Economic potential of potassic feldspar-rich gneisses in Tysfjord/Hamar0Y, northern Norway

NGU-BULL436,2000-PAGE129

Economic potential of potassic feldspar-rich gneisses in Tysfjord/Hamar0Y, northern Norway

TORARNEKARLSEN

Karlsen,TA 2000:Econ omicpotentialof potassic feldspar-richgneisses inTysfjord/Hamaroy,north ern Norway.

NorgesgeologiskeundersokelseBulletin436,129-135.

Potassicfeldspargneiss intheTysfjord/Hamaroyareamaybeapotentialresourceforfutureexploitation.Therock consists primarily ofmicrocline(upto 84%)andquartz(up to35%).togeth erwithsmallamo untsof plagioclase(1- 12%),commonlyalbite.Accessorymineralsinclude epidote,micasand magnetite.Sixdepositshavebeen indicated bymap ping.Allaresit uated wit hina supracrustalsuiteof Precamb rianage(2500-2100 Ma)dominated by a feldspath ic gneiss.Thequalit y oftherockislargelydependent onthetexture andgrainsize,asafinegrainsize and comp lex grainboundariesmake separat ionof thedifferent mineralsdifficult.

Tor ArneKarlsen,Geological SurveyofNorway,N-7491Trondheim,Norway.

Introduction

Tradit io nal ly, feld spar was extracted from pegmat ites by hand sorting.Now adays,processingtechniques such asflo- tat ion make it possible to extra ct feldsparfrom many rock type s. Theparent rocksworldwidearedom inatedby several typ esofgranitoi dand alkalin e int rusive rocks,includingleu- cocratic granites,albit ites,alaskite and aplites.North Cape Minerals AS at Lillesand, sout hern most Norw ay, separate quartzand feld sparfrom a graph ictexturedgraniteby flota- tion.

Feldspars of commercial interestcommonly fallwithin the range of microcline-perthite-albite-oligoclase. They are frequent ly used in glass manufacture and in ceramic s.In glass applicat ions feldsparisusedfor contain er and flat glass, fibreglass,TV-tube glass,and other more specialised uses.

The chemical composition of thefeldsparproduct is impor- tant for the applicati onsin glassmanufacture.Feldspar is princip ally a source of alum ina, which acts asa sta bil iser, im pro vesdurabi lity,increasesviscosit y during glassfor ma- tio n,andactsasamatrixformer.Ingeneral,around1.5-2% Al₂0_Jisreq uired for containerand flatglass, andupto 15% for certain glassfibres.Thealkalisinfeldsparactas afluxby chemica llyatt acking theot herglassbatch mineralssuchas quart z(Harben&KuZvart1997).Inceramics,sodic feld spar is part icularly useful inceramicbody and glaze.Pot assic feld- spar ismoreexpensive, but ispreferredinporcelain ename ls andinhigh-voltageelectri calporcelain.

At the end of the 1970s, K-rich gneisses in Tysfjo rd/ Harnarey,north ern Norway,werelocated and investig ated by NGU(Am li 1975, 1978).More comp rehensive mapping and further dep osit studies were carried out by Karlsen (1990).In thepresentpaper, asum maryof the earlierworkis present ed wit h special em phasison deposit geolog y and composition of theore.

Geological setting

Theinvestiga t ed depo sit s are sit uatedat the borderbetween themunicip alities ofTysfjo rdand Harnarey,nort hernNorw ay (Fig.1).Allrocks in the area are of Precamb rian age, and are part of the Lofot en-Tysfj ord basem ent .IntheTysfj ord and Harnarey area,thebasem ent isdominatedbygranitoid rocks wit h ages around 1800 Ma. The granito id bodies have intruded into volcanic and sedimentary supracrustal rocks wit h ages of 2500-2100 Ma or 1910-1880 Ma.Prior to the intrusion of thegranites,the suprac rusta l rockswere affec ted bytheSvecokareliandeform ation eventat 1900-1 800Ma;in manyof thesup racrustal lenses,foliati on and foldsare visi- ble.These st ruct ures are not present inthe granitoid rocks.

