Coal Studies ELK VALLEY COALFIELD, NORTH HALF (825102, 07, 10, 11) By R. J. Morris and D. A. Grieve
KEYWORDS: Coalgeology, Elk Valley coalfield, Mount the area is formed by Hmretta andBritt creeks, and is Veits, Mount Tuxford, HenretlaRidge, Bourgeau thrust, coal immediately northof the Fc'rdingRiver operations of Fording rank, Elk River syncline, Alexander Creek syncline. Coal Ltd.(Figure 4-1-1).The northernboundary is the British Columbia - Alberta border. The map area includes INTRODUCTION the upper Elk Valley and a portion of the upper Fording Detailed geological mapping and sampling of the north Valley. half of theElk Valley coalfieldbegan in 1986 and were Most of the area is Crown land and includes three c:od completed in 1987. The end poduct, a preliminary map at a properties. The most southerly comprises the north end ol'tbe scale of 1: IO OOO, will extend available map coverage in the Fording Coal Ltd. Fording River property. Adjacent to the coalfield north from the areas covered by Preliminary Maps north is theElk River property, in which Fording Coal 51 and 60 (Figure 4-l-l),which in turn expanded previous currently holds aSO-per-cent interest. Coal rights to the most coverage in the adjacent Crowsnest coalfield (Preliminary northerly property, formerly known as tlne Vincent option, Maps 24, 27,31 and 42). are reserved to the Crown Work in 1986 (Grieve, 1987) was mainly concentrated in Exploration history of the Weary Ridge - Bleasdell Creek the Weary Ridge ~ Bleasdell Creek area. Themore extensive area was summarized by Grieve (1987). Of the remailing 1987 field program was completed by R.J. Morris. parts of the study area, onlyLittle Weary Ridge and vicinity The study area, which includes some of the least well- has received a significant exploration effort. Little W:ary explored parts of the southeast coalfields, extends 40 kilo- Ridge was the focus of considerable attention in the 1970s ds metres in a north-south direction. The southern boundary of the proposed site of the planned Elco mine development. Otherparts of the area Ihave received some exploralion, including drilling programs in the north end of the reserve ', area by Rio Tinto CanadianExploration L,td.,and at Henretta ', ELK L4KES PROVINCIAL PARK Ridge and in the Aldridge Creek area by Fording. Mount Tuxford on the Fording River property has received e:,sen- tially no exploration and as such is the largest unassessed block of coal-bearing land in the southeast coalfields. The part of the map area north of Cadorna Creek has been the subject of two previous geological studies. Pearsor and Duff ( 1977) carried out B mapping and core logging pro- gram. Graham et al. (1977) carried out a study whicl in- cluded mapping and drillingof four diamond-drill hole!., tor a total of 1641 metres, at the extreme north end of the Elk Valley. Access to most parts of the area is good,ultilizing the Elk Valley road, Fording mine access roads (permission re- quired), the powerline access road and subsidiaryexploration roads. The upper Fording Valley, however, has no vehicle access, and consequently most of Mount Tuxford can only be reached by helicopter. The west side of the Elk River norh of CadornaCreek, andHenretta Ridge, also have no road access. PRELIMINARY MAP 60 Relief varies throughout the area from very low il the north, wherethe coalfield. essentially ocmxpies the bottom of the Elk Valley, to relatively extreme on Mount Tuxford and MountVeits. Elevation:; range from 1500 to over 2400 0- 0- 5 10 A5 - metres. A PRODUCING MINE FIELDWORK AND METHODS OF STUDY Field data were plotted directly on British Columbia gov- -Figure 4-1-1. The Elk Kiver valley north of Elkford. ernment air photograph!;, enlarged to a scale of approx- British Columbia Ministry of Energy, Mines and Petrulcurn Resources, Geological Fieldwork. 1987. Paper 1988-1 421 INDEX MAP
ARCTIC SHELF
LEGEND
LOWER CRETACEOUS flIRMORE GROUP
JURASSIC AND CRETACEOUS
$J'ZaYoYp
Mist Mountain Formation
Morrissey Formation
TICAND OLDER Fernie Formation and older strata T!? Position of measured section a - Coal Creek b - Mount Veits c - Mount Tuxford South d - Mount Tuxford South e - Henretta Ridge A' Cross-section line
Figure 4-1-2. General geology of the north half of the Elk Valley coalfield
