Magnesium is a critical raw material of high importance to the European Union economy.Magnesium has versatile applications in many industries: the automotive industry (48%), packaging applications (23%), the construction industry (13%), desulphurisation of steel (12%), heavy transportation (air, marine, train; 4%) as well as in medical equipment, sport applications, electrochemical and organic chemistry applications.The Republic of Croatia hosts two major sources of magnesium: (1) primary dolostone deposits and occurrences, mainly used as a high-quality crushed stone aggregate and carbonate mineral raw material for industrial processing, and (2) secondary Mg reject brine from the Nin, Pag and Ston saltpans: (1) Deposits and occurrences of early and late diagenetic dolostone are associated with the South Tethyan Megaplatform (STM; Upper Triassic Hauptdolomite and Lower Jurassic limestone and dolostone) or the Adriatic Carbonate Platform (AdCP; Jurassic limestone and dolostone and Upper Jurassic boundstones, layered and massive dolostone and Lower to Middle Cretaceous dolostone and post-sedimentary, diagenetic breccia).Based on their lithological, mineralogical, and chemical characteristics, STM deposits are considered high-potential magnesium sources, whereas AdCP deposits belong to medium-to-high (Jurassic) and low-potential (Cretaceous) magnesium sources.The overall geological potential of primary magnesium sources at a scale of 1:300,000 has been calculated by excluding areas where exploitation is prohibited.In the resulting areas, exploitation is possible, but additional restrictions arising from the three levels of spatial plans (national, county, and local) must additionally be taken into account.(2) Average annual salt production in Croatia is around 20,000 t.The calculated amount of discharged magnesium from highsaline brines remaining after the precipitation of sodium-chloride is about 2.38 t/annually.The case study on the ipalo dolostone deposit near Sinj (STM dolostone; exploitation reserves of 5.9 Mt) shows high purity dolostone with MgO > 22 wt%, whereas the sum content of SiO 2 , Fe 2 O 3 and Al 2 O 3 remains below 1 wt%.The ipalo dolostone can be used in the refractory material industry, as an agent of fusion in ferrous metallurgy, in the production of cement, glass, ceramics, paper or for magnesium metal production.The prices of various Mg-products range from 1.7 /t construction mineral raw material, 10 /t for crushed stone aggregate, 100 /t for refractory (roasted) dolostone and about 2,250 /t for 99,0% pure magnesium (February 2024).Dolostone consumption for the ipalo deposit is estimated to be about 10-15 t of dolostone per tonne of Mg metal produced, depending on the process, however, the estimated CO 2 emissions remain a significant negative factor.of the mineral raw materials that were initially used, and most importantly on the quantities of the complementary material left for disposal.At this point, the average citizen might ask himself "Are we doing any mining and extraction in Croatia?" Croatian Critical Mineral Commodity Letters are a serial of review publications focused on selected critical raw materials (CRM) in Croatia.Critical raw materials are non energy raw materials of high importance to the European Union's economy across the industrial value chain, irreplaceable in modern and environmentalfriendly clean technologies such as solar panels, wind turbines, electric vehicles, and energy-efficient lighting.At the same time, there is a high risk associated with their supply, where the EU mainly relies on their import (GROHOL & VEEH, 2023).

Optical polarizing microscopy, X-ray powder diffraction and transmission electron microscopy with energy-dispersive spectroscopy have been used to study microstructures in feldspars from two structurally and texturally different granite types from Pakra Creek valley (Papuk Mt., Croatia).The porphyritic texture granite contains pink potassium feldspar megacrysts with cross-hatched extinction and tweed pattern, which proved to be intermediate microcline to orthoclase.These crystals have Or > 90% and An=0 composition, and coexist with low albite Or(1.2)Ab(98.8)An(0).The feldspars from the granite with homogenous finegrained microstructure are white in colour and proved to be mixture of lamellar and zoned plagioclase and intermediate microcline.The plagioclase has a Na:Ca ratio close to 3:1 and minor K content (72.2%<Ab<76.5%,23%<An<26.8%,Or<1.4%).Pure albite (Ab=97-99%) and anorthite (An=99%) grains were also detected.The higher content of plagioclase in the granite with homogenous fine-grained microstructure indicates a higher crystallization temperature compared to the porphyritic type.The microstructure of the feldspar crystals suggests a parent melt close to the eutectic composition for the studied granites.

