Conadian MineralogistYol. ?-6, pp. 343-353 (1988)

ABSTRACT

Lignite and bituminous coal were sampled,predominantly from drillholes, in the Moose River Basin(northern Ontario) and Monkman (North East Coal Block'British Columbia), respectively. Quartz, kaolinite, and sub-sidiary mixed-layer clays, siderite, gypsum, pyrite, gibb-site and illite are present in the Moose River Basin lignites.The Monkman coals contain a more drverse assemblage:quartz, kaolinite, ankerite, illite, calcite, siderite, pyrite'plagioclase feldspar, mica, galena and barite. The detritalminerals, i.e., qtartz, feldspar and certain cliays, occurpredominantly in mineral-rich partings, durain and, to alesser extent, finely distributed throughout the vitrinitemacerals. The early authigenic minerals, i.e., kaolinite,some illite, pyrite, quartz, and certain carbonates, are com-monly associated with fusinite. The distribution of lat+stageauthigenic or "cleat" minerals, such as ankerite or pyrite,bears no relationship to maceral or litlotype content ofthecoal. Many of the common minerals have a variety of modesof occurrence. For example, pyrite in the Moose River Basinreplaced organic structures' infilled pore spaces, coatedorganic surfaces, and infilled later stage cracks. The his-tory of mineral formationinthe coals is mmplo<and seernsto be controlled primarily by source-rock litiology' degreeof weathering, nature of the coal-forming envhonment,hydrology, conditions ofburial, and degree of coalilication.

Keywords: Lower Cretaceous, lignite, bituminous coal'detrital minerals, autligenic minerals, Ontario, BritishColumbia.

SolvffviArRE

Des s6quences de lipuite et de charbon bitumineux ont€t€ dchantillonn€es, principalement d partir de forages' dansle bassin de la rivibre Moose (nord de l'Ontario), ainsi qu'iMonkman (terrain houiller du Nord-Est, Colombie-Britannique). Quartz, kaolinite et argiles interstratifi€esaccessoires, sid6rite, emse, pyrite, gibbsite et illite sontpr6sents dans les lignites du bassin de la rividre Moose. Lescharbons de Monkman contiennent un assemblage plus

diversifi6: quartz, kaolinite, ank6rite, illite, calcite' sid6-rite, pyrite, pla€roclase, mica, galbne et baryte. Les min6-

raux d6tritiques, c'est-i-dire quartz, feldspath et certainesargiles, sont localisds suf,out le long de plans de s6para-tion et dans le durain; i un degr€ moindre, ils sont fine-

MINERALOGY OF LOWER CRETACEOUS COALS FROM THEMOOSE RIVER BASIN, ONTARIO. AND MONKMAN, BRITISH COLUMBIA

EILEEN VAN DER FLIER.KELLERDepailment of Geogrophl, (lniversity of Victoria, P.O. Box 1700, Victoria, British Columbia V8W 2Y2

WILLIAM S. FYFEDeportment of Ceologt, University of Western Ontario, London, Ontorio N6A 587

ment dispers6 parmi les macdraux de la vitrinite. Les mine-raux authigeniques pr6coces (kaolinite, une partie de I'illite,pyrite, quartz et certains caxbonates) sont courammtnt asso-ci* e U tuslnlte. La disribution des mindraux authigdniqueset de ceux qui ddfinissent le clivage' tels que fank6rite etla pyrite, ne d€pend pas du contenu de mac6raux et deslitholype$ du charbon. Certains min6raux communs ontptusieurs origines. Par exemple, dans le bassin de la rivibreMoose, la pyrite a remplac6 des structures organiques' rem-pli les pores, recouvert la surface de mat6riaux organiques'et rempli des fissures d'origine tardive. La formation desmindraux dans les charbons est complexe, et semble €1rer6gie par la lithologie des roches h6tes, l'intensi$ du les-sivage, le milieu de formation du charbon, l'hydrologie dumilizu, la profondeur de l'enfouissement, et le degr6 de car-bonisation.

(Traduit par la R&action)

Mots-cl6s: Cr6tac6 inf6rieur, lignite, charbon bitumineux,mindraux d6tritiques, min6raux authig&nes, Ontario,Colombie-Britannique.

INTRODUCTION

Coal, although primarily organic in composition,contains a sienificant quantity of inorganic mattertlat may be present as minerals and trace elements.The minerals most commonly found in coals axe clayminerals, qvartz, carbonates (such as calcite, ankeriteand siderite), sulfides (including pyrite and marca-site) and, to a lesser extent, phosphates, silicates(such as feldspars), sulfates and salts (Mackowsky1982, Gluskoter lnT.In' addition, a rapidly increas-ing number of accessory minerals has recently beenidentified in coal; for example, Finkelman (1980)

listed over 125 minerals, which include a wide vari-ety of silicates, sulfides, carbonates, oxides and rare-earth-bearing minerals. Some of the common andaccessory ph€rses present problems in the utilizationof coal. Many of these problems may be addressedby understanding the associations, modes of occur-rence and origins of minerals in coal.

