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Iron Oxide-Copper-Gold Deposits in Finland:case studies from the Per pohja schist belt and

the Central Lapland greenstone belt

Tero Niiranen

Aca emic issertation

To be presented with permission of the Faculty of Science of the University of Helsinki, for public

criticism in t e au itorium D101 o P ysicum, Kumpu a, on Decem er 9t , at 12 o’c oc noon

ublications of the Department of Geology D6

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hD-thesis No. 187 of the Department of Geology, University of Helsinki

Supervisors

r. Pasi EiluGeo og ca Survey o F n an

spooinland

ro essor N c o as H.S. O ver chool of Earth Sciencesames Cook University

Queens anustralia

eviwers

ro essor Pär We euleå Technical Universitywe en

r. Erkki Vanhanenuolanka Municipalityn an

Opponent

ro essor Dav Lentzepartment of Geologyniversity of New Brunswick

Cana a

Cover: Laur no a Fe-Cu-Au ore. Po s e r core a . ~ 45 % Fe, ~ 2.5 % Cu, an ~ 5 g t Au.Chalcopyrite (yellow), magnetite (gray), and clinopyroxene (green) comprise the main minerals.

ield of view is 17 mm.

SSN 1795-3499SBN 952-10-2160-8 (paperback)SBN 952-10-2161-6 (Pdf-version)ttp: et es s. e s n .

liopistopainoe s n 2005

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Tero Niiranen Iron Oxide-Copper-Gold Deposits in Finland: case studies from the Peräpohja schist belt and the Central Lapland greenstone belt. Academic dissertation, University of Helsinki, 2005.

u cat ons o t e Department o Geo ogy D6, ISSN 1795-3499, ISBN 952-10-2160-8 paper ac ,SBN 952-10-2161-6 (Pdf-version).

Abstract

ron oxide-copper-gold (IOCG) deposits define a group of diverse, epigenetic Cu-Au deposits to whichsevera econom ca y mportant epos ts e ong. T e r typ ca c aracter st cs are: 1 Fe-Cu-Au-Co-U-

EE-Ba-F element association, (2) high Fe-S ratio manifested by magnetite- and/or hematite-rich hostocks of the ores, (3) extensive, commonly spatially and temporally zoned Na-Ca-K-Fe metasomatismn an aroun t e epos ts, 4 g y sa ne aqueous ± car on c u s re ate to a terat on an m ne-alisation, and (5) spatial correlation with crustal-scale fault and shear zones. Host rock sequence, ,

an ept as we as temperature o t e m nera sat on events vary extens ve y etween t e nown

deposits causing considerable diversity in their characteristics.The purpose of this work is to evaluate the IOCG potential of northern Finland. This is done by

stu y ng ve ron ox e-r c epos ts rom two erent reg ons: 1 Raa ärv an Puro magnet tedeposits in the Misi region located in the easternmost part of the Peräpohja schist belt, and (2) Hannu-a nen, Kuerv t o an Cu-Rautuvaara Fe-Cu-Au epos ts n t e Ko ar reg on ocate n t e western

part of the Central Lapland greenstone belt. The study covers alteration, mineralogy, geochemistry,uid inclusion characteristics, and geochronology. The data achieved are further compared to the ex-

st ng ata on t e IOCG epos ts e sew ere an to genet c mo e s t at ave een propose or IOCGdeposits.

n ot Ko ar an M s reg ons, t e geo og ca eatures o t e epos ts are compara e to t e

OCG deposits elsewhere and consistent with proposed magmatic source models. The Kolari depositsalso contain Cu and Au in grades typical for IOCG deposits and thus they best fit to the IOCG category.

t oug at east Cu was mo e ur ng t e m nera sat on an a terat on events re ate to magnet tedeposits in the Misi region, only anomalous values of Cu and Au have been detected. However, thea terat on sty e, u nc us on compos t on, O- an C- sotope c aracter st cs, an t e propose genet c

odel of the magnetite deposits at Misi are consistent with what has been described with IOCG de po-sits. Therefore, the magnetite deposits in the Misi region are considered to be representatives of IOCGepos ts arren w t respect to Cu an Au.

According to the data presented, northern Finland is a IOCG potential region. The most prospec-ve str ct or IOCG s t e western part o t e Centra Lap an greenstone e t, t e area a acent to t e

ajor Kolari shear zone system. Based on the age data on the studied deposits, favourable time periodsfor IOCG mineralisation in northern Finland were 2.44 – 2.05 Ga and 1.83 – 1.77 Ga. These periodsepresent t e crusta -sca e r t ng stage t at pre ates t e 1.92 – 1.77 Ga Sveco enn an orogen c events,

and the D -stage thrusting event(s) of the Svecofennian orogeny post-dating the peak of regional meta-orp sm, respect ve y. T e most prospect ve ocat ons or IOCG epos ts n nort ern Fennoscan a

are old cratonic margins and intracratonic regions with abundant rift-related magmatism and extensive,etal-depleting sodic alteration.

Keywords: IOCG deposits, Skarn deposits, Iron deposits, Copper deposits, Gold deposits, Hydrother-

al alteration, Palaeoproterozoic, Peräpohja Schist Belt, Central Lapland Greenstone Belt, Misi,

Kolari, Finland, Geochemistry, Fluid inclusions, U-Pb age, O-isotopes, C-isotopes, SIMS, PIXE

Tero Niiranen

ort an Resources, Te notie 14-16, O ce 11, FIN-96930 Rovaniemi, Fin an . tero.n nrmine.com

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Preface

ron oxide-copper-gold deposit class (IOCG)nc u e wor c ass epos ts e O ymp cam (Gawler craton, Australia), Ernest Henry

C oncurry str ct, Austra a an Can e ar a(Punta del Cobre, Chile). The mentioned depositsare very large in size (e.g. Olympic Dam, about

Gt an t e r or g ns controvers a , ence t e rdiscovery has captured the attention of explora-

on compan es an aca em cs, an t e num erof deposits classified into the IOCG category hasdrastically increased as is the understanding of

e genes s o t s en gmat c epos t c ass ur nghe past 15 years.

T s wor s part o t e pro ect “Iron ox e-copper-gold in northern Finland” of the Geologi-cal Survey of Finland (GTK), initiated in 2001.T e a m o t e pro ect s to ver y t e occurrenceof this ore type in Finland, and to create genetic

o e s an exp orat on too s app ca e to t eennoscandian Shield. The ultimate goal is to

ocate economically interesting prospects for pri-ate n ustry an to promote m nera exp orat on

by providing information on host rocks, geneticore mo e s, an exp orat on n cators o IOCG

ineralisation in Finland.The original GTK project scheme focused the

esearc to nort ern F n an ecause t e geo og -cal environment is similar to the regions whereOCG epos ts are nown to occur. Furt ermore,he plan was to focus the research to the knownron oxide-rich deposits that have at least anoma-ous concentrat ons Cu an Au an ave prev -

ously been classified as skarn deposits. Therefore,e sc ent c part o t e pro ect was ocuse on

deposits in the Misi region in the easternmost cor-er of the Peräpohja schist belt, and on deposits ine Ko ar reg on n t e western part o t e Cen-

ral Lapland greenstone belt.On my account, t s pro ect was n t ate y

a phone call in the late autumn 2000. Caller wasr. Pasi Eilu from the Geological Survey of Fin-

an w o to me r e y a out t e IOCG pro ecthat was due to start in January 2001, and asked

et er I was ntereste n o ng a P D wor onhe topic as a part of the GTK’s project. This washe first time ever I had heard about the IOCG de-

posits, and some of the methods I was supposed touse I knew only by their name. However, withoutu y rea s ng w at I was up to o, I answere yes

to Pasi’s question. And so it began.T e t me spent on t s pro ect as certa n y

been interesting and challenging for me. I’ve been

n places I probably otherwise would never wind-e up, met num er o nterest ng peop e, an aopportunity to work with some of the top-rankingore geo og sts. So I am appy t at I too t e c a -enge. Now, writing this, I am even happier that its done and I never have to do it again.

