Overview of talc resources in the Altermark talc province, northern Norway, and possible uses of the talc ore

NGU-BULL436,20 00-PAGE93

Overview of talc resources in the Altermark talc province, northern Norway, and possible uses of the talc ore

TORARNEKARLS EN,EDVIN RIAN&ODLEIVOLESEN

Karlsen,TA, Rian,E.&Olesen,0.:2000:Overview of talcresourcesand reserves intheAltermarktalc province, northernNorwayandpossibleusesof thetalc ore.Norg es geolog iskeundersekelseBulletin,436,93-102.

Acti ve prospect ingduring thepast10 yearshasprovedthat theAltermark area contains muchmoretalc than previously recogni sed In theNakkan-Esjeklumpenarea,10Mtonnes or moreoftalc-carbon ateoreare probably present,dist rib uted in ultramafic bodies. The ore,which occursas one ofseverallayerswithin compositionallyzoned ultramafic lensesdominated by antigorit eserpentinites,hasthefollowing general mineralogy:talc(45-65 %l.

carbonate(30-50%),chlorite(0-4%)and magnetite(0-3%).Relati vetootherknown similardeposits,the oreisrather coarse-grained,and themineralstendto be idioblastic.Severalproducts canbemade fromthe talc-carbonateore.

By app lying flot ation or other kindsof mineralseparat iontechniques,itislikelythat high-qu alitytalc-con centrate could be madeinadditio ntotalc-carbonate mixtures.A concentr ate of by-pro ductbreunn eritewould possibly be of economicvalue.

TorArneKarisen,Geolo gicalSu rvey of Norway,N-7491Tron d heim,Nor way;EdvinRian,No rw egianTa lc AltermarkAS,N- 8616, Norway; Odleivotesen,^{GeologicalSurv ey}of Norwa y,N-7491 Trondheim,Norway.

Introduction

Economi ctalc¹mineralisat io n is norma llyassociate deit her with dol om ite or wit h ult ram afic rocks(i.e.'ultramafic' talc).

All known major occurrencesoftalc in Norw ay areof the ultram afictyp e, andareassociat edwit hserpent inisedophi- olitic ult ramafites,ult ramaficconglomerates or solitary ult ra- maficlenses.

Nor wegi anTalc AS, owned by Pluss Sta ufer AG,isthe maj or talccompany in Norway, and produces talcfromultra- mafic rocks inAltermark,Nordland county, northern Norway (Fig. 1).In theAlt erm ark area,theultram afi clensesare found to be parti cularly welltalcified, and the area isdescribed as a talc province.Due to a shortage of ore reserves inthe late 1980s,a prospecti ng campaign was carried outduring the foll owin g years(1989- 1995).Work started with drilling and investigat ion of the Stra umdalen talcdeposit (Holter 1990), and was followed up by a more intensive survey including airbo rne geophysics (Mogaard & Walker 1991, Karlsen &

Olesen 1991), regio nalmappin g,det ailed deposi t mapping, and comprehensive mineralogical studies (Karlsen 1995).

This campaign, which has been followed up by drilling, turned out to be successful,andseveral million s of tonsof talc-carb on ate rockswere detected,bot hwit hinand outsi de theexist ing talcmine.The Nakkandepositwas detected by airbornegeophysical exploration(Mogaard & Walker 1991, Karlsen & Olesen1991,1996), and istod aythemaj ortarget for future exploi tatio n.In the present paper, the general geologyand prospectsin the Altermark area arepresent ed.

1. Talc- bot h pure mineralogical talc andindustrialtalcwhich may containvariable amounts of magnesite,chloriteetc.

Geological settin g

TheAlterm ark area is situatedabout20 kmwest of Moi Rana, nort hern Norway (Fig.1).Therocks belong to the Rod inq sfj al- let Nap peComplex(Gustavson&Gje lle 1991)of the Upper- mostAllochth on (Roberts&Gee 1985)ofthe Caledonides.

The Rodinqsfjallet Nappe Complex and the overlying Helg eland NappeComplex arethetwo dominating nappe com plexes alo ng the Nordl and coast. These nappe com - plexescontai nnumerousultramafic lenses of somewhatdis- puted origin (Karlsen 1995).Immediat ely to the south of Helg eland, ophioliticultram afit e wit hassociated talcoccurs on the island of Leka in Nord-Tronde lag. North of Redey (Bang 1985),ophiolitecomplexesas such have notbeenrec- ognised,and the ultramafitesoccur assolit arylenses.Around thebasem ent windows Sjona,Hogt uva and Svartisen, soli- taryultramafic orult ramafic/maficlenses arewidespread,sit- uated predominantly within the RodinqsfjalletNappe Com- plex(Fig.1).