Studies of the mineral matter in Canadian coals(Williams & Ross 1979, Goodara et al. 1985)haYeconcentrated on specific aspects of coal mineralogy

343

344 THE CANADIAN MINERALOGIST

and are generally restricted to identification of themineral phases. In this study, we examine theminerals present in Cretaceous coals from the MooseRiver Basin in northern Ontario and the peace RiverBasin in northeastern British Columbia, their modeof occurrenoe, and history of formation. The major-and trace-element chemistry of these coals has biendiscussed by Van der Flier-Keller & Fyfe (1937).

The generally accepted classification of mineralsin coal differentiates between authigenic and detri-tal phases. On the basis of timing of mineral forma-tion, authigenic phases can be further subdivided@avis et al. 1984) into minerals formed duringsedimentation of the peat, after deposition or b!diagenetic alteration of pre-existing minerals, andepigenetically such as cleat infills.

Minerals formed in each of these groups may bedistinguished using characteristics related to condi-tions and timing of formation. These include: natureof associated minerals and macerals, mode of occur-rence of the mineral, its geochemistry, texturalcharacteristics such as rounding and crystal form,and 'paragenetic' associations. For example, thedetrital minerals, which are generally rounded tosubangular, occur either associated in mineral-richbands with intermixed macerals, which in some casesare broken and rounded, or isolated within thegrganic matter. Syngenetic authigenic minerals,fo119d at an early stage in the coalification process,exhibit crystal faces, are intimately intergrown withother syngenetic minerals, and generally occur in cellcavities (lumens) within the organic material.Epigenetic minerals occur in distinct fractures, cleats,or on slickenside surfaces in the coal. These mineralsmayexhibit crystal faces, and their occurrence gener_ally bears no relationship to the inherent structurein the coal.

Locanox AND GENERAT- Gpor,ocyThe Moose River Basin deposit is located in the

James Bay Lowlands, Cochrane District, of north-ern Ontario between 5lo and 5lo 30,N and 82o and83o W (Frg. l). The basin is fault-bounded to thesouth and consists of a gently dipping succession ofstrata ranging from Devonian to Cretaceous in age.The coal-bearing succession is Middle to Late Albianin age (Norris 1982) and consists of largely uncon-solidated kaolinitic gravels and sands, silt, clay andlignite, deposited in alluvial channel and floodplainsettings respectively (lry et al. 1984). The successionis thickest in the northeast and southeast of the basin,where accumulation occurred in structural lows adja-cent to Precambrian highs.

The Monkman coal deposit is located toward.thesouth of the Peace River or North East Coal Block,in northeastern British Colnmbia (Fig. l). The areais structurally complex, and the coal-bearing Gates

Formation is folded and thrust-faulted. This forma-tion is ofearlyAlbian age (Stott 1982) and consislsof 270 meters of cyclically interbedded bituminouscoal, claystone, siltstone, sandstone and lesser con-glomerate. The coal is generally underlain and over-lain by carbonaceous claystone, with coarser clas-tics occurring towards the base of each cycle. Up to12 seams are present, and are thickest and mostextensive at the base of the section, and thinner andmore nufirerous toward the top. The sediments weredeposited in floodplain or interdistributary, andchannel settings, in an alluvial or upper-delta plainenvironment (Carmichael 1983, Van der Flier 1985).

Field and laboratory methods

Analyses were carried out on 79 coal and sedimenrsamples from the Moose River Basin. The samoleswere derived predominantly from two drillholes'andthe recently exposed channel banks of the AdamCreek dam outflow, located in the southeast of thebasin. Additional samples were collected from theOnakawana test-pit site in the northeast of the basin.In the Monkman €uea, 40 coal and sediment sam-ples taken from seven drillholes located in the mostnortherly proposed pit site (the Honeymoon pit) wereanalyzed. In both areas all the coal seams were exten-sively sampled, and sediments were collectedthroughout the sequences. The samples were trans-ported to the laboratory in sealed plastic bags.

Whole-sample mineralogy was determined usinga philips Norelco or Rigaku X-ray diffractometer.Samples were air-dried and crushed using a mortarand pestle, and subsequently analyzed as dry cavity-mounts. Qualitative mineral abundances were deter-mined from the X-ray spectra. In order to determinethe location of the minerals in the coal and theirassociation with the organic components, reflected-light microscopy and scanning electron microscopy(SEM) coupled with energy-dispersion X-ray analy-sis @DX) were used. An ISI DS-130 SEM, run ar30 kV and 25 mm working distance, utilized the widerange of magnifications available. The EDX analyzer@GT system III), which is capable of detecting allelements with an atomic number of ll and greaterat concentrations above l0 ppm, was used primar-ily to list component elements in mineral grains.Relative peak-heights were used to estimate the rela-tive amounts of the elements present, thus allowingminefal erains to be identified. The results were sub-stantiated in a number of test cases by opticalmicroscopy or microprobe analysis. In addition toanalyzing isolated grains or locations, element win-dows were run over larger areas to establish relativedistributions of various elements. In this way ele-meuts associated with and homogenously distributed'in the organic matter were identified.

