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Introduction
The Štiavnica Stratovolcano in Central Slovakia is the largest
volcano among Neogene to Quaternary volcanoes at the in-
ner side of the Carpathian arc. Despite a long lasting denuda-
tion, rocks of the volcano still cover the area of 2200 km
2
. It
shows a complex structure involving differentiated rocks, an
extensive multiple stage subvolcanic intrusive complex, a
caldera 18 22 km and a late stage resurgent horst accompa-
nied by rhyolite volcanic activity. The central zone of the
volcano hosts rich intrusion-related and epithermal base/pre-
cious metal mineralizations that have been the basis for a
long lasting mining tradition and for the rise of the famous
medieval mining city of Banská Štiavnica.
Evolution of the stratovolcano took place in five stages
during the Early Badenian to Early Pannonian time. While
the succession of volcanic formations, subvolcanic intrusive
rocks and related metallogenetic processes is quite well es-
tablished (Konečný et al. 1983, 1998; Lexa et al. 1999a;
Koděra & Lexa 2003), the exact timing and duration of vol-
canic, intrusive and hydrothermal activity remains uncertain.
Available biostratigraphic data, including extensive palynol-
ogy records (Planderová in Konečný et al. 1983; Planderová
K-Ar and Rb-Sr geochronology and evolution of the
Štiavnica Stratovolcano (Central Slovakia)
IGOR V. CHERNYSHEV
1
, VLASTIMIL KONEČNÝ
2
, JAROSLAV LEXA
3
, VLADIMIR A.
KOVALENKER
1
, STANISLAV JELEŇ
4,5
, VLADIMIR A. LEBEDEV
1
and YURIJ V. GOLTSMAN
1
1
Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Staromonetny per. 35,
119 017 Moscow, Russian Federation; kva@igem.ru
2
State Geological Institute of Dionýz Štúr, Mlynská dolina 1, 817 04 Bratislava, Slovak Republic; vlasto.konecny@gmail.com
3
Geological Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 840 05 Bratislava, Slovak Republic; jaroslav.lexa@savbb.sk
4
Geological Institute, Slovak Academy of Sciences; Branch: Ďumbierska 1, 974 01 Banská, Bystrica, Slovak Republic; jelen@savbb.sk
5
Faculty of Natural Sciences, Matej Bel University, Tajovského 40, 974 01 Banská Bystrica, Slovak Republic
(Manuscript received June 11, 2012; accepted in revised form March 14, 2013)
Abstract: The Štiavnica Stratovolcano in Central Slovakia is the largest volcano in the Neogene to Quaternary Carpathian
volcanic arc. A large caldera, an extensive subvolcanic intrusive complex and a resurgent horst with late stage rhyolite
volcanites are the most characteristic features. The results of new K-Ar and Rb-Sr isotope dating using more sophisti-
cated methodical approaches have changed our view on the timing of volcanic and intrusive activity. K-Ar dating of
groundmass fractions combined with Rb-Sr isochron dating in the cases of possible rejuvenation has provided highly
reliable results. The lifespan of the stratovolcano is apparently shorter than assumed earlier. Evolution of the stratovol-
cano took place in five stages during the Early Badenian to beginning of Early Pannonian time: (1) construction of the
extensive andesite stratovolcano during the interval 15.0—13.5 Ma; (2) denudation of the volcano concluded with the
initial subsidence of a caldera and the contemporaneous emplacement of a subvolcanic intrusive complex of diorite,
granodiorite, granodiorite porphyries and quartz-diorite porphyries during the interval 13.5—12.9 Ma; (3) subsidence of
the caldera and its filling by differentiated andesites during the interval 13.1—12.7 Ma – volcanic activity overlapping
with the emplacement of the youngest intrusions; (4) renewed explosive and effusive activity of less differentiated
andesites during the interval 12.7—12.2 Ma; (5) uplift of the resurgent horst in the central part of the caldera accompa-
nied by rhyolite volcanic/intrusive activity during the interval 12.2—11.4 Ma. Extensive epithermal mineralization was
contemporaneous with the uplift of the resurgent horst and rhyolite volcanic activity and continued till 10.7 Ma.
Key words: Central Slovakia, evolution, resurgent horst, andesite stratovolcano, caldera, K-Ar and Rb-Sr isotope
dating, subvolcanic intrusions, rhyolite.
1990) and isotope dating results are often contradictory due
to remaining problems in the chronostratigraphic assignment
of lithostratigraphic units, in the correlation of Paratethys
stratigraphic stages with isotope ages, in the complexity of
isotope data interpretation in areas of repeated magmatic ac-
tivity and hydrothermal alterations, and also due to a rather
low quality of some of the past isotope datings.
Uncertainty in the timing and duration of volcanic, intrusive
and hydrothermal activities has been a reason for additional
effort based on more advanced and sophisticated methods of
isotope dating and their interpretation. As the outcome of the
effort we present an updated evolutionary scheme of the Štiav-
nica Stratovolcano based on new results of K-Ar and Rb-Sr
isotope dating, critical evaluation of available biostratigraphic
data and published results of previous isotope dating.
Correlation of biostratigraphic and isotope chronology data
is based on the chronostratigraphic assignment of relevant
lithostratigraphic units by Kováč et al. (2005) and the newest
version of the isotope time scale for the central and eastern
Paratethys by Harzhauser & Piller (2007). The relevant time
intervals are as follows: Early Badenian 16.3—13.65 Ma,
Late Badenian 13.65—12.7 Ma (two-fold division of the
Badenian is accepted as definition of the Middle Badenian is
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CHERNYSHEV, KONEČNÝ, LEXA, KOVALENKER, JELEŇ, LEBEDEV and GOLTSMAN
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problematic; Kováč et al. 2005), Sarmatian 12.7—11.6 Ma
(Early and Late Sarmatian are well defined only in the
Eastern Paratethys with boundary at 12.0 Ma), Pannonian
11.6—7.2 Ma (with boundaries Early/Middle and Middle/
Late Pannonian at 10.5 Ma and 9.0 Ma, respectively;
Kováč et al. 2005), Pontian 7.2—5.3 Ma.
Structure of the stratovolcano and stages of
volcanic and intrusive activity
The Štiavnica Stratovolcano occupies the SW part of
the Central Slovakia Neogene Volcanic Field (Fig. 1). It
is the largest as well as the most complex volcano of the
field. Its volcanic products extend over an area exceeding
2000 km
2
. At the outskirts its rocks overlap mutually with
rocks of neighboring stratovolcanoes – Javorie Strato-
volcano in the east, stratovolcanoes of Kremnické vrchy
mountain range in the north and Vtáčnik Stratovolcano in
the northwest. Most of the volcano evolved in a terrestrial
environment and volcanic facies grade in the distal zone
into volcano-sedimentary complexes that were laid down
in the ephemeral stream, fluvial, and/or limnic environ-
ments (Fig. 2). However, in the south volcanic products
reached the coastal zone of an epi-continental sea, so vol-
canic facies in the distal zone grade into volcano-sedimen-
tary complexes laid down in the littoral and sublittoral
marine environments.
The structure and evolutionary stages of the Štiavnica
Stratovolcano have already been described in greater de-
tail elsewhere (Konečný et al. 1995, 1998). Here we
present a summary as a basis for the discussion on the
timing of volcanic activity. The main structural units of
the stratovolcano correspond to five essential stages distin-
guished in its evolution (Konečný 1970, 1971; Konečný et
al. 1995, 1998; Konečný & Lexa 2001): (1) the lower struc-
tural unit representing products of the first, pre-caldera
stage andesite volcanic activity; (2) the subvolcanic/intra-
volcanic intrusive complexes that were emplaced during a
break in volcanic activity (the second stage); (3) the mid-
dle structural unit representing products of the third,
caldera stage volcanic activity of differentiated rocks, fill-
ing the caldera and paleovalleys on the slopes of the stra-
tovolcano; (4) the upper structural unit representing
products of the fourth, post-caldera stage andesite volca-
nic activity; (5) the Jastrabá Formation representing
products of the fifth, late-stage rhyolite volcanic activity
associated with the uplift of the resurgent horst. Rocks of
the lower structural unit rest variably directly on pre-Neo-
gene basement, pre-volcanic sedimentary rocks and/or
early volcanic products of garnet-bearing andesites. Suc-
cession of units/stages is based on superposition and ma-
jor unconformities established by geological mapping and
sporadic biostratigraphic data including evaluation of pa-
lynomorphs. The results of previous isotopic dating are
reviewed in the discussion.
The terms complex and formation are used in the text to
designate both formal lithostratigraphic units, in which
case they are written in italics with capitalized first letters,
Fig. 1. Position of the Štiavnica Stratovolcano in the structural frame-
work of the Carpathian arc and Pannonian Basin (A) and in the structural
scheme of the Central Slovakia Neogene Volcanic Field (B). Modified
after Konečný et al. (1995) and Pécskay et al. (2006).
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and informal units (complexes) describing groups of rocks at
variable hierarchal levels.
Volcanic formations preceding the Štiavnica Stratovolcano
Evolution of the stratovolcano itself was preceded by volca-
nic activity of garnet-bearing hypersthene-amphibole andes-
ites at dispersed volcanic centers. Groups of extrusive domes
are associated with accumulations of breccias in their sur-
roundings and reworked material in the distal zone. Volcanic
activity occurred in the time of the initial stage of back-arc ex-
tension in the area of the Central Slovakia Neogene Volcanic
Field that gave rise to horsts and grabens and caused a marine
transgression. A complex of garnet-bearing andesite extrusive
domes and volcaniclastic rocks cropping out between the Ja-
vorie and Štiavnica Stratovolcanoes has been defined as the
Neresnica Formation (Konečný et al. 1983).
Lower structural unit – the first stage
The first stage in the evolution of the stratovolcano corre-
sponds to rocks of the lower structural unit. This unit comprises
pyroxene and hornblende-pyroxene andesite stratovolcanic
complexes/formations of the Badenian volcanic activity that
took place before the caldera subsidence. Paleovolcanic recon-
struction reveals remnants of a large stratovolcano, over
40 km in diameter, surrounded by accumulations of epiclastic
volcanic rocks. Rocks of the lower structural unit are often
covered by younger volcanic products of the caldera and
post-caldera stages (Fig. 2).
In the central zone of the stratovolcano the lower structural
unit is exposed in the eastern half of the resurgent horst
(Figs. 2, 3). Here, the former stratovolcano has been deeply
eroded and the lower structural unit consists of pyroxene,
amphibole-pyroxene and biotite-amphibole-pyroxene andesite
porphyry sills and laccoliths that crop out in the lower part of
the andesite stratovolcanic complex.
In the proximal zone (outside of the caldera), the pre-
caldera stage stratovolcanic complexes of the lower structural
unit are not uniform. Mutual age relationships among rocks
exposed in different sectors of the stratovolcano are not
known. In the northeast, the lower part of the exposed strato-
volcanic complex consists of biotite-amphibole-pyroxene
andesites, while the upper part consists mostly of pyroxene
andesites. The complex also hosts a large biotite-bearing
hornblende-pyroxene andesite porphyry laccolith.
In the western sector pyroxene and amphibole-pyroxene
andesite lava flows dominate over sporadic epiclastic volcanic
breccias. At the lowermost part of the volcanic complex there
are glassy and leucocratic pyroxene andesites accompanied by
hyaloclastite breccias. In the borehole PKŠ-1 Gondovo rocks
of the first stage rest on marine sedimentary rocks of the late
Early Badenian age (Brestenská in Karolus et al. 1975). Closer
to the central zone, the complex of lava flows has been in-
vaded by andesite porphyry sills and laccoliths, as well as py-
roxene-amphibole andesite extrusive domes.
Several volcanic formations have been distinguished in the
lower structural unit in the south-eastern sector of the strato-
volcano (Figs. 4, 5). The oldest effusive complex of pyroxene
andesites is locally covered by hypersthene-amphibole andes-
ite extrusive domes and related pyroclastic flows and epiclas-
tic volcanic breccias. Both are covered by a slightly younger
extensive stratovolcanic complex of amphibole-pyroxene
andesite lava flows, extrusive domes, pyroclastic flows and
epiclastic volcanic breccias of the Sebechleby Formation.
The formation extends southward into the marine environ-
ment where it comprises laharic breccias, conglomerates and
sandstones that alternate eventually with fauna-bearing ma-
rine sedimentary rocks (Fig. 4). Mafic pyroxene andesite
lava flows of the Žibritov Effusive Complex conclude the
succession of the lower structural unit in the SE sector of the
stratovolcano.
It follows that the first, pre-caldera stage in evolution of the
stratovolcano involved a gradual formation of a large andesite
stratovolcano with related aprons of epiclastic volcanic rocks.
Generally, the early activity of dominantly pyroxene andesites
was followed by activity of more evolved and often porphy-
ritic amphibole-pyroxene, pyroxene-amphibole and biotite
amphibole-pyroxene andesites (Figs. 4, 5). However, mafic
pyroxene andesites also appeared among the youngest volca-
nic products of the first stage. During maturity of the first
stage stratovolcano, emplacement of extrusive domes, diorite
porphyry intrusions and andesite to andesite porphyry sills
and laccoliths took place, with the exception of the extrusive
domes preferentially into the lower parts of volcanic complex
in the central and proximal zones of the stratovolcano.
The south distal zone of the stratovolcano evolved in a shal-
low marine environment (Konečný et al. 1998) and bio-
stratigraphic evidence is available for timing of the beginning
of volcanic activity. In the borehole PKŠ-1 Gondovo in the
SW sector of the stratovolcano (Fig. 2), the beginning of vol-
canic activity is recorded by reworked pumice tuffs at the
depth of 822.4 m covered by breccias and lava flows of the
lower structural unit (Karolus et al. 1975). Fauna in underly-
ing marine sedimentary rocks points to the uppermost Lower
to lowermost Upper(?) Badenian stage (Brestenská in Karolus
et al. 1975). In the borehole ŠV-8 (Dolné Semerovce) tuf-
faceous sediments corresponding to the first stage of the Štiav-
nica Stratovolcano occur in the interval 194—430 m (Fig. 2).
Macrofauna, foraminifera, palynomorphs and calcareous nan-
nofossils at the interval 270—430 m imply the late Early Bad-
enian age (Zone NN5), while in the interval 194—270 m they
imply the early Late Badenian age (beginning of the Zone
NN6) (Vass et al. 1981; Ozdínová 2008). In the borehole
GK-3 Horné Rykynčice in the southern sector of the strato-
volcano (Fig. 2), the beginning of volcanic activity is recorded
by reworked pumice tuffs in marine sedimentary rocks at the
depth of 618 m covered by pyroclastic flow breccia and a
complex of epiclastic volcanic breccias, conglomerates and
sandstones representing the distal zone of the first stage
andesite stratovolcano (Konečný et al. 1966). Palynological
evidence from underlying marine sedimentary rocks with re-
worked material of garnet-bearing andesites points to the
Early Badenian age (Planderová in Konečný et al. 1983).
Middle to late Early Badenian age is implied by microfauna
and palynomorphs in marine siltstones interbedded with epi-
clastic volcanic sandstones in the interval 237—0 m (Leho-
tayová in Konečný et al. 1966; Brestenská et al. 1980;
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Fig. 2. Structural scheme of the Štiavnica Stratovolcano including localization of samples. Modified after Konečný & Lexa 2001.
The legend is on the next page.
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Fig. 2. Legend.
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Planderová in Konečný et al. 1983). Overlying
epiclastic volcanic breccias and conglomerates
belong to the Sebechleby Formation.
Subvolcanic/intravolcanic intrusive com-
plexes – the second stage
The second stage in the evolution of the
Štiavnica Stratovolcano corresponded to a long
lasting break in volcanic activity and extensive
denudation of the former stratovolcano down to
a thickness of 500—1000 m. In the SW sector of
the stratovolcano the break in volcanic activity
is indicated by shallow marine tuffaceous sedi-
mentary rocks that rest on top of the Sebechleby
Formation (first stage) and are covered by
pumice tuffs of the Lower Sarmatian Ladzany
Formation (fourth stage). In the borehole ŠV-8
Dolné Semerovce (Vass et al. 1981) (Fig. 2)
they are represented by marly clays and sandy
clays with tuffitic intercalations in the interval
21—194 m. Macrofauna, foraminifera, palyno-
morphs and calcareous nannofossils at this in-
terval imply the Upper Badenian stage (Zone
NN6) (Vass et al. 1981; Ozdínová 2008). The
period of denudation was concluded by the ini-
tial subsidence in the central part of the strato-
volcano, giving rise to local depressions with
lacustrine and/or limnic environments. Related
volcano-sedimentary deposits of the Červená
studňa Formation are described as a part of the
middle structural unit below. Palynology has
confirmed the uppermost Upper Badenian stage
(Planderová in Konečný et al. 1983).