Maficdykesthat cross-cut both thesupracrustalsand the granito idsare the youngestrocksin thearea.

TheK-rich rockdescribed in thispaperhasanalkali-rhy- olit ic compo sition and belon g sto the supracrusta l series, comprising 1)K-feldspar gneiss,2)calc-silicate,K-feldspar- rich gneiss, 3) biotite-b earin g K-fel dspa r-poor gneiss, 4) bioti teschist,5)cale-silicaterockand6)calcitemarble.The K- feldspar depositsare allsit uate dwithin the dominantK-feld- spar gneiss.

Sim ilar rocks, but lessdeformed and lesspotassic,out- cropping in the Rom bakwindow farth er north,have been inter p rete dasvolcanic(Korneliussen&Saw yer 1990, Saw yer

&Korne liussen 1990).Thepot assic gneissesin Tysfj ord form amoreor lessst ruct uralconti nuatio nofsimilar rockspresent in theLofot enregi on where they are more com mon.

Previous processing tests

Pot assium feld spar-richgneisses are knowntooccuratsev- eral placesinNorway,andthefollowingdepositshavebeen st udied invarying detailfor com me rcial use:

NGU-BULL436,2000-PAGE130 TORARNEKARLSEN

Metamorphosed sedimentary and volcanicrocks (supracrustals) c:::J FeldspathJc gneiss.FIne- 10 medlulllilralned,white to pink.

- Biolk&-bearlng,pola88lcfeldepar-poor gneiss.FIn&-gralned,grey.

c:::J Calo-sUlcategneiss.

c:::::J POIa88Ic feldspar-poorgneiss.Finetomedium-grained,white.

Magnellt&-rlch.

Calo-sillcat&-rock

c:::J Skam

c:::J Bioln&-schlst

Biollt&-homblendegnel88l~hibolne - Mixed tormalloo:amphbollte,blotlt&-schlst.

Intruded by granltold dykes

Banded,epldot&-rich gnel88.Thullte-bear1ng,nn~graJned

c::::J Mixed formalloo:~eUlcate^rock(do rnnanl),martlle,gneiss c::::J Granitic gneissr:Adisputed origin,medlUlllilraJned

LEGEND

o,

Scale

2.5 km

.

N

t

TYSFJORDEN

Magm atic rocks

c:::J Gran tte.Med ium 10coarse-qramed, follaled,grey,whh~plnk

c:::::J ^{Gran tte.}Fln~^{to med}lulllilraJned.grey.

okI81thanthegraniteabove Gnelss lcgranite.MedlUlllilralned. Mangerlte

~ Covered area c:::J No!mapped

U1hologlcalboundary ,30 Strikeanddip(dipIndegr&88) .-/ Fold axis

(youngerthanfollal loo)

; ' lineation

- Foldaxis^andIInea1lon / " Macroscopicfoldaxle.

whichdel'o rmsthedominantfoltatlon

Industrialminerals andores

• Pegmatlte (f Iron

, Chalcopyrlte,pyr1le

@ Uranium,thorium

- Graphite J: Potass ic feldspar

Fig. 1.Geologicalmap of the investiga te darea.

TOR ARNE KARLSEN

o,Ion

~kken

5,9

30

Fig. 2.Det ailed geo logical map showi ng the deposi tsof K-feld spar rich gneisses.

NGU- BULL 436,2000-PAGE131

LEGEND

o

o

o

o

o

o

o

o

o

Ampht>ol~8dyke(yOUngetlt orthemappedrocke) lithologicaJboUndary

Fau~

-1D

)0Uneation

.,.. Fold axis,(younger thanfoliation) , Chalcopyrite,pyrite:!:.sphalerite

e UraniumIthorium

• Sampling point

Produced by T.S"rdaJ

,

1. Gasland svann.Be in Vesteralen (Arnl] 1976)

2) Storjord-Tiltvi ka, Tysfjord/Harnarey (Am li 1975, 1978, Karlsen1990)

