BCGS: Carbonatites, Nepheline Syenites & Related Rocks in British Columbia (Chapter 1) (Pell, 1994)

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The British Columbia Geological Survey's 1994 report on Carbonatites, Nepheline Syenites, Kimberlites and Related Rocks in British Columbia by Jennifer Pell.

The British Columbia Geological Survey's 1994 report on Carbonatites, Nepheline Syenites, Kimberlites and Related Rocks in British Columbia by Jennifer Pell.

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  • 1. Province of British Columbia MINERAL RESOURCES DIVISIONMinistry of Energy, Mines and Geological Survey BranchPetroleum ResourcesHon. Anne Edwards, Minister CARBONATITES, NEPHELINE SYENITES, KIMBERLITES AND RELATED ROCKS;IN BRITISH COLUMBIA This is a Contribution to the CanaddBritish Columbia Mineral Development Agreement1985-1990 By Jennifer Pel1 BULLETIN 88
  • 2. ~~~~~~~ ~ Pell, Jennifer,1956- -~ Canadian Catalooulno in Publication Data ~~ Carbonatites, nepheline syenites, kimberlites and related rocks in British Columbia (Bulletin, ISSN 0226-7497;88) Issued byGeologicalSurveyBranch. This is a Contribution to the CanadaIBritisb Columbia Mineral Development Agreement 1985-1990." Indudes bibliographical references:p. ISBN 0-77262170-5 1 Carbonatites -British Columbia. 2. Nepheline . Field Research furthis project was caniec! uut syenite -British Columbia. 3. Kimberlite - British durizgtheperiod 1984 to 1990 Columbia. 4. Geology, Economic - British Columbia. 5. Geochemistry - British Columbia, 6. Petrology - British Columbia. I. British Columbia. Ministry of Energy, Mines and Petroleum Resources. 11. British Columbia. GeologicalSurveyBranch. 111.CanadalBritish Columbia Mineral Development Agreement. IV. Title. V. Series: VICTORIA Bulletin (British Columbia. Ministry of Energy, Mines and BRITISH COLUMBIA Petroleum Resources) ; 8 . 8 CANADA553.609711 TN27.B7P44 C94-960219-1 1994 July 1994
  • 3. Ministry of Energx Minesand Petroleum Resources TABLE OF CONTENTS ” INTRODUCTION........................................................................ 1 Geochemistry...................................................... Distribution and general characteristics of Geochronology ................................................... 36 carbonatites and nephelinesyenites .................... 2 CARBONATITES AND SYENITE GNEISS COMPLliXES IN Distribution and general characteristics of TO METAMORPHOSED PRECAMBRIAN EARLY kimberlites and alkaline ultrabasic diatreme CAMBRIAN STRATA. OMINECA BELT............................... 31 breccias ................................................................ 3 Manson Creek area (93N/9) ..................................... 37 Geological work .......................................................... 5 Carbonatites ........................................................ 37 Acknowledgments....................................................... 38 5 Silicate phases ..................................................... Fenites ................................................................. 38 CARBONATITE AND SYENITE COMPLEXES IN Geochemistry ...................................................... 39 PALEOZOIC STRATA, ROCKYAND CASSIAR Geochronology ................................................... MOUNTAINS. FORELAND BELT ............................................ 7 - Mount Bisson Mnnroe Creekarea (93N/9; The Aley Carbonatite complex (94B/5)...................... 7 930/5. 12).......................................................... 41 Rauhangite core zone ............................................ 7 41 rocks Alkalic dike ............................................... Sovite zones ........................................................... 7 Pegmatites........................................................... 42margin ‘Amphibolitic’ ........................................... 7 Intrusive breccias ................................................ 42 Alteration halo ....................................................... 8 Fenites ................................................................. 42 Rare-earth-bearing dikes ..................................... 11 Quartz monzonites quartz syenites .............. and 42 Geochemistry ...................................................... 11 Geochemistry...................................................... 42 Geochronology.................................................... 11 Wicheeda Lake complex(Prince and George Geochronology ................................................... 43 Blue River area (83D/3. 6. 7) ................................... 43 claims, 93V5; 93J/8,9) ...................................... 11 Carbonatites ........................................................ 44 Carbonatites and associated syenitic rocks.........13 Nepheline syenites .............................................. 44 Alkaline dikes...................................................... 13 Mafic Silicate Rocks........................................... 44 Geochemistry ...................................................... 13 Fenites ................................................................ 47 Geochronology.................................................... 14 Geochemistry ..................................................... 47 Bearpaw Ridge sodalite syenite (93V4).................... 14 Geochronology .................................................. 53 Sodalite syenite ................................................... 15 Trident Mountain (82M/16) .................................... 53 Nonda formation volcaniclastic rocks ................ 16 Geochemistry..................................................... 54 Orthogneiss.......................................................... 16 Geochronology .................................................. 54 Postorogenic syenite ........................................... 17 Geochemistry ...................................................... 17 CARBONATITES AND SYENITE GNEISSCOMPLEXES Geochronology.................................................... 18 ASSOCIATED WITH CORE GNEISSES IN THE Oh! INECA Ice River complex (82N/1) ....................................... 18 BELT .......................................................................................... 55 Ultramafic series ................................................. 18 Mount Copeland nepheline syenite gneisses Zoned syenite complex ....................................... 19 (82W2) ............................................................. 55 Carbonatites......................................................... 19 Nepheline syenite gneisses ................................ 55 Lamprophyres ..................................................... 20 Alkaline amphibolite .. ......................................... 58 Geochemistry ...................................................... 22 Grey syenruc gneiss ........................................... 58 Geochronology.................................................... 23 Geochemistry ..................................................... 59 Rock Canyon Creek fluorite and rare-earth Geochronology ................................................... 60 element showing (82J13E) ................................. 24 Carbonatites and associated rocks. west flank, . . Minerahzatlon ..................................................... Frenchman Cap 25 (82W2, 7, 10)............... dome 60 Geochemistry ...................................................... 25 Perry River intrusive carbonatites (82Wr)........60 Geochronology.................................................... 27 Fenites - Perry River area .................................. 60 Kechika Riverarea (94L/ll, 12, 13) ........................ 27 Ratchford Creek (Ren) intrusive carbona:ite Distribution and field relationships of (82W7) ........................................................ alkaline rocks ............................................... 28 Intrusive syenite - Perry River area Petrography: syenites .......................................... 30 (82W7, 10).................................................. 62 Petrography: trachytes......................................... 31 Mount Graceextrusive carbonatite Petrography: (82W7, 10).................................................. 63 feldspar-quartz-carbonate-sericiterocks .....31 Geochemistry ...................................................... 66 Petrography: carbonatites.................................... 34 Geochronology ................................................... 68 _- Bulletin 88 iii
  • 4. Three Valley Gap (82L/16)....................................... 68 Carbonatites and syenite gneisses........................... 111 Carbonatites, fenites, syenites ............................. 69 Kimberlites. lamprophyres and other ultrabasic Geochemistry....................................................... 70 diatremes.......................................................... 111 Geochronology .................................................... 70 . . . . Tectonlc lmphcattons.............................................. 113 ULTRABASIC DIATREMESIN NORTHERN BRITISH REFERENCES ........................................................................ 119 COLUMBIA............................................................................... 71 The Kechika River diatreme and related rocks APPENDICES ......................................................................... 125 (94L/12, 13)........................................................ 71 COLOUR PHOTOS ................................................................. 135 Lithology ............................................................. 71 Geochemistry....................................................... 73 FIGURES Geochronology.................................................... 1. Index map, carbonatite and syenite gneiss 74 Ospika Pipe (94B/5) .................................................. 74 complexes..................................................................... 2 Lithology ............................................................. 2.74 Index map, alkaline ultrabasic diatreme swanns ......... 4 Geochemistry....................................................... 3. Geologicalmap, Aleycarbonatite complex................ 75 6 Geochronology.................................................... 76 4.Major element ternary plots of carbonatites and ULTRABASIC DIATREMES IN THE GOLDEN- "amphibolite" margin, Aley complex......................... 10 COLUMBIAICEFIELDSAREA ............................................. 77 . 5 Chondrite-normalizedrare-earth element plots, Bush Riverarea (Larry claims) (83C13) ................... complex 77 Aley ............................................................ 10 Lens Mountainand Mons Creekareas (Jack and 6. Ternary plots for fenites. Aley complex.................... 10 Mike claims) (82N/14. 15)................................. 81 7 .Location map of the intrusive bodies on the Prince Valenciennes Riverpipes and George groups of claims. Wicheeda Lake..........11 (Mark claims) (82N115) ..................................... 83 8. Geological map of the Prince grid, Wicheeda Lakt: 12 .. The HPPipe (82N/10) ............................................... 84 9. Chondrite-normalized rare-earth element plot. Geochemistry o diatremes andf related dikes ........... 87 Wicheeda Lake alkaline complex .............................. 13 Geochronology.......................................................... 87 10. Geologicalmap of Bearpaw Ridge ............................ 14 11. Alkali-silica and agpaitic index plots, ULTRABASIC DIATREMES IN THEBULL RIVER - ELK RIVER AREA. SOUTHERN BRITISH COLUMBIA 17 Bearpaw Ridge ........................................................... (82G. 3) ....................................................................................... 91 12. Major element ternary plots. Bearpaw Ridge ............ 17 Shatch Mountain area (Joff claims) (82Jlll) ............ 91 13. Geology ofthe Ice River complex ............................. 19 The Russell Peak diatremes (82J/6) .......................... 92 14. Alkali-silica and agpaitic index plots. Ice River Blackfoot andQninn diatremes (82G114)................. 94 ultramafic suite ........................................................... 22 Mount Haynes- Swanson Peakarea (Swan 15. Ternary majorelement plots. Ice River ultramafic claims) (82G/14) ................................................ 95 suite............................................................................. 22 The Mary Creek - White River breccia dike 16.Alkali-silica and agpaitic index plots, Ice River (823/3W) ............................................................. 96 . . . syenltlc sulte ............................................................... 23Summer The pipes96 (82G/ll) ..................................... 17. Ternary major element plots, Ice River syenitic Geochemistry of diatremes and dikes ....................... 99 suite ............................................................................. 23 Geochronology........................................................ 101 18. Major element ternary plot. Ice River complex ................................................................. 23 KIMBERLITES IN BRITISH COLUMBIA ........................... 103 I9.carbonatitesthe Rock Canyon Creek Geology of fluorite/ The Cross kimherlite (82J/2) ................................... 103 Geochemistry ..................................................... 105 rare-earth showing...................................................... 25 Geochronology.................................................. 105 20. Chondrite-normalizedrare-earth plot. Rock Canyon Creek fenites ............................................................... 27 ECONOMIC CONSIDERATIONSAND EXPLORATION 21. Generalized geology, Kechika area ........................... 28 POTENTIAL ............................................................................ 107 22 . Geology of the central part of the belt of alkaline Niobium and tantalum ............................................. 107 rocks. Kechikaarea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Rare-earth elements and yttrium ............................. 107 23. Alkali-silica and agpaitic index diagrams. Kechika Zirconium ................................................................ 108 syenites ....................................................................... 32 Phosphates ............................................................... 108 24. Major element ternary plots. Kechika igneous Nepheline and nepheline syenite............................. Vermrcuhte . . .............................................................. 109 109 suite ............................................................................. 32 25. Carbonatite ternary plot, Kechika suite ..................... 34 Molybdenum ........................................................... 109 26. Chondrite-normalizedrare-earth plots, Kechika Wollastonite ............................................................. 109 suite ............................................................................. 34 Titanium................................................................... 109 Diamond .................................................................. 109 27 .Geological map ofthe Lonnie carbonatite complex..37 Gemstones ............................................................... 110 28 .Carbonatite plot. Lonnie complex ............................. 39 29.Major element ternary plots, Manson Creekarea SUMMARY AND CONCLUSIONS ....................................... 11 1 carbonatite complexes................................................ 40 iV Geological Suwey Branch
