S T U D I A G E O L O G I C A P O L O N I C AVol. 123, Kraków 2004, pp. 279–294.

Geology of the Pieniny Klippen Belt and the Tatra Mts, CarpathiansEdited by K. Birkenmajer

Part XVII

Krzysztof BIRKENMAJER1, Zoltán PÉCSKAY2 & Wojciech SZELIGA3

Age relationships between Miocene volcanismand hydrothermal activity at Mt Jarmuta,

Pieniny Klippen Belt, West Carpathians, Poland4

(Figs 1–8; Tab. 1)

Abstract. In the Pieniny Volcanic Arc (Miocene), the northernmost volcanic arc of the WestCarpathians, hydrothermal activity produced some ore-bearing veins associated with moderate-sizeandesite intrusions. They were subjected to prospecting and mining for gold, silver and lead for a shortperiod at the beginning of the 18th century. K-Ar dating of secondary chlorine-biotite from themineralized zone at Mt Jarmuta, yielded a K-Ar date of 11.35±0.45 Ma. This K-Ar date fits well withthe average K-Ar age (11.34±0.50 Ma) obtained on unaltered andesite sills exposed at Mt Jarmuta. Itindicates a close age-relationship between the emplacement of the andesite intrusion and thesubsequent ore-mineralization during Miocene (Sarmatian) time.

Key words: K-Ar dating, Miocene (Sarmatian), hydrothermal activity, Mt Jarmuta, Pieniny KlippenBelt, West Carpathians

GEOLOGICAL SETTING

Pieniny Volcanic Arc

The Miocene (Sarmatian) volcanics of the Pieniny Mts, West Carpathians (Fig.1), form a swarm of small- to moderate-size hypabyssal andesite bodies, dykes andsills (Fig. 2). They intrude strongly folded Palaeogene flysch rocks in the innermost(southernmost) part of the Magura Nappe (Outer Carpathians), the Jurassic through

1 Institute of Geological Sciences, Polish Academy of Sciences, Cracow Research Centre, ul.Senacka 1, 31-002 Kraków, Poland. E-mail: ndbirken@cyf-kr.edu.pl

2 Institute of Nuclear Research, Hungarian Academy of Sciences, Bem tér. 18/c, 4001 Debrecen,Hungary. E-mail: pecskay@namafia.atomki.hu

3 Institute of Geological Sciences, Jagiellonian University, ul. Oleandry 2a, 30-063 Kraków,Poland. E-mail: szeliga@geos.ing.uj.edu.pl

4 Manuscript accepted for publication September 10, 2004.

280 K. BIRKENMAJER et al.

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The Pieniny Mts andesite intrusions, representing the northernmost sites of theMiocene volcanism in the West Carpathians, occur along a WNW–ESE-trendingline – the Pieniny Andesite Line (PAL) some 20 km long, between the villagesKluszkowce-Czorsztyn in the west and Szlachtowa-Jaworki in the east, parallel/subparallel with the PKB (see Fig. 2). The PAL obliquely traverses the early Mio-cene (late Savian) northern strike-slip boundary fault (NBF) of the PKB (Birken-majer, 1983, 1984). The NBF divides the folded Palaeogene rocks of the MaguraNappe from still stronger folded Mesozoic and Palaeogene rocks of the PKB.

The Grajcarek Unit, hosting about one third of the Pieniny Mts andesite intru-sions, consists of deep-water Jurassic and Cretaceous marine deposits originallylaid down in southern part of the Magura sedimentary basin (Birkenmajer, 1977,1986). They were stripped off their supposedly oceanic crust basement, folded andthrust during the Laramian phase (Cretaceous/Palaeogene boundary), finally ac-creted to leading age of the overriding PKB orogenic arc (Birkenmajer, 1986).Northward from the NBF, the Grajcarek Unit forms basement of the Palaeogeneflysch cover of the innermost part of the Tertiary Magura Nappe.

