New styles of intrusive related copper-gold deposits in ...

LICENTIATE T H E S I S

New Styles of Intrusive Related Copper-Gold

Deposits in Northern Sweden

Therese Bejgarn

Department of Chemical Engineering and GeosciencesDivision of Geosciences

ISSN: 1402-1757 ISBN 978-91-7439-057-5

Luleå University of Technologyy 2009

Printed by Universitetstryckeriet, Luleå 2009

ISSN: 1402-1757 ISBN 978-91-7439-057-5

Luleå

www.ltu.se

Front coverLeft: Gold (yellow) among silicate minerals (black) and pyrite (beige).Right: Gold bearing sulphide vein with pyrite chalcopyrite and sphalerite, drill core diameter 41 mm.

a

e

c

d

b

GIV

GIII

GI

GII

5 km

N

Tona

lite-

Gra

nodi

orite

(Jör

n G

rani

toid

Com

plex

, GI)

~188

5 M

a�'�

Porp

hyrit

ic in

trus

ive

(~18

86 M

a in

the

Tallb

erg

area

)�

Gra

nodi

orite

-Gra

ntite

(Jör

n G

rani

toid

Com

plex

, GII)

~18

73 M

a�'�

Coar

se g

rain

ed G

rant

ite (J

örn

Gra

nito

id C

ompl

ex, G

III) ~

1865

Ma�

Gab

bro/

hybr

id g

abbr

o

Fine

grai

ned

mafi

c dy

kes

Fels

ic m

etav

olca

nic

rock

s, Sk

elle

fte

Gro

up (~

1885

Ma)

6

Met

avol

cani

c ro

cks,V

argf

ors

Gro

up (~

1875

Ma)

6

Maj

or fa

ults

/she

ar z

ones

Tona

litic

enc

lave

s

Mag

netit

e-ric

h ga

bbro

Dril

l hol

e lo

catio

n in

pro

files

Intr

usiv

e ro

cks

Supr

acru

stal

rock

s

Alt

erat

ion

and

min

eral

isat

ion

Mafi

c en

clav

es

Qua

rtz-

porp

hyrit

ic g

rano

dior

ite (G

I), Ä

lgtr

äsk

Prop

yliti

c al

tere

d qu

artz

por

phyr

itic

gran

odio

rite

(GI,

Älg

träs

k)

Älg

liden

ultr

amafi

c in

trus

ion

~187

6 M

a (p

relim

inar

y ag

e)4

Duc

tile

defo

rmat

ion

HH

ybrid

rock

Crus

hed

rock

Min

eral

ised

rock

with

phy

llic

to s

ilici

c al

tera

tion

(Älg

träs

k an

d Ta

llber

g Au

-zon

e)

Post

-oro

geni

c gr

anito

id

Gal

leja

ur a

nd A

ntak

mon

zoni

te s

uite

(~18

75 M

a)5

Inte

rmed

iate

-mafi

c m

etav

olca

nic

rock

s, Sk

ellft

e an

d A

rvid

sjau

r Gro

ups

Met

ased

imen

tary

rock

s, A

rvid

sjau

r Gro

up (~

1876

Ma)

7

Min

eral

dep

osit

a-e

Intr

usiv

e ho

sted

min

eral

dep

osits

Mis

cella

neou

s

Ä W

ilson

et a

l. 19

87

ÄGon

zále

s-Ro

ldán

200

9 ÄW

eihe

d &

Sch

öber

g 19

91

4Bej

garn

, Söd

erbe

rg, Å

rebä

ck, W

eihe

d 20

09 (u

npub

lishe

d da

ta)

5 Ski

öld

1988

6Bill

strö

m &

Wei

hed

1996

7S

kiöl

d et

al.

1993

Hy

Lege

nd ,

Figu

re 1

& 2

Fres

h to

wea

kly

prop

yliti

c qu

artz

por

phyr

itic

gran

odio

rite

(GI,

Älg

träs

k)

Med

ium

-gra

ined

lam

inat

ed to

oph

itic

oliv

ine

gabb

rono

rite

Med

ium

-gra

ined

sul

phid

e-be

arin

g ga

bbro

norit

e

Coar

se-g

rain

ed, F

e-Ti

oxi

de ri

ch g

abbr

onor

ite/o

livin

gabb

rono

rite

Fine

-gra

ined

, Fe-

Ti o

xide

rich

gab

bron

orite

/oliv

inga

bbro

norit

e

Rens

tröm

min

e

50 m

50 m

More intensemineralization

50 m

50 m

a) b) c)

d)

e)

GIV

GIII

GI

GII

Post orogenic granitoid

Jörn granitoid batholith (GI)

Jörn granitoid batholith (GII)

Jörn granitoid batholith (GIII-GIV)Älgliden dyke

Gallejaur and Antak monzoniteGabbro-diorite

Major faultFelsic metavolcanic rocks,Skellefte group

Intermediate-mafic metavolcanic rocks, Skellefte and Arvidsjaur groups

Metasedimentary rocks,Arvidsjaur group

Metavolcanic rocks, Vargfors group

Major VMS deposit

Porphyry dykeRenström

JörnTallberg porphyry Cu deposit

Älgträsk Au deposit

7250

000

7230

000

7210

000

1690000 1710000

Unaltered to weakly altered quartz porphyritic granodioritePropylitic altered quartzporphyritic granodiorite

Quartz-feldspar porphyritic dyke

Finegrained mafic dyke

”Episyenite”

Aplitic dyke

Mafic microgranular enclaves

Mineralized rock withphyllic to silicic alteration

Ductile deformation

Gabbro

H Hybrid rock

Crushed rock

Tonalite

50 m

A)

B)

7219000

1695

000

PROFILE

Drill core location

1 km

H

H

H

H

H

H

HH

GI data from the Älgträsk area, this study.

