Norwegian anorthosites and their industrial uses, with emphasis on the massifs of the Inner Sogn-Voss area in western Norway

NGU-BULL436, 2000-PAGE103

Norwegian anorthosites and their industrial uses, with emphasis on the massifs of the Inner Sogn-Voss area in western Norway

JANEGILWANVIK

Wanvik,J.E.2000: Norwegiananorthositesandtheir indust rial uses,with emphasis on the massifs ofthe Inner Soqn- Vossarea in westernNorway.Norges geologiskeundersokelseBulle ti n436,103-112.

Anort hosit icrocksarecommon inseveralgeologicalprovincesinNo rway.Many occuratscattered localitiesin differentparts oftheco untry, but thetw olargestanort hositecomplexes inweste rn Europ earesituatedinwestern No rway.Thesetw oPrecambrianmassifs,theInnerSoqn-Vossprovince(- 1700 Mal.and theRogalandprovince(- 930 Ma)havebeen investigatedforuseas a rawmaterial for variousind ust rialapplications.Anorthositewith a high anorthite content(An>70)is easilysoluble in mineralacids,and thebyt owniteplagioclase oftheSoqnanorthosite makesitwellsuit ed forindust rial processesbasedon acid leachin g.Thehigh alumini umcontent,ca. 31%A1₂0_3,has madetheseoccurrencesinterestingforvariousindust rialapp licat ions,especiallyas analternativerawmate rialfor theNorw egianalumi nium industry.Wit h thisgoal inmind,geologicalinvestigation sand processingst udieshave beencarriedoutatvarioustimesduring thepastcentu ry.Atpresent,a refined processutilising bot h thesiliconand the calciumcontents of the anort hositehas renewed industrialinterestin these acidsolubleanort hosit es.

JanEgil Wanv ik,Geol ogical Surveyof Nor way,N-749 1Tron dheim,Norway.

Introduction

Anort hosit icroc ks are common in seve ral geol ogicalprov- inces in Norwayand occurat manylocalit iesin differentpart s of the country(Fig.1).Mostof thebodies areof relatively smallsize,but afew are of app reciably larger dimension s.

Among these are theBergen Arcanor t hosi t es(Kolderup&

Kolder up 1940),and most prominently, the 500 km²Roga- land prov ince and the700 km² Inner Sogn -Vossprov inc e.

These are thetwolargestano rt hositeoccurrencesinweste rn Europe and are ofconsiderable interestforindust rial ap plica- tion s.

Anorthosit e isanalmost monomi neralic,feld spathi c rock wit h a great variety of industrial appl ications (Table 1).

Anorthositemassifs areknown to hostimport antoredepos- its suchas ilmeniteand are, in manycases,excellent sources for high-quality rock aggregate and also for dimension- stone. The explo itationofanort hosite forindustrialmineral productsis growing,and the pote ntial forfuture prod uct io n of alu miniu m and ot her im portan t constit uents from anort hositesis considere d tobequiteconsid erable.

It isprimarily thehighaluminium conte nt of the Sogn anorthosite which makes itattract ive for avarietyof indus- trial end uses.The alumi niumconte nt canbeutilised in vari- ousprocesses.Mostimporta ntly,anort hositecan be leached wit h mineralacidsinorder to facili tate the liberation ofalu- minium. Simultaneou sly,the calcium com ponent is lib er- at ed,and isthus availablefor other potenti al ap plicat ions.

Labo ratoryinvestigations(Graff1981)have shown thatplagi- oclase(albite NaAISi₃0₈-ano rth it eCaAI_2Si20₈)hasa solubil- itywhichis highly dependentupontheAnconte ntofplagi- oclase(Fig. 2). Anorth osite with An<sois almost non-sol ubl e

Egersund

Fig.1.Distributionofanort hosites(red)in No rway.Modifiedafte rQvale (1982b).Boxed area-Fig.3.

