IN CENTRAL FINNISH LAPLAND Introduction orogeny (Mänttäri

Geological Survey
Survey of
of Finland,
Finland, eurrent
Geological
Current Research
Research 1999-2000,
1999-2000,
Edited by
by Sini
Edited
Sini Autio.
Autio.
Geological Survey
Survey of
of Finland,
Finland, Special
Geological
Special Paper
Paper 331,251, 25- 29
, 200 I.
29,2001
AND CARBON
CARBON ISOTOPE
ISOTOPE COMPOSITIONS
OXYGEN AND
COMPOSITIONS OF
OF CARBONATES
CARBONATES IN
ALTERATION
THE ALTE
RA TI ON ZONES OF
OF OROGENIC GOLD DEPOSITS
IN CENTRAL
IN
CENTRAL FINNISH
FINNISH LAPLAND
LAPLAND
by
Pentti Hölttä and Juha
Juha Karhu
Karhu**
Geological Survey of Finland,
151 ESPOO,
Finland, P.O. Box 96
FIN-02151
96,, FIN-02
ESPOO, FINLAND
E-mail: Pentti
E-mail:
.Holtta @gsf.fi
Penrti.Holtta@
gsf.fi
*present address: Department of Geology, FIN-OOOI4
*present
FIN-00014 HELSINGIN YLIOPISTO
sinki.fi
E-mail: luha.Karhu
Juha.Karhu @hel
@ helsinki.fi
(GeoRef Thesaurus
Thesaurus,, AGI): gold ores, metavolcanic rocks,
Key words (GeoRef
rocks, hydrothermal
hydrothermal alteration
alteration,, carbonates, stable isotopes, 0
O-1 8/O-16,
C-131C-12, Proterozoic
Proterozoic,, central Lapland, Finland
18/016, C-13/C-12,
Introduction
In Central
Central Finnish
Finnish Lapland
Lapland there
In
there are
are ca.
ca. thirty
known gold mineralisations in an area covering ca.
4000km2,
some of
of those
those being
being economicl
4000
km2, some
viable. The
economiclyy viable.
deposits are
are mostly
mostly associated
deposits
associated with
with late shear
shear zones
zones in
a greenschist facies metamorphic
metamorphie environment.
environment. A Pb
isotope study of some of these gold mineralizations
mineralizations
given ages, indicating
and
country rocks has given
and their
their country
indicating syn
to
late-orogenic ore
formation during
during the
to late-orogenic
ore formation
the Svecofennian
orogeny (Mänttäri
orogeny
(Mänttäri 1995)
the gold
1995).. Therefore the
mineralisations
mineralisations in Central
Central Lapland seem
seem to represent
the orogenic
orogenie ore type
type following
the classification
classification by
following the
Groves et
et al.
al. (1998).
(1998). According to
to Groves et
et al.
(1998),
(1998), orogenic
orogenie gold deposits
deposits are
are ores
ores that were
formed during compressional
compressional to transpressional
transpressional deformation
processes
at convergent
formation
convergent plate margins in
accretionary
accretionary and collisional
collisional orogens.
Mostof
Most of the
the goldmineralisations
gold mineralisations in
in Central
Central Lapland
are hostedby
hosted by mafic
mafic andultramafic
and ultramafic volcanic
volcanic rocks,
rocks, and
are
they
they are
are surrounded
surrounded by
by alteration
alteration zones characterised
characterised
by K-metasomatism
K-metasomatism with abundant biotitization
biotitization and
sericitization.
sericitization. Albitization and carbonation are also
typical
typical features
features of the
the alteration
alteration zones. There are
several
several interpretations for the origin of the
the fluids
causing
causing such alteration, the main alternatives
alternatives being
premetamorphic
premetamorphic sea-floor
sea-floor hydrothermal
hydrothermal and
synmetamorphic fluid system connected
connected with shear
shear
zones,
zones, as
as proposed
proposed for
for Central
Central Lapland
Lapland by
by Korkiakoski
Korkiakoski
(1992) and
(1994). Different
(1992)
and Eilu
Eilu (1994).
Different rock
rock types
types and
formation
formation environments have different oxygen and
carbon
carbon isotope
isotope signatures
signatures and so stable
stable isotope
isotope studies
studies
can be used as
as a tool for constraining the origin of
fluids causing the alteration. In the case of the gold
quantities of
deposits,
large quantities
fluid is needed
to infiltrate
deposits,large
of fluidis
neededto
the rock to precipitate gold in economic abundance.
abundance.
