GEOLOGICA CARPATHICA, 52, 5, BRATISLAVA, OCTOBER 2001
277 — 286
FLUID INCLUSION STUDY ON HYDROTHERMAL As-Au-Sb-Cu-Pb-Zn
VEINS IN THE MLYNNÁ DOLINA VALLEY (WESTERN
CARPATHIANS, SLOVAKIA)
JURAJ MAJZLAN
1
, VRATISLAV HURAI
2
and MARTIN CHOVAN
3
1
Department of Geology, University of California at Davis, Davis, California 95616, USA; jmajzlan@ucdavis.edu
2
Dionýz Štúr Geological Institute, Mlynská dolina 1, 817 04, Bratislava, Slovak Republic
3
Department of Mineralogy and Petrology, Comenius University, Mlynská dolina G, 842 15 Bratislava, Slovak Republic
(Manuscript received October 31, 2000; accepted in revised form June 13, 2001)
Abstract: A study of fluid inclusions from the ore samples from the Mlynná dolina valley (Nízke Tatry Mts, Western
Carpathians) has provided information on the formation conditions of the mineralization. Arsenopyrite and pyrite are
accompanied by quartz with CO
2
-rich, low-to-moderately saline (3.6—15.4 wt. % NaCl eq.) fluid inclusions with homog-
enization temperatures of 281—365 °C and estimated trapping pressures between 150 and 350 MPa. Arsenopyrite ther-
mometry suggests a crystallization temperature of 320—380 °C, thus overlapping the fluid inclusion data. Subsequent
decrease in temperature and pressure were probably responsible for the fluid devolatilization and the precipitation of
stibnite and berthierite at temperatures of 200—250 °C and pressure <100 MPa. Formation conditions of chalcopyrite—
tetrahedrite assemblage are poorly constrained due to the paucity of fluid inclusions. These homogenize at 157—187 °C
and indicate an aqueous fluid with a salinity of 17.9—22.0 wt. % NaCl eq. Superimposed galena-sphalerite assemblage is
hosted by quartz containing fluid inclusions with a salinity of 16.3—22.5 wt. % CaCl
2
eq. and homogenization tempera-
tures between 95—202 °C. Preliminary thermometry and mineralogical data for mineralizations of the Mlynná dolina
valley suggest a close genetic similarity to other ore deposits in the Nízke Tatry Mts.
Key words: Western Carpathians, Nízke Tatry Mts, ore mineralizations, fluid inclusions.
Introduction
There is a long mining history in the Nízke Tatry Mountains
which contain rich ore accumulations (Chovan et al. 1996). In
addition to the large ore deposits (cf. Dúbrava, Magurka), nu-
merous smaller deposits were mined in the past. A number of
small abandoned mines have been found in the Mlynná dolina
valley (Andrusov et al. 1951) but there have been only a few
mineralogical studies on these ores (Turan 1961; Stankovič
1976; Majzlan & Chovan 1997).
A detailed fluid inclusion study of the Dúbrava deposit was
presented by Chovan et al. (1995) and Chovan et al. (1999).
As a continuing effort to understand the conditions of ore dep-
osition in the Nízke Tatry Mts, we have conducted a micro-
thermometric study on the vein quartz associated with miner-
alization in the Mlynná dolina valley. Our objectives are to
determine the fluid inclusion composition, to correlate the tim-
ing of inclusion trapping with the growth of ore minerals, and
to derive thermodynamic information from equilibrium miner-
al assemblages in order to understand the conditions under
which the mineralization has formed. The ore veins in the
Mlynná dolina valley are then compared with other deposits in
the Nízke Tatry Mts, and with similar hydrothermal deposits
elsewhere, in terms of their mineralogical composition and
evolution of hydrothermal fluids.
Geological settings
The Western Carpathians (Fig. 1a) are a collisional Alpidic
orogen, which formed after closure of the Tethys Ocean due to
the folding and thrusting of the rock complexes. The Western
Carpathians can be subdivided into the Outer, Central and In-
ner Western Carpathians (Plašienka et al. 1997).
The Outer Western Carpathians are represented by the Car-
pathian Foredeep infilled by Oligocene-Miocene molasse sed-
iments. Only the southernmost part of the Foredeep was incor-
porated into orogen nappe structure and can be compared with
the Subalpine Mollasse Zone in the Eastern Alps. The Central
Western Carpathians are further subdivided into the Tatric, Ve-
poric, and Gemeric superunits separated by major mid-Creta-
ceous thrust-faults. Inner Western Carpathians comprise the
Meliatic and Silicic superunits. The oceanic crust of the Meli-
ata Ocean was subducted and metamorphosed into blueschist
facies, and later thrust over the Gemeric Superunit. The Silicic
Superunit represents the uppermost, mostly non-metamor-
phosed allochthonous unit.
The Tatric basement of the Central Western Carpathians
(Fig. 1b) is composed of large fragments with Variscan nappe
structure, composed of Variscan granitoid plutons emplaced
within medium- to high-grade metamorphic rocks (Putiš
1992). The Tatric unmetamorphosed sedimentary cover com-
prises Upper Carboniferous-to-Albian lithological members.
