GEOLOGICA CARPATHICA, 49, 5, BRATISLAVA, OCTOBER 1998
HYDROTHERMAL ALTERATION OF GRANITOID ROCKS
AND GNEISSES IN THE DÚBRAVA Sb-Au DEPOSIT,
, JURAJ MAJZLAN
and MARTIN CHOVAN
Slovak Museum of Nature Protection and Speleology, kolská 4, 031 01 Liptovský Mikulá, Slovak Republic
Department of Mineralogy and Petrology, Faculty of Sciences, Comenius University, Mlynská dolina,
842 15 Bratislava, Slovak Republic
(Manuscript received October 15, 1997; accepted in revised form September 1, 1998)
Abstract: Three alteration zones are recognized in hydrothermally altered granitoid rocks at the Dúbrava Sb-Au
deposit, Nízke Tatry Mts., Western Carpathians: the outermost chlorite zone, muscovite zone and the innermost illite-
carbonate zone. Chlorite replacing biotite originated at temperature about 320±40
C (according to Cathelineau 1988)
and the frequency distribution of Al
in chlorite suggests its re-equilibration during later hydrothermal events. The
muscovite and illite-carbonate zones are superimposed on the chlorite zone. Muscovite appears to be of both mag-
matic and hydrothermal origin, as deciphered from its TiO
content. Hydrothermal muscovite replaces plagioclase
and chlorite. In the innermost zone, carbonates and sulphides become abundant, muscovite and feldspars are replaced
by illite. Measurements of crystallinity index values of illite gave an estimate of 180200
C for the illite-carbonate
zone. The altered rocks were enriched in K
, Sb and S and depleted in CaO, MgO, Fe
, and Na
Minor changes in Al
content are ascribed either to the variations of the composition of the primary
magmatic precursor or local redistribution of these elements. Limited data on alteration of amphibole gneisses and
migmatites suggest that the main processes were chloritization and illitization; SiO
O wereremoved and K
added to these rocks.
Key words: Nízke Tatry Mts., granitoids, hydrothermal alteration, illite, muscovite, chlorite.
Recent effort to understand the processes governing the for-
mation of the Dúbrava Sb-Au deposit, including detailed
mineralogical studies (Chovan 1990), fluid inclusion and sta-
ble isotope investigation (Sachan 1989; Chovan et al. 1995)
as well as structural data (Sasvári 1997) calls also for a clos-
er inspection of the environment that hosts the ore bodies.
This paper presents new data on mineralogical and chemical
changes of the wall rocks in the process of alteration induced
by hydrothermal fluids responsible for the formation of eco-
nomic accumulation of antimony and subeconomic amounts
of other elements (Au, Cu, Ag).
In the past, little attention was paid to the rock alteration
linked to hydrothermal events in the Nízke Tatry Mts. Èillík
& Michálek (1983) dealt with the mutual influence of rock
environment and hydrothermal mineralization and reported
increasing amounts of Pb, Cu, Bi and Ag and decreasing
amounts of K, Na, Ca and Mg with increasing Sb. They found
that sericitization and silicification is typical for granitoids,
while carbonatization, chloritization and saussuritization is
characteristic for migmatites. The authors made no attempt to
compare the results of chemical analyses with petrographic
studies of the rocks. Gubaè (1983) mentioned alteration of the
rocks hosting W-Au mineralization (Jasenie-Kyslá, Nízke Ta-
The Dúbrava deposit is located in the valley of Kriianka,
on the northern slopes of the Ïumbier part of Nízke Tatry
Mts., Western Carpathians, Slovakia. It has been known for a
long time. It became an important source of Sb in the 1950s
and the exploitation ceased in 1991.