NGU-BULL436,2000 - PAGE104 JAN EGIL WANVIK

Processing Products Uses Specifics

Physical. Plagioclasegrainswith crystal Aggregates Lightcoloured road surfaces,gardens, structureintact

(dry or wet mineral Building materials Concreteelements,dimensionstone, industrialfloors

processing) Abrasives Scouringpowder,toothpaste, sand

blasting

Fillers,extenders,coatings Paint,plastics,rubber Chemical Aluminium chlorides Aluminiummetal

Aluminiumoxide(alumina) Flocculent Waterandwastewatertreatment (acid oralkaline Aluminium sulphate(alum) FlocculentJsizing Papermanufacture

leaching) Calcium carbonate Binder Asphalt

Calcium nitrate Catalyst Organic reactions

Calciumsilicate Alumina speciality products

Ammoniumnitrate Cellulose insulation

Silicagelsandsols Cementcomponents

Sodiumsilicates Cosmeticsandpharmaceuticals

Sodiumcarbonate Foodprocessing

Nitrogenfertiliser Specia lity metallurgical uses Syntheticwollastoniteand zeolite Silicaresidue Fillersandextenders Polyesterandepoxyresins,Poly-

urethanevarnishes

Coating Whiteenamel

Absorbent Kittylitter,radioactive pactides Siliconproduction

Cement additive

Melting Fullyor partial meltingof Ceramics Floorandwalltiles,electricalporcelain,

plagioclase grains bioceramics,ceramic glazes

Glassfibre

MineralWool Rockwool

Weldingf1uxes

AI-productioncells Cryolitebathinsulation Direct reduction AI-S-alloys,AI- andSi-metal.

Table1.Various industrial usesof anorthosite.Norwegian commer- cialandtested uses markedinital- ics.

inmineralacids,whereas labradorit e plagioc lase(AnSO-70)is part lysoluble.Only anorthos itescontain ingplagioclase wit h more than 70%An(byt ownite)are proven to be fullysoluble.

Such basicanorthos itesare relative ly rare,but thelargemas- sifs in the Sogn-Vossregion containimmensequantit iesof easilysoluble anorthosites wit h an AI₂0₃content ofabout 31%. This makesthese bytown ite-anor thos ite s apotent ial alternativeto importedbauxiteasasourceof aluminiumore forthe large Norwegian aluminiumindustry, and theyhave been evaluate d forthispurpose at varioustimessince early in the 20^thcent u ry.

Main Norwegian anorthosite deposits

With regard to indu st rial uses it is adequate to grou p

anorthositesinto twocategories;acidsoluble and not acid solu ble .

Large areas of theVoss-Sogn massifs(Fig s.3 and 6)areof outstandingqualityconcerning acidsolub ility,making them id eallysuitedforseveral industrialapplicat ions(see below).

Acid-soluble anorthosite might also be present in some of the much smaller occurrences in Norway,but noneof the other major anorthosite deposits are composed of soluble plagioclase (Qvale 1982b). The -75 km² Bergen Arc anorthosites,for example,are dominat ed by a plagioclase withAn<so(Kolderup&Kolde rup1940).

Theanorthosit esofthe 500 km²Rogalandprovince(Fig.

1)are dominated by andesine-plagioclase(An_4o-so)(Duch- esne et al.1987)and arethus alsoinsoluble in acids.Th is anort hosit e complexisbest known foritslarge no rite-hosted ilmenitedeposit at Tellnes. However,theanorthosite it self

JANEGILWANVIK NGU-BULL436,2000-PAGE 105

,

20km

o

6 •

Mjolfjell

drill ing werecarriedout inKinsedalby NorskHyd ro(Carstens 1942).The work culmin ated in the building of a complete plant for undergrou nd mining,transport and shipping of anort hosite.Up to 300men were employedthere and some 15,000 tonn esof rock were produced before sabotageended the workin 1945.

In the mid 1960s, underground mining of whit e anort hosite beganin Nee reyd al (Figs.4,7and8)inthe altered zone along thethrust at thebase oftheGudvangen-Mjolfjell massif.Production has continued since thattime. Products have included white road aggregate, white concrete ele- ments, and abrasivesfor use in toot hpaste and cleaning agents. Annualproductionhas varied between 10,000and 100,000tonnes of anorthosite. Part of the production has beenexported,and the mostrecent developmentis the ship- pingof anorthosite to aSw edish producer of mineral wool.