The Pieniny Mts andesites, which occur at or near to the Outer/Inner Carpathiantectonic junction (see Fig. 1: P), find their equivalents in the west in the MoravianCarpathians (see Fig. 1: M), and in the east – in Transcarpathian Ukraine (see Fig. 1:T), moreover at Vihorlat, Gutai (Baia Mare region, NW Romania), and as a subvol-canic unit at Toroiaga, Radna and Borgon (NW Romania). At these locations, theandesite intrusions belong to the outermost (northernmost) post-collisional lateMiddle Miocene (Sarmatian) volcanic arc of the West Carpathian orogen some 400km long – the Pieniny Volcanic Arc (Birkenmajer, 2003).

Phases of intrusive activity

Two phases of the Miocene intrusive activity have been recognized in the Pie-niny Mts (Birkenmajer, 1962, 1984, 1996; Birkenmajer & Nairn, 1969). Andesitesof both phases are reversely magnetized (Birkenmajer & Nairn, 1965, 1969;Kruczyk, 1968).

The first-phase intrusions, mainly dykes, subordinately sills, are the most nu-merous. Predominantly, they run WNW–ESE and W–E parallel/subparallel withthe NBF. The intrusions are represented by basic to normal to acidic rocks, de-scribed in various papers as magnetite-andesite, amphibole-andesite, amphibole-augite andesite, plagioclase-andesite, etc. (see, e.g., Ma³kowski, 1921, 1958;Youssef, 1978). The andesite bodies are dissected by transverse faults, some synin-trusive (Birkenmajer, 1958a), but mainly post-intrusive (Birkenmajer, 1962, 1984;Birkenmajer & Nairn, 1969).

MIOCENE VOLCANISM 281

282 K. BIRKENMAJER et al.

The second-phase intrusions are areally restricted to thewesternmost part of the PAL (Mt W¿ar and its vicinity). Theyform narrow, tectonically undeformed vertical dykes directedNNW–SSE (Birkenmajer, 1962; Birkenmajer & Nairn, 1969),consisting of fresh, usually coarse-porphyritic amphibole-augite andesite (Ma³kowski, 1921, 1958; Youssef, 1978).

Plate-tectonic position and possible depth of andesitemagma chamber

Xenoliths collected from the Pieniny Mts andesites includea variety of moderately to strongly thermally altered, resp.metasomatized, sedimentary rocks, moreover metamorphic,plutonic and volcanic rocks (Ma³kowski, 1921; Kardymowicz,1957). Most of the sedimentary xenoliths were derived fromJurassic and Cretaceous formations of the Grajcarek Unit andfrom Palaeogene flysch formations of the Magura Nappe,moreover from the Magura-type Palaeogene cover of the PKB(Birkenmajer, 2003).

The metamorphic and plutonic xenoliths are represented bycontinental-crust type rocks. They could have derived, at leastin part, from Upper Cretaceous and Palaeogene exotic-bearingconglomerates which are known from the Grajcarek Unit andthe Magura Nappe. Another source could be tectonic slices oforiginal crystalline basement of flysch nappes, if present underthe innermost part of the Outer Carpathian accretionary prismwhich overrides the North European Plate (Fig. 3).

The volcanic xenoliths could have derived from ?olderhypabyssal/abyssal intrusions associated with the Pieniny Vol -canic Arc (Birkenmajer, 2003) – Fig. 3.

Magmatic chamber of the Pieniny Mts andesites had proba-bly formed in basal, innermost part of the Outer Carpathian ac-cretionary prism, possibly at a depth of 10–20 km (Trua et al.,in preparation; Birkenmajer, 2003, fig. 4).

Age of andesite intrusions by K-Ar dating

The first whole-rock K-Ar dating of the 2nd phase andesiteintrusions at Mt W¿ar, yielded an isochron age of 12.6 Ma(Birkenmajer et al., 1987). A slightly older date, 13.5±1 Ma,was obtained on monomineral hornblende fraction from thesame site ten years later (Bukowski et al., 1997). The K-Ar dat-ing programme of the Hungarian and Polish Academies of Sci-ences that followed, included the whole-rock, groundmass andmonomineral (hornblende and feldspar) fractions of the 1st and

MIOCENE VOLCANISM 283

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the 2nd phase andesites from 27 sites in the Pieniny Mts. Altogether, 40 K-Ar dateswere obtained, their age-range varying between 13.5 and 11 Ma (Birkenmajer &Pécskay, 1999, 2000). This implied the Sarmatian age of the andesite intrusive ac-tivity. Its upper age limit (ca 10.8 Ma) coincides well with the Middle/Late Miocene(Sarmatian/Pannonian) boundary age established at 11 Ma (Vass & Balogh, 1989).

