GEOLOGY OF DUKE AND HONEYMOON PIT AREAS, MONKMAN COAL DEPOSIT, NORTHEAST COALFIELD* (93U15) By C. B. Wightson

KEYWORDS: Coal geology, Monkman coal deposit, com- The joint venture group has presented a proposal to the puter modelling, Minnes Group, , Fort St. provincial government for an open-pit mine capable of pro- John Group, . ducing 3 million tonnes per year of metallurgical coal. This proposal has obtained Stage I1 approval. The objectives of INTRODUCTION the author's project are 'to provide a detailed geolo;:ical Coallicences were initiallyacquired on the Monkman interpretation of the proposed mine area and to develop a computer-based model of Ithe coal deposit. Information built property by Mclntyre Mines Limited in 1970. Exploration mapping and drilling programs have been conducted over a into the model will be used to calculate: coal reserves and 17-yearperiod by Mclntyre Mines Limited, Canadian stripping ratios. An assessment of the coal deposit will be Superior Exploration Ltd., Pacific Ltd. and Pe- available to the provincid government at thetime that a trocanada Inc.The Monkman project is a joint venture mining project is initiatecl at Monkman. Methodology and between Petro-, Mobil Oil Ltd., Coal computer technology developed during this project will be Ltd. and Sumitomo Corporation, with Petro-Canada acting used to model and assess other coal deposits and to assist as operator. with the interpretation of ruuctural geology. LOCATION AND ACCESS The Monkman coal deposit is located in the southern part of the Northeast British Columbia Coalfield approxim;ltely 30 kilometres southeast of the Quintette mine and 35 tilo- metres southeast of Tumbler Ridge (Figwe 4-7-11,The pro- ject area covers 140 square kilometres in the inner foolhills region of theRocky Molmtains. The Monkmanproperty consists of 169 coal liceom which COVI:~39 587 hect;ues. The Duke Mountain Block, in which Duke and Honeymoon pits are located (Figure4-7-Z), encompas:ies 20 745 hect:ms. Coallicences owned by Petro-Canadamark the northern boundary of the study ar,:a and Fearless Creek mark!; the southernboundary. Kinuseo Creek valley cuts acros!: the northernpart of thearea. The valley contains upto 100 metres of unconsolidated overburden (Figure 4-7-2)hhich covers part of theproposed Duke and Honeymoon pirs. Elevations vary from 9580 metres in the valley floor of Kinuseo Creek to 1742 metres at the top of Duke Mountain. Vegetation ranges from spceforests to alpine tundra. sl Access into the Monkman areais via the Monkman High- way, a dry-weather road which parallels Kinuseo Creek. and extends to just west of Kinuseo Falls OCI the Murray River. The Monkman Highway c.an be reached by gravel roads From Tumbler Ridge; Elmworth, ; or from Dawson Creek along the HeritageHighway. An airstrip near Thunder Moun- tain permits access by light plane. Numerous coal explora- tion roads, industry access roads and seismiclines provide excellent access I:O most parts of the project ;area. FIELDWORK -10 krn Prior to the 1987 field season, all pertinent open file coal assessment reports were examined. Geological maps of the Figure 4-7-1.Study area location map with Monkman property area were used to obtain digitized outc~rop informatioxA coal licences. computer-based outcrop database was designed to ston: the ~ ____ * This project is a contribution to the CanaddBritish Columbia Mineral Development Agreement. British Columbia Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork, 1987. Wper 1'988.1 47 I LEGEND

[(3 GATES FM.