Throughoutmostof the 20^thcentury,the major potential end-use oftheSogn-ty pe anorthosit ehas been conside red to be as an alternative aluminium raw materialto bauxite, based on the solubility of this anorthosite type in mineral acids.Leaching wit h acids, suchasHCI and H_2S04is very well establishedin the Norwegi anAnort al process(Kvande1987, Braaten1991).In the mid 1970s,the formationof the Interna- tional Bauxit e Association (IBA) triggered Elkem A/S and Ardalog Sunndal Verk AlS into renewing their int erest in anort hositeas an alternative alumi niumrawmaterial.During theperiod 1976-1982,majo r geologicalinvestig ation s and process development were carried out on the Sogn Fig.3.Anorth osit ic rocks of Inner Sogn and Voss.

100

70 90 50

40 60 80

An ofplagioclase

30 20

10

~ ^{Oligoclase Andesine} LabradoriteBytownite

<{:

0 1..== ==;== :=:...,....-- ---,.---.:..- --.-- ----.

o

100

0 :

«

.Q 0 60

~0

.S

q

«

s:Ql

o 20 roQl --l

Norwegian investigations and developments

Historical perspective

The potenti alfor explo it ation of the anort hosite for various purpo ses has been evaluated at different timessince the beginningofthe20^thcentury.Goldschmidt(1919) was the first to propose the idea of utilising anorthosite as a raw material for the production of alum iniumand aluminium in combinat ion wit h otherelements.Two years earlier, he intro- ducedhis idea to AlSElekt rokemisk Industriand also carried outthe first regional investigationof the anorthosites ofthe InnerSogn area(Goldschmidt 1917).Gold schmid tfoundthat themassifinthe Neereydalarea contai ned thebestqualityof easily soluble anorthosit e. He also located a deposit in Kinsedal, east of Lust rafjord,which was suita ble for a leach- ing processtolib eratethe aluminium compon ent .lnvestig a- tionsinKinsedal continued until1920.

Interestfor anorthosite as analt ernat iverawmaterialfor alumi nium production was revived during the secondworld war. Extensivefield invest igati ons,sampling and diam ond has several industrial applications.The altered,white variety ismined for aggregateand filler purposes,and an attra ctive, massive brown variety with blue labradorescence in some plagio clase crystal sis quarriedas dimension stone(Heldal&

Lund 1995).

A summaryof the anorthositeoccurrencesin Norwayhas been givenby Ovale(1982a). In thisrepo rtOvale also givesa comprehensiveoverview ofthe geologyand min eralogy of the Sogn-Voss anorth osit e provinces. Wanvik (1999) pre- sentedan overview of the sameareawit hemphasis on the criteria and geograph ical variations regardi ng potential indust rial use.

Fig.2.Plotofso lubilit y vs.ano rth it econtent ofplagioclase. Modified af- terGraft(1981) and Qvale (1982al.

NGU-BULL436,2000-PAGE106

Fig.4.Anort hositeinNeeroyd alen near Gudvangen,asseenfrom Stal- heim.Mang eriticgneissesarelocatedbelowthe ano rthositeofthewell- knownJordalsnut.

anorthosite bythe joint ventu re com panyliSAnortal (Wan- vik1981,Braat en1991).The mainobject iveof thefieldwork

wastolocate a depositcontaini ngatleast100 milliontonnes

of readily soluble anorthosite,which contains only minor amou nt s ofmafic minerals.Areaswithtop-qu alityrockwere located and drilled at two separate locations;the Hylland field and the Kaldafj ell field,southof Neeroydal (Fig. 7).The Geolog icalSurvey of Norwayhascontributedto the project wit him portantfieldinvestig at ionsona regional scale(Qvale 1982b).

TheAnort alprojectwassuccessful concerning adequate raw mater ial and the developm ent of a technically viable process,and thus the mainissues of establ ishing apossible Norwegian alte rnat iveto imported bauxitewas solved.The project,however,wastermin ated,astheconcept wasnot foundto becommerciallycomp atib lewit h existingbauxite- basedalu mi na produc t ion.

Recent developments

At the sta rt ofthe 1990s,thecompany AISPolym er (now Polymer NorgeAS)introduced the concept of produci nga polymericcoagu lant (polyaluminium chlorid e)forcleaning drin king wat er and wastewater,employ ing anorthosite as the raw material.The processinvolves acidleaching of the

JAN EGILWANVIK

raw materialandth usadoptsparts of the processing results develop ed in the Anortalproject. New alte rnative sitesfor quarry ingsuitable ano rt ho sitehave,inthisconnectionbeen locat ed bytheGeolog icalSurvey ofNorway(Wanvik 1997, 1999).Thecomp any is at present carrying out a pilot-scale processing develop mentinPoland. Results so far have been very encouraging. The highl y polluted waste water from Polishand EastEurop eanindustryisseenasthemain target for theproduct.

