Stable isotope (δD, δ18O) data on the structural water of two sericite samples from the Cu-Au high-sulphidation deposit Chelopech, Bulgaria – a tentative study

The epithermal high-sulphidation Cu-Au Chelopech deposit is characterized by a well-developed and well-traceable hydrothermal footprint manifested in the volcanic host rocks. The economic ore mineralization is embedded in the strong silicification, included among the advanced argillic zone of alteration, smoothly transitioning to quartz-sericite alteration that evolves into widespread propylitics. The quartz-sericite alteration zone is accessible for exploration only in underground mining galleries and exploration drillings. The main mineral assemblage in this zone is quartz, sericite, pyrite, minor rutile/anatase and relics of apatite and feldspar. According to XRD data from the studied samples, sericite was defined as illite and muscovite/sericite 2M1 polytype. The abundance of heavy stable isotopes (D, 18O) in the structural water of two sericite samples is the object of this study. A special attention was paid to the separation of extraneous waters from the structural one by thermal fractionation. The extracted structural water was converted to hydrogen and carbon dioxide before the isotopic measurements. The obtained results, put into a δD vs. δ18O plot, indicate that sericite structural water is “heavier” than meteoric water, within uncertainty limits.

Use of multivariate statistical methods to determine spatial distributions of chemical elements in soils (Mariovo region, North Macedonia)

The main objective of this study is to present the distribution of different chemical elements in soil samples from the Mariovo region, North Macedonia. To determine the level of presence of chemical elements, soil samples were collected from a total of 33 locations in a 5×5 km area. From each location, two samples of soil were collected: topsoil (0–5 cm) and bottom soil (20–30 cm). The analyses of soil samples were used to assess the prevalence of the chemical elements and the presence of heavy metals in the studied area. The analysis was carried out, using two instrumental methods: atomic emission spectrometry with inductively coupled plasma (ICP-AES) for macro-elements, and mass spectrometry with inductively coupled plasma (ICP-MS) for trace elements. A factor analysis was applied to reveal the relationships between the investigated variables (chemical elements). From the obtained results, spatial distribution maps of factors for the separate groups were prepared, as well as distribution maps for the analyzed elements. It was found that the distributions of most elements follow the lithology of the examined area. Factor analysis revealed the relationships between the investigated variables and could provide dimensionality reduction based on them.

Assessment of the factors affecting slope stability in the southern part of the Sofia Kettle

A specific sample area was selected, where an assessment model was made for the stability of a slope subjected to anthropogenic impacts. A hillside slope zone from the foot of the Vitosha and Lozen mountains in the southern periphery of the Sofia Kettle was chosen as an exemplary area for a part of the hazards arising in the Trans-Balkan valleys. The anthropogenic impact on their slope stability was studied on three particular slopes. The study area is about 1.25 km2 and has a maximum distance of up to 3.80 km between the slopes. Landslide processes resulting from anthropogenic impact often occur on the territory of the Sofia Valley. The rise of construction, the development of hard-to-reach terrains with steep slopes, their undercutting, the seismic impact and the low values of the strength-deformation parameters of the geological varieties building up the respective terrains contribute to their occurrence. The deforestation, the loads with heavy embankments, the hydration and the inhomogeneity of the layers of the earth base have a strong destabilizing effect. The paper presents the results of field and laboratory tests and analyses of slope stability by the method of Fellenius. The severity of the impact of the various destabilizing factors was assessed.

Correlation between the liquid limit of clay derived by the Vasiliev and Casagrande test methods

The liquid limit is one of the most commonly used index properties of soils. The paper compares liquid limit values determined by the Vasiliev cone penetrometer method and by the Casagrande cup method, based on 45 natural clay samples collected from the Kozloduy Town area (North Bulgaria). An empirical correlation based on these liquid limit results has been derived.

Risk assessment of geological disaster in the region of Primorsko Municipality

Risk assessment methodology is described in detail and applied for assessing the geological hazard for potential landslides and earthquakes. This methodology follows the guidelines of ISO 31010 and the JRC recommendations, and is applied for the first time in Bulgaria. The obtained results have high practical applicability. The flexibility of the methodology allows the final result to be presented as either a risk matrix or risk profiles. It depends on the specific tasks, issues and scientific problems that need to be solved.