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Acknowledgements

am very grate u to Dr. Pas E u GTK w oacted as a leading supervisor during my work,ntro uce me to t e wor o a tere roc s anass balance calculations. Besides that he was a

co-author in one paper, he reviewed all my man-scr pts w t an amaz ng e c ency an r gor. I

am also grateful to Professor Nick Oliver (JamesCoo Un vers ty or t e e orts e put nto my

ork and for his hospitality during my stay in Oz.r. Matti Poutianen was one of the key persons

n t e pro ect an eserves very g t an s. Be-sides introducing me to the world of fluid inclu-s ons an e ng an nsp r ng co-aut or, Matt sup-

ported me during the frustrating times (yes, there

ere quite a few) of the project. I am also verygrate u to Dr. Irme Mänttär GTK w o aremendous work on the age determinations andas a co-aut or n two o t e papers. I am a so

grateful to Professor Eero Hanski (University ofOulu) who introduced me to the geology of the

s reg on an acte as a co-aut or n one paper.r. Akseli Torppa (University of Helsinki) is ap-

prec ate or t e car onate sotope ana yses. Pro-fessor Martti Lehtinen (University of Helsinki) is

hanked for the XRD work and Dr. Bo JohanssonGTK or t e m cropro e wor . I am grate u orr. Jodie Miller (University of Cape Town) fore sta e sotope ana yses an Dr. Satu Mertanen

(GTK) for the AMS measurements. Mr. Rikuaitala (University of Helsinki) owes my grati-

u e or t e ass stance n t e ore m croscopy anfor “turning-that-one-diagram”. Dr. Arto LuttinenUn vers ty o He s n s t an e or en g ten-ng discussions on the geochemical issues. Dr.

Chris Ryan and Mrs. Esme van Achterberg at theCSIRO a orator es n Nort Ry e, Sy ney arehanked for the kind assistance with the PIXE.

am grate u to Pro essor Pär We e Lu eTechnical University) and Dr. Erkki Vanhanen(Puolanka Municipality) for constructive criti-c sm t at e pe to mprove t s wor .

This work was carried out mainly in the Uni-ers ty o He s n an I am very grate u to t e

following persons at the University of Helsinki

ot directly related to my project but for the in-sp r ng an or ar ous co ee ta e scuss ons

an e ng won er u e ow wor ers: Dr. M aRäisänen, Dr. Saku Vuori, Dr. Paula Kosunen, Dr.Laura Lauri, Mr. Matti Kurhila, Mrs. Kirsi-MarjaÄyräs, Mrs. Helena Korkka, Mrs. Sari Lukkari,and Mr. Pasi Heikkilä.

Emer tus Pro essor I mar Haapa a s t an e

for his part in initiation of the project and for thesupporting attitude he always had towards mywor . Pro essors Ragnar Törnroos, Tapan Rämö,Juha Karhu, and Veli-Pekka Salonen are thankedor pos t ve att tu e towar s my wor .

The work was done in co-operation with theGeological Survey of Finland Rovaniemi andEspoo o ces w ere t e o ow ng persons arethanked for their support during my work: Dr.Ra mo La t nen, Dr. Ju an O a a, Dr. Pe a Nur-

mi, Dr. Erkki Vanhanen, and Mr. Jorma Isomaa.I am grateful to all organisations from which I

ave rece ve nanc a support ur ng t e pro ect.Outokumpu Oyj Foundation was the main finan-c a supporter. I a so rece ve un ng rom t eFinnish Academy (project n:o 202628), FinnishGraduate School in Geology, Australian ResearchCounc D scovery Grant, an a t ree mont sgrant from the University of Helsinki for finishingt e octora t es s. T e Geo og ca Survey o F n-

and provided most of the geochemical and agedating analyses and thin sections. Management oft e Geo og ca Survey o F n an s t an e orthe possibility to finish my work.

My very goo r en s Mr. Sam Partam esand Mr. Jouni Rautiainen are thanked for all theirmental support during the work and for remind-ng me t at t ere s e outs e t e wor , too. My

spouse, Ms. Virve Heilimo deserves very specialt an s or a er pat ence ur ng t e pro ect an

enjoyable life outside the office.

Ste n um Ste n

He s n , Octo er, 21s , 2005.

Tero N ranen

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7

ontents

ist of publications..................................................................................................................................8

Introduction........................................................................................................................................9

1.1 Element association............................................................................................................9 1.2 Iron-r c osts..................................................................................................................15

1.3 Alteration..........................................................................................................................15

1.4 Propose genet c mo e s or IOCG epos ts..................................................................16

1.5 Fennoscandian IOCG deposits.........................................................................................18

Rev ew o t e or g na papers........................................................................................................19

2.1 Paper I...............................................................................................................................19

2.2 Paper II..............................................................................................................................19

2.3 Paper III.............................................................................................................................20

D scuss on.........................................................................................................................................21

Summary..........................................................................................................................................23

4.1 Conclusions.......................................................................................................................23

4.2 Imp cat ons or exp orat on..............................................................................................23

5 References........................................................................................................................................24

apers I-III

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8

List of Publications

T s t es s cons sts o a synops s an t e o ow ng t ree papers t at are re erre n t e synops s noman numerals:

Niiranen, T., Hanski, E., Eilu, P., 2002. General geology, alteration, and iron deposits in the

alaeoproterozoic Misi region, northern Finland. Bulletin of the Geological Society of Finland 75, pp. 69-92.

N ranen, T., Mänttär , I., Pout a nen, M., O ver, N.H.S., M er, J. Genes s o t e ear y Proterozo cron skarns in Misi region, northern Finland. ineralium Deposita 40, pp. 192-217.

N ranen, T., Pout a nen, M., Mänttär , I. Geo ogy, Geoc em stry, F u nc us on c aracter st cs,and U-Pb age studies on Iron oxide-Cu-Au deposits in the Kolari region, northern Finland. Ore

eo ogy Reviews Accepte .

T. Niiranen’s contribution to paper I includes everything except the construction of the geological mapo t e reg on an part o t e e o servat ons an samp ng re ate to t e reg ona geo og ca survey.T. Niiranen contributed everything except U-Pb age determinations and stable isotope analytical workor paper II. Furt ermore, t e ma or ty o t e u nc us on escr pt ons an eat ng- reez ng measure-ents were carried out by a co-author. Everything except U-Pb age determinations and fluid inclusionork in paper III was done by T. Niiranen.

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9

1 Introduction

ron ox e-copper-go epos ts IOCG are nowa widely recognised ore class into which hun-

re s o ron an copper-go epos ts aroun t eorld have been included since the synthesis of

he concept by Hitzman et al. (1992). The IOCGepos ts orm a group w t verse age, tecton c

setting, host rock package, and mineralisationsty e e.g. H tzman et a . 1992; Haynes, 2000;

illiams and Skirrow, 2000; Pollard, 2001; Wil-iams and Pollard, 2001; Tables 1 and 2). Never-e ess, t ere appear to e eatures t at are c ar-

acteristic for all deposits, although none of thema one s agnost c y tse . T e most commonfeatures include: (1) the element association Fe-

Cu-Au-Co-U-REE-Ba-F, (2) host rock for Cu-Aunera sat on s typ ca y r c n ron ox es, 3

an extensive metasomatism in and around the depos ts, 4 g -sa n ty aqueous ± car on c ore

uids, (5) high mineralisation temperature (up to00oC for oxide stage) evolving towards moder-

ate temperatures 500 – 300 C or su p e stage ,(6) deposits appear to be located in the regions

t vo um nous gneous act v ty ut, w t someexceptions, lack intimate relationship with intru-

sions, and (7) deposits are located in or next toau t or s ear zones, an n reg ona sca e appearo be proximal to crustal-scale faults, shear zones

or neaments e.g. H tzman et a ., 1992; Bartonand Johnson, 1996; Pollard, 2000; Williams andPo ar , 2001; O ver et a ., 2004; Ta es 1 an 2 .Be ow s a r e escr pt on o some t e most es-sential features and their genetic significance.