The high fluid-rock
fluid-rock ratio should be reflected in the
stable
isotope
compositions
ofhost
rocks. In
work,
isotope
stable
compositions of
host rocks.
In this
this work,
a test set of sampIes
samples was analysed from carbonated
in the
alteration zones
gold deposits
rocks in
the alteration
zones of
ofgold
deposits (and also
similarly
rocks without
without gold)
gold) in
in Central
Central Lapland
similarly altered
altered rocks
Lapland
(Fig. 1). For comparison,
comparison, carbonates were also analysed from unaltered rocks atthe
at the neighbourhood
neighbourhood ofthe
lysedfromunalteredrocks
of the
alteration zones.
alteration
method
Analytical method
Carbonate was sampled from the fresh surface of
Carbonate
unaltered
a sawed rock using a dentist drill. From unaltered
tholeiitic
volcanite
specimens
carbonate
was
tholeiitic volcanite specimens carbonate was sampled
from carbonate-bearing
carbonate-bearing vesicles
vesicles or veinlets. Isotope
Isotope
from
methods were
were chosen
chosen according to
to the
analytical methods
carbonate species
species in
in question.
question. An
An aliquot
aliquot of the
carbonate
sampIe powder
powder was used to
to determine
deterrnine the
the proportion
proportion
sample
of calcite,
calcite, dolomite
dolomite and
and magnesite
magnesite in
in the
the total
total carboncarbonof
by a semi-quantitative
semi-quantitative X-ray diffraction
diffraction method
ates by
described by Karhu (1993). Carbon
Carbon and
and oxygen
oxygen isoisodescribed
tope ratios in carbonates were measured using the
the
25
Geological
and , Special
Finland,
Paper 3311
Geological Survey
Survey of
of Finl
Special Paper
Pentti Hö
lttä and
a Karhu
Ka rhu
Pentti
Hölttä
and Juh
Juha
o0-F
20
km
20km
LEGEN
TEGEN 0
D
gneisses and
rnI1
Tonalite-trondhjemite
T^onolile.-trondhjemite gneisses
ond migmatites
migmotites
m
oEi Gronitoids
Gronitoids
g Quartzite
~
nd conglomerate
ond
conqlomerole
Quorfzite a
Q
-silicate rock, bla
c k sc
hist, basic
ic intercalates
block
schist,
bosic volcan
volconic
intercololes
Colc-silicote
N Calc
~
Quartzite
wilh intercalates
intercolotes
Quorlzife with
= Mafic
5!!!!
nd felsic volcanic
volconic rocks
Mofic,, intermediate
intermediote aond
=
(after Korsman et
Fi
g. 1.
fied lithological
and (after
e locations
Fig.
l. Simpli
Simplified
lithological map
map of Central
Central Finnish Lapl
Lapland
et al.
al. 1997).
1997). Sampi
Sample
locations are
black dots.
marked with
with small
small black
conventional
conventional phosphoric acid
acid method
method at
at SODC
50"C for
calcite and
and lOODC
100"C for dolomite and magnesite.
magnesite. The
analytical methods are described in detail by Karhu
(1993).
(1993).
Results
Results and
and discussion
Oxygen
Oxygen isotopes
The isotope ratios
oxygen and carbon in carbonratios of
ofoxygen
carbonates are
1 and illustrated
illustrated in Figure
are given in Table 1
Figure 2. The
18
8ö18O
0 values
rocks fall in aanarrowrange
narrow range from
values in altered
alterr:drocks
(SMOIV), with
11 to 13 %0
%o (SMOW),
with aa few outliers at lower and
higher values
values.. The small variation in oxygen
oxygen isotope
pattern observed in
composition contrasts with the
the pattern
Archean
Archean hydrothermal
hydrothermal carbonates
carbonates associated with
gold mineralizations in
gold
in eastem
eastern Finland.
Finland. There the
18
0 values
variation in 8
ör80
varlues is considerably
considerably largerrelative
largerrelative
13
C (Karhu et al.
to the variation observed in 8ö13C
al. 1993).
1993).
26
18
The variable 8Et8O
0 values in Archean deposits have
been interpreted to be
be related
been
related to
to Proterozoic metamorphic overprinting
overprinting (Karhu et al.
al. 1993).
