BCGS: Carbonatites, Nepheline Syenites & Related Rocks in British Columbia (Chapters 2&3) (Pell, 1994)

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Historical report by the British Columbia Geological Survey on carbonatites and related rocks. Ther report was completed by geologist Jennifer Pell who has spent several years studying rare metals in …

Historical report by the British Columbia Geological Survey on carbonatites and related rocks. Ther report was completed by geologist Jennifer Pell who has spent several years studying rare metals in British Columbia's Rocky Mountain Rare Metal Belt.

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  • 1. Ministry o Eneqy, Mines and Petroleum Resources f CARBONATITES AND SYENITE GNE,ISS COMPLEXES IN METAMORPH0SE:D PRECAMBRIAN TO EARLYCAMIBR1:A:N STRATA. OMINECA BELTMANSON CREEK AREA (93N/9) been deformed and metamorphosedto lower amphibolite facies. The hostrocks include psammitic semipelitic mica to Syenite, monzonite and calmnatite occur together on schists,micaceousquartzitesandsomemarbleswhichstrikeboth the Lonnie (Granite Creek) andVergil (Brent) claims. southeasterly (15Oo-17O0)and dip steeply to the southwestThe two showings arelocated 3 kilometres apart, approxi- (7Oo-8O0)on average.mately 8 kilometres east of the placer mining village of The various rock units within each intrusive zone areManson Creek, 230 kilometres northwest of Prince George. distributed in interfingering lenses (Hankinson, 1958;Exposures are in trenches, between loo0 and 1.100metres Rowe, 1958; Halleran, 1980). The Lonniecarbonatite is upelevation, on wooded slopes; elsewhere outcrop is sparse. to 50 metres thick and traceable for nearly 500 metres (Fig-TheLonniecarbonatitecanbereachedbyanoldroad,which ure 27);theVergil showing is approximately30 mftres thickis passable by four-wheel-drivevehicle to within 1 kilome- and canbe traced for a few hundred metres.The effects oftre of the showing (latitude 55”40’45”N, longitude alkali metasomatism(fenitization) can be detected for a few124°23’15”W). The Vergil showing,approximately5.5 kil- tens of metres beyond the intrusions.ometres from the nearest road, is accessible by helicopter oron foot (latitude 55”42’45”N,longitude 124°25’15”W). CARBONATITES At both showings, theintrusive rocks occurin single, W o varieties of carbonatite are present within the Lon-northwest-trending, sill-like sheets within uppermost Pre- nie complex: one is aegirine sovite in which the principalCambrian metasedimentary rocks the Wolverine Complex of components are calcite, microcline, perthite and aegirine;(Lang ef al., 1946). Both intrusive rocks and hostrocks have the other is biotite sovite, comprising calcite, b.iotite and ~~ ~~~~ _- ~~~~~ LEGEND S y e n i t em o n z o n i t em o n z a d i o r i t e , , Aegerine-amphiboleenite f Mylonitized biotite sovite Biotite sovite Aegerine sovite lnferiayered ovife nd emipelitic chisl s a s s Wolverine omplex iotite sammit?, C b p s e m i D e l i t i c c h i s tm i n o a u a r t z i l e s , r Figure 21. Geological map of the Lonnie (GraniteCreek) carbonatite complex (contours metric), after Rowe, 1958Bulletin 88 37
  • 2. usually plagioclase. Only biotite sovite occurs at the Vergil tain accessory muscovite, biotite, calcite and apntite.showing. Both the biotite and aegirine sovites are variably Nepheline syenite is also locally present and contains: sig-foliated and containapatite (up to 20%). magnetite and py- nificant amounts of zircon (3-15%).rochlore as accessory minerals. The biotite sovite may alsocontain zircon; columbite, ilmenorutile and ilmenite have FENZTESalso been reported (Hankinson, 1958). At the Lonnie show-ing, aegirine sovite occurs along the southwestern margin Pods andlayers of fenite occur within both the Lonnieof the complex and biotite sovite along the northwestern and Vergil intrusive complexes. The fenite is medium to dark green in colour and rusty weathering. It consists ofmargin (Figure 27). The biotite sovite is variably myloni- aegirine and sodic amphibole (Plate 14) with microcline.tized, with the most intense shearing near the contact withthe country rocks. Enrichmentin zircon, pyrochlore, colum- plagioclase and calcite in varying amounts. The amphibolebite, pyrite and pyrrhotite has been noted nearthe contacts is strongly pleochroic, x -turquoise, y - colourless, z - PNS-of the sovites with syenites (Hankinson, 1958). sian blue, with colour strongest at the rims. It issimilar to the amphibole at the Aley complex, which has been itlenti- fied as magnesio-arfvedsonite(Miider, 1986, 1987). ‘TraceSILICATE PHASES constituents in fenites include pyrochlore, magnetite and Feldspathic intrusive rocks, monzodiorite, monzonite zircon.and syenite, outcrop as lenticular masses separating the car- The hosting psammitic and semipelitic schists arc rec-bonatite units (Figure 27). These intrusive rocks consist of ognizably fenitized for a fewtens of metres beyond the in-potassium feldspar (orthoclase or microcline) and plagio- trusive contacts. Microcline, plagioclase and quartz areclase in varying proportions; plagioclase greatly exceeds major constituents, with aegiriue and arfvedsonite dissemi-potassium feldspar in the monzodiorites,in the monzonites nated throughout, presumably replacing the original maficthe proportions approach equality and potash feldspar silicate minerals. Biotite is present in trace amounts only.greatly exceeds plagioclase in the syenites. All phases con- Calcite, apatite, magnetite and zircon may be present andPlate 14. Blue pleochroic amphibole (rnagnesio-arfvedsonite)and finer grained aegirine (light green) in ultrafenite, Lonnie area. Longdimension of photomicrograph is2.5 millimetres, (colourpkoto,page 135).38 Geological Survey €!ranch
  • 3. ~~~ ~ ~~~ ~ ~~~ ~~ ~~ ~ ~ coarse-grained arfvedsonite, magnetite andfeldspar segre- gations are developed locally. GEOCHEMISTRY Carbonatites in the Manson Creek area are all true sovites, no magnesio- or ferrocarbonatites were observed (Figure 28; Table7. Aegirine sovites are depleted in silica ) and aluminum and enriched strontium, relative to biotite in sovites. Fenites are notably enriched in iron and sodium, relative to other lithologies (Figure 29; Table 7. With in- ) creasing degree of fenitization, that is from recognizable metasedimentsto ultrafenite, the rocks exhibit a systematic increase in iron and alkalis relative to calcium (Figure 30a) and fenitization appears to be a combination of typical iron-magnesium andalkali fenitization trends. The fenites, even ultrafenites (aegirine and arfvedsonite rich) are en- riched in sodium relative to typical pyroxene-amphibole fenites (Figure 30b). J Syenitic rocks are quite vaned in composition (Figures Figure 28. CaO-MgO-Fez03t+MnO carbonatite pht, Lonnie 29and31;Table7)but,onaverage,plotwithinthemiaskitic complex. TABLE 7 CHEMICAL ANALYSES OF ALKALINE ROCKS, MANSON CREEK AREA " ~ ~~~ ~ ~ ~~ ~~~ ~ Syenites and contact syenites Fenite 7 6 8 9 10 141113 12 15 15 - Si02 1.70 12.70 12.00 13.70 7.81 4 0 56.70 53.77 36.44 1.0 51.09 32.88 44.5035.9638.8273.1557.82 Ti02 0.02 0.67 0.71 0.01 0.08 0.03 0.02 0.530.03 0.40 0.20 0.66 0.38 0.28 0 6 0.83 .4 3.653.26 7.46 0.367.573.06 16.70 15.38 12.14 2.4811.61A12036.792.2214.30 14.93 11.74 Fe203T 1.40 6.21 5.70 0.37 5.39 1.44 0.57 0.80 4.84 0.59 2.63 19.60 6.91 18.63 11.66 4.52 0.59 0.37 0.24 0.16 0.28 0.23 0.11 0.26 0.15 0.25 0.37 0.24 0.30 0.34 0.24 0.115 0.31 2.20 1.85 0.60 1.21 0.17 0.12 1.73 0.18 1.36 1.15 2.48 2.11 1.13 1.11 2.112 CaO 52.90 36.10 43.72 6.09 9.78 20.19 36.60 48.29 16.30 8.85 23.12 10.90 14.56 0.34 24.21 1.34 Na20 0.44 1.21 0.99 5.57 2.46 5.79 10.33 3.48 4.97 5.37 10.30 5.55 0.36 6.94 3.53 3.99 0.12 2.45 2.04 0.49 0.19 5.36 5.84 1.89 4.82 1.50 4.43 0.24 0.50 1.14 1.61 0.ZI 4.417.48 17.89 7.9817.47 6.56 18.06 0.46 11.48 0.77 0.61 1.05 1.29 1.65 0.34 0.76 0.71 1.13 0.05 0.04 99.27 98.8298.7498.24 99.8985.9399.2799.5599.5998.13 ppm Ni <2 <2 <2 2 9 8 4 4 4 33 7 28 5 65 5 Cr e20 7 9 <20 e 20 36 52 1415 < 20 <20 153 24 34 77 6: 7 8 co 10 10 7 5 3 12 11 9 9 < 5 2 8 3 8 3 1 Sr 12009 6643 7959 6907 8780 4125 1110 1940 3143 2303 5360 5095 6738 233 1506 3: Ba 9861097662 14551926 26341191 22302479 1321215 27522084 387 129 4: Zr 76 127 10363 154 77 385 2030 1062 170 298 322 756 641 198 2324 311 Nb < 5 78306 2 43 1444 358 8831589 1274884 2465 19 253 387 1756 33 44 78 46 77 Y 66 54 69 62 53 16 19 36 YO 11 La 247 345 43 371 135347 398 401 222 265 88 254 102 1 0 173 9 22 Ce 600 172 426 483 130 392 107 673 325 470 286 176 398 660 741 31 Nd 245 179 206 102 35 56 Yb 6.27.7 5.2 3.5 3.8 2.1 sc 30 17 4.8 23 16.820.5 7.24.1 37 46 16.318.5 8.4 41 11.2 31 Ta c2 2 4 < 2 11 c 2 37 17 25 9 3 < 2 <2 <2 8 <2 Th <<6 <66 <66 < 25 28 17 8 < 6 18 6 8 65 244 19 I-LA179C oegirine sovite, Lonnieclaim 12- ultrafenire, LA174B Lonnie claim 2-01242B biotite sovite, Vergil claim 13- ultmfenite, LA197E Lonnie claim 3-011184 biotite sovite,Lonnie claim 14- LAl79E banded, calcareous fenite, Lonnie claim 4-LA242C white. massive sovite, Vergil claim IS- l.4178 fenitired metasediment with carbonaiite 5-LA252 carbowrite breccia, Vergil claim veinle:, Lonnie claims 6-l.41978 syenite, Lonnie claim 16- l.41740fenirired mefasediment, Lonnie claim 74.42408 syenite, Vergil claim Samples 1,2,3.6,7,12%- majorelementsnmlyred 8-01250 syenitic breccia, Vergilclaim by ICAP; trace elements by XRF; 9-LAl74A marsive syenite, Lonnie claim REE by INAA at Bondar-Clegg. IO-LA248 mixed syenitdcarbonatite, Vergil claim Sampbs4, 5,8,9,10,11.13,14,15,16,- II-LA197D carbonatitdsyenife contact, Lonnie claim Major and tmce elements byXRF. Bulletin 88 39
  • 4. %% carbonatites A fenite 0 syenite trend Creek "normal.. fe-Mg fenite trem pyroxene amphibod< fenitesFigure 29. Majorelementternary plots, MansonCreekarea Figure 30. Ternary fenite plots, Manson Creek area carbsnatitccarbonatite complexes. complexes.syenite field (Figure 31). These rocksmay contain signifi- GEOCHRONOLOGYcant amounts of zirconium, upto 1.23%, and are enriched The Lonnie and Vergil carbonatites contain zircm, p yin barium and niobium relative to other igneous andmeta- rochlore and other uranium-bearing minerals arc: ame-- thatsomatic rocks the area. Niobium pentoxide in values of be- nable to uranium-lead geochronoIogy. Zircons fromtween 0.1 and 0.3% have been reported from the Lonnie samples collected from the Lonnie andVergil carbonatite-showing. Azone in the centre of the property averages 0.3% syenite complexes are generally large crystals that areNbzOs across a width of 7.6 metres and a length of 240 equant and clear. Analyses fromthese samples are ciscor-metres (Vaillancourt and Payne, 1979). dant, but indicate a uranium-lead age of 340 Ma anc. lead.. Rare-earth element abundancesrocks in the Manson of lead ages of 351 to 365 Ma (Appendix which is similar 2),Creek area are uniformly low, compared to those at Aley, to the age of the zircons from the Ice River complexin theKechika River and Rock Canyon Creek (Appendix and, 1) Rocky Mountains. Preliminary uranium-lead syste~natic!ias indicated by the shallow slope on chondrite-nomalized do not yield precise ages for these zircons, but do suggestplots, the light rare-earth enrichment is not as marked (Fig- that the Lonnie and Vergil carbonatites were emplaced iuure 32). Late Devonian early Mississippiantime. to __40 Geological Survey .3ranch