.1 Element associationCopper an go are t e ma n commo t es IOCGepos ts are m ne or. T e gra es or Cu an Au

are commonly relatively low (0.5 – 1.5 wt.% Cu,0.2 – 1 g t Au, c . Ta e 1 s m ar to porp yrysystems, but high grade IOCG deposits (> 1.5wt.% Cu, > 1 g t Au are nown, too e.g. Starra,Osborne, Mt Elliott, Eloise; Table 1). Averageron concentration, where reported, is usuallyetween 15 – 35 wt.% Fe, ut a so over 40 wt.%

concentrations in the ironstone hosts are commone.g. H tzman et a ., 1992; Marsc et a ., 2000;

Requ a an Font oté, 2000; Wang an W ams,2001; Paper III). In addition to the Fe-Cu-Au as-soc at on, t e epos ts typ ca y sp ay at eastelevated values, if not ore grades, of Ag, Ba, Bi,Co, F, Mo, P, Se, Te, U an REE Ta e 1 . Lessfrequently, the deposits are enriched in As, B, Ni,Sn, W, or Zn. In some deposits, which in otherrespects c ear y are o IOCG type, even Cu or Au

may occur in concentrations only in slightly overoca ac groun eve s e.g. NICO, Goa et a .,

2000 .

CandelariaOlympic Dam

Cloncurry district

NICO and

Sue-Dianne

Salobo

Kiruna district Finnish deposits

igure 1. Location of the deposits listed in Tables 1 and 2.

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11

D e p o s i t a n d

s e l e c t e d

r e f e r e n

c e

S i z e a n d

g r a d e , e l e m e n t

a s s o c i a t i o n 1

O r e m i n e r

a l o g y 2

S t r u c t u r e s , h o s t s e q u e n c e

A g e a n d P - T e s t i m a t e s 3

C h i l e

C a n d e l a

r i a

( M a r s c h

i k e t a l . , 2 0 0 0 ;

M a r s c h i k a n d F o n t b o t é , 2 0 0 1 )

4 7 0 M t a t

1 . 0 % C u , 0 . 2 g / t A u ,

3 . 1 g / t A g

;

F e , C u , A u , A g , M o , L R E E ,

Z n , A s

M g t , c p y , p y ± h m , p o , s p h ,

a p y , m o , g o

l d ;

B t , K f s , q t z

, a m ± a b , e p , t o u ,

c c

N e a r t o i n t e r s e c t i o n b e t w e e n

l i t h o s t r a t i g r a p h i c b o u n d a r y

a n d m a j o r s h e a r z o n e ;

A n d e s i t i c - b a s a l t i c

m e t a v o l c a n i c

r o c k s , d i o r i t e ,

d a c i t e d y k e s ,

l i m e s t o n e

1 1 5 M a ( A r - A r , b t & h b l ) ;

> 4 7 0 - 3 3 0 C ( F . I . )

B r a z i l

S a l o b o

( R e q u i a

a n d F o n t b o t é , 2 0 0 0 ;

R e q u i a e t a l . , 2 0 0 3 )

7 8 9 M t a t

1 . 0 % C u , 0 . 5 g / t A u ;

F e , C u , A g , A s , F , M o , M n , U ,

C o , L R E E

M g t , c p y , b o r , c h a ± h m , m o ,

c o b , u r a , g o

l d ;

C u m - g r u , b

t , K f s , g r ± q t z ,

t o u , fl u , a p ,

a l l , c h l

w i t h i n a m a j o r s h e a r s y s t e m ;

M e t a g r e y w a c k e s , a m p h i b o l i t e ;

q u a r t z i t e , B I F , g n e i s s , d o l e r i t e

2 5 7 6 - 2 5 6 2 M a

( R e - O s , m o ) ;

5 5 0 C

C a n a d a

N I C O

( G o a d e

t a l . , 2 0 0 0 )

4 2 M t a t 0 . 1 % C o , 0 . 5 g / t A u ,

0 . 1 % B i ;

F e , A u , C o , A s , B i , W , T e , B a ,

B , P , F , L R E E

M g t / h m , a p

y , c o b , b i s , p y , p o ,

c p y ;

B t , a m , K f s

± c a r b , c h l , t o u

D i a t r e m e a n d

f r a c t u r e b r e c c i a

a t i n t e r s e c t i o n o f s t r u c t u r a l

l i n e a m e n t s ;

S u b - a r k o s i c w a c k e , r h y o l i t e ,

s i l t s t o n e

1 8 5 0 M a ;

s h a l l o w l e v e l d

e p o s i t i o n .

S u e - D i a

n n e

( G o a d e

t a l . , 2 0 0 0 )

1 7 . 3 M t a t 0 . 7 2 % C u , 2 . 7 A g ,

0 . 0 6 g / t A

u ;

F e , C u , A g , U , M o , B a , P , B i ,

C o , F , R E

E

H m / m g t , c p

y , b o r ± c h a , c o v ,

u r a , p y , g o l d , m o ;

K f s , e p , c h l , g r , fl u , q t z , a l l

D i a t r e m e b r e

c c i a a t

i n t e r s e c t i o n o

f s t r u c t u r a l

l i n e a m e n t s ;

R h y o d a c i t e i g n i m b r i t e ,

m a r g i n a l t o r a p a k i v i p l u t o n

1 8 5 0 M a ;

s h a l l o w l e v e l d

e p o s i t i o n .

S w e d e n

T j å r r o j å

k k a - C u

( E d f e l t a n d M a r t i n s s o n , 2 0 0 3 ;

E d f e l d e

t a l . , 2 0 0 5 )

3 . 2 M t a t

0 . 9 % C u ;

C u , F e , P ,

F , B a ± A u , A g , T e ,

M o , T h , R

E E

C p y , b o r , m

g t ± p y , c h a , c o v ,

m o ;

K f s , a c t , q t z , c c , a p

S h e a r / f a u l t n e x t t o i n t e r s e c t i o n

o f t w o m a j o r

s h e a r z o n e s , c a .

7 0 0 m f r o m 5

3 M t ( 5 2 % F e )

m a g n e t i t e b o d y ;

A n d e s i t i c m e

t a v o l c a n i c r o c k ,

d o l e r i t e s

P a l a e o p r o t e r o z

o i c

N a u t a n e

n

( M a r t i n s o n a n d A a l t o n e n ,

2 0 0 4 )

0 . 6 3 M t a t 2 . 4 % C u , 1 . 3 g / t

A u , 1 1 g / t A g ;

C u , F e , A u , A g , B a ± B , C o ,

Z n , W

C p y , m g t , p

y ± s p h , g a l , c a r r ,

m o , b o r , c h a ;

A m , p x , e p , q t z , s e r , t o u

S h e a r z o n e ;

I n t e r m e d i a t e

m e t a v o l c a n i c

r o c k ( ? )

P a l a e o p r o t e r o z

o i c

T a b l e 1 .

C o n t i n u e d

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13

eposit Alteration luid inclusion chemistry S, C, O isotopes (‰)

ustraliaOlympic Dam Early: K-Fe (ser-hm-qtz)

Intermediate: Cu-Au-U-Ba-F-S (qtz-hm-sid-bar-flu-sulphides)

Late: Ca-Ba-F-CO (bar, flu, sid, do,sulphides)

(A) High salinity L-V-halite, up to 42 wt.% NaCl

eq,

(B) Moderate salinity L-V,-24 wt.% NaCl

eq,

(C) CO -rich

δ Csid

= -4 to -2,δ O

s = 14 to 21,

δ Ofluid

~ 10 (early)

and < 9 (late)

rnest Henry Distal: Na ± Ca (ab ± act, di)Proximal: (I) K-Fe (Kfs-mgt-bt-cc-

r),(II) K-Fe-Cu-Au-S-CO (Kfs, mgt,carb, qtz, py, cpy).Post mineralisation: cc, do, qtz ± hmveining

(A) hypersaline L-V-halite± 5 daughter minerals, 33-55 wt.% NaCl .(B) moderate salinity L-V ±halite, ca. 20 wt.% NaCl .(C) CO

2 -rich

δ S = -2 to 4,δ34S

py = -1 to 4,

δ C = -6 to 0,δ O

cc = 10 to 13,

δ O u

= 8 to 11

Starra Distal: Na-Ca (ab-qtz-act-sca)Proximal: (I) K-Fe (bt-mgt-qtz ± hm, py), (II) CO -SO -S-Au-Cu (anh-cc-hm-chl-sulphides ± ser, mu)

(A) hypersaline L-V-halite± 3 daughter minerals, 34-52 wt.% NaCl .(B) hypersaline L-V-halite± 4 daughter minerals, 29-