Unaltered
Unaltered carbonate
carbonate bearing
bearing volcanic
volcanic rocks
rocks in
greenschist
greenschist facies
facies areas
areas do
do not
not show
show any
any marked
deviations
deviations from the isotopic composition of carbonates
ates in
in the
the alteration
alteration zone. These
These regions include
Saattopora, Iso-Kuotko and Atri
Atri.. However, regions
with
peak metamorphic
with peak
metamorphic conditions
conditions in
in amphibolite
amphibolite facies
show a different
pattern.
The
volcanic
host rocks of
different
the Pahtavaara
Pahtavaara deposit have been metamorphosed
metamorphosed in
lower
lower amphibolite
amphibolite facies with
with homblende-plagioclase
hornblende-plagioclase
assemblages,
assemblages, whereas the gold-related metasomatic
metasomatic
place
alteration
in upper greenschist facies conalteration took
took
(Korkiakoski 1992).
ditions
ditions (Korkiakoski
1992). The
The carbonates in the
gold-related alteration zone
zone are
are tightly grouped with
18
0 values between
between 11.2
8ö18O
lI.2 and
and 12.8
12.8 %0,
but both
%q but
altered
altered and
and unaltered
unaltered rocks
rocks outside the
the immediate
180
vicinity
vicinity of
of the gold ore have distinctively lower 88r8O
Table
l=calcite , dol=dolomite
dol=dolomite,, ank=ankerite
ank=ankerite,, mgs=magnesite.
mgs=magnesite. Locations
Locations ofthe
of the sampie
sample sites
sites are presented in Figure
Figure 1.
1
Table 1.
1 . Analytical data
dala.. Mineral
Mineral abbreviations:
abbreviations: ca
cal=calcite,
Outcrop
Sampie
Sample Site
northing
northing easting
Ö
" C PDS
613C
PDB
Rock
type, a =
Rocktype,
allered, uu =
unallered
= altered,
= unaltered
PSH-98-102
Keinotusjänkkä
Keinotusjänkkä
7527580
7527580 2531360
ca
call
11
.50
11.fi
-2.74
mafie
volcanic rock
maficvolcanic
rock,, U
u
Levi
7522280
7522280 2534390
25U390
doVank
dol/ank
14.05
14.05
-1.80
-1
.80
ck brecciated
schistose
rock
schistose mafie
mafic volcani
volcanicc ro
brecciated by brown
brown carbonate
veins, , U
carbonate veins
u
PSH
-98-113
PSH-98-1
13
Kuukerinmaa
Kuukerinmaa
7525400
7525/.OO 2532130
doVank
doYank
11
.58
1 1,58
-5.1 5
-5.15
chlorite
chlorite schist
schist brecciated by Fe-carbonate veins
veins,, a
,l
Kuukerinmaa
Kuukerinmaa
7525400
7525400 2532130
mgs
m9s
12.07
12.O7
-3.14
-3.'t4
chlorite
st brecciated by Fe-carbonate veins
chlorite schi
schist
veins, , a
1
PSH-9813
PSH-98-1113
2
Kuukerinmaa
Kuukerinmaa
7525400
7525400 2532130
dol/ank
12.08
12.O8
-5.'t7
-5.17
chlorite
chlorite schist
schist brecciated by Fe-carbonate veins,
veins, a
PSH-98-113
PSH-98-1 13
2
Kuukerinmaa
Kuukerinmaa
7525400
7525400 2532130
mgs
'12.78
12.78
-2.83
chlorite
st brecciated by Fe-carbonate veins
chlorite schi
schist
veins,, a
PSH-98-113
PSH-98-1 13
3
Kuukerinmaa
Kuukerinmaa
7525400
752il00 2532130
mgs
12.04
12.O4
-5.01
chlorite schi
st brecciated by Fe-carbonate
veins , a
Fe-carbonate veins,
schist
Pahtavuoma
7523480
752UAO 2512090
ca
call
12.88
12.48
-8.35
s, a
chlorite
chlorite schist brecciated by Fe-carbonate
Fe-carbonale vein
