Province of British Columbia MINERAL RESOURCES DIVISION Ministry oi Energy, Mines and Geological Survey Branch Petroleum Resources Hon. Anne Edwards, Minister GEOLOGY OF THE EARLY JURASSIC TOODOGGONE FORMATION AND GOLD-SILVER DEPOSITS IN THE TOODOGGONE RIVER MAP AREA, NORTHERN BRITISH COLUMBIA By Larry J. Diakow, Andrejs Panteleyev, and Tom G. Schroeter BULLETIN 86 MINERAL RESOURCES DIVISION Geological Survey Branch Canadian Cataloguing in Publication Data Diakow, Larry, I. Geology of the early Jurassic Toodoggone Formation and gold-silvei depositsin the Toodoggone River map area, northern British Columbia VICTORIA BRITISH COLUMBIA (Bulletin, ISSN 0226-7497; 86) CANADA Issued by Geological Survey Branch. Includes bibliographical references: p January 1993 ISBNO-7718-9277-2 1. Geology - Stratigraphic - Jurassic. 2. Gold ores Geological researchfor this -Geology - British Columbia - Toodoggone River Region. 3. Silver ores - British Columbia - Toodoggone River publication was completed during Region. 4. Geology - British Columbia - Toodoggone the period 1981 to 1984. River Region. 5. Toodoggone Formation (B.C.) I. Fanteleyev, Andrejs, 1942- 11. Schroeter, T. G. In. British Columbia. Geological Survey Branch. IV. British Columbia. V. Title. VI. Series: Bulletin (British Columbia. Minisrry of Energy, Mines and Petroleum Resources); 86. TN414C32B731992 551.7'66'0971185 C92-092349.6 Lawyers gold-silver deposit looking northwesterly with Amethyst Gold Breccia (AGB) and Cliff Creek (CC) zones indicated. Cheni Gold Mines camp is in the lower centre and the mill site at the left of the photograph. Flat-lying ash-flow tuffs of the Saunders Member (Unit 6) form the dissected plateauand scarps in the foreground. Silica-clay-alunite capping Alberts Hump, similar to nearby precious metal bearing advanced argillic altered rocks of the A1 deposit (AI), are barely visible to the north of Toodoggone River and 5 kilometres beyond Metsantan Mountain. Gently inclined temgenous sedimentary beds of the Late Cretaceous Sustut Group are unconformable on the Toodoggone Formation to the west and northwest. TABLE OF CONTENTS Page 46 49 49 49 51 51 52 52 52 54 54 55 55 55 55 55 51 57 60 60 60 63 67 68 75 75 16 76 76 1 2 3 6 11 12 25 26 27 27 ... 111 TABLE OF CONTENTS - Continued Page Page 11.Na,O-K,O-CaO temary diagram for volcanic 7. Light stableisotope compositions of volcanic rocks of the Toodoggone Formation ................................ 28 rocks and mineral separates in the study area ...... 58 12. Total alkalis-silica diagram for volcanic rocks of the Toodoggone Formation......................................................... 29 PHOTOGRAPHS 13. AFM diagram for volcanic rocks of the Toodog- Plate gone Formation ........................................................................................ 29 Frontispiece .................................................................. Opposite title page 14. Variation in SO,, Feo" and TiO, versus Few/ 1. Adoogacho Member ........................................................................... 13 MgO for volcanic rocks of the Toodoggone For- A. Flat-lying dacite ash-flow tuffs in the type mation ................................................................................................................ 29 area 15. Comparison of K-Ar and Ar-Ar age determina- B. Blocky weathering in partly welded ash- tions on volcanic rocks of the Toodoggone For- flow tuff mation ................................................................................................................ 30 16. Distribution of Early Jurassic Black Lake intru- 2. Adoogacho Member ........................................................................... 14 sions and subvolcanic domes ................................................... 31 A. Compactionfoliation in partlywelded 17. Distribution of Late Triassic and Early Jurassic ash-flow tuff plutons along the axes of the Stikine and Skeena B. Typical partly welded, crystal-rich dacite arches.................................................................................................................. 32 ash-flow tuff 18. Published K-AI age determinations from inhw C. Unwelded dacite ash-flow tuff slons ..................................................................................................................... 33 3. Adoogacho Member ........................................................................... 15 19. Major faults in the study area ................................................. 37 A. Photomicrographshowing crystal frag- 20. Stratigraphic cross-sections of the Toodoggone ments diagnostic of dacite ash-flow tuff Formation (and in back pocket) ............................................ 