GeolCarp_Vol53_No5_303

GEOLOGICA CARPATHICA, 53, 5, BRATISLAVA, OCTOBER 2002

303 — 314

RELATIONSHIPS BETWEEN VOLCANISM AND HYDROTHERMAL

ACTIVITY IN THE TOKAJ MOUNTAINS, NORTHEAST HUNGARY,

BASED ON K-Ar AGES

ZOLTÁN PÉCSKAY

and FERENC MOLNÁR

Institute of Nuclear Research, Hungarian Academy of Sciences (ATOMKI), Bem tér 18, 4026 Debrecen, Hungary;

pecskay@moon.atomki.hu

Department of Mineralogy, Eötvös Loránd University (ELTE), Pázmány Péter sétány 1/C, 1117 Budapest, Hungary; molnar@abyss.elte.hu

(Manuscript received June 27, 2001; accepted in revised form March 19, 2002)

Abstract: Conventional K-Ar studies of volcanic rocks, rock-forming minerals and hydrothermal adularia and alunite
from different volcanic centres of the Tokaj Mts indicate that volcanic activity took place between 15.2 and 9.4 Ma
(Badenian—Sarmatian—Pannonian). In the northern part of the Tokaj Mts, ages for the relatively deeply eroded hydrother-
mal systems (Rudabányácska and Telkibánya Au-Ag deposits and parts of the Regéc caldera), formed mainly by the
adularia-bearing low-sulphidation epithermal deposits, are between 13.0 and 12.2 Ma. These systems were developed
within andesitic-dacitic volcanic centres with calderas and subvolcanic intrusions. In the southern parts of the Tokaj Mts
(near Mád and in the Szerencs Hills region) exposures of hydrothermal systems mainly represent shallow acid-sulphate
steam-heated zones of low-sulphidation-type systems, and the K-Ar ages are between 12.1 and 10.4 Ma. Radiometric
ages also suggest that in some parts of this latter area, repeated hydrothermal activity occurred, suggesting that hydro-
thermal circulation developed in relation to different magmatic centres that were active at different times.

Key words: Carpathians, Miocene volcanism, epithermal deposits, K-Ar ages.

Introduction

The  Neogene-Quaternary  volcanic  units  of  the  Carpathians
and  connected  basin  areas  (Pannonian  Basin,  Transylvanian
Basin) are divided into four major groups (Pécskay et al. 1995;
Lexa 1999). The calc-alkaline ignimbrite and felsic tuff units
are  regionally  distributed  in  the  basin  areas  where  they  are
largely  covered  by  young  sediments.  K-Ar  dating  of  these
units (Pécskay et al. 1995) showed that most deposition took
place  between  20  and  10  Ma.  The  low-  to  high-potassium
calc-alkaline  intermediate-felsic  units  are  associated  with
large stratovolcanoes in the Western Carpathians (Central Slo-
vak Volcanic Field, Börzsöny-Dunazug Mts, Mátra Mts, Tokaj
Mts, covered volcanics of the Trans-Tisza Region of Hungary)
and in the Apuseni Mts were formed in the Miocene, between
16  and  7  Ma  (Karpatian—Badenian—Sarmatian—Pannonian).
The  arc-type,  low-  to  high  potassium  calc-alkaline  andesite,
basaltic andesite units are distributed from the Slanské and Vi-
horlat  Mts  through  the  Oas-Gutâi  Mts  to  the  Harghita  Mts.
The major stages of volcanic eruption in this arc occurred from
13 to 0.2 Ma ago. The K-Ar ages for the local alkaline basaltic
volcanism developed in the back-arc extensional regime, are
between 11.5 and 0.35 Ma.

Among the different volcanic groups only the intermediate-

felsic units associated with stratovolcanoes and the andesitic
arc-type units are characterized by metallogenetically impor-
tant hydrothermal activity. Although there is abundant K-Ar
data for the various volcanic rocks from these units (Pécskay
et al. 1995), systematic radiometric age determination of hy-
drothermal activity has rarely been conducted (there are some
data from the Gutâi Mts and the Central Slovak Volcanic
Field; Kovacs et al. 1997; Chernyshev et al. 1995). Thus the
age relationships between the various eruption stages and dep-

osition of hydrothermal minerals in volcanic centers has not
yet been documented. In this paper we present the results of
comparative radiometric dating of volcanic rocks and hydro-
thermal minerals from various volcanic centers and related
mineralized areas of the Tokaj Mts.

General characteristics of volcanism and

hydrothermal activity in the Tokaj Mts

The intermediate-felsic calc-alkaline volcanic rocks of Bad-

enian to Pannonian age of the Tokaj Mts were deposited in a
N-S trending graben-like structure in northeast Hungary (ca.
100 km long and 25—30 km wide; Pantó 1968; Gyarmati
1977). The basement units consist of various Precambrian and
Paleozoic metamorphic rocks, which crop out along the north-
eastern boundary of the graben (Fig. 1).