In 1993,a Norwe gia n com pany(Borgestad FabrikkerA.S.) wished totestthe high AI andCaSogn anorthositeas a raw materialfor a newrefractoryprod uct designed as a sealantof aluminium electr olyt ic cells in the alumi nium indust ry (Brantzzeq etal.1993,Feereyvik1994).Thehighmeltingpoint of the calcicplagioclase from the Sogn anorthositeis,inthis case,advantageouscompa redto the lowermeltingpoint of the mor e Na-ri ch anorthosi t e of the Egersund region. Alt ho ug htheprojectinit iallyseemed very promising,it has met wit hprob lems relating to the viscosity of the sealant productand is thus so faronlypartially successful.

Liberationof the alum iniu mcomp onent is still the main issue of a process(Fig. 5)that hasrecentlybeen developedby theNorweg ian Insti t uteforEnergy Technology(IFE)(Raheim etal. 1998,Raheim 1999).IFEwas responsiblefor the process- ing developm ent in the Anortalproject. In this new refined concept,more orlessall compon ents(AI,Ca and Si)of the rockareutilised,yieldin g prod uct s suchas calcium carbon- ate,ammoniumnitr ate and silica-productsin additionto the alumi niu moxide.Inaddition,the processincorporates the consumptionof CO₂,andsincethiscanbe obtained from the em issions ofnat uralgaspower plants,suchaclean,'tot al-uti- lisatio n'processcanbeconsideredto havea very good envi- ronm ental profile. At present the institute is seeking an ind ustry partn erin order to be able to develop thisproject further.

Theleachresidu efromanacid processis awhite,highly porou s,low -density,amorph ou s silica gel.Theresid uehas a poten tialuseasafillerand extende r in the paint,plast ics and paper indu st ries,aswell asabind ing material in cement pro- ductio n.The very highporosity might alsomakeit suitableas anabsorbantofvarious products,including radioact ivepar- ticles.

This high-Si residueisalso interesting asanalterna tive rawmat erialinanew innovativ eind ustri al process,which at presentis being developedbythe company NorwegianSili- con Refinery AS.Both AI and Si are being produced in a refined,continuous,elect rical melt ing operation wit h feld- sparastheraw materi al(Stuberg h 1994,1996).The silicon productisof solarcell quality and thehigh silico ncontentof the plagio clase of theEgersund anorthositeis suitable for such a process, as well as the residue of leached Sogn anor t hosite.

As a raw material for the produ ct ion of ceramicsand sanitary porcelain,a lowmeltingpointisadva ntageo us.For thisapp licatio n, whit eanort hosit e from Hellvik,near Eger- sund,is shipped to European customers (internetreference:

http:/ /www.edel splitt.no).

Sintering processes have also been attempted with

Silicaresiduum

•

;Vatercleaning,Filler Leachingin nitric

HNO,

I

I

Additivesconcrete ~ ^acid

Raw materialfor Filtration

I

silicon production

•

I I- o },.)'gen

Precipitation

n nn

Production alntnininm ..NH,

alnmina

-

^Producti~

^I

I

Fill er in paper Industrial CO.-source:

production Precipitation

Environ men tal

1 -

chem ical Filtration Hydr ogenproduction

Cemen tproducti on Ammonia production

n n _~

~/ Evaporation of

--e

Raw material water

f-- Productionof Nitrogen fertilizer ammoniumnitrate JAN EGILWANVIK

Anor thosite (CaA~Si. OJ

SOIU"c efor calcium, alu mln ium

and silica

Fig.5.TheNo rwe gia n InstituteforEnergyTechnologyhas developed a new COrbas ed concept ofuti lising several compo nentsof the Soqn anorthosit e.

Acid Ot her Quant it y

Use so lu bi- AI Fe Ca LOI

Iity criteria needed

AIproducti on high high low large

AItSitCa high high low large

(COrfree gas powerprocess)

Watercleaning high high low not quartz medium SitAlproduc- high low high Si,low large

tion(electroly- P, BandK

sis)

Refractory high low high low not quartz small

Ceramics low low low melting medium

point

Mineralwool high high lowSi medium

Aggregates whiteness, medium!

mechanical large qualities

Dimension fracturing, small

stone block size,

colour

Tabl e 2.Impo rt ant characterisation criteriafor anorthosite used in differ- entapplicat ions.

