GEOLOGICA CARPATHICA, 50, 4, BRATISLAVA, AUGUST 1999
295–303
THE ORIGIN OF GRAPHITE IN THE CRYSTALLINE BASEMENT
OF THE WESTERN TATRA MTS.
(WESTERN CARPATHIANS, S-POLAND)
ALEKSANDRA GAWĘDA
*
and STEFAN CEBULAK
University of Silesia, Faculty of Earth Sciences, Dept. of Geochemistry, Mineralogy and Petrography, Będzińska st. 60,
41-200 Sosnowiec, Poland; *gaweda@us.edu.pl
(Manuscript received July 22, 1998; accepted in revised form March 17, 1999)
Abstract:
Metamorphic rocks with graphite contents from 0.1 wt. % to 4 wt. % were analysed using Oxyreactive
Thermal Analysis as a main tool with supporting X-ray and optical methods. Two generations of graphite were found
in these rocks: 1. predominant graphite Gph
1
of organic origin (graphitized petroleum coke); 2. hydrothermal graphite
Gph
2
,
in association with postmagmatic muscovite, albite and quartz. The P-T conditions of final graphitization for
Gph
1
were assumed as 7.5–10 kbar and 700–780
°C. The hydrothermal graphite precipitation took place at the tem-
perature of 700–730
°C and pressure about 6 kbar and continued during cooling up to 400 °C and 2 kbar of pressure.
Key words:
Western Tatra Mts., shear zones, oxyreactive thermal analysis, graphite.
Introduction
Graphite present in metamorphic rocks in thought to be a
product of two geological processes: 1. transformation of or-
ganic matter of different origin, related mainly to heat; 2.
precipitation from fluid saturated with respect to C, with the
typical association with hydrous silicates (muscovite) and
Fe-Ti oxides (Wopenka & Pasteris 1993; Connolly 1995).
The type of graphite we observe in natural circumstances in
the result of the following factors: A. temperature; B. pres-
sure (stress and hydrostatic pressure); C. type of organic pre-
cursors; D. catalytic properties of inorganic host-minerals; E.
fluid composition (by means of oxidizing/reduction condi-
tions); F. porosity/compaction and permeability of the host
rocks; G. geological time.
Temperature is thought to be the most important factor in
graphite formation, but graphitization in nature could be
caused by all the above mentioned geological factors, pro-
moting or inhibiting the process of carbon transformation
(Bonijoly et al. 1982; Wilks et al. 1993). Strain — in addi-
tion to temperature — is needed not only to initiate the
graphitization process but it significantly lowers the critical
temperature, at which the transformation of organic matter
into graphite could occur. The critical P-T conditions of syn-
kinematic metamorphism, documented in many natural oc-
currences show at least greenschist or lower amphibolite
metamorphism (300–500
°C and 4–5 kbar of pressure) as
well as much higher — upper amphibolite to granulite facies
conditions (Landis 1971; Diessel & Offler 1975; Wilks et al.
1993). The polytype of graphite (3R or 2H) depends on the
kind of pressure: stress facilitates the 2H polytype formation,
while hydrostatic pressure dominated conditions could — in
some cases — facilitate 3R polytype crystallization. The sig-
nificance of oxygen fugacity in graphite bearing assemblages
was demonstrated in detail by Connolly (1995). Low oxygen
fugacity (f
02
)
is indispensably required for the graphitization
of organic matter, regardless of the type of the actual process.
In the case of high oxygen fugacity (oxidizing conditions)
all carbon present in rocks would be transformed into CO
2
(gas) and possibly removed from the system. The removal of
the gaseous products of carbon transformation is important
for the P-T conditions of graphitization: under conditions
preventing the escape of gaseous product graphitization
would take place slowly and would require higher tempera-
tures and pressures (Diessel et al. 1978).
The aim of this paper is to describe graphites present in
metamorphic rocks of the Western Tatra Mts. and to determine
their origin as well the relative time of graphitization. An addi-
tional, but not the least, aim is to check the usefulness of the
oxyreactive thermal analysis for graphite investigations.
