Giulio Casini

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.

Bauxites, a key source of multiple critical raw materials, including aluminum, rare earth elements (REEs), titanium, and gallium, have gained renewed interest due to Europe's ambition of becoming the first carbon-neutral economy by 2050. The External Dinarides, part of the Alpine orogenic system, provide an ideal setting for examining the interplay between lithospheric deformation and surface processes in fold-thrust belts, with a particular focus on the formation and preservation of karst bauxite deposits. Multiple emersions with associated bauxite deposits and occurrences have been reported from the Adriatic microplate throughout its tectonio-stratigraphic evolution from rifting to passive margin and tectonic inversion, including Triassic, Jurassic, Lower and Upper Cretaceous, and Paleocene-Eocene age deposits.This study investigates the tectono-stratigraphic evolution of a portion of the External Dinarides and its controls on the generation and preservation of Late Cretaceous-Paleogene karst bauxites in the Posušje area, Bosnia and Herzegovina.A 3D geological model was developed using detailed geological maps, borehole data, and remote sensing, integrating structural interpretations and cross-section analyses to determine deformation style, and tectonic control over basin evolution and paleogeography.The study reveals a complex structural history characterized by both thin- and thick-skinned tectonics, with multiple detachment levels and the inversion of inherited normal faults. Late Cretaceous-Paleogene bauxite deposits are closely associated with the Late Cretaceous to Early Paleocene forebulge uplift and subsequent erosion, where karst-related depressions served as primary traps for bauxite accumulation and preservation. Paleocene to Oligocene syn-orogenic deposits are reviewed in the context of the Dinaric Foredeep Basin's evolution and its progressive migration towards the foreland. Finally, the 3D-modeled top Cretaceous unconformity highlights extensive underexplored areas where bauxite deposits might exist at mineable depths, offering improved targeting efficiency for future exploration campaigns.Through the integration of tectono-stratigraphic data within a validated structural model, this work provides new insights into the evolution of the External Dinarides and valuable information on the formation and preservation of Late Cretaceous-Paleogene karst bauxites. These findings contribute to enhancing exploration strategies for critical mineral resources in this portion of the fold-thrust belt and other regions with similar geological settings.

The interaction of the lithosphere with surface processes in fold-and-thrust belts often leads to the formation of mineral ore deposits, including economically significant resources like bauxites. These interactions are driven by complex geological dynamics, including crustal deformation, sedimentation, and erosion, which create favourable conditions for ore deposition. Bauxite, an essential ore for aluminium production, has become increasingly critical due to global demand and is now included in the European Union's fifth list of critical raw materials. The Dinarides, a branch of the Alpine Belt in south-eastern Europe, are notable for their multiple bauxite levels, making them an important case study for understanding bauxite ore deposits. The External Dinarides are traditionally divided into two tectonic units: the High Karst Unit and the Dalmatian Unit. Historically, these external Dinarides have been interpreted as a thin-skinned fold-and-thrust belt, characterized by significant horizontal shortening and detachment along sedimentary layers.This study proposes a new model for the evolution of the Dinarides, mapping the spatial and temporal distribution of bauxites providing valuable insights into the processes that control their formation, with the ultimate aim to provide broader implications for exploration strategies in similar geological settings.The new model is based on regional balanced and restored cross-section through the External Dinarides of Bosnia and Herzegovina and Croatia that integrates offshore 2D seismic data, borehole data, fieldwork and remote sensing to determine style of deformation, and paleogeographic evolution of this portion of the belt.The balanced and restored cross-section revises the traditional view, proposing a mixed thin-skinned/thick-skinned tectonic model that emphasizes the role of deep-seated structures and salt tectonics in shaping the region, with much less shortening than previous models. Salt tectonics, involving the deformation of evaporite layers, plays a critical role both in the passive margin stage and its subsequent inversion, localising the deformation and controlling the structural style. In this revised tectono-stratigraphic framework, potential scenarios for bauxite generation, accumulation and preservation are outlined. The combination of surface processes and tectonic activity creates zones where bauxite deposits are likely to be concentrated, both at local (thrust ramp anticlines, diapir roof uplift or extensional footwall uplift) and regional (see level fluctuation, forebulge migration) scales. Understanding these scenarios not only enhances the exploration potential in the Dinarides but also offers valuable analogues for bauxite exploration in other fold-and-thrust belts worldwide.

