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BCGS: Carbonatites, Nepheline Syenites & Related Rocks in British Columbia (Chapters 4,5&6) (Pell, 1994)
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BCGS: Carbonatites, Nepheline Syenites & Related Rocks in British Columbia (Chapters 4,5&6) (Pell, 1994)


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  • 1. ULTRABASIC DIATREMES IN NORTHERN BRITISH COLUMBLQ " Only twobreccia pipes have so far been recognized in pearance of a stretched-pebble conglomerate. The northernBritish Columbia north Prince George of (Figure 2); the Os- and central parts of the diatreme havebeen cut by fluorite-pika pipe near Peace Reach,east of Williston Lake and the calcite and fluorite-calcite-pyrite stockwork veins contain-a small diatremein the Kecbika Riverarea of the Cassiar ing minor amounts of galena and molybdenite. SimilarMountains, westof the Rocky Mountain Trench. Both are breccias (minus thephlogopite) arepresent the E d River inhosted by middle Paleozoic carbonate rocks are associ- and -White River area of the southern Rocky Mountains (Yell,ated with carbonatite/alkaline rock complexes. The dia- 1987).treme in the Kechika River area is the only one documentedwest of the Rocky Mountain Trench. Associated dikes are quite common periphcal to the main diatreme and on ridges to the north (Figures 21 and theTHE KECHIKA RIVER DIATREME AND 22). They crosscut both the carbonate hostrock!; and the mottled phyllites. The dikes, in general, are extremely wellRELATED ROCKS (94L/12,13) foliated and average 1 to 2 metres in thickness. They are A suite of alkaline igneous r 9 k s in the Kechika Ranges similar in composition and appearance the matrix of the toof the Cassiar Mountains is intermittently exposed in a main diatreme, comprised predominantly iron and mag- ofnorthwest-trending zone excess of 20 kilometres long, the incentre of which is approximately latitnde 58"42north and TABLE 13longitude 127"3Owest.Tracbytes,syenites,malignites,car- GEOCHEMISTRY OF SELECTED DIATREMEbonatites and related tuffs and agglomeratesare present in BRECCIAS AND RELATED DIKESAND T JFFS , Ithissuite(seeChapter2);adiatremebrecciapipeandrelated KECHIKA AREAdikes and tuffs are also exposed in this area. The igneous - ~~~~~~ ~. "rocks are hosted by middle Paleozoic (Silurian?) carbonate Diatreme brecciastrata and have been deformed and metamorphosed to 13.34 35.68 36.75 41.46 34.35 37.04 19.82greenschist facies. 0.85 1.14 1.18 1.12 0.74 0.81 0.95 A1203 6.07 10.07 6.32 5.35 10.35 10.42 A complex diatreme containing a numbes of breccia 9.78 9.48 5.96 7.13 6.92 7.4: 6.81phases, related tuffs and breccia dikes crops out near the 0.14 0.12 0.38 0.39 0.48 0.41. 0.26centre of the belt of alkaline igneous rocks(Figures 21 and 5.1.1 3.65 15.11 8.45 10.68 10.01 9.3;22). These rocks weather greenish to rusty orange and silver 9.55 5.44 12.55 9.89 11.27 20.21 11.7are weakly to extremely well foliated. The main diatreme is 0.06 2.13 2.10 2.74 2.96 0.2:; 0.72exposed in acreek at approximately 1560 metres elevation; 4.80 1.71 7.74 6.04 4.20 4.0:: 3.76dikes and tuffs are present on the slopes and ridges to the 16.87 14.79 14.2215.88 23.31 13.05 28.4:north and west of the diatreme, at elevations of up to 2230 11 L0.24 0.19 0.26 0.21 1.3: 218metres. Exposure in the area is moderate to excellent; buck- 6.68 99.30 98.71 97.51; 99.11 98.04 95.49brush andscattered trees are present in the valley bottoms,while the upperslopes are barren. Access to the area is by 689210600 270514 71 1 1G2 1100 1108 510 720 - 32r1 641helicopter from Watson Lake, Yukon or Dease Lake, B.C., - 82 - 269 2 1 56150 and 160 kilometres distant, respectively. 390 95314 230 320 105 127 295 212 790 610 708 81 92 420LITHOLOGY Ba 970 179 500 430 412 411 174 Zr 105 106 225 440 181 56 175 The main diatreme (Figure 22) comprisesvery inhomo- Nb 9 60 20 <5 92 43,3 80geneous, heterolithic tuffisitic breccias with roundedto an- 32 23 32 55 50 3885 46gular xenoliths up to 7 centimetres in diameter. Quartzite 15 341 199 44026 317 360and carbonate rock fragments dominate xenolith popu- the 33 35270 560 423 440 510 - 47 204 -lation; some autoliths, rare syenite fragments and someblack argillite clasts were also noted. Quartz xenocrysts,rare chrome spinels, juvenile and vesiculated glass lapilli,and crystal fragments (predominantly potassium feldspar : ;1 Nd Ta < s < 3< 5 < 5 201 75 9, 23 5 areand minor phlogopite) also present. The breccia matrixconsists of carbonate minerals, potassium feldspars, minor 161muscoviteandlocally.chromemicas.Inp1acesnearitsoutercontacts, the breccia is intensely deformed andhas the ap-Bulletin 88 71
  • 2. Brifish Columbianesium-rich carbonate minerals, feldspars, muscovite andserpentine. Some quartz and apatite may also be present.The dikes locally contain chrome spinels, small lithic frag-ments and fragments of devitrified glass. Some contain orchrome-green (chrome mica) dark green (chlorite and bi-otite) elliptical patches which probably represent shearedand altered fragments or crystals. One dark green weather- rocking dike contains abundant small fragments and alteredolivine macrocrysts. Tuffs outcrop on ridges near the centre of the property,immediatelynorth of the main diatreme and the north end atof the property, south of Boreal Lake (Figures 21 and 22).These pyroclastic rocks are rusty orange to silver-greenweathering with a pale green fresh surfaces, very similar inappearanceto some of the dikes. They are conformable withthe host carbonate succession and are interbedded withbrown, blocky weathering agglomerates and aplitictrachytes. Chrome spinels are present locally. In thin sec-tion, these rocks are seen to contain plagioclase laths,siderite spots and altered, six-sided crystals (clinopy-roxenes) in a fine-grained matrix of carbonate, sericite or IC,feldspar and oiaqnes. These rocks be the extrusi! ~~~~ ~ ~~ ~~~ ~~may~ ~- @ 0 didreme dike X + tuff ultramafic Figure 58. Major element ternary plots, Kechika diatrelre and 00 .0 5.00 15.00 10.00 20.00 25.00 related rocks. 0 0 Kechiko dialreme 25.00 20.00 0 diatreme X dike + tuff 1500.00 4 * and dikes Kechika tuffs V 15.00 baranifiie tephriie alkollne larnprophyre 5.00 0.00 m 30.00 20.00 40.00 50.00 60.00 70.00 S I 0L 7 C r Darn gure57.Majorelementdiscriminantplots,Kechikadiafremear Figure 59. "Average" compositionsfrom Wederhi.1and lated dikes and tuffs. Maramatsu, 1979.Nivs Crplot, Kechikadiatreme, dikes an(ituffs.72 Geological Survey llranch
  • 3. Minisrry of Energy, Mines and Petmleun: Resources " Based on modal mineralogy (olivine, clinopyroxene, plagioclase and/or potassium feldspar and minor phlo- gopite) it is difficult to classify these r o c k they showsome CHONDRITE-NORMA1 17Fn REE PLOT similarities to alkaline basalts (basanites). RELATED GEOCHEMISTRY Major element analyses of samples fromth,: Kechika 0 diatreme diatreme and related dikes and tuffs (Table 13) in(licatethat X dike these rocks are relatively low in silica and aluniinum and + tuff moderately enriched calcium and in magnesium. On a K20- MgO discriminant plot samples from Kechikt pipe and the related rocks fall predominantly within or near the leucitite field (Figure 57a), while on an alkali-silica discriminant plot they fall between the alkaline lamprophyre and alnoite .field (Figure 57b). On the ternary Fe-Al-Mg plot, samples fall within the melilitite (alkaline lamprophyre) field (Figure 58a). On an AFM plot,samples plot closer to the: base (the A-M side) than alnoites or typical basalts (Fignrt: 58b); the diatreme samples are similar, in this respect, to samples of other rock types in the Kechika area (see Figure 24b). Based on major elementchemistry, it is difficult to c1ar:sify these rocks although they do show some chemicalaffinity to al- kaline lamprophyres (nephelinites) or leucitites. Alteration may have affected major element chemistry to pre- clude definitive classification. Diatreme anddike samples show afair rangc: of nickel and chrome values; some are moderately enriched, contain- 1 ing up to 0.11% chrome and 0.07% nickel. Tht:y contain Lo Ce Pr Nd Srn Eu Tb Dy Ho Trn Yb Li higher concentrations of these two elements than do there- Rare-earthElements latedtuffs,inwhichtheigneouscomponenthasbeendiluted (Figure 59). Diatreme and dike samples also moderately areFigure 60. Chondrite-normalized REE plot - K e c W diatremes enriched in fluorine, containing between 0.18 and 1.9% (Ta-and related dikes and tuffs. ble 13). They contain low to moderate amounts ::areearths of ~~ Plate 31. Dolostone clastwith reaction rim, Ospika pipe. ~-Bulletin 88 73