  • 5. Ministry of Enemy. Minesand Petmleum Resouxes 30. Ternary fenite plots. Manson Creek area carbonatite . 64 General geology anddiatreme locations in the complexes ................................................................... 40 Golden . Columbia Icefields area .............................. 77 31.Alkali-silica and agpaitic index plots, Lonnie 65. Diatreme breccias and dikes. Bush Riverarea ..........77 complex silicate rocks ................................................ 41 66. Sketch showing distribution of diatreme and related 32. Chondrite-normalizedrare-earth plots, Lonnie rocks on theJack claims. Lens Mountainarea ..........81 and Vergil showings, Manson Creek area .................. 41 67. Diatreme breccias and dikes. Valenciennes River 33. Geology and carbonatitekyenite localities in area ............................................................................. 82 the Blue River ..................................................... 42 area 68. Geology ofthe HP pipe ............................................. 84 34. Geological map the Howard Creek carbonatite of . 69 Major element discriminant diagrams, Golden occurrence................................................................... 44 diatreme swarm .......................................................... 88 35. Geological map and cross-section, Paradise Lake . 70 Major element ternary pIots, Golden diatremes ........88 area .............................................................................. 45 71. Ni-Cr plot, Golden diatremes .................................... 88 . 36 Major elementternary plots, Blue River area . 72 SrRb vs.TiOz, Golden diatremes and related alkaline rocks .............................................................. 48 dikes ........................................................................... 89 37.Carbonatite plot, River Blue area............................... 48 73. General geology and diatreme locations in tht: 38. Ternary fenite plots, Blue River area rocks................ 48 Bull River- White River area .................................... 90 39. Alkali-silica and agpaitic index plots. Blue 74. Geology ofthe Joff pipe, Shatch Mountain .......91 ar.a River area syenites...................................................... 50 75. Geology of the Russell Peak diatreme ...................... 92 40. Chondrite-normalizedrare-earth plots, Blue River area showings ............................................................. 50 76. Geology of the Blackfoot diatreme .......................... 94 77. Stratigraphy, Swanson Peak .............................. area 95 41 . Geology of theTrident Mountain Area, Selkirk Mountains ................................................................... 51 78. Diatreme breccias, Summer andGalbraith 42.Alkali-silica and agpaitic index plots, Trident creeks area ................................................................. 97 Mountain syenites....................................................... 52 79. Major element ternary plots, southern diatremes 99 ...... 43. Major element ternary plots, Trident Mountain 80. Major element discriminant plots, southern syenites ....................................................................... 100 swarm 53 diatreme ........................................................ . 44 Geology of the Frenchman Cap area ......................... 56 Ni . = Cr plot, southern 100 81 diatremes ............................. 45. Geological map, Mount Copeland ..................... 57 area 82. Sketch of the Crossing Creek kimberlite pipe 46. Alkali-silica and agpaitic index plots, Mount facing north .............................................................. 102 Copeland syenites ....................................................... 59 . 83 Major element discriminant plots, Cross 47.Major elementternary plots, Mount Copeland kimberlite ................................................................. 103 syenites ....................................................................... 59 84.Majorelement ternary plots, Cross kimberlite ........103 48. Carbonatite plot, Mount Grace and Perry River 85.Ni = Cr plot, Cross kimberlite ................................. 104 areas ............................................................................ 65 86. Structural position ofdiatremes............................... 112 49. Chondrite-normalizedrare-earth plots. carbonatites, 87. (a) Carbonatites and related rocks in Western west flank, Frenchman Cap dome .............................. 65 North America (b)Diamonds and diatremes i:1 50. Detailed section of the Mount Grace carbonatite, Western North America ............................................ 116 Blais Creek showing ................................................... 66 51. Alkali-silica and agpaitic index plots. Perry River TABLES syenites ....................................................................... 66 1. Chemical analyses. Aley carbonatite complex ............ 9 52. Major element ternary plots, Perry River and 2. Chemical analyses. Bearpaw Ridge.......................... 16 Mount Grace area alkaline rocks................................ 67 3. Chemical compositions Ice River of 53. Fenite plots. Perry Riverarea ..................................... 67 complex rocks ............................................................ 21 54. Carbonatite plot. Three Valley Gap............................ 69 4 . Ice River complex geochronologysummary .......... - 24 55.Major element ternary plots. Three Valley Gap ......... 69 5. Chemical analyses. Rock Canyon Creek................... 26 56. Chondrite-normalizedrare-earth plot, Three 6. Geochemistry ofselected samples, Kechika area .....33 Valley Gap .................................................................. 69 7. Chemical analyses of alkaline rocks, Manson 57. Major elementdiscriminant plots. Kechika diatreme Creek area................................................................... 39 and related dikes and tuffs .......................................... 72 8. Chemical analyses of alkaline rocks, Blue River 58. Major elementternary plots, Kechika diatreme and area ............................................................................. 49 related rocks ................................................................ 72 9. Chemical analyses of Trident Mountain syenites......53 59. Ni-Cr plot, Kechika diatreme, dikes and tuffs ...........72 10. Chemical composition of selected rocks from the 60. Chondrite-normalizedrare-earth plot, Kechika Mount Copelandsyenite complex ............................. 58 diatreme andrelated dikes and tuffs ........................... 73 11. Chemical analyses of alkaline rocks, west fla.~k. 61.Major elementdiscriminant plots. Ospika pipe ......... 74 Frenchman Cap Dome ............................................... 64 62. Major element ternary plots, Ospika pipe .................. 75 12.Chemical analyses, Three Valley Gap,alkalir e 63. Ni-Cr plot, Ospika pipe .............................................. 75 rocks ........................................................................... 68 Bulletin 88 V
  • 6. 13. Geochemistry of selected diatreme breccias and 24. Intrusive carbonatite band surrounded by dark related dikes and tuffs, Kechika area .......................... 71 amphibolitefenite and some grey syenitic fenite,14. Chemical analyses, Ospika pipe ................................. 74 Perry River area .......................................................... 6015. Field characteristics of HP pipe breccia phases ......... 84 25. Swirled carbonatite in amphibole fenite, Peny16. Chemical analyses, Golden area diatremes ................ 86 River area.................................................................... 6117. Chemical analyses, Bull River- Elk River 26. Interlayered amphibolitic fenite and syenitic fenite, and diatremes related rocks ........................................ 98 Peny River area .......................................................... 6118. Chemical analyses, CrossingCreek kimberlite........ 104 27. Ratchford Creek carbonatite interlayered with19. Timingof alkaline intrusion and orogenesis ............114 amphibolitic fenite and containing fenitized fragments of country rock .......................................... 62PLATES 28. Part of the thickened section of the Mount Grace 1. Xenoliths of quartzite and syenite in the breccia extrusive carbonatite .................................................. 63 phase of the "amphibolitic" margin, Aley complex..... 8 29. Interbedded sedimentary marble with carbonatite 2. Quartzite xenoliths weathering ontof the agglomerate and tuff layers; Mount Grace "amphibolite"margin, Aley complex ........................... 8 carbonatite near Blais Creek ...................................... 63 30. Large feldspar clots in biotite-rich carbonatite, 3. REE-enriched dikes in carbonate hostrocks, Aley complex......................................................................... 8 Three Valley Gap area ................................................ 68 31. Dolostone clast with reaction rim, Ospikapipe ......... 73 4. Boulder containing syenite dike crosscutting bonded volcaniclastic rocks, Bearpaw Ridge............. 15 32. Rusty weathering,clast-supported megabreccia, Bush River area ......................................................... 78 5. White-weathering syenite with disseminated sodalite, Bearpaw Ridge ............................................. 15 33. Dark greenweathering breccia, Bush Riverarea ... ..78 6. Folded andfoliated dioritic orthogneiss exposed, 34. Limestone-cored annoured xenolith in diatreme Bearpaw ............................................................ 15 breccia, Bush River area ......................................... ..79 35. Alteredmica macrocryst diatreme breccia,in 7. Contact between syenites of the Ice River complex River Bush area ......................................................... 79 and steeply dipping carbonate rocks, Bntress Peak ....18 36. Boulder from dike, Bush Riverarea with breccia a 8. Jacupirangite cut by fine-grained nepheline syenite core and finer grained, macrocryst-rich rim .............79 dikelets, north of Mount Mollison, River Ice complex....................................................................... 20 37. Laminated margin of a fine-grained dike, Bush River area................................................................... 79 9. White-weathering, coarse-grained carbonatite dike, Mount Sharp area, Ice River complex ........................ 20 38. Photomicrograph ofan altered pyroxene crystal in a matrix containing abundant altered mica10. Intrafonnational conglomerate with fluorite matrix, from a dike, Bush River area ...................................... 80 Rock Canyon Creek .................................................... 27 39. Fragments of sedimentary rocks a buff- in11. Potassium feldspar porphyroclasts in a fine-grained weathering, quartz xenocryst-rich breccia, carbonate-sericite-feldspar-quartz Creek matrix from a Mons ................................................................ 80 sheared leucosyenite, Kechika area ............................ 30 40. Photomicrograph ofquartz xenocryst-rich breccia,12. Typicaltrachyte, Kechika area .................................. ,30 similar to that shown in previous plate ...................... 8013. An apatite-rich zone in the quartz-feldspar-sericite- 41. Serpentinized olivine macrocrysts in a fine- carbonate-(apatite) rocks, Kechika area ..................... 31 grained, massive diatreme phase, Valenciennes14. Blue pleochroic amphibole and grained finer River area.................................................................... 82 aegirine in ultrafenite, Lonnie area ............................. 38 42. Boudinaged dikesubparallel to bedding in15. Fz folds in banded nephelinesyenite, Paradise buff-coloured carbonates, Valenciennes River area ...83 Lake............................................................................. 43 43. Alteredphenocrysts in a dike, Valenciennes16. Phlogopite in carbonatite, from Verity ....................... 46 River area.................................................................... 8317. Welllayered carbonatite, Howard Creek ................... 46 44.Sharp contact between breccia phases, HP pipe ........8518. Migmatitic lencosome layered syenites, in 45. Large gabbroicxenolith in a strongly foliated Paradise Lake .............................................................. pipe 47 breccia, HP .......................................................... 8519. Migmatitic segregations of coarse perthite 46. Optically zoned andradite garnets, HP pipe............... 85 crystals in layered nepheline syenite gneiss, 47. Biotite macrocryst coring accretionary lapilli, Paradise .............................................................. pipe HP ....................................................................... 8520. Coarse-grained ilmenite segregation in 48. Graded bedding in extrusive epiclastic layer, leucosyenite, Trident pipe .................................. Mountain 51 Joff ...................................................................... 9121. Typicalbanded nephelinesyenites, Trident 49. Epiclastic crater-infill breccia, Joff pipe, Mountain ..................................................................... 51 immediately overlain by well-bedded, pink and22. Leucosyenite dikes cutting mafic, biotite-amphibole buff-weatheringstrata of the basalDevonian unit .....92 gneiss, Trident Mountain ............................................ 52 50. Well-bedded crater-infill material, Russell Peak23. Xenolith of mafic gneiss in biotite-rich syenite, diatreme .................................................................... ..93 Trident Mountain ........................................................ 52 51. Porphyritic volcanic rock, Russell Peak diatreme 93 ..... -vi Geological Survey Bnznch
  • 7. Minisfry of Energy, Mines and Petroleum52. Vesiculated glass lapilli in diatreme breccia, APPENDICES Quinn Creek................................................................ 94 1. Rare-earth element analysesfrom some carbonatite53. Pillowed flow, Swansou Peak .................................... 96 suites ......................................................................... x2754. Chrome spine1 macrocryst, Summer diatreme 2. (A) U-Pb zircon data, British Columbia breccia ......................................................................... 97 carhnatites and nephelinesyenites .................. 12855. Pyroxenite inclusion forming the core of an (B) Uranium-lead analytical data, accretionary lapillus, central breccia phase, Cross B.C. diatrernes .................................................. 129 kimberlite .................................................................. 102 (C) Summary of RblSr analytical data,56. Alteredolivine macrocrysts and phenocrysts, B.C. diatremes ................................................... :I30 phlogopite phenocrysts and opaque oxidesa in (D) Summary of K-Ar analytical data, magmatic matrix, Cross kimberlite .......................... 102 B.C. diatremes .................................................. ~131Bulletin 88 vii
  • 8. ~.British Columbia -viii Geological Survey B n
  • 9. Ministry of Energy, Mines and Petroleum Resources " INTRODUCTION A previously poorly documented alkaline igneous may contain diamond, but only as a rare constihtent. h eprovince is present in the Canadian Cordillera. It comprises term kimberlite was introduced into geological literature thecarbonatites, nepheline and sodalite syenites, some ijolite- in 1887to describe the hostrocksof diamonds at Kimberley,series rocks, one kimberlite locality and numerous ul- South Africa. Since that time many rocks carrying oli-tramafic and lamprophyric diatreme breccias, all of whichintruded the Cordilleran miogeoclinal succession prior to vine+phlogopite+carbonat&clinopyroxene+feldspathoid+the deformation and metamorphism associated with the spinel have erroneously been referred to as kinberlites,Jura-Cretaceous Columbian orogeny. rocks which should be placed in the 1amprophSre group Carbonatites are ultrabasic igneous rocks composed of (Clement etal., 1984). Inaccurate orincorrectclasrificationmore than 50%carbonate minerals. They may contain sig- only complicates understandingof petrogenetic: eco- the andnificant amounts of olivine, magnetite, pyroxene, sodic am- nomic implications.phibole, biotite, vermiculite, apatite, columbite, zircon, Kimberlite has traditionally heeu considered the onlyrare-earth minerals and pyrochlore. Carbonatites occur most important primary source of diamond. Recent studiescommonly as intrusive bodies, generally associated with (Scott-Smith and Skinner, 1984a, 1984b; Jacques et al.,other alkalineigneous rocks (Pecora, 1956;Heinrich, 1966) 1986; Scott-Smith et al., 1986) have shown that diamondssuch as nepheline syenites, ijolites, urtites, melteigites may also be present in economic concentrations in lamproi-(nepheline+maficsilicateskfeldspathoidsinvariouspropor-tions) and jacupirangites (alkaline pyroxenites). Metaso- tes. Lamproites are ultrapotassic rocks that are chemicallymatic rocks (fenites), which are generally enriched in andmineralogically distinct fromkimberlites. characterizedsodium andferric iron and depleted in silica, are also com- by thepresence of phenocrystic and/or groundmass leucite,monly associated with carbonatites, often marginal to the titanium-rich phlogopite, clinopyroxene, amphihole (!.ita-intrusive complexes. Extrusive carbonatites are less com- nium and potassium-rich richterite), olivine and !;anidinertmon, but havebeen described westemUganda (von Knor- in glass (Scott-Smith and Skinner, 1984b).Diamonds;have oc-ring and du Bois, 1961). northern Tanzania (Dawson,1962, casionally been reported from carbonatites and pt:ridotites, 1964, Hay, 1983). Kenya (Le Bas and Dixon, 1965; Le Bas, 1977; Deans and Roberts, 1984) and Germany (Keller, but, to date, the only known economic primary sources re-1981). main kimberlites and lamproites. Diatreme breccia pipes in Many cabonatite bodies are valuable sources a num- of British Columbia have been targets diamond exploration forber of commodities. Niobium has producedat Oka and been since the mid-1970s (Grieve, 1981; Dummett et tzl., 1985)St. Honor&, Quebec and at Araxa, Brazil; the Mountain Pass even though mostare nottrue kimberlites; microdiamondscarbonatite in California is the largest producer of rare-earth have been discovered in heavy mineralseparates from twoelements in the westem world; and copper and byproduct of these pipes (Dummett et al., 1985). Diamondr are alsoapatite, magnetite, vermiculite and zirconium oxide are pro- known to occur in kimberlites from the Colorado-Wyomingduced at Palabora, South Africa (Heinrich, 1966; Currie, State-Line district (McCallum and Marbarak,1976), from1976a). Nepheline syenite is an important raw material used the Mountain diatreme in Yukon (Godwin andPrice, 1987)in the glass and ceramics industries. Small amounts have and from placer deposits in Alaska (Forbes et d, 1987)also been usedin paints and as fillers in plastics. The BlueMountain region Ontario is the largest western world pro- of where stones over 1 carat in size have been recovered.ducer of nepheline syenite (Cume, 1976a). Since the 1950s The parental magmas of alkaline igneous rocks area number of carbonatite complexes in British Columbia meltswhichformdeepinthemant1e.Thesemeltsc~ostcom-have been prospected for various commodities at different monly intrude cratonic or shield areas with a longhistorytimes; their vermiculite, niobium, zirconium and rare-earth of tectonic stability (Heinrich, 1966; Dawson, 1980) andpotential has been explored. None haveany history ofpro- their emplacementis often indirectly associated with normalduction. faults, grabens or failed rifts. In British Columbia, the car- Kimberlites arevolatile-rich, potassic, ultrabasic igne- bonatites and related rocks wereintruded into the sedinlen-ous rocks which occur as small volcanic pipes, dikes andsills. They have adistinctly inequigranular texture resulting tary prism deposited along the rifted continental margin,from the presenceof macrocrysts (olivinefphlogopite, pi- making this a somewhat anomalous alkaline province in acroilmenite, chrome spinel, magnesian garnet, clinopy- structural setting which differsfrommostothers worldwide.roxene and orthopyroxene) in a fine-grained matrix. The set Consequently, thissuite has important implications becausematrix contains phenocrystic and/or groundmass it documents the characteristics of carhonatites and relatedolivinefphlogopite, carbonate, serpentine, clinopyroxene rocks emplaced in a continental margin environ~nent, andandmany otherminerals (Clementetal., 1984). Kimberlites details the subsequent effects of orogenesis. "Bullefin 88 I