Geology
The crystalline basement of the Western Tatra Mts. is com-
posed of metamorphic rocks, intruded by the Variscan Ro-
háče granitoid pluton. In the metamorphic complex both
metasedimentary rocks (paragneisses, migmatites and mica
schists) and orthoamphibolites and orthogneisses can be dis-
tinguished (Fig. 1a). The metasedimentary (metapelitic-
metapsamitic) origin of most of the gneisses, migmatites and
micaschists was confirmed by mineralogical investigations
(Gawęda & Burda 1995) and geochemical analyses of major
and trace elements (Gawęda et al. 1996). The coarse-grained
orthogneisses, found both on the Polish and Slovak sides of
the metamorphic cover in question, were recently dated by
the U-Pb method to 380 Ma (Poller et al. 1997). The main
tectono-metamorphic event, which formed the peak meta-
morphic conditions is assumed to have occurred at 340–350
Ma (Poller et al. 1997). The Main Tatra Granite cooling ages
296 GAWÊDA
and CEBULAK
were calculated as 305–327 Ma (Janák & Onstott 1993). In
the Polish (northern) part of the crystalline basement one can
distinguish several parallel shear zones, running NE–SW and
dipping gently (5–15
°) to SE–SSE intruded by alaskitic
leucogranites and their pegmatites (Gawęda 1995). Graphite-
bearing rocks were found in the shear zones, mainly in the
westernmost part of the investigated area (Fig. 1b).
Different origins have been presumed for the so-called
graphitoid schists: a biogenic-tuffogenic origin of these rocks
was considered by Bober et al. (1966); later on, a pneuma-
tolytic or hydrothermal origin was assumed (Skupinski 1975;
Kapera & Michalik 1995). The latter authors suggested meta-
morphic conditions in the sillimanite zone of the amphibolite
facies and — using the “graphite geothermometer” of Shenge-
lia et al. (1978) calculated the temperature of graphite crystal-
lization as 500
°C (for graphite from schists) and 600 °C (for
graphite from quartzites).
Analytical methods
Preliminary investigations on all samples of graphite-bear-
ing rocks were conducted in transmitted light and in reflected
light. From the samples with graphite content of 2–4 wt. %
concentrates of different grain sizes were prepared for X-ray
investigations. Minor changes in structural state of graphite
were observed after the demineralization with HCl-HF mix-
tures. After the set of experiments on the separated pure
graphites we stated that the mixture of HCl + HF (5 : 1) had
the smallest infuence on both X-ray characteristics and the
Fig. 1b.
Simplified geological map of the Polish Western Tatra Mts. and sampling places. Explanations: 1 — metasedimentary rocks; 2 —
amphibolites; 3 — alaskites; 4 — mylonitized orthogneiss; 5 — Roháče Granite; 6 — sedimentary cover (T+J); 7 — Quaternary deposits;
8 — shear zones.
Fig. 1a.
Simplified geological sketch of the Tatra Mts. (after Kohút & Janák 1994; all symbols according to these authors).
THE ORIGIN OF GRAPHITE IN THE CRYSTALLINE BASEMENT 297
thermal analysis pattern of graphite under investigations. X-
ray analyses were carried out at the Dept. of Geochemistry,
Mineralogy and Petrography, Univ. of Silesia (Rigaku Denki;
CoK
α
) and — for comparison — at the Dept. of Geochemis-
try, Mineralogy and Petrography, University of Mining and
Metallurgy (Philips X’Pert; CuK
α
).
Thermal analyses were carried out using an oxyreactive
variety of this method at the Dept. of Geochemistry, Mineral-
ogy and Petrography, University of Silesia. The oxyreactive
modification of the thermal anylysis is based on the maxi-
mum accesibility of oxygen to reacting particles during heat-
ing at the time of analysis. The size of particles of the analy-
sed substance should enable such a run of reaction, that the
stoichiometry of the reagents is maintained in minute time
intervals. During the carbonization process the size of react-
ing particles should guarantee that the reaction takes place in
the whole particle, and avoid the formation of lag of reaction
products. To fulfill these conditions we need: thin layers of
substance, particle sizes below 0.1
µ
m and their dispersion in
a neutral medium (Al
2
O
3
) as well as a dynamic atmosphere.
