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GEOLOGICA CARPATHICA, 50, 5, BRATISLAVA, OCTOBER 1999

353–364

USE OF ILLITE FOR K/Ar DATING OF HYDROTHERMAL PRECIOUS

AND BASE METAL MINERALIZATION IN CENTRAL SLOVAK

NEOGENE VOLCANIC ROCKS

IVAN KRAUS

1

, IGOR V. CHERNYSHEV

2

, VLADIMÍR ŠUCHA

1

, VLADIMÍR A. KOVALENKER

2

,

VLADIMÍR A. LEBEDEV

2

 and EVA ŠAMAJOVÁ

1

1

Faculty of Science, Comenius University, Mlynská dolina, 842 15 Bratislava, Slovak Republic

2

Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences,

Staromonetny Pereulok 35, 109017 Moscow, Russia

(Manuscript received December 9, 1998; accepted in revised form June 22, 1999)

Abstract:

 In all important stages of hydrothermal precious and base metal mineralization in the Central Slovak

Neogene volcanic rocks the characteristic assemblages of clay minerals can be distinguished, in which illite and
mixed-layer illite/smectite of various polytypes play an important role. Our study has confirmed that the illite polytypes
can provide information on the thermodynamic conditions that prevailed during the formation of precious and base
metal mineralization in the Central Slovak Neogene volcanic area. The results of K/Ar dating of illites from hydro-
thermally altered zones, such as those observed in most hydrothermal precious and base metal mineralizations in the
Central Slovak Neogene volcanic area are reported for the first time. They bring new information on the time interval
of the hydrothermal mineralization. The main stages took place 12.4±0.1–11.03±0.1 Ma in all the important ore
districts within the Central Slovak Neogene volcanics.

Key words:

 stratovolcanoes, advanced argillitic alteration, mineral assemblage, illite polytypes, mixed-layer illite/smectite.

Introduction

The age determinations performed by radiometric/isotopic
geochronological methods are an important part of the metal-
logenetic model of the hydrothermal, precious and base met-
al mineralization in the Banská Štiavnica and Kremnica stra-
tovolcanoes. Onačila et al. (1995) proposed a metallogenetic
model for the Central Zone of the Banská Štiavnica strato-
volcano which visualizes several stages of mineralization
spanning the time of some 6 Ma. The age determination
made on the intrusive rocks from the Central Zone of the
Banská Štiavnica stratovolcano and on sericite

1

 from epith-

ermal, vein precious and base metal mineralization using K/
Ar dating, reported in the paper of Chernyshev et al. (1995),
reduced the time span of the Banská Štiavnica stratovolcano
rocks and the base metal mineralization to approximately 1–
2 Ma. Geochronological datings of analogous epithermal,
precious and base metal mineralizations, made worldwide
during the past 25 years confirmed a similar time range (Sil-
berman et al. 1972; Ashley & Silberman 1976; Silberman
1985; Noble et al. 1991; Setterfield et al. 1992; Conrad et al.
1993; Alderton et al. 1998). One of the reasons why the tim-
ing used in the metallogenetic model of the Central Zone of
the Banská Štiavnica stratovolcano is incompatible with the
world-wide data is the absence of geochronological study of
clay minerals which occur in the altered salband zones, or di-
rectly within the vein fillings. The illite appears to be most
suitable for the K/Ar dating, especially when its origin is
concurrent with the hydrothermal mineralization and when
its development was monomineral.

This is the reason why a complex mineralogical-geochemi-

cal study of altered zones, especially in the epithermal pre-

cious and base metal deposits in the areas underlain by Neo-
gene volcanic rocks, is so important. In the area of outcrop of
Neogene volcanic rocks in Central Slovakia we used this
method to date illite and mixed-layer illite/smectite, which
formed during the most significant stages of hydrothermal
mineralization in the Banská Štiavnica and Kremnica strato-
volcanoes. Our work was inspired by the results of Cherny-
shev et al. (1995) who presented the first K/Ar datings made
on illite from epithermal, precious and base metal veiny min-
eralization of the Banská Štiavnica-Hodruša ore district
(Terézia vein).

In present paper we do not intend to address the problems

related to the geology and mineralizing conditions of the
Banská Štiavnica and Kremnica stratovolcano, because these
were already addressed in detail and reported by several au-
thors (Štohl 1976; Burian et al. 1985; Štohl & Kaličiak 1989;
Knésl & Knéslová 1991; Kovalenker et al. 1991; Onačila &
Rojkovičová 1992; Onačila et al. 1995; Lexa et al. 1997). We
do, however, focus on the synoptic characterization and tim-
ing of different stages of hydrothermal mineralization and of
the altered zones in the Banská Štiavnica and Kremnica stra-
tovolcanoes.

Characteristic features of the hydrothermal

mineralization of the Banská Štiavnica and

Kremnica stratovolcanoes

Our classification of the hydrothermal mineralization of the

Central Zone of the Banská Štiavnica stratovolcano is based
on the concepts of Štohl & Lexa (1990), Štohl et al. (1994) and
Onačila et al. (1995), and we summarize it as follows:

In the paper of Chernyshev et al.  (1995) the term sericite has only a petrological meaning. We use this term for the mineral in separated fraction composed of particles

measuring less then 4 

µ

m across and having on the XRD difractogram the d(001) reflex within the range 1.0 nm, as in illite.

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354                                                                                                KRAUS et al.

The older types of hydrothermal mineralizations, which in-

clude the stockwork-disseminated base metal mineralization
of the Šobov hydrothermal system near Banská Štiavnica
(Štohl & Lexa 1990), the stockwork-disseminated base metal
mineralization in the surroundings of the Rozália vein near
Banská Hodruša (Gavora 1983) and the porphyry-copper
mineralization of skarn type, among which the Zlatno depos-
it is the most important (Rozložník & Zábranský 1971), de-
veloped under compressional, disjunctive, tectonic condi-
tions during the pre-caldera stage. The presumed sources of
energy and fluids are related to quartz-diorite, granodiorite
and quartz-diorite porphyry intrusions of the Central Zone of

the Banská Štiavnica stratovolcano. Hydrothermal wallrock
alteration associated with the above mentioned types of ore
mineralization is predominantly of zonal character. Using
Nakovnik’s (1964) concept, it can be assigned to the forma-
tion of secondary quartzites, whereas in the Sillitoe’s (1973)
concept, it belongs to the advanced argillitic alteration, or to
a phyllic zone.