Tectonostratig raphy

Inthe investigated area, the RodinqsfjalletNappeComplex consistsofthree tectonic units: theTj orn rasta Nappe,the Straumbotn Nappe(Sovegj art o et al. 1988)and theSlet te fje l- let Unit (Fig. 2). The Tjorn rasta Nappe is dominat ed by quartz o-feld spath ic gneisses and quartz-rich mica schists while the Straumbotn Nappe comprises kyanite-staurol it e bearing garnet-mica schists,marblesand amphibolites.The tect onisedtransitionfromthe Tjornrasta Napp eto theover- lyin g Straumbot n Nappe is marked by occurrences of st rongly deformed graphitic schists, which outline the thrust zone of the 'St raum bot n Nappefloorthrust' (SNft).TheSlet-

NGU-BULL436,2000- PAGE94 TORARNE KARLSEN,EDVIN RIAN

s

ODLEIVOLESEN

Helgeland Napp eComplex

Helgeland NappeComplexsolethrust Rbd ingsfjbllet Nap pe Complex

Thrust planeabove Precambrianbasement Preca m brianbasement

Ultramaficlens

<

N

1

30 km

Fig.1.Tectonostratigraph icmap of western Helgeland and occurrences of ultra mafic rocks.Scale ofult ramaf ic rocksis exagge rat- edbyaround 100%.The investigated areais outlined.Compiledfrom Soveg jarto(1977), Jo hnsen(1983),Sovegja rto etal.(1988,1989) andGustavson&Gjelle(1991).

tefj elletUnit,whic h is sit uatedabovethe Straum bo t nNappe, isinte rp retedto be a structuralrepetit ion oftheTjornrasta Nappe,andcontains simi lar rocktypes(Karlsen1995).

Theultramafic rocks,whichcan be classifie dasso-called solitaryalpi ne-ty pe ultramafites (Quale&Stigh 1985),occur as lenses wit hin the StraumbotnNappe and are usually asso- ciated wit h theSNft(Fig. 2).ltispossibl e thatcertainrevisions will haveto be mad e to the standard tectonostratigraphyof the region.

The structu ral history of theareaiscomplex,andwill be describ ed in detail in a separate paper;only a sum maryis givenhere.Four deformation events havebeenrecognised, 0_1,O₂,0₃and 0₄(Karlsen 1995).Thefirst deformationevent, 0_1, created the well-develope d met amo rph ic foliation,51' which is the dominant micro-/mesoscop ic structure, and defined by mica,hornblende , kyanite,staurolite,graphite, epidoteand elongat ed aggregatesof quartzand feldspars.

0₁alsocreated micro scop ic to macroscopicF, folds, which are moderatel y inclined, andweakly plunging isocli nal folds wit h a strongly developed penetrativeaxialplane cleavage (51)'Most of the F₁fold axesparallel themainE-plun ging, L₁ stretching lineation .L_1a is a micro-/mesoscopic stretch ing lineation defined by strongly elongat ed aggregates of quartz and/or feldspars and by aparallel orienta tionofthe minerals kyanit e,stauro lit e and hornblend e.The L_1alineation gener- allyplunges atabout0-30°towardsEorESE.Llbisa meso-/

macroscopi c stre tc hing lin eati on definedbythelongestaxes of meso- and macroscaleboud insof serpentin it es andlocally amphibolitesplunging at around20-30°towardsE.Allof the interpreted nappe boundaries within the Rodinqsfjallet Nappe Complexareint erpr eted to beof early0₁age.

Deformation events post-dating the peak of metamor- phism are representedby O₂and 0₃,which createdrneso-to macrosco picscale folds thatdeform the 0₁structures.The Slette fj ellet fold, which isthedominant macroscopic struc- ture inthe area,isinter pre ted to be an overturned,tight,F₂ antifo rmwith an axial surface dipping at about 40°towards SE. The Slett efje llet fold changes trend when traced west- ward alongthe Sjona gneiss dome(interpret ed fromGustav- son&Gjelle 1991),probab ly as a result of the dome geometry of thePrecam brian window.

Decollernent thrustingisobservedalong the outermost part sof the ult ramafic rocks where the enveloping rocks havebeenint ensively foldedbyF₂/F₃and slidalong the bor- derofthe ultramafites.

Geoth ermobarometric investigationshaveindicated that all the rocks of the Rcdinqsfjallet Nappe Complex in the investigated area were metamorphosed at amphibo lit e facies at high -pr essure conditionsduring

°

^{1(Karlsen1995).}

Compositional zoning of the ultramafic lenses

The ult ramafic lenses are actuallyparts of compositemafic/

ultr amafic lenses,although themafic parts,now represented by amphi bolite,are notalways easyto recognise.The ultra- maficpart s of the lenses are mineralogicallyzoned,and three major zones occur(Fig.3):(1) Serpent initic core,(2) Talc-car- bonate zone,(3)Monomineral icrocksin the rim .The

setpen-

tinite con sists predominantly of interpenet rati ng text ured antigor it e and 5-20%magnetite.Especially ferrite-chromi te, but locally also relics of olivine and c1inopyroxene, are

TORARNEKARLSEN,EDVINRIAN&ODLEIVOLESEN NGU-BU LL436, 2000-PAGE95

---Cl-

S traumbotn Nappe floor thrust and equ ivalents

p:l' Axial tra ce of ov erturned F

²

antiform ( Slettefjellet fold)

% Axia l tra ce of overturned F

²

sy nfo rm

- 'it"' Axia l trac e of ove rturned F

¹

antiform

( Stra um botn fold)

40 ^{Fol iation}

A-I\ Cross sec tio n

~

Altermark tal c m ine Quartzo-feldspathic gneiss

r=~=~

Quartz-rich mi c a gne iss, ± garnet Carbonate-mica schist

1=~""--'="'"1

Ga rnet-m ica schist ± kyanite/staurolite Graphitic mic a schist

Marb les, calcitic/do lomitic Amphibo lite

Ultramafic rocks

Fig.2.Sim plifiedgeolo gicalmapof theinvestigat ed areawit h nam esof theultramaficlenses and localitiesofcross-sections.Abb revat ions:A