NGU- BULL 436,2000-PAG E107

anorthosite (Dolan et. al. 1991). How ever, these have prov en to be energy intensi ve,and testing using the Norw egi an Pedersen process(Kvand e 1987) has not been found to be of commercial interest.

The most recentapplicationofanort hositeina high-th ermalprocess is for mineral wool produc - tion.The Sw ed ish company Paroc AB, operating 3 rockwool factories,has now start ed using Nor- wegianano rthositein theirproduct ion.In this case, it isthe high-AI variety,which is interesting;thus favouring theSog n type.

Concern ing more direct applica tion s,the white altere d variety ofboth the Sognand theRogaland ano rt hosite has been mined/qu arried for aggre- gatefor somedecades.Macadam,for useinthe top layer of asphalt,in Norw ay and abroad, is thepri- mary prod uct, with its white colo ur and good mechanical propertiesas the main advantage.In addition ,concret e eleme nt s, for ext erior walls as wellasstr eet/tr afficap plicati ons, have been pro- duced wit h this whiteanort hosit eas avital ingredi- ent.Thewhite variety from bothregion shas also beenused as anadditi veinwashi ng powd er andas agrindingagent in toothpaste.

Unaltered anor thosite is att ract ive both as dimension stone and aggre gate. Mellegren &

Dalseg(198 1)havedescrib ed future plans for the opening ofagiant aggr egate quarry nearJessinqf- jord. Product ion fromthis quarry, inthe southernmost part of themassif,is principally designate dfor directexport.Export is also the main issuewith the successful,new, dimension stone quarry operated by the comp anyGranit -1893 AS in brown anort hositewestof Egersund.

Table 2 givesan indicativeovervi ewofthemaincrit eria of anort hositeastheraw material invario usrelevantindustrial applications.Further detailed information on the indust rial uses ofanort hosit es hasbeengivenby Dolan et al.(1991)in the context of their thorough study of Canadian anort hosites.

The Sogn-Voss occurrences

Geology

The anorthositic rocks of the Inner Sogn-Voss regio n belon g totheJotun Nappe,athick block of Proterozoic crystalline rocks lyin g in a NE-SW trending faul ted trench.Below the basal thrust there areyounger schists, phyllites,quart zit es and gneissesoverly ingPrecamb rian baseme ntgneisses.The Jotun Nap peitselfis subdividedint o severalseparate sheets.

The anorthosit ic rocks are situ ate d within an upper unit toget her with gabbroi c rocks and, in northern areas,also granodioriticrocks. They belong totheMiddle Alloc ht hon of the Caledonid es.Thecalcic characterof the Sogn anort hosite isa common featureof Archaeananorthosites (Ashwa I1993).

However,theSognanorthosit eis generally considered to be of Proterozoicage, probablyca.1700 Ma(Sigmond 1988).

The anortho sitic rocks mainly occurintwodistin ct geo-

Fig.6. Variationincon tentof(a)darkmineralsand(b)acidsolubility in the vario usareasoftheSognanorthositic massifs.

o00

zCl cCo

Cr r

..,.

9'w IVo oo

10 km I

• >HU1y',

• 70- 110%

• 611-70%

• <60'Yo

• <30%

Ill; with_~ra lludiurlticdyk l'S Ano rthositeso//III11'r.'logllatul Vo ss

Acid suluhlc AI,O,in%oftut ul AI,O,

"

/lOrda", -.

~<i Hcrmanvvvrk

\

'· 7

~.

B

J,,, I·,.lll ft'.·..

"

.;r

Ilk

Ifl~m

I

• >.'5%

• 22.5--'5'Y..

15-22.5%

o

o

III

• ~ahhro

Cun tcnt of ma li c minerals Anorthosites

of

FMm

\

: S"I:J"IK.f·

/ ~" _ '. .J<)~/,,""

"

Halt/a/ " .'

"':<I

..

:~. L

I '·7

A

11k

"

JANEGIL WANVIK NGU-BULL436,2000-PAGE109

Location Si02 AI20 Fe20 Ti02 MgO CaO Na2 K20 P20S LOI Acid solub.