SEM samples were prepared from thin sections,grain mounts, polished blocks, and broken sample

345LOWER CRETACEOUS COALS

GRANDRAPIDSHIGH

(. ('\)!

..*MONKIUAN -

i i (

li,

Frc. l. Location and general geology of the Moose River Basin and Monkman coal deposits (maps modified from Van

der Flier 1985, and Schiller el al. 1983, respectively).

/ i.2 i

ADAMCREEK

MOOSE RIVER BASIN

Fault ContaclUnconformable Contact

a

( /

/oevonnu

U/ ,r.""', E l

t

PRECAMBRIAN

NN\{PDJ-.9{2 \

D80.04

:.{

^* ^ Thrust, showlng- direction of diP

*+--i-- Antlcllne, Syncllne

o ilD0lt-05 Drlll Hole Slte

iiilliiii*$.ift Gates FormatlonEXpOSUTS

DOKKEN Proposed Pit Areas

346 TI{E CANADIAN MINERALOGIST

Quartz

Kaoll nlte

Il I l te

iltca

l'llxed-layer clay

Pyrlte

5'lderlte

qtpsun

Gibbslte

TAELE 1. ABUIIDANCE AND MODE OF OCCURREI{CE OF !.III{ERALSIII'II1E }MOSE RIVER BASIII LIGIIITE

fragments. These were fixed to aluminum-stud sam-ple holders using silver paint, and gold- or carbon-coated prior to analysis. Surface analyses of 2lie-nite and 4 bituminous coal samples were nrn usingX-ray photoelectron spectroscopy (ESCA).

RrsurmThe results of XRD analysis of the Moose River

Basin and Monkman coal samples are summarizedin Tables I and,2, respectively.

Moose River Basin

The Moose River Basin lignitc are generally clean;isolated samples show no traces of mineral matter.Approximately 8090 of the samples contain quartzand kaolinite as major or trace components scatteredthroughout the organic fraction. Quantities varydepending on the detrital input (proximity to a majorchannel with splays), and the amount of shemicalprecipitation. The lignites can be differentiated fromadjacent sediments in that the accessory clays are res-tricted to trace amounts of mixed-layer clays withno (or trace) illite. Kaolinite varies from absent toa major component and occrus in the clastic horizonsin the lignite as well as associated with the organicmaterial. Gypsum and pyrite occur in less than halfof the samples analyzed. High values of the Al:Siratio, on the order of 8:1, were determined by ESCAin some lignite samples, indicating the possiblepresence of gibbsite. There is no definite relation-ship between stratigraphic level of the samples andtheir mineral content.

Quartz and kaolinite are the major constituentsin the majority of the associated sediment samples.Trace amounts of illite and some undifferentiatedmixedJayer clays are also present. Trace ocqurencesof K-feldspar, hematite, gypsum, dolomite, ilmenite,calcite and galena were recorded in 50% of the sam-ples. Siderite, pyrite and goethite were observed asmajor components in 890 of the samples. Milleritewas detected in one sample, AC-10-82. The iron sul-fide in isolated samples is in the form of marcasite,and g5psum is commonly associated with both mar-casite and pyrite. Traces of gibbsite were detectedby XRD in only one sample (AC-18-82).

Monkman

In the Monkman coal samples, quartz, kaoliniteand ankerite are the most common and most abun-dant minerals. Illite, calcite, siderite, pyrite andplagioclase feldspar are also common and occur astrace constituents in 70t/o to 25a/o of the samples.Mica was detected in only one sample, 1296, as atrace constituent. Other minerals identified in thecoals are galena (trace constituent in approximately1090 of the samples) and barite (trace constituent in

&ggestedAbundance !{ode(s) of 0ccumence

P - liD dett ltalinfi l l lng cell ho1lors

P - ND detrltalauthlgentc (syngenetic)

T - llD detrttal

N0 (r)

T - N D

T . I { D

ND (T)

r{D (T)

xD (r)

detrltal

detrltal

in f l l l l ng ce l l ho l lo rsreplaclng cell rallslnfl l l lng cracls

recent ,eatherlng ofpyrlte

auth igen lc , coa t ingquartz grain surface

,P : l'laJor _conponent, T : -Trqce cmponent, ND : Not detected,O : Ir| lneral present at thls level of abundance ln only one

saBple.

