigranular, and contains coarse pyrite i n fractures with quartz. The rock has a hypidiomorphic granular texture and consists of 1 to 2-millimetre euhedral, zoned plagioclase, 70 per cent; quartz, 15 per cent; K-feldspar, 5 per cent; biotite, 10 per cent; and metallies, 5 per cent. Biotite occurs as 0.5 to 1.0-millimetre plates and as fine-grained aggregates which replace original hornblende. Biotite i s essentially unaltered. 140. NC-70-3 - Quartz Monzonite Porphyry Sample of this late porphyry phase was collected from d r i l l core from a vertical depth 900 feet below the original surface level i n the northeast section of the ore zone. The rock i s a fine to medium-grained porphyry with 2 to 4-millimetre phenocrysts of euhedral plagioclase (An^), K-feldspar, and anhedral quartz which make up 25 per cent of the rock by volume. These are set i n a fine-grained matrix of quartz, feldspar, carbonate, pyrite, and sphene. Biotite constitutes 7 per cent of the rock and occurs primarily as 1-millimetre plates and books which are up to 30 per cent chloritized. C.1.2 Bell Molybdenum (after Carter, 1967) The Bell Molybdenum property i s situated 6 miles southeast of Alice Arm. Molybdenum mineralization i s associated with an e l l i p t i c a l stock of quartz monzonite porphyry which i s elongate i n an east-northeast direction and measures 2,200 by 1,100 feet (Fig. C.2). The stock intrudes a sequence of dark grey to black siltstones and greywackes which are thermally metamorphosed to biotite hornfels adjacent to the stock. Flat-lying olivine basalts of Pleistocene age and of variable thickness overlie the sedimentary rocks north and south of the stock. Quartz monzonite porphyries of the stock include three major types. The main type, leucocratic quartz monzonite porphyry, occupies the central part of the stock. Two to 4-millimetre phenocrysts of quartz, plagioclase (An„_ O Q)> 2U"2o and perthitic orthoclase make up 30 per cent of the rock, and are set i n a fine-grained matrix of quartz and feldspar. Original biotite i s bleached to 142. a mixture of chlorite and sericite. Phenocrysts of euhedral orthoclase range up to 1 centimetre in size. Accessory minerals include s e r i c i t e , carbonate, apatite, sphene, and pyrite. Near the stock contacts and i n dykes peripheral to the stock, the leuco-cratic quartz monzonite porphyry i s gradational to a quartz monzonite or granodiorite porphyry. This rock contains a more calcic plagioclase, a lesser amount of orthoclase, and fresh biotite and hornblende. The southwestern part of the stock i s composed of a crowded 'quartz-eye' porphyry of distinctive appearance. Phenocrysts which make up 50 per cent of the rock by volume, include 4-millimetre quartz anhedra, 2 to 4-millimetre euhedral crystals of plagioclase, and randomly distributed 1 to 2-centimetre euhedral crystals of perthitic orthoclase.- Average rock composition, which i s similar to the leucocratic quartz monzonite porphyry, i s : quartz, 27 per cent; plagioclase (^20-28^' ^ ^ e r c e n t » orthoclase, 25 per cent; biotite, 5 per cent; hornblende, 5 per cent; sphene, apatite, and opaques, 3 per cent. The distinguishing feature of this phase i s i t s relative lack of alteration. A similar porphyry was encountered at depth i n a d r i l l hole near the central part of the stock where i t appeared to have a gradational contact with the leucocratic quartz monzonite porphyry. The relative lack of quartz veinlets and fractures and attendant mineralization suggests that the 'quartz-eye' quartz monzonite porphyry represents a late, possibly post-mineral intrusive phase. Narrow granitic dykes cut the leucocratic quartz monzonites in the central part of the stock. One drill-hole intersected 1-foot-wide dykes of fine-grained alaskite, consisting of interlocking grains of quartz, perthitic orthoclase, s e r i c i t e , and some granophyre. Near the stock contacts, short 143. sections of grey-green, fine-grained quartz monzonite porphyry breccias were noted. These cut the quartz monzonites and are distinguished by the presence of one-half-inch angular hornfels fragments in a granulated matrix. Narrow dykes of fine-grained light green quartz feldspar porphyry were noted i n several d r i l l holes. Two varieties of basic dykes cut the granitic rocks of the stock. These include a fine to medium-grained porphyritic lamprophyre consisting of plagio-clase, hornblende, and clinopyroxene, and fine-grained basalt and andesite dykes which are locally vesicular and may be related to the young lava flows nearby. Both varieties generally have a northeasterly strike and are 1 to 2 feet wide. Sedimentary rocks have been contact metamorphosed to brown biotite hornfels a distance of between 1,200 and 1,500 feet outward from the stock contact. Near the contact, the hornfels i s a dense fine-grained rock exhibiting a grano-blastic texture and consisting of interlocking grains of quartz and biotite. Alteration of the biotite hornfels includes pale green chlorite-sericite bleaching marginal to fractures and quartz veinlets. Intensity of metamorphism decreases outward from the stock contact to colour-banded argillaceous sediments in which only certain beds contain secondary biotite. Within the stock, the central leucocratic quartz monzonite porphyry exhibits the greatest degree of alteration. Most prevalent i s s e r i c i t e -carbonate alteration of plagioclase. In addition, plagioclase locally i s altered to K-feldspar, particularly along the margins of quartz veinlets. Secondary reddish brown biotite was noted i n both the 'quartz-eye' quartz monzonite porphyry and the quartz monzonite-granodiorite porphyry i n the 144. marginal areas of the stock. In both rock types, the original biotite has been altered to a mixture of chlorite and sericite. Intense a r g i l l i c and sericite alteration i s common i n fault zones, as are chlorite-coated s l i p surfaces. The major structural trends in the area of the porphyry stock are east-northeast and north-northwest, as reflected by the elongation of the stock i t s e l f , the strike of fractures, joints, faults, and basic dykes, and by the trend of creeks and airphoto lineaments. The stock contact, which dips steeply outward, i s not well defined, rather i t consists of a transitional zone of hornfels cut by numerous porphyry dykes. A large horse of hornfelsed sedi-mentary rocks within the stock, measuring 1,000 by 200 feet, parallels the long direction of the stock (Figure C.2) and i s cut by numerous porphyry dykes. Dr i l l i n g information suggests that this block of country rock decreases in size with depth. Major faults preceded the period of intrusion and intersections of east-northeast and north-northwest faults and fractures were undoubtedly important in the localization of the stock. Later movement along these faults, particu-l a r l y the north-northwest set, i s documented by the apparent offsetting of the stock contacts along two major faults and by the presence of numerous post-mineral shears noted i n d r i l l cores (Figure C.2). Molybdenum mineralization occurs i n both the quartz monzonite porphyry and biotite hornfels adjacent to the central and eastern parts of the stock. The company has stated that d r i l l i n g has indicated 35.8 million tons having an average grade of 0.11 per cent molybdenite (Carter, 1967a). Molybdenite occurs mainly as selvages i n one-eighth to one-quarter-inch steeply dipping quartz veinlets which follow major fracture directions. Three 145. stages of quartz veining and mineralization have been noted. A f i r s t stage of barren quartz veinlets i s followed by the second, the most important stage, consisting of quartz-molybdenite-pyrite veinlets which are steeply inclined. These are offset locally by flat quartz-molybdenite veins and hairline fractures. The third stage consists of 1-inch-wide and larger veins of quartz and carbonate which contain variable amounts of pyrite, pyrrhotite, galena, and sphalerite. In Clary Creek, 1,500 feet east of the stock, a 10-inch-wide quartz-carbonate vein containing pyrite, pyrrhotite, galena, and sphalerite was noted i n a shear zone in argillaceous sediments. The quartz monzonite porphyries and biotite hornfels contain abundant disseminated pyrite and pyrrhotite. Three samples for potassium-argon dating were collected from and adjacent to the Bell Molybdenum stock. Locations are shown on Figure C.2. NC-67-30 - 'Quartz-eye' Quartz Monzonite Porphyry Sample i s from the late, possibly post-mineral porphyry phase and was collected from d r i l l core from a hole i n the central part of the stock. Fifty per cent of the rock consists of 4-millimetre phenocrysts of euhedral plagioclase ^^n20-26^' a n n e d r a l quartz, and occasional 1-centimetre K-feldspar crystals. The rock contains both hornblende and biotite. Hornblende exhibits incipient alteration to biotite. Primary biotite occurs as 1-millimetre plates and books which contain up to 15 per cent chlorite alteration. NC-67-32 - Biotite Hornfels Sample was collected from d r i l l core recovered from a hole south of the stock but within the contact metamorphic aureole. The hornfels i s fine 146. grained and i s a uniform brown colour. Numerous one-sixteenth-inch quartz v e i n l e t s cut the rock. In t h i n s e c t i o n , the rock has a granoblastic texture and consists of a very fine-grained mosaic of quartz and subhedral b i o t i t e . The o r i g i n a l rock was probably an argillaceous microgreywacke. B i o t i t e constitutes 15 per cent of the rock and i s unaltered. NC-68-2 - Granodiorite Porphyry Sample i s from the border phase of the stock and i s a core sample c o l l e c t e d from a d r i l l hole near the northern contact. The rock i s cut by one-eighth-inch quartz-molybdenite v e i n l e t s and i s a medium grey colour. Phenocrysts of euhedral p l a g i o c l a s e ( A n ^ . ^ ) , 1 to 2 millimetres i n s i z e , constitute 20 per cent of the rock by volume. These are set i n a f i n e r grained matrix of quartz, p l a g i o c l a s e , K-feldspar, b i o t i t e , hornblende, and c h l o r i t e . B i o t i t e occurs as 0.5 to 1.0-millimetre shredded plates which feature only i n c i p i e n t c h l o r i t e a l t e r a t i o n . Very fine-grained shredded b i o t i t e i n the matrix appears secondary a f t e r hornblende. C.1.3 Ajax ( a f t e r Carter, 1966) The Ajax property i s on the east slope of Mount McGuire, 8 miles northeast of A l i c e Arm. Argillaceous sedimentary rocks and some interbedded volcanics are intruded by four small c l o s e l y spaced stocks of quartz monzonite porphyry i n the ce n t r a l 147. part of the claim group (Fig. C.3). Molybdenum mi n e r a l i z a t i o n occurs both i n the i n t r u s i v e rocks and adjacent hornfelsed sedimentary rocks. Black a r g i l l i t e s , s i l t s t o n e s , and microgreywackes, which s t r i k e north-northwest and dip steeply east, underlie most of the eastern h a l f of Mount McGuire. At lower e l e v a t i o n s , calcareous a r g i l l i t e s and buff-coloured limy s i l t s t o n e s were noted. Dark grey to black argillaceous sedimentary rocks i n a l l parts of the area contain 2 per cent 0.05-millimetre plates of brown b i o t i t e and up to 5 per cent p y r i t e and p y r t h o t i t e as fin e disseminations and as coatings on fracture planes. With increasing proximity to the quartz monzonite porphyry stocks, the sediments grade to b i o t i t e hornfels. Augite andesites, weathering a reddish brown colour, occur as 3-foot-thick interbeds within the sedimentary rocks. A larger area of v o l c a n i c rocks, on the west slope of Mount McGuire, consists of purple t u f f s and breccias. Intrusive rocks, i n the form of four small stocks of quartz monzonite porphyry, are grouped close together i n a 2,500-foot-square area i n the c e n t r a l part of the claim group between 3,000 and 4,200 feet e l e v ation. The stocks are roughly r e c t i l i n e a r i n plan, and the l a r g e s t , the most southerly one, i s elongate i n a north-northwesterly d i r e c t i o n , measuring 1,500 to 1,000 fee t . The remaining three measure 1,000 by 500 feet and are elongate i n an east-northeast d i r e c t i o n . The area between the stocks features an abundance of dykes of s i m i l a r composition. The l a r g e s t stock and the one immediately northwest of i t are composed of l e u c o c r a t i c white to pink quartz feldspar porphyry. Twenty-five to 30 per cent of the rock consists of 3 to 6-millimetre phenocrysts of anhedral quartz, subhedral s e r i c i t i z e d p l a g i o c l a s e , and ragged p e r t h i t i c orthoclase i n a fine-grained matrix of quartz, feldspar, and s e r i c i t e . 148. 149. Sericite, in part an alteration of original biotite, i s the major mafic mineral. One-eighth to one-quarter-inch quartz veinlets are common. The other two intrusive bodies, which are essentially a network of closely spaced east-northeast and north-northwest dykes, are of similar composition , but dif f e r from the quartz feldspar porphyries by being medium grey in colour and by having a biotite content of between 7 and 10 per cent, and some chlorite and hornblende. Two to 4-millimetre phenocrysts of quartz and normally zoned oligoclase-andesine make up 25 per cent of the rock. In contrast to the quartz feldspar porphyries, plagioclase i s essentially fresh and K-feldspar i s largely restricted to the matrix. Some of the narrow dykes have a seriate texture. Dykes of quartz feldspar porphyry and biotite-bearing quartz monzonite porphyry, striking east to east-northeast and not exceeding 25 feet i n width, cut sedimentary rocks on top of Mount McGuire. Felsite dykes, porphyritic i n part and containing some disseminated pyrite, were noted south of the main area of intrusive rocks. Northeast-striking 6-foot-wide dykes of fine-grained hornblende and biotite lamprophyres were noted south and east of the quartz monzonite porphyry stocks. These weather a brown colour, have chilled contacts, and are of post-mineral age. Contact metamorphism associated with the intrusion of the porphyry stocks has converted a large area of sedimentary rocks i n the central part of the property to brown and purple-coloured biotite hornfels. The hornfels zone surrounding the stocks, elongate i n a north-northwest direction and measuring 7,000 to 5,000 feet, i s gradational outward from a fine-grained granoblastic 150. textured rock c o n s i s t i n g of anhedral quartz and b i o t i t e to an a l t e r n a t i n g sequence of banded black a r g i l l i t e and brown hornfels. The b i o t i t e hornfels i s featured by c l o s e l y spaced f r a c t u r i n g and widespread limonite s t a i n due to abundant disseminated p y r r h o t i t e and p y r i t e . The inner zone of hornfels, extending outward from the stocks a distance of between 500 and 1,000 feet, has been aff e c t e d by a more intense a l t e r a t i o n , r e s u l t i n g i n the transformation of b i o t i t e hornfels to a pale green fine-grained quartz-albite-epidote hornfels. In the outer part of t h i s zone, h a i r l i n e fractures i n b i o t i t e hornfels con-t a i n i n g quartz and a c t i n o l i t e and l e s s e r amounts of clinopyroxene and p y r r h o t i t e are rimmed by 4-millimetre-wide zones of quartz-albite-epidote h o r n f e l s . Adjacent to and between the four stocks, where f r a c t u r i n g i s most intense, q u a r t z - a l b i t e -epidote hornfels has almost completely replaced b i o t i t e h o r n f e l s , and i s prob-ably a r e f l e c t i o n of the degree of quartz v e i n i n g and s i l i c i f i c a t i o n w i t h i n and adjacent to the i n t r u s i v e rocks coupled with higher temperatures p r e v a i l i n g near the contacts. East of the stocks, near the outer l i m i t s of the zone of quartz-albite-epidote h ornfels, a narrow band of limestone contains 4-millimetre porphyroblasts of pink garnet• The e f f e c t s of contact metamorphism on interbedded augite andesites includes p a r t i a l to complete a l t e r a t i o n of o r i g i n a l clinopyroxene to fibrous a c t i n o l i t i c hornblende and s e r i c i t i z a t i o n of p l a g i o c l a s e . A l t e r a t i o n of the i n t r u s i v e rocks, which i s most widespread i n l e u c o c r a t i c quartz feldspar porphyries, includes s e r i c i t i z a t i o n of p l a g i o c l a s e phenocrysts, a l t e r a t i o n of b i o t i t e to muscovite, and development of ragged porphyroblasts of K-feldspar. Flakes of b i o t i t e i n the quartz monzonite porphyries may be of secondary o r i g i n . D r i l l i n g information indicates l i g h t grey prevasive s i l i c i f i -c ation adjacent to quartz v e i n l e t s i n deeper parts of the i n t r u s i v e bodies. 