3 3

Kaldafjell,drillcores 50.0 29.6 1.4 0.15 0.7 13.7 3.1

°

1982,202samples 50.05 30.53 0.65 0.16 0.82 13.70 3.46 0.25 0.02

Fresh,Ncer0ydal 48.99 30.70 0.68 0.10 0.42 14.22 3.00 0.16 0.08 0.77 42.05

Fresh,Brandsetdal 49.75 31.02 0.43 0.07 0.08 14.18 2.94 0.14 0.08 0.55 41.6'1

Fresh,0vsthusdal 49,39 30.55 1.05 0.14 0.63 14.09 3.15 0.16 0.03 0.59 42.63

Alteredwhite,Jordalsnut 48.15 29.43 0.41 0.08 0.02 15.65 2.21 0.19 0.06 2.24 12.1

Alteredwhite,Fyrde 48.69 29.77 0.60 0.10 0.12 13.83 3.25 0.31 0.06 1.69 32.9

Minefines,Ncemydal 48.19 29.4 1.46 0.24 0.83 13.58 3.02 0.27 0.08 2.40 15.3

Table 3.Majorelements andacidsolubilityoftypicalsamples fromtheGudvangen-Mjolfjellmassif (wt%,XRF).

graphicalareas(Figs.3 and 6).The southe rnarea, betwee n Gudvangen and Mj0lfj ell,consistsofasingl elargemassif and several smaller satel lite bodi es.The north ern area,whic h ext ends from Dyrd al inoute rNeereyfjordto Kinseda linLus- trafj ord,isdomi nated byonelarge massif,separatedinto4-5 separate bodies by the Sognefjord.Several satel litebodies are also present.In addition to Qvale (1982b) and Wanvik (1999),informationonparts ofthe sout hernareas have been publishedbyHedal (1945),Dugstad(1965)andBryhniet al.

(1983).

In the Fresvikarea(westof thenorth ernpart oftheAur- landsfjord ),theupper sheet of the Jotun Nappe displays a primary intrusivelayering seenona regio nalscale(Bryhniet al. 1977); wit halternat ingano rt hositeandgabb ro layerswith thicknesses from tens to hund reds of metres. The anort hosites themselves are inte rnally isoclin allyfold ed, and thus thetotalthic kness of the massifscanbe as muchas 2000 m, asobserved,forexample,onthe easternside oftheAur- landsfjord.

The anorthositic massifs displaylarge variations in their conten t of mafic minerals (Fig. 6). Areas with proper anort hosite « 10%maficminerals)are totally dominantin the southern Nzereydal-Mjelfje llarea. Inthe nort hern areas, leucogabbr o (10-35% mafic minerals) predo m inates, anort hosite-gab bro (22.5-35 % mafics) is also prom in ent , whereasano rt hosite isrestrictedto only minorlocal occur- rences.In themorepure,andmost com mercia lly interesting ano rt hosite areas,the dark mineralsconsistof epidoteand brown amphibole withminor amountsofgarnet, biotiteand sericite. The leucogabbro containslessepidote,but clinopy- roxene,in places alteredto greenamphibole, as wellas some garnet,are common constituents.The latter mineralsform patches, spotsandbands,dependingonthetypeandgener- at ionof theanort hositicrock.

The Sognanort hositeis characterisedby ahigh-Anplagi- oclase (AnSS-80)'The sout hern Gudvan qen-Mj alfj ell Massif hasbeen show n to beparti cularlycalcic (An6S-78)while the north ern region s areless calcic (An40-60dominates) (Qvale 1982b). Based on region al field studies, Qvale (1982b) dividedthe Sogn anor thositic rocks into 9 sub-types,rep re- senti ngfour differentgenerations.Of these only the second generation wit h granular coarse- to medium -grain ed

ano rt hositeis attractivefor ind ustrialuses. TheGudvange n- Mj01fjellmassif isdom inate d bythis sub-ty pe.The ot hervari- et ies,dominantin theother massifs, generallyshow toohigh conte ntsof dark mineralsto be considered as commercially attractive.