TABLE 2. ABUNDII.ICE AIID !IODE(S) OF OCq'IRNENCE OF MIiIERAI.SI[ fiE MoNK{At'l CoAt_

SuggestedAbundance !lode(s) of kcurrence

P - T ( x D ) d e t r l t a lQuartz

Knol lnite

Il 1 ite

Mlca

Mlxed-layer c'lay

Pyrlte

Siderite

Ankedte

Calc l te

Feldspar

Ga I ena

Barite

Sphalerlte

lnfi l l lng cell hollors

lnfi l l ing ce'l l hollorsauthl genl c,/assocl ated

rlth lnertodetrlnlte

detrltalinfi l l lng cell hollors

detrital?

franboidscoalesclng euhedral

crystalsln f l l l l ng ce l l ho l lo lsin f l l l l ng n lc rcscop lc

shrinkage cracks lnmacerals

infl l l lng cell holl0!|sc lea t ln f l l l l ngs

lnfi l l lng cell hollors

detrital

assoclated with pyrlte

lnfi l l in9 cell hollorsassociated rith calclte

and pho'sphorusauthlgenlc crystals ln

coal and associatedsedlments

T . I I D

T - N D

ND (T)

T - I { D

I - I { D

T - I { D

T - N D

r - t { 0

I - I { D

I . I I D

T . l I D

r{0 {T)

Synbols: As ln Table 1.

LOWER CRETACEOUS COALfi 347

approximately 2090 of the samples). In the clay-richhorizons in the Monkman coals, zircon also is found.A relationship between stratigraphic level andmineral distribution is exhibited only by pyrite andsiderite. In certain drillholes (e.g., MDD 80.0l) side-rite occurs only in the upper seams @3 and B5),

whereas pyrite is restricted to the lowest seam (Bl).In the sediments associated with the Monkman

coals, quartz is present in most samples as a majorconstituent. Illite is a common minor to trace phase.Two types have been identified, namely mica and aless-well-ordered illite phase. The illite, which occurs

Frc. 2. A. SEM micrograph of a detrital quartz grain in Moose River Basin lignite (scale bar zl0 pm). B. Photomicro-graph of quartz (grey) infill of cell porosity in fusinite, Moose River Basin (scale bar 2.0 mm). C. SEM micrographshowing total replacement of organic matter by plirite, Moose River Basin lignite (scale bar 40 pm). D. SEM micro-graph showing a pyrite crystal that fills a cell lumen, Moose River Basin lignite (scale bar 20 pm). E. SEM micro-graph showing pyrite infill of a crack, Moose River Basin lignite (scale bar 40 pm). F, SEM micrograph showingillite (ight exey) and pynte Origh0 infi[ing of cell lumens in fusinite, Monkman (scale bar N pm). Figures 2C,D and E from Brown et al. (1986).

348 THE CANADIAN MINERALOGIST

Ftc. 3. A. SEM micrograph of a kaolinite-rich mineral band in vitrinite, Monkman (scale bar 80 pm). B. Photomicro-graph showing single and coalesced euhedral pyrite crystals in fusinite, Monkman (scale bar 0.5 mm). C. SEM micro-graph of fusinite showing ankerite (grey) and pyrite (bright) infilling of cell lumens, Monkman (scale bar 40 pm).D. SEM micrograph showing epigenetic ankerite as crack filling, Monkman (scale bar 80 pm).

in most samples, is likely the lMd variety, which isthe most common illite polymorph (Levinson 1955,Velde & Hower 1963). The mica was found inapproximately 25a/o of the sediment samples as aminsl s1 trace constituent, Kaolinite ranges from atrace constituent to absent in some samples. Mixed-layer clays were detected by XRD as a trace compo-nent in approximately 6290 of the samples. Ankerite,siderite, pyrite, calcite, plagioclase feldspar andgalena occur either as major constituents (e.g.,ankerite in 33-6) or as minor components in up to9090 of the samples.

MoDES oF OccURRENcE AND ORIGIN oFMnERALS rN TI{E CoAL

Summaries of the lmineral occurrences in theMoose River Basin and Monkrnan coals, as deter-mined usingSEM-EDX and optical microscopy, aregiven in Tables I and 2, respectively.

Moose River Basin

Several different modes of occurrence were notedfor all of the common minerals. For example, in theMoose River Basin lignites, quartz occurspredominantly as detrital grains (Fig. 2A), but in anisolated sample of laminated fusinitic coal and sand-stone (AC-12-82), cell infillings of quartz wereobserved (Fig. 2B). The detrital quartz is commonlyassociated with clay minerals (kaolinite and mica),normally in mineral-rich bands in the coal, but theseminerals are also found isolated in the organicmaterial.

Mica generally occurs associated with the detritalquaxtz, whereas the illite and kaolinite may be poorlyformed and more commonly are intimatelyassociated with the organic material. Kaolinite, whichis the most cotnmon clay mineral in the Moose RiverBasin lignites, occurs associated with detrital quartzin clastic horizons and is also associated with theorganic matter.

LowEl cRErAcEous coAls 349

In the pyrite-rich lignite or wood samples, pyritemay replace the whole wood structure (Fig. 2C), infillthe pore spaces (Fig. 2D), or occur as crystal coat-ings on organic surfaces or in cracks (Fig. 2E). Sul-fides are also present as nodules, e.g., in AC-10-82.Gypsum and pyrite are commonly associated,indicating oxidation of the pyrite.