Miocene volcanism in the Tokaj Mts took place in two ma-

jor  stages  (Gyarmati  1977).  The  older  (Badenian)  volcanic
stage began with ignimbrite and felsic tuff eruptions along the
Szamos Line (Fig. 1). The subsidence of the basement resulted
in marine transgression, and the accumulation of thick Bade-
nian andesitic and dacitic lava flows took place under subma-
rine conditions along the axis of the graben. For the late stage
of Badenian volcanism, some areas were uplifted and andesit-
ic-dacitic subvolcanic bodies intruded into the earlier volcanic
and  sedimentary  units.  The  Badenian  rocks  crop  out  only  in
the  northeastern  part  of  the  Tokaj  Mts;  they  are  covered  by
Sarmatian-Pannonian  volcanic  and  sedimentary  accumula-
tions in other parts of the mountains.

The initial stages of the Sarmatian-Pannonian volcanic cycle

in the Tokaj Mts started in partly subaqueous and partly sub-
aerial conditions, corresponding to a terrestrial environment

VOLCANISM AND HYDROTHERMAL ACTIVITY IN THE TOKAJ MTS 305

dissected by lagoons and bays. This initial stage was charac-
terized by accumulation of felsic tuff commonly intercalated
with shallow marine clay and marl. In the central and northern
part of the Tokaj Mts, initial felsic pyroclastic deposition was
followed  by  formation  of  subaerial  andesitic  stratovolcanoes
(Telkibánya  and  Regéc;  Fig.  1).  Synchronous  with  andesitic
volcanism, rhyolite dome-flow complexes were formed in the
Mád  area  as  well  as  southeast  of  Telkibánya  (Fig.  1).  In  the
late stages of Sarmatian-Pannonian volcanism, andesitic dikes
and  flows  related  to  fissure-volcanism  were  emplaced  in  the
axial part of the mountains. Dacite extruded along the margin-
al zones of the graben-structure. The youngest product of vol-
canism is olivine basalt known from drilling along the eastern
boundary of the graben (Fig. 1).

The magmatism related to both Badenian and Sarmatian-

Pannonian volcanism generated hydrothermal activity. How-
ever, hydrothermal environments in Badenian volcanic rocks
are known mostly from deep drilling; their exposures are limit-
ed  to  the  northeastern  part  of  the  Tokaj  Mts.  (e.g.  the  Rud-
abányácska area; Fig. 1). The mineralized zones in both Bade-
nian  and  Sarmatian  sequences  are  typical  examples  of
low-sulphidation-type epithermal environments, with different
levels of erosion in exposures of various parts of the Tokaj Mts
(Molnár et al. 1999). The most deeply eroded zones are char-
acterized by adularia-sericite alteration, which crops out in the
vicinity  of  Rudabányácska,  Telkibánya  and  Regéc  (Fig.  1).
Remnants of the shallower, acid-sulphate steam-heated alter-
ation zones are also present at Telkibánya and Regéc; howev-
er,  this  type  of  hydrothermal  alteration  predominates  on  the
surface  at  Mád  and  in  the  Szerencs  Hills,  north  of  Szerencs
(Fig.  1).  The  essentially  non-eroded,  distal  environments  of
hydrothermal systems are represented by limnic siliceous and
clay deposits near Mád and Regéc and in several other parts of
the Tokaj Mts.

Detailed K-Ar studies have been conducted on the volcanic

rocks and hydrothermal minerals from the following volcanic
and hydrothermal centers: Rudabányácska, Telkibánya,
Regéc, Mád and the Szerencs Hills.

Method of K-Ar study

The K-Ar age determinations of all samples were carried out

at the Institute of Nuclear Research of the Hungarian Acade-
my of Sciences (ATOMKI), Debrecen, Hungary, except for
some alunite samples (with S35 sample numbers, see Tables 2,
4 and 5) which were analysed at the Okayama University of
Science, Japan.

Fresh to highly altered (>8 wt. % K

O content due to K-

metasomatic  alteration)  volcanic  rocks  from  drillcores  and
outcrops were crushed, then a sample of the crushed rocks was
selected and pulverized. Rock-forming minerals (biotite, am-
phibole, and sanidine) were separated from the host rocks by a
combination  of  magnetic  and  heavy-liquid  methods.  Hydro-
thermal minerals (adularia and alunite) were handpicked from
fractures  and  cavities  of  host  rocks.  Ultrasonic  washing  in
tubes produced clean mineral surfaces. Alunite samples were
chemically treated following the method of Itaya et al. (1996)
to remove small amounts of contaminant phases such as iron

minerals. As a consequence of this treatment, atmospheric ar-
gon contamination was significantly reduced.

Potassium determinations were made on about 100 mg por-

tions of the pulverized samples by means of a flame photome-
ter.  For  Ar  analyses,  approximately  500  mg  of  sample  were
used.  Details  of  analytical  procedures  (potassium  determina-
tions,  Ar  extraction  lines  and  mass  spectrometers)  are  de-
scribed by Balogh (1985) and Itaya et al. (1996). All analytical
errors in this paper represent one sigma standard deviation (i.e.
a 68 % analytical confidence level).