  • 5. Ministry of Energy, Mines and Petmleum Resources CHONDRITE-NORMALIZED REE PLOl average Lonnie syenite 105 Lonnie & V e r g iS h o w i n g s l X overagemonzonite - Monson C r e e k r e a A . . . Carbonatite A Fanile 104 - D syenite . . . . .Subalkaline basalt Alkali rocks mmrr 30.00 40.00 50.00 60.00 70.01 Si02 Agpaitic 1 !O.OO- syenite La Ce Pr Nd Sm Eu Tb Dy Ho lm Yb LI family Rare-Earth lements E Mlaskitlc __ syenite family Figure 32. Chondrite-normalized REE plots, Lonnie and Vergil 5.00 showings, Manson creek area. Nephelinite family The alkalic rocks are hosted by high-grade metarnor- phic rocks assigned to the Wolverine complex, 0 ; probable 0.00- late Proterozoic age, and are exposed in a 5 hy 10kilometre area, south andeast of the Manson River, in the Wolverine Ranges of the Omineca Mountains. Within this arxa,num- a - 0 ber of discrete alkalic dikes and dike swarms arepresent, 5.00- ." . Subalkaline associated with alkalic pegmatite dikes or segreg&ions,in- rocks trusive breccias and large metasomatic alteration halos U " (fenites); unfoliated, fine-grained quartz morzonite to 0.00 quartz syenite intrusions are also present, but may or may 30.00 40.00 50.00 60.00 70.0 not berelated to the alkaline syenites. The relationship be- Si07 tween the intrusion of alkaline rocks andmetamorphism is Figure 31. Alkali-silica and agpaitic index plots, Lonnie complex unclear from available literature. the silicate rocks. (A) Agpiatic index plot - Lonnie complex silicate The area is accessible from good logging roads run that rocks; (B) Lonnie - alkali vs silica diagram. along the west side of WillistonLake fromWindy Point,at the south tip of the lake, to Manson Creek. MOUNT BISSON - MUNROE CREEK AREA (93N/9; 930/5,12) ALKALIC DIKE ROCKS Alkalic syenites are exposed in the Mount Bisson - Three types of syenite dikes are present in the Mount Munroe Creekarea of north-central British Columbia (lati- Bisson - Munroe Creek area: the fzst rich in alkali feldspar; the second containing abundant aegirine-augitc:; and the tude 553100"N, longitude 124"0000W), 64 kilometres third a suite of rare-earthelement enriched dikes which con- northwest of the town of Mackenzie (Figure 1). They were tain allanite as the main rare-earth mineral. The alkali ield- discovered in 1986 and 1987 A.A.D. Halleran.The min- by spar dikes contain 90% potassium feldspar rimmed with eralogy andfield relationships were describedby Halleran plagioclase, and 10% mafic minerals, predominantly aegir- (1988) andHalleran andRussel1 (1990) and summarized are ine-augite. The aegirine-augite dikes contain, 011 average, from these works. 40 to 60% aegirine-augite grains, up to 1.5 centimetres " Bulletin 88 41
  • 6. across, 35% perthite, 3% sphene with rare allanite inclu- gioclase (Anzz-uI), potassium feldspar, biotite, chloritz andsions, 1%apatite and traces of allanite, magnetite, chalco- traces of magnetite, allanite, apatite and zircon.pyrite and malachite. These dikes are banded, with mafic theminerals concentratedin thin, discrete zones. The allanitic GEOCHEMISTRYdikes are also rich in aegirine-augite: they consist of ap-proximately 80% aegirine-augite, 8% potassium feldspar,5% apatite, 3% allanite and 2%sphene, withaccessory cal-cite and biotite.PEGMATITES Two types of alkalic pegmatites are described by Hal-leran and Russell (1990),aegirine-augite pegmatites and al-lanite pegmatites. They occur in zones l to 4 metres wideby in excess of 30 metres long; it is unclear, however,whether they are distinct dikes or, simply, coarse-grainedsegregations or pods within fenite zones. The aegirine-augite pegmatites contain zoned antiperthite (Anz3), sub-hedral aegirine-augite grains [with inclusions of plagioclase(An34). sphene, hornblende and biotite], minor perthitic po-tassium feldspar, occasional elongate quartz crystals andlate, fracture-filling epidote. The allanite pegmatites consistof perthite, up to 35% allanite, 5 % sphene, plagioclase(Anzs.27). apatite and minor to trace amounts of aegirine-augite, quartz, zircon and opaques. Allanite crystals are 0.03to 2.0 centimetres in size and commonly occur with spheneand apatite. Late quartz veins, up to 5 centimetres wide, lo-cally cut the allanite pegmatites.INTRUSIVE BRECCIAS An intrusive breccia zone, over 40 metres long, is ex-posed in one area. It consists of intrusive clasts supportedby a fine-grained, green matrix which contains 25% relicpotassium feldspar, 10%plagioclase, altered blue-greenamphibole and traces of sphene and apatite. LEGENDFENITES Fenitized Wolverine Complex rocks are exposed over &@ A e uncertainplutonic rocks G r o n o d i k , quartzmonzonite, tonollle;iocaliy pegmolitica broad area. The fenites are generally banded, with melano-cratic layers consisting of aegirine-augite, sphene, allanite, Hadvnian- Windermere Supergroupapatite and minor hornblende, andleucocratic layers domi- Horsethief Creek Group, Upper Clastic Unit/Koza Group: granule conglomerote,nated by plagioclase or potassium feldspar and apatite. psammite; minorpeiife carbonate andBanding in the fenites reflects original bedding or layeringin the Wolverine rocks which the fenite zones grade into: a Horse!hie! Creek Group, Amphlboilte Middle ond Semipelile/ Marbleunils;melanocratic bands were probably amphibolite or biotite amphibolite, semipelite, marble, minorschist layers while the leococratic bands were probably peliteoriginal quartzofeldspathic layers. Fenites are differentiated Horsethief Creek Group, Aluminousfrom hostrocks the presence aegirine-augite and rare- by of Peiite unit: pslite predominates:mayearth element bearing minerals, an increase in alkali feld- also contain minoramounts of Lower Gril Unitspar and a decrease quartz. in Hadrynian Older and (Proterozoic) Malton gneiss: ortho and parogneissQUARTZ MONZONITESAND QUARTZSYENITES Geological contact .......... ----------- Fault .............................. Fine-grained, massive, leucocratic quartz monronite Thrust fouit .................... -7-cand quartz syenite intrusions are also present in the Mount Corbonatite/nepheiineBisson - Munroe Creek area. They are very fresh in appear- rvenite localities ............................ 0ance and maybe unrelated to the more alkaline rocks. There -are at least four large intrusions (1 by 3 km in size) and a Fig,ure33. Geology and CarbonatiteJsyenite localitiesin the Illuenumber ofsmaller satellite bodies. They contain quartz, pla- Ri rer m a .42 Geological Survey Branch
  • 7. -~ ~~~~~~~~ ~ Ministry of Energy, Mines and Petmleurn ResouxesThese values represent total rare-earth concentrations; how- of Kamloops (Figures 1 and 33). All are sill-like bodiesever, the values are mainly in the light rare earths. Fenites which were intruded prior to the deformation and ~netan~or-contain 0.07 to 0.64% light rare earths over widths 1to 2 of phism associated with the Columbian orogeny. The car-metres. bonatites, syenites and hosting sedimentary rocks been have subjected to three phases of deformation (Plate: 15) andGEOCHRONOLOGY metamorphosed to upper amphibolite grade (kyanite to sil- No absolute dating has been done on the alkaline rocks. limanite zone). TheMudLake (83D/3, latitude52c07’55”N.They obviouslypostdate the Late Proterozoic rocks of the longitude 119°10’44”W), Bone Creek (83D/6: latitudeWolverine Complex; from published data, the timingof em- 52°17’09”N, longitude 119°09’42”W) and Verity (831Y6,placement relative to metamorphism is unclear and an upperlimit on the agedifficult to establish. Within the sequence, latitude 52”23’51”N, longitude 119”09’13’W) !showingsthe syenitic dikes appear to be the latest alkaline rocks em- (Figure 33) occurbelow treeline at elevations bet ween 600placed as they crosscut both the alkaline pegmatites andthe and 900 metres; consequently exposure limited. ‘ThePara- isfenites. dise Lake (83D/6, latitude 52”24’19”N, longitude Quartz monzonites and quartz syenites probably post- 119°05’47”W) and Howard Creek (83D17, latitudedate the alkaline rocks andmay he completely unrelated to 52”23’OO”N, longitude 118”53’26‘W) carbonatites arethem; angular fenite xenoliths are reported to occur within above treeline, well exposed and were mapped in datailthe quartz-hearing intrusions. From descriptions given, (Figures 34,35a and 35h).these intrusions sound as if theyare postorogenic; however, The Verity carbonatites can be reached by trails anduntil some radiometricdating is completed, their ages will logging roads which cross the North Thompson River andremain unknown. intersect Highway 5 at Lempriere Station, approxi.nately 40 kilometres north of Blue River. The Bone Creek showingsBLUE RIVER AREA (83D/3,6,7) are accessed from logging roadwhich leaves Highway 5 a A number of carbonatite and nepheline syenite layers approximately 23 kilometres of Blue River. The Mud northoccur within the semipelite-amphibolite division of the Lake carbonatite crops out along Red Sands road, which theHadrynian Horsethief Creek Group the Monashee Moun- in intersects Highway 5, three kilometres north of B lne River.tains near BlueRiver, approximately 250kilometres north All roads are passable with four-wheel-drive vehicles. The Plate 15. Fz folds in banded nepheline syenite, Paradise Lake.Bulletin 88 43