However, the break in volcanic activity did
not represent a break in magmatic activity.
Evolution of magma in a shallow magma
chamber (Lexa et al. 1998b; Konečný 2002)
led to a repeated emplacement of extensive
subvolcanic/intravolcanic intrusive bodies and
complexes. These crop out in the uplifted
block of the resurgent horst, in the central
zone of the stratovolcano (Figs. 2, 3). The age
of subvolcanic intrusions is not equally con-
strained. Taking into account mutual crosscut-
ting their emplacement took place in the
following order (Konečný et al. 1993, 1998;
Konečný & Lexa 2001):
The oldest Hodruša-Štiavnica Intrusive
Complex, that crops out in the central part of
the resurgent horst comprises an older diorite
subvolcanic intrusion and a younger grano-
diorite bell-jar pluton that extends over an area
of 100 km
2
. Both intrusions invaded basement
rocks underlying the volcanic complex.
Granodiorite to quartz-diorite porphyry
dyke clusters and small stocks of the Zlatno
Intrusive Complex situated at the periphery of
the granodiorite pluton postdate the pluton.
Fig. 3.
Section
of
the
Štiavnica
Caldera
and
Hodruša-Štiavnica
resurge
nt
horst.
Modified
after
Konečný
&
Lexa
2001.
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Stocks in basement rocks pass upward into dyke
clusters that are emplaced in andesites and andesite
porphyries of the lower structural unit.
Diorite to quartz-diorite porphyry sills and dykes
of the Banisko Intrusive Complex show some fea-
tures that are characteristic of ring dykes. They have
invaded major discontinuities in the basement, the
granodiorite pluton, the contact between basement
and volcanic complex and the overlying volcanic
complex of the lower structural unit. The highest
level sills have reached the lower part of the caldera
filling. Outward dipping dykes show a preferential
orientation in the directions N-S to NE-SW.
All the intrusions are younger than andesites and
andesite porphyries of the first stage. Their rela-
tionship to the caldera filling of the third stage is
not known with one exception – quartz-diorite por-
phyry sills and dykes of the youngest Banisko Intru-
sive Complex are also emplaced in the lowermost
parts of the caldera filling. That implies a partial
overlap among the second and third stages.
Middle structural unit (caldera filling) – the
third stage
The third stage is also called the caldera stage.
During this stage the Štiavnica Stratovolcano
Caldera subsided and was filled by differentiated
rocks of biotite-hornblende andesite to dacite com-
position. The caldera 18 22 km is of a oval form
(Fig. 2). The extent of its subsidence is estimated at
500 m. At the base of the caldera filling there are
lacustrine and limnic sediments of the Červená
studňa Formation – reworked tuffs, fine epiclastic
volcanic breccias and sandstones, siltstones and
tuffaceous clays including lignite seams. Close to
the margins of the caldera, the formation also in-
cludes coarse epiclastic volcanic breccias and a sin-
gle biotite-amphibole-pyroxene andesite lava flow
in the south.
The caldera is filled with rocks of the Studenec
Formation comprising biotite-amphibole andesite
to amphibole-biotite dacite extrusive domes, dome
flows, pyroclastic flow breccias, ignimbrites and
epiclastic volcanic breccias (Figs. 3, 5). The early
stage of the subsidence associated with explosive
activity that gave rise to pumice fall and pumice
flow deposits that along with reworked tuffs and
epiclastic volcanic sandstones/siltstones rest upon
sedimentary rocks of the Červená studňa Forma-
tion (Figs. 4, 5). Subsequent extrusive activity
filled the caldera with extrusive domes, dome-
flows, pyroclastic flow breccias and related coarse
epiclastic volcanic breccias of the Studenec Forma-
tion 350—500 m in thickness. Remaining local mor-
phological depressions hosted marshes and
temporary lakes giving rise to overlying horizons
of the lacustrine and limnic type deposits with
diatomaceous earth and/or silicite intercalations.
Fig. 4.
Schematic
section
of
the
lower
structural
unit
in
the
SE
secto
r
of
the
Štiavnica
Stratovolcano.
Modified
after
Konečný
&
Lexa
2001.
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Fig. 5. Stratigraphic columns in different sectors of the Štiavnica Stratovolcano.
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Where former paleovalleys were cut off by the caldera
fault, the caldera walls were rather low and products of the
caldera-related volcanic activity passed over on the slopes of
the stratovolcano filling the paleovalleys up to a thickness of
200 meters (mostly thick lava flows, pyroclastic flow deposits
and epiclastic volcanic breccias). At the foot of the stratovol-
cano epiclastic volcanic rocks in filling of the paleovalleys
passed outward into distal facies ephemeral stream, lacus-
trine and limnic deposits, including locally lignite seams
(Obyce lignite deposit at west, Zvolenská kotlina Basin at
northeast) (Fig. 2).
There are no marine sedimentary rocks interbedded with
rocks of the Studenec Formation and no biostratigraphic
data based on marine fauna are available. Palynomorphs in
lacustrine siltstones and claystones at the base and top of the
Studenec Formation in the caldera as well as in sediments
interbedded with distal facies rocks at the outskirts of the
stratovolcano point to the time interval: end of Late Bade-
nian – beginning of Early Sarmatian (Planderová in
Konečný et al. 1983). Macroflora in diatomaceous limnic de-
posits overlying caldera filling in its northern part has been
assigned to the Lower Sarmatian (Sitár 1973).
Upper structural unit – the fourth stage
The unit comprises andesite explosive, stratovolcanic and
effusive volcanic complexes and formations that represent
volcanic activity post-dating the caldera subsidence and pre-
dating the uplift of the resurgent horst and related rhyolitic
volcanic activity. Individual complexes/formations are spa-
tially limited to certain sectors of the volcano (Fig. 2), and
often separated by short periods of erosion. Relevant volca-
nic centers were situated on slopes of the stratovolcano,
along the caldera margin and inside the caldera. Volcanic
rocks covered the caldera, accumulated in paleovalleys on
slopes of the stratovolcano and spread into broader accumu-
lations at the foot of the stratovolcano. Hyaloclastite breccias
and extensive horizons of conglomerates, sandstones and re-
worked tuffs reveal a shallow marine environment in the
southern sector of the stratovolcano.
Accumulation of volcanic rocks in different sectors of the
stratovolcano reflected a successive activation of individual
volcanic centers. No individual section provides a complete
record. A complete succession of formations and complexes
is based on the correlation of local stratigraphic columns
(Fig. 5) (Konečný et al. 1998): (1) biotite-amphibole-pyro-
xene andesite pumice tuffs of the Ladzany Formation;
(2) pyroxene andesite lava flows and related hyaloclastite
breccias and epiclastic volcanic conglomerates and sand-
stones of the Ba an Formation and Humenica Complex;
(3) biotite-amphibole-pyroxene andesite pumice tuffs of the
Biely Kameň Formation; amphibole-pyroxene andesite lava
flows, pyroclastic flow deposits and epiclastic volcanic brec-
cias in the lower part of the Breznica Complex; (4) biotite-
amphibole-pyroxene andesite lava flows of the Sitno Effusive
Complex and biotite-amphibole-pyroxene andesite epiclastic
breccias in the middle part of the Breznica Complex; (5) bio-
tite-amphibole-pyroxene andesite ignimbrites of the Drastvica
Formation; (6) amphibole-pyroxene andesite lava flows of
the Priesil and Žiar Effusive Complexes; (7) pyroxene andes-
ite lava flows of the Inovec Formation, Jabloňový vrch Com-
plex and upper part of the Breznica Complex.
Distal facies volcanic products of the fourth stage reached
a marine environment in the south. Reworked tuffs and tuf-
faceous sediments corresponding to the Ladzany and
Drastvica Formations include macrofauna of the Early Sar-
matian age (Brestenská 1970; Karolus & Váňová 1973).
Freshwater lacustrine deposits interbedded with volcanic
formations of the fourth stage elsewhere contain remnants of
macroflora and palynomorphs pointing to the Early Sarma-
tian age of the Ba an Formation and Biely Kameň Forma-
tion and Breznica Complex (Němejc 1967; Sitár 1973;
Planderová in Konečný et al. 1983).
Rhyolites of the Jastrabá Formation – the fifth stage
Rhyolite volcanic activity of the fifth, late stage associated
with an uplift of the asymmetric resurgent horst in the center
of the caldera and its denudation to the level of basement
rocks and with a contemporaneous subsidence of the Žiar
Depression at the northern sector of the stratovolcano. We
explain these phenomena using the model of Smith & Bailey
(1968) for resurgent cauldrons as being caused by a large
scale relocation of rhyolite magma from underneath the Žiar
Depression to the roots of the resurgent horst and related
isostatic equilibration (Konečný 1971; Konečný et al. 1998).
The volcanic centers of the rhyolite volcanic activity were
situated on marginal faults of the resurgent horst, marginal
faults of the Žiar Depression and N-S striking fault systems
west of the Žiar Depression (Nová Baňa—K ak fault system)
(Fig. 2).
Products of the rhyolite magmatism (Jastrabá Formation)
appear as dykes, intrusions and extrusive domes on N-S to
NE-SW striking faults. West of the caldera they associate
with faults of the Nová Baňa—K ak volcano-tectonic zone. In
the central zone of the Štiavnica Stratovolcano rhyolite
dykes and extrusive domes follow marginal faults of the re-
surgent horst, especially at its western and north-western
sides. In the northern sector of the stratovolcano an extensive
dome/flow complex with related pyroclastic and epiclastic
volcanic rocks spreads along the south-eastern and eastern
marginal faults of the Žiar Depression.
Early sporadic extrusive and explosive activity of rhyo-
dacites was followed by a widespread activity of plagioclase
and plagioclase-sanidine rhyolites. Products of the late activ-
ity of plagioclase-quartz-sanidine rhyolites are found in the
northern part of the Žiar Depression interbedded with lacus-
trine and/or limnic type deposits with horizons of sedimentary
and/or hot spring silicites that are related to the outflow of
fluids from the Kremnica epithermal system (Koděra et al.
2010). Dark silicites and associated carbonaceous clays are
rich in palynomorphs implying the Late Sarmatian to Early
Pannonian age (Planderová in Konečný et al. 1983). No other
direct biostratigraphic data are available. In the Žiar Depres-
sion rhyolite volcanites of the Jastrabá Formation rest upon
sedimentary rocks of the Upper Sarmatian stage and are cov-
ered by sedimentary rocks of the Upper Pannonian and Pon-
tian stages (Konečný et al. 1983; Lexa et al. 1998a).
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Post-rhyolite volcanic formations
In the Štiavnica Stratovolcano area there are minor occur-
rences of younger volcanic activity represented by high alu-
mina and alkali basalts (Fig. 2). High alumina basalt dykes,
sills, lava flows and tuff cone of the Šibeničný vrch Complex
in the surroundings of the town of Žiar nad Hronom post-
date rhyolite volcanic activity. Sporadic activity of alkali ba-
salts (nepheline basanites) created two necks east of the town
of Banská Štiavnica, extensive lava flows at the eastern base
of the stratovolcano and a small volcano, Pútikov vŕšok, next
to the town of Nová Baňa to the west. Its lava flows rest upon
Quaternary terrace accumulations of the river Hron.
Related ore mineralizations
The Štiavnica Stratovolcano hosts intrusion-related, as
well as extensive epithermal base metal, silver and gold min-
eralizations. Details of metallogeny have been treated exten-
sively elsewhere (e.g. Lexa et al. 1999a; Lexa 2001;
references in these papers). Here we refer only to the estab-
lished relationship between the metallogenetic processes and
the structure and evolution of the stratovolcano.
No metallogenetic processes are related to the andesites
and andesite porphyries of the lower structural unit. However,
rocks of this unit host many of the younger mineralizations.
The diorite intrusion of the Hodruša-Štiavnica Intrusive
Complex is the parental intrusion of the high sulphidation
system of Šobov that is hosted by andesites of the lower
structural unit (Onačila et al. 1995; Lexa et al. 1999a,b).
The granodiorite intrusion of the Hodruša-Štiavnica Intru-
sive Complex is the parental body for the magnetite skarn min-
eralization that affected surrounding carbonate rocks. It is also
the parental body as well as the host for the intrusion-related
stockwork/disseminated base metal mineralization (Onačila et
al. 1995; Koděra et al. 1998, 2004; Lexa et al. 1999a).
The granodiorite to quartz-diorite porphyry stocks and
dyke clusters of the Zlatno Intrusive Complex are the paren-
tal intrusions of the porphyry/skarn Cu ± Au, Mo mineraliza-
tion at the localities Zlatno, Šementlov, Medené, Kozí potok,
Handerlová and Sklené Teplice—Vydričná dolina (Onačila et
al. 1995; Lexa et al. 1999a).
The Rozália mine epithermal gold mineralization in Hod-
ruša is hosted by andesites and andesite porphyries of the lower
structural unit. It evolved during the early stage of the caldera
subsidence, prior to the emplacement of quartz-diorite sills of
the Banisko Intrusive Complex (Koděra & Lexa 2003; Koděra
et al. 2005). The barren hot spring systems of Dekýš and Čer-
vená studňa, hosted by rocks of the Červená studňa Forma-
tion and lower part of the Studenec Formation, evolved roughly
in the same time interval (Onačila et al. 1995; Lexa 2001).
The Varta high sulphidation system next to the town of
Banská Belá is situated in rocks of the Studenec Formation
filling the caldera. We assume a relationship to the hypothet-
ical porphyry intrusion emplaced during the caldera stage of
the stratovolcano.
The extensive system of base metal, silver-base metal and
gold-silver epithermal veins is hosted by faults of the resur-
gent horst. The rather long living system evolved during the
uplift of the resurgent horst. Evolution of the system took
place during and after the late stage rhyolitic magmatic activity
(Kovalenker et al. 1991; Onačila et al. 1995; Chernyshev et al.
1995; Lexa et al. 1999a; Háber et al. 2001; Lexa 2001).
Methodology of the new K-Ar and Rb-Sr isotope
dating
K-Ar method
Radiogenic
40
Ar content measurements were performed by
isotope dilution method with
38
Ar as a spike. The MI-1201
IG mass spectrometer with low-blank argon extraction and
purification device was used. The overall analytical system
was developed and calibrated for young (Neogene—Quater-
nary) magmatic rock dating (Chernyshev et al. 2002, 2006).
Argon isotope analyses were conducted in static regime of
mass-spectrometer measurements at resolving power ~1200.
The last provided the interference elimination on the 36 m/e
mass peak: the argon isotope peak (
36
Ar
+
, 35.98 m/e) was re-
solved from the isobaric peak (
12
C
3
+
, 36.01 m/e). The overall
system sensitivity in argon was 5 10
—3
A/tor, total blank did
not exceed 3 10
—3
and 1 10
—5
ng in isotopes
40
Ar and
36
Ar
respectively. The potassium content was determined by the
flame spectrophotometry method. In the case of plagioclase
monomineral samples having low ( < 0.5 %) potassium con-
tent the isotope dilution method with
39
K spike was used. The
accuracy was controlled by systematic analyses of the geo-
chronological standard samples Bern-4 (muscovite), P-207
(muscovite) and 1/76 (basalt).
Rb-Sr method
The isotope dilution method with
85
Rb +
84
Rb as mixed
spike was used to assess Rb and Sr contents. Whole rock and
monomineral samples, 10—20 mg in mass, were decomposed
in acid and then subjected to Rb and Sr extraction at the col-
umn with the Dowex 50 8 (200—400 mesh) anion exchange
resin. Rb and Sr mass-spectrometric measurements were per-
formed on the thermal ionization 7-collector Micromass Sec-
tor 54 mass-spectrometer. The accuracy was controlled by
systematic analyses of the Sr SRM-987 standard sample. The
overall errors of the
87
Rb/
86
Sr and
87
Sr/
86
Sr ratios determina-
tion that were used in isochron calculations averaged ± 0.5 %
and ± 0.005 % respectively.
Precision of the K-Ar and Rb-Sr age data
Errors of all isotope age values that are summarized and
discussed in the present paper correspond to the ± 2 level.
They differ for individual samples. Errors of K-Ar ages aver-
age around ± 3.5 % relative (around ± 0.35 Ma in the case of
our results) and represent exclusively analytical errors.
Roughly ± 1.5 % relative of this error value constitutes the
error of the potassium content determination. The rest repre-
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sents the error of the radiogenic
40
Ar determination that in
turn depends on the sum of mass-spectrometric measurement
errors as well as on the non-radiogenic
40
Ar content in indi-
vidual samples. The K-Ar age determination errors were cal-
culated using the formula of Baksi et al. (1967) as
recommended by Baksi (1982) for the case of individual Ar
isotopes error estimates.
The 2 -errors of Rb-Sr isochron ages are less than the er-
rors of K-Ar ages. Their value varies around 0.33 Ma. In this
case the error does not represent as much a sum of analytical
errors. It is rather given by deviation of data points incorpo-
rated into the isochron calculation relative to the isochron re-
gression line.