GI data from the Tallberg area, from Weihed (1992).

Average data from 54 analyses of GI from Boliden Mineral AB, previously published in Weihed et al. (1987).

Average data from 16 analyses of GI, from Gonzáles Roldán et al. (2007).

Average data from 10 analyses of GI, from Wilson et al. (1987).

a) b)

c)

A P

Q

quartzolite

quartz-rich

granitoid

a

l

k

-

f

s

p

.

g

r

a

n

i

t

e

syeno-

granite

monzo-

granite

grano-

diorite

t

o

n

a

l

i

t

e

q-alk-fsp

syenite

quartz-

syenite

quartz-

monzonite

q-monzodiorite

q-monzogabbro

q-diorite

q-gabbro

q-anorthosite

1

syenite

monzonite 2 3

1 - alkali-feldspar

syenite

2 - monzodiorite

monzogabbro

3 - diorite, gabbro

a

b

c

d

e

f

a bccp

apy

sp

Au

apyI

apyII ccp

Au

Te-minerals

GIV

GIII

GI

GII

Post orogenic granitoid

Jörn granitoid batholith (GI)

Jörn granitoid batholith (GII)

Jörn granitoid batholith (GIII-GIV)Älgliden dyke

Gallejaur and Antak monzoniteGabbro-diorite

Major faultFelsic metavolcanic rocks,Skellefte group

Intermediate-mafic metavolcanic rocks, Skellefte and Arvidsjaur groups

Metasedimentary rocks,Arvidsjaur group

Metavolcanic rocks, Vargfors group

Major VMS deposit

Porphyry dykeRenström

JörnTallberg porphyry Cu deposit

Älgträsk Au deposit

7250

000

7230

000

7210

000

1690000 1710000

N

Unaltered to weakly altered quartz porphyritic granodiorite (GI), Älgträsk

Propylitic altered quartzporphyritic granodiorite

Quartz-feldspar porphyritic dykeFinegrained mafic dyke

”Episyenite”, Älgträsk

Älgliden ultramafic intrusion

Mineralized rock withphyllic to silicic alteration,Älgträsk

Ductile deformation

Gabbro (GI)

H Hybrid rockCrushed rock

Tonalite, Älgträsk

Au-deposit,Tallberg

Porphyry Cu-Mo-Au deposit, Tallberg

Tonalite, Tallberg (GI)

No geological information

1695

000

7219000

500 m

Profile b

Profile a

Näverliden

Unaltered to weakly altered quartz porphyritic granodiorite (GI)

Quartz-feldspar porphyritic dykeFinegrained mafic dyke

Propylitic altered quartzporphyritic granodiorite (GI)

