1 NGU-BULL 436, PAGE 93 Overview f talc resurces in the Altermark talc prvince, nrthern Nrway, and pssible uses f the talc re TORARNE KARLSEN, EDVIN RIAN & ODLEIV OLESEN Karlsen, TA, Rian, E. & Olesen, 0.: 2000 : Overview f talc resurces and reserves in the Altermark talc prvince, nrthern Nrway and pssible uses f th e talc re. Nrgesgelgiske undersekelse Bulletin, 436, Acti ve prspecting during the past 10 years has prved that th e Altermark area cntains much mre talc than previ usly recgni sed In the Nakkan-Esjeklumpen area, 10 M tnnes r mre f talc-carbnate re are prbably present, distributed in ultr amafic bdies.the re, which ccursasne f several layerswithin cmpsiti nally zned ultramafic lenses dmi nated by antigrite serpentinites, has th e fllwing general min eralgy: talc (45-65 %l. carbn ate (30-50 %), chlrite (0-4 %) and magnetite (0-3 %). Relati ve t ther knwn similar depsits, the re is rather carse-grained, and the minerals tend t be idiblastic. Several prduc ts can be made frm the talc-carbnate re. By app lying fltatin r th er kinds f mi neral separatin techniques, it is likely that high -quality talc-cncentrate culd be made in additi n t talc-carbnate mixtures. A cncentrate f by-prduct breunn erite wuld pssibly be f ecnmic value. Tr Arne Karisen, Gelgical Survey f Nrway, N-7491 Trn dheim, Nrway; Edvin Rian, Nrw egian Talc Altermark AS, N 86 16, Nrway; Odleiv tesen, Gelg ical Survey f Nrway, N-749 1Trndheim, Nrway. Intrductin Ecnmi c talc 1 mineralisatin is nrma lly assciated eit her with dlmite r wi t h ultramafic rcks (i.e. 'ultramafic' talc ). All knwn majr ccurrences f ta lc in Nrway are f th e ultramafic typ e, and are assciated wit h serpentinised phili tic ult ramafites, ultramafic cnglmerates r slita ry ultramafic lenses. Nrwegi an Talc AS, w ned by Pluss Staufer AG, is t he maj r talc cmpany in Nrway, and prduces talc frm ultramafic rcks in Alt ermark, Nrdland cunty, nrthern Nrway (Fig. 1). In the Altermark area, th e ultramafic lenses are f und t be parti cularly we ll talcified, and th e area is described as a talc prvince. Due t a shrtage f re reserves in the late 1980s, a prspecti ng campaign was carried ut during the fll win g years ( ). Wrk started w ith drilling and investigatin f t he Stra umdalen talc depsit (Hlter 1990), and was fllwed up by a mre intensive survey including airb rne gephysics (Mgaard & Walker 1991, Karlsen & Olesen 1991), regi nal mapping, detailed depsit mapping, and cmprehensive mineralgical studies (Karlsen 1995). This campaign, which has been fllwed up by drilling, turned ut t be successful, and several millins f tn s f talc-carbnate rcks were detected, bt h wit hin and utside the exist ing ta lc mine. The Nakkan depsit was detected by airbrne gephysical explratin (Mgaard & Walker 1991, Karlsen & Olesen 1991, 1996), and is td ay th e maj r target f r future exp li tatin. In the present paper, the general gelgy and prspects in the Altermark area are present ed. 1. Talc - bth pure mineralgical talc and indu strial talc which may cntain variable amunts f magnesite, chlrite etc. Gelgical setting The Alt ermark area is situ ated abut 20 km west f M i Rana, nrthern Nrway (Fig. 1). The rcksbelng t the Rd inqsfjallet Nappe Cmplex (Gustavsn & Gje lle 1991) f the Uppermst Allchthn (Rberts & Gee 1985) f the Calednides. The Rdinqsfja llet Nappe Cmplex and the verlying Helgeland Nappe Cmp lex are the t w dminating nap pe cmplexes alng the Nrdl and cast. These nappe cm plexes cntai n numerus ultramafic lenses f smewhat disputed rigin (Karlsen 1995). Immediat ely t th e suth f Helgeland, p hilitic ultramafit e wi t h assciated talc ccur s n th e island f Leka in Nrd- Trndelag. Nrth f Redey (Bang 1985), p hilite cmplexes as such have nt been recgnised, and the ultram afites ccur asslitary lenses. Aru nd th e basement wi ndws Sjna, Hgt uva and Svartisen, slitary ult ramafic r ult ramafic/ mafic lenses are wi despread, situated predminantly within the Rdinq sfjallet Nappe Cmplex (Fig. 1). Tectnstratigraphy In t he investigated area, th e Rdinqsfja llet Nappe Cmplex cnsists f th ree tectnic units: th e Tj rnrasta Napp e, th e Straumbtn Nappe (Svegjart et al. 1988) and the Slettefjellet Unit (Fig. 2). The Tj rnrasta Nappe is dminated by quartz-feldspath ic gneisses and quartz-rich mica schists while t he Straumbtn Napp e cmprises kyanite-staurlite bearing garnet-mica schists, marbles and amphiblites. The tectni sed tr ansit in fr m th e Tj rnrasta Napp e t t he verlying Straumbt n Nappe is marked by ccurrences f strngly defrmed graphitic schists, which utline the thrust zne f the 'St raumbt n Napp e flr thrust' (SNft). The Slet-