The following constants recommended by the IUGS Sub-
comission for Geochronology (Steiger & Jäger 1977) were
used in age calculations:
= 0.581 10
—10
year
—1
,
= 4.962 10
—10
year
—1
,
40
K/K = 0.01167 at. % (K-Ar method)
and 1.42 10
—10
year
—1
,
85
Rb/
87
Rb = 2.59265 (Rb—Sr method).
Excess radiogenic argon in young volcanic rocks: rock
groundmass as the K-Ar geochronometer
Matsumoto & Kobayashi (1995), Singer et al. (1998) and
Chernyshev et al. (1999) have demonstrated that different
components inside one rock might be distinct in K-Ar age
values. As the initial
40
Ar/
36
Ar isotope ratio in geochronologi-
cal calculations is the accepted air value equal to 295.5 the
above mentioned phenomena are attributable most often to the
Ar isotope composition un-equilibration in associated min-
eral components of the rock – some components (especially
low-K mineral phenocrysts) may have an initial
40
Ar/
36
Ar iso-
tope ratio higher than 295.5, indicating an excess radiogenic
argon presence. The geological mechanisms of this phenom-
enon are related to the earlier phenocryst crystallization in
respect to rock groundmass crystallization. For argon sources
with increased
40
Ar/
36
Ar isotope ratio ( > 295.5) the follow-
ing processes might be relevant: 1) melt inclusions in phe-
nocrysts; 2) the argon contained in melt as gaseous
component captured in lattice of crystallizing phenocrysts;
3) the argon retained in cores of phenocrysts during magma
contamination by older sialic crustal material – cores of
phenocrysts in this case represent remnants of assimilated
crustal rocks that later played the role of phenocryst crystal-
lization centers (Chernyshev et al. 1999, 2002, 2006). The
phenomenon of excess radiogenic argon is characteristic es-
pecially for phenocrysts with low potassium content – pyro-
xene, plagioclase and amphibole. Its effect in the case of
potassium-rich biotite is questionable for Miocene rocks. If
different ages are obtained for biotite—groundmass pairs an
effect of radiogenic argon loss of one of the fractions due to
reheating or secondary processes is a more probable cause.
Biotite, as well as groundmass K-feldspars and glass, are
sensitive to these processes. In such a case the higher age of
the pair is considered as the more dependable one.
The data set forth here and the above considerations give
us a basis for concluding that volcanic rock groundmass, that
evolved from erupted and consequently mostly out-gassed
material, represents the most acceptable K-Ar geochronometer
with the exception of samples affected by rejuvenation. Its
usage for geochronological studies of young volcanic rock
does not exclude a parallel, more detailed study involving
also K-Ar measurements of phenocrysts. In this respect we
believe, that such a detailed study as performed on volcanic
rocks of the Štiavnica Stratovolcano also brings methodo-
logical benefits (Appendix 1). Out of 9 rocks studied with
data on both, plagioclase phenocrysts and groundmass, in 3
cases K-Ar age values obtained from plagioclase pheno-
crysts and groundmass of the same rock are consistent within
the analytical error intervals. However, in the case of 6 rocks
(GK-110, GP-11/02, GK-16, GP-57, GK-105, GK-21) the
K-Ar ages obtained from groundmass and plagioclase phe-
nocrysts differ significantly by 1.6 to 3.3 Ma, the age values
of plagioclase phenocrysts being older than the age values of
groundmass in the same rock. It follows that a whole-rock
sample K-Ar dating of the Štiavnica Stratovolcano rocks
generally could lead to acquisition of incorrect age data. The
discussed phenomenon is one of the causes of many discre-
pancies and contradictions among age estimations based pre-
viously upon K-Ar dating of whole-rock samples (Konečný et
al. 1969; Bagdasarjan et al. 1970; Merlitsh & Spitkovskaya in
Štohl 1976; Bagdasarjan in Konečný et al. 1983; Kantor et
al. 1988). Another cause could be connected with the signifi-
cant ( ± 2—3 Ma) errors of earlier results due to the limitations
of analytical isotope techniques more than 30 years ago. The
third cause is related to a possible partial or complete rejuve-
nation of minerals with low closing temperature due to re-
heating by an extensive hydrothermal system in the central
zone of the stratovolcano.
To eliminate a possible influence of excess radiogenic ar-
gon in phenocrysts of plagioclase, pyroxenes and amphi-
boles upon the age of dated rocks the present work is based
especially upon the K-Ar dating results obtained by analyses
of groundmass (matrix, glass) separated from phenocrysts.
Some andesites, out of studied ones, contain subordinate
biotite phenocrysts in sufficient quantity to enable Rb-Sr
analyses. The Rb-Sr method of dating was applied to intru-
sive rocks as well as to felsic volcanic rocks of the Štiavnica
Stratovolcano.
The results of Rb-Sr isochrone dating require few com-
ments. The
87
Rb/
86
Sr of biotites is an order of magnitude
higher than the
87
Rb/
86
Sr of other phases. In such a case it is
especially biotite that determines the isochrone slope and the
isochrone age is more or less the biotite age. With the excep-
tion of two samples, the MSWD parameter is greater than 1.
This suggests that a geochemical dispersion of the data rela-
tively to the isochrone regression line exists beside an analyti-
cal scatter of data points. Such a situation appears to be bound
to young magmatic rocks, including rocks of the Štiavnica
Stratovolcano. At low radiogenic
87
Sr content, inherent to
such young rocks, the initial
87
Sr/
86
Sr ratio variations affect re-
markably the data point position in respect of the isochrone re-
gression line as well as the MSWD isochrone parameter value.
This effect is manifested in Rb-Sr data for rocks of the Štiavnica
Stratovolcano in an unconformable position of data points
representing fractions with high common Sr content (hun-
dreds ppm) close to the
87
Sr/
86
Sr coordinate (Fig. A in Appen-
dix 2). The same data points determine the I
0
isochrone
parameter value. As demonstrated in the Appendix 2 this pa-
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rameter varies significantly between 0.7053 and 0.7085 re-
flecting the Sr isotope heterogeneity of the rocks studied.
New K-Ar and Rb-Sr data
The set of studied samples represents main structural units
(evolutionary stages) of the Štiavnica Stratovolcano that are
recognized on the 1 : 50,000 map (Konečný et al. 1998).
Sampling localities are marked in the structural scheme of
the stratovolcano (Fig. 2). Their geographical and geological
positions are provided in electronic Appendix 3, whereas
short petrographic description and chemical characteristics
of analysed samples are given in Appendices 3 and 4, re-
spectively (available only in the electronic version). Appen-
dices 1 and 2 include the obtained K-Ar and Rb-Sr ages
along with source analytical data and their individual errors.
The chemical compositions of the Štiavnica Stratovolcano
samples that were used for isotope dating are given in Appen-
Table 1: Summary of reliable K-Ar and Rb-Sr isotope geochronological data for rocks of the Štiavnica Stratovolcano.
* – data published already by Chernyshev et al. (1995). Numbers 1—42 correspond to sample numbers on the structural scheme (Fig. 2).
No. Sample Rock type
Volcanic form
Formation Complex
K-Ar age
(Ma)
Rb-Sr age
(Ma)
Volcanic formations pre-dating Štiavnica Stratovolcano
1 GP-4
Pyroxene-amphibole andesite with garnet Extrusive dome
Neresnica Formation
15.0 ± 0.4
Lower structural unit (1
st
stage)
3 GK-111
Amphibole-pyroxene andesite
Lava flow
Sebechleby Formation
14.8 ± 0.3
4 GK-110
Amphibole-pyroxene andesite
Fragment in lahar breccia Sebechleby Formation
14.0 ± 0.4
5 St-6/06
Amphibole-pyroxene andesite
Lava flow
Sebechleby Formation
14.0 ± 0.4
6 St-4/06
Pyroxene andesite matrix
Welded tuff/breccia
Lower structural unit
13.8 ± 0.4
7 St-5/06
Pyroxene andesite fragment
Welded tuff/breccia
Lower structural unit
13.8 ± 0.4
8 GK-107
Pyroxene andesite
Lava flow
Zibritov Complex
14.1 ± 0.3
9 GK-106
Pyroxene andesite
Lava flow
Zibritov Complex
13.8 ± 0.4
13.7 ± 0.3
10 GP-13
Pyroxene andesite
Lava flow
Zibritov Complex
13.4 ± 0.4
11 St-7/06
Pyroxene andesite
Lava flow
Lower structural unit
13.5 ± 0.3
12 St-14/06
Pyroxene andesite
Lava flow
Lower structural unit
13.5 ± 0.4
13 GK-57
Pyroxene andesite
Lava flow
Lower structural unit
13.2 ± 0.4
14 GP-11
Pyroxene andesite
Lava flow
Lower structural unit
13.1 ± 0.4
Subvolcanic/intravolcanic intrusive complexes (2
nd
stage)
15 St-5/99
Granodiorite
Bell-jar type pluton
Hodr.-Štiavn. Intr. Complex
13.4 ± 0.2
16 St-2/04
Granodiorite
Bell-jar type pluton
Hodr.-Štiavn. Intr. Complex
13.3 ± 0.6
17 St-4/08
Diorite
Bell-jar type pluton
Hodr.-Štiavn. Intr. Complex
13.3 ± 0.2
Middle structural unit (caldera filling, 3
rd
stage)
18 St-83/91* Biotite-amphibole andesite
Extrusive dome
Studenec Formation
12.7 ± 0.4*
12.4 ± 0.1
19 GK-100
Pyroxene-biotite-amphibole andesite
Lava flow
Studenec Formation
13.1 ± 0.3
20 GK-16
Biotite-amphibole andesite
Extrusive dome
Studenec Formation
12.8 ± 0.3
12.9 ± 0.5
21 GK-20
Pyroxene-biotite-amphibole andesite
Extrusive dome
Studenec Formation
13.0 ± 0.4
12.4 ± 0.6
Upper structural unit (4
th
stage)
22 St-9/06
Pyroxene andesite
Lava flow
Baďan Formation
12.6 ± 0.3
23 St-10/06
Pyroxene andesite
Lava flow
Baďan Formation
12.5 ± 0.3
24 GK-105
Biotite-amphibole-pyroxene andesite
Lava flow
Sitno Effusive Complex
12.7 ± 0.3
12.3 ± 0.2
25 KSD-2
Biotite-amphibole-pyroxene ignimbrite
Welded tuff
Drastvica Formation
12.0 ± 0.2
26 St-1/06
Pyroxene andesite
Lava flow
Breznica Complex
12.9 ± 0.3
27 St-11/06
Pyroxene andesite ± biotite
Lava flow
Priesil Formation
13.0 ± 0.3
28 St-12/06
Amphibole-pyroxene andesite ± biotite
Lava flow
Priesil Formation
12.4 ± 0.3
12.3 ± 0.7
29 St-15/06
Pyroxene andesite
Lava flow
Inovec Formation
12.2 ± 0.3
30 St-16/06
Amphibole-pyroxene andesite
Lava flow
Ziar Complex
12.0 ± 0.3
Rhyolites of the Jastrabá Formation (5
th
stage)
31 St-18/06
Rhyolite
Dyke
Jastrabá Formation
12.2 ± 0.8
32 GK-21 Rhyolite
Dyke
Jastrabá
Formation
12.2 ± 0.3
11.9 ± 0.3
33 KSD-1
Rhyolite (K-metasomatism)
Extrusive dome
Jastrabá Formation
11.5 ± 0.3
34 V-7/91c
*
Rhyolite (K-metasomatism)
Extrusive dome
Jastrabá Formation
11.6 ± 0.3*
35 L-8/91
*
Rhyolite (perlite)
Fragment in extr. breccia Jastrabá Formation
11.4 ± 0.4*
12.1 ± 0.1
36 St-6/08B
Rhyolite (perlite)
Fragment in extr. breccia Jastrabá Formation
11.8 ± 0.1
37 Kl-1/91*
Rhyolite
Dyke
Jastrabá Formation
11.4 ± 0.3*
Post-rhyolite volcanic formations — alkali basalts
38 St-84/91* Nepheline basanite
Lava neck
7.8 ± 0.4*
39 St-85/91B* Nepheline basanite
Lava neck
5.7 ± 0.4*
40 S-B3/02
Nepheline basanite
Lava flow
0.45 ± 0.03
41 S-B7/02
Nepheline basanite
Lava neck
0.42 ± 0.03
42 S-B8/02
Nepheline basanite
Lava flow
0.43 ± 0.03
ˇ
ˇ
ˇ
ˇ
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dix 4 along with a short commentary. The data as shown in the
diagram Na
2
O + K
2
O—SiO
2
(Fig. B in electronic Appendix 4)
are comparable to earlier results obtained from volcanic rocks
of the Central Slovakia Volcanic Field (Konečný at al. 1995).
Their composition is close to high-potassium rocks of andes-
ite-dacite suites in volcanic belts of the developed island arcs
or continental margins (Lexa & Konečný 1998).
Appendix 1 presents all new K-Ar data. It also demonstrates
the relationship among the K-Ar ages of groundmass, plagio-
clase and/or biotite separated from common samples. Results
that are considered reliable and serve as a basis of the follow-
ing discussion and conclusions, are indicated by bold type and
grey background. Reliability of results has been evaluated on
the basis of criteria mentioned in the part on methodology and
compatibility with other results. Comments on the selection of
reliable results in the case of individual samples are given be-
low. Appendix 2 presents the results of Rb-Sr isochron dating,
whereas Table 1 presents reliable results of K-Ar and Rb-Sr
dating as accepted age values with 2 errors. Here we have
also included results published by Chernyshev et al. (1995) as
they were not discussed yet in the context of other data and the
evolution of the Štiavnica Stratovolcano.
The primary objective of the Rb-Sr isochrone dating appli-
cation in the present work was dating of intrusive rocks in the
area of younger hydrothermal system overprint (regional pro-
pylitic alteration associated with the extensive system of epi-
thermal veins) as the closure temperature of the Rb-Sr system
rock-forming minerals (biotite, feldspars) is higher than for
the K-Ar system. This is an important feature of the Rb-Sr sys-
tem if we take into account that the younger hydrothermal sys-
tem has reached temperatures of 250—300 °C (Kovalenker et
al. 1991; Onačila et al. 1995). Moreover, Rb-Sr age data repre-
sent the independent information that can be used to control
results of K-Ar dating. Such a possibility has been used in the
case of rocks containing biotite. In so doing 3—5 mineral frac-
tions separated from a common rock were analysed. In two
cases (samples GK-105, L-8/91) Rb-Sr measurements were
limited to analyses of pairs biotite—whole rock, or biotite—
glass. Out of 6 samples studied by both methods 4 andesite
samples show a concordant K-Ar and Rb-Sr isochron ages that
agree within the 2 error intervals while two felsic rock sam-
ples (L-8/91 rhyolite, GK-21 rhyodacite) exhibit a differences
between the K-Ar ages and Rb-Sr ages that exceed the error
intervals as much as 1.5—2 times.
Comments on the reliability of individual results
Most of the results of K-Ar dating obtained from ground-
mass fraction and Rb-Sr isochrone dating are reliable and
need no comments. However, some of the results are contra-
dictory and require comments on how reliable results have
been chosen.
No. 1 (sample GP-4): The obtained K-Ar isotope age of
15.0 ± 0.4 Ma on groundmass fraction corresponds to Early
Badenian. That is in agreement with the structural position
below the base of the Štiavnica Stratovolcano. The apparent
age of 14.6 ± 0.4 Ma from plagioclase phenocrysts overlaps
with results from the overlying rocks, so it is not considered
representative.
No. 2 (sample GK-2/01): The sample represents a lava
flow filling a paleovalley eroded in rocks of the Sebechleby
Formation. However, the age of 15.2 ± 0.4 Ma obtained from
pyroxene andesite groundmass is older if compared with
ages of the underlying formation in the range 14.8 ± 0.3 to
14.0 ± 0.4 Ma (Appendix 1 and Table 1).
No. 4 (sample GK-110): K-Ar dating of groundmass frac-
tion has provided the reliable age 14.0 ± 0.4 Ma. The result
15.6 ± 0.5 Ma from plagioclase phenocrysts is not considered
representative, probably due to excess radiogenic argon.
No. 9 (sample GK-106): K-Ar dating of groundmass frac-
tion has provided the age 13.7 ± 0.3 Ma. In this case plagio-
clase phenocrysts have provided a compatible result
13.8 ± 0.4 Ma.
Nos. 12 and 13 (samples St-14/06 and GK-57): Results of
K-Ar dating of groundmass fractions 13.5 ± 0.3 and 13.2 ± 0.4
place these lava flows into the upper parts of the lower struc-
tural unit (first stage). The result 15.1 ± 0.7 Ma from plagio-
clase phenocrysts of the sample No. 13 is not considered
representative, probably due to excess radiogenic argon.