GEOCHEMICAL FEATURES OF THE PIENINY MTS ANDESITES

The Pieniny Mts calc-alkaline igneous rocks are represented by high-K basalticandesites (HKBA), and medium-K andesites (MKA). Their major and trace ele-ments characteristics range between subduction- to collision-related magmas,while multi-element patterns with positive LILE (e.g., K, Rb, Ba) anomalies in re-

284 K. BIRKENMAJER et al.

Fig. 3. Position of the post-collisional Pieniny Volcanic Arc (Sarmatian), West Carpathians: aplate-tectonic model (after Birkenmajer, 2003, fig. 4). Inner Carpathian Overriding Slab: 1 – Tatriccrystalline core (pre-Triassic); 2 – Subtatric (Fatric) meso-Cretaceous nappes; 3 – post-orogenicPalaeogene cover (Oligocene Podhale flysch basin with Eocene sedimentary base); 4 – PieninyKlippen Belt (PKB). Outer Carpathian Accretionary Prism: 5 – Savian–Styrian flysch nappes (MNF– Magura Nappe front; CF – Carpathian front); 6 – hypabyssal andesite intrusions (A) and supposedlocation of their magmatic chamber; 7 – bottom thrust surface of the overriding slab and itsaccretionary prism. North European Platform Underthrust Slab: 8 – Miocene Foredeep molassebasin, inner part; 9 – Precambrian crystalline rocks overlain by Palaeozoic and Mesozoic platformdeposits

spect to HFSE (Nb, Ta) are characteristic of subduction-related magmas. A strongPb positive anomaly observed in the HKBA rocks (1st phase andesites) suggeststhat a continent crust-derived component had been involved in their petrogenesis(Birkenmajer et al., 2000; Trua et al., in preparation).

ANDESITE ALTERATION AND ORE-MINERALIZATION

In the eastern part of the PAL, at Kroœcienko, Szczawnica and Mt Jarmuta, the1st phase andesites are often strongly carbonatized/calcitized (Ma³kowski, 1921;Birkenmajer, 1956, 1958a; Kardymowicz, 1957). East of Szczawnica, at Mt Jar-muta and Mt Krupianka, these andesites were locally affected by propylitizationand mineralization caused by hydrothermal activity (Gajda, 1958a, b). As a result,small metalliferous ore bodies were formed at contact of andesite intrusion withsedimentary country rocks (Ma³kowski, 1918, 1921, 1958; Wojciechowski, 1950,1955, 1965; Banaœ et al., 1993; Soko³owska & Wojciechowski, 1996; Szeliga &Michalik, 2003). From 1732 to 1738, these ore bodies were mined for gold, silverand lead (Matras, 1959) at three locations: (1) Mt Krupianka (a horizontal miningshaft); (2) Pa³kowski Stream (a vertical shaft); and (3) Mt Jarmuta, eastern slope(two horizontal adits linked by a dip-slip shaft). The first site is not available anymore for detailed geological and mineralogical studies due to the shaft collapse.The second one is completely filled with stream water. Fortunately, the Mt Jarmutasite (Figs 4, 5) is still well preserved, being accessible for studies of mineralizationprocesses and their age.

MT JARMUTA MINING SITE

The Mt Jarmuta mining site has recently been re-examined by Szeliga and Mi-chalik (2003). Samples were taken from mineralized amphibole-augite andesitebody (Fig. 5) for K-Ar dating of biotite, aimed at age determination of ore-forminghydrothermal processes. At Mt Jarmuta, there is a good background for determin-ing geological age of intrusive activity, with four K-Ar whole-rock dates,11.09±0.55 Ma through 11.64±0.51 Ma (Tab. 1), obtained from several fresh-preserved amphibole- and amphibole-augite andesite bodies (Birkenmajer &Pécskay, 1999, 2000) – see Fig. 4.