Monkman

Minerals in the Monkman coal have a wide rangeof occurrences. Quartz is present both as detritalrounded grains in the mineral-rich areas and as cellfillings. Similar modes of occurrence are noted forthe clay minerals. Figure 2F shows authigenic illiteas a cell filling, and Figure 3A provides an exampleof kaolinite associated with inertodetrinite. The mostcommon modes of occrurence of pyrite are ascoalescing euhedral crystals @ig. 3B) and as fram-boids. These are both commonly associated with theinertinite macerals and coaly claystones; however,crystals (in the same sample) are larger whenassociated with organic matter. Pyrite, precipitatedin cell lumens (Ftg. 3C) and microfissures caused byshrinkage in the macerals, was also observed. Thecarbonates inlill fusinite cell lumens (Fig. 3C) anddiagenetic cracks (Fig. 3D).

MacSRAL-MTNSRAL AssocrATroNS

Moose River Bqsin

In the Moose River Basin the soily Iignite containsthe majority of the mineral matter. The associatedorganic material is commonly comminuted, whichindicates the important influence of flowing wateron its formation. The woody (xylite) and fusinitic(fusain) materials are generally very clean but con-tain isolated detrital quartz grains and clay minssals.Cell walls are in rare cases altered to pyrite, andpyrite also occasionally infills cell lumens.

Monkmon

In the Monkman coals, apart from the mineral-rich bands and lenses that are occasionally associatedwith the coal, fusinite contains 11e highest propor-tion of minelzl matter. Partings in the clean coalsalso contain a sigpificant amount of mineral mat-terl however, these bands are relatively uncommon.Vitrinite contains few mineral particles and they arein general detrital as opposed to the authigenic typefound in fusinite.

Minerals found in the fusinites occur mostly asinfillings of cell hollows. Illite, quartz and pyrite arethe most common, whereas ankerite and kaoliniteare less cornmon. Sphalerite was found in 514-1(sandy coal) as infillings of some cell lumens,associated with a phosphorus-rich phase and calcite.In S2-5 (sandy coal) galena is associated with pyrite,

where it occurs as overgrowths on illite cell fills andin the maceral in general. Illite and silica, and cal-cite to a lesser extent, are the primary authigenicminerals that infill the cell hollows in most of thefusinites examined; pyrite is observed as overgrowthson these phases (e.9., Fie. 3C).

Vitrinite is clean compared to fusinite and containsrare isolated mineral grains scattered throughout themaceral. Occasional concentration of the mineralsin bands parallel to the bedding of the coal, forexample in S1-4 (Fie. 3A), may indicate depositionof a greater concentration of minerals at that time,or the breakup and compression of a band of vitrinite(precursor), concentrating the small amounts ofauthigenic and detrital mineral matter present. Theminerals occasionally appear to be broken pore-fillings, as tleir shapes match those found in crushedfusinite grains. These bands were not observed to becontinuous. Minerals found in the vitrinite aredominantly kaolinite and silica; however, occasionalpyrite, illite, feldspar, and mica grains were alsoobserved. The minerals are typically smaller than inthe fusinites and are rounded to irregular in shape.Minerals present in the vitrinite, therefore, proba-bly include both detrital and authigenic phases.

Compared to the abundant authigenic and detri-tal mineral matter in the macerals of the Monkmancoals, the Moose River Basin lignite is very clean.In particular, very little authigenic mineral matter(with the exception of pyrite and some kaolinite, andquartz and calcite in AC-12-82) was observed inti-mately associated with the lie;nite. Thus the porosityin the lignites is high and the pores largely unfilled,compared to the Monkman coals.

MoDEs aro fiulNc or Mntrnql FoRMATIoN

Figures 4 and 5 classify and illustrate the proposedrelative timing of mineral formation in the MooseRiver Basin and Monkman coals (and associatedsediments).

Moose River Basin

The detrital minerals introduced into the basininclude quartz, K-feldspar, muscovite, and a num-ber of heary minerals (Hamblin 1982). Carbonatefragments are cornmon where bedrock was exposedabove the level of the basin. Feldspar in the gravelsis partly altered to kaolinite, which is also commonas poorly formed crystals in the lienite. The occur-rence of some kaolinite associated with quartzin clas-tic horizons in the lignite may indicate a detrital ori-gin for this material; however, the kaolinite is morelikely to have formed in situby alteration of detri-tal feldspar. Other syngenetic minerals include illite(which may have formed through the alteration ofdetrital muscovite), gibbsite, siderite, pyrite andgeothite. Siderite occurs predominantly as nodules

350 THE CANADIAN MINERALOGIST

Ftc. 4. Mineral genesis in the Moose River Basin,Mattagami Formation.

associated with an inertodetrinite maceral. Illiteformed at an early stage (syngenetic) in the coals,infilling cell lumens. In a number of samples the illitein the macerals is overgrown by pyrite. In other sam-ples, where the relationship with illite is not observed,pyrite nodules associated with the organic materialare oriented parallel to the bedding planes, whichindicates either an early syngenetic origin or preferen-tial flow of groundwater along these horizons. Thecarbonates generally represent the latest stage ofmineralization in the Monkman samples; however,as in the case of pyrite, carbonate minerals may haveformed syngenetically, i.e., infilling cell pores, inaddition to overgrowing the matrix and cryst4lliz-ing in late-stage cracks and on slickenside surfaces.Ankerite is the most common carbonate phase.