  • 10. DISTRIBUTION AND GENERAL Rocky Mountain Trench; the eastern edge of the OminecaCHARACTERISTICS OF Belt; and in the vicinity of Frenchman Cap dome, a core gneiss complex, also within the Omineca Belt. The eaiiternCARBONATITESAND NEPHELINE or Foreland Belt (Figure 1) hosts carbonatites and d a t e dSYENITES rocks within Paleozoic strata, predominantly in the Main and Western rangesof the Rocky Mountains. This con- belt In British Columbia, carbonatites, nepheline and so- tains the Aley carbonatite complex (Mader, 1986, 1!)87),dalite syenite gneisses and related alkaline rocks are found Wicheeda Lake showing (Prince and George claims, Bet-in a broad zone which parallel to, and on either side of the isRocky Mountain Trench. Carbonatites relatedrocks are and manis, 1987; Maderand Greenwood, 1988),BearpawRidge sodalite syenite, the Ice River syenite and carbonatite corn-also reported from anumber of areas in the western UnitedStates, for example, the McClure Mountain, Iron Hill, Gem plex (Cnrrie,1975,1976a) and Rock Canyon Creek fluo- the rite and rare-earth showing, a carbonatite-related depositPark and Wet Mountain areas of Colorado (Lmen, 1942;Olson and Wallace, 1956; Parker and Sharp, 1970; Nash, (Hora and Kwong, 1986). The Aley, Ice River and Bearpaw1972; Hildebrand and Conklin, 1974; Armbrustmacher, Ridge intrusions are subcircular to elliptical in plan, gcner- ally have extensive metasomaticalteration or contact meta-1979, 1984; Armbrustmacher et al., 1979), the Lemitar morphic halos and are hosted by Middle Cambrir.n toMountains, central New Mexico (McLemore, 1987) and theMountain Pass area, California-Nevada State-Line (Olson Middle Devonian miogeoclinal rocks. Alkalic rocks i:1theetal., 1954; Jaffe, 1955; Warhol, 1980; Woyski, 1980). Wicheeda Lake area define a linear zone, and consist of small plugs, dikes and sills. The Rock Canyon Creek show- Three discrete areas hosting carbonatites can be defined ing is an elongate zone of fluorite and rare-earth metaso-within British Columbia: the Foreland Belt, east of the matic alteration in Devonian carbonate rocks, possibly Figure 1. Index map, carbonatite and nepheline syenite gneiss complexes.2 Geological Survey Bxanck
  • 11. ~~ ____ ____~ ~~~ ~~ ~related to a buriedcarbonatite. Carbonatites in this belt ex- syenite gneiss (Fyles, 1970;Cnme, 1976b) occurs along thehibit varied mineralogy andare enriched in niobium, fluo- southern margin of the gneiss dome. The extrusive Mountrine and rare-earth elements relative to other British Grace carbonatite tuff, intrusive carbonatites with thickColumbia occurrences. During the Colnmbian orogeny the fenitited margins and syenite gneisses occur along theintrusions were subjected to sub-greenschist to greenschist northern and western flanks of the dome. Bothof .he inm-facies metamorphism. The obviouseffects of deformation sive andextrusive carbonatites are moderately enriched inare minor, the intrusions appear to have behaved as rigid rare-earth elements, but no significant niobium mineraliza-bodies during orogenesis and were simply rotated, tilted tion has beenreported.and/or transported eastwards in thrust slices. Locally, small Several tens of kilometres to the south of tht: French-faults cut the alkalic rocks. man Cap Dome, near Three Valley Gap, another carbonatite The Kechika River complex is located a few kilometres is hosted bymigmatitic gneisses of uncertain affinity. It ex-west of the Rocky Mountain Trench, in the Cassiar Moun- hibits many similarities in fieldrelationships and geochemi-tains (Fox, 1987; Pell et al., 1989). It is morphologically cal signatures to the intrusions of the Blue River andsimilar to the Wicheeda Lake showing,consisting of dikes Manson Creek areas along the eastern margin of theand plugs and probable pyroclastic layers distributed in a Omineca Belt.linear belt. Although not the Rocky Mountains,it exhibits inmany similarities to alkalic rocks in the Foreland Belt and DISTRIBUTION AND GENERALfor the purposes of this discussion, will be consideredwith CHARACTERISTICS OF KIMBERLITESthem. AND ALKALINE ULTRABASIC Carbonatites and syenites are found along the eastern DIATREME BRECCIASmargin of the Omineca Belt, extending westward from theRocky Mountain Trench for 50 kilometres or more. All the Alkaline ultrabasic diatremes anddikes have been dis-intrusions within this belt are hosted by late Precambrian covered in the Western and Main ranges of the Rocky Moun-(Upper Proterozoic) to Early Cambrian metasedimentary tains and in the Cassiar Mountains of British Columbiarocks. They generally form foliated, sill-like bodies that (Figure 2). With the exception of the Cross diatrenle, all arehave been multiply deformed and metamorphosed to am- hosted byCambrianto Silurian miogeoclinalrocks (Robertspbibolite facies during the middle Mesozoic orogeny; some et al., 1980; Grieve, 1981; Pell, 1986~. 1987b). The Crosssmall plugs and discordant dikes are also present. The car- diatreme, which is located in a moreeasterly structural po-bonatites have thin sodic pyroxene and amphibole-rich feni- sition, is hosted by carbonate rocks the Pennsylvanianto oftic margins. The belt comprisescarbonatites associated with Permian Rocky Mountain Group (Hovdebo,195:‘; Grieve,monzonites and some syenites in the Manson Creek area at 1985). A11 thediatremesintNdedthemiogeoclina1 sequencethe Lonnie and Vergil showings (Rowe, 1958; Currie, of platformal carbonate and clastic rocks prior to the Colum- 1976a). syenites and monzonites in the Mount Bisson - biau orogeny. The effects of deformation and metamor-Munroe Creekarea (Halleran, 1988; Halleran and Russell, phism are manifest in a weak to strongly dweloped 1990), carbonatites with nepheline and sodalite syenites and foliation, some flattening and the development 01: chlorite.some nrtites in the Blue River area, including the Verity, The diatremes weretransported eastwards in thnlst sheetsParadise and Howard Creek localities (Rowe, 1958; Cnme, during orogenesis therefore, have presumably and, been cut1976a; Pell, 1987) and nepheline and sodalite syenites at off from their roots. Diatreme breccias are also fomd in theTrident Mountain and Kinbasket Lake (Cnrrie, 1976a; MackenzieMountains, Yukon (Mountaindiatremc:, GodwinPerkins, 1983). No carbonatites in this zone are known to and Price 1987; Coates Lake diatreme, C. Jeffeison, per-contain potentially economic concentrations of niobiumor sonalcommunication, 1987);kimberlites andrelatedalkalicrare-earth elements; however, pegmatites dramatically en- ultramafic diatremeshave been found in north-central Mon-riched in light rare-earth element havebeen reported from tana (Hearn, 1968; Hearn and McGee, 1983); kimberlitesthe Mount Bissonarea (Halleran and Russell, 1990). also occur in the Colorado-Wyoming State-Lin: District The most westerly contains intrusive and extrusive area (e.g. Sloanpipe,HauseletaL, 1979,1981;McCal:umeraZ.,carhonatites and syenite gneiss bodies in a mixed paragneiss 1975; McCallum and Marbarak, 1976).succession along the margins of the Frenchman Cap gneiss Ultrabasic diatremes are present in five geographic: re-domenorth ofRevelstoke (Wheeler, 1965;McNlillan, 1970; gions of British Columbia. Within each area the ,diatremesMcMillan and Moore, 1974; Hoy and Kwong, 1986; Hoy are, for the most part, petrologically similar. The first suiteand Pell, 1986) in the core of the Omineca Bele (Figure l). is found in the Cranbrook- Bull River (Figure 2) where areaThe Frenchman Cap gneiss dome is one of several late do- examples of crater facies and extrusive rocks have been rec-mal structures located near the eastern margin of the ognized. The upper parts of the diatremes are chwacterizedShuswap Complex (Wheeler, 1965; Read and Brown, by bedded epiclastic and/or pyroclastic material overlying1981). The core of the dome comprisesmixed gneisses of a chaotic fragmental breccia containing abundant vesicu-probable Aphebian age that are nnconformably overlain by lated glass lapilli. In one pipe, small mafic flows dikes and‘mantlinggneiss’, an autochthonous cover sequence which are exposed near top of the crater zone. These rocks the arehosts the carbonatites and syenites. The intrusive and extru- porphyritic and consist of abundant clinopyroxene less andsive alkaline rocks in this area are conformable bodies that abundant olivine phenocrysts, clinopyroxene, oxide and po-were deformed and metamorphosed to upper amphibolite tassium feldspar microphenocrysts in a fine-grainedfacies during the Columbian orogeny. The Mount Copeland groundmass. Deeper levels within the craters are charac-Bulletin 88 3
  • 12. terized by juvenile lapilli-rich breccias with rare macro- (1986). These diatremes and dikes are associated withcrysts of chrome spinel, altered pyroxenes andaltered oli- quartzxenocryst rich breccias,containingsedimentaryarylockvines sporadically distributed throughout. Micas are not fragments and little recognizable igneous material. Mi-present in these rocks. Sedimentaryrock fragments, granitic crodiamonds have reportedly been recovered from hc:avyclasts and a variety ofpyroxenite andperiodotite xenoliths mineral separates taken from two pipes of this type (Dum-have been recovered from these pipes. Tentatively, these mett etal., 1985).rocks are interpreted to have an alkaline lamprophyre affin- In a third area, near Williston Lake and the Os:?ikaity. River, northern Rocky Mountains, a single pipe has k e n The secondsuite, found north of Golden (Figure 2). is discovered near the Aley carbonatite complex. It exhibitscharacterized by macrocryst-rich breccias and dikes. The many similarities to the pipes inthe Golden area; it is a ~nnl-macrocryst population consists of titaniferous augite or tiphase diatreme characterized by macrocrystic greensalite, phlogopite, green chrome diopside, spinel and rare chrome pyroxene,augite, pholgopite and spinel. Basei onolivine, with either clinopyroxeneor phlogopite most abnn- mineralogy it can be classified as an aillikite, a type of ul-dant (Ijewliw, 1987;Pell 1987a). Sedimentary fragments are trabasic lamprophyre.predominant in the breccias; gabbroic and granitic xeno- A diatreme breccia and related dikes are also known inliths, as well as cognate material, spherical structnres and the Kechika area of the Cassiar Mountains northern :Brit- innucleated autoliths are also present locally. These pipes are ish Columbia. These breccias are richin juvenilelapilli, con-multiphase intrusions, with massive and multiple breccia tain abundant sedimentary rock fragments, rare chromephases cut by related dikes. Petrologically, the diatremes spinels and are devoid of xenocrystic micas (Pell ei al.,appear to bear someaffinity to alkaline and ultrabasic mica 1989), similar to breccias in the Cranbrook - Bull Piverlamprophyres (alnoites and aillikites) as defined by Rock area.Figure 2. Index map, alkaline ultrabasic diafxeme swarms (from Pelf, 1987). For details on the Ospika Pipe see Figure 3 or Miider ( 1987).4 Geofogical S u n q Eranch
  • 13. Ministry of Energy, Mines andPetroleum l E c 3 The last geographically and petrologically distinct rock All the carbonatite-syenite localities (with the exception oftypeis represented by one example, Cross diatreme, lo- the theWicheedaLakeandMountBissonshowings,di:rcove:redcated at Crossing Creek, north of the town of Elkford. To late in the project) and alarge number ofthe diatreme brec-date, this breccia pipe is the only true kimberlite recognized cias were mapped and sampled. The purpose tllis study ofin the southern Canadian Cordillera (Grieve, 1981, 1982; is to document alkaline rock occurrences in British Colm-Hall e#al., 1986; Ijewliw, 1986,1987). It is a multiple intru- bia; to describe their petrography, geochemistry, economicsion with massive and breccia phases containing xenoliths geology and field relationships; and to determine the timingof garnet and spinel lherzolite, serpentinized peridotite, and tectonic controls of emplacement, providing basis for agimmerite and sedimentary material as well as pelletal future, detailed studies. Most new work concenmted onlapilli and xenocrystsof olivine, pyrope garnet, spinel and previously undocumented occurrences; previous1:r studiedphlogopite. Massive phases have a magmatic matrix of ser- suites were examinedfor comparison purposes.pentine, carbonate, microphenocrystic olivine and spinels.No diamonds havebeen reported from this pipe. The ratioof ultramafic to sedimentaryxenoliths is greater in the Cross ACKNOWLEDGMENTSdiatreme than in any the other breccia pipes andit is char- ofacteristic of the diatreme facies of kimberlites (Hawthorne, The Canadaritish Columbia Mineral Development1978; Clement and Reid, 1986). Agreement 1985-1990 has provided the financial support which made this project possible; the Natural Sciences andGEOLOGICALWORK Engineering Research Council of Canada supplied addi- Prior to this study, documentation of carbonatites, tional funding. R.L. Armstrong, The University of Britishsyenite gneisses and alkaline ultramafic diatreme breccias Columbia, provided the rubidium-strontium dating;was limited to studies of a few complexes and brief descrip- J. Harakal and Scott, The University K. ofBritish Columbia,tions of some of the others. In the Foreland Belt, the Ice the potassium-argondating; and R. Parrish, GeologicalSur-River complex had been subject of a number ofstudies, the vey of Canada, the uranium-lead zircon dating. Neutron ac-dating back to the turn of the century (Dawson, 1885; Bar- tivation analyses were provided by Bondar-#:lege &low, 1902; Allan, 1914; Jones, 1955; Rapson, 1963; 1964). Company L dt.The most comprehensive studyof the complex was com- I would like to thank Z.D. Hora for proposin]: the pro-pleted by Currie (1975). Other carbonatite complexes, ject in 1984 and for his continued help and ;pidancesyenites, kimherlites and diatremes the Rocky Mountains in throughout; thanks also go to T.HBy, D.J. Schulze, D.C.had only received brief mention in the literature. Carbona- Hall, J.A.Mott, C. Graf,B.H. Scott-Smith, C.E.Fipke,K.R.tites hosted by metamorphosedstrata along the eastern mar- Pride, U.K. Mader, H.H. Helmstaedt, D.A. Grieve, G.P.E.gin of the Omineca Belt had also received only brief White, M.Fox, R.R Culbert, A. Betmanis, B. French, !LA.mention in overview publications (Rowe, 1958; Currie, Almond, D.L. Pighin and J.K. Russell for helpfill disr:us-1976a). Carbonatites and syenite gneisses associated with sions both in and out of the field; thanks are also extendedcore complexes in the Omineca Belt were discovered and to W.J. McMillan, J.M. Newel1 and B. Grant for review ofstudied in the course of regional mapping (Fyles, 1970; this and related manuscripts. A special thanks goesto OlgaMcMillan, 1970, 1973; McMillan Moore, 1974). Sub- and Ijewliw for two seasonsof capable field assistance and. forsequent studies (Currie, 1976b;HBy and Kwong, 1986; Hay, of agreeing to help unravel some the story hiddell in these1988) provide detail on these suites. rocks, through her Master’s thesis research. Gwen3a Loren- Work by the author was begun in 1984 and included zetti also provided capable and cheerful assistance duringfield mapping during the summers of1984,1985 and 1986. one field season.Bulletin 88 5
  • 14. British Columbia - LEGEND 1 Fenitized Group alkali-syenitt River Rood (dolostone) Rood River Group (sandstone, shole) a amphibolite Carbonatite >Devoniar Rare-earth Group Road River (shale) carbonatitedikes SkokiFm. (dolostone, volcanics) KechikoFm. (limestone, marl, siltstone) Figure 3. Geological mapof the Aley carbonatite complex (fromMader), 1987.6 Geological Survey Bnznch