  • 8. CARBONATITES Three types of carbonatite occur within this suite. One is a whitish weathering olivine sovite which contains pre- dominantly calcite (60-8556). olivine (3-20%) and apatite (2-20%). Accessory minerals which may be present are phlogopite (Plate 16), with either normal or reverse pleo- chroism (up to 8%). diopside (10% or less), magnetitz, il- menite, pyrite, pyrrhotite, pyrochlore, columbite, zircon, monazite, allanite and baddelyite. The sovite is usually me- dium grained and massive, but locally may contain pegma- titic phases with calcite and olivine crystals 2.5 to 3 centimetres long and magnetite clusters over20 centimtres in diameter. Zircon crystals up to 3 centimetres long have also been found. The second type is a buff-weathering dolomitic car- bonatite (ranhaugite) with accessory amphibole (5-1 S) %, apatite (2-10%). magnetite and minor phlogopite.Ilmenite, pyrochlore, columbite and zircon may be present in trace amounts. The amphibolemay be richterite, soda-tremolite, tremolite or actinolite. Apatite and amphibole, within the rauhaugite, define a foliation parallel to both the edg:s of the carbouatite and the external schistosity. Locally, compo- sitional banding with alternating apatite-amphibole-rich and carbonate-rich layers parallels foliation and contacts (Plate 17). Pegmatitic segregations are not found in the ranhaugite, but coarse pyrochlore and crystals ( 1-1.5 zircon cm long) may be present. Separate bands of sovite and rauhaugite occur at Verity, Paradise Lake and Hoxard Creek. Rauhaugiteis present at both the Mud Lake and I3one Creek localities. LEGEND The third type ofcarbonatite, biotite sovite, is found at Carbona{ite, ou{crop Bedding SYMBOLS F, fold axes Minor folds - ............... 4 y 2 ........16 .......... Paradise Lake only. It occurs as segregations or pods ;asso- ciated with nepheline syenite. Calcite, biotite, apatite and magnetite are the primary constituents and nephelinemay also be present. 4 Sohene-amohibalite Fault - ................... NEPHELINE SYENITES Contour Interval = 30m Nepheline and sodalite syenite gneisses crop out in the ParadiseLakearea (Figure 35). In general, the syenitescom- prise white to grey-weathering, medium-grained, layered yE:&ian Psarnmite, sernipelite, and foliated gneisses, concordant with hostrocks of the and amphibolite Hadrynian Horsethief Creek Group. Layering and foliation are parallel to the margins of the gneisses, to bedding inFigure 34. Geologicalmap of the Howard Creek carbouatite surrounding metasedimentary rocks andto regional lolia-occurrence. tion. These syenites are typically composed of micrcclineHoward Creek and Paradise Lake localities are reached by (25-35%). plagioclase (An30 - Ana, 25-35%), nephelinehelicopter, from Valemount. (10-30%) and biotite (7-15%). Accessory minerals may in- Carbonatites in the Blue River area have been exam- clude muscovite, sodalite, cancrinite, zircon and perthite. Trace minerals present are calcite, magnetite, pyrrbotitl:, py-ined periodically since the 1950s, for their vermiculite, ura- rochlore and uranopyrochlore. The syenite gneisses r e lo-nium, niobium and tantalum potential. Previous cally migmatitic, with massive, medium to coarse-grained,descriptions are given by McCammon (1951,1953,1955), of lensoidal leucosomesthat are composed either nephdine,Rowe (1958). Currie (1976a). Meyers (1977). Ahroon microcline, plagioclase and sodalite or large perthite crys- tals (Plates 18 and 19).(1979, 1980), Aaquist (1981, 1982a,1982b, 1982c), White(1982, 1985) and Pel1 (1987). Lithologies are very similar MAFIC SILICATE ROCKSthroughout this area and will be described by rock type Mafic and ultramafic silicate rocks are present atrather than locality. Howard Creek (Figure 34). The most common varicty is44 Geological Survey Branch
  • 9. Ministry of Energy, Mines and Petroleum Resouxes Geologicalconloct Moraine or talus defined, assumed approx, .......-" "- INTRUSIVE ROCKS Orientation bedding of and parallel foliation (SI and S2) F2 Fold axis ............................................. - ................................................ c- ....................................... xp HOST ROCKS Hadrynian Minor F2 folds Fault....................................................... S I axid race t - Bonded amphibolite ~ syncline, anticline ................................ * I 0 .i Psammlte,semipelite. and thin omphibollte layers S 2 axial antiform trace, ......................... olcsilicate SI axial trace ......................................... Sa Il + Figure 35. (A) Geology of the area south of Paradise Lake; (Next page) Cross-sectionA-A, area south (B) of Paradise Lake.Bulletin 88 45
  • 10. INTRUSIVE ROCKS A Figure 358 (continued) Plate 17. Well layered carbonatite, Howard Creek. Layering isPlate 16. Phlogopite in carbonatite with reverse pleochroism and produced bycompositional variation within the carbonatite and isdistinctive orange colour, from Verity. Long dimension of parallel to the marginsof the layer, external sedimentary b:ddingphotomicrograph is 2.5 millimetres, (colourphoto, page 136). and regional foliation.46 Geological Survey 3runclr
  • 11. Plate 18. Migmatitic leucosome (tine-grained leucosyenite segregations) present in layered syenites, Paradise Lake calcite with or without biotite, allanite and apatite The rock is generally coarse grained with pyroxenecrystals exceed- ing 3.5 centimetres in length and sphene crystas up to 2 centimetres long. In the strongly foliated varieties, hom- blende predominates (50-55%), with aegirine-augite, sphene and biotite abundant and calcite, plagioc1ar.e. apatite, pyrite and sometimes nephelinetrace constituents. At one as locality, themelteigiteis transitional to, and locallycrosscnt by, a coarse-grained, massive urtite composed of :25 to 40% nepheline, 10 to 15% potassiumfeldspar, 8 to 15% plagio- clase, 8 to 15%aegirine, 15 to 20% hornblende and sphene, biotite and calcite. FENITES Mafic fenites, 1 to 30 centimetres thick, separate car- bonatites and host metasedimentaryrocks. They v a q from medium to coarse grained and massive to foliated. They are generally composed of amphiboles (hornblende-actinolite, 45-80%), clinopyroxene(generally diopside or augite, up to 35%). apatite and opaques.Accessory minerals which may be present are titanaugite, biotite, plagioclase, sphene, epi- dote, quartz (remnant) and calcite. In some loca:.itiesa bi-Plate 19. Migmatitic segregations of coarse perthite crystals in otite-vermiculite layer is developed in place of thelayered nepheline syenite gneiss, Paradise Lake. amphibole fenites. In all cases the metasedimentary rocks adjacent to the fenites appear unaltered.sphene-pyroxene-amphibolerock or melteigite, which maybe layered andfoliated or massive. It consists of aegirine- GEOCHEMISTRYaugite (approximately 50%), strongly pleochroic horn- The alkaline rocks in the Blue River area shclw distinctblende (x - honey-yellow, y - dark bluish green, z - dark major element trends of increasing alkalis from carbonatitesforest-green to opaque: 15.30%) and sphene (10-20%).Ac- to syenites, with fenites most similar in composition to thecessory minerals include nepheline, plagioclase, pyrite and carbonatites (Figure 36; Table 8). Carbonatites (b~th calciteBulletin 88 47
  • 12. British Columbia - albiie fenite fieldFigure 36. Major elementternary plots, Blue River area alkaline;ocks. Figure 38. Ternary fenite plots, Blue River area rocks and dolomite-rich varieties) are distinct from marbles the in host Horsethief Creek Group;the carbonatites c0nta.n s i g nificantly less silica, aluminum and alkalis than the average marble and are enrichediron, phosphorus, strontium and in rare earths (Table 8). Enrichment in niobium and tartalum also occurs in the carbonatites (Table 8), %Os values of up to 0.46%(Aaquist, 1982b) and tantalum ppm (Aaquist, 1982c) have been values tc.2400 reported. Calcite carbona.. tites range fromme sovites to ferrocarbonatites. dolomitic carbonatites may be classified as magnesiocarborlatites (Figure 37). Fenites are all typical pyroxene-amphibolt: fenites, pIotting within pyroxene-amphibolefenite fields; the rnognesio- ferro- o n b o t h N a20-KzO-Fe203 a n d C a 0 - N a20i-KzO.. corbonatite corbonatite MgO+FezO3 plots (Figure 38a and b). Syenites frcm tht: Paradise Lake are miaskitic, generally compositionally area close to the average nepheline syenite (Figure 39a m d b).Figure 37. CaO-MgO-Fe203ttMnO carbonatite plot, Blue River Alkaline rocks contain anomalous amounts of rare:-eartharea. elements, but not to the extent of manyof the comp1t:xes in -48 Geological Survey Branch
  • 13. TABLE 8 CHEMICAL ANALYSES,ALKALINE ROCKS, BLUE RIVER AREA 5 6 3.82 6.60 5.26 2.73 7.642.03 12.30 41.03 42.30 59.20 47.01 12.W 35.86 58.W 44.12 58.20 4530 31.80 50.80 47.10 55.80 41.80 46.60 60.50Ti02 0.16 0.80 0.62 0.02 00 .2 0.70 0.09 0.85 0.13 0.60 0.44 0.82 0.02 0.29 5.65 4.15 0.25 218 1.84 0.40 0.23 0.40 06 .0 0.64 0.65 0.72 0.15 0.15 on 0.24 0.22 2.22 9.62 6.51 10.51 I250 22.60 20.80 20.10 8.42 5.93 9.72 20.10 18.W 4.88 1.03 13.30 853 4.28 10.70 10.30 4.35 7.356.48 7.61 8.41 0.305.177.449.409.68 2.62 2.69 2.20 15.10 856 12.90 3.67 5.36 1.10 7.19 11.10 3.31 0.21 0.23 0.24 0.31 0.38 0.21 0.41 0.37 0 2 0.20 .0.22 0.27 4 0.18 0.01 0.M 0.03 0.41 023 0.12 0.34 0.06 0.15 0.19 0.20 0.03 2.60 6.88 5.59 14.50 19.W 14.80 16.30 15.W 2.65 11.12 9.23 10.76 2.02 0.W 0.310.17 7.14 459 1.40 11.70 1.44 1.W 1290 7.98 4.74 45.40 39.80 40.90 28.10 28.70 32.90 30.64 29.10 20.W 16.81 15.26 42.90 14.40 0.54 0.698.20 13.58 0.83 16.80 23.10 28.70 2. 3 9 14.90 11.50 5.35Na20 0.10 0.15 0.15 0.10 0.27 0.11 0.05 4.03 1.11 3.60 3.28 0.40 4.06 7.488.27 9.70 4.462.08 9.52 0.12 1.01 1.13 054 26 6 3.wK20 4.10 0.38 0 4 4.10 .8 02 .5 o . ~ 0.12 0.12 2: 0 0.59 0.64 153 ;:$ 1.66 3.78 8.W 5.49 5.08 1.201.71 3.50 4.10 1.69 09 .7 0.81 0.13 2.71 d 40.38 35.46 27.12 37.21 20.73 4.98 2.57 0.90 2.02 1.75 1.18 19.29 0.71 2.12 0.21 -.4 2 8 24~ 098 1.11 04 .4 0.23 4.W 4 9 . 0 4.W am 4.W $9.78 99.86 97.98 97.10 97.W lW.11 98.R 99.63 91.17 98.18 97.601 lW.48 99.31 98.98 99.46 99.29 lW.39 2 4 <2 1 24 6s 58 I7 5 9 92 <w 2 < 20 CW 75 88 52 IC4 124 I27 3w 16 16 10 18 28 32 18 22 8 22 25 3 6 1 1 9 7 46Sr 4223 2995 3372 4092 4459 IS25 3276 3549 5312 534 1334 I641 78 2W3 134 152 71Ba 248 316 315 157 127 427 113 87 467 196 803 810 31912161 238 367s I59 934 712 27 M 1118 50 28 159 734 276 462 63 119 155 M3 37Nb % 41 42 470 7w 1 W 491 117 E5 181 185 303 6 I64 3 16 1Y 76 68 67 IS 9 2 5 22 16 68 32 33 48 36 19 26 42 17La 280 254 171 241 103 134 m 174 2H 74 91 183 42 18 33 162 2cc 539 548371 530 208 279 415 339 470 169 187 370 32 70 302 164 I5Nd 234 223 147 119 81 114rn 4 4 1.4 1 1.8 12 39k 41 36 40 41 3 4 4 4 34 29 22T* 19 <2 CZ 12s I78 8 IO CZ c2 c2 <2?h- ~ ~~ ~ c6 0.11 6 6 c6 ~6 , c6 5 13 W ~ 1 Porndire&;
  • 14. I Nephelinite CHONDRITE-NORMALIZEDREE PLOT PARADISE, VERITY,HOWARD CREEK lo5j SHOWINGS BLUE RIVER AREA i Carbmatife A Fenile 1 o4 Subalkaline rocks 00 I .0 30.00 I I I , , , I , I , I I , , I I I , , 40.00 50.00 ,,,,, I , , 60.00 ,,,, I , , , 70.C ,, Si09 0 nepheline syenite m eDlCore0"S nepheline syenile Agpaitic family syenite fornily Miaskilic t overage nepheline - .- - " syenite 1 1 ~ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 , 1 1 1 11, La Ce Pr Nd Srn Tb Eu Dy Ho Tm Yb LL 1 Rare-earth lements E -- Alkali basalt Subalkaline rocks Figure 40. Chondrite-normalized REE plot - Paradise, V:rity, Howard Creek showings Blue Riverarea. 30.00 50.00 40.00 60.00 70.0 Si09Figure 39. Alkali-silica and agpaitic index plots,Blue River areasyenites.50 Geological Survey Brmch
  • 15. LEGEND 11 2 Nepheline syenite /IjHorsethief creek met ore dim en la^ rocks 1 Axial 7 trace o f early antiforms Figure 41. Geology of the Trident Mountain area, Selkirk Mountains(from Pell, 1986b; Perldns, 1983). IPlate 20. Coarse-grainedilmenitesegregationin leucosyenite.Trident Mountain. Plate 21. Typical banded nepheline syenites, Trident Mountain.