=

^Anna-

berg an ult ramafite,SE

=

St or eEsj eklu m pen,LE

=

LilleEsjeklum pen, R

=

Remlia.N

=

Nakkan (situated about 150m belowsurface).Napp es:Tj.Na

=

Tjern- rastaNappe,Tj.Na2=Tj er nrastaNapp einverted, Str.Na=St raum bo t n Napp e.Cross-secti ons areshown inFigs.4& 6.

present in subordinate amounts. Some of the ultra mafic cores carry lensesof prim aryc1inopyroxenite,dunite,chrom- itite and alsorodingite.Therodingite,whichprobably repre- sent metasomati sedmafic rocks,has been described only once previously in Norwegian ultramafites(B0e 1985)and consistsof theassemblage:epidote+amphibole+chlorite ± hydrogro ssular± serpentine. The talc-carbonate zone con- sists of about 40-70% talc, 30-45% carbonate and trace amounts of chlorite,magnetite and chromite.In the inner- most part s of the zone,trace amounts of antigorite occur, commonlyasporphyroclasts pre-dating thetalc-carbonate formation, but also asporphyroblastspost-dating the talc- carbonate.The carbonate is dominated by textu rally and

chemically zoned breunnerite, while dolomite may be present locally in subordinate amounts. A more detailed descript ionof this rock,which isthe primaryore,is given below.The monomineralicrocks in the rim consist of talc schist,(±trernolitlte).chlorititeandbiotitite. The talcschistis alsoa part ofthe ore,butin general it is much thinn er and more chloriterich than the talc-carbonaterock,and therefor e of lessinterest .The tremolite in the tremolitite occurspre- dominantly as green-coloured,idioblasticgrains.Theult ra- mafic lenses areisofacial with themetamorphic envelope.

The compositional zoning pattern was created by prograde metamorphismduringD₁(Karlsen1995).

--- Ma gnetite boundar y (high/Iow magnetite)

Fiq,3_Idealisedlitholog icalzon ingpatte rn oftheAlt ermark ult rama fi c lenses.

NGU-BULL436,2000-PAGE96

Upper pressure sha dow

Low ma gneti te

~::=~:;....~~High magnetite

I 0-200m I

Legend

• Serpentinite

• Serpentine-talc-carbonaterock

• Talc-ca rbo na terock

n

^{Talcsc hist}

• Blac kwa llrocks

Lower pressure shadow

TORARNEKARLSEN,EDVINRIAN

s

ODLEIVOLESEN

Deposit geometry and size

All of the described deposits,except fortheRemlia deposit, occur as rimsaround serpentinites,butwit h differentserpen - tine/talc-carbonateratios.Insomeof thetalcbod ies in the mine,thereare onlysmallremnan ts of serp ent init e,whilein others it is the dominating lithology.Ashort int roducti on to the geometry and size of the depositsisgiven below.Esti- mates of tonnage are based on differentpremisesduetodif- ferent levelsofinvest igat ion,and theterm spro ven,proba ble and possibleare used.In the presentpaper,howe ver,only the totalestimati ons are given.

The Store Esieklumoenultramafite(Fig s. 2&4)is an 800 m long and up to 180mthick, exposed ultram afite consisting primarily of antigorit e.Itsmaximumdepth below surfaceis 140m at a height of240 m abovesealevel.Thetalc-carbo n- ate zone that surrounds the serpent inite is noteasy to see on the surface,part lybecause theboundary iscoveredbyover- burden and partlybecause the majo rityof the talc-carbo nate zone is sit uat ed well below surface. The ult ramafic body probably consistsof 4 coresof serpent in it ethat aresepa- rated by thinzones of talc-carbonate and,toalimitedextent, ch loritite.

Thrustzo ne

200

lOO

0

-lOO

-200

A ²⁰⁰

^m

Thrustzo ne, inve rted

I

Drillho le

Straumbo tn Nappe floor thrust

Fig. 4.Crosssection A-A'(Fig. 2)show ing the StoreEsjeklumpen andNakkanultr am afit es.

Tj ornrasta Nappcincl.Slcttcfjcll ctUnit

_ Quart z-rich garnet-micaschist. minorquart zo-feld sp athi cgneiss

StraumbotnNappe Graphitic micaschist

Quartz-richgarnet-mica schist.minorquartzo-feld spathic gneiss

J

Garnet-m ica schist.partly staurolite and kyanite bearing Arnphibolite

Calcit icmarble Dolomiticmarble Predomin antlyserpentinite Talc-carb onat e,minor talcschist

Blackwall rocks

TORARNEKARLSEN,EOVINRIAN&ODLEIV OLESEN

50m

N

1

NGU- BU LL 436,20 00 - PAGE97

Fig.S.Simplifiedgeolog icalmapof the Main Level,Alter marktalcmine. Minelayoutfrom 1995 .