Volcanism, hydrothermal processes and K-Ar ages

in different parts of the Tokaj Mts

Rudabányácska

The felsic pyroclastic deposits (ignimbrite, welded ignim-

brite,  crystal  tuff)  of  Badenian  age  are  only  a  few  hundred
meters thick and they cover Triassic-Jurassic carbonate units
that  are  underlain  by  metamorphic  rocks  at  Rudabányácska
(Gyarmati & Pentelényi 1973). K-Ar ages for biotite and sani-
dine from the pyroclastic deposits are between 15.2 and 13.1
Ma (Fig. 2, Table 1). The eruption centers for ignimbrite are
probably  along  the  Szamos  Line  (Gyarmati  1977);  however,
there  are  also  small  rhyolite  domes  in  the  vicinity  of  Rud-
abányácska that have similar ages (13.0 Ma, Table 1). The py-
roclastic  rocks  were  intruded  by  dacitic  bodies  (Száva  Hill;
Fig.  2),  which  suffered  hydrothermal  alteration.  Subsequent
andesitic dacitic-andesitic lava flows covering ignimbrites are
fresh. K-Ar data for whole-rock and amphibole samples sug-
gest a Sarmatian age for intermediate lava flows in this area
(12.4—12.2 Ma, Table 1).

The hydrothermally altered rocks of the area occur in a NW-

SE oriented zone nearly parallel to the Szamos Line (Fig. 2).
The  most  intense  adularia-sericite-pyrite-hematite  alteration
affected the felsic pyroclastic units of the Bányi Hill and the
dacite intrusion of Száva Hill (Fig. 2). The zone with adularia-
bearing alteration assemblage is surrounded by regional pro-
pylitized  rocks  (Varga-Máthé  1961).  Rocks  with  adularia-
sericite alteration host a siliceous-pyritic disseminated-stock-
work  gold  deposit,  which  was  exploited  in  medieval  times.
According to fluid inclusion data, the deeper zones of the gold
deposit  (Bányi  Hill)  formed  at  temperatures  of  230—300 °C
during boiling of fluids, at a minimum depth of about 300 m
below the paleogroundwater table (Molnár 1994).

The K-Ar age of intrusive dacite from Száva Hill affected

by intense K-metasomatic (K-feldspar-sericite) alteration, is
13.2 Ma (Table 1). The K-Ar age for adularia from the stock-
work deposit of Bányi Hill is 13.0 Ma (Table 1). These data
suggest that hydrothermal mineralization of the area near Rud-
abányácska took place at the end of the Badenian rhyolitic-
dacitic volcanic stage and may be related to emplacement of
shallow intrusions.

Telkibánya

The volcanic and sedimentary sequence of Sarmatian-Pan-

nonian age that is exposed in the vicinity of Telkibánya is

306 PÉCSKAY and MOLNÁR

about 1 km thick and is underlain by Badenian intermediate
volcanic rocks, based on data from the 1240 m deep Telkibán-
ya-2 borehole (Széky-Fux 1970; Gyarmati 1977; Molnár et al.
1999). Interpretation of geophysical data by Zentai (1991) sug-
gests that the depth to the basement is about 2000 m.

Sarmatian volcanism started with ignimbrite and rhyolitic

tuff eruptions from a still recognizable volcanic center at the

northwestern end of Telkibánya village (Horváth et al. 1989;
Fig. 3). The early products of explosive activity accumulated
in subaqueous conditions and are interbedded with clay and
marl as well as coarse siliciclastic sedimentary rocks. The next
stage of volcanic evolution was characterized by the formation
of subaerial andesite stratovolcanic and caldera-like structures.
Horváth & Zelenka (1997) recognized two caldera structures,

Fig. 2. Simplified geological map of the Rudabányácska area (redrawn after Gyarmati et al. 1976), with the locations of samples for K-Ar dating.

Table 1: K-Ar data for fresh and altered rocks and hydrothermal minerals from the Rudabányácska area. 1 – Pécskay et al. (1986).

Volcanic stage,

type of hydro-

thermal alteration

Sample

Location

Type of rock and

mineral

K (%)

40Ar rad

(%)

40Ar rad

(10

-6

ccSTP/g)

Age (Ma)

Reference

1187

Kovácsvágás,
Hallós Valley

rhyolite tuff

biotite

6.71

68.0

3.966

15.2±0.6

pyroclastic

4246

Sátoraljaújhely,

Kopaszka Hill

rhyolite tuff

biotite

6.19

55.9

3.201

13.3±0.5

this study

eruptions

2133

Sátoraljaújhely,

Boglyaska Hill

dacite tuff

biotite

6.58

23.6

3.374

13.2±0.8

this study

699

Sárospatak,

Somlyód Hill

rhyolite tuff

sanidine

5.33

76.0

2.724

13.1±0.5

1181

Sárospatak,

Ciróka Hill

rhyolite

biotite

5.97

59.0

3.015

13.0±0.5

Domes and

479

Rudabányácska,

Kövespatak

amphibole dacite

2.27

17.0

1.101

12.4±1.0

flows

1112

Sátoraljaújhely

Néma Hill

pyroxene

amphibole dacite

2.22

45.0

1.075

12.4±0.5

1111

Sátoraljaújhely

Sátor Hill

pyroxene

amphibole dacite,

amphibole

2.37

0.50

52.0

18.0

1.123

2.420

12.1±0.6

12.3±1.0

Intrusion,

adularia-sericite

477

Rudabányácska,

Nagy Szava Hill

K-metasomatized

dacite

4.94
5.19

61.0
63.0

2.606
2.656

13.3±0.6
13.1±0.6

neutral-alkaline

boiling

5475

Rudabányácska,

Bányi Hill

adularia

10.49

73.3

5.320

13.0±0.5

this study

FRESH ROCKS

ALTERED ROCKS

HYDROTHERMAL MINERALS

308 PÉCSKAY and MOLNÁR

tures (Fig. 3). Gold and silver from these veins was exploited
during the midle ages. The intermediate and felsic volcanic
rocks related to the caldera-like structures are characterized by
strong K-metasomatic (adularia-sericite) alteration along these
veins (Fig. 3) with >8 wt. % K