  • 16. Plate 22. Leucosyenite dikescutting mafic, biotite-amphibolegneiss, Trident Mountain. - Carbonalile average 1 family . . 1.00- 1 < b ? 0 nepheline syenite bosolt Alkali rn mafic ~ ( ~ I c o r e o u ! ; nepheline family syenite 0.00 60.00 73.0 Si07 Figure 42. Alkali-silica and agpaitic index plots, Trident Mountain syenites.Plate 23. Xenolith of mafic gneiss inbiotite-rich syenite, TridentMountain.52 Geological Survey Branch
  • 17. Minishy of Energy, Mines and Petmleum .Pesources "the Rocky and Cassiarmountains (Appendix Enrichment 1). More recent uranium-lead data have been obtainedin light rare earths is greater than in heavy rare earths, as from zircon separates and indicate a mid-Paleoz.oic (1%-indicated by the shallow slope on the chondrite-normalized vono-Mississippian) age of emplacement. A sample fromrare-earth element plot (Figure 40). Verity yielded an age of approximately 325 Ma (G.l.E. White, personal communication, 1984); a prelimi!~ary dateGEOCHRONOLOGY of approximately 328f30 was obtained from Mud Lake Early attemptsat dating did not providedefinitive re- samples (R.R. Parrish,personalcommnnication,1!)85).Zir-sults on the ageof the alkaline intrusions in the Blue River cons separated from Paradise Lake syenites, which were large, equant andclear, provided slightly discordant analy-area. Potassium-argon dates of 205f8 Ma on phlogopite ses which suggesteda uranium-lead age of apprc7ximatelyfrom Howard Creek, and 92.5f3.2 and 80.2S.8 Ma on 340 Ma and lead-lead ages of 351 and 363 Ma (Appendixrichterite from Verity were obtained (White, 1982). Suh- 2).sequently, potassium-argon dates of 20of7 Ma on phlo-gopite and 94.4+3.3Ma on hornblende from Howard Creekwere obtained (G.P.E. White, personal communication. TRIDENT MOUNTAIN (82M/16)1984). The young dates (circa 80-90 Ma) are most likely Nepheline syenites were first recognized in tk e Tridentrepresentative of the timing of metamorphism and not the MountainareabyWheeler(1965)andsubsequentkfmappedemplacement of the igneous rocks. byPerkins(l983).TridentMountain(latitude5lo.L~4N,lon- gitude 118"09 west) is located in the Big Bend cf the Co- lumbia River, about 85 kilometres northeast of Rxelstoke and 20 kilometres southeast of Mica Creek (Figwe The 1). 0 nepheline syenite area is very rugged; the syenites are exposed 011 cliffs at maficcalcareous elevations of 2200 to 3000 metres, adjacent to largc:icefields nepheline syenite (Figure 41). Access is by helicopter from Revelsbke. The syenite gneisses at Trident Mountain are whiteto grey weathering, medium grained and moderately to well foliated. They are composed of white to pinkish nucrocline TABLE 9 CHEMICAL ANALYSES OF TRIDENT MOUNTAIN SYENITES Si02 5i.59 56.66 57.64 53.72 41.76 T0 i2 0.02 0.802.04 0.26 41.04 21.69 22.39 22.35 15.45 24.36 A1203 81.59 6.24 0.17 2.71 13.15 Fez03 MnO 00 .1 0.44 0.14 00 .8 *>.01 MgO 0.05 1.59 3.10 0.46 i0.W cao 6.820.59 0.33 8 . 6 0 9 15 .1 Na20 1.72 8.16 6.27 75 .1 1.39 K207.527.968.22 1.986.94 Ni 3 6 11 4 8 CI 21 < 20 19 13 18 CO 16 18 13 14 18 Sr 1234 1713 625 730 1116 B3 E 2992 1211 1156 584 1520 zr 210 338 1562 57 43 Nb <5 358 229 249 33 Y 6 22 16 4 2 La 8 197 1 6 21 Ce 16 275 10 22 32 Nd Yb SC 0.1 99 . 0.4 <I Cl <2 2 11 12 1020 COOFigure 43. Major element ternary plots, Trident Mountain syenites. -Bulletin 88 53
  • 18. (25-50%), albitic plagioclase (10-30%) and nepheline(10- River, approximately 15 kilometres northeast of Tcdent40%). Nepheline generally has an irregular poikiloblastic Mountain. The nepheline-bearing lithologies display atexture and is often partially altered to clay minerals. Green strong foliation, conformable to the surrounding metasedi-to olive-pleochroic biotite is commonly the mafic silicate mentary rocks, which are assigned to the Lower Cambrianphase present and comprises from trace amounts to more Hamill Group. The only known outcrops of this intrusionthan 30% of the rock. Locally,coarse-grained aggregates of were in the Sullivan River delta, which is now flooded byrandomly oriented biotite crystals are developed. Greenish the Mica Dam reservoir.acmitic pyroxene has also been reported from nepheline-rich phases (Cnme, 1976a). Accessory minerals may in- GEOCHEMISTRYclude sodalite, cancrinite, calcite, apatite, sphene, ilmenite, The leucosyenites at Trident Mountain are miarkiticpyrochlore and zircon (crystals up to 1.5 cm in size). I1- (Figure 42), and are compositionally similar to the ‘aver.age’menite segregations, 20 to 40 centimetres in size, are some- nepheline syenite. Mafic calcareous phases plot withi:1thetimes present (Plate 20). Local pegmatiticsegregations are nephelinite field. Melanocratic and leucocratic varieties ap-sporadically developed. parently form a cogenetic sequence (Figure 43). The The syenites occur as a concordant lenticular mass high syenites are locally enriched in strontium, barium, zirco-on the slopes of Trident Mountain and adjacent ridges. The nium and niobium (Table 9). Rare-earth element concentra-hostrocks are psammitic and kyanite-bearing pelitic schists tions are generally low. Chemically (and mineralogically)(with rare calcsilicate bands) of the Hadrynian Horsethief they are very similar to those at Paradise Lakein the BlueCreek Group and are exposed core of an early isoclinal in the River area.antifonn which is refolded by later upright to overturnedstructures (Perkins, 1983). The syenites display composi- GEOCHRONOLOGYtional layering and afoliation parallel to the margins of the Two zircon fractions from the Trident Mountain syenitebody, the axial plane of the antifonn and bedding in the were collected and hand picked. They consisted of clear tometasedimentary rocks. The layering is defined by leu- slightly cloudy, equant, multifaceted roundish grains. Thecocratic (biotite less than 10%)and melanocratic (biotite two analyses were somewhat discordant and, because cf the30-40%)phases (Plate 21) withoccasionalcalcareouslayers low uraniumcontent, it has been interpreted that both meta-(sovitic sweats?). Leuococratic syenites are the most abun- morphic and igneouszircons are present. This is also sng-dant phase. gested by the fact that a number of crystals havepefiztly the clear rims surrounding cloudycores (Le., two generaions Melauocratic syenite gneisses rich in amphibole, bi- of zircon growth). Also morphology of grains is typi- the theotite and sphene are also present at Trident Mountain, but cal of metamorphic zircon (R.R. Parrish, personal conunn-were not seen in outcrop. They are cnt by dikes of lenco- nication, 1987). On concordia a diagram (Appendix2) 2. linesyenite. Contacts between the mafic gneisses and syenite joining the two analytical points has upper and lower i nter-dikes are sharp (Plate 22). Xenoliths of country rock ormafic orthogneiss were observed in the melanocratic cepts of 378+7 Ma and 138f9 Ma). The 378 Ma date issyenites. The xenoliths have very diffuse contacts, suggest- consistent with the Devono-Mississippian age obtaineding reaction with, or partial digestion by, the syenitic magma from Paradise Lake syenites which resemble the Trident(Plate 23). Mafic gneisses apparently represent an early Mountain gneisses, and withinterpreted ages of other car-phase of intrusion, cut by later leucocratic nepheline bonatite complexes in British Columbia. The 138Ma datesyenites. may be indicative of a period ofresetting during a Jnrwsic metamorphic event. Uranium-lead data on pyrochloreyield Another mass of nepheline syenite is reported (Fyles, a 60 Ma date (R.R. Pamsh, personal communication, 1,387)1959, 1960; Cume, 1976a) at the mouth of the Sullivan which may indicate a late metamorphic resetting.54 Geological Survey Brmch
  • 19. Ministry of Energy, Mines and Petroleum . e n = CARBONATITES AND SYENITE GNEISS COMPLEXES ASSOCIATED WITH COIRE GNEISSES IN THE OMINECA m r r " Intrusive and extrusive carbonatites and syenite gneiss MOUNT COPELAND NEPHELINEbodies occur within a mixed paragneiss succession along SYENITE GNEISSES (82M/2)the margin ofFrenchman Cap gneiss dome (Figure 4 ) one 4,of several late domal structures near the eastern margin of The Mount Copelandsyenite gneisses crop out along Hren Creek and the slopes south of Mount Copeland, on inthe Sbnswap complex in southeastern British Columbia the Jordan Riverarea (Figure 45) on the southeastern flank(Wheeler, 1965). The dome exposed as a window between is of the Frenchman Cap dome (latitude 51"05N, longitudethe Columbia River fault to the east and the Monashee 118"25W) approximately 25 kilometres northwest ofd6collementto the west (Read and Brown, 1981). Revelstoke. The alkaline rocks arereadily accessible by an The core of Frenchman Cap dome comprises mixed a old mine road whichleaves the TransCanada Highway justparagneiss and orthogneiss succession of probable Aphe- west of Revelstoke. During the summer of 1985 this roadbian age. It is basement to an unconformably overlying was passable with a four-wheel-drive vehicle to within 2 mantling gneiss or autochthonous cover succession, com- kilometres of outcroppings of syenite gneiss.prising a basal quartzite and overlying pelitic and calcareous Alkaline rocks the Mount Copeland in region werefirstrocks. The autochthonous cover successionhosts the car- identified byWheeler (1965) the course regicmal m.ap- in of ping. The area was studied in detail by Fyles (1970) andbonatites and syenite gneisses. Its depositional environment Curie (1976b). The readeris referred to previou!; authors,is interpreted as shallow