Mesozoic sedimentary nappes (Krížna, Choč, and Strážov)
were thrust from the south and overlie the Tatric basement/
cover complexes. Alpine low-grade metamorphism influenced
only the marginal domains of the Central Western Car-
pathians.
The Nízke Tatry Mountains (Fig. 1b), located in the Central
Western Carpathians, are the most extensive mountain range
of the Western Carpathians. The Čertovica fault, a major mid-
Cretaceous thrust fault, divides the Nízke Tatry Mts into the
278 MAJZLAN, HURAI and CHOVAN
western Tatric part (with Au-Sb deposits Dúbrava, Magurka,
Dve Vody, and others), and the eastern Veporic part.
The Paleozoic crystalline complex of the Tatric part of the
Nízke Tatry Mts consists of Variscan granites and medium- to
high-grade metamorphic rocks, comprising anatectic migma-
tites, various types of gneisses, and amphibolites (Krist et al.
1988). The crystalline complex and its autochthonous Meso-
zoic sedimentary cover were overthrusted by the Mesozoic
(Krížna and Choč) nappes.
The most important sulphide mineralizations in the Nízke
Tatry Mts are hosted by the Tatric crystalline complex. The
formation of these mineralizations is believed to be linked
with Variscan metamorphism and the final stages of the grani-
toid plutons emplacement (Putiš 1992) in an overthickened
continental crust of the Variscan orogen. The veins, stringers,
and disseminated ores of Au-Sb±(As, Pb, Cu, W) are localized
inside regional mylonite zones of N-S and E-W direction, ac-
companied by brittle fault structures penetrating the crystalline
complex. A weak Alpine reactivation induced fault formation
within the crystalline complex and the overlying Permian-Me-
sozoic sequences. It is generally accepted that despite being
insufficient for a large-scale metal remobilization, the low-
grade Alpine metamorphism generated smaller siderite-sul-
phide veins.
The ore occurrences in the Tatric crystalline complex of the
Nízke Tatry Mts were classified by Chovan et al. (1996) who
distinguished the uranium, molybdenum, tungsten (scheelite),
As-Fe-Au (arsenopyrite-pyrite with gold), Au-quartz, antimo-
ny with Fe, Cu, Pb, Sb, Bi, Ag sulphides, Pb (galena) – base-
metals, siderite with Cu sulphides, and hematite mineraliza-
tions.
The Mlynná dolina is a north-south-oriented valley in the
Nízke Tatry Mts (Fig. 1c), north of the town of Brezno (Fig.
1b). The dominant rock types are migmatites with small am-
phibolite and lamprophyre bodies belonging to the Tatric crys-
talline complex (Biely & Bezák 1997). The northern part of
the Mlynná dolina valley is developed in the Carboniferous
granitoid rocks of the Králička and Ďumbier types (Biely &
Bezák 1997). The Čertovica lineament crops out several kilo-
meters east of the valley, thus defining the contact between the
high-grade metamorphic rocks and granitoids of the Tatric
complex, and the weakly metamorphosed rocks of the Veporic
complex (Fig. 1b). In the southern part of the Mlynná dolina
Fig. 1. a) A sketch of Central Europe showing the Outer, Central,
and Inner Western Carpathians. The thin solid line is the state bor-
der of the Slovak Republic. The area delimited by the heavy out-
lined box is expanded in 1b; b) a schematic geological map of the
Nízke Tatry Mountains (after Slavkay & Chovan 1996). 1 – Tat-
ric (Cretaceous—Permian and crystalline core), 2 – Veporic (crys-
talline core) and Krížna Nappe (Cretaceous—Permian), 3 – Choč
Nappe (Cretaceous—Upper Carboniferous). Elevation points indi-
cated by crosses, elevation given in meters above sea level. The
area delimited by the heavy outlined box is expanded in 1c; c) lo-
cation of the abandoned mine fields and waste dumps in the area
of the Mlynná dolina valley. Elevation points indicated by crosses,
elevation given in meters above sea level. Solid lines represent
streams.
▲
FLUID INCLUSION STUDY ON HYDROTHERMAL VEINS 279
valley, the crystalline complex dips beneath the sub-autochtho-
nous and allochthonous Mesozoic sedimentary sequences.
Methods
Shallow pits and abandoned mine dumps were sampled at
Valachovo, Hviezda, Brestová, Uhlisko, Hviezda-juh, and
Brezina occurrences in the Mlynná dolina valley (Fig. 1c).
