Comprehensive characterization of bentonites from Croatia and neighboring countries

Bentonites are an important industrial resource and are also interesting from the mineralogical point of view. The main component of bentonites is a mineral from the smectite group in which chemical and structural variations, influencing bentonite properties, provide a great deal of interesting research topics. The aim of this study was to better describe bentonites from 11 known deposits from Croatia and neighbouring countries: Bednja, Bunarić, Draga, Divoselo, Sjeničak, Paripovac, Lončarski Vis and Poljanska Luka (Croatia), Zaloška Gorica (Slovenia), Šipovo (Bosnia and Herzegovina) and Vranjska Banja (Serbia). Thirteen samples were analysed using several available techniques in order to obtain the data necessary for currently accepted bentonite classification. The mineralogical composition was analysed using XRD and FTIR, and crystallo-chemical properties were investigated by thermal analysis, CEC determination with ammonium index cations, chemical analyses (ICP-AES and ICP-MS) and Mössbauer spectroscopy. The results showed that the main mineral constituent of most local bentonite deposits is a Fe-poor smectite, with a predominantly medium layer charge mostly as a result of octahedral substitutions, with calcium or sodium cations occupying the interlayer. Nevertheless, the variations between samples are prominent enough to provide a good overview of the range of crystallo-chemical properties which exist in different smectites resulting in varying bentonite properties.</p

Estuarine Sediments from the Boreal Region – an Indication of Weathering

Öre estuary (Northern Sweden) was chosen as a model for other anthropogenically unpolluted estuaries in the boreal region. Sediments were studied in detail in order to characterize the weathering products of silicate rocks. Primary rocks are mostly composed of granite and gneiss. Chemical analysis of total sediments was performed by the XRF method. SiO2 predominated (71.1–59.2 %) in all samples, decreasing seaward. Al2O3 (11.58–12.89 %) and Fe2O3 (3.71–6.92 %) were the other main chemical components and they increased seaward. Fourteen elements within the fine silt and clay fraction (f < 32 &micro;m) were analyzed by the ICP-AES method. The most abundant microelement was Ti, followed by Mn, Zn, Ba, Cr, Sr, V, while Cu, Co and Ni were the least abundant. Organic matter was characterized as total carbon, hydrogen and nitrogen. Mineralogical composition was studied by the XRD method. The minerals found were quartz, different minerals from the feldspar group (albite, microcline, plagioclase, sanidine), biotite, chlorite and hornblende. Some weathering products, such as montmorillonite-15&#197; and Al(OH)3, were detected in the fine silt and clay fraction (f < 32 &micro;m). Amorphous iron hydroxide could not be detected by the XRD method. Most of the trace elements determined by ICP-AES (Co, Mg, Cr, Ni, Cu, Mn, Zn) were in very good correlation with iron. 57Fe Mössbauer spectroscopy was used for further characterization. Measured at room temperature, Mössbauer spectra did not display magnetic ordering. In only one sample, closest to the river mouth, a better fit was obtained by adding one sextet pattern, but it was of minor significance. Relative amounts of Fe(II) and of Fe(III) were determined in each sample and the Fe(III)/Fe(II) ratio was calculated. It was observed that the amount of Fe(III) increased with the distance from the river mouth and it was either retained at the silicate sites or precipitated as amorphous iron oxide. Mössbauer spectroscopy indicates that the sediments sampled are mostly formed from metamorphic rocks due to the presence of altered biotite and chlorite. The results of this work demonstrate that sediments can be used to study weathering. Some of the reactions, according to the literature, are connected with the consumption of CO2. Examples of such reactions include the weathering of K-feldspar, albite and hornblende

Some Geological Observations in Slovačka jama Cave (-1268m) in Velebit Mountain, Croatia

Tekom zadnjih treh speleoloških odprav je bila Slovaška jama raziskana do globine 1268 m. V njej je več rovov freatičnih oblik. Hipsometrično najvišji ostanki takih rovov so najbrž v zvezi s ponori iz časa, ko je nastajala uvala Veliki Lubenovac. Spodnji, recentni in subrecentni freatični horizonti v jamskem “dnu” so verjetno del kanalov podzemeljske reke Like, ki ponika na severovzhodni strani Velebita in teče skozenj v podmorske izvire v Jadranskem morju. Ostali rovi so predvsem brezna in meandri z vadoznimi oblikami. Analize izotopa 14C dokazujejo, da so najstarejše sige v obojih, v starih in v subrecentnih freatičnih rovih, medtem ko so mlajše sige v vadoznih meandrihDuring three speleological expeditions the Slovačka jama cave has been explored to the depth of 1268m. In the cave there are several channels with phreatic forms. The highest relict phreatic channel is probably due to sinkholes formed on the karst uvala Veliki Lubenovac at the time of uvala formation. Lower, recent and subrecent, phreatic horizons at the cave bottom are probably a part of the underground route of the Lika river which sinks on the north-eastern side of Velebit mountain and flows through the mountain to the submarine springs in the Adriatic sea. Other channels are mostly shafts and channels with meandering vadose forms. 14C isotope analysis of speleothems shows that the oldest are situated in both ancient and subrecent phreatic channels, while younger ones are found in the vadose meandering channel

Influence of Support Materials on Phosphate Removal by the Pure Culture of Acinetobacter calcoaceticus