  • 4. (up to 510 ppm La) and, on chondrite-normalizedrare-earth OSPIKA PIPE (94B/5)plots, generally display shallow, negatively sloping curves The Ospika pipe is a small diatreme located on(Figure 60) which are indicative of a low moderate degree to Comincos Aley claims (latitude 56"27N, longitudeof light rare-earth enrichment. The diatreme and related 123"45W) approximately 140kilometres north-nortttwestrocks are anomalously enriched rubidium and have in very of Mackenzie, on the east side of Williston Lake bemeen the Peace Reach and Ospika River. Access to the area is bylow total strontium:rubidium ratios that average around 2: 1 helicopter from Mackenzie.(Table 13). The diatreme crops outon forested slopes at approxi- mately 1550 metres elevation (Figure 3). It is only 2, fewGEOCHRONOLOGY hundred metres from the large Aley carbnatite coniplex (see Chapter 2), butthe relationships between the carlmna- No radiometric dating has been done on alkaline rocks tite and the diatreme are unclear.from the Kechika area. Field relationships suggest that theyare similar in age to the host strata, Silurian or slightly LITHOLOGYyounger. The Ospika pipeis a composite diatreme(roughly 20 by 50 metres inarea) containing at least five distinct brxcia TABLE 14 and massive phases and intruding Ordovician carbonms of CHEMICAL ANALYSIS - OSPIKAPIPE the Skoki Formation. is massive to foliated and red-brown It ~ ~ ~ ~~~ weatheringinoutcrop,withfluoritepresentnearthemargins 1 2 3 4 75 6 27.9032.0926.660.99 24.1830.5928.65Ti02 2.76 2.15 2.76 1.67 2.25 2.58 0.38Ai203 5.43 4.77 6.25 5.01 5.19 5.61 0.25Fe203T 9.47 7.94 9.25 9.56 7.61 8.67 5.21 0.20 0.19 0.17 0.22 0.16 0.17 0.55 12.72 10.04 14.65 10.62 12.47 14.07 14.69 15.63 17.26 13.40 17.20 17.52 14.84 27.53 0.01 1.23 0.95 2.29 1.55 1.85 0.00 1.43 4.01 5.55 3.80 4.01 4.02 0.12 10.00- 11.51 24.79 10.83 14.32 18.07 17.05 41.59 1.12 0.84 0.09 1.80 0.99 0.08 0.28 0.12 0.16 0.01 0.80 0.41 I %.25 97.67 96.93 97.25 97.50 99.2691.81 9 5;0 . 5.00- 230 190 360 220 290 40 330 455 331 481 185 409 232 387 co 48 24 46 39 40 10 47 Rb 48 42 160 115 148 <8 118 Sr I 514 1257 1134 1650 1448 837 1601 0.00 Ba 788 1163 1248 1741 1737 1290 20138 Zr 300 53 263 682 261 303 4 Nb 241 625 180 245 147 168 226 Y 36 72 32 51 26 26 34 La 183 177 124 170 96 199 3858 25.00 Ce 322 332 217 369 85 166 6298 Nd -; Yb <-2 2 <-4 <-7 0 <-1 6 20.00 sc 33.2 29 32.1 29 32.6 28.8 31.5 Ta 13 15 10 16 6 a 16 Th 90 36 21 40 16 1731 17 15.00 +phonolite u 16 13 16 19 5 16 8 V 317 398 353 261 342 253320 4cu 109 74 73 103 112 119 _______ 80 10.00 from Alno frachybaaalf 5.00 barall +andesite I klrnberlife 0.00 rn 902 Figure 61. Major element discriminant plots, Ospika pipe.74 Geological Survey Branch
  • 5. Ministry of Energy, Mines and Petroleum llesoumeson the pipe. The phases are differentiated by size and per- Phlogopite dominates the macrocryst assemblages,centage of fragments of sedimentay rock, macrocrysts and comprising 5 to 20% of the rock, with titaniferous augite,pelletal lapilli. Contacts between phases may be sharp or rare altered olivine and bright green diopside also presentgradational. Locally, narrow dolomitic dikes crosscut dia- locally. Phlogopites range from few millimetres to 3 cen- a timetres in size, augites from a few millimetres tc. 2 centi-treme breccias. metres. The phlogopites are orange in colour and have The breccias contain 2 to 25% subangnlar to snb- normal pleochroism. In some samples, they have thin,rounded fragments of sedimentary rock. These range from bleached rims; in others, the rims are darker than the corea fewmillimetres to 50 centimetres across, with most in the of the grains.2 to IO-centimetre range. Larger fragments are dolomitic The matrix to most phases is fine grained and lightwith prominent reaction rims (Plate 31). Rare cognate xeno- green-grey in colour.It is a g o d igneous or magmatic ma-liths are present, but no exotic xenoliths were found. One trix, consisting of fine-grained dolomite and felled plrlo-distinct phase is composed of abundant small pelletal lapilli gopite, chlorite, amphibole with or without talc. It contains abundant fine-grained opaque oxides and, in some places,(50-60%).macrocryptic phlogopite (5-10%) and small frag- pyrite.ments of sedimentary rock(less than 10%) in a fine to me- Clast andmacrocryst-rich brecciadikes, 50centimetresdium-grained carbonate matrix. wide, crop out onridges 0.5 to 1 kilometre away fromthe main breccia pipe. These dikes do not appear be continu- to ous with the diatreme at surface, but have very similar clast and macrocryst populations. Locally, the matrix the of dikes is considerably morecalcareous than that of the diatreme. Both thedikes and mainpipe havesuffered some (degreeof alteration. Bluepleochroic sodium amphiboleis ukdquitous, often rimming other phases. The Ospika pipe and related dikes may be classified, on the basis of petrography, as ultramafic lamprophyresusing the criteria given byRock (1986)and, more speci:ically, as aillikites. These arerelatively common ultramafic lampro- phyres that are often associated with carbonatites. They are similar to alnoites, but lack goodevidence of meltlite. GEOCHEMISTRY Major element analyses of samples from the Ospika pipe and relateddike rocks (Table 14) indicate that the pipe is low in silica and high in calcium, magnesium andiron. On a KzO-MgO discriminant diagram (Figure 61a:r analyses group in an area which is overlappedby the leucitii e, olivine melilitite and alkaline lamprophyre fields. It should be noted, however,that on this diagram, alnoites from Alno fall ~~ ~ ~~~~~~~~ ~ __ ~ ~~ 0 Ospika pipe 1500.00 Average basalt Average kirnbtrliles 0.00 1000.00 500.00 1500.00 Cr ppm _- Figure 62. Major element ternary plots, Ospika pipe Figure 63. Ni-Cr plot, Ospika pipe.
  • 6. ~ ~ ~~ ~~~~~~within the alkaline lamprophyre field, which suggests that The geochemical data do not conflict with thc pet-the ultramafic lamprophyre field should be extended; this rographic classification of the pipe as an ailliki:e, orplot is not strictly adhered to in attempting a chemical clas- melilite-free variety of alnoite, which, according to Rocksification. Analyses from the Ospika pipe plot relatively (1986) is a member ofthe ultramafic lamprophyre family.close to the type alnoite. The sameis true on an alkali-silicaplot (Figure 61b). Ternary AFM and MgO-AIz03-Fe~03plots (Figure 62) show that analyses from the Ospika pipe GEOCHRONOLOGYplot in or near the alonite and/or aillikite (a melilite-free Rubidium-strontium isotopic studies on mica sep,uatesalnoite) fields. from the Ospika pipe give an age of 334f7 Ma. Potas-’1111- ,1 1 The Ospika pipe has a restricted range of nickel and argon studies on the same sample yielded 323f10 Ma (Ap-chrome values and contains relatively low concentrations ofthese elements, similar to the ‘average’ nephelinite (Figure pendix 2). These data suggest that the pipe very similar in is63). It is somewhat enriched titanium, barium,strontium in age to the Aley carbonatite complex, which it flanks. Theand niobium, and has fairly restricted range of total stron- a temporal and spatial association between carbonatites andtiummbidinm ratios, averaging around 13:l (Table 14). alnoites or aillikites is well documented (Rock,1986:..76 Geologicul Survey B m c h
  • 7. Minisiry o Energy, Mines and Peiroleum Resourres f " ULTRABASIC DIATREMES IN THlE GOLDEN - COLUMBIA ICEFIELDS AR:EA Numerous diatremes are located along the Alberta - suggests that these rocks are neither kimberlites nor lam-British Columbia border @2N, 83C) between 50 and 90 proites, the twolithologies currently known to contain eco-kilometres north of Golden (Figures 2 and 64).The terrain nomic concentrations of the area is rugged and the diatremes outcrop elevations atof 2200 to 3000 metres. In all cases access is by helicopter. BUSH RIVER AREA (LARRY CLAIMS)Most of the diatremes are hosted by Upper Cambrian car- (83CP)bonate rocksand, in most cases, consanguineousdikes are Near the headwaters of the Bush River :latitudealso present. 52"0420"N, longitude 1172350W Figure 64), I suite of Microdiamonds havereportedly been recovered from dikes and small diatremes intrudes Upper Cambrianstrata.heavy mineralseparates taken fromtwo of the pipes inthis Three diatremes were examinedin this study (Figure 6 3 ,swarm (Northcote, 1983a. b; Dummett et al., 1985; George revealing two breccia types. The breccias appear ,quitedif-CrossNewsLetter,Jan.23,1990).Preliminaryinvestigation ferent in the field, but the division is somewhat arbitrary. A Bush Riverpipes dikes and B Lens ountain ipe M p C Mons reek rea C a LEGEND D V a l e n c i e n n e sR i v e ra r e a Foliated breccia phose with pelletal lapilli E HP p i p e Rusty weathering quartz xenocrystic bre:cia Fine grained massive phose dike Mocrocryrt rich dikes (micas, pyroxenes, etc.)Figure 64.General geology and diatreme locations the Golden in Macrocryst rich dikes with breccia core:$- Columbia Icefields area. indicates diatremes or dike swarms.GeologymodifiedfromWheeler(1962)andPrice(1967a,1967b). _-For legend see Figure 73. Figure 65. Diatreme brecciasand dikes, Bush River m a (83CL3).Bulletin 88 77
  • 8. Plate 32. Rusty weathering, clast-supported megabreccia, Bush River aea.78 Geological Survey Branch
  • 9. ~ .~ . _ r: : ..... .. ~. l -. .. ~ ~ ~ ~ .". , Minisrry o Energy, Mines and Pefmleum Resources fPlate 34. Limestone-cored armoured xenolith in diatreme breccia,Bush River area. Plate 36. Boulder from adike, Bush River area. Dike has a brcccia core containing abundant fragments of sedimentary ~.ockand a finer grained, macrocryst rich rim.Plate 35.Altered micamacrocryst in diabeme breccia, Bush River Plate 37. Laminated (flow-banded) margin a fine-grained dike, ofarea. Bush River area.Bulletin 88 79