  • 15. Ministry of Energy, Mines and Petroleum . e s o u x e s " CARBONATITE AND SYENITE COMPLEXES IN PALEOZOIC STRATA, ROCKY AND CASSIAR MOUNTAIINS, FORELAND BEXI "THE ALEY CARBONATITE COMPLEX [(Ca,Ce,Na)(Nb,Ta,Ti)2(0,OH,F)61 forms fibrous to fine- grained aggregatesreplacing pyrochlore; primary fersnute(94BI9 is rare. Columbite [(Fe,Mn)(Nb,Ta)z06] is present as a re- The Aleycarbonatite complex was discovered 1980 in placement of fersmite.and staked by Cominco Ltd. in 1982 (Pride, 1983) for its Mineral banding or layering is common, particularlyniobium potential. It is located approximately 140 kilome- near the margins of the complex, and is charactmized bytres north-northwest of Mackenzie, on the east side of Wil- aligned flattened grains and aggregates apatite. In miner- ofliston Lake between the Peace Reach and the Ospika River alized zones, magnetite, pyrochlore, fersmite and biotiteat latitude 56"27 north, longitude 12345 west. The area is also exhibit some alignment and compositional zoning.generally above treeline (1450 - 2200 melevation) and has Field studies indicate that the mineral layering i:r steeplyexcellent exposure. It is fairly remote; access is by helicop- dipping and strikes approximatelyparallel to the margins ofter from Mackenzie. the complex. It has been interpreted as vertical flow band- The Aley Creek area is underlain by Cambrian to Silu- ing, a primary igneous texture (Mader, 1986) as is observedrian carbonate andclastic rocks of the Kechika, Skoki and in many other carbonatite complexes (e.g., Oka).Road River groups (Thompson, 1978; Pride, 1983). Thismiogeoclinal succession, deposited near the outer edge of SOVITE ZONESthe continental shelf, was intruded by the Aley carbonatite Sovite zones (dikes and sweats) occur locally near thecomplex prior to the main Late Jurassic to Early Cretaceous margin of the rauhaugite core zone andin the sunaundingorogenic event. The youngest unit affected by the intrusion amphibolite zone. The sovites exhibit a more variable min-is the mid-Ordovician(?) Skoki volcanic sequence. Much of eralogy than the rauhaugites. Calcite with or without dalo-the following description of the carbonatite complexis sum- mite dominates (40.95%) and there are accessory to majormarized fromthe work of Mader (1986,1987). amounts of apatite (2-lo%), biotite (0-5%),magnetite (0 to The complexis oval in outline with a diameter of 3 to 40%), richterite, a sodic amphibole (0-5%),pyrochlore (O-3.5 kilometres, occupying an of approximately 7 square 2%). fersmite and pyrite (Pride et al.,1986). Zircon rare area andkilometres. It is cylindrical, with a near-vertical axis and baddeleyite associated with zirkelite have also been re-consists of a rauhaugite (dolomitic carbonatite) core zone ported; mineral banding well developed. issurrounded by an older, outer ring of amphibolite. Somesovite (calcitic carbonatite) and rare-earth carbonate AMPHIBOLITICMARGINsweats occur in the rauhaugite core. A contact aureole of An amphibolitic margin, approximately 1 kilometrerecrystallized carbonate rocks surrounds the amphibolite in width, encircles and complexly interfngers with themargin. Rare-earth-enriched carbonatite dikes intrude the rauhaugite core. The marginal zone includes massive andcontact aureole (Figure 3). Ultrabasic lamprophyre dikes breccia phases. No distinct pattern to the spatial dis ributionand a diatreme breccia pipe (Ospika pipe) intrude altered of the two phases is evident. Carbonatite dikes cut bothand fresh carbonates outside the complex. These will be dis- members, indicating the amphibolite margin pred %ted em-cussed later in thisreport. placement of the carbonatite core zone. The massive phasea medium to coarse-grained, dark isRAUHAUGITE CORE ZONE green rock consisting primarily of sodic amphibole (mag- The coreof the Aley complex is approximately 2 kilo- nesio-arfvedsonite), quartz, albite and aegirine. It is moremetres in diameter. It comprises morethan 50% of the ex- extensively developed than the breccia phase and resemblesposed complex and consists of dolomite (80.99%) and fenites associated with some of the other carhonatite com-apatite (1-10%) witb minor amounts of phlogopite, pyrite, plexes in British Columbia. Mader (1986,1987) recog- h2.smagnetite, monazite, strontianite and zircon. It is generally nized microsyenite textures in the massive amphibolite. anda massive and homogeneous unit, weathering a buff to suggests that it is a primary igneous phase with a metaso-brownish colour. Pyrochlore [(Na,Ca,Ce)2 (Nb,Ta,Ti)z Os matic (fenitic) overprint, as opposed to fenitized country(OH,F)] may b e p r e s e n t i n t h i s z o n e . F e r s m i t e rock. This appearsto be the most reasonableinterpretationBulletin 88 7
  • 16. -~ ~British Columbia - for the origin of this rock; however, the true nature of the primary igneous phaseis so obscured that classificatim is difficult. The breccia phase contains subroundedclasts of domi- nantly orthoquartzite, with some siltstone, albitite and mi- crosyenite fragments in a matrix that is similar to the massive phase and locally grades into it. The clast-to-natrix ratio is highly variable and clast-supported breccias ate de- veloped locally; on average, clasts comprise l to 30%of the rock volume. Their subrounded nature gives this unit the appearanceof a conglomerate (Plates 1 and 2). The quartzite and siltstone xenoliths range from a milliietres l o ap- few proximately 30 centimetres in diameter. Reaction rims con- sisting predominantly of fine-grained aegirine commonly envelop the xenoliths. The quartzite xenoliths are probably derived from Lower Cambrian quartzite formations which the complex must have sampled during its ascent. Niicro- syenite and albitite clasts may represent deeper level mtru- sives or fenites associated with the original magma chanber. The extreme roundnessof clasts is similar to many of the diatremebreccias and may be a result of gas-streamingabra- sion. ALTERATION HALO Sedimentary rocksadjacent to the Aley complex have been altered for a distance of approximately500 metn:s be-Plate 1. Rounded xenolithsof quartzite and syenitein the breccia yond the amphibolite margin. This alteration halo is char-phase of the "amphibolitic" margin, Aley complex. acterized by a colour change from greyish to a distinct buff hue. The altered rocks may superficially resemble mzlterialPlate 2. Roundedquartzitexenolithsweatheringout of the Plate 3. Chocolatebrown-weathering,REE-enricheddikes in"amphibolite" margin, Aley complex. carbonate hostrocks, Aley complex, (colourphoto, page,3) 5.8 Geological Survey Branch
  • 17. TABLE 1 CHEMICAL ANALYSES, ALEY CARBONATITE COMPLEX 0.50 0.28 0.52 1.08 0.69 5.80 2.42 7.22 2.17 3.84 3.53 1.67 1.02 0.65 7.30 0.56 2.31 0.80 0.40 75.15 60.17 66.36 53.W 4 . 20.41 4W 7.934.01 4.01 0.01 0.72 0.18 020 0.20 0.14 0 0 0.10 .2 0.08 0.02 0.03 0.01 0.04 0.02 0.01 0.00 0.01 0.68 0.41 1.31 0.35 0.15 0.15 0.41 0.26 0.14 0.16 0.12 0.49 0.34 0.15 0.30 0.02 0.03 0.51 0.24 0.18 0.21 0.67 0.49 0.08 0.04 6.39 1.33 8.30 4.28 0.12 0.08 1.73 8.69 16.50 - 2.50 4.91 5.48 256 2.29 4.34 13.68 3.59 1.80 - - 5.82 3.94 5.33 11.10 5.61 - 12.91 10.98 4.36 2.54 19.92 2.95 108 0.761.92 . . - . . - 8.41 10.49 - 3.88 . - . . 0.26 0.87 0.77 0.25 0.22 0.90 0.22 0.22 ND ND ND 0.23 0.40 3.30 4.11 1.58 1.37 1.66 0.45 0.35 0.14 0.27 2.68 1.37 0.49 044 0.1717.34 16.68 14.79 18.02 16.50 14.90 16.60 12.77 7.71 5.85 2.92 2.M) 1.80 7.91 11.29 13.48 14.77 13.74 13.07 2.55 0.87 16.W 3.61 5.22 3.72 9.18 1.6632.89 34.82 34.29 31.20 31.W 33.71 28.20 32.74 15.69 41.47 41.34 45.50 46.W 28.14 24.59 n.73 30.44 29.39 3.98 28.18 3.50 2.28 4.05 14.80 35.88 25.32 4.590.08 0.63 ND ND 0.06 0.05 0.08 0.W 0.48 0.46 0.18 0.08 0.12 0.79 1.13 01 .0 ND ND ND 8.727.71 3.85 7.79 2.83 3.83 0.04 8.86 0.01 0.02 0.02 0.01 4.10 026 0.13 0.02 0.05 0.13 0.03 0.11 0.13 0.06 0.04 0.02 ND ND ND 1.153.68 0.24 020 0.03 0.52 3.10 0.3743.52 40.16 36.46 37.08 42.00 41.96 39.96 27.86 38.72 39.69 36.06 142.55 30.20 35.36 33-11 - 40.38 41.08 41.42 1 0.84 1-16 - . 15.45 2639 20.02 5.16 1 . 7 4 x p ~: 9 ~3.15 6.07 1.81 5.29 86 . 11.42 0.14 0.09 0.34- 0.60 0.90 0.52 0.70 0.20 0.68 0.60 9.13 3.23 0.4500.11- 97.32 101.33 99.78 97.35 99.03 93.97 95.34 93.90 92.01 99.92 92.94 98.86 %98 96.41 98.77 1W.54 92.50 I - <2 c25 IO . . c2 . . 7 14 c2 - CZO c20 E20 c20 . . < 20 . . 36 <20 c 20 - 10 4 10 I1 . . 12 . . - 15C5 359 4377 44493391 831 457 1426 2023 5281 4630 686 3506 141 670 - 3663 642 2023 39 1% 59 45 33 85 24 38 314 248 308 323 I84 540 461 1665 - 450 66 465146 499 35 497 70 290 M)4 559 308 563 887 390 40 79 290 490 168 1796 683 1384 5699 6759 13525 3290 4610 5M0 891 n 280 10 803 119 5697 41 14 140 69 18 122 249 138 97 93 122 129 18 21 48 227 138 310 142 388322 205355 598 558 314 248 308 307 7046 8725 63 2789 60 235 . 813 l o u l 379 750 224 909 1115 1215 390 816 856 708 8 2 1318 590 l 2 l W 125W 4ooo 170 110 143 . 1260 2070 905 210 59 310 297 - . - ND ND ND 2940 3260 56 1080 46 - 941 . . . " . . 11.6 10.0 3.5 - . . - 21 - 33 28 41 36 . . 46 26 2.6 1.7 - . . 32 5.6 31 18 ND 17 16 6 1 <2 c2 171 <20 c20 59 230 c2 <2 <2 - " Q 53 579 130 ND 21 184 375 5 23 712 65 106 4 4 253 6 151 105 61 <7 <7 <m 12 67 108 592 3.5 0.56 0.34 0.63 0.35 ~ 1.32 0.32 0.07 - - 0.90 0.30 ND . -
  • 18. Lo Ca Pr Nd Sm Eu Tb Dy Ho Tm Yb lu Rore-earth Elements Figure 5. Chondrite-normalized rare-earth element plots- Aley.Figure 4. Major element ternary plots of carbonatites and Figure 6. Ternary plots for fenites, Aley;Figure 6a after Hay, 88;"amphibolitic" margin. Aley; Plot 4b after Wooley, 1982. Figure 6b after Le Bas, 1981.10 Geological Survey Bra1
  • 19. Ministry of Energy, Mines and Petroleum Resortruesfrom the rauhaugite core zone. Apatite, pyrite and magnetite 339f12 Ma and 349k12 Ma. The data suggest an age ofare locally developed in the alteration zone. Silicification emplacement inlatest Devonian to early Mississippiantime.and development of green amphibole occursimmediatelyadjacent to the contact (10-40 cm). White mica and potas- WICHEEDA LAKE COMPLEX (PRINCEsium feldspar are the only commonmetamorphic mineralsobserved in impure marles, mark and siltstones and the de- AND GEORGE CLAIMS, 931/5; 93J/lt,9)gree of alteration decreases outward from the complex. A series of carbonatite plugs, sills and dikes, mociatedTrace element abnudances (Nb,REE, Th, F) can be corre- with alkaline silicate rocks, are located on the Prince andlated with the degree of alteration, also decreasing outward. George claims near Wicheeda Lake, approximately 80 kilometres northeast of Prince George (latitude 54”3:1’N,RARE-EARTH-BEARING DIKES longitude 122%4W; Figure Access to the area is by heli- 1). Dikes or ‘sweats’enriched in rare-earthelements (REE) copter. Elevations range from 820to 1490 metre:;, and theoccur throughoutthe complex but are most common in the area is largely forested. Outcrops arelimited to ridge topsouter alteration halo. The dikes weather adistinct, dark red- and some rock bluffs. The claims were stakedin 1986 bydish brown (Plate 3). are generally intruded parallel to bed- TeckExplorations Limited when anomalousniobium valnesding and average 0.5 to 1.5 metres in thickness. Their were detected in samples previously collected from a minorprimary component ankerite. Accessory minerals is include base metal showing.purple fluorite, quartz, pyrite, barite, bastnaesite The alkaline rocks intrude northwest-striking, steeply[(Ce,La)C03F] and other rare-earth carbonate minerals to subvertically dipping dolostones, limestones 2nd argil-(K.R. Pride and U.K. Mader, personal communications, laceous rocks of uncertain age. The Wicheeda Lake area1986). Rare-earth carbonate minerals fine grained, com- are straddles the boundary of two map sheets, mapped by dif-monly intergrown and comprise 3 to 6% of the rock. ferent workers (Armstrong et al., 1969; Taylor and Stott, 1979) and lithologic formations do not correlate across theGEOCHEMISTRY map-sheet boundaries. On one map sheet (Armstrcng et al., 1969), strata which host the alkaline rocks are as:;igned to Carbonatites, both rauhaugites and sovites, are very the UpperCambrian Kechika Group, which is in thrust con-low insilica, aluminumand alkalis, and high in phosphorus, tact, to the southwest of the property, withLower Cambrian 1).up to 11.42% P2O5 (Table Calcite carbonatites predomi- clastic rocks of the Misinchinka Group. Taylor 2nd Stottnantly plot within the sovite field on a CaO-MgO- (1979) correlate strata hosting the carbonatites with theFe203+FeO+MnO carbonatite diagram, dolomiticcarbonatites within the magnesio-carbonatitefield and rare-earth-enriched dikes span the magnesio- to ferrocarbonatiteboundary (Figure 4h). All are enriched in the incompatibleelements thorium, niobium, zirconium light rare earths. andExtensive zones within the rauhaugite core containing be-tween two-thirds and three-quarters of a percent niobiumhave been defined, and local concentrations of over 2%Nb2os are present (K.R. Pride, personat communication, 1987). Barium, strontium total rare-earth elements may andreach major element concentrations of 7.74, 0.5 and ap-proximately 2%, respectively (Table 1 and Appendix 1) inthe rare-earth- bearing dikes. Cerium is the dominantrare-earth element present; lanthanum and neodymium are alsoabundant. Fluorine, manganese, barium and, to a lesser ex-tent, iron are also enriched in the dikes relative torauhaugites and sovites, while niobium and tantalum are de-pleted. The ‘amphibolitic’ marginhas variable major elementconcentrations (Table 1 and Figures 4 5) and trace ele- andment patterns similar to typical carbonatites, but with muchlower concentrations. It is compositionally different from‘typical’ pyroxene-amphibolefenites in that it contains sig-nificantly more sodium and potassium (Figure 6), whichmay be a result of its original alkaline igneous or syeniticcomposition. carbonatite plug alkaline dikes gg soil anomaly (NE), g exposedcorbonatiie >some GEORGE GRID LAKE GRIC andGEOCHRONOLOGY I syenite ~~ ~~ ~~ I Figure 7. Locationmap of the intrusive bodiesof the Prince and Two potassium-argon dates have been obtained from Georgegroupsofclaims,Wicheeda Lake from MBder andmica separates from the Aley complex (Miider, 1986), Greenwood, 1988. __Bulletin 88 I1
  • 20. .British Columbia : Corbonatite, syenite roult ................................. -- a r/:.Contact rocks related and Limestone,argillaceous limestone, ~ P P ~ O Xinfered Interbedded argillite Bedding . .......................... / 75-85 * .......................... - pz85-90 Calcareous argillite minor arglllaceous limestone,locally Bedding, where different phyllitic from foliotion ...................1 0 30 Minerallayeringin Nodular locally argillite, calcareous massive intrusive rocks -- .................. Metres l 0 =Layered calcite carbonatit< (K-feldspar, aegirine. sphene, biotite) 0 t I L e u c o - to m e r o t v D e Ieucii like Figure 8. Geological map the southwesternpart of the Prince grid (enlargement) from Mader and Greenwood, 1988. of12 Geological Survey Bronch
  • 21. ~~~~ ~~ Ministry of Energy, Mines and Pefmleum ResourcesLower Ordovician Chushina and Middle Ordovician Skoki A third carbonatite body is poorly exposed west of theformations, overthrust by Precambrian Misinchinka Group southern end of Wicheeda Lake (Lake grid; Betmanis, 1987;metasedimentary rocks. The following descriptions of the Mader and Greenwood, 1988). It consists of sovite with ac-complex are summarized from the work of Mader and cessory apatite, feldspar, aegirine and, locally, coarse (0.1Greenwood (1988). to 0.8 millimetre) enhedral pyrochlore crystals. Sane sam- The carbonatite sills, plugs anddikes are distributed in ples collected from this area contained slightly in excess ofa northwest-sttiking linear zone in excess of 8 kilometres 1% total rare earths (Betmanis, 1988).long (Figure 7). All the intrusions show mineralogy typicalof igneous alkaline rocks, but each stock has distinctive pet- ALKALINE DIKESrographic features. As a whole, thesuite is characterized by Three varieties of alkaline dikes are present peripheralthe ubiquitous presence of ilmenite and sodic pyroxene. to the ankeritic carbonatite plug south-southeast ofCarbonatites range from almostpure sovites to pyroxene- Wicheeda Lake. They are quite thin (50-150 cm) andbiotite-rich varieties to rare-earth-rich ferrocarbonatites. slightly discordant to bedding and schistosity. The first typeSilicate rocks include syenites and leucitites rich in albite is a potassium feldspar porphyry with a fine-grai:nedand potassium feldspar. Most of the rocks are medium groundmasscontaining albite, biotite and accessoly calcite,grained and often display mineral Iayering. In all cases, ther- ilmenite and zircon. The second type comprises abundantmal and metasomatic effects on country rocks are appar- blue sodalite phenocrysts in a fine-grained groundmas:$ ofently minimal. albite and sodalite with accessory calcite, ilmenite, sphalerite and zircon. Rare xenoliths of microsyenite are also present. A third type of dike, which cuts the scdalite-CARBONATITES AND ASSOCIATED SYENITIC rich dikes, consists of an intermediate feldspar augite por-ROCKS phyry with an aphanitic groundmass. A carbonatite-syenite sill complex has been traced for GEOCHEMISTRYnearly 3 kilometres alongstrike on thesoutheastern part ofthe property (Prince grid; Betmanis, 1987; Mader and Whole-rock geochemical data are not available forGreenwood, 1988).Approximately halfway along itslength samples from Wicheeda Lake the area. Limited data indicatethe sill is cut by a northerly striking fault (Figure 8) and that the intrusive rocks are enriched in elements typical. oflithologies to the northwest of the fault differ from those to alkaline rocks and carbonatite comdexes (.e x . NI.Ba, Sr. ~~~ ~~ ~~ _ . .the southeast. Southeast of the fault, where the sill is the CHONDRITE-NORMALIZED REE PLOTthickest, white, layered sovite intrudes coarse-grained leu- WICHEEDA LAKE ALKALINE COMPLEXcosyenite, augite-leucite-syenite and layered, fine-grainedaugite-syenite. All rock types are in sphene. Northwest richof the fault, medium to coarse-grained sovites which contain ‘OS 3feldspars, aegirine, biotite, pyrite, apatite and pyrochloreare #+ Rare-earth elemmipresent. These rocks exhibit a pronounced mineral layering enriched dikeand are intercalated with syenites rich in albite and potas- 104sium feldspar and also contain aegirine and biotite. Contactsbetween carbonate and silicate rocks are locally either dis-tinct or gradational. Locally, analyses of nearly 1% Nb205were returned from samples taken treuches in this area from(Betmanis, 1987). An oval carbonatite plug, approximately 250 metres indiameter, is exposed south-southeast of Wicbeeda Lake(Figure 7) on the northwestern part of the property (Georgegrid; Betmanis, 1987; Mader and Greenwood,1988). Theintrusion is predominantly anankeritic carbonatite, locallycontaining ankerite phenocrysts up to 5 centimetres longand pyrite cubes which reach 2 centimetres across. Potas-sium feldspar, ilmenite, monazite andrare-earth carbonateminerals are present as minor constituents. Along the south-western margin of plug, albite-rich rocks are intermixed thewith ilmenite-rich carbonatite. Some rare-earth mineraliza-tion is hosted by this carhonatite. Samples from trench, one42 metres long, averaged 2.60% total rare-earth elements,including a shorter sample interval of over 4% total rare 1 1 , ~ 1 1 ~ ~ 1 1 1 , , 1 ~ , 1 1 , 1 1 1 1 1 1 , 1earths (Betmanis, 1988). Soils in the vicinity also contain Lo Ce Pr Nd Sm Eu Tb Dy Ha Tm I b Luhigh rare-earth concentrations, with one sample containing Rare-earth lements Eover 4%total rare earths (Betmanis, 1987). The majority of WicheedaLakealkaliae Figure9.ChondritenormalizedREEplot-these values are concentrated in the light rare earths. complex.