Mineralized rock withphyllic to silicic alterationDuctile deformation

Crushed rock

Drill hole

50 m

b

a

65-140

Quartz-

destructive

alteration

54.69

19.52

8.03

1.50

2.29

7.37

1.67

0.28

0.04

0.09

17.0

4.4

99.86

381.0

2

8.3

0.8

18.5

5.4

7.6

29.0

6

233.7

0.7

7.9

6.3

60

1.8

160.7

29.9

29.0

56.9

6.54

25.2

4.39

1.16

4.22

0.76

4.55

0.99

3.07

0.52

3.30

0.54

0.23

3.42

265-84

Sodic

alteration

71.08

14.11

1.48

0.93

6.14

4.52

0.16

0.32

0.06

0.01

12.0

1.0

99.85

83.0

1.6

0.2

13.5

4.7

6.5

2.7

265.9

0.5

6.7

2.2

32

157.9

28.2

31.4

60.5

6.94

24.1

4.76

0.91

4.37

0.74

4.43

0.92

2.88

0.46

3.00

0.48

0.16

0.06

0701

Silicic

alteration

56.04

2.59

25.99

0.14

0.06

0.04

1.41

0.08

0.01

0.02

0.004

7.0

13.6

99.95

202.0

58.3

0.2

4.2

0.3

0.8

13.8

2

6.9

0.1

0.2

38

6.3

11.6

2.4

1.0

2.0

0.24

0.9

0.23

0.03

0.22

0.05

0.39

0.08

0.24

0.04

0.28

0.04

19.33

83-125

Phyllic

alteration

69.49

10.65

10.16

1.33

0.58

0.30

2.83

0.21

0.06

0.14

0.003

11.0

4.1

99.89

506.0

8.3

1.5

14.3

3.7

6.2

59.2

6

22.3

0.6

4.2

5.0

39

7.8

110.1

20.3

8.7

17.9

2.28

9.0

1.90

0.26

2.06

0.41

2.88

0.66

2.18

0.39

2.45

0.41

0.05

3.11

83-126

Propylitic

alteration

70.68

13.46

3.83

0.80

2.35

2.82

2.82

0.21

0.06

0.10

0.002

11.0

2.8

99.92

575.0

4.2

1.0

12.9

3.8

6.2

50.7

2

100.8

0.7

5.9

5.4

39

1.8

110.7

23.3

12.7

27.1

3.48

13.4

3.01

0.54

2.99

0.55

3.44

0.73

2.33

0.41

2.64

0.43

0.28

0.09

118-45

Low Ti

mafic dyke

48.7

14.2

9.13

8.7

8.51

3.01

1.27

0.71

0.265

0.19

0.081

172

28

5

99.76

325

37.9

1.8

15.7

1.8

3.5

31.6

452.0

0.2

2.4

1.8

179

0.7

61.2

11.9

17.7

39.7

5.62

23.6

4.68

1.13

3.71

0.41

2.44

0.4

1.02

0.14

0.95

0.15

0.61

0.03

99-62

High Ti

mafic dyke

48.61

15.18

11.60

5.85

7.96

2.35

1.02

1.72

0.55

0.18

0.022

60

28

4.7

99.76

225

2

36.8

3.0

19.0

3.2

9.8

43.4

348.2

0.5

1.4

0.7

212

<0.5

126.2

25.2

21.4

49.6

6.93

29.6

6.04

2.02

5.78

0.90

4.86

0.93

2.58

0.38

2.32

0.34

0.47

0.05

47-80

Älgliden

intrusion

41.90

7.68

19.93

18.94

3.93

0.95

0.53

0.71

0.14

0.22

0.306

685.0

17

4.2

99.48

189

1

126.1

1.6

10.9

1.2

3.2

12.3

1

192.0

0.2

0.8

0.9

165

1.3

38.6

9.6

7.4

15.4

2.07

9.3

1.92

0.58

1.87

0.31

1.60

0.33

1.00

0.16

0.96

0.15

0.04

0.97

55-130

Aplite

76.99

12.18

0.91

0.18

2.25

4.78

0.93

0.06

0.004

0.02

2

1.6

99.88

443

2.3

0.3

11.4

3.3

4.2

15.5

131.3

0.3

3.3

2.9

0.9

71.8

16.8

13.9

30.8

3.96

14.8

2.45

0.11

2.22

0.35

2.49

0.54

1.62

0.26

1.83

0.29

0.30

0.07

58-38

QFP,

Älgträsk

69.21

15.40

3.04

1.02

3.73

4.50

1.05

0.23

0.08

0.06

0.003

5

1.5

99.86

492

2

5.0

1.0

17.5

2.2

3.2

17.9

591.0

0.3

1.3

0.9

32

0.6

70.9

5.6

9.3

19.0

2.26

8.7

1.48

0.40

1.09

0.17

0.96

0.18

0.56

0.09

0.57

0.09

0.18

169-33

QFP,

Tallberg

68.55

15.05

2.56

1.00

3.25

4.82

0.55

0.21

0.07

0.03

4

3.8

99.86

334

2.4

0.5

16.8

1.9

2.6

10.2

508.6

0.1

1.2

1.0

28

1.3

56.5

4.8

7.8

16.4

2.09

7.7

1.40

0.40

1.10

0.16

0.87

0.17

0.41

0.07

0.46

0.08

0.07

0.04

48-45

Gabbro,

Älgträsk

51.19

16.64

8.87

5.50

8.13

1.39

1.32

0.56

0.11

0.24

0.005

21

26

5.8

99.70

324

26.8

0.6

17.0

1.3

2.7

23.6

414.0

0.2

1.5

0.9

195

0.8

39.1

11.2

8.4

17.9

2.40

10.2

2.19

0.64

2.01

0.35

1.93

0.41

1.17

0.19

1.14

0.18

0.64

0.16

22-104

Tonalite,

Tallberg

64.63

14.01

7.61

2.92

4.63

2.23

1.09

0.41

0.09

0.07

0.005

27

2.2

99.93

261

1

10.6

1.1

16.2

1.5

3.7

25.2

205.6

0.2

2.7

2.1

155

0.7

45.0

12.9

9.3

17.7

2.18

9.1

1.79

0.45

1.88

0.34

2.02

0.43

1.35

0.21

1.40

0.21

0.08

0.10

27-77

Tonalite,

Älgträsk

66.71

16.23

3.78

1.07

4.72

4.17

1.03

0.26

0.12

0.05

5

1.7

99.81

389

3.8

0.4

17.7

2.4

3.4

14.8

508.0

0.2

1.2

1.0

32

83.8

9.2

9.2

19.2

2.47

9.8

1.85

0.54

1.67

0.27

1.47

0.31

0.86

0.15

0.98

0.14

0.13

0.04

146-89

QPG,

Älgträsk

71.79

13.61

3.66

0.79

3.26

3.35

2.01

0.23

0.027

0.06

bd

25

12

1.1

99.89

508

6.0

1.2

12.6

4.1

5.9

41.3

1

145.3

0.5

8.1

4.6

43

0.7

136.2

18.6

29.3

53.7

5.90

20.6

3.43

0.40

3.03

0.41

3.23

0.66

2.01

0.25

2.22

0.33

0.05

0.08

0.01

0.01

0.04

0.01

0.01

0.01

0.01

0.01

0.01

0.01

0.002

20

1

0.01

1

1

0.2

0.1

0.5

0.1

0.1

0.1

1

0.5

0.1

0.2

0.1

8

0.5

0.1

0.1

0.1

0.1

0.02

0.3

0.05

0.02

0.05

0.01

0.05

0.02

0.03

0.01

0.05

0.01

0.02

0.02

Sample

SiO2Al2O3Fe2O3(t)MgOCaONa2OK2OTiO2P2O5MnOCr2O3NiScLOISumBaBeCoCsGaHfNbRbSnSrTaThUVWZrYLaCePrNdSmEuGdTbDyHoErTmYbLuCS

