DETAILED GEOLOGICAL MAPPING AND INTERPRETATION OP THE GRAND FORKS-EHOLT AREA, BOUNDARY DISTRICT BRITISH COLUMBIA by ARNE REINSBAKKEN B.Sc, University of British Columbia, 1968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OP THE REQUIREMENTS FOR- THE DEGREE OP MASTER OF SCIENCE in the Department or Geology We accept this thesis as conforming to the required standard THE UNIVERSITY OP BRITISH COLUMBIA December, 1970 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree tha permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Depa rtment The University of British Columbia Vancouver 8, Canada A northward view up Granby River Valley from Thimble Mountain. The ridge in the foreground and across the Valley is underlain by the Middle Triassic Sharpstone Conglomerate and Brooklyn Limestone sequence. iii ABSTRACT The Grand. Forks-Eholt map area is underlain predominantly by a sequence of moderately deformed and slightly metamorphosed sedimentary and volcanic rocks, previously termed the "Anarchist Group" and ranging in age from Permian/or Earlier to Middle Jurassic. These rocks are divisible into two distinct sequences: (a) cherts (Knob Hill), quartzites, phyllites, and greenstones of Permian/or Earlier age. The term Anarchist Group is now restricted to this lower sequence which resembles the Cache Creek Assemblage (Penn.-Lower Triassic) widespread throughout southcentral B.C.; (b) Sharp- stone Conglomerate/Brooklyn Limestone sequence (Middle-Upper Triassic), and overlying Pragmental Andesites (Middle Jurassic) which correlates with the Takla-Hazelton Assemblage (Middle Triassic - Middle Jurassic) in north central B.C. This upper sequence rests unconformably on -the lower and the Sharpstone Conglomerate forms the basal conglomerate separating the two sequences. The Grand Forks Group (pre-Cambrian/or Early Paleozoic), consisting of paragneisses, minor marble and amphibolites crops out east of the Granby River Fault. The fault forms approximately the eastern boundary of the map area. Latest Jurassic Nelson granodiorites; Latest Cretaceous quartz-diorite, quartz-monzonite porphyries, leuco-gabbros and diorites; and Eocene Coryell syenites and related alkalic rocks intrude the sediments and volcanics pre• dominantly in the northern part of the map area. The Nelson granodiorites occur as large batholith-like masses and the younger intrusions form small irregular plugs, dykes and sills. iv A NNE to N trending nearly recumbent synclinal structure is outlined within the Sharpstone Conglomerate/Brooklyn Limestone/Fragmental Andesite sequence. It is transected by prominent NW trending shear/fault zones and has been broken by these into blocks that are downdropped and shifted to the southwest from north to south in the map area. The eastern part of the map area is transected by the NNE trending Granby River Fault which forms the northern projection of the Eastern Boundary Fault of the Republic Graben - a major structural element to the south in Washington State. Prominent NW and NE Late Cretaceous to Tertiary fractures are ubiquitous and often filled by sheared serpentinites and Tertiary pulaskite and diorite dykes. The Middle Jurassic and older sediments and volcanics have been regionally metamorphosed to the Greenschist Facies. The Grand Forks Group to the east has undergone metamorphism to the Almandine-Amphibolite Facies. Large hornfelsed metasedimentary aureoles surround the larger Nelson granodiorite masses. The Brooklyn Limestone has been thermally altered to marble and locally to chalcopyrite-magnetite bearing calc- silicate skarns, which are often of economic value. Thin contact thermal aureoles surround the Latest Cretaceous quartz-diorite and quartz- monzonite porphyry plugs and dykes, indicating high level intrusion. V TABLE OF CONTENTS Page SECTION I; INTRODUCTION a. Nature and Scope of Project 1 b. Field Approach and Laboratory Studies 2 c. Location and Accessibility 3 d. Previous Work 6 e. General Geology 7 SECTION II; STRATIGRAPHY A. SEDIMENTARY SUCCESSION 10 a. Grand Forks Group 10 b. Anarchist Group 13 c. Sharpstone Conglomerate Sequence 19 d. Brooklyn Limestone Formation 30 e. Fragmental Andesites 38 f. Tertiary Layered Rock 44 - Kettle River Formation 44 - Marron Volcanic Formation 47 B. SERPENTINITES 51 C. INTRUSIVE ROCKS 54 a. Nelson Intrusions 54 b. Valhalla Intrusions 56 c. Diorites and Gabbros 57 d. Tertiary Intrusions - Quartz-diorite and quartz-monzonite porphyry intrusions; includes "Scatter Creek Formation" rocks 63 vi Page - Coryell Syenite and Pulaskite Dykes 66 SECTION III; STRUCTURES 71 a. Republic Graben 71 b. Northwest and Northeast Fault Patterns 73 c. Dyke s 74 d. Folds 75 e. Tertiary Block Faulting and Tilting 80 SECTION IV: METAMORPHISM 84 a. Regional Metamorphism 84 b. Contact Thermal Metamorphism 87 SECTION V: SUMMARY AND CONCLUSION 91 a. Summary 91 b. Conclusions 97 c. Suggestions for Further Work 101 SECTION VI; REFERENCES 103 APPENDIX I; ECONOMIC GEOLOGY 106 - Mining History 106 - Mineralization 107 APPENDIX II: FOSSIL LOCATION AND DESCRIPTION 111 LIST OF TABLES Table " Page 1 Table of Formations 11 LIST OF FIGURES Figure Page 1 Location map of the Grand Forks-Eholt map area, Boundary District, British Columbia. 