The mineral diversity of the Urdini Lakes and the glacial valley of the Urdina River (Rila Mountain) – an overview

An overview of different types of mineralization in the area of the Urdini Lakes and the glacial valley of the Urdina River (northwestern Rila Mountain) has been made. Currently, it is the only protected area for minerals in Bulgaria. In this area, mainly pegmatite, but also skarn and alpine-type mineralizations, have been found to date. Of particular interest are the hybrid desilicified type pegmatites containing emerald, aquamarine and chrysoberyl crystals and the extremely rare native aluminum. The skarn mineralizations from this area are characterized by wollastonite, diopside, garnet (grossular, andradite), zoisite, clinozoisite, scapolite, vesuvianite and others. In the alpine-type mineralizations, well-formed crystals of quartz, adular, epidote and pyrite, as well as nests of almandine with albite, were observed as recrystallization of the minerals previously formed in the cavities of the host rocks. These cavities may also occasionally contain zeolites.

The thermal waters in Sofia City (Bulgaria): importance, condition and problems

Sofia, the capital of Bulgaria, is situated in a region rich in thermal waters, which were a major factor for the establishment and development of the city. The thermal spring in the city center of Sofia has been in use since ancient times. As the city expanded rapidly in the 19th and 20th centuries, it absorbed many other sources of thermal water. In addition, the available volume of usable thermal water increased with the construction of abstraction wells. The prevailing types of thermal waters are sourced from Mesozoic rocks at the base of the Sofia graben. The water temperatures are in the range between 21 °C and 54 °C, and the mineralization is up to approximately 1 g/L total dissolved solids (TDS). There is only one source in deeper rock formations with approximately 4 g/L TDS. The population of the city utilizes the thermal water resources to a various degree, mainly for bottling of natural mineral water. Some sources are used for balneology, sport, recreation and sanitation; however, their potential is not sufficiently utilized. Considering the importance of the thermal water resources for the city and its population, a numerical model was set up to study the impact of subway construction on the thermal spring in the center of Sofia.

First record of an erymid lobster (Crustacea, Decapoda) from the upper Bajocian of Northwest Bulgaria

Fossil chela of an erymid lobster from a single locality of the upper Bajocian in the Western Fore-Balkan Mts (NW Bulgaria) was studied. Two segments of the thoracic appendages, probably belonging to one individual, were described: 1) P1 propodus with partially preserved pollex and dactylus; and 2) P1 carpus and P1 merus attached. These elements of the first pair of pereiopods of a lobster were identified as Eryma compressum (Eudes-Deslongchamps, 1842). Eryma compressum a is well-known taxon from numerous Jurassic localities in Europe but has not been recorded in Bulgaria to date. Therefore, albeit being an isolated finding with only a few elements, the Bulgarian example contributes to the overall record of European erymid faunas from the Middle Jurassic, and especially in Eastern Europe, from where only a few erymids have been reported.

Review of investigations into the vadose zone’s variable state of saturation in connection with the assessment of radon potential in Bulgaria

Natural radon (222Rn) is a radioactive noble gas that occurs as the immediate decay product of radium (226Ra), part of the 238U family, in the lithosphere. Radon is driven by advection and diffusion with soil gas throughout connected and water-unsaturated pores and/or cracks in permeable rocks and soils. The aim of the present study is to do a review of the existing so far research activities in Bulgaria in connection with the observation and/or evaluation of the degree of water saturation of the near-surface layer, and on that base to distinguish the up-to-date achievements in regards to the radon potential in situ evaluation. Due to this review, the studies in Bulgaria concerning moisture dynamics in the near-surface layers can be divided mainly into two groups. The first one investigates the hydraulic characteristics (parameters) of soils in the vadose zone. Based on that, conclusions or computer simulations for the saturation degree estimation can be drawn. The other group includes in situ observations by sensors on the change of moisture with time. The results of these studies may serve as a base for more precise moisture dynamics assessment at sites with specific radon potential tendencies.