No. 14 (sample GP-11): K-Ar dating on groundmass frac-
tion has provided the age 13.1 ± 0.4 Ma. The result
11.8 ± 0.5 Ma obtained from plagioclase phenocrysts is not
considered representative.
No. 17a (sample St-2/08): An attempt to date the dyke by
Rb-Sr isochrone method has not been successful (Fig. A in
Appendix 2). Analyses of individual fractions do not fall on
a well-defined isochrone. The upper and lower limits for the
age are 16 and 11 Ma.
No. 18 (sample St-83/91): K-Ar dating of mineral fractions
provided the following ages: plagioclase – 15.8 ± 2.0 Ma,
amphibole – 14.8 ± 1.2 Ma and biotite – 12.7 ± 0.4 Ma; K-Ar
isochrone provided the age 12.4 ± 0.2 Ma; Rb-Sr isochrone
dating provided the age 12.4 ± 0.1 Ma. Both, K-Ar and Rb-Sr
isochrone ages overlap with data from overlying andesites of
the upper structural unit. As the K-Ar isochrone is affected
by excess argon in plagioclase and amphibole the K-Ar age
of biotite is considered the most representative.
No. 20 (sample GK-16): K-Ar dating provided the age
11.8 ± 0.3 Ma from groundmass fraction and 12.8 ± 0.3 Ma
on biotite fraction; the result 15.1 ± 0.5 Ma obtained from pla-
gioclase phenocrysts reflects excess radiogenic argon. Rb-Sr
isochrone dating (Fig. A in Appendix 2) provided the age
12.9 ± 0.5 Ma. In this case we assume that groundmass has
been affected by radiogenic argon loss (due to unrecognized
alteration?). It follows that the K-Ar age for the biotite fraction
and Rb-Sr isochrone age are considered representative.
No. 21 (sample GK-20): K-Ar dating provided the age
11.8 ± 0.3 Ma from the groundmass fraction and 12.1 ± 0.3 Ma
from the biotite fraction. The plagioclase fraction provided the
result 13.0 ± 0.4 Ma. Rb-Sr isochrone dating pointed to the age
12.4 ± 0.6 Ma. Usually the Rb-Sr isochrone age is considered
the most reliable one and plagioclase apparent K-Ar ages are
affected by the excess argon phenomena. However, in this
case only the K-Ar age on plagioclase fits the geological po-
sition. Other results are too young considering the ages of
overlying andesites of the upper structural unit.
No. 24 (sample GK-105): K-Ar dating of groundmass frac-
tion provided the age 12.7 ± 0.3 Ma that is within the error lim-
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its from the Rb-Sr isochron age 12.3 ± 0.2 Ma. The result
15.4 ± 0.6 Ma from plagioclase phenocrysts is not considered
representative, most probably due to excess radiogenic argon.
No. 28 (sample St-12/06): K-Ar dating of groundmass
fraction provided the age 12.4 ± 0.3 Ma that is within the error
limits from the Rb-Sr isochron age 12.3 ± 0.7 Ma.
No. 32 (sample GK-21): K-Ar dating of groundmass pro-
vided the age 11.9 ± 0.3 Ma, the biotite fraction produced the
age 12.2 ± 0.3 Ma, and the plagioclase fraction 13.7 ± 0.4 Ma
perhaps reflecting excess radiogenic argon. Rb-Sr isochron
dating provided the age 10.5 ± 0.2 Ma. The K-Ar ages of the
groundmass and biotite fraction are considered the most reli-
able ones.
No. 35 (sample L-8/91): K-Ar dating of biotite and glass
provided the ages 12.7 ± 0.4 Ma and 11.4 ± 0.4 Ma respectively.
The Rb-Sr isochron dating provided the age 12.1 ± 0.1 Ma. The
result obtained on biotite overlaps with ages of older andes-
ites. Perlite glass is sensitive to possible radiogenic argon loss.
The Rb-Sr isochron age is considered the most representative.
Discussion — evolution of the Štiavnica Stratovolcano
Volcanic formations preceding the Štiavnica Stratovolcano
Biostratigraphic dating of associated sedimentary and vol-
cano-sedimentary rocks suggests the Early Badenian age
(Zone NN5) for volcanic activity of garnet-bearing andesites
(Kantorová 1962; Čechovič & Vass 1962; Lehotayová 1962;
Lehotayová in Vass et al. 1979; Konečný et al. 1983; Kováč
et al. 2005). The same age is applicable for the early volcanic
activity of garnet-bearing andesites/dacites in the Börzsöny
mountain range, located further southward (Karátson et al.
2000). According to Kováč et al. (2005) sedimentary rocks
of the lowermost Badenian corresponding to the nanno-
plankton Zone NN4 are missing in the Slovak territory. The
Early Badenian transgression reached the territory early dur-
ing the NN5 Zone ( < 15.5 Ma), or early during the planktonic
foraminiferal Zone Orbulina suturalis ( < 15.1 Ma). K-Ar
dating of garnet-bearing andesite from the locality Breziny
south of Zvolen (No. 1) to 15.0 ± 0.4 Ma fits well the bio-
stratigraphic data. Older results of isotope dating of garnet-
bearing andesites in the range 16.2 ± 0.2 Ma to 15.7 ± 1.4 Ma
(Bagdasarjan in Konečný et al. 1969; Repčok 1978, 1981) are
either erroneous or they imply volcanic activity before the
Early Badenian transgression. Equivalent garnet-bearing andes-
ites of the Börzsöny mountain range in Hungary show K-Ar
ages in the interval 16.0—14.5 Ma (Karátson et al. 2000). Ap-
parently, garnet-bearing andesites represent a longer lasting
volcanic activity. A partial overlap with volcanic activity of
the first stage of the Štiavnica Stratovolcano (the oldest reli-
able age obtained is 14.8 ± 0.3 Ma) cannot be excluded on the
basis of available data. We consider 14.8 Ma as a probable up-
per limit on their age in the area of the Štiavnica Stratovolcano.
Lower structural unit (1
st
stage) of the Štiavnica Stratovolcano
Previous dating of the 1
st
stage rocks by the FT method
provided ages in the interval 16.5 ± 0.5 Ma to 15.9 ± 0.8 Ma
(Repčok 1980, 1981, 1984). New dating has provided a set of
reliable results in the interval 14.8 ± 0.3 Ma to 13.1 ± 0.4 Ma,
with most results in the interval 14.0 ± 0.4 Ma to 13.5 ± 0.3 Ma
(Table 1).
The Sebechleby Formation in the southern sector of the
stratovolcano represents a relatively older lithostratigraphic
unit of the 1
st
stage (Konečný et al. 1998). Relationship of
the formation to biostratigraphically dated volcano-sedimen-
tary rocks in the boreholes GK-3 Rykynčice (Lehotayová in
Konečný et al. 1966; Brestenská et al. 1980; Planderová in
Konečný et al. 1983) and ŠV-8 Dolné Semerovce (Vass et al.
1981; Ozdínová 2008) points to the middle(?) to late Early
Badenian age of the formation. The results of new dating in
the range 14.8 ± 0.3 Ma to 13.8 ± 0.4 Ma (Nos. 3—7) are com-
patible with such a biostratigraphic assignment. The result
15.2 ± 0.4 Ma (No. 2) would be compatible with biostrati-
graphic assignment of the formation as well as with the iso-
tope age of underlying volcanic products of garnet-bearing
andesites (see above) only in the case that the real age is
close to the lower limit of the error interval. This lava flow is
also relatively younger as it fills a paleovalley in older rocks
of the formation. Because of incompatibility with younger
ages on underlying rocks it is not considered reliable. Taking
into account the reliable results (Table 1), the biostratigraphic
evidence and a possible overlap of the 1
st
stage with activity
of garnet-bearing andesites, 15.0 Ma seems to be the best
choice for the lower limit of the 1
st
stage volcanic activity.
However, volcanic activity of the 1
st
stage has not started at
the same time in all sectors of the stratovolcano. In the SW
sector of the stratovolcano rocks of the 1
st
stage rest on upper-
most Lower Badenian marine sedimentary rocks (Brestenská
in Karolus et al. 1975). Considering correlation of chrono-
stratigraphic units with the time scale (Kováč et al. 2005;
Harzhauser & Piller 2007) volcanic activity of the 1
st
stage
started here as late as 14.0 to 13.6 Ma. That correlates with
the absence of the Sebechleby Formation in this sector of the
stratovolcano (Konečný et al. 1998).
The Žibritov Effusive Complex in the south-eastern sector
of the stratovolcano represents a relatively younger litho-
stratigraphic unit of the 1
st
stage overlying the Sebechleby
Formation (Konečný et al. 1998). There is no biostratigraphic
evidence available. New isotope dating has provided 4 results
(Nos. 8—11) in the interval 14.1 ± 0.8 Ma to 13.4 ± 0.6 Ma
(Table 6) around the Early/Late Badenian boundary. The lava
flow at the locality Ficberg (No. 11) has formerly been as-
signed to the upper structural unit (4
th
stage) of the stratovol-
cano on the basis of erroneous K-Ar dating to 11.4 ± 0.3 Ma
(Bagdasarjan et al. 1970).
New results of isotope dating of two pyroxene andesite
lava flows next to Machulince in the western sector of the
stratovolcano, namely 13.5 ± 0.3 Ma and 13.2 ± 0.4 Ma, re-
spectively, assign these lava flows to the youngest products of
the 1
st
stage of the stratovolcano, corresponding to the Late
Badenian. However, on the basis of geological mapping these
lava flows have formerly been assigned to the upper structural
unit (4
th
stage) (Konečný et al. 1998) and their real assignment
should be further clarified by detailed field investigation. Py-
roxene-rich sandy deposits in the interval 194—230 m of the
borehole ŠV-8 Dolné Semerovce assigned to the lowermost
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Upper Badenian (Vass et al. 1981; Ozdínová 2008) may repre-
sent a volcano-sedimentary equivalent.
K-Ar dating of the 1
st
stage pyroxene andesite lava flow
south of Nová Baňa (No. 14) provided the age of
13.1 ± 0.4 Ma. As the lava flow is relatively close to the
Nová Baňa epithermal system and shows signs of weak hy-
drothermal alteration its relatively young age might be a re-
sult of partial rejuvenation.
The upper limit for the time interval of the 1
st
stage of the
stratovolcano is set forth by (1) the Late Badenian age of
overlying sedimentary rocks in the borehole ŠV-8 Dolné Se-
merovce (see below) and (2) by results of isotope dating of
rocks from the Hodruša-Štiavnica Intrusive Complex
(Nos. 15—17) in the range 13.4 ± 0.2 Ma to 13.3 ± 0.2 Ma.
The intrusive complex is younger than rocks of the 1
st
stage
(Konečný et al. 1998; Konečný & Lexa 2001). It follows that
the most probable interval of the 1
st
stage volcanic activity of
the Štiavnica Stratovolcano is 15.0—13.5 Ma (middle Early
Badenian to early Late Badenian).
Denudation and emplacement of subvolcanic intrusive
complexes (2
nd
stage)
Biostratigraphic evidence points to a Late Badenian age
(Zone NN6) for sedimentary rocks corresponding to the den-
udation of the 1
st
stage stratovolcano (Vass et al. 1981;
Ozdínová 2008) and to a late Late Badenian age for lacus-
trine sediments related to the early caldera subsidence (Plan-
derová in Konečný et al. 1983).
Previous attempts to date rocks of subvolcanic intrusive
complexes by the K-Ar method on whole-rock samples
(Bagdasarjan et al. 1970; Merlitsh & Spitkovskaya in Štohl
1976; Konečný et al. 1983) and by the FT method on mineral
fractions (Repčok 1981, 1984) failed due to extreme scatter
(19.5 ± 0.8 to 10.5 ± 0.5 Ma) and contradiction between indi-
vidual results reflecting variably contamination by Hercyn-
ian basement rocks, excess radiogenic argon in low-K phases
and/or rejuvenation. Discordant ages obtained from amphib-
oles and biotites (Repčok 1981, 1984) imply resetting of bio-
tite ages. Only single K-Ar dating of the biotite mineral
fraction provided a reasonable result of 13.9 ± 0.1 Ma (Kantor
et al. 1988).
The most reliable results obtained in the present work
come from samples of the Hodruša-Štiavnica Intrusive Com-
plex. Isotope dating of granodiorite pluton at two localities
(Nos. 15—16) by the Rb-Sr method provided very close ages
of 13.4 ± 0.2 Ma and 13.3 ± 0.6 Ma. Dating of diorite intru-
sion provided the same age 13.3 ± 0.2 Ma. These results as-
sign the Hodruša-Štiavnica Intrusive Complex to the Late
Badenian as assumed on the basis of geological data
(Konečný et al. 1998; Konečný & Lexa 2001).
Dating of granodiorite to quartz-diorite porphyry stocks and
dyke clusters of the Zlatno and Tatiar Intrusive Complexes
has not been successful. Attempts to date these rocks failed
because of alterations of related porphyry hydrothermal sys-
tems and possible rejuvenation by younger epithermal sys-
tems. K-Ar dating of granodiorite porphyry from the locality
Šementlov by Chernyshev et al. (1995) to 11.4 ± 1.2 Ma serves
as an example. An attempt to date the granodiorite porphyry
Fig. 6. Sums of radiometric age normal distribution densities for evo-
lutionary stages of the Štiavnica Stratovolcano based on K-Ar and
Rb-Sr ages presented in Table 1. The curves for individual stages
reflect the number of individual results, values of individual results
and their errors. In that way they summarize results of individual
stages and allow for their mutual comparison.
intrusion at the locality Zlatno by the Rb-Sr method (Krá et
al. 2002) has failed too. The rock, including mafic enclaves up
to 0.5 m in diameter, was isotopically homogenized at sub-
solidus temperatures. Results from separated amphiboles and
biotites imply, that amphibole was enriched in radiogenic Sr
lost by biotite during a younger event. The biotite—whole-rock
isochron gave the apparent age 10.6 Ma.
The same applies to the younger Banisko Intrusive Com-
plex. Owing to regional alteration related to thermal anomaly
of extensive system of epithermal veins no reliable results
have been obtained. FT dating of a quartz-diorite sill close to
the locality Zlatno has provided apparent ages for amphibole
and biotite of 13.4 ± 0.6 Ma and 13.6 ± 0.8 Ma respectively
(Repčok 1984). As some of the sills of the complex intruded
into the lowermost parts of the Štiavnica Caldera filling
(Figs. 3, 5) the age of the caldera filling (13.1—12.7 Ma) also
represents the upper limit for the age of the intrusive com-
plex (compare Fig. 6). The value 12.9 Ma in the middle of
this interval is considered the most probable upper limit. It
follows that the subvolcanic intrusive complexes of the
Štiavnica Stratovolcano were emplaced in the time interval
13.4—12.9 Ma, corresponding to the Late Badenian.
Middle structural unit (caldera filling, 3
rd
stage)
Palynomorphs in sediments interbedded with rocks of the
Studenec Formation within the caldera as well as at the out-
skirts of the stratovolcano point to the interval late Late Bad-
enian to Early Sarmatian (Planderová in Konečný et al.
1983). Overlying sediments have been assigned to the Lower
Sarmatian (Sitár 1973; Planderová in Konečný et al. 1983).
Previous isotope dating by the K-Ar and FT methods pro-
vided erroneous ages in the interval 16.4—14.8 Ma (Konečný
et al. 1969; Repčok 1978—1981). New isotope dating by
both, K-Ar and Rb-Sr methods, provided reliable ages in the
interval 13.1 ± 0.3 Ma to 12.4 ± 0.1 Ma (see discussion to in-
dividual samples above and Table 1) that are in agreement
with biostratigraphic evidence. However, the youngest data
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are not compatible with ages on some of the overlying rocks
of the upper structural level (4
th
stage) (see bellow). Consid-
ering the mutual overlap of apparent ages of the 3
rd
and 4
th
stages (Fig. 6) the best choice for the upper limit of the 3
rd
stage and lower limit of the 4
th
stage is 12.7 Ma. Consider-
ing correlation of chronostratigraphic units with the time
scale (Kováč et al. 2005; Harzhauser & Piller 2007), the vol-
canic activity of the 3
rd
stage took place during the late Late
Badenian and despite the palynological evidence probably
did not extend into the Early Sarmatian.
Upper structural unit (4
th
stage)
Biostratigraphic data from marine sediments interbedded
with rocks of the upper structural unit in the SW sector of the
stratovolcano reveal the Early Sarmatian age (Brestenská
1970; Karolus & Váňová 1973). Freshwater lacustrine depos-
its interbedded with volcanic formations of the fourth stage
elsewhere contain remnants of macroflora and palynomorphs
implying the same age (Němejc 1967; Sitár 1973; Planderová
in Konečný et al. 1983). However, Kováč et al. (2005) ques-
tioned the ability to distinguish Early and Late Sarmatian.