The ganister quartzites which occur near Šobov and next

to the Rozália vein near Banská Hodruša (Fig. 1) and are the
products of these hydrothermal alteration processes in the
Central Zone of the Banská Štiavnica stratovolcano, became
the subjects of our study.

Fig. 1. 

Structural and metallogenetic scheme of the Banská Štiavnica-Hodruša ore district of the Central Zone of the Štiavnica stratovol-

cano. Settled according to Lexa et al. (1999). Explanations: 1 — basement; 2 — granodiorite, diorite, granodiorite porphyry,  and quartz-
diorite porphyry (Upper Badenian); 3 — propylitized andesite and andesite porphyry complex (Upper Badenian); 4 — rhyolites (Upper
Sarmatian-Lower Pannonian); 5 — ore veins (a) and unmineralized faults (b); 6 — marginal faults of the resurgent horst; 7 — porphyry/
skarn copper deposits and occurrences; 8 — stockwork/disseminated base metal deposits and occurrences; 9 — advanced argillic (high
sulphidation)  alterations; 10 — location of the samples collected for K/Ar dating from the Banská Štiavnica stratovolcano.

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USE  OF  ILLITE  FOR   K/Ar  DATING  OF  HYDROTHERMAL  MINERALIZATION                                     355

The younger type of hydrothermal, precious and base vein

metal mineralization developed under extensional tectonic
conditions, during the post-caldera stage and with intensive
participation of meteoric waters. The rhyolites of the Jastra-
bá Formation, defined by Konečný et al. (1983) are pre-
sumed sources of energy and fluids. Hydrothermal wallrock
alteration associated with the vein mineralization has a linear
character. For a detailed study of the hydrothermal alteration
products found within the Central Zone of the Banská Štia-
vnica stratovolcano, we selected those from the Svetozár and
Rozália vein systems near Banská Hodruša, from the Terézia

vein near Banská Štiavnica (Fig. 1) and from the Central and
Southern parts of the Kremnica stratovolcano (Fig. 2).

Analytical methods

Samples from hydrothermally altered zones of the precious

and base metals vein mineralization of the Banská Štiavnica
and Kremnica stratovolcanoes were studied using optical po-
larization microscope. The fraction below 2 

µ

m was isolated

using the sedimentation method and both, oriented and non-
oriented slides were prepared for the XRD analysis. The lat-
ter were prepared by mixing the clay fraction with the melted
colophony. The oriented preparates were studied in natural
form and after saturation with ethylene glycol (8 hours in
ethylene glycol vapour at 60 °C). The lattice parameters in
the assemblages of clay minerals selected from samples con-
taining illite and/or mixed layer illite/smectite and their poly-
types were measured using the PW 1710 Philips XRD instru-
ments, operating with Ni filtered Cu/K

α

 radiation.

The K-Ar dating of illite samples was performed with use

of a highly-sensitive mass-spectrometer low-blank complex
which includes a M1-1330 mass-spectrometer as well as a
gas extraction system. Static regime of argon isotope analy-
sis was realized. A total blank of all the system units was less
than 8

×

10

-3

 ng of 

40

Ar. The isotope dilution method with the

38

Ar monoisotope was used. The 

40

Ar

rad

 and potassium deter-

minations errors exhibited in the Table are individual for

40

Ar

rad

 and K, whereas K-Ar age values attended by 1

σ

-er-

rors. The age calculations were made using the following
constants: 

λ

β

 

= 4.962

×

10

-10

 years, 

λ

e

 = 0.581

×

10

-1 

years

-1

,

40

K/K = 0.01167 at. %.

Fig. 2. 

Scheme of diagenetic and hydrothermal alteration of the

Kremnica ore district in the Central and Southern parts of the
Kremnica stratovolcano (according to Kraus et al. 1994). Explana-
tions: the Jastrabá Formation (Upper Sarmatian-Lower Pannonian)
1 — hydrothermally altered rhyolite extrusions with prevalence of
smectite; 2 — hydrothermally altered rhyolite intrusions with
prevalence of kaolinite; 3 — rhyolite extrusions, intrusions and
lava flows not affected by hydrothermal alterations; 4 — limno-
quartzites; 5 — diagenetically altered rhyolite volcanoclastics
with prevalence of smectite and clinoptilolite; 6 — hydrothermal-
ly altered rhyolite volcanoclastics with prevalence of mixed-layer
illite/smectite and kaolinite; 7 — volcanoclastics  not affected by
hydrothermal alterations. The Zlatá Studňa Formation (Lower and
Upper Badenian); 8 — hydrothermal wall rock alteration of andes-
ites and andesite porphyries with kaolinite, illite, mixed-layer il-
lite/smectite and adularia; 9 — propylitized andesites and andesite
porphyres with prevalence of smectite; 10 — intrusive body of
amphibolite-pyroxenic andesite porphyry; 11 — effusive complex
of pyroxenic and leucocrate andesite; 12 — The Turček Formation
(Upper Badenian-Lower Sarmatian): lava flows, pyroclastics and
epiclastics of basaltoids and pyroxenic and leucocrate andesite; 13
— The Kremnický Peak Formation (Upper Badenian): effusive
amphibolite-pyroxenic andesite; 14 — The Krahule Formation
(Lower Sarmatian): extrusions of biotitic-amphibolite andesite; 15
— aluvium; 16 — ore veins (a) and weakly mineralized faults (b);
17 — faults; 18 — boreholes; 19 — location of the samples col-
lected for K/Ar dating from the Kremnica stratovolcano.

v

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356                                                                                                KRAUS et al.

Assemblages of clay minerals from the Banská

Štiavnica and Kremnica stratovolcanoes

All important stages of hydrothermal, precious and base

metal mineralization in the Banská Štiavnica and Kremnica
stratovolcanoes have the characteristic assemblages of clay
minerals. Illite and/or mixed layer illite/smectite of various
polytypes are common constituents.

The Sillitoe’s (1973) stage of advanced argillitic alteration

is in the Central Zone of the Banská Štiavnica stratovolcano
genetically and spatially bound to an older, stockwork/dis-
seminated base metal mineralization. For several years it was
a subject of studies in the broader surroundings of the quartz-
ite deposit at Šobov, a source of ganister production, in the
Rozália vein and at other occurrences studied in detail by
Žáková in Štohl et al. (1988). Advanced argillitic alteration
of the Šobov hydrothermal system has the spatial and chro-
nological links to the quartz-diorite intrusive activity. On the
other hand, the advanced argillitic alteration associated with
the stockwork/disseminated base metal mineralization in the
Rozália vein is spatially and temporally linked to the grano-
diorite (Štohl et al. 1988).