2 NGU -BUL L 43 6, PAGE 94 TORARNE KARLSEN, EDVIN RIAN s ODLEIV OLESEN Fig. 1. Tectnstrat igraphic map f western Helgeland and ccur rences f ultramafic rcks. Scale f ultramaf ic rcks is exaggerated by arund 100 %. The investigated area is ut lined. Cmp iled frm Svegjart (1977), Jhnsen (1983), Svegja rt et al. (1988, 1989) and Gustavsn & Gjelle (1991). N 130 km Helgeland Napp e Cmplex Helgeland Nappe Cmplex sle thrust Rbd ingsfjbllet Nappe Cmplex Thrust plane abve Precambrian basement Preca mbrian ba sement Ultramafic lens < tefjellet Unit, which is sit uated abve th e Straumbt n Nappe, is inte rpreted t be a struct ural repet itin f th e Tjrnrasta Nappe, and cnta ins simi lar rck types (Karlsen 1995). The ult ramafic rcks, w hich can be classified as s-called slitary alpine-ty pe ultramafites (Quale & Stigh 1985), ccur as lenses wi thin the Straumbtn Nappe and are usually assciated with t he SN ft (Fig. 2).l t is pssibl e that certain revisins wi ll have t be made t th e standard tectnstratigraphy f the regin. The structu ral histry f the area is cm plex, and will be described in deta il in a separate paper; nly a sum mary is given here. Fur defrmatin events have been recgnised, 0 1, O 2,0 3 and 0 4 (Karlsen 1995). The first defrmatin event, 0 1, created the well-develped metam rph ic fliatin, 51' w hich is th e dminant micr-/ messcpic structure, and defined by mica, hrnblende, kyanite, staurlite, graphite, epidte and elngated aggregates f quartz and feldspars. 0 1 als created micrscp ic t macrscpic F, flds, w hich are md erately inclined, and weakly plunging isclinal fld s with a strngly develped penetrative axial plane cleavage (51)' Mst f the F 1 fld axes parallel th e main E-plun ging, L 1 stretching lineatin. L 1a is a micr-/m esscpic stretch ing lineatin defined by strngly elngated aggregatesf qu artz and/ r feldspars and by a parallel rienta tin f t he min erals kyanite, staur lite and hrnblende. The L 1a lineatin generally plunges at abut 0-30 t wards E r ESE. Ll b is a mes-/ macrscpi c stretching lineatin defined by th e lngest axes f mes- and macrscale b udins f serpentinites and lcally amp hib lites plunging at arund twards E. All f th e interpreted nappe b undaries w it hin the Rdinqsfj allet Nappe Cmp lex are interpreted t be f early 0 1 age. Defrmat in events pst-dating the peak f metamrphism are represented by O 2 and 0 3, which created rnes- t macrscpic scale flds tha t defrm the 0 1 structures. The Slettefj ellet fld, which is th e d minant macrscpic struc ture in the area, is inter preted t be an verturned, tight, F 2 antifrm with an axial surface dipping at abut 40 t wards SE. The Slett efje llet fld changes trend when traced west ward alng the Sjna gneiss dme (interpreted fr m Gustavsn & Gjelle 1991), prbably asa result fthe dme gemetry f th e Precambrian win dw. Decllernent thrusting is bserved alng the utermst part s f t he ult ramafic rcks where the envelping rcks have been int ensively flded by F 2 /F 3 and slid alng the br der f the ultramafites. Geth ermbarmetric investigatins have indi cated that all the rcks f the Rcdinqsfjallet Nappe Cmp lex in the investigated area were metamrphsed at amph ib lite facies at high -pr essure cnditins during 1 (Karlsen 1995). Cmpsitinal zning f the ultramafic lenses The ult ramafic lenses are actuall y parts f cmpsite mafic/ ultr amafic lenses, althugh t he mafic parts, nw represented by amphi blite, are nt always easy t recgnise. The ultramafic parts f the lensesare mineralgically zned, and three majr znes ccur (Fig. 3): (1) Serpent init ic cre, (2) Talc-carbnate zne, (3) Mnmineral ic rcks in the rim. The setpentinite cnsists predminantly f interpenetrati ng text ured anti gr ite and 5-20 % mag netite. Especially ferrite-chrmite, but lcally als relics f livine and c1 inpyrxene, are
3 TORARNEKARLSEN, EDVINRIAN& ODLEIVOLESEN NGU -BU LL 436, PAGE 95 Quartz-feldspathic gneiss r=~=~ Quartz-rich mic a gneiss, ± garnet 1=~""--'="'"1 Carbnate-mica schist Garnet-m ica schist ± kyanite/staurlite Graphitic mic a schist Marb les, calcitic/dlmitic Amphiblite Ultramafic rcks ---Cl- Straumbtn Nappe flr thrust and equivalents p:l' Axial tra ce f verturned F2 antifrm (Slettefjellet fld) % Axial trace f verturned F2 synfrm - 'it"' Axial trac e f verturned F1 antifrm (Straum btn fld) 40 Fliatin A-I\ Crss sec tin ~ Altermark talc m ine Fig. 2. Sim plified gelg ical map f th e in vestigated area w it h names f th e ultr amafic lenses and lcalities f crss-sect ins. Abb revati ns: A =Annaberg an ultramafite, SE=Stre Esjeklu mpen, LE=Lille Esjeklum pen, R=Remli a. N =Nakkan (situated abut 150 m belw surface). Napp es: Tj.Na =Tjernrasta Nap pe, Tj.Na2 = Tj er nrasta Napp e invert ed, Str.Na = St raumb t n Napp e. Crss-secti n s are shw n in Figs. 4 & 6. present in subrdinate amunts. Sme f the ultramafic cres carry lenses f primary c1inpyrxenite, dunite, chrmitite and als rdingite. The rdingite, whic h prbably represent metasmati sed mafic rcks, has been described nly nce previusly in Nrwegian ultramafites (B0e 1985) and cnsists f the assemblage: epidte + amphible + chlrite ± hyd rgr ssular ± serpentine. The talc-carbnate zne cnsists f abut 40-70% talc, 30-45% carbnate and trace amunts f chlrite, magnetite and chrm ite. In the innermst parts f the zne, trace amunts f antigrite ccur, cmmnly as prphyrclasts pre-dating th e talc-carbnate frmatin, but als as prphyrblasts pst-dati ng the talccarbnate. The carbnate is dm inated by textu rally and chemically zned breu nnerite, w hile d lmite may be present lcally in subrdinate amunts. A mre detailed descript in f t his rck, which is t he prim ary re, is give n belw. The mnmineralic rcks in the rim cnsist f talc schist, (± tre rnlitlte). chlritite and bititite. The talc schist is als a part f the re, but in general it is much th inn er and mre chlr ite rich than the talc-carbnate rck, and therefre f less interest. The t remlite in the tremlitite ccurs predminantly as green-clured, idiblastic grains. The ultramafic lenses are isfacial with the metamrphic envelpe. The cmpsitinal zni ng pattern was created by prgrade metamrphism during D 1 (Karlsen 1995).
4 NGU -BULL 43 6, PAGE 96 TORARNEKARLSEN, EDVIN RIAN s ODLEIVOLESEN Upper pressure shadw Lw magneti te ~::=~:;...~~ High magnetite I 0-200m I Legend Serpentinite Serpentine-talc-carbnate rc k Talc-carb nate rck n Talc schist Blac kwall rcks Magnetite bundar y (high/iw magnetite) Fiq, 3Idealised lithlgical zning patte rn f the Altermark ult ramafic lenses. Lwer pressure shadw Depsit gemetry and size All f the described deps its, except fr th e Remlia deps it, ccur asrims arund serpent inites, but wi th different serpen tine/talc-carbnate ratis. In sme f th e talc bd ies in the mine, ther e are nly small remnan ts f serp ent inite, wh ile in thers it is the dminating lithlgy. A shrt intrducti n t the gemetry and size f the dep sits is given belw. Estimates f tnnage are based n different prem isesdu e t different levels f investigatin, and th e term s prven, pr bable and p ssible are used. In the present paper, hwever, nly the ttal estimatins are given. The Stre Esieklumen ultramafite (Figs. 2 & 4) is an 800 m lng and up t 180 m th ick, expsed ultram afite cnsisting primarily f ant igrit e. Its maximum depth belw surface is 140 m at a height f 240 m abve sea level. The talc-carb n ate zne that surrunds the serpent inite is nt easy t see n the surface, partly because t he bundary is cvered by verburden and part ly because the maj rity f the talc-carb nate zne is sit uated well bel w surface. The ult ramafic bd y prbably cnsists f 4 cres f serpent in ite that are separated by th in znes f talc-carbnate and, t a limited extent, chlritite. Thrust z ne Thrust zne, inverted I 200 loo 0 -loo Fig. 4. Crss sectin A-A' (Fig. 2) shwing th e Stre Esjeklumpen and Nakkan ultramafit es. A m Tjrnrasta Nappc incl. Slcttcfjcllct Unit Quartz-rich garnet-mica schist. minr quartz-feldspathi c gneiss Straumbtn Nappe Graph itic mica schist Quartz-rich garne t-mi ca schist. minr quartz-feldspathic gneiss J Garnet-mica schi st. partly staurlite and kyanite bearing Arnp hiblite Ca lcitic marble Dlmitic marble Pred min antly serp ent inite Straumbtn Nappe flr thrust Talc- carbnat e, minr talc schist Drillhle Blackwall rcks
5 TORARNEKARLSEN, EOVINRIAN& ODLEIV OLESEN NGU- BULL 436, PAGE 9 7 Fig. S. Simplified ge lg ical map f th e Main Level, Alter mark talc mine. Mine layut frm D Legend Serpentinite Talc-carbnate, minr talc schist Blac kwall rcks Amphiblite Marble Garnet-mica schist 50m \40 S, fliatin,...,. 20 F 2 fld axis, plunge N 1 -..lk- Axial trace f verturned F 2synfrm - Axial traces f F3 fld s During the years , an inclined shaft was driven in a talc-carbnate rck in the suthwestern part f Stre Esjeklumpen in rder t investigate the re, but the wrk was subsequently stpped at the time f pening f the Altermark talc mine (1934). In 1990 and 1991, Stre Esjeklumpen was the subject f drilling, and 1460 m and 2260 m were drilled, respectively, in 16 crss-sectins. The prspecting wrk was suppl emented by surface mapping in 1991 (Karlsen 1995). The gemetry f the talc-carbnate depsit is relatively simple as it ccurs mainly as a regular zne arund the serpentinite cre.the th icknessf the talc zne varies accrding t the structural ccurrence; it is always much thicker in the 'nse', pinting twards S-SE in the dip directin, i.e. in