The geochemical signature of weathering and pedogenesis in a temperate humid climate on two parent material types in the foothills of Medvednica Mt. was studied. Five soil profiles on Miocene marls and three sections of Plio-Quaternary (PlQ) proluvial sediments with overlying soil and weathered material were analyzed. The (clay) mineralogy of all profiles and sections had been determined in previous studies. The chemical composition of the samples was determined by inductively coupled plasma emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectroscopy (ICP-MS). Poorly ordered Fe and Mn oxides were determined in the PlQ sediment and overlying soil samples by atomic absorption spectroscopy (AAS), after oxalate dissolution in the dark. The concentrations and element ratios were used to determine element enrichment/mobility and intensity of chemical weathering, material provenance, and to compare the geochemical signatures with previously obtained clay mineralogy results. Trace elements in the Miocene marls, including rare earth elements (REE), indicate the continental origin of the marl siliciclastic component, while more scattered geochemical data of the PlQ sediments reflect their proluvial/torrential nature. The mass transfer coefficient (τ) for major elements and element ratios of the Miocene marl profiles indicate chemical weathering and pedogenesis of lower intensity. The geochemistry of these samples shows homogeneity within the profiles. In the geochemical signature of the PlQ sections, a chaotic proluvial deposition of the material is visible, as well as the heterogeneity with the overlying soil and weathered material. Overall, the geochemistry results largely support the clay mineralogy of the samples and demonstrate how a multiproxy approach can help test hypotheses about past environments and provide valuable additional information for complex paleoenvironmental studies.

Microboring traces in carbonate skeletal fragments deposited in aphotic depths of the oceans are studied, evaluated, and described with respect to their marine ecology and palaeoecology as well as ichnotaxonomy. Sand-size deep sea sediment particles dredged from depths ranging between 600 and 3266 m of the Bermuda Pedestal, Central Atlantic Ocean, the Florida Escarpment, the Mediterranean Sea, the Red Sea and the Indian Ocean were studied. Following ichnological rules, trace fossils are described as ichnogenera and ichnospecies, defined as products of organismal behaviour. This, in our view, refers to the growth habit of microboring organisms in response to environmental stimuli within the substrate they penetrate. The problem of palaeobathymetry is discussed in conjunction with the distinction between light-dependent and light independent microboring organisms, with the emphasis on the latter. We considered this distinction to be important because only the light-dependent microborers have been recognized as indicators of ancient depositional depths, whereas the light-independent ones are expected to occur at any depth, subject to the availability of organic nutrients. Microboring organisms often leave morphologically similar traces due to convergent evolution. Their responses may change during their life cycle; they may produce different traces when pursuing their vegetative vs. reproductive functions. New ichnotaxa are described. All are regarded as organotrophs given their aphotic zone deep sea origin. This work presents the most complete set of deep sea microbial euendolith traces, to date.

The provenance of the Upper Miocene sandstones from the Sava and Drava depressions of the North Croatian Basin was investigated using petrographic, geochemical, and heavy mineral analyses, including Raman spectroscopy. The study of these sandstones, which represent important oil and gas reservoirs in Croatia, allowed reconstruction of the Late Miocene source-to-sink model of the Lake Pannon drainage system and the evolution of the southwestern Pannonian Basin. The studied feldspatho-litho-quartzose sandstones consist of a mixture of sedimentary, metamorphic, and igneous detritus. Heavy-mineral assemblages are dominated by almandine-rich garnet with apatite, epidote, tourmaline, rutile, zircon, staurolite, and zoisite, indicative of low to medium-grade metamorphic source rocks. Higher concentrations of Ca and Mg than in the Upper Continental Crust standard (UCC) additionally reflect the abundance of limestone and dolostone rock fragments as well as carbonate cement. Geochemical compositional variations between sandstone samples from the Sava and Drava depressions primarily stem from diagenetic processes. CIX and alpha values indicate only minor weathering. Compositional features indicate an orogenic source located in the Eastern Alps and primarily represented by Austroalpine and Penninic nappes. This research offers a novel perspective to distinguish the Upper Miocene reservoirs from other sedimentary units within the basin, contributing to a more comprehensive understanding of the regional geological dynamics and supporting future exploration projects also related to energy transition.

Lower Cretaceous (Aptian) shallow-marine limestones with intercalated polymictic conglomerates were investigated with respect to their biostratigraphic age and their microfacies. They are the younger part of the generally carbonate-siliciclastic Lower Cretaceous deep-water (max. few hundred metres) turbiditic sequences (“Paraflysch”) of the so-called East Vardar zone in the Belgrade area. The biostratigraphic age of the limestones was determined by orbitolinid foraminifera: the co-occurrence of Dictyoconus? pachymarginalis SCHROEDER and Mesorbitolina texana (ROEMER) besides various other microfossils suggest a biostratigraphic age of this shallow- marine limestone succession as middle Aptian (Gargasian). Radiolarite components in the conglomerates are Triassic in age and were derived from the obducted Middle Triassic to Middle Jurassic Neo-Tethys ophiolites and/or their ophiolitic mélanges on the wider Adria plate. From both the first precise biostratigraphic age dating as middle Aptian combined with microfacies analysis of these shallow-marine limestones and the component spectrum in the intercalated conglomerates, it can be concluded that the Lower Cretaceous turbiditic “Paraflysch” succession was deposited on the eastern rim of the Dinarides. The results will allow a better comparison of the different Lower Cretaceous sedimentary successions deposited on the eastern margin of the Dinarides.