Mineral associations in these localities have been studied by
Majzlan & Chovan (1997) in polished and thin sections in re-
flected and transmitted light. Fluid inclusions described in this
work were studied in 0.2—0.3 mm thick doubly polished wa-
fers. After petrographic documentation at room temperature,
phase transitions in the inclusions have been measured using a
LINKAM THMSG-600 freezing-heating stage. The instru-
ment was calibrated using synthetic K
2
Cr
2
O
7
(398 °C) and
with natural inclusions of known composition at the triple
point of pure CO
2
(—56.6 °C), and at the melting point of bi-
distilled water (0 °C). The calibration at the triple point of CO
2
was performed daily when measurements at sub-ambient tem-
peratures were carried out. The precision of the measurements
between —50 and +100 °C is ±0.2 °C. The precision of the
measurements T > 100 °C for homogenization to the liquid
phase is about ±2 °C. Salinities of the fluids were calculated
from the equations of Oakes et al. (1990), Darling (1991), Dia-
mond (1992), and Bodnar (1993) for the appropriate systems.
The isochores for the fluid inclusions were calculated using the
FLINCOR software (Brown 1989) for the H
2
O—NaCl and
H
2
O—NaCl—CO
2
systems, and by the algorithm of Zhang &
Frantz (1987) for the H
2
O—CaCl
2
system.
Results
Mineralogy
Ore veins in the Mlynná dolina valley comprise several dis-
tinct mineral assemblages (Majzlan & Chovan 1997). Their
tentative crystallization sequence is depicted in Fig. 2. A more
reliable temporal relationship is unclear due to poor exposure
and the inaccessibility of the underground workings. Conse-
quently, the strike, slope, and thickness of the veins is not ex-
actly known. The only direct evidence for a cross-cutting rela-
tionship is the occurrence of tetrahedrite veinlets in fractured
arsenopyrite and pyrite crystals, as observed on a microscopic
scale in reflected light. Additional indirect evidence comes
from the degree of deformation in the gangue minerals (Table 1),
formation PT conditions estimated in this work, and a compar-
ison with other ore bodies in the Nízke Tatry Mts. The miner-
al assemblages are listed in Table 1.
Arsenopyrite and pyrite of the arsenopyrite-pyrite assem-
blage form large (1—2 mm) euhedral crystals uniformly dis-
persed in quartz and feldspar. Minute gold grains (average
size 20
µ
m, maximum size 90
µ
m) are enclosed by arsenopy-
rite or are found in cracks within the arsenopyrite. The tempo-
ral relationship between quartz and the sulphides could not be
discerned from the available samples.
The sulphides of the stibnite assemblage form aggregates
and veinlets that appear to post-date quartz. Textural relation-
ships show that berthierite postdates stibnite. In some cases,
the emplacement veinlets and acicular crystals of berthierite
have been accompanied by the recrystallization of quartz and
resulted in a ‘halo’ of quartz surrounding the berthierite.
The chalcopyrite-tetrahedrite assemblage was emplaced in
pre-existing vein structures that contained arsenopyrite and
pyrite.
Magnetite and hematite of the magnetite-tetrahedrite as-
semblage form octahedral and tabular crystals, respectively.
Pseudomorphs of magnetite after hematite and vice versa can
be commonly observed in polished sections. Both oxides ap-
pear to be younger than abundant siderite. Tetrahedrite and
chalcopyrite form veinlets in the weathered iron oxyhydroxide
matrix. The samples were collected from shallow pits and ad-
vanced weathering to a mixture of earthy iron oxyhydroxides,
Table 1: Mineral assemblages of the ore veins in Mlynná dolina
valley (after Majzlan & Chovan 1997) and the deformation fea-
tures of their minerals. Electron microprobe analyses of the sul-
phides and identification schemes for some rarer sulphosalts were
taken from Majzlan & Chovan (1997).
Assemblage Major minerals
Minor minerals Deformation features
tourmaline tourmaline,
quartz
pyrite
quartz strongly deformed
into ribbons; tourmaline
crystals fragmented and
bent
arsenopyrite
-pyrite
arsenopyrite,
pyrite, quartz
gold, rutile,
K-feldspar
quartz with undulatory
extinction; arsenopyrite
and pyrite crystals
fractured
stibnite
stibnite, pyrite,
quartz
berthierite,
zinckenite,
gold, Fe-
dolomite
quartz and stibnite with
undulatory extinction;
stibnite shows pressure-
induced twinning
chalcopyrite
-tetrahedrite
chalcopyrite,
tetrahedrite,
quartz
chalcostibite,
Bi-jamesonite,
Bi-berthierite,
kobellite,
krupkaite
quartz with undulatory
extinction; sulphides not
affected by deformation
magnetite-
tetrahedrite
magnetite,
hematite,
tetrahedrite,
chalcopyrite,
siderite, quartz
quartz with undulatory
extinction; Fe-oxides
and sulphides not
affected by deformation
galena-
sphalerite
galena,
sphalerite, quartz
pyrite,
chalcopyrite
none
Fig. 2. A tentative paragenetic sequence of the mineral assemblag-
es distinguished in the Mlynná dolina valley. The localities of the
mineral assemblages after Majzlan & Chovan (1997).
280 MAJZLAN, HURAI and CHOVAN
covelline, and malachite precluded more precise determination
of the mineral succession.
The sulphides of the galena-sphalerite assemblage post-
date quartz.