Sampling

Samples for petrological investigations were collected from two sites at Mt Jar-muta: (1) from an amphibole-andesite intrusion exposed at Malinowa quarry (sites11–12 of Birkenmajer & Pécskay, 1999, fig. 4; Birkenmajer & Pécskay, 2000, fig.5); and (2) from ore-bearing vein exposed in an early 18th century (Matras, 1959)exploitation adit (Birkenmajer & Pécskay, 2000, fig. 5: S; Szeliga & Michalik,2003).

(1) Mt Jarmuta: Malinowa quarry. This is an amphibole-andesite (Ma³-kowski, 1921, 1958) 1st phase intrusion, a south-dipping sill emplaced in folded

MIOCENE VOLCANISM 285

Lower Jurassic through Upper Cretaceus rocks of the Grajcarek Unit (Birkenmajer,1956, 1958a, b, 1979). Its K-Ar whole-rock age is: 11.09±0.55 Ma (site 11) and11.40±0.47 Ma (site 12), respectively (Tab. 1; Birkenmajer & Pécskay, 1999,tab. 2).

(2) Mt Jarmuta: old mine. Samples S1J13–15 for mineralogical investigation(contact metamorphism alterations), and sample S2J21 for K-Ar dating of hydro-thermal Cl-enriched biotite, were collected from altered amphibole-augite andesiteat its contact with ore-bearing vein of the old adit (Fig. 5).

Methods applied in petrographic/mineralogical study

The above samples (1, 2) were studied using optical microscopy, both in trans-mitting and reflected light. X-ray diffractometry (Philips X’Pert APD apparatus)was used for identification of mineral components. Powdered preparations were in-vestigated in Cu monochromatized radiation using graphite monochromator. Peli-tic fraction was separated using Mery-Jackson method. Infrared spectrometry

286 K. BIRKENMAJER et al.

Fig. 4. Simplified geology of Mt Jarmuta and location of K-Ar dated sites (geology partly afterBirkenmajer, 1958a, b, 1979; ages of sedimentary rocks after Birkenmajer, 1977; K-Ar dated sites –after Birkenmajer & Pécskay, 1999, 2000). 1, 2 – Grajcarek Unit (1 – Jarmuta Fm.: Maastrichtian; 2 –Campanian–Toarcian deposits); 3 – 1st phase amphibole-andesite sills; 4 – 1st phase amphibole-augite andesite sills; 5 – contact and hydrothermally altered deposits; 6 – Middle Miocene transversalfaults; 7 – Quaternary cover; 8 – K-Ar whole rock-dated andesite sites; S – old mining site at Jarmuta(site of K-Ar dated biotite sample – cf. Fig. 4, Tab. 1)

MIOCENE VOLCANISM 287

Table 1

K-Ar dates from fresh-preserved andesite intrusions (sites 11, 12, 20, 21), and fromhydrothermally-altered andesite intrusion (site S), at Mt Jarmuta (data from Birkenmajer& Pécskay, 1999, 2000, and the present paper). The K-Ar dating was performed at the

Institute of Nuclear Research, Hungarian Academy of Sciences, Debrecen

Lab. No Sample No K % 40Ar rad. (%)40Ar rad.(ccSTP/g)

K-Ar age (Ma)

4643 11 (wr)1.361.40

av 1.38

36.2 5.880 × 10–7 11.09 ± 0.55

4694 12 (wr) 1.37 54.4 6.091 × 10–7 11.40 ± 0.47

5011 20 (wr)1.591.67

av 1.63

54.6 7.131 × 10–7 11.22 ± 0.46

5010 21 (wr)1.261.28

av 1.27

45.2 5.766 × 10–7 11.64 ± 0.51

6341 S2J21 (bio) 6.66 60.3 2.948 × 10–6 11.35 ± 0.45

(av – average; bio – biotite; wr – whole rock)

Fig. 5. Sketch-map of old adit, Mt Jarmuta mine (cf. Fig. 4), with location of investigated samples.High-temperature alteration zone shaded. S1J15 – andesite/altered sedimentary rock contact; S1J24 –andesite with small amount of high-temperature minerals; S1J21 – andesite with chlorine-rich biotiteused for K-Ar dating of hydrothermal processes

(Bio-Rad FTS-135 type spectrometer) analysis, and a study using scanning electronmicroscope (JEOL JSM 5410) with energy dispersive spectrometry (NORAN,Voyager 3100), were also performed. The samples studied were coated with carbonfilm.