O content in the rocks (Széky-

Fux 1970; Molnár et al. 1999; Molnár & Pécskay 2000). The
K-metasomatic alteration pinches out at depth and is surround-
ed by a propylitic alteration halo. In some rhyolitic tuff and ig-
nimbrite  units  situated  above  the  adularia-bearing  alteration
zones, an acid-sulphate type steam-heated alteration zone with
kaolinite-alunite  assemblage  is  also  present  (Molnár  1993;
Molnár et al. 1999). The formation of the quartz veins and hy-
drothermal  wall  rock  alteration  occurred  at  temperatures  of
250 to 180 °C, during boiling of hydrothermal fluids. The min-
imum paleodepth of hydrothermal activity was around 200 to
500 m below the groundwater table (Molnár & Zelenka 1995).

The youngest pyroxene andesite dikes of the mineralized

area do not show hydrothermal alteration. This suggests that
the age of hydrothermal activity is older than the 10.9—10.6
Ma. K-Ar ages of the very strongly altered rocks with >8 wt.
% K

O are between 12.4 and 11.5 Ma, and for adularia and

alunite from quartz veinlets and steam-heated alteration zones,
respectively, ages are between 12.5—12.2 Ma (Table 2). These
data  reveal  that  hydrothermal  activity  immediately  followed
the formation of the host rocks related to the caldera-like struc-
tures. The identical K-Ar ages of adularia and alunite indicate
that  precipitation  of  alunite  in  the  steam-heated  alteration
zones  was  synchronous  with  the  deposition  of  adularia  in
veins  formed  during  boiling  within  the  same  hydrothermal
system.

Regéc

In the central part of the Tokaj Mts, around Regéc, there is a

caldera-like  circular  structure,  about  4 km  in  diameter  (Ba-
jnóczi  et  al.  2000).  Data  from  the  Baskó-3  drillhole  (Fig.  4)
shows  that  a  subaerial  stratovolcanic  sequence  consisting  of
andesitic  lava  and  pyroclastic  units  approximately  850  m
thick,  as  well  as  subvolcanic  andesite  bodies,  accumulated
over the Badenian subaqueous intermediate lava flows during
the  Lower  Sarmatian.  The  K-Ar  ages  for  the  stratovolcanic
andesite  lava  flows  and  subvolcanic  units  are  between  13.6
and 12.1 Ma (Table 3). The average of whole rock and biotite
K-Ar data from the dacitic dome situated in the center of the
caldera structure (Fig. 4) is 11.6 Ma (Table 3). The late-stage
pyroxene andesite flows related to fissure volcanism in the vi-
cinity  of  the  caldera  have  K-Ar  ages  between  10.4  and  10.7
Ma (Table 3).

In the area of the caldera at Regéc, there are several hydro-

thermal centers hosted by regionally propylitized stratovolca-
nic andesite units. K-metasomatic (adularia-sericite) alteration
occurs along the quartz veins (Fig. 4). These veins formed at a
temperature  between  170  and  190 °C.  Boiling  hydrothermal
fluids of mainly meteoric origin reacted with igneous rocks at
a minimum depth of 90—150 meters below the paleogroundwa-
ter table (Bajnóczi et al. 2000). In the tuffaceous units of the
stratovolcanic  sequence,  shallow  steam-heated  alteration
zones  with  alunite-argillite  alteration  assemblages  are  also
present. At some places in the caldera, the paleosurface of hy-
drothermal activity is still preserved with hydrothermal erup-
tion breccia and related layered siliceous deposits (Fig. 4).

Table 2: K-Ar data for fresh and altered rocks and hydrothermal minerals from Telkibánya. Reference: 1 – Pécskay et al. (1986).