Typology of fluid inclusions and microthermometry data
The number of observable phases in fluid inclusions at room
temperature was the basis for distinguishing several inclusion
types, which are listed in Table 2. Most inclusions are
monophase (liquid-only), less commonly two (liquid + gas)
phases have been observed. The size of the inclusions ranges
from <5
µ
m up to 20
µ
m. The samples of chalcopyrite-tetrahe-
drite and magnetite-tetrahedrite assemblages contain few pri-
mary fluid inclusions, and no inclusions were found in the
samples of the tourmaline assemblage. Therefore, in the re-
maining text, most emphasis is laid on the arsenopyrite-pyrite,
stibnite, and galena-sphalerite assemblages. No measurements
were performed on the secondary inclusions, whose trails are
ubiquitous in quartz accompanying all mineral assemblages.
Microthermometric measurements were interpreted in terms
of available experimental data (Oakes et al. 1990; Darling
1991; Diamond 1992; Bodnar 1993). The phase transitions
measured were the melting temperature of carbon dioxide
(TmCO
2
), eutectic temperature (Te), melting temperature of
the gas clathrate (Tm
clat
), and ice (Tm
ice
), the partial homoge-
nization temperature of the CO
2
-rich phase (ThCO
2
) and total
homogenization temperature (Th). All phase transitions were
estimated at a heating rate of 0.1 °C/min. The Tm
clat
values
were obtained using the sequential freezing method (Collins
1979). The results of the microthermometric measurements
are listed in Table 3.
Arsenopyrite-pyrite assemblage
Quartz that hosts arsenopyrite, pyrite and gold contains
abundant carbonic-aqueous, and sparse carbonic fluid inclu-
sions. Small (<1
µ
m) inclusions are the most abundant, caus-
ing ‘cloudiness’ of the quartz. Larger inclusions that survived
tectonic deformation occur either randomly in areas with
abundant small inclusions or in small clusters in clearer quartz.
The inclusions bear no clear signs of a secondary origin ac-
cording to conventional criteria (Roedder 1984), however,
they cannot be unambiguously assigned a primary origin.
The ThCO
2
values divided the inclusions with the carbonic
phase into two groups (Fig. 3a,b): the inclusions with relative-
ly low ThCO
2
(—15 to +12 °C) (hereafter referred to as carbon-
ic-aqueous I) and inclusions with higher ThCO
2
(+15 to +28
°C) (hereafter carbonic-aqueous II). In the quartz with arse-
nopyrite and pyrite, the former group of inclusions is more
Fig. 3. a,b) Histogram of ThCO
2
values of the carbonic-aqueous I
and II (light gray bars) and carbonic inclusions (dark gray bars): a
– from quartz associated with stibnite and berthierite, b – from
quartz associated with arsenopyrite and pyrite. c) Histogram of
TmCO
2
values for the carbonic-aqueous I and II (light gray bars)
and carbonic inclusions (dark gray bars). d) Histogram of Th values
for the aqueous inclusions from quartz associated with galena and
sphalerite.
▲
FLUID INCLUSION STUDY ON HYDROTHERMAL VEINS 281
abundant than the latter. No Th values have been obtained for
the carbonic-aqueous I inclusions due to their decrepitation
prior to total homogenization. The TmCO
2
values in all CO
2
-
bearing inclusions have been close to the triple point of pure
CO
2
(Fig. 3c, Table 3), indicating only minor amounts of other
gaseous components besides CO
2
.
Stibnite assemblage
Quartz associated with stibnite, berthierite and gold contains
numerous carbonic-aqueous and aqueous inclusions, and rare
carbonic-aqueous-halite inclusions. The carbonic-aqueous in-
clusions I are rarely found in the quartz associated with stib-
nite. The carbonic-aqueous inclusions II (Fig. 4) occur either
isolated or in small clusters but their secondary or primary ori-
gin is equivocal. A total of 17 Th measurements (Fig. 5, Table
3) were made for the carbonic-aqueous II inclusions that ho-
mogenized to either liquid or gas. Most carbonic-aqueous II
inclusions decrepitated between 250 and 300 °C due to high
internal overpressure. Therefore, each successful Th measure-
ment was checked by repeated ThCO
2
measurement to ensure
that the inclusion has not undergone stretching or decrepita-
tion. The carbonic-aqueous-halite fluid inclusions were only
found in a small quartz crystal isolated in massive stibnite.
Their relationship to other inclusions in the sample is not clear
and they were not further characterized.
