Provenance and characteristics of the pavement stone from the courtyard of the Ljubljana Castle

The pavement stone used in the central courtyard of Ljubljana Castle originates from the Kukul area northeast of the town of Prilep in Republic of Macedonia. Several pavers were badly damaged and partly replaced by two other natural stones, because the original stone from Kukul is no longer available on the market. The natural stone that is recently used as a replacement is commercially named “Bianco Sardo” and differs from original rock from Kukul in both, structure and composition. The advancement of the replacement of original pavers with “Bianco Sardo” is resulting in extremely uneven and disturbing appearance of the courtyard. The original Kukul stone used in the central courtyard of Ljubljana Castle is of metamorphic origin and belongs to gneisses. Two types of pavers were identifid, the light coloured and the dark coloured varieties. They have similar mineral composition consisting of quartz, feldspars (orthoclase, microcline and plagioclases), minerals of the epidote group, micas (muscovite and biotite), titanite, zircon, clinopyroxene, kyanite, pyrite and calcite. Light coloured pavers have porphyroclastic, protomylonitic to mylonitic structures. Dark coloured pavers display gneissic structure, contain more quartz and epidote, less feldspars, and no clinopyroxene. They show intensive recrystallization and granoblastic textures. Both analysed rock types belong to the same rock massif, only that the blocks were extracted from various parts of the rock massif. The variations are due to the process of metamorphic differentiation, which resulted in segregation and separation of light and dark coloured minerals. In the past, the natural stone that was coming from Kukul, was known and classifyed as a type of granite. The rock that is used in the central courtyard of Ljubljana Castle is not granite but granitic gneiss, therefore, we assume that in the last stages of quarrying in the Prilep area, they were extracting also the metamorphic country rocks for some time. The broader area of Prilep belongs to the Pelagonian massif. Its thick metamorphic complex contains also granitoid (granodiorite) intrusives, which crop out in the Prilep anticline and used to be quarried at the locality of Kukul. According to national regulations of the Republic of Macedonia the area is now protected as a natural monument and further exploitation was no longer possible. Today, there is only one open granite exploitation fild in the wider surroundings of Prilep, the locality of Lozjanska Reka–Kruševica and a few localities of gneiss-granites of high potential. It would be necessary to consider these solutions for the conservationrestoration of the Ljubljana Castle central courtyard instead of using an inappropriate stone replacement

Pohorje eclogites revisited: Evidence for ultrahigh-pressure metamorphic conditions

Kyanite eclogites from the Pohorje Mountains, Slovenia, are providing the first evidence of ultrahigh-pressureEo-Alpine metamorphism in the Eastern Alps. Polycrystalline quartz inclusions in garnet, omphacite and kyaniteare surrounded by radial fractures and exhibit microtextures diagnostic for the recovery after coesite breakdown.The non-stoichiometric supersilicic omphacites found in Pohorje eclogites contain up to 5 mol % of Ca-Eskola molecule.Such clinopyroxenes are known to be stable exclusively at high-pressure conditions exceeding 3 GPa. Theirbreakdown during decompression resulted in exolution of quartz rods and needles that are oriented parallel toomphacite c-axis. The absence of coesite is a consequence of near-isothermal decompression during the first stagesof exhumation.Pressure and temperature conditions for the formation of the peak metamorphic mineral assemblages have beenassessed through a consideration of a) Fe2+-Mg partitioning between garnet and omphacite pairs, based on differentcalibrations; b) the equilibrium between garnet + clinopyroxene + phengite ± kyanite ± quartz/coesite assemblage.Estimated peak pressure and temperature conditions of 3.0-3.1 GPa and 750-783 °C are well within the coesite, i.e.the ultrahigh-pressure stability field

Garnet peridotites from Pohorje: Petrography, geothermobarometry and metamorphic evolution

Ultrahigh-pressure (UHP) metamorphism has been recorded in Eo-Alpine garnet peridotites from the PohorjeMts., Slovenia, belonging to the Eastern Alps. The garnet peridotite bodies are found within serpentinized metaultrabasitesin the SE edge of Pohorje and are closely associated with UHP kyanite eclogites. These rocks belongto the Lower Central Austroalpine basement unit of the Eastern Alps, exposed in the proximity of the Periadriaticfault system.Garnet peridotites show signs of a complex four-stage metamorphic history. The protolith stage is represented bya low-P high-T assemblage of olivine + Al-rich orthopyroxene + Al-rich clinopyroxene + Cr-spinel. Due to metamorphism,primary clinopyroxene shows exsolutions of garnet, orthopyroxene, amphibole, Cr-spinel and ilmenite. TheUHP metamorphic stage is defined by the assemblage garnet + olivine + Al-poor orthopyroxene + clinopyroxene +Cr-spinel. Subsequent decompression and final retrogression stage resulted in formation of kelyphitic rims aroundgarnet and crystallization of tremolite, chlorite, serpentine and talc.Pressure and temperature estimates indicate that garnet peridotites reached the peak of metamorphism at 4 GPaand 900 °C, that is well within the UHP stability field. Garnet peridotites in the Pohorje Mountains experiencedUHP metamorphism during the Cretaceous orogeny and thus record the highest-pressure conditions of all Eo-Alpinemetamorphism in the Alps

Geochemical and mineralogical approaches in unraveling paleoweathering, provenance, and tectonic setting of the clastic sedimentary succession (Western Central Paratethys)