One of the more geologically (b ut not commercially) interestingtypes is a late-generationcorona anorthosit ethat occurs in several parts of the massifs.Lens-shaped aggre- gates of mafic minerals, up to 10 cm in size, commonly appear as well developed corona textures.Primary olivine reacted with plagioclase, resulting in a dunite core sur- roundedby zonesofort hopyroxene,clinopyroxene,amphib- ole, garnet and spinel in the outer rim(Griffin&Heier1970, Griffin 1971).

Alon g thethrust base ofthe upper Jotu n Nappe sheet (Fig.8),therocks arest rongly deformed.Where anorthosite is present in this thrust zone,as in the Gudvanqen-Mjelfje!l Massif,the primary rockhas been saussuritised,resulting in the formation of albitic plagioclase and epidote minerals.

Since the An content is low(An20)'this anorthositeisnotacid soluble .This low solubility,12-15%(of total rock)as opposed to 41-42%in unalt ered rock, is indicatedinTable3.This table also shows that altera tio ndoes not produce a significant changeinthe maj or elementcomposit io nof theanort hosit e.

Geological criteria in relation to industrial applications

The types ofmineralogica landgeological factorsto look for whenevaluatingan anorthositedepositdepends on the end use.Apartfrom theplagioclasecomposition, the lowcontent of dark minerals and a minimal number of dykes ofother rocks wit hin the anor t hosites are favourable factors in all cases.

Inview of thehigh conten t of mafic minerals in maj or part s of the Sognanort hosites(Fig.6), onlyrest rict edareas areofindust rial interest.In theGudvanq en-Mj olfj ell Massif though,a content of5- 10%darkmineralsdom inates, and thebest areas have only3-5%mafics.

Dykes of other rocks are very common within the anorthosites of the Jotun Nappe. The most prominent are early gabbro and garnet-amph ibolitedykes occurr ing aslay-

NGU-BULL436,2000-PAGE110

. -

Dominatedby good qualityanorthosi tc Topqualityareas Anorthositegabbro Gabbro

..-.bor ~ Anorthositcmine

0"

flggl

fI1J'.

Fig.7.Location ofthe high qualityGudvangen-Mjo lfje llmassif.

ersandlenses of varyingthickness and frequ ency. Theseare a major negativefactor againstexploitation in many areas.

Their widespread occurrence, for example in the Gudvan- qen-Mje lfje!l massif,excludes many areas for exploitation which otherw ise areofopt im um anort hosite quality.Map- ping ofswarmsof thesedykes (Ottesen1979)has shown that the anorthosite massifsare intensely folded .Among other dykes,granodioritic intrusion sare the most common.Ordi- narily they are not frequent andthus do not greatly affect anort hosite quality,butin nort hernand northeasternareas, they are very common (Fig.6).Thinner,granitic pegmatite dykesalso occur,but they aresporadic and do not influence anorthosite quality.

The hig h Ancontentofthe plagioclaseischaracteristicof theSogn anorthosite,andisthe mostimport ant factormak- ing thesedepositsespecially attractive.SinceGoldschmidt's daysit has beenknown that onlyhigh-Anplagiocl ase is solu- ble inmineralacids.Such high-An plagioclase is thus essen- tialforapplications requiring liberation of AI and ot herele- ments from anort hosite.Duringthe Anorta lprojec t Gj elsvik (1980)stated that leachabilityis a function ofthe Si:AIratio,

JAN EGILWANVIK

which must be belo wabou t 1.5:1to prevent the dissolut ionof AI ions being masked by aninsolu ble silicatest ructu re.The condition that appears to be necessaryfor acceptabledissolutionis the collapse of the silicatestr uct ur easAI ionsareleachedfrom it.

Dueto the regionalvariationsofthe An content of theSog n anor thosi te,only smaller areasin the centraland nort hern reg ions have optimumsolu- bilit ycharacteristic s.The remaind erison ly mode r- ately to poo rlysoluble(Fig.6);anorthi tecontents betw een 40and60 dominatein these areas.The plagioclase inthe Gud vanqen-Mj elfj ellmassif,on the otherhand, is dominated byAn65-78and most parts of this massif are of very high solub ility.The

/ " altered anort hositeat thethrustbaseofthe massif

isa clearexception .

