Šime Bilić

This study examines impure grey marble occurring as interlayers in amphibolite and diopside-amphibole schists which belong to the magmatic-metamorphic complex of Mt. Moslavačka Gora in Croatia. The marble is composed mainly of calcite with abundant accessory minerals: dolomite, forsterite, spinel, pargasite, phlogopite, ilmenite, apatite, Ti-clinohumite, tremolite, chlorite, serpentine and talc. Detailed descriptions of mineral assemblages, their textural relationships and mineral chemistry analyses in situ, as well as compositional maps of characteristic mineral assemblages, revealed that the marble experienced at least three different metamorphic stages. These can be summarized as follows: a) the regional metamorphic stage characterised by peak metamorphic stage in granulite facies and a mineral assemblage consisting of calcite + dolomite + forsterite + spinel + pargasite + phlogopite + ilmenite + apatite; b) the stage of subsequent infiltration of an external Ti-rich, fluorinated fluid into the marble giving rise to the origin of Ti-clinohumite, the Ti content of which varies from 0.070 to 0.325 pfu and its XF value, defined as F/(F + OH), is in the range of 0.32 to 0.57; c) the stage of uplift and exhumation of the terrain causing diverse retrograde metamorphic reactions such as the replacement of Ti-clinohumite, spinel and pargasite by chlorite, formation of tremolite on the rims of pargasite and forsterite, as well as the replacement of forsterite by serpentine and talc. Due to the differences in the age determinations of both metamorphisms and magmatic intrusions, good correlation between the occurrence of the Ti-clinohumite bearing marbles of Mt. Moslavačka Gora with those found in surrounding terrains, for instance in Alps (Switzerland/Italy, Austria, Czech Republic) and Rhodope massif (Greece), could not be established at this stage of the investigation.

In the Posušje region of the External Dinarides (Bosnia and Herzegovina), bauxite deposits are hosted along a Late Cretaceous–Paleogene forebulge unconformity that records an extended emersion phase of the Adriatic Carbonate Platform. Historically, open-pit mining has targeted surface and shallow subsurface bauxite bodies, but ongoing exploration must now focus on deeper structurally preserved deposits. To address this challenge, we integrate remote sensing, geological mapping, borehole data, and 3D structural modeling to assess the distribution and structural controls of bauxite deposits. Balanced and restored cross-sections reveal a complex interplay between inverted normal faults, fold structures, and foredeep burial, which collectively influenced bauxite accumulation and preservation. Statistical analyses of deposit size, shape, and orientation indicate that larger bauxite bodies are concentrated in the footwalls of inverted normal faults, where prolonged or repeated exposure enhanced karst development and bauxite accumulation. Additionally, the predominant NW–SE elongation of bauxite bodies suggests that pre-existing structural lineaments played a key role in paleokarst morphology, supporting the influence of syn-depositional extensional faulting on bauxite distribution. These findings demonstrate that bauxite exploration in fold–thrust belts requires an integrated structural approach, where 3D geological modeling can delineate prospective areas prior to costly geophysical surveys and drilling campaigns. Insights from the Posušje region can refine mineral exploration strategies in other orogenic settings, highlighting the importance of structural inheritance in karst bauxite accumulation and preservation.

Numerous outcrops of ultramafic rocks consisting mostly of peridotites occur in the area of Banovina, in Croatia. These rocks were formed as parts of the former Earth's mantle and belong to the Central Dinaride Ophiolite Belt (CDOB), which is direct proof of the existence and closure of the Neothetys ocean in the northern part of the Balkan area. Previous studies have considered these peridotites as fertile, subcontinental parts of the mantle with complex chemistry. This research presents a more detailed petrographic and chemical analysis, focused solely on peridotites as dominant ophiolitic member, with the intention to sort between different types of Banovina peridotites and offer the model for their petrogenesis.    Detailed field work, mapping and petrographic analyses have revealed that Banovina peridotites occur as two texturally, lithologicaly and mineralogicaly different types, that crop out in two geographically different belts, the northern (N-belt) and the southern (S-belt). The N-belt contains mostly serpentinite breccias and serpentinized, depleted and mostly porphyroclastic spinel lherzolites that occur in the form of mélange, while S-belt comprises larger masses of peridotites which consist predominantly of fertile spinel lherzolites with equigranular to porphyroclastic textures. Bulk rock analyses have shown that spinel lherzolites from the S-belt have lower Cr# and Mg# and higher content of Al2O3, CaO, Na2O, TiO2 and REE than spinel lherzolites from N-belt, and same relations, excluding the REE, can be seen in the chemistry of clinopyroxenes and orthopyroxenes. Spinels from the N-belt spinel lherzolites have a significantly higher Cr# (12,7 – 50,7) then those from the S-belt spinel lherzolites (7,7 – 10,8). Two types of dunites, which were found only within S-belt peridotites, have very different petrographic and chemical characteristics. Pyroxene rich dunite is characterized by a coarse-grained protogranular to porphyroclastic texture, high modal pyroxenes (up to 10 vol. %) and spinels enriched in MgO, Al2O3 and NiO. The second type of dunite has small-grained equigranular texture, contains amphibole (up to 1 vol. %), pyroxene (< 1 vol. %) and spinels enriched in Cr2O3 and FeOT. Geochemical analysis of all peridotites indicate that the S-belt peridotites represent a subcontinental mantle which have been formed through the initial rifting phase during which they ascended to the upper crust. Peridotites from the S-belt are classified as orogenic peridotites. The geochemical characteristics of N-belt peridotites indicate their origin from a suboceanic mantle formed within mid ocean ridge environment and are classified as ophiolitic peridotites. Dunites show different geochemical characteristics and may have been formed by different geological processes. The diverse lithology of ultramafics in the limited space of the S-belt indicates very heterogeneous nature of the subcontinental mantle. As a part of the CDOBs, peridotites from Banovina indicate that the CDOB record three different phases of ocean evolution, the early phase of the initial rift and opening of the ocean (S-belt peridotites), later phase of the already developed ocean (N-belt peridotites) and also the phase of ocean closure which is evident from the mélange occurrences.

In the scope of this research, the petrographic and geochemical analyses of clastic sedimentary rocks from the St. Barbara, copper and iron ore mine in Rude near Samobor, have been made, aiming to classify and determine the provenance and environment of formation of clastic sedimentary rocks, as well as the influence of hydrothermal fluids on their properties. Eight samples were collected in total from different locations in the mine. Six of those samples have been studied in detail. The results showed structural and geochemical variability and uneven hydrothermal alteration intensity in the samples. Based on petrographic analyses, three rocks are classified as sublithoarenite, quartz arenite and quartz greywacke. Three of the samples are classified as ore breccia, ore sandstone, and ore silt-sandstone due to the pronounced hydrothermal alterations and ore mineralisation. Comprehensively, petrographic and geochemical analyses indicate that the source rocks of the investigated clastic sedimentary rocks were felsic (La/Sc = 0.9-6.2; Th/Sc = 1.3-2.4), most probably sedimentary, possibly resedimented rocks. The extent of source rock weathering was very high (Chemical Index of Alteration CIA = 52.1-81.3 %) and the geotectonic position of the sedimentary basin was very likely to be at the passive continental margin.