The upper structural unit comprises a succession of poorly
correlated volcanic formations and complexes post-dating
the Štiavnica Caldera and pre-dating rhyolite volcanism of
the 5
th
stage. Fig. 5 shows their probable succession. Previous
isotope dating by the K-Ar and FT methods provided mostly
erroneous ages in the interval 15.0—9.9 Ma (Konečný et al.
1969; Bagdasarjan et al. 1970; Repčok 1978, 1981). New
isotope dating of the 4
th
stage rocks (Nos. 22—30, Table 1)
by K-Ar as well as Rb-Sr methods provided ages in the inter-
val 13.0 ± 0.3 Ma to 12.0 ± 0.2 Ma. We have already dis-
cussed above that the probable lower limit on the age of the
4
th
stage rocks is 12.7 Ma. The upper limit is constrained to
12.2 Ma by the overlap with results obtained from younger
rhyolites (Table 1, Fig. 6) and by ages of rhyolites in the
Nová Baňa area in the interval 12.31 ± 0.44—12.03 ± 0.38 Ma
(Lexa & Pécskay 2010). Considering correlation of chrono-
stratigraphic units with the time scale (Kováč et al. 2005;
Harzhauser & Piller 2007), the volcanic activity of the 4
th
stage took place during Early Sarmatian.
Rhyolites of the Jastrabá Formation (5
th
stage)
Rhyolite activity accompanied the resurgent horst uplift
and contemporaneous subsidence of the Žiar Depression. Pa-
lynological evidence points to the Late Sarmatian to Early
Pannonian age (Planderová in Konečný et al. 1983).
With few exceptions the results of previous isotope dating
by the K-Ar and FT methods fall in the interval 12.9—10.7 Ma
(Konečný et al. 1969; Bagdasarjan et al. 1970; Bojko et al. in
Štohl 1976; Merlitsh & Spitkovskaya in Štohl 1976; Repčok
1981, 1982). The results of new dating by K-Ar, as well as
Rb-Sr methods (Nos. 31—37, Table 1) fall in the interval
12.2 ± 0.8 Ma to 11.4 ± 0.4 Ma. This interval is comparable
with the results of K-Ar dating of the Jastrabá Formation
rhyolites in the Nová Baňa area and Kremnické vrchy moun-
tain range that fall into the intervals 12.3 ± 0.4—12.0 ± 0.4 Ma
and 12.3 ± 0.4—11.5 ± 0.4 Ma, respectively (Lexa & Pécskay
2010). Considering correlation of chronostratigraphic units
with the time scale (Kováč et al. 2005; Harzhauser & Piller
2007), the rhyolite volcanic activity of the Jastrabá Forma-
tion (5
th
stage) took place during the Late Sarmatian to earliest
Pannonian time.
Post-rhyolite volcanic formations – high alumina basalts
The volcanic activity of high alumina basalts and basaltic
andesites of the Šibeničný vrch Complex post-dated rhyolite
volcanites of the Jastrabá Formation in the Žiar Depression.
The reported K-Ar ages fall in the range 11.1 ± 0.8 to
8.2 ± 0.5 Ma (Balogh et al. 1998), that corresponds to the
Early to Late Pannonian time. New data are not available.
Post-rhyolite volcanic formations – alkali basalts
K-Ar dating of alkali basalt necks at Kysihýbel (No. 38) and
Banská Štiavnica (No. 39) on whole-rock samples provided
results of 7.8 ± 0.4 Ma and 5.7 ± 0.4 Ma, respectively. While
the first result is compatible with the result of previous dating
(7.31 ± 0.24 Ma, Konečný et al. 1999) the second result seems
to be erroneous as previous dating provided results of
7.24 ± 0.25 Ma (Konečný et al. 1999) and 7.32 ± 0.23 Ma
(Kantor & Wiegerová 1981). The ages of both alkali basalt
necks correspond to the latest Pannonian to Pontian time.
The alkali basalt volcano Pútikov vŕšok is the youngest
volcano in Slovakia. Previous K-Ar dating of its lava flow
using a whole-rock sample provided an age of 0.53 ± 0.16 Ma
(Balogh et al. 1981). Superposition over the Hron river Riss
terrace points to age in the interval 0.15—0.12 Ma (Šimon &
Halouzka 1996), while optically stimulated luminescence
(OSL) dating of underlying sediments provided an age of
102 ± 11 ka (Šimon & Maglay 2005). New K-Ar dating of
groundmass fractions carried out on 3 samples from different
parts of the volcano provided very consistent results of
0.45 ± 0.06 Ma, 0.42 ± 0.06 Ma and 0.43 ± 0.06 Ma, respec-
tively. It follows that the younger ages reported by Šimon &
Halouzka (1996) and Šimon & Maglay (2005) obtained by
indirect methods are questionable.
Ages of mineralization types
The high sulphidation system of Šobov is a part of the
magmatic-hydrothermal system driven by diorite intrusion
(Onačila et al. 1995; Lexa et al. 1999a,b). Such systems are
almost contemporaneous with emplacement of the parental
intrusion (Sillitoe 2010). The Rb-Sr isochron age of diorite
13.3 ± 0.2 Ma (Table 1) represents the best estimate of the
mineralization age. The same type of argument is also appli-
cable for the magnetite skarn and intrusion-related stockwork/
disseminated base metal mineralizations with granodiorite as
the parental intrusion (Onačila et al. 1995; Koděra et al. 1998,
2004; Lexa et al. 1999a). Their age is approximated by Rb-Sr
isochron ages of granodiorite 13.4 ± 0.2 and 13.3 ± 0.6 Ma.
However, considering the relative ages of diorite and grano-
diorite intrusions, these mineralizations are relatively young-
er than the Šobov high sulphidation system. We have no
K-Ar data for the porphyry/skarn Cu ± Au, Mo mineraliza-
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Fig. 7. Evolution of the Štiavnica Stratovolcano. Modified after Konečný & Lexa 2001. Continued on the next page.
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Fig. 7. Continued from the previous page.
tion related to the emplacement of granodiorite porphyry
stocks and dyke clusters (Onačila et al. 1995; Lexa et al.
1999a) and an attempt to apply Rb-Sr isochron method has
not been successful due to rejuvenation (Krá et al. 2002).
Parental intrusions of granodiorite porphyry cross-cut grano-
diorite and are cross-cut by quartz-diorite porphyry dykes of
the Banisko Intrusive Complex. This geological position places
their origin into the time interval 13.1 ± 0.2 Ma.
Association of the epithermal gold mineralization at the
Rozália mine with the early stage of the caldera subsidence
and its origin prior to the emplacement of the quartz-diorite
sills of the Banisko Intrusive Complex (Koděra & Lexa 2003;
Koděra et al. 2005) place evolution of this mineralization into
the time interval 13.0 ± 0.1 Ma.
Kraus et al. (1999) dated illites from the above mentioned
mineralizations. K-Ar dating of 2M
1
type illite from Šobov
provided the age 12.4 ± 0.1 Ma, of 2M
1
> > 1M type illite from
argillites of the stockwork/disseminated base metal mineral-
ization provided the age 11.5 ± 0.3 Ma, while 2M
1
> > 1M type
illite from the epithermal gold mineralization at the Rozália
mine provided the age 11.9 ± 0.3 Ma. Such results are in con-
flict with the established geological position. The Šobov high
sulphidation system is cross-cut by younger base metal epither-
mal veins showing temperatures over 300 °C (Kovalenker et
al. 1991) and the stockwork/disseminated base metal mineral-
ization and epithermal gold mineralization extend next to the
Rozália vein in the hottest Cu-zone of the younger epithermal
system (Onačila et al. 1995), where temperature could reach
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350 °C. A partial to complete rejuvenation due to long lasting
reheating by younger epithermal system is highly probable.
The extensive system of precious/base metal low to inter-
mediate sulphidation epithermal veins evolved during the
uplift of the resurgent horst. K-Ar dating of adularia in epi-
thermal veins provided the ages 12.0—10.7 Ma (Kantor &
Ďurkovičová 1985; Kantor et al. 1988). K-Ar dating of
1M> > 2M
1
type illite from the Terézia vein at the Weiden
gallery provided the age 11.4 ± 0.2 Ma (Kraus et al. 1999).
Rejuvenated ages of 11.5 ± 0.3 Ma and 11.9 ± 0.3 Ma also ob-
tained from 2M
1
> > 1M type illites from older mineraliza-
tions (see above) are considered as indirect data. Dating of
rhyolites to the time interval 12.2—11.4 Ma confirmed that
evolution of the epithermal system took place during and af-
ter magmatic activity of the rhyolites (Kovalenker et al.
1991; Onačila et al. 1995; Chernyshev et al. 1995; Lexa et
al. 1999a; Háber et al. 2001; Lexa 2001). Lexa & Pécskay
(2010) confirmed the same relationship in the case of rhyo-
lites and epithermal system in the Nová Baňa ore deposit.
Lifespan of the Štiavnica Stratovolcano and breaks in vol-
canic activity
The lifespan of the stratovolcano is definitely shorter than
assumed earlier. While Konečný et al. (1983, 1998) assumed
its evolution in the Early Badenian through Early Pannonian
time (16.4—10.7 Ma), the presented results from new K-Ar
and Rb-Sr isotopic dating imply that it was active in the in-
terval 15.0—11.4 Ma (middle Early Badenian—earliest Pan-
nonian). The most prolonged first stage, representing
construction of the compound andesite stratovolcano, took
almost a half of the total duration of volcanic activity
(1.5 Ma out of 3.6 Ma), whereas three later evolutionary
stages representing emplacement of subvolcanic/intravolca-
nic intrusions, caldera subsidence and activity of post-
caldera andesite volcanoes lasted only around 0.5 Ma each
and the 5
th
stage of rhyolite activity lasted around 0.8 Ma.
The results of isotopic dating and their errors provide an il-
lusion of continuous volcanic/magmatic activity. However,
frequent unconformities and evidence for associated exten-
sive erosion (Konečný et al. 1998; Konečný & Lexa 2001)
point to frequent breaks in volcanic activity of variable dura-
tion. Analogy with recent volcanoes implies that in reality
shorter periods of volcanic/magmatic activity were separated
by longer lasting breaks giving opportunities for erosion. Thus
several unconformities between lithostratigraphic units of the
1
st
stage explain its unusually long duration. A longer lasting
break in volcanic activity took place between the 1
st
and 3
rd
stages – prior to initial subsidence of the caldera. During
this break the former compound andesite stratovolcano with
elevation 3000—4000 m had been denudated down to the level
of intravolcanic intrusions and thickness 500—1000 m in the
central zone. However, this break in volcanic activity only
partially overlapped with a break in magmatic activity as
emplacement of subvolcanic/intravolcanic intrusive com-
plexes took place towards its end. Another significant break
in volcanic activity took place following the caldera subsid-
ence. Volcanic rocks of the 4
th
stage andesite volcanoes rest
at many places on a levelled surface over the caldera fault.
Lithostratigraphic units of the 4
th
stage are often separated by
minor unconformities (Fig. 5) implying minor breaks in vol-
canic activity also during this stage. Finally, a major unconfor-
mity and related break in volcanic activity separated the
rhyolites of the 5
th
stage from the andesites of the 4
th
stage.
Conclusions
We have applied the low-blank K-Ar method coupled with
the Rb-Sr isochron method to a representative set of mag-
matic rocks that systematically cover the different structural
units and evolutionary stages of the Neogene Štiavnica Stra-
tovolcano. The K-Ar study of mineral components of com-
mon volcanic rocks has confirmed the phenomena of the
excess radiogenic
40
Ar in plagioclase phenocrysts. There-
fore, our recent geochronological study of the Štiavnica Stra-
tovolcano was based especially upon K-Ar dating of
groundmass fractions. Its combination with the Rb-Sr isoch-
ron dating provided highly reliable results.
Former attempts to date subvolcanic intrusive rocks using
whole-rock samples failed owing to possible effects of con-
tamination and partial rejuvenation due to regional hydro-
thermal alteration associated with the extensive systems of
late stage epithermal veins overlapping with the extent of
subvolcanic intrusions. We have managed to obtain reliable
results for the granodiorite/diorite pluton of the Hodruša
Intrusive Complex using the Rb-Sr isochron method.
Results of new K-Ar and Rb-Sr isotopic dating confirmed
the succession of volcanic/magmatic activity based on re-
sults of geological mapping, superposition of lithostrati-
graphic units and major unconformities. At the same time we
have achieved compatibility between the isotope and bio-
stratigraphic ages of lithostratigraphic units by using the lat-
est version of the geological time scale (Harzhauser & Piller
2007) and biostratigraphic assignment of sedimentary for-
mations (Kováč et al. 2005).
On the basis of new data and critical evaluation of older
evidence, we are able to assign the most probable time inter-
vals to the established evolutionary stages of the Štiavnica
Stratovolcano and volcanic formations below and above.
Based on the above discussion evolution of the Štiavnica
Stratovolcano can be summarized as follows (Fig. 7):
1. Volcanic activity of garnet-bearing andesites at dispersed
centers took place prior to the evolution of the Štiavnica Stra-
tovolcano in the time interval 16.0—14.8 Ma (early to middle
Early Badenian). A partial overlap with volcanic activity of
the lower structural unit (1
st
stage) cannot be excluded.
2. Evolution of the extensive compound stratovolcano of
pyroxene and amphibole-pyroxene andesites took place dur-
ing the time interval 14.8—13.5 Ma (middle Early Badenian
to early Late Badenian). Periods of volcanic activity alternated
with breaks of variable duration represented by internal ero-
sion surfaces and unconformities. The stratovolcano reached
a diameter of 35 to 40 km at the base of the volcanic cone
and a probable elevation of 3000 to 4000 m.
3. Construction of the compound stratovolcano was fol-
lowed by a period of denudation and emplacement of the ex-
tensive subvolcanic intrusive complex of diorite, granodiorite,
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granodiorite porphyry and quartz-diorite porphyry during the
time interval 13.5—12.9 Ma (Late Badenian). The youngest
quartz-diorite sills were emplaced at the time of the initial sub-
sidence of the Štiavnica Caldera.
4. Subsidence of the Štiavnica Caldera accompanied by ac-
tivity of differentiated biotite-amphibole andesites occurred
during the time interval 13.1—12.7 Ma (late Late Badenian).
Volcanic activity overlapped partially with the emplacement
of the youngest quartz-diorite porphyry sills.
5. Renewed explosive and effusive activity of andesites at
centers in the caldera and on the slopes of the stratovolcano
occurred during the time interval 12.7—12.2 Ma (Early Sar-
matian).
6. Resurgent horst uplift accompanied by rhyolite volcanic
activity along marginal faults took place during the time in-
terval 12.2—11.4 Ma (Late Sarmatian to earliest Pannonian).
Uplift of the resurgent horst and activity of the associated
epithermal system continued till 10.7 Ma (Early Pannonian).
7. Sporadic activity of high alumina basalts in the northern
sector of the stratovolcano took place during the time inter-
val 11.1—8.2 Ma (Early to Late Pannonian).
8. Sporadic activity of alkali basalts took place in the time
interval 7.8—7.2 Ma and 0.5—0.25 Ma. The younger age as
reported on the basis of the position above one of the Quater-
nary terraces and OSL dating of underlying sedimentary
rocks is problematic.
The lifespan of the stratovolcano is apparently shorter than
assumed earlier. It was active in the interval 15.0 to 11.4 Ma
(middle Early Badenian to earliest Pannonian), hydrothermal
activity of the late stage epithermal system extending for
1.3 Myr since 12.0 till 10.7 Ma. Periods of volcanic/magmatic
activity were separated by breaks of variable duration repre-
sented by unconformities and related denudation.
Our success in isotope dating of the granodiorite/diorite
pluton and differentiated rocks filling the caldera enabled an
indirect dating of associated mineralizations. Results ob-
tained from rhyolites confirm association of the extensive
late stage epithermal systems with rhyolite magmatism.
We have confirmed that K-Ar dating of groundmass frac-
tion combined with Rb-Sr isochron dating in the cases of
possible rejuvenation provides highly reliable results even in
the case of complex evolution and deeply eroded volcanoes
with exposed subvolcanic intrusions and related hydrother-
mal systems. The precision of the Rb-Sr method “internal”
isochrones applied to Neogene volcanic rocks is limited by
in-homogeneity of the initial
87
Sr/
86
Sr ratios in mineral com-
ponents. Nevertheless, in most cases when the Rb-Sr method
was applied to dating the volcanic and intrusive rocks of the
Štiavnica Stratovolcano, it has provided reliable results with
precision of ± 0.2—0.5 Ma.