All analyses were performed on a MOM Derivatograph
(Hungary) in an air atmosphere. The analytical conditions
were as follows: dynamic conditions for air suction of 1.9
cm
3
min
-1
and inflations rate of 1 cm
3
min
-1
; multiple sample
holders (3–10 Pt plates) [3]. The weight of each sample de-
pended on the carbon content and is in the range of 40 mg to
1500 mg. Samples with high carbon content were ground
with Al
2
O
3
powder in proportions of 1 : 2 to 1 : 3 to increase
porosity of the samples and to enable the reactions between
the oxygen and the sample components.
The Oxyreactive Thermal Analysis (OTA) was successfully
used for examination of unmetamorphosed and weakly meta-
morphosed organic matter by means of its origin and tempera-
ture or metamorphism (Cebulak & Langier-Kuźniarowa 1997;
Cebulak et al. 1997a). The preliminary results, obtained from
the rocks of different metamorphic degree and different organ-
ic matter contents (Cebulak et al. 1997b, 1998) encouraged us
to use OTA as the main tool for graphite investigations and de-
scription. This is in agreement with previous studies
(Kwiecińska & Parachoniak 1976; Kwiecińska 1980) estab-
lishing a correlation between metamorphic degree and the
peak temperature of DTA for graphites and related materials,
as well as a correlation between DTA maximum and interlay-
ered spacing d
002
.
For Oxyreactive Thermal Analysis we used a collection of
graphite standards (both natural and synthetic ones) with dif-
ferent degrees of crystallinity, different origins and different
parent organic materials, obtained from A. Szymanski (Tech-
nical University, Warsaw, Poland), Carbon Electrode Plants
(Racibórz, Poland) Museum of Earth (Univ. of Silesia, Sos-
nowiec, Poland).
The chemistry of associated minerals were investigated by
electron microprobe at the Dept. of Mineralogy and Petrog-
raphy, University of Wroclaw (Cambridge Microscan M9
electron microprobe, donation of the Vrije Universiteit Am-
sterdam). Analytical conditions: 15 kV accelerating voltage,
20 s counting time, ZAF correction procedure with sets of in-
ternationally recognized natural and synthetic mineral stan-
dards. The associated ore minerals were investigated in the
Dept. of Geochemistry, Mineralogy and Petrography, Uni-
versity of Silesia.
Abbreviations and phase notations used here:
Q — quartz, Kfs — K-feldspar, Ab — albite, An — anorthite,
Mt — magnetite, Ilm — ilmenite, Bt — biotite, Ms — muscovite,
Gph — graphite, AS — Al
2
SiO
5
polymorphs, V — vapour phase.
Petrography of graphite-bearing rocks
Graphite was found in quartzites, quartz-rich gneisses
(sample Nos.: Q2, Q3, DUx, DU1–DU6, Or.17, SP1, Ł3),
mica schists (W1, K l), mylonitic orthogneisses with S-C
structures (Ł6) and blastomylonites (Ch22, Ch17a) present in
the shear zones (Fig. lb). In quartzites and quartz-rich gneiss-
es the graphite content ranges from 2 to 4 wt. % (Table 1).
Most of the graphite is concentrated in micro-laminae 0.2–
0.3 mm thick (Fig. 2), subordinate amounts of graphite flakes
are scattered among the quartz grains. In the sample Or.17
one can observe both graphite scattered in the quartz matrix
and graphite inclusions in the muscovite flakes (Fig. 3).
Blastomylonites and mica schists contain 0.1–1.0 wt. % of
graphite. In the S-C mylonitic orthogneisses graphite is a
component of the black “impregnant” (1.5 wt. % of graphite)
found on the S and C surfaces (Fig. 4) and associated with
the large muscovite flakes. The phengitic muscovite (Table
2A) and almost pure albite (Table 2B) are the products of sil-
limanite + alkali feldspar decomposition (Fig. 5).
Sample No
Quartz
Feldspars
Mica
Graphite
O.M.