Legend

_ Serpen tinite

_ Talc-carbonate, minor talc schist _ Blac kwall rocks

_ Amphibolite D Marble

Garnet-mi caschist

\40 S,foliat ion

,...,.20 F₂fold axis,plunge

-..lk-

Axialtraceofove rturned F2synform

___ - Axialtracesof F3fold s

During the years1932-1934,an inclined shaft was driven in a talc-carbonate rock in the southwestern part of Store Esjeklumpen in order to investigate the ore, but the work was subsequently stopped at the time of opening of the Altermark talc mine (1934). In 1990 and 1991, Store Esjek- lumpen was the subject of drilling,and 1460 m and 2260 m were drilled,respectively,in 16 cross-section s.The prospect- ing work wassupplemented by surface mapping in 1991 (Karlsen 1995).

The geometry of the talc-carbonatedeposit is relatively simple asit occursmainly asa regular zone around the ser- pentinitecore.Thethicknessof the talc zone varies according to the structural occurrence;it is alwaysmuch thicker in the 'nose',pointing towardsS-SE in the dip direction, i.e. in the direction of the lineationLlb,and up to 40 m of talc-intersec- tions are presentin drillholes.Along the hanging-and foot- wall of the serpentinite,the talc-carbonate oreis much thin- ner« 2-3 m thick).The thicknessof the talc rocksalso varies along theE-Wtrend:it is generallymuch thicker in its western parts than in the east where the thickness gradually decreasesto less than 2-3 m.In spiteof the relatively simple geometry of the Store Esjeklumpen talc deposit, some few zones of chlorit it ecrosscut the orebody.

The LineEsieklump enultramafite has not been investi- gated by drilling,but detailed surface mapping has proved

that talc mineralisation also occurs in this ultramafic lens.

Thin talc-carbon atelayersare present in the northern,east- ern andwestern parts of the body, while the southern part is not exposed(Karlsen 1995).Based on our knowledgeof the geometry of other talc deposits in the area, most of the talc- carbonate is probably present in a pressureshadow(Fig. 9)at the S-SE,deep-seatedend of the body.Magnetic modelling (Karlsen & Olesen 1997)indicates that the magneticpart of the body does not continue deeper than 150 m below the surface. Investigations carried out so far indicatethat4 M tonnes or more of talc ore are presentin the Store/LilleEsjek- lumpen area.

The Nakkan ultramafite (Figs.2 & 4)was discovered by geophysical exploration (Karlsen & Olesen 1991, 1996)and subsequent(1992) core drilling (Karlsen 1995).The ultramafic body is situated in the S-SE continuation of the Store Esjek- lumpen ultramafite, with a minimum distancebetweenthem of approximately 150 m. Its uppermost part is situated approximately215 m above sea leveland minimum 130 m below the surface.The ultramafic body is approximately 800 m wide along the E-Wtrending strike,and has a general dip of 40-45°towards S-SE,as at Store Esjeklumpen.ltsmaximum thickness is more than 200 m.The length of the bodyin the dip direction is unknown,but it is probably more than500- 600 m.The ultramafic body iscomposed of at leastthree dif-

NGU-BULL 436,2000-PAGE98 TORARNEKARLSEN,EDVINRIAN&ODLEIV OLESEN

o

100

-200 -100

lOOm

level 3 level 2

_ - - - -- - - ---,--- 8 '

M.o.s

• Drive

~ Inclined shaft / Drillholeintersect ion

B

'-<l...Thrustfault

Legend

_ Serpentinite

_ Talc-carb. rock,minortalcschist - Blackwall rocks

_ Amphibolite _ Maib le

D

Garnet-micaschist

Fig.6.Sim plifie dcross-sect ion B-B'(Fig.

2)of theno rthern part oftheAltermark Talcmine.Theinterpretedthrustfaults are primarilyof D,agebutwerestro ng ly react ivated during D₂.

ferentserp ent inite coresseparated by thinzon esof talc-car- bonat e rocks and,in some cases,black wall rockssuch as chloritite and biotitit e.The upper part ofthe Nakkan ultrarna- fite has been investigated by drill ing in 1992, 1996,1997, 1998 and 1999with a total lengt h of drillcoreof 16,260m.

As in the otherlargeult ramafic lensesin Altermark,the talc rocksoccur primarily asrim saround the serpentinit e cores.Thethickestpartsof thetalc-carbon atezone(-20 m) are found on the hanging-wall ,notfar from the'no se' point- ing N-NWtowardsStoreEsjeklum pen.Basedon thecom mon occurrenceof pressure shadow saround compet entunits,as well asonour know ledgeof the geometryof similarultr ama- fites in thetalc mine, it isprobable that a sim ilar pressure shadow existsat theopposite, deeply buried sout heastern end ofthe lens(cf.Fig.6).This area,however,has not been investigateddue to the greatdepth below surface and the high drilling costsinvolv ed.Investigation of thispart of the lens can onlybedone fromanent rance drive.Int ernal cross- cutting 'veins' (up to 10 m wid e)of talc-carbonate can, at least to some extent,be regarded as addit ion al resources, though they partly carry unusuallyhigh amountsof magn et- ite leadingto lower recovery.In total,the Nakkanultramafit e isbelievedto containsa tonnage of 5 M tonnesor more.

The total length of theAltermark talcmineisapproxi- mately 800 m from NEto SW.The mine is operatedat5diff er- ent levels (Fig. 6).Today,the Main Level(Fig. 5) is used asthe accessand transport drive,and the oreisbeing mined in inclined (20-50°) st opes between the Main Level and the Level2.