- PIT BOUNDARY \ \ OVERBURDENTHICKNESS 4 I

Figure 4-72, Subcmp map of the Gates Formation showing unconsolidated overburden thickness and Duke and Honeymoon pits

412 information. Once completed, outcrop maps were produced record. Data points can be referenced and retrieved based and examined to identify areas which lacked dataand to upon locational parameters. drill-hole identification, or strat- indicate areas with structural complexities or interpretation igraphic horizon. problems.Subsequent field mapping concentrated on COIL Outcrop data were digitlzed using a GTCO digitizer 'con- lecting additional outcrop data at these locations and verify- nected to a Compaq portable 286 compu1.er. Database main- ing the informationover the remaining parts of themap tainance and data processing and display were managed on a sheet. New data were plotted on topographic maps at a scale Wyse pc286 computer. Peripheral dcvices inc1ud1:d a of 15000. Airphotos at a scale of 1:40 000 were used to Houston Instrument DMP-52plotter and an Epson FX-:!86e produce enlargements at a scale of 1:lO 000. Outcrop infor- printer. mation was also plotted on the photo enlargements. Database construction and maintainance were performed Field mapping was conducted in conjunction with map- using the Geological Analysis Package of Cal Data Ltd. ping carried out by W. Kilby and S. Johnston (1988) on NTS Display of the geological data was facilitated by the Slruc- map sheets 931114,931i15 and 93Pi02 at a scale of 150 000. tural Analysis module of !.he Geological Analysis Package, Some outcrop datain the southeast comer of the geology map with a number of modifications by the author. StNc:ural (Figure 4-7-3) is from this source. Information from 1955 analysis of the outcrop data and drill-hole information pro- outcrop data points and 21 1 drill holes was examined and cessing was performed wil:h programs written by the author. incorporated into the geological interpretation. Outcrop data were digitized from geologicalmaps using programs written by W. Kilby. Figures were produced using the ECAD computer-aided drafting program. METHODOLOGY AND DATA HANDLING Computer-based methods have been used extensively to assist with data handling and display. Orientation parameters Strataexposed in thearea range from theLower describing the geological structural features were calculated to M.innes Group, to the Upper Cre- using computer-based numerical procedures (Charlesworth taceous Kaskapau Formati,sn.The stratigraphy in the are.i has ef a/.,1976). beendescribed extensive!!y by Stott (1968 and 1982) and others. Descriptions of sedimentology and depositional en- Cross-sections were constructed by projecting outcropand vironments are beyond the scope of thi:s study and arc not drill-hole data down plunge onto planes of cross-section. includedhere. Table 4-7-.1 summarizes each formatica in Assuming that the folded surfaces approximate cylindricity, terms of a general description and the thickness specific to the data can be reliably projected parallel to the fold axis. the Monkman location. Thicknesses and descriptions were Lack of data, or poordistribution of orientations along both obtained from outcrop information, coalexploration drill limbsand across thehinge zone of a fold, may result in holes and petroleum industry exploration wells. Texaco Ex- unreliable fold axes orientations. In these cases an appropri- ploration CanadaLtd. drilled an explaration well, ExEx ate projection axisor fold axis orientation may he obtained by Flatbed a-21-Fi93-1-15, in the northeas): comer of the map visually best-fitting the data by trial and error, using several area (Figure The entire stratigraphic sequence, from different projection orientations. 4-7-3). the Minnes to the Kaskapau, is penetratemi by this hole. Brief Thick unconsolidated overburden covers parts of both the descriptions of the stratigaphy follow. Duke andHoneymoon pit areas. Visual best-fit fold axes orientations were determined in these areas. MINNES GROUP General data-handling methods are similar to those de- scribed by Kilby and Wrightson (1987). Drill-hole data have The Minnes Group con,iistsof both marine and nonmarine been incorporated into this study in a computer processible strata rangingin age from Jurassic to Early Cretaceous. format. Information wasdivided intoprimary,secondary and Lithologiesinclude interbedded sandstones, siltstone!; and tertiary categories and entered into three independent raw with minor coal seams. data files. Primary data consist of drill-hole identification, location (easting, northing and elevation), overburden thick- BULLHEADGROUP ness, total depth and original hole orientation measured as the hole trend and plunge. Secondary data consist of drill- CADOMINFORMATION hole deviation data entered as the measurement depth, the The Cadomin Formationunconfonnably overlie$ the hole trend and the deviation measured in degrees from ver- Minnes Group. It is approximately 45 metres thick and tical.Tertiary data consist of thedrilled depths and the consists of two hands of chert and qua.rtzite conglom.erate identifying names of the horizons of interest. The raw data separated by sandstone.The conglomerate framework is files were then processed to yield three additional files con- poorly sorted and ranges From grit to cobhle-size fragments. taining the data in formats ready to be processed or plotted on The is easily mappable with prominent maps or cross-sections. Primary data for each drill hole are ridges often indicating its; outcrop. stored as separate records with indexing information used to locate the specific secondary and tertiary data for that hole. Secondary and tertiary data are stored in separate files as GETHINCFORMATION eastings, northings and elevationsin format ready for posting Gething strata consist of 140 metres of interbedded sand- to maps or cross-sections. Each entry is an independent stone, siltstone, and coal.Lent:~cular conglonlerate