  • 22. REE). Rare-earth element analyses (Betmanis, 1987; sum- 54”03’00”N, longitude 12lo35’30”E). The ridge reaches amarized in Appendix 1) indicate that these rocks are en- maximum elevation of 1700 metres this area and is largely inriched in light rare earths; chondrite-normalized plots forested. Best exposureis found in subalpine meadowson(Figure 9) display patterns typical of other alkaline intru- north-facing slopes. The lowerslopes are easily reachzd bysions in British Columbia. logging roads from McGregor and Prince George;toaccms the ridge crest is on foot or by helicopter.GEOCHRONOLOGY The syenite intrudes Silurian Nonda Formation vol- No radiometric has been obtained the Wicheeda date on caniclastic rocks (Figure lo), which are predominantly al-Lake rocks. Due to lack of outcrop, unambiguous field re- kaline mafic tuffs, locally containing limestone clasts.lationships are not exposed. The intrusive rocks display Regionally, the hostrocks have attained lower greenxhistwell-developed fabrics in thin section and outcropthat are facies metamorphism; however,biotite is present in thf: vol-concordant with the regional schistosity. They are, there- canics immediately adjacent to the sodalite syenite. Thefore, interpreted as having been intruded prior to the Colum- syenite is massive, medium grained and white weathering.bian orogeny and, together with their host strata. were Three apparently separate bodies crop out; an oval stock,subsequently deformed during orogenesis (Mader andGreenwood, 1988). 500 metres by loo0 metres in area, flanked by two smaller is sill-like bodies (Figure IO). The stock contains rand,mlyBEARPAW RIDGE SODALITE SYENITE oriented feldspar laths (1-5 centimetres long) with inemti- tial mafic silicate, feldspathoid and opaque minerals. The(9W) sills have feldspar phenocrysts upto 4 centimetres lorg, in Abody of sodalite syenite and twoflanking syenite sills a groundmassof felted feldspar laths. The main intnwionscrop ont on Bearpaw Ridge in the Rocky Mountains ap- are roughly parallel to bedding in the hostrocks; how:ver,proximately 60 kilometres east of Prince George (latitude crosscutting dikelets (Plate 4) were observed.Intrusion ap-14 Geological Survey Branch
  • 23. Ministry o Energy, Mines nnd Petroleum ResouKes f parently occurred prior to orogenesis. The syenites contain a low-grade metamorphic mineral assemblage(albite-epi- dote) and are exposedin the core of a synform. A folded and foliated orthogneiss of unknown age crops out on the western lower slopes of Bearpaw Ridge(Figure 10). It is not shown on previous maps the area (lhylor and of Stott, 1979) andits extent is unknown. Where exposed, the contacthetween the volcaniclastics and thegneiss isparallel to the bedding in the volcaniclastics, hut may be either de- positional or faulted. A second body of syenite, also previously unmapped, crops out on the southwestern end of the ridge, intruding both the dioritic gneiss and the volcaniclastics (Figure 10). It is a massive, coarse-grained rock with huff to pink fresh a surface containing randomly oriented feldspar hths up to 1.5 centimetres long. Clinopyroxene, amphibole and opaques, predominantly magnetite, comprise up !o 10% of the rock. This syenite appears to he postorogenic and unre- lated to the sodalite syenite on the ridge crest. It is, however, petrographically similar to Cretaceous syenites described elsewhere in the Cordillera. SODALITE SYENITE The white-weathering sodalite and related feld- spathoid-poor syenites generally comprise 80 to 90% feld- spars. Due to metamorphism, much of the feldspar is nowPlate 4. Bouldercontainingsyenitedike(white)crosscutting altered to albitic plagioclase and original potasic leld-banded volcaniclastic rocks. Banding parallel to pen,Bearpaw spar/plagioclase ratios are difficult to establish. Other meta-Ridge. morphic minerals include epidote (npto 10%). :nnscovitePlate 5 . Whiteweatheringsyenite with disseminatedsodalite, Plate 6. Folded and foliated dioritic orthogneiss, present on theBearpaw Ridge. lower slopes of Bearpaw Ridge.Bullefin 88 I5
  • 24. British Columbia -(generally only a few percent) and traces of chlorite. In one minor basaltic flows. Flow-rocks contain clinopyrcxenesample, alteration patches, consisting of fine-grained mus- phenocrysts and altered phenocrysts (now chlorite) in acovite and epidote, comprise 30% of the rock. clay a h a - groundmass of opaque oxides, plagioclase and cliropy-tion was also noted locally. roxene microphenocrysts and chlorite. Some vesicles are Feldspathoid-bearingsyenites occur near the centre of present.the large syenite stock. They may contain up to 10% feld-spathoid minerals, generally sodalite and cancrinite or can- ORTHOGNEISScrinite alone (Plate 5. No nepheline was noted. Aegirine )(strongly pleochroic from marsh to blue-green)and biotite Folded and foliated dioritic orthogneiss (Plate 6 ) cropsare also locally present in minor amounts. Trace minerals, out on the lower slopes of the western end of Bearpawidentified by scanning electron microscopy, include mag- Ridge. It varies from a banded gneiss containing approxi-netite (titanium free), allanite, zircon, monazite, apatite, py- mately 70%calcic plagioclase (bytownite) with olivine, 5%r o c h l o r et h o r i t e T h S i 0 4 ) n d h e r a l i t e , ( a c 15%augite,5tolO%magnetite-ilmeniteandatraceolapa-[(Ca,Ce,Tht(P,Si)041. tite. mafic to a - eneiss with 10%calcic Dlaeioclase. 3046 oli- vine, 35% augite, 15 to 20%magnetite-ilmeniteand 2 to 3% . -NONDA FORMATION VOLCANICLASTIC apatite. In both the feldspar-rich and feldspar-poor phases, . .ROCKS brown amphibole present rimming pyroxenes and is locally The Nonda Formation rocks in this vicinity largely as an intercnmnlate phase comprising 5 to 7% of the morecomprise clinopyroxene crystal tuffs, calcareous tuffs and mafic gneiss. In some localities, the gneiss is remar1:ably TABLE 2 CHEMICAL ANALYSES, BEARPAWRIDGE ~. ~ /mB Nonda Formation Other rocks Si02 1 2 3 42.40 47.70 58.30 45.50 68.80 Ti02 0.12 0.11 0.09 0.13 0.47 0.10 2.06 0.59 0.80 2.01 0.27 A1203 22.80 19.40 21.65 22.10 21.80 21.10 15.20 15.80 17.90 15.60 15.70 Fe203T 2.50 2.68 3.95 2.50 4.38 2.00 14.50 6.88 7.12 11.20 1.50 MOO 0.10 0.10 0.16 0.09 0.11 0.10 0.29 0.08 0.11 0.18 0.01 ME0 0.13 0.12 0.33 0.13 0.33 0.15 9.80 4.58 0.33 5.25 0.16 1 CaO 0.81 0.85 5.74 0.78 3.13 4.92 11.50 17.50 0.36 12.90 0.97 Na20 11.10 6.59 6.02 11.30 6.64 4.91 1.56 0.65 7.68 3.75 4.54 K20 6.39 4.60 5.52 6.47 6.87 5.77 1.84 4.33 6.42 1.46 6.28 0.89 1.12 1.45 1.23 1.69 2.32 2.34 1.96 2.26 2.37 2.55 ~ 4 . 0 9 <0.08 <0.09 <0.09 <0.09 <0.09 0.23 ~~ <O.W Total 99.36 100.46 100.831W.2899.21 98.08 99.85 1W.16101.08 99.64 97.80 i PPm INi < 34 <37 7 - 2 c 28 24 219 1 Cr 62 67 50 -30 44 51 Co 4 1.4 1.9 - 5 17 1.6 56 Sr 501751205 - 1023 55 2903421 288 Ba 50722 170 - 1079 486545 445 zr I 613 1831756 - 717 134 103 429 133 110 232 Y La Nb Ce Nd 1 9 155 : 108 135 222 28 156 32 - - 147 - 58 - 167 11 - 35 21 - 122 78i ~ 174 111: 71 22 44 25 20 11 38 14 34 45 10 61 24 26 Yb 2.7 2.9 - 1.9 sc 0.3 3.8 0.2 - 2.7 0.3 23 33 21 1.4 Ta 8.5 10 17 - 8 7.5 <2 - ~ Th ~ 36.3 38.3 56 29.4 39 l; <l;l 1; 15 1 .84211A - sodalire syenite(?); 2 - B4211 -grey ropink granular syenite; 3 - B4203A -white porphyritic syenite dik; 4 - b4212A - greyish sodaliresyenite; 5 - b4216 - syenite sill; 6 - B4212B - sodalire syenife; 7 - 84213 - N o h Formorion mafic volcanic rock; 8 - 84226 - N o h Formorion inremediate ro mafic tuff; 9 - B4147 - posrorogenic oegirine syenite; I O - B4170C - diroite gneiss;I 1 - B4163 - granire. Major elements analyzed by ICAP, alkalinefusion. Trace elements nmlyred byXRF; 1,2 & 6 ,traces byINAA, Bohr-Clegg.16 Geological Survey B ~ n c h
  • 25. Ministv o Energy, Mines and Petmleurn Resources f " Y Bear aw Ridgesyenile @ O on8 Formotion volcclnics N a 0 Portorogenic syenite 0 Beorpow Ridge syenite t Nonda Formalion Y O I C ~ I I ~ E E 0 Porlorgogenlc syeniie 30.00 40.00 50.00 60.00 70.01 Si02 I / Agpaitic syenite fomily nephelin ** /syenite Alkali bosall fomily 0 Postorogenic syenite __ 0.00 , , , , , , , 30.00 50.00 , , , , , , , , , , , , , , , , , , ~, , , , , , w, 40.00 601ao 70.0 020 __ CO Si07 Figure 12. Major element ternary plots, Bearpaw RidgeFigure 11. (A) Alkali vs. silica diagram Bearpaw Ridge; beckite). Accessory minerals, identified by scann:ng elec-(B) Agpaitic index plot Bearpaw Ridge syenites. - tron microscopy, include ilmenite, pyrite, barite, monazite, sphalerite and arsenopyrite.well preserved; inothers it isstrongly altered, consisting ofchlorite, epidote, plagioclase, sericite and prehnite. GEOCHEMISTRY The preorogenic feldspathoidal syenites on the crest ofPOSTOROGENIC SYENITE Bearpaw Ridge are variable in major element conteilt (Table A second type of syenite outcrops on the southwest end 21, and alkali-silica and agpaitic index plots (Figure 11) in-of Bearpaw Ridge. It is massive, coarse grained andpink dicate they span the range from saturated syenites, throughweathering with randomly oriented feldspar laths up to 1.5 miaskitic syenites to agpaitic syenites, with anavert ge co m-centimetres long. It comprises 30 to 35% potassic feldspar, positional range in the miaskitic syenite field. Composi-20 to 25% plagioclase and 10to 20% microperthite with up tional differences with the postorogenicsyenite whichcropsto 10% clinopyroxene (aegirine-augite to aegirine), 5% out on the lower slopes of Bearpaw Ridge are s1.ght; thehornblende, 5 to 7% magnetite (withtitanium) ilmenite plus feldspathoidal syenites are higher Al2O3, CaO, 2 ,Nb,Ta inand minor biotite and apatite. The clinopyroxenes are and Th and, on average, lower in SiOz, Fez03, IiOz andstrongly pleochroic, from yellowish to blue-green and often PzOs than the postorogenic syenite (Table 2; Figures 11andrimmed by strongly pleochroic blue sodic amphibole (rie- 12).Other major elements show no systematic variation. OnBulletin 88 17
  • 26. alkali-silica andagpaiticindexplots (Figure 11) thepostoro- metres, most of which lies within Kootenay and Yoho Na-genic syenite falls within the agpaitic syenite field, however tional Parks (Figure 13). Access is difficult due to iiteepit wouldbe erroneousclassify this rock to type as suchbased mountainous topography, lack of roads andregulations im-on asingle analysis. posed by Parks Canada. The Nonda Formation volcanic and volcaniclastic The Ice River complexwas the first alkaline intnlsionrocks havealkaliisilica ratios which allow them to be clas- to be recognized British Columbia. It was discovered and insified as alkali basalts (Figure 11). Chemical trends suggest described around the tnm of the century (Dawson, 1885;that they may he genetically related to the syenites on the Barlow, 1902; Bonney, 1902). Work by Allan (1911,1914)ridge crest (Figure 12). established it as one of the worlds major alkaline com- plexes. During the 1950s and 1960s there was renewed in-GEOCHRONOLOGY terest and anumber ofadditional studies undertaken (Jones, Taylor and Stott (1979) suggested that the sodalite 1955; Gussow and Hunt, 1959; Campbell, 1961; Rapson,syenite is a subvolcanicintrusion, related to the formation 1963, 1964, Deans al., 1966). The most recent conipre- etof the Nonda volcaniclastics. If so, it would be approxi- hensive study is by Cunie (1975); much of the followingmately Silurian in age. The chemistry of these rocks sug- description is summarized from Curries Memoir anti thegests that this may be a viable interpretation; however, this reader is referred there for additional details. An excdlentalone is not snfticient to establish this relationship and there- bachelors thesis (Peterson, 1983) deals withtheminernlogyfore the age ofthe intrusion. No radiometric dates are avail- is and petrology ofthe complex and also drawn upon ewten-able and, until the intrusion has been dated, its age is sively. In view of many previous studies of the Ice Itiver theuncertain. complex, only brief description will be given here. a h o distinct suites are present within the complex: anICE RIVER COMPLEX (82N/1) early, rhythmically layered, feldspar-free intrusion of ,jam- The Ice River complexis an alkaline ultramafic intrn- pirangite, ijolite and urtite, cored by a carhonatite phi: andsion located 23 kilometres south of Field, at latitude crosscut by carbonatite dikes rich in mafic silicates an43 ox-51"10N, longitude 116°25W. It is an arcuate mass, some ides; and a later zoned andcrosscutting syenitic sene;$, as-18 kilometres long, with atotal exposure of 29 squarekilo- sociated withazeoliteandfeldspar-hearingcarhonatite. The alkaline rocks intruded Cambrian and Ordovician slales and carbonates the Chancellor, Ottertail and McKay for- of mations (Plate 7; Figure 13). Contact metamorphism cC the enclosing sedimentary rocks resulted in the formation of hornfels and skarns. Some limited soda metasomatism also occurred. The complex and its hostrocks were deformed and subjected to low-grade regional metamorphism during the Columbian orogeny. ULTRAMAFIC SERIES The older part of the complex comprises a semiconcor- dant, rhythmically layered intrusion of feldspar-free litholo- gies ranging from jacupirangite through melaniteijolite to melanite urtite, and characterized by a repetitive seqcence of gradedlayers, 10 to 200 metres thick, with nepheline in- creasing in abundance toward top of each layer. Ja:upi- the rangite is the most mafic lithology in this series. It conlains, in decreasing abundance,titanaugite, titaniferous ma,;net- ite, perovskite and phlogopite. Accessory minerals include apatite, calcite, pyrrhotite, cancrinite and natrolite; the:.atter two minerals present as alteration products of nepheline. are In many cases, the jacnpirangite has been fractured and in- truded by later, more felsic phases (Plate 8). Ijolites are the most common component the layered of series. They vary from slightly more maficvariety (rnela- a ijolite) to true ijolite. The mela-ijolites contain clinopy- roxene, either titanaugite or hedenbergite, nepheline, phlogopite, magnetite and perovskite or sphene, in order of decreasing abundance. Accessory mineralsinclude calcite,Plate 7. Contact between syenites(light grey massive) of the Ice apatite, cancrinite and natrolite. Some varieties contai~~ sig-River complex and steeply dipping Paleozoic carbonate rocks, nificant amounts of black melanite garnet and biotite. TrueButress Peak. The contact is clearly intrusive. here ijolites differ in that the pyroxenemephelineratio is 1::I and18 Geological Survey B,.anch
  • 27. Figure 13. Geology of the Ice River complex (from Cume,1976a).opaques are uncommon.Locally, kaersutite amphibole re- The syenites are all dominatedby the presence of alkaliplaces pyroxene. feldspar, generally with subordinate amounts pwthite and of Urtites contain greater amounts of nepheline than py- albitic plagioclase. Mafic minerals vary from minorroxene (generally aegirine) and wollastonite may be pre- amounts to comprising approximately 50% of the rock.sent. They are generally coarse grained, with a fabric Melanocratic varieties are characterized by the presence ofdeveloped due to the parallel orientation of elongate py- titanaugite to hedenbergitic pyroxeneeaersutitekbiotite.roxene or wollastonite. Kaersutite, melanite, albite, Leucocratic syenites generally contain minor amounts ofnepheline alteration products, sphene, calcite and apatite aegirine; hedenbergitic pyroxene, kaersutite, hastingsite ormay also be present. biotite may also be present. In all varieties, nepheline may comprise up 30%of the rock. Sodalite is preser~t quan- to in tities from trace amounts to 20%,and is generally moreZONED SYENITE COMPLEX abundant inthe leucocratic syenites. It occurs bot1 dissemi- The youngerportion of the Ice River complex has in- nated throughout syenite and concentrated veins cut- the intruded the older mafic portion and consists of feldspar-rich ling the syenites. Accessory minerals include s:?hene (nosyenitic rocks. The syenites are unlayered, however, there perovskite), apatite, cancrinite and minor opaquen. Zeolite-is a strong alignment and segregation of minerals. They rich syenites are present locally; fluorite and pyrochloreform an elliptical pipe-like mass, zoned from a greenish so- have also been reported (Peterson, 1983).dalite syenite core through pale grey nepheline syenite todarker coloured mafic-rich rocks at the margin. The com- CARBONATITESplex is surrounded by a thin rim of saturated fine-grained Carbonatites crop out in a number of localities in theleucosyenite in contact with the country rocks. This phase Ice River complex and display considerable lithologic .vari-is commonly full of inclusions. ation. Complex relationships with other alkaline rocks pre-