Contact- and hydrothermal alterations in sedimentary country rocks

The Upper Cretaceous sedimentary rocks around the andesite intrusion and theore-bearing vein were subjected to alterations by contact-metamorphism and hy-drothermal processes, respectively (Szeliga & Michalik, 2003). The contact ther-mal alterations in sedimentary rocks were recognizable already in the field due tochange of their colouration, from greenish and red (if unaltered) to black (if al-tered).Two main contact-metamorphic mineral zones have been recognized.

The first zone, located closest to the contact with the andesite intrusion, yieldedsanidine, diopside, wollastonite, pigeonite and cristobalite. Determination of sani-dine and cristobalite was based on the XRD pattern study; it also indicated that thesanidine phase was accompanied by another potassium feldspar phase (?orthoclase– samples S1J13–15 – Fig. 6).

The second zone, located farther off the contact with the andesite intrusion,yielded wollastonite, diopside and garnet.

Still farther off the contact with the andesite, only recrystallization of detritalminerals, accompanied by enrichment in Fe, Ti and Fe-Ti oxides, has been ob-served in altered sedimentary rocks. Farthest from the contact, calcite, siderite andclay minerals (chlorite and kaolinite) occur in practically unaltered sedimentaryrocks. Sulphides (pyrrhotite, chalcopyrite and pyrite) – products of hydrothermalactivity – occur both in altered and unaltered sedimentary country rocks.

Stages of alterations in andesite intrusion and ore-bearing vein

A rich mineral assemblage occurs in the andesite intrusion adjoining the ore-bearing vein. The thermal-contact type minerals, sanidine and wollastonite, formanhedral grains, discrete grains and complex intergrowths with other secondaryminerals.

The hydrothermal type minerals originated during several consecutive stages,depending on changing conditions of hydrothermal regime, on distance from theore vein and the core of the intrusion:

(1) During the first stage, probably at highest temperatures, poikilitic, ratherhigh-chlorine biotite growths, with inclusions of quartz, chlorine apatite and,rarely, feldspars, had been formed (Fig. 6). Presence of high Cl content in the biotiteindicates that it is a secondary, and not primary, mineral of the andesite, thus beingsuitable for K-Ar dating of the hydrothermal processes (sample S2J21 – Radiocar-bon Laboratory sample No 6341 – see Tab. 1);

(2) During the second stage, at lower temperatures, pyrrhotite, pyrite, chalcopy-rite, very rarely also electrum and epidote, had grown. This stage corresponds topropylitization;

288 K. BIRKENMAJER et al.

(3) During the third stage, carbonatization of the andesite (e.g., Ma³kowski,1921, 1958; Birkenmajer, 1956, 1958a) was caused by cool carbon dioxide-richwaters;

(4) During the fourth stage, under low pH and temperature conditions, primarysulphides were being replaced by products of their alteration, e.g., chalcopyrite bycovelite (Fig. 7), and pyrrhotite by marcasite. In strongly altered rocks, Fe-hydroxides replaced earlier minerals, such as pyroxene, sulphides, etc.

Silicification and argillitization (chloritization) accompanied the hydrothermalprocesses in question during the first and the second stages.

The ore-bearing vein was subject to alterations similar to those recognized in theandesite intrusion and its country rocks (see Wojciechowski, 1950, 1955, 1965;Soko³owska & Wojciechowski, 1996; Banaœ et al., 1993; Szeliga & Michalik,2003), with addition of kaolinitization of the biotite, and the appearance of coarse-crystalline vermiculite (Fig. 8).