The studied samples were collected from visible alteration
zones of cm to dm thickness around the ore veins of all min-
eralization stages. Sampling was carried out in four chief
mining works in order to detect any horizontal or vertical
changes of rock alteration. Additional samples were collected
in the periphery of the ore field. The alteration zonality in the
scale of meters was studied in a traverse across the alteration
envelope of Terézia vein, Martin adit with a sampling
distance of 3 m. Changes of mineral composition of the stud-
ied rocks were monitored by planimetric analyses of 20 sam-
ples. The clay material was size-fractionated by gravity set-
tling. XRD analyses were performed on a DRON
diffractometer with Cu K
radiation and a Ni filter. Oriented
samples were prepared by sedimentation of clay suspension
) on glass plates. Samples were analyzed both be-
fore and after saturation by ethylene glycol (8 h at 60
Electron microprobe analyses were performed on JXA 840A
(CLEOM, Comenius University) (feldspars, biotite, chlorite,
illite, Ti-oxides) at 15 kV, 10 nA, standards: albite (Na), anor-
thite (Ca), spinel (Al), SiO
(Si), MgO (Mg), hematite (Fe),
adularia (K), MnO (Mn), chromite (Cr) and rutile (Ti); JEOL
*Current address: Department of Geology, University of California at Davis, Davis 95616, USA; E-mail: email@example.com
378 ORVOOVÁ, MAJZLAN and CHOVAN
733 Superprobe (Geological Survey of Slovakia) (muscovite)
at 15 kV, 20 nA, standards: albite (Na), wollastonite (Ca), co-
rundum (Al), quartz (Si), MgO (Mg), hematite (Fe). Bulk rock
chemistry was determined by wet chemical analysis (major ox-
ides) and combination of AAS and ICP (trace elements). Densi-
ty of the samples was determined by repeated measurements in
Geological setting and petrography
The Dúbrava deposit is hosted by granitoid rocks; high-
grade metamorphic rocks outcrop to the north of the deposit.
Xenoliths (up to tens of meters) of migmatites and amphibole
gneisses occur as relics of the metamorphic mantle of the
granitoids (Fig. 1).
Emplacement of a large pluton composed of granites, gran-
odiorites to tonalites, took place approximately 300 Ma B.P.
(Petrík et al. 1994 and references therein). The granitoid
rocks represent I-type plagioclase-rich Variscan granitoids
(Petrík et al. l.c.) or IS-type granitoids with affinity to I-type
granitoids (Kohút 1997). The rock-forming mineral assem-
blage comprises Mg-biotite, strongly saussuritized plagio-
clase and quartz (Petrík et al. 1994). Variscan structural
scheme was modified by Alpine tectonometamorphic events
which caused weak retrograde metamorphism in this area.
The large granitoid pluton of the Nízke Tatry Mts. is built
by two principal rock types: the first one (type Ïumbier) be-
ing composed of granodiorite to tonalite, the second one
(type Praivá), dominating around the Dúbrava deposit, of
granitic to granodioritic composition with porphyric K-feld-
Modal composition of the granitoid rocks (Lukáèik 1983)
is shown in Fig. 2 (column 1, 2). Mafic minerals are not
specified, but according to several authors, biotite greatly
predominates. Chemical composition of biotite in unaltered
rocks of the pluton falls on the boundary between the fields
of Fe- and Mg-biotites (according to Foster 1960, Fig. 3).
Magmatic muscovite and amphibole are scarce. Chemical
composition of plagioclases and K-feldspars is depicted in
Fig. 4. Plagioclases (mostly andesine) are more abundant
than K-feldspars. Their composition ranges between An
(type Ïumbier) and An
(type Praivá) (Fig. 4). K-feld-
spar, the principal phase of the phenocrysts, belongs mostly
to microcline (Lukáèik 1983) and contains poikilic inclu-
sions of quartz, biotite and plagioclase. On cooling, plagio-
clase enclosed in K-feldspar phenocrysts developed albite-
Xenoliths of amphibole-biotite gneisses and migmatites
underwent alteration similarly as granitoid rocks. Their neo-
some is compositionally close to biotite granodiorite (quartz,
albiteoligoclase, biotite). Paleosome contains amphibole,
biotite, plagioclase (albiteoligoclase).
Fig. 1. Sketch cross-section of the Dúbrava deposit (after Michálek
1992). 1 granitoids, 2 gneisses and migmatites, 3 ore veins,
4 faults. Inset shows localization of Dúbrava deposit in Slovakia.
Fig. 2. Modal composition of unaltered granitoid rocks (after
Lukáèik 1983, columns 1, 2) and the altered granitoids (columns 3
5) from the Dúbrava deposit. 1 granodiorite to tonalite (type
Ïumbier), 2 granite to granodiorite (type Praivá), 3 chlorite
zone, 4 muscovite zone, 5 illite-carbonate zone. Lukáèik
(1983) did not specify mafic minerals but the dominating one is bi-
otite; amphibole is rare.