Thenorthern halfof the mine is geomet ricallycomp lex

with numeroustalc-bearing lenses(Fig s. 5&6)which com- monlyhave relativ ely hig h ratios of talc rock to serpen tini te.

The majo rit y ofthese bod iescon sists mainlyoftalc-carbon- ate rockswith small cores of serpenti nite lenses'floating' wit hin them. The serpentin it e bod ies are generally cigar- shaped with their longest axes oriented E-W and with a plungeof about 20°toward s east.Frequent ly,decollernent thru sting has occurredalong the contact betw een the ultra- mafitesand the coun t ry rocks,leading to inte nsively fold ed country rocksbeing placedon topof non-fo ld edultramafic assemblages. In the Altermarktalcmine,reserves for several years have been mapped.

Ore quality

In theindustry,severalcriteriaareusedto describethequal- ityofindustrialtalc, e.g. white ness,oil absorptio n, cont ent of damagingminerals,hard ness and smoothness,and electrical and thermalproperties.Allsuch criteria,which are measured in thefinalprod uct s, are cont rolled bythe mineralogyofthe ore and the beneficiationprocessesused.Themineralog y of the ore isdescribed below, focusing on the possible end prod uct s. Whiteness,whichis also discusse d,is a very impor- tant parameter for the present day prod uct ion oftalc-car- bonateprod ucts,buthas a limitedvaluewhenother poten- tial products of the talc-carbonate mixtureare evaluated. Thisis because the white nesswould be changed if other processeswere applied.

Exam plesofthechem ist ry of the Altermark talc oresis given inTable 1.Except forthe contentof Ni and Cr,the ore

TORARNEKARLSEN,EDVINRIAN&ODLEIV OLESEN NGU-BULL 436,2000-PAGE99

A,Etg.5 "'AK920 1ESK9008A ESK9008A ESK 9008A ESK 9008A NAK 9201

321III 133III 163.2m 180.3m 371m

o

21 10 19 31 1733 52 3337

o

37

o

o o

34,25 0,02

<0.3 7,05 0,13 37,10 0,17

<0.2

<0.1

<0.02

o

33 7 12 24 1450 62 2771 8

71 o

2 840 99,69 29,90 0,01 0,37 8,20 0,16 35,04 0,63

<0.2

<0.1

<0.02 25,36

Fig.7.Phot omicrographofthetalc-carbonate ore,showingthe idioblas- ticgrainshape oftalc(g reen) andcarbo nate(g rey).Horizontalscale of fieldofview:1cm.

Rim

o 51 11 22 22 1054 41 1927

o

40

o o o

29,71 0,01

<0.3

99,59 7,50 0,16 35,42 1,15

<0.2

<0.1

<0.02 25,63

Rim Rim Vein/joint

Rim

99,42 99,93 99,98 99,79

0 0 0 0

21 22 23 53

11 8 10 8

19 16 15 18

40 58 33 35

1735 3634 1860 2085

63 74 55 51

3644 3766 2612 2297

0 0 0 7

40 96 59 66

0 0 0 0

2 0 0 0

0 0 40 1250

32,04 36,08 30,45 35,27 0,02 0,05 0,02 0.02 0,38 1,58 0,33 0,48 7,36 11,36 8,18 8,93 0,10 0,15 0,15 0,19 35,82 33,54 36,35 34,42 0,13 0,1 2 0,25 1,29

<0.2 <0.2 <0.2 <0.2

<0.1 <0.1 <0.1 <0.1

<0.02 <0.02 <0.02 <0.02

23,57 17,05 24,26 19,19

reg ard edasa deposit,and is not dis- cussedfurther.Thedeposits at Store Esj e klu m p en, Nakkan and at the Alterm ark talc mine (Fig. 2), how-

Rim Vein/joint ev er, hav e quite simi lar mineralo- gies.

The talc-carbon at e ore (Fig. 7) consistsmainlyof talc (abo ut 45-65

%)and carbo nates(30-50%). Add- itio nal const it uentsare chlorite(typ- ically0-4%,locallyhigher)and mag- netite / chromite / ferrite-chromit e (0-3%,locallyhig he r).Trem olite and ant ho p hy lli te are usually abse nt in the ore, but have been id enti f ied lo cally in distin ct zo nesin the talc- 21,84 carbonate rock. Zones conta ini ng

-- ---- - --- - - - ----- --- ----- ------ --------- --- --- - -- ----- - - -----

am p hi bole are not regarde das ore. 100,55

Antigorite ispresentclose to the ser- pentinitic cores. Sulphides are present in very sm allam o u nts«0.5

%)and are dominated by pyrit e,pyr- rhotite and pentlandite.Thecarbon- ates are commonly chem icall y zoned breunn erites wit hanincreas- ing contentof FeC03from the core towardsthe rim(u p to abo ut 21 mol.