The aim of this study was to investigate the influence and performance of the addition of support material on the phosphate uptake in a pure culture of phosphate-accumulating bacteria Acinetobacter calcoaceticus (DSM, 1532). Materials (natural zeolite and clay from Hrvatsko zagorje, Croatia) of different physical, chemical and mineral characteristics as well as different particle size were tested. In anaerobic/aerobic sequencing batch reactors with the pure culture of A. calcoaceticus, the addition of natural zeolite or clay in the aerobic phase resulted in a significantly higher final efficiency of phosphate removal. The amount of phosphate removed depended on particle size and type of material used. The number of A. calcoaceticus cells was significantly higher in reactors with support materials than in control reactors. After 24 h of incubation with support materials, the cells were present in colonies on the outer layer, strongly adsorbed and adhering to one another by extracellular substances. The main contribution of the support material to the phosphate removal was the increase of biomass, and in a lesser extent the adsorption of phosphate on the material particles

Preliminary results on degree of thermal alteration recorded in the eastern part of Mt. Papuk, Slavonia, Croatia

Samples from the Radlovac metamorphic complex, together with others from the overlying sedimentary rocks, and parts of Psunj metamorphic complex beneath it were studied in order to better constrain metamorphic conditions that have prevailed in the area. Rocks from Mt. Papuk were investigated, in order to determine thermal conditions, by Kübler index (illite “crystallinity”) and Árkai index (chlorite “crystallinity”) while the b0-parameter of K-white mica was used to estimate the pressure conditions. Treatment with dimethyl-sulfoxide (DMSO) was used in order to extend application of chlorite “crystallinity” measurements to kaolinite bearing samples. Results suggest temperatures between 250–300°C and pressures of 2–3 kb. Similar temperature data recorded from various lithologies implies the existence of a previously unknown post lower Triassic thermal event, (Alpine very low to low-grade metamorphism) affecting different complexes on Mt. Papuk. New data presented and discussed in this paper provides the basis for further research and interpretation of the tectono-metamorphic history of the studied area and its correlation with other similar European metamorphic complexes

Corrensite in metabasalts and metagabbros from Mt. Medvednica, Croatia

Complex mineral paragenetic and mineral structural and -chemical studies were carried out on metabasite samples from the ophiolitic mélange unit of Mt. Medvednica, Croatia using pétrographie microscopic, XRPD and EMP techniques. According to XRPD studies of the <2 pm and < 0.6 |xm grain-size fractions, chlorite and corrensite (regularly interstratified chlorite/smectite) are the predominant phyllosilicate components. Randomly interstratified chlorite/smectite and discrete smectite are also found in minor amounts. On the basis of the EMP analyses chemical composition of "chloritic materials" from different textural positions reveals that they contain not only chlorite layers but certain amount of trioctahedral smectite (saponite) interlayers also occur being responsible for their relatively high Ca and/or Na contents, large excess of A1(V1) relative to Al(IV) and high octahedral vacancy. The formation temperature of the "chloritic materials" is suggested to be in the range of ca. 160- 200 °C using the geothermometer of Cathelineau (1988). Metabasalt samples from the ophiolitic mélange could be affected by minimum alteration, and the appearance of corrensite, together with mixed-layered chlorite/smectite and discrete smectite suggest "intermediate" temperature conditions (Shau and Peacor, 1992). According to Proust (1982) and Proust et al. (1986) corrensite as chlorite/vermiculite forms as an intermediate product of the weathering but the occurrence of chlorite/smectite in the studied samples may indicate that rather the diageneticincipient metamorphic alteration is the process that may be the main mechanism responsible for its formation

Tidal deposits in the Early Miocene Central Paratethys: the Vučji Jarek and Čemernica members of the Macelj formation (NW Croatia)

The Macelj formation is an informal Eggenburgian-early Ottnangian lithostratigraphic unit that is established in the area of the Hrvatsko Zagorje Basin, which represented a marginal zone of the Early Miocene Central Paratethys Sea. Modern studies, as a part of the Geologic Map of the Republic of Croatia 1:50 000 project, yielded new data that improves the knowledge of the depositional and stratigraphic characteristics of the formation. The sedimentological research within this study was focused on the two older lithostratigraphic units of the Macelj formation: the Vučji Jarek member and the Čemernica member. The Vučji Jarek mb. is represented by three facies. The Facies of horizontally bedded sandstones is characterized by mostly medium-grained, moderately sorted sandstones that reflect deposition on the foreshore to the upper shoreface. The facies of horizontally and cross-bedded glauconitic sandstones is composed of fine- to coarsegrained, well-sorted sandstones that indicate foreshore to shoreface deposition under tidal influence. The Facies of horizontally and cross-bedded pyroclastics consists of tuff, pumice, lapilli and large blocks, showing a chaotic structure in places. Deposition occurred at the shoreface under tidal influence. The Čemernica mb. is represented by the Facies of structureless clayey-silty sands that are poorly sorted and bioturbated, and indicates deposition below the fairweather wavebase, in the offshore-transition zone. Deposits of the members include marine macro- and microfossil associations.K-Ar dating of separated glauconite mineral fractions yielded an early Eggenburgian age for the Vučji Jarek mb. glauconitic sandstones (19.2±0.64 Ma) which is in accordance with biostratigraphical analyses. Sedimentological characteristics of the Eggenburgian Macelj fm., especially those that reflect the tidal influence, fit the general characteristics of the Central Paratethys Sea in the Early Miocene