Our investigations, as well as the results of other authors

(Polák 1963; Radzo 1969; Oružinský 1989; Žáková & Štohl
1992; Žáková et al. 1995; Onačila et al. 1995; Uhlík & Šucha
1997) have shown that four mineral associations, all important
in terms of the alterations and formation of clay minerals (Table
1), can be distinguished in the Šobov hydrothermal system.

The first is the mineral assemblage dominated by pyrophyl-

lite. Another most common mineral is kaolinite which occurs
mainly in marginal parts of the quartzite bodies. Alunite and
diaspore occur only sporadically.

The second is the mineral assemblage in which the illite of

the polytype 2M

1

 is the most common clay mineral of the

Šobov hydrotermal system. It associates with pyrophyllite,
but the two minerals may also occur separately (Fig. 3).
There are indications that illite preferably concentrates in the
marginal parts of the quartzite bodies (Uhlík & Šucha 1997).
Chlorite sporadically associates with illite.

The third is the mineral assemblage dominated by mixed-

layer illite/smectite, which occurs in the area of Červená
Studňa, at the western end of Šobov. The XRD difractogram
and the crystallochemical formulas indicate the presence of
regular mixed-layer illite/smectite-like rectorite, but its K

2

O

content is low (Table 2, Fig. 4).

The fourth assemblage consists of adularia and illite, iden-

tified by Štohl et al. (1987) in the 12

th

 horizon of the Šobov

hydrothermal system, 500 m below the Šobov quarry. How-
ever, we did not study the illite from this assemblage.

Advanced argillitic alteration in the surroundings of the

Rozália vein has several features in common with the Šobov
hydrothermal system (Table 1). However, a different situation
is found in the surroundings of the Rozália vein where the il-
lite predominates over pyrophyllite. Diaspore and alunite are
totally absent, as is adularia. The presence of a mixed-layer
mineral is very probable, but was not yet identified precisely.

Hydrothermal alteration adjacent to precious and base met-

al veins always has a linear course. Ma o et al. (1996) distin-
guish “mesothermal” and “epithermal” stages here. Because

Fig. 3. 

XRD-pattern of pyrophyllite /P/ and pyrophyllite with ad-

mixture of illite /I/. Mineralization of advanced argillic alteration,
Banská Štiavnica-Šobov.

Table 1:

 The assemblages of clay minerals on advanced argillic

alteration. *The sample with K/Ar dating.

Deposit

Banská Štiavnica-Šobov

Banská Hodruša-Rozalia vein

mineral

assemblage

I.

pyrophyllite±kaolinite, diaspor,

alunite

±pyrophyllite, kaolinite

II.

*

illite 2M

1

±pyrophyllite, chlorite

*

illite 2M

1

>>1M

III.

regular mixed-layer I/S

like rectorite

?

IV.

illite + adularia

Table 2:

 Crystallochemical formulas of regular mixed-layer rec-

torite like minerals. Explantions: 4488 and 4490 — the Červená
Studňa Formation, near the Šobov hydrothermal system; B-2/590
m — bore hole Banská Belá, the North eastern part of the Banská
Štiavnica-Hodruša ore district; DV-4 — bore hole Dolná Ves, the
Southern part of the Kremnica ore district. *Analyzed in Sr form,
** analyzed in Na form.

Sample type of

illite/smectite

Si

Al

(IV)

Al

(VI)

Fe

Mg

Na

K

Sr

4488

rectorite

6.77

1.23

3.67

0.16

0.28

0.37

0.43

0.22

*

4490

rectorite

6.71

1.29

3.72

0.11

0.33

0.30

0.40

0.22

*

B-2/590 K-rectorite

7.07

0.93

3.71

0.08

0.33

0.07

0.85

DV-4

K-rectorite

7.00

1.00

3.62

0.16

0.26   0.18

**

0.85

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USE  OF  ILLITE  FOR   K/Ar  DATING  OF  HYDROTHERMAL  MINERALIZATION                                     357

we think that the term “higher temperature epithermal stage”
is more suitable instead “mesothermal”, we adhere to it in
the following text.

We assign the assemblage of clay minerals with adularia

from the Svetozár vein, a part of the precious and base metal
deposit of Banská Hodruša, to the higher temperature epith-
ermal stage. It consists of several generations of quartz and

carbonates, with gold of high fineness (Ma o et al. 1996).
The wallrock alteration appears in a narrow zone along the
vein. The illite in it occurs as the 2M

1

 and 1M polytypes. In

some sections in the external part, chlorite predominates. In
the higher temperature stage, kaolinite and mixed-layer ilite/
smectite are absent (Table 3).

Compared with the higher temperature epithermal stage,

the mineral assemblage of the epithermal stage is more com-
plicated. The materials from the Rozália and Terézia veins
and from the Central and Southern Zones of the Kremnica
ore district were studied. In the wallrock alteration zone of
the Rozália and Terézia veins, the polytypes of illite 1M and
2M

1

 were found, which is analogous to the findings of Rusi-

nov et al. (1993).

Gold of low fineness and electrum, both hosted by quartz

and sulphides, predominate in the epithermal veins of the
Kremnica ore district (Böhmer 1966). In the Kremnica ore dis-
trict, the altered salbands of the epithermal stage are more in-
tensely disintegrated than those in the Rozália deposit, near
Banská Hodruša and attain a thickness of some 10 m. In the
epithermal, precious and base metal vein mineralization we
distinguished three mineral assemblages, as did Böhmer et al.
(1969), Kraus (1989), Šucha et al. (1992) and Kraus et al.
(1994) before. During the first, the conditions were favourable
for the development of kaolinite with local smectite and chlo-
rite admixtures. During the second, the 1M polytype illite and
adularia formed and as at deposits with the advanced argillitic
alteration, the mineralization was concluded when the condi-
tions became suitable for the formation of regular mixed layer
illite/smectite-like rectorite. The XRD difractogram and crys-
tallochemical formulas indicate a presence of regular mixed
layer illite/smectite, with increased content of K

2

O, similar to

K-rectorite (Table 2, Fig. 4). It is of interest that regular mixed
layer illite/smectite-like K-rectorite was not only found in the
southern part of the Kremnica ore district, near Dolná Ves, but
also in the northeastern part of the Banská Štiavnica-Hodruša
ore district near Banská Belá (Table 2).