38 B. Photomicrograph of typical partly welded 21. Major transcurrent faults in the Omineca and ash-flow tuff Cassiar mountains ................................................................................. 40 22. Mineral deposit types and the distribution of 4. Moyez Member ....................................................................................... 17 mineralized occurrences in the study area ................ 44 A. Well-bedded lapilli-ash tuff in thetype 23. Diagrammatic northwest-southeast section area through the study area showing the relative rela- B. Conglomerate at the base of the Moyez tionship of major mineral deposits with structure Member and stratigraphy 46 C. Interbed of impure limestone with laminae of chert and mudstone 24. Geology of the Lawyers deposit .......................................... 48 25. Geology of the Chappelle deposit ...................................... 50 5. Metsantan Member .............................................................................. 18 26. Geology of the Shas deposit..................................................... 51 A. Typical porphyritic latite flow of the Met- 27. Surfacedistribution of secondarymineral santan Member assemblages at Silver Pond ........................................................ 52 B. Variety of porphyriticlatite flow with 28. Barite-gold concentrations at the AI deposit .......... 54 orthoclase megacrysts 29. Distribution of whole rock and quartz 180 in C. Photomicrograph showing phenocrysts Toodoggone and other epithermal deposits .............. diagnostic 59 of the flowslatite 30. Conceptual model of Early Jurassic metallogenic 6. Attycelley Member .............................................................................. 20 relationships in the Toodoggone River map area 61 A. Interbedded sandstone overlainby tuff and breccia -. "" B. Typical lapilli-ashunwelded dacitic tuff 'IABLES C. P&y welded air-fall tuff with pronounced I. Regional stratigraphy of the Toodoggone River comnaction~ .~~~~~~~~~.~~ foliation~.~~~~~~.~~ map area5 (NTS 094E) ...................................................................... 2. Composition of volcanic rocks and meanmajor 7. Saunders Member ................................................................................. 22 element abundance of maior ma0 units,Toodoe- - A. Resistant,cliff-forming dacite ash-flow gone Formation ........................................................................................ 26 tuffs 3. Phenocryst assemblage and the main features of B. Typical incipientto partly welded dacite CIPW norms in major stratigraphic members of ash-flow tuff C. Dacite ash-flow tuff the Toodoggone Formation ......................................................... 21 .. 4. Publishedaierage compositions of selected vol- 8. Saunders Member ................................................................................. 24 canic rocks .................................................................................................... 28 A. Photomicrograph.showing crystal frag- 5. Comparativefeatures of major mineral deposit ments diagnostic of the dacite ash-flow types ..................................................................................................................... 47 tuffs 6. Fluid inclusion data for various mineral pros- B. Photomicrographshowing crystal frag- pects and deposits ................................................................................. 56 ments in a partly devitrified matrix iv TABLE OF CONTENTS - Continued Page Page 9. Dikes ................................................................................................................... 35 11. View of acid-sulphate altered rocks at Silver A. Coarse porphyritic andesite Pond and well-laveredstrata of the Sustut Grow B. Coarse porphyritic andesite ................................................................................................................................... 53 C. Aphyric basalt with calcite filled vugs D. Porphyritic rhyolite MAPS (in back pocket) 10. Dikes ................................................................................................................... 36 1. Geology of the Toodoggone Formation, Toodog- A. Photomicrograph of aphyric basalt dike goneRiver map area, north-central British B. Photomicrograph of porphyritic rhyolite Columbia dike 2. Mineral deposits, prospects and sample locations SUMMARY The Early Jurassic Toodoggone Formation is a new stratigraphic division of the Hazelton Group in the ToodoggoneRiver maparea, north-central British Columbia. The ToodoggoneFormation consists of six lithostratigraphic members comprising high-potassium (3.1% K,O at 57.5% SiO,), calcalkaline latite and dacite subaerial volcanic rocks. Hornblende-biotite-quartz 2 sanidine phenocrysts