151. Sedimentary and volcanic rocks underlying Mount McGuire are part of the steep east limb of a regional a n t i c l i n a l structure. East and west ,of the porphyry stocks, s t r i k e s are uniformly north-northwest, while a t t i t u d e s north and south of the stocks ind i c a t e contortion of the sediments along s t r i k e . Attitudes adjacent to the stocks suggest the presence of a large dragfold modified by doming associated with the i n t r u s i o n of the stocks. Most creeks on Mount McGuire follow f a u l t s which s t r i k e north-northwest and east-northeast. The r e c t i l i n e a r nature of the porphyry stock contacts, which follow steep f r a c t u r e s , and the trends of smaller dykes r e f l e c t the north-northwest and east-northeast f a u l t and fracture pattern and i n d i c a t e the importance of major f a u l t s i n the l o c a l i z a t i o n of the stocks. P y r r h o t i t e and l e s s e r amounts of p y r i t e coat fracture planes and occur as fin e disseminations i n the sedimentary rocks on the east slope of Mount McGuire. P y r r h o t i t e i s p a r t i c u l a r l y widespread i n the i n t r u s i v e rocks and adjacent a l t e r e d sedimentary and v o l c a n i c rocks. Limonite s t a i n i n g i s prominent. Molybdenum mi n e r a l i z a t i o n occurs i n both the i n t r u s i v e rocks and i n the marginal zone of hornfels affected by quartz-albite-epidote a l t e r a t i o n . The most common form of occurrence i s that of fine-grained quartz and molybdenite coating randomly oriented, h a i r l i n e f r a c t u r e s . Disseminated molybdenite also occurs i n a stockwork of one-eighth to one-quarter-inch quartz v e i n l e t s and i n the s i l i c i f i e d zones i n the deeper parts of the stocks. At l e a s t two stages of quartz-molybdenum mineralization follow an i n i t i a l stage of quartz-pyrrhotite m i n e r a l i z a t i o n . The l a t e s t stage of m i n e r a l i z a t i o n i s represented by coarse-grained quartz veins several inches wide, containing 152. s p h a l e r i t e and l e s s e r amounts of p y r i t e , galena, and chalcopyrite. On surface these veins s t r i k e north-northeast and dip to the west at shallow angles. One sample for potassium-argon dating was c o l l e c t e d from the Ajax property and the l o c a t i o n i s shown on Figure C.3. NC-67-33 - Granodiorite Porphyry Sample was c o l l e c t e d from a roadcut i n the easternmost of the four small stocks. The granodiorite i s a mesocratic p o r p h y r i t i c rock i n which fresh, euhedral, zoned p l a g i o c l a s e (^n25-3o^ phenocrysts constitute 30 per cent. These are set i n a fine-grained matrix of quartz and feldspar. Hornblende i s uniformly d i s -t r i b u t e d through the matrix and d i s p l a y s p a r t i a l a l t e r a t i o n to b i o t i t e . Primary b i o t i t e books, 1 to 2 millimetres i n s i z e , amount to 7 per cent of the rock and are p o i k i l i t i c , d i s p l a y i n g only i n c i p i e n t c h l o r i t e a l t e r a t i o n . C.1.4 Roundy Creek ( a f t e r Carter, 1964, 1968, 1970, 1971) This property i s south of A l i c e Arm Inlet on Roundy Creek, 1.5 miles from tidewater. Molybdenum min e r a l i z a t i o n i s associated with a small, elongate composite i n t r u s i o n of quartz monzonite porphyry. The i n t r u s i o n i s s t o c k - l i k e i n part and has been segmented by northwest f a u l t s along and adjacent to Roundy Creek (Figure C.4). The i n t r u s i o n consists of a number of recognizable phases, which are of s i m i l a r compostion. The most widespread of these i s a l e u c o c r a t i c 'quartz-eye' 154. quartz monzonite porphyry which forms the core of the intrusion. Twenty-five per cent of the rock i s composed of 2 to 4-millimetre phenocrysts of subhedral quartz, perthitic K-feldspar, and euhedral plagioclase ( A n 28-32^' w n l c h a r e set i n a very fine-grained matrix of quartz and feldspar. The rock contains only minor biotite, with sericite being the chief mafic mineral. Where intensely sheared and fractured, the 'quartz-eye' quartz monzonite porphyry grades into brecciated quartz monzonite in which feldspar phenocrysts are p a r t i a l l y broken down and the many randomly oriented fractures are coated with chlorite, s e r i c i t e , carbonate, and molybdenite. The 'quartz-eye' quartz monzonite porphyry i s apparently gradational to biotite-quartz monzonite and i s most abundant i n the central and border areas of the intrusion. This rock type has a seriate texture and consists essentially of 2 to 4-millimetre grains of quartz, fresh euhedral plagioclase (An^g), and perthitic orthoclase, plus scattered flakes of biotite which are pa r t i a l l y altered to chlorite and sericite. Dykes and irregular masses of fine-grained white alaskite cut a l l of the aforementioned rock types. Alaskites consist of a fine-grained mosaic of quartz, sodic plagioclase, granophyre, and some ser i c i t e . In some areas the alaskite i s gradational to a quartz feldspar porphyry. A late intrusive phase i s represented by narrow dykes of fine-grained, light grey biotite-quartz monzonite which were seen i n one of the underground levels and i n a few d r i l l holes. The last phase contains only trace amounts of molybdenite. Narrow, northeast-striking and steeply dipping hornblende and biotite lamprophyre dykes cut a l l granitic rocks and mineralized veinlets and fractures. Many terminate at, or are offset by, northwesterly trending faults (Figure C.4). 155. Sedimentary rocks have been contact metamorphosed to biotite hornfels in a zone roughly 200 feet wide surrounding the intrusion. Structural relationships of the intrusion are complex. In addition to the faulted segments in plan, d r i l l i n g evidence indicates inward dipping intrusive contacts sug-gesting that parts of the intrusive may be sheet-like in form about a central feeder pipe. The eastern segment i s apparently tabular i n section. Alteration of the intrusive rocks includes a potassic zone, which i s best developed within and marginal to better grades of molybenum mineralization. Potassic alteration occurs as abundant sericite and lesser biotite-coated fracture planes particularly i n the leucocratic quartz monzonite porphyry. Secondary b i o t i t e , principally on fractures, i s best developed i n the biotite-quartz monzonite peripheral to the main zones of mineralization. Two zones of molybdenum mineralization are known within the intrusive. The eastern segment i s host to uniform grades of molybdenite occurring as selvages i n numerous randomly oriented quartz veinlets and as fracture f i l l i n g s . D r i l l i n g has indicated the presence of 7 to 8 million tons of 0.11 per cent molybdenite in this zone. High-grade molybdenum mineralization occurs along and south of Sunshine Creek (Figure C.4) where d r i l l i n g and underground work has indicated 1.5 million tons of 0.347 per cent molybdenite i n the southern zone and some 39,000 tons grading 0.668 per cent in a small zone explored on the north side of Sunshine Creek. In both zones, higher grades of molybdenum mineralization are contained in alaskites. On the 1050 level (Figure C.4), closely spaced parallel one-quarter to one-half-inch bands of molybdenite are crudely par a l l e l to the 156. trend of the enclosing alaskite body. One-quarter-inch rosettes of molybdenite also are uniformly distributed i n the alaskite. Molybdenite also occurs i n numerous randomly oriented hairline fractures with chlorite i n brecciated quartz monzonite and i n closely spaced one-eighth to one-quarter-inch quartz veinlets i n alaskites and leucocratic 'quartz-eye' quartz monzonite porphyries. D r i l l i n g and underground exploratton indicate that the zones of molybdenum mineralization are lens-like i n form and extremely erratic in lateral and ve r t i c a l extent. The distribution of the higher grade zones suggests they are spatially related to the intrusive centre or feeder pipe. One sample was collected from the Roundy Creek intrusion, the location of which i s shown on Figure C.4. NC-67-35 - Biotite Quartz Monzonite Sample was collected from a d r i l l hole in the central part of the intrusion. The rock i s leucocratic, has a seriate texture, and i s featured by flakes of reddish brown biotite which make up 10 per cent of the rock. Feldspars are equally divided between perthitic K-feldspar and plagioclase (An^) and are essentially unaltered. Biotite occurs as 0.5 to 1.0-millimetre shredded plates which display only incipient chlorite alteration along cleavage planes. C.1.5 Molly Mack (after Carter, 1965) The Molly Mack property i s situated on the west shore of Observatory Inlet near the south end of Granby Point, 15 miles west of Alice Arm (Figure 19). 157. The main mineralized showing i s at sea level immediately south of the contact between granitic rocks and sedimentary rocks to the north. South and west of the showing, leucocratic quartz monzonite porphyries form low ridges and weather to a uniform near white colour. Two-millimetre phenocrysts of anhedral glassy quartz and euhedral feldspars make up most of the rock, with muscovite as the dominant mafic mineral. Sedimentary rocks in the area have been metamorphosed to a biotite-quartz hornfels and are cut by numerous 1-foot-wide s i l l s of fine-grained quartz monzonite near their contact with the quartz monzonite porphyry. The main zone of molybdenum mineralization i s confined to a small area of biotite-rich granite within the quartz monzonite porphyries. The granite, which consists essentially of anhedral quartz, subhedral perthitic K-feldspar, and coarse flakes of b i o t i t e , contains irregular inclusions of hornfelsed sediments and i s cut by lenses of quartz monzonite porphyry and fine-grained f e l s i t e dykes. Coarse-grained molybdenum mineralization within this zone occurs along the biotite cleavages and near the margins of 1-foot-wide quartz veins and lenses. The zone i s oriented i n a north-south direction and measures 4 by 10 feet. A chip sample from the zone assayed 12.7 per cent M0S2 with trace amounts of copper and lead. A few specks of molybdenite were noted in the intrusive rocks to the north and south of the main showing. NC-68-11 - Biotite Granite Sample i s from a test p i t near tide line and i s a medium-grained, foliated granitic rock i n which coarse grains of molybdenite are interleaved with biotite. The rock has a hypidiomorphic granular texture and consists of subhedral, perthitic K-feldpsar and microcline, 60 per cent; anhedral quartz, 158. 10 per cent; finer grained i n t e r s t i t i a l sodic plagioclase, 5 per cent; b i o t i t e , 20 per cent; and epidote and apatite, 2 per cent. The biotite i s acicular, occurring as 1 to 2-millimetre plates and appears to have been introduced along fractures. Only minor chlorite alteration was noted. C.1.6 Nass River Molybdenum Deposits (after Carter, 1967) Four small molybdenite-bearing quartz feldspar porphyry stocks intrude argillaceous sedimentary rocks near their contact with the Coast Plutonic rocks along the south side of the Nass River. The stocks are clustered around the western edge of a thin, Recent lava flow (Figure C.5). The Snafu property i s situated directly south of the lava f i e l d . In the central part of the claim group, a subcircular stock of quartz feldspar porphyry, roughly 3,500 feet i n diameter, intrudes northeast-striking, banded argillaceous sediments. A smaller mass of similar intrusive rock outcrops northwest of the main stock. The porphyry i s typically leucocratic and i s of quartz monzonite composition. Phenocrysts constitute 40 per cent of the rock and include 1 to 2-centimetre euhedral crystals of perthitic orthoclase and 4-millimetre euhedral grains of plagioclase (oligoclase) and subhedral quartz crystals which are set in a very fine-grained matrix of quartz, feldspar, and biotite. The rock i s essentially fresh, with only minor s i l i c i f i c a t i o n and secondary K-feldspar occurring adjacent to some quartz veinlets. Iron oxide staining i s widespread, due to the presence of finely disseminated pyrite and pyrrhotite. Fine-grained dykes of alaskite, consisting of interlocking anhedral 160. grains of quartz and microgranophyre, follow northeast and northwest fractures in the porphyry near the west contact of the stock. In the same area a 100-foot-wide northwest-striking dyke of grey hornblende-biotite feldspar porphyry of quartz-diorite composition cuts both the quartz feldspar porphyry and adjacent hornfelsed sediments. Numerous small screens of hornfels were noted within the stock near the irregular west-central contact, and peripheral dykes of porphyry are locally abundant. Molybdenite occurs i n northeast and northwest fractures and quartz veinlets i n quartz feldspar porphyry, alaskite, and hornfelsed sediments along the western stock contact. The Valley and Ridge properties are situated 4 miles west of the Snafu showing (Figure C.5). Two small circular stocks of porphyritic granite 1,000 feet i n diameter occur 2,000 feet apart on opposite sides of a west-northwest-trending topographic lineament which i s probably a fault. The stocks, while par t i a l l y enclosed i n quartz diorite of the Coast Plutonic Complex, also are i n contact with hornfelsed sedimentary rocks along their northern contact. The granites have a seriate to porphyritic texture and consist essentially of quartz and microcline perthite with only minor plagioclase (oligoclase) and scattered flakes of biotite. Near the northwest contact of the stock on the Ridge group, the granite i s gradational to quartz monzonite. Narrow dykes of fine-grained alaskite cut the Valley stock near i t s western contact. Dykes of hornblende-biotite feldspar porphyry, 100 feet wide and striking northwest, cut the granites i n both the Valley and Ridge stocks. These are post-mineral in age and are similar to the late dyke on the Snafu group. The Coast quartz diorite i s typically a grey medium-grained equigranular rock consisting mainly of fresh, zoned plagioclase (oligoclase-andesine) with lesser amounts of quartz, hornblende, and biotite. 161. Molybdenum mineralization i s exposed i n trenches near the central part of the Valley stock, where i t occurs as fine disseminations, irregular coarse replacements, and i n northwest fractures i n porphyritic granites and alaskite dykes. Iron oxide staining i s widespread. The Kay property i s 3 miles southwest of the Valley and Ridge prospects on the Greenville road (Figure C.5). The claims cover an e l l i p t i c a l stock of quartz feldspar porphyry, elongate i n a northeasterly direction and measuring 4,000 by 1,200 feet. The stock underlies a prominent ridge which i s bounded by steep c l i f f s at i t s northern end. The leucocratic quartz feldspar porphyry i s of quartz monzonite composition, and 0.4 to 2-centimetre phenocrysts make up between 20 and 50 per cent of the rock. These include euhedral perthitic orthoclase and microcline plus quartz and plagioclase (oligoclase) which are set i n a fine-grained quartzofeldspathic matrix containing some biotite. Prominent sheeting in the intrusive strikes north and dips moderately to the west. Contacts between the intrusive and adjacent biotite hornfels were observed only at the base of the steep c l i f f at the northeast end of the stock. Quartz feldspar porphyry containing coarse rosettes of molybdenite was observed i n several trenches near the central part of the stock. Diamond d r i l l i n g i n 1969 indicated the presence of late, possible post-mineral, fine-grained grey porphyry dykes which cut the leucocratic quartz feldspar porphyry. The following potassium-argon samples were collected from the Nass River molybdenum prospects. Locations are shown on Figure C.5. NC-67-25 - Hornblende-biotite Feldspar Porphyry Sample i s from a post-mineral porphyry dyke which cuts quartz monzonite porphyry at the Ridge prospect. 162. The rock, of quartz diorite composition , i s a light grey porphyry with 25 per cent of the rock consisting of 4-millimetre phenocrysts of plagioclase (An 2 Q_^ 5), biotite books, and hornblende needles set i n a very fine-grained matrix of quartz and feldspar. Corroded quartz phenocrysts are also present. Hornblende i s completely altered to chlorite and b i o t i t e , and biotite displays incipient to 50 per cent alteration to chlorite, principally along cleavage planes. NC-67-26 - Porphyritic Granite Sample was collected from a test p i t on the Valley prospect. The granite i s a pink colour and has occasional resorbed quartz eyes as phenocrysts. Major constituents are subhedral microcline and perthitic K-feldspar. Biotite amounts to 7 per cent of the rock and occurs as fresh 0.5-millimetre discrete grains scattered through the matrix. Molybdenite occurs in close association with bio t i t e , principally along cleavage planes. NC-67-27 - Quartz Monzonite Porphyry Sample i s from a test p i t near the central part of the Kay prospect. The rock i s pink to white and has a porphyritic texture with 1 -centimetre phenocrysts of p o i k i l i t i c and perthitic K-feldspar contained i n a medium-grained matrix of microcline, plagioclase, and quartz. Molybdenite i s disseminated i n the matrix. Biotite displays only incipient alteration to sericite and epidote and occurs as 1-millimetre shredded flakes throughout the rock matrix. 