the directin f the lineatin Llb, and up t 40 m f talc-intersec tins are present in drillhles. Alng the hanging- and ftwall f the serpentinite, the talc-carbnate re is much thin ner «2-3 m thick). The thicknessf the talc rcks als varies alng th e E-W trend: it is generally much thicker in its western part s than in the east wh ere the th ickness gradually decreases t less than 2-3 m. In spite f the relatively simple gemetry f the Stre Esjeklumpen talc depsit, sme few znes f chlr it ite crsscut the rebdy. The Line Esieklump en ultramafite has nt been investigated by drilling, but detailed surface mapping has prved that talc mineralisatin als ccurs in this ultramafic lens. Thin talc-carbn ate layers are present in the nrthern, eastern and western parts f the bdy, while the suthern part is nt expsed (Karlsen 1995). Based n ur knwledge f th e gemetry f ther talc depsits in the area, mst f the talccarbnate is prbably present in a pressure shadw (Fig. 9) at the S-SE, deep-seated end f the bdy. Magnetic mdelling (Karlsen & Olesen 1997) indicates that the magnetic part f the bdy des nt cntinue deeper than 150 m belw th e surface. Investigatins carried ut s far indicate th at 4 M tnnes r mre f talc re are present in the Stre/Lille Esjeklumpen area. The Nakkan ultramafite (Figs. 2 & 4) was discvered by gephysical explratin (Karlsen & Olesen 1991, 1996) and subsequent (1992) cre drilling (Karlsen 1995).The ultramafic bdy is situated in the S-SE cntinuatin f the Stre Esjeklumpen ultramafite, with a minimum distance between them f appr ximately 150 m. Its uppermst part is situated apprximately 215 m abve sea level and min imum 130 m belw the surface. The ultramafic bdy is apprximately 800 m wide alng the E-W trending strike, and has a general dip f twards S-SE, asat Stre Esjeklumpen.lts maximum thickness is mre than 200 m. The length f the bdy in the dip directin is unknwn, but it is prbably mre th an m. The ultramafic bdy is cmpsed f at least three dif-
6 NGU-BU LL 436, PAGE 98 TORARNEKARLSEN, EDVIN RIAN & ODLEIV OLESEN Fig. 6. Simplified crss-sectin B-B' (Fig. 2) f th e nrth ern part f the Alt ermark Talc mine. The interpreted th rust faults are primarily f D, age but were str ngly react ivated during D 2. B , ' M..s level level 3 Legend Serpentinite Talc-carb. rck, minr talc schist - Blackwall rcks Amphiblite Maib le Drive D Garnet-mica schist ~ Inclined shaft '-<l... Thrust fault / Drillhle intersectin loom ferent serpent inite cres separated by thin zn es f talc-carbn ate rcks and, in sme cases, black wall rcks such as chlritite and bititite. The upper part f th e Nakkan ult rarnafite has been investigated by drill ing in 1992, 1996, 1997, 1998 and 1999 w it h a ttal length f dri llcre f 16,260 m. As in the th er large ult ramafic lenses in Altermark, th e talc rcks ccur primarily as rims arund the serpentinit e cres. The th ickest parts f the talc-carbn ate zne (- 20 m) are fund n the hanging-wall, nt far frm th e 'nse' pinting N-NW t wards Stre Esjeklum pen. Based n th e cm mn ccurren ce f pressure shadws arund cmp etent units, as well as n ur knw ledge f the gemetry f sim ilar ultr amafites in th e talc mine, it is prbable that a sim ilar pressure shadw exists at th e ppsite, deeply bur ied sutheastern end f t he lens (cf. Fig. 6). This area, hwever, has nt been inv estigated due t the great depth bel w surface and th e high drilling csts invlv ed. Investigatin f thi s part f th e lens can nly be dne frm an ent rance driv e. Internal crsscutting 'veins' (up t 10 m wide) f talc-carbnate can, at least t sme extent, be regard ed as add itin al resurces, th ugh they partly carry unusuall y high am unts f magn etite leading t lwer recvery. In ttal, the Nakkan ultramafit e is believed t cnta ins a t nnage f 5 M tnnes r m re. The ttal length f th e Altermark talc mine is appr ximatel y 800 m frm NEt SW.The mine is p erated at 5 different levels (Fig. 6).Tday, the Main Level (Fig. 5) is used as th e access and transprt dr ive, and the re is being mi ned in inclin ed (20-50 ) stpes bet ween the Main Level and t he Level 2. The nrthern half f the mi ne is gemetrically cmp lex with numerus talc-bearing lenses (Figs. 5 & 6) wh ich cmmn ly have relativ ely hig h ratis f talc rck t serpentini te. The majrity f these bd ies cn sists mainly f talc-carbnate rcks wit h small cres f serpenti nite lenses 'flating' wi thin them. The serpent inite bd ies are generally cigarshaped with their lngest axes riented E-W and with a plung e f abut 20 twards east. Frequent ly, decllernent thru sting has ccurred alng the cntact between the ultramafites and the cun try rcks, leading t intensively flded cuntry rcks being placed