Sedimentary Zeolite Deposits in Croatia

I = Italy; SLO = Slovenia; H = Hungary; SRB = Serbia; BIH = Bosnia and Herzegovina; MNE = Montenegro

Introduction: Both of the sedimentary zeolite deposits in Croatia (see map) are of Early Miocene
Age. They are located in the northern part of Croatia, which geologically belongs to
the Pannonian Basin System (PBS), extension structure formed at the beginning of
the Miocene as a result of continental collision of Africa (Adriatic microplate) and
Europe. The PBS is surrounded by mountain chains comprising the Alps,
Carpathians and Dinarides, and palaeogeographically it occupies most of the
Central Paratethys realm. Two basins with different depositional histories evolved
in the area of north Croatia during the Early Miocene: the Hrvatsko Zagorje Basin
(HZB), which occupied a small area in the north-westernmost part extending
westwards into Slovenia, and the North Croatian Basin (NCB), that covered almost
the entire area of north Croatia. Very important depositional differences occurred
between the basins in the Early Miocene. The HZB was a part of the Central
Paratethys characterized by brackish to marine deposition from the end of
Oligocene/beginning of Miocene (Egerian and Eggenburgian) through almost the
whole Miocene, except from the second part of Early Miocene (i.e. during late
Ottnangian and Karpatian) till early Middle Miocene (i.e early Badenian). In the
NCB deposition commenced later, in the Ottnangian, with the formation of
continental environments after a long-lasting emersion. This was replaced by
marine sedimentation in the Middle Miocene, i.e. in the middle Badenian (Pavelić
and Kovačić, 2018 and references therein).
 POLJANSKA

Zeolite occurrence: Analcime bearing sedimentary rocks.

Poljanska quarry: (left) general view; (right) typical laminated carbonate-analcime sedimentary rock.

Geology: The Early Miocene (Ottnangian) Poljanska deposit was formed in the NCB, an
elongated rift-type basin generated by continental passive rifting that commenced
in the Early Miocene, when normal listric faulting generated extension of the
basin. The extensional tectonics formed four half-grabens as elongated
subbasins that represented main depocentres. The Poljanska deposit is located
in one of them, namely the Bjelovar Depression that continues into the Požega
Depression. The basin evolved in two phases: the syn-rift phase which lasted
from the Ottnangian until the middle Badenian, and the late Badenian to the
Quaternary post-rift phase. The syn-rift phase was characterized by depositional
environments that changed from continental to marine environments (Šćavničar
et al., 1983; Pavelić et al., 2016; Kovačić et al., 2017). The rocks exposed in the
Poljanska quarry were deposited in shallow lacustrine environments which
predate the Middle Miocene marine transgression of the Paratethys Sea. The
lacustrine deposition most probably commenced in the Early Miocene and
continued during the Middle Miocene. These geological periods are characterised
by the alternation of warm and wet subtropical periods and periods of hot and
arid climate, together with abundant volcanic activity. During the humid climate in
fresh- or brackish-water lacustrine environments, pelites and marls were
deposited. In contrast, during arid climate periods dolomites and hydrous Ca-
bearing magnesium carbonate (HCMC) were deposited in a lake which had
characteristics of an isolated salina-type lake. Dolomite layers alternate with
analcimolite layers, which are a result of the alteration of tuff and/or clay minerals
in an alkaline lake environment (Šćavničar et al., 1983). Tuff and tuffite layers
indicate abundant volcanic activity at the end of the Early Miocene and the
beginning of the Middle Miocene in the area of the SW PBS. Such activity
produced large quantities of pyroclastic material, which altered into smectite
during humid periods or into analcime during more arid periods. Sandstone beds
from the upper part of the succession indicate that metamorphic and granitoid
basement rocks of the PBS were exposed on the surface, providing clastic
material. The increased supply of the sandy material, along with the deposition of
marly sediments, indicates a gradual establishment of more humid conditions and
the formation of a large open lake in the Lower Badenian, which was later, during
the Badenian, around 15 Ma ago replaced by a marine setting (Šćavničar et al.,
1983; Pavelić et al., 2016; Kovačić et al., 2017).
Mineralogy: In the quarry a more than 40 m thick sedimentary succession is exposed at the
surface. The succession is divided in three parts. The lower part is characterised by
the alternation of calcitic marls and tuffitic layers. Calcitic marls rich in fossil macro
flora contain analcime. The tuffite layers, 10-30 cm thick, consist of altered
vitroclasts, feldspar crystaloclasts, analcime, carbonate minerals, and detrital grains
of quartz, feldspar, amphibole and mica. The thickest, middle part of the section is
mostly composed of a few cm to several dm thick, massive, horizontally laminated
or tectonically deformed carbonate-analcime sedimentary rocks. Carbonate
minerals are crypto- to microcrystalline, concentrated in some lamina or
homogeneously dispersed in rock. Dolomite is the most abundant carbonate
mineral, but HCMC characteristic of playa environments is also detected in almost
all samples. The analcime is cryptocrystalline and homogeneously dispersed within
the rock or concentrated within the laminae in the up to 50 μm-sized isometric
crystals. Minor natrolite, the other zeolite mineral characteristic of a saline
environment, is also present. In the middle part of the succession sandstone layers
(cm-2 m thick) occur beside the dominant analcime-carbonate layers. The
sandstone is poorly sorted with grains derived from the locally uplifted metamorphic
and granitoid basement rocks of the Pannonian basin. The upper part of the
section, which is exposed laterally in the quarry, consists of thin layered
fossiliferous marls (Kovačić et al., 2017). Mineral composition of dominant rock
types is shown in Table 1.