2 wt.% NaCleq

.(C) CO -rich

δS = -10 to -3,

δ13Ccc

= -7 to -1,δ O = 10 to 13,δ18O

fluid = 7 to 10

Osborne Distal/Regional: Na-Ca (ab-sca-act)Proximal: Fe-K-Ca-CO

2-S (mgt-bt-

qtz-ab-cpy-py-po ± am, cc, mu, hm)

(A) hypersaline L-V-halite± 4 daughter minerals, ≤ 70wt.% NaCl .(B) CO

2-CH

4 -rich

δ S = -4 to 3,δ18O

fluid = 5 to 12

t Elliott Distal: Na (ab ± sca),Proximal: (I) Ca-Fe ± Na (di-mgt-sca-act), (II) Ca-Cu-S-CO -Au (cpy-act-sca-cc ± adr, tou, all, ap, mgt, py, po)

(A) hypersaline L-V-halite± 4 daughter minerals,(B) CO -rich

δ34S = 0 to 2,δ S 1 to 2,δ13C = -10 to -8,δ O = 12 to 13,δ18O

fluid = 9 to 10

loise Distal: ab ± ap, qtz and bt-hbl,Proximal: hbl-bt-qtz-mgt-cpy-po-pyLate/post-ore: chl, Kfs, cc, qtz, bt,cpy, py, mu, tou, sph, gal, flu, hm, sid

(A) hypersaline L-V-halite± 4 daughter minerals,(B) CO -rich

δ S = 0 to 2,δ S

o = 1 to 2,

δ34S = 1 to 2,δ C = -10 to -8,δ18O = 9 to 10,δ O

fluid = 5 to 10

ChileCandelaria Distal: Na-Ca (ab-qtz-bt-mgt & sca ±

r, px, Ca-am);Proximal: (I) K-Fe ± Ca (bt-mgt-qtz-

ru/cum ± Kfs, gr, crd, (II) Cu-Au-Ca-S (sulphides ± Ca-am, anh)

(A) hypersaline,(B) CO -rich

δ34S py

= 0 to 3,δ S

n = 15 to 18,

δ Ofluid

= 6 to 9

razil

Salobo Distal (pre-mineralisation): weak Na(ab); Proximal: (I) K-Fe-Ca (Kfs-cum/gru-bt-mgt ± tou, flu, apa, all)(II) Cu-Au-S ± K, Ca (cpy-cha-bor ±cum/gru, bt, mo, cob, gold, saff)

(A) hypersaline, up to 58wt.% NaCl .,(B) low to moderatesalinity, 1-29 wt.% NaCl

.,

(C) CO2-CH

4-rich,

δ34S py & bor

= 0 to 2

able 2. Alteration, fluid inclusion and stable isotope data on deposits shown in Table 1

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Deposit Alteration luid inclusion chemistry S, C, O isotopes (‰)

Canada NICO Distal: extensive & intense K ± Fe

(Kfs ± mgt)Proximal: K-Fe ± Ca (mgt-bt-hbl/act-hm-Kfs ± carb, chl, tour) in multiplestages accompanied with sulphidesand gold

no data no data

Sue-Dianne Distal: extensive & intense K ± Fe(Kfs ± hm)Proximal: K-Fe (hem-mgt-kfsp ±ep, qtz, gr, flu) accompanied withsulphides

no data no data

Sweden

Tjårrojåkka-Cu Distal: Na (sca ± bt and ab-mgt-ap);Proximal: K-Cu-S ± Ca, Fe (Kfs-sulphides ± am, qtz, mgt, ap, carb)

high to moderate salinity no data

Nautanen Distal (?): Na-K (sca-bt),Proximal(?): K-Fe ± Ba-Cu-Au-S(Kfs-bt-gr-mgt and ser-gr-mgt-tou-qtz)

no data no data

Finland

Vähäjoki Proximal: tre/act-cum-chl-mgt ± bt,r, hbl, qtz, hm, cc, bar; sulphides andold overprint(?)

(A) low salinity L-V ±nahcolite 2-14 wt.% NaCl

q.

(B) CO -rich

no data

Laurinoja(Hannukainen)

Distal: Na (ab ± sca)Inner distal: K ± Na (bt-Kfs ± ab, sca)

Proximal: Ca-Fe-Cu-Au-S (cpx-act/hbl-mgt-sulphides-gold ± sca, cc, bt, ab)

(A) hypersaline L-V-halite± 5 daughter minerals, 45-

8 wt.% NaCl .(B) hypersaline L-V-halite32-56 wt.% NaCl .(C) CO

2 -rich

δ S = -1 to 7,δ34S = 2 to 6,

δ C = -7 to -3,δ18O

cc = 10 to 14,

δ Ofluid

= 8 to 13

Kuervitikko Distal: Na (ab ± sca)Inner distal: K ± Na (bt-Kfs ± ab, sca)Proximal: Ca-Fe-Cu-Au-S (cpx-act/hbl-mgt-sulphides-gold ± sca, cc, bt, ab)

(A) hypersaline L-V-halite± 5 daughter minerals, 45-

8 wt.% NaCl .(B) hypersaline L-V-halite32-56 wt.% NaCl .(C) CO

2 -rich

no data

Cu-Rautuvaara Distal: Na ± K, Ca (ab ± bt, kfs, sca

cpx, am)Proximal: Na-Fe-Cu-Au-S ± K (ab-mgt-atp ± bt) accompanied withsulphides and gold

no direct data, probably

similar to Laurinoja anduervitikko

δ34S py, py, po

= 4 to 6

Raajärvi &uro

Distal: Na ± Ca (ab ± sca, act),Proximal: act/tre-chl-mgt ± cc, bt,ab, ap,Retrograde post-ore srp-chl-tlc-cc-hm

(A) hypersaline L-V-halite± 4 daughter minerals, 29-58 wt.% NaCl .(B) low to moderatesalinity 0-22 wt.% NaCl .(retrograde stage)(C) CO -rich

δ C = -8 to 11,δ C

naltered marble = 13,

δ18O = 12 to 19,δ O

fluid = 6 to 10

Table 2. continued.

or references and mineral abbreviations see Table 1. The stable isotopes are given relative to CDT, PDB andMOW for S, C, and O, respectively.

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.2 Iron oxide-rich hostsT e ro e an or g n o t e ronstones t at osthe Cu-Au mineralisation in IOCG systems haseen un er e ate ever s nce t e IOCG conceptas created. Hitzman et al. (1992) included Kiru-

a apatite-iron ores in the IOCG class. On theot er an , some aut ors cons er t at t e g ant

iruna ores were formed via direct crystallisa-on rom Fe-O- P-Ca-F me ts e.g. Nyström anenriquez, 1994), and there is still controversyhether there is a link or continuum between

K runa-type” apat te- ron ores an IOCG epo-sits. Typically, the ironstone hosts are metaso-

at c rep acement o es, an numerous arrenexamples of these are known to occur in conjunc-

ion with IOCG occurrences (Williams, 1994).ven n epos ts t at sp ay a roa spat a re-

ationship with syngenetic iron formations (i.e.IFs t e ron ox e-r c osts or Cu-Au m ner-

alisation are considered epigenetic (e.g. Salobo,equia and Fontboté, 2000).

n a num er o epos ts, ron ox es appearo be paragenetic precursors to the copper-gold

assem ages, an n some cases t as een proposed that magnetite-rich ironstones have acted

as a redox trap for the sulphur-rich fluids (e.g. attarra, Rot er am et a ., 1998 . Su p at on o

he pre-existing iron-rich assemblages is proposedn some epos ts as a prec p tat on mec an sm o

Cu and Au (e.g. Eloise, Baker, 1998). Groves andielreicher (2001) suggest that the complex and

epet t ve nature o t e ore-paragenes s re ect a prolonged and discrete hydrothermal event related

o mu t p e ntrus ve stages w t an a a ne mag-atic fluid source. Recent geochemical model-

ing suggests that precipitation of iron oxides andCu-Au m nera s n IOCG epos ts not neces-sarily take place in discrete episodes, but rather

e Fe an Cu-Au assem ages express pro ongeevolution of a single hydrothermal system (Oli-

er et al., 2004). Nevertheless, the ultimate roleo t e ron-r c osts n t e genes s o t e IOCGdeposits is still unclear. While in some deposits

ey appear to e t e cause or prec p tat on o t eCu and Au bearing minerals, in others they may

just be a “by-product” of Cu and Au mineralisa-on e.g. W ams an Po ar , 2001; O ver et

al., 2004).

