Selected pegmatite dyke intruded within the gneiss-marble-amphibolite sequence of the Rhodope Metamorphic Complex was studied for its REY+ACT mineralization in attempt to assess the potential of these pegmatites for critical and strategic raw materials. Mineral composition of K-feldspar and albite is complemented by abundant common accessories of zircon, apatite, monazite, allanite, and titanite. The REY+ACT mineralization is presented as single euhedral crystals (zircon, thorianite, Y-Nb oxide, titanite and fluorapatite) or as complex multimineral nodule-like aggregates. The nodule core typically consists of decomposed Th-bearing monazite-(Ce) altered to different degree by intergrown Th-bearing apatite/thorite assemblage. Fluid-involved reactions led to mineral transformations and redistribution of the elements like LREE, Y, Th, U, and formation of the inhomogeneous allanite-(Ce)/REE-epidote rims enveloping the aggregated earlier phases.

The formation of the Elatsite deposit is related to the emplacement of several Upper Cretaceous porphyritic intrusions with the most significant intrusions of quartz-monzodiorite and granodiorite porphyries. The surface exposure of the Elatsite deposit provides an opportunity for investigating the lithogeochemical features of different hydrothermal alteration types. Petrographic observation combined with detailed geochemical analysis of the hydrothermal alteration types and chemical features of secondary biotite, amphibole, plagioclase and chlorite, led to the assessment of gains and losses of major, trace and REE elements and the origin of fluids for the variety of alterations. The Na–Ca alteration is probably formed from a mixture of magmatic and external fluids. The Na–Ca–K-silicate alteration is formed during fluid–fluid interaction of magmatic and external fluid, with predominance of the magmatic one, and occurs in the zone of primary neutralization. The K-silicate alteration is formed by magmatic fluids with a high oxygen fugacity, high temperature, high aK+ and aMg2+. The upward superimposition of the K-silicate–sericitic alteration is related to the incorporation of meteoric fluids into magmatic fluids in an initial high oxygen fugacity environment and a high aMg2+. The quartz–sericitic alteration occurs from admixture of meteoric fluid into evolving magmatic fluids, with the predominance of the meteoric fluid, inducing an environment with a low aK+/aH+ ratio. The quartz–adularia–carbonate alteration is probably resulting of the admixture of a magmatic fluid with external and meteoric fluids, in an environment with high aK+. The propylitic alteration is observed only in the periphery zones of the deposit and clear relations with other alteration types were not observed.

The Djurkovo and Govedarnika deposits represent hydrothermal Pb-Zn systems spatially associated with the Eocene–Oligocene tectono-magmatic evolution of the Rhodope Metamorphic Complex. This study presents new mineralogical and geochemical data for galena, sphalerite, pyrite, and chalcopyrite obtained by electron probe microanalysis (EPMA) and LA-ICP-MS in order to evaluate the compositional variations of sulphides among the vein and metasomatic mineralization types and between the two deposits. The analysed sulphides exhibit distinct compositional signatures reflecting the different mineralization stages and hydrothermal environments. Sphalerite from the Govedarnika metasomatic ores is enriched in Mn (up to 5200 ppm), Fe (up to 5.13 wt.%) and Co due to interaction with Mn-rich skarn assemblages, whereas Djurkovo sphalerite shows elevated Cd (up to 3000 ppm), In and Hg concentrations. Trace-element systematics indicate coupled Fe-Mn incorporation, competitive Cd-Fe substitution and local re-equilibration processes associated with “chalcopyrite disease” textures. Late pyrite from the quartz-carbonate stage is enriched in As (up to 3.87 wt.%), Au (up to 78 ppm), Ag, Se, Sb and Tl, with positive Au-As and Au-Ag correlations suggesting invisible gold and possible submicroscopic precious-metal inclusions. The obtained data demonstrate prolonged hydrothermal evolution and highlight the potential role of the studied sulphides as concentrators of economically important elements.

The Djurkovo base-metal vein deposit in Laki ore field, is hosted by a heterogeneous gneiss/amphibolite/marble rock sequence of the high-grade metamorphic complex of the Central Rhodopes. Mineralogical and geochemical investigation was conducted on slightly deformed, and hydrothermally altered thin pegmatite dykes intruded in the marbles. The pegmatite bodies consist mostly of K-feldspar, albite and quartz, with minor garnet present. Clear textural zonation within the bodies is absent except for the preferential crystallization of garnet in the innermost parts. The main pegmatite accessories include ishikawaite, zircon, apatite, monazite-(Ce), allanite-(Ce), and titanite. The post-magmatic hydrothermal overprint on the pegmatites resulted in the formation of the assemblage including epidote, sericite, chlorite, carbonate, quartz, hematite, and leucoxene. The accessory oxide, silicate, and phosphate minerals bearing rare earth elements (REE), actinides (ACT), Nb, Ta, and Ti have undergone partial replacement by secondary mineral phases (thortveitite, fergusonite, fersmite, uraninite, thorianite, REE-epidote, xenotime) observed as irregular grains or veinlets along fractures and dissolved zones, either inside or near the primary minerals.