A distinct increase in the concentration of W in the topsoil (from 19–20 to 71 ppm) is found in the vertical profile of the alluvial soil at the Grantcharitsa deposit. The distribution of W, Fe, and C is well correlated, which indicates a significant role of organic material and iron oxides/hydroxides formed in the soil in the chemical behavior of W. The role in these processes of scheelite, W-containing goethite and rutile identified in the soil is insignificant.

Geopolymers based on Bulgarian natural zeolite (clinoptilolite) were synthesized using alkaline activators in order to prepare plaster/render mortar. The influence of the alkali concentrations of the activator solution was examined in regard to tensile strength and adhesion to concrete. Microstructure of the obtained geopolymer pastes was analysed by XRD, FTIR, SEM. The results showed adhesive strength to concrete up to 3.6 MPa and tensile strength up to 5.44 MPa. The present study shows a promising potential of the geopolymers as coating material for concrete.

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A combination of methods is applied in the present study to define the exact age of the Petrohan and Mezdreya plutons and trace their magma evolution. Field, petrological, and geochemical studies of the Petrohan pluton revealed its complex evolution and emphasized the role of magma mingling and mixing, complementary to the normal assimilation and fractional crystallization (AFC) processes. Using high-precision conventional U-Pb (CA)-ID-TIMS zircon and titanite dating in combination with CA-LA-ICP-MS zircon dating and tracing, we suggest an incremental growth of a common Petrohan-Mezdreya pluton. It was assembled over minimum 4.5 Ma from 311.14±0.48 Ma to 307.54±0.54 Ma. The younger age of the gabbro (308.12±0.33 Ma), compared with the age of granodiorites (311.14±0.48 Ma), provides numerical proofs for magma replenishment during the assembling of the Petrohan pluton. Whole-rock strontium-neodymium (initial 87Sr/86Sr ratios of 0.70521–0.70527 to 0.70462 and 143Nd/144Nd of 0.51221 to 0.51210) and Hf-zircon isotope data (ε-Hf from –5.8 to +3.6) argue for interaction of mantle derived magma with crustal melts but also mixing and mingling and transfer of zircon grains between the gabbroic and granitic melts. Possible petrogenetic scenario includes melting of subcontinental mantle lithosphere and crust and evolution trough AFC, FC and mingling/mixing processes. Considering the Petrohan-Mezdreya pluton as part of the Variscan orogeny in SE Europe, our new data support the accretion/collision of both the Balkan and Sredna Gora/Getic units with Moesia in the Early Carboniferous followed by syn- and post-collisional Carboniferous and Permian magmatism.

This paper presents a study on boiling assemblages in the Kupel occurrence, as boiling was evidenced by the presence of vein adularia and platy calcite. Fluid inclusion evidence is not available since the present fluid inclusions are very small in size for investigation under optical microscope. Boiling assemblages occur in two types of auriferous mineralization hosted by supradetachment, grey fine-grained arkosic sandstones and presented by (i) veinlets of quartzadularia and (ii) veinlets of platy calcite. In quartz-adularia veinlets micron-sized electrum aggregates form globular shapes, which reach 800 µ m across and are arranged along the veinlet length. In cross-sections electrum aggregates display abundant silicate-filled pores of a few microns in size. Globular geometry of the electrum aggregates and their arrangement along the veinlet length suggest collectively that these globules were flowing particles-flocs but not colloidal particles since the latter are much smaller. In these veinlets electrum is intergrown with micron-sized chalcopyrite, galena, hessite and greenockite. The auriferous calcite veinlets are formed later than the auriferous quartz-adularia ones, since the first clearly has intersected or brecciated the latter. Electrum in the calcite veinlets forms accumulations only in portions of sharp thickness expansions after throttle portions, which are barren. This suggests that electrum has been transported by a flowing fluid, in a particulate form and deposited due to pressure drop during hydrofracturing, as the electrum particles have been arrested in low velocity (expanded) portions of ore conduits. The auriferous assemblages in the Kupel occurrence indicate high effectiveness of boiling for deposition of Au, Ag, Cu, Pb, Cd and Te through collective loss of H2, CO2, H2S and H2Te what is in complete accord with recent studies on modern terrestrial geothermal fields. Methods used comprise observations under binocular, optical and scanning electron microscope, and electron microprobe analysis.