%)(Fig.8).In places,the FeC03con- tent in the coreislessthan 5mo l.% (-2.1wt.%FeO)and thecarb on ate may be termed magnesite.There is a break in carbonate composit ion in the area between 10.3 and 12.6% FeC03,a feature alsorecognisedin theRaudberg etdepos it in Stolsheimen(Karlsen1990),but at alo w er level. Dolomite is present locally in su bo rd inate amounts .Thetalccrystals carry0-4wt.%FeO (t ot al)and0-0.3wt .%NiO in theirlatt ices (Tab le2),a common feature in talcassociat ed withultrama- fites.Two typesof magnetite occur:a)chemicallyzoned larg e grains with cores of chromitesor altere d chromi tes;and b) moreseldom,small,unzoned,pure magnetite grain s.Chlo- rite occurswitha widerange of compositions, the most com- mon beinga c1inochlore composition.Chlorite in the talc-car- bonate rock may carry up to about3wt.%Cr20 3and0.15wt.

%NiO in the lattice(Table2).

The mineralogyof the ore variesso m ew hat betweenthe different deposits,and alsowit h in each of the deposit s;Most of the variations are,however,systematically related to the structureof the ultramafic lenses (Fig.9);

1 Antigorite occurs only close to the serp ent in it e core, eitherasrem na nt s of pre-existing serpe nt init e,as inclu- sionswithin carbonate ,oras late-growthporphyro bl ast s that crosscutthetalc-carbonate assemblage.

2 Chlorite ismoreabunda ntclose to the black wall rocks than elsewhere.

Ni

Table1.Selectedwhole-rockanalyses ofthe talc-carbonateore.

SAM PLE

S

SITEII'ULTRAi\1.

Su m

Cu Zn Ba Pb Cr Co

Traceele me n ts(p p m) Rb

Sr y Zr V

Majorelements(%) SiO,

TiO, AI,03 Fe,O"(tot.) MnO i\tg O CaO :\a,O K,O 1',0, L.0.1.

is very pure and elements regarde d asbeing damaging to the environmentor healthare at concentrationsbelowanalytical detectionlimits.

The mine ralogy of four selected ult ramafites has been investigated;Store Esjeklumpen,Nakkan,Remliaand Alter- mark talc mine.The Remliaultramafite (Fig.2)is quite differ- ent from theothersbecause parts of the talc-carbonaterock carr yant ho p hyllite, a mineralnot wanted in mineralproducts because of its fibroushabit.The Remlia body is therefore not

NGU- BULL 436, 2000-PAGE100 TORARNEKARLSEN,EDVINRIAN&ODLEIVOLESEN

Fig.8.Zoning profile acrosstwozoned magnes- ite/breunneritegrainsof about 1 cmdiameter.

50.0 48 .0

T

^46.0

44.0 MgO

:

⁹

~:~

^.0

t ^T

7.0

5.0

1

^42.0

3.0 ~--,./

I.

^{40 .0}

1.0 + I - - - + - - - - + - - - + - - - - + - - - - f - - - ' - -- - - - i 38.0

2 3 4 5

Analysis

6 7

MgO

FeO

2 3 4 5 6 7 8 9 10 II

Ana ly sis

3 Magnetiteis more abundant in the innerpart sof thetalc- carbonatezone.

The conte ntof magn etite,whichisformedbytheprocess ofserpe ntinisa tio n, isameasureofmaturity of talc-carbon ate alte ratio n. Duringtheformationof thetalc-carbon at e assem- blagefrom serpenti nite,serpenti neis rapid lybroken down , while magneti te/ferrite-chro mite takes longer. Forthis rea- son, int ernal parts of the oremigh t cont ain high amounts of magn etite(up to10%inext remecases)whiletheouterpart normally contai ns<1%.When magn etite isbrokendown,Fe entersthecarbon at e,thuscausing the chemical zoningwith increased Fe conten t from coretorim.The changefrom alow magneti te content to ahig hcontenttakes placein a narrow

zone. Thedistribution ofmagnetite,as described above,has the follow ing generalim plicationsfor the ore:

Ore excavatedfrom nearbytheserpentinites hashigh amounts of magnetite,whil eoreexcavat ed frommo re distalpart s has low amounts ofmagnetite.

When the talc-carb onatezoneis thin,theamoun t of magne tite presentisalw ayshighduetothe shor t distancefromtheser- pentinitecor e.

Because ofthis relation ship andgeometrical differences, theamountof magn etit e inthedifferent deposits is variab le.

IntheAlterm arktalc mine,contentsinthe range0-8%mag- netit e are recorded.The StoreEsj eklum pen depositgenerally contains<1%magneti te.In the Nakkandeposit,the mag- netite contentis in general higher than elsewhere,and on Tabl e 2.Selecte d microp rob e analyses of the mineralspresent inthe talc-carb onate ore.