**
Or.17
84.8
1.8
8.6
4.0
0.8 (H+M)
SP1
84.5
3.05 (An
3-4
)
7.55
4.0
0.9 (H)
DU2
84.4
2.6
9.6
2.1
1.3 (I+M)
DU3
84.4
8.5 (An
20
)
2.8
2.8(.)
1.5 (I+H)
W1
9.0
5.0 (An
14-18
)
84.0
0.2
1.8 (G+H)
£6
51.8
35.14 (An
0.1-0.3
)
9.06
1.5
*
2.5 (M+G)
*
percent of graphite in the black "impregnant" (2.5 vol. % of the rock) counted
from thermal analysis of the separated impregnant;
**
O.M. = ore minerals: ilmenite (I), hematite (H), magnetite (M), goethite (G).
(In brackets
–
the anorthite content in plagioclase)
Table 1:
Modal analyses of representative graphite-bearing rocks
(in vol. %).
Fig. 2.
Graphitic quartzite (DU4) from Dlhý Uplaz. Graphite
flakes (Gph) concentrate in thin lamellae among the quartz grains
(Q). Scale bar = 0.5 mm.
298 GAWÊDA
and CEBULAK
hours. Their values change a little with the time of acid treat-
ment which influenced the calculated temperatures of graphite
crystallization (Table 3a). The temperatures obtained from
curves presented by Demeny (1989) are significantly lower
than those obtained by Shengelia (1978) and temperatures ob-
tained in our experiments. We should remember that all curves
presented in the paper of Demeny (1989) are almost parallel to
the temperature axis in the interval over 500
°C, that is for
graphite samples with good structural ordering, which can re-
sult in inprecise temperature estimations.
Oxyreactive thermal analysis (OTA) was carried out for
raw samples, to calculate the amount of graphitic carbon and
then for homogenized samples, ground for 30’ with Al
2
O
3
.
The ground samples showed lowering of the peak tempera-
ture (approx. 100
°C; Fig. 6a), but the grinding allowed us to
distinguish the peaks from organic matter of different origin
and/or metamorphic degree, and to avoid the influence of
crystal-size on the temperature of the graphite decomposi-
tion. The large graphite flakes (Ø > 0.2 mm) usaully show a
higher degree of ordering and higher temperatures of crystal-
lization, observed both in X-ray and OTA methods (Table 3b;
Fig. 6a).
A
Sample
Msl(C)
Msl(M)
Ms2(C)
Ms2(M)
SiO
2
47.01
46.34
46.29
45.56
TiO
2
0.89
0.95
1.19
1.45
Al
2
O
3
34.88
36.02
35.56
34.84
FeO
0.95
0.92
1.00
0.92
MnO
0.02
0.00
0.05
0.03
MgO
0.64
0.45
0.60
0.63
Na
2
O
0.40
0.51
0.67
0.49
K
2
O
10.48
10.90
10.48
10.81
Total
95.27
96.09
95.84
94.73
formula
Si
6.234
6.115
6.120
6.111
Al
IV
1.766
1.885
1.880
1.889
Al
VI
3.685
3.717
3.662
3.620
Ti
0.089
0.094
0.118
0.146
Fe
0.110
0.102
0.111
0.104
Mg
0.127
0.088
0.118
0.126
Mn
0.002
0.000
0.005
0.004
K
1.774
1.835
1.767
1.850
Na
0.102
0.131
0.171
0.126
C –
core; M –
margin
B
Sample
Ab1(C)
Ab1(M)
Ab2(C)
Ab2(M)
SiO
2
69.91
70.75
70.53
69.73
Al
2
O
3
19.96
19.77
20.28
19.90
FeO
0.08
0.07
0.05
0.01
CaO
0.04
0.03
0.07
0.06
Na
2
O
11.55
11.82
11.87
11.80
K
2
O
0.06
0.11
0.06
0.06
An
0.2
0.1 0.3 0.3
Ab
99.5
99.3 99.4
99.4
Or
0.3
0.6 0.3 0.3
C –
core; M –
margin
Table 2: A.
chemical analyses and crystall-chemical formulae of
muscovites (22 O
2-
). B. Chemical analyses and crystall-chemical
formulae of albites (8 O
2-
).
Fig. 3.