MAIN FA TORS DETERMININC OCCURRENCE ANDFonuartoN oF MINERALS, AND

Mnrr,nar-MacsRAr. REr.anroNsHrps

The accumulation of plant material and its matu-ration to form coal involves a continually changingset of geochemical and physical conditions. Thechanging conditions strongly influence the nature ofthe inorganic matter associated with the coal and inmany cases result in mineral suites that reflect con-ditions at various stages in the accumulation andcoalifi cation processes.

Certain factors dominate mineral genesis duringthe main stages of coal formation (Fig. O. The detri-tal minerals in coal are controlled by the lithologi-cal nature of the $ource area, its climatic regime, andthe extent to which weathering has taken place. Thepredominantly granitic source area for the Mat-tagami Formation gave rise to detrital minerals suchas quartz, K-feldspar and mica, whereas the occur-rence of abundant lithic fragments and a larger rangeof detrital minerals in the Gates Formation resultedfrom sedimentary, igneous, and metamorphic sourcerocks. In addition, the abundance of quartz andkaolinite, and the appearance of gibbsite in theMoose River Basin lignite indicate a highly weatheredenvironment, whereas a less weathered setting isimplied by the preservation of a greater range ofdetrital and syngenetic minerals in the Monkmancoals.

Syngenetic minerals (authigenically formed dur-ing early stages of coalification) reflect the natureof the depositional environment (i.e., alluvial, del-taic, back-barrier or lacustrine), and its physical,hydrological and geochemical characteristics. Thesyngenetic minerals in both the Moose River Basinand Monkman coals reflect the freshwater alluvialor upper delta-plain depositional environments pro-posed for the deposits. Hence pyrite is less commonthan in marine-influenced coals, and the syngeneticclay minerals consist of kaolinite and illite rather than

DETR]TALAUTHICENIC

SYNCENETIC EPIOETEnC

Krollnltg

flGcorltorlllhe

Ptttlregalana

- Ptrno

Sphalorlto,aalcfio

Ankotto i- Ankstno.&rEdta....'.....-+llllts(tonimrlllonltol \ Kmflnhe

Ftc. 5. Mineral genesis in the Monkman samples, GatesFormation.

in the clay, whereas pyrite is more common in thegravels and coals. The relative timing of formationof the syngenetic minerals is difficult to establish,as many of the minerals are restricted to certain rypesof sediment. Kaolinite and illite may have formedsynchronously from degradation products of thefeldspar and muscovite, respectively, with the drierand more acidic conditions in the coals favoring thecrystallization of kaolinite, whereas both illite andkaolinite may have crystallized in the clays andcliaystones. Authigenic silica occurs in the cell lumensof a finely laminated fusinitic sandstone (AC-12-S2);however, this appears to be an isolated situation,with the silica possibly derived from pressure solu-tion of the quartz sand grains. The most importantdiagenetic mineral, pyrite, occurs most commonlyin crack fillings and as an alteration orpseudomorphof organic mafter. Gypsum is a product of the recentweathering of pyrite.

Monkman

In the Monkm2r samples, the dominant detritalminerals axe quartz, muscovite, zhcon, plagioclasefeldspar and some illite. Carbonates, kaolinite, illite,barite, some quartz, and the sulfides are consideredto be authigenic. The earliest syngenetic mineral toform in the coal may be kaolinite, as broken frag-ments of kaolinite cell fillings are intimately

LOWER CRETACEOUS COALS 351

illite, smectite, and lesser kaolinite. The latter groupwould be more typical of back-barrier or lower deltaplain coals (Ceal et al. 1981, Styan & Bustin 1983).In particular, the pH and EH of the peat are impor-tant controls on both minslzl and maceral contents(Cecrl et al. l98l). Although no strict relationshiphas been identified in coals between macerals andthe minerals which are associated with them @aviset sl. 1984), the natue of the original organic mat-ter (plant type) and subsequent conditions ofmaceralformation are known to give rise to c€rtain minssalgand mineral-maceral associations in some coals(Finkelman 1980, Cecil el al. 1981, Chandra & Tay-lor 1982). The strong association in the Monkmancoal between fusinite and early-formed authigenicminerals may be due either to the higher porosity offusinite [5-50 nm compared with 2-20 nm in vitrinite(Harris et al. l98l)l or to the oxidizing conditionsrequired for its formation (or both).

Diagenetic minerals (formed in cleats and crackfills) are controlled by factors such as the composi-tion and flow rates ofgroundwater, temperature andpresure of burial, permability, and time. In the caseof the Moose River Basin sequence, proximity to sur-face during ice retreat must have caused a majorcold-leaching or accelerated weathering event (aprocess that would be accelerated by release ofrebound stress), which resulted in a relatively cleancoal with few authigenic (both syngenetic andepigenetic) minerals.