3. Bleikvassli (Larsenetal. 1995).

Potassium-rich rocksat Gasland svann were investiga ted by NGU in1976-1977 (Amli1976). Theraw material consistsof 60%orthoclase, 21%quartz, 6%plagioclase, 6%cordierite, 2%sillimaniteand4%magn et it e+ilmenite.Inaddit io n, the

following accessoriesoccur:biotite,apatite, garnet, zirco n, corundumandwhit e mica.Sampl es of 50 kgwere takenfrom 3 locat ions.Asimple processing by flot ati on andstrong-field magnetic separatio n gave promi sing results regardi ng K- feld sparconcent rates.Inad di ti on to a K-fel dsparprodu ct,it was realised that production of quart z and cor dierit e/silli- maniteconcentratesmightbe achievabl e.The achieved feld- spar concentratecontained 85-90%feld spar (ca. 85%K-feld- spar and the remai nde r aIbite), and 10-15 % quart z and

NGU-BULL436,2000-PAGE132 TORARNEKARLSEN

sill iman ite.A labo rat o ryrepo rtfrom SINTEFconc lude d that a feldsp ar conce nt rate conta ining ca.13.5%K20 ,1.8%Na20 and0.10-0.12%Fe203shou ld be at ta ina ble by more compre- hensivetests.

The indus t rialpote ntia l forpot assicfeld spargneissin Tys- fjord/Harn a re y was pointe d out by Am li (1975). Partl y becauseof this, a radio metric(gamma spectrosco py) survey was undert aken fro m heli copter in partsof Tysfjord and Harn arey (Hab rekke 1979).Themeasurem entsgave promis- ingresults andwere foll ow ed up by gro und measurem ent s (Amli 1978).Tw o deposits,Solt uva and Ramnflag ura,were identif ied(Fig.2).Chemi cal andpet rogr aphi c descript io ns,as wellas sim ple processing testswere made.Fro mthe process- ingtests itwas conclude d thatit ispossible to makeconcen- trat es ofK-fe ldspa rcontai ni ng lo w amo un tsof Feby conven- tionalmeth od s, includi ng flo t ati on.

400 kg of raw mater ial from both the Solt uva and the Rarnnflaqur a dep osit s were collected for processing tests (Am li 1978).Thetests were perfo rmed in 197 8 onaverage samp les by Oppred nings laborato riet,NTNU,andNorfloa tAI S,andwere reporte d byAmli(1978).A lat er test made by Nor- float AlS conclude d that theprocessproduced too great a prop ort ion of fin es.

Oppred ningslabo rato rietdidasim pletestbyst rong-field magnet icseparatio n inorde r to removeFe-bea ringminera ls, and the achieved prod ucts contained 0.12 % and 0.09 % Fe203' respecti vely.Itwas concluded that Fe-p oo r feldspar conce ntra tes cou ld be ach ieved by relat ively sim ple proc- esses.

Norfloat A/S(no w part of Nort h Cape Minerals AS) at Glam sland made high magnet ic separatio n and flotati on tests of the same mat erial inorderto findoutifitwaspossible to achievea pureK-fe ldsparconce nt rate.Two samples were tested.The followi ngpro d uctswere achieve d:

Deposit characterisation

In addition to theSoltuva andRarnnfl aqu radep ositsinvesti- gatedby Amli(1978),the sup racrusta lseriesinthe Tysfjord- Harnar ey area contains addi t io nal deposits.Det ailed map- ping in the regio n(Karlsen1990)revealed depositsatthe fol- lo win gloca lit ies: Forbardnes N,Fo rbardn esS,Tilt vikbakken, VassliaWandVassliaE(Fig.2&Karlsen1990).The three larg- est depo sit s aredescrib edbelow :