. terat onThe IOCG deposits typically are surrounded byun re s o meters to ometre-sca e y rot er-

mal alteration haloes and the immediate wall rocks

are intensely altered. The alteration styles varyrom so c to potass c to ca c c or com nat on o

these (Table 2). The distal alteration is typicallyc aracter se y extens ve so c ± ca c c m neraassemblages, chiefly albite ± scapolite, actinolite,and it is accompanied by a loss of a number of el-ements, espec a y Fe, K ± Ca an ga n n Na e.g.Williams, 1994; Oliver et al., 2004; Paper II). Thesty es o t e prox ma a terat on somew at e-

pends on the lithology of the host rock sequence,

varying between potassic and calcic assemblagesan accompan e y prec p tat on o ron ox es(Table 2). The potassic alteration products areK- e spar an ot te or ser c te, an t e ca c calteration assemblages are dominated by skarnminerals, i.e. diopside-hedenbergite, andradite-grossu ar, an Ca-amp o es. In some cases,such as parts of the Candelaria (Marschik et al.,2000; Marsc an Font oté, 2001 , t e s arnassemblages are related to the presence of car-

bonate rocks in the host rock package, whereas inot ers e.g. Mt. E ott, Wang an W ams, 2001calcium is externally derived. In some shallow-eve recc a-sty e epos ts e.g. O ymp c Dam,

NICO, Sue-Dianne; cf. Table 1), the sodic distalalteration zone is missing or not exposed, and the

sta a terat on s om nant y potass c.Hitzman et al. (1992) suggested that the alter-

at on patterns epen on t e ept o a terat on,sodic alteration prevailing at deep levels, potassic

at intermediate to shallow levels, and sericitic al-terat on an s c cat on at very s a ow eve s(Fig. 2). The level of deposition also appears toe re ecte n t e ore m nera ogy Ta e 1 . In

deeper levels, the dominant iron oxide is mag-netite, and chalcopyrite, pyrite, and pyrrhotiteare t e ma n su p e m nera s. In s a ow- evedeposits, the mineral assemblages indicate moreox ze con t ons, emat te e ng t e om nantron oxide, and chalcocite and bornite comprising

the typical Cu-sulphide minerals.

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1

k m

2 km

Paleosurface

Sericite alteration

hematite-sericite-carbonate-

chlorite ± quartz

Potassic alteration

K-feldspar-sericite-magnetite

± biotite, actinolite, chlorite

Sodic alterationalbite-magnetite-actinolite

Magnetite stockwork

Massive magnetite

Massive hematite

Sericitic/Silicic alteration

Hematite - sericite ± quartz breccia

Figure 2. Schematic cross section of alteration zoning in IOCG deposits after Hitzman et al. (1992).

. ropose genet c mo e s orOCG deposits

The original proposal by Hitzman et al. (1992)as t at IOCG epos ts are express ons o eep-

seated, volatile-rich igneous-hydrothermal sys-ems tappe y eep crusta structures an pos-

sibly related to global-scale rifting events chieflyduring the Mesoproterozoic. Since that work,

ot Arc aean an P anerozo c IOCG epos tsand districts have been recognized and recentage ata n cate t at some epos ts are n e toorogenic processes (e.g. Williams, 2000; Oliveret al., 2004). Therefore, it is becoming more and

ore apparent t at IOCG epos ts are not m teo a certain time period or tectonic environment,ut were orme t roug out t e geo og ca s-ory in various tectonic environments.

Several genetic models for the IOCG depositsave een propose ur ng t e past 15 years. Re-ease of the ore constituents, especially the con-

st tuents o t e ron ox e-r c osts v a a t sa-ion reactions caused by circulating high salinity

brines is emphasised in number of these modelse.g. H tzman et a ., 1992; W ams, 1994; Bar-on and Johnson, 1996; and 2000; Oliver et al.,004 . T e ma n contra ct ng ssue etween t e

presented models is the ultimate source of the

albitising brines (i.e. magmatic versus non-mag-mat c source . Vo at e-r c a a ne magmas en-riched in incompatible elements (e.g. A-type orshoshonitic felsic intrusives) are favored in themagmat c u source mo e s e.g. Po ar et a .,

998). A genetic link to carbonatite intrusivesas a so een propose Groves an V e re c er,

2001). Brief reviews are given below on the ge-netic models by Barton and Johnson (2000) andO ver et a . 2004 w c suggest non-magmat cand magmatic brine sources for the mineralising

u , respect ve y F gs 3 an 4 .Barton and Johnson (1996 and 2000) pro-

posed that the ore fluids are connate basinalr nes an t e gan s carr e y t ese r nes are

possibly derived from ancient evaporates. Thec rcu at on o t e r nes s contro e y t er-mal convection, and extensive albite alteration(with metal depletion) is expected in the inflowan own ow zones o t e r ne F g. 3 . Nearmagmatic heat sources the fluids focus into struc-tura y an or t o og ca y avoura e ocat ons

producing intense sodic (mafic host) or potassic(felsic host) proximal alteration and the metalsare prec p tate . M x ng o sur ace- er ve u swith brines can be a significant factor in metal

prec p tat on at s a ower eve s. Barton an

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ab-chl-ep

+ Kfs-hm

(connate/marine

evaporite recharge)

(continental brine recharge)

Fe and base metals

leached, Na±Ca fixed

olig-act/

sca-hbl-px

fluids, metals, sulphurexternal and/or rock source

fluid flow due to thermal convection

fluids, metals, sulphurfrom magma

flow due to fluid release

± magmatic fluid

component

bt-act-Kfs/

ab-act-chl

mu-pph-qtz/

chl-mu-carb

hm-cpy-py/

mgt-ap

qtz-pph-alun-py/

mu-qtz-py/

Kfs-bi-qtz-mgt

py-en/

cpy-py/

mgt-cpy-bor

Iron oxide-copper-gold system Porphyry Cu system

igure 3. Conceptual genetic model for IOCG deposits, and a possible link to porphyry Cu-Au deposits, by Bartonand Johnson (1996 & 2000). Solid arrows display the path of the externally derived brines, dashed arrows the pathof fluid derived from magmatic source. Mineral abbreviations as in Tables 1 and 2, except alun = alunite, en =enargite, olig = oligoclase. Figure modified after Barton and Johnson (2000).

o nson 2000 po nt out t at t s n o systemends to produce sulphide poor deposits with only

geochemically anomalous concentrations of chal-cop e e ements. T ere ore, t ey propose t at

agmatic metal, sulphur, and fluid input mixingt t e externa y er ve u s or super mpos-

ng the oxide-rich system is probably significantn Cu-Au-richer deposits. Although the modely Barton an Jo nson 1996 oes exp a n t e

extensive sodic alteration noted in number of theOCG str cts, t a s to exp a n t e a most con-

sistent magmatic stable isotope signatures in theajority of the deposits (Table 2).

O ver et a . 2004 comp e t e ata on t edeposits from the Cloncurry region and made theo ow ng o servat ons. 1 Severa a t sat on

stages exists in the region covering temporally both the metamorphic events related to the 1600 – 1580 Ma Isan orogeny an t e t erma events

elated to Williams Suite intrusives during 1550 – 1500 Ma. 2 Most o t e IOCG epos ts n t e

egion post-date the peak of regional metamor-

phism being contemporaneous with the Williamsu te ntrus ves. T us t e evaporate source mo efor the deposits is unlikely since the evaporate

un ts wou ave een consume n a te anscapolite producing reactions prior to or duringthe peak of regional metamorphism. (3) Geo-c em ca ata on t e a t se country roc s othe Cloncurry deposits suggest consistent gain in

Na an oss o Fe, K, Ba, R ± Ca, Sr, Co, V,Mn, Pb, and Zn during the alteration. Most theelements lost from the albitised rocks are foundenr c e n t e metasomat c ronstones t at ostthe Cu-Au occurrencess, and are also detected ine evate concentrat ons n t e u nc us ons nthe IOCG deposits of the region. Thus a geneticink between sodic alteration, high-salinity brines,

an t e IOCG epos ts appears ev ent. However,Cu is not consistently lost from the albitised rockssuggest ng t at anot er source s s nee e .