  • 10. The pipes are massive; onlythe southeastern diatreme hasa margin that is foliated, with the foliation subparallel to thecontacts (Pell, 1987; Ijewliw and Schulze, 1989). The northeastern pipe comprises rusty orange weather-ing, clast-dominated megabreccia (Plate 32). The clastma-trix ratio is approximately 39. Over 99% of the clasts are ofsubrounded to subangular fragments the hosting carbon-ate lithologies, ranging in size from 1 to 75 centimetres, withan average size of 10 to 40 centimetres. Altered granitoidsand, less commonly, gabbroic rocks make the balance of upthe xenolith population. The matrix is predominantly car-bonate and quartz-sand grains. The second type breccia, exhibited by the central and ofsouthern pipes, is also clast dominated andgenerally mas-sive, but is rusty to dark green weathering (Plate 33) ratherthan orange in colour.The clastmatrixratio is greater thanin the first breccia type and clast population more the varied.Approximately 50% of the clasts are subangular fragmentsof sedimentary rock, carbonates, shales and some ortho-quartzites. Two to five percent of the xenoliths consist ofgranitic material; these fragments may be either rounded orangular and are in the 5 to 15-centimetre size range.Rounded, 8 to 25-centitnetre fragments of altered igneous-looking material comprise 10 to 20% of the xenoliths. These Plate 39. Fragments of sedimentary rocks in a buff-weathering,clasts consist of coarse, randomly oriented carbonategrains, quartz xenocryst-rich breccia, Mons Creek area. Plate 40. Photomicrograph of quartzxenocryst-richbn:ccia,Plate 38. Photomicrograph of an altered pyroxene crystai in a similar to that shown in previous photograph.Quartz xenwrystsmatrix containing abundant altered mica; dike, Bush River area. are enclosed in a matrix of carbonate, chlorite and iron-o:ddes.Long dimensionof photograph is2.5 mm. Long dimension of photograph is2.5 m .m80 Geological Survey Branch
  • 11. Ministry o Energs Minesand Petroleum Resources fFigure 66. Sketch showing distribution diatreme related rocks the lack claims Lens Mountain area; sketch drawn from photog,raph of ontaken by C. Fipke. View is of the ridge southeast of Lens Mountain, facing mica and opaqueoxides. Spectrographic analyses surfaces are generally a dull greenish grey colour. They haveindicate high silica content; these clasts are possibly altered coarse xenolith andlor macrocryst-rich cores and finersyenites. Many of the rounded xenoliths are armoured, or grained margins (Plate 36). Contacts withiuthe (dikes maymantled bya rim fine-grained mica-rich igneous of material be gradational or distinct and often the margins have asimilar to the breccia matrix. An additional 5 to 10% of the strongly flow-banded texture (Plate 37). In thin swtion, thebreccia fragments arecognate xenoliths. The remainderof dikes are porphyrytic with altered macrocrysts, phenoclyststhe clast population is made upof spherical structure (also and glomerocrystsof olivine, pyroxene (Plate 33) and bi-referred to as accretionary lapilli or globular segregations) otite. The olivine crystals, some of which contain inclusionsranging from a few millimetres to 3 centimetres in size and of red-brown spinel, are altered to calcite, serptmtine andfrequently cored by small fine-grained limestone fragments talc. The groundmass consists of a network altered of biotite(Plate 34). Armoured xenoliths and accretionary lapilli are with dusty secondaq calcite, minor serpentine, soinels andfeatures common to pyroclastic rocks (Fisher and opaques (Ijewliw and Schulze, 1989).Schmincke, 1984). Silvery, altered mica macrocrysts, up to Based on modal mineralogy, including the pseudomor-3 centimetres in diameter, are abundant (Plate 35); they phed phases (olivine, pyroxene, biotite, plagiodase). thewere, most likely, originally biotites. The matrix the brec- of dikes and diatremes the Bush River can be in area classifiedcia consists of chlorite>calcitequartz>trace apatite. In thin as lamprophyres of either alkaline or calcalka1ir.e affinity.section, it is seen to comprise 25% euhedral to suhhedral The best designation appears to be as olivine-kzrsantites,olivine crystals that have been pseudomorphedbyeither ser- which are part of the calcalkaline lamprophyre familypentine, or calcite and quartz with magnetite rims, cloudy, or (Ijewliw and Schulze, 1989) biotite-camptonites, whichbrown plagioclase, biotite, euhedral calcite and trace are alkaline lamprophyres.amounts of magnetite and apatite phenocrysts in a fine-grained aggregate of dusty carbonate, quartz, serpentine, LENS MOUNTAIN AND MONS CRJ3EKmagnetite, chlorite, felsic microlites and unidentifiable ma- AREAS (JACK AND MIKE CLAIMS)terial (Ijewliw and Schulze, 1989). (82N/14,15) Numerous subparallel dikes are present in the BushRiver area, some of which crosscut the diatreme breccias; At both Lens Mountain (latitude 5 l”54’30”N. longitudethey range in length from 50 to 600 metres and width from in 117°07‘30”W) and Mons Creek (latitude 51”49’:;O”N, lon-0.5 to 2.5 metres. Bifurcation and remerging occurs along gitude 117°00’30”W; Figure 64)the dominant intrusive li-the length of some dikes and narrow, fine-grained apophyses thology consists of a buff-weathering, weakly foliatedare common. Both homogeneous and zoned dikes are seen breccia with a low clastmatrix ratio (approximalely 1:3 or(Figure 65). The homogeneous dikes are fine grained and 1:4). The ‘Jackdiamond‘(Northcote,1983b)was recoveredmedium to dark green in colour. They may contain up to from this lithology and two additional microdiamonds have10% small, silvery, mica phenocrysts and minor amounts of recently been recovered from core (George C ross News drillspinel or other opaque oxides. A dike with unaltered phlo- Letter, Jan.23,1990, p. 2).Clasts are small subaugnlarfi‘ag-gopite megacrysts was observed one locality.The zoned in ments of sedimentary rock, predominantly carbpnates, indikes are rusty to dull green on weathered surfaces and fresh the 2-millimetre to 2-centimetre size range (Plate 39). The __Buliefin 88 81
  • 12. British Columbiamatrix is pale green to buff incolour and consists ofabun- dark red and have dark greyfresh surfaces. They consist ofdant rounded quartz grains (xenocrysts), carbonate, chlorite subangular clasts of limestone and relict phenocrysts in aand iron oxides (Plate 40). Relict lapilli, with a preferred carbonate matrix. The matrix consists of 15%phenocrystsorientation, have also been observed(Ijewliw and Schulze, that are entirely pseudomorphed by fine-grained quartz1989). At Mons Creek,this breccia grades into a clast-poor andor calcite. Some of the phenocrystsretain traces of sim-(5 to 10% clasts) green breccia with a foliated matrix con- ple twinning, with a morphology suggestive of sana4line.taining carbonate, chlorite and talc(?) or serpentine. In both Altered crystals of titanamphibole or sphene are also pre-areas, the enclosing sedimentary strata are steeply dipping; sent; they have been replaced calcite but retain a rimof bythe breccias, however, display a weakly developed subhori- inclusions of very fine grained sphene.The groundmrss iszontal to shallow-dipping planar fabric. At Lens Mountain, extremely fined grained and contains calcite patchesa shallow-dipping layer of boulder breccia is enclosed in the (Ijewliw and Schulze,1989).sandy breccias. At Mons Creek, a small, light green, strongly foliated, It has been proposed (C.E. Fipke, personal communi- tine-grained breccia crops out the north of the main sandy tocation, 1987) that these breccias are crater-infill material. diatreme. It contains fragments of sedimentary rock lessAlternatively, they may be intrusive, formed through than 1 centimetre across and opaque oxides a matrix con- influidizing of sediments by introdnction of volatiles explo- sisting of dolomite>quartz2pyrophyllite~inor chlorite,sively exsolved fromrising and vesicnlating magmas. The calcite, muscovite and trace apatite. In thin section, lhesesubhorizontal fabric locally displayed in the breccias would rocks have a porphyrytic texture, but arehighly altered. Cal-have originally been steeply dipping (prior to deformation), cite replaces some phenocrysts, which may have been oli-which would favour the latter hypothesis. vine, manyof which have red-brown spinel inclusions. The original composition of other psendomorphed phenocrysts At Lens Mountain,two additional small breccia pipes is undeterminable (Ijewliw and Schulze, 1989).or dikes and light green, clast-free aphanitic rock are alsopresent (Figure 66). The breccias are very coarse, weather At Mons Creek, one small, altered dike cutting the main diatreme and a second parallel dike outside the diatreme ~~. ~ LEGEND @Green foliated breccia phase @Quartz xenocrystic breccia a Massive diatremephase a Fine-graineddikes Dikes with pyroxene and olivine mocrocrvrtr Dikes with mica rnocrocrysts pyroxene olivine and /LI Host limestone Plate 41. Serpentinizedolivinemacrocrysts in a fine-grained, Figure 67. Diatreme breccias and dikes, Valenciennes River. massive diatreme phase, Valenciennes River area.82 Geological 6ranch