TheSoltuvadep osit,situat ed alo ng thebord er between thecommunit iesofTysfj ord and Harnareyat an altit ude of 300-375m,covers an area of appro xim at ely200 x700 m. In general, thedeposit st rikes SE-NW,and dipsat around30°

towardsNE.In thehanging wall,theore lies in contactwitha sim ilar, butmo reepidote-rich andlessK-richgneiss. To ward s thenorth the ore becom eslesspot assicas the plag ioclase content increasesat the expenseof microcline.Towards the weste rn footwa ll,the bound ary is more difficultto defi neby eye,but asudd en dropinK20 wasencountered by theradi- ometricsurvey. Geoc hem ical analys esof33samples(Karlsen 1990)indicate K20 contents of 6-9.5% wit h anaverage of 7.6%(Table1).Variations areshownin Fig.3.Petrog raphic analyses by point -counting ind icatea microcli neconten tat arou nd65%.

The

Ro mnilaquro

<0.5mm:

<0.3mm:

63.3 % feldspar concen tra te with9.7 % Kp and0.19%Fe203

13.7%quart z conce nt ratewit h0.34%AI20 3 18.7%'Fe-concentrate'

26.3 %K20 -concent rateI wit h13.2%K20and 0.07 %Fe203

23.8 %K20-concent rateI1wit h8.7%K20 and

Sampleb:

<0.5 mm:

<0.3mm:

0.08%Fe203

18.1%Quart z concentra te wit h0.26 %AI203 and0.06%Fe203

24.6%'Fe-concent rate'

63.6 %feldsparco ncent rat e with 11.8%K20 and0.25%Fe203

9.1% quartz concentratewit h0.17%AI20 3 20.1%'Fe-co ncent rate'

51.9%feldsparconc entrat e wit h 12.7%K20 and0.11%Fe20 3

11.6%quartz concent rate

Itwas concludedthatthe finegrain sizeof the rock and im p regnations of mafic minerals make beneficiati on to hig h-g rade feldsparor quartz/feld sparprodu ct s difficu lt.

Tabl e 1.Averagewhole-rockmajorelementXRFanaly sesof theK-f eldsp ardep o sits.For comparison,single sam p lesfro m Gasland svan n in Ve steralenandfrom Bleikvassli(Larsenet al.1995)areincluded.

Deposit No.of sample s Si02 AI20 3 Fe203 Ti02 MgO CaO Na20 K20 MnO P20_S LOI

Solt uva 33 68.52 14.91 2.96 0.26 0.33 1.24 2.70 7.58 0.04 0.08 0.25

Ramnflagura 12 66.08 15.52 3.15 0.34 0.43 0.93 1.75 10.17 0.06 0.10 0.17

Tiltv.b.,VassI.W/E 9 71.79 13.36 2.18 0.16 0.28 0.57 2.07 7.65 0.03 0.04 0.27

ForbardnesN&5 7 71.46 13.53 2.58 0.22 0.53 0.40 1.75 8.05 0.04 0.04 0.27

Bleikvassli 1 63.66 17.69 2.60 0.38 0.26 1.17 3.79 8.74 0.02 0.16 0.34

Gaslandsvann 1 62.92 17.00 6.42 0.65 0.68 0.41 1.26 9.38 0.10 0.24 0.45

TORARNEKARLSEN ^NGU-BULL436, 20 0 0 - PAGE 133

Table2.Mineralogical content(modal%)ofsele ctedsamples of the ore.'x'

=

Sample Deposit Kfsp Qtz Pla g Ep Biot Muse Mgt/llm Apat. Zirc. Ca lc. Grt Chi Amph Tita. Othe rs