5 2 General geological setting of the Boundary District and adjacent Curlew quadrangle in northern Washington. 8 3 Idealized diagram of the possible source and formation of Triassic marine basins and the related deposition of the Sharpstone Conglomerate sequence and the Brooklyn Limestone. 28 4 NW-SE diagrammatic cross-section (looking NE) from the Rathmullen Creek - C.P.R. track intersection to where Lime Creek flows into the Granby Valley. 81 5i E-W diagrammatic cross-section through Baker Ridge. 82 6. SW-NE diagrammatic cross-section through Hardy and Goat Mountains. 83 7. Observed stratigraphic range of metamorphic minerals and other features of the Early Paleozoic, Permian, and Triassic-Jurassic rocks (after Parker and Calkins (1964), with modifications). 85 8. Possible outside correlations of various rock units and formations outcropping throughout the Grand Forks area. 96 9. Sketch and Measurements of Megaphyllites. 113 10. Mature to Juvenile Suture Patterns of Megaphyllites 114 viii LIST OF PLATES Plate Page Frontispiece A northward view up Granby River Valley from Thimble Mountain. The ridge in the foreground and across the valley is under• lain by the Middle Triassic Sharpstone Conglomerate and Brooklyn Limestone sequence. ii 1. Photograph Typical bedded sharpstone conglomerate with distinct alignment of angular chert pebbles. Note large weathered pits still containing limestone cobble remnants, and an increase in maroon colour towards the top of the picture. 22 2. Photograph Sharpstone conglomerate. Showing predominance of light green to grey angular chert pebbles. Several dark red jasper pebbles can be seen. 22 3. Photograph Typical "Puddingstone" or limestone cobble conglomerate from exposure along C.P.R. tracks north of Neff Creek. The white elongate rounded cobbles are aligned roughly parallel to bedding. 26. 4. Photograph A thin lens of sharpstone conglomerate interbedded with a maroon-coloured fine• grained wacke of the uppermost "Puddingstone" sequence, found west of Baker Ridge. 26. 5. Photograph "Aeolian limestone" or Seraphim's "Peanut Brittle" limestone forming the basal section of the Brooklyn limestone NW of Baker Ridge. Note alignment of the frosted chert ovoids. 34 6. Photograph Brooklyn Limestone, thinly bedded, well banded,unit from area immediately west of Grand Forks. Thin more resistant beds are tuffaceous and impure limestone. 34. ix Page 7. Photograph Typical fragmental andesite from Goat Mountain. Note several large rounded porphyritic frag• ments and the light green-yellow epidote and chlorite alteration. 41 8. Photograph Spectacular andesite agglomerate outcropping along the southern Provincial Highway in the July Creek Valley. Camera case - extreme left for scale. 41 9. Photograph Intensely sheared, steeply dipping serpentinite body found within a NW trending fault zone northeast of Hardy Mountain. 53 10. Photograph Coarse-grained slightly foliated leuco- gabbro or mela-diorite from east of Hardy Mountain. Composed of plagioclase and hornblende. 53 11. Photograph Coarse-grained quartz-monzonite porphyry ("Scatter Creek Formation"?) from easterly trending dyke at Eagle Mountain. 68 12. Photograph Coryell syenite "clot porphyry" variety from east of Wilgress Lake. 68 13. Photograph A NE view of the limestone cliff directly opposite the Granby River from the Hummingbird showing. Shows synclinal fold minor structure within the well banded limestone unit and several flat dipping Tertiary dykes. 77 X MAP I. GEOLOGY Grand Forks-Eholt Area (l"=2000') in pocket at back xi ACKNOWLEDGEMENTS The author wishes to thank Texas Gulf Sulphur Company for the opportunity of working on the project and for allowing full use of all data and maps on which this thesis is based. The author was ably assisted in the field by C.N. Forster, K.A. Komenac, R.Taylor and P.T. Edwards at various times throughout the summer. Special thanks goes to J.M. Newell, who supervised the field mapping and with whom