163. C.1.7 Coast Plutonic Complex - Alice Arm-Nass River Penny Creek The Penny Creek prospect i s situated within the Coast Plutonic Complex, 16 miles south of Alice Arm (Figure 19). The principal showings are i n a cirque near the headwaters of Penny Creek. Medium-grained quartz diorites of the Coast Plutonic Complex are cut by drusy quartz veinlets containing rosettes of molybdenite. The sparse mineralization i s apparently marginal to a younger, equigranular, pink granite exposed near the head of the cirque. NC-67-45 - Granite Sample was collected from near the head of the cirque and i s a leucocratic medium-grained pink rock which consists of quartz, 20 per cent; perthitic K-feldspar, 72 per cent; b i o t i t e , 3 per cent; opaque minerals, 2 per cent; and epidote and sphene, 3 per cent. Biotite occurs as 1-millimetre plates and exhibits only incipient alteration to chlorite. Dawson Ridge Sparse amounts of molybdenum mineralization are associated with veins and dyke-like masses of alaskite and pegmatite, which cut equigranular quartz monzonites and quartz diorites near the summit of Dawson Ridge, near the headwaters of Roundy Creek (Figure 19). 164. NC-67-29 - Quartz Monzonite Sample i s a leucocratic medium-grained rock i n which plagioclase (An28-32^ makes up 40 per cent; K-feldspar, 28 per cent; biotite, 8 per cent; hornblende, 5 per cent; and accessories, including sphene and magnetite, 5 per cent. Biotite plates are 1-millimetre size and exhibit some alteration (10 to 20 per cent) to chlorite. Mount Priestly Mount Priestly, 8 miles east of Aiyansh on the Nass River (Figure 19), i s underlain by a granitic stock related to the Coast Plutonic Complex. Light grey, medium-grained, equigranular quartz diorites near the peak of the mountain contain some disseminated molybdenite in fractures. NC-67-24 - Granodiorite The sample i s a mesocratic, medium-grained, equigranular rock, having a hypidiomorphic granular texture and consisting of euhedral, fresh, zoned plagioclase (^20-28^' 5 7 p e r c e n t » i n t e r s t i t i a l quartz, 15 per cent; green hornblende, 10 per cent; b i o t i t e , 7 per cent; K-feldspar, 5 per cent; and apatite, sphene, and opaques, 5 per cent. Biotite occurs as 1-millimetre plates which show only incipient chlorite alteration. Some biotite also occurs as a deuteric alteration of hornblende. 165. Nass River Granitic rocks of the Coast Plutonic Complex are well exposed i n roadcuts between the Valley and Kay molybdenite prospects on the south side of the Nass River (Figure 21). NC-67-28 - Quartz Diorite The sample i s a mesocratic, medium-grained rock with hornblende and biotite as mafic minerals. The rock i s of quartz diorite composition, has a hypidiomorphic granular texture, and consists essentially of euhedral, fresh, zoned plagioclase (^28-35^ w* t* 1 i n t e r s t i t i a l quartz and 1 to 2-millimetre grains of fresh hornblende and biotite. Biotite makes up 10 per cent of the rock and exhibits only very minor chlorite alteration. Lava Lake Coat Plutonic Complex rocks are exposed i n a roadcut near the southeast side of Lava Lake, 15 miles south of the Nass River (Figure 19). NC-69-3 - Quartz Monzonite Sample i s leucocratic and contains abundant 2-millimetre plates of biotite. Fresh plagioclase (An^) and K-feldspar occur i n nearly equal proportions and quartz i s i n t e r s t i t i a l . Green hornblende i s partially altered to chlorite. Biotite makes up 10 per cent of the rock and i s only weakly altered to chlorite. 166. C.1.8 Lamprophyre Dykes NC-70-1 - Biotite Lamprophyre Sample i s from a 1-foot-wide, northeast-striking, steeply dipping dyke which intrudes quartz monzonite porphyry i n the northeast part of the British Columbia Molybdenum ore zone. The rock i s fine grained, dark grey, and slightly magnetic with 1 to 2-millimetre carbonate amygdules. Forty per cent of the rock i s made up of fresh brown hornblende needles 1 to 2-millimetres long, and equant 1-millimetre grains of chlorite (originally pyroxene). The remainder consists of unaltered plagioclase and minor carbonate and magnetite. NC-68-3 - Quartz Biotite Schist Sample i s from the dump at the portal of the old Bonanza copper mine south of Anyox (Figure 19). Quartz and biotite are the major constituents of the rock, along with chalcopyrite which i s intimately associated with biotite. Biotite i s unaltered and may be the product of contact metamorphism related to the lamprophyre dyke swarm which cuts the ore zone. NC-68-4 - Biotite Lamprophyre Sample i s from a 1-foot-wide dyke which parallels a silver-bearing quartz vein near the headwaters of the Illiance River, 10 miles northeast of Alice Arm (Figure 19). 167. The rock, i s a dark green colour and i s fine-grained with 1-millimetre plates of biotite distributed through the matrix. The biotite i s essentially unaltered and imparts a flow texture to the rock. The very fine-grained matrix consists of biotite, clinopyroxene (altered to carbonate), and plagioclase. C.1.9 Basalt Lava Flows NC-67-32 - Olivine Basalt Sample was collected from d r i l l core recovered from a hole through a basalt outlier north of the Bell Molybdenum stock (Figure C.2). The lava flow i s fine grained, light grey, vesicular, and has chilled contacts with underlying rocks. The rock has a trachytic texture as imparted by plagioclase (A^g.^g) laths which make up 70 per cent of the rock. Inter-s t i t i a l areas are made up of olivine, clinopyroxene, and magnetite. The basalt i s essentially unaltered. NC-70-4 - Olivine Basalt Sample was collected from the south side of Widdzech or Table Mountain, a basalt outlier one-half mile northeast of the British Columbia Molybdenum open p i t (Figure 19). The rock i s a fine-grained, dark grey porphyry with scattered 1 to 2-millimetre euhedral phenocrysts of unzoned plagioclase (An 0, . _ ) , set i n a 36-40 fine-grained matrix, featuring a trachytic texture as imparted by plagioclase laths. I n t e r s t i t i a l areas are occupied by olivine, clinopyroxene, and magnetite. The rock i s fresh. 168. C.2 BULKLEY INTRUSIONS AND ASSOCIATED COPPER AND MOLYBDENUM DEPOSITS C.2.1 Glacier Gulch-Hudson Bay Mountain (after Kirkham, 1966 and Jonson, et a l . , 1968) The property i s centred on Glacier Gulch on the east side of Hudson Bay Mountain, a few miles northwest of the town of Smithers. On surface, molybdenum mineralization occurs over an area of about 1 by 1.5 miles i n Glacier Gulch, and i s known to extend to depths greater than 3,000 feet. Most of this area i s underlain by an altered and metamorphosed bedded pyroclastic sequence and some cla s t i c sedimentary rocks, both of Jurassic age. Aphanitic f e l s i t i c intrusions cut the pyroclastic sequence. A concealed discordant and differentiated granodiorite sheet which intrudes the pyroclastic rocks i s host to much of the higher grade molybdenum mineralization (Figure C.6). The granodiorite i s intensely altered and original mafic minerals have been obliterated. Numerous basic dykes cut the granodiorite sheet and the volcanic rocks. Also intruding the volcanic rocks and the lower portion of the granodiorite sheet i s an oval quartz porphyry plug 1,100 feet in diameter. Occurring above the porphyry plug are dykes and breccias of similar composition which both truncate, and are veined by, quartz-molybdenite mineralization and are therefore inter-mineral i n age. A stock of quartz monzonite porphyry truncates the mineralized quartz porphyry plug at depth, and i s i t s e l f only weakly mineralized (Figure C.6). It i s therefore a late phase in the intrusion-mineralization sequence. The stock i s the apparent source of a subradial swarm of dykes which extends for at least 2 miles north and south of the glacier. V VEIN PATTERNS FIG.-C.6 GLACIER GULCH 170. The volcanic and sedimentary rocks in the Glacier Gulch area and the granodiorite sheet have been thermally metamorphosed by the intrusion of the quartz porphyry plug and the quartz monzonite porphyry stock. Hydrothermal alteration and bleaching are common both inside and outside the area of molybdenum mineralization. The quartz porphyry plug i s overlain by a zone of intense s i l l c i f i c a t i o n . In the vi c i n i t y of the molybdenum deposit, hydrothermal alteration i s superimposed on products of thermal metamorphism, involving bleaching of the wallrocks, particularly adjacent to quartz veinlets. Molybdenite occurs almost entirely i n a stockwork of quartz veinlets. Lesser amounts of scheelite-powellite and chalcopyrite also occur in the veinlets. Most quartz veins are one-half inch wide, but locally they may be up to 2 feet in width. At least two main periods of molybdenite have been distinguished. An area of quartz veining extends beyond the molybdenum zone and i s gradational to a pyrite halo 2.5 by 4 miles i n area. The molybdenum deposit i s central to a great number of small, complex sulphide-sulphosalt veins rich i n lead and zinc. These have a zonal arrange-ment and include a zone of zinc-gold-copper-arsenic mineralization surrounded by a zone of lead-silver-copper-arsenic mineralization. A l l of the mineral deposits on Hudson Bay Mountain appear to be genetically related, but the zonal arrangement i s complicated by several stages of mineralization. Two potassium-argon samples were collected from the molybdenum deposit, duplicates of which were also analysed at the Geochronology Laboratories of the Geological Survey of Canada (Wanlesst et a l . , 1970). NC-67-41 - Quartz-biotite Veinlets i n Granodiorite Sample was collected from the 3,500-foot level adit (Figure C.6). 171. Biotite i s contained in one-eighth-inch quartz-molybdenite veinlets which cut intensely altered granodiorite. The biotite occurs as medium to coarse-grained reddish brown flakes. Minor chlorite alteration occurs on the edges of some biotite grains. NC-68-6 - Quartz Monzonite Porphyry Sample i s from d r i l l core from a hole collared on the north side of Hudson Bay Mountain and d r i l l e d into the concealed quartz monzonite porphyry stock. The rock i s a pink to grey porphyry with scattered 1-centimetre pheno-crysts of K-feldspar and 3 to 4-millimetre phenocrysts of euhedral plagioclase (An ) set in a finer grained matrix of quartz, plagioclase, hornblende, and 25 biotite. Some quartz phenocrysts are also present. Hornblende exhibits deuteric alteration to biotite. Biotite constitutes 3 to 5 per cent of the rock and occurs primarily as 1-millimetre plates which exhibit up to 10 per cent chlorite alteration along cleavages. Fine-grained, shredded biotite i s up to 50 per cent chloritized. C.2.2 Huber (after Sutherland Brown, 1965) This property i s about 8 miles north of Houston and the showings are about a mile east of Highway 16. The property was formerly known as Mineral H i l l and was explored for copper, lead, and zinc i n 1926 to 1928 by means of a shaft, an adit, and some trenching. The geology of the Huber group i s shown on Figure C.7. Hornfelsic sand-stones, siltstones, and crystal tuffs of Jurassic age are intruded by three 173. bodies. At the west i s a tongue-like body of coarse alaskite, whereas the main mass of the h i l l i s underlain by porphyritic granite that has a p l i t i c border facies. A large dyke of fine-grained monzonite i s unmineralized and unmetamorphosed. The hornfelses are dense, dark purplish to brownish rocks that weather a light grey where leached or rusty colour where oxidized. The degree of metamorphism i s f a i r l y uniform, with an overlay of fine-felted brown biotite throughout. The alaskite i s a relatively coarse-grained rock i n which quartz i s rounded, the plagioclase (An^g) lathy, perthite lathy to irregular, and the muscovite and opaque minerals are interleaved. The porphyritic granite i s composed of about 65 per cent phenocrysts of perthite, quartz, and plagioclase (A^Q) and minor mica i n an a p l i t i c fine-grained matrix of quartz, perthite, and micrographic granite and lesser small laths of plagioclase (An^^) with angular hornblende and interstices of quartz and micrographic granite. Alteration i s moderately intense, with plagioclase partly altered to clinozoisite and s e r i c i t e , and hornblende i s altered to clinozoisite and chlorite. Most of the hornfels i s shattered and contains numerous closely spaced one-eighth-inch quartz veinlets in a stockwork pattern. The alaskite i s cut by larger veins. Pyrite and some molybdenite occur in veinlets and fractures. Lead, zinc, and silver minerals occur i n larger veins peripheral to the molybdenum mineralization, principally near the old shaft and i n a breccia zone to the north. One sample for potassium-argon dating was analysed, that being a whole-rock biotite hornfels. A sample collected from the monzonite dyke was con-sidered to be unsuitable due to intense alteration of hornblende. 174. NC-67-16 - Biotite Hornfels Sample was collected from a trench within the zone of molybdenum miner-alization (Figure C.6). Rock i s fine grained, dense, and brown i n colour. Quartz-carbonate veinlets have bleached borders. In thin section, very fine-grained unaltered biotite occurs i n a matrix of quartz. The rock was originally a crystal tuff. Epidote occurs i n the quartz-carbonate veinlets. C.2.3 Sunsets Creek (Fog, Fly) (after Sutherland Brown, 1967) This prospect i s situated at the head of Sunsets Creek i n the Telkwa Range, 19 miles south of Smithers. The Telkwa Range i s underlain by maroon pyroclastic rocks of the Hazelton Group. The Sunsets Creek pluton occurs i n the centre of the range and has domed the surrounding pyroclastic rocks. Volcanic rocks i n close proximity to the pluton have been hornfelsed. The Sunsets Creek pluton i s a steep-sided plug, approximately 6,000 feet i n diameter (Figure C.8). It i s composed entirely of quartz monzonite of nearly constant composition and texture. The rock i s light grey and has a porphyritic texture with scattered 1 to 2-centimetre phenocrysts of feldspar i n addition to numerous 1-millimetre plagioclase (A^Q.-JQ) phenocrysts which are set i n a fine-grained matrix. The ratio of K-feldspar to total feldspar i s 1:3. Other phenocrysts include resorbed quartz grains and hornblende and biotite. Phenocrysts form 50 per cent of the rock. The matrix consists of very fine-grained quartz, K-feldspar, and minor plagioclase. L E G E N D SUNSETS PLUTON P l j r Ouort2 monionite porphyry HAZELTON GROUP Pyrotloitic rocks with lilli o! pyroxene ondejitt 3 Outcrop — Limit of gosson 1C T r m c h i t - ^ * * Joint) C —™J> Pyritic zones-minor alteration jf rntamc quortt- sericitt - pyrite oil •ration Scot* lOOO 0 IOOO 200CL I I i Fee! FIG.-C.8 SUNSETS CK. 176. A gossan zone surrounds the stock and roughly corresponds to the area of intense hornfelsing. Widely spaced 1-inch quartz veins containing pyrite, chalcopyrite, and minor molybdenite occur at many places along the periphery of the stock. Two altered zones with associated sulphide mineralization occur i n the interior of the stock. A broad area 2,000 by 3,000 feet i n the west part of the stock contains abundant pyrite as disseminations and as coatings on fracture planes. In the southern part of this zone, molybdenite occurs with pyrite i n a wide-spaced stockwork of quartz veins, veinlets, and dry fractures. A smaller area of quartz-sericite-pyrite alteration to the east contains minor disseminated chalcopyrite. One sample for potassium-argon dating was collected by A. Sutherland Brown from quartz monzonite i n the southeastern part of the stock, south of the zone of quartz-sericite-pyrite alteration. NC-67-39 - Porphyritic Quartz Monzonite The sample i s a leucocratic porphyritic rock with scattered 1 to 2-centimetre phenocrysts of K-feldspar plus 4-millimetre phenocrysts of plagioclase (^£0-30^ "hich a r e s e t i n a finer grained matrix of quartz, plagioclase , K-feldspar, hornblende, and biotite. Biotite occurs as 1 to 2-millimetre plates and books which are only partly (less than 10 per cent) altered to chlorite. Biotite equals 3 to 5 per cent of the rock volume. C.2.4 Rocher Deboule A sample for potassium-argon dating was collected by R. V. Kirkham from near the 1200 level portal of the Rocher Deboule mine, 5 miles south of Hazelton. 