The main mineralogical differences between thetwo coals are mineral diversity, nature of the clayminerals, and proportions of detrital yer,sas authi-genic phases. The Monkman coals contain a morediverse mineral assemblage than the lignites. Thewider range of detrital minerals is related to grcaterdiversity of source rocks, and also to tle degree ofweathering in both tlte source area and basin of depo-sition. The presence of gibbsite, with quartz andkaolinite as the major mineral phases in the MooseRiver Basin lignite, indicates an intensely weatheredsituation, whereas the survival of plagioclase feld-

spar, for example, in the Monkman coals shows thatin this area weathering was less intense.

The most abundant clay mineral in the MooseRiver Basin is kaolinite. In the Monkman coal bothillite and kaolinite are coulmon. This may be relatedto the extent of weathering, soluce materials (e.g.,the greater abundance of detrital mica in the Monk-man sediments) and/or differences in wetness andacidity in the coal-forming environment (related toproximity to channels, precursor vegetation types,hydrology, e/c.).

The relative lack of autligenic (e.g., pore fillingand epigenetic) minerals in the Moose River Basinlignite compared with the Monkman coal may beexplained by a) the intense leaching event caused byice retreat which affected the Moose Nver Basin lig-nite, and b) the higher rank of the Monkman coal(which in turn is related to overburdenthickness dur-ing coalification, and structural setting). In particu-lar, the occurrence of minerals infiling cleats in theMonkman coal may be related to the abundance ofthese structures in higher rank coals compared withthe lower rank lignites.

CONCLUSION

The minerals present in the Moose River Basin lig-nites are limited to quartz, kaolinite, and lessermixed-layer clays, siderite, illite, gypsum, pyrite andgibbsite. The Monkman soals contain amore diverseassemblage which includes quartz, kaolinite,ankerite, illite, calcite, siderite, pyrite, plagioclasefeldspar, mica, galena and barite.

The highest proportions of mineral matter axe con-tained in rock partings and in the durain and fusainlithotypes. The majority of the detrital minerals islocated in the former, and the early authigenicminslals occur associated with fusinite and otherinertinile macerals. The distribution of cleat mineralsexhibits little relationship to maceral or lithotlpe con-tent.

Quartz and the clay mine131g are the dominant

@llcttr""t" 1lffillof weathedng I

lD"e""lrl""rl IlEnrlronmont I

SYNGENETIC

.alluvlal

. deltalc

. back banler

. lacustrlne1"r"",*, Ilr''. Ilt"-""blllr-l

DETRITAL EPIGENETIC

Frc. 6. Factors which influence the mineral matter of coals.

3s2 THE CANADIAN MINERALOGIST

detrital minerals in both deposits. Authigenickaolinite and illite also occur. Other common authi-genic minerals are pyrite and the carbonates, formedboth at early and later stages in the coalificationprocess. In both deposits, many of the commonminerals have a variety of modes of occurrence,indicating that these minerals may have formed orbeen incorporated into the coal at several stages dur-ing the history of coal formation.

The sequence of mineral formation in both coaldeposits is therefore complex; differences in mineralcontent and characteristics are related primarily tosource lithologies, degree of weathering, nature ofthe coal-forming environment, and postdepositionaleffects such as conditions ofburial, degree ofcoalifi-cation, and groundwater-flow characteristics.

The environmental impact of coal burning isassociated with the occurrence and habit of certainminerals and trace elements. The minerals which areof most importance are the sulfides. The MooseRiver Basin lignite is low in both ash and S, andmuch of the pyrite is present in habits which are read-ily removed during washing. Finer grained pyrite andcrystals intimately associated with the organic mat-ter, for example pore fillings, are more difficult toremove. Similarly, pore-filling pyrite in the Monk-man coal is difficult to remove by conventional clean-ing techniques, but the framboids, crack infills, andother coarse pyrite phases can be cleaned readily.

AcKNowLEDCEMENTS

We thank PetroCanada and Lignasco Resourcesfor access to drill core, and Mike Powell forassistance v/ith the SEM. The original manuscriptwas improved by two anonymous reviewers. Thestudy was funded in part by an Ontario CeologicalSurvey Grant to W.S. Fyfe.

REFERENcES

BnowN, J.R., Fvnn W.S., Knolnenc, B.I., LoNc,D.G.F., Munnav, F.H., Pownrr, M., Tnv, C.F.,VeN opn Flren, E. & Wrxorn, C.G. (1986):Geochemistry and petrography of the MattagamiFormation fgnites (Northern Ontario). Ont. Geol.Sum. Open File Rep.5617. Ont. Geoscience Res.Grant Prog., Grant No. lM.

CannrcHarr, S.M.M. (1983\ Sedimentology of theLower Cretaceow Gats and Moosebar Formations,Noftheast British Columbia. Ph.D. thesis, Univ.British Columbia, Vancouver, 8.C..