The aqueous inclusions appear to be pseudosecondary or
secondary with respect to the host quartz. In a few cases, the
aqueous inclusions were found in healed cracks extending be-
yond the quartz-penetrating stibnite veinlets. The aqueous in-
clusions are also found in clear quartz halos around berthierite
veinlets or in trails extending from berthierite aggregates and
crystals. Occasionally, a jagged interface between the vapor
bubble and the liquid phase at temperatures <10 °C suggested
the presence of CO
2
hydrate. Many aqueous inclusions de-
crepitated upon heating. The data for the inclusions for which
Table 2: Types of fluid inclusions from the Mlynná dolina valley.
phases discernible at room temperature
type
liquid, gas, or supercritical
CO
2
carbonic
liquid, gas, or supercritical
CO
2
with aqueous phase
carbonic-aqueous
liquid, gas, or supercritical
CO
2
with aqueous phase and
halite crystal
carbonic-aqueous-
halite
aqueous phase and vapour
aqueous
aqueous phase and vapour, crystals of solid phases
aqueous-solid
Table 3: Chemical and physical properties of the fluids trapped in fluid inclusions in the samples from the Mlynná dolina valley. For the
microthermometry measurements, only the minimum and maximum values are reported, with the exception for Te where all data are giv-
en. Volume estimates have been made at room temperature. (f.i. – fluid inclusions.)
f.i. type and
mineral assemblage
measured temperatures
of phase transitions
size and shape,
phase proportions
chemical system, salinity of the
aqueous phase, and f.i. density
carbonic f.i. in Q from
arsenopyrite-pyrite and
chalcopyrite-tetrahedrite
assemblages
TmCO
2
-57.4 to -56.7
°C,
ThCO
2
-15.4 to +29.0
°C
≤5 µm, regular shape
system CO
2
,
density 0.631–1.011 g/cm
3
carbonic-aqueous f.i. I in Q
from arsenopyrite-pyrite,
stibnite, and chalcopyrite-
tetrahedrite assemblages
TmCO
2
-57.4 to -56.7
°C,
ThCO
2
-15.4 to +12.0
°C,
Tm
clat
1.5–8.6
°C
≤10 µm, regular shape,
occasional necking-down
system H
2
O–CO
2
–NaCl
±KCl,
salinity 4.4–14.8 wt.% NaCl eq.,
density 0.936–1.046 g/cm
3
carbonic-aqueous f.i. II in Q
from arsenopyrite-pyrite and
stibnite assemblages
TmCO
2
-57.6 to -56.7 °C,
Te -22.5, -22.5, -22.5 °C,
ThCO
2
15.6 to 28.3 °C,
Tm
clat
0.2–8.2 °C,
Th 281–428 °C
<10
µm, regular, commonly negative
crystal shapes, occasional necking-
down, CO
2
-rich phase ~20–95 vol.%
system H
2
O–CO
2
–NaCl
±KCl,
salinity 3.6–15.4 wt.% NaCl eq.,
density 0.670–1.007 g/cm
3
aqueous f.i. in Q from
stibnite assemblage
Te -22.5, -22.7
°C,
Tm
ice
-7.3 to -11.7
°C,
Th 205–292
°C
usually <10
µm, occasionally up to
20
µm, regular, common negative
crystal shapes, low density phase
~20 vol.%
system H
2
O–NaCl
±KCl, traces of CO
2
,
salinity 10.9–15.7 wt.% NaCl eq.,
density 0.904–0.943 g/cm
3
aqueous f.i. in Q from
chalcopyrite-tetrahedrite
assemblage
Tm
ice
-19.5 to -14.1
°C,
Th 157–187
°C
≤5 µm, regular, occasionally negative
crystal shapes, low density phase
~20 vol.%
system H
2
O–NaCl,
salinity 17.9–22.0 wt.% NaCl eq.,
density 1.016–1.063 g/cm
3
aqueous f.i. in Q from
galena-sphalerite assemblage
Te -43, -50
°C,
Tm
ice
-12.8 to -24.1
°C,
Th 95–202
°C
<10
µm, usually regular in shape,
occasional signs of necking-down,
low density phase ~15 vol.%
system H
2
O–NaCl–CaCl
2
,
salinity 16.3–22.5 wt.% CaCl
2
eq.
(density not calculated because
NaCl/CaCl
2
ratio is not known)
282 MAJZLAN, HURAI and CHOVAN
both Th and Tm
ice
values have been measured are plotted in
Fig. 5.
Chalcopyrite-tetrahedrite assemblage
Quartz associated with chalcopyrite and tetrahedrite con-
tains carbonic-aqueous and aqueous inclusions. The carbonic-
aqueous inclusions are uncommon and found only in a few
clusters in clearer quartz. All measured inclusions belong to
the carbonic-aqueous I inclusion type (Table 3). Their relation-
ship to the quartz host or the ore minerals is, because of their
paucity, unclear. We consider the carbonic-aqueous inclusions
in these samples to be related to the early arsenopyrite-pyrite
mineralization present in the samples. The aqueous inclusions
occur either in cloudy quartz or in clear quartz grains inter-
grown with copper-bearing minerals, suggesting that they may
be related to the copper-bearing ore fluids.
Galena-sphalerite assemblage
Quartz associated with galena and sphalerite contains nu-
merous aqueous inclusions and rare aqueous-solid inclusions.
The inclusions occur isolated or as trails that do not intersect
grain boundaries or as smaller inclusions delineating the
growth zones of the quartz crystals (Fig. 6). The solid phases
occur as either transparent cubes, probably halite, or more
rarely as unidentified anisotropic acicular crystals. Sphalerite
contains sparse, large aqueous fluid inclusions.