177. This dormant copper-gold-silver vein deposit i s situated on the western periphery of the northern dome of the Rocher Deboule stock (Sutherland Brown, 1960). Siltstones of the Middle Cretaceous Red Rose Formation have been hornfelsed marginal to the stock contact. The main country rock of the mine i s typical porphyritic granodiorite of the Rocher Deboule stock. The rock i s formed of 20 to 35 per cent of 4-millimetre plagioclase (^20-40^ Phenocrysts and hornblende and biotite total 15 per cent of the rock volume. The matrix i s formed of plagioclase, perthitic K-feldspar, and quartz, and the accessory minerals sphene, apatite, zircon, and metallic minerals. NC-67-46 - Porphyritic Granodiorite Sample i s a mesocratic porphyritic rock with crowded phenocrysts of plagioclase (^20-40^ s e t i n 3 m e^ u m"& v a^- n e^ matrix of quartz, K-feldspar, and hornblende and biotite. Biotite occurs as 1-millimetre plates exhibiting only minor chlorite alteration and as a deuteric alteration of green hornblende. C.2.5 Bear (Laura) (after Sutherland Brown, 1968) This property i s situated on the western flank of Mount Thomlinson between McCutcheon and Sterrett Creeks, 20 miles north of Hazelton. Molybdenum and copper mineralization i s associated with a subcircular porphyry plug of roughly one-half mile diameter. The plug occurs i n the western flank of a major anticline i n Bowser Group volcanic sandstones , which have been thermally metamorphosed to biotite hornfels i n an irregular halo up to 1,500 feet wide. 178. L E G E N D | + + + 4 . ' > ' | P2 G r o n o d i o r i t e p o r p h y r y I" | P I G r a n o d i o r i t e p o r p h y r y B o w s e r G r o u p , h o r n f e l s e d D i a m o n d - d r i II h o l e s B u l l d o z e r t r e n c h O u t c r o p Sca le 400 " F e e * FIG.-C.9 BEAR 179. The pluton consists of two nearly identical phases. The earlier phase i s porphyritic, irregular i n plan, and occupies the peripheral areas of the plug (Figure C.9). The later phase, a crowded porphyry bordering on a granitic texture , i s concentric with the f i r s t and makes up the bulk of the pluton. Both phases are rusty weathering, medium grey rocks with prominent plagioclase, hornblende, and scattered biotite books. Both are of granodiorite composition. The major difference between the two phases i s the greater abundance of 1 to 4-millimetre zoned plagioclase (^20-45^ P n e n o c r y s t s a n d the coarser grain size of the matrix. Hornblende prisms and biotite books occur as phenocrysts and apatite and sphene are accessory minerals. Hydrothermal ateration i s erratic i n distribution and consists of clay minerals , or sericite with pyrite and quartz. Disseminated pyrite and pyrrhotite are also erratically distributed. Molybdenum and copper mineralization i s widely distributed in the pluton, with better grades most common near the periphery. Molybdenite and chalcopyrite occur i n quartz veinlets and i n dry fractures i n a stockwork. Late-stage quartz-carbonate veins contain minor pyrite, sphalerite specularite , arsenopyrite , and stibnite or bismuthinite. A sample for potassium-argon dating was collected by A. Sutherland Brown from a hole d r i l l e d near the south end of the plug (Figure C.9). NC-68-12 - Granodiorite Porphyry Sample i s a crowded porphyry; with abundant 2 to 4-millimetre phenocrysts of euhedral plagioclase (^0-30^ a n d 2 " m i l l i m e t r e p o i k i l i t i c biotite books set in a finer grained matrix consisting essentially of quartz and hornblende. 180. Biotite displays up to 15 per cent alteration to chlorite, principally along cleavages. Secondary, fine-grained biotite occurs as an alteration of primary hornblende. C.2.6 Huckleberry (after Carter, 1970) The Huckleberry copper-molybdenum deposit i s situated between Tahtsa Reach and Sweeney Lake, 50 miles southwest of Houston. Copper and molybdenum mineralization i s associated with an e l l i p t i c a l plug of granodiorite porphyry, oriented with i t s long axis i n a northeast direction and measuring 2,200 by 1,400 feet. The plug intrudes fine-grained crystal tuffs of the Hazelton Group (Figure C.10). As exposed i n the trenches i n the central part of the plug, the intrusive i s a lig h t grey crowded porphyry with phenocrysts constituting 50 per cent of the rock. These include 2 to 4-millimetre phenocrysts of euhedral, fresh, zoned plagioclase (An^Q^j), and subsidiary 2-millimetre plates and books of fresh biotite and 2-millimetre anhedral quartz phenocrysts , a l l set i n a fine-grained matrix of quartz, feldspar, and biotite. Locally the rock has a pinkish cast due to the presence of K-feldspar i n the matrix and marginal to narrow quartz veinlets. Biotite may constitute 10 to 15 per cent of the rock by volume, occurring both as primary, fresh 1 to 2-millimetre plates and books and as fine-grained clusters of secondary biotite, partly chloritized, altering from original hornblende. Porphyry dykes cut the volcanic rocks marginal to the plug as seen i n d r i l l core from holes east of the intrusive. These biotite feldspar porphyries, 0 400 800 IJMO CRYSTAL TUFFS AND HORNFELSIC —I EQUIVALENTS. - ' LIMIT OF BIOTITE ALTERATION. AREA OF TRENCHING. BASED ON COMPANY PLANS FIG. - C.10 HUCKLEBERRY GRANODIORITE PORPHYRY 'GEOLOGIC CONTACT, APPROXIMATE * w ~ v FAULT ZONE 182. while of similar composition, are finer grained than the main intrusive, consisting mainly of crowded 2-millimetre phenocrysts of unzoned plagioclase (An^g) and 1-millimetre biotite plates set i n a fine-grained quartz-rich matrix. L i t t l e K-feldspar was seen except marginal to quartz-filled fractures. Plagioclase exhibits a f a i r degree of sericite and a r g i l l i c alteration and biotite i s mostly altered to chlorite. Intrusion of the granodiorite porphyry has caused hornfelsing of the adjacent fine-grained crystal tuffs. These rocks are mainly light to dark grey, but are local l y tinged brown due to the selective development of secondary biotite within an oval zone extending outward from a plug a distance of up to 600 feet. Typically, the hornfelses contain 2-millimetre crystal fragments of plagioclase i n a very fine-grained mosaic of quartz, plagioclase, and biotite. Abundant fine-grained biotite and actinolite were noted f i l l i n g fractures i n a few d r i l l sections. Light grey hornfelsed volcanic rocks consist mainly of quartz, s e r i c i t e , and carbonate and contain abundant disseminated pyrite. The hornfelses are well fractured, with many of the fractures f i l l e d with quartz and rimmed by bleached zones up to one-quarter-inch wide. These bleached haloes are made up of very fine-grained quartz, s e r i c i t e , carbonate, and some K-feldspar or granophyre. Lamprophyre dykes, fine grained and dark green, intrude a l l rocks i n the area. Northeast and northwest linear features, often marking the course of creeks, are common on airphotos covering the Huckleberry Mountain area, and some of these represent faults. The northwest faults appear to be terminated by the northeasterly ones. As suggested by Carr (1964), the porphyry plug was 183. apparently localized by the two northeast faults which bound i t closely on the north and south (Figure C.10). These faults also caused fracturing of the volcanic rocks which was intensified by the intrusion of the porphyry plug. The major fracture directions i n the volcanic rocks and the porphyry plug also trend northeast and northwest. Copper and molybdenum mineralization i s associated with the granodiorite porphyry plug and, i n particular, the hornfelsed rocks peripheral to the intrusive. The best mineralized sections occur i n the hornfelsed rocks east and north of the granodiorite porphyry plug. Typically, these hornfelses are cut by closely spaced hairline fractures which are coated with chalcopyrite and lesser amounts of quartz and magnetite. Magnetite may also be disseminated in the matrix of the rock with pyrite. Chalcopyrite and lesser molybdenite also occur i n vertical one-eighth-inch quartz veinlets which may also contain some K-feldspar. These fractures are commonly bordered by bleached zones up to one-quarter-inch wide. Biotite feldspar porphyry dykes seen cutting hornfels i n this area east of the main intrusive also contain one-eighth-inch vertical quartz-chalcopyrite-molybdenite veinlets. These veinlets, which may be rimmed by K-feldspar, are cut by horizontal gypsum-healed fractures. Some fluorite was also seen i n fractures and chalcopyrite was noted replacing mafic minerals i n one section. In the trench area within the main intrusive, chalcopyrite occurs i n 1 to 2-inch-spaced hairline fractures with quartz and minor K-feldspar and also in one-eighth to one-half-inch quartz veinlets. Magnetite i s also common i n fractures. Chalcopyrite also occurs as disseminations i n the granodiorite porphyry. 184. A pyrite halo extends outward from the granodiorite porphyry a distance of up to 2,000 feet, and i s marked by a gossan on the south slope of Huckleberry Mountain. This gossan occurs i n an east-trending zone some 2 miles long, with the porphyry plug situated near the western end of the zone. A sample for potassium-argon dating from the east-west trench i n the central part of the plug (Figure C.10) was provided by P. T. Black, formerly of Kennco Explorations, (Western) Limited. NC-67-44 - Granodiorite Porphyry Sample i s a medium grey crowded porphyry. Fifty per cent of the sample i s composed of 2 to 4-millimetre phenocrysts of euhedral, zoned plagioclase ( A ^ Q ^ Q ) , 2-millimetre books of b i o t i t e , and anhedral quartz phenocrysts. These are set i n a fine-grained matrix of quartz, feldspar, and bi o t i t e . K-feldspar occurs i n the matrix and adjacent to quartz veinlets and fractures which contain chalcopyrite. The rock i s essentially fresh. Biotite makes up between 5 and 10 per cent of the sample and occurs both as primary, fresh, 1 to 2-millimetre plates and books, and as very fine-grained aggregates secondary after hornblende. The edges of some biotite plates are chloritized. C.2.7 Ox Lake (after Sutherland Brown, 1969) The Ox Lake deposit i s peripheral to a small granodiorite porphyry plug that intrudes a mixed pyroclastic and sedimentary sequence of the Hazelton Group (Figure C.11). The plutonic rocks of the plug are nearly identical to those of the Huckleberry deposit 5 miles west. f7G.-C.lJ OX L A K E P R O P E R T Y LEGEND Diabase EARLY TERTIARY ? OX L A K E PLUTON Granodior i te porphyry Qua r t z monzonite porphyry pluton Fe ldspar porphyry dykes i + + 4 + + + + « + < J U R A S S I C HAZELTON GROUP Volcanic sandstone and pebbly sandstone ( f o l ^ Fanglomerale Lapi l l i luff ~ L q Very f ine tuff or s i ltstone Hornfelsic equivalent 5 0 0 1000 F E E J ^Jr ' _ * - Margin of intense pyrite halo ~r'T~~r">- Surfoce margin of main mineralized body —I— Vein o 1 Drill holes <7=^' Bulldozer cuts and trails C^) Outcrop Geological contact , approximate - J I O O — Contour interval 100 feet 186. Volcanic tuffs marginal to the porphyry plug are hornfelsed and pyritized in a halo up to 1,000 feet wide. The st r a t i f i e d sequence outside this zone i s cut by northerly trending feldspar porphyry dykes and s i l l s which are older than the main porphyry plug. These occur mainly to the northeast of the plug and may be related to a quartz monzonite porphyry to the northwest (Figure C.11). The porphyry plug i s e l l i p t i c a l i n outline and measures 2,000 feet by 1,300 feet. It i s a distinctive crowded porphyry with prominent plagioclase ( A ^ ^ ^ Q ) ^ a t' i s 3 to 10 millimetres long and books of biotite and long hornblende needles i n a finely speckled pink and black matrix. The most intense alteration within the plug i s adjacent to the mineralized zone where plagioclase i s altered to sericite and carbonate, mafic minerals to chlorite and muscovite, and K-feldspar partly to zeolite. In the hornfelsed rocks , metamorphic biotite has been completely obliterated by sericite i n a zone 300 feet wide bordering the plug. This decreases i n intensity outward to a point where secondary bleaching i s only present marginal to quartz veinlets and fractures. The main mineralized zone of copper and molybdenum i s contained i n a crescent-shaped body west of the plug. Chalcopyrite and molybdenite occur in a stockwork of dry fractures and quartz veinlets best developed adjacent to the plug. In general, copper mineralization i s dominant i n the hornfels while molybdenum i s concentrated i n porphyry dykes and near the granodiorite porphyry contact. Pyrite, up to 5 or 10 per cent, occurs i n a halo extending beyond the ore zone. Minor late veins occur, formed of sphalerite, pyrite, quartz, and carbonate. A sample for potassium-argon dating was collected by A. Sutherland Brown from a trench near the southwest end of Ox Lake (Figure C.11). 187. NC-69-5 - Granodiorite Porphyry Sample i s a crowded porphyry with up to 50 per cent of the rock consisting of 2 to 5-millimetre phenocrysts of euhedral plagioclase ( A n ^ ^ ) , and 2-millimetre phenocrysts of biotite, hornblende, and quartz. These are contained i n a fine-grained matrix of quartz, K-feldspar, chlorite, and opaque minerals. Biotite occurs principally as 1-millimetre, ragged, p o i k i l i t i c plates, some of which exhibit up to 20 per cent chlorite alteration. Hornblende i s mainly altered to chlorite although some biotite alteration was also noted. C.2.8 Coles Creek A biotite separate from the Coles Creek porphyry copper-molybdenum prospect was supplied by D. G. Maclntyre and the analytical results are included i n this study. The property i s situated south of Troitsa Lake on a tributary of Coles Creek 80 miles north of Houston. A stock of quartz monzonite porphyry, 2,500 feet i n diameter, intrudes Jurassic volcanic and sedimentary rocks. Possible extrusive equivalents of the stock include rhyolite tuffs and breccias. An inner phase of the quartz monzonite porphyry i s a feldspar biotite porphyry of granodiorite composition which i s host to chalcopyrite and molybdenite mineralization. A pyrite halo 4,000 feet wide surrounds the stock and galena and sphalerite mineralization occurs i n fractures south of the stock. MC-9 - Feldspar Biotite Porphyry Sample i s from a tributary of Coles Creek. The rock i s of granodiorite composition and i s texturally similar to the granodiorite porphyry at the Ox 188. Lake and Huckleberry deposits (Maclntyre, personal communication). Both primary and secondary biotite are contained i n the sample. C.3 NANIKA INTRUSIONS AND ASSOCIATED COPPER AND MOLYBDENUM DEPOSITS C.3.1 Mount Thomlinson (after Kirkham, 1964) This molybdenum prospect i s situated 24 miles north of Hazelton on a northerly trending ridge of Mount Thomlinson. Massive black argillaceous siltstones of Jurassic-Cretaceous age have been intruded by a circular stock of leucocratic quartz monzonite poprhyry (Figure C.12). Near the contact, the sedimentary rocks have been deformed and metamorphosed to medium or dark grey schists i n a zone 300 to 500 feet wide. Biotite, muscovite, cordierite, and andalusite have been formed i n the contact aureole. Stock contacts are sharp. The margins of the stock are foliated parallel to the contact and to the schistosity i n the intruded rocks. Much of the stock i s a coarse-grained porphyry with K-feldspar pheno-crysts up to 5 centimetres long and quartz and plagioclase (^20-30^ P n e n o " crysts up to 1 centimetre in size. In many areas, the stock i s cut by narrow aplite dykes which occur in swarms. Molybdenite, chalcopyrite, and pyrite occur i n a stockwork of quartz veinlets with minor amounts of magnetite and scheelite. The quartz stockwork i s best developed along the northwest stock contact. A sample for potassium-argon dating from the mineralized zone was supplied by R. V. Kirkham. 189. i ; "...'•] M o l y b d e n i t e a n d ch a Ic o p y r i t e **•* *—' m i n e r a l i z a t i o n A p l i t e d y k l e t s w a r m s I | Q u a r t z m o n z o n i t e p o r p h y r y B l a c k a r g i 11 i t e 5 a n d m e t a m o r p h o s e d e q u i v a l e n t s L E G E N D O D i a m o n d - d r i l l s t a t i o n F o l i a t i o n , s c h i s t o s i t y , s l a t y c l e a v a g e * T r e n c h f.'-'* C o n t a c t , o b s e r v e d , i n f e r r e d A p p r o x i m a t e l i m i t s o f s c h i s t o s i t y a n d f o I i a t i o n S c a l e F e e t P o s i t i o n of i n t r u s i v e c o n t a c t t o k e n f r o m c o m p a n y m o p FIG.