MIOCENE VOLCANISM 289

Fig. 6. Sample S2J21, Mt Jarmuta, old adit. SEM image of poikilitic biotite and its EDS spectrum.Poikilitic minerals include mainly quartz, plagioclase, and Cl-bearing apatite

RADIOMETRIC DATE AND GEOLOGICAL AGE OFHYDROTHERMAL PROCESSES AT MT JARMUTA

Fresh to slightly altered intrusive andesites from Mt Jarmuta yielded four K-Ardates between 11.64±0.51 Ma and 11.09±0.55 Ma (Birkenmajer & Pécskay, 1999,2000). Taking into account possible alterations by hydrothermal activity, the oldestdate (11.64±0.51 Ma) gives the best approximation of the real geological age of em-placement of the andesite magma. The youngest date (11.09±0.55 Ma) may beslightly younger than the geological age of the intrusion because of some argon lossdue to hydrothermal activity.

The Cl-enriched biotite was separated from sample S1J21 collected at the MtJarmuta mine (see Fig. 4). It was K-Ar dated at the Institute of Nuclear Research,Hungarian Academy of Sciences (ATOMKI) in Debrecen, Hungary (Lab. No 6341– Tab. 1). Potassium determination was made on about 100 mg pulverized mo-nomineral fraction of this secondary biotite using flame photometry with a Li inter-nal standard and Na buffer. Approximately 200 mg biotite sample was degassed byhigh frequency induction heating.

Details of analytical procedures (Ar extraction, purification, and isotope dilu-tion method for Ar analyses) were those described by Balogh (1985). The K-Ar age

290 K. BIRKENMAJER et al.

Fig. 7. Chalcopyrite replaced by covelite (late stage of hydrothermal activity), sample S2J20. MtJarmuta, old mine

was calculated using the decay constants proposed by Steiger and Jäger (1977). Allanalytical errors represent one sigma standard deviation, i.e. a 68% analytical con-fidence level.

Considering that the monomineral fraction of our biotite is suitable for K-A de-termination, because of its purity, high potassium content, and high 40Arrad percent-age, its K-Ar date, 11.35±0.45 Ma, can be regarded as a reliable geological age ofthe hydrothermal processes which produced ore-bearing vein at Mt Jarmuta. Verysimilar K-Ar ages of the andesites and of the Cl-enriched biotite (Tab. 1) indicatethat the hydrothermal system obviously was related to the intrusive magmatism: thehydrothermal waters subsequently followed the intrusion emplacement in sedi-mentary rocks. Similar conclusions have been drawn on K-Ar dating of differenthydrothermal systems within the Carpathian–Pannonian region (Chernyshev et al.,1995; Kovács et al., 1999; Pécskay & Molnár, 2000).

REFERENCES

Balogh, K., 1985. K/Ar dating of Neogene volcanic activity in Hungary: experimental technique,experiences and methods of chronological studies. ATOMKI Report, D/1: 277–288.

Banaœ, J., Nieæ, M. & Salomon, W., 1993. Bismuth tellurides from the Jarmuta hill (Pieniny Mts).Mineralogia Polonica, 24: 33–40.

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Fig. 8. Coarse vermiculite from hydrothermal ore-vein, sample S2J26. Mt Jarmuta, old mine

Birkenmajer, K., 1956. Badania geologiczne andezytów okolic Szczawnicy (Geological researches ofandesites in the vicinity of Szczawnica, Pieniny Klippen Belt). Przegl¹d Geologiczny(Warszawa), 2: 72–74.

Birkenmajer, K., 1958a. Nowe dane o geologii ska³ magmowych okolic Szczawnicy (Newcontributions to the geology of magmatic rocks of the Szczawnica area within the Pieniny KlippenBelt). Prace Muzeum Ziemi (Warszawa), 1: 89–103.

Birkenmajer, K., 1958b. Przewodnik geologiczny po pieniñskim pasie ska³kowym, cz. I–IV (PieninyKlippen Belt of Poland. Geological Guide. Parts I–IV – in Polish). Wydawnictwa Geologiczne,Warszawa.

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