n tp f nn-flded ult ramafic assemblages. In th e Altermark talc mi ne, reserves fr several years have been mapped. Ore quality In th e industry, several criteria are used t describe t he quality f industr ial talc, e.g. whiteness,il absrpti n, cnt ent f damag ing minerals, hardness and smthness, and electrica l and thermal prperties. All such criteria, which are measured in the final prd ucts, are cntrlled by the mineralgy f the re and th e benefi ciatin prcesses used. The mineralgy f th e re is described belw, fcusing n the pssible end prd ucts. Whiteness, which is als discussed, is a very imprtan t parameter fr t he present day prd uct in f talc-carbnate prd ucts, but has a limi ted value when ther pten tial prducts f the talc-carbnate mixture are evaluated. This is because th e whiteness wuld be changed if ther prcesses were applied. Examples f the chemistry f the Altermark talc res is given in Table 1. Except fr th e cntent f Ni and Cr, the re
7 TORARNEKARLSEN, EDVINRIAN & ODLEIVOLESEN NGU-BULL 436, PAGE 99 Table 1. Selected whle-rck analyses f the talc-carbnate re. SAMPLE SITE II' ULT RAi\1. Majr elem ents (%) SiO, TiO, AI,0 3 Fe, O" (tt.) MnO i\tgo Ca O :\a,o K,O 1',0, L.0.1. Su m Trace eleme nts (ppm) Rb Sr y Zr V Cr C Ni Cu Zn Ba Pb S 32,04 36,08 30,45 35,27 0,02 0,05 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 < ,57 17,05 24,26 19,1 9 99,42 99,93 99,98 99, ,71 0,01 < 0.3 7,50 0,16 35,42 1,1 5 < 0.2 < 0.1 < ,63 99, ,90 0,01 0,37 8,20 0,16 35,04 0,63 < 0.2 < 0.1 < ,36 99, ,25 0,02 < 0.3 7,05 0,1 3 37,10 0, is very pure and elements regarded as being damaging t the envirnment r hea lth are at cncentratins be lw analytical detectin limits. The m ine ralgy f fur selected ult ramafites has been investigated; Stre Esjeklumpen, Nakkan, Remlia and Altermark talc mine. The Rem lia ultramafite (Fig. 2) is quite different frm th e thers because parts f the talc-carbnate rck carry ant hphy llite, a mineral nt wanted in minera l prducts because f its fibrus habit. The Remlia bdy is therefre nt regard ed as a depsit, and is nt discu ssed further. The depsits at Stre A, Etg.5 "' AK 9201 ESK 9008A ESK 9008A ESK 9008A ESK 9008A NAK 9201 Esjeklum pen, Nakkan and at th e 32 1 III 133 III m m 371 m Alterm ark talc m ine (Fig. 2), hw- Rim Vein/ji nt Rim Rim Rim Rim Vein/j int ever, have quite simi lar mineralgies. The t alc-carbnat e re (Fig. 7) cn sists m ain ly f t alc (abut %) and carb nate s (30-50 %). Addit i nal c nst it uents are ch lrite (typically 0-4 %, lc ally higher) and m agnetite / chrmite / ferrite-chrmite (0-3 %, lcally highe r). Trem lite and < 0.2 ant hphy lli te are usually absent in < 0.1 the re, but have been id enti fied < 0.02 lcally in di stin ct znes in the talc- 21,84 carbnate rc k. Znes c nta ini ng 100,55 am phi b le are n t regarde d as re. Antig rite is pre sent clse t the serpentinitic cr es. Sulphides are 21 present in very small amunts «0.5 %) and are dminated by py rit e, py r 7 10 rhtite and pentlandite. The carbnates are cmmnly ch em ically zn ed breunnerites wi t h an increasing cntent f FeC frm th e cre tward s the rim (up t ab ut 21 ml %) (Fig. 8). In plac es, the FeC0 3 cn tent in the cre is less th an 5 m l. % (-2.1 wt. % FeO) and th e carb n at e 2 may be termed magnesite. There is a 840 break in carbnate cmpsit in in the area between 10.3 and 12.6 % FeC0 3, a feature als recgnised in th e Raudb erg et depsit in Stlsheimen (Karlsen 1990), but at a lw er level. Dlmite is present lc ally in subrdinate amunts. The t alc crystals carry 0-4 wt. % FeO (t t al) and w t. % NiO in their lattices (Table 2), a cmmn feature in talc assci at ed w it h ultra mafites.tw types f magnetite ccur: a) chemically zned larg e grains with cres f chrmites r altered chrmi tes; and b) mre seldm, sma ll, un zned, pure magnetite gr ain s. Chlrite ccurs with a w ide range f cmpsitins, the mst cmmn be ing a c1inchlre cmpsitin.chlrit e in the talc-carbnate rck may carry up t abut 3 w t. % Cr20 3and 0.15 w t. % NiO in the lattice (Tab le 2). The mineralgy f the re varies s mew hat between the different depsits, and als w it hin each f the depsit s; Mst f the variatins are, hwever, systematically relat ed t th e structure fthe ultramafic lenses (Fig. 9); 1 Antigrite ccurs n ly clse t th e serpent inite cre, either as rem nant s f pr e-existing serpe nt inite, as inclusins within carbnate, r as lat e-grwth prphyrbl asts t hat cr sscut th e talc-carbnate assemblage. 2 Chlrite is mre abu nda nt clse t the black wall rcks than elsewhere. Fig. 7. Phtmicrgraph f t he talc-carbnate re, shwing th e idiblastic grain shape f talc (green) and carbnate (grey). Hrizntal scale f field f view: 1 cm.