HYDROTHERMAL ALTERATION OF GRANITOID ROCKS AND GNEISSES 379
Fig. 3. Composition of biotite in terms of octahedral cations (clas-
sification after Foster 1960): biotite from unaltered granitoids
(Lukáèik 1983, open circles) and biotite from altered granitoids
(chlorite zone, solid squares).
Fig. 4. Composition of feldspars in terms of Na, K, and Ca: feld-
spars from unaltered granitoid rocks (Lukáèik 1983, open circles)
and from altered granitoids (solid squares).
Fig. 5. Macroscopic appearance of altered rocks from chlorite
zone (top), muscovite zone (bottom left) and illite-carbonate zone
(bottom right). Scale in cm.
THtot of fluid
+3.5 to +5.1
+3.3 to +5.6
+5.5 to +8.5
-9.3 to 1.7
-3.8 to +1.5
-4.9 to +1.4
Table 1: Mineral stages and phases at the Dúbrava deposit and
values of THtot and
O of the associated fluid inclusions (after
Chovan et al. 1995, completed by new unpubl. data). The stages
and phases are listed in successive order.
The mineralization occurs in veins, stockworks and impreg-
nations in granitoid rocks and xenoliths of metamorphic rocks
(Fig. 1). Two major phases of mineral deposition were identi-
fied by the mineralogical studies (Chovan 1990): an earlier
scheelite phase and later sulphide phase, both of them further
subdivided into several stages (Table 1). The distinction be-
tween phases and stages is based on mineral assemblages and
structural arrangements of the veins bearing different assem-
blages. Quartz from scheelite, molybdenite and pyrite-arse-
nopyrite stage contains CO
-rich and aqueous fluid inclusions
with relatively high total homogenization temperature (TH
(Table 1). Oxygen isotope data suggest endogeneous source of
these fluids. Fluids in quartz of the later stages are richer in
dissolved salts and they lack CO
; contemporaneous decrease
and salinity and oxygen isotope data indicates the in-
troduction of meteoric waters into the hydrothermal system.
Fluids of the last, barite stage contained appreciable amounts
. Similar evolution of the fluids is expected in the case
of Au-W deposit Jasenie-Kyslá (Nízke Tatry Mts.) where the
O values of water extracted from fluid inclusions in
arsenopyrite fall in the field of metamorphic water close to the
boundary with the field of magmatic water (Bláha & Bartoò
1991). There is no direct geological or other evidence about
the age (Variscan or Alpine) of the Dúbrava deposit. Chovan et
al. (1995) argue that the major mineralization event was
Variscan, with Alpine remobilization. The Sb-Au deposits of
380 ORVOOVÁ, MAJZLAN and CHOVAN
Fig. 6. Alteration halo of a quartz-stibnite vein (in the left part of the photograph). ill-carb illite-carbonate zone, mus muscovite
zone, chl chlorite zone. Scale bar = 2 cm.
Table 2: Electron microprobe analyses of biotite, muscovite, chlorite and illite from the altered rocks in Dúbrava. Analyses of chlorite
recalculated on the basis of 14 oxygen atoms, analyses of other minerals on the basis of 22 oxygen atoms.
Nízke Tatry Mts. appear to be genetically close to the Variscan
Sb-Au mineralization of Massif Central, Iberian massif (e.g.,
Boiron et al. 1989, 1996; Ortega et al. 1996) and elsewhere.
There are no unaltered wall rocks left in the Dúbrava de-
posit. Field work, petrographic observation, mineralogical
studies and chemical analyses supplied evidence of hydro-
thermal alteration of the studied rocks. Samples collected in
the periphery of the ore field show also weak alteration.
Thickness of the inner alteration zones reaches centimetres
to decimeters. The alteration envelope is best developed
around the major veins with economic accumulation of met-
als, but it is found also around minor (few cm thick) veinlets
or even fractures without ore mineralization. The study of
alteration at the scale of meters was limited due to strong tec-
HYDROTHERMAL ALTERATION OF GRANITOID ROCKS AND GNEISSES 381
tonic fracturing (and consequent alteration) in the surround-
ing of the veins. In the thin sections, secondary trails of CO
rich as well as aqueous fluid inclusions, corresponding to the
two major phases of deposit formation, can be found.