413 Figure 4-7-3. Geology of the Monkman coal deposit in the Duke and Honeymoon area 474 TABLE 4-7-1 STRATIGRAPHIC COLUMN, MONKMAN AREA

~~ THICKNESS SERIES GROUP FORMATION LITHOLOGYIN METRES

Darkgrey marine shales; KASKAPAU interbeddedsandstone end shale in lowerpart UPPER SMOKY Non-marine aandmtone, soma DUNVEGAN LRETACEOUS 30 shaleand coal

Darkgrey marino shele, locallysilty with sidoritic concretions;minor oon- iHAFTESBURY 250 glomorsteand sanda~tono. Includes theGoodrich aend- atone

Fino-grsinnd, w.11 aortod BOULDER sandatone;msaaive con- CREEK 90 glomersto;non-marin~o send- mtonoand mudstone end coal FORT

ST I Darkgrey marino mhalo JOHN HULCROSS 80 I I with sideriticconcrakions

Fine-grained,marine, end non-marinasandstones; con- GATES 250 glomerate; coal; shaleand mudstone LOWER Darkgrey marine chsle :RETACEOUS with sideritic concrations; MOOSEBAR 2o gleuconiticssndstone, end pebblesat base, coarsens UD. Torrensmember st toD

Fine- to coarse-grained, brown,calcareous, cor- GETHING bonaceoussandstone,; coal, 1 40 cerbonsceous shale, end conglomerate KILLHEAD Massiveconglomerate con- tainingchwt endquartzit. CADOMIN 45 pebblesand some sandstont

UNDIFFEREN- Thinly-thicklyinterbeddod, MINNES TIATED shale, ssndetone.niltstone JURASSIC andcoals