Volcanic stage,

type of hydro-

thermal alteration

Sample

Location

Type of rock and

mineral

K (%)

40Ar rad

(%)

40Ar rad

(10

-6

ccSTP/g)

Age (Ma)

Average

age (Ma)

Reference

211

Telkibánya-2 drillhole,

173.6 m

amphibole-

pyroxene andesite

1.57

15
33

0.762
0.824

12.4±1.8
13.5±1.5

13.1±1.2

1119

Telkibánya. Fehér Hill

pyroxene andesite

1.65

0.802

12.4±0.7

283

Telkibánya. Csengő adit

pyroxene andesite

1.58

0.749

12.3±0.8

2690

Telkibánya. Kánya Hill

andesite

3.11

1.477

12.2±0.5

this study

Stratovolcanic

1209

Hollóháza. Szurok Hill

pyroxene andesite

1.15

0.542

12.1±0.6

lava flows and

post-caldera

192

Telkibánya-2 drillhole,

182.5-183 m

pyroxene andesite

1.87

20
16

0.870
0.850

12.0±1.3
11.6±1.5

11.8±1.0

domes and cones

3363

Telkibánya, Gyepű Hill

pyroxene andesite

1.51

0.696

11.8±0.5

this study

1117

Telkibánya, Teréz adit

amphibole andesite

2.51

1.132

11.6±0.5

695

Telkibánya. Jó Hill

rhyodacite

4.83

2.373

12.6±0.6

3362

Nyíri Fehér Hill

rhyolite

6.93

3.113

11.5±0.4

this study

Late dikes

360

Telkibánya, Medve Hill

pyroxene andesite

1.79

0.762

10.6±1.4

641

Telkibánya, Baglyas Valley

pyroxene andesite

2.46

1.43

10.9±0.5

Adularia-sericite

2533

Telkibánya. Kánya Hill

K-metasomatized

andesite

10.68

85.1

5.003

12.0±0.5

this study

189

Telkibánya-2. drillhole

19.2-20.0 m

K-metasomatized

andesite

9.03

72
91

4.165
1.696

11.7±0.9
13.2±1.3

12.4±0.8

Neutral-alkaline

2917

Telkibánya. Veresvíz

Valley

adularia

12.46

24.4

5.930

12.2±0.7

this study

boiling

2728

Telkibánya. Veresvíz

Valley

adularia

13.33

95.2

6.442

12.4±0.5

this study

Acid-sulphate

S35-229

Telkibánya. Kánya Hill

alunite

5.97

64.6

2.902

12.5±0.5

this study

steam-heated

S35-231

Telkibánya. Kánya Hill

alunite

8.16

69.3

3.899

12.3±0.6

this study

FRESH ROCKS

ALTERED ROCKS

HYDROTHERMAL MINERALS

VOLCANISM AND HYDROTHERMAL ACTIVITY IN THE TOKAJ MTS 309

Table 3: K-Ar data for fresh and altered rocks and hydrothermal minerals from the Regéc area. Reference: 1 – Pécskay et al. (1986).

Fig. 4. Simplified geological map of the Regéc area (modified from Bajnóczi et al. 2000), with the locations of samples for K-Ar dating.

Volcanic stage,

type of hydro-

thermal alteration

Sample

Location

Type of rock and

mineral

K (%)

40Ar rad

(%)

40Ar rad

(10

-6

ccSTP/g)

Age (Ma)

Average

age (Ma)

Reference

4244

Regéc brook

pyroxene andesite

1.65

0.833

13.0±0.5

this study

4058

Regéc

pyroxene andesite

2.02

1.068

13.6±0.7

this study

4409

Regéc

pyroxene andesite

1.99

1.017

13.1±1.2

this study

4134

Regéc, Soltész Valley

pyroxene andesite

1.89

9.324

12.6±0.8

this study

Stratovolcanic
lava flows and

1196

Baskó-3 drillhole,

879.3-885.3 m

pyroxene andesite

3.29

1.571

12.1±0.5

subvolcanic

bodies

481

Baskó-3 drillhole,

782.4 m

pyroxene andesite

1.69

0.810

12.3±0.6

1217

Baskó-3 drillhole,

660.4-664 m

pyroxene andesite

2.24

1.061

12.1±0.5

1199

Baskó-3 drillhole,

522.1-524.6 m

pyroxene andesite

1.87

0.907

12.4±0.5

Post-caldera

dome

814

Regéc, Vár Hill

dacite

biotite
biotite
biotite
biotite

3.33
4.26

4.1

4.38
6.07

10
58
67
29
62

1.550
1.897
1.848
1.949
2.849

11.9±1.6
11.4±0.5
11.5±0.5
11.4±0.6
12.0±0.5

11.6±0.6

Late dikes and

1198

Baskó-3 drillhole,

158.6-162.6 m

pyroxene andesite

1.99

0.807

10.4±0.5

lava flows

642

Regéc, Tokár Hill

pyroxene andesite

2.00

0.836

10.7±0.6

4031

Regéc, east of the Vár Hill

K-metasomatized

andesite

7.8

3.747

12.3±0.5

this study

Adularia-sericite

4032

Regéc, east of the Vár Hill

K-metasomatized

andesite

8.78

4.105

12.0±0.5

this study

4133

Regéc, Csonkás Hill

K-metasomatized

andesite

6.73

3.103

11.8±0.5

this study

acid-sulphate
steam-heated

4030

Regéc, southern

caldera rim

alunite

6.98

3.315

12.2±0.5

this study

FRESH ROCKS

ALTERED ROCKS

HYDROTHERMAL MINERALS

310 PÉCSKAY and MOLNÁR

The dacite dome in the center of the caldera, as well as the

late-stage andesitic lava flows do not show the hydrothermal
alteration. This suggests that the age of the hydrothermal ac-
tivity is older than 11.6 Ma. In agreement with this, the K-Ar
ages for the rocks enriched in potassium due to adularia-seric-
ite alteration along the veins are between 12.3 and 11.8 Ma
and the age of alunite from a steam-heated alteration zone is
12.2 Ma.