Grain of postmagmatic muscovite (Ms) among the quartz
grains (Q) in the graphitic quartzite from Ornak (Or.17) enclosing
the graphite flakes (Gph). Scale bar = 0.5 mm.
Fig. 5.
Sillimanitic nodule (Sil) in the core of the postmagmatic
muscovite (Ms). Sample Ł6. Scale bar = 0.1 mm.
Fig. 4.
S-C structure of orthogneiss from Łopata (Ł6). The post-
magmatic muscovite (Ms) and graphite (Gph) crystallized on the
S-C planes. Pl = albitic plagioclase. Scale bar = 0.3 mm.
Experimentals and results
X-ray analyses of both raw pure graphites and samples after
acidification showed that the graphite represents 2H polytype,
with high ordering degree (G.D.= 0.83; method after Tagiri
1981, updated by Barrenechea et al. 1992). In the classifica-
tion of Landis (1971) it represents d1 type with high crystallin-
ity. The a
0
and c
0
parameters were calculated for raw concen-
trates and for samples after acidification during 48 and 120
THE ORIGIN OF GRAPHITE IN THE CRYSTALLINE BASEMENT 299
ent origin. Two thermal points are important in the OTA
characteristics of graphites: 1. the beginning of reaction
marks the lowest temperature threshold at which the organic
matter was transformed and carbonized; 2. the peak of exo-
thermal reaction marks the maximum thermal stability of the
carbon structure. The beginning temperature of the exother-
mal reaction for the analysed graphites is quite stable and oc-
curs in the range of 570–590
°C. The peaks of reactions for
raw samples can be grouped into two intervals: 640–650
°C
and 698–780
°C (Table 4). One exception is the sample Ł3
with the first peak about 450
°C. This could be evidence for
the possible presence of weakly metamorphosed (antracithic)
carbon.
The thermal characteristics of the graphites under investiga-
tion are typical for bituminous precursor material: petroleum
cokes originated from metamorphosed pyrobitumins, such as:
asphalts, ozokerite or heavy fractions of rock-oil. The high de-
gree of metamorphism of the graphitized organic substance is
shown in Fig. 7. Different and high temperature oxyreactive
patterns of graphites are results of both degree of metamor-
phism and the genetic diversification of the parent organic
substance. Graphites originated from bituminous substances
metamorphosed in amphibolite facies conditions usually show
oxyreactive effects at high temperatures — i.e. above 700
°C.
A
Sample
a
o
c
o
Ts [
o
C]
Td [
o
C]
Or.17 (raw)
2.4570(0.0015)
6.7075(0.0038)
730
600
Or.17 (48 h)
2.4601(0.0002)
6.7111(0.0005)
680
590
Or.17 (120 h) 2.4613(0.0003)
6.7124(0.0006)
660
570
B
Sample
a
o
c
o
Ts [°C]
Td [°C]
SP
XL
2.4612(0.0007)
6.7127(0.0008)
666
575
SP
L
2.4611(0.0008)
6.7151(0.0008)
630
560
SP
M
2.4630(0.0008)
6.7164(0.0007)
625
530
XL–crystal size > 0.2 mm; L– crystal size 0.01-0.2 mm; M–crystal size < 0.01 mm
Table 3: A.
Unit cell parameters of graphites (raw and after acidi-
fication — time of treatment in brakets) and estimated tempera-
tures of crystallization. B. Unit cell parameters and estimated tem-
peratures of crystallization of raw graphites. (Ts = according to
Sengelia et al. 1978; Td = Demeny 1989).
Fig. 6b.
Oxyreactive thermal patterns of graphite (sample SP) raw
and after acid treatment.
Fig. 6a.
Oxyreactive thermal patterns of graphite (sample Or.17)
raw and after grinding.
Samples after treatment with (HCL + HF) mixture were
analysed in the same conditions as raw samples. During the
experiments we observed a decrease of peak temperatures af-
ter acidification (Fig. 6b), and the effect was comparable
with the shift observed for X-ray analysis. The acid treatment
didn’t influence the shape of the exothermal peak. The exper-
iments carried out previously allowed us to determine the
typical features of metamorphosed organic matter of differ-
Raw sample
Sample after
grinding for 30’
Sample after
grinding for 60’
Rock concentrate (30 %
of graphite) after grinding
for 30’
Sample after
grinding for 30’
Raw sample
Sample after grinding and
(HCl+HF) treatment for
24 h.