475 hands are oftenfound in the lower third of the Gething. In the preted to have penetrated the lower portionof the Shaftesbury Monkmanarea the coal seams aregenerally poorly de- Formation. The sandstone interval is overlain by about 170 veloped and are of little economic interest. metres of marine shales. The top oltheseshales marksthe top of the Shaftesbury Formation. Discontinuity of the marine FORT ST. JOHN GROUP sandstone interval makes mappingdifficult and prevents division of the Shafteshury Formation. MOOSEBARFORMATION The MoosebarFormation is about I20 metres thick. Athin SMOKY GROUP glauconiticconglomeratic band marks the lower contact. This is overlain by bioturbated marine mudstonefollowed by DUNVEGANFORMATION a seriesof coarsening-up cycles. TheTorrens member, which The consists of 30 metres of argill- lies at the top of the Moosebdr Formation, is a well-sorted acenus fluvial sandstones with minor amounts of shale and beach sand 20 metres thick. coal GATES FORMATION KASKAPAUFORMATION The Gates Formation is comprised of approximately 250 The is comprised of about 400 metres metres of interbedded sandstone, siltstone, shale, coal and of recessive, dark, marine shales with minor sandstone inter- some conglomerate. Twelve coal seams, identified from beds near the base. oldest to youngest as B1 to B12, are distributed throughout the formation. Well-developed coal seams are present in the STRUCTURE Gates Formation from justnorth of Bullmoose Creek south- wards into Alberta. Folds in the Monkman areagenerally displaynarrow hinge zones and planarlimbs. Majorstructures are continuous Potentially mineable coal reserves have been identified in along strike for severalkilometres. Along strike the folds are seams BI toB9 in the Monkman area. Seams83 and 84are characterized by variations in fold axis trend and plunge. of most economic interest and constitute the mdjority of the Fold structures tend to die out with abruptterminations. coal reserves estimatedby Petro-Canada in Duke and Honey- Duke syncline, Quintette syncline andQuintette anticline moon pits. (Figure 4-7-3) display these characteristics. At the north end of the map sheet Quintette anticline has a HULCROSSFORMATION calculated trend and plunge of 113"/5". Along strike to the lnterbedded marine shale and siltstone, with some fine- southeast the fold axis orientation changes to I18"/2" and grained sandstone, make up the Hullcross Formation. It is then to 125"/5". Further south, outcrop data are rare where approximately 80 metres thick. thick overburden covers KinuseoCreek valley. Calculated foldaxis orientationscannot be determined in this area. BOULDERCREEK FORMATION Numerouscoal exploration drill holes are present in the valley and the continuation of the anticline was examined The Boulder Creek Formation compises from 70 to 90 using these data. Visual best-fit fold axis orientations con- metres of conglomerate, sandstone, siltstone, shale and tinue to increase in both trend and plunge to the southeast to minor coals.The lowermost 30 metresconsist of pebble maximums of 141"i1I0. Rapid hut consistent changes in conglomerate which is overlain by a finer grained interval. trend, accompanied by an increase in plunge of macroscopic The upper 5 metres may be either pebble conglomerate or folds, may be indicative of a termination of the fold. Cross- sandstone. sections further south show noindication of the continuation of Quintette anticline. Fold terminations will be examined in SHAFTESBURYFORMATION the next field season and outcrop data will he numerically analysed to determine if the folds display conical geometry. To the northwest, the Shaftesbury Formation is differenti- ated into the Hasler, Goodrich and Cruiser formations, hut At the northern end of Quintette syncline, the orientation these divisions have not been recognized in the vicinityof the of the fold axis is 121"/20". To the southeast, the orientation Monkman deposit (Stott, 1982). The ShafteshuryFormation gradually changes to 130"/2". With the exception ofthe north may be closely examined with outcrop data in the south- end, orientation data are poorly distributed around the eastern quadrant of the map sheet, in coal exploration drill syncline. holes MDH-X107 and MDH-8108 and inTexEx Flatbed Outcrop information is abundantalong both limbs and a-21-Fi93-1-15, The Boulder Creek Formation is overlain by across the hinge zone of Duke syncline. Calculated fold axis 35 to 65 metres of marine