  • 28. Plate9. White-weathering,coarse-grainedcarbonatitedike,AlountPlate 8. Jacupirangite (dark grey massive) Ice of the River complex Sharp area, Ice River complex. Coarse-grained dark minerals areand steely dipping carbonate rocks, Butress Peak. contact here The books of biotite. Sugary appearance of white matrixproduced byis clearlyintrusive. coarse apatitegrains mixed in with the calcite.clude the unambiguous establishment of an emplacement generally coarse grained and composedcalcite, aeglrine, ofsequence. Currie (1975)suggests there may be some remo- apatite, pyrite and trace pyrochlore.bilization of carbonatite during deformation and metamor- White-weathering carbonatite dikes (Plate 9) inlrudephism whichresults in complex crosscutting relationships; the ultramafics exposed on Sharp Mountain (Figure 1 ) 3.alternatively there may be more than one period of carbona- They consist predominantlyof calcite and fluorapatite withtite emplacement. aegirine (occasionally containing hedenbergitic cores), in Carbonatite occurs the layered ultramafic sequence, phlogopite, pyrite and ilmenite/magnetite. Some sampleswestoftheIceRiver(Figure13)aslayeredlenticularmasses contain feldspar-rich xenoliths (microcline plus a1hite:l andand as smaller dikes. Three types are recognized: ablack- garnet (melanite?), analcime, natrolite, cancrinite andweathering, iron-rich variety which is associated with a sphene.buff-weatheringcalcite-rich type, and ared-weathering va- The carbonatite associated with the syenites is radit:allyriety, which crosscuts the buff carbonatite. The black car- different from occurring within the ultramafic series in thatbonatites commonly occur as dikes containing elemental that the only silicate minerals present are feldspars (albitecarbon and tetranatrolite concentrated near the margins, and in some localities microcline), zeolites (natrolite, mal-with calcite, siderite and grass-green berthierine cime and rarely, edingtonite) and rare phlogopite. In some[(Fe2t,Fe3,Mg)z-3(Si,Al)zO~(0H)~,a serpentine mineral] localities the carbonate is pure calcite, in others ankcrite,as major components. Other mineralsthe black carbona- in barytocalcite and strontianite have been identified in addi-tite are: iron-rich biotite, aegirine, edingtonite (a barium tion to calcite. Minor and trace minerals include ilmenite,zeolite), perovskite, ilmenite, minor sphalerite and traces of pyrite, rutile, barite and apatite.pyrite. The red-weathering carbonatite is similar to theblack, but it contains fewer non-carbonate minerals (less LAMPROPHYRESthan 10%);both siderite and zeolites are absent, serpentine Many dark-weathering lamprophyric dikes o;curis distinctly yellow-brown rather than grass-green, and py- within the Ice River complex and contiguous country rocks.rochlore and xenotimeare present. The buff carbonatite is They contain phenocrysts of strongly pleochroic orange-20 Geological Survey Branch
  • 29. ~ ~~~~ "" Ministry of Energy, Mines and Petrnleum Resources TABLE 3 CHEMICAL COMPOSITIONS OF ICE RIVER COMPLEX ROCKS 1 7 ljolote Jacutpimgje Melanie Mch-ijolie j0- Uni* carbonatill 1 1 -1 si02 34.2 37.9 33.6 41.6 42 40 35.9 39 40.2 43.7 43.9 40.3 43.5 44.2 1.2 7.7 1.6 9.92 12.38 9.65 20.24 12.93 16.24 Ti02 5.62 5.64 7.14 2.21 3.22 2.42 4.4 2.04 3.48 1.2 2.44 3.58 0.19 0.14 0.02 0.09 0.05 0.07 0.38 0.07 0.73 0.77 2.21 5.6 8,7 9.9 11.6 12.4 12.5 19.1 20.2 19.8 25.8 19.3 21.3 26.2 26.1 0.3 2.6 0.4 2.84 1.62 2.76 4.65 6.14 4.$1 8.9 2.1 6.4 2.9 4.1 2.8 4.8 3.3 2.5 1.6 2.4 2.4 1.1 1.3 0.1 2 0.2 1.62 5.9 0.53 5.37 8.7 5.89 4.9 5.4 3.7 5.7 8.2 4.3 6.9 7.4 7.4 8.2 8.5 6.2 21 0.7 0.8 8.9 3.2 - - 0.140.41.750.5 0.120.20.170.20.2 0.130.31 0.120.150.28 0.51 0.2 0.06 0.18 0.18 0.07 1.15 0.98 1.1 12.7 0.42.75.1 5.64.74.1 11.6 9.88.4 0.7 0.27 10.411.6 10.6 0.5 0.44 1.258.85 2.01 0.2 4.27 0.4 5.411.7 10.111.7 9.521.4 12.3 12.3 27.2 21.8 6.6 I 145.55 51.86 30.69.7 44.62 39.73 47.12 27.58 19.13 6.4 :27.8 0.13 10.47.6 1.089.9 7.4 7.7 8.7 4 3.5 3.3 10.6Na2O 7.4 0.7 0.8 1.12 1.79 0.3 0.2 1.44 nd 1.91 2.25 Kzo 0.12 4.6 2.60.4 0.10.32 0.03 1.9 4.6 4.9 3.9 5.4 4.5 3.5 3.7 0.3 3.3 2.74 0.36 0.05 0.11 1.45 3.6 H20 0.7 0.8 0.8 15 0.9 0.7 0.7 0.6 2.1 0.9 1.2 0.7 0.9 0.9 1.3 0.5 0.5 . A nil 0.02 0.M 0.10.3 1.9 0.2 0.5 0.2 0.8 0.1 43.4421.87 36.9:!5.27 43.6 29.37 23.43 0.7 35.03 23.76 0.3 2.54 l.W 1.94 1.24 0.51 1.12 0.56 0.62 0.33 0.09 0.11 0.05 0.67 0.36 0.01 0.05 0.1 2.06 8.23 7.81 0 0.20.92 99.7 99.0 100.6 98.0 99.5 1W.9 IW.7 IW.O 1 0 9 IW.4 99.9 99.4 lW.2 99.51 99.9 98.64 94.9 100.8 95.62 99.6 99.13 !nU9%.l5 I __- 110 nd 190 40 61 49 3W nd 6 6 2 6 303 nd 2 nd 1 1 4 0 3600 11 nd nd 2wO 5 13 nd 3 28 10 2 W 13763 12768 10 40 43 34 13628 3954 . 11610 8 65 lS 2 7907 16 3W 190 470 1300 210 320 220 m 2M)/ 1IW nd 890 340 360 213% 221 392 21511 528 nd 35 587 415 248 60 62 370 22 68 81 450 86 150 50 230 170 98 250 1701 4 0 60 :: 81 650 7W 2M) 439 930 4 4 4 10a0 145 43143 620 535 224 159 €1 4 1x7 125 418 nd 650 nd nd nd nd 1oW 880 4 W 1562 7M 878 852 1530 nd IlW 830 nd nd nd 820 1wO nd " . 5.1 4 4.7 4 c4 c4 <40 <4 <4 <4 . . . ;1 c40 52 26 39 nd nd . " Od; - . 41 36 39 2 6 2 6 . . . " " " Q Q Q 14 6 13 I. . . " . " " . . 79<6 81 703 511 ____ Lampmphyrs Melanacmtic syeoite lrucOcraG0 syenie sodalite syenite (1) (2) (3) si02 46.7 62.1 51.9 44.4 44.7 41.6 45.3 58.654.t 53.9 54.6 52 54.4 Ti02 1.140.41 1.930.63 0.28 4.3 0.19 0 2.77 1.010.7 1.68 0.11 0.81 0.12 0 2 0.C . A1203 20.1 23.3 21.8 21.6 24.1 18.322.4 23.1 19.1 20.4 18.4 23.8 20.721.9 16.420.8 16.3 15.6 13.4 22.1 Fern3 2.1 2.6 1.2 2.1 1.2 1 0.81.3 0.62 3.1 04 . 4.6 7.1 4.35.1 4.1 0.1 5.8 1.4 4.8 3 7.8 2.1 7.1 5.9 0.8 5.5 0.3 0.4 0.9 (MnO 0.12 Fd) 0.15 0.18 0.19 0.13 0.42 0.32 0.05 0.16 0.07 0.11 0.16 0.22 0.2 0.C2.8 0.2 4.$ 4.2 MgO 6.1 11.6 0.4 0.1 0.8 0.1 cao 14.4 13.8 0.73.41.61.97.8 6.5 3.66.10.20.54.1 16.7 16.3 12.111.8 0.3 1.2 0.74 5.8 5.1 2.8 7.85.9 5.7 4.7 7.1 7.6 9 9.9 7.997.8 5.7 8.3 6.8 11.5 10.7 10.1 Kzo 2.1 2.3 2.3 5 0.4 6.3 5.4 3.2 2.3 6.9 8.6 7.8 4.1 2.1 4.4 3.6 6.3 7.56.35.3 1.4 1.6 1.2 1.9 0.9 1.3 1.6 0.9 O h 0.7 O S 0.9 5.4 0.9 0.9 1 0.7 0.8 0.8 0.7 1.4 1.2 1.3 0.9 0 0.2 0 0.1 0.03 0.9 0.2 00.2 0.05 0 0.1 0.1 0.7 0.2 0.8 0.470.91 0.030.96 0.020.74 0.28 0.05 0.47 0.W 0.22 0.31 0.19 0.77 0.09 0 0.08 0.02 0.01 0.1 99.8 99.71W.8 1W.2 99.7 1W.S 1W.6IW.5 10.0 1W.3 100.5 98.2 100.1 99.4 98.4 IW.5 100.0 99.3 99.8 101.1 Ni __ 150 220 40 24 40 36 nd nd 4 0 nd 21 nd nd nd - I " - i 5wJ MD 16 16 4 0 17 4 0 nd nd nd nd 4 0 4 0 nd 45 nd nd 40 nd 31 nd nd nd nd nd nd nd nd - %o 920 2 W 1700 % 12W 990 25W ZoW 118% 1800 770 2600 380 ZM) - 490 280 2wO 1wO 17W 1wO 37W 26(M 34w 14M 350 2SW 130 280 . 350 I80 120 410 690 390 280 330 190 300 370 160 270 310 ,450 - 1mO 110 nd 203510310 180 270 1 4 w 2 4 0 , 140580 2W 140 140 - 980 22 33 nd 4235 51 47 94 28 4 0 61 nd nd nd - 300 59 40 73 55 170 150 93 94 110 99 1500 nd nd 210 - 180 Ce nd 22 nd nd nd nd nd 17W ndnd nd nd nd 290 - nd Nd nd od nd nd nd nd nd 740 nd nd nd nd nd 160 - yb <40 <40 <4 c4 <4 c4<4 <4 c4 5.7 4 4 - - - SC 34 27 d l 2 0 od 17 nd 14 nd nd nd nd- - - Ta . . . . " . . _ . _ . _ . ll l ~ . . . . . . . . . . . . . . Bullerin 88 21
  • 30. brown phlogopite, zoned crystals of angitekitanangite, grams (Figure 14). They form a cogenetic suite and eAibit zoned kaersutite and olivine in a groundmass of pyroxene, systematic major element variation with Si02, Na2Cl and pale orange phlogopite, calcite, alkali feldspar and opaque &O increasing and CaO, TiOz, Fez03 and FeO decreasing oxides. Sphene and apatite have also been reported. Field with decreasing colour index is, from jacupirangite to (that relationships indicate that the dikes were emplacedlate in urtite, Table3; Figure 15). Rocks of the ultramafic sui:e are history of the complex. generally lower in Si02 and higher in CaO and Ti02 than those of the syenitic series (Table 3). GEOCHEMISTRY Syenites of the Ice River complex range from nephelin- Rocks of the layeredultramafic complex belong theto itic (melanocratic varieties) to agpaitic (leucocratic and nephelinite family and plot predominantly within the feldspathoidal varieties) in composition (Figure 16). They nephelinite fields on alkali-silica and agpaitic index dia- exhibit systematic major element variation with decreasing CaO, MgO and total iron, and increasing alkalis with de- creasing colour index (from melanocratic to leucocratic and feldspathoidal varieties, Figure 17). / "51 @ Corbomtite,/ family A 0 0 * ljolite and melanite Wile ijuiite Melo-ijolife Josupirongiie Agpoiiic syenite family Miaskitic / A b Mela-ijolite ljolite and melanite ijolitt Urtite Alkoli basalt rocks family0 0 . 0 I * * */ 30.00 40.00 50.00 60.00 ?I ;% Figure14.Alkali-silica and agpaiticindexplots,IceRiver ultramafic suite. Figure 15. Ternary major elementplots, IceRiverultramafk suite. 22 Geological Survey €:ranch
  • 31. A Meianocratic ryenil 0 Contactsyenite b breccia an, Leucocratic syenila Sodalite breccia 1 syenite LBUCOCratiC ryeniter Melonocratic syenite Zeolite ryeniter & Contact syenite - Sodalife syenife Nepheline syenite LeucOCrOtiC syenites Melonosrafic syenif 30.00 40.0060.00 50.00 Contact ryenite & breccia Si02 T t M e l a n o c r a t i c :yenit DContact syenbte an breccia /D 0 0 Leucocratic syenile 4 0 Sodalitesyenite *Zeolite svenitear+ CIz 0 Figure 17. Ternary major element plots, Ice River syenitic suite. .- -- " . " Subalkaline rocks Alkali basalt family 0.00 30.00 40.00 60.00 50.00 si09Figure 16. Alkali-silica and agpaitic index Ice River syenite pbts,suite. Carbonatites &e predominantly sovites and ferrocar- Ibonatites (Figure 18) and, togetherwith some the melano- of * Corbonolites near M o m 1cratic syenites, have relatively high concentrations ofincompatible trace elements (Nb, Y REE), barium and , Mollison a n d Eultress Peak * Corbonolites associated strontium (Table 3).GEOCHRONOLOGY with theultramafic complex, S h a r p Mt. Xundifferentiated Other, I The ageof emplacement of the Ice River complex haslong been a topic ofdebate. Allan (1914) suggested that em- Figure 18. Majorelementternaryplot,IceRiver Zoom[placement was post-Cretaceous, Gussow and Hunt (1959) carbonatites.Bulletin 88 23
  • 32. TABLE 4 ICE RIVER COMPLEX -~GiOCHRONOLOGY SUMMARY ~ ~~ ~ ~~ ~~ - I ~~ ~ Publishedlated* Date - 392t10 374t10 Rapson, rock whole K-Ar, 1963 Pyroxenite; age possibly slightly old, excess tm argon possiblein pyroxene (2s~f3o) Rb-Sr, separate 1963 pegmatite: mica Rapson,Biotite Sr tm low for satisfactory data but K-Ar shouldbe reliable 336*5 3216 K-Ar, Rapson, mica separate 1763 Minene sill; Sr too low for satisfactory data but (244*45) Rb-Sr, mica separate K-Ar should be reliable 327*5 312G separate mica K-AI, 34Ot23 348~27 IC-Ar, mica sepmte Lowdon, 1960 Syenite d%e, no chlorite 330+23 334t26 separate chlorite K-Ar,Fyroxenite; mica 1960 no Lowdon, 355+18 362t18 K-Ar, mica Baadsgaard, separate 1961 Jacupirangite 3&18 367t18 micaseparate K-AI, 1961 Baadsgaard, Minette 304+15 31045 separateBaadsgaard, mica 1761 K-AI, Pegmatite (233+11) (231+10) mica K-AI, Separate 1975; Cumie, Wanless, Me@-ijolite: 1973 no alteration(discordant, low) (22Df8) (227t10) K-Ar, separate 1775: mica Cume, Wanless, Nepheline no 1973 syenite; alteration (discordant, low) (408k15) K-Ar, (415*15) mica separate 1966 Wanless, Altered lamptnphyre (421+11) K-Ar, Stevens, hornblende Hornblende 1982 from syenite: excess argon separate 368-370 Ma U-Pb, zircon sphene Parrish, 1987 207PbDMPb ageson zircon as follows:359.9i2.2: 363.1*2.2: 364.9t2.2; sphene368.8t7.D: 357.3*8.4;361.2t9.0;356.6~16.1. Dola m e reealnrloted using currenflyoccepled decay con~lenls, A m l r o n g , persoml communicolion, 198% R.L examined contact relationships and concluded that the com- 1979, mapping, soil and rock geochemistty andtrenching plex wasa sample of Precambrianbasement and the contact were doneto assess the fluorspar-lead-zinc potential of the with thesediments was unconformity.Radiometricdates an property (Bending,1978; Alonis, 1979). More recent work obtained in the early 1960s (Lowdon,1960; Baadsgaard et (Graf, 1981,1985) attempted establish the economic po- to al., 1961; Rapson, 1963) suggested a mid-Paleozoic age, tential of the property interms of other commodities.Duing circa Devono-Mississippian (Table 4). Cunie (197.51, un- certain of the validity of the early radiometric work, had this latter work it was discovered that the property also :on- additional material analysed and obtained Early Triassic tained anomalous concentrations of rare-earth elements ages (see Table 4). In evaluating his, and earlier work, Cume WE). suggested a preferred age of emplacement of circa 245 Ma. The Rock Canyon Creek area is underlain by a Cam- Recent work on uranium-lead zircon systematics (Panish et bro-Ordovician to Middle Devonian carbonate-dominated al., 1987;also see Table 4) indicates that the mid-Paleozoic sequence (Leech, 1979; Mott etal., 1986). Theregionahtra- dates most closely represent the true age of emplacement. tigraphy has been previously described Mott et al. and by only relevant points willbe reiterated here. The southu,est- ROCK CANYON CREEK FLUORITE AND em boundary of the property is marked by the eastemmost RARE-EARTH ELEMENT SHOWING in a series of west-dipping thrust faults which place Cam- (825/3E) brian and Ordovician strata over younger rocks (Figure 19). The Rock Canyon Creek showing (Candy and Deep The remainderof tbe area is underlain by an overturned to Purple claims) occurs near headwaters of Rock Canyon the upright homoclinal sequence, yonnging to the east. This Creek (Figure 19) in theeastern White Riverdrainage, ap- succession comprisescoral-rich limestones of the Ordovi- proximately 40 kilometres east of Canal Flats (latitude cianBeaverfootFormationinthenorthwest,unconformably 5012N. longitude 115"OSW). It is accessible by conven- overlain by buff-weathering dolomites and solution brec4:ias tional vehicles along the White River and Canyon Creek of the basal Devonian unit which are, in turn, conformably forestryroads, whichjoinHighway3Atwokilometressouth overlain by fossiliferous and nodular grey limestones of the of Canal Flats.The main mineralized zone between the lies Fairholm Group. The fluorspar and REE mineralization is 1525 and 2000-metre elevations in a valley that has been stratabound, hosted mainly by the basal Devonian unit. burnt-overand subsequently logged. Access is excellent, but exposure poor due to thick drift cover. Acarbonatite-related origin has been suggested the for The prospect was discovered 1977 during regional in a showing (Graf, 1985; Hora andKwong, 1986; Pell, 19117), exploration program camed out by Riocanex (then Rio which consists of metasomatically altered (fenitized) :De- Tinto Canadian ExplorationLtd.), in search of Mississippi vonian carbonate rocks, possibly associated with a deep- Valley-type lead-zinc mineralization. Between 1977 and seated carhnatite intrusion. 24 Geological Survey Branch