The results of K-Ar age determinations in the vicinity of

Regéc confirm that hydrothermal activity was related to the
formation of the stratovolcanic and caldera structures and pre-
ceded the last stages of volcanism within the caldera and its
surroundings.

Mád

In the southern part of the Tokaj Mts, near Mád, volcanic

rocks of Sarmatian-Pannonian age are exposed. Igneous rocks
of Badenian age are known only from the Tállya-15 drillhole
(Fig. 5) below 1000 m depth (Gyarmati 1977); K-Ar data for a
submarine andesite flow of the Badenian sequence is 14.2 Ma
(Table 4).

The major part of the Sarmatian-Pannonian volcanic se-

quence consists of pumiceous glass tuff, pumiceous tuff, rhyo-
lite crystal tuff and ignimbrite. These pyroclastic rocks accu-
mulated both under subaqueous and subaerial conditions and
are interbedded and intercalated with shallow marine clay and
marl beds, as well as lacustrine clay and silica deposits. Zelen-
ka (1964) recognized five major periods of accumulation of py-
roclastic rocks. The eruption centres are marked by rhyolitic-
dacitic domes and associated pumiceous lava flows (Fig. 5).

The most intensive hydrothermally altered zone is situated

northeast of Mád. In this area, the exposures of volcanic rocks
consist of felsic pyroclastic deposits and dacitic-rhyolitic ex-
trusions and lava flows of the fourth major eruptive period of
the volcanic evolution (Zelenka 1964). K-Ar ages for dacitic
and  rhyolitic  rocks  from  the  fourth  volcanic  period  are  be-
tween 12.8 and 11.1 Ma (Table 4). Accumulation of andesitic
lava  flows,  agglomerates  and  tuffs  followed  this  stage.  The
centre of the andesitic volcanism may be related to the loca-
tion of the subvolcanic andesitic intrusions found in the Mád
23  drillhole  (Fig.  5).  Radiometric  ages  for  the  subvolcanic
andesite  and  andesitic  lava  flows  are  between  11.8  and  11.5
Ma (Table 4). K-Ar data for the rhyolite domes and dacitic ex-
trusions of the fifth volcanic period of the area range from 10.8
to 9.8 Ma (Table 4).

In the area northeast of Mád, the hydrothermal alteration of

rhyolitic tuffs of the fourth and fifth volcanic stages represents
shallow acid-sulphate steam-heated zones of low sulphidation
type epithermal systems (Molnár et al. 1999). The typical al-
teration minerals are kaolinite and alunite associated with si-
licification.  However,  the  steam-heated  alteration  zones  also
contain N-S and NE-SW oriented quartz veins containing 1.7—
2.4 g/t Au in some places (Csongrádi & Zelenka 1995). Some
of these veins have quartz pseudomorphs after bladed calcite
suggesting  that  they  were  formed  in  a  deeper  position  com-
pared to a steam-heated alteration level, during boiling of near-
neutral  hydrothermal  solutions  (at  around  180—200 °C,  at  a
depth of 100—160 m below the paleogroundwater table; Mol-
nár & Bajnóczi 1997). Field and paragenetic observations sup-
port a shallow steam-heated alteration which overprinted the
earlier wall rock alteration and vein formation. Thus we con-

Table 4: K-Ar ages of volcanic rocks and hydrothermal minerals from the Mád area. Reference: 1 – Pécskay et al. (1986); 2 – Itaya et al. (1996).

Volcanic stage,

type of hydro-

thermal alteration

Sample

Location

Type of rock

and mineral

K (%)

40Ar rad

(%)

40Ar rad

(10

-6

ccSTP/g)

Age (Ma)

Average

age (Ma)

Reference

submarine flows

1191

Tállya-15 drillhole,

1195-1200 m

pyroxene

andesite

0.65

0.363

14.2±1.3

1189

Tállya-15 drillhole,

899-904 m

dacite

0.85

0.367

11.1±0.7

4th volcanic

stage, domes and

flows

1197

Tállya-15 drillhole,

518.6-556.7 m

rhyolite

1.29

0.604

12.0±0.8

1008

Mád-24 drillhole,

17.2 m

rhyolite

3.95

0.187

12.2±0.7

879

Bodrogszegi,

Cigány Hill

pyroxene

dacite

2.83

12
35

1.331
1.278

12.1±1.4
11.6±0.9

11.8±0.5

4238

Bodrogkeresztúr

Kakas quarry

rhyolite

4.27

2.124

12.8±0.5

this study

4th volcanic

stage,

intrusions and

1147

Mád-23 drillhole,

189.3-192 m

pyroxene

andesite

1.44

0.645

11.5±1.2

flows

1137

Tállya, Kopasz Hill

pyroxene

andesite

1.92

0.873

11.7±1.1

897

Mád, Harcsa Hill

rhyolite

4.16

1.761

10.8±0.8

5th volcanic stage

832

Bodrogszegi,

Cigány Hill

pyroxene

dacite

2.89

52
58

1.163
1.071

10.3±0.5

9.5±0.4

9.8±0.5

domes and flows

880

Bodrogszegi,

Cigány Hill

dacite

3.07

1.214

10.1±0.8

acid-sulphate

S35-134

Mád, Király Hill

alunite

8.7

25.4

3.705

10.9±0.3

this study

steam-heated

S35-232

Mád, Mogyorós Hill

alunite

7.0

67.8

3.194

11.7±0.5

this study

MAD FM

Mád, Mogyorós Hill

alunite

8.4

30.5

3.822

11.7±0.3

HYDROTHERMAL MINERALS

FRESH ROCKS

312 PÉCSKAY and MOLNÁR

Table 5: K-Ar data for fresh rocks and hydrothermal mineral from the Szerencs area. Reference: 1 – Pécskay et al. (1986).