Alt eration of the anorthosite is acommon phe- nomenon, caused by local defor matio n of the anorthositemassifs. The plagioclase is crushed and saussuritised, withalt erationto a more albiticplagi- oclase.Amp hibo le,clin op yroxene and garnet have been partly replaced by epido te, biot ite,chlorite and muscovite.Some quartz and calcit emay also bepresent.Thisgneissic,alt eredvariety is easy to recognise and has a dull, fine-grained whitish appearance. Themostintensealteration took place wit hin the thrust zones at the base of the anort hosite massifs, where up to hundreds of metres mighthavebeen affecte d(Fig.8).Higher up in the anort hosites,deformation and alteration is primarilyrestricte d to narrow shearzones,up to a fewm thick.Outsideof such zones, saussuri ti satio n is rest ricted to grain boundaries in massive anort hosites,andhas resulted in a beehive texture on weathere d outcrop s. The low-An rims of the grain sprotrudeatthe surf ace, whilethe more calcic cores areweat hered and eroded.

Thecolourofthe anortho sitevaries andgives nodefin ite indi cati on of quality.Eventhoug h alteredlow-An anorthosite is white (fine-grained and with dull lustre).unalteredtypes might also be white(medium- to coarse-gr ained and crystal- line).Grey and violet-greyvarietie sare mostcom mon, but dark viol etand darkbrown varieti esalso occur.These two lat- tertypesarenormallyhighinAn,and for mostindustrialuses they areexcelle nt;butthey are foun d to often contain large amounts of microscopic inclusionsof iron oxidesand this mightbe disadvantag eous in som e applications.

Environ mental issues

TheSogn anorthos itesaresit uatedina verypicturesquepart of Norway.The Nzereyfjordregi oninpart icular is considered tobe very specialwithits narrow fjord and steepmountains, andis visite dbynumerous tourists every year. Largepartsof this area arethus now proposed asa new national park, includingsome of themostint eresti ng part softheGudvan- qen-Mjel fje!lmassif(Fig.7).This posesdefiniterestrict ionson

JANEGIL WANVIK NGU-BULL436,2000 -PAGE111

a

b

NGU~

County/communeborder Glasha~mar

r.:I:

_ _L _

SW

Ovsthusnipa

I

Aurlund ;Vo~s

Verticalprofile alongtheNaroyvalley Hyllandtcltct

.\1angcritic rocks Acid-leachableanonbositc Vallevbottom

c==J White.non-solubleanonhos itc

NE

SE

100m.u..\.I.

-- -

NW

Fig.8.Vertical sect ions(a) across and(b) along the Neereydal,showingthealte red thrust (border)zoneat thebaseof the anort hosite massif.Diamond drillholes of investig ated areasare marked wit h redlinesinsectio ns.

open mine quarrying, and the locationsselectedasbeing most favou rablefor mining during theAnort alproj ectmight then becom e inaccessible in thefuture. Furthermo re,the anort hositeareato thesouthof theprop osedparkis already occupiedas a military training area(Fig. 7).Thus, the Sogn anort hositeprovidesa'good' exampleof thediff iculti es one often is confronted wit h today when prospecti ng for new mineral depo sit s.Luckily,more recent invest igatio nshave revealedthat high -q uality,acid-solubleanor th ositeisacces- sible even with regular und erg round mining from the Neereyd alvalley, and thatsuchminesarepossible tooperate in a narrow'open'zone along thebottomofthevalley.

Conclusions and future perspectives

As analmost monomineralicfeld sparresource, anort hosite has avaried spect rum of industrialapplicati ons.Especially theSognanort hosite has along and interesting history of various companies involved in investigation sto utilisethis large resource. Industrial application s of anort hosite are expected to increasein scopeand possibilitiesin thefuture.

The very largedepositsin Sognand Rogaland aresituated close to thecoast, andare thusfavour ableforboat transport.

The acid-soluble, high-An Sogn ano rt hosite and the medium-An Rogaland ano rt hosite thusprovid eNor way wit h anexcellent basefor variou scommerciallyinterestingfuture industrial applicat ions.

Acknowledgements

I wanttothankNigel Cook,Tom Heldal,IdunnKjolleandthe lateBrianA.

Sturtfor suggestio ns and corrections regarding bot h linguist icissues and the structureandcontentof the manuscriptitself.Special thanksare also due to Tor Arne Karlsen,who initia ted my writingof thisarticle.

Finally I wantto expre ssmy appreciation for havingthe good fortune of enjoyingmany daysduringseveral periods inthismostbeautifulpartof No rw ay.

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