  • 33. Ministry of Energy, Mines and Petroleum Resources [(Ba,Ca,Ce)A13(P04)z(OH)3HzO], calcite, limorite, illite and barite are common accessory minerals (IIora and Kwong, 1986). Parisite [CaCez(C03)3Fz] has also been identified from fy of the Rock luorite veins by scanning electron microscopy and may be associated a i t h bast- naesite. Neutron activation analyses of up to 2.3% lare-earth elements and 2.7% barium have been reported (Gl,af, 1985; also Appendix 1). Niobium,strontium and yttrium also are present in measurable amounts (Table 5). Contacts between mineralized and unmineralized dolomitic rocks are grada- tional; the amount of fluorite veining decreases and col- the our of the rocks changes gradually from dark brown grey to or buff, the characteristic colonr o unaltered dolomites in f the area. This type of mineralization defines a northwest- trending zone mappable over a for kilometre, subparal1c:l to strike (Figure 19). The second type mineralization consists olmassive, of fine-grained purple and white fluorite, which csmmonly comprises greater than 40% of the rock, together with ac- cessory prosopite [CaAlz(F,OH)3], gorceixite, pyrite and minor barite, calcite, rutile and kaolinite (Hora a d Kwong, 1986). Chemical analyses indicate that this type of miner- alization can contain up to 71% CaFz. The rare-earth ele- ment and pyrite contents of these rocks arerelatively low. Massive fluorite mineralization has not been found in place, hut abundant float occurs at the southeast end of the zone of Type 1 mineralization, near the nortb-flowing Ixanch of Rock Canyon Creek (Figure 19). Fine-grained purple fluorite disseminatedin white cal- cite whichis locally interbeddedwithbuff-weatheringdolo- LEGEND mite and forms the matrix of solution breccias constitutes UPPER DEVONIAN the third type of mineralization. Fluorspar is prese nt in con- m F a i r h o l m Group-grey limestone centrations from trace amounts to a few percent. Minor sare- nodular limestone,dolomite and earth element enrichment also reported (Graf,11385).This is argillaceous limestone type of mineralization is found randomly distributed MIDDLEAND/OR UPPER DEVONIAN throughout the basal Devonian unit. m B a s a l Devonian Unit-dolomite, mudstone and solution breccia The fourth type of fluorspar mineralization occurs in rocks tentatively assigned to the Devonian Fairhalm Group UPPER ORDOVICIAN LOWER AND SILURIAN M B e o v e r f o o t Formation-limestone, and is found in one locality, the2135-metre elwationon at dolomite and abundant corals the ridge east of the headwaters of Rock Canyon Creek (Fig- LOWER MIDDLE AND ORDOVICIAN ure 19). Massive purple fluorite which constitutes greater Losk/Skoki Formation-dolomite, limestone than 20% of the rock, forms the matrix of an irttrafonna- and sandstone tional conglomerate(Plate 10) and locally replaces the irag- m G l e n o g l e Formation-shale ments. Minor barite, pyrite and magnetite may also be present. CAMBRIAN ORDOVICIAN AND M M c K o y Group-limestone shale and GEOCHEMISTRYFigure 19. Geology of the Rock Canyon Creek fluorite rare-earth The interpretation that the Rock Canyon Creek show-showing. Modified from Pel1 and Hora (1987) and Mott (1986). ing is carbonatite related appears to be consistenl with pre- liminary geochemical data (Table 5; Appendix 1). InMINERALIZATION addition to high fluorine, REE and barium, the rock:! are Four main types of fluorite mineralization are identifi- enriched in Fez03, MnO, MgO, strontium, yttrium, phos-able in the field. The first and most widespread consists of phorus and niobium (Table 5) relative to the unaltered De-disseminations and fine veinlets of dark purplefluorite in a vonian carbonates. Chondrite-normalized rare-earthdark brown to dark orange-brown weatheringdolomitic ma- element abundance patterns are typical of carboniltites (Fig-trix. Fluorite content generally varies from 2 greater than to ure 20) and fall within the field defined by off ler Blitish10% of the rock. Bastnaesite (CeC03F) often occurs along Columbia carbonatites, however, the Rock Can:,on Creekthe margins of fluorite veins, as does coarsely crystalline showing is more enriched rare earths than most other ex- indolomite. Disseminated pyrite, gorceixite amples, comparable only withthe REE sweats and dikesBulletin 88 25
  • 34. TABLE 5 CHEMICALANALYSES, ROCKCANYON CREEK Weakly altered carbonates, adjacent to Type1 .. Type 1 mineralization Type 2 mineralization mineralization A1203 Fe203 4 li 31 2 0.39 3.16 0.85 0.02 0.02 0.01 2.32 1.07 0.20 2.80 2.80 2.95 2.89 0.03 1.10 3.26 5 _ 0.94 2.82 0.03 0.03 0.37 0.43 " _ 0.06 1.24 5.28 3.641 5.49 7.41 6 _ . 1.04 7 ~ 1.10 0.39 2.04 0.02 0.04 0.41 15 13 17.16 15.31 17.05 1.061 1.810.53 14 0.64 6.39 9.34 16 7.84 22.79 0.10 2.25 1.29 <.01 0.01 1.62 1.11 1.01 0.16 0.09 1.49 0.961 1.09 0.78 0.11 <.01 0.021 <.01 <.011 11.790.17 2.408.9611.8014.40 0.22 4.2310.5314.2612.86 14.0012.61 13.4010.30 34.7026.3619.0539.59 29.4029.0046.60 37.4530.811 42.08 37.57 32.10 0.08 32.89 40.491 0.05 nd nd 0.22 0.16 0.23 <0.03 0.55 0.18 0.06 nd 0.08 0.01 0.24 4 Z I 2;:fi;I 0.23 0.25 nd nd 0.01 0.02 0.06 0.58 3.27 2.47 0.931 0.05 0.13 29.97 35.49 33.30 35.36 35.61 34.28 39.78 32.80 25.68 40.80 34.04 12.88 12.021.670.17 0.120.26<.090.921.520.340.310.360.591.49 0.14, 0.14, 2iil 83.2988.76 88.3493.14 90.12~ 87.23 ~92.85 93.02 82.49 95.29 99.87 79.24 98.01 77.89 94.99 8 9 4 3 - 3 6 24 11 2 7 3 Q 12 28 22 40 39 - 17 26 27 QO 34 10 12 7 7 7 10 6 10 6 8 11 2 4 1129 > l o o 0 0 7759 1369 3428 981 735 1260 1334 608 1676 1024 3723 1358 1483 300 9820 4078 950 24226 1306 11538 10942 14953 790 46 54 5352 13840 12215 13582 136 4137 49 42 28 52 21 34 75 45 23 41 303149158 54 181 40 162 20 5 53 63 48 224 317 174 157 146 165 147 278 15 90 <5 157 17 163 15 21 56542683 2833 4876 453803 2318 5319 24 6072 5 18 530 125 111 44 8596 4365 6285 3957 7858 8986 6302 5009 48 42 95 19 142 948 178 45 4 :43 70-I - - -I i :I <3-I 107 81 92 428 407 201 188 69 81 <2 263 412 305 1120 7 < 2 < 2 < 3 2.00% 4.80% 4.50% 2.96% 1.75% 6.52% 6.40% 3.13% Sample descriptions: 1- massivefluorite in altered carbonate: 2 - brown, alteredcarbonate with streakroffluorite; 3 - brown, altered carbonate abundantfluorite; with 47 - - 38 < 2 32 < 2 a a a 36 47 52 43 460 134 2.90% 0.90% 1.43% 0.51% 47 5 33.28% 34.56% 32.00% 10 - grey to bug laminated carbonate with minorfluorite; 45 11 - light grey laminafed carbonate with grey altemtion patches; 12 - grey to bufj laminated carbonate with traces offluorite; - A 6.08% 4 - brown, alteredcarbonate withfluorite; 13 - massive purple and whitefluorite with some calcite; 5 -fluorite veins in altered carbonate; 14 - purplefluorite; 6 -fluorite in altered carbonate; 15 -massive white andpurplefluorite; 7 - chocolate-weathering altered carbonate rockwithfluorite; 16 - i n t r a f o m t i o d limestone conglomerate withfluoritematrix; 8 - brown, altered carbonate; -.- . Samples1,2,5,6,7,9,11nnd13tol6majorelementsbylCP;trace 0 , a. ." , L _ n Y*,, "" I~ .. ~UIYVIUT ~.~ wu,uunz,ruunrr; ..I WL,, ."v . elements byXKForlNA.4; Samples3,4,8,10,12 majorandtrace elements byXRF
  • 35. CHONDRITE-NORMALIZED REE PLOl ROCK CANYONCREEK FENITES La Ce Pr Nd Sm Eu Tb Dy Ho Ttn Yb L Rare-earfh Elements Figure 20. Chondrite normalizedREE plot - Rock CanyonCreek fenites.Plate 10. Intraformationalconglomerate with matrix entirely KECHIKA RIVER AREA(94L/ll, 12,13)consisting of dark purple fluorite from the Devonian Fairholm A suite of alkaline igneous rocks consisting ofGroup along the ridge crest eastof the Rock Canyon Creek (rype4 fluorspar mineralization). trachytes, trachytic breccias, crystal and lapi:!.li tuffs, syenites, melanocratic augite syenites, an alkaline diatremeassociated with the Aley complex(Mader, 1987). and pos- and related dikes and numerous strongly sheared and alteredsibly some lithologies in the Kecbika River area. rocks, crops out the Kechika Ranges the Cassim Moun- in of tains (RAR and REE claims). These rocks have been ex- plored for their yttrium and rare-earth element potlmtial.GEOCHRONOLOGY The alkaline rocks are intermittently expored in a Timing of metasomatism is poorly defined. Minerali- northwest-trending zone in excess of 20 kilometres!ong, thezation apparently occurred prior to the Jura-Cretaceousde- centre of which i s approximately 58O42 north and 127O30formation, as no fluorite is observed west of the west (Figure 21). Elevations in the area range from 1180 towest-boundary fault, and postdated at least part of the depo- 2315 metres, and there is excellent exposure above treeline.sition of basal Devonianunit. This broadly defines a time the Access is by helicopter from Dease Lake, approximately 160 kilometres to the west or from Watson Lake, Yukon,span of 280 Ma during which mineralization must have oc- which is approximately 150 kilometresnorth of the prop-curred. Some mineralization (Vpes 3 and 4, fluorite asso- erty.ciated with solution breccias and intraformational The area is underlain by unmetamorphosedto weaklyconglomeratematrix) may have resulted from elemental re- metamorphosed Cambrian to middle Paleozoic stratamobilization, and therefore postdate the Type 1 and 2fluo- (Gabrielse, 1962).To the northeast of the area (Figure 2 0 ,rite and rare-earth deposits. It has been suggested that thick-bedded quartzites of probable Early Cambriar age aremineralization may have been synchronous with deposition folded in a broad open antiformwith a northwest-trending axis. Along the southwestern limb of the antiform, theof the basal Devonian unit (Graf, 1985). A slightly younger quartzites areincontact with athick, southwest-dippingsec-age is favoured as most other carbonatites in the province tion of phyllites, thin-bedded marblesand massive, bloclcyare Devono-Mississippian early Mississippian(circa 350 to weathering dolostones probable Middle Uppt:r Carn- of andMa) in age. brian and Ordovician age (Gabrielse, 1962). Chlorite,Bulletin 88 27
  • 36. sericite, sericite-graphite and calcareous phyllites are all (malignites), displaying good igneous textures, predomi-present within this succession. To the southwest, the phyl- nate in the south. These syenites contain some irregula: leu-lites are bounded by a gently southwest-dippingfault, which cocratic zones and are brecciated along their margins.juxtaposes greentuffs and cherty tuffs overlain by fossilif- Numerous small sills, dikes and metasomatic alterationerous grey limestones and pink andquartzites with the black zones are present peripheral to the main intrusive body.phyllites. The limestones, which contain beds rich in ru- A diatreme breccia pipe is exposed near the cenlre ofgosan corals, favosites-type corals, bryozoans and brachi- the property (Figures 21 and 22; see Chapter 5). The pipeopod fragments are probably of middle Paleozoic age contains xenoliths of numerous sedimentary and igrmus (Silurian). The cherts, tuffs and limestones the fault panel in rock types and rare chrome spinel xenocrysts, in a pale outline an overturned antiform and, to the southwest, are in green, carbonate-rich tuffisitic matrix.The diatreme, which fault contact with graphite-sericite and chlorite-sericite is close to the northeast bounding fault, is weakly to stronglyphyllites similar to those to the northeast. The gently dip- deformed andlocally cut by carbonatite dikes and cwbon-ping, northeastern boundingfault apparently has had normal ate-sulphide veins. movement along as younger strata are present in hang- it, the A large area underlain by igneous rocks, including the ingwall package, however, geometry and the presence of the main mineralizedzone, is present immediately northwmt of hangingwall anticline imply that at one time there probably diatreme (Figure 22). It consists of a complex, southwest- was thrust motion along this fault. The southwestern fault is a moderate steeply southwest-dippingthrust which places to of dipping homoclinal sequence moderately to strongly de- formed (sheared) igneous andpyroclastic rocks. older rocks over younger rocks. The alkaline rocks are pre- sent in the tuff-chert-limestone thrust panel, between the The base of the sequence is composed of pale green to two phyllitic units. pale orange weathering,variably calcareous rocks that lo- cally contain rare chrome spinels. These rocks are interlay- ered with a minor amount of grey aplite and buff toDISTRIBUTIONAND FIELDRELATIONSHIPS brown-weathering, fine to coarse breccias interlayered withOF ALXALINE ROCKS fine-grained, laminatedbeds. Well-developed gradedhyers Alkaline igneous rocks occur four main areas of the in are present locally.The coarse breccias and the bases of theproperty (Figure 21). Dark green, intrusive mafic syenites graded beds consist of lithic fragments, 1 to 3 centimetres Figure 21. Generalized geologyKechika area. -28 Geological Survey Branch
  • 37. Ministry of Energy, Mines and Petroleum Resources N I Figure 22. Geology of the central part of the belt of alkaline rocks, Kechikaarea.across, in a welded tuff matrix containingabundantflattened weathering, extremely carbonate and sericite-rich varieties.pumice fragments and altered crystals. Fine-grained, car- This unit is generally weakly to moderately foliated,bonate-rich material is present at the of the graded beds. top strongly lineated and, in thin section, displays a myloniticThis part of the section is interpreted as comprising a series fabric. These rocks tentatively interpreted as trxhytic or areof fine-grained, locally calcareous tuffs, crystal and lapilli syenitic tuffs or flows with, possibly, a minor sedimentarywelded tuffs with some interlayered sedimentary material component;the degree of deformation makes recognition ofand, locally, sills. the protolith very difficult. It is overlain by predominantly whitelocally buff and to Dark green mafic syenites that grade from medium-pinkish weathering rocks containing varying amounts of grained, igneous-textured rocksto foliated chlorite schistsquartz, feldspar, apatite, carbonate and sericite. Yttrium near the margins, are present near the top of the :sequence.minerals occur within white-weathering this horizon, appar- The mafic syenites appear to have been intrusiv: into theently related to phosphate-rich areas. Locally this rock type white-weathering, quartz-feldspar-apatite-cmbonate-grades into grey-weathering (graphitic?) varieties or rusty sericite sequence and are now present as a megaboudin.Bulletin 88 29
