Rossitsa D. Vassileva

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.

Calcic skarns are formed on the pegmatite/marble contact in the region of Dzhendemski Ezera, NW Rila, Bulgaria. The garnet/vesuvianite-dominated association is formed in the marbles of the Malyovitsa Lithotectonic Unit as a result of emplacement of crosscutting pegmatite injections. Large (up to 3 cm) prismatic vesuvianite crystals and their radiating aggregates are associated with garnet masses, diopside, scapolite, and zoisite. Representative samples were selected for mineralogical and geochemical study, focused on the vesuvianite composition and its associated minerals. Significant incorporation of fluorine is an important compositional characteristic in vesuvianite and garnet evidencing for the fluid/rock interaction and diffusion-involved bimetasomatic processes due to pegmatite intrusion. Trace-element signatures of the skarn minerals reveal constant isomorphic incorporation of large set of elements including V, Zn, Ga, Ge, Sn, Ni, Bi, REE, HFSE, U.

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.

Mineralogical and geochemical LA-ICP-MS trace element study was conducted on sulphides from the Djurkovo Pb-Zn deposit, Central Rhodopes. The studied ore mineralization consists mainly of sphalerite, galena, pyrite, and chalcopyrite precipitated in three mineral parageneses, part of the main polymetallic and quartz-carbonate stages as it is indicated by the textural relationships. The first paragenesis is developed as massive metasomatic replacement occurring in the marble horizons and consisting of sphalerite, galena, and chalcopyrite. The second para­genesis represents later veins composed mainly of quartz, pyrite, galena, and sphalerite crosscutting the metasomatic bodies. The third paragenesis represents late thin carbonate veins with translucent greenish sphalerite (cleiophane) and pyrite/marcasite aggregations, parts of the quartz-carbonate stage. The trace element signatures of the studied sphalerites indicate incorporation of Fe, Cd, Mn, Cu, Co, In, and Hg. Important elements in pyrites are Co, As, Pb, Mn, and Se. Chalcopyrite is the main carrier of Ag among the studied sulphides. The latest pyrite/marcasite aggregations show significant incorporations of As, Sb, and Tl.

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.

The Sedefche Au-Ag deposit is located in the eastern Rhodopes, Bulgaria and is part of the Zvezdel-Pcheloyad ore field. The deposit is of low-sulphidation epithermal type, hosted in Oligocene highly silicificated intermediate volcanic tuffs, which lie above shallow marine sediments of organogenic limestones. The orebody has stratiform shape partly outcroping onto the surface. The ore mineralization is represented by small crystals and fine grained aggregates of sulphides (mainly pyrite, arsenopyrite, marcasite, chalcopyrite, galena, sphalerite) and associated sulphosalts (tetrahedrite, pyrargyrite, freibergite, and miargyrite) within matrix of quartz, formed in several stages of deposition. Gold in the deposit is detected in significant amounts in bulk ore samples, while native gold (a single < 1 μm gold nugget) and gold-bearing phases were sporadically discovered. The form of gold presence in the deposit is nevertheless debatable. Using combined SEM-EDS, EPMA and LA-ICP-MS approach, the highest concentrations of gold have been established in the arsenopyrite – the gold content there is up to hundredfold higher than in other ore minerals being potential concentrators of gold such as pyrite, marcasite and chalcopyrite. The presence of gold in arsenopyrite predominantly as nanoparticles, irregularly disseminated in the crystals as clusters of inclusions is suggested.