L12 Soltuva 67 23 6 x x 2.5 1.5 x

US Soltuva 48 35 3 12 1 x 0.5 x

L41 Soltuva 63 20 12 1 1 1 1 x x

L43 Soltuva 66 17 5 5 3 3.5 x x x x

L53 Soltuva 62 33 3.5 x 0.5 x x x x

L55 Soltuva 66 23 1.5 4 0.5 3.5 1 x x x

L61 Soltuva 54 32 6 2 x 4 1 x x x x

L69 Soltuva 65 16 9 3.5 2.5 1.5 1 x x

L73 Soltuva 68 22 5 4 x x 0.5 x x x

L93 Ramnfl. 81 11 4 1 1.5 x 1 x x x x

L97 Ramnfl. 84 3.5 3 4 3 2 x x x x x

Ll03 Ramnfl. 74 15 5.5 3 0.5 0.5 1.5 x x x

L120 5kardv. 34 23 38 x 0.5 x 4

L148 Vass.w 79 8 2 7 2.5 1 x x x x x x

Ll56 Forb.5 61 23 7 3 5 x 0.5 x

Ll58 Forb.5 49 45 3 1 x 1 1 x x

OppF Forb.5 65 22 x 3 2 7 1 x x

Tabl e 3.Microprobeanalysesofplag ioclase andmicroclinefeld spar. -=not detec ted.

Sample L12 L12 L12 L12 L1S8 L1S8 L12 L12 L1S8 L1S8 OppF OppF

Deposit Soltuva Soltuva Soltuva Soltuva Forb.5 Forb.5 Soltuva Soltuva Forb.5 Forb.5 Forb.5 Forb.5

5i02 67.30 66.76 64.76 67.39 61.19 67.86 63.02 62.75 63.16 65.28 63.32 63.75

AI203 19.59 18.64 21.65 19.85 22.25 19.62 17.41 17.73 17.17 17.72 17.39 17.37

Ti02 0.15 - 0.04 0.07 0.48 0.12 0.08 0.81

FeO 0.02 0.03 0.03 0.02 0.14 0.06 0.02 0.04 - 0.09 0.10

MnO 0.01 - - 0.02 0.01 0.05 0.03 0.02 0.02

MgO 0.02 0.02 0.02 0.01 0.04 0.03 ^- 0.04 0.01 0.08 0.03

CaO 0.50 0.34 2.26 0.55 4.33 0.05 - 0.02 0.01 0.03 0.03 0.01

Na20 11.02 11.32 9.93 11.04 8.76 11.12 0.50 0.64 1.18 0.76 0.75 0.57

K20 0.09 0.11 0.13 0.12 0.19 0.11 15.76 15.77 15.59 15.45 15.83 16.06

BaO 0.10 0.11 1.10 0.94 0.10 0.15 0.19 0.19

Total 98.68 97.45 98.80 99.05 97.04 99.02 98.34 98.07 97.32 99.52 97.73 98.96

Type Plag Plag Plag Plag Plag Plag Microcl. Microcl. Microcl. Microcl. Microcl. Microcl.

TORARNEKARLSEN NGU-BULL 436,2000 -PAGE 134

Fig.3.Variatio ndiagramsof the K-feldspar-richgneisses,basedonXRF analyses.

250m. The oreisin thefo rm ofaplate, strikingE-Wand dip- ping ataro und50⁰toward s NE,withathickness of 100mand lengthof800m.In thesouthandwest,the orelies incontact with theTysfj ordgranit e wit h,inso me places,a cale-silicate rockor marble in bet w een.Inthenorth,the potassicgneiss becomes poorer in K20 close to the contact to theTysfjo rd granit e.Thismeansthat onlyaround2/3 of thegneissic lens isrichinK20.Geochemicalanalysesof13 samples(Karlsen 1990)indicate thatthe ore has avery highand constant K20 contentwit h an average of 10-11%(Table 1,Fig.3).Petr o- graphic analysesindicatemicroclinecontentsofupto 84%.

The Forbardnes5deposit is situa ted in Ham aroy munici- pality,easilyaccessiblefro mthe coast just north of Tiltvika.

The size of the depositis notknow nasthebordershavenot beenmapped, butit maywellbe the largest ofthedeposits.

Thelensdips ataround40⁰towa rdsNE.Inthesout h,theore bo rdersamo re biotite-rich,less potassicgneiss and, insome

•SOltUV3

Ramnff gura Tiltvikbakken Vasvlia\V VassliaE Forb ardn c-,S For bardncs:--:

0 Othe rs Lo fotc n

.

^.

- - - -.

.