428 imately 1:7SoO. Data and interpretations will be transferred per centof the total thickness. An almost complete sectionof to specially prepared 1:10 000-scale orthophoto base maps. Mist Mountain Formation measuredon Weary Ridge in 1986 Stratigraphic sections were measured on Mount Veits, (Grieve, 1987, Figure 5-14) is 507 metres thick, and cm- Mount Tuxford and Henretta Ridge andat Coal Creek, using tains 63.8 metres of coal. Good exposures of the formation pogo stick, compass and chain. They have been generalized occur throughout muchof the southern partof the area; same for inclusion here. Coal units thinner than 1.0 metre are not of these were measured and are generalized here in Figure included in the generalized sections. 4-1-3 and arediscussed below. North ofLittle Weary Ridge, Grab samples of coal were taken frequently to provide however, exposures of MistMountain Formation are ex- material for petrographic rank determinations. In all cases, tremely poor and little can be saidabout its general features. bloom and other highly degraded coal was avoided, usually Logs of drill cores from the extremenorth end of the area are by sampling from fresh-looking cuts or by digging through shown in Graham et al. (1977). softer material. Average sample size was 250 grams and no attempt was made to make the samples representative. COALCREEK Petrographic rank of coal was determined by the Rpax At Coal Creek, a tributary of Bleasdell Creek, a pmtial method (mean maximum vitrinite reflectance in oil) on pel- section of Mist Mountain Formation in the immediate fm- letized particulate samples.Samples were lightlycrushed wall of the Bourgeau thrust fault was ~neasured (Figure using mortar andpestle; only the -20-mesh fraction was 4-1-3). At this location the MorrisseyFormation and thetsase utilized. Maximum readings on 50 grains per sample were of the MistMountain are not present due tomovement on the measuredand averaged.Coals are classifiedinto ASTM Bourgeau thrust (see Figure 4-1-2). The baseof the sec:ion categories as follows: high volatile bituminous, R,max chosen was an arbitrary point beneath a prominent coal scam
Predominantly coal 1 .O ELK FORMATION lnterbedded coal /r and shale -1 -1 Predominantly siltstone and finer E:-:- E:-:- lnterbedded Siltstone and sandstone Predominantly sandstone
Covered interval
5.2 Coal seam thickness in metres - 1.22 R0max (Ob)
5010 metres
I MORRISSEY FORMATION I
Figure 4-1-3. Generalized measured sections of parts of the Mist Mountain and Elk formations in the north half of the Elk Valley coalfield. See Figure 4-1-2 for locations; sections are described in the text. 430 seams range from 1 .0 to 5.6metres thick, and four seams are topcorresponds with theMist Mountain - Elk contact. in the range of 4.8 to 5.6metres. Channel sandstone units are Unfortunately, the section location is Characterized by struc- mainly confined to the lowermost and uppermost200 metres tural complications and poor exposure. A thrust repeat of of the section. Theintervening, 150 metres of predominantly roughly 135 metres of strtlta in the lower Mist Mountain recessive strata contains twoclosely spaced coal seams each Formation was noted and split out (Figure 4-1-31, At just greater than 5 metres in thickness. under 700 metres, however. the total Mist Mountain sectlon is still anomalously thick, which suggests that other struc- MOUNTTUXFORDSOUTH tural repetitionsprobably occur within thick recessive or covered intervals. A partial section of upper Mist Mountain Formation was The partof the section occupying thefootwall of the thrust measured on the east-facingslope of Mount Tuxford. roughly (plotted on the left in Figure 4- 1-3) is well (enoughexposed to kilometres south of the previous section. The base of the 3.5 permit the observation that it is remarkably lacking in coal (it section was chosen arbitrarily and represents thelowest point contains only two coal seams, one I .O metre thick and the of consistently good exposure. The top of the section corre- other 5.3 metres thick), and contains a relatively large thick- sponds with thebase of a prominentchannel sandstone ness of channel sandstone units. The prtsence of charnel believed to mark the base of the Elk Formation. sands may have a bearing on the lack of coal; chartnel The Mount Tuxford south section is 181.6 metres thick sandstones often fill washouts of coal seams. and contains only two coal sedms (1 .0 and 3.1 metres thick) The hangingwall portionof the