marine or platformal (McMillan, in particular the work by Cume (1976b), for delailed d e1973; Hoy and McMillan, 1979; Brown, 1980). scriptions; much of what follows is summarized From that The ages of mantlingparagneiss successionand car- the work.bonatites have not yet been unequivocally established. The Mount Copeland syenites (Figure 45) a r c exposedBased on regional correlations with platformal rocks to the in a large antiformal structure and have been sutljected toeast, a number authors (Wheeler, 1965;Fyles, 1970;HOy of more than one phase of folding. They are apparently con-and McMillan, 1979) tentatively assigned Eocambrian to cordant with metasedimentary hostrocks. All contacts within the igneous rocks appear to be gradational. Threeearly Paleozoic ages to these rocks. Recent lead isotopic alkaline rock units have been defined; a basal ~lephelinedata from a syngenetic lead-zinc layer within the upper part syenite gneiss, overlain by alkaline amphibolite, ahich is inof the succession support Eocambrian to Early Cambrian an turn overlain by calcareous and saturated syenite:;. The al-age for that part of the sequence (HOy and Godwin, 1988). kaline rocks intrude micaceous quartzites and c~lcsilicateUranium-lead systematics on a syenite intrusive into the gneisses of the Frenchman Cap autochthonous ,:over se-lower part of the sequence suggest late Precambrian(circa a qnence. The metasedimentary succession has been corre-770 Ma) age the syenite (Oknlitch e#al., 1981); this sug- for lated with a similar successionin the Perry River and Mountgests that the lower part of the mantling gneiss succession Grace areas (HOy and McMillan, 1979; brow^,^, 19110). Based on these correlations, it appears that the gneisses atmust be younger than 780 Ma. Mount Copeland lie stratigraphically beneath the Mount Two phases of folding are prominent in the mantling Grace extrusive carbonatite. Postorogenic lamprophyregneiss succession and various generations of minor folds are dikes are also present in the Mount Copelandarer..also developed (Fyles, 1970; McMillan, 1970). All phasesof folding deform both extrusive and intrusive carbona- the NEPHELINE SYENlTE GNEISSEStites and the syenite gneisses. Amphibolite facies regional The nepheline syenite gneisses (unit A1 of Cuirie,metamorpbism alongthe margin of Frenchman Cap dome 1976b) contain nepheline in excess of 10%.The:l may be weakly to strongly foliated, and locally have a spectacularlyhas produced sillimanite-kyanite, sillimanite and sillimanite-potassic feldspar assemblagesin pelitic rocks. Calcsilicate developed augen texture with large porphyroblastr: of nepheline and alkali feldspar in a fine-grained groundmass.assemblages contain diopside, garnet and actinolite. Car- The augen gneisses (unit Ala) are found in outlying areasbonates and carbonatites are recrystallized to medium to lo- and as lenticles within the calcsilicate hostrocks; they arecally coarse-grainedgranoblasticmarbles (Hdy andKwong, mesocratic rocks with a faint purplish tinge and are pre-1986). dominantly composed nepheline, alkali feldspar,perthite, ofBulletin 88 55
  • 20. British Columbia - Figure 44. Geology of the Frenchman Cap area (from Hoy and Kwong, 1986).56 Geological Survey $:ranch
  • 21. LEGEND Talus, glacial deposits, recent stream gravels snow and iceaccumuiations 100, biotileschist gneiss prominent and with augen gneiss zones, abundantpegmatite; lob, porphyroblostic granite gneiss Eiocky whitequartzite containing biotite schist Purplishquart-diopside-biotitegneisswith glossyquortz layers, rare morbie lenlicler; Ea bronzymicaschistwithquortrileand calssilicate layers Grey green t o white syenite gneiss; A h , caiwreous Alkolineamphibolite, amphibole-biotiteschist, clmphiboiecaicite pegmatite Finelybanded muscovitequartzite mica with schistintercalations Grey biotite gneiss and quortzitewithmeionocrotic biotiteschistintercalotions Eiosky whitequartzite misoceous and quartzite withdeformed pebble conglomerate layer near base100 SYMBOLS (defined, Approximate. Rood assumed) .................................................... -"- ._....... - " (from K.L. Currie. 1976 GSC Memoir 2 6 5 ) Figure 45. Geological map, Mount Copeland area
  • 22. calcite, biotite and fluorite. Cancrinite is often present mar- ALKALINEAMPHIBOLITE ginal to nepheline grains. Accessory minerals include tour- A thin lens, or numerous parallel lenses, of alkaline maline, apatite, sphene, riebeckite and rarely, poikilitic ‘amphibolite’ (unit A2) can be traced for more than aegirine. 10 kilometres. It consists of gneissic and fissile medium to The corepart of the nepheline syenite (unit Alb) con- coarse-grained mesocratic to melanocratic rocks. Aeg;rine, sists of a weakly foliated, pale pink leucocratic rock that biotite and sphenearethemajor constituents; calcite, apatite and potash feldspar may be present in minor amounts Pla- contains nepheline, potash feldspar and albite with lesser gioclase is rare and, where present, often partially rep: aced aegirine and sphene. Accessory minerals include calcite, by scapolite. present as small grains along narrow seams, fluorite, garnet and zircon. Tracesof biotite, muscovite and cancrinite may GREY SYENITIC GNEISS also be present. The strongly alkaline rocks (units AI and A2) arcsnr- The third type of nepheline gneiss (unit Alc), which rounded by a thick shell of less alkaline rocks. Three prin- may be transitional to the nepheline-free syenites, is creamy cipal types are recognized: a fine-grained greenish grey to buff weathering and exhibits the best-developed gneissic syenite with slight gneissic banding (unit A3a); white, apli- a foliation of all the nepheline syenites. Microcline, perthite tic lencosyenite (unit A3b); and buff to pale pink, me f a lum to coarse-grained syenite (unit A3c). and fine-grained nepheline, commonly replaced by can- The fine-grained, greenish grey syenite is dominatedby crinite and thompsonite, are the dominant constituents. plagioclase (An39 and potash feldspar. Themostprominent Phlogopitic mica is the principal mafic mineral, although it mafic mineral biotite, although a diopsidic pyroxene may is is rarely present inamounts greater than 5%. Small amounts also be present. Calcite, sphene and epidote are common. of aegirine and hastingsite may also be present. Accessory Accessory minerals include apatite, muscovite and zeJlite, a minerals include sphene, apatite, calcite and specularite. either analcite or thompsonite. Quartz very rarely fcnnd. is TABLE 10 CHEMICAL COMPOSITION OF SELECTED ROCKS FROM THE MOUNT COPELAND SYENITE C0MPLE:X ~ ~ WI % Alc A2 A3a A3b A3c D Si02 54.11 44.18 48.90 57.97 53.60 49.09 39.70 39.73 54.97 Ti02 0.49 5.49 3.07 2.53 1.63 0.47 1.28 1.24 0.62 A1203 21.69 11.30 7.51 18.48 18.08 15.40 13.50 14.44 21.82 Fe203 2.48 1.300.22 0.04 2.60 8.06 2.60 2.71 3.81 FeO 0.62 0.51 6.10 10.20 7.17 7.20 0.49 5.40 4.92 MnO 0.11 0.15 0.37 0.05 0.16 0.23 0.14 0.14 0.12 MgO 0.19 7.76 8.40 2.81 0.11 7.34 6.00 0.29 7.60 CaO 3.01 9.68 10.10 6.53 4.80 11.57 11.00 9.41 2.51 Na20 5.85 2.30 3.69 2.63 2.50 9.32 4.33 1.32 1.90 1 1 K20 7.21 7.47 7.53 0.91 4.30 6.20 HZ0 0.30 0.88 0.49 4.72 0.50 1.11 1.26 1.21 2.20 0.82 0.18 1.70 2.29 1.90 2.03 c02 0.12 0.80 0.23 1.11 0.20 0.10 0.24 0.26 0.60 0.88 5.22 0.10 0.28 8.20 7.09 ~ P205 0.01 0.03 0.02 0.02 0.02 0.03 0.01 0.59 0.28 0.49 0.14 0.37 0.01 1.68 1.77 3.77 Total 39.47 99.85 100.36 99.71 100.5* 99.99 99.43 99.77 100.4* 99.94 99.71 100.1* 98.98 99.3* 98.34 ppm 4.62 7.50 ~ 11.39 9.37 1.60 3.20 ~ ~ 5.101 7.621 Ni Cr co Sr 1900 1800 940 - 1200 3100 - 3400 - Ba 1200 320 280 - loo0 33 - 130 - ZI 1600 2200 600 - 290 2400 - 2700 -340 260 140 Nb 510 - 300 - 470 - 100 Y 39 230 6.8 - 5.8 9.5 - 15 - - - - ~ La - 270 44 83 34 500 Ce 1300 99 - <500 - 510 780 - 540 - 820 - Nd 310 420 - 550 330 - 630 - 270 - Yb - 11 6.5 ~ 150 - 5.6 7.6 ~ sc 7.2 -i - 31 7.8 - 12 < 4 - 6.8 - *From Currie (1976a) From Currie (1976b) -all other analyses A l a - leucocratic nepheline augen syenites; A l b - nepheline syenite gneisses, pink and white; Alc -pink and grey nepheline-biotite syenites A2 - black alkaline amphibolite; A3a - grey granular syenite; A3b - grey syenite; A3c-greenish granular syenite; D - ocellar biotite lamprophyre dike. 58 Geological Suwey Blanch
  • 23. Ministry of Energy, Mines and Pefmleum Resources " The aplitic leucosyenites contain albitic plagioclase, be present in combination or separately. Zircon, magnetitepotash feldspar, muscovite and either calcite or diopside. and apatite are common accessory minerals; tourmaline andBiotite, zircon, apatite, pyrite and molybdenite be pre- may fluorite have also been noted.sent in trace amounts. This rock is the host of the MountCopeland molybdenite deposit. In the vicinity ofthe deposit, GEOCHEMISTRYmolybdenite is more abundantthan elsewhere andepidote Thenepheline syenitegneisses show amarkecl increaseis present. in silica content from Ala to unit Alc (Table 10) that is unit The third group of syenites are, in general, buff to pink proportional to a decrease in modal nepheline. Unit Ala isin colour andgneissic. This is an extremely heterogeneous also richer in alkalis than the other nepheline gneimes. Unitunit, exhibiting a great variation in mineralogy. Potash feld- A2 has an extremely high soda and potash content (Tablespar and albitic plagioclase are generally present. Calcite orfine-grained aggregates of analcite and cancrinite are found 10) for normal igneous rocks comparable silicz. and alu- ofin some specimens.Biotite, aegirine and a hastingsitic am- mina contents.Cume (1976b) feels this could be rlttributedphibole are the mafic mineralswhich may occur; they may to fenitization. Major element data (Table 10) fo~. syenites ~ ~~~~~~ ~ ~~ ~~~~~~ ~ ~ ~ ~~~ ~~~~~~ in unit 3A indicate that they are only mildly alkaline. The syenites at Mount Copeland all tend to be enriched in in- 0 A1 Syenites V A3 Syenites compatible elements (e.&Sr, Zr,Nb, Y and REE, Table I ) O. - Subalkaline rocks L 30.00 40.00 50.00 60.00 70.1 Si07 0 A1 Syenites 0 A3 Syenites Corbonatite 0 A1 syen fer Agpaitic syenite fomily 0 A3 syen fer Alkali basalt family Subalkaline rocks 0.00 30.00 40.00 50.00 60.00 70. Si09Figure 46. Alkali-silica and agpaitic index plots, Mount Copelandsyenites. Figure 47. Major element ternary plots, Mount Copelan syenites.Bulletin 88 59