Sample after grinding and
(HCl+HF) treatment for
72 h.
Sample after grinding and
(HCl+HF) treatment for
144 h.
300 GAWÊDA
and CEBULAK
The oxyreactive peaks in the temperature range of 600–700
°C
are typical of humolitic precursor material (metamorphosed in
the same conditions in amphibolite facies). Such a conclusion
is supported by a series of OTA experiments led for the car-
bonization products of antracites and pitches of different ori-
gin as well as petroleum coke carbonization products obtained
from Carbon Electrode Plants — Racibórz (Poland).
Table 4:
Thermal characteristic of graphites from the W-Tatra Mts.
Sample
beginning of
peak of reaction
No
reaction [°C]
[°C]
Or.17
570
650
660
780
SP1
570
650
£6
590
730
Q2
580
698
Q3
580
698
DUx
590
650
700
DU5
580
670
DU6
590
720
Ch22
590
660
Ch17a
590
640
£3
420
450
590
650
Fig. 7.
Oxyreactive thermal analyses of graphites from the West-
ern Tatra Mts.
Discussion
The origin of graphite
The high concentration of graphite in rocks that have un-
dergone significant polymetamorphic changes as well as lo-
cations of graphite-rich rocks in the shear-zones and the un-
equivocal mineral relations raise the question if all the
graphite is of organic or hydrothermal origin in the Western
Tatras crystalline basement. To solve the problem of its ori-
gin we considered both hydrothermal and organic hypothe-
ses, taking into account the geological and thermodynamic
aspects of graphite occurrence as well.
The hydrothermal hypothesis
Hydrothermal graphite precipitation can occur from C-O-
H (± Fe, Ti, Si, Na) fluids saturated with respect to carbon,
during cooling and exhumation of metamorphic terranes (Ce-
sare 1995). The most important feature which determine if
graphite would precipitate is the composition of the fluid, ex-
pressed by X
0
(atomic fraction of oxygen relative to oxygen
plus hydrogen — Fig. 8). The mineral devolatilization reac-
tions or the C-O-H ± Fe fluid influx are factors determining
the redox conditions in natural systems (Connolly 1995). In
the first case siderite decarbonization and oxidation can lead
to graphite + magnetite precipitation. The next possibility
can result in hydration of the K-feldspar + Al
2
SiO
5
system to
produce muscovite, graphite and quartz. The general reaction
can be written as:
AS + Kfs + V (C, Fe, Ti, Na) = Ms + Q + Ab + Gph ± Mt/Ilm
or
Bt(Fe, Ti) + AS + Kfs + V (C, Na) = Ms + Q + Ab + Gph ± Mt/Ilm
In that case the amount of graphite precipitated can be cor-
related with the amount of muscovite (as the hydrated phase)
so that the production of 1 cm
3
muscovite involve the precip-
itation of 0.0002 cm
3
graphite (Connolly 1995).
The sample adequate to that model is the S-C orthogneiss
(Ł6). In that sample graphite is a component (1.5 wt. %) of
the black “impregnant” found on the S-C surfaces (Fig. 4). In
the whole sample muscovite content is 9.06 vol. %, and the
“impregnant” content is 2.5 vol. %, what makes the real
graphite content 0.0004 wt.% (for simplification we recalcu-
late every number as wt. % taking specific gravities as: for
muscovite = 2.79 g/cm
3
; for graphite = 2.2 g/cm
3
; for the
whole rock = 2.7 g/cm
3
; for the black “impregnant” = 4 g/
cm
3
). Taking into account that the graphite in the Ł6 sample
occurs only as mineralization on cleavage (C) and schistosity
(S) planes it seems to be possible that in this particular case
graphite could precipitate from the carbon-saturated vapour
phase. The same interpretation can be assumed for the mica
schists with very small graphite content (i.e. W1) or for the
graphite cogenetic with muscovite flakes found in the quartz-
ite sample Or.17 (Fig. 3). The above intrepretation can sup-
port the suggestion of Kapera & Michalik (1996) about the
hydrothermal precipitation of graphite in the so called “chlo-
rite” schists (in fact mica schists, with no chlorite present).