Early beginnings of the Middle Triassic extension in the areas surrounding the western embayment of the Neotethys are evidenced in formation of small half-graben basins, local emergences of the underlying platform, and/or deposition of coarse-grained breccia. The succession related to the creation and infilling of one of these half-grabens is exposed on the slopes of the base of Mt. Vernar in eastern Julian Alps, Slovenia. The lowermost exposed unit within the half-graben is the Uggowitz Breccia, which attains thickness of up to 150 m. It is followed by a few tens of meters of red nodular limestone (the informal 'Vernar member'), followed by the second, thinner Uggowitz Breccia unit, succeeded by sandstone and sandy limestone (the informal “Krma member”), rich in shallow marine foraminifers and plant material. The basin-filling succession is followed by indistinctly bedded and then massive limestone of the Schlern Formation. Late Anisian (Ilyrian) age is assumed for the sediments of the half-graben based on the clast composition and comparison with regional sequence stratigraphic schemes. Breccias likely deposited in shallow marine or marginal marine setting. Individual beds are interpreted as subaqueous debris-flow deposits.

A sediment infill of a small, late Anisian-earliest Ladinian half-graben, sealed by massive limestone of the Schlern Formation is exposed on the northeastern slopes of Mt.Vernar in the eastern Julian Alps, Slovenia.The pre-rift base of the succession is formed by a chaotic mixture of massive limestone and limestone breccia of the Anisian platform.Sedimentation in the half-graben started with a 20 m thick thinly bedded pink nodular limestone which is informally named here as the Vernar member.It consists of microbial carbonate and was probably deposited within the photic zone.The Vernar member is overlain by poorly sorted polymict breccias of the Uggowitz Breccia Formation which reaches a thickness of at least 150 m, but pinches out rapidly towards the SE graben margin, reflecting the highly asymmetric basin geometry.Individual beds of breccia represent successive debris flow deposits.The Uggowitz Breccia Formation is followed by a few metres of sandstone and sandy limestone of the Buchenstein Formation.The limestone contains abundant grains of shallow marine origin and terrestrial plant fragments.The overlying post-rift Schlern Formation consists of crudely bedded and massive limestone, covering the graben.The consistent NE-SW strike of the graben-bounding faults and of the smallscale conjugate normal faults observed in the Uggowitz Breccia Formation suggests that the half-graben originated from NW-SE directed extension.

The Rupnica geosite, a key locality of the UNESCO-protected Papuk Geopark in northern Croatia, is well-known for an excellent exposure of columnar jointing in volcanic rock. This rock is defined as an albite rhyolite that comprises almost pure albite phenocrysts within a fine-grained matrix composed of microphenocrysts of albite, quartz and devitrified volcanic glass. Primary accessory minerals are clinopyroxene, apatite, zircon and magnetite. Haematite, apatite and anatase were found as inclusions in zircon. The albite rhyolite is characterized by a highly siliceous, peraluminous, oxidized (ferroan), dry, alkali-calcic to alkalic composition, with low CaO, MgO, and MnO contents and high FeOT/(FeOT+MgO) ratios. Normalized trace element contents display positive anomalies of K, Pb, and Zr as well as negative anomalies of Nb, P, Ti, Ba and Eu, together with an enrichment of light rare-earth elements (REE) relative to heavy REE. Zircon from the rhyolite of Rupnica is characterized by ratios of Th/U=1.13 and Zr/Hf=55 and contents of HfO2=1.04 wt. % typical for an early-stage igneous zircon crystallized from a dry high-temperature magma in a deep magma chamber. Apatite REE patterns show enrichment of light REE over heavy REE and a pronounced Eu anomaly, typical for apatite from granitoids formed in an oxidizing environment. The magma is of A-type and was generated at high temperatures at 800–900 °C by partial melting of lower- to mid-crustal rocks. The age of the albite rhyolite of Rupnica is Late Cretaceous at 80.8±1.8 (2σ) Ma, according to U-Pb dating of zircon, coeval with geochemically similar igneous rocks of Mt. Požeška Gora and Mt. Kozara within the Sava Zone.