bd

bd bd

bd

bdbd

bd

bd

bd

bd

bd

bd

bd

bd bd bd

bd

bd

bd

bd

bd

bd

bd bd bd

bd bd

bd bdbd

bd

bd

bd

bd

bd

bd

bd

bd

bd bd

0.1

Detection limit

2.4

3.4

3.6

50.0

1.5

4.4

bd

0.5

0.2

0.2

86.9

0.03

bd

bd

bd

0.4

3.4

2.2

20.0

0.5

1.6

bd

0.3

bd

bd

bd

0.02

bd

bd

bd

22.9

157.1

35.6

89.0

4.2

300.6

0.2

2.0

7.2

3.1

2157

0.15

bd

3.5

12

1.2

93.8

5.6

84.0

1.5

22.3

bd

0.4

1.5

1.5

1456

0.02

0.2

0.5

2

0.7

18.4

1.9

43.0

1.2

4.3

bd

0.4

bd

bd

14.8

0.01

bd

bd

bd

0.6

69.2

5.4

113

112.4

18.2

bd

0.5

bd

0.2

1.6

bd

0.4

bd

bd

0.8

51.8

3.2

122

55.1

52.1

bd

0.3

bd

0.1

0.9

bd

0.5

bd

bd

4.6

923.1

4.3

59

618.8

bd

0.2

bd

0.2

0.6

64.7

0.01

0.8

1.2

bd

3.9

24.2

1.5

2

0.9

3.8

bd

0.4

bd

bd

5.0

0.01

bd

bd

bd

0.4

6.5

1.9

55

6.1

1.8

bd

0.3

bd

bd

5.3

bd

bd

bd

bd

1.0

61.0

2.3

53

6.8

5.7

bd

0.4

bd

bd

2.5

bd

bd

bd

bd

0.2

52.6

2.6

266

21.5

7.7

bd

0.3

bd

0.1

3.6

0.16

bd

bd

bd

1.4

64.3

2.0

69

7.6

3.3

bd

0.4

bd

bd

4.5

0.02

0.1

bd

bd

0.7

24.6

0.8

35

1.5

2.8

bd

0.2

bd

bd

bd

bd

bd

bd

bd

2.5

6.2

3.8

36

1.3

3.7

bd

0.2

bd

bd

bd

bd

0.2

bd

bd

0.1

0.1

0.1

1

0.1

0.5

0.1

0.1

0.1

0.1

0.5

0.01

0.1

0.5

1

Mo

Cu

Pb

Zn

Ni

As

Cd

Sb

Bi

Ag

Au

Hg

Tl

Se

Te

Phonolite

Trachyte

Rhyolite/Dacite

Rhyodacite/Dacite

Sub-AB

TrAn

AB

Com/Pant

Bas/Trach/Neph

Andesite

0.001 0.010 0.100 1.000

40

50

60

70

80

Zr/TiO2

SiO2

A M

F

Tholeiite Series

Calc-alkaline Series

Tholeiite series

Calc-alkaline series

High-K calc-alkaline series

Shoshonite series

45 50 55 60 65 70 75

0

12

34

56

7

K2O

SiO240

Peridot

gabbro

Gabbro

Gabbroic

diorite

Diorite

Granodiorite

Granite

Syenite

Quartz

monzonite

Monzonite

Monzo

diorite

Monzo-

gabbro

Foid

gabbro

Foid

monzo-

gabbro

Foid

monzo-

syenite

Foid

syenite

Foidolite

Tawite/Urtite/Italite

Quartzolite

40 50 60 70 80 90

05

10

15

SiO2

Na2O

+K2O

A) B)

C) D)

Tonalite, Tallberg3Tonalite, Näverliden2Tonalite, Älgträsk1

Quarts Feldspar Porphyry, Älgträsk1,2Quartz Porphyritic Granodiorite, Älgträsk1,2