The AGEMERA project (Agile Exploration and Geo-Modelling for European Critical Raw Materials) advances the exploration of critical raw materials in the EU by deploying innovative, non-invasive geophysical technologies. Funded by the Horizon Europe programme, it aligns with the European Critical Raw Materials Act to enhance resource security and sustainability. Utilising passive seismic methods, drone-based electromagnetic sensing, and muography, the project maps subsurface characteristics across multiple countries in Europe and Zambia. Outcomes are integrated into a dynamic web-based platform for enhanced co-visualisation of different data sets.

Reinterpretation of the Organyà Basin, based on new detailed field observations and subsurface data, emphasizes the key contribution of Upper Triassic evaporites in the tectono‐sedimentary evolution of the South‐Central Pyrenees. Results are integrated in a 65‐km long restored cross‐section through the Serres Marginals, Montsec and eastern Organyà salt‐related depocenters. The reconstructed part of the Jurassic–Cretaceous northern Iberian salt‐rich rifted margin shows a template characterized by inherited Permo‐Triassic basement normal faults and an initial salt thickness of 0.7 km to the south and 1.5 km to the north. The Organyà Basin is part of the South Pyrenean Diapiric Province, a large system of salt related depocenters and minibasins, that is limited to the north by the more than 120‐km long Senterada salt wall complex separating the supra‐salt and sub‐salt domains in the Southern Pyrenees. Three main stages of diapiric activity are recognized along the northern Iberian margin from Asturias to the Eastern Pyrenees: a Jurassic early salt mobilization; a latest Jurassic–middle Albian main diapiric evolution associated with rifting; and a Campanian–Miocene diapiric reactivation during basin inversion that produced salt welds and thrust welds and translated the salt province some 60 km to the south.

Fieldwork and remote-sensing data from the Siah Kuh anticline, simply folded belt, Zagros, Iran indicate that specific structures and fracture systems formed during the development of its sigmoidal shape, and that conceptual fracture models developed for cylindrical folds are inadequate for the correct evaluation and development of hydrocarbon accumulations in this type of anticline. The sigmoidal shape of the Siah Kuh anticline was achieved in the Pliocene due to vertical axis rotations of an already existing anticline. These rotations promoted the development of (1) two systems of normal faults in the outer arcs of the sigmoidal shape, (2) a low-angle thrust, and (3) the north–south Danan anticline in the inner arc of its easternmost bend. The passive margin to syn-folding structures, typically observed in nearby cylindrical and periclinal anticlines, predated the development of the sigmoidal shape and were passively rotated into the segments of the anticline. The sigmoid-related structures are spatially, geometrically, and kinematically related to the bends of the anticline trend, hence they can be predicted and modeled in the subsurface. The sigmoid-related normal faults have a great potential to preserve porosity and promote localized high flow rates or early water breakthrough. However, if they cut through thin reservoir and seal units, sigmoid-related thrusts and normal faults might compromise lateral reservoir continuity and seal integrity. The results of this study can help in reducing risks and uncertainty in the evaluation and development of business opportunities in secondary sigmoidal anticlines within the Zagros or any other fold-thrust belt.

Flow simulations of fractured and faulted reservoirs require representation of subseismic structures about which subsurface data are limited. We describe a method for simulating fracture growth that is mechanically based but heuristic, allowing for realistic modelling of fracture networks with reasonable run times. The method takes a triangulated meshed surface as input, together with an initial stress field. Fractures initiate and grow based on the stress field, and the growing fractures relieve the stress in the mesh. We show that a wide range of bedding-plane joint networks can be modelled simply by varying the distribution and anisotropy of the initial stress field. The results are in good qualitative agreement with natural joint patterns. We then apply the method to a set of parallel veins and demonstrate how the variations in thickness of the veins can be represented. Lastly, we apply the method to the simulation of normal fault patterns on salt domes. We derive the stress field on the bedding surface using the horizon curvature. The modelled fault network shows both radial and concentric faults. The new method provides an effective means of modelling joint and fault networks that can be imported to the flow simulator.