Table 1: Mineral composition (wt%) of representative samples of marls, dolomite- and

analcime-rich rocks from Poljanska.

Dolomite with Dolomitic

Phase Marl
analcime analcimolite

Analcime 18 15 50
Dolomite 45 30
Calcite 40
HCMC 15 5
Plagioclase feldspar 10 5 5
K-feldspar 5 10 7
Illite/muscovite 14 3 1
Chlorite 2 1 2
Montmorillonite 2
Pyrite 3 1
Organic material 5 5
Amorphous 1

Chemistry Table 2: Chemical composition (wt%) of the representative samples of Table 1.

Sedimentary rocks:
SiO2 32.85 25.31 38.29
Al2O3 13.69 10.15 16.43
Fe2O3 4.72 5.06 3.73
MgO 3.02 11.25 5.98
CaO 18.03 12.99 7.73
Na2O 2.37 2.06 7.23
K2O 2.19 3.16 1.27
TiO2 0.58 0.46 0.30
P2O5 0.10 0.04 0.19
MnO 0.09 0.11 0.08
Cr2O3 0.01 0.01 0.02
LOI 22.10 29.00 18.50
Analcime: The chemical composition of analcime from Poljanska, analysed by microprobe, is
shown in Table 3 (Jelavić, 2012). The corresponding crystal chemical formula of
analcime is:
(Na14.72K0.08Ca0.15Mg0.23)[Si32.46Al15.21Fe0.28Mn0.05O96].19.65H2O.

Table 3: Chemical composition (wt%) of analcime from Poljanska.

SiO2 54.44
Al2O3 21.64
Fe2O3 0.61
MgO 0.25
CaO 0.24
Na2O 12.73
K2O 2.19
TiO2 n.d.
MnO 0.11
H2O 9.88
Total 100.00
E% -0.45

n.d. = not determined.

E% = balance error according to Gottardi and Galli (1985).

Crystallography: The unit cell parameters of analcime from Poljanska are (Jelavić, 2012):

a [Å] V [Å3]
13.710(4) 2577

Physical and Table 4: Main physical properties of rocks from Poljanska.

mechanical properties:
Appearance (colour) Greenish or brownish grey
Pozzolanic activity class 50-100
Density 2.46-2.68 g/cm3
Bulk density 1.84-2.38 g/cm3
Compressive strength 4.2-13.8 MPa
Bending strength 1.5-3.7 MPa

Reserves, production Estimated reserves in Poljanska quarry (at the end of 2016) are approximately
and main applications: 3,900,000 tonnes. Exploitation started in 1980, till 2018 approximately 730,000
tonnes were exploited, with average annual production in last years in the order of
10,000 tonnes. The material is used exclusively as a pozzolanic addition in the
cement industry.

DONJE JESENJE

Zeolite occurrence: Clinoptilolite-rich tuff.