Based on this data and geochemical model-ing, Oliver et al. (2004) propose a genetic modelor IOCG epos ts n t e C oncurry reg on w ere:

(1) brines are released from crystallising WilliamsSu te ntrus ons, 2 c rcu at ng r nes evo vevia albitisation reactions where Na is fixed and

constituents that are enriched in proximal altera-t on zones an ronstones espec a y K an Feare stripped to the brine, (3) the circulation of

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Pegmatites

Breccia

Barren calcite veins

Proximal alteration, formation

of metasomatic ironstones

Barren granitoid tops: not enough Fe, K;

no sulphur Barren calcite veins: Host rock wrong

composition, not enough sulphur?

Barren ironstone: no sulphur

1

2

3

1

2

3

Heat source

Williams Suite (or similar)

felsic and mafic intrusive

rocks

Cu-Au mineralisation

Cu source NaCl source

Sulphur

source

Gabbro releases

sulphur, possibly

by mingling

Mixing Cu-bearing brine

with S-bearing fluid,

possible deposit

Albitisation:

Fe+K source

Previous S-source

(black shale or

ironstone), possible

deposit

5 0 0 t o 3 0 0 0 m e t e r s

igure 4. The genetic model for IOCG deposits in the Cloncurry region, Queensland, Australia by Oliver et al.(2004). Solid arrows illustrate the path of the brines derived from intrusions. Dashed arrows illustrate path of thesulphur bearing fluids. Figure modified after Oliver et al. (2004).

e meta -enr c e r ne s a e an ocuse y

faulting and/or shearing, (4) metals are precipi-ate n structura y e.g. at ona ogs an ort o og ca y avoura e ocat ons poss y a e

by mixing with external lower-salinity fluid (Fig.. Barren ronstones are pro uce t e a t s-

ng fluids were initially poor in Cu or S or both.or ormat on o arge tonnage c a copyr te e-

pos ts n t e reg on e.g. Ernest Henry , m x ng oa metal-rich brine with S-bearing wall rocks or anexterna S- ear ng u s pro a y requ re .

. ennoscan an epos tses es t e K runa-type magnet te-apat te ores,

severa epos ts n t e nort ern Fennoscan a

have been proposed to belong to the IOCG classe.g. H tzman et a ., 1992; Po ar , 2000; We e

an E u, 2003 . In nort ern F n an , numerous,chiefly orogenic, Au ± Cu deposits are knownE u, 1999 , an t e Fe-Co-Au- U epos ts n

the Kuusamo schist belt have been suggestedto e ong to t e IOCG c ass Van anen, 2001 .However, unt recent y, t e ma n ocus o exp o-ration and research in northern Finland has beenn PGE an orogen c go epos ts an tt e e ort

has been put on the IOCG deposits. The purposeo t s wor s to esta s t e IOCG potent a ot e nort ern F n an – w et er suc epos ts ex-

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sts there, and if so, what are their characteristics,and how do they compare to IOCG deposits else-

ere.

2 Review of the original pa-

. aperaper I describes (1) the general geological fea-

ures o t e M s reg on, 2 geo og ca an t egeochemical features of the magnetite occur-ences in the area focusing on the Raajärvi anduro epos ts, an 3 reg ona an oca a tera-

ion styles.T e e roc o t e M s reg on cons sts o

a supracrustal sequence of dolomitic marbles,

quartzites, mafic metalavas, mafic tuffs, micasc sts, ac sc sts, ca c-s cate roc s an

eta-arkosite. Gabbros and granites comprise thentrus ves n t e reg on. Base on t e r c em ca

composition, the mafic metavolcanic units aredivided into LREE-depleted and slightly LREE-enr c e t o e t c avas, an a tu un t w c

as a flat chondrite-normalised REE pattern. Twogeoc em ca y erent ga ros occur n t e re-gion: differentiated, LREE-enriched, 2117 ± 7

a gabbros, and gabbros of unknown age witha at c on r te-norma se REE pattern. T egranites, that occur mainly in the northern parto t e reg on, are t e youngest roc s n t e areaand belong to the ca. 1800 Ma aged intrusive suiteof the Central Lapland Granitoid Complex. Thegeoc em ca an sta e sotope eatures o t e

isi supracrustal rocks display similarities withe K va o Group roc s n t e western part o t eeräpohja schist belt.

Several skarn-like magnetite occurrences ex-sts n t e M s reg on. O t ese, t e Raa ärv anuro deposits were investigated in more detail.

T e magnet te occurrences are oste y s arnocks within a ca. 2.22 – 2.12 Ga dolomitic mar-

ble-quartzite sequence and within albitites whichare g y a tere var et es o t e LREE-enr c egabbro intrusions and their granophyric roofones. T e ma n opaque m nera n t e occurrenc-

es is magnetite with minor hematite, pyrite and

chalcopyrite. Besides iron, the occurrences con-a n e evate concentrat ons o V ≤ 2400 ppm ,

and locally elevated values of P (≤ 1.44 wt.%).The average sulphur concentration at Raajärvian Puro s 0.1 wt.% an 0.3 wt.%, respect ve y.However, locally up to 3.7 wt.% S was assayedrom pyr te- an c a copyr te- ear ng parts o t e

deposits. The sulphide-bearing parts of the ores

and skarn hosts also show elevated concentrationso Au, Cu, Co, an Te.

Characteristic for the Misi region is a re-g ona -sca e, mu t stage so c a terat on a te-scapolite) that has effected all rocks in the regionexcept the granites in variable degrees. Alterationn an aroun t e Raa ärv an Puro epos ts s

dominated by intense, pervasive sodic alterationa te-scapo te an s arn-a terat on act no te-

tremolite-chlorite-serpentine). The intense sodic

alteration and the skarn-alteration are related toau t ng or s ear ng e ore or ur ng t e reg ona

D deformation stage.Base on t e a terat on eatures, an geo-

chemical and mineralogical constrains of the Raa- järvi and Puro deposits and their country rocks,

t s suggeste t at t e ron n t e epos ts maywell have been derived from the altered countryroc s.

2.2 Paper IIPaper II 1 tests t s poss e t at t e ron n t emagnetite deposits in the Misi region was derivedrom t e ma c country roc s v a a t sat on y

circulating high-salinity brines, (2) investigateswhether the albitisation and mineralisation took

p ace ur ng t e crusta -sca e extens ona stages pre-dating the 1.9 – 1.8 Ga Svecofennian orog-eny or ur ng t e Sveco enn an orogen c events,(3) evaluates the sources of the fluids related to

the albitisation and mineralisation events, and (4)eva uates t e poss e mec an sms o mo sa-tion and precipitation of the metals in the mag-net te epos ts. T s wor s one ase on t egeochemical, fluid inclusion, stable isotope (Oand C), U-Pb and Pb-Pb isotopic data presentedn Paper II.