Gabbro/gabbro hybride, Älgträsk1,2

Quartz Feldspar Porphyry, Tallberg3Tallberg Tonalite1,2

Mafic dykes (high/low Ti), Älgträsk1,2Älgliden intrusion1,2

1 Data from this study. 2 Previously unpublished data from Boliden Mineral AB. 3 Data from Weihed et al. 1992.

a

b

c

d

e

f

g

h

i

j

Sam

ple/

REE

cho

ndrit

e

Tonalite, Älgträsk¹

La Ce Pr Nd SmPm Eu Gd Tb Dy Ho Er Tm Yb Lu

1

10

10

0

Tonalite, Näverliden²


Tonalite, Tallberg¹,²


Tonalite, Tallberg³


Quatz Feldspar porphyry , Tallberg ³


Quartz feldspar porphyry, Älgträsk¹,²

Tallberg porphyry, this study


Quartz porphyritic granodiorite, Älgträsk¹,²


Microgranular mafic enclaves, Älgträsk¹,²


Aplite¹,²


Älgliden intrusion¹


Mafic dykes¹,²


Gabbro, Älgträsk¹,²


11

01

00

11

01

00

11

01

00

1

10

10

0

100

0

a b c

d e f

g h i

j k l

a

b

c

d

e

Phyllic alteration1,2


Silicic alteration1,2


Prophylitic alteration1,2


Quartz destructive alteration1,2


Least altered1,2


0.1

11

01

00

Sodic-Calcic alteration1


0.1

11

01

00

Sample/

REE

cho

ndrite

a b c

d e f

65-140

Qu

artz-

de

stru

ctive

alte

ra

tio

n

-25

3

3

0

-1

3

-1

0

3

-185

-17

53

8

1

3

1

0

-3

-1

6

0

0

73

265-84

So

dic

alte

ra

tio

n

-10

-1

-2

0

2

1

-2

0

0

-436

-39

84

-15

-1

0

-5

-2

-3

-2

-19

-1

-2

0

0701

Silicic

alte

ra

tio

n

586

17

301

1

-3

-3

15

1

159

1864

121

-64

403

73

227

679

266

1838

414

1009

48

3526

25326

83-125

Ph

yllic

alte

ra

tio

n

14

0

9

1

-3

-3

1

0

4

118

32

-118

5

9

4

4

-1

110

3

68

1

24

1801

83-126

Pro

pylitic

alte

ra

tio

n

15

3

1

0

0

0

1

0

2

199

21

-21

5

2

0

-1

-2

16

-1

17

0

2

18

Sample

Alteration style

SiO2

Al2O3

Fe2O3

MgO

CaO

Na2O

K2O

TiO2

LOI

Ba

Rb

Sr

V

W

S

Co

Mo

Cu

Pb

Zn

Ni

As

Au

T

Least altered

0

5

10

15

20

25

30

5 10 15 20 25 30

0.25SiO2

20Ho

50Tb

Al2O3

Fe2O3

20MgO5CaO5Na2O

K2O

50TiO2

100P2O5

100MnO

Sc

LOI

0.01BaCo

Hf

2Nb

0.5Rb

0.1Sr

Th

U

0.5V

10W

0.1Zr

Y

La0.5Ce

50Lu

100S

10Mo

Cu

5Pb

0.5Zn

Ni

As

100Au

0.25SiO2

20Ho

50Tb

Al2O3

Fe2O3

20MgO

5CaO

5Na2O

K2O

50TiO2100P2O5100MnO

Sc

LOI

0.01Ba

CoHf

Nb

0.5Rb

0.1Sr

ThU

0.5V

10W

0.1Zr

Y

La

0.25Ce

50Lu

100S

10Mo

Cu

5Pb

0.5Zn

Ni

As

Au

0 5 10 15 20 25 30

5

10

15

20

25

30Propylitic alteration

0.25SiO2

20Ho

50Tb

Al2O3Fe2O3

20MgO

5CaO5Na2O

K2O

100TiO2

100P2O5

100MnO

Sc

LOI

0.025Ba

Co

5Hf

Nb

0.5Rb

0.2SrTh

U

0.5V

2W

0.2ZrY

La0.5Ce20Lu

5S

Mo

0.25Cu

Pb

0.25Zn

Ni

As

0.02Au Phyllic alteration

0 5 10 15 20 25 30

5

10

15

20

25

30

0.25SiO2

20Ho20Tb

Al2O3

Fe2O3

10MgO

5CaO

5Na2O

10K2O

100TiO2

100P2O5

100MnO

Sc

LOI

0.05Ba

0.5Co

5HfNb

0.5Rb

0.2Sr2Th

5U

0.5V

2W

0.2ZrY

La0.5Ce

50Lu

S

Mo

0.1Cu

0.5Pb

0.25Zn

Ni

0.05As

0.01Au

0 5 10 15 20 25 30

5

10

15

20

25

30Silicic alteration

0.25SiO2

10Ho

10Tb

Al2O3

Fe2O3

10MgO

CaO

Na2O

10K2O

20TiO2100P2O5

100MnO

Sc

LOI0.025BaCo

5Hf

Nb

0.5Rb

0.05Sr 2Th

2U

0.5V

2W

0.1Zr

Y 0.9La

0.1Ce10Lu 100S

10MoCuPb

0.5Zn

10Ni

As10Au

Sodic-Calcic alteration

0 5 10 15 20 25 30

5

10

15

20

25

30

0.25SiO210Ho

10Tb

Al2O3

Fe2O3

5MgO

5CaO

Na2O

10K2O

10TiO2

100P2O5

100MnOSc

LOI

0.05Ba

Co

Hf

Nb

0.5Rb

0.2Sr

Th

U

0.5V

10W

0.1Zr0.5Y La

0.5Ce

10Lu

100S 10Mo2Cu

Pb

0.1Zn

Ni

As

100Au

Quartz destructive alteration

0 5 10 15 20 25 30

5

10

15

20

25

30

y=1.25xy=2.10x

y=0.94xy=1.14x

y=0.90xy=1.28x

y=0.84xy=1.11

y=0.19xy=0.13x

y=1.11xy=1.51x

Concentration in protolith (wt%/ppm)

Conc

entration in

alte

red ro

ck (w

t%/ppm

)

a b

c d

e f

586

-25

301

Propylitic alterationPhyllic alterationSilicic alteration

Sodic calcic alterationQuartz destructive alteration

-15

-10

-5

0

5

10

15

20

SiO2

Al2O3

Fe2O3

MgO CaO Na2O

K2OTiO

2 LOI

1863

-436

678

227

266

1838 41

4

1009

3525

1801

2532

6

-185

-118

199

BaCo

Rb

Sr

S Mo Cu PbZn

Ni As Au

150

100

50

0

-50

-100

g/10

0g ro

ckpp

m/ppb

Ca, Na lo

st

AlbitePlagioclase

K-gainNa, Ca lossK-mica

KaoliniteChlorite

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0

0.1 0.2 0.3 0.4 0.5 0.6 0.7

2Ca+Na+K/Al (molar)

K/A

l (m

olar

)