veins,
PSH-98-120
PSH-98-1 20
PSH-98-64
PSH-98-64
1
Pahtavaara
Pahtavaara
7505400
7fi5400 3477040
U77UO
cal
10.26
10.26
-8.74
-4.74
pillow lava, 1.83
pillow
1 .83 km NE
from the main
NE from
main ore,
ore, u
PSH-98-64
PSH-98-64
2
Pahtavaara
Pahtavaara
7505400
7fü0o
cal
10.06
10.06
-4
.78
4.74
pillow lava
pillow
lava,, 1.83
1 .83 km NE
NE from
from the main
main ore,
ore, u
PSH-98-64
PSH-98-64
4
Pahtavaara
PahtavaaE
7505140
7505140 3475360
dol/ank
10.44
10.44
-1.23
tale
talc breccia
breccia,, 200 mN
m N from
from the
the main
main are,
ore, a
PSH-98-64
PSH-98-64
8
Pahtavaara
PahtavaaE
7505140
7505140 3475360
dol/ank
10.19
10.19
-1
.76
-1.76
tremol
ite rock
tremolite
rock,, 200 m N from
from the main
main ore
ore,, a
PSH-98-65
PSH-98-65
1
pit ofthe main ore
Pahtavaara
Pahtavaara, , open
open pitofthe
7504950
7504950 3475280
v752AO
mgs
11
.78
11.78
-2.08
-2.O8
ba
rite vein with grey
grey Fe-carbonate
barite
Fe-carbonate,, main are
ore,, a
3477040
v77UO
PSH-98-65
PSH-98-65
't.1
1.1
pit ofthe main ore
Pahtavaara
Pahtavaara, , open pitofthe
7504950
7504950 3475280
mgs
11
.36
11.36
-1.83
grey Fe-carbonate, main are,
barite
barite vein with grey
ore, a
a
PSH-98-65
PSH-98-65
2
the main ore
Pahtavaara,
pit of
Pahtavaara, open pit
ofthe
7504960
7504960 3475280
dol/ank
11
.62
11.62
-4.11
komatiite
komatiite brecciated
brecciated bytalc, main ore
ore,, a
PSH-98-65
PSH-98-65
3
pit ofthe
Pahtavaara,
Pahtavaara, open
open pit
ofthe main ore
7504960
7504960 3475280
dol/ank
11
.86
11.86
-1
.18
-1.18
karnati
ite brecciated
komatiite
brecciated by
by talc, main ore
ore,, a
PSH-98-65
PSH-98-65
4
pit ofthe
Pahtavaara,
Pahtavaara, open
open pit
ofthe main ore
7504960
7504960 3475280
mgs
11
.52
11.52
-1.62
-1.62
komatiite
talc , main
ore , a
komatiite brecciated
brecciated by
bytalc,
mainore,
PSH-98-65
PSH-98-65
4
pit ofthe
Pahtavaara
Pahtavaara, , open
open pit
ofthe main ore
7504960
7504960 3475280
dol/ank
11
.24
11.24
-2.39
komatiite
komatiite brecciated
brecciated by
by talc,
talc, main ore
ore,, a
PSH-98-65
PSH-98-65
7
pit of
Pahtavaara
the main
Pahtavaara, , open
open pit
ofthe
main ore
7504970
7504970 3475280
doVank
douank
12.13
't2.13
-3.77
-3.77
biotite-amphibole
biotite-amphibole schist brecciated by talc,
talc, 9
from the ore,
9 m N from
ore, a
PSH-98-65
PSH-98-65
8I
pit ofthe
Pahtavaara
Pahtavaara, , open
open pit
ofthe main
main ore
7504985
7504985 3475280
doVank
dovank
11
.68
11.68
-4.13
-4.1 3
biotite-amphibole
biotite-amphibole schist brecciated by talc,
talc, 22 m N
N from
from the ore
ore,, a
PSH-98-65
PSH-98-65
9
pit ofthe main
Pahtavaara
main ore
Pahtavaara, , open pitofthe
y75273
7504967
7fi4$;7 3475273
doVank
douank
12.19
12.19
-1
.66
-1.66
Fe-carbonate vein with
with blue
blue amphibole,
amphibole, 6 m N
N from
from the ore, a
PSH-98-65
PSH-98-65
10
pit ofthe main ore
Pahtavaara
Pahtavaara, , open
open pitofthe
7504990
750/.990 3475270
3/'75270
doVank
dovank
12.84
12.U
-4.42
4.42
biotite-amphibole
biotite-amphibole schist, 30 m N from
from the ore, a
PSH-98-66
PSH-98-66
2
Pahtavaara
Pahtavaara