Mass balance calculations on variably albi-t se ga ro next to t e Raa ärv an Puro e-

posits indicate that significant amounts of Fe, Ca,

Mg, K, Cu, V, and Ba were lost, and Na and Siwere ga ne ur ng t e a terat on o t e roc w t

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l, Ga, Ti, and Zr remaining immobile. Calcu-ated loss of Fe O (t) in respect to 100 g of rocks 3.3 g an 14.7 g or mo erate y an ntense y

albitised gabbro, respectively. This indicates thaton y one m o ga ro w t a ens ty o 2.9 g× dm- can release 67 Mt of Fe through moderate

albite alteration. This is more than 20 times theron n t e Raa ärv an Puro epos ts com ne

and, considering the extent of the albite alterationaroun t e epos ts .e. at east 3 m mo erate yo intensely albitised rock in the immediate vi-

cinity), the iron in the deposits could easily haveeen er ve rom t e country roc s. Mass a -

ance calculations on skarn-alteration indicate thats gn cant quant t es o S , Ca, Fe, Na, Cr, an

a were gained, K, Mg, and V were lost and Al,

Ti and Zr remained immobile during the skarn-a terat on o a m ca sc st at Raa ärv .

luid inclusion data from the Raajärvi anduro epos ts suggest t at u s re ate to ore

formation, albitisation, and skarn-alteration wereighly saline (up to 58 wt.% NaCl

q, oxidizing,

aqueous-car on c u s. Base on eat ng- reez-ng measurements and proton induced X-ray

em ss on PIXE ana yses, t e u s conta neigh concentrations of Na, Cl, Ca, K, Fe, and Ba,

as well as elevated concentrations of Mn, Sr, Cu,n, an P . T e u s t at c rcu ate ur ng t e

post-ore serpentinisation were low to moderatesa n ty aqueous-car on c u s conta n ng mo -erate concentrations of Na, Cl, Ca, and K. The

r-Cl ratio of the fluids that circulated during thenera sat on an t e post-ore retrogra e stages

differ significantly suggesting a different originor t e u s.

ased on oxygen isotope thermometry, the

emperature during the skarn-alteration and for-at on o t e magnet te epos ts was etween

90o and 490oC. Based on the analysed δ Oa ues o t e magnet tes, an s cates rom t e

ores and skarns the calculated O u

during theineralisation stage was between 6.1 and 9.8 ‰MOW at 450 C. T s, toget er w t t e ana yse

δ C values of the calcites in the ores and skarnsat are etween -7.7 an 10.9 ‰ PDB, most e-

y reflect admixture of magmatic- or mantle-de-

ived carbon with the marble wall rocks that showC va ues o aroun 13 ‰ PDB.

SIMS U-Pb age data on zircons from the albi-tised gabbro next to the Raajärvi and Puro depos-ts suggest t at t e ntrus on o t e ga ro too

place at 2123 ± 7 Ma. TIMS U-Pb data on meta-somat c t tan tes n t e a t ze ga ro re ate toalbite alteration yield ages of 2062 ± 2 Ma and

2017 ± 3 Ma. These ages are roughly contempora-neous to magmat c events re ate to crusta -sca eextensional stages in northern Finland.

Base on t e ata presente , t e o ow ngconclusions are made. (1) The oldest skarn as-semblage, the diopside skarn, was formed due tocontact metasomat c react ons cause y t e n-trusion of the 2123 ± 7 Ma gabbro into the Raa-ärv ormat on supracrusta sequence. 2 T eronstones and actinolite-dominated skarns were

formed during metasomatic events that took placeetween 2062 ± 2 Ma an 2017 ± 3 Ma. T e ot,

highly saline, fluids that circulated during thisstage cause t e w e sprea a te a terat on anstripped the mafic country rocks of Ca, Fe, K, Cu,Ba, and V. The fluid was possibly derived froma eep-seate magmat c source. T e c rcu at onof the metal-rich fluid was aided and focused byau t ng re ate to crusta -sca e extens on an t e

metal precipitation was due to a drop in tempera-

ture, wall rock reaction, or mixing of the brinew t coo er, ess-sa ne u s, or com nat on othese. (3) The present low-temperature mineralassem ages at Raa ärv an Puro were ormeduring the later Svecofennian orogenic eventsthat post-date the iron mineralisation in the Misireg on.

. aperPaper III (1) describes the geology of three iron

oxide-copper-gold deposits in the Kolari region,nort ern F n an , 2 escr es t e a terat on nand around the deposits, (3) presents new geo-c em ca ata on t e epos ts an a tere roc s,(4) presents new fluid inclusion data, and (5)

presents new U-Pb age data. Based on the previ-ous y reporte ata an t e new ata presente ,a new genetic model, alternative to the previouss arn mo e , or t e Ko ar epos ts s presente .

Several iron oxide-copper-gold deposits are

known in the Kolari region, in the western parto t e Centra Lap an greenstone e t, nort ern

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inland. They are hosted by clinopyroxene-domi-ated skarns overprinting the > 2.05 Ga Savukos- Group supracrusta roc s an t e ca. 1.86 Gaaparanda Suite intrusions. All deposits are lo-

cate w t n or next to s ear an au t zones orm-ng parts of the major, NNE-trending, Kolari shear

one (KSZ) which in turn form the northernmost part o t e Ba t c-Bot n an Megas ear BBMS .

aper III focuses on three of the deposits whichconta n s gn cant amounts o Cu an Au: t e

aurinoja ore body at the Hannukainen mine, andhe Kuervitikko and Cu-Rautuvaara deposits. Ataur no a an Kuerv t o, t e copper an go

are hosted by ironstone and skarn. At Cu-Rautu-aara, t e ost roc s a magnet te- ssem nate

albitite.

The deposits have a distinct metal associationo Fe-Cu-Au ± Ag, B , Ba, Co, Mo, S , Se, Te, T ,

, LREE. The concentration of copper and golds 0.1 – 4.5 wt.% an 0.1 – 6.6 g t, respect ve y.

The wall and host rocks are intensely altered anddisplay a deposit-scale zonation at Laurinoja and

uerv t o w ere t e structura contro s t eost prominent. The outer distal alteration zone

s c aracter se y a te ± Na-scapo te, t e n-er distal alteration zone by biotite-K-feldspar ±

albite, scapolite, and the proximal alteration zoney c nopyroxene-magnet te ± Ca-amp o e,

scapolite, calcite, sulphides.T e rat os o t e mmo e A , T , Zr n cate

hat the dominant protolith for the clinopyrox-ene-dominated skarns and ironstones is the mafic

etavo can c roc o t e > 2.05 Ga supracrustasequence. Mass balance calculations suggest thats gn cant quant t es o Fe, Ca, CO , S, Cu, Au,

i, and Te were added to the proximally altered

ocks (skarn and ironstone) at near constant Al,T , an Zr. Mass a ance eva uat ons or t e s-ally altered rocks suggest gains in Na, K, and Ba

an oss n Ca.luid inclusion data from Laurinoja and

uervitikko suggest that fluids that circulated ine roc s ur ng t e ma n m nera sat on event

and the subsequent brittle stage(s) were complexg -sa n ty ≤ 56 wt.% NaC . aqueous-car-

bonic fluids. The temperature during the minerali-

sation event was between 450o and 550oC whichs cons stent w t t e g -temperature m nera

assemblages of the skarn. The pressure at the timeof the mineralisation was between 1.5 and 3.5

ars.The age limits for the alteration and ore for-

mat on are e ne y t e 1864 ± 5 Ma age omagmatic zircons in the hanging wall diorite and

the 1797 ± 5 Ma age of the magmatic zircons int e gran te t at recc ates t e ore at Hannu a -nen mine. The 1797 ± 5 Ma age of the zircons ins arn com ne w t t e 1.81 – 1.78 Ga ages othe metamorphic titanites in the altered wall rocksand skarns suggest that the deposits were formedat ca. 1.80 Ga. T s age post- ates t e reg onametamorphic peak in northern Finland, and isnterprete to e roa y contemporaneous w t

the eastward directed, 1.83 – 1.77 Ga D thrusting

event in the Kolari region during which the KSZwas react vate .

The data presented is inconsistent with the prev ous mo e s o t e Ko ar epos ts w csuggested that the deposits either are metamor-

phic expressions of syngenetic iron formations ors arn epos ts orme un er contact-metasomat cconditions related to ca. 1.86 Ga monzonite in-trus ons. Instea , t e a ternat ve mo e presentehere is that the Kolari ironstones and Cu-Au oc-

currences are epigenetic deposits structurally con-tro e y t e KSZ au t an s ear zones. T e newdata suggest that the deposits best fit into the cat-egory o t e ron ox e-copper-go epos ts.

3 Discussion

Characteristics of five potential IOCG occur-rences rom nort ern F n an are s own n Ta es

and 2: Laurinoja, Kuervitikko, and Cu-Rautu-

vaara from the Kolari region, western part of theCentra Lap an greenstone e t CLGB , Raa-

järvi with its small satellite (Puro) from the Misireg on, eastern part o t e Peräpo a sc st e t(PSB), and Vähäjoki in the western part of thePSB (Fig. 5). All, except Vähäjoki which is be-yon t e scope o t s wor , are escr e n moredetail in papers I, II, and III.