  • 38. British Columbia These rocks are structurally overlain by an unusual lower unit. At the north end of the zone, this unit is in faultbreccia unit. To the north, this breccia consists of predomi- contact with lower Paleozoic phyllites; to the south it inter-nantly subangularclasts a very fine grained, buff to light in fingers with black siltstones and is overlain by a p d e togrey matrix rich in p u m i c e fragments. To the south, it is medium green weathering, medium-grained igneous :flowsrusty weathering and contains predominantly subrounded or sills ofuncertain affiliation. Rusty weatheringcarbolatitefragments in a carbonate-rich matrix. Inboth areas the brec- dikes and green to orange-weathering fragmentaldikes orcia is multilithic, containing a variety of sedimentary and sills occur in numerous locations throughout the sequmce.igneous rock fragments; notably absent the fragment within At the north end of the property a thick section of alka-suite are mafic syenites. Fluorite and pyrite are common line igneous rocks is exposed. It consists mainly of a com-accessoryminerals in the breccias, both disseminated within plex sequence of pale green to orange to buff-weatberingthe matrix and replacing fragments. Locally, a unique, buff- agglomeratebreccias and tuffs, buffand greyaplite layers,weathering feldspar-porphyrytic trachyte structurally un- white-weathering quartz-feldspar-carbonate-sericite rocksderlies the breccias and contributes clasts to the breccias. and some sedimentary interlayers. Only reconnaissanceThe trachytes are interpreted as flows or sills, and the brec- traverses have been completed in this area and a detailedcias as volcanic tuff-breccias with a matrix that varies later- stratigraphy has notbeen established. Although lithologiesally from lapilli tuff to fine-grained calcareous tuff. are superficially similar to those in the central part of the area, no zones of high-grade mineralization have yet been The breccia sequence is overlain by a second buff to discovered.white-weatheringfeldspathic unit. It is quite similar to themineralized, white-weathering quartz-feldspar-carbonate-sericite-apatite unit, however, it generally does notcontain PETROGRAPHE SYENlTESas much sericite or carbonate and is more massivethan the Syenites and melanocratictitaniferous augite sy:nites (malignites) are exposed at the south end of the property. The melanocratic syenites, which arepresent as large dikes Plate 12. Typical trachyte, Kechika area, note feldsparphe~rocrystPlate 11. Potassiumfeldsparporphyroclasts in a fine-grained in a matrix predominantly consisting of felted feldspar laths withcarbonate-sericite-feldspar-quartz matrix from a sheared minordisseminatedcarbonate and opaque, (colour photo,leucosyenite, Kechika area. Long dimension is mm. 7 page 135).30 Geological Survey .8ranch
  • 39. Ministry o EneTy, Mines and Petroleum Resources f ”or elongate stocks, are fineto medium-grained, dark green PETROGRAPHE TRACHYTESto bluish grey rocks with small pyroxene feldspar phe- and Buff,greyorpinkishweatheringtrachytedikesandsillsnocrysts. They contain 40 to 60%microcline, 5 to 20% al- (or flows) are exposed in the central and northernparts ofbite and 10 to 20% augite with titaniferous rims. Garnet the area. For the most part, they appear aplitic in hmd speci-(melanite), biotite, sodalite, cancrinite, allanite, magnet- men, however, some varieties contain 2 to 5-millinletre feld-itehlmenite, pyrite, fluorite and apatitehonazite are pre- all spar phenocrysts in an aplitic matrix. In thin section, thesent as accessory phases. Veins or segregations containing porphyritic feldspars are generally polycrystalline and ex-coarse calcite and dark purpleflnoritekbiotitekepidote are hibit both simple and ‘checkerboard’ twinning; they appearlocally present within the malignites. In the central and to beperthitic in composition. The phenocrysts present arenorthern parts of the property, melanocratic syenites are in a fine-grained groundmass of felted feldspar ~nicrolitesstrongly sheared andchlorite rich. with minor disseminated carbonate and opaques 12). (Plate Leucocratic syenites crop out the southern part the in ofproperty, generally as irregular zones within the melano- PETROGRAPHE FELDSPAR-QUARTZ-cratic syenites. They are light grey, medium-grained, mas- CARBONATE-SERICITE ROCKSsive rocks containing35 to 40% microcline and10 to 20% Fine-grained, extremely fissile and micaceon!; phyIlitesalbite, with fluorite, sodalite, cancrinite, sphene, biotite, py- to massive, white to buff-weathering rocks are commonlyrite and pyrochlorepresent in variable amounts. Crosscut- associated with other alkaline rocks in the central and north-ting calcite-pyrite-fluorite veinlets are common. The em areas of the property. They locally have myklnitic tex-syenites vary from massive and relatively unaltered to tures and contain varying amounts of quartz, carbonatesheared. Sheared syenites contain potassium feldspar por- (generally dolomite, although calcite and iron-rich magne-phyroclasts in a tine-grained recrystallized and altered ma- site have also been noted), muscovite, potassium feldspar,trix Containingabundant clay minerals, quartz, plagioclase, phosphates and pyrite. Massive varieties commonly havedolomite and muscovite (Plate 11). irregular dolomitic patches in a siliceous matrix.Plate 13. An apatite-rich zone the quartz-feldspar-sericite-carbonate-(apatite)rocks. The high relief, low birefringent material in (mediumto dark grey) is all apatite with rare earth enriched phosphate minerals. relief material(white to black) is quartz and felispar. The Lowlath shaped grains are sericite. Plane polarized light and crossed nicols. __Bulletin 88 31
  • 40. British Columbia Locally phosphate minerals comprise in excess of 25% In some samples, potassium feldspar porphyroclar.tsareof the sample (Plate 13). In such rocks, a number of phos- preserved in a fine-grained quartz-carbonate-sericie: ma-phate minerals may be intergrown, with apatite the most trix, which suggests that the mylonite had a syenii:ic or trachytic protolith. In other cases, the rocks are very finecommon species. Monazite (containing cerium, neodym- grained and completely recrystallized; no textural evidenceium, lanthanum, calcium, thorium), xenotime (yttrium of the protolith remains. Fieldevidence indicates that thesephosphate, with minor dysprosium, gadolinium and cal- rocks are confomahle to bedding inthe hosting limestonescium) and ytirium-thorium-calcium-dysprosium-gadolin- a and werepossibly flows or tuff layers. The high d e g m ofium-bearing phosphate have been identified by scanningelectron microscopy. Minor amounts of an iron-thorium-ytrium-calcium silicate mineral havealso been noted. * mofic syenites * leucocraticsyeniies x shearedleucosyeniles 20.00 1 Nephelinite /,, Miaskitic syenite 3 iamilv / carbonatiter Ah 9 1020 F (FeOtC0.98 TiOZ) - COC D Subolkaiine A rocks 30.00 40.00 50.00 60.00 70.0 Si02 - * mafic syenites * ieucocraticsyenites X sheared leucosyeniter Carbondite Agpoific syenite family qveroge mofic syenite x XY mafic syenites j / Subalkaline rocks 0 quarlz-feidrpar-carbonate- Alkali-basalt rericite apatite rock fomiiy corbonatites 0.00 , , ,,,,,,, , , , I I I , , , I I I I I I I I I , , , I , rm 0 rounded cobble breccia 30!00 40100 50,OO 60100 70.0 0 brown bedded oggiomerate Si07 -k dikesFigure 23. Alkali-silica and agpaiticindexdiagrams,Kechikasyenites. Figure 24. Major element ternary plots, Kechika igneous su:te. - -32 Geological Survey Bnmch
  • 41. Ministry o Enemy, Mines and Petmleum Resources f TABLE 6 GEOCHEMISTRY OF SELECTED KECHIKA SAMPLES T syenite 43.39 51.05 67.28 29.86 58.35 39.38 46.85 72.17 72.47 65.84 55.0~ 0.76 0.46 0.45 0.02 0.04 1.80 0.08 0.68 0.15 0.49 0.08 4 3 19.42 19.86 14.96 7.92 7.44 10.83 7.52 14.67 11.05 17.52 9.63 4.67 2.39 2.22 5.40 4.01 4.69 5.28 1.53 3.96 1.68 1.95 0.26 0.23 0.16 0.200.17 0.140.43 0.23 0.05 0.25 0.17 0.13 0.01 0.01 0.01 0.M 0.04 1.413.27 3.267.23 8.0113.92 1.74 1.22 0.42 3.88 4.75 1.03 0.57 4.73 0.32 4.9~ 0.94 11.65 13.17 5.97 5.16 9.55 6.17 9.07 14.12 8.40 12.79 10.90 1.10 0.96 0.87 7.96 3.48 2.98 6.78 6.14 3.24 3.09 0.90 0.15 0.21 0.37 0.20 0.17 0.24 0.95 0.24 4.48 4.34 6.96 6.33 4.92 8.28 9.06 6.60 5.32 8.82 5.52 5.05 8.48 10.90 7 2 2.78 6.02 3.23 1.84 2.96 2.66 8.13 20.88 11.95 14.20 15.93 2.35 2.14 1.72 12.63 0.36 0.33 ~ 0.29 -0.26 0.25 - 0.14 - ~ 0.16 0.04 - 2.42 - 0.34 - 0.01 0.03 ~ 0.02 0.07 ~ ~ " 0.M 98.14 97.59 101.27 98.57 96.09 98.19 100.17 96.74 99.96 100.53 92.72 99.88 1w.18 97.20 99.10 99.85 1W.56 99.81 76 180 56 18 168 -30 0 0 7 11 19 QO 40 150 350 1W 19 354 40 4 0 10 12 13 110 <SO 35 24 39 17 18 18 270 220 316 316 285 230 220 279 248 a3 160 170 16M) 1IW 2153 2198 2438 2800 ISW 1593 5534 sa 4w 65 1600 3100 1245 1949 1720 19w 2wO 4059 1881 679 307W 230 120 140 270 380 143 120 415 257 169 357 a9 325 130 81 194 241 272 140 405 303 141 136 43 270 4 20 41 31 62 4 24 33 2747 38 63 100 77 120 134 342 130 120 99 71 39 120 640 49 52 15 18 101 71 71 170 183130 174 613 zw 210 170 128 93 240 960 86 IO1 15 60 208 162 140 46 248 46 sa 31 29 22 41 a8 ::~ 4 4 a s s 4 4 a s 1 1 4 7 48 5 11 II I1 3 5 8.6 19.0 10.7 6.5 22.8 3.7 3.3 7.9 5.1 0.2 2.7 3.6 I7 10.2 <.2 c.5 <.7 6.9 0.7 11 8.2 I1 10 5 IO 7.8 19 12 IS cl <I 10 5 10 12 21 5 I7 22 ;4 46 37 3; 54.5 Is1 269 583 208 56 58 22 45 138 57.3 3.5 2.4 48 41 40 5.4 34 52 25 1.4 2.3 51 33 51 26 34 35 10 122 112 239 27 155 121 72 49 6 94 L6200 7w0 31W 4700 75W 32W 1 5 w O 53W 1 5 w O 320 460 700 2900 320 1800 am ~ 760 " 4s " 2900 0.05 0.07 0.08 0.26 0.3 0.38 0.42 0.64 0.21 0.18 0.16 0.19 0.06 0.37 0.14 0.680.29 1.20 0.43 2.15 6.20 2.47 10.11 10.00 11.36 11.28 7.24 3.90 7.19 0.64 3.09 8.29 6.92 3.74 3.05 1:72 20.71 22.02 24.60 20.86 20.57 19.82 24.34 25.44 16.01 15.25 10.42 2.03 6.86 18.23 17.95 13.25 48.64 50.30 0.14 0.16 0.26 0.26 1.20 0.11 0.13 0.15 0.13 0.18 0.23 0.25 0.29 0.26 2.69 0.11 0.13 0.14 3.46 3.19 1.66 3.85 3.11 0.76 0.28 6.40 7.49 6.43 0.29 9.07 10.35 5.96 2.85 0.63 1.06 0.20 1.82 6.38 7.15 18.66 32.53 30.97 30.83 38.71 20.83 18.58 14.93 3.56 9.31 21.53 7.73 25.86 19.30 13.70 18.20 8.30 0.23 0.02 0.03 0.08 0.12 0.16 0.01 0 0 0.47 0.19 .9 0.25 0.14 96.13 98.02 95.67 96.94 100.91 98.06 96.86 98.491 92.82 86.54 83.w _. .. 85 a8 39 95 <49 69 0 1 43 I60 160 220 63 130 210 27 4 3 4 5 430 4w 624 68s 505 275 510 467 660 570 140 71 I50 815 3500 185 I1W 1300 17W 310 1898 522 ISW 310 39w 713 2Mx) I500 130 270 5200 5W 590 <IW ow 010 4 4 190 100 75 68 59 26 a3 76 130 470 180 95 d 70 53 32 1:1 120 43 32 130 37 195 38 85 62 60 94 34 30 93 23 125 130 43W 6671 2645 103 20 120 61 4 9 9 62 21 37 35 450 340 250 222 51 a75 60 360 478 41 53 23 130 20 450 480 1120 1810 440 543 105 I020 110 320 628 59 95 54 270 48 630 210 610 I050 1970 402 140 166 420 227 157; a 2 4 a 1 <4 4 4 4 6 4 4 c37 4 0 5.7 28.7 22.9, 8.8 1.7 6.4 27.1 4.3 11 2.2 6.; 7.9 3.8 5.8 4 1.7 60 22 2.2 1.1 <I 3.4 3.7 10 5.2 <I <1 a.2 2380 3312 1322. 620748 55.4 55.6 11 36 13 54.9 778 972 37 99 101 2.2 4 4.6 1.8 0.7 6.5 7.1 <.5 1.4 4.3 47 69 213 llS00 127W 62W 720 140 1 5 -~ 40 "Bulletin 88 33
  • 42. deformation within these rocks, compared with the other rock types, may be a result of original incompetence, in which case a tuffaceous protolith is favoured. Phosphate- rich rocks are distributed in discontinuouslenses up to :I few metres thick and several tens of metres parallel to oyerall layering. PETROGRAPHE CARBONATITES Fine-grained igneous carbonate rocks, with a di:;tinc- tive orange-brown-weathering colour also present :n the are Kechika area. They occur as dikes which aregenerally less than a metre wide and crosscut both other alkaline rocks and the carbonatehostrocks. Volumetrically the carbonatites are an insignificant part of the alkaline suite. The carbonatites are dolomite or ankerite rich (SO%), and contain quartz. Accessory phases include microdine, muscovite, barite, iron oxides, pyrite, fluorapatite, gor- ceixite, xenotime and an unidentified thorium-calcium- ytrium-iron phosphate mineral. The carbonatites are locally fragmental, containing subangular to rounded lithic :lasts Figure 25. CaO-MgO-FezO,t+MnO carbonatite plot, Kechika. of various rock types. ~~ ~~ ~ .~ . . - ~~~~ ~ - CHONDRITE-NORMALIZED PLOT REE CHONDRITE-NORMALIZED PLOT REE KECHIKAMAFIC SYENITES KECHIKA LEUCOCRATIC SYENITES i 1 7 - 1 I Lo Ce Pr Nd Sm Eu Tb Dy Ho Tm Yb L LO Ce Pr Nd Sm Eu Dy Tb Ho Tm Yb LI Rare-earth Elements Rare-earth ElementsFigure 26. (A) Chondrite normalized REE plot - Kechika mafic syenites; (B) Chondrite-normalized REE plot - Kechika leucocraticsyenites: (C) Chondrite-normalizedREE plot - Kechika quartz-feldspar-carbanate-sericite rocks; (D) Chondrite-normalizedREI; plot -Kechika quartz-feldspar-carbonate-sericite-apatiterocks; (E) Chondrite-normalized REE plot - Kechika carhoratites;(F)Chondrite-normalizedREE plot - Kechika veins, shearsand alteration zones.34 Geological Survey Branch
  • 43. Ministry o Energy, Mines and Petroleum Resources f ~ ~~ ~ ~ ~~ ~~ ~~~~~~ ~~~~ ~~~~ ~~ ~~ ~ ~~ ~~~~~~ ~ ~~ ~ CHONDRITE-NORMALIZED REE PLOT CHONDRITE-NORMALIZED REE PLOT KECHIKA QUARTZ-FELDSPAR-CARBONATE- KECHIKA OUARTZ-FELDSPAR-CARBONATE-io5 ROCKS SERICITE 105 SERICITE-APATITE ROCKS104 I@ 1 La Ce Pr Nd Tb Dy Ho Sm Eu Tm Yb 1 Lo Ce Pr Nd Sm Eu Tb Dy Ho Trn Yb LC Rare-earth lements E Rare-earth Elements CHONDRITE-NORMALIZED REE PLOT CHONDRITE-NORMALIZED REE PLOT KECHIKACAR80NATITES KECHIKA VEINS, SHEARSAND ALTERATION ZONElo4 4 104 103 102 10 1 1 La Ce Pr Nd Sm Eu Tb Dy Ho Tm Yb L Lo Ce Pr Nd Sm Eu Tb Dy Ho l m Yb LI Rare-earth lements E Rare-earth lements E Figure 26 (continued)
  • 44. GEOCHEMISTRY middle and heavyrare-earth elements and yttrium. Values Syenites from Kechika have variable alkalilsilica ratios ofupto1.13%Y~0~,0.30%Nd20~,0.ll%Sm~0~,0.03%(Figures 23a andb: Table 6); however, the ‘average’ lenco- EuO, 0.14% DyZ03 and 0.05% Tb203 are reported by Pel1syenite plots in the miaskitic syenite field and the ‘average’ et al. (1990). The samples enrichedmiddle and heavy in raremafic syenite plots in the nephelinite field, near the miaski- earths give convex-upward, positively sloping chondrite-tic syenite boundary. Syenites are enriched in sodium (Fig- normalized rare-earth patterns (Figure 26d) which are noture 24a) and moderately enriched barium andstrontium in typical of carbouatite suites. Almost flat chondrite-no~mal-relative to other rock types in the Kechika area (Table 6). ized rare-earth patterns are occasionally produced by leu-On an AFM diagram, the syenites define a trend subparallel cocratic syenites as well (Figure 26b).to a typical basalt trend, but displaced away from the ironapex (Figure 24b). Carbonatites fall within the magnesio- GEOCHRONOLOGYcarbonatite field, close to the boundary with the ferrocar-bonatite field and well removed from calcite carbonatites No radiometric dating has been completed on the(Figure 25). Quartz-feldspar-carbonate-sericiteand quartz- Kechika River alkaline rocks. The presence of mylcnitesfeldspar-carbonate-sericite-apatite rocks are variable in and their distribution suggest that they were emplaced priorcomposition (Figure 24, Table 6). They are generally so- to orogenesis. Fieldrelationships, in particular the pre.ence s ordium poor and calcium potassium rich. Apatite-rich va- ofbedded agglomerates tuffswith sedimentary and interlay-rieties can contain over 19%PzOs. ers, suggest that the alkaline suite is coeval with the host carbonate sequence, is, midPaleozoic. that As with other alkaline suites, rocks in the KechikaRiver area are generally enriched in rare-earth elements Clear crosscutting relationships between many of the(Appendix 1). Chondrite-normalized rare-earth element alkaline phases are largely obscuredby deformationand, forplots of most rock typesfrom the Kechika area (Figure 26A the most part,the sequence of deformation cannot estab- heto F) showlight rare-earth enrichmenttypical of carhouatite lished. Mafic syenites in the central part of the area mustand alkaline rock complexes. Some carbonatites locally have been emplaced late in the sequence, as clasts of thesecontaining np to 3.77% cerium and lanthanum oxides. Of rocks were never found in the agglomeratesor breccias. Car-particular interest are the quartz-feldspar-carbonate- bonatite dikes, which crosscut quartz-feldspar-carbollate-sericite-apatite rocks which, as well as containing signifi- sericite rocks and some tuffs, appear to be some 0.: thecant amounts of PzOs, have anomalous concentrations of youngest igneous rocks the sequence. in36 Geological Survey Bnznch