The stibnite mineralization at Rizana (Kilkis ore district; Serbo-Macedonian metallogenic province; northern Greece) occurs along a NE–SW-trending brittle shear-zone, which transects a two-mica and an augen-gneiss of the Vertiskos Unit. Barren Triassic A-type granites and satellite pegmatites and aplites, as well as Oligocene-Miocene plutonic, subvolcanic and volcanic rocks that are variably hydrothermally altered and mineralized, outcrop in the broader region. The mineralization appears as veins, discordant lodes and disseminations. Veins and discordant lodes exhibit massive and brecciated textures. Historic underground mining (1930s–1950s) produced 9000 t of stibnite ore, grading 40% Sb on average. The main ore mineral assemblage includes stibnite + berthierite + sphalerite + pyrite + chalcopyrite + native antimony and traces of wolframite, galena, tetrahedrite, marcasite, pyrrhotite, arsenopyrite, realgar, native arsenic and native gold. Quartz, minor barite and ankerite are the gangue minerals. Sericitization and silicification developed along the shear-zone, forming hydrothermal halos of moderate intensity in the two-mica gneiss. Locally, valentinite, goethite and claudetite are present due to the supergene oxidation of the stibnite mineralization. Bulk ore geochemistry shows enrichments in specific elements including As, Au, Cd, Se, Tl and W. Fluid inclusion microthermometry showed that the mineralization was formed under a limited range of temperatures and salinities. The fluids had low to slightly moderate salinities (6.6–8.1 wt% equiv. NaCl) with low homogenization temperatures (217–254 °C, with a maximum at 220 °C).

Supply risk and economic importance are the key aspects controlling the metals classified as critical. Several of the critical metals are also classified as rare based on their restricted geological availability. In Europe, numerous mineralizations have been reported as being enriched in critical, strategic, and rare metals, and could potentially facilitate the production of these metals as by-products. Within this context, this paper reviews the critical and rare metals incorporated in the vein-type mineralization hosted in the Vertiskos unit in Greece. Several Cenozoic polymetallic mineralizations hosted in quartz veins and metamorphic rocks, which are enriched in Cu–As–Pb–Bi–Ag–Au–Te or in Sb-W are being reported in the region. The polymetallic mineral assemblages are characterized by base metal sulfides—Bi-sulfosalts, Bi-sulfotellurides, and tellurides—associated with Au and Ag. On the contrary, Bi-Te mineral phases are lacking or are completely absent from the Sb-W mineralization. The highest critical metals enrichments are reported from Kolchiko and include Bi (995 ppm), Co (320 ppm) and W (844 ppm). Gold is up to 28.3 ppm in Koronouda, while Ag reaches up to 2433 ppm in Laodikino.

The sulfide mineralization at Xylagani is hosted in metamorphosed mafic massive and pillow lava. It has an Early–Middle Jurassic age and belongs to the Makri unit, which represents the upper crustal section of the Evros ophiolite in the Circum Rhodope Belt, Northern Greece. The protolith of the host rock is basalt that has a boninitic-to-low-Ti tholeiitic composition and was formed in an intra-oceanic supra-subduction zone within a juvenile forearc-to-volcanic arc setting. The volcanic rocks were subjected to ocean-floor metamorphism at very low-grade prehnite–pumpellyite facies and low-grade greenschist facies at temperatures of up to 360 °C and pressures between 1 and 4 kbar. The mineralization shows typical features of a stratabound–stratiform deposit and occurs as silicified lenses and layers with disseminated and massive sulfides and gold. Based on host rock composition, geotectonic setting, and base metal content, the mineralization at Xylagani is classified as a Cu-rich mafic volcanic-associated deposit, i.e., Cyprus-type VMS (volcanogenic massive sulfide). The mineralization consists of pyrite, chalcopyrite, gold, pyrrhotite, sphalerite, galena, and tennantite-(Zn). It was formed at a subseafloor setting where hydrothermal fluids circulated through the host volcanic rocks, resulting in a pervasive alteration (silicification and chloritization) and the development of a replacement VMS deposit. The very low-to-low-grade orogenic metamorphism and related deformation during the Alpine collision in the Middle Jurassic to Early Cretaceous periods remobilized the mineralization and formed milky quartz veins with rare sulfides, crosscutting the metavolcanic rocks.

The high global demand for critical elements required for continuously advancing technologies has intensified the research interest in gold deposits that are enriched in elements such as Te, Se, Bi, Sb, W, and Mo

Hydrothermal alteration assemblages provide valuable information on epithermal mineralization, but superimposed events may obscure their relationships with ore formation. This study characterizes the gangue and alteration architecture of the Pefka-Loutros high- to intermediate-sulfidation (HS-IS) epithermal district, NE Greece, and evaluates which assemblages and spectral features distinguish higher-grade mineralization from alteration in the surrounding volcanic rocks. Particularly, the enrichment of the Pefka deposit in critical and precious metals, including In, Te, Se, Au, and Ag, provides an opportunity to assess alteration-based exploration vectors in a complex polymetallic system. We integrate 764 portable visible-near-infrared and shortwave-infrared (pVNIR-SWIR) measurements and X-ray diffraction (XRD) analyses of 60 samples with petrography, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and bulk-rock geochemistry of 136 samples. At Pefka, adularia-bearing volcanic rocks surrounding the mineralized veins contain Mg-bearing muscovite with relatively long Al-OH absorption wavelengths, commonly around 2210 nm. In contrast, the white mica in the immediate vein wall rocks and ore-bearing assemblages is predominantly muscovitic, while higher-grade samples tend to exhibit shorter Al-OH wavelengths, commonly around 2200 nm. The HS quartz-barite veins contain white mica and aluminum phosphate-sulfate minerals, whereas later IS veins are associated with carbonate gangue and white mica-carbonate wall-rock alteration. Principal component analysis (PCA) of centered log-ratio-transformed bulk-rock geochemical data identifies a mineralization-related association involving Cu, In, As, Te, Au, and Ag toward negative PC1 scores, mainly related to samples containing white mica and/or carbonate. In contrast quartz-“adularia” veinlets and associated altered rocks show positive PC1 scores and represent a comparatively lower-grade mineralized stage, and the replacement of “adularia” by white mica near the HS and IS veins supports alteration overprinting. In the southern sector of the Pefka-Loutros area, alunite-bearing gangue and wall-rock alteration occur along silicified faults and hydrothermal breccias, whereas hilltop opaline silica blankets and associated kaolinite-alunite alteration indicate a shallow steam-heated environment. These results define a multistage alteration architecture in which mineral assemblages and spectral variations help distinguish mineralizing stages and guide exploration when interpreted alongside structural, textural, and geochemical evidence.