section(plotted on the r ght which exceed I metre in thickness. Covered zones within the in Figure 4-1-3) defies generalization. It contains almos no section may hide more coal seams. In contrast with the upper coal, althoughthe thick covered intervals are almost ;er- 200 metres of the MountTuxford north section, this sectionis tainlyhiding some coal seams. However, the lowest 250 relatively recessive and devoid of major channel sandstone metres is well exposed, and contains no coal. Thecontinuous units. thick intervals of fine-grained rocks are extremely anomalous. HENRETTARIDGE It is noteworthy that the overlapping portion of the Mist A section, representing all Mist Mountain strata underly- Mountain Formation on Henretta Ridge IS very differerit in ing Henretta Ridge, was measured 3 kilometres south of the each of the two thrust sheets (Figure4-1-31, The hangingwall Mount Tuxford south section. The base of the section corre- portion contains a predominantly recessive sequence, 1.1ck- sponds with the Morrissey - Mist Mountain contact and the ing the major sandstoneunit present in the footwall. Further- r
1
Figure 4-1-4. Generalized cross-sections throughthe north half of the Elk Valley coalfield. See Figure 4-1-2 for locations 43 1 more, the 5.3-metre seam just beneath the thrust is appar- STRUCTURE ently absent in the hangingwall. The study area lies inthe Front Ranges of theRocky Mountains and is part of the Lewis thrust sheet. The domi- ELK FORMATION nant structures are therefore thrust faulting and folding. The area can be divided at Aldridge Creek into two distinct The overlying Elk Formation is a coarser grained facies zones with contrasting structural elements. The zone south of than the Mist Mountain and distinguished from it in several Aldridge Creek contains north-plunging folds, northward ways. In particular it generally lacks thick coal seams and extensions of those affecting the adjoining part of the contains unusual sapropelic coals known as “needle coals” coalfield. The major folds are, from east to west, the Alex- (see Kalkreuth, 1982). In the Mount Tuxford and Henretta ander Creek syncline, the Greenhills syncline and the Ford- Ridge areas the Elk Formation is distinguished by a yellow or ing Mountain anticline (Figure 4-1-2); minor folds are also orange-brown weathering colour to the resistant sandstone observed. These folds are open and roughly symmetrical units. (Figure 4-1-4, Section D-D’). Based on cross-sections, the thickness of the Elkis Until now it was believed that the Alexander Creek syn- approximately 350 to 400 metres throughout the study area cline was continuous throughout the Elk Valley coalfield (for (Figure 4-1-4). example, Pearsonand Grieve, 1980; Grieve, 1987). It is A partial section containing 177.9 metres of the lower Elk evident now,however, that north of Aldridge Creek the Formation was measured on the north end of Mount Tuxford, coalfield is underlain by another newly defined major fold, and is included in Figure 4-1-3 (Section c). The base of the theElk River syncline (proposed name). The Elk River section is the Mist Mountain - Elk contact and the top isat an syncline is east and north of the Alexander Creek syncline, arbitrary point. The relatively coarse-grained nature of the although its east limb becomes the east limb of the Alexander Elk, in comparison with the Mist Mountain Formation at this Creek syncline and is possibly related to it in an en echelon point, is noticeable in Figure 4-1-3. The lower two-thirds of fashion (Figure 4-1-2). the section consists of several stacked channel-sandstone The Elk River syncline is asymmetrical, with a steep to units separated by thin, recessive, finer grained intervals, overturned west limb and a shallow to moderately west- including a 1.0-metre coal seam. The upper third is a re- dipping east limb (Figure 4-1-4). It is doubly plunging with a cessive interval including coal seams 1.0 and 1.6 metres depression in the vicinity of Cadoma Creek (Cadoma Creek thick. The section is overlain by a prominent cliff-forming depression of Pearson and Grieve, 1980). Itis cylindrical sandstone which marks the base of another sequence of throughout except for the area of its origin where it isconical. stacked sandstone units. In many areas its east limb is modified by zones of shallow At Elkan Creek, at the extreme north end of the