Geology: The Early Miocene (Eggenburgian) Donje Jesenje deposit was developed within
the HZB. Due to the collision of the Adriatic microplate and the European foreland,
the regional stress was characterized by a main NS compression axis with EW
extension during the Oligocene and Miocene. Dextral strike slip fault systems were
formed, representing the eastern continuation of the Periadriatic lineament.
Associated with these fault systems is the occurrence of synsedimentary volcanism
in the Egerian (andesite and pyroclastic rocks), Eggenburgian and Ottnangian
(tuffs, tuffites and bentonites). The onset of the Eggenburgian was marked by a
transgression and deposition of sands, glauconitic sands and pyroclastics in the
coastal environment, coinciding with sea level rise in the Central Paratethys. Tuffs
 prevail among the Eggenburgian pyroclastics which were probably deposited in a
marine environment. They are best exposed in the Donje Jesenje quarry, where
vertical alternation of vitroclastic, vitrocrystalloclastic, crystalloclastic and
crystallolithoclastic types is visible. Pyroclastic rocks have variable primary
composition: the main constituents of vitroclastic and crystalloclastic tuffs are
volcanic glass, plagioclase feldspars (andesine) and biotite, while amphibole and
quartz are rare. Lithoclastic tuffs are composed of tuff and effusive rocks fragments,
and in smaller quantities mineral fragments and glass. In the quarry SiO2 content
varies between 65 and 70 %, and therefore the tuff is dacitic. Alteration of volcanic
glass is the result of burial diagenesis. Different alteration products are most
probably due to temperature increase with increasing depth of burial. Clinoptilolite
was transformed to mordenite and analcime, while opal-CT changed to opal-C and
recrystallized to quartz. However different immobile element content of rocks
containing different alteration products indicates that alteration was probably also
dependent on chemical composition of the rocks. In some instances, the type of
alteration product was also dependent on the grain size of the primary material
(Avanić et al., 2018a, b and references therein).

Eggenburgian pyroclastic rocks in Donje Jesenje quarry Typical tuff from Donje Jesenje.

Mineralogy The pyroclastic rocks contain various alteration products of volcanic glass. The
alteration products comprise zeolites, clay minerals (smectite, authigenic mica),
SiO2 phases and authigenic feldspars. Clinoptilolite (based on the Si/Al ratio) is the
most abundant zeolite, however minor mordenite and analcime are also present
(Table 5). The type of exchangeable cations in clinoptilolite is variable; therefore,
clinoptilolites were divided into two subgroups: Ca-K- (present in the upper part of
the quarry), and Na-rich (present in the lower part). Clinoptilolite content varies; the
average content of clinoptilolite is approximately 50 wt% (Tibljaš, 1996; Tibljaš and
Šćavničar, 2007).

Table 5: Mineral composition of representative tuff sample from Donje Jesenje (Hrenović
et al., 2011).

Phase Wt%

Clinoptilolite 50-55
Plagioclase feldspar 10-15
Opal-CT 10-15
Illite/celedonite 10-15
Quartz traces
Analcime traces
Chemistry: The following table (Table 6) reports the chemical composition (wt%) of the
Clinoptilolite representative sample of clinoptilolite-bearing tuff from Donje Jesenje (Tibljaš, 1996).

SiO2 70.09
Al2O3 11.03
TiO2 0.09
Fe2O3 1.25
MnO n.d.
CaO 2.43
MgO 0.88
K2O 2.93
Na2O 0.61
P2O5 0.04
H2O 10.50

n.d. = not determined.

The cation exchange capacity (CEC), based on cation displacement by a NH4+

solution (Minato, 1997) followed by determination of NH4+ ions by an ion-selective
electrode ranges from 40 to 160 mequiv/100 g.

The chemical composition of clinoptilolite from a representative Donje Jesenje

sample, analysed by microprobe, is shown in Table 7 (Tibljaš, 1996). The
corresponding crystal chemical formula of clinoptilolite is:
(Na0.25K1.00Ba0.01)(Ca1.58Mg0.73)[Al6.24Si29.85O72].18.46H2O.

Table 7: Chemical composition (wt%) of clinoptilolite from Donje Jesenje.

SiO2 68.48
Al2O3 12.14
Fe2O3 <0.01
MgO 1.12
CaO 3.39
BaO 0.09
Na2O 0.29
K2O 1.79
H2O 12.70
Total 100.00
E% 5.95

E% = balance error according to Gottardi and Galli (1985).

Crystallography: The unit cell parameters of clinoptilolite from Donje Jesenje are as follows (Tibljaš
and Šćavničar, 1988):

a [Å] b [Å] c [Å] β [°] V [Å3]

17.647(6) 18.007(8) 7.396(3) 116.34(2) 2106

Physical and Table 8: Physical and mechanical properties of clinoptilolite-bearing tuffs from Donje
mechanical properties: Jesenje (Kruk et al., 2014; Tušek et al., 2017):.
Appearance (colour) Mostly light-green
Pozzolanic activity class Almost 150
Density 2.39g/cm3
Surface area (3–60 µm powder) 12,055 m2/g
Reserves, production In the Donje Jesenje quarry, abandoned in the first decade of 21st century, the
and main applications: thickness of the pyroclastic rocks as determined by exploration drilling is
approximately 60 m (Golub and Brajdić, 1969; Marković, 2002). The material was
first used as ornamental building stone, then as an additive in cement industry, and
lately as a soil additive, litter additive and for wastewater and sewage water
purification. Estimated zeolitized rock reserves are in the order of 3,000,000 tonnes
(Kruk et al., 2014).