8 NGU- BULL 436, PAGE 100 TORARNEKARLSEN, EDVIN RIAN & ODLEIVOLESEN : ~ : ~t T 9.0 M go T46.0 Fig. 8. Zning prfi le acrss tw zned magnesite/ breunnerite grainsf abut 1 cm diameter ~--,./ I I f------'------i A na ly s is 6 7 M go FeO II A na ly s is 3 Magnetite is mre abundant in th e inner parts f t he talccarbnate zne. The cnte nt f magn etite, which is frm ed by th e prcess f serpentinisa ti n, is a measure f maturity f talc-carbnate alterati n. During th e frmatin f th e talc-carbnate assemblage frm serpenti nite, serpenti ne is rapidly brken d wn, while magn etite/ferrite -chrmite takes l nger. Fr t his reasn, internal parts f th e re migh t cnt ain high amunts f magn etite (up t 10 % in ext reme cases) while the uter part nrm ally cntai ns < 1 %. When magnetite is brken d wn, Fe enters the carbnate, th us causing the chemical zni ng wit h increased Fe cnten t frm cre t rim.the change frm a lw mag neti te cntent t a high cntent takes place in a narr w zne. The distributin f magnetite, as described abve, has th e fllwing general implicatins fr the re: Ore excavated frm nearby the serpentinites has high amunts f magnetite, w hil e re excavated frm mre distal part s has lw am unts f mag netite. When the talc-carb nate zne is th in, the amunt f magne t ite present is always high du e t th e shr t distance frm the serpentin ite cre. Because f t his relat in ship and gemetrical differences, th e amunt f magnetit e in t he different depsits is variable. In t he Altermark talc mine, cntents in the range 0-8 % magnet ite are recrded. The Stre Esjeklumpen deps it genera lly cntains < 1 % magne tite. In the Nakkan deps it, the magneti te cntent is in general higher than elsewhere, and n Table 2. Selected micrprbe analyses f the mine rals present in the talc-carb nate re. Samp le F6 FI Area Talc mine SI.Esjekl. akkan Talc mine SI. Esj ekl. 1 akkan SI. Esj ekl. SI. Esje kl. Talc min e Talc mine vein Si0 2 62,24 62,24 61,26 30,08 30,40 32, 84 n.a. n.a. 0, Ti02 0,00 0,00 0, 00 0, 18 0,00 0,00 n.a. n.a. 0,47 0,35 A I203 0,06 0,06 0,04 16,71 17, 11 12,92 n.a. n.a FeO 3,32 3,11 0,73 7,32 6,30 3,98 2, , MnO 0,00 0,00 0,05 0,00 0,06 0,04 0, m 0.22 MgO 30,5 8 29,93 31,87 29, 88 31, 31 36,06 46,55 40, O. 5 CaO 0,00 0,Q3 0,00 0,01 0,Q3 0,03 0, ,02 0,01 a20 0,Q3 0,00 0,00 0,00 0,00 0,07 n.a. n.a. 0, K20 0,00 0,01 0,00 0,00 0,0 1 0,00 n.a. n.a ,00 Cr203 0,04 0,03 0,04 1,98 2,75 1,28 n.a. n.a. 6 1,03 53,3 1 io 0,23 0,08 0,2 8 0,0 8 0,1 1 0,25 n.a. n.a. 0, T ta l 96,50 95,49 94,2 7 86,24 88,08 87,47 49, ,02 Cre Rim C re Rim Mineral Talc Talc Talc Ch lrite Chlrite Chlrite Magne site Breunnerite Fe-chrmite Fe-chrrn ite
9 TORARNEKARLSEN, EDVIN RIAN& ODLEIV OLESEN NGU-BULL 436, PAGE 101 Serpentintte Dunite Clinpyrxenite Rdingite Talc -Carbnate Talc -schist m I "Blacxwa!l rcks": Chlcrinte. rtmte. smaragditite, epidte rcks Fig. 9. Generalised zning pattern shwing sme imp rtant features related t the quality f th e re (see text). average it may cntain arund 2 % magnetite, w hile the lcal cnte nt may be high er. When th e re is magn etically separated, th e magnetic fractin tend s t cntain th er min erals in additin t magnetite. Fr th is reasn th ere might be a lwer recvery f th e re w hen the cnt ent f magnetit e is high. In th e evaluat in f th e Nakkan depsit, this aspect has t be cnsidered. Whiteness is a measure f reflectance at thr ee differ ent wavelengths, here designated Rx, Ryand Rz, where the wavelengths are m, 560 I-Im and 450 I-Im, respectiv ely. A high whiteness% means a white clur. The statistics frm whiteness measurement s in Alterm ark shw that th e variatins between the Rx, Ry and Rzare small (Ka rlsen 1995). Fr thi s reasn, nly Rx is referred t belw. The degree f wh iten ess f the fin al prducts depend s n 1) mine ralgy, 2) grain size f th e sample w hen measured (grade f crushing and micrnisatin), and 3) blacking frm technical equipment like the crusher and th e micr ni ser. In th e investigatin f the re qual ity the grain size is kept cnstant, and th e blacking frm instrum ent s is negl ected (micrnisatin has nt been applied). The w hiteness values given belw are th erefr e assumed t be essentially related t mineralgy. In practice, the values will increase by arund 2 % when micrnised. Tests shw that th ere is a negative crrel atin between th e w hite ness and th e cntent f magnetite and chlr ite (Karlsen 1995). In samples that nt have been magn etically separate d, th e cntent f magnetit e will determ ine the w hiteness. Fr example, a sampl e cntaining % magnetite gives a w hite ness f arund %, w hile a sample cntaining 