  • 24. British Columbia - On agpaitic index and alkali-silica plots, nepheline up-section to the south. The carbonatites consist of dixon-syenites (unit Al) predominantly plot within the miaskitic tinuous lenses associated with mafic (pyroxene-amphhole)syenite field. The leucocratic nepheline augen syenites (unit and syenitic fenites. Within the volumetrically more abun-Ala) fall within the agpaitic field on the alkali-silica plot, dantfenites,carbonatites may occuras relatively thick, buff-but are closer to the miaskitic field on the agpaitic index plot weathering, foliated and laminated layers (Plate 24); as(Figure 46). The bordering syenites (unit A3) contain sig- swirled, discontinuouslenses (Plate 25); or as small, irregu-nificantly less alkalis, and plot in the miaskitic syenite to lar coarse-grained pods.alkali basalt (alkaline gabbro) fields. The bordersyenites are The carbonatites are sovites and consist of 70 to90%also somewhat enriched in calcium, magnesium and iron calcite and variable amounts of sodic amphibole (rie-relative to the nepheline syenites (Figure 47). beckite), apatite and phlogopite. Phlogopites may di:;play reversed pleochroism. Sphene, aegirine, plagioclase, mag-GEOCHRONOLOGY netite, pyrrhotite, pyrochlore, chalcopyrite, pyrite, The isotopic ratios resulting from lead and uranium molybdenite and ilmenite may be present as accessory min-analyses on zircons separated from Mount Copeland syenite erals.gneisses yielded an early Hadrynian age of emplacement,circa 770 Ma (Okulitch et al., 1981). Subsequent analyses FENITES -PERRY RIVER AREA(R.R. Parrish, personal communication, 1986) in agree- arement. Fenites are well layered, probably reflecting oripinal compositionalvariations in sedimentary strata. Three lypes are recognized; mafic pyroxene-amphibole fenite, syeniticCARBONATITES AND ASSOCIATED albite - potassium feldspar fenite and albite fenite. TheROCKS, WEST FLANK, FRENCHMAN mafic fenite isby far the most abundant;jt has gradationalCAP DOME (82M/2,7,10) contacts with interlayered albite fenite and sharpcoctacts with syenitic fenites (Plate 26). Remnant metasedimmtary Carbonatites alongthe western margin of the Irench- calcsilicate gneiss, quartzofeldspathic paragneiss and nunorman Cap dome in the Perry River area (latitude 51°15N,longitude 118"41W Figure 44) were originally describedby McMillan (1970) and McMillan Moore (1974). W o andtypes were recognized. Type 1carbonatites are conformablewith bedding inmetasedimentary hostrocks and meta- havesomatic envelopes whichmay extend from l to more than30 metres beyond the intrusive contacts. They are inter-preted to be sills or dikes. Type carbonatites are concordant 2bodies, associated with whitemarbles, which have no con-tact alteration zones. They crop out strata which overlie inthose hosting Q p e 1 carbonatites. Detailed mapping theinMount Grace area north of the Perry River (latitude51"27N, longitude 118"49W, Hoy and McMillan, 1979)led to the discovery of new occurrences of the Type 2 car-bonatite layer, referred to as the Mount Grace carbonatite(Hoy and Kwong, 1986) and confirmed suggestion that theit is an extrusive layer. More recent work (Pilcher, 1983;Hoy and Pell, 1986; Hoy, 1988) has shown that intrusivecarbonatites occur at two stratigraphic levels. Anew occur-rence (Pilcher, 1983) is located stratigraphically above theMount Graceextrusive layer and is referred to as the Ren,or Ratchford Creekcarbonatite (latitude5l022N, longitude118"44W). Adetailed account of carbonatites on the westflank ofthe Frenchman Cap Dome given in Hoy (1988) isand the reader is referred there for additional information.PERRY RIVER INTRUSIVECARBONATITES(82Mf7) Several lenses of intrusive carbonatite are recognizedin the Perry Riverarea (McMillan and Moore, 1974). Theyoccur low in the mantling gneiss stratigraphy, locally withina few metres of the core gneisses. These occurrences appearto be p a t of a single continuous zoneat least 4 kilometresin length (Figure 3 of McMillan and Moore, 1974)that is Plate 24. Intrusivecarbonatite band (light grey) surrounded by darkconcordant withlayering, but on a regional scale may cut amphibolite fenite and some grey syenitic fenite, Perry River area.60 Geological Survey Bi.anck
  • 25. ~~ ~~ Plate 25. Swirled carbonatite (light colour) in amphibole fenite, Perry River area. Plate 26. Interlayered amphibolitic fenit (dark) and syenitic fenite (light), Perry River area.Bulletin 88 61
  • 26. British Columbiamarble layers occur withinthe fenites. In general, the con-tacts between mafic fenites and quartzofeldspatbic parag-neisses are sharp, whereas those with more calcareous strataare gradational. Toward the centre of the fenitized zones,paragneiss layers may be present but not calcsilicategneisses. These relationships suggest that fenitization is se-lective, preferentially affecting more calcareous layers andonly with increasing intensity affecting quartzofeldspathicstrata to produce syenitic fenites (Hoy, 1988). Pyroxene amphibole fenites are dark greenblack and to ormay he massive foliated. They consist primarily of aegir-ine-augite, or rarely, aegirine, sodic amphibole, sphene andbiotite. Biotite content ranges from trace amounts to over50%. Calcite, apatite, plagioclase (albite), epidote, zircon,chalcopyrite, magnetite and ilmenite may be present as ac-cessory minerals. Potassium feldspar and nepheline havealso been noted (Hoy, 1988). Pegmatitic lenses consistingof calcite, amphibole, pyroxene, enhedral sphene, magnetiteand ilmenite are common throughout fenites. Individual thecrystals of these minerals may be in excess of 7 centimetreslong. The maficfenites are locally interlayered and grada-tional with leucocratic fenites (or albitites) consisting of ap-proximately 90% albite with aegirine-augite and minoramounts of biotite, sphene, apatite, epidote, microcline,magnetite, and locally, coarse molybdenite. Syenitic fenites are foliated, compositionally handedand contain rare thin metasedimentarylayers and occasionalsmall discontinuouscarbonatite lenses. They are composedof 70 to 80% plagioclase (andesine) and microcline in vary-ing proportions. TNe syenites are less common that mon-zonites (microcline is generally less abundant than Plate 27. RatchfordCreek (REN) carbonatite(lightgrey) aegirine or aegir-plagioclase). Principal mafic minerals are interlayered with amphibolitic fenite (dark grey) and conlainingine-augite with or without biotite. Calcite, muscovite, fenitizedcountry rock fragments (grey), (colourphoto,pug,?136).sphene, magnetite, apatite, chalcopyrite and allanite arecommon accessory minerals. Variable amounts ofnephelinemay also be present.RATCHFORD CREEK(REN) INTRUSIVE INTRUSIVE SYENITE- PERRYRIVER AREACARBONATITE (82M/7) (82M/7,10) A large intrusive syenite body crops out in the Peny The Ratchford Creekcarbonatite is a concordantunit River area(see Figure 44). It is a concordant unit, up 1.0 300at least 3 kilometres in length and, on average, 10 to 30 metres thick and 12 kilometres long (McMillan,1973), tbaf.metres thick. It is associated with pyroxene-amphibole is internally foliated and layered with alternating bands 01fenites similar to those occurring with Type 1 carbonatites. syenitic and feldspathoidal rock. Country rocks along itsIt crops ont south of Ratchford Creek, in the core of the margins are metasomaticallyaltered; a rusty zone en~ichedMount Grace syncline (Figure 44) and intrusive into strata is in feldspar,pyroxene, muscovite andor pyrrhotite is devel-.which overlie those hosting the other known carbonatites oped adjacent to the syenite. The syenite gneiss infruded(intrusive and extrusive) and syenites. strata which underlie those hosting the extrusive carbona The Ren carbonatite weathers to a mottled orange- tite.brown colour and bas well-handed to salt-and-pepper tex- a The main minerals in the syenite are microcline:, per-.ture. It is intimately intermixed with pyroxene-amphibole thite, plagioclase (albite to labradorite) and nepheline. A pfenites and locally contains weakly fenitized inclusions of proximately 60% of the rocks contain nepheline, with orcountry rock(Plate 27). The carbonatite comprises, on av- without feldspars. Biotite is the predominant mafic mineralerage, 60 to 80% carbonate minerals (calcite and dolomite) aegirine or aegirine-augite may also be present. Acc~:ssoryand 10 to 30% apatite, with accessory biotite, magnetite, minerals include muscovite, phlogopite, calcite, cancrinite,amphibole, pyroxene and sphene, minorpyrrhotite, py- and apatite, sphene, zircon, allanite, pyrochlore, grossnlsr gar..rite, sphalerite, chalcopyrite, pyrochloref?) and monazite(?) net, fluorite, molybdenite, magnetite and pyrrhotite.(Pilcher, 1983). (McMillan and Moore, 1974).62 Geological Survey i?ronch