Eutectic melting and Tm
ice
values below eutectic point of
the H
2
O—NaCl system (Table 3) suggests the presence of chlo-
rides of divalent cations in the fluid (Davis et al. 1990). The
aqueous fluid inclusions displayed a range of Th values (Table
3) with no sharp maxima (Fig. 3d) and little correlation of sa-
linity with Th (Fig. 7). The halite cubes in the aqueous-solid
inclusions are too small to reliably measure their dissolution
temperature. After cooling to room temperature, the halite
crystals did not re-nucleate. Attempts to measure the tempera-
ture of incongruent hydrohalite melting indicated metastable
hydrohalite transformation at temperatures above 10 °C.
Discussion
The results from fluid inclusion studies combined with pet-
rographic research of ore samples can constrain the P-T-X con-
ditions of ore formation. In the samples from the Mlynná doli-
na valley, however, there are only a few links between the
fluid inclusions trapped in quartz and the sulphidic mineraliza-
tion hosted by the gangue minerals.
Variability of the volumetric ratio between the CO
2
- and
H
2
O-rich phases in the carbonic-aqueous inclusions (Table 3,
Fig. 4) accompanying arsenopyrite-pyrite and stibnite indi-
cates a heterogeneous trapping of the CO
2
-rich fluid. There-
fore, Th values of the carbonic-aqueous II inclusions (281—428
°C, Fig. 5) represent the highest possible temperatures of for-
mation. The lowest estimates approach the actual trapping
temperatures, while the higher values could correspond either
to trapping temperature or to a solvus of a particular random
mixture of two coexisting – gas- and liquid-dominated phas-
Fig. 6. A subhedral crystal of quartz, hosting galena and sphalerite.
Arrows point at fluid inclusions outlining the growth zone of the
quartz crystal. The width of the microphotograph corresponds to
appr. 1 mm.
Fig. 4. Two carbonic-aqueous II fluid inclusions in quartz associat-
ed with stibnite and berthierite. The inclusions contain different
phase proportions, thus indicating a heterogeneous entrapment of
two immiscible CO
2
-rich and water-rich phases. Microphotograph
taken at appr. 20 °C, scale bar represents 10
µ
m.
Fig. 5. Plot of salinity and total homogenization temperature of the
carbonic-aqueous II (gray squares) and aqueous (open squares) in-
clusions from quartz associated with stibnite and berthierite.
FLUID INCLUSION STUDY ON HYDROTHERMAL VEINS 283
es trapped in the individual inclusions. The higher density of
the carbonic-aqueous I inclusions in comparison with that of
the carbonic-aqueous II inclusions points indirectly to an earli-
er origin of the former. Therefore, we assume that Th values
for the carbonic-aqueous I inclusions would be equal or higher
than those of the carbonic-aqueous II inclusions. A higher
trapping temperature also means a higher trapping pressure. A
calculation of the trapping pressure for the carbonic-aqueous
inclusions I was precluded by the lack of their Th values. The
homogenization pressure was calculated for all carbonic-aque-
ous inclusions II for which the necessary data exist (Fig. 8a),
even if the Th values have been below the lower applicability
limit (350 °C) for the equation of state of Bowers & Helgeson
(1983). The carbonic-aqueous inclusions I are interpreted as
representing an earlier hydrothermal fluid with temperature
and pressure higher than the fluid sampled by the carbonic-
aqueous inclusions II. Isochores for the carbonic-aqueous fluid
inclusions (Fig. 8a) indicate the lowest approximate formation
PT conditions at 280 °C and 150 MPa, or higher, possibly
reaching ~365 °C and ~350 MPa.
Temperature of arsenopyrite-pyrite deposition may also be
constrained using arsenopyrite geothermometry (Kretschmar
& Scott 1976). Arsenopyrite crystals contain 30.4 ± 0.2 atomic
% As and 0.8 ± 0.2 (2
σ
) atomic % Co + Ni + Sb (Majzlan &
Chovan 1997). Chemical homogeneity of the arsenopyrite and
pyrite seen in back-scattered electron images and intergrowth
of the two sulphides with no signs of replacement suggests
thermodynamic equilibrium between the two phases during
crystallization. According to the geothermometer, arsenopyrite
should have crystallized at temperatures of 320—380 °C. This
estimate allows arsenopyrite composition to deviate from the
FeS
2
—FeAs
2
join and neglects the influence of pressure on the
geothermometer (Sharp et al. 1985). The spatial association of
arsenopyrite, pyrite and quartz-hosted carbonic-aqueous fluid
inclusions, and the overlap between the homogenization tem-
peratures of the inclusions and the arsenopyrite thermometry
suggest that the arsenopyrite-pyrite mineralization was derived
Fig. 8. a) Isochoric envelopes for the inclusions from the arsenopy-
rite-pyrite (shaded) and stibnite (hatched) assemblages. Homogeni-
zation temperatures and pressures are shown for arsenopyrite-pyrite
(grey circles) and stibnite (open circles) assemblages. b) Isochoric
envelopes for the chalcopyrite-tetrahedrite (hatched) and galena-
sphalerite (shaded) assemblages, with squares (chalcopyrite-tetrahe-
drite) and circles (galena-sphalerite assemblage) corresponding to
homogenization temperatures and pressures. The isochores for the
galena-sphalerite assemblage have been calculated using the volu-
metric properties of the H
2
O—CaCl
2
system because the inclusions
have been too small to measure temperature of halite dissolution
and to derive the NaCl/CaCl
2
ratio.
from the CO
2
-rich fluids at a temperature range of 280—380 °C.