Changes of mineral composition of granitoids
The least altered rocks are greenish in color, equigranular,
medium- to coarse-grained with occasional transitions into
porphyric types (Figs. 5, 6). Illitization of plagioclase in this
zone is weak; illite represents only about 12 vol. % of the
feldspar (Fig. 2). Acidic reaction rims between plagioclase
and K-feldspar contain no illite (Fig. 7a). Chessboard albite
and various forms of pertites are common in the K-feldspar
phenocrysts but they show no signs of alteration due to hy-
drothermal metasomatic processes. The Mg/(Mg+Fe) ratio of
biotite in the altered rocks (0.450.48) is identical to the ratio
for biotite from unaltered granitoid rocks (0.450.49)
(Table 2, Fig. 3). Biotite is partially or completely converted
to chlorite (brunsvigite, ripidolite, according to Foster 1962)
(Figs. 7b, 8a, Table 2) and needle-like crystals or fine-grained
aggregates of rutile, rarely also epidote or sphene. Chlorites
(Mg/(Mg+Fe) = 0.390.64) are formed exclusively at the ex-
pense of biotite. Chemical composition of feldspars from al-
tered samples and unaltered rocks (Lukáèik 1983) does not
differ (Fig. 4).
Decomposition of biotite and chlorite leads to bleached ap-
pearance of the rocks (Figs. 5, 6) closer to the contact with
ore veins. The rocks appear as equigranular, medium- to
coarse-grained. Illitization is still not intensive and the
proportion of illite does not increase (Fig. 2). Chlorite is
preserved only rarely and is mostly replaced by muscovite
with inherited cleavage planes clearly marked by fine-grained
aggregates of Ti-oxides, identified by electron microprobe
analyses. Sporadic epidote and sphene are products of
decomposition of biotite and plagioclase. Minute anhedral
grains of Fe-dolomite and calcite become more abundant,
replacing plagioclase and chlorite. K-feldspars are still
relatively resistant to alteration.
Strongly altered rocks, confined to immediate vicinity of ore
veins, are grayish or white in color, medium to fine-grained
(Figs. 5, 6). Relics of muscovite flakes, replaced by illite (Fig.
7c), Ti-oxides, epidote and carbonates represent the original
biotite crystals. In thin sections, muscovite and illite were dis-
tinguished on the basis of crystal size; fine-grained aggregates
were considered to be illite and separate large flakes musco-
vite. Other rock-forming minerals, except of quartz, are almost
totally transformed to illite which represents up to 33 vol. % of
the rock (Fig. 2). Chessboard albite and pertites in K-feldspars
are preferentially replaced by illite. Increasingly abundant car-
bonates form aggregates of veinlets in plagioclase, less in K-
feldspars. Strongly altered rocks bear larger quantities of euhe-
Fig. 7. (a) partially sericitized plagioclase crystals in unaltered K-
feldspar, note the unaltered rims on the plagioclase crystals; (b) bi-
otite bt flakes partially altered to chlorite chl; (c) muscovite
mus replaced by fine-grained aggregate of illite ill.
382 ORVOOVÁ, MAJZLAN and CHOVAN
Fig. 8. a chemical composition of chlorites in the classification di-
agram of Foster (1962); b histogram of Al
content in chlorites.
Fig. 9. Ternary diagram of TiO
, and MgO in muscovite (cir-
cles) and illite (squares) from the altered rocks from the Dúbrava
deposit. Fields after Monier et al. (1984): 1 magmatic muscovite,
2 late to post-magmatic muscovite, 3 hydrothermal illite.
dral crystals, veinlets and impregnations of pyrite, arsenopy-
rite, and stibnite.
Changes of mineral composition of migmatites
The collected migmatite samples do not display as pro-
found mineral changes as in the case of granitoid rocks. The
chief processes induced by hydrothermal fluids are chloriti-
zation and illitization. Muscovitization of mafic minerals
was not observed. Alteration intensity may be assessed ac-
cording to the degree of amphibole preservation and the vari-
able volume proportion of the secondary minerals.