  • 27. Plate 28. Part of the thickened section the Mount Grace extrusive carbonatite; the whole cliff is part of the carbonatite zone; note larg ofsyenitic inclusions immediately above the person.MOUNT GRACE EXTRUSIVE CARBONATITE(82M/7,10) The Mount Grace carbonatite layer averages 3 to 5 me-tres in thickness. Locally, it narrows to less than a metre andnear its mapped northern limit (Figure 44). it isestimated tobe greater than 20 metres thick (Plate 28). An associatedincrease in clast sizes here indicates close proximity to asource or vent area. Although in most places it is a singlelayer, it locally comprises a main layer plus a number ofthinner layers separated by paragneiss and marble. It hasbeen traced or projected beneath overburden for a strikelength of at least 100 kilometres (Hay, 1988).The contactsof the Mount Gracecarbonatite with overlying and under-lying calcareous gneisses are sharp, hut in places they gradethrough approximately1 metre into grey-weathering, mas-sive to thin-beddedcalcite marble. In contrast with intrusivecarbonatites in the Perry River area, it has no fenitized mar-gins. Detailed descriptions of the Mount Gracecarbonatitehave previously been published (Hoy and Kwong, 1986;Hoy and Pell, 1986; HOy, 1988) and onlybrief reviewwill abe presented here. In the field, the carbonatite is recognized and charac-terized by an unusual pale to medium brown weatheringcolour. Grains of dark brown phlogopite, colourless apatiteand needlesof amphibole weatherin relief. Pyrrhotite, py-rochlore and zirconare locally developed accessory miner- Plate 29. Interbedded grey sedimentary marble (light ):rey) withals. Monazite, barite, strontianite and possibly rare earth buff carbonatite agglomerate tuff (darkergreys) layers; and Mount arecarbonate minerals present in trace amounts. Grace carbonatite nearBlais Creek.Bulletin 88 63
  • 28. TABLE 11 CHEMICAL ANALYSES OF ALKALINE ROCKS, WEST FLANK, FRENCHMAN CAP DOMEI Z 2 - L 51.44 57.34 0.27 0.30 0.94 Nepheline syenite gneiss 2- 2 2 2- -2- -~ 46.18 55.67 51.33 0.28 0.38 41.77 0.52 53.02 0.21 0.60 Mount Grace carbanatite & 5.1 6.77 1.32 ,,P 5.1 5.15,1 River inrmsivs carbonatitn 0.39 6.38 0.79 4.10 < . 1 0.86 0.03 0.05 00 5.1 5.1 5.1 Ren InWsIve cartonatite 5.1 1.51 4.57 0.06 0.04 0.85 0.04 5 1 4.15 0.06 24.42 22.98 28.11 23.57 23.59 31.71 27.12 19.76 0.36 0.16 1.57 0.30 0.91 0.22 0.55 0.07 0.72 1.40 0.59 4.08 0.63 0.44 0.29 1.14 4.10 4.14 0.38 4.66 0.68 1.20 3.45 2.87 2.71 3.29 1.32 1.33 2.57 1.45 2.37 1.49 0.46 1.30 . . 0.10 0.07 0.29 0.09 0.09 0.10 0.09 0.15 0.38 0.44 0.44 0.17 0 9 0.31 . 9 0.43 0.41 0.43 0.15 0.24 1.12 0.15 0.79 0 4 . 6 0.31 0.37 2.38 0.46 1.85 0.62 0.10 6.30 17.30 16.6915.40 4.23 0.59 4.63 2.06 2.973.47 6.33 2.79 45.34 51.0442.7252.44 45.29 31.05 43.82 33.83 32.86 9.44 5.06 3.00 4.12 7.51 12.23 4.24 6.04 0.37 0.13 0.64 0.14 0.37 0.08 0.24 0.04 0.16 10.18 3.55 5.80 8 9 6.41 . 9 4.70 6.69 10.90 10.30 4 3 0.38 1.74 1.41 0.63 0.97 1.08 1.23 1.53 0.50 1.42 0.36 0.50 0.53 0.41 1.22 0.12 2.17 0.35 2.49 0.62 0.70 31.10 40.72 0.16 0.60 0.10 0.36 0.1s 0.31 ~ 0 8 COS 0.06 0.06 I 7 mr ~ %.0s~l00.00iw.l2 99.02 99.46 98.54 101:70 9 5 98.68 .4 98.63 . " . " " . . . " . . . . . . . _ . - - 33W 57W 46M 54M) 6600 58W 16w 31W 2103 1wO 5188 4628 4271 4828 . . " - .3500 28W 31W 3500 3203 36w 213 162 1205 6761155 1133 2539 1217 1403 3700 LIS0 1915 23W 2540 2185 - . . - i - - . . - 297 208 % 92 108 IZW - 2380 - 1 2 w lZm . - . <IO 1W 3W IW Zm 50 8 50 30 203 clW M) 27 25 1516S-. 1 A B B B Fy~x~e-amphibolcfenilc~ 55.70 ~63.9662.29 63.23 62.81 59.02 "6262 "49.19 56.58 64.31 61.26 62.87 38.44 38.88 35.64 53.76 57.45 57.66 55.91 35.66 41.94 37.24 I-~talironuyrr~Ul.~Fa203 2.22 0.86 0.68 0.54 1.17 0.78 0.46 0.04 0.22 0 0 0.31 .1 0.03 0.22 0.37 0.06 4.352.34 2.17 2.64 2.86 4.01 2-fmmMcMihundMoorrflPM 15.24 17.91 17.92 16.41 17.35 18.14 17.19 13.18 20.53 17.72 17.08 16.09 19.75 1858 19.37 20.02 8.508.M 1.44 7.27 1.37 7.64 3-hHdyundPdlf1986) 2.90 7.05 5.76 3.76 5.59 5.39 4.60 0.65 3.71 0.89 3.14 0.52 0.43 1.65 2.70 0 6 15.74 .6 10.73 11.66 11.4010.72 13.62 4-/mnHdyundXw~~(l9S5) :,04B B B C i 5 -h. . . . Hm 119871 0.22 0.07 0.16 0.13 0.15 0.15 0.12 0.12 2.22 0.28 0.14 0.04 0.10 0.06 0.10 0.02 0.31 0.15 0.23 0.15 0.27 0 2.5 1.61 0.56 0.19 0.37 0.91 0.35 0.50 1.02 3.16 0.33 1.76 0.08 0.16 0.41 0.66 0.36 8.20 12.41 6.82 1237 9.527.91 A.A~~~~"a~~~~rrdw;huunuiw~.~~~,~~P~rryRiur 3.72 2.81 1.90 1.58 2.54 1.68 1.99 15.79 9.14 8.12 2.24 3.16 6.93 3.58 3.55 3.48 13.66 16.70 21.70 21.80 14.63 12.05 B - l ~ ~ ~ f ~ " i i ~ ( ~ j , ~ , ~ J ~ ~ " ~ " M ~ ~ G * 7.38 9.22 7.21 7.45 7.97 6.48 7.83 7.06 9.14 9.24 7.82 6.61 4.81 7.69 5.90 9.04 3.12 1.84 4.11 4.10 1.41 2.63 C-rU6j,~/mdrauaiurdv~,hR~h/~~C,~~fRln)in(nuivr~nr&-.; 1.34 0.78 4.27 3.57 2.02 4.01 3.12 0.32 1.16 0.30 2.01 5.12 6.40 3.36 5.36 1.34 1.43 0.43 0.80 0.53 3.64 3.46 2.94 1.32 0.88 0.21 0.41 0.845.896.46 7.4412.38 6.615.76 4.64 3.39 5.30 3.21 1.6118.% 4.070.791 4.08 2.50 0.37 0.07 0.03 0.02 0.06 0.02 -. 2.68 0.03 0.24 0.16 0.36 0.08 0.75 00 .s 0.35 0.05/ 3.19 1.81 3.32 2.12 0.99 1.82 97.79 100.69 101.09 98.80 96. 9 99.59 9 99.01 101.45 99.373% 102.28 99.36 99.88 98.35 99.511 97.16 98.81 98.81 98.69 101.07 96.541 99.98) . . " " " . . " " " 10 c10 <IO <IO 17 c 10 I5 <IO 10 <IO 13 <IO <IO c10 c t 0 <IO 14 124 25202 IS 242 " " . " . . . . " " . 71p.l A??< 77n7 n a p 7 y n .m a 77011 hM? X7A 7.767 R?7 1 9 6 1 2251 1693 1674 1446 2616 2654 3120 2 M O 5307 6785 851 560 962 1074 613 628 996 183 IWO 1060 5227 5732 2928 830 3 m 423 2961995 2701 229 187 521 476 352 713 1275 1613 569 117 8181 22 675 28 38 79 30 815 286 loxl 1142 203 w) 937 1116 S2 1% i3c 179 248 139 47 i 4 592 339 559 8% 6I :5 2 W 493 ? !?S 22 24 ?3 74 I17I. 36 37 32 43 65 31 19 62 9 18 16 10 18 10 28 15 79 47 79 47 65 85
  • 29. ~- ~ " ~ ~ I _, Minisfry ofEnergy, Mines Petmleun!Resomes and CHONDRITE-NORMALIZED REE Pl.OT PERRY RIVER INTRUSIVE CARBONAITES Figure 48. Carbonatite plot, Mount Grace Perry River area. and l I I I I I I i I I I I I I I i I I Trr , , I I I I I I Lo Ce Pr Nd Sm Eu Tb Dy Ho Yb Tm I. Rare-earth lements E ~ ~~ ~~ ~ ~ ~~ ~ ~ ~~ ~~ ~. CHONDRITE-NORMALIZED REE PLOT CHONDRITE-NORMALIZED REE PLOT RENCARBONAllTES MOUNT GRACE INTRUSIVECAREONLTITES 103 i j 102 I ri La Ce Pr Nd Sm Eu Tb [ly Ho Yb Tm LI 10 La Ce Pr Nd Srn Eu Tb Dy Ho z Tnr Y i b Rare-earth lements E Rare-earth lements E Figure 49. Chondrite normalized rare earthplots, carbonatites, west flank, Frenchman Cap Dome. (A) Chondrite-normalizedKEE plot - - - Perry River intrusive carbonatites;(B) Chondrite-normalized REE plot Ren carbonatites; (C) Chondrite-normalized REE plot Mount Grace extrusive carbonatites. Buliefin 88 65
  • 30. Brifish Columbia The carbonatite is commonly internally banded, with characteristicofcarhonatiteselsewhere(e.g.,LeBas, 1981).one or several layers of blocky tephra interbedded with All the carbonatites show typical light rare-earth elementfiner grained, massive or laminated carhonatite (Plate 29). enrichment patterns on chondrite-normalizedplots (FigureThe blocky tephra layers contain three types of matrix-sup- 49a, b, and c). Light rare-earth enrichment is not as markedported clasts: small granular albitite clasts, commonly upto as that displayedby samples from Aleyor Rock Canyon the3 centimetres in diameter, consisting of pure albite or albite Creek showings; however, total rare-earth values andslopewith variable amounts of phlogopite; syenite clasts, gener- (measure of enrichment) are greater than those for carmna-ally 1 to 10centimetres in diameter,consisting of potassiumfeldspar with variable amounts of plagioclase, calcite, apa- tites hosted by Precambrian or Early Cambrian strata in thetite and rare feldspathoids; and larger rounded to sub- Omineca Belt.rounded biotite-plagioclase gneiss, schist and quartzite The Mount Gracecarbonatite has total rare-earth ele-clasts that are commonly up to 20 centimetres in diameter. ment concentrations ranging from approximately ppm 6oE1The lithic clasts may be internally folded and have a pro- to greater than So00 ppm (Appendix significantly h igher I),nounced layering or foliation that is randomly oriented withrespect to the regional mineral foliation. The lithic and al-bitite clasts are generally randomly distributed throughouta tephra layer, hut in some layers they are concentratedinthe centre or occasionally graded withclast size increasingup-section. Near the northern mapped limit of the carbona-tite layer, where it is thickest, unusually large syenitic clasts,over 1 metre in diameter, occur within it.GEOCHEMISTRY Carbonatites from the Perry River, Mount Grace andRatchford Creek (Ren) areas display a large compositionalrange with respect to major and trace elements (Table 11; /Appendix 1). The majority of the Mount Grace extrusiveand Perry River intrusive carhonatites are sovites while atthe Ratchford Creek showing magnesio-carbonatites pre-dominate (Figure 48). All are highly enriched in strontium,barium, niobiumand rare-earth elements relative to carbon- Subalkalineates of sedimentaryorigin (Table 11).These high values are rocks rT 30.00 40.00 50.00 60.00 7. 0 Si07 x overageintrusive syenite, Perry River area Marble impure marble, coic. schist 0- a locality Sample 30.00 40.00 50.00 60.00 70, Si09Figure 50. Detailed sectionof the Mount Grace carbonatite, BlaisCreek showing. La, Ce and Nd values of selected samples from Figure 51. Alkali-silica and agpaiticindex plots, Peny RiverHBy (1988). syenites.66 Geological Survey Branch