Sample 63 77 44 64 78 45 74 75 F6 FI

Area Talcmine SI.Esjekl. akkan Talc mine SI.Esj ekl. ¹akkan SI.Esj ekl. SI.Esjekl. Talcmine Talcmine vein

-- - - ---- -- - -- -- -- ---- -- --- ------ - - - - --- - - ----- --- - ---- -- --- --------- --- ---- --- - -- ----- - - -- -------

Si02 62,24 62,24 61,26 30,08 30,40 32,84 n.a. n.a. 0,05 0.00

Ti02 0,00 0,00 0,00 0,18 0,00 0,00 n.a. n.a. 0,47 0,35

AI203 0,06 0,06 0,04 16,71 17,11 12,92 n.a. n.a. 6.58 4.5 1

FeO 3,32 3,11 0,73 7,32 6,30 3,98 2,0 2 10.34 32,36 40.67

MnO 0,00 0,00 0,05 0,00 0,06 0,04 0,18 0.20

om

^0.22

MgO 30,58 29,93 31,87 29,88 31,31 36,06 46,55 40,36 1.78 O. 5

CaO 0,00 0,Q3 0,00 0,01 0,Q3 0,03 0,29 0.2 0,02 0,01

a20 0,Q3 0,00 0,00 0,00 0,00 0,07 n.a. n.a. 0,06 0.10

K20 0,00 0,01 0,00 0,00 0,01 0,00 n.a. n.a. 0.00 0,00

Cr203 0,04 0,03 0,04 1,98 2,75 1,2 8 n.a. n.a. 61,03 53,3 1

iO 0,23 0,08 0,28 0,08 0,11 0,25 n.a. n.a. 0,09 0.00

Tota l 96,50 95,49 94,27 86,24 88,0 8 87,47 49,04 51.18 102.5 1 100,02

Core Rim Core Rim

Mineral Talc Talc Talc Chlorite Chlo rite Ch lorite Magne site Breunner ite Fe-c hromite Fe-chrorn ite

TORARNEKARLSEN, EDVIN RIAN&ODLEIV OLESEN NGU-BULL436,2000 -PAG E 101

Fig.9.Generalised zoning patternshowing someimpo rtantfeatu resre- latedtothe quality of the ore (seetext).

Possible products

Talc is anext remely versatil emineral,and hasapplicationsin the following sectors : paint s, paper, ceramic s, cosmetics, plastics,roofing, agriculture,and in therubber indust ry.Its manyusespartlyreflectthefactthatthe properties of talc are highly valuedby industry. Italso indicates that there is agreat varietyof differenttalcproducts on the market.Talc produ cts may beclassifi edinseveralways. One way isby their content of talc, e.g.talc>95%,talc75-95%,talc 60-75%,talc<60%. Alternativ ely,the origi nof thetalc isused as a criteria:e.g., ultramafite-derivedtalc and dol omi t e-derivedtalc.

High-purit ytalc(talc content>95%)isusedincosmetics, steat ite, cordierit e ceramic s, paper and plastics. Medium- puritytalc (e.g.,talccontent75-95%)isusedinpaper,plas- tics,walltiling,paint and rubber.Low-purit ytalc(e.g., <75%) isusedin paint, roofing materials,flooring and fert ilisers.

There are cert ain distinction s betw een ultramafite- derived talc and dolomite-d erived talc, in that some small amounts of Fe and Ni are site d in thecrystallattice of the former, while thedolomit ictalcis analmost pureMg-silicat e.

This isimportantfor someap plicat io ns;for examp le,ultrama- fic talc is not used in plasticswhere a low Fe conte nt is requi red.

There are several product possibilitiesfor the talc raw material from Altermark (Fig. 10):1)talc-carbon ateproduct, 2) talc concentrate, 3) carbonat e concentra te.The first of theseistheeasiestone to produ ceand involvescrushing, grinding and magnetic separat ion. This is the meth od applied by NorwegianTalcAS today,but inaddi t io n,micro- nising techniques areap plied.Theirproduct s,'AT1' &'ATX', containaro und60%talc and 40%magnesite.Theother two possibleproductsnotedabove wouldall haveto bemadeby flotationor other kindsof mineralseparation method s.Flota- tion is the method employedbyMondoMinerals in Finl and, which producestalcconcentrates wit h morethan 90%talc from talc-carbonaterocks.Asulphideconcent rateanda car- bonate,concentrate are produced asby-pr oducts.The sul- phide product is Ni-rich, becausethe prim ary sulp hide is pentlandite.The carbonateconcentr at econtainsmostlybre- unnerit e, i.e.the Fe-richvarietyof magn esite.Thereis a great diffe rence betw een the Finnish raw material and the raw material from Altermark.lnFinland,two quite differentultra- mafictalc-carbon ateoresexist:1)sulphide-rich,magnetite- poorand2)sulphide-poor,magnetite-rich.Therawmaterial is takenfromthefirsttype, while the second typeisthe one that most closelyresemblesthe oresin Alterm ark.

By applying flotation techniquesto the Alterm arktalc- carbonate ore,it isprobable that high-gradepure talc prod- uctscould be produced.Coarse grain size and idioblastic crysta l shapesareadvantageous for suchamineral separa- tion. It isexpectedthat pure talc concentrateswill havecon- side rably higher whitenessthan the talc-carbon ateproduct produced today.Thereasonfor this isthat whit eness-red uc- ing mineralslike magnetite and chlorite would be morethor- oughly remov edinsuchaprocess.A carbonateproductfrom flotation would have achem istrycloseto the average com- position of magnesit e/breunnerite wit h an FeO content

"Blacxwa!lrocks":Chlcrinte.orotmte.

smaragditite,epidoterocks

0-200m I

Talc -Carbonate Talc-s chist Clinopyroxenite

Serpentintte

Rodingite Dunite

average it maycontainaround2%magn etit e, while thelocal conte nt may behigher.Whenthe oreismagnetically sepa- rated,themagneticfractiontend s to conta in otherminerals inad di t ion to magnetite.For this reason theremightbe a lower recovery of the orewhen the contentof magnetit e is high.In the evaluat ionof theNakkandeposit ,this aspecthas tobeconside red .