  • 13. Ministry o Eneqy, Mines and Perroleunr Resources fwere observed. Oneunaltered porphyrytic dike and abun-dant unaltered float of porphyrytic dike-rock are presentelsewhere onthe property. The altered dikes contain quartzaggregates replacing a lath-shaped, twinned mineral thatmay have been feldspar, some minute plagioclase grains(An25) that are partly replaced by calcite, and a phyllosili-cate mineral, partially replaced by calcite, with sphene in-clusions and rims in a fine-grained groundmass ofcarbonate, chlorite and minor quartz and pyrite (Ijewliw andSchulze, 1989). The unaltered dike material contains 5%primary phenocrystic clinopyroxene,commonly augite ordiopsidic augite with pinkish brown titaniferrous rims.Some grains also have titanium-rich cores, and an iuterme-diate, nonpleochroic zone. Other phenocrysts present in-clude biotite, some amphiboles and olivine, completelypseudomorphed by calcite or chlorite, with red-brownspinel inclusions. The matrixcontains microphenocrystsofclinopyroxene, biotite, sphene and plagioclase (Anzs) in agroundmass of carbonate, chlorite, interstitial quartz, fine-grained serpentine and opaqueoxides. The main diatremes in the Lens Mountain and MonsCreek areas have only minor igneous components duetointense sedimentary rock contamination and difficult to areclassify. The dikes at Mons Creek, however, have a pre-served mineralogy (titanaugite, plagioclase, biotite, ampbi-bole, olivine) which allows classification as alkaline Plate 42. Fine-grained boudinageddike subparallel to tedding inlamprophyres, or more specifically, biotite camptonites buff-coloured carbonates. Diatreme breccia in the right(Ijewliw and Schulze, 1989). background. Valenciennes River area.VALENCIENNES RIVER PIPES(MARK CLAIMS) (82N/15) Four or more diatremes and numerous dikes intrudeUpper Cambrian rocks near headwater of Valenciennes theRiver (latitude 51"470O"N, longitude 116"5800W, Fig-ures 64 and 67). Two distinctly different diatreme types arepresent. The first are rusty brown to pale green weathering,weakly to well-foliated, composite pipes with both massiveand breccia phases. Two such diatremes are exposed at thesouthern end of the area examined. Serpentinized olivinemacrucrysts (Plate 41). coarse nonmagnetic oxides(greenspinels) and altered spinel peridotite xenoliths are presentin some phases. Typical breccias contain 30 to 40% clasts,mostofwhicharesmall(l-5cm,withamodeofZcm),withrare xenoliths up to 15 centimetres across. Limestone,dolostone, shale and minorquartzite comprise the majorityof the breccia fragments. Rare oxide macrucrysts may bepresent. The matrix typically light green to grey in colour isand contains calcite and/or dolomite, quartz, chlorite, mus-covite, and traces of pyrite, apatite, talc and clay minerals.Bright green mica is commonly seen in band sample(chrome-rich muscovite?). Chromite and ilmenite havebeen identified in heavy mineral separates and a mi-crodiamond is reported to have been recovered from thelargest diatreme (Northcote, 1983a). Associated dike rocks fine to medium grained, rusty areto dark green weathering, with a light greenish grey tome-dium greenfresh surfaces. They occurin a number of ori- Plate 43. Altered phenocrysts (zonedpyroxenesfolivinehica)inentations, varying from almost concordant discordant to to a dike, Valenciennes River area. "be degree of alteration in thisbedding. Dikes which are nearly parallel to bedding and sample is typical. Long dimension of photograph is2.5 m . the m "Bulletin 88 83
  • 14. cleavage are strongly baudinaged (Plate 42). Some of thedikes are porphyritic and all are altered. The phenoclyst as-semblage, so far as can be recognized, consists of sieve-tex-tured olivine pseudomorphs, altered euhedralclinopyroxene with relict zoning, mica and rare spinels. Pla-gioclase phenocrysts have been observed (Ijewliw and alsoSchulze, 1989). In some phases, olivine appears to he moreabundant than pyroxene (olivine+pyroxenehica) and inothers pyroxene is far more abundant (py-roxenekolivinehica). Some dikes are predominantly mi-caceous. It is difficult to accurately estimate proportions ofphenocrystsas they are altered and only morphology canbeused plate 43). The groundmass generally consists of veryfine grained carbonate, chlorite, serpentine and altered bi-otite (Ijewliw and Schulze, 1989). Oxides are also a com-mon groundmass constituent. The dikes are generallyperipheral to the diatremes, but locally crosscut them. The second type breccia is present in the diatremes ofin the northern part of the area examined (Figure 67). Theyare brown weathering and moderately well foliated with an-gular to subangular fragments sedimentary rock set in a ofmatrix ofquartz grains, chlorite and carbonate. Clasts aver-age 1 to 5 centimetres across, with some up 20 centime- totres. The clastmatrix ratio is 2:3. These diatremes aresimilar to the orange-weathering pipe the Bush River area in(the first type described). Intense alteration makes petrological classification dif- Figure 68. Geology of the HPpipe, south the Campbell Ice field. of Details on breccia and dike phasessupplied in Table 15. See textficult. The rocks in the Valenciennes River area, as evi- for geographic coordinates.denced by phenocryst assemblages in dikes (olivine,clinopyroxene,mica, plagioclase) also bear astrong resem- in the Golden - Columbia Icefields area (Figure 64).It isblance to those in the Bush Riverarea and probablybelong located approximately 50 kilometres due north of Goldento the calcalkaline or alkaline lamprophyre clans. The best and is exposed at an elevation of 2400 metres, near the toedesignation appears to be as olivine kersantites, which arepart of the calcalkaline lamprophyre family alternatively, or, of the Campbell Icefield. The pipe small, covering an area isbiotite camptonites, which are alkaline lamprophyres. of only 40 by 70 metres; however, it is exposed in a flat, recently deglaciated basin which offers nearly 100% expo-THE HP PIPE (82N/10) sure and is therefore ideal for study. The pipe has sharp, steeply dipping contacts with the T h e H P p i p e ( l a t i t u d e 5l04l3O"N, longitude horizontal to shallow-dipping grey Cambrian limestone116"57W) is the most southerly diatreme so farrecognized beds which it intrudes (Figure 68). It is a composite dia- TABLE 15 FELD CHARACTERISTICSOF HP PIPE BRECCIA PHASES84 Geological Survey Branch
  • 15. Plate 46. Optically zonedandraditegarnets, HP pipe. Long dimension of thephotomicrographis 2.5 mm. C!arbonatePIate 44. Sharp contact between breccia phases & 3, HPpipe. (82 ) segregation forms matrix.Plate 45. Large gabbroic xenolith a strongly foliated breccia in (BI Plate 47. Biotite macrocryst coring spherical smclure, HP pipe.phase), HP pipe. Long dimensionof the photomicrographis I m . m
  • 16. TABLE 16 - CHEMICAL ANALYSES GOLDEN AREA DIATREMES - Si02 TI02 A1203 Fe203 0.14 0.13 0.18 0.06 0.17 0.12 0.13 0.18 0.18 0.06 0.12 0.12 0.06 0.16 13.21 11.79 8.67 5.18 9.69 14.67 11.03 12.27 12.79 6.16 6.51 9.48 5.02 7.25 19.92 20.39 17.41 17.74 16.15 13.28 9.48 16.11 13.36 14.51 11.28 12.36 15.61 12.77 0.29 0.27 1.65 1.87 0.25 0.06 0.42 1.32 1.60 0.06 2.73 0.29 0.01 0.18 0.06 4.131 1.01 4.18 4.47 0.01 1.361 0.93 4.031 0.53 0.21 0.70 3.70 0.601 6.44 10.70 7.27 16.29 19.88 16.02 14.05 7.71 5.84 14.50 11.73 14.08 16.11 13.90 P205 0.58 0.61 0.95 0.74 0.81 0.77 0.47 0.88 0.65 0.42 0.11 0.04 0.09 0.07 0.79 0.11 0.16 0.08 0.07 0.08 0.20 0.04 0.31 0.02 Tora, 98.45 97.63 97.54 98.951,401 98.66 98.89 99.43 98.99 98.93 99.02 98.93 98.88 98.21 99.63 0.051 0,581 0.91~ 240 210 140 150 330 200 200 270 230 200 270 230 200 786 904 313 335 301 805 386 493 527 849 399 589 744 387 1101 co 40 40 38 30 42 55 43 45 4 j 48 38 36 56 40 137 121 1301 40 17 8112 3 24 39 < <8 12 85 5 SI 99s lizi lis51 579 881 528 1191 1410 640 1026 821 781 513 595 Ba 1933 1868 3131; 390 202 3791 1975 514 2136 360 91 227 322 589 Zr 156 Nb Y 17 191 244 175 24 90 34 31 78 261 :z 188 361 172 294 20 345 301 22 22 26 25 29 229 265 160 262 200 204 112 198 312 140 229 338 24 24 26 96 111 18 La 92 121 91 78 197 120 119 162 165 145 123 Ce 181 169 193 208 149171 321 206 247 267 29 1 278 220 Nd 4491 Yb 1 <-4 3 <-2 1 0 0 0 <-2 c- 1 33 26.1 31.3 34.328.2 35 25 28.8 31.1 25.1 6 17 18 6 10 9 3 11 11 31 12 14 15 10 21 6 7 . A1 .. 4 _. 17" 7X _. 14 0 7 .^ 23 3L I 33 16 hI 221 322 232 305 206 306 339 356 189278 67 49 11057 80 65 69 109 7 83 73 215 30 _"86 Geoiogicai Survey .Trunci
  • 17. Minisfry of Energy, Mines and Petmleum Resoumestreme, comprising five distinctly different breccia phases garnet. In thin section, all phases contain some, ,:enerallyand numerousdikes. The breccias differ in clast-to-matrix fine-grained, garnet.ratios, megacryst ahuudances @lack salitic pyroxenelgreen The HP pipeunique, in many respects, from the other isdiopside/biotite) and the presence or absence of additional pipes in the Golden area. Petrography and mineral chemis-phases such as oxides and spherical structures (Table 15). try suggestthat it is ultramafic lamprophyre with an ailliiticContacts between breccia phases may he gradational or affinity. There also appears to be a significant metasomaticsharp (Plate 44). A well-developed foliation, at high angles or metamorphic overprint introducing phases such asto the pipes eastern and western margins, is present in melanite/andradite and clinoamphihole.phases B1 and B2 (Plate 45). The other phases aremoder-ately to weakly foliated. GEOCHEMISTRY OF DIATREMES AND The matrix of breccia phases B1, B2 and B3 is com- RELATED DIKESposed of calcitefbiotitQcolourless clinoamphihole (tre-molite?)