Changes of chemical composition of granitoids
Investigation of chemical composition of the rocks is an-
other way of alteration assessment. In this study, alteration
index (A.I. = (MgO + K
O) / (Na
O + K
O + CaO + MgO))
defined by Hashiguchi et al. (in Vivallo 1987) was found to
be a useful tool. The degree of alteration estimated from
petrographic study correlates well with the A.I. The least
altered rocks are typical of A.I. < 50, while the most altered
ones reveal A.I. > 60, with a maximum at more than 80.
Chemical analyses of the altered rocks are listed in Table 4.
The first 16 analyses (A-9 to A-11) represent granitoid rocks
and are arranged, with an exception of A-9, in the order of in-
creasing A.I. The sample A-9 was selected as the least altered
one according to petrographic observation, (the degree of bi-
otite preservation), even if it does not hold the lowest A.I. val-
ue. The last three analyses are migmatite samples, with in-
creasing degree of alteration from A-23 to A-34. Approaching
to the ore veins, density of the samples slightly decreases and
then increases sharply due to the abundant sulfide grains in the
immediate vicinity of the veins.
The principal wall-rock alteration products in the Dúbrava
Sb-Au deposit are chlorite, muscovite and illite, together with
lesser amounts of rutile, epidote, Fe-dolomite, calcite, and other
minerals formed by decomposition of biotite, plagioclase and
K-feldspar. Progressive alteration caused transformation of orig-
inal magmatic biotite to chlorite, muscovite and illite. The three
latter sheet silicate minerals are abundant and typical for a
specific alteration zone and govern the textures and color of the
rocks. Three zones of alteration are recognized in the Dúbrava
II. muscovite zone,
III. illite-carbonate zone.
Chlorite is preserved only in the most external (chlorite)
zone. Recently, De Caritat et al. (1993) gave critical evalua-
tion of available empirical and thermodynamic chlorite ther-
mometers and concluded that none of them performs satisfac-
HYDROTHERMAL ALTERATION OF GRANITOID ROCKS AND GNEISSES 383
Fig. 10. Distribution of K/O
in muscovite and illite from
the altered rocks.
torily in the full range of chlorite composition, bulk rock min-
eralogy and P-T conditions examined. Empirical thermome-
ters, such as the one developed by Cathelineau (1988) are val-
id only for specific geological environment and produce large
errors if used in geochemically different environments. Later
thermal events may also override the original chemistry of
chlorite, thus affecting any thermometric data. Although there
was undoubtedly a later event related to the formation of sul-
fidic stages the studied chlorite seem to record, at least partial-
ly, action of the higher thermal fluids linked to the older miner-
alization stages. In the case of alteration, chlorite may inherit
compositional features of its precursor. Application of chlorite
thermometers to the samples from Dúbrava gives wide range
of formation temperatures, summarized in Table 3. Asymme-
try of Al
frequency distribution (Fig. 8b) in chlorite suggests
re-equilibration of studied chlorite during later mineralization
stages. We believe that the calculated average temperature
C (Cathelineau 1988; Jowett 1991; Table 3) is rea-
sonable when compared to the previous results of fluid inclu-
sion investigation (Chovan et al. 1995).
Several authors investigated reactions of rock-forming min-
erals under hydrothermal conditions. Ferry (1979) reports
breakdown of biotite to chlorite, sphene and release of silica,
into the fluid. In their experimental work with
iron chloride complexes, Fein et al. (1992) found that no
annite was formed in the presence of sulfur in agreement with
the data of Hammarback & Lidqvist (in Fein et al. 1992) who
suggested that annite component is destabilized by sulfur.
Destabilization of biotite and amphibole by S-rich fluid is
reported also by Tso et al. (1979) and Popp et al. (1977).
Furthermore, if the fluid contains As-bearing complexes, the
reaction will proceed according to Heinrich & Eadington
(1986) as follows:
biotite + chlorite + H
muscovite + quartz + arsenopyrite + water + O
K-feldspar + chlorite + H
muscovite + quartz + arsenopyrite + water + O
Bryndzia & Scott (1987) mention also destabilization of Fe-
chlorite by sulfidation, although at temperatures and pressures
higher than those assumed for the Dúbrava deposit. All these
reactions may account for release of silica in the hydrothermal
fluid and development of impregnations of pyrite and arse-
nopyrite in the altered rocks.