0.6 % magnetite giv es a w hiteness f 78.7 %. By remving magnetite by magnetic separatin, th e w hiteness is increased cnsiderably. The high est measured w hiteness in magnetic ally separated samples is apprximately 84 %. Chlrite is th e majr mineral determ ining th e whiteness w hen magnetite has been remved. Since the cntent f chlrite varies, s will the w hite ness. The talc-carbnate rcks at Nakkan and in th e Altermark talc mine have th e high est recrded magnetically separated whiteness, % and %, respect ively, whilst th at at th e Stre Esjeklump en depsit has a w hiteness f arund %. Pssible prducts Talc is an ext remely versatil e mineral, and has applicatin s in the fllwing sectrs: paint s, paper, ceramics, csmetics, plastics, rfing, agriculture, and in th e rubb er indust ry. Its many uses partly reflect th e fact th at the prperties f talc are highly valued by industry. It als indicates that th ere is a great variety f different talc prducts n the market. Talc prdu cts may be classified in several ways. One way is by th eir cntent f talc, e.g. talc >95 %, talc %, talc %, talc < 60 %. Alternativ ely, t he rigi n f t he talc is used as a criteria : e.g., ult ramafite-derived talc and dlmi te-derived talc. High -pu rity talc (talc cntent >95 %) is used in csmetics, steat ite, crdi erit e ceramic s, paper and plastics. Mediumpurity talc (e.g., talc cntent %) is used in paper, plastic s, wall tiling, paint and rubber. Lw-purity talc (e.g., <75 %) is used in paint, rfing mater ials, flring and fertilisers. There are certain distinctins between ultramafitederived talc and dlmite-derived talc, in th at sme small amunts f Fe and Ni are sited in th e crystal lattice f th e frmer, while th e dlmit ic talc is an almst pure Mg-silicate. This isimprtant fr sme applicatins; fr example, ult ramafic talc is nt used in plastics w here a lw Fe cntent is requi red. There are several prduct pssibilities fr th e talc raw material frm Alt ermark (Fig. 10): 1) talc-carbn ate prduct, 2) talc cncentrate, 3) carbnat e cncentrate. The first f th ese is th e easiest ne t prdu ce and invlves crushing, grinding and magnetic separatin. This is th e meth d applied by Nrw egian Talc AS tda y, but in addit in, micrnising techniques are applied. Their prducts, 'AT1' & 'ATX', cntain arund 60 % talc and 40 % magne site. The ther tw pssible prducts nted abve wuld all have t be made by fltatin r th er kinds f min eral separatin meth d s. Fltatin is the methd emplyed by Mnd Minerals in Finland, which prduces talc cncentrates wit h mre than 90% talc frm talc-c arbnate rcks. A sulphide cncent rate and a carbn ate, cncentrate are prduced as by-prducts. The sulphide prduct is Ni-rich, because the primary sulphide is pentlandite.the carbnate cncentr ate cntains m stly breunn erit e, i.e. the Fe-rich variety f magnesite. There is a great difference between th e Finnish raw materi al and th e raw material frm Alte rmark.ln Finland, tw quite different ult ramafic talc-carbn ate res exist: 1) sulph ide-rich, magnetitepr and 2) sulph ide-pr, magn etite-rich. The raw material is taken fr m th e first type, w hile th e secnd typ e is th e ne that mst clsely resembl es the res in Alterm ark. By applying fltatin techniques t th e Alterm ark talccarbnate re, it is prbable that high-grade pure talc prducts culd be prduced. Carse grain size and idiblastic crystal shapes are advantageus fr such a min eral separatin. It is expected that pure talc cncentrates will have cnsiderably higher whiteness than the talc-carbnate prduct prduced tday. The reasn fr this is th at w hiteness-reducing minerals like magnetite and chlrite wuld be mre th r ughly remved in such a prcess. A carbn ate prduct frm fltatin wuld have a chemistry clse t th e average cm psitin f magnesit e/breunn erite wit h an FeO cntent
10 NGU-BULL 436, PAGE 10 2 TORARNEKARLSEN, EDVIN RIAN & ODLEIV OLESEN Talc-magnesite Raw material 55-65% talc % magnesite. 