>chlorite. Serpentine, talc and pyrite are also Diatreme breccias and dikes in the Golden area are nl-reported to he present (Ijewliw and Schulze, 1989). Fine- 20 trahasic; silica values predominantly range from to 40%grained spinel and garnet are disseminatedthroughout. The (Table 16)with theexception dikes from theVa1f:nciennes ofgarnets are suhhedralto euhedral in outline, light green to River area which contain from to 45% silica. Analyses 40golden or brown in colour andoften optically zoned (Plate are varied with respect to the other major elemenrs (Figure46). X-ray spectra indicate that the brown garnet is melanite, 69; Table 16) and chemical classification is difficult. Altera-a titanium-bearing andradite, and the green gamet is tita- tion is intense, and may have affected some elemmts morenium-free andradite (Ijewliw, 1986, 1987). In addition to than others (e& potassium, as is suggested byth~: that fact most micas havebeen strongly altered and potassium maysmall disseminated garnets, larger garnets commonly occur have been removed). Ingeneral, analyses plot in or near thein dikes and associated with calcite segregations in clast andspherical structure-supported breccias, Groundrnass spinels alkaline to ultramafic lamprophyre fields (Wgurw 69 andare titanium-bearing magnetites. The groundmass has a 70); the HP pipe borders on alnoitic in composit:on, dikesmagmatic texture, hut apparently has been altered, eitherby from the Bush River area and from Mons Creek more fallmetamorphism or metasomatism. The matrix ofthe spheri- within the alkaline lamprophyre range anddikes from thecal structure-rich breccias is predominantly calcite with or Valenciennes River area (all strongly altered) trend towardwithout amphibole (colourless to slightly bluish). Euhedral a basaltic composition.garnets commonly form rims on the spheres. The spheres As is the case with major element compositims, traceare composed of material similar to the matrix of the other element ahundances diatremes and in dikes from the Goldenbreccia phases and are commonly cored by pyroxene or area are quite varied. There is a fairly wide range elements icmica megacrysts(Plate 47). such as chrome (Figure 7 l), strontium, rubidium and barium (Table 16).The HPpipe, in general, shows more restricted Black clinopyroxene (salite; C.E. Fipke, personal com- compositionsthan the others, has higher average rubidium,munication, 1987) bright green chrome diopside and biotite strontium and barium concentrations and has much moreare the dominant megacrysts. The black clinopyroxenesare restricted total strontiummhidium ratios (Figure72). Rocksrich in titanium (up to 2.6%) and aluminum (up 14.5%). to from the Valenciennes River and Bush River generally areasThe clinopyroxenes are compositionally similar to those show the most variation and have large ranges in total stron-found in the Isle Bizard alnoite and in South African olivine tium:ruhidium ratios, which may indicative of higher de- bemelilitites. Biotite x-ray spectra show high ironmagnesium grees of alteration. Rocks collected from BushRiver wereratios and occasional zoning to iron-rich rims. Red-brown more enriched titanium than those from elsewhere the in inchrome spinels with minor amountsof aluminum, magne- Golden area (Figure 72).sium and titanium have also been identified. The spinelshave a very limited compositional range; Fe2+/(Fe2++Mg) Although chemistry alone is not sufficient grounds tovalues of 0.34 to 0.38, Cr/(Cr+Al) values of 0.54 to 0.68 and classify rocks, especially altered rocks, it does ba2k nppet-Ti02 of less than 1%. The spinels are also compositionally rographic observations. The HP pipe appears to share manysimilar to those from Isle Bizard. Euhedral apatite phe- characteristics with ultramafic lamprophyres; the othernocrysts are also present (Ijewliw, 1987; 1,jewliw and pipes and dikes in the Golden area are slightly different, inShulze, 1988). general more similar to alkaline lamprophyres. The breccia pipe and surrounding sediments cut by are GEOCHRONOLOGYnumerous dikes (Figure 68). The dikes are generally finegrained andmassive, but are variable with respect to xeno- In the Golden area, the HP pipe and some the dikes 01lith, macrocryst,spherical structureand obviousgametcon- in the Bush River area are relatively unaltered and containtent. D l dikes are massive and free of inclusions. They abundant micas. These two locations were sampled, micacontain biotite and spinel phenocrysts; the biotites are often separates obtained and potassium-argon and ~uhidinm-aligned (flow foliation?). D2 dikes have some (less than 5% strontium analyses performed in order to establish the agetotal) small limestone xenoliths and macrocrysts; they may of the intrusions. Elsewhere, the rocks are either loo alteredalso contain minor amounts of spherical structures. D3a or too poorin micato attempt to date. Biotites from th~:HPdikes are megacryst rich (1520%); D3h dikes are also pipeyieldpotassinm-argondatesof39lf12and396flOMamegacryst rich and containspherical structnres and visible (Appendix2). Initial rubidium-strontiumanalyse; yielded a -Bulletin 88 87
  • 18. date of 34W7 Ma; these analyses were rerun, using amoreaccurate ion-exchange technique and date of approxi- a newmately 400 Ma was obtained (Appendix 2). Close agree-ment of potassium-argon and rubidium-strontium datessuggests that the HP pipe was emplacedat approximately400 Ma. Recent paleomagnetic work (Symons and Lew-chnk, in press) established that samples fromthe HP pipe,after tilt corrections, give a concordant Mississippian pole,which is slightly younger than the isotopic age. Preliminary results of rubidium-strontium ion ex-change analyses of micas from alkaline dikes in the BushRiver area suggest an ageof 410 Ma (Appendix 2), whichis in close agreement with results from the HPpipe. Zircon separates were obtained from rocksin the Va-lenciennes River, Lens Mountain and Mons Creek In areas.all cases, the zircon populations are very heterogeneous.Zircons from the Mons Creek area vary from rounded,frosted, colourless to pale yellow spheres, to clear, equantfragments. In the Valenciennes River sampleszircons varyin shape from round to rounded prisms. Some grains arerounded andbroken. Colours range clear to colourless, fromfrosted to pink. In the Lens Mountain sample clear and both / A (NozO+K20) Figure 70.Major element ternary plots, Golden diatremes. A HP 25.00 * 4 * Mark Lorry Mons 20.00 a1noite from Alno I 1500.00 1 Averoge (Mark) u15.00 1000.00- alkali-olivine ,v E a bpsalt ! 10.00 (alkaline larnprophyre) a Average mei1titite & naphslinito ._ z bosalt 500.00- 5.00 0.00 2 m m 500.00 1000.00 1500.00 I Cr w mFigure 69. Major element discriminant diagrams, diatreme Goldenswarm. Figure 71. Ni vs Cr plot,Golden diatremes.88 GeologicalSurvey Branch
  • 19. Ministry o Energ3 Mines and Petroleum Resources f pink roundedzircons are present, as well as clear, frosted to clear, colourless, rounded prisms. Euhedral zircons from Mons Creekyielded .1 concor- dantlead-lead ageof 469iz17 Ma (Appendix 2), which pos- sibly represents the age of zircon crystallization in the lamprophyricmagma. This may equivalent to, or slightly be older than, the actual age of emplacement. This dzte is con- sistent with the fact that the igneous rocks are hosted by Lower to Middle Cambrian strata. Rounded zircons from the same sample gave ages of 1917 to 1907 Ma(Appendix 2); these zircons are clearly xenocrystic and thedates may . be representative of the age of the basement. Zircons separated from a diatreme in the Va1,:nciennes River area are all xenocrystic in origin and gavelead-lead-00.0 ages of approximately 1525,1825,2550 and 2565 Ma (Ap- 0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 pendix 2). All analyses are discordant. Zircons separated Sr/Rb from the Lens Mountain sample werealso all xlnocrysts. Resultant lead-lead ages are approximately 1790,2050 andFigure 12. SrRb vs Ti&, Golden diatremesand related dikes. 2685 Ma (Appendix 2). Bulletin 88 89
  • 20. British Columbia - LEGEND p m H e l i k i a n Purcell Supergroup, 1 and Hadrynian Windermere Supergroup aCarnbrian aOrdovicianMckayGroup Upper Cambrian/Lower through Ordovicianand/or SilurianBeaverfoot Frn. a MiddleDevonian:Cedared, Burnais Harrogate and Fm. Middleand/orUpper Devonianthrough Mississippian m P e r r n i a na n d Pennsylvanian, Rocky Mountain Group m T r i a s s i ca n dJ u r a s s i c or younger 0 Alkalic ultrabasic diatreme ordikelocation 1 Joff Pipe 2 Rus Pipe 3 Mary Creek-White River brecciadike 4 BlackfootDiatremes 6 Swanson Peak volcanics anddiatreme (Swan Claims) 6 QuinnDiatremes 7 Summer 1 & 2 Pipes 8 CrossingCreek Kimberlite I 0 15 Kilometres Figure 73. General geology and diatreme locations Bull River - White River area. Geology modified the in from Leech(1960, 1979) and Price (1981). ~-90 Geological