Muscovite is found in all alteration zones, but it dominates
only in the muscovite zone. The least altered rocks contain
muscovite flakes only along grain boundaries of plagioclases;
in the course of alteration, muscovite replaces chlorite and
plagioclase. Electron microprobe analyses (Table 2) revealed
that the textural variety of muscovite found in the least
altered samples with still preserved biotite contains the
largest amounts of Ti. This muscovite is considered to be of
magmatic or late magmatic origin (Fig. 9). Muscovite that ob-
viously replaces chlorite contains less Ti, representing the
product of hydrothermal activity. Fig. 9 depicts comparison of
chemical composition of muscovite from Dúbrava with com-
positional fields of magmatic and hydrothermal muscovite in
the Millevaches Massif outlined by Monier et al. (1984). Posi-
tion of our analyses outside of the magmatic muscovite field is
most probably due to differences in bulk rock chemistry; the
general trend is clearly preserved, however. In more altered
samples, distinction between magmatic and hydrothermal
muscovite, based exclusively on the petrographic observa-
tions, becomes ambiguous. Beside TiO
, Monier et al. (1984)
showed that magmatic muscovites exhibit a higher Na
O + K
O) ratio (0.070.12) while hydrothermal white mi-
cas are characterized by substantially lower ratio (0.020.06).
On the other hand, in their discrimination of magmatic and hy-
drothermal muscovites in granites, Villa et al. (1997) found no
differences between the two groups in Na
O and K
although the difference in TiO
concentration is obvious. A lit-
tle variation in Na
O + K
O) ratio with changing TiO
concentration in muscovite was observed also in the studied
samples from the Dúbrava deposit (Table 2).
Illite from Dúbrava is characterized by lower content of K/
than muscovite, FeO
content up to 3 wt.
% and low TiO
content (Table 2, Fig. 9), comparable to the
published data on illite composition (rodoñ & Eberl 1984).
content shows distribution with two maxima
between 0.60.7 and 0.80.9 K/O
contains 1.02±0.02 (1
(Fig. 10). It is not clear
whether the analyses correspond to mixed-layer illite-smectite
or merely to a mixture of illite with later smectite. The end-
member illite was found to contain 0.88 (Yates & Rosenberg
1997) or 0.85 (Aja 1991) K/O
. Aja (1991) implies also
K ranidiotis & MacLean (1987)
Jowett (1991 in De Caritat et al. 1993)
Table 3: Estimated temperature of chlorite formation according to
various chlorite thermometers.
384 ORVOOVÁ, MAJZLAN and CHOVAN
the existence of stable solubility-controlling phase with 0.69
Table 5 lists the results of XRD analyses of the most altered
granodiorites, performed to determine their mineral composi-
tion and the crystallinity index (CI) value. The measured val-
ues, compared to the data of ucha & Eberl (1992) gave an es-
timate of illite crystallization interval of 180200
C. The CI
values are similar to those measured for hydrothermal illite in
Silverton caldera by Eberl et al. (1987) who determined crys-
tallization temperature from
O data to 170320
Some XRD patterns reveal the presence of minor amounts of
smectite which probably originated during final, lower, ther-
mal stages of the alteration process.
Mylonite zones, apparently reactivated during the Alpine
orogeny, including the ¼ubelská fault, a major structure run-
ning throughout the deposit, contain mostly illite and traces
of smectite and kaolinite.
The isocon method of Grant (1986) was adopted in the cal-
culation of gains and losses during wall-rock alteration. Field
observations suggest little or no volume change during alter-
ation, but its quantification is not feasible. The isocons de-
fined for no mass change are almost identical with those for
constant volume. The solution of Gresens (1967) equation
gave no single datum for the volume change for the pairs of
the least altered sample and other analyzed samples, a con-
siderable scatter of values was obtained instead. The isocons
for constant alumina imply volume changes in range between
8.2 to +9.5 %, but aluminum needs not to be immobile (cf.
Robert & Brown 1986; Boiron et al. 1989), although in other
cases it seems to be (Ferry 1985;MacLean & Kranidiotis
1987; Ortega et al. 1996). Enrichment or depletion was quan-
tified on the basis of constant volume assumption.