Acknowledgments: This study has been carried out in the
framework of the Russian-Slovak scientific cooperation be-
tween the Institute of Geology of Ore Deposits, Petrography,
Mineralogy and Geochemistry of the Russian Academy of
Sciences, Moscow and the Geological Institute of the Slo-
vak Academy of Sciences, Bratislava, project “Genetic and
chronological relations of magmatism and epithermal ore
genesis in the Neogene volcanostructures, Central Slovakia”
(2008—2011). The authors appreciate support by the VEGA
Grant 2/0162/11, Slovakia and Russian Foundation of Basic
Research Grants 09-05-00870, 10-05-00354. Our thanks also
go to our colleagues Dr. M. Háber and Ing. R. Kaňa for their
assistance during the sample collection in field. We are grate-
ful to anonymous reviewers for their constructive remarks that
helped to improve the presentation of our results.
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No. Sample
Rock
type
Fraction
K
(%) ± σ
40
Ar
rad
(ng/g) ± σ
40
Ar
atm
(%)
Age
(Ma) ± 2σ
Volcanic formations pre-dating Štiavnica Stratovolcano
plag
0.454 ± 0.004
0.460 ± 0.005
41.4
14.6 ± 0.4
1
GP-4
px-amph andesite with garnet
gdm
2.19 ± 0.03
2.289 ± 0.009
9.6
15.0 ± 0.4
Lower structural unit (1
st
stage)
2
GK-2/01
Px andesite
gdm
1.80 ± 0.02
1.907 ± 0.010
12.6
15.2 ± 0.4
3
GK-111 Amph-px
andesite
gdm
1.83 ± 0.02
1.880 ± 0.007
12.6
14.8 ± 0.3
plag
0.288 ± 0.003
0.312 ± 0.003
37.3
15.6 ± 0.5
4
GK-110 Amph-px
andesite
gdm
2.07 ± 0.03
2.013 ± 0.011
22.5
14.0 ± 0.4
5
St-6/06 Amph-px
andesite
gdm
1.44 ± 0.02
1.407 ± 0.005
6.7
14.0 ± 0.4
6
St-4/06
Px andesite matrix
gdm
1.61 ± 0.02
1.542 ± 0.016
24.4
13.8 ± 0.4
7
St-5/06
Px andesite fragment
gdm
1.84 ± 0.03
1.762 ± 0.007
6.6
13.8 ± 0.4
8
GK-107 Px
andesite
gdm
1.83 ± 0.02
1.801 ± 0.009
20.5
14.1 ± 0.3
plag
0.421 ± 0.004
0.404 ± 0.003
34.2
13.8 ± 0.4
9
GK-106 Px
andesite
gdm
2.57 ± 0.03
2.460 ± 0.009
11.3
13.7 ± 0.3
10
GP-13 Px
andesite
gdm
2.27 ± 0.03
2.121 ± 0.008
12.8
13.4 ± 0.4
11
St-7/06 Px
andesite
gdm
2.90 ± 0.03
2.740 ± 0.012
23.5
13.5 ± 0.3
12
St-14/06 Px
andesite
gdm
2.67 ± 0.03
2.510 ± 0.020
74.0
13.5 ± 0.4
plag
0.158 ± 0.002
0.165 ± 0.003
73.4
15.1 ± 0.7
13
GK-57 Px
andesite
gdm
2.15 ± 0.03
1.982 ± 0.014
71
13.2 ± 0.4
plag
0.260 ± 0.003
0.213 ± 0.004
71.4
11.8 ± 0.5
14
GP-11 Px
andesite
gdm
2.22 ± 0.03
2.031 ± 0.010
35.7
13.1 ± 0.4
Middle structural unit (caldera filling, 3
rd
stage)
19
GK-100 Px-bt-amph
andesite
gdm
1.85 ± 0.02
1.682 ± 0.010
22.9
13.1 ± 0.3
plag
0.259 ± 0.003
0.273 ± 0.003
39.4
15.1 ± 0.5
bt
7.02 ± 0.08
6.23 ± 0.02
19.1
12.8 ± 0.3
20
GK-16 Bt-amph
andesite
gdm
2.76 ± 0.03
2.27 ± 0.02
36.3
11.8 ± 0.3
plag
0.279 ± 0.003
0.252 ± 0.003
46.5
13.0 ± 0.4
bt
6.04 ± 0.07
5.08 ± 0.04
76.1
12.1 ± 0.3
21
GK-20 Px-bt-amph
andesite
gdm
2.85 ± 0.03
2.345 ± 0.010
41.1
11.8 ± 0.3
Upper structural unit (4
th
stage)
22
St-9/06
Px andesite
gdm
2.60 ± 0.03
2.285 ± 0.013
14.2
12.6 ± 0.3
23
St-10/06
Px andesite
gdm
3.35 ± 0.04
2.914 ± 0.013
17.2
12.5 ± 0.3
plag
0.307 ± 0.012
0.328 ± 0.005
60
15.4 ± 0.6
24
GK-105 Bt-amph-px
andesite
gdm
3.18 ± 0.04
2.818 ± 0.011
20.2
12.7 ± 0.3
26
St-1/06 Px
andesite
gdm
2.55 ± 0.03
2.291 ± 0.011
13.5
12.9 ± 0.3
27
St-11/06
Px andesite ± bt
gdm
3.55 ± 0.04
3.203 ± 0.013
14.4
13.0 ± 0.3
28
St-12/06 Amph-px
andesite
±
bt
gdm
3.61 ± 0.04
3.102 ± 0.016
56.6
12.4 ± 0.3
29
St-15/06 Px
andesite
gdm
2.58 ± 0.03
2.195 ± 0.009
8.5
12.2 ± 0.3
30
St-16/06 Amph-px
andesite
gdm
2.93 ± 0.03
2.451 ± 0.011
9.6
12.0 ± 0.3
Rhyolites of the Jastrabá Formation (5
th
stage)
plag
0.257 ± 0.003
0.245 ± 0.002
17.9
13.7 ± 0.4
bt
6.79 ± 0.07
5.79 ± 0.02
35.3
12.2 ± 0.3
32
GK-21 Rhyolite
gdm
4.48 ± 0.05
3.712 ± 0.013
16.7
11.9 ± 0.3
33
KSD-1 Rhyolite
gdm
8.00 ± 0.09
6.42 ± 0.02
34.2
11.5 ± 0.3
Post-rhyolite volcanic formations — alkali basalts
40
S-B3/02 Nepheline
basanite
gdm
1.50 ± 0.02
0.047 ± 0.001
82.4
0.45 ± 0.03
41
S-B7/02 Nepheline
basanite
gdm
1.32 ± 0.02
0.038 ± 0.002
89.9
0.42 ± 0.03
42
S-B8/02 Nepheline
basanite
gdm
1.05 ± 0.02
0.031 ± 0.001
80.4
0.43 ± 0.03
Results considered as reliable (see text) are indicated by bold letters on grey background. Dated mineral fraction abbreviations: plag – plagioclase, bt – bio-
tite, gdm – groundmass.
Appendix 1
New K-Ar data for rocks of the Štiavnica Stratovolcano.
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Appendix 2
No.
Sample
Rock type
Fraction
Rb (ppm)
Sr (ppm)
87
Rb/
86
Sr ± 2σ
87
Sr/
86
Sr ± 2σ
Isochron age (Ma ± 2σ)
Subvolcanic/intravolcanic intrusive complexes (2
nd
stage)
w.r.
165
382
1.2514 ± 28
0.706937 ± 14
plag
86
790
0.3167 ± 9
0.706790 ± 13
kfs
470
360
3.753 ± 9
0.707464 ± 14
bt I
420
27
45.24 ± 21
0.715240 ± 30
15
St-5/99 Granodiorite
bt II
512
15.6
94.98 ± 47
0.724741 ± 12
13.4 ± 0.2
I
0
= 0.70668 ± 0.00011
MSWD = 10.1
w.r.
176
396
1.282 ± 3
0.706899 ± 13
plag
53
800
0.1911 ± 5
0.706533 ± 14
kfs
456
337
3.911 ± 10
0.707456 ± 13
bt I
422
37
32.901 ± 9
0.713167 ± 14
16
St-2/04 Granodiorite
bt II
528
16
94.14 ± 45
0.724350 ± 12
13.3 ± 0.6
I
0
= 0.70668 ± 0.00036
MSWD = 71
w.r.
60
306
0.567 ± 2
0.708591 ± 10
plag
22
133
0.471 ± 3
0.708652 ± 13
amph
16
25
1.857 ± 9
0.709014 ± 20
17
St-4/08 Diorite
bt
450
6.1
215.3 ± 8
0.749253 ± 17
13.3 ± 0.2
I
0
= 0.70857 ± 0.00022
MSWD = 26
w.r.
91
381
0.6876 ± 20
0.707093 ± 10
plag
29
846
0.0975 ± 5
0.707226 ± 10
amph I
4.7
58
0.235 ± 2
0.707411 ± 12
amph II
5.5
62
0.259 ± 2
0.707337 ± 13
bt I
223
59
10.91 ± 6
0.709426 ± 11
bt II
212
213
2.888 ± 15
0.708360 ± 10
17a
St-2/08
Quartz-diorite
porphyry
matrix
118
339
1.010 ± 3
0.707218 ± 9
(16–11)
Middle structural unit (caldera filling, 3
rd
stage)
plag
2.9
1079
0.00790 ± 12
0.706603 ± 16
amph
19
74
0.7479 ± 22
0.706754 ± 20
18
St-83/91
Bt-amph
andesite
bt
458
32
41.30 ± 17
0.713873 ± 16
12.4 ± 0.1
I
0
= 0.706612 ± 0.000025
MSWD = 0.70
w.r.
120
370
0.939 ± 2
0.707291 ± 14
plag
3.1
1125
0.00798 ± 21
0.706864 ± 18
amph
30
80
1.107 ± 3
0.707217 ± 14
bt I
420
28
43.22 ± 11
0.714890 ± 20
bt II
376
43
25.12 ± 8
0.711653 ± 19
20
GK-16
Bt-amph
andesite
gdm
136
295
1.331 ± 3
0.707265 ± 13
12.9 ± 0.5
I
0
= 0.70701 ± 0.00013
MSWD = 28
Upper structural unit (4
th
stage)
w.r.
74
330
0.6538 ± 15
0.706604 ± 13
24
GK-105
Bt-amph-px
andesite
bt
107
42
26.44 ± 7
0.711121 ± 17
12.3 ± 0.2
I
0
= 0.70649 ± 0.00004
w.r.
147
279
1.527 ± 4
0.706904 ± 14
plag
5.2
767
0.0195 ± 2
0.706574 ± 16
amph
3.8
73
0.1482 ± 7
0.706699 ± 20
bt
387
21
54.40 ± 13
0.715879 ± 24
25
KSD-2
Bt-amph-px
ignimbrite
gdm
206
160
3.702 ± 9
0.707252 ± 16
12.0 ± 0.2
I
0
= 0.706628 ± 0.000071
MSWD = 6.1
w.r.
148
308
1.388 ± 3
0.705541 ± 10
plag
7
888
0.0227 ± 3
0.705257 ± 10
bt
430
31.4
39.76 ± 12
0.712273 ± 10
28
St-12/06
Amph-px
andesite ± bt
gdm
218
190
3.305 ± 8
0.705975 ± 11
12.3 ± 0.7
I
0
= 0.70531 ± 0.00019
MSWD = 17
Rhyolites of the Jastrabá Formation (5
th
stage)
w.r.
226
52
12.52 ± 3
0.708685 ± 14
kfs
147
290
1.469 ± 4
0.706605 ± 10
31
St-18/06 Rhyolite
bt
480
7.5 184.3 ± 5
0.738288 ± 14
12.2 ± 0.8
I
0
= 0.7064 ± 0.0011
MSWD = 42
w.r.
195
116
4.869 ± 11
0.707271 ± 17
plag
3.6
165
0.0657 ± 10
0.706576 ± 20
bt
390
7.8 145.0 ± 4
0.728204 ± 36
32
GK-21 Rhyolite
gdm
252
49
14.94 ± 4
0.708878 ± 18
10.5 ± 0.2
I
0
= 0.70658 ± 0.00015
MSWD = 8.9
bt
470
23
58.81 ± 26
0.716625 ± 11
35
L-8/91 Rhyolite
glass
204
107
5.503 ± 16
0.707486 ± 13
12.1 ± 0.1
I
0
= 0.70654 ± 0.00004
w.r.
206
153
3.901 ± 9
0.707313 ± 11
plag
10.7
936
0.0330 ± 3
0.706673 ± 14
bt
416
20.2
59.50 ± 18
0.716648 ± 10
36
St-6/08B Rhyolite
gdm
212
126
4.808 ± 12
0.707456 ± 11
11.8 ± 0.1
I
0
= 0.706659 ± 0.000021
MSWD = 0.28
Mineral fractions: w.r. – whole rock, plag – plagioclase, kfs – K-feldspar, amph – amphibole, bt – biotite, gdm – groundmass.
Table: The Rb-Sr isotope data and isochrone ages for rocks of the Štiavnica Stratovolcano.
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Fig. A. Rb-Sr isochrone plots for rocks of the Štiavnica Stratovolcano.
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Appendix 3
Localization, geology and petrography of rock samples collected from lithostratigraphic units of the Štiavnica Stratovolcano for
K-Ar and Rb-Sr dating.
For each of the dated samples there are given: number used throughout this paper including the Figure 2; original sample name;
WGS 84 coordinates in the degree/minute/second format; localization in italic; geological position; petrographic description (mineral
abbreviations: Amf – amphibole, Bt – biotite, Cpx – clinopyroxene (augite), Gdm – groundmass, Gnt – garnet, Kfs – K-feldspar,
Ol – olivine, Opx – orthopyroxene (hypersthene), Pl – plagioclase, Px – pyroxene, Q – quartz).
Volcanic formations pre-dating Štiavnica Stratovolcano
1
GP-4
48 31 15.4 N
19 05 55.7 E
Quarry at the Breziny settlement, SW of the city Zvolen.
Lithostratigraphic unit: Neresnica Formation
Geology:
Massive, blocky andesite with obscured banded texture from the internal part of the extrusive dome
Petrography:
Pyroxene–amphibole andesite with garnet
Phenocrysts:
Pl – 2–6 mm, 10–12 %, An
30–50
; Amf – 3–8 mm, 10–11 %, opacitized; Px (glomeroporphyric grains) –
2.3 %; Gnt – 0.4–0.8 cm, 0.7 %
Groundmass:
Microhyalopilitic to micropilotaxitic
Alteration:
Low autometamorphic – chloritization, limonitization
Štiavnica Stratovolcano
Lower structural unit (1
st
stage)
2
GK–2/01
48 19 17.4 N
18 58 42.1 E
Quarry bellow b.m. 408 Žarnosek, loc. Tepličky south of the village Prenčov, southern slope of the stratovolcano.
Lithostratigraphic unit: undefined, position above the Sebechleby Formation
Geology:
Lava flow with a well developed platy and blocky jointing fills up a N–S oriented paleovalley in rocks of
the Sebechleby Formation; owing to its geological setting it was formerly assigned to lava flows of the
upper structural unit
Petrography:
Pyroxene andesite
Phenocrysts:
Pl – 0.2–2 mm, 25–30 %, An
50
; Cpx + Opx – 0.2–2 mm, 10 – 15 %; Q – 0.4 mm, rare
Groundmass:
Cryptocrystalline
3
GK–111
48 18 59.3 N
18 52 14.9 E
Quarry south of the village Baďan, southern slope of the stratovolcano.
Lithostratigraphic unit: Sebechleby Formation
Geology:
Lava flow of massive andesite showing platy to blocky jointing
Petrography:
Amphibole–pyroxene andesite
Phenocrysts:
Pl – 0.5–2.5 mm, An
35–50
; Opx + Cpx – 0.2–2 mm; Amf – rare, opacitized
Groundmass:
Hyalopilitic
4
GK–110
48 23 36.1 N
18 55 51.9 E
Outcrop at the state road south of the village Sv. Anton, southern slope of the stratovolcano.
Lithostratigraphic unit: Sebechleby Formation
Geology:
Block in coarse to blocky epiclastic volcanic breccia; breccia laid down by a lahar makes up a thick horizon
among andesite lava flows
Petrography:
Amphibole–pyroxene andesite
Phenocrysts:
Pl – 3–5 mm, 15 %, An
35–55
; Px – 0.4–2.2 mm, 10 %, Cpx > Opx; Amf – up to 2 mm; Bt – rare
Groundmass:
Hyalopilitic
5
St–6/06
48 17 59.0 N
18 55 13.3 E
Quarry bellow b.m. 529 Šibač, north of the village Sebechleby, southern slope of the stratovolcano.