Similar estimates have been obtained for the same assemblage
from the Sb-Au deposit at Dúbrava (Sachan & Chovan 1991;
Chovan et al. 1995).
Petrographic observations (occurrence of aqueous inclu-
sions in cracks extending beyond the stibnite veinlets, in halos
around berthierite aggregates) suggest that aqueous fluids have
precipitated stibnite and berthierite. We suppose that the aque-
ous fluid was derived from the CO
2
-rich fluid by devolatiliza-
Fig. 7. Plot of salinity and total homogenization temperature for
the aqueous inclusions from quartz associated with galena and
sphalerite.
284 MAJZLAN, HURAI and CHOVAN
tion and followed the solvus in the H
2
O-rich part of the H
2
O—
CO
2
—NaCl system during decompression. Therefore, the esti-
mated homogenization temperatures (205—292 °C) of the
aqueous inclusion should be close to the actual trapping tem-
peratures. Isochores of the fluid inclusions (Fig. 8a) suggest
trapping pressure of <100 MPa. The estimated temperature
range is also consistent with conditions for Sb and S saturation
and stibnite precipitation at about
≤
250 °C (Williams-Jones &
Normand 1997). The predominant Sb and Au species in a
near-neutral fluid at temperatures < 275 °C are metal thiocom-
plexes (Seward 1973; Krupp 1988). Loss of sulphur via effer-
vescence causes destabilization of the thiocomplexes and pre-
cipitation of sulphides and gold (Krupp 1988). Formation of
berthierite post-dating stibnite may correspond to a decrease in
sulphur fugacity (Vaughan & Craig 1997) that is induced by
effervescence.
The presented data enable a comparison between the miner-
alizations in the Mlynná dolina valley and elsewhere in the
Nízke Tatry Mts, as well as with similar ores in the European
Hercynides. Fluid inclusion data from the Dúbrava deposit
(Chovan et al. 1995) show the early scheelite and arsenopy-
rite-pyrite stages precipitated from a CO
2
-rich, low salinity
(H
2
O-NaCl) fluid at 305—355 °C and >200 MPa. We have also
found carbonic fluid inclusions in fine-grained pyrite-arse-
nopyrite ores containing gold from the Dve Vody Sb-Au de-
posit. Adamia et al. (1989) reported on CO
2
and CH
4
from the
Jasenie-Kyslá W-Au deposit indicated by chromatographic
analysis of gases liberated during decrepitation of fluid inclu-
sions. In summary, the CO
2
-rich, low salinity fluid inclusions
commonly occur in the arsenopyrite-pyrite and auriferous
mineralizations throughout the Nízke Tatry Mts. They record
the PT conditions (>300 °C, >100 MPa) of the earliest hydro-
thermal fluid. Contrasting with this behavior is quartz associ-
ated with arsenopyrite, pyrite, and gold from the Vyšná Boca
locality, containing only aqueous inclusions with salinities of
2.7—16.3 wt. % NaCl eq. (Smirnov 2000).
Deposition of the early auriferous pyrite-arsenopyrite ores
has often been related to low salinity, CO
2
-rich fluids contain-
ing reduced sulphur species, at a relatively high temperature of
250—400 °C (Lattanzi et al. 1989; Boiron et al. 1990; Ortega et
al. 1996). In general, the lode-gold deposits are associated
with metamorphic terranes, CO
2
-rich fluids, sericitization of
the wall-rocks, quartz-dominated veins that are relatively poor
in sulphides, and with a high Au : Ag ratio (~10) (Groves et al.
1998). However, the CO
2
-rich fluids have not been observed
in all Au-As-Sb deposits (Boiron et al. 1989), thus bringing
into question the importance of carbon dioxide for transport of
these metals.
A common later stage (or stages) following the deposition
of the Fe-As sulphides is an assemblage with Sb-Pb-Cu-Zn
sulphides, precipitating from lower temperature (150—250 °C)
aqueous fluids (e.g. Boiron et al. 1990). Ortega et al. (1996)
and Clayton & Spiro (2000) inferred that the aqueous fluids
evolved by CO
2
-outgassing.