Permeability in fractured carbonate reservoirs is very heterogeneous due to fracturing at different scales superimposed on inherent textures from deposition and diagenesis. Observations of fractures in core and outcrop indicate that flow in open fractures in carbonate rock tends to be channelled rather than through fissures. Most of the flow takes place along a few dominating channels in the fracture plane, whereas most of the fracture plane is not effective for fluid flow. The formation of flow channels is caused by a combination of mechanical and, in particular, diagenetic processes. Single extension fractures occur as partly open or vuggy fractures, and their hydraulic properties are controlled by dissolution and cementation. Single shear fractures are typically open at local steps in the fault plane controlled by shearing along irregular fracture surfaces. Fault damage zones tend to be concentrated at fault tips, intersections, pull-aparts and overlap zones that represent areas of dilation. These damage zones represent elongated features in three dimensions with a high fracture density that will result in channelled flow at reservoir scales. The effect of channelled flow should be taken into account during evaluation of fractured carbonate reservoirs and when building dynamic flow models.

Advances in virtual outcrop technologies and their introduction to fracture characterization allow extraction of fracture data from very large and inaccessible areas. The recent development of automated or semiautomated methods for fracture extraction aims to reduce or avoid tedious, time-consuming, and biased manual interpretation of fractures from virtual outcrops. We present a benchmarking exercise between a previously proposed automated fracture picking method, manual picking, and fieldwork methods. Comparison between the three methods highlighted their relative advantages and limitations. The automated fracture picking method provided excellent results in terms of fracture orientation, size, spatial distribution, and density. Fieldwork is complementary to fracture extraction from virtual outcrops, and it should focus on quality control of remote sensing data, poorly exposed areas, small-scale observations, diagenesis, timing of fracture development, building conceptual models, and linking fracture stratigraphy to rock properties. We propose a best practice for the use and integration of manual and/or automated fracture extraction from virtual outcrop and fieldwork data for fracture characterization and modeling from outcrop analogs. We consider integration of different methods as the best way to improve the modeling exercise while reducing operational costs and risks.

In recent years, fracture-controlled (hydrothermal) dolomitization in association with igneous activity has gained interest in hydrocarbon exploration. The geometry and distribution of dolomite bodies in this setting are of major importance for these new plays. The Latemar platform presents a spectacularly exposed outcrop analogue for carbonate reservoirs affected by igneous activity and dolomitization. Light detection and ranging (LIDAR) scanning and digital outcrop models (DOMs) of outcrops offer a great opportunity to derive geometrical information. Only a few analysis methods exist to quantitatively assess huge amounts of georeferenced three-dimensional lithology data. This study presents a novel quantitative approach to describe three-dimensional spatial variation of lithology derived from DOMs. This approach is applied to the Latemar platform to determine dolomite body geometry and distribution in relation to crosscutting dikes. A high-resolution photorealistic DOM of the Latemar platform allows description of dolomite occurrences in three dimensions, with high precision at platform scale. This results in a unique lithology dataset of limestone, dolomite, and dike positions. This dataset is analyzed by true three-dimensional variography for the geospatial description of dolomite distribution. In most studies, three-dimensional geostatistics is the combination of two-dimensional horizontal and one-dimensional vertical variation. In this study, the dolomite occurrences are extensive in three dimensions and cannot be reduced to a two-dimensional + one-dimensional case. Therefore, the concept of two-dimensional variogram maps is expanded to a three-dimensional description of lithology variation. Three-dimensional anisotropy detection is used to derive principal directions in the occurrence of dolomite. Two small-scale (<200 m [656 ft]) anisotropy directions emerge, one vertical and one subhorizontal, which describe the geometry of the dolomite bodies. These principal directions are perfectly aligned parallel to the average dike orientation. On platform scale (200–1600 m [656–5249 ft]) a bedding-parallel anisotropy direction indicates stratigraphic control on dolomite occurrences.