Cecr, C.B., SraNroN, R.W., Dur.oNc, F.T. & RsN-roN, J.J. (1981): Geological factors that controlmineral matter in coal. In Proc. Amer. NuclearSoc./Amer. Chem. Soc. Conf. on Atomic andNuclear Methods in Fossil Energy Research, PuertoRico. Amer. Chem. Soc., Wash., D.C.

CUaNDRA, D. & Teylon, G.H. (1982): Gondwanacoals. Iz Stach's Textbook of Coal Petrology @.Stach, M.-Th. Mackowsky, M. Teichmuller, G.H.Taylor, D. Chandra & R. Teichmuller, eds.).Gebruder Borntraeger, Berlin, Stuttgart.

Devrs, A., Russrlr, S.J., fuurrlrn, S.M. & Yrarnl,J.D. (1984): Some genetic implications of silica andaluminosilicates in peat and coal. Int. J. Coql Geol,3,293-314.

FrtncrtueN, R.B. (1980): Modes of Occutence ofTrace Elements in Coal. Ph.D. thesis, Univ.Maryland, College Park, Md.

Grusxornn, H.J. (1977): An introduction to the occur-rence of mineral matter in coal. .tre Ash Deposits andCorrosion Due to Impurities in Combustion Gases(R.W. Bryers, ed.). Hemisphere Publ. Corp.,Washington, D.C..

Goooanzr, F., Foscoros, A.E. & CarrannoN, A.R.(1985): Mineral matter and elemental concentrationsin selected Western Canadian coals, Fuel 64.1599-1605.

HalrnLrN, A.P. (1982): Petrography of Mesozoic andPleistocene sands in the Moose River Basin. .[zMesozoic Geology of the Moose River Basin (P.G.Telford & H.M. Verma, eds.). Ont. Geol. Surv.,Study 2li Toronto, Ont.

Henms, L.A., CavrN, O.8., Cnousn, R.S. & Yusr,C.S. (1981): Scanning electron microscopical obser-vations and energy dispersive X-ray analysis ofsecondary mineralization in a bituminous coal.Microsc. Actu A, 343-349.

LrvrNsoN, A.A. (1955): Studies in the mica group:polymorphism among illites and hydrous micas.Amer. Mineral. N,4149.

Macrowsrv, M.-Tn. (1982): Minerals and trace ele-ments occurring tn coaJ. In Stach's Textbook of CoalPetrologl (E. Stach, M.-Th. Mackowsky, M. Teich-muller, G.H. Taylor, D. Chandra&R. Teichmuller,eds.). Getrruder Borntraeger, Berlin, Stuttgart.

Nonrus, G. (1982): Mesozoic palynology of the MooseRiver Basin. .Ia Mesozoic Geology and MineralPotential of the Moose River Basin (P.G. Telford& H.M. Verma, eds.). Ont. Geol. Surv., Study 21,Toronto, Ont.

Scmrlen, E.A., Sexrraco, S.P. & PrecuNen, W.A.(1983): Monkman coal property, British Columbia.Can. Inst. Mining Metall.76, 65-71.

Srorr, D.F. (1982): Lower Cretaceous Fort St. JohnGroup and Upper Cretaceous Dunvegan Formationof the foothills and plains of Alberta, British Colum-bia, District of Mackenzie and Yukon Territory.Geol. Sun. Can. Bull.3?8.

LOWER CRETACEOUS COALS 353

Srver, W.B. &BusrrN, R.M. (1983): Sedimentology ofFraser River delta peat deposits: a modern analoguefor some deltaic coals. Int. J. Coal Geol. 3, l0l-143.

Tnv, C.F., LoNc, D.G.F. & Wrworn, C.G. (1984):Sedimentology of the Lower Cretaceous MattagamiFormation, Moose River Basin, James BayLowlands, Ontario, Canada. In The Mesozoic ofMiddle North America (D.F. Stott & D.J. Glass,eds.). Can. Soc. Petroleum Geol. Mem.9,345-359.

VaN osn Furn, E. (1985): Geochmistry ond Sedimen-tologt of Two Cretaceous Coal lreposits in Conada.Ph.D. thesis, Univ. Western Ontario, London, Ont.

VaN oen Furn-Knnrn, E. & Frrn, W.S. (1987):Geochemistry of two Cretaceous coal-bearing

sequences: James Bay Lowlands, N. Ontario andPeace River Basin, N.E. British Columbia. Can. J.Earth Sci. A, rc38-1052,

Vnlnr, B. & Howen, J. (1963): Petrological sig-nificance of illite polymorphism in Paleozoicsedimentary r ocks. A me r. Minera l. 8, 1239 - l2S 4.

Wrruaus, V.E. & Ross, A.R. (1979): Depositional set-ting and coal petrology ofTulameen coalfield, south-central British Columbia. Amer. Assoc. PetroleumGeol. Bull. 63, 2058-2069.

Received April 2, 1987; revised manuscript acceptedJuly 2, 1987.