Fig. 6. Summary of K-Ar data from the various volcanic and hydrothermal centres of the Tokaj Mts. Shaded boxes: range of K-Ar data;
Empty boxes: range of K-Ar data +/- standard deviations.

Volcanic stage,

type of hydro-

thermal alteration

Sample

Location

Type of rock and

mineral

K (%)

40Ar rad

(%)

40Ar rad

(10

-6

ccSTP/g)

Age (Ma)

Reference

1204

Abaújszántó Sulyom Hill

rhyolite

3.80

75.0

1.717

11.6±0.4

Domes and flows

with pyroclastics

1211

Golop, drillhole 51.2-

52.0 m (Somos Hill)

rhyolite, biotite

5.13

39.0

2.337

11.7±0.5

this study

1212

Monok Őr Hill

rhyolite

3.86

30.0

1.697

11.3±0.5

this study

1215

Monok Zsebrik

dacite, biotite

5.76

46.0

2.749

12.2±0.5

this study

725

Legyesbénye, quarry

alunite

7.96
8.11

43 51

3.423
3.422

11.0±0.5
10.9±0.5

acid-sulphate

930

Monok, Kassa Hill

alunite

8.79

3.677

10.7±0.7

steam-heated

932

Megyaszó, Pipiske

alunite

2.75

1.112

10.4±0.7

S35-235

Monok, Kassa Hill

alunite

8.52

59.3

3.760

11.3±0.4

this study

S35-236

Szerencs, Fekete Hill

alunite

3.93

43.1

1.846

12.1±0.3

this study

HYDROTHERMAL MINERALS

FRESH ROCKS

VOLCANISM AND HYDROTHERMAL ACTIVITY IN THE TOKAJ MTS 313

Ma (Fig. 6). This extended magmatism generated several hy-
drothermal systems in different parts of the region and there
was repeated hydrothermal activity in some areas.

The K-Ar ages for the oldest hydrothermal systems are be-

tween 13.0 and 12.2 Ma (Fig. 6). These systems are related to
intermediate (andesitic-dacitic) eruption centres characterized
by subvolcanic bodies which locally intruded into stratovolca-
no and caldera-like structures in the northern part of the Tokaj
Mts. Among these volcanic centres, the hydrothermal activity
may be connected to the emplacement of dacitic intrusions at
Rudabányácska.  However,  in  the  caldera-like  structure  near
Regéc, hydrothermal alteration can be related to the evolution
of an andesitic volcanism and extrusion of the dacite occurred
after  the  hydrothermal  mineralization.  At  Telkibánya,  hydro-
thermal activity appears to be contemporaneous with andesitic
and rhyolitic magmatism. The identical K-Ar ages for strongly
altered  (K-metasomatized)  rocks  with  greater  than  8  wt.  %
K

O content and hydrothermal minerals from the same areas,

indicate that such datings  of  completely  altered  rocks can be
used to determine the ages of hydrothermal activity with a high
confidence. The same ages for strongly altered (K-metasoma-
tized)  rocks,  adularia,  and  alunite  from  some  of  these  occur-
rences  indicate  that  acid-sulphate  steam-heated  alteration  at
shallow  levels  was  contemporaneous  with  adularia-sericite
mineralization in the deeper levels of the same hydrothermal
system.

In the southern part of the Tokaj Mts (in the vicinity of Mád

and in the Szerencs Hills area), the ages of hydrothermal
alunite are between 12.1 and 10.4 Ma; thus, the hydrothermal
systems of this area are slightly younger compared to those of
the northern part of the Tokaj Mts (Fig. 6). In agreement with
this, hydrothermally altered areas in the southern Tokaj Mts are
also less eroded in comparison to the northern Tokaj Mts. In
the southern Tokaj Mts, the hydrothermal activity had an ex-
tended and polystage nature, suggesting that the felsic eruption
centres that were active at different times generated several in-
dependent hydrothermal systems. Succeeding hydrothermal
pulses at some localities are also recognized on the basis of an
overprint of contrasting mineral assemblages.

Acknowledgments: The National Science and Research Fund
(OTKA) No. T 029898 Project supported this work as well as
the  Project  Jap-26  of  the  Hungarian-Japanese  Science  and
Technology Agreement. The authors also express their thanks
to  Dr  Tibor  Zelenka  (Geological  Survey  of  Hungary)  for
countless discussions during this work and to Prof. David H.
Watkinson  (Carleton  U.,  Ottawa),  Dr  Jeffrey  W.  Hedenquist
(Ottawa),  Dr  Jaroslav  Lexa  (Geological  Survey  of  Slovakia,
Bratislava) and to Dr Kadosa Balogh (Nuclear Research Cen-
tre,  Hungarian  Academy  of  Sciences)  for  critical  revision  of
the manuscript.