The younger mineralizations in the Nízke Tatry Mts that are
rich in Sb, Pb, Zn, and Cu have formed from fluids of higher
salinity and lower temperature, with little or no CO
2
. Fluid in-
clusions in quartz with stibnite, sulphosalt, and tetrahedrite in-
dicate a relatively low temperature (105—170 °C), H
2
O-NaCl
fluid at the Dúbrava deposit (Chovan et al. 1995). Infrared mi-
crothermometry data on fluid inclusions in stibnite at Dúbrava
indicate primary aqueous fluid inclusion with 3—16 wt. %
NaCl eq. and homogenization temperatures mostly between
100—150 °C (Chovan et al. 1999). Preliminary results suggest
that the conditions of stibnite precipitation at Dúbrava and
Mlynná dolina may be different.
No fluid inclusions related to the magnetite-tetrahedrite
mineralization have been found so far. This mineralization is
characterized by high oxygen fugacity reflected by presence of
di-trivalent (magnetite) and trivalent (hematite) iron oxides.
Both chalcopyrite-tetrahedrite and magnetite-tetrahedrite as-
semblages bear a strong resemblance to the siderite-sulphide
ore veins of the Nízke Tatry Mts with respect to their mineral-
ogical composition and textural appearance (cf. Ozdín & Cho-
van 1999; Ozdín & Pršek 2000).
The latest mineralizations in the Nízke Tatry Mts are related
to fluids rich in solutes of divalent metals, most probably
CaCl
2
. The barite stage at Dúbrava originated from H
2
O-
NaCl-CaCl
2
fluids at 105—160 °C (Chovan et al. 1995). Simi-
larly, the lead and zinc ores of the Mlynná dolina valley have
formed from a low-temperature, high-salinity NaCl-CaCl
2
aqueous fluid. Luptáková et al. (2000) have found CaCl
2
-rich
fluid inclusions with higher Th values (170—320 °C) in quartz
associated with galena from the Jasenie-Soviansko deposit.
The abundance of galena, sphalerite, and barite in these miner-
alizations is a consequence of the high solubility of lead and
zinc as chloride complexes and barite in Cl
—
-rich hydrothermal
solutions (Holland & Malinin 1979; Seward 1984; Ruaya &
Seward 1986). There are no constraints on the temperature and
pressure of formation of the chalcopyrite-tetrahedrite and gale-
na-sphalerite assemblages from the Mlynná dolina valley oth-
er than those from the fluid inclusion study. Isochores of the
inclusions of the two associations (Fig. 8b) show that estimat-
ed formation temperature of < 200 °C corresponds to a pres-
sure of 150 MPa. Chovan et al. (1995) have assumed epither-
mal formation conditions for the late stages of mineralization
in the Dúbrava deposit. This assumption applies likely also to
the Mlynná dolina valley, implying pressures significantly
lower than the maximum estimate.
Conclusions
Several spatially and probably temporally separated mineral
assemblages have been distinguished in the Mlynná dolina
valley. Each assemblage can be assigned to one of the miner-
alizations distinguished by Chovan et al. (1996) in the Nízke
Tatry Mts. The early arsenopyrite-pyrite assemblage corre-
sponds to the As-Fe-Au mineralization sensu Chovan et al.
(1996). The association can be linked to H
2
O-CO
2
-NaCl±KCl
fluids with formation conditions of 280—365 °C and 150—350
MPa. The fluid inclusion-derived temperature estimates coin-
cide with those obtained from the arsenopyrite thermometry,
ranging between 320 and 380 °C. The stibnite assemblage cor-
responds to Fe, Cu, Pb, Sb, Bi, Ag sulphides, occurring
throughout the Nízke Tatry Mts (sensu Chovan et al. 1996).
The Sb sulphides from the Mlynná dolina valley have crystal-
lized from a CO
2
-unsaturated H
2
O-NaCl fluid derived from
FLUID INCLUSION STUDY ON HYDROTHERMAL VEINS 285
the earlier H
2
O-NaCl-CO
2
fluid at temperature of 200—250 °C
and pressure <100 MPa. The late chalcopyrite-tetrahedrite and
galena-sphalerite assemblages coincide with the siderite veins
containing Cu sulphides and Pb (galena) – base-metals min-
eralizations (sensu Chovan et al. 1996). The chalcopyrite-tet-
rahedrite assemblage can be correlated with H
2
O-NaCl fluids,
and the galena-sphalerite assemblage to H
2
O-NaCl-CaCl
2
flu-
ids, which circulated at temperatures < 200 °C.
Acknowledgments: We are thankful to F. Molnár (ELTE
Budapest) for his help and discussions about the issues of fluid
inclusion study. We also appreciate the critical comments of
N. Tabor and B. Joy. Thorough review by M.C. Boiron, R.E.
Clayton, and I. Rojkovič significantly improved the quality of
the manuscript. The microprobe analyses were performed by
D. Ozdín (Geological Survey of Slovak Republic, Bratislava).
All the thin and polished sections, as well as double-sided pol-
ished wafers were produced by cheerful V. Szabadová (Come-
nius University, Bratislava). The research was financially sup-
ported by a Grants VEGA No. 1/5218/98 and 1/8318/01.
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