7505150
7505150 3475270
3/75270
doVank
doUank
10.24
10.24
-1.97
komatiite
komatiite,, 200 m N
N from the main
main ore, u
PSH-98-76
PSH-98-76
1
Atri
Atri,, open
open pit
7525590
7525590 2531070
dol/ank
12.50
12.50
-5.84
ca
rbonate breccia
carbonate
breccia, , a
PSH-98-76
PSH-98-76
1b
Atri, open
open pit
7525590
7525590 2531070
dol/ank
12.83
12.83
-5.97
-5.97
carbonate
carbonate breccia,
breccia, a
PSH-98-76
PSH-98-76
2
Atri
Atri,, open
open pit
7525590
7525590 2531070
dol/ank
'I t.95
11.95
-5.20
carbonate
carbonate breccia,
breccia, a
PSH-98-76
PSH-98-76
2b
h
Atri
Atri,, open
open pit
7525590
7525590 2531070
dol/ank
12.38
12.ß
-4.83
carbonate
carbonate breccia,
breccia. a
PSH-98-76
PSH-98-76
3
Atri
Atri,, open
open pit
7525590
7525590 2531070
cal
11
.81
11.81
-6.70
folded
folded carbonate
carbonale breccia,
breccia, a
PSH-99PSH-99- 106
1 06
'l
Iso-Kuotko
lso-Kuotko
7550340
7550340 2559050
cal
19.79
19.79
-4.86
chlorite-carbonate
rock,, a
chlorite-carbonate rock
o><
'<
@
"""o
"
"'"
p..
o
o
p
o
@
oo
a'. m
PSH-99-106
Iso-Kuotko
lseKuotko
7550340
7550340 2559050
dol/ank
11
.02
11.02
-7.43
albite-carbonate
rock , a
albite-carbonalerock,
lrn
PSH
-99-107
PSH-99-107
Iso-Kuotko
lsGKuotko
7550300
7550300 2558780
cal
'11.26
11
.26
-3.91
mafic
volcanic rock
with crb-filled ve
inlets, U
maficvolcanic
rockwith
veinlets,
u
s3
PSH-99-109
Lauttasselkä
Lauttasselkä
7530670
7530670 2518030
cal
10.31
-2.85
mafic
lcanic rock
lled vesicles,
mafic vo
volcanic
rock rock with crb-fi
crb-filled
vesicles, u
PSH-99PSH-99-1113
1 3
2
Sinermäjärvi
Sinermäjärvi
7512680
7512680 2554690
mgs
11
.90
11.90
-6.86
chromian
chromian marble,
marble, withoutAu
withoutAu,, a
PSH-99-113
PSH-99-1 1 3
4
Sinermäjärvi
Sinermäjärui
7512680
7512680 2554690
dol/ank
11
.66
11.66
-5.85
chromian
withoutAu, a
chromian marble,
marble, withoutAu,
PSH-99-73
PSH-99-73
'l
Kettukuusikko
7522280
7522280 2547440
2il7440
doVank
doUank
't1.42
11.42
-5.03
mafic
mafic volcanic
volcanic rock with
with Fe-carbonate, a
PSH-99-80
PSH-99-80
2
Pikku
Pikku Rouravaara
Rouravaara
7538380
7538380 2560350
ca
call
13.75
-0.77
-0.77
mafic
lcan ic rock
mafic vo
volcanic
rock with
with crb-filled veinlets
veinlets,, u
PSH-99-82
PSH-99-82
'l
Kapsajoki
Kapsajoki
7548400
7UU00 2552350
ca
call
12.05
12.05
-3.58
mafic
lcanic rock
lets , u
mafic vo
volcanic
rock with
with crb
crb,, ab and ep-filled vein
veinlets,
Saattopora
Saattopora
7523560
7523fiO 2517130
ca
call
12.10
12.10
-6.87
mafic
led veinlets,
mafic volcanic rock
rock with
with crb-fil
crb-filled
veinlets. 700 m north
north ofthe
ofthe mine,
mine. Uu
PSH-98
-111l
PSH-98-1't
'l
Saattopora,
Saattopora, open pit
7522810
7522a10 2517210
doVank
douank
12.63
12.63
.6.85
-6.85
Fe-carbonate
Fe-carbonale breccia
breccia, , a
PSH-99-96
PSH-99-96
1
Saattopora,
Saattopora, open pit
7522910
75229'tO 2517380
doVank
doUank
13.18
13.18
-7.22
banded
deformed Fe-carbonate
banded and
Fe-caöonate rock,
rock, a
anddeformed
PSH-99-95
PSH-99-95
{
ö"OSMOW
ö130SMOW
PSH-98-103
PSH
-98-113
13
PSH-98-1
N)
Analysed
Analy$d
mineral
no.
no.