study area, dip which have been interpreted as minor step folds. Thrust- a series of several thick, cliff-forming conglomerates and ing in the east limb is also common. conglomeratic sandstones occurs within the Elk Formation. Concomitant with the change in structural style which The coarseness of this occurrence is unusual for the Elk takes place at Aldridge Creek is a pronounced change in the Formation inthe Elk Valleycoalfield, but we see reason to no width of the coalfield (Figure 4- 1-2).This isprimarily due to place these strata in the Blairmore Group as was done by the behaviour of the Bourgeau thrust fault. The Bourgeau Graham et al. (1 977). We feel this occurrence is analagous to fault is a regional feature which marks the westernboundary the Elk Formation occurrences on the west side of the of the surface exposures of the Lewis thrust sheet and, from Crowsnest coalfield, including the type area near Fernie. The Bingay Creek northward, the western boundary of the Elk type area isbelieved to represent an alluvial fan facies of Elk Valley coalfield. Starting at a point roughly corresponding Formation (Gibson, 1985; Grieve and Ollerenshaw, in prepa- with the southern boundary of the study area, the trace of the I ration) and perhaps the north end of the Elk Valley coalfield is Bourgeau fault begins to step to the northeast, possibly on the fringes of another fan system. reflecting lateral ramping. In the process the fault cuts up- Precise identification of the Elk- Mist Mountain contact in section relative to itsfootwall and cutsoff thetraces of all fold southeastern British Columbia is generally difficult (Grieve axes in the footwall, including the Greenhills and Alexander and Ollerenshaw, in preparation). The study area is no excep- Creek synclines. At the point where the Elk River syncline tion. In the case of the good exposures near the summit of begins to develop, the trace of the Bourgeau faultreturns to a Mount Tuxford, it waspossible to detect a significant colour more normal northerly orientation. change in the sandstone units at a stratigraphic horizon which also seemed to mark the base of a more resistant, coarser From Aldridge Creek northwards, the Bourgeau thrust grained facies devoid of thick coal seams. The so-called remains parallel to, and in contact with, the west limb of the needle coals were only observed near the top of the Kootenay Elk River syncline. The stratigraphic position of its footwall at this location. This horizon was mappable for a short varies along its trace from the uppermost Fernie Formation to distance to the north and south, although confidence in its uppermost Kootenay (Figure 4-1-2). At the north end of the position decreases with distance. Using airphoto interpreta- study area the Bourgeau fault is offset 2 kilometres to the tion it waspossible to extend it from Mount Tuxford to Weary northeast by a transverse fault (Leech, 1979). Ridge, where the contact was mapped previously (Grieve, Minor sttuctures associated with the Bourgeau thrust are 1987). Definition of the contact lacks precision on the west not generally observable because of poor exposure. At Coal side of the Elk River and throughout the area north of Weary Creek, the location of measured section A in Figure 4-1-3, a Creek. highly disturbed zone of Mist Mountain Formation occurs in
432 the footwall of the thrust.This zone containsstructures of I.38 per cent represents a coal seam within 20 metres 01 similar in style and orientation to the Bourgeau fault itself, as the baseof the formation. The othertwo va:lues, in ascending well as a transverse fault, parallel to the creek (roughly east- stratigraphic order, are 1.36 and 1.31 per 'cent. west). The former structures have caused local thickening of Sixsamples from Mount Tuxford have been analysd the strata, including onecoal seam, while the latter has representing stratigraphic positions ranging from 56 metres resulted in a dramatic contrast in the degree of structural above the base of the Mist Mountain Folmation to irnoie-. deformation of the strata on opposite sides of the creek. In diately beneath theElk contact. All correspond with :he particular, the thickened coal seam referred to above, which measured section of Mount Tuxford north, and are plotted outcrops onthe south side of the creek, is undisturbed on the alongside it in Figure 4-1-3. The