(1)
(1a)
650
780
650
730
698
698
650
700
696
Or.17
SP
Ł6
Q2
Q3
DUx
DU4
Ch17a
DU5
DU6
Ch22
Ł3
670
710
640
450
750
660
650
THE ORIGIN OF GRAPHITE IN THE CRYSTALLINE BASEMENT 301
agreement with the high crystallinity index of graphite, the
type of organic matter (the Early Paleozoic rocks could not
contain more evolved organic matter) and the high tempera-
tures of decomposition.
The problem to consider is the amount of primary organic
matter (possibly bitumins from Lower Paleozoic algae),
present in the rocks before metamorphism. To obtain the
presently observed 2–4 wt. % of graphite we need the prima-
ry bitumins concentration in the range of 15–20 wt. %. Such
a concentration can be found in the Early Paleozoic rocks
from the Baltic area. The fingerprints of the oxyreactive fea-
tures of the organic matter from the Baltic area is shown on
the Fig. 9 and was discussed in a recent paper (Cebulak &
Langier-Kuźniarowa 1997). The present host-rocks —
quartzites, previously sandstones, cannot be considered as
favourable oil-bearing host rocks for primary bitumins but
they could serve as good collectors for migrating bitumins.
In such an interpretation in the described rocks we can ob-
serve the bitumin deposits, conserved during metamorphism.
Special attention should be paid to sample Or.17. It shows
two-peak characteristics and two modes of graphite occur-
rence: both the disseminated graphite and graphite flakes
growing together with muscovite. Such a situation could sug-
gest the presence of both types of graphite in this sample.
P-T conditions and time relations of graphitization
The conditions of post-magmatic graphite (Gph
2
)
crystalli-
zation are quite easy to estimate. This type of graphite is asso-
ciated with the mineral reaction 1a: AS + Kfs + Bt + V (C, Na)
= Ms + Q + Ab + Gph + Mt/Ilm. Applying the phengite-in-
muscovite geobarometer (Massonne & Schreyer 1987), the
critical curve of the reaction and the muscovite stability field,
we can assume the maximum temperature and pressure of pre-
cipitation as 700–730
°C and 6 kbar. The minimum conditions
are as low as 450
°C and approx. 2 kbar (Fig. 10). We can ob-
serve the similarity of peak temperature obtained from OTA
(Fig. 7 — sample Ł6) and maximum temperature estimated
from mineral reactions. The origin of hydrothermal fluids
could be related to the Roháče granite emplacement and fluid
migration along the cracks, cleavage and schistosity — best
developed in the shear zones.
The fluid composition is a result of the interaction of mag-
matic vapour phase and the envelope rocks. Taking into ac-
count that the hydrothermal graphite isn’t very common
phase in the metamorphic rocks we can assume that the pres-
ence of graphite-saturated CH
4
-CO-CO
2
-H
2
O fluid (Fig. 8)
originated as the result of assimilation of organic compo-
nents present in some metasedimentary rocks.
The graphite with organic precursors (Gph
1
),
metamor-
phosed in situ, is more difficult to investigate. The richest
graphite occurrences are situated rather close to the tonalite-
granodiorite Roháče intrusion. This granitoid was character-
ized by the high oxygen fugacity, manifested by the oxida-
tion of Fe-minerals (Kohút & Janák 1994) and the
temperatures of emplacement as high as 850
°C, thus in the
contact aureole the temperature could exceed 700
°C (Lud-
hová & Janák 1996). In such a situation the carbon present in
any unmetamorphosed form in country rocks should be oxi-
Fig. 8.
C-H-O phase diagram with the graphite growth limits in
CH
4
-CO-CO
2
-H
2
O fluids (combined from Connolly 1995; Bach-
mann et al. 1991).