  • 31. Ministry of Energy, Mines and Petroleum Resources b syenites MI. Grace corbonotite A k-feldspar-albito fenite / I I R& carbonatite albite fenite fenit* / Veniter amphiboleFigure 52. Major element ternary plots, Perry River and Mount Grace area alkaline rocks. (A) CaO-Na20-KZO plot, Pen) River and (B)Mount Grace areas; A F M diagram, Perry River syenites and fenites. iFigure 53.Fenite plots,Perry River area. (A) CaO-Na20-KZO-MgO+Fez03fenite plot, Perry River area; (B) NazO-KzO-Fez03 feniteplot, Perry River area.than sedimentary marbles; rare-earth element analyses can miaskitic varieties are present, but on average, the Perrybe used to differentiate the layered Mount Grace carbonatite River syenites are miaskitic in nature (Figure 51). Alkali andfrom its hostrocks (Figure 50). Thin tuff layers, with high iron-magnesium fenites occur in the Perry Riverarea, andrare-earth element concentrations, are present within me- can be clearly differentiated on ternary plots (Figure 53).tasedimentary marble the top of the carbonatite unit (sam- at The alkali fenites may be further subdivided intc, soda-richple H85P25B) and some of the fine-grained marble layers (albite) fenites and soda and potash-rich (albite - potassiumwithin the basal part of the carbonatite unit (those that havelow REE concentrations, e.&, H85F26B, H85P261)may be feldspar or syenitic) fenites; however, these two typesarelargely of sedimentaryorigin with only a minor tuff compo- compositionally gradational (Figure 53). Syenitic fenitesnent (Hoy and Pell, 1986). This intimate interlayering of cannot be easily distinguished from igneous syenites oncarbonatite and sedimentary marble supports argument for AFM or Naz0-Kz0-Ca0 ternary plots (Figure 52). Albitean extrusive origin for the Mount Gracecarbonatite. fenites are most common as clasts in the Mount (Gracecar- Intrusive syenites are quite varied in major element bonatite and Hoy (1988) suggests that this mayindicate thatcomposition (Table 1; Figures 51 and 52); both agpaitic and sodium fenitization is more importantat depth adjacent toBulletin 88 67
  • 32. the parent magmas, and more potassic and iron-magne- the which it is intruded by). A Lower Cambrian lead-lead datesinm fenitization occurs at higher structural levels. obtained from galena the stratiform Cottonbelt lead-zinc in deposit higher in the succession (H6y and Godwin, 1988)GEOCHRONOLOGY supports the interpretation that the age of the mafitling Uranium-lead analyses of zircons from the Mount gneiss succession spans Late Proterozoic early Pa1a)zoic toGrace carbonatite produce nearly concordant agesof 70 to time (Hoy, 1988). The Mount Gracecarbonatite also must 100 Ma (R.R. Parrish, personal communication, 1987) be Late Proterozoic to early Paleozoic in age.It occurs highwhich indicates that the zircons are mainly metamorphic in in the mantling gneiss stratigraphy, only 110 metres beloworigin. Uranium-lead systematics on pyrochlore from the the Cottonbelt deposit; and based on this, it is reasonable toMount Gracecarbonatite yield a 60 Ma date, which is also assume that it is close in age to the Cottonbeltdeposit, ]?rob-indicative ofmetamorphism. ably latest Hadrynian to Eocambrian (circa 570 Ma). Addi- tional work on uranium-lead systematics is currenlly in Because absolute dating methods have notbeen effec- progress in an attemptto verify these conclusions.tive in establishing the age of Mount Grace and Perry Rivercarbouatites, other methods must be attempted. The MountGrace andPerry River carbonatites are hosted in the man- THREE VALLEY GAP (82L/16)tling gneisses of the Frenchman Cap dome, a rock sequence Carbonatites and leucosyenites are found along Vic-thethat also contains the Mount Copelandsyenite gneiss (un- tor Lake Main logging road (latitude 50°5534"N, longitudederlying the carhonatites) and the Cottonbelt stratiformlead-zinc layer (overlying the carbonatites). The Mount TABLE 12Grace carbonatite, which is extrusive, must be the same age CHEMICAL ANALYSES, THREE VALLEY GAPas the sediments with which is interbedded. it ALKALINE ROCKS The date of approximately 770 Ma, obtained from zir-cons in the Mount Copeland syenite gneiss (Oknlitch et al., wi % 1 2 3 4 51981) whichintrudes the basal part of the succession in the Si02 18.70 46.50 21.60 50.96 33.40 Ti02 0.680.72 0.67 0.81 0.64 0.42Jordan River area, suggests that the basal part of the succes- A1203 21.26 6.29 17.62 8.29 11.02 13.80sion is Late Proterozoic (it must at least as old as rocks be Fe203T 8.16 8.7 6.20 8.33 2.70 4.34 MnO 0.26 0.23 0.16 0.21 0.08 0.07 IMeO 2.70 2.42 2.44 2.15 1.85 0.891 Cab 33.20 29.80 21.95 18.90 11.29 5.17 Na20 0.92 1.60 1.93 2.18 3.35 3.64 K20 2.85 3.26 3.59 2.40 2.37 6.76 LO1 22.25 20.75 14.63 2.26 1.29 P205 3.21 3.20 2.10 2.40 2.27 Tofal 99.80 100.1 98.09 99.81 99.7 ppm Ni <2 <2 1 30 1 Cr 3 3 <20 63 <20 e20 20 12 co15 13 14 28 %St 1313 1730 1418 3279 3135 3433 Ba 1643 2405 826 1726 836 1568 Zr 207 296 79 21731 177 Nb 429 114 110 96 92 33 Y 51 47 37 3424 42 La 212 55206 131 60 148 Ce 140 256 401 275 396 154! .1Nd 140 151 - 111 yb 4.2 4.4 - 2.8 sc 24 29 20 Ta 82 1 <2 19 1 21 Th 0 10 6 < 6 4 4 1. - 3VG136A - biotite sovite; 2. - 3VG135A - sovile; 3. - 3VG139A - biotite sovite 4. - 3VG137 - border zonebehveen carbonatite and associated syeniiic rocks; 5. - 3VG137B - syenificfenite, confabzone; 6. - 3VG139B -pegmaiiiic sphene-rich syenite. Major elements analysed by ICAP, alkalinefusion, in samples 1,2,4:All irace elemenis analysedPlate 30. Large feldspar clots in biotite-rich carbonatite, T h r e e by XRF except REE in 1,2, & 4 whichValley Gap area. were analysedby INAA.68 Geological Survey 1:ranch
  • 33. Minisfy of Energy, Mines and Petroleum ResourcesFigure 54. CaO-MgO-FQOjt+MnO carhonatite plot, Valley ThreeGap. 1 Lo Ce Pr N d Sm Eu Tb Dy Ho Tm Yb LI Rare-earth Elements ___ Figure 56. Chondrite-normalizedREE plot - Three Valley Gap. 118"2329"W) which joins TransCanada Highwayfrom the the south, approximately 3 kilometres east of Three Valley Gap. Outcrop is limited to roadcuts, at elevations between 900 and 1500metres. The road is in good condi:ion, pass- able by conventional vehicles. The carbonatites and syenites occur as thin, discontinu- ous bedding-parallel lenses in pelitic metasedimentary rocks. Both the intrusions and hostrocks have been meta- morphosed to upper amphibolite facies (sillimanite zone) and the pelites have been extensively migmatized. The host- rocks are of uncertain affiliation, they crop out near the mapped boundary (Joumeay and Brown, 1986) between Hadrynian Horsethief Creek Group strat;r and the autochthonous mantling gneiss succession of Irenchman Cap dome. Tentatively they are assigned to tht: mantling gneisses. Carhonatite lenses are generally 20 to 63 centime- tres in width andhave envelopesof mafic feniter, 10 to 30 centimetres thick, developed between them and adjacent rocks. Everywhere observed, thefenites in dirxt contact are with, and gradational to, syenites. Commonly th- carbona- tite occurs as lenses within the fenite. CARBONATITES, FENITES, SYENITES The carbonatites are buff to brown-weathering rocks that are primarily composed of calcite (45-50%), biotite (5-20%). apatite (5-15%), perthite (up to lo%), hornblende (5-30%),augite(1-10%)andtracesofsphene.In]~lacesthey contain feldspathic lenses or augen (Plate 30). sirnilar inap- Figure 55. Major element ternary plots, Three Valley Gap. pearance to migmatitic leucosomes. Hornblende and augiteBullefin88 69
  • 34. are more abundant the marginsof the carbonatite lenses: at veloped within them than is typical and hence have highbiotite is the dominant maficsilicate mineral in the centre. Si02 (Table 12). They are also relatively enriched in ironAll carbonatites display a well-defined biotite-amphibole and plot within the ferrocarbonatite field on a Ca0-Ivlg0-foliation. Fez03+MnO ternary plot (Figure 54). Samples collectcd ad- Fenites are green on weathered fresh surfaces and and j a c e n t to t h e c a r b o n a t i t e s h a v e m a j o r e l e l n e n tgenerally containabnndant augite, hornblende, calcite(25% concentrations intermediate between the carbonatites andor less), scapolite and plagioclase. Accessory mineralsin- the ‘syenitic’rocks (Figure 55). Rare-earth element contentsclude biotite, apatite, sphene andnepheline. Potassiumfeld- are low, relative to Perry River, Ren and Mount Grac: car-spar, perthite, allanite, zircon and garnet (coarse grained, bonatites (Appendix 1) and slopes on chondrite-nomillizedbrown body-colour) mayalso be present. rare-earth plots (Figure 56) are flatter than for carbonatites The leucosyenites are massive, white, medium to on the west flank of the Frenchman Cap dome (less lightcoarse-grained rocks that generally contain potassium feld- rare-earth enrichment).sparzplagioclasehugite+sphene.Their origin is unclear;unambiguous field relationships are not exposed. These GEOCHRONOLOGYsyenites may actually be syenitic fenites, rather than intrn-sive phases. Uranium-lead analyses of zircons separated from the Three Valley Gap carbonatite produce nearly conccrdantGEOCHEMISTRY ages of 70to 1 0Ma, as was the case with Mount Grace 0 the The carbonatites at Three Valley Gapare calcitic (high carbonatite, indicating that the zircons are mainly metamor-Ca0:MgO ratio), but tendto have moresilicate phases de- phic in origin.70 Geologicul Survey Binnch