T e genera c aracter st cs o t e Ko ardeposits best fit into the IOCG category; they

display similar element association, alteration pattern, an u nc us on c aracter st cs to t e

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< 1.8 Ga Volcanic rocks

< 1.7 Ga Rapakivi intrusionsTranscandinavian magmatic belts

Paleoproterozoic undivided

Archean basement

C a l e d o

n i a n

o r o g

e n (

5 1 0

- 4 0 0

M a )

Sveconorwegian

orogen (1.1-0.9 Ga)

Svecokarelian

orogen (1.92-1.80 Ga)

27°E

60°N

400 km

B B M S

SWEDEN

RUSSIA

PSBKSB

CLGB

1.

2.

Ca. 1.80 Ga granitoids

Proterozoic greenstone and schist belts

Archean basement

Lapland granulite belt

150 km

a. b.

3.

igure 5. (a) General geological features of northern Fennoscandia. Dashed lines indicate major structuralineaments. Dashed box indicates the area covered in (b). Modified after Gorbatchev and Bogdanova (1993). (b)

General geological features of northern Finland and the location of the Kolari region (1), Misi region (2), andähäjoki deposit (3). CLGB = Central Lapland greenstone belt, KSB = Kuusamo schist belt, PSB = Peräpohja

schist belt. BBMS = Baltic-Bothnian megashear (after Berthelsen and Marker, 1986).

other deposits listed in Tables 1 and 2. The Kolariepos ts are re ate to a ma or crusta sca e s ear

one system (Berthelsen and Marker, 1986) thats cons ere to represent t e cont nent-cont -ent collisional boundary between the Norrbotten

and Karelian cratons in the recent plate tectonico e o t e Fennoscan an s e y La t nen

et al. (2003). The deposits were formed duringe ate part o t e cont nent-cont nent co s ona

stage (1.85 – 1.79 Ga), near to the extensionalorogenic collapse and stabilisation stage (1.79

– 1.77 Ga n t e tecton c mo e . T e pre m -

ary C- and O-isotope data on the Kolari depos-ts suggest t at t e u source was om nant yagmatic, S-isotopic values implying a combina-

ion of magmatic and sedimentary sources for thesu p ur H tunen, 1982; Ta e 2 . T e propose

.80 Ga age of the Kolari deposits (Paper III) iscontemporaneous to a t erma event re ate to t entrusion of the voluminous S-type potassic gran-toids throughout northern Finland and Swedene.g. Hans et a ., 2001 . Anot er nterest ng, ut

poorly known, group of roughly contemporane-ous ntrus ons n nort ern F n an are t e ca. 1.79Ga appinites that display enrichment in K, Na,

Ba, Sr, P, Cl, F, and LREE, and locally containa un ant Cu-N -Fe su p e ssem nat on w t

elevated PGE-Au-Te concentrations (Mutanenan Väänänen, 2004 . Regar es o w et er t e brine source for the Kolari deposits was the felsic

ntrusives, appinites or some other, possibly deep-seate magmat c source, t e genet c mo e y O -ver et al. (2004) best fits with the characteristicso t e Ko ar epos t.

The barren ironstones in the Misi region showa number of features common for IOCG depositsesp te conta n ng on y oca y geoc em ca y

anomalous concentrations of Cu, Au, Co, and TeTa es 1 an 2; Paper I an II . T e ata sug-

gest that it is likely that the Misi ironstones wereformed by a mechanism proposed by Oliver et al.2004 or ronstone osts or IOCG epos ts see

Fig. 4). In addition, the data from the Raajärvian Puro epos ts n cate t at Cu an poss yAu were mobile during the alteration and pre-cipitation of iron but, possibly due to lack of S,t e c a cop e e ements not prec p tate see

Paper II).T e age ata suggests t at t e so c a terat on

and formation of the ironstones in the Misi region

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ook place in an intracratonic rift setting prior tohe 1.92 – 1.79 Ga Svecofennian orogenic events.

T us, t e oca supracrusta sequence con-ain evaporate beds as it has been suggested (e.g.r etsc et a ., 1997 , t e so c a terat on n t eisi region could have been related to the brines

eleased from the evaporates by a mechanisms m ar to t at propose y Barton an Jo nson(1996). However, the stable isotope data and

a ogen rat os o t e r nes at Raa ärv an Purosuggest that the fluid source was dominantly mag-

atic (Paper II). Therefore, like with the Kolariepos ts, t appears t at a so n t e M s reg on t eagmatic-source model is more probable.

Summary

.1 Conclusionsollowing conclusions can be made based on theata presente :

. Northern Finland is a potential region forhe formation of IOCG deposits. Of the Fe-Cu-Auepos ts present y nown n t e reg on t e Ko ar

occurrences best fit into the IOCG category.. T e metasomat c ronstones n t e M s

egion are formed by mechanism similar to the

ronstone hosts for IOCG deposits elsewhere.Copper an pro a y go was mo e ur ng t ealteration and formation of the ironstones in the

s reg on, ut ue to a ow amount o su p urn the system they did not precipitate. Therefore,he ironstones at Misi are considered to representarren examp es o IOCG epos ts.

3. In light of the current data, it appearsat t e most avoura e per o s or ormat on

of IOCG deposits in northern Finland were: (1)

during the extensional events at 2.44 – 2.05 Ga,an 2 ur ng tecton c events at 1.83 – 1.77 Gahat post-date the peak of the regional metamor-

p sm.. The data supports magmatic source models

of the mineralising fluids and that the elementsenr c e n t e ronstones were er ve rom t ecountry rocks of the ores by albitisation process.

5. So c a terat on n nort ern F n an too place in multiple stages, especially during the

crustal scale extensional events between 2.44 and.05 Ga, ut a so ur ng post-pea metamorp c

tectonic events at 1.83 – 1.77 Ga.. The sodic alteration events in northern Fin-

an were accompan e y mass ve ux o mo- bilised metals, especially iron, which may have

ocuse to structura an or t o og ca ocat onssuitable for metal precipitation. Great care should

be taken in interpretation of the origin of ironox e-r c t o og es n reg ons w t a un ant a -

bite alteration, especially if the host rock is highlya tere , e ore a e ng t em to “metamorp cexpressions of syngenetic iron formations”. Epi-genetic origin should also be considered.

4.2 Implications for exploration. In t e g t o current ata, t e most pro-

mising area for exploration of IOCG type deposits

n northern Finland is the area around the KolariS ear Zone system n t e western part o t e Cen-tral Lapland greenstone belt. Also the Misi regionappears nterest ng w t arren ronstones n cat-ng that favourable hydrothermal activity did take

place in there. However, the focus of the explora-t on at M s s ou per aps to e put nto t e areaswith sulphur-rich lithologies.

2. So c-a tere roc s n cate act v ty ohigh-salinity brines and mobility of metals. Re-

gions with albitised and scapolised rocks shoulde avore . However, n s a ower- eve systems

sodic-altered rocks may not be exposed, instead potass c- ron an or ca c c- ron a terat on may prevail and indicate high-prospectivity areas.

3. Key locations for exploration are fault ands ear zones, t o og ca contacts, an ntersec-tions of these.

4. Numerous ronstones t at ave een nter- preted, in some cases only based on their banded

appearance, to be syngenetic iron formations (i.e.BIFs o occur n nort ern F n an . T ese s ou

be reviewed, especially if they do contain evensma amounts o Cu, Ba, Co, Au, an S, anthere appears to be a spatial correlation with faultor shear structures.

5. Geop ys cs an t geoc em stry s ou be used to focus the exploration. A number of thecurrent y m ne arge IOCG epos ts are nand were discovered by using geophysics and soil

geochemistry. The combination of distal sodic al-terat on an ron ox e-r c ost roc s s ou g ve

7/27/2019 Iron Oxid


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good response in magnetic maps. In addition, U,, and/or Th anomalies in radiogenic maps andu, Cu, Co, Ba, U, T , an or P anoma es n

soil geochemistry may indicate the presence of a prox ma a terat on zone an m nera sat on.

. Drilling should not be limited to ironstones

only. Cases like Cu-Rautuvaara in Finland andT rro a n Swe en suggest t at Cu-Au m n-eralisation and ironstones may be located tens or

un re s o meters away rom eac ot er.

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iron oxid

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