Pronounced tectonic and paleogeographic changes were detected in the Alpine–Pannonian region during the Miocene at the interface between the Alps, the Dinarides, and the Pannonian Basin. To understand the major tectonic, paleogeographic, and paleoclimatic changes during this period, geochemical and mineralogical investigations were carried out on the fine-grained clastic sedimentary rocks in the Tunjice Hills. The paleoweathering indicates a cold and/or arid to a warm and humid period. The paleoclimate and the regional climatic conditions correspond well with the Middle Miocene Climatic Optimum. The mineral composition shows an abundance of quartz and calcite. Quartz is associated with detrital origin from volcanic and metamorphic rocks of the Eastern and Southern Alps and with authigenic processes in sediments. Calcite is related to authigenic origin formed in shallow marine environments and to detrital provenance from the Southern Alps. Not all discriminant functions based on major oxides provided adequate results in determining the tectonic setting. The source rocks were subjected to oceanic island arc and collision. Moreover, sedimentation was influenced by both active and passive margin settings. The former is related to the Alpine collision, which continued from the Cenozoic onward, and the latter is connected to the processes associated with the formation of the Pannonian Basin System, which began in the late Early Miocene

Calcite deformation twins in Pohorje marbles

Marbles in Pohorje occur in lenses and smaller bodies in the southern and southeastern part of the massif. Marbles are very pure, predominantly calcitic and rarely calcitic-dolomitic, containing a maximum of 5 % of non-carbonate mineral phases. The latter comprise pyroxenes (diopside), amphiboles (tremolite), olivines (forsterite) in places replaced by serpentine, quartz, feldspars (potassium feldspars and plagioclases), epidote, zoisite, vesuvianite, scapolite, muscovite, biotite partly replaced by chlorite, phlogopite, rare grains of titanite, rutile, zircone, apatite, and small grains of ferric oxides and sulfies. Calcite exhibits intensive deformational e-twinning whereas dolomite is undeformed and untwined. All four known types of mechanical twins in calcite were recognized: thin Type I twins, straight thick Type II twins, curved, lensoid and tapered thick Type III twins, and thick patchy Type IV twins. Type III twins are the dominant mechanical twins in the Pohorje marbles indicating the temperature of deformation somewhat above 200 °C. Since they lack signs of grain boundary recrystallization, we assume that the twinning was followed by a decrease temperature during exhumation. With increasing temperature the process of recrystallization along calcite grain becomes pronounced. Small individual untwined calcite crystals are progressively replacing bigger calcite grains. In few examples second generation of Type I deformational twins develop in recrystallized calcite grains, which also implies lowering of temperature due to exhumation

Authigenic Mineralization in Low-rank Coals from the Velenje Basin, Slovenia

he purpose of this study is to characterize sedimentologically and isotopically authigenic mineralization and low-rank coals (lignite) from the Velenje basin, Slovenia. Six structural types of calcite mineralization in a fine lignite gelified matrix were recognized, namely: (A) laminae and thin beds, (B) small lenses and lenticular bodies, (C) dispersed mineral matter in minute detritus, (D) calcite-substituted xylite fragments, (E) encrusted xylite fragments, and (F) calcite-coated and calcite-filled pores. Scanning electron microscopy revealed that in parts the calcified lignite is almost pure calcite. The carbon (–4.3 to +16.4‰) and oxygen (–14.5‰ to –6.6‰) isotopic composition indicates a carbonate precipitation temperature of between 5.7 and 45.5°C. The δ13Corg. values and δ15Nbulk of organic compounds were from –29.4‰ to –23.7‰ and from +1.8‰ to +5.9‰, respectively. The lower δ13Corg. values (up to –29.4‰) in the Velenje lignite indicate a high degree of gelification, while the δ15Nbulk values (up to +5.9‰) are indicative of intense mineralization. Furthermore, a carbon isotope fractionation factor (εTOC) of more than 32% suggests that unlike in recent lake sediments from Slovenia, Croatia, and Argentina, where oxic processes dominate, there was intense microbial activity (methane formation in anoxic conditions). In addition, the εTOC values in the Velenje samples are unrelated to mineralization type but are related to the degree of gelification (bacterial activity). The investigation of mineral occurrence is important since cleat-filling minerals reduce coal permeability, which in turn can trigger gas outbursts and inhibit gas extraction.Published201-2137SR AMBIENTE – Servizi e ricerca per la societàJCR Journa

Influence of alkalis on the phase development of belite-sulfoaluminate clinkers

This paper presents a study on the influence of different amounts of alkalis (K2O and Na2O) on clinker phase formation, microstructure, phase composition and reactivity of belite-sulfoaluminate cement clinker. Using X-ray powder diffraction and scanning electron microscopy with energy dispersive spectrometry, it was found that the amount of C2S and C4AF increases with the incorporation of alkalis, while the amount of C4A3Ś and CŚ decreases. In addition to the major phases, the samples with alkalis also consist of minor phases such as C3A (tricalcium aluminate), KŚ (arcanite), and KC2Ś3 (Ca-langbeinite). The major ions in the major phases were substituted by alkali cations and some other ions (Ca2+, Al3+, Fe3+, S2-, S6+, Si4+). The alkalis also affect the microstructure of the clinker, e.g., the shape of the grains. Consequently, isothermal calorimetry was used to detect differences in hydration kinetics. The clinker with 2 wt. % K2O content was the most reactive, while the sample with 0.5 wt. % Na content was the least reactive. The latter was primarily influenced by the content of the main and minor phases of the clinker