Saattopora
Saattopora, , open pit
7522910
75229'tO 2517380
doVank
douank
12.38
12.&
-7.68
grained Au-bearing Fe-carbonate
coarse
coarse grained
Fe-carbonate veins
veins in N-S direction
direction,, cutting 96.1,
96.1, aa
PSH-99-96
PSH-99-96
3
Saattopora
Saattopora, , open pit
7522910
7522910 2517380
dol/ank
12.19
12.19
-6.87
grained Au-bearing Fe-carbonate
coarse
.1,, a
coaße grained
Fe-carbonate veins
veins in N-S direction
direction,, cutting 96
96.1
PSH-99-96
PSH-99-96
4
Saattopora
Saattopora, , open pit
7522910
75229't0 2517380
dol/ank
12.44
-7.37
coarse
.1,, a
grained Au-bearing Fe-carbonate
coarse grained
Fe-carbonate veins
veins in N-S direction
direction,, cutting 96
96.1
PSH-99-96
PSH-99-96
o<
:H
Ä;l
mr
ää
oe
u)
x^v
äö
Geological
Paper 3311
Special Paper
Geological Survey
Survey of Finland, Special
Pentti
Pentti Hölttä
Hölttd and
and Juha
Juha Karhu
values,
between 10.0
10.4 %0.
Similarly, the
10.0 and
and 10.4
Voo. Similarly,
values, between
unaltered
tholeiitic
amphibolite
facies
rock
facies
rock from
unaltered tholeiitic amphibolite
18
Lauttasselkä
0
(PSFI-99-109) has a slightly lower 8
ör8O
Lauttasselkä (PSH-99-109)
(Table 1).
value
l).
to the
the altered
altered sampies
samples (Table
value compared
compared to
Sampie
06.1 differs from all other carbonPSH-99-106.1
Sample PSH-99-1
18
ate
samples
having
aa high
0 value
value of
of 19.8
19.8 %0.
%,
havirrg
high 8
8r8O
ate
Calcite
fluid infiltramay represent
represent late fluid
sample may
Calcite in this sampie
tion
possibly during weak
lower temperatures,
temperatures, possibly
tion at
at lower
weathering.
weathering.
Oxygen
depend on the
isotope, ratios of
of carbonates
carbonates depend
Oxygen isotope
temperature
the isotopic
isotopic composition
of fonnation and
andthe
temperature of
ofthe
of the fluidis,
fluid is, in
isotopic composition
composition ofthe
of the fluid. The isotopic
turn, related
of the fluid and to the waterl
related to the source of
rock (WIR)
(WR) ratio during alteration.
Relatively homoalteration. Relatively
18
geneous 8öt80
0 in alteration-related
alteration-related carbonates
carbonates suggest
large crustal scale
processes with high WIR
scal: processes
WR ratios.
18
More variable 8
0 values
values outside the
the cores of the
öt8O
alteration
n:ray result from differences
differences in any of
alteration zones may
these
these factors.
13
tion
C
with 88t3C
show more
more scatter,
scatter, with
of carbonates
carbonates show
tion of
values
varyingfrom-8.7
to-0.8
%0(PDB,
Table
1).
No
values varying from -8.7 to -0.8 %o(PDB,
clear
in carbon isotope values
values can
can be
clear differences in
observed
between altered
altered and
and unaltered
unaltered volcanic
observed between
Pahtavaara, where the altered rocks
rocks apart from Pahtavaara,
13
generally
C values compared to unalgenerally have higher 8
ö13C
13
tered rocks (Fig. 2). The large spread in 8öt3C
C may be
related
presence ofblack
host rock
related to the
the presence
ofblack schists
schists in the host
association
gold mineralizations.
of most
most gold
mineralizations. Sedimentary
association of
organic
characteized by carbon depleted in
organic matter is characterized
13C,
I3C, and progressive
progressive additions
additions of
of organic
organic carbon
carbon to the
13
fluid system
C values
system will
will tend to shift the 8813C
values to more
negative
been observed
negative values.
values. Black
Black schists have not
notbeen
to
to occur close
close to
to the
the Pahtavaara ore
ore deposits,
deposits, and
13
accordingly
C values
thermal
accordingly the
the 8öt3C
values of
of the
the hydro
hydrothermal
carbonates
there are relatively
relatively high
high compared
compared to other
carbonates there
mineralizations.
mineralizations.