MacLean & Kranidiotis (1987) advise investigation of the
relationship of pairs of elements, where one of them serves as
a reference and is shown or considered to be immobile. If the
data points for the two elements form a linear array with high
positive correlation passing through the origin then the
second element is also immobile, provided that the two
elements are not decoupled geochemically. The most suitable
reference element in most cases appears to be zirconium.
High positive correlation coefficients were found only in the
(r = 0.92, Fig. 11a) and ZrSc (r = 0.83,
Fig. 11b), suggesting that these three elements behaved as
immobile throughout the alteration process. Contrary to this,
rutile is a common constituent of the pyrite-arsenopyrite as-
semblage of hydrothermal veins and the trends for both ele-
, Sc) are but a copy of the magmatic trends
(Figs. 11a, b). Investigation of the relationships ZrAl
(Fig. 11c) and ZrK
O (Fig. 11d) shows that they follow the
magmatic trends as well, with an evident gain of K
(Fig. 11d). The application of this method seems to be ques-
tionable. We suppose that TiO
was released from primary
magmatic minerals (biotite) but its migration was limited. We
are unable to judge the degree of Sc mobility.
Figs. 12ag demonstrate gains and losses in the analyzed
samples arranged in the order of increasing alteration index.
Variations in alumina and silica content (Figs. 12a,b) are as-
cribed either to the variable chemical composition of the
magmatic precursor, or, more probably, to local redistribu-
tion of Al
. Chlorite is occasionally found in the
fractures of the vein quartz, indicating extraction of Al from
the ambient rocks into the veins. Therefore, calculations of
chemical changes on the basis of constant Al
ed and the constant volume approach was used instead.
From the change in mineralogy across alteration zones it is
obvious that K
O, Sb, S were added to the rocks during
alteration, whereas CaO, Na
O, MgO, Fe
(Figs. 12cg). Conversion of biotite to chlorite in the chlorite
Table 4: Bulk chemical composition of altered rocks from the Dúbrava deposit. Oxides in wt.%, trace elements in ppm. LOI = loss on ig-
nition, D = density, A.I. = alteration index (see text). Analyses of altered granitoids are arranged in the order of increasing A.I.
A-9 A-38 A-44
A-7 A-27 A-37 A-16 A-14 A-32 A-6a A-25 A-10
66.06 67.88 68.45 66.51 68.72 65.69 64.05 54.67 69.05 71.20 64.50 64.85 66.80 70.08 65.87
68.62 56.53 54.10
15.28 15.04 14.57 14.79 15.01 15.70 16.46 14.69 14.49 14.27 16.97 16.57 16.23 15.90 17.26
17.09 15.06 15.54
0.582 0.470 0.521 0.676 0.465 0.614 0.549 0.580 0.380 0.188 0.514 0.304 0.513 0.570 0.375
0.480 0.916 1.089
0.069 0.049 0.045 0.060 0.043 0.061 0.107 0.230 0.057 0.098 0.037 0.150 0.176 0.021 0.140
0.067 0.146 0.182
99.18 99.50 99.73 99.30 99.72 99.07 99.57 99.35 98.65 99.85 99.90 99.26 99.84 99.33 100.10
99.68 99.00 98.96
63.95 69.95 54.88 87.37 41.95 37.28 32.00 24.95 20.40 15.83 16.74 21.88 26.04 33.84 34.86
22.13 119.20 158.30 107.30
9.456 8.178 9.445 10.13 9.037 9.324 8.178 11.060 5.776
5 7.903 5.975 7.407
6.129 23.830 24.610 27.670
4.786 4.711 3.396 5.537 3.044 3.452 4.885 12.090 3.479 5.461 2.709
1.763 15.990 12.430 19.630
7.761 5.836 4.645 7.021 3.921 3.235 3.778 20.450 2.562 9.886 1.716 4.455 1.582 3.552 1.468
4.478 12.850 6.271 25.810
2.707 2.703 2.714 2.709 2.696 2.791 2.713 2.738 2.659 2.682 2.732 2.751 2.731 2.706 2.744
2.723 2.759 2.798
0.432 0.370 0.405 0.433 0.448 0.503 0.587 0.592 0.593 0.616 0.624 0.644 0.685 0.685 0.717
HYDROTHERMAL ALTERATION OF GRANITOID ROCKS AND GNEISSES 385
zone is responsible for K
O loss in the less altered samples
(Fig. 12d). Illitization accounts for most of the gain of K
O. Loss of Na
O (Fig. 12c) and CaO (Fig. 12g) is due
to decomposition of plagioclases. MgO (Fig. 12f) and Fe
(Fig. 12e) were removed during destruction of biotite and
chlorite. Fixation of Ca, Mg and Fe in carbonates was not suf-