0-3% magnetite D ~ Crushing, grind ing ~.. milling, magnetic separatin """, ",,,,,.,,,~;,, tt' D Mineral separatin, e.g. fltatin Fig. 10. Pssibl e prcessing rutes fr the talc-carbnate re (see text ). arund 8-10 %. While pure magnesite prducts are cmmn n the market, the Fe-bearing breunnerite prducts are nt. Such Fe-bearing Mg prducts are nt easily sld, r are sld at lw prices (Olerud 1990). Since almst all carbnates cntain substantial amunts f Fe, it wuld nt be pssible t make a pure Mg prduct by furt her physical separatin methds. Hwever, it might perhaps be pssible t achieve a purer Mg prduct by applying sme methds t change the chemistry f the carbnates.anyh w, mre research n such a carbnate prduct wit h respect t bth prperties and market pssibilities wuld have t be carried ut. Since t he sulphides ccur nly in very limited amunts «1%) and cnsist f a mixture f pyrite, pyrrhtite and pentland ite, an ecnm ic sulphide prduct is nt pssible t achieve. A similar cnclusin can prbably be made fr the magnet ite/ferrite chrmite cntent remved by magn etic separatin. Cnclusins Active prspecting du ring the last 8 years has prved th at the Altermark area cntains much mre talc th an previu sly knwn. In the Nakkan-Esjeklumpen area, the re are prbably arund 10 millin tnnes r mre f talc-carbnate re, di s tributed in three ultramafic bd ies. In the present mining area, a cnsiderable reserve has been added t the previusly knwn tnnage. The re, which ccur sasne f several layers wit hin crnpsitinally zned ultramafic lenses dminated byantigrite serpentinites, has the fll wing general min eralgy : talc (45 65 %). carbnate (30-50 %), chlrite (0-4 %), magnetite (0-3 %). Relative t ther similar knwn depsits, the re is rat her carse-grained, and the minerals tend t be idiblastic. There are variatins in the mineralgical cntent, bt h w ithin and bet ween th e deps its. Variatins in magnetite and chlrite are systemat ically related t the psitin f the sample relat ive t t he serpentinite cre and the external rim. The cnt ent and grain sizef magnetite will effect t he recvery f th e re during magnetic separatin and shuld be fcused n du rin g fut ure develpment. Several prducts can be made frm t he talc-carbnate re. By applyi ng fltat in it is likely th at high-quality talc cncent rate culd be made. A by-prduct f breunnerit e cncent rate might als be ecnmic, but mre research and develp ment need t be carried ut t find app licatins. Ackn wledgements The da ta in th e present paper are largely ext racted frm a PhD. t he sis by the fi rst authr, financed by Nrwegian Talc ASand the Ryal Nrwegian Cu ncil f r Scient ific and Ind ust rial Research (Grant BF t Nrwegian Talc AS). Nrwegian Talc AS is thanked fr the p ssibility t publish t his paper. Prfes srs H. Papunen, E. K. Ravna and researc h assciate K. Kullerud are thanked fr t heir helpful reviews n the ma nus cript. References Bang, N.A. 1985: The stratigraphy and structural develpment f the Ry Haltey area, uter Vefsn Fj rd. Unpublished Cand. Scient. thesis, University f Bergen, Gelgical Insti tu te. Be, R. 1985: Rdingite frm Lindas. w estern Nrway. Nrsk Gelgisk Tidsskrift 65, Gustavsn, M. & Gjelle, S : Ge lg isk kart ver Nrge. Berggru nnskart M i Rana, M 1: Nrgesgel giske underskelse. Hlt er, K.G. 1990: En qelqis k/mineratq isk underskelse av talkfrekm ster i Ahermark-mradet i Ran i Nrd land. Unpublished thes is, University ftrndheim, 47 pp. Jhnsen, : Svartisen , Prelim inary map 1:50,000. Nrges gelg iske unders kelse. Karlsen, TA 1990: Minera lgisk underskelse av talk-karbnat -ma lm, Raudb erg-felt et, Vik i sgn. Nrges gelgiske undersekelse Reprt ,71 pp. Karlsen, TA 1995 : Gelgical and geph ysical studi es fultr am afit e assciated talc dep sit s, Altermark, Nrthern Nrway. De. Ing. th esis 1995:49, University f Trndheim. 229 pp. Karlsen, TA & Olesen, O. 1991: Tlkning av gefysiske heli kpterrnalln ger, Alterrnark-rnradet, M i Rana, Nrdland. Nrges gelgiske underskelsereprt pp. Karlsen, TA & Olesen, O : Airbrne gephysical prspecting fr ultramafite assciated talc, Altermark, nrthern Nrw ay. Jurnal f Applied Gephysics 35, Karlsen, TA & Olesen, : Gephysical mdelling f aermagn etic anmalies in Altermark, nrthern N rwa y. Nrges gelg iske und erskelse Reprt pp. Mgaard, J.O. & Walke r, P. 1991: Magnetiske malinger ver Alt erm arkmradet. Nrges gelgiske underskelse Reprt pp. Olerud, S. 1990: Anvendelse av magnesitt fra ta lk- karb nat -fre kmstene pa Rauberget, Vik i sgn. Nrges gelg iske underskelse Reprt pp. Quale, H. & Stiqh, J. 1985: Ultramafic rcks in the scandinavian Caled nides. ln: Gee, D.G. & Sturt, B. Ed s.: The Caledn ideorgen - Scandinavia and Related Areas. Jhn Wiley & S ns Ltd., Chic hester, Rbe rts, D. & Gee, D.G. 1985: An intrductin t th e st ructu re f the scandinavian Calednides.ln: Gee, D.G. & Sturt, B.A.(eds.): The Calednide Orgen - Scandinav ia and Related Areas, Jhn Wiley & Sns Ltd., Chichester, Sveq jart, U. 1977: Field map 1:5,000 f parts f map sheet M i Rana 1:50,000. Unpublished map in the NGU archive s. Seveqjart, U., Marker, M., Graversen, O.&Gjelle, S. 1988: Berggrunn skart M i Rana 1927 I, M 1: Nrgesgelgiske unders kelse. svegjart, U., Marker, M., & Gjelle, S : Berggrunns kart Strfrshei 2027 IV, M 1: Nrges gelgiske underskelse.