Determination of illite polytypes

The illite polytypes are suitable for use in modeling of the

geological and metallogenetic processes (Velde 1965; Eberl et
al. 1987). Our study has confirmed that the illite polytypes can
provide information on the thermodynamic conditions that pre-

Fig. 4. 

XRD-pattern of regular mixed-layer minerals illite/smec-

tite-like rectorite, Banská Štiavnica stratovolcano. Explanations:
4490 — mineralization of advanced argillic alteration, Banská
Štiavnica-Červená Studňa, B-2/590 m — mineralization of epith-
ermal vein precious and base metal, bore hole B-2, Banská Belá.

Table 3:

 The assemblages of clay minerals on higher temperature epithermal and epithermal vein precious and base metal deposits.

*The sample with K/Ar dating.

stage

higher

temperature

epithermal

epithermal

deposit

Banská Hodruša

Svetozár vein

Banská Hodruša

Rozália vein

Banská  Štiavnica

Terézia vein

Kremnica and Dolná Ves Central and Southern part of
Kremnica ore district

mineral

assemblage

I.

*2M

1

>>1M illite +

chlorite, adularia

kaolinite ± smectite, chlorite

II.

*1M>>2M

illite + adularia

*1M 

 

illite + adularia

III.

*regular mixed-layer I/S-like K-rectorite

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358                                                                                                KRAUS et al.

vailed during the formation of precious and base metal mineral-
ization in the Central Slovak Neogene volcanic rocks (Fig. 5).

The presence of 2M

1

 polytype in the stockwork/dissemi-

nated base metal mineralization, accompanied at Šobov by
advanced argillitic alteration, has been confirmed. In the sur-
roundings of Rozália vein, where the advanced argillitic al-
teration is accompanied by the stockwork/disseminated min-
eralization, as well as in the Svetozár vein, in which the
higher temperature epithermal precious and base metal min-
eralization occurs, the 2M

1

 illite polytype contains an admix-

ture of 1M(2M

1

>>1M). In the epithermal precious and base

metal vein mineralization found in the Terézia vein in Ban-
ská Štiavnica, the predominance of 1M illite polytype was
confirmed, but small amounts of 2M

1

 illite polytype and

(1M>>2M

1

) also occur. A specific feature of the epithermal

precious and base metal vein mineralization in the Central
and Southern Zones of the Kremnica ore district is the exclu-
sive presence of 1M illite polytype. A similar pattern of illite
polytypes was also confirmed in the altered zones of the epi-

thermal precious metal Neoid mineralization in Nevada
(Hauff et al. 1991).

At the same time at all occurrences relationships exist be-

tween the Kubler’s crystallinity indexes obtained from illites
and illite polytypes. The highest degree of crystallinity was
found in the illite of the 2M

1

 polytype, which forms exclu-

sively under advanced argillitic alteration conditions in the
stockwork disseminated base metal mineralization of the
Šobov hydrothermal system. The crystallinity of illite gradu-
ally decreases through the higher temperature epithermal to
epithermal precious and base metal vein mineralization of
the Banská Štiavnica and Kremnica statovolcanoes. In the
Kremnica stratovolcano, a more advanced differentiation
took place within the Central and Southern Zones of the
Kremnica ore district. With increasing content of expanded
layers in mixed-layer illite/smectite, the crystallinity of illite
layers decreases from north to south indicating that the tem-
peratures of hydrothermal solutions dropped.

High sulphidation and low sulphidation types of

hydrothermal alterations in the Banská Štiavnica

and Kremnica stratovolcanoes

Since the second half of eighties, the importance of study

of the alteration processes at epithermal, precious and base
metal vein deposits dramatically increased. This is mainly
because the knowledge of hydrothermal alteration processes
in many world deposits, located mostly in Neogene volcanic
rocks, became standard criteria to determine which of the
two contrasting fluid types was involved in the mineraliza-
tion. One of them has the pH value indicative of an acid en-
vironment and the other has values close to a neutral envi-
ronment. To classify them, Bonham (1986) coined the term
“high sulphur” and “low sulphur”. Meanwhile, Heald et al.
(1987) introduced the terms “acid sulphate” and “adularia-
sericite”. Hedenquist (1987) recommended use of the terms
“high sulphidation” and “low sulphidation” and it is these
terms that are now mostly used in the Western Carpathians.

It was shown that it is not right to classify the hydrothermal

deposits as two types on the basis of minerals present in the al-
tered zones alone, but it is also necessary to determine the tem-
perature, pressure and salinity of the hydrothermal solutions, as
well as the changes in the 

34

S isotope ratio in coexisting sul-

phides and sulphates, in the CO

2

/H

2

S ratios etc. Most data from

the region made up of the Central Slovak Neogene volcanic
rocks were obtained very recently (Kovalenker et al. 1991; Rus-
inov et al. 1993; Háber et al. 1998; Štohl et al. 1994; Onačila et
al. 1995) and the age determinations are reliable, thus they can
be fully used in modeling of metallogenetic processes.

All illites and mixed-layer illite/smectite in the altered sal-

bands located in the Banská Štiavnica and Kremnica stratovol-
canoes, which were used for K/Ar dating or age determination
of precious and base metal mineralization, can be assigned to
two contrasting mineralization types, characterized above.

Most high sulphidation types of hydrothermal alteration in

the Central Slovak Neogene volcanic rocks associate with
the advanced argillitic alteration which was brought about by
the stockwork/disseminated base metal mineralization. Pyro-

Fig. 5. 

Plot of illite crystallinity index (Kubler 1968) versus Ir in-

dex (Środoń 1984). Ir index  should represent trace contents of ex-
pandable interlayers in illite structure. Explanations:  q advanced
argillic alteration of the Šobov hydrothermal system, Banská Štia-
vnica-Šobov; 

×××××

 

advanced argillic alteration of the stockwork/dis-

seminated base metal mineralization, Banská Hodruša-Rozalia
vein, outcrop; 

×××××

  higher temperature epithermal vein precious and

base metal mineralization Banská Hodruša-Svetozár vein; s epith-
ermal vein precious and base metal mineralization, Banská Štia-
vnica-Terézia vein; v epithermal vein precious and base metal
mineralization, Kremnica ore district — Central part;    epithermal
vein precious and base metal mineralization, Kremnica ore dis-
trict—Southern part.

v

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USE  OF  ILLITE  FOR   K/Ar  DATING  OF  HYDROTHERMAL  MINERALIZATION                                     359

phyllite was shown to be a typomorphic mineral for the high
sulphidation systems, probably for the whole region of the
Central Slovak Neogene volcanic rocks and, unambiguously,
also for the Central Zone of the Štiavnica stratovolcano.
High amounts of illite belonging exclusively to the 2M

1

polytype and a low share of alunite and diaspore are charac-
teristic features of the high sulphidation in the Šobov hydro-
thermal system. Onačila et al. (1995) explain the sporadic
presence of alunite as a consequence of erosion of the upper
part of the Šobov quartzites.