  • 21. Ministry of Energy, Mines and Petroleum Resources ULTRABASIC DIATREMESIN THE BIJLL RIVER - ELK RIVER AREA, SOUTHElRW BRITISH COLUMBIA (82Gr, 3) " Forty or more breccia pipes and related dike-rocks oc- ing fine-grained altered clinopyroxene and somefeldspar.cur within the Bull, White and Palliser river drainages (Fig- Microprobe analyses indicate that the feldspar is e:;sentiallyures 2 and 73) east of Cranbrook and Invermere (Grieve, pure albite; the albite, however, may be secondary, having1981). The majority are hosted the Ordovician-Silurian hyBeaverfoot Formation and underlying Mount andlor Wilson replaced an earlier, more calcic plagioclase or potassiumSkoki formations and exhibit similarities in petrography,de- feldspar. Some feldspar laths have been partially altered togree of alteration and morphology. white mica or clay minerals. Some mafic phenocrysts have been pseudomorphed by quartz and chlorite. Opaqile oxides (JOFFSHATCH MOUNTAIN AREA are abundant.CLAIMS) (825/11) A number of small diatremes and dikes have been re-ported (D.L. Pighin, personal communication, 1984) southof the Palliser River on the ridges around Shatch Mountain,west of Joffrey Creek (latitude 50"3107"h, longitude 115"1633W) approximately 55 kilometres east of In-vermere (Figure 73). Two were examined, both exposed atthe 2750-metreelevation and accessible by helicopter. Bothare hosted by moderately to steeply east-dipping Ordovi-cian-Silurian Beaverfoot-Brisco strata which are charac-teristically massive thick-bedded grey limestones whichcontain rugosan corals. The main breccia pipe (Figure 74) consists of small (upto 10-centimetre) subrounded to subangular fragments a instrongly foliated light green matrix. Clasts are predomi-nantly limestone, dolostone andshale; some cognate xeno-liths and rare pyroxenite nodules present. In thin section, arehoney-coloured altered vesicular glass lapilli are the pre-dominant constituents; locally the glass is completely de-vitrified. Juvenile lapilli are also present and in somesamples quite abundant. The matrix the breccia consists ofof calcite with some quartz and chlorite and minor talc,anatase and apatite. This is a tuffisitic crater-infill breccia. East (stratigraphically up-section) ofthe main breccia,intensely hematized, discontinuous layers consisting of ju-venile lapilli, suhangular lithic fragments, quartz and car-bonate are apparently interbedded with grey limestone.These agglomerate layers locally display moderate to well- ;DIMENTARY SEQUENCE INTRUSIVE AND RELATECdeveloped graded bedding (Plate 48). Elsewhere, graded SEQUENCE DOLE AND/OR UPPER DEVONIANbreccia layers are immediately overlain by pink and huff a 8 A S A L UNITpink and bulldolostones, sandy crosshedded dolostones and sandstones, Eandrlone. dolonfone. mud- stone and 101uIion brecciawell-bedded siltstones and dolomiticsiltstones of the basal ~OOV~C~AN/SILUR~ANDevonian unit (Plate 49). a 8 E lhiok Rbedded.FORMATION: AVE FOOT -Epicloolic ond/or pyro~laslic grey tuff breccia beds South of the main tuffkitic breccia, a medium to fine- forsilifemus limerfane -Folioled tuf,isilic brecc ~grained, massive igneous intrusive crops ont (Figure 74). -Marrive. magmoiis phasethat is medium to dark greenin colour withintensely hrec-ciated and hematized margins. It contains 10 to 15%altered Figure 14. Geology of theJoffpipe,ShatchMountainareaclinopyroxene and olivine phenocrysts in a matrix contain- (modified from Pell, 1986a). See text for geographic coordinates.Bulletin 88 91
  • 22. British Columbia - Due to intensity of alteration, classification is d i f f i d t . The presence of glass lapilli and absence of biotitdphlo- gopite exclude these rocks from ultramafic lamprophyre the clan. The phenocryst and microphenocryst assemblage of olivine, two generations of clinopyroxene and a m a l l amount of feldspar (albite) in the groundmass of the por- phyrytic dike-rocks suggest that they mayshare some affin- ity to limburgites or alkaline basalts. THE RUSSELL PEAK DIATREMES (825/6) Diatremes in southern British Columbia are typified by those near Russell Peak (latitude 5Oo2540"N, longitude 115"1330"W, Figure 73). There are at least three small pipes in the immediate vicinity of Russell Peak, two more small intrusions crop out approximatelykilometres to the 7 north (latitude 5Oo2915"N, longitude 115°1540W). All of these pipes can be reached helicopter from Fairmonr.Hot by Springs. One, immediately southRussell Peak, is particu- of larly well exposed on a cliff face anddisplays many feawes of pipe morphology (Figure 75). The lower poaionof the exposed pipe comprises well-foliated, tuffisitic breccia con- taining abundant subangular fragmentssedimentaryrock ofPlate 48.Graded bedding in extrusive epiclastic layer, pipe. Joff m C 0 o r z . e contact breccia Dialreme material/tuffite a Epiclarlicand/orpyrocioslic material mixed with sediment =Mafic volcanic rock Snow patch 0Limestone rafts Db = Basol Devonian unit Ob = Ordovician Beaverfoot Formation . Otp = Ordovician TipperaryPlate 49. Epiclastic crater-infill breccia, Joff pipe, immediately Formation L - 3 Metresoverlain by well-bedded, pink and buff-weathering strata of thebasal DevonianUnit, (colourphoro, page136). Figure 75. Geology of the Russell Peak diatreme., .92 Geological Survey Branch
  • 23. and subrounded cognate xenoliths (autoliths) in a matrix of A small, black-weathering, mafic body (flc~w?)out-vesicular altered glass lapilli, monocrystalline quartz crops near exposed top of the crater zone (Figwe and the 75)xenocrysts, calcite, dolomite, chlorite, minor talc, serpen- represents the only unaltered material present ir. the dia-tine and opaque oxides. Exotic material is rare, if present. treme complex (Plate 51). It is extremely porphyritic and up 25Rock fragments to centimetres across are present, but comprises 5 to 20% titanaugite (Appendix 3) and,approxi-the population mode is 2 centimetres and the clastmatrix mately 10% altered olivine phenocrysts set in a ma.trix of35ratio is approximately 1:l.The tuffisitic breccia is medium to 40% titanaugite microphenocrysts, 0 to 5% olivine, ap-green in colonr except along pipe walls where it isred, the proximately 10% altered feldspar and 5 to 10% opaque ox-due to the presence of abundant hematite. At the western ide microphenocrysts with 15 to 25% f i n e g a i n e dmargin of the pipe, near the base of the exposure, a coarse groundmass. The groundmass, in part, consistr. of fine-contact breccia crops out. It contains large (up t 4 or 5 m), o grained material of essentially albitic composition. Somechaotic fragments of angular wallrock and subordinate ma- quartz and calcite are present as alteration minerals. Micro-trix. probe analyses indicate that some essentially unaltered Between 50 and 100 metres of well-bedded, greenish labradorite is present (Appendix 3) together u.ith traceweatbering pyroclastic and/or epiclastic material (Plate 50) amounts of chrome spinel. In a nearby diatreme, similar ma-is exposed overlying tussitic breccia. At the base of this the terial occurs as small dikes crosscutting diatreme-zonetuf-zone, the material is similar in composition to the tuffisitic fisitic breccia, suggesting that this phase was emp:aced latebreccia, with increasing amounts of sedimentary material in the intrusive sequence.and interbeds of dolomitic siltstone or silty dolostone, up- The modal mineralogy of the magmatic ghase (ti-section. Thin layers of igneous material are apparently in- tanaugite and olivine phenocrysts, titanaugite, olivine,terbedded with, or injected into, the Ordovician-Silurian labradorite and opaque oxide microphenocrysts In a fiue-Beaverfoot Formation carbonate rocks, near the top andmargins of the exposed pipe. The succession is unconfor-mably overlain by Middle and/or Upper Devonian strata. Plate 51. Porphyritic volcanic rock, Russell Peak diatreme. Large euhedralgrainsarezoned,titaniferiousclinopyroxene phenocrysts:thelargeanhedralcrystal is ana1teri:dolivine phenocryst; the microphenocrystpopulation cmsists of titaniferousclinopyroxenes,feldsparlaths and opaqle oxides.Plate 50. Well bedded craterinfill material, Russell Peak diatreme. Long dimension of the photo micrograph is mrn. 7Bullefin 88 93
  • 24. grained groundmass) suggests that these rocks have affinity BLACKFOOT ANDQUINN DIATREMESto limburgites or alkaline basalts, but do notfit exactly into (826/14)either category. They differ from limburgites in that the feld- The Blackfoot diatreme crops out 2650 metre!; ele- atspar present is calcic (labradorite) rather than sodic. They vation on ridges east of the headwaters Blackfoot (!reek ofexhibit some mineralogic similarities to basanites or (latitude 49"5823"N, longitude 115"1645"W) approxi-tephrites (alkaline basalts), but lack modal feldspathoids mately 65 kilometres northeast of Cranbrook (Figurf: 73). Access is by helicopter or on foot from a logging road the inand contain considerably feldspar than commonlypre- less Blackfoot - Quinn Creekvalley. TWO small diatreme!; (thesent in these rock types. Quinn pipes) are present near the head of Goat Creek, a tributary of Quinn Creek (latitude 49"5305N, longitude 115°2030"W). One is exposed westof Goat Creek, at ap- proximately 1980 metreselevation and can be reachcdby hiking along Goat Creekfor slightly less than a kilometre from the end of alogging road. The other is exposed e,xst of Goat Creek, asaddle at 2315 metres in elevation and i:;best reached by helicopter. These pipes are very similar to the Blackfoot diatreme will be discussed together with it. and The Blackfoot pipe is a recessive, green-weathering body, discordant with rocks mapped byLeech (1960) Or-2s dovician to Silurian Beaverfoot-Brisco Formation. :.?olds are evident in the hostrocks nearthe diatreme, where there is a deviation from the regional steep westerly dips (Figure HOST ROCKS OLimestone, halyimestones s l Beaverfoot-Erisco ormation) F M a s s i v e r e yo s s i l i f e r o u si m e s t o n e s g f l t h i n - b e d d e d u r p l i s hi m e s t o n e p l a n d h a l yi m e s t o n e s l Plate 52. Vesiculated glass lapilliindiatreme breccia, Quinn;:reek. Figure 76.Geology of the Blackfoot diatreme. Long dimension of photo micrograph is2.5 m . m ~~~~94 Geological Survey llranch