K gain, Na, C

a loss

Possible

Na, Ca gain

K loss

K-feld

spar

Biotite

Least altered

Propylitic alterationPhyllic alteration

Silicic alteration

Sodic-Calcic alterationQuartz destructive alteration

a b c

d e f

apyII

Te-id

Au

sp

apy

py

py

py

py

py

ccp

ccp

ccp

ccp

Au

Au

Au

AuAu Te-id

Te-ids

apyI

Te-id

Intrusion-related mineralization in the Palaeo-proterozoic Jörn Granitoid Complex, northern Sweden. Therese Bejgarn Division of Geosciences, Luleå University of Technology, SE-971 87 Luleå, Sweden

Pär Weihed Division of Geosciences, Luleå University of Technology, SE-971 87 Luleå, Sweden

Hans Årebäck Boliden Mineral AB, SE-936 81 Boliden, Sweden

Juhani Nylander Boliden Mineral AB, SE-936 81 Boliden, Sweden

Abstract: Immediately north of the Skellefte mining district, northern Sweden, the early orogenic-synvolcanic Jörn granitoid complex hosts several mineral deposits. The Jörn granitoid batholith intruded into a continental margin arc or island arc volcanic succession during the early Proterozoic, and comprises a composite, I-type, calc-alkaline batholith, ranging from granite to gabbro in composition. Several mineral deposits occur in the heterogeneous margin of the complex, i.e. the Tallberg porphyry Cu-Au-Mo, the Älgträsk Au and the Älgliden Ni-Cu-Au deposits in the south and the Näsberg Fe±PGE and Granberg porphyry Cu mineralization in the north. The known deposits indicate that the intrusion is fertile for further exploration activities and that Palaeoproterozioc synvolcanic intrusions close to VMS districts should be studied more closely to further develop genetic models which can be used to reconstruct the ore forming environments and tectonic evolution. This knowledge might be used as guidelines when exploring for new districts with economic potential in Palaeoproterozoic terrains.

Keywords: intrusion-related mineralization, Skellefte district, gold, copper, Palaeoproterozoic.

1 Introduction

The Skellefte mining district in northern Sweden (Fig. 1) is well known for its many economic and sub-economic VMS deposits, eg. the Boliden, Renström, Petiknäs, Kristineberg and Maurliden deposits (Allen et al. 1996; Barrett et al. 2005; Bergman Weihed et al. 1996; Montelius et al. 2007; Årebäck et al. 2005). Less known are the intrusive hosted mineral deposits north of the Skellefte district. These mineral deposits are hosted by the marginal and oldest out of four (GI-GIV) magmatic phases in the Jörn granitoid complex (JCG). The JGC is a complex, calc-alkaline, I-type intrusion of which the oldest phase, the GI, is the least fractionated and heterogeneous by character, with compositions ranging from gabbro to granodiorite (Wilson et al. 1987). The JGC was emplaced into the coeval c. 1.89 Ga Skellefte Group volcanic succession, which is interpreted as a remnant of an early Proterozoic island arc or continental margin arc succession (Allen et al. 1996; Weihed et al. 1992). In the southern part of the JGC there are three known deposits, the Älgträsk,

Tallberg and Älgliden deposits. The Älgträsk Au-deposit is structurally controlled and associated with zones of strong alteration (Bejgarn et al. 2008), and constitutes a major gold exploration target with, at present, an inferred mineral resource of 1.6 Mt grading 3g/t Au (Boliden 2007). The Palaeoproterozoic Tallberg porphyry Cu-Au-Mo deposit (Weihed and Schöberg 1991) is situated three km to the west of the Älgträsk deposit and close to these two deposits, the mafic-ultramafic Älgliden dyke with Ni-Cu-Au mineralization occurs. In the northern part of the JGC, the Näsberg Fe±PGE mineralization is hosted by a layered gabbro. The Granberg Cu-mineralization is situated SW of Näsberg and shares many characteristics with the Tallberg porphyry deposit in the south.

In this abstract we present a summary of the geology and mineralization, discuss a possible relationship between of the intrusive-related deposits in the JGC and discuss the exploration potential for similar intrusive hosted base and precious metal deposits in Palaeoproterozoic terrains.

2 Regional geology

The Skellefte district (Fig. 1) situated in the northern part of the Fennoscandian shield developed during the early Proterozoic and has been interpreted as the remnant of an ancient volcanic arc behind a northward dipping subduction zone (Allen et al. 1996; Lundberg 1980; Weihed et al. 1992).

The district consists of a complex volcanosedimentary succession which historically has been divided in to three major stratigraphic groups; the Skellefte, Vargfors and Arvidsjaur Groups (Allen et al. 1996; Lundberg 1980; Rickard and Zweifel 1975; Weihed et al. 1992). The lower stratigraphic units are dominated by juvenile volcaniclastic rocks, lavas, porphyritic intrusions with intercalated sedimentary rocks such as mudstone, siltstone, sandstone and breccia-conglomerate (Allen et al. 1996). The oldest unit, the Skellefte group, has been dated at 1884 ± 6 Ma by U-Pb in zircon (Billström and Weihed 1996). The VMS deposits are hosted within the Skellefte group. The overlying Vargfors Group is dominated by fine and coarse grained sedimentary succession with intercalated volcanic rocks (Allen et al. 1996) yielding a U-Pb zircon age of 1875 ± 4 Ma (Billström and Weihed 1996). Subaerial volcanic rocks such as ignimbrites, ash-

fall tuff and volcaniclastic rocks characterize the Arvidsjaur Group which yield a U-Pb zircon age of 1876 ± 3 Ma (Skiöld et al. 1993).