A characteristic feature of the high sulphidation type of the

hydrothermal alteration in the area of Rozália vein is that
2M

1

>>1M illite prevails over pyrophyllite.

On the basis of the stability diagram of the mineral phases in

the altered rocks and the dependence on the activity of individ-
ual components and sulphur (Titley & Bean 1981; Hayba et al.
1986) in the Šobov hydrothermal system we presume the fol-
lowing time succession for the high sulphidation alteration
process: alunite (?) 

 diaspore 

 pyrophyllite + kaolinite 

illite 2M

1

 

 regular illite/smectite-like rectorite (?).

The stability of pyrophyllite begins at temperatures around

270 

°C and diaspore is usually present in the deeper parts of

the high sulphidation systems. Using our present knowledge
of the distribution of alunite, its position is problematic. To
assign its position in the succession scheme we set out from
the assumption that in the Šobov hydrothermal system, the
content of sulphur was either gradually reduced, or its oxida-
tion state has changed. This is indicated by the younger, low
sulphidation type of mineralization consisting of sericite–
adularia mineral assemblage, found by Štohl et al. (1987)
some 500 m below the level of the Šobov quarry. This im-
plies that illite, uncontaminated by illite polytypes and be-
longing to other, younger mineralization stages (Fig. 5)
formed within the longest interval, during the existence of
the Šobov hydrothermal system. The regular mixed-layer
mineral illite/smectite-like rectorite with a low content of
K

2

O (Table 2) may belong to the high sulphidation type, but

this is not yet unambiguously confirmed. This is due to the
fact that the hydrothermal alteration of the Červená Studňa
Formation, in which this mineral was found, was not defi-
nitely identified as part of the Šobov hydrothermal system
(Lexa et al. 1997).

The statement of Žáková (in Onačila et al. 1995) is of es-

sential importance for the characterization of the high sulphi-
dation hydrothermal alteration in the area of Rozália mine
near Banská Hodruša. She discovered that the presence of an
illite generation belonging to the younger, epithermal, pre-
cious and base metal mineralization at Rozália vein cannot
be excluded. This is a contrary to the Šobov hydrothermal
system. It is superimposed on the generation of illite which
belongs to the high sulphidation type of hydrothermal alter-
ation which formed in connection with the stockwork/dis-
seminated base metal mineralization. This circumstance may
be indicated by the presence of two illite polytypes, the 2M

1

,

present exclusively in the Šobov hydrothermal system and
the 1M, represented mostly in the epithermal vein precious
and base metal mineralization.

In the Central Slovak Neogene volcanic rocks, low sulphi-

dation types of hydrothermal alterations form in association

with the epithermal vein precious and base metal mineraliza-
tion. Of the clay minerals, the illite and regular mixed-layer
illite/smectite-like K-rectorite are shown to be typomorphic
minerals of the low sulphidation systems, probably for the
whole region of the Central Slovak Neogene volcanic rocks
outcrop, which is definitely also valid for the epithermal vein
precious and base metal mineralization in the Banská Štia-
vnica-Hodruša and Kremnica ore districts. With decreasing
temperature, the share of 2M

1

 polytype in the low sulphida-

tion type of the Banská Štiavnica-Hodruša ore district also
decreases at the expense of 1M polytype (Fig. 5). In the low
sulphidation type of the Kremnica ore district, the 1M poly-
type is exclusively present in illite, and the regular mixed-
layer illite/smectite-like K-rectorite.

In the low sulphidation type of the higher temperature epi-

thermal vein precious and base metal mineralization, the
conditions in the altered salband zone are relatively simple.
Of the clay minerals, the 2M

1

>>1M illite polytype forms in

the inner part of the zone, while chlorite prevails in the outer
part of the zone.

The succession of clay mineral formation in the low sulphi-

dation type of epithermal vein precious and base metal miner-
alization in the Kremnica ore district was studied by Kraus
(1989) and Kraus et al. (1994). These results, as well as the
temperature determinations, pH values and fluid salinities
from the epithermal, vein precious and base metal mineraliza-
tion in the Banská Štiavnica-Hodruša and Kremnica ore dis-
tricts (reported by Onačila et al. (1995), Háber et al. (1998)
and Bebej & Dubaj (1993)) confirm the concept that clay min-
erals of the low sulphidation type developed in two stages.

During the first stage, the conditions were suitable for

transformation of kaolinite and with the increasing pH value
of fluids, smectite and chlorite developed. At the beginning
of the second stage, potassium metasomatism caused the for-
mation of 1M illite (Kremnica ore district) or illite
1M>>2M

1

 (Banská Štiavnica-Hodruša ore district). At the

end of this stage the conditions were favourable for the for-
mation of regular mixed-layer illite/smectite-like K-rectorite.
This is shown by the conditions that prevailed in the north-
eastern part of the Banská Štiavnica-Hodruša ore district
near Banská Belá, or in the southern part of the Kremnica ore
district near Dolná Ves (Table 2, Fig. 4).

Šucha et al. (1992) and Fuchs (1994) confirmed that the

degree of K-rectorite illitization during the K-metasomatism
decreases from north to south, that is towards the sinking
temperature of hydrothermal solutions. This is in good agree-
ment with the results of study of gaseous-fluid inclusions
(Bebej & Dubaj 1993).

There is no doubt that adularia is a typomorphic, non-clay

mineral of the low sulphidation type of hydrothermal alter-
ations throughout the Central Slovak Neogene volcanic
rocks. According to information from various authors (Böh-
mer 1966; Hojstričová in Štohl et al. 1987; Kraus 1989), adu-
laria forms due to metasomatic replacement of plagioclases
and of the matrix of andesites, rhyolites and their volcano-
clastic derivatives. Adularia is a part of quartz veins in these
rocks, or forms separate crystals in rhyolite tuffs. The con-
tents of K

2

O in hydrothermally altered rocks of this type var-

ies within the range between 7 and 10 %.

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360                                                                                                KRAUS et al.