  • 25. Ministry of Eneqy, Mines and Petroleum Resorrrces76). The Beaverfoot-Brisco Formation the hangingwall in Haynes - Swanson Peak (latitude 49°5620", longitude areais characterized by thick-bedded, massive, medium grey 115"163O"W). Igneous rocks outcrop at approximatelylimestones containing rngosan corals, and light grey lime- 2400 metres elevation and can be reached by hekopter.stones in which chain corals (favosites and halosites type) Extrusive flows and a small diatreme arc: exposedare present. Thin-bedded to laminated, nonfossiliferous, within a few hundred metres of each other. The main flow -purplish weathering limestones and shaly limestones are is approximately 3 metres thick. It overlies al orange-present in the footwall. The contacts between the diatreme weathering, coarse, intraformational limestone cimglomer-and the limestones arewell exposed andno thermal meta-morphic effects are evident. ate that, in turn,overlies graptolitic shale. The volcanics are overlain by a few tens of centimetres of mixed shaly tuff The Blackfoot diatreme is a composite or branching which is in turn overlain by a thin orange-weatheringquartz-pipe-like body that is intensely foliated near its margins and ite. The quartzite displays graded beddingand, lit its base,contains fragments that have been flattened in the plane of contains small (centimetre-size) greenish clasts Df the un-the foliation. The centre of the diatreme is moderately tostrongly foliated. Foliation is generally parallel or subparal- derlying volcanic rocks. The quartzite is overlaiu by a thinlel to the margins (Figure 76). This wasapparently a site of black shale unit which is in turn overlain by 1.5 to 2 metreslocalized shearing during deformation. This pipecontains of white to pinkish weathering orthoqnartzite (Figure 77).approximately 30% inclusions, most of which are sedimen- Thin to thick-bedded grey carbonates the Beawrfoot For- oftary in origin (largely limestone, some shale and dolostone). mation, containing abundant fossil corals, orerlie theThese inclusions are subronnded to subangular and geuer- quartzite. The stratigraphic position of this flow, .which un-ally small (up to 10 cm in diameter). The largest xenolithsare purple-grey huff-weathering carbonates to probably de-rived from the Beaverfoot-Brisco Formation. The Quinn STRATIGRAPHY-SWAN CLAIMSpipes are very similar in appearance and composition, hutsomewhat less deformed. Exotic xenoliths, predominantly clinopyroxenites, greycarbonatehornblendites and dunites, are relatively common and re-markably fresh. Eclogite nodules have also been reported Beaverfoot-Brirco Formation(C.I. Godwin, personal communication, 1984). Clinopy- coral* locally prerertroxenite nodules consist of 30 to 57% green diopside, 0 to 3 15% enstatite, 0 to 40% olivine plus serpentine, 0 to 22%hornhlende with calcite, talc and minor ilmenite, spinel andpyrite. Hornblendites contain approximately 75% horn-blende, 10% clinopyroxene and 10% ilmenite, with calcite, 2 white orthoquartzite L1serpentine and traces ofpyrite. Dunites contain 63% olivine, ? + 14%clinopyroxene and 17% talc with accessory orthopy-roxene and hornblende (Ijewliw, 1986). Exotic xenoliths . . . . . . E 1were not found in the Quinn pipes. Altered vesicular glass lapilli, yellow in colour, pre- are black shalesent in the breccias (Plate 52), as are juvenile lapilli. Theglass lapilli are extremely well preserved in Quinn pipes. the orange quortzitewith 0-Lapilli constitute about 25 to 30%of the rock volume. Diop- green CILIDIO near tl(lLBside, altered olivine, minor orthopyroxene and chrome greyshale greanish andspinel macrocrysts are also present. The matrix, which fragmentolsmakes up a significant proportion of the sample volume, isamixtnreofcalcite>talc?chloritekplagioclase,minorpotas-sium feldspar, sphene and apatite with a fibrous, matted tex-ture. Bryozoan and brachiopod fragments have noted been green volcanic locally shearedfrom tnffisitic material in the western Qninn pipe. central portion appears Massive, fine-grained, dark green dikes cut the breccias pillowedat both the Blackfoot and Qninn diatremes. These dikes areintensely altered. The Blackfoot and Qninn diatremes areextremely similar to both the Shatch Mountain and RussellPeak pipes and are therefore probably also of limburgitic oralkaline basaltic affhity.MOUNT HAYNES - SWANSON PEAK orange weothering (+domitic?AREA (SWAN CLAIMS) (826/14) intraformoiionol conciomerate The Swan claims are located approximately 5 kilome-tres south of the Blackfoot pipe (Figure 73) in the Mount Figure 77.Stratigraphy, Swanson Peak areaBulletin 88 95
  • 26. Plate 53.Pillowed flow, Swanson ]?e&,derlies 5 . quartzite (Tipperary Formation?) beneath the THE MARY CREEK- WHITE RIVERBeaverfcsot Formation, indicates that it is of probable Late BRECCIA DIKE (82Jj3W)Ordovician age. The flow is fine grained and dark green in hand sample. A narrow dike crops out the head of Mary Creek, a atSpherical pillow strnctures are preserved in the centre of the small tribufary ofthe White River, east of Whiteswan Lakeunit (P1a:e 53). In thin section, the rock displays a fine por- (latitude 5O01O’3O”N, longitude 115”22’15”W; Figure 73).phyritic texture consisting of approximately 10% altered It is exposed at the 2010-metre elevation and is most easily accessed by helicopter. 2olivine @pyroxene?) phenocrysts and to 5% feldspar phe-nocrysts in a he-grained altered groundmass that contains The is 1 to 2 metres wide, steeply dipping andapproximately 40% feldspar microphenocrysts and a few slightly discordant to bedding. It mainly consists of a mas-percent opaque oxides. Microprobe analyses indicate that sive, fine-grained, dark green weathering phase locally thatthe feldspars, both phenocrysts and microphenocrysts, are grades into a red and green-weathering, strongly foliated phase that contains small round globular segregations or ac-very pun: potassium feldspars (Appendix 3). cretionary :lapilli. The massive phaselocally contains clasts The diatreme is exposed on a small ridge, approxi- of host sedimentary strata. In thin section, accretionarymately 200 metres south where the volcanics outcrop. It of lapilli were observed to be cored by olivine macrocrystsis light greenish to buff weathering,massive, and has grey- a with large red-brown spinel inclusions; some fine-grainedish to buff fresh surface. It consists of a matrix-supported biotite was also noted.breccia that predominantly contains small, subroundedfrag-ments of sedimentary rock. THE SUMMER PIPES (826/11) Bas-d OTI the modal mineralogy (olivineAc1inopy-roxene and generations of potassium feldspar), the vol- tw’a Two small intrusive bodies are exposed at the conflu-canic rock is difficult to classify; it exhibits similarities to ence of Galbraith and Summer creeks (latitude 49’44’50’’the trachybasalt or the nephelinite family of rocks, but con- longitude 1.15°20’32’W, Figures 73 and 78) approximatelytains potassium feldspar alone rather than with plagioclase 40 kilometres northeast of Cranbrook. Outcrops occur be-in the fo~mer, feldspathoids, in the latter case. It is impos- !or tween 1250 and 1350 metres elevation and canbe reachedsible to :say, however, if the potassium feldspar is primary from a logging road leading to a forest recreation site ator pseudomoq?hing a pre-existing phase. Summer Lake to the Top of the World Park. These pipes and96 Geological Survey Branch
  • 27. ” Minisfry o Energy. Mines and Petroleum Resources f 1 have beenpreviouslyreported on by Grieve (1981) and Pel1 (1987). The Summer diatremes form weatheringresistant rusty knolls and arehosted by rocks mapped by Leech (1960)as Late Cambrian Ordovician McKay Group. In the vicinity to of the diatremes, the McKay Group consists of thin-bedded, grey micritic limestone, argillaceous limestone and intrafor- mational limestone conglomerate. only one place is the In contact between limestone andbreccia exposed and there, is subparallel to bedding in the limestones. This is most likely a local phenomenon, as the overall outcrop pattern indicates discordance. The limestones within0.5 metre of the ex,posed contact are strongly brecciated and material similar to the diatreme matrix forms veinlets in the lime- stone breccia. No other contact effects are evident. The breccia pipes consist of angular to snbrounded clasts in a medium green to grey matrix which is locally calcareous.Theclast:matrixratioisontheorderofl:l,with clasts ranging from granuleto cobble size. The largest and most numerous inclusions are angular limestone, limestone conglomerate and shale fragments, up to 70 centimetres of across, which comprise 90% all the clasts. The remaining 10% are buff dolostones, crinoidal limestones, red-weather- ing, thinly laminated dolostones, granites, granitic gneisses, phlogopite - chrome mica - marbles (altered syenites?), fine-grained cognate xenoliths and autobreccia fragments. Resistant reaction rims were noted around many sedimen- tary clasts. The matrix is predominantly chlorite, serpentine and carbonate (Grieve, 1981). Abundant juvenile lapilli (20-40%) and altered olivine and clinopyroxene macro- crysts are evident in thin section; some of the lapilli arePlate 54. Chrome spinel macrocryst (dark crystal rimmed by light cored by altered feldspar or clinopyroxene grains. Minorcoloured tc, transparent minerals - mainly carbonates), Summer chrome spinel may also be present (Plate 54). No vesiculardiatnme breccia. Long dimension the photograph is 2.5 mm. of glass lapilli were observed.