Multiple phases of the early orogenic JGC and the Gallejaur type magma intruded the volcanosedimentary succession at c. 1.89-1.87 Ma (Wilson et al. 1987) and c 1.87 Ma (Skiöld et al. 1993) respectively. Mafic dykes cutting the JGC are tentatively correlated with the younger Gallejaur magmatism (Kathol and Weihed 2005). The JGC is composed of I-type, calc-alkaline, early orogenic granitoids, which evolved from at least three different initial magmas (Wilson et al. 1987). The GI outer zone is heterogeneous in composition, though dominated by a coarse-grained grey granodiorite-tonalite. Younger units of the JGC are more felsic in character, ranging from granodiorite to granite in composition (González Roldán et al. 2006; Wilson et al. 1987). The intrusions have been dated with the U-Pb zircon method at 1888+40-14 Ma (GI), 1874+45-26 Ma (GII) and 1873+18-14 Ma (GIII) (Wilson et al. 1987). The intrusion of the GII-GIV phases into the GI unit likely caused metamorphism, hydrothermal alteration and deformation of the GI (González Roldán et al. 2006; Wilson et al. 1987). Similarities in composition and age led many authors to suggest that the volcanic rocks of the Skellefte Group are comagmatic with the JGC (Claesson 1985; Lundberg 1980; Wilson et al. 1987).

Two major phases of folding have been proposed for the central Skellefte district; tight to isoclinal upright folds with variably plunging fold axes (D2) formed during E-W shortening at 1.87-1.82 Ga, and a set of later open folds (D3) with steep north to north-east striking axial surfaces and fold axis that are coaxial with earlier folds (Bergman Weihed 2001). Generally, west-northwest striking shear zones are correlated with the D2 event and the north-north east trending shear zones correlated with the D3 event (Bergman Weihed 2001).

3 Intrusive hosted mineral deposits

3.1 Southern area

The porphyry Cu deposit in Tallberg (Fig. 1, a) is hosted by a medium-grained equigranular tonalite, associated with mainly propylitic and phyllic alteration and quartz-feldspar porphyritic dykes dated at c. 1.88 Ga (Weihed and Schöberg 1991). The deposit is characterized by disseminated pyrite, chalcopyrite, molybdenite, pyrrhotite, magnetite and quartz vein stockworks with similar sulphide mineral assemblage.

The Älgträsk deposit (Fig. 1, b) situated approximately 3 km east of the Tallberg deposit, is mainly hosted by a coarse-grained quartz-porphyritic granodiorite. It is characterised by several steeply dipping, sub-parallel, NW-SE striking zones of varying width with disseminations and veins of pyrite locally enriched in chalcopyrite, sphalerite, arsenopyrite and accessory Te-minerals and Au. The mineralized zones are structurally controlled and accompanied by intense proximal phyllic-silicic alteration and distal propylitic alteration in the host rock. The mineralization crosscuts

gabbroic rocks and quartz-feldspar porphyritic dykes similar to the dykes in Tallberg, but is in turn crosscut by mafic dykes.

A steeply dipping, NE striking ultramafic-mafic dyke (Fig. 1, c) crosscut the JGC at Älgliden (referred to as the Älgliden dyke), just northeast of the Tallberg and Älgträsk deposits. The dyke is approximately 50 m wide and 3 km long. The dyke contains mainly disseminated magnetite, pyrrhotite, chalcopyrite and pentlandite with minor pyrite and gold. Pyrite is more common within 10 m from the contact, subsequently replaced by pyrrhotite towards the centre of the dyke. A 0.5 m massive lens of sulphides is present in the central-lower part of the dyke. The Älgliden dyke is in turn crosscut by mafic dykes with similar characteristics as in Älgträsk.

Figure 1. Outline of the Fennoscandian shield with the Skellefte district indicated (upper left corner). Simplified geological map of the central part of the Skellefte district with major VMS deposits indicated (modified after Allen et al. 1996; Wilson et al. 1987; Årebäck 2005). Jörn Granitod Complex with the intrusive hosted a) Tallberg deposit, b) Älgträsk deposit c) Älgliden deposit d) Näsberg mineralization and e) Granberg mineralization.

3.2 Northern area

The Näsberg Fe+PGE mineralization is hosted by the Näsberg gabbro (Fig. 1, d) in the northern part of the JGC. The Näsberg intrusion exhibit cryptic and rhytmic lamination (Filén 2001; Årebäck et al. 2006). The Fe-

mineralization was mined periodically for iron from the 1830’s to c. 1910. The mined magnetite occurs in veins cross-cutting the gabbro, associated with actinolite±quartz±feldspar±apatite± sulphides (Årebäck et al. 2006). A boulder found by Swedish Geological Survey in the southern part of the intrusion contained 1.2 ppm Pt, 3.9 ppm Pd and 0.2 ppm Au (Filén 2001).

The Granberg Cu-mineralization (Fig. 1, e) is situated in the northern part of the GI, and is similar to the Tallberg deposit in the south (Weihed 2001). It comprise disseminated chalcopyrite, pyrite and molybdenite, hosted in a granodiorite an in a quartz feldspar porphyry.

4 Discussion

The Palaeoproterozoic JGC hosts several different types of mineralizations, among them porphyry Cu-Au-Mo deposits, Au only deposits (Bejgarn et al. 2008) and ultramafic-mafic hosted Cu-Ni±Au±PGE. All these mineral deposits are situated in the outer, older parts of a synvolcanic composite intrusion. In the southern part, the mineralization predates the last magmatic phase of the JGC. The role and timing of the mafic magmatism and its related Fe-PGE-Au and Cu-Ni-Au mineralizations needs to be further investigated. In this model the VMS deposits formed in a rifted volcanic arc environment with the porphyry type deposits in on the continent side of the arc (Weihed et al. 1992). Porphyry Cu-Au and VMS deposits thus seem to occur in the same tectonic environment, are temporal and spatially related in the Palaeoproterozoic. Faster moving plates, microcontinent accretion and possibly a higher geothermal gradient may explain this. Though the restricted areal extent, the early orogenic-synvolcanic JGC intrusion has proven to have a good exploration potential and a large variety of deposit styles. Similar tectonic regimes and related synvolcanic intrusions in other Palaeoproterozoic districts should not be overlooked when exploring for potential new ore districts.