- C. 12 MT. THOMLINSON 190. NC-68-13 - Quartz Monzonite Porphyry Sample i s a pink leucocratic porphyry with 5-centimetre euhedral phenocrysts of K-feldspar, 4-millimetre anhedral quartz eyes , and 2-millimetre biotite plates set in a medium-grained matrix of quartz, K-feldspar, and plagioclase (A^Q) . Accessory minerals include muscovite, apatite, and opaque minerals. Biotite plates are p o i k i l i t i c and are unaltered. C.3.2 Big Onion (after Sutherland Brown, 1966) The property i s on the south side of Astlais Mountain, 12 miles east of Smithers. The Big Onion property i s underlain by Hazelton andesitic volcanic rocks that are intruded by an elongate complex pluton (Figure C.13). The pluton i s formed of two phases: an early quartz feldspar porphyry which forms a sheath around a later quartz diorite porphyry. The quartz feldspar porphyry i s a white aphanitic rock with a few scattered quartz phenocrysts 1 to 4 millimetres i n size. Pyrite may form up to 3 per cent of the rock and exposures are commonly iron stained. The quartz diorite porphyry i s a medium-grained grey rock with sericitized plagioclase and chloritized hornblende and biotite phenocrysts 3 to 7 millimetres i n size. Copper and molybdenum mineralization i s widely distributed near the contacts of the two intrusive phases and i n the peripheral volcanic rocks. Chalcopyrite, molybdenite, and minor bornite occur in a stockwork of quartz-f i l l e d fractures and as disseminations. The best copper mineralization occurs 192. within the quartz diorite porphyry and molybdenite i s mainly restricted to the quartz feldspar porphyry. Pyrite i s best developed i n volcanic rocks near the intrusive contact. Post-mineralization dykes include a northerly striking quartz monzonite dyke and several varieties of late hornblende andesite dykes. NC-67-7 - Quartz Monzonite Sample i s from a roadcut i n the post-mineral quartz monzonite dyke (Figure C.13). The rock i s dark grey, medium grained, and i s slightly magnetic. It i s formed of 33 per cent plagioclase, 25 per cent orthoclase, 10 per cent quartz, 20 per cent b i o t i t e , 5 per cent granophyre, with the remainder consisting of magnetite and minor hornblende. Biotite plates are 1 to 2 millimetres i n length and exhibit up to 10 per cent chlorite alteration, mainly along cleavage planes. C.3.3 Lucky Ship (after Sutherland Brown, 1965) The Lucky Ship molybdenum deposit i s on a ridge between Morice Lake and the Nanika River, 50 miles south of Houston. Molybdenum mineralization i s associated with a rhyolite plug, 2,000 by 3,000 feet i n diameter, that cuts Hazelton Group volcanic, pyroclastic, and sedimentary rocks (Figure C.14). The rhyolite porphyry plug consists of four phases including two porphyries and two breccias, The porphyry forming the major part of the plug i s a white aphanitic rock with sparse phenocrysts of 193. 194. quartz and feldspar. This phase intrudes an earlier breccia i n which fragments of the porphyry occur along with fragments of country rock. The porphyry i s intruded by a second breccia composed mainly of porphyry fragments and a small (800 feet in diameter) plug of quartz monzonite porphyry. A r g i l l i t e s and l a p i l l i tuffs marginal to the intrusion are hornfelsed and contain biotite and actinolite throughout the matrix. S i l i c i f i c a t i o n i s the most intense alteration and i s developed i n an annular zone around the periphery of the younger porphyry plug, where a stockwork of quartz veins and fractures i s developed (Figure C.14). Molybdenum mineralization i s contained within the s i l i c i f i e d zone and better grades occur i n a zone immediately peripheral to the contact of the younger porphyry plug. A pyrite halo i s developed i n the earlier porphyry phase, the breccias, and the hornfels, surrounding the s i l i c i f i e d zone. NC-67-42 - Biotite Hornfels Sample was collected from an outcrop immediately adjacent to the east contact of the intrusion (Figure C.14). The rock i s iron stained on weathered surface and i s transected by parallel hairline fractures. On a fresh surface, the dark grey to dark brown rock exhibits a conchoidal fracture. In thin section, the rock i s seen to be a fine-grained crystal tuff. Very fine-grained metamorphic biotite i s best developed adjacent to fractures. 195. C.3.4 Goosly (after Church, 1969 and Ney, et a l . , 1972) The Goosly property i s northeast of Goosly Lake, 33 miles by road southeast of Houston. The property i s underlain principally by Hazelton Group sedimentary and pyroclastic rocks. Gently inclined Tertiary volcanic rocks unconformably overlie the Mesozoic rocks. Hazelton Group rocks are intruded by a granitic stock and a syenodiorite stock about a mile apart (Figure C.15). Both are of Tertiary age, with the granitic stock emplaced about 7 m.y. prior to the intrusion of the syenodiorite. Major economic mineralization at the Goosly property i s a northerly trending slab of copper-silver mineralization which i s roughly conformable with the enclosing volcanic and sedimentary rocks. The mineralized zone i s between the two intrusive bodies. Weak copper-molybdenum mineralization in fractures occurs near the northern contact of the granitic stock. The leucocratic, medium-grained quartz monzonite porphyry contains 2 to 4-millimetre phenocrysts of subhedral plagioclase and biotite set i n a matrix of quartz and K-feldspar. A sample for potassium-argon dating was collected by B. N. Church from a trench near the centre of the intrusion. NC-69-6 - Quartz Monzonite Porphyry The sample i s a medium grey, crowded porphyry with 50 per cent euhedral, zoned plagioclase (An 2 5 -.j 0) a s 1 t o 2 " m i l l i m e t r e phenocrysts. Biotite pheno-crysts of similar size are scattered through the rock. The fine-grained matrix consists mainly of quartz, plagioclase, K-feldspar, and hornblende, which i s F/G.-CJ5 S A M G O O S L Y P R O P E R T Y G E O L O G Y LEGEND ^ ftJCk CREF.K VOLCANlCS ( Endofco Group ) -Basaltic Flows ond Breccia / GOOSLY LAKE VOLCANtCS (Oolso Group) / . (• t;.;;. J Biotite Trachyte Float X~\ 1 Tmchyqndtjili Flow* [ * . V J Tlow Breceio HYPABVSSAL PHASES [f"*jn:.^ ] Montonite L'^ ifl] Monionite Porphyry GARPRO-MONZONITE COMPLEX DionN EFi*fa] Monionile Etttiii) W t f H » * r t i Phase C_K3 Gnbbro QUART* MONZONITE STOCK D " 3 HAZtl TON GROUP [ Se&'nenlory- Vokonic Divisro [T?~J Pyrotlostic Division IX£3 Mineroliied Zone Coarse Clostic" Division • V % * * 4 8 , f l my # / ^ :^^ ^•v":•"^'•)I^S'^'•• :-*^;/'v;::;;\':.:.C^:/-x::;:':S SA-:' ; : ; : ; : : : : :^ : : ; : : : : : : N. -p«3:J?.-..1 mlillllii'ilaiuuX \ rm) //: ?•<.•; j-CV. . W > ~ 4 i y • • / I ^V-v.V??--:/.:-v/v^-- '• V O 197. altered to chlorite and some biotite. Biotite plates are p o i k i l i t i c and exhibit up to 15 per cent chlorite alteration. C.3.5 Berg (after Sutherland Brown, 1966 and Ney, 1972) The property i s in the Tahtsa Range about 70 miles south of Smithers. The area i s underlain by massive and cl a s t i c volcanic and sedimentary rocks of the Hazelton Group. These rocks have been intruded by an elongate quartz diorite stock several square miles in area and by a circular, composite porphyry stock of one-half-mile diameter. The porphyry stock i s host to copper and molybdenum mineralization (Figure C.16). The quartz diorite i s a fine to medium-grained equigranular rock of uniform appearance. Scattered hornblende phenocrysts up to 8 millimetres long occur throughout the rock. The quartz monzonite porphyry which constitutes the bulk of the stock i s a light grey to buff rock i n which 4 to 6-millimetre phenocrysts of plagioclase, biotite, and quartz are prominent. These are set in a very fine-grained matrix of quartz, plagioclase, and perthitic K-feldspar. Post-dating the quartz monzonite porphyry are a breccia pipe and dykes of quartz l a t i t e porphyry. The breccia occurs south of the stock and partly intrudes the earlier quartz diorite (Figure C.16). It i s a cream-coloured rock composed mainly of subangular, 15-millimetre fragments of quartz monzonite porphyry, siltstone, and andesite i n a finely communited matrix. Pyrite i s widely disseminated throughout the breccia. The quartz l a t i t e porphyry dykes occur both within and marginal to the quartz monzonite porphyry stock. One such dyke outcrops as a conspicuous northeast-trending spine through the central FIG.-U6 199. part of the stock (Figure C.16). In hand specimen, the quartz l a t i t e greatly resembles the quartz monzonite, but crosscutting relationships and lack of mineralization indicate that i t i s of post-mineral age. Also of post-mineral age are narrow andesite dykes. Volcanic and sedimentary rocks marginal to the quartz monzonite porphyry stock have been thermally metamorphosed to biotite hornfels. The earlier quartz diorite within the zone of thermal metamorphism features abundant secondary biotite, an alteration of magmatic hornblende. Superimposed on the metamorphic zone are alteration minerals related to mineralization, including K-feldspar, topaz, and s i l i c a . Molybdenum and copper mineralization i s contained i n an annular zone , co-axial with the quartz monzonite porphyry stock. The mineralized zone i s best developed around the eastern contacts of the stock where chalcopyrite and molybdenite are contained i n a stockwork of quartz veinlets. In general, best molybdenum mineralization i s within and adjacent to the stock whereas copper has i t s greatest concentrations 200 feet or more beyond the contact. A pyrite halo extends outward 1,000 to 2,000 feet from the stock contact. Primary mineralization has been subjected to oxidation, leaching, and enrichment. The depth of leaching may extend to 300 feet, below which supergene chalcocite appears as coatings on pyrite i n an irregular blanket. NC-67-8 - Quartz Diorite Sample i s from an elevation of 7,200 feet at the head of the cirque, to the east of the Berg stock (Figure C.16). 200. The quartz diorite i s a fine-grained, grey, equigranular rock with scattered 4-millimetre phenocrysts of hornblende. The rock has a hypidiomorphic granular texture and i s composed essentially of plagioclase (An^) with sub-ordinate hornblende, b i o t i t e , and quartz. Plagioclase i s f a i r l y fresh, while hornblende shows partial alteration to chlorite. Biotite occurs as one-half to 1-millimetre plates which are up to 50 per cent altered to chlorite. NC-67-4 - Quartz Latite Porphyry Sample i s from d r i l l core from a hole d r i l l e d i n the south-central part of the stock (Figure C.16). The quartz l a t i t e porphyry i s composed mainly of 2 to 4-millimetre phenocrysts of euhedral plagioclase (An^g), 2 to 4-millimetre biotite books, and 1 to 2-millimetre quartz phenocrysts , a l l set i n a very fine-grained matrix of quartz, feldspar, and chloritized hornblende. Biotite i s p o i k i l i t i c and i s relatively unaltered except for minor chlorite alteration along the edges of some grains. NC-67-10 - Quartz Latite Porphyry Sample i s from d r i l l core from a hole d r i l l e d near the southern contact of the Berg stock (Figure C.16). Sample i s similar to NC-67-9, except for a greater number of larger (4-millimetre) quartz phenocrysts and some hairline fractures containing quartz. Original hornblende i s altered to a mixture of chlorite and bi o t i t e . Biotite occurs as 4-millimetre shredded, p o i k i l i t i c plates exhibiting only minor chlorite alteration. 201. NC-67-11 - Quartz Monzonite Porphyry Sample i s from d r i l l core from a hole d r i l l e d into the north part of the stock (Figure C.16). Phenocrysts make up 35 to 50 per cent of the rock and include 4-millimetre euhedral plagioclase (An^), biotite books, and anhedral quartz. Matrix i s a very fine-grained mosaic of quartz and feldspar. Feldspars exhibit sericite alteration and hairline fractures cut through some phenocrysts. Biotite i s p o i k i l i t i c and minor chlorite and carbonate alteration (10 per cent) occurs along the edges of some grains. NC-67-12 - Biotite Hornblende Sample i s from a d r i l l hole collared near the southern contact of the stock (Figure C.16). The hornfels i s a dense, aphanitic, dark brown rock, transected by numerous hairline fractures f i l l e d with quartz. It consists principally of a mosaic of quartz grains and extremely fine-grained, unaltered biotite plates. NC-67-13 - Quartz Diorite Sample i s from a d r i l l hole which intersected quartz diorite i n the contact metamorphic aureole northeast of the stock (Figure C.16). The rock i s fine grained, equigranular, and dark grey i n colour. Quartz and biotite have been introduced. Biotite occurs as 1-millimetre plates which make up to 10 per cent of the rock. Biotite plates are p o i k i l i t i c and are up to 10 per cent chloritized. 202. C.3.6 Red Bird (after Sutherland Brown, 1966, 1972) This property i s several miles west of Eutsuk Lake, 100 miles south of Smithers. Middle Jurassic Hazelton Group pyroclastic rocks are intruded by an e l l i p t i c a l stock of quartz monzonite porphyry, 3,000 feet in diameter. A semicircular ring dyke occurs around the northern circumference of the stock (Figure C.16). The stock consists largely of a single-phase, quartz monzonite porphyry. Where fresh, the rock i s light grey to pink and contains phenocrysts of slightly corroded quartz, plagioclase, K-feldspar, and biotite , set i n a matrix of quartz and feldspar. Grey monzonite porphyry, of post-mineral age, occurs as small crosscutting dykes and larger masses within the stock. Four-millimetre phenocrysts of plagioclase, quartz, and biotite are contained i n a very fine-grained matrix of feldspar. Fine-grained volcanic rocks adjacent to the stock have been converted to biotite hornfels. Hydrothermal alteration, involving the development of secondary K-feldspar, has affected some of the hornfelsed country rocks and the core of the stock where half the plagioclase phenocrysts have been con-verted to K-feldspar. The quartz monzonite porphyry stock i s host to a concentric zone of molybdenum mineralization contained mainly within a peripheral ring of the main mass of the stock. Molybdenite i s contained i n a stockwork of quartz veinlets, best develped near the stock contact. A prominent gossan developed in the volcanic rocks i s about 2 miles i n maximum diameter. 203. NC-67-17 - Biotite Hornfels Sample i s from a roadcut to the east of the Red Bird stock (Figure C.16). The rock i s dense, fine grained, dark brown, and i s cut by numerous one-eighth-inch quartz-pyrite veinlets. Biotite and quartz constitute the bulk of the rock. Biotite occurs as unaltered one-half millimetre plates which are uniformly distributed throughout the rock. NC-67-19 - Quartz Monzonite Porphyry Sample was collected from near the south end of the stock (Figure C.16). The quartz monzonite i s a pink, leucocratic, crowded porphyry with 4-millimetre phenocrysts of quartz, plagioclase (An25-30^' a n c* K-feldspar making up 50 per cent of the rock. Matrix i s composed of a mosaic of quartz, feldspar, and biotite. One-millimetre p o i k i l i t i c biotite plates are weakly altered to chlorite. NC-67-20 - Monzonite Porphyry Sample i s from a roadcut i n the central part of the stock (Figure C.16). The monzonite i s a medium grey rock containing scattered 2 to 6-millimetre phenocrysts of euhedral plagioclase and partly resorbed quartz. Quartz-pyrite one-eighth-inch veinlets cut the rock. The fine-grained matrix i s composed mainly of quartz and sericitized feldspar. Biotite occurs as 1 to 2-millimetre plates and books, and i s p o i k i l i t i c . Chlorite alteration amounts to 10 per cent and i s principally along cleavages. Original hornblende i s completely altered to a mosaic of fine biotite. 204. C.3.7 Nadina Mountain A granitic stock underlies most of Nadina Mountain and i s exposed on the eastern and western flanks of the mountain. The stock intrudes a sedimentary sequence blieved to be equivalent to the Sustut Group of Late Cretaceous -Early Tertiary age (Figure 14). The intrusive i s not known to contain sulphide mineralization. A sample from near the top of the mountain was collected by A. Sutherland Brown. NC-68-7 - Quartz Monzonite The quartz monzonite i s a pink to grey, medium-grained, equigranular rock containing abundant biotite plates. The rock has a hypidiomorphic granular texture and consists of quartz , 15 per cent; plagioclase (^25-30^* ^ p e r c e n t » perthitic K-feldspar, 25 per cent; b i o t i t e , 7 per cent; chlorite, 10 per cent; and sphene, apatite, and opaque minerals, 12 per cent. Feldspars are slightly sericitized and original hornblende i s entirely altered to chlorite. Biotite occurs as 1-millimetre plates with only incipient chlorite alteration. C.3.8 Goosly A sample from the syenodiorite stock at the Goosly property was collected by B. N. Church (Figure C.15). The stock i s interpreted by Church (1969) as being a feeder for the extensive Tertiary volcanic rocks which occur nearby. NC-69-7 - Syenodiorite Sample i s a medium-grained grey rock consisting essentially of feldspar and mafic minerals. 205. Laths of plagioclase (An^), up to 2 centimetres long, make up most of the rock. I n t e r s t i t i a l areas contain K-feldspar, clinopyroxene, and biotite. The rock i s unaltered. Shredded, p o i k i l i t i c unaltered biotite plates are intimately associated with clinopyroxene. C.3.9 Morice Lake A sample from the granitic stock at Morice Lake was collected to deter-mine i t s possible relationship to the Lucky Ship molybdenum-bearing pluton (Figure 14). Sulphide mineralization i s not known within the Morice Lake stock. NC-67-15 - Quartz Monzonite Sample was collected from the east shore of Morice Lake , 12 miles from the north end of the lake. The quartz monzonite i s a pink, leucocratic, medium-grained, equigranular rock, which consists mainly of quartz, plagioclase (A^Q) and perthitic K-feldspar plus biotite. Biotite occurs as 1-millimetre p o i k i l i t i c plates which are up to 15 per cent chloritized. C.4 BABINE INTRUSIONS AND ASSOCIATED COPPER DEPOSITS C.4.1 Granisle (after Carter, 1972b) The Granisle mine i s on McDonald Island near the north end of Babine Lake, 40 miles northeast of Smithers. 