ficient to counterpart their release; only a single anomalous
sample (A-37) shows a positive change (gain) for these ele-
ments (Figs. 12eg). The samples were not analyzed for CO
but according to abundant occurrence of carbonates, the rocks
were also enriched in CO
Evaluation of the element migration in migmatites is limit-
ed due to few analyzed samples. It seems that SiO
were removed and K
O added to these rocks (Table 4). Mi-
nor losses were determined also in the case of Fe
and CaO. The same fluids drove hydrothermal alteration of
both granitoids and migmatites and therefore the differences
in alteration patterns are caused only by the variability of the
Changes of chemical and mineralogical composition of
rocks altered by hydrothermal fluids at the Dúbrava Sb-Au
deposit, Nízke Tatry Mts. enabled to distinguish three zones
of alteration: I. chlorite zone (outermost), II. muscovite zone,
III. illite-carbonate zone (innermost).
Every wall rock sample from the deposit represents an al-
tered rock. Increasing degree of alteration results in progres-
sive decomposition of plagioclase, K-feldspar and complete
disappearance of biotite. Primary magmatic minerals and tex-
tures are completely erased in the most internal alteration zone.
The presented data indicate a temperature decrease from
the external chlorite zone (320±40
C, chlorite thermometry)
toward the inner zone rich in illite and carbonates (180
C, crystallinity index). The initial stages of alteration
Table 5. Crystallinity index values of illite from the altered rocks
from the Dúbrava deposit (in º2Q).
CI (air dried)
Fig. 11. Plots of Zr vs. TiO
, Sc, Al
, and K
O for unaltered granitoids (Cambel and Janák, unpubl.data, solid circles) and altered grani-
toids from the Dúbrava deposit (open squares). Zr and Sc in ppm, oxides in wt. %.
Fig. 12. Percentage gains and losses of oxides in altered granitoid rocks from the Dúbrava deposit based on data listed in Table 4 arranged
in order of increasing alteration index. The calculation was performed from 15 samples, the sample A-9 was used for normalization.
386 ORVOOVÁ, MAJZLAN and CHOVAN
bore pervasive character, altering mostly biotite in large vol-
umes of rocks within the ore field. Muscovite and illite-car-
bonate zones are superimposed on the most external chlorite
zone. They are a product of action of cooler thermal fluids
whose circulation was restricted to open tectonic structures
and channelways. Gradual sealing of the walls of the veins
and temperature decrease led to isolation of external chlorite
zone and preservation of its mineral assemblage even during
In the course of alteration, the rocks were enriched in K
, Sb, S and depleted in CaO, Na
O, MgO and
(Figs. 12cg). Local redistribution and/or variation in
the chemical composition of the primary magmatic precursor
caused small changes in Al
content (Figs. 12a,
b). Zr, TiO
and Sc seem to be the least mobile elements, al-
though rutile appears in pyrite-arsenopyrite assemblage of
the quartz veins.
Similar features of alteration accompanying the ore min-
eralization are expected, according to our observations, also
in other Sb-Au deposits (Magurka, Dve Vody) in the Nízke
Acknowledgements: This paper includes results of Master
thesis of M. Orvoová. We are grateful to doc. V. ucha for
the help with interpretation of XRD patterns of clay minerals.
We thank Dr. J. Kritín (CLEOM, Comenius University) and
Dr. M. Köhlerová (GS SR) for electron microprobe analyses
of minerals. The preliminary versions of the paper benefited
greatly from critical remarks of Dr. J. rodoñ, Prof. Z. Pertold,
Prof. I. Kraus and doc. I. Rojkoviè. We are indebted to Dr. I.
Petrík for advice and valuable remarks with the problems on
granitoid rocks. The field work and bulk rock analyses were fi-
nanced by Dr. M. Arvensis and Dr. J. Michálek (ENVIGEO).
The work was financially supported also from VEGA Grant
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