Whiteness is ameasureofrefle ctanceat threediffer ent wavelengt hs,heredesign atedRx,Ryand Rz, where the wave- lengthsare 6001-1m,560 I-Im and 450 I-Im,respectiv ely.A high whiteness%meansa white colour. The statistics from white- ness measurement s in Alterm ark show that thevariations between the Rx,Ryand Rzare small(Ka rlsen1995). For this reason,only Rxisreferredto below .Thedegreeof whiten ess of the finalproductsdepend son 1)mineralogy, 2)grainsize of the sam plewhen measured (grade of crushingand micro- nisation),and3)blacking from technicalequipment like the crusherand the microni ser.In theinvestigation of the ore qualit ythegrainsizeis keptconsta nt,and theblacking from instrum ents is negl ected (micro nisati on has not been applied).The whitenessvaluesgiven below are therefor e assumed to be essent iallyrelate d to mineralogy.In practice, the valueswill increasebyaround2%whenmicronised.

Tests show that thereis anegativecorrelation between the white ness and the content of magnetite and chlorit e (Karlsen 1995).Insam p les that not havebeenmagnetically separate d, the cont ent of magnet ite will determ ine the whiteness.For exam ple,asampl econtaining10-15%mag - neti tegives awhite ness ofaround60-70%,while a sample cont aining 0.6%magnetitegives a white ness of 78.7%.By removing magn etitebymagn etic separatio n,the white ness is increasedconsiderably.Thehighestmeasured white ness in magn etic ally separated sam plesis approximately 84%.

Chlorite is the major mineral determ ining the whiteness when magn etite has been removed. Since the content of chloritevaries,sowill thewhite ness.

The talc-carb on at e rocksat Nakkan andin theAltermark talcminehavethehigh est recorde d magneticallyseparated whit eness,76-83%and72-84%,respect ively,whilst that at the Store Esj eklu mp endep osithas a white nessofaround76- 80%.

Talc-magnesite

NGU-BULL 436,2000 -PAGE102

Raw mat erial 55-65%talc.35-45%magnesite.

0-3%magnetite

D

~ Crushing,grinding

~ .. millin g,magnetic separation

""",",,,,,.,,,~;,, tt' D

Mine ralseparation,e.g .flotation

Fig .10.Possibl e processingro u tesforthe talc-carbon ate ore(see text).

around 8-10%.While pure magnesite productsare common on the market,the Fe-bearing breunnerite products are not.

Such Fe-bearing Mg products are noteasily sold,oraresold at low prices (Olerud 1990).Since almost all carbonates con- tain substantial amountsof Fe, itwould not bepossibleto make a pure Mg product by furt her physical separation methods.However,it might perhaps be possibl etoachievea purer Mg product by applyingsomemet hods to changethe chemistry of the carbonates.Anyhow,more researchon such a carbonate product wit h respect to both propertiesand market possibilities wou ld have to be carried out. Sincethe sulphides occur only in verylimited amounts« 1%)and con- sist of a mixtureof pyrite,pyrrhotiteand pentl and it e,an eco- nomicsulphide productisnot possibleto achieve.Asimilar conclusion can probablybe made for the magnet it e/ferrit e chromite contentremoved bymagnet ic separati on.

Conclusions

Active prospecting duringthe last 8 yearshasprovedthatthe Altermark area contains much more talc than previou sly known.In the Nakkan-Esjeklumpen area, thereareprobably around 10 million tonnes ormore of talc-carbonateore,dis- tributed in three ultramafic bodies. In the present mining area, a considerable reservehas been added to the previ- ouslyknowntonnage.

The ore, which occurs as one of severallayers wit hincorn- positionally zoned ultramafic lensesdominatedbyantigorite serpentinites,has the following general mineralogy :talc(45- 65%).carbonate(30-50%),chlorite(0-4%), magneti te(0-3

%).Relative to other similarknowndeposits,the oreisrat her coarse-grained, and theminerals tend to be idioblastic.

There are variations in the mineralogical content,both wit hin and between thedeposits.Variations in magneti te

TORARNE KARLSEN,EDVINRIAN & ODLEIVOLES EN

andchloriteare syst ematicallyrelated to the posit ion of the sample relat ivetotheserpentinitecoreand the externalrim.

Thecont ent andgrainsize of magnetite willeffectthe recov- ery of the ore during magnetic separation and should be focused on durin g futuredevelopment.

Severalproducts canbe made from the talc-carbonate ore.By applyingflotation it islikely that high-qu ality talccon- cent ratecould bemade.Aby-productof breunnerit econ- cent ratemight also be economic, but more research and develop mentneedto be carriedout tofindapplications.

Ackno wledgements

The datain thepresentpap er are largelyext ractedfro ma PhD.the sisby thefirst author,financed byNorwegian Talc AS and the Royal Norwegian CouncilforScientificandInd u st rial Research(GrantBF 26917to Norwe- gian Talc AS).Norwegian Talc AS isth an ked for the possib il ityto publi sh this paper.ProfessorsH.Papunen,E.K.Ravnaand research associa t eK.

Kull er ud arethanked fortheir helpfulrev iews onthemanus cript.

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