Age of hydrothermal alterations

To determine the age of hydrothermal alterations that took

place during separate ore-forming processes in the Banská
Štiavnica and Kremnica stratovolcanoes using K/Ar dating,
we strictly selected the monomineral and precisely defined
illite polytypes. Detailed investigation of altered salband
zones with determination of the mineral assemblage with
which illite is associated in different deposits confirmed its
synchronous position within the individual mineralizing
stages. The characterization of individual samples and the re-
sults of K/Ar datings are shown in Tables 4 and 5.

The oldest hydrothermal alteration process in the area under

study is the advanced argillitic alteration found in the deposit
of ganister quartzite at Šobov, which gave the age 12.4 ± 0.1
Ma. Štohl & Lexa (1990) associate the stockwork/disseminat-
ed base metal mineralization of the Šobov hydrothermal sys-
tem with quartz diorite. Onačila et al. (1995) do not report any
datings of quartz diorites from the Šobov hydrothermal sys-
tem, because they are intensely altered.

Our age determination of advanced argillitic alteration as-

sociated with the stockwork/disseminated base metal miner-
alization in the surroundings of Rozália vein gave the age
11.5 ± 0.3 Ma. On the basis of geological criteria, Štohl &
Lexa (1990) genetically and spatially associate this mineral-
ization with the granodiorite body which intruded the Central
Zone of the Banská Štiavnica stratovolcano after the intru-
sion of quartz diorite. On the basis of K/Ar dating of amphib-
ole from the granodiorite located near the stockwork/dissem-
inated base metal mineralization, Štohl et al. (1994) report its
age as 15.9 ± 0.7 Ma. Chernyshev et al. (1995) published the
age of 12.6 ± 0.8 and 12.5 ± 0.6 Ma for granodiorite porphy-
ry and for quartz porphyry of the second and third volcanic
stage of the Central Zone of the Banská Štiavnica stratovol-
cano as defined by Onačila et al. (1995). On the basis of
structural-superpositional relations, biostratigraphical data
and the results of K/Ar dating of pyroxenic and amphibole-
pyroxene andesites of the first volcano-tectonic stage of the
Central Zone of the Banská Štiavnica stratovolcano (Kantor
& Durkovičová 1985; Kantor et al. 1988), the pre-caldera

stage of the Central Zone of the Banská Štiavnica stratovol-
cano and of the mineralization associated with it, is placed
within the time interval 16.4–14.8 Ma (Onačila et al. 1995).

Considering the K/Ar dating of 2M

1

>>1M illite polytype

which gave the age of 11.9 ± 0.3 Ma, the setting of the higher
temperature epithermal vein precious and base metal miner-
alization distinguished by Ma o et al. (1996) in the Svetozár
vein system in the 14

th

 horizon of the Rozália mine seems to

be justified.

Most K/Ar datings made so far on the 1M>>2M

1

 polytype

of illites were obtained from epithermal vein precious and
base metal mineralization from the Terézia vein. The isoch-
rone from four samples constructed by Chernyshev et al.
(1995) gives the age 12.1 ± 0.2 Ma. The sample of a monom-
ineral illite, taken from the Terézia vein to support the results
of this paper gave an age of 11.4 ± 0.2 Ma.

In the metallogenetic model of Onačila et al. (1995), the

epithermal vein precious and base metal mineralization of
the Central Zone of the Banská Štiavnica stratovolcano is as-
signed to the post-caldera stage on the basis of dating of rhy-
olite of the Jastrabá Formation (12.4–10.7 Ma) and on struc-
tural-superpositional and biostratigraphical grounds. An age
of 13.5–12.0 Ma is assigned to the initial stage of epithermal,
mostly base metal mineralization. The subsequent stage of
epithermal, mostly precious metal mineralization, was as-
signed an age of 12.0–10.5 Ma.

We have paid much attention to the dating of 1M polytype

illite and to regular mixed-layer illite/smectite such as K-rec-
torite from the Central and Southern parts of the Kremnica ore
district. The illite developed during the main phase of epither-
mal vein precious and base metal mineralization. K/Ar dating
of two samples gave practically identical ages of 11.1 ± 0.1
and 11.03 ± 0.1 Ma. The closing stage of the epithermal vein
formation was already free of significant precious metal min-
eralization. The conditions became suitable for the develop-
ment of regular mixed-layer illite/smectite-like K-rectorite.
K/Ar dating of two samples taken from the southern part of the
Kremnica ore district (Fig. 2) gave the youngest ages corre-
sponding to 10.4 ± 0.1 and 10.1 ± 0.1 Ma. Both represent the
mixed-layer illite/smectite with a high amount of expanded

Table 4: 

Location and brief description of the samples collected for K/Ar dating from the Banská Štiavnica (BS) and Kremnica (KRA)

stratovolcanoes.

No

Sample

Location

Stratovolcano

Mineralization

Polytype of illite

1

ŠI

Banská Štiavnica-Šobov,
surface outcrop

BS

advanced argillic alteration
of Šobov hydrothermal system

2M

1

2

P-22/94

Banská Hodruša-Rozalia vein,
surface outcrop

BS

advanced argillic alteration
of stockwork/disseminated
base metal

2M

1  

» 1M

3

4673

Banská Hodruša-Rozália mine,
14-th horizon, Svetozár vein

BS

higher temperature epithermal
vein precious and base metal

2M

1  

» 1M

4

4830

Banská Štiavnica-Weiden,
Terézia vein

BS

epithermal vein precious
and base metal

1M  » 2M

1

5

DV-8

Dolná ves, southern part of
Kremnica ore district bore hole

KRA

epithermal vein precious
and base metal

1M

6

31

Kremnica, central part of
2-nd vein system, Václav vein

KRA

epithermal vein precious
and base metal

1M

7

DV-7

Dolná Ves, southern part of
Kremnica vein system, bore hole

KRA

epithermal vein precious
and base metal

1M

8

2931

Dolná Ves, southern part of
Kremnica vein system, bore hole

KRA

epithermal vein precious
and base metal

1M

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USE  OF  ILLITE  FOR   K/Ar  DATING  OF  HYDROTHERMAL  MINERALIZATION                                     361

layers and come from the most external part of the Kremnica
ore district.

The age data obtained from illite and mixed-layer illite/

smectite from the altered salband zones of the Kremnica ore
district are in good agreement with the data obtained from
rhyolites and perlite of the Jastrabá Formation of Chernyshev
et al. (1995), which vary within the range between 11.6 ± 0.3
and 11.4 ± 0.4 Ma.