"" : ..- >- , - . - -

!- - - - - ,

.

0' " ...,

-

Solruva

c - - - Ramnflgura

Tiltvikbakken

-~. Vasslia\\'

vassliaE

- _-,~~---

• . -:- , - .

Forba rd ne s;-.:

- -o-~ -

'.~ , Oth_{Lofot en}ers

- .- -'-

0

I

- - ^{~ ~}

0 ~

,

- - ^~

..

,

places,also theTysfjordgranite .Geochem icalanalyses indi- catethat theorehasa K20 content bet ween 6 and 10.2% wit hanaverageof ca.8%(Table1,Fig.3).Petrographic anal- ysesindi catemicro clineco nt ent s up to65%.

In general,the depositsconta inprimarily microcline(48- 84%)and quartz(3-35%),and some smallamount sofplagi- oclase(1-12%).Traceminera lsinclud e, indecreasingord er, epid ot e,biotite,muscovite,mag netite,ilm enit e,apatit e,zir- con,garn et,chlorite,titaniteand calcite (Tables2&3).The microclinehasa rather constantcomposit ion with 15-16% K20 and less than 1% Na20 (Table3).Plag ioclase is domi- nated by alb ite, although olig oclase may occur predo mi- nantlyas intergro wth lamellae within albite. Epidot ehas a very variablechemistry;somegrainsarerichinFe,othersrich inMn.Magneti tecontainsfrom 0to 13%Ti02.Radioacti ve mineralscontain ingThandSi inthe co re,and Nb,YandU in the rimoccurasmet am ictphasesina sam ple fro m oneof the deposits.Thehig h conte nt of microclin e in the deposit sis ind icatedinthe chemica lanalyseswit hK20inthe range6-11

%.The Fe203contentisnorm ally in therange 1-4%(Table 1, Fig.3).

Textural rela tionships

A prim ary concern when dealing wit h feldspar or feldspar/

quart z forglass andcerami csisthe content of Fe inthe prod- uct, whichsho uld be aslowaspossib le.SinceFeislocatedin

Table 4.Grain-sizevariatio nsof microcline.

Samp le Depo sit Grain size int erval Most commo n grain size

12 Soltuva 0.05- 0.8mm OAmm

41 Soltuva 0.05-1.5mm OAmm

43 Soltuva 0.05-2.8mm 0.8mm

53 Soltuva 0.08 -2.0mm 0.6mm

55 Soltuva 0.05-l Amm 0.6mm

61 Soltuva 0.02 -1.5mm OA mm 73 Soltuva 0.1 -1.5mm 0.6 mm 93 Ramnflagura W 0.15-2.8mm 1.0 mm 97 Rarnnflaqura W 0.05-1.5mm 0.6mm 98 RamnflaquraW 0.05-2.3mm 0.6mm 103 RarnnflaquraE 0.05-1.6mm 0.6mm 105 RarnnflaquraE ^{0.2 -2.5mm} 0.6mm

120 Skardvika 0.05- 1.5mm OAmm 148 VassliaW 0.2 -4.5mm l.3mm 156 Forbardnes 0.15 -1.6 mm 0.5mm 158 Forbardnes 0.05-2.5mm 0.5mm OppF Forbardnes 0.05-1.0mm 0.3mm 80

12 ..Soltuva ..Ramnflagura

•Tilrvikba k ken ..Va....slia\\' ..VawliaE

•Forb ard nesS ..Forbardn c..:-':

oOthers

I Loforcn

11 75

. ...

75

10 9 70

8 70 5i0₂%

• 0° 0°

7

.'

.

- -,---;--'---'-' - 0. -. -_ 65

- -,-~ - ';;-' -- - . - -

65

6 11

10 60 3 2

o

60

19 18 17 16

0:

o

i 14 13 12

:

E

11"- I

q. ^4-;

'"

z 2

1

1

0

4 5

9 8 7 6

TOR ARNEKARLSEN

thelatticesof mineralssuchas magneti te,ilmenite, biot ite andepidote, it isim port ant that theseareremoved during proc essing.Forpurefeld sparproducts, itis also import antto succeed in separati ng microcline fro m quartz and plagi- oclase,orfeldsparin generalfrom quartz.An important fac- to rinsuc h processesisthegrain size(Table 4)andthetyp e of grain bound ariesin the raw material(seeKarlsen1990).