206. The property was originally worked on in the early 1900's and d r i l l e d i n 1929. The Granby Mining Company Limited acquired the property i n 1955 and mining began i n 1966. The m i l l capacity i s 14,000 tons per day and published reserves are 80 million tons of 0.43 per cent copper. The Granisle mine i s in the central part of McDonald Island, which i s triangular shaped, each side being about 1 mile long. The island i s underlain chiefly by volcanic and sedimentary rocks of the Lower Jurassic Hazelton Group which are divisible into two distinct members. Green to purple waterlain andesite tuffs and breccias with intercalated chert pebble conglomerates and shales underlie the central and eastern part of the island. These rocks, which strike northerly and dip at moderate angles to the west are apparently overlain i n the western part of the island by massive and amygdaloidal andesitic flow rocks (Figure C.17). Copper mineralization i s associated with a series of porphyry intrusions which occur i n the central part of the island. The oldest of these i s an e l l i p t i c a l plug of quartz diorite, however the largest and most prominent i s a 400 to 600-foot-wide dyke of biotite feldspar porphyry which strikes north-easterly across the island. This wide dyke i s evident as a ridge which before mining culminated as a 300-foot h i l l above lake level. There are small dykes very similar in composition that post-date mineralization. The multiple intrusions are well displayed i n the present open p i t . The f i r s t intrusive stage i s represented by a northeast-oriented ovaloid cylindrical pluton of fine-grained dark grey quartz diorite , the original dimensions of which were approximately 1,000 by 1,500 feet i n plan. The quartz diorite i s commonly a microporphyry with 1-millimetre phenocrysts of GRANISLE GEOLOGY OF MCDONALD ISLAND . IJQCOII. -N-BABINE LAKE 2332' b==j BIOTITE -FELDSPAR-PORPHYRY • • - DACITE PORPHYRY QUARTZ [HORITE AND RELATED • , . • BRECCIAS f.Vi.-H MASSIVE ANDAMYGOALDIDAL 1 '•' ANUESITi: • FRAGMENTAL VOLCANIC ROCKS SHALE, SILTSTONE, PEBBLE CONGLOMERATE ('"'"'; LIMITS OF SECONDARY BIOTITE ALTERATION .--N LIMITS OF QUARTZ -( 1 SERICITE-CARBONATE-^ ' PYRITE ALTERATION s , CONTACT,DEFINED, r-* ASSUMEO • w FAULT X . BEDDING <«•** EDGE OF OPEN PIT S# CAUSEWAY, ROCK DAM GRANISLE GENERALIZED PIT PLAN GEOLOGY - JULY 1970 PIT OUTLINE - JUNE 1971 -7 - BENCH NUMBER mm M 'Pyx ?:-:->:vCfc EQ GLOLOGY OF GRANISLE MINE BIOTITt - FELDSPAR PORPHYRY , DARK GRAY BIOTIT E - FELDSPAR PORPHYRY , LEUCOCRATIC BIOTITE - FELDSPAR PORPHYRY , GRAY MASSIVE BIOTITC-FELDSPAR PORPHYRY,MEDIUM GRAY, FRACTURED, MINERALIZED V mm - 11 t •:•/ l.,V-;,0 j QUARTZ DIORITE .FINE-GRAINED METAVOLCANIC AND METASEDIMENTARY ROCKS O ^ J FIG.-C.17 208. zoned andesine set in a fine-grained quartz-plagioclase-biotite matrix. Original amphibole grains , now completely altered to fine masses of biotite , locally impart a foliation to the rock. Within the quartz diorite, particularly along i t s eastern edge, are irregular inclusions of metavolcanic and metasedimentary rocks which had a wider distribution i n the original outcrop. Three varieties occur, two of which are breccias believed to be the product of recrystallization and meta-somatism of the fragmental volcanic and sedimetnary rocks marginal to the intrusive. One variety of breccia includes 1 to 3-centimetre rounded chert and volcanic fragments i n a fine-grained diorite matrix, while another consists of chert fragments in a white f e l s i c matrix which also contains 4-millimetre clots of very fine-grained quartz and chloritized biotite. The third variety of inclusions consists of fine-grained, light to dark grey, hornfelsed volcanic and sedimentary rocks. The most important intrusions are biotite feldspar porphyries of several distinct but very similar phases that overlap the period of mineralization. The largest and oldest i s the wide northeasterly trending dyke which i s intrusive into the western edge of the quartz diorite pluton. In plan, a salient of this porphyry projects into the quartz diorite in the p i t area and the contact between the two i s nearly ver t i c a l . Small dykes of porphyry radiate outward from the main dyke. The main porphyry i s light to dark grey and ranges i n composition from quartz diorite to granodiorite depending on the amount of K-feldspar present, most of which i s of secondary origin. Characteristically the rock i s a crowded porphyry with between 35 and 50 per cent by volume consisting of 2-millimetre euhedral, fresh, zoned plagioclase (oligoclase-andesine) phenocrysts and 1^millimetre flakes and books of fresh brown biotite. 209. These phenocrysts are set i n a fine-grained matrix consisting essentially of quartz, plagioclase, patches of fine-grained bi o t i t e , some of which i s pseudomorphic after amphibole, K-feldspar, and apatite. Outside of the p i t area, the porphyry i s a uniform grey colour and contains hornblende phenocrysts as well as biotite and plagioclase. Several of the phases of porphyry intrusions can be recognized within the pit area. While these are a l l grossly similar in appearance and composition as described above, they can be distinguished by slight differences i n the colour of the matrix, resulting mainly from variations i n grain size , by crosscutting relationships, and by the presence of inclusions of earlier phases contained in later ones. The earliest and most widespread porphyry phase i s the medium-grained, well-fractured, and mineralized biotite feldspar porphyry exposed i n the central part of the p i t . Small dykes of similar material were noted cutting the quartz diorite. Bordering this type on the west i s a massive grey porphyry of uniform appearance, differing mainly by having a slightly coarser matrix and by a relative absence of fracturing and mineralization. These two varieties of biotite feldspar porphyry are probably products of the i n i t i a l stage of porphyry intrusion with fracturing being best developed i n the contact area between the porphyry and the quartz diorite. Occurring along the contact between the biotite feldspar porphyry and the quartz diorite are narrow discontinuous dykes and stringers of intrusive breccia which range i n width from several inches to several feet and follow the principal fracture directions. The dykes and stringers are contained i n a northerly trending, vertical zone which i s up to 200 feet wide. The intrusive breccias commonly contain 1 to 2-centimetre rounded fragments of 210. both the medium grey mineralized porphyry and the quartz diorite i n a fine-grained light to dark grey granulated matrix of strained and fractured quartz, broken plagioclase grains, and locally abundant very fine-grained biotite. The breccias are also mineralized, with some disseminated chalcopyrite occur-ring i n the matrix. Dykes of light grey, relatively leucocratic biotite feldspar porphyry up to 10 feet wide, that also parallel the dominant fracture pattern, occur as northwest-trending, vertical dykes i n the main porphyry mass and northeast-trending vertical to steeply dipping dykes i n the marginal quartz diorites. These dykes have a coarse matrix which has a lower biotite content. Rounded inclusions of mineralized porphyry are common in the leucocratic type which are only locally mineralized themselves by minor disseminated pyrite and chalcopyrite. The latest porphyry phase, post-mineral i n age, occurs as dykes of dark grey biotite feldspar porphyry which intrude diorite rocks i n the eastern part of the p i t . The plagioclase phenocrysts are sparser than in earlier phases and the dark grey matrix i s due to the presence of very fine-grained biotite and uniformly disseminated magnetite. Only minor disseminated pyrite and chalcopyrite were noted i n this phase. The porphyry dyke on McDonald Island i s bounded by two parallel northwest block faults. The westernmost of these i s marked by a topographic lineament which crosses the island to the south of the mine and extends through the western part of McDonald Island i n the v i c i n i t y of the plant site. The eastern fault extends along the channel separating McDonald Island from the east shore of Babine Lake. 211 . Within the pit area, the main fractures are vertical to steeply dipping and include the following sets: north 20 degrees to 40 degrees east; north 70 degrees to 85 degrees east; and north 30 degrees to 60 degrees west. Horizontal to slightly inclined fractures are also common. In general the resulting fracture spacing may vary from 0.1 to 1 metre. Movement has occurred along many of the fractures; the most common faulting directions being north 20 degrees east and north 30 degrees to 60 degrees west. An oval zone of potassic alteration i s roughly coincident with the ore zone or the p i t outline (Figure C.17). Within this zone, the intrusive rocks appear fresh i n hand specimen and plagioclase phenocrysts are essentially unaltered. The main alteration product i s secondary biotite which occurs as very fine-grained aggregates which retain original amphibole outlines in both the porphyries and the quartz diorites. Fine-grained biotite i s also uniformly distributed in the matrix of the intrusive rocks. However secondary K-feldspar i s also present within the ore zone, occurring most commonly as fine grains i n the matrix of the biotite feldspar porphyry, and only detectable by staining. Pink K-feldspar also forms thin envelopes enclosing veinlets and fractures i n the lower benches of the p i t . Similar alteration was noted at depth in cores of holes d r i l l e d in the centre of the orebody. The potassic alteration zone i s gradational outward to a quartz-sericite-carbonate-pyrite zone. This zone, apparent by iron staining on weathered surfaces, i s visible on the higher benches at the north end of the p i t , and along roads south of the p i t . This pyrite halo i s e l l i p t i c a l i n plan and i s roughly coaxial with the ore zone, extending 500 to 800 feet beyond. It merges 212. with a similar alteration along the regional fault southwest of the p i t . The entire quartz-sericite-carbonate-pyrite zone measures 3,000 to 4,000 feet. Within this zone, the intrusive rocks and most of the volcanic rocks are weathered to a uniform buff colour. Abundant fine-grained quartz has been introduced, mafic minerals have been altered to a mixture of sericite and carbonate, and plagioclase i s clouded by sericite. Pyrite occurs both as disseminations and as fracture f i l l i n g s . Outside the pyrite halo, most of the rocks on McDonald Island display varying degrees of propylitic alteration; chlorite, carbonate, and epidote are common constituents i n the matrix of volcanic rocks and carbonate-filled fractures are widespread. Pyrite also occurs in fractured zones. Clay mineral alteration i s confined to narrow gouge and fault zones. The principal minerals within the ore zone are chalcopyrite , bornite, and some pyrite. Medium to coarse-grained chalcopyrite i s most widespread, occurring principally i n quartz-filled fractures which vary from 1 to 5 millimetres i n width. The mineralized fractures have preferred orientations of north 35 degrees to 60 degrees east and north 30 degrees to 60 degrees west, and dip steeply. A horizontal fracture set i n the pit i s only weakly mineralized. Chalcopyrite i s also disseminated in the quartz diorite and associated metasediraentary and metavolcanic rocks. Bornite i s most widespread in the southern half of the ore zone where i t occurs with chalcopyrite and quartz i n fractures. The greatest concen-trations of bornite were confined to the upper 250 feet of the south end of the orebody. During the f i r s t few years of mining operations , a number of veins up to 0.3 metre wide and composed of coarse-grained bornite, chalcopyrite, 213. quartz, biotite, and apatite were uncovered. They were vertical and had a strike of north 50 degrees east but were discontinuous. Gold and silver are recovered from the copper concentrates. Molybdenite occurs locally within the ore zone, most commonly i n drusy quartz veinlets which appear to be later than the main mineralizing stage. Magnetite and specularite are common i n the north half of the ore zone where they occur i n fractures with chalcopyrite and pyrite. The greatest concentration of pyrite i s peripheral to the copper orebody where i t occurs as blebs, stringers, and disseminations. Near the southwest end of the island, approximately 4,000 feet south-west of the p i t , a narrow quartz-carbonate-pyrite-galena-sphalerite-chalcopyrite vein containing silver values follows a northeast-striking fault for a limited distance. NC-67-4 - Biotite Feldspar Porphyry Sample was collected from the open p i t i n the southwestern part of the orebody (Figure C.17). The rock i s a medium grey, fine to medium-grained crowded porphyry of granodiorite composition. The porphyry i s cut by numerous hairline fractures and one-eighth to one-quarter-inch quartz veinlets containing chalcopyrite and a l i t t l e bornite. Minor chalcopyrite i s also contained i n the matrix. Forty per cent of the rock i s composed of 1 to 2-millimetre phenocrysts of fresh, euhedral, zoned plagioclase (An^_^) and plates and books of biotite. These are contained i n a very fine-grained matrix of quartz, plagioclase, 214. Biotite, and minor K-feldspar. Accessory minerals include apatite and magnetite. Biotite occurs as primary books and plates and as an alteration of original hornblende, and makes up 10 per cent of the rock by volume. Both varieties are free of chlorite alteration. NC-67-5 - Biotite Feldspar Porphyry Samples were collected from a 10-foot-wide dyke outside the quartz-sericite-pyrite zone on the north end of Sterrett Island (Figure C.17). The porphyry i s a light grey, fine-grained rock containing minor amounts of pyrite on hairline fractures. One to 2-millimetre phenocrysts of plagio-clase (A^^) and biotite constitute 25 per cent of the rock. These are con-tained in a fine-grained matrix of quartz, sericitized feldspar, and hornblende which i s completely altered to chlorite and carbonate. Biotite plates are primary and are fresh. NC-68-1 - Biotite Feldspar Porphyry Sample i s from a late porphyry dyke in the eastern part of the p i t area and contains only minor disseminated sulphide minerals (Figure C.17). Thirty per cent of the rock consists of 2-millimetre phenocrysts of plagioclase (^£5-35^ 3 1 1 ( 1 2-millimetre plates of biotite and chloritized hornblende. The matrix features abundant carbonate alteration. P o i k i l i t i c biotite plates exhibit no chlorite alteration. 215. NC-69-8 - Quartz-bornite-chalcopyrite-biotite-apatite Vein o Sample was collected from a 1-foot-wide vein i n the central part of the open p i t . The vein contains abundant coarse-grained bornite and chalcopyrite i n a quartz, apatite, and biotite gangue. Apatite occurs as one-half to 1-centimetre crystals. Biotite i s in the form of one-half to 1-centimetre plates and books and i s 20 to 50 per cent altered to chlorite. C.4.2 Newman (Bell Copper) (after Carter, 1965 and Carson and Jambor, 1974) The Newman mine of Noranda Mines, Limited, Bell Copper Division, i s on Newman Peninsula, 4 miles northwest of the Granisle mine. I n i t i a l work on the property, dating back to 1913, was directed to mineralized showings on the west shore of the peninsula opposite Newman Island. By 1927 three adits had been driven along small shear zones containing pyrite, pyrrhotite, and some chalcopyrite and sphalerite. The property was located by Noranda Exploration Company, Limited in 1962. Production began in 1972 at a daily milling rate of 10,000 tons. Reserves are i n the order of 50 to 100 million tons of 0.5 per cent copper. Copper mineralization i s associated with a plug-like intrusion of biotite feldspar porphyry 2,600 feet in diameter. Radial dykes projecting from the west side of the plug suggest i t i s probably a volcanic neck which has come up along the fault contact between siltstones on the west and fragmental rocks on the east (Figure C.18). 