  • 28. TABLE 17 CHEMICAL ANALYSES BULL RIVER - ELK RIVER DIATREMES AND RELATEDROCKS ,2. 74- Si02 Ti02 A1203 Fez037 MnO 0.19 MgO 58 .5, cao~ Nd.0 K20 LO1 E05 480 140 420 420 80 160 140 490 400 480 2w 3W 210 158 380 520 430 280 200 85 116 340 754 236 579 564 176 201 476 8115 592 1050 542 709 508 450 898 994 1454 471 134 237 131 540 40 32 33 30 30 51 42 34 45 47 48 56 50 42 43 52 40 39 36 8 32 43 8 22 5 11 21 16 6 <8 26 11 40 33 18 46 4 <E 20 12 73 68 77 27 157 152 438 457 681 901 108 2 4 40 538 135 818 115 574 270 490 490 239 450 212 96 354 395 1415 106 553 2050 2158 1335 1016 443 4 1109 425 990 630 1461 676 140 67 88 73 2002 1320 1983 999 126 147 82 116 127 166 73 35 26 212 131 182 125 186 186 173 157 70 216 191 214 180 101 205 63 34 60 67 63 44 5 10 72 50 82 54 100 98 84 77 27 131 73 70 67 63 21 20 15 20 30 22 16 d 25 21 29 17 25 24 25 22 14 29 28 29 28 16 8 9 27 23 35 24 CI 4 31 ~~ 6 39 12 40 42 42 32 - 3 59 24 22 20 27 46 50 54 77 68 70 38 14 63 60 88 84 63 90 91 95 11 0 32 139 61 69 56 61 122 NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA 0 2 <-4 0 2 <-E <-7 d 0 0 <-2 <-2 0 0 <-2 0 0 c2 0 2 0 <-2 21 A 38.4 59.9 43 23.3 24.00 2. 99 2. 60 2. 80 2. 75 23.5 20.5 22.6 20.4 I;: 19.3 2: 4. 2. 16 22.8 " n 2 " . i-5 . I 6 4 5 3 4 4 b 0 12 1 12 3 9 26 3 1 1 0 15 <-5 9 4 10 7 10 8 10 20 3 4 5 9 4 5 4 188 156 129 130 261 650 511 280 258 319 313 338 325 292 143 219 331 296 323 215 263 24 _____ ~ 22 52 ~ 51 -54 61 76 ." __68 ~ 6 ~ 62 __ 39 55 ~ "~" 7 ~~ 4 6 57 38
  • 29. Minisfry of Eneqy, Minesand PefmleumResources / @ Diotreme breccia by Swonron PeakFigure 79. Major element (B) ternary plots. (A) Fez03-MgO-AIz03 plot, southern diatremes: Fe?,03-MgO-A1203 plot, Swan volcanics:(C) fiF" diagram, southern pipe swarm: (D) AFM diagram, Swan volcanics. Related dikes and sills occur peripheral to the diatre- slightl:, deeper level intrusions or blind diatremes of alka-mes. The dikes are fine grained, porphyritic and strongly line basalt affinity that did not breachthe surface.altexed. Theyare texturally similar to dikes and flows in theRus:;ell Pcak area. They contain what appear to be altered GEOCHEMISTRY OF DIATREMES ANDolivine, c:linopyroxene and feldspar phenocrysts and mi- DIKEScrophenoc:rysts. These dikes are locally vesicular; the ves-icles are rimmed bycoarse crystalline carbonate and infilled - Al.kaline rocks in the Bull River Elk River area arewith serpentine. varied in composition. Silica contents are in the ultrabasic range to marginally basic, from 28 to 45% and the aluminum Thou,!h still probably part of the same petrologic fam-ily, the Summer diatremes differ from those previously de- to alkali ratios place them in the metaluminousfields (Table 17). Other major elements significantly (Table Fig- vary 17:scrihed in a number of ways: they are hosted by Late nres 79 and 8 ) On the Fe203-MgO-Alz03 ternary dis- 0.Cambrian McKay Formation strata, not by Ordovician-si- criminant plot, these rocks generally fall in or peripheral tolurien formations; they are massive, brown-weathering, the alkaline lamprophyre (melilitite) fields (Figure 79),weakly foliated breccias as opposed to dominantly green- while on the AFM ternary plot they plot in the ultramaficwealherin,!, well-foliated tuffisitic breccias: and they de- are lamprophyre field and betweenit and the kimberlite field,void of volcanic glass lapilli. These rocks may represent generally removed from thearea of typical basaltic compo-"Built tin 88 99
  • 30. British (!oluml?ia" _sitions (Figure 79c). Relatively unaltered dike and flow ma- tremely potassic. They do not fall consistently into onetelial from the Russell Peak area plot in the alkaline lampro- category on the various discriminant plots: on the FeZ03-phyre fjeld on a K20-MgO discriminant plot; dikes from MgO-Al203 ternary plot they fall on the aluminous sideofMary Creek rdot the alkaline and ultramafic lamprophyre in the alkali basalt fields (Figure 79b); on an AFM diagramfields (I9gnre 8Oa). Samplesfromotherareasgenerally have they plot along the basalt trend and closer to the AM side ofMgO values in the alkaline to ultramafic lamprophyre the triangle than typical basalts (Figure 79d); on a KzO-range, but are depleted in potassium. On the alkali-silica MgO plot they fall within or marginal to the leucitite fieldplot, re1 3tivel:y fresh dike material from the Russell Peak and (Figure 80a); and, on an alkali-silica plot they fall wellMary Creek areas plots peripheral to the melilitite- within the melelitite-nephelinite field (Figure 8Ob). Majornephelhite and hasanite fields; the other samples are quite element chemistry and conventional do not help un- plots invaned, :some plotting in the typical basalt field and others equivocally classifying the Swanson Peak volcanics; theyexhibiting a depletion in alkalis relative to alkaline lampro- do, however, suggest that these rocks share some chemicalpbyres (Figure Sob). Much of the scattering of chemical similarities with members of the nephelinite family, al-compos.tions may, in part, be due to alteration or to dilution though lacking modal feldspathoids. infrom inciorporation offoreign material. The chemistrysug- Trace elementconcentrations of rocks fromthe south-gests th;H the,re rocks are morebasic than typical alkaline em diatreme swarm are somewhatvariable, particularly inhasalts m d m;iy be transitional to nephelinites, but have not terms of elements such as shontium, barium, nickel anddeve1op:d modal feldspathiods. chrome(Table17).SwansonPeakvolcanicshavenickeland The volc.mic rocksat Swanson Peak havean nunsual chrome concentrations similar to typical hasalts, while dia-composition; like other igneous rocks in southern British tremes and dikes from elsewhere in the southern swarm areColumbia, thEy are ultrabasic, but are peraluminons and ex- enriched in these elements (particularly in chrome) relativer to basalts lor nephelinites (Figure 81), with dikes generally more enriched breccia phases. Most ultrabasic rocks in than this area contain low concentrations of rubidium and low to moderate mounts of strontium, relative to the others exam- ined from the Golden, Ospika and Kechika areas. Total strontium:mhidium ratios for diatreme breccias throughout the area, and for dikes from the Summer area, are quite vari- able (3 to 1221),while dikes and flows from Russell Peak and the B:lackfoot area have restricted ranges, averaging around 22:l. The volcanics from the Swanson Peak area have higher than average rubidium concentrations and lower than average strontium concentrations compared to other members of the southern diatreme swarm, resulting in low total strontiummbidium ratios (around 2:l). On aver- age, dikes and flowsin the Bull River- Elk Riverarea are significantly more enriched in titanium than related brec- MQO I cias; the Swanson Peak volcanics contain more titanium, on e Blackfoot 25.00- @ Quinn, Joff X Rus 0 Joff. Ouinn, Blackfoot 8 Summer RUES dialremes n Mary Creek 20.00- . Swan + Hayner Creek 1500.00$ 0 Rum V O I C ~ I E I . * Swan diker grobbroicsill Average Plveroge 1000.00 alkali-olivine kimberliteo c basalt Dikaa v ~ l c a n i c s Russell Peak and Summer are0 Chrome spinel rich breccia 500.00 0.00 1000.00 1500.00Figure 80. Major element discriminant plots, southern diatremeswarm. (P.)Soulhdiatremeswarm: (B)Alkali-silicaplot, southernpipes.100 Geological Survey Branch
  • 31. " Ministry of Energy, Mines und Petroleum Resourcesaverage, lhan the other ultrabasic rocks in the area (Table fractio,ns plotted on concordia, yielding Paleozoic ages of17). 529 and 532S.5 Ma. Although tantalizingly young, it is unlikely that these ages are related to diatreme emplace-GEOCHRONOLOGY ment: the Blackfoot pipeis hosted by the Ordovician to Si- Diatreme breccias and related rocks in the BullRiver - lurian (circa 440 Ma) Beaverfoot Formation carbonateElk River area for the most part do not contain micaor other rocks.minzrals ;amenable to Rb-Sr or K-Ar radiometric dating. In As radiometric dating methods have yet proved use- notlieu of this,other methods havebeen attempted in order to ful, age determinations must on relative methods. In the relyestablish the ages emplacementof these rocks. Crater-in- of case a the Swanson Peak F volcanics, this task is not too dif- Rusfill material from the pipe on Russell Peak was sampled ficult. The volcanics clearly underlie a quartzite unit imme-for conodonts. It was barren. Samples werecollected from diately beneath the Late Ordovician to Early Silurianthe .loff pipe on Shatch Mountain and from the Blackfoot Beaverfoot Formation. Adiatreme in theNorth WhiteRiverpipe and xircon separates were obtained. Zircons recoveredfrom the Joff pipe were colourless and rounded, with an valley is of apparently the same age. It cuts Middle Ordovi-oblate to )prismaticshape. Results of analyses indicate that cian Slkoki Formation strata and contains bedded epiclasticthe :zircons are xenocrystic in origin (Appendix 2). giving crater-infill material in the upper portion of the pipe (Helm-lead-lead ages of 1046, 1780, 1820 and 2085 Ma. Two of staedt ,eral., 1988). The crater-fill sediments are overlain bythe .dnaly!;es, whichyielded the oldest and youngest ages, a quantziteunit which underlies the Beaverfoot Formation,p1ot:ed very close to concordia (Appendix 2). snggeriting an age of emplacement of circa 450 Ma. A ma- Zircons obtained from the Blackfoot diatreme are of jority of the other pipes in the area cut through part or all offour diffelrenr types: round and colourless; round and pink- the Beaverfoot Formation, but not breachthe basal De- doish; clear, colourless, enhedral and abraided; and clear, vonian unconformity surface; they are, therefore, post-Lateeuhcdral, multifaceted. The rounded zircons gave lead-lead Ordovician to Early Silurian and pre-Middle Devonianinages of 1918 and 2052 Ma (Appendix 2). The other two age, probably circa 400 Ma.
  • 32. "- "- Metres 10 Pile I Figure 82. Sketch of the Crossing Creek kimberlite pipe, facing north. Plate 56. Altered olivine macrwrysts and phenocrysts, phlogcpitePlate 55. Pyroxenite inclusion forming the core of a accretionary n phenocrysts andopaque oxides in a magmaticmatrix,Crosslapillus, central breccia phase, Cross kimberlite. kimberlite.I02 Geological Survey Bmnch