References

Balogh K. 1985: K-Ar dating of the Neogene volcanic activity in

Hungary: Experimental technique, experiments and methods of
chronological studies. ATOMKI Report D/1, 277—288.

Bajnóczi B., Molnár F., Maeda K. & Izawa E. 2000: Shallow level

low-sulphidation type epithermal systems in the Regéc
caldera, Central Tokaj Mtns., NE-Hungary. Geol. Carpathica
51, 217—227.

Chernyshev I.V., Háber M., Kovalenker V.A., Ivanenko V.V., Jeleň

S. & Karpenko M.I. 1995: The age of the magmatic events and
epithermal Au-Ag-base metals mineralization in the central
zone of the Banská Štiavnica stratovolcano: K-Ar data. Geol.
Carpathica 46, 327—334.

Csongrádi J. & Zelenka T. 1995: Hot-spring type gold-silver miner-

alization in the Tokaj Mts, northeastern Hungary. Geological
Survey of Greece, Spec. Publ. 4, 659—693.

Gyarmati P. 1977: Intermediate volcanism in the Tokaj Mts. Ann.

Inst. Geol. Publ. Hung. LVIII, 1—196 (in Hungarian with ex-
tended English abstract).

Gyarmati P. & Pentelényi L. 1973: Explanation to the geological

map of the Tokaj Mts, 1:25,000, Makkoshotyka-Sátoraljaújhe-
ly. Geological Institute of Hungary, 1—101 (in Hungarian).

Gyarmati P., Perlaki E. & Pentelényi L. 1976: Geological map of

the Tokaj Mts, 1:50,000. Geological Institute of Hungary.

Horváth J. & Zelenka T. 1997: New data on the Telkibánya precious

metal mineralization and their evaluation. Földt. Közl. 127,
405—430 (in Hungarian).

Horváth J., Zelenka T. & Fegyvári T. 1989: Paleovolcanic struc-

tures in the North Tokaj Mountains interpreted on the basis of
satellite imagery and aerial photography. Acta Geol. Hung. 32,
181—190.

Itaya T., Arribas A.Jr. & Okada T. 1996: Argon release systematics

if hypogene and supergene alunite based on progressive heat-
ing experiments from 100 to 1000 °C. Geochim. Cosmochim.
Acta 60, 4525—4535.

Kovacs M., Edelstein O., Gabor M., Bonhomme M. & Pécskay Z.

1997: Neogene magmatism and metallogeny in the Oas-Gutai-
Tibles Mts; a new approach basd on radiometric datings. Ro-
manian J. Miner. Dep. 78, 35—45.

Lexa J. 1999: Outline of the Alpine geology and metallogeny of the

Carpatho-Pannonian region. In: Molnár F., Lexa J. & Heden-
quist J.W. (Eds.): Epithermal mineralization of the Western
Carpatians. Soc. Econ. Geol. Guidebook Ser. 31, 65—18.

Molnár F. 1993: Genesis of epithermal mineralization of the Tokaj

Mts on the basis of fluid inclusion studies. Unpublished PhD
Theses, Eötvös Loránd University, Budapest (in Hungarian).

Molnár F. 1994: Reconstruction of hydrothermal processes accom-

pained by precious-metal enrichment in the area between Sá-
toraljaújhely-Rudabányácska and Vágáshuta, Tokaj Mts,
NE-Hungary. Földt. Közl. 124, 25—42 (in Hungarian).

Molnár F. & Zelenka T. 1995: Fluid inclusion characteristics and

paleothermal structure of the adularia-sericite type epithermal
deposit at Telkibánya, Tokaj Mts, northeast Hungary. Geol.
Carpathica 46, 205—215.

Molnár F. & Bajnóczi B. 1997: Fluid inclusion studies on the sam-

ples from the BD-3 and BD-4 drillholes (Mád, Bomboly) and
genetic interpretation of results. Unpublished reserach report,
Humex Ltd., Hungary (in Hungarian).

Molnár F. & Pécskay Z. 2000: Genesis of processes leading to the

potassium-enrichments in the Tokaj Mts. Földt. Kut. XXXVII/
3, 5—13 (in Hungarian).

Molnár F., Zelenka T., Mátyás E., Pécskay Z., Bajnóczi B., Kiss J.

&  Horváth  I.  1999:  Epithermal  mineralization  of  the  Tokaj
Mtns,  Northeast  Hungary:  Shallow  levels  of  low-sulphidation
type systems. In: Molnár F., Lexa J. & Hedenquist J.W. (Eds.):
Epithermal  mineralization  of  the  Western  Carpathians.  Soc.
Econ. Geol. Guidebook Ser. 31, 109—153.

Pantó G. 1968: Structural-volcanological relationship between the

Tokaj Mts and its surroundings. A. R. Geol. Inst. Hungary from
1964, 215—225 (in Hungarian).