216. E Purple basalt, amygdular, tuffaceous Dacite porphyry, quartz latite porphyry Biotite feldspar porphyry; hornblende biotite fe ldspar porphyry Fe ldspar porphyry Predominant ly volcanic rocks, andesite, tuf fs and brecc ia s - , I000 0 bcale i i i Predominantly sedimentary rocks, silt-nLiV.Vv^ J stones, graywacke, arkose, arg i l l i te f Bedd ing Jo i n t s . — Geolog ica l contact, defined, i n fe r red I V \ A / , * / " Fault, def ined, assumed Limits of best minera li zation ( a pprox.) I000 ZOOCy i Feet FIG-C.18 NEWMAN (BELL COPPER) 217. Supergene weathering has transformed the biotite feldspar porphyry to a feldspar porphyry in the upper several hundred feet of the intrusive. This i s a porous white rock composed of numerous 1 to 2-millimetre chalky white feldspar phenocrysts set in a quartz-rich matrix. Along the western contact, sericite and carbonate alteration of feldspar i s extreme, i n some cases obliterating the original texture. The rock i s cut by numerous randomly oriented quartz and carbonate veinlets. Original biotite has been leached out, leaving golden-brown-stained areas i n the matrix. Metallic minerals, including pyrite and chalcopyrite, are finely disseminated throughout the rock matrix and the quartz veinlets. Quartz veining and s i l i c i f i c a t i o n of the feldspar porphyry i s most extensive throughout the northern part of the western contact of the plug, where irregular areas of light purple and grey quartz contain ragged inclusions of the feldspar porphyry. The degree of quartz veining and s i l i c i f i c i a t i o n has not been as extreme i n the southern part of the western contact area, where larger 2-millimetre phenocrysts of sericite and carbonate, pseudomorphic after plagioclase, are contained i n an altered quartz feldspar matrix. Irregular siltstone inclusions, having both sharp and grada-tional contacts , are common within the feldspar porphyry along the western contact. A northerly trending dyke-like body of relatively unaltered biotite feldspar porphyry occurs i n the central part of the intrusive (Figure C.18) and also forms a 500-foot capping over mineralized porphyry i n the northeast part of the plug. It i s interpreted as being a later, possibly post-mineral intrusive phase. The rock contains f a i r l y fresh 2-millimetre phenocrysts of oligoclase-andesine and brown biotite with some hornblende. 218. Hydrothermal alteration patterns are similar to those developed at Granisle, but are masked i n the upper part of the intrusion by supergene quartz-sericite alteration (Carson and Jambor, 1974). The potassic zone i s best developed coincident with the zone of copper mineralization and consists almost entirely of secondary biotite alteration in the porphyry. The quartz-sericite-pyrite zone i s best developed i n the sedimentary and volcanic rocks marginal to the intrusive and extends to the western shore of Newman Peninsula. Enveloping this i s a chlorite-carbonate zone of several thousand feet diameter. Copper mineralization occurs in a crescent-shaped zone along the western contact of the porphyry plug. Better grades of copper mineralization are contained in a 200 to 300-foot-thick fl a t - l y i n g , blanket-type deposit which i s connected to a central pipe-like zone, centred on the western contact of the intrusive. The pipe-like zone of copper mineralization i s 500 feet i n diameter and extends to a depth of at least 2,500 feet. Primary mineralization, consisting of pyrite, chalcopyrite, and some bornite, occurs as fine disseminations in the rock matrix, and in irregular quartz lenses and a stockwork of one-eighth to one-quarter-inch quartz veinlets which cut the feldspar porphyries and the siltstones. Quartz veinlets and hairline fractures containing specularite and magnetite are also common. Disseminations of molybdenite occur locally i n the feldspar porphyry i n the northern part of the zone. A zone of secondary enrichment, i n the form of chalcocite coating chalcopyrite, i s present over the entire mineralized body, extending to a depth of 500 feet over the central pipe-like zone. Elsewhere the depth of enrichment corresponds to the limits of the better grade mineralization in the northeast and southeast extensions of the zone of mineralization. 219. Relationships in the d r i l l cores suggest several ages of fracturing and quartz veining, including at least two stages of primary copper mineralization. Hairline fractures and one-quarter-inch quartz veinlets containing specularite and magnetite represent the i n i t i a l stage of mineralization, and these are cut by nearly flat-lying light grey quartz-pyrite veinlets containing some chalcopyrite. Offsetting these are chalcopyrite-bearing hairline fractures and veinlets of purple quartz oriented at angles of 40 degrees with respect to core surfaces in vertical d r i l l holes. Associated with this stage i s pervasive purple quartz s i l i c i f i c a t i o n . Milky white quartz veins, several inches wide, and 2-foot lenses of pink calcite cut a l l other veinlets. Secondary enrichment, consisting of sooty chalcocite coating chalcopyrite, represents the fin a l stage bf copper mineralization. Controls for the zone of copper mineralization are incompletely known. The crescent-shaped form of the zone accentuates the regional pattern of northeast and northwest fractures and the plug contact acted as a locus for intense fracturing and brecciation of the siltstones and feldspar porphyry. In general, areas of better grade primary copper mineralization are situated in the central and northeast parts of the zone, where s i l i c i f i c a t i o n i s more extensive and the quartz veinlets are more numerous than in the southern part of the zone. Pyrite, with some chalcopyrite and sphalerite, occurs in narrow northeasterly trending shear zones i n the adits on the lakeshore. A well-developed pyrite halo surrounds the orebody and i s approximately 6,500 feet i n diameter. 220. NC-67-22 - Biotite Feldspar Porphyry Sample i s from a d r i l l hole collared in late phase, weakly mineralized porphyry in the south-central part of the plug (Figure C.18). The rock i s light grey to buff in colour and i s composed of 2-millimetre phenocrysts of plagioclase almost totally altered to carbonate, and 1-millimetre plates of biotite i n a fine-grained, quartz-rich matrix. Original hornblende i s altered to biotite and carbonate. Biotite occurs both as 1-millimetre plates and as very fine-shredded grains in the rock matrix. Both varieties are unaltered. NC-67-23 - Biotite Feldspar Porphyry Sample i s from d r i l l core from a hole collared i n the northeast part of the intrusion (Figure C.18). The porphyry i s cut by numerous quartz veinlets containing chalcopyrite. The section sampled i s well below the zone of supergene alteration and mineralization. The rock i s a dark grey crowded porphyry with 2 to 4-millimetre pheno-crysts of plagioclase (An.^) and 1-millimetre biotite plates and books con-stituting 35 per cent of the rock. The matrix i s composed essentially of quartz. Biotite occurs as primary plates and books and as secondary fine-grained aggregates after hornblende. Both varieties are fresh. C.4.3 Morrison (after Carter, 1966 and Carson and Jambor, 1974) The Morrison copper deposit, owned by Noranda Exploration Company, Limited, i s on the southeast side of Morrison Lake about 14 miles north of 221. the Newman mine. Copper mineralization was discovered i n 1962 and d r i l l i n g since that time has indicated a copper zone containing 70 million tons averaging 0.4 to 0.45 per cent copper. Chalcopyrite mineralization i s associated with a small plug and peripheral dykes and s i l l s of biotite feldspar porphyry which intrude a northerly trending sedimentary sequence (Figure C.19). Post-intrusive faulting has horizontally Offset the central plug 1,000 feet. Argillaceous siltstones adjacent to the plug and peripheral dykes have been thermally metamorphosed to biotite hornfels. Best exposures are i n trenched areas east and west of the central plug, where dykes of porphyry are closely spaced and vary from 10 to 20 feet i n width. Contacts between the dykes and the hornfelsed siltstones are sharp. The biotite feldspar porphyries are dark grey and of quartz diorite composition. One-quarter to one-third of the rock consists of 2 to 3-millimetre phenocrysts of fresh, euhedral , normally zoned oligoclase-andesine. Abundant one-half to 1 -millimetre plates and books of fresh brown biotite, partly an alteration of hornblende, are also a characteristic feature of these rocks. The biotite feldspar porphyries are gradational to an altered variety i n which plagioclase i s altered to sericite and biotite i s mainly converted to sericite. A biotite alteration zone envelops the zone of copper mineralization and extends several hundred feet outward from i t . Within this zone, sugary textured brown hydrothermal biotite has replaced hornblende phenocrysts and invaded the matrix of the porphyry. Some K-feldspar alteration adjacent to fractures was also noted, The biotite zone i s gradational outward to a chlorite-carbonate zone several thousand feet in diameter. 222. \ A ^ A A V V < A ' / Biotite-Feldspar Porphyry Siltstone Andesite tuffs & breccias 1000 2000 Morrison Lake FEET 300 METERS FIG.-C.19 MORRISON/ 223. Chalcopyrite occurs i n closely spaced fractures and narrow quartz veinlets i n the contact areas of the central plug and i n the peripheral porphyry dykes and hornfelsed siltstones. Some bornite i s contained in the central part of the deposit. A pyrite halo overlaps part of the copper zone and extends outward 1,000 feet from i t . NC-67-40 - Biotite Feldspar Porphyry Sample was collected from a trench i n the northwest part of the deposit. The porphyry i s dark grey and i s featured by the presence of abundant biotite. Quartz-filled fractures cut the rock and contain chalcopyrite and a l i t t l e bornite. One to 2-millimetre phenocrysts of euhedral plagiocoase make up 25 per cent of the rock. Biotite occurs mainly i n fine-grained aggregates as an alteration of primary hornblende. The matrix consists of quartz, plagioclase, and some chlorite. Biotite aggregates show l i t t l e , i f any, alteration to chlorite. C.4.4 Old Fort (after Carter, 1966) The property i s on the southeast slope of Old Fort Mountain at the north end of the main part of Babine Lake (Figure C.20). An e l l i p t i c a l stock of quartz diorite, elongated in an easterly direction and measuring 3,000 to 2,000 feet, intrudes argillaceous siltstones and inter-bedded andesite tuffs i n the central part of the property (Figure C.20). Within the stock, quartz diorites have been intruded by a small elongate mass of quartz monzonite and related hornblende-biotite-feldspar porphyry dykes. 224. 225. Chalcopyrite and lesser amounts of molybdenite occur as disseminations and i n fractures in both the quartz diorite and porphyry dykes adjacent to the western margin of the inner quartz monzonite body. The quartz diorite which constitutes the greater part of the stock i s a fine to medium-grained light grey equigranular rock having an average composition of 67 per cent euhedral, normally zoned oligoclase-andesine , 15 per cent quartz, 10 per cent hornblende, and 5 per cent b i o t i t e , with the remainder consisting of apatite, epidote, and opaque minerals. Alignment of 3-millimetre hornblende needles was noted near the margins of the stock. The quartz diorite i s an essentially fresh rock, with only local sericitization of feldspar and chloritization of mafic minerals. Contacts between the quartz diorite and later quartz monzonite are sharp to gradational. The quartz monzonite i s distinguished by a slightly coarser equigranular to seriate texture, and a lighter grey colour with pinkish cast due to the presence of ragged, p o i k i l i t i c K-feldspar. Biotite i s the dominant mafic mineral, and occurs both as 1 to 2-millimetre books and flakes and as a fine alteration of hornblende. A typical specimen i s composed of 45 per cent euhedral, normally zoned oligoclase-andesine, 20 per cent orthoclase, 15 per cent quartz, 10 per cent b i o t i t e , 5 per cent horbnlende , and 5 per cent accessory minerals including apatite, epidote, and opaque minerals. Varying degrees of a r g i l l i c alteration of feldspar and bleaching of mafic minerals were noted i n some sections of d r i l l core. A porphyritic texture i s developed along the western margin of the quartz monzonite body, and dykes of hornblende-biotite-feldspar porphyry, not exceeding 100 feet i n width, radiate outward from this zone into the quartz diorites. Two-millimetre phenocrysts of euhedral oligoclase-andesine and 226. plates and books of fresh brown biotite constitute 30 per cent of the rock, the remainder being composed of finer grained quartz, plagioclase, and amphibole, largely altered to fine biotite. Argillaceous siltstones, including dense dark grey and light to dark grey well-banded varieties, have been metamorphosed to chocolate-brown-coloured biotite hornfels , for a distance of between 1,000 and 3,000 feet outward from the quartz diorite stock. Pyrite and pyrrhotite are widely disseminated i n a l l intrusive and adjacent sedimentary rocks. Several small isolated zones containing variable amounts of copper mineralization are grouped i n a semicircular pattern within the area of porphyry dykes adjacent to the western margin of the central quartz monzonite mass. Chalcopyrite and minor bornite occur with magnetite as disseminations and i n fractures i n both the quartz diorite and hornblende-biotite-feldspar porphyry dykes. Molybdenite flakes are found i n some fracture planes rimmed by one-eighth to one-quarter-inch fine-grained pink K-feldspar veinlets. The most northerly zone of mineralization, near the central part of the stock, has been exposed i n a 200-foot-long trench. Copper mineralization i s most widespread i n the eastern half of the trench, where porphyry dykes intrude quartz diorites. Chalcopyrite occurs as disseminations i n both rock types and i n north-trending fractures and irregular 1-inch zones rich i n mafic minerals and magnetite i n quartz diorites. A grab sample from the east end of the trench assayed 0.43 per cent copper. 227. NC-67-1 - Biotite Feldspar Porphyry Sample i s from a trench i n the most northerly mineralized zone near the central part of the stock (Figure C.20). The porphyry i s a medium to dark grey rock with hairline fractures containing chalcopyrite and molybdenite. Chalco-pyrite i s also finely disseminated i n the rock matrix. The rock i s a crowded porphyry with 1 to 2-millimetre phenocrysts of euhedral plagioclase (Aja25-35^ biotite making up 50 per cent of the rock volume. Original hornblende phenocrysts are altered to a mixture of chlorite and hornblende. The matrix i s a cryptocrystalline mixture of quartz and feldspar. P o i k i l i t i c biotite plates and books are unaltered. NC-67-2 - Biotite Quartz Monzonite Sample i s from a s i l l which intrudes argillaceous sedimentary rocks 2 miles south of the Old Fort stock (Figure C.20). The rock i s light grey and medium grained, and i s actually a crowded porphyry with 2-millimetre phenocrysts of plagioclase (An ^Q), quartz, hornblende , and biotite making up 50 per cent of the rock. The matrix i s a fine-grained mosaic of quartz and K-feldspar. Biotite occurs as 1-millimetre, shredded, p o i k i l i t i c plates and as fine-grained aggregates i n the matrix. Up to 15 per cent chlorite alteration was noted. C.4.5 T r a i l Peak (after Carter, 1969) The property i s on the south slope of T r a i l Peak, north of Babine Lake and 70 miles northeast of Smithers. 