References
Avanić, R., Kovačić, M., Pavelić, D., Peh, Z. (2018a): Stop 2: The Neogene of Hrvatsko Zagorje. In: Tibljaš, D., Horvat, M.,
Tomašić, N., Mileusnić, M., Grizelj, A. (Eds.): Conference Book 9thMid-European Clay Conference - MECC2018. 128-131,
Zagreb.
Avanić, R., Tibljaš, D., Pavelić, D., Gverić, Z. (2018b): Stop 2: Zeolitized pyroclastics of the Donje Jesenje. In: Tibljaš, D.,
Horvat, M., Tomašić, N., Mileusnić, M., Grizelj, A. (Eds.): Conference Book 9thMid-European Clay Conference -
MECC2018. 137-140, Zagreb.
Golub, Lj., Brajdić, V. (1969): Pyroclastic rocks from the Donje Jesenje (Hrvatsko Zagorje). Geološki vjesnik, 22, 411-422. (in
Croatian, English summary)
Gottardi, G., Galli, E. (1985): Natural zeolites. Springer, 409 p.
Hrenović, J., Kovačević, D., Ivanković, T., Tibljaš, D. (2011): Selective immobilization of Acinetobacter junii on the natural
zeolitized tuff in municipal wastewater. Colloids and Surfaces B: Biointerfaces, 88, 208-214.
Jelavić, S. (2012): Sedimentological and mineralogical characteristics of Ottnangian deposits in Poljanska quarry. Ms Thesis,
University of Zagreb, 80 p. (in Croatian)
Kovačić, M., Tibljaš, D., Pavelić, D., Hajek-Tadesse, V., Bakrač, K., Mandic, O., Galović, I., Wacha, L., Filjak, R., Marković, F.
(2017): Stop 1. Early-Middle Miocene salina-type and open lake deposits. In: Kovačić, M., Wacha, L., Horvat, M. (Eds.),
Fieldtrip Guidebook. 7NCSEE Workshop, 11–15.
Kruk, B., Dedić, Ž. Kruk, Lj., Kovačević-Galović, E., Miko, S., Crnogaj, S., Peh, Z., Avanić, R. (2014): Mining-geological study of
Krapina-Zagorje County. HGI-CGS, Zagreb, 375 p. (in Croatian)
Marković, S. (2002): Croatian mineral raw materials. Croatian Geological Survey, Zagreb. 544 p. (in Croatian)
Minato, H. (1997): Standardization of methods for zeolite speciality determination and techniques for zeolite resources
utilization. In: Kirov, G., Filizova, I., Petrov, O. (Eds.), Natural Zeolites- SOFIA’95, 282–292.
Pavelić, D., Kovačić, M. (2018): Sedimentology and stratigraphy of the Neogene rift-type North Croatian Basin (Pannonian
Basin System, Croatia). Marine and Petroleum Geology, 91, 455-469.
Pavelić, D., Kovačić, M., Banak, A., Jiménez-Moreno, G., Marković, F., Pikelj, K., Vranjković, A., Premužak, L., Tibljaš, D.,
Belak, M. (2016): Early Miocene European loess: A new record of aridity in southern Europe. Geological Society of America
Bulletin, 128, 110–121.
Šćavničar, S., Krkalo, E., Šćavničar, B., Halle, R., Tibljaš, D. (1983): Analcime bearing beds in Poljanska. Rad JAZU, 404, 137–
169.
Tibljaš, D. (1996): Zeolites and other products of the alteration processes in the Oligocene and Early Miocene pyroclastic rocks
from the Macelj area. PhD Thesis, University of Zagreb, 167 p. (in Croatian, English summary)
Tibljaš, D. & Šćavničar, S. (1988): Mineralogical investigation of clinoptilolite, plagioclase and celadonite in tuff from Donje
Jesenje (Hrvatsko Zagorje). Geološki vjesnik, 41, 99-117. (in Croatian, English summary)
Tibljaš, D. & Šćavničar, S. (2007): Zeolitized tuff deposits in the Krapina area. - In: Filipan, T., Tišma, S. & Farkaš, A. (Eds.):
Natural zeolitized tuff from Croatia in environment protection. Institute for International Relations, Zagreb, 13-23. (in
Croatian, English summary)
Tušek, D., Ašperger, D., Bačić, I., Ćurković, L., Macan, J. (2017): Environmentally acceptable sorbents of chemical warfare
agent simulants. Journal of Material Science, 52, 2591–2604.

This text was prepared in October 2018 by D. Tibljaš and M. Kovačić. Further information on zeolite deposits in Croatia
is available from Professor Darko Tibljaš (dtibljas@geol.pmf.hr).