Concluding
Concluding remarks
Carbon
Carbon isotopes
Compared
oxygen, the carbon isotope composicomposiCompared to oxygen,
gold related alteration
Carbonates
alteration zones in CenCarbonates in gold
tral
tral Lapland
Lapland are
are characterized
characterized by
by relatively
relatively small
0U
t
Pahtavaara , altered rocks
-1
-1
200 m from the
Pikku Rouravaara
Pikku
•
m~
1
•
-2
KeinotusJänkkä
Keinotusjänkkä
Pahtavaara, altered roc
ks <30 m
rocks
from the main ore
-3
Lauttass
elkä
Lauttasselkä
-4
IsoKuotko ,
lso-Kuotko,
unaltered
una ltered tholeiite
tholeiite --------......
ca
m
Levi
Kapsajoki, unaltered
unaltered tholeiite
tholeiite
Kuu
kerinmaa ------------.....
Kuukerinmaa
o
a..
IL -5
U
u-c
0
------fa
Iso-Kuotko,
lso-Kuotkc, altered
altered rock 0O
next to
tE the ore
Kettukuusikko ----+--+-.....-h
'"'-10
tO
Atri
-6
SinermäJäNi
Sinermäjäwi
-7
Iso-Kuotko,
red
lso-Kuotko, alte
altered
roc
k next
'rext to the ore
roEk
-8
Gaaffnnnra
q
Saattopora
essLruPU,
--+-~ O
Pahtavaara,
altered-----.
Pahtavaara. un
unaltered
tholeiite
.83 km from
tholeiitess 11.83
the rnain
rnaln ore
-9
oo Pahtavuoma
Prhtruro*,
-10+----.----,---,---,r---.---,----,---.---,----r---,----.---.---,---,r-~
-10
5
6
7
8
9
10
'I
11
1
12 13
13
12
6{80
14
15
16
17
18
19
20
21
sMow
Fig. 2.
arbon isotope
2. Oxygen and
and carbon
isotope compositions
compositions of carbonates
carbonates from
from Central
Lapland.. Black dots
Central Lapland
dots == unaltered mafic vo1canic
volcanic rocks,
open
open dots
dots == altered
altered rocks.
28
Geological
Geological Survey
Survey of
of Finland,
Finland, Special
Special Paper
Paper 31
31
Oxygen and
and isotope
isotope composition
Oxygen
composition of
of carbonates
carbonates in
in the
the alteration
alteration zones
zones of
gold deposits
of orogenie
orogenic gold
deposits ..,
18
variation in
in Ö
ö18O
values compared
compared to
variation
0 values
to more
more spread
spread in
in
r3C.
ö 13c. Because
Because oxygen
oxygen isotope
isotope values
Ö
values are
are affected
affected by
by
both the
the fluid
fluid composition
composition and
both
and the ambient
ambient temperatemperature, it
it is
is difficult
difficult to
to draw
draw any
any definitive
definitive conclusions
ture,
conclusions
about the
the source
source of
of the
the fluid.
fluid. Furthermore,
about
Furthennore, carbon
carbon
isotope ratios
ratios seem
seem to
to be more affected
isotope
affected by local
local host
host
rock
lithologies.
Nevertheless,
rock lithologies. Nevertheless, in
in some
some study
study sites,
sites,
such as
as Pahtavaara,
Pahtavaara, the
mineralized zone
the rnineralized
such
zone seems
seems to
to
have distinctive
distinctive stable
stable isotope
isotope characteristics,
characteristics, and
have
and
stable isope ratios may therefore have potential as
stable
as an
an
exploration
tool.
Apparently,
each local
exploration too1.
each
local fluid system
system
has its
its own
own characteistics
characteistics and
and detailed
has
detailed studies
studies are
are
needed for
for each
each prospect.
needed
Acknowledgements
authors want to thank Arja Henttinen
The authors
Henttinen from the
Geological
Survey
Finland
for assisting
Geological Survey of Finland for
assisting in
in the
analytical work.
TerraMining
work. Terra
analytical
Mining Co., especially
especially Markku
Kilpelä and Kari Niiranen from the Pahtavaara
PahtavaaraMine,
Kilpelä
Mine,
are thanked
thanked for
for helping
helping to
to sampie
sample the
are
the Pahtavaara
Pahtavaara
rocks.
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