reflectance values range north side of the creek, where exposed at the base of our from 1.45 to I.02 per cent, decreasingwith ascending strat- measured section. For this reason, the probability that the igraphic position. economic potential of this seam may be enhanced by struc- The number of analyses is not sufficient to define rank tural thickening is believed to be low. trends. However, it appears that ranks along the east limtl of Late-stage, crosscutting normal faults occur in the Mount the Elk River syncline are at a maximum in the vicinit) of Tuxford and Mount Veits area parallel to prominent joint Weary Ridge and Little W~aryRidge, and decrease to the orientations. They have resulted in mass wasting of the Mor- south. rissey Formation, forming both topographic steps and land- slide blocks. A large slide-block of Morrissey Formation on BLEASDELL CREEK TI3 CADORNA. CREEK the north end of Weary Ridge is probably a related feature. (WEST LIMB) Reflectances of six samples of Mist Mountain Formalion RANK DISTRIBUTION from north of Bleasdell Creek, onthe west limb, range fiom to 0.84 percent.Although stratigraphic control poor Preliminary data on the coalrank distribution in the Weary 0.63 is in this area, this range appears to represent the entire hlist Ridge - Bleasdell Creek area were given by Grieve (1987). Mountain Formation. These results are compatible with They indicated an extreme rank contrast between opposite those obtained last year from the Bleasdell Creek area. limbs of the syncline in this area. Coals from Weary Ridge, on the east limb, have reflectance values anomalously high for southeastern British Columbia, while reflectance values ELK LAKES AREA in the Bleasdell Creek area are anomalously low. For exam- Five samples from the Mist Mountain ]Formation and one ple, the Mist Mountain Formation on Weary Ridge contains from the Elk Formation collectedat the nonh end of the study coals which range in reflectance from I .59 per centdown to area have been analysed. Reflectances of the Mist Mountain 0.99 per cent, with a general decrease up-section. In con- samples decrease from I.06 to 0.70 perc:ent with ascendng trast, Mist MountainFormation coals fromthe Bleasdell stratigraphic position. Thehighest value corresponds with a Creek area rangein rank from 1 .OO per centdown to 0.65 per seam in the lower part of Ithe formation, but its exact srat- cent, with a less well-defined stratigraphic variation. Values igraphicposition is unknown.The sample fromthe Elk plotted alongside the Coal Creek Section A in Figure 4-1-3 Formation has a reflectance of 0.57 per cent. range from1 .oO per cent to 0.85 per cent,providing a further These values are anomalously low, and are in general example of the low relative ranks in this area. A possible agreement with results of Pearson and Grieve (1980) .who explanation for this contrast was briefly reviewed by Grieve found the entire sectionin this area to be high volatile (R,nax (1987) based on work by Hughes and Cameron (1986).
~ (1985): Stratigraphy, Sedimentology and Depsi- Kalkreuth, W.D. (1982): Rank and Petrographic Composi- tionalEnvironments of theCoal-bearing Jurassic- tion of Selected Jurassic-Lower Cretaceous Coals of Cretaceous Kootenay Group, Alberta and British Co- British Columbia, Canada, Bulletin, Canadian Pe- lumbia, Geological Survey of Canada, Bulletin 357. troleum Geology, Volume 30, pages 112-139. Graham,P.S., Gunther, P.R. and Gibson, D.W. (1977): Leech,G.B. (1979): KananaskisLakes Map-area, Geo- Geological Investigations of the Coal-bearing Kwtenay logical Survey of Canada, Open File 634. Formation in the Subsurface of the Upper Elk River Pearson, D.E. and Duff, P.McL.D. (1977): Studies in the Valley, British Columbia, Geological Survey of Can- EastKootenay Coalfields, B.C. Ministry of Energy, ada, Report of Activities, Part B, Paper 77-lB, pages Mines andPetroleum Resources, Geology in British 203-210. Columbia, 1975, pages G94G99. Grieve, D.A.(1987): Weary Ridge and Bleasdell Creek Pearson,D.E. and Grieve, D.A. (1980): Elk Valley Areas, Elk Valley Coalfield (823/7), B.C. Ministry of Coalfield, B.C. Ministp of Energy, Mines and Pe- Energy, Mines andPetroleum Resources, Geological troleum Resources, Geological Fieldwork, 1979, Paper Fieldwork, 1986, Paper 1987-1, pages 345-350. 1980-1. pages 91-96.
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