228. T r a i l Peak i s underlain by dark grey to black cherty siltstone which i s intensely fractured and iron-stained due to the presence of disseminated pyrite. Light grey crystal l i t h i c tuffs are interbedded with the sedimentary rocks on the west side of T r a i l Peak. The cherty siltstones have been intruded by medium-grained diorites and granodiorites and by dykes and irregular masses of biotite feldspar porphyry which host copper mineralization. Hornblende feldspar porphyries may i n part be extrusive equivalents of the biotite feldspar porphyry dykes (Figure C.21). The earliest intrusive rocks are medium-grained diorites and grano-diorites which occur i n small stock-like masses 1,500 feet or so i n diameter in the central part of the map-area. An unaltered variety, on the south side of T r a i l Peak, has a hypidiomorphic granular texture and consists of the following: euhedral plagioclase (An^g^g), 57 per cent; hornblende, 13 per cent; reddish brown bi o t i t e , 7 per cent; i n t e r s t i t i a l perthitic K-feldspar, 7 per cent; anhedral quartz, 5 per cent; and chlorite, opaque minerals, etc., 11 per cent. Cutting the diorites and granodiorites and the sedimentary rocks are northwest-striking dykes and irregular masses of biotite feldspar porphyry which are most abundant i n the western trench area (Figure C.21). These porphyries are typical of the Babine Lake area and are of quartz diorite composition. Typically, the rock i s medium to dark grey with phenocrysts making up 25 per cent of the rock by volume. These include 1 to 2-millimetre euhedral zoned plagioclase ( ^ 2 5 - 3 5 ) a n c i * "millimetre books and plates of fresh biotite which are set in a fine-grained matrix of quartz, feldspar, and biotite. Secondary biotite i s present as an aggregate of fine flakes replacing WG-C2J GEOLOGY OF THE CAVZ GROUP TRAIL PEAK H Hornblende •feldspar porphyry.locally blotilic BiOliH-feldspOf porphyry 1 Dionle, monionilt ~J Sandstone 7:^j Sholy tiltilofli [r- r f"j Andsillt Cryttol-lilhiC tuff Block iiltslone , cherty in port > ——< Bulldozer trench Outcrop area f Bedding, inclined, vertical Jointing, inclined, virlicof * w w * Foul I - •• Geologtcot contocl,defined, inferred 230. original hornblende and as fine flakes i n the matrix. The porphyry i s relatively fresh, with only minor sericite-carbonate alteration of feldspar and incipient chloritization of biotite. A typical specimen from the west trench area consists of plagioclase, 46 per cent; quartz, 23 per cent; bio t i t e , 23 per cent; chlorite, 6 per cent; apatite, 1 per cent; and sphene, 1 per cent. Hornblende feldspar porphyries are closely related to the biotite feldspar porphyries. These occur as narrow northwest-striking dykes or s i l l s on the north slope of Tr a i l Peak, as larger dyke-like masses i n the west trench area, and as a large mass capping the h i l l southeast of the trench area. A l l varieties display a trachytic texture in which phenocrysts of plagioclase and hornblende are aligned in subparallel fashion as are the fine-grained feldspar laths which make up the matrix. Crude columnar jointing noted i n the large area of hornblende feldspar porphyry southeast of the trenches suggests that some phases may be partly of extrusive origin. The sedimentary rocks of the T r a i l Peak area are contained i n a north-west-trending synform. Northeast and northwest faults dominate the structure of the area and were no doubt instrumental i n localizing intrusive activity near the axis of the fold structure. Later post-intrusive movement along these faults has contributed to the complex form of the intrusive bodies. Copper mineralization was observed i n close proximity to the major northeast fault through the central part of the area. In the creek north of the east trenches at an elevation of 4,600 feet, fractures spaced 2 to 6 inches apart i n hornblende feldspar porphyry contain pyrite and chalcopyrite with quartz and tourmaline. One-quarter to one-half-inch-wide quartz veins 231. contain chalcopyrite and tourmaline needles and are rimmed by an alteration envelope i n which plagioclase i s altered to K-feldspar, hornblende to actinolite , and abundant quartz has been introduced. In the western trench area, chalcopyrite i s mainly associated with biotite feldspar porphyry i n which i t occurs with pyrite as disseminations on fracture planes and i n one-quarter-inch-wide quartz veinlets which also contain magnetite. Malachite staining i s common. In the same area, tourmaline i s abundant in the rocks near the northeast fault zone, occurring in fractures and veinlets and as irregular clots in brecciated hornblende feldspar porphyry and diorite. Southeast of the trenches, a 2-inch-wide quartz vein, containing galena and sphalerite , occurs in a northwest-striking shear zone in shaly siltstone. NC-68-10 - Biotite Feldspar Porphyry Sample i s from the trenched area south of T r a i l Peak (Figure C.21). The rock i s dark grey and contains scattered 2 to 3-millimetre pheno-crysts of subhedral plagioclase (An ) and 1-millimetre plates of biotite. Original hornblende i s almost completely altered to chlorite. P o i k i l i t i c biotite plates are up to 15 per cent chloritized. NC-69-1 - Granodiorite Sample i s from a small stock that underlies T r a i l Peak. The granodiorite i s a grey, medium-grained, equigranular rock which contains prominent biotite plates. The rock has a hypidiomorphic granular 232. texture and consists of quartz, plagioclase (^38-45)» K-feldspar, hornblende, and biotite. Hornblende and biotite are intimately associated and most of the biotite may represent a deuteric alteration of hornblende. The biotite occurs as 1-millimetre p o i k i l i t i c , shredded plates and i s unaltered. C.4.6 Newman Peninsula Extrusive equivalents of intrusive biotite feldspar porphyries are exposed near the south end of Newman Peninsula on Babine Lake (Figure 26). These rocks are sheet-like i n form and may have a vertical thickness of several hundred feet. Well-devloped columnar jointing i s exposed along the southwest shore of the peninsula. The extrusive equivalents are fine to medium-grained hornblende feldspar porphyries of andesite composition. Parallel arrangement of the hornblende and feldspar phenocrysts impart a flow texture to the rock. NC-67-43 - Hornblende Feldspar Porphyry Sample i s from columnar-jointed porphyry exposed along the southwest shore of Newman Peninsula (Figure 26). The porphyry i s fine to medium grained, grey i n colour, and has a trachytic texture. One to 2-millimetre phenocrysts of plagioclase (An^) and hornblende make up 35 per cent of the rock and are contained i n a matrix of very fine-grained plagioclase laths. Hornblende needles are slightly p o i k i l i t i c and are essentially free of alteration. 233. C.4.7 Lennac Lake (after Carter, 1972) The Lennac Lake porphyry copper prospect i s 9 miles southwest of Topley Landing (Figure 26). Hazelton Group volcanic rocks are intruded by an oval stock-like body of quartz-horbnlende-biotite-feldspar porphyry, elongate in a northeast direction and measuring 4,000 by 2,000 feet. The porphyry i s of granodiorite composition and phenocrysts constitute 30 per cent of the rock. Trenches south of the small lake expose relatively unaltered porphyry and a typical specimen from this area consists of quartz, 15 per cent, usually occurring as 2 to 4-millimetre anhedral phenocrysts; plagioclase (An^Q.,^), 45 per cent, occurring both i n the matrix and as 4 to 7-millimetre euhedral pheno-crysts; K-feldspar, 15 per cent, restricted to the matrix and marginal to fractures; biotite, 10 per cent, i n the form of 5-millimetre books; and hornblende, 5 per cent, usually exhibiting incipient alteration to fine-grained brown biotite. Potassic alteration i s weak to moderate within the main trench area and consists of secondary K-feldspar adjacent to fractures and secondary b i o t i t e , an alteration of hornblende. To the east of the stock are two northeast-striking porphyry dykes and there the intrusive rocks exhibit features typical of a quartz-sericite-pyrite alteration zone. Plagioclase i s almost totally altered to sericite-carbonate, hornblende i s altered to a mixture of chlorite and epidote , and biotite i s completely chloritized. Pyrite i s disseminated throughout the rock as well as being intimately associated with altered mafic minerals. 234. Hazelton Group volcanic rocks have been metamorphosed to biotite hornfels marginal to the porphyry stock and dykes. Inclusions of hornfelsed Hazelton volcanic rocks are numerous within the stock and these rocks also contain significant amounts of magnetite. Sulphide mineralization i s centred about the porphyry stock and occurs over an area of 1.5 by 1 mile. The major copper showings are within the porphyry stock where chalcopyrite, pyrite, magnetite, and minor chalcocite and molybdenite occur i n northwest-striking one-sixteenth to one-eighth-inch veinlets with quartz and some K-feldspar. Chalcopyrite mineralization was also noted as films on dry fractures i n inclusions of volcanic rocks within the stock and i n hornfelsed rocks i n a trenched area 1 mile to the east. NC-72-1 - Quartz-hornblende-biotite Feldspar Porphyry Sample was collected from a trench near the central part of the stock. Chalcopyrite occurs in narrow quartz-filled fractures. Thirty per cent of the rock i s composed of 4 to 7-millimetre pheno-crysts of plagioclase ( ^ 3 0 - 3 5 ) ' biotite books and hornblende needles to 5 millimetres , and 2-millimetre quartz eyes. These are set i n a fine-grained matrix of quartz, biotite, plagioclase, and K-feldspar. Magnetite also occurs in the matrix. Green hornblende i s partially altered to biotite and primary biotite books are p o i k i l i t i c and exhibit incipient (10 per cent) alteration to chlorite. 235. C.4.8 Tachek Creek (after Carter, 1969) The Tachek Creek copper-molybdenum prospect i s 4 miles south of Topley Landing (Figure 26). The oldest rocks exposed are intermediate volcanic rocks of Lower Jurassic age. These are intruded by Topley granitic rocks which underlie the central part of the property. These rocks range from granodiorite to quartz monzonite in composition. Biotite-quartz feldspar porphyry dykes were observed cutting the granitic rocks in the v i c i n i t y of the principal mineral showings near 2,900 feet elevation on Tachek Creek. The dykes have irregular, commonly brecciated contacts with the granites and strike predominasntly east. Where seen i n the creek, they are several feet wide, although d r i l l intersections i n the order of 50 feet were encountered. The dyke rock, while lithologically similar to the typical Babine porphyries with which the copper deposits of the region are associated, differs from them i n age and by having quartz phenocrysts. Typically, the rock i s a crowded porphyry, with phenocrysts making up 50 per cent of the rock by volume, including 2 to 4-millimetre euhedral, zoned, plagioclase crystals, 2-millimetre resorbed quartz pheno-crysts , and 1 to 2-millimetre books of fresh b i o t i t e , a l l set i n a fine-grained matrix of quartz, feldspar, and secondary shredded biotite. Hornblende phenocrysts, 2 to 4 millimetres i n size, are not uncommon, and these are commonly altered to a mixture of chlorite, s e r i c i t e , and flaky biotite. A typical specimen of porphyry i s of quartz diorite composition and contains the following constituents: quartz, 35 per cent; plagioclase (^28-35)' 4 5 per cent; b i o t i t e , 7 per cent; chlorite and s e r i c i t e , 10 per cent; and metallic minerals, 3 per cent. 236. Sulphide mineralization, in the form of pyrite, chalcopyrite, and molybdenite , appears to be most widespread marginal to biotite-quartz feldspar porphyry dykes. In general, molybdenite i s restricted to K-feldspar-rimmed fractures, while chalcopyrite occurs both i n fractures and as disseminations in both the granitic rocks and the porphyries. Biotite-lamprophyre dykes, 3 feet wide and magnetic, were seen cutting the granitic rocks and are apparently of post-mineral age. NC-69-4 - Biotite-quartz Feldspar Porphyry Sample i s from a porphyry dyke near the main mineralized zone i n Tachek Creek. The rock i s a crowded porphyry, with about 50 per cent of the rock composed of 2 to 3-millimetre phenocrysts of euhedral plagioclase (An 0 0 o c ) , biotite books, hornblende needles, and anhedral quartz eyes. The matrix i s very fine-grained anhedral quartz, feldspar, and shredded biotite and chlorite. Hornblende i s partially altered to chlorite and biotite. Biotite plates are p o i k i l i t i c and display some chlorite alteration along grain boundaries. PUBLICATIONS: Carter, N. C. (1970): Copper and Molybdenum Porphyry Deposits i n Central British Columbia, Cdn. Min. Jour., Vol. 91, No. 4, pp. 74-76. (1972a): Faults, Lineaments, and Porphyry Copper Deposits, Babine Lake Area, B.C. (Abstract), G.A.C., Symposium, Faults, Fractures, Lineaments, and Related Mineralization in the Canadian Cordillera. (1972b): Granisle, XXIV International Geological Congress, Guidebook, Field Excursion A09-C09, Copper and Molybdenum Deposits of the Western Cordillera (C. S. Ney and A. Sutherland Brown, Eds.), pp. 27-36. (1973a): Geochronology of Porphyry Copper and Molybdenum Deposits i n West-central British Columbia (Abstract), C.I.M., Ann. Gen. Mtg., Gen. Program, 1973. (1973b): Geology of the Northern Babine Lake Area, B.C. Dept. of Mines and Petroleum Resources, Preliminary Map No. 12. Contributions to 'Minister of Mines Annual Reports' and 'Geology, Exploration, and Mining,' B.C. Dept. of Mines and Petroleum Resources, 1964 - 1973. 00*00 S6'00 !24°00 53°00 130 00' 56 00' U4 00 128°00' 126°00' PORTLAND, CANAL 0 op * N 0 0 s 9 0 o | | g BABINE RANGE 0r ° 55 00 GENERA W E S T - C E N T R A L • 1*3 67 l17if A I Cil L E G E N D S E D I M E N T A R Y A N D V O L C A N I C R O C K S Q U A T E R N A R Y P L E I S T O C E N E A N D R E C E N T j P L A T E A U B A S A L T S , B A S A L T F L O W S . A N D C I N D E R C O N E S T E R T I A R Y E O C E N E - M I O C E N E E N D A K O G R O U P . G O O S L Y L A K E A N D B U C K C R E E K V O L C A N I C R O C K S P L A T E A U B A S A L T . A N D E S I T E F L O W S A N D B R E C C I A S . S O M E R H Y O L I T E A N D D A C I T E C R E T A C E O U S A N D T E R T I A R Y U P P E R C R E T A C E O U S — P A L E O C E N E O O T S A L A K E G R O U P . T IP T O P H I L L V O L C A N I C R O C K S -B A S A L T . A N D E S I T E , D A C I T E , A N D R E L A T E D T U F F S A N D B R E C C I A S . S O M E R H Y O L I T E F L O W S A N D I N T R U S I V E E Q U I V A L E N T S S U S T U T G R O U P ( I N P A R T I - S A N D S T O N E . C O N G L O M E R A T E . M U D S T O N E . S H A L E C R E T A C E O U S L O W E R C R E T A C E O U S ^ ^ ^ S K E E N A G R O U P , B R I A N B O R U A N D R E D R O S E • F O R M A T I O N S - S I L T S T O N E , S A N D S T O N E . S H A L E . A N D 8 8 8 — 1 P O R P H Y R I T I C A N D E S I T E F L O W S , B R E C C I A S . A N D T U F F S J U R A S S I C A N D C R E T A C E O U S U P P E R J U R A S S I C - L O W E R C R E T A C E O U S H A Z E L T O N G R O U P ( IN P A R T ) - S I L T S T O N E , G R E Y W A C K E , S A N D S T O N E , C O N G L O M E R A T E . A R G I L L I T E . M I N O R L I M E S T O N E , A N D C O A L J U R A S S I C ( H A Z E L T O N G R O U P ) M I D D L E J U R A S S I C l iJJJJfJfJANDESITE- B A S A L T A N D D A C I T E T U F F S A N D B R E C C I A S . V i l l i A N I C S A N D S T O N E A N D C O N G L O M E R A T E . S I L T S T O N E . ' A N D G R E Y W A C K E L O W E R J U R A S S I C G R E E N . R E D , A N D P U R P L E A N D E S I T E A N D B A S A L T T U F F S A N D B R E C C I A S , V O L C A N I C S A N D S T O N E A N D C O N G L O M E R A T E , A R G I L L I T E . A N D G R E Y W A C K E T R I A S S I C A N D O L D E R T A K L A G R O U P (IN P A R T ) - M A F I C V O L C A N I C R O C K S . V O L C A N I C S A N D S T O N E . A R G I L L I T E . L I M E S T O N E , C H E R T , S O M E A C I D I C M E T A V O L C A N I C R O C K S . A N D C H L O R I T E . S E R I C I T E . A N D B I O T I T E S C H I S T S L GEOLOGY BRITISH COLUMBIA FIG-8 I N T R U S I V E R O C K S T E R T I A R Y O L I G O C E N E IHHlJ L A M P R O P H Y R E D Y K E S W A R M S E O C E N E P O R T L A N D C A N A L D Y K E S W A R M - G R A N I T I C R O C K S M I D D L E E O C E N E G R A N I T I C R O C K S , G O O S L Y L A K E . A L I C E A R M . N A N I K A . B A B I N E I N T R U S I O N S T E R T I A R Y A N D O L D E R (?) C O A S T P L U T O N I C C O M P L E X - G R A N I T I C R O C K S , Q U A R T Z D I O R I T E . G R A N O D I O R I T E . Q U A R T Z M O N Z O N I T E . L O C A L L Y F O L I A T E D A N D / O R G N E I S S I C C R E T A C E O U S U P P E R C R E T A C E O U S B B B U L K L E V I N T R U S I O N S P O R P H Y R I T I C Q U A R T Z M O N Z O N I T E A N D G R A N O D I O R I T E J U R A S S I C A N D C R E T A C E O U S • • M K I T S A U L T I N T R U S I O N S ^ - T E L D S P A R P O R P H Y R Y , A U G I T E • • • P O R P H Y R Y . H O R N B L E N D E D I O R I T E J U R A S S I C U P P E R J U R A S S I C F R A N C O I S L A K E I N T R U S I O N S . P O R P H Y R I T I C O U A R T Z M O N Z O N I T E . G R A N O D I O R I T E , A N D Q U A R T Z D I O R I T E L O W E R A N D M I D D L E J U R A S S I C • O M I N E C A I N T R U S I O N S - G R A N O D I R O I T E . Q U A R T Z D I O R I T E , S Y E N I T E . G A B B R O . M O N Z O N I T E . A N D D I O R I T E T R I A S S I C A N D J U R A S S I C U P P E R T R I A S S I C - L O W E R J U R A S S I C T O P L E Y I N T R U S I O N S - Q U A R T Z M O N Z O N I T E . G R A N O D I O R I T E , A N D Q U A R T Z D I O R I T E A N D P O R P H Y R I T I C V A R I E T I E S P E R M I A N - T R I A S S I C J T R E M B L E U R I N T R U S I O N S - U L T R A M A F I C R O C K S H O R N B L E N D E S C H I S T S C H L O R I T E S Y M BOLS A N D S T O N E . A M P H I B O L I T E . A N D S C H I S T E N F A U L T S T H R U S T F A U L T S NANIKA LAKE 54 00' ^ O 0 C OOTSAJ) LAKE ]0 o 2? u 0 0 Q » EUTSUKTAKE o 0 o o 53 00' i 1 48 MOLLY MACK LEGEND QUATERNARY \MM BASALT FLOWS PLEISTOCENE PLATEAU BASALTS •RTIARY COAST PLUTONIC COMPLEX I ALICE ARM INTRUSIONS JURASSIC AND CRETACEOUS SEDIMENTARY ROCKS MIDDLE AND UPPER JURASSIC ] VOLCANIC AND SEDIMENTARY ROCKS N i FIG.19 ALICE ARM—NASS RIVER AREA F/G-26 PORPHYRY COPPER DEPOSITS BABINE LAKE AREA INTRUSIVE ROCKS Tertiary (Eocene) I \BABINE INTRUSIONS BFP,QD,QM. RMS EXTRUSIVE EQUIVALENTS Upper Cretaceous IQZ-HB-B/O. FELDSPAR PORPHYRY RHYOLITE PORPHYRY Jurassic } TOPLEY-OMINECA INTRUSIONS SEDIMENTARY& VOLCANIC ROCKS Jurassic-Cretaceous • CLASTIC VOLCANIC & SEDIMENTARY ROCKS E 5 2 AGES IN M.Y 0 b 5 1.0 MILES 

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