The organic hypothesis
If we consider the graphitic quartzites (2–4 wt. % of graph-
ite) with only 2.8 vol. % of sericite/muscovite such a hypoth-
esis looks improbably. Hydrothermal precipitation cannot
produce the laminar structures characteristic for graphite-rich
rocks. Both the rock fabric and the thermal characteristics of
the graphites point to the organic origin of the graphite in
question. Their geological position — xenoliths inside the
sheared orthogneiss — suggests that they were fragments of
the metasediments emplaced in the older granite (possibly
380–400 Ma ago) and their metamorphism was much older
than the Roháče granite intrusion. Such interpretation is in
H
O
C
H
2
O
CO
2
CO
CH
4
Borehole II
depth [m]
1297.19-1297.23
1311.05-1311.09
1312.1-1312.16
1321.53-1321.59
1312.17-1312.21
1321.74-1321.77
Borehole III
depth [m]
1386-1386.2
1388
1390.2-1390.22
1446.23-1446.26
Borehole II depth [m]
Borehole III depth [m]
Fig. 9.
Examples of the Early Paleozoic kerogens from the Baltic
area (after Cebulak & Langier-Kuźniarowa 1997).
1297.19-1297.23
1311.05-1311.09
1312.10-1312.16
1312.17-1312.21
1321.53-1321.59
1321.74-1321.77
1386-1386.2
1388
1390.2-1390.22
1446.23-1446.26
302 GAWÊDA
and CEBULAK
Fig. 10.
P-T diagram with the suggested graphitization conditions.
Explanations: Gph
1
—graphitization conditions of the primary or-
ganic matter; Gph
2
—post-magmatic graphite precipitation.
dized to CO
2
. The only solution is to assume that carbon was
present as graphite before the Roháče granite intrusion,
meaning that its transformation to the mineralogically stable
form took place during an older metamorphic event.
The graphite polytype 2H is thought to be typical of stress
conditions. That fact, together with the location points — in
the shear zones — could suggest that the Old Variscan shear-
ing episode, which occurred at about 345 Ma (Gawęda et al.
1998), had formed the graphitic structure. The P-T conditions
in the sheared complex were estimated at 710–780
°C and
7.5–10 kbar (Gawęda & Burda 1995; Gawęda & Kozlowski
1997). It is possible, that in the rocks outside the shear zones
the form of carbon was more weakly metamorphosed and was
oxidized during or after granite intrusion. That could be the
explanation for the graphite presence only in shear zones. A
further consequence of the carbon oxidation could be that the
CO
2
enrichment in postmagmatic fluids resulted in carbonate
mineralization — very rich in that part of the Tatra crystalline
basement (Paulo 1970, 1979; Wątocki 1950).
Conclusions
We can conclude that in the investigated area it is possible
to distinguish two genetic types of graphite:
1. Most of the graphite (= Ghp
1
), present in the Western
Tatra metamorphic rocks was formed as the result of poly-
metamorphism of the older organic matter (possibly bitumins
such as: ozokerite, asphalt, heavy fractions of rock-oil, etc.).
Final graphitization took place before the Roháče granitoid
intrusion and was possibly the result of the shearing event
(345 Ma).
2. A minor amount of graphite (= Gph
2
) was precipitated
from the post-magmatic CO
2
-CH
4
-H
2
O fluids and is synge-
netic with secondary muscovite and albite. The origin of this
type of graphite is connected with the postmagmatic fluids
circulation in the vicinity of the Roháče granitoid pluton.
3. The remobilization of carbon (not as resistant as the
graphite) to the volatile phase as CO
2
is a possible source of
carbonate mineralization in the Western Tatra Mts.
4. The shear zones in the crystalline basement preserved
graphite G
1
and contain younger graphite G
2
precipitated
from the hydrothermal fluid phase.
Acknowledgements:
The authors thank Prof. R. Kryza for
the assistance during microprobe analyses, Prof. A. Szyman-
ski for the graphite standarts for the thermal analyses, Prof.
B. Kwiecińska for the critical and constructive discussion,
Msc B. Ptak for the assistance during X-ray analyses and
Msc Ewa Teper for the assistance during the preparation of
computer drawings. Dr. Attila Demeny and two other anony-
mous referees are deeply acknowledged for valuable com-
ments.
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