shales, silty shales and thin fine- orientations were determined for four distinct segments or grained sandstones. Above this lies upto 18 metres of marine domains alongthe trendof the structure. At the north end, the sandstone. TexEx a-21-F intersects two coarsening-up off- fold axis trend and plunge are313"10". The trend and plunge shore-bar sandstones which are probably a marineequivalent change toI25"iS" in the north-central part of the structure and to the Goodrich Formation. Marine sandstones in a similar shallow slightly to 124'12" in the south-central portion of the stratigraphic position were located at several outcrops. Drill fold. At the south end of Duke synclinethe fold axis orienta- holes MDH-X 107 andMDH-8108, however, did not intersect tion changes dramatically to a trend of 290" and a plunge of a recognizable sandstone horizon even though they are inter- 15". 476 In the extreme northwest comer of the map sheet Duke Kelker, D. and Langenber;:, C.W. (1982): A Mathematical thrust fault displaces Minnes strataover the Cadomin Forma- Model for Orientation Data from Macroscopic Conical tion in Quintette syncline. Thewestern limb ofthe syncline is Folds, Mathematical #Geology, Volume 14, Number 4, vertical to slightly overturned. Along strike to the southeast pages 289-307 the fault cannot be traced by outcrop data, due to the over- Kilby, W.E. (1978): The :Structure and !Stratigraphy of the burden Kinuseo Creek valley. Drill-hole information indi- in Coal-bearing and Adjacent Strata Near Mountain Park, cates continuity of the thrust to the southeast. where it is Alberta,Unpublished M.Sc. Thesis, University of indicated by the positions of Dunvegan outcrops. Alberla ECONOMIC GEOLOGY Kilby, W.B. and Wnghtson, C.B. (1987): Bullmoose Map- ping and Compilation Project (93P/3,4),B.C. Minrstry Major economic interest in the area is in the Monkman of Energy, Mines and Petroleum Resources, Geolopical coal deposit which contains large reserves of metallurgical Fieldwork, 1986, Paper 1987-1, pages 373-378. coal. The deposithas reached an advanced stage of explora- tion and engineering planningand has received Stage I1 Kilby, W.E. and Johnston, S.T. (1988): Kinuseo Mapping approval from the provincial government. Further develop- and Compilation Projcct (931114, IS: 93P/3), B.C. Min- ment awaits tightening in the slack world coal markets. istry of Energ): Miner and Petroleum Resourcrs, This Gas from Mississippian to Jurassic sediments is exploited Volume to the east and north of the study area. Langenberg,C.W. (1985): TheGeomctry of Folded and Thrusted Rocks in the Rocky Mountain Foothills near AKNOWLEDGMENTS GrandeCache, Albe:rta, Canadian Journal of Earth The author would like to aknowledge field and office Sciences, Volume 12.. Number 11, pages 1711-1719. assistanceprovided by David Thomas. Cal Data Ltd. Stott, D.F. (1968): Lower Cretaceous Bullhead and Fort St. provided the Geological Analysis Package on loan. Petro- John Groups betweerl Smoky and P(:ace Rivers, Rocky Canada lnc. provided a computer tape containing surveyed Mountain Foothills, Alberta and British Colurrbia, drill-holelocations and drill-hole deviation data for coal Geological Survey of Canada, Bulletin 152,279 pi.ges. exploration holes drilled in the Duke and Honeymoon pit areas. In addition Petro-Canada provided topographic base ~ (1973):Lower Cretaceous Bullhead Group maps at scales of 1 :5000 and 1 : I0 000. Between Bullmoose Mountain and Tetsa Rivet; Rocky Mountain Foothills, Northeastern British Colun,bia, REFERENCES GeologicalSurvey of Canada, Bulle.tin 219,228 pages. Carmichael, S.M.M. (1983): Sedimentology of the Lower "--(1982):LowerCretaceousFortSt. JohnGmupand Cretaceous Gatesand Moosebdr Formations, Northeast Upper Cretaceous DmveganFormation of the Foo~hiils Coalfields,British Columbia, Unpublished Ph.D. and Plains of Alber::a, British Columbia, District of Thesis, The University LfBrirish Columbia, 285 pages. MacKenrie and Yukon Territory. Geological Surwy of Canada, Bulletin 323, 124 pages. Charlesworth, H.A.K., Langenberg, C.W.and Ramsden, J. (1976): Determining Axes, Axial Planes and Sections Wrightson, C.B. (1978): Structural Geology and Stratigra- of Macroscopic Folds using Computer-based Methods, phy of Campbell Flats Anticlinonum, Grande Cache, CanadiunJournal of EarrhSciences, Volume 13, Alberta,Unpublished M.Sc. Thesis, Univerui'y of Number 13, pages 54-65 Alberta.

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