Discussion

Comparison of hydrothermal mineralizations, but mainly of

high sulphidation and low sulphidation alteration systems as-
sociated with them indicates some asymmetry between the
Banská Štiavnica and Kremnica stratovolcanoes. In the Ban-
ská Štiavnica stratovolcano, especially in its Central Zone, the
older, stockwork/disseminated base metal mineralizations and
the younger, hydrothermal vein and base metal mineralizations
can be reliably distinguished (Štohl & Lexa 1990; Štohl et al.
1994; Onačila et al. 1995). Besides other features, the older
base metal mineralizations are characterized by alterations at
regional scale, in which the associated clay minerals are reli-
able indicators of the high-sulphidation type of deposits. Al-
though, there are some indications justifying the assignment to
an older base metal mineralization in the Kremnica stratovol-
cano, we still do not have reasonable proofs to specify their
character. The first indication was found in the borehole KR-3,
in the northern part of the Kremnica ore district (Fig. 2). Böh-
mer & Šímová (1976) observed a diorite body at a depth of
some 700 m below the surface, with an indistinct stockwork/
disseminated base metal mineralization at the contact zone
where the andesites also occur, accompanied by an association
of sillimanite, andalusite, cordierite, topaz and garnet which
suggests that secondary quartzites occur there. This finding led
several authors studying the metallogeny of the Kremnica stra-
tovolcano (Böhmer 1981; Burian et al. 1985; Knésl & Knés-
lová 1991), to presume that an older metallogenetic stage ex-
ists in the Kremnica ore district. On the basis of this data Štohl
et al. (1994), examining the northern part of the Kremnica ore
district, distinguished a stockwork/disseminated base metal
mineralization of a high-sulphidation type, equivalent to the
mineralization in the central zone of the Banská Štiavnica stra-
tovolcano.

Mineralogical study of samples taken from the boreholes

KV and KVŠ drilled in the northern part of the Kremnica ore

No Sample

K (%)

40

Ar

rad.

1

(ng/g)

40

Ar

rad.

1

(%)

Age ± 2

δ

(Ma)

1

ŠI

6.96 ± 0.05

5.99 ± 0.06

81.4

12.4   ± 0.1

2

P-22/94

5.64 ± 0.05

4.52 ± 0.13

16.9

11.5   ± 0.3

3

4673

7.18 ± 0.04

5.95 ± 0.15

19.1

11.9   ± 0.3

4

4830

7.77 ± 0.08

6.16 ± 0.06

77.1

11.4   ± 0.2

5

DV-8

7.29 ± 0.04

5.65 ± 0.05

82.6

11.1   ± 0.3

6

31

6.90 ± 0.04

5.30 ± 0.05

79.1

11.03 ± 0.1

7

DV-7

4.05 ± 0.04

2.93 ± 0.04

50.0

10.4   ± 0.2

8

2931

6.30 ± 0.10

4.43 ± 0.05

65.0

10.1   ± 0.2

1 — radiogen 

40

Ar

Table 5: 

K/Ar isotope data of the illite from the Banská Štiavnica

and Kremnica stratovolcanoes.

district to intersect the mineralization at the contact with the
diorite body, did not confirm the presence of pyrophyllite
and alunite in any of them. In the altered zones, the associa-
tion of kaolinite, illite and mixed-layer illite/smectite, which
corresponds to associations encountered in the epithermal,
precious and base metal vein mineralizations in the southern
part of Kremnica ore district, is always present.

Polák (1957) reported an occurrence of alunite accompa-

nied by opal and pyrite in an altered pyroxenic andesite host
in the old tunnels driven in the past to follow the precious
metallic veins in the mentioned, northern part of the Kremni-
ca ore district near Horný Turček village. At that time we
confirmed this finding using the XRD analysis. Alunite has a
kaolinite admixture in opalline matrix. The isotopic research
can give clues as to the origin of the high-sulphidation alter-
ations (Rye et al. 1992). To obtain this information it is nec-
essary to determine 

δ

DOH, 

δ

18

O/SO

4

,

 

δ

18

O/OH and 

δ

34

S/

SO

4

/ in alunite. Up to now only the 

δ

34

S/SO

4

/ + 10.04 ‰

value was determined in the alunite from the surroundings of
Horný Turček (Repčok et al. in Žáková et al. 1995), which
can neither confirm, nor discard its supergene origin.

The problems discussed above, related to the existence of

an older metallogenetic stage in the Kremnica ore district in-
dicate that exact data on mineral associations in the hydro-
thermally altered systems are needed, but are not available
for the northern part of Kremnica stratovolcano, the only ex-
ception being those reported in the paper of Bebej & Dubaj
(1993). On the other hand, a good example is available from
the epithermal precious metal veins of the “Kremnica type”
which occur in the surroundings of Banská Belá, at the NE
margin of the Banská Štiavnica-Hodruša ore district, show-
ing how helpful an exact identification of clay minerals from
the altered perivenous zones can be (Fig. 1). Lexa et al.
(1997) studied the structures and concluded that the Banská
Belá veins cannot represent the NE continuation of the Ban-
ská Štiavnica veins. Thus, they are usually assigned to an in-
dependent, “Kremnica type” of mineralization which was the
main source of precious metals in the past. This setting is
also supported by the presence in the borehole B-2/520 m, of
regular mixed-layer illite/smectite, similar to K-rectorite
with parameters almost identical with those found in this
mineral in the southern part of the Kremnica ore district, near
Dolná Ves (Table 2, Fig. 4). It would be very useful to date
this mineral from the Banská Belá vein system using the
K/Ar method, and thus to date this hydrothermal mineraliza-
tion. This type of regular mixed-layer illite/smectite-like K-
rectorite from Banská Štiavnica, from predominantly base
metal vein mineralization, was not yet determined.

The results of K/Ar dating of the illites from the hydrother-

mally altered zones, such as those affecting most hydrothermal
precious and base metal mineralizations in the Banská Štiavnica
and Kremnica stratovolcanoes, are reported for the first time.
They bring a new aspect into the time interval of the hydrother-
mal mineralization. The main stages took place within the range
12.4 ± 0.1–11.03 ± 0.1 Ma in all the important ore districts lo-
cated within the Central Slovak Neogene volcanics.