Lithostratigraphic unit: Sebechleby Formation
Geology:
Lava flow formed of massive andesite with irregular blocky jointing
Petrography:
Amphibole–pyroxene andesite
Phenocrysts:
Pl – 0.5–3 mm, 3 %, An
60
; Opx – 0.5–2 mm, 5–8 %; Amf – 0.3–2 mm, rare
Groundmass:
Hyalopilitic to microlitic
ELECTRONIC SUPPLEMENT — CHERNYSHEV ET AL.: K-Ar AND Rb-Sr GEOGRONOLOGY OF THE ŠTIAVNICA STRATOVOLCANO
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Appendix 3 Continued
6
St–4/06
48 21 39.6 N
18 57 52.7 E
Outcrop at the forest road northwest of the village Královce–Krnišov, southeastern slope of the stratovolcano
Lithostratigraphic unit: undefined, position bellow rocks of the Sebechleby Formation
Geology:
Welded pyroclastic flow deposits or froth lava situated underneath block and ash pyroclastic flow breccias
of the Sebechleby Formation
Petrography:
Pyroxene andesite, welded matrix of breccia
Phenocrysts:
Pl – 1–2 mm, An
30–35
; Opx – 2 mm; Cpx – 0.5 mm
Groundmass:
recrystallized, micropoikilitic
Alteration:
Partial oxidation
7
St–5/06
48 21 39.6 N
18 57 52.7 E
Outcrop at the forest road northwest of the village Královce–Krnišov, southeastern slope of the stratovolcano
Lithostratigraphic unit: undefined, position bellow rocks of the Sebechleby Formation
Geology:
Fragment in welded pyroclastic flow deposits or froth lava situated under–neath block and ash pyroclastic
flow breccias of the Sebechleby Formation
Petrography:
Pyroxene andesite
Phenocrysts:
Pl – up to 1.2 mm, 20 %, An
40–60
; Cpx – 0.6 mm, 5–8 %; Opx – 0.8 mm, 5–8 %
Groundmass:
Microphelsitic, locally micropoikilitic
8
GK–107
48 23 59.8 N
18 57 11.1 E
Small quarry at the state road Sv. Anton – Žibritov, southeastern slope of the stratovolcano
Lithostratigraphic unit: Žibritov Effusive Complex
Geology:
Lava flow of massive andesite shows lamination and platy jointing; it rests upon the eroded surface of the
Sebechleby Formation
Petrography:
Pyroxene andesite
Phenocrysts:
15–25 %, Pl >Px; Pl – up to 2 mm, An
40–70
; Opx – up to 1 mm, Cpx – up to 0.8 mm
Groundmass:
Hyalopilitic
9
GK–106
48 24 00.6 N
18 56 52.7 E
Outcrop at the forest road west of the village Žibritov, southeastern slope of the stratovolcano
Lithostratigraphic unit: Žibritov Effusive Complex
Geology:
Lava flow of massive andesite shows lamination and platy jointing; it rests upon the eroded surface of the
Sebechleby Formation
Petrography:
Pyroxene andesite
Phenocrysts:
20 %, Pl >Px; Pl – up to 1.5 mm, 10–12 %, An
25–40
; Opx; Cpx; Bt – rare
Groundmass:
Hyalopilitic
10
GP–13
48 23 51.3 N
19 05 17.0 E
Cliff bellow the hill Mäsiarsky bok north of the town Krupina, eastern slope of the stratovolcano
Lithostratigraphic unit: Žibritov Effusive Complex
Geology:
Lava flow of massive andesite shows lamination and platy jointing
Petrography:
Pyroxene andesite
Phenocrysts:
35 %, Pl/Px = 2/1; Pl – up to 0.3–0.5 mm, An
35
; Opx – up to 2.5 mm; Cpx; Amph – 0.3–0.5 mm, rare
Groundmass:
Hyalopilitic, locally micropoikilitic
11
St–7/06
48 22 35.2 N
19 02 13.5 E
Quarry Ficberg northwest of the town Krupina, eastern slope of the stratovolcano
Lithostratigraphic unit: Žibritov Effusive Complex
Geology:
Lava flow of massive andesite showing platy or columnar jointing; it rests on rocks of the Sebechleby
Formation
Petrography:
Pyroxene andesite
Phenocrysts:
25 %; Pl – up to 1.5 mm, 15 %, An
60–65
; Opx – up to 1 mm, Cpx – up to 1 mm
Groundmass:
Hyalopilitic
12
St–14/06
48 24 47.9 N
18 26 40.1 E
Abandoned quarry next to the village Machulince, lower one of two lava flows, northwestern slope of the stratovolcano
Lithostratigraphic unit: top of the lower structural unit
Geology:
Andesite lava flow associated with hyaloclastite breccias; it has been formerly assigned to the Inovec
Formation of the fourth stage (Konečný et al. 1998) without any specific arguments
Petrography:
Pyroxene andesite
Phenocrysts:
15–20 %; Pl – 1–3 mm, An
30–35
; Opx; Cpx
Groundmass:
Hyalopilitic
ELECTRONIC SUPPLEMENT — CHERNYSHEV ET AL.: K-Ar AND Rb-Sr GEOGRONOLOGY OF THE ŠTIAVNICA STRATOVOLCANO
iii
Appendix 3 Continued
13
GK–57
48 24 53.1 N
18 26 48.0 E
Abandoned quarry next to the village Machulince, upper one of two lava flows, northwestern slope of the stratovolcano
Lithostratigraphic unit: top of the lower structural unit
Geology:
Andesite lava flow associated with hyaloclastite breccias; it has been formerly assigned to the Inovec
Formation of the fourth stage (Konečný et al. 1998) without any specific arguments
Petrography:
Pyroxene andesite
Phenocrysts:
15 %, Pl >Px; Pl – 2.3 mm, An
45–55
; Px – up to 1.2 mm, Cpx > Opx
Groundmass:
Cryptocrystalline
14
GP–11
48 22 58.6 N
18 37 38.7 E
Outcrop in the valley southeast of the village Tekovská Breznica, western slope of the stratovolcano
Lithostratigraphic unit: middle part of the lower structural unit
Geology:
Lava flow of massive andesite showing irregular blocky jointing
Petrography:
Pyroxene andesite
Phenocrysts:
30 %, Pl/Px = 1/1; Pl – up to 2,5 mm, An
35–50
; Px – up to 2,5 mm, Opx > Cpx
Groundmass:
Microlitic locally microlite–hyalopilitic
Subvolcanic/intravolcanic intrusive complexes (2
nd
stage)
15
St–5/99
48 27 11.0 N
18 46 48.2 E
Small quarry near the Mayer shaft, Hodruša Valley, western part of the resurgent horst
Lithostratigraphic unit: Hodruša–Štiavnica Intrusive Complex
Geology:
Granodiorite pluton, roughly 50 – 100 m below its former roof; it is partially affected by propylitic alteration
Petrography:
Equigranular granodiorite, hypidiomorphic–granular texture, grains 4–5 mm
Minerals:
Hypidiomorphic grains of Pl – An
40–51
, Bt, Amf; allotriomorphic grains of Kfs, Q; rare apatite, titanite,
zircon, magnetite, tourmaline
Alteration:
Propylitization – albitization of Pl, sericite, carbonate, pyrite, secondary quartz
16
St–2/04
48 27 18.9 N
18 46 22.7 E
Outcrop next to gallery entrance, Sandrik in the Hodruša Valley, western part of the resurgent horst
Lithostratigraphic unit: Hodruša–Štiavnica Intrusive Complex
Geology:
Granodiorite pluton, roughly 50 – 100 m below its former roof; it is partially affected by propylitic alteration
Petrography:
Equigranular granodiorite, hypidiomorphic–granular texture, grains 4–5 mm
Phenocrysts:
Hypidiomorphic grains of Pl – An
40–51
, Bt, Amf; allotriomorphic grains of Kfs, Q; rare apatite, titanite,
zircon, magnetite, tourmaline
Alteration:
Propylitization – albitization of Pl, sericite, carbonate, pyrite, secondary quartz
17
St–4/08
48 29 12.6 N
18 51 05.7 E
Pivná dolina Valley, northwest of the village Banky, northern part of the resurgent horst
Lithostratigraphic unit: Hodruša–Štiavnica Intrusive Complex
Geology:
Diorite intrusion at the northern side of the granodiorite pluton, roughly 100 m below the former roof
Petrography:
Equigranular diorite, hypidiomorphic–granular texture, grains 1–2 mm
Minerals:
Hypidiomorphic grains of Pl – An
55–72
, Cpx, Amf, minor Bt; minor allotriomorphic grains of Q and Kfs
Alteration:
Weak propylitization
17a
St–2/08
48 25 20.7 N
18 48 30.1 E
Road–cut in the Richňava Valley, 1 km south of the settlement Banisko, western part of the resurgent horst
Lithostratigraphic unit: Banisko Intrusive Complex
Geology:
Dyke crosscutting andesites of the Lower structural unit; the rock is slightly affected by regional
propylitization
Petrography:
Quartz–diorite porphyry
Phenocrysts:
35 %; Pl, Amf, Bt, rare Q
Groundmass:
Microallotriomorphic granular
Alteration:
Weak propylitization
ELECTRONIC SUPPLEMENT — CHERNYSHEV ET AL.: K-Ar AND Rb-Sr GEOGRONOLOGY OF THE ŠTIAVNICA STRATOVOLCANO
iv
Appendix 3 Continued
Middle structural unit (3
rd
stage)
18
St–83/91
48 27 18.9 N
18 56 34.8 E
Barlangi quarry next to the settlement Kysihýbel, east of the town Banská Štiavnica, southeastern part of the caldera
Lithostratigraphic unit: Studenec Formation
Geology:
The internal part of a large extrusive dome; massive to slightly porous andesite of reddish color shows
blocky jointing and a weak autometamorphic alteration; the locality is quite close the outer zone of argillic
alterations related to the extensive system of younger epithermal veins
Petrography:
Biotite–amphibole andesite
Phenocrysts:
40 %, up to 5 mm; Pl – An
15–35
; Amf, Opx, Q
Groundmass:
Glassy, locally microspherulitic
Alteration:
Weak oxidation
19
GK–100
48 24 54.8 N
18 53 19.0 E
Cliff on to northeastern slope of the hill Sitno, southwest of the village Ilija, southern part of the caldera
Lithostratigraphic unit: Studenec Formation
Geology:
Thick lava flow of massive andesite with blocky jointing; the lava flow is in the upper part of the formation;
the locality is not affected by younger hydrothermal processes
Petrography:
Pyroxene–biotite –amphibole andesite
Phenocrysts:
20–25 %, Pl, Amf>Bt, Opx; Pl – 1.5–2 mm, An
15–35
; Amf – 0.8 mm, Bt – 0.7–3 mm; Opx – up to 0.8 mm
Groundmass:
Glassy, locally partially spherulitic
20
GK–16
48 30 43.9 N
18 54 39.6 E
Cliff northwest of the village Podhorie, eastern part of the caldera
Lithostratigraphic unit: Studenec Formation
Geology:
The marginal part of an extrusive dome; the locality is outside of the zone affected visibly by younger
hydrothermal processes
Petrography:
Biotite-amphibole andesite
Phenocrysts:
30–35 %, mostly Pl; Pl – 3–3.5 mm, An
25–40
; Amf – 2.5–3 mm; Bt – 0.5–3.5 mm
Groundmass:
Spherulitic–microlitic, locally passing into hyalopilitic to microlitic
21
GK–20
48 32 40.6 N
18 56 34.8 E
Outcrop in the roadcut north of the village Močiar, northeastern part of the caldera
Lithostratigraphic unit: Studenec Formation
Geology:
The internal part of an extrusive dome; the locality is outside of the zone affected visibly by younger
hydrothermal processes
Petrography:
Pyroxene–biotite–amphibole andesite
Phenocrysts:
20–25 %; Pl – up to 4.5 mm, An
30–65
,10–15 %; Amf – up to 3.5 mm; Bt – up to 1.5 mm; Opx – 0.8 mm;
Groundmass:
Hyalomicrolitic
Upper structural unit (4
th
stage)
22
ST–9/06
48 13 16.6 N
18 46 41.4 E
Quarry next to Kamenný chotár, southeast of the village Žemberovce, southwestern slope of the stratovolcano
Lithostratigraphic unit: Baďan Formation
Geology:
Andesite lava flow showing blocky to platy jointing; the lava flow associates with hyaloclastite breccia
Petrography:
Pyroxene andesite
Phenocrysts:
10–15 %, Pl>Amf>Px; Pl – 1.5 mm, An
40–60
; Amf, Px – rare
Groundmass:
Pilotaxitic, partially glassy
23
ST–10/06
48 13 30.0 N
18 40 22.1 E
Quarry next to the village Krškany, southwestern slope of the stratovolcano
Lithostratigraphic unit: Baďan Formation
Geology:
Andesite lava flow showing blocky to platy jointing; the lava flow associates with hyaloclastite breccia
Petrography:
Pyroxene andesite
Phenocrysts:
15–20 %, mostly Pl; Pl – 1–2 mm, An
60–70
; Amf – rare, Px – rare
Groundmass:
Hyalopilitic, locally micropoikilitic
ELECTRONIC SUPPLEMENT — CHERNYSHEV ET AL.: K-Ar AND Rb-Sr GEOGRONOLOGY OF THE ŠTIAVNICA STRATOVOLCANO
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Appendix 3 Continued
24
GK–105
48 23 37.1 N
18 55 08.8 E
Cliff at the top of Biely Kameň Hill, north of the village Prenčov, southeastern part of the caldera
Lithostratigraphic unit: Sitno Effusive Complex
Geology:
Andesite with blocky jointing represents the central part of a thick lava flow; the lava flow filled originally
a paleovalley at the top of caldera filling in the southern part of the Štiavnica Caldera
Petrography:
Biotite–amphibole–pyroxene andesite
Phenocrysts:
10–15 %; Pl – up to 3 mm, An
45–60
, 8–10 %; Amf – 0.8 mm, opacitized; Bt – up to 3–3.5 mm
Groundmass:
Hyalopilitic
25
KSD–2
48 25 43.8 N
18 39 48.1 E
Cliffs in the slope above the river Hron, 1.5 km east of the town Nová Baňa, eastern slope of the stratovolcano
Lithostratigraphic unit: Drastvica Formation
Geology:
Andesitic ignimbrite is strongly welded, almost homogenized. Fiamme as well as other oriented texture are
obscured. The sample represents the central part of roughly 100 m thick ignimbrite flow with un–welded
pumice tuffs at the base. Ignimbrite is not affected by hydrothermal alteration, however, west of the locality
there is an extensive extrusive dome of younger rhyolite.
