The Elatsite–Chelopech ore field in the northern part of the Panagyurishte district in Central Bulgaria comprises numerous spatially associated porphyry copper and epithermal gold deposits and prospects. In addition to the mineralization and alteration features, trace elements, lead and sulfur isotope signatures of sulfide minerals from porphyry copper, base metal and gold-base metal deposits/prospects have been studied. LA-ICP-MS analyses of pyrite, arsenopyrite and sulfosalt minerals validate them as major carriers for Au, Ag, Sb, Se and Co. Pyrite from the three types of mineralization has specific geochemical characteristics. Pyrite from the porphyry copper deposits/prospects has generally lower total trace element content compared to pyrite from the epithermal prospects, except for Se, Co and Ni. Pyrite from the base metal and gold-base metal veins is enriched in As, Au, Ag, Sb and Pb. In pyrite from the base metal deposits, Co and Ni have contents comparable to the pyrite from the porphyry copper deposits, while pyrite from the gold-base metal veins shows lower Co and Ni. Arsenopyrite from these deposits shows similar features. Similarly, sphalerite from the gold-base metal veins also has lower Co content compared to sphalerite from the base metal veins but higher In and Cu contents. In addition to the close spatial relationships between the Elatsite and Gorna Kamenitsa porphyry Cu deposits and Negarstitsa-West and Dolna Kamenitsa base metal prospects, as well as similarities in the mineralization and alteration styles, the lead isotopic (²⁰⁶Pb/²⁰⁴Pb = 18.61–18.68, ²⁰⁷Pb/²⁰⁴Pb = 15.64–15.65 for porphyry and ²⁰⁶Pb/²⁰⁴Pb = 18.55–18.67, ²⁰⁷Pb/²⁰⁴Pb = 15.64–15.68 for base metal) and sulfur isotopic (δ³⁴S values of −3 to +1‰ for porphyry and δ³⁴S values of −1.7 to +3.5‰ for base metal) signatures of sulfides support the idea of a genetic link between these two types of deposits. The porphyry and base-metal mineralization result from a common major ore-forming event during the Late Cretaceous, corresponding to deep/higher-temperature and shallower/distal/lower-temperature environments, respectively. In particular, more radiogenic lead (²⁰⁶Pb/²⁰⁴Pb = 18.41–18.47, ²⁰⁷Pb/²⁰⁴Pb = 15.67–15.76) and slightly different sulfur isotopic compositions (δ³⁴S values of +3.5 to +10.6‰) of sulfides from the distal gold-base metal veins of Kordunsko Dere, Svishti Plaz and Shipkite might be a consequence of the interaction of the ore-forming fluids with an external older crustal and isotopically positive S source. Alternatively, a different fluid source/event for the formation of these gold-base metal veins may be suggested.

Deep-sea Fe-Mn polymetallic nodules formed nowadays at the deep-sea ocean floor were evaluated as promising critical raw materials (CRMs). Here, we report results of polymetallic nodules from the H22_NE block of the Interoceanmetal (IOM) exploration area in the eastern part of the Clarion–Clipperton Zone (CCZ), NE Pacific Ocean. The polymetallic nodules were studied with X-ray Diffraction, Raman spectroscopy, SEM-EDS, and LA-ICP-MS (bulk nodules and in situ nodule layers). Additionally, we combine geochemical data of polymetallic nodules with the previously reported data of pore waters and sediments from six stations. Our study aims to define the mineral composition and determine the content of CRMs in the polymetallic nodules and to assess the main factors controlling metal deposition and nodule enrichment in some CRMs. Mn content and the Mn/Fe ratio of the nodules classify them mostly as mixed hydrogenetic–diagenetic type. They are also enriched in Ni, Cu, Co, Zn, Mo, W, Li, Tl, and REE. The in situ REE patterns exhibit MREE and HREE enrichment and a variable Ce anomaly that argues for a changing oxic/suboxic environment and periodically changing of diagenetic and hydrogenetic nodule growth. The results of the joint study of the bottom sediments, pore waters, and polymetallic nodules show a complexity of processes that influence the formation of these deposits. The changing oxic and anoxic conditions are well documented in the chemistry of the nodule layers. Probably the most important controlling factors are sedimentation rate, bioturbation, adsorption, desorption, and oxidation. In addition, growth rates, water depth variations, electro-chemical speciation, phosphatization, and the structures of the Fe-Mn adsorbents are also considered. The polymetallic nodule deposits in the IOM contract area are estimated for future mining for Ni, Cu, Co, and Mn resources. They, however, contain additional metals of economic importance, such as REE and other trace elements (referred to as CRMs) that are potential by-products for metal mining. They can significantly increase the economic importance of exploited polymetallic nodules.

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.

The calcareous nannofossil assemblages in three sections (Dalgi Rid, Milkova Cheshma and Toplika) of the clayey-carbonate Mirkovo Formation in the Central Srednogorie Zone have been investigated. These sections were specifically chosen because, at their basal parts, they contain silica-manganese (± iron) mineralisations, which, according to recent studies, may prove useful for investigations into their potential as a source of ore and critical elements. The nannofloras exhibit very poor preservation and comparatively-low taxonomic diversity. Nevertheless, the presence of some biostratigraphically-significant taxa has been detected. Micula staurophora occurs consistently in sections Dalgi Rid and Milkova Cheshma, which, in the absence of Lithastrinus grillii, indicates the middle to late Coniacian UC10. The latter species was recognised, with a relatively-consistent stratigraphical range, in section Toplika. Although Lithastrinus septenarius and Arkhangelskiella cymbiformis are absent at Toplika, the studied sediments could not confidently be assigned solely to UC12, and thus a tentative late Coniacian (pars.)–Santonian (pars.) age was adopted for the strata in this section. This is consistent with the obtained LA-ICP-MS U-Pb age (86.2±1.4 Ma) of the youngest zircons from the volcaniclastics in the uppermost part of the Chelopech Formation at the same locality, immediately below the boundary with the overlying Mirkovo Formation.

The concentrations of Fe, Mn, Co, Cd, Zn, Cu, Mo, and As were registered in broad intervals and are elevated compared to the mean values for the ocean water. Vertical distributions of the element concentrations in the pore waters along four sediment cores show distinct differences, mainly for the elements Fe, Mn, Cu, and Zn. Bioturbation activities developed in the depth interval 7–15 cm could be a probable reason for the variation trends. The distributions for the elements As, Cd, Co and Zn are conservative type and the patterns for the Mo and Ni – scavenged type. The obtained pore water profiles are similar to the distribution trends for areas in the Eastern Equatorial Pacific and show different patterns from the pore waters from the Western Pacific.

Asarel-Medet JSC Mining and Processing Complex is the first, biggest and leading Bulgarian company for open pit mining and processing of copper and other types of ores. Asarel-Medet JSC is the only Bulgarian company that participates in the international research project AGEMERA to study the potential of Europe regarding critical raw materials for the green transition. The supply of European critical raw materials (CRMs) does not currently meet the European demand. This gap is predicted to increase, making Europe even more dependent on outside suppliers. AGEMERA is a project to help tackle this strategic problem by studying several CRM sites in Finland, Poland, Spain, the Balkans, and Zambia in different deposit types. To check the potential of the porphyry systems in Europe as a source of CRMs, the Asarel porphyry-Cu deposit was selected as a test site. Here we present preliminary geochemical and mineral chemistry data for hydrothermal ore and alteration minerals in Asarel that reveal the potential of the deposit to source some CRMs as by-products. Further studies will combine the geochemical data with innovative geophysical methods for an improved deposit model and provide enhanced knowledge about effective exploration techniques for CRMs.