At present, the valid model of the metallogenetic develop-

ment of the Banská Štiavnica stratovolcano is based on the
combination of structural-superpositional relationships, bios-

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362                                                                                                KRAUS et al.

tratigraphic and geochronological data. It places the main
stages of hydrothermal precious and base metal mineraliza-
tion within the approximate time interval between 16.0 and
10.5 Ma (Štohl & Lexa 1990; Onačila et al. 1995). The re-
sults of K/Ar dating of illites from hydrothermal altered
zones clearly confirmed the existence of the succession of in-
dividual metallogenetic stages in the valid metallogenetic
model of the Central Zone of the Banská Štiavnica stratovol-
cano (Tables 4, 5). At the same time, both schemes could
bring similar dating of the metallogenetic stage associated
with the epithermal hydrothermal vein precious and base
metal mineralization, which shows that fluids were energeti-
cally and substantially linked to the rhyolite volcanism of the
Jastrabá Formation defined by Konečný et al. (1983). This is
because previous K/Ar determinations gave the age range of
the Jastrabá Formation between 12.4 and 10.7 Ma (Bagdasar-
ian et al. 1968; Konečný et al. 1969; Burian et al. 1985),
which are in good agreement with the ages of 11.6 ± 0.3–
11.4 ± 0.3 Ma obtained for the rhyolites and perlites of the
Jastrabá Formation by Chernyshev et al. (1995). Besides, our
K/Ar data obtained from illites and mixed-layer illites/smec-
tites of the Kremnica ore district show that the main stage of
precious metal mineralization probably took place during a
narrow time period, from 11.1 ± 0.1 to 11.03 ± 0.1 Ma. More
K/Ar datings must be available to determine the age more
precisely. The hydrothermal process, especially the one that
took place in the area of Bartošova Lehôtka, in the southern
part of the Kremnica ore district (Fig. 2), faded out without
detectable precious metal mineralization between 11.0 ± 0.2
and 10.1 ± 0.2 Ma ago. This means that the whole process of
epithermal vein precious and base metal mineralization in
the Banská Štiavnica and Kremnica stratovolcanoes took
place approximately during the time span 12.0 ± 0.2–11.0 ±
0.1 Ma. This is why we do not consider that the assignment
of epithermal, vein precious and base metal mineralization to
two stages, 1) Ag-Pb-Zn veins and base metal metasomatic
mineralization ± Ag, Au with the age 13.5–12.0 Ma, and 2)
Au-Ag veins with the age 12.5–10.5 as proposed by Onačila
et al. (1995) is reasonably supported. This also applies to
structural-superpositional relationships.

The main point why the metallogenetic model of Onačila et

al. (1995) disagrees with our results is the dating of the older
stockwork/disseminated base metal mineralizations associated
with the advanced argillitic alteration of the pre-caldera stage,
defined by Štohl & Lexa (1990). This model is supported by
fairly small number of K/Ar dates, mainly from quartz diorites
and granodiorites of the Central Zone of the Banská Štiavnica
stratovolcano, which they tried to outweigh with arguments
based on structural-superpositionl relationships. Other prob-
lems are of methodological types, which were already ad-
dressed by Chernyshev et al. (1995). As was shown, the selec-
tion of suitable minerals for the K/Ar dating of rocks is
important. Minerals with relatively low K

2

O contents, be it

amphiboles, or plagioclases, give substantially older ages than
biotites. This difference may reach 3 Ma for the biotite-am-
phibole andesites and may serve as a key argument in solving
the disputed problem. It could also affect the age of the grano-
diorite which is spatially close to the stockwork/disseminated
base metal mineralizations in the surroundings of Rozália

Mine near Banská Štiavnica, and its age of 15.9 ± 0.7 Ma was
determined from amphibole (Štohl et al. 1994).

In our dispute, Lexa proposed that the ages obtained from

the illites of the older stockwork/disseminated base metal
mineralizations in the surroundings of Rozália vein near
Banská Štiavnica were either partly, or completely rejuvenat-
ed as a result of long-term overheating during the formation
of the younger epithermal precious and base metal mineral-
ization (Central zone of the Banská Štiavnica and Kremnica
stratovolcano).

On the other hand, our K/Ar dating of illites, based on an

analysis of mineral associations and on assessment of poly-
types confirms their synchronous relationship to individual
mineralization stages. It contains a younger, superimposed il-
lite generation which developed during a younger epither-
mal, vein precious and base metal mineralization may be
present at the Rozália vein. This is indicated by the age of
11.5 ± 0.3 Ma, practically identical with the age of 11.4 ± 0.2
Ma for an illite collected from the epithermal vein precious
and base metal mineralization of the Terézia vein.

Conclusions

1) In all important stages of hydrothermal precious and

base metal mineralizations of the Banská Štiavnica and
Kremnica stratovolcanoes, associations of clay minerals can
be distinguished, in which illite and mixed-layer illite/smec-
tite play an important role.

2) All the illites and mixed-layer illite/smectites which we

used for K/Ar age determination of hydrothermal precious
and base metal mineralizations in the Banská Štiavnica and
Kremnica stratovolcanoes, belong to the high-sulphidation
and low-sulphidation types of Hedenquist (1987).

3) The high-sulphidation types of hydrothermal alterations

in the Central Slovak Neogene volcanics developed in associa-
tion with the advanced argillitic alteration, which was brought
about by stockwork/disseminated base metal mineralization.
Pyrophyllite is the typomorphic mineral for the high-sulphida-
tion type of deposits. The low-sulphidation types of hydrother-
mal alterations in the Central Slovak Neogene volcanics de-
veloped in association with the epithermal, vein precious and
base metal mineralization. Apart from adularia, the illite and
the regular mixed-layer illite/smectite such as K-rectorite are the
typomorphic minerals for the low-sulphidation types of deposit.

4) K/Ar dating of illite and of mixed-layer illite/smectite

confirmed that the entire process of hydrothermal precious
and base metal mineralization in the Banská Štiavnica and
Kremnica stratovolcanoes took place approximately within
the period 12.5 ± 0.1–11.0 ± 0.1 Ma.

Acknowledgements: 

This research was carried out as part of

scientific technical cooperation between the Institute of Ge-
ology of Ore Deposits, Petrography, Mineralogy and
Geochemistry of the Russian Academy of Sciences, the Fac-
ulty of Sciences Comenius University and the Geological In-
stitute of the Slovak Academy of Siences, with the financial
support of project Grant No. 1/4090/97 and project Grant No.
98-05-64052 of Russian Basic Research Foundation.

background image

USE  OF  ILLITE  FOR   K/Ar  DATING  OF  HYDROTHERMAL  MINERALIZATION                                     363

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