Petrography:
Biotite–amphibole–pyroxene andesitic ignimbrite
Phenocrysts:
45 – 50 %; Pl, Px, Amf, Bt
Groundmass:
Devitrified, cryptocrystalline, pseudofluidal structure
26
St–1/06
48 35 05.2 N
18 59 48.6 E
Small quarry at the road south of the village Hronská Dúbrava, northern slope of the stratovolcano
Lithostratigraphic unit: upper part of the Breznica Complex
Geology:
Lava flow – massive andesite with blocky to platy jointing
Petrography:
Pyroxene andesite
Phenocrysts:
25–30 %, mostly Pl; Pl – up to 3 mm, An
35–55
; Opx –up to 3 mm, Cpx – up to 2 mm
Groundmass:
Hyalopilitic
27
St–11/06
48 16 55.4 N
18 29 51.6 E
Quarry northwest of the village Malé Kozmálovce, western slope of the stratovolcano
Lithostratigraphic unit: Priesil Formation
Geology:
Andesite lava flow passing laterally into hyaloclastite breccias
Petrography:
Pyroxene andesite with rare biotite
Phenocrysts:
25 %, mostly Pl; Pl – 2.5 mm, An
40–60
, 15 %; Cpx – 0.4–1.5 mm, Opx, Bt – rare
Groundmass:
Hyalopilitic, locally micropoikilitic
28
St–12/06
48 18 17.3 N
18 31 52.2 E
Quarry next to the village Kozárovce, southwestern slope of the stratovolcano
Lithostratigraphic unit: Priesil Formation
Geology:
Andesite lava flow passing laterally into hyaloclastite breccias
Petrography:
Amphibole–pyroxene andesite with minor biotite
Phenocrysts:
15 %; Pl – up to 2.5 mm, An
40–60
, 8–10 %; Px – up to 1 mm, Amf – 0.7 mm, Bt – 1.5 mm
Groundmass:
Hyalopilitic
29
St–15/06
48 24 01.3 N
18 28 14.6 E
Quarry at the ridge Krivá 4 km southeast of the village Machulince, western slope of the stratovolcano
Lithostratigraphic unit: Inovec Formation
Geology:
Lava flow – gray massive andesite showing lamination and well developed platy jointing
Petrography:
Pyroxene andesite
Phenocrysts:
20 %, mostly Pl; Pl – up to 1.4 mm; Opx – up to 1.2 mm, Cpx – 0.5 mm, Amf – 0.6 mm, opacitized, rare
Groundmass:
Hyalopilitic to microlitic
30
St–16/06
48 34 14.3 N
18 38 01.8 E
Cliff at the slope of the hill Klenový vrch, 2 km west of the village Ostrý Grúň, northwestern slope of the stratovolcano
Lithostratigraphic unit: Žiar Effusive Complex
Geology:
Lava flow of massive andesite showing blocky to platy jointing
Petrography:
Amphibole–pyroxene andesite
Phenocrysts:
35 %, mostly Pl; Pl – up to 2.5 mm, An
40–65
; Px – up to 2.5 mm, Amf – 0.5 mm, opacitized
Groundmass:
Hyalopilitic to pilotaxitic
ELECTRONIC SUPPLEMENT — CHERNYSHEV ET AL.: K-Ar AND Rb-Sr GEOGRONOLOGY OF THE ŠTIAVNICA STRATOVOLCANO
vi
Appendix 3 Continued
Rhyolites of the Jastrabá Formation (5
th
stage)
31
St–18/06
48 26 24.3 N
18 58 35.0 E
Outcrop at the field road south of the village Banský Studenec, southeastern part of the caldera
Lithostratigraphic unit: Jastrabá Formation
Geology:
Dyke emplaced along the Štiavnica Caldera fault
Petrography:
Rhyolite
Phenocrysts:
15–20 %; Q – up to 2 mm; Pl – 1.5 mm, Kfs, Bt – 1–1.3 mm
Groundmass:
Spherulitic
32
GK–21
48 33 23.5 N
18 56 42.7 E
Outcrop 2 km north of the village Močiar, northern part of the caldera
Lithostratigraphic unit: Jastrabá Formation
Geology:
The central part of a 25 m thick N–S oriented dyke with blocky jointing; the dyke crosscuts rocks of the
Studenec Formation and a lava flow of the Sitno Effusive Complex
Petrography:
Rhyolite
Phenocrysts:
30 %; Q – up to 2 mm; Pl – 3.5 mm, An
35–55
; Kfs – 2.5 mm, Bt – 2 mm
Groundmass:
Felsitic with transition to micropoikilitic
33
KSD–1
48 26 47.8 N
18 38 49.9 E
Northern Štamproch quarry, north of the town Nová Baňa, northwestern part of the stratovolcano
Lithostratigraphic unit: Jastrabá Formation
Geology:
The marginal part of an extensive extrusive dome. Rhyolite at the sampling site is not visibly affected by
hydrothermal alteration. However, visible alteration of the Nová Baňa epithermal system starts about 500 m
south of the sampling site. K
2
O content 9.11 % (Appendix 2) implies K-metasomatism (adularization?).
Petrography:
Rhyolite
Phenocrysts:
20–25 %; Q – 2.5 mm; Kfs – 4.5 mm, Bt – 2 mm, partly altered
Groundmass:
Felsitic with transition to mikropoikilitic
Alteration:
Adularization
34
V–7/91c
48 30 33.7 N
18 47 30.0 E
Cliffs above stone sea west of the town Vyhne, western part of the resurgent horst
Lithostratigraphic unit: Jastrabá Formation
Geology:
The central part of a cryptodome emplaced along marginal faults of the resurgent horst in the center of the
Štiavnica Caldera; rhyolite is affected by subsolidus recrystallization and K-metasomatism – K
2
O content is
10.38 % (Appendix 2)
Petrography:
Rhyolite
Phenocrysts:
35 %; Pl – mostly replaced by adularia, Q – 2.5 mm; Kfs – 4.5 mm, Bt – altered to chlorite
Groundmass:
Felsitic
Alteration:
Subsolidus recrystallization + adularization, chloritization of Bt
35
L–8/91
48 32 24.1 N
18 48 36.7 E
Perlite quarry next to the village Lehôtka pod Brehmi, northwestern edge of the resurgent horst
Lithostratigraphic unit: Jastrabá Formation
Geology:
Perlite block in hyaloclastite breccia; hyaloclastite breccia associates with extrusive dome situated at the
fault zone between the resurgent horst and Žiar Depression
Petrography:
Glassy rhyolite – perlite
Phenocrysts:
10 %, 1–2 mm; Pl, Bt
Groundmass:
Hyaline, locally vesicular
36
St–6/08B
48 32 24.1 N
18 48 36.7 E
Perlite quarry next to the village Lehôtka pod Brehmi, northwestern edge of the resurgent horst
Lithostratigraphic unit: Jastrabá Formation
Geology:
Perlite block in hyaloclastite breccia; hyaloclastite breccia associates with extrusive dome situated at the
fault zone between the resurgent horst and Žiar Depression
Petrography:
Glassy rhyolite – perlite
Phenocrysts:
Pl – 1.7 mm, 8 %; Bt – 1 mm, 7 %; Pl and Bt form glomeroporphyric aggregates
Groundmass:
Hyaline
ELECTRONIC SUPPLEMENT — CHERNYSHEV ET AL.: K-Ar AND Rb-Sr GEOGRONOLOGY OF THE ŠTIAVNICA STRATOVOLCANO
vii
Appendix 3 Continued
37
Kl–1/91
48 27 40.4 N
18 54 36.9 E
Klotilda vein at the12
th
level of New Shaft, Banská Štiavnica; eastern side of the resurgent horst
Lithostratigraphic unit: Jastrabá Formation
Geology:
Rhyolite dyke invading a base metal rich epithermal vein structure; it is affected by strong
hydrothermal alteration
Petrography:
Rhyolite
Phenocrysts:
15 %; Kfs, minor Q, pseudomorphoses of adularia after Pl, altered Bt
Groundmass:
Aggregate of secondary Q and adularia with pyrite grains (0.5–1 %)
Alteration:
Adularization, silicification + pyrite
Post-rhyolite volcanic formations – alkali basalts
38
St–84/91
48 27 40.0 N
18 56 16.5 E
Abandoned quarry at the side of railroad next to the settlement Kysihýbel, east of the town Banská Štiavnica
Lithostratigraphic unit: Alkali basalts
Geology:
Nepheline basanite lava neck – the lava part of a volcanic pipe
Petrography:
Nepheline basanite
Phenocrysts:
Around 40 %; Pl, Cpx, Ol
Groundmass:
Fine-grained
Alteration:
Zeolites in vesicules
39
St–85/91
48 27 42.6 N
18 54 51.3 E
Cliff at the southern side of the Kalvária Hill, eastern side of the town Banská Štiavnica
Lithostratigraphic unit: Alkali basalts
Geology:
Lava neck – remnant of a lava lake in the former maar crater
Petrography:
Nepheline basanite
Phenocrysts:
Fine-grained
Groundmass:
45 %; Pl, Cpx, Ol, minor Bt
40
S–B3/02
48 24 13.5 N
18 38 02.0 E
Quarry next to the road west of the village Brehy, south of the town Nová Baňa
Lithostratigraphic unit: Alkali basalts
Geology:
Lava flow of massive basanite with blocky to columnar jointing
Petrography:
Nepheline basanite
Phenocrysts:
Pl rare, Px rare, Ol – 0.8 mm, minor Bt
Groundmass:
Fine-grained with glass and microlites of Pl, Ol, Cpx, magnetite, ilmenite
41
S–B7/02
48 22 37.0 N
18 38 14.8 E
Cliff at the southwestern side of Pútikov vŕšok Hill, east of the village Tekovská Breznica
Lithostratigraphic unit: Alkali basalts
Geology:
Sample comes from a basanite lava neck in the central part of a scoria cone
Petrography:
Nepheline basanite
Phenocrysts:
10 %; Ol – 0.5–0.6 mm; rare Cpx
Groundmass:
Fine-grained with glass and microlites of Pl, Ol, Cpx, ore minerals, vesicules are rimed by plagioclase
microlites
42
S–B8/02
48 22 29.4 N
18 38 25.6 E
Outcrop at the southern side of Pútikov vŕšok Hill, east of the village Tekovská Breznica
Lithostratigraphic unit: Alkali basalts
Geology:
Sample comes from a thin basanite lava flow at the foot of a scoria cone
Petrography:
Nepheline basanite
Phenocrysts:
10 %; Ol – 1.1–3 mm, rare Pl, Cpx
Groundmass:
Hyaline, porous, showing transitions into hyalopilitic
ELECTRONIC SUPPLEMENT — CHERNYSHEV ET AL.: K-Ar AND Rb-Sr GEOGRONOLOGY OF THE ŠTIAVNICA STRATOVOLCANO
viii
Appendix 4
Major element composition (wt. %) of Štiavnica Stratovolcano dated rocks.
No.
Sample
SiO
2
TiO
2
AI
2
O
3
Fe
2
O
3
MnO MgO CaO Na
2
O K
2
O P
2
O
5
S
LOI Total
Volcanic formation pre-dating Štiavnica Stratovolcano
1
GP - 4
62.48
0.71
14.69
7.24 0.148
2.35
5.16
2.62
2.13 0.173
0.85
98.55
Lower structural unit (1
st
stage)
2
GK - 2/01
60.60
0.58
17.36
6.24 0.112
1.69
6.44
2.78
1.58 0.111 0.01
1.31
98.81
3
GK - 111
60.25
0.68
17.37
6.49 0.105
1.28
6.57
2.69
1.61 0.106
0
1.34
98.49
4
GK - 110
62.44
0.57
16.63
5.31 0.082
1.24
6.37
2.57
1.52 0.097 0.01
1.09
97.93
5
St - 6/06
56.35
0.78
19.16
7.81 0.133
3.56
7.21
2.86
1.40 0.149
0.05
99.46
6
St - 4/06
56.45
0.86
18.52
8.36
0.18
3.58
6.73
2.82
1.50 0.129
0.66
99.79
7
St - 5/06
57.24
0.80
18.79
7.66 0.110
2.82
6.48
2.92
1.65 0.138
1.16
99.77
8
GK - 107
58.74
0.87
16.58
7.41 0.105
1.62
6.61
2.57
1.77 0.122
0
1.38
97.78
9
GK - 106
63.02
0.63
16.45
5.98 0.092
1.38
5.24
2.48
2.60 0.153 0.01
0.27
98.31
10
GP - 13
60.74
0.91
15.33
7.40 0.117
2.75
5.72
2.41
2.49 0.149
0.84
98.86
11
St - 7/06
57.72
0.83
17.12
7.67 0.130
3.83
6.54
2.61
2.33 0.178
0.70
99.66
12
St - 14/06
57.87
1.06
19.25
6.46 0.101
1.62
6.85
2.81
2.68 0.307
0.75
99.76
13
GK - 57
59.68
1.28
16.70
7.23 0.104
1.65
6.13
2.90
2.39 0.272
0.90
99.24
14
GP - 11
60.30
0.85
14.94
7.86 0.145
3.88
5.78
2.34
2.11 0.156
1.37
99.73
Subvolcanic/intravolcanic intrusive complexes (2
nd
stage)
15
St - 5/99
62.45
0.65
15.57
5.69 0.118
2.41
4.57
2.73
3.52
0.19
1.87
97.90
16
St - 2/04
63.90
0.66
15.66
5.48 0.091
2.50
4.56
2.68
3.56
0.18
0.52
99.27
17
St - 4/08
56.47
0.78
16.90
8.32 0.137
4.60
7.36
2.44
1.52
0.15
0.96
99.64
Middle structural unit (caldera filling, 3
rd
stage)
19
GK - 100
65.43
0.46
14.91
4.88 0.082
1.60
4.99
2.03
2.46 0.168 0.02
1.44
98.47
20
GK - 16
65.93
0.58
14.56
4.90 0.095
2.17
4.55
2.32
2.71 0.178
1.85
99.84
21
GK - 20
65.73
0.53
15.48
4.99 0.097
1.82
4.48
2.15
2.85 0.136
2.45 100.71
Upper structural unit (4
th
stage)
22
St - 9/06
56.99
0.91
19.62
6.19 0.118
0.94
7.13
3.28
2.43 0.245
1.56
99.41
23
St - 10/06
63.72
0.91
16.28
5.99 0.035
0.36
3.41
3.69
3.61 0.256
1.37
99.63
24
GK - 105
62.30
0.70
16.82
6.96 0.123
1.91
6.74
2.55
1.64 0.127 0.01
0.80 100.68
25
KSD - 2
69.36
0.62
14.47
2.84 0.024
0.59
3.72
2.43
3.26 0.112
1.18
98.61
26
St - 1/06
56.77
0.91
18.01
7.68 0.107
3.78
6.51
2.83
1.90 0.217
1.09
99.80
27
St - 11/06
58.60
0.96
17.32
6.85 0.113
1.50
5.70
3.37
3.37 0.236
1.73
99.75
28
St - 12/06
65.58
0.72
15.55
4.46
0.05
1.29
4.58
3.13
3.22 0.208
0.92
99.71
29
St - 15/06
59.23
0.69
17.64
7.21 0.172
2.83
5.73
2.98
2.19 0.198
0.77
99.64
30
Št - 16/06
58.66
0.82
17.50
7.45 0.126
3.13
5.88
2.79
2.34 0.198
0.97
99.86
Rhyolites of the Jastrabá Formation
31
St - 18/06
73.73
0.14
13.96
1.85 0.016
0.28
0.48
2.08
5.15 0.010
2.12
99.82
32
GK - 21
77.80
0.12
11.77
1.16 0.022
0.21
1.08
2.50
4.64 0.018
0.82 100.14
33
KSD - 1
72.90
0.14
12.59
1.26 0.012
0.03
0.57
1.12
9.11 0.014
0.53
98.28
34
V - 7/91c
70.98
0.30
14.30
0.36 0.012
0.06
1.12
0.76
10.38 0.020
1.48
98.29
35
L - 8/91
71.36
0.22
13.57
1.70 0.043
0.34
1.30
2.55
5.13 0.040
3.37
99.62
36
St - 6/08B
70.81
0.26
13.78
1.95 0.043
0.43
1.44
2.41
5.20 0.060
3.24
99.62
Post-rhyolite volcanic formations – alkali basalts
38
St - 84/91
48.12
2.65
16.73
11.43 0.162
5.67
8.59
4.00
1.54 0.520
0.46
99.41
39
St- 85/91B
46.52
2.69
14.21
11.49 0.159 10.22
9.02
3.05
1.21 0.430
0.84
99.00
40
S - B3/02
45.61
2.39
14.43
10.59
0.16
6.60
9.27
4.07
1.93 0.693
1.27
97.01
41
S - B7/02
46.70
2.23
15.13
9.65 0.145
6.53
9.70
3.98
1.77 0.731
1.68
98.25
42
S - B8/02
45.43
2.61
13.96
11.73 0.172
9.90 10.32
2.58
1.21 0.526
1.31
99.75
ELECTRONIC SUPPLEMENT — CHERNYSHEV ET AL.: K-Ar AND Rb-Sr GEOGRONOLOGY OF THE ŠTIAVNICA STRATOVOLCANO
ix
Appendix 4 Continued
Comments: Composition of the sample No. 1, representing garnet-bearing andesites pre-dating Štiavnica Stratovolcano, overlaps
with the array of samples No. 2–14, representing the lower structural unit of the stratovolcano. This array lays almost completely in
the field of andesites, only two samples No. 5 and 6 lay in the field of basaltic andesite in respect of the silica contents (Fig. B). On
other side, volcanic rocks of the middle structural unit (caldera filling) correspond to dacite. Rocks of the upper structural unit No.
22–30 show compositions from andesite up to dacite and as a whole are slightly enriched in alkalies, especially Potassium. Analysed
samples of subvolcanic intrusions No. 15–17 show diorite–granodiorite trend. (Fig. B). Composition of rhyolites No. 31–36
corresponds to high-potassium trend with moderate variations of silica content. Two of analysed rhyolite samples No. 33 and 34
show very high K
2
O and low Na
2
O contents as a result of hydrothermal adularization. Alkali basalt samples No. 38–42 project close
to the boundaries of basalt, trachybasalt and basanite fields (Fig. B).
80
70
60
75
65
50
55
40
45
35
10
8
6
4
2
0
12
14
16
SiO (%)
2
N
a
(
%
)
2
O
+
K
O
2
Volcanic formation pre-dating
stratovolcano
Lower structural unit
(1 stage)
st
Subvolcanic intrusions
(2 stage)
nd
Middle structural unit
(caldera filling, 3 stage)
rd
Upper structural unit
(4 stage)
th
Rhyolites of the
Jastrabá Formation
Post-rhyolite volcanic
formations — alkali basalts
++
+
+
+
+
+
+
+
+
trachyte/trachydacite
trac
hyand
esite
rhyolite
basalt
p
ic
ro
b
a
sa
lt
dacite
andesite
basaltic
andesite
basaltic
trachy
andesite
trachy
basalt
tephrite/
basanite
Fig. B. TAS plot for dated rocks of the Štiavnica Stratovolcano.