Acknowledgements

Boliden Mineral AB is greatly acknowledged for providing geological information on the deposits. This work has been sponsored by New Boliden, The Geological Survey of Sweden and the Luleå University of Technology.

References

Allen RL, Weihed P, Svenson SA (1996) Setting of Zn-Cu-Au-Ag massive sulfide deposits in the evolution and facies architecture of a 1.9 Ga marine volcanic arc, Skellefte district, Sweden. Economic Geology 91: 1022-1053.

Årebäck H (2005) Geology and gold mineralisations in Älgträsk: results from 2004–2005 exploration. New Boliden, Internal Exploration Report 2005:18: 38.

Årebäck H, Barrett TJ, Abrahamsson S, Fagerström P (2005) The Palaeoproterozoic Kristineberg VMS deposit, Skellefte district, northern Sweden, part I: geology. Mineralium Deposita 40: 351-367.

Årebäck H, Wasström A, Mattsson B (2006) Petrology and geochemistry of the Näsberget layered intrusion, Skellefte district, Northern Sweden. Bulletin of the Geological Society of Finland, Special issue Abstract Volume 1.

Barrett TJ, MacLean WH, Areback H (2005) The Palaeoproterozoic Kristineberg VMS deposit, Skellefte district, northern Sweden. Part II: chemostratigraphy and alteration. Mineralium Deposita 40: 368-395.

Bejgarn T, Weihed P, Nylander J, Årebäck H (2008) The Älgträsk intrusive hosted Au(-Cu) deposit, northern Sweden (abstract). International Geological Congress, Oslo.

Bergman Weihed J (2001) Palaeoproterozoic deformation zones in the Skellefte and Arvidsjaur areas, northern Sweden. In Weihed, P. (ed.): In Weihed, P. (ed): Economic geology research, Sveriges Geologiska Undersökning C833 1: 46-68.

Bergman Weihed J, Bergström U, Billström K, Weihed P (1996) Geology, tectonic setting, and origin of the Paleoproterozoic Boliden Au-Cu-As deposit, Skellefte District, northern Sweden Economic Geology 91: 1073-1097.

Billström K, Weihed P (1996) Age and Provenance of Host Rocks and Ores in the Paleoproterozoic Skellefte District, northern Sweden. Economic Geology 91: 1054-1072.

Boliden (2007) Boliden Annual Report. 95-97. Claesson L-Å (1985) The geochemistry of early Proterozoic

metavolcanic rocks hosting massive sulphide deposits in the Skellefte district, northern Sweden. Journal of the Geological Society of London 142: 899-909.

Filén B (2001) Swedish layered intrusions anomalous in PGE-Au. In Weihed, P. (ed): Economic geology research, Sveriges Geologiska Undersökning C833 1: 33-45.

González Roldán MJ, Allen RL, Donaire T, Pascual E (2006) Secuencia de Emplazamiento, Alteración Hidrotermal y Metamorfismo en el Complejo Intrusivo de Jörn, Distrito Minero de Skellefte, Norte de Suecia. Geogaceta 40: 115-118.

Kathol B, Weihed Pe (2005) Description of regional geological and geophysical maps of the Skellefte District and surrounding areas. Gological Survey of Sweden Serie Ba 57: 197 pages.

Lundberg B (1980) Aspects of the geology of the Skellefte fiield, northern Sweden. Geologiska Föreningens i Stockholms Förhandlingar 102: 156-166.

Montelius C, Allen RL, Svenson SA, Weihed P (2007) Facies architecture of the Palaeoproterozoic VMS-bearing Maurliden volcanic centre, Skellefte district, Sweden. GFF 129: 177-196.

Rickard DT, Zweifel H (1975) Genesis of Precambrian sulfide ores, Skellefte District, Sweden. Economic Geology 70: 255-274.

Skiöld T, Öhlander B, Markkula H, Widenfalk L, Claesson LA (1993) Chronology of Proterozoic Orogenic Processes at the Archean Continental-Margin in Northern Sweden. Precambrian Research 64: 225-238.

Weihed P (2001) A review of Palaeoproterozoic intrusive hosted Cu-Au-Fe-oxide deposits in northern Sweden. In Weihed, P. (ed): Economic geology research, Sveriges Geologiska Undersökning C833 1: 4-32.

Weihed P, Bergman J, Bergström U (1992) Metallogeny and Tectonic Evolution of the Early Proterozoic Skellefte District, Northern Sweden. Precambrian Research 58: 143-167.

Weihed P, Schöberg H (1991) Age of Porphyry-type deposits in the Skellefte District, northern Sweden. Geologiska Föreningens i Stockholms Förhandlingar 113: 289-294.

Wilson MR, Sehlstedt S, Claesson L-Å, Smellie JAT, Aftalion M, Hamilton PJ, Fallick AJ (1987) Jörn: an early proterozoic intrusive complex in a volcanic-arc environment, north Sweden. Precambrian Research 36: 201-225.

New styles of intrusive related copper-gold deposits in ...

Documents