Microcline occurs as xeno-hy pi dioblastic grains,0.05to 4.5 mminsize, wit htheirlong estaxesusually orie nted paral- leltothefol iation.Thegrain sconta inonlyvery few inclu- sions,but very small grainsof magn et it eare common.Inclu- sio ns of epi d ote occur in lesser amounts . Microperthite lam ellaearerareand,whenobserved,are on lyweaklydevel- oped. The grain bound aries are relatively welldefined,and vary between being stra ig ht to weakly undu lating .Quart z usually occursassingle, scat te red grain s,but is some time s localised in aggreg ates defin ing band s. Quartz grains are co mmonly sm aller thanfeldspars:0.05- 1.2mm.Plagiocl ase has a similar appearance to K-fe ldspar,but the grainsizeis typicallysmaller.White micaandbio titeoccurasparallel-or i- ente d idiobl astic grains« 0.05-2.2 mm).Epidoteoccurs as xeno blastic to hypi d ioblastic grains,<0.05-1mm, eit her in mono m ineralic aggregates or as scat tered sing le grains.

Largergrain sare commonly compositionallyzoned wit ha coreof allaniteanda norma lepidote rim.The allanite, which contain srad ioact iv e eleme nts causesradialjointsin thesur- rou nd in g epidoteorpleoch roichaloes whensitedinbiot it e.

Magnetiteandilmeniteoccu ras xenob last ic-hyp id io bl asti c grains(up to2.5mm,butgene rally<0.15mm).Thesegrain s are generallyassociate dwit hepidoteand biotite.Oth erwi se, veryfine-g rain ed oxidesoccur in smallamou ntsevenly dis- tributedthrough outthe ent iresam ple.

Texturalrelationshi ps,andespeciallygrainsize, are criti- calto the eco no mic potentialof therock.To obtai nopt imal resultswhensepara t ing themineralsthe rock sho uld be as coarse-grainedaspossible.The grainsizeis so mewhat varia- blebet w eensam ples(Table 4),andfor possibl efut ure inve s- tigat ion it will beimpor tan t tocharact erisethe depositsalso in term s ofgrainsize.

Conclusions

Several signi ficant dep ositsof K-feldspar-ric hgneissesoccur in the Tysfj or d and Harnarey municipa lities. Three maj or deposits aredefin ed:Rarnnf laq ura,So lt uvaand Forbardn es S. TheRarnnflaquradepositcontains10- 11%K₂₀and isthe

NGU-BULL436,20 00 -PAGE135

richestinmicrocline.The Soltuva and Forbard nes5 deposits contai nK₂0 in the range6-9.5 %with a microclineco nt ent aro und 65%.Thesmall grain size makes separatio n of the minera ls difficult.Proc essingtestshavegivenratherpro mis- ing results, but wit h the prod uct io n of a large quant it y of fines.Itisconcluded that a moredetailed character isat ionof thedepos itsin term s ofmineralogy and grain-size variations isnecessary in orderto obtainmo rerepr esentat iv e sam ples for testing. It is possible that the variations between the deposit s arelargeeno ug h to inf luence theresult sofmineral processingtests.Finally,achem icaland miner alogicalcom - parison betw een the Tysfjord/Hamaroy depositsand those present in Bleikvassli and Vesteralen sho uld be carriedout.

The depositsare, neverth eless, an impor t ant reso urce for potentialexploitationin the future.

Ackno wledgements

Theautho r than ksPlant Manag erN.E.Johann esen, Nort h Cape Minerals AS and Profe ssorT.Prestvik ,NTNU,fortheir criticalreadingof themanu- script,andT.Serdal,NGU,fordraftingthemaps.

References

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