Eastern Rhodope Research Articles

Arsenopyrite from the Low-sulphidation Sedefche Au-Ag deposit, Eastern Rhodopes: Mineral Association and Gold Potential

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.

Iron Age ceramics from Thracian rock-cut complexes from Bulgaria – Mineral magnetic relics of technological production and use

The Gluhite kamani Thracian rock-cut complex in the Eastern Rhodopes Mountain is famous with its more than 500 rock niches carved in the rock at heights up to 20 m. Continuous habitation starting from the final Chalcolithic (the second quarter of the 4th millenium BCE) until the Late Classical – Early Hellenistic period (late 5th – 4th century BCE) provides unique opportunity for studying diachronic changes in pottery production and use. In this contribution, systematic analysis of a collection of 135 ceramic sherds from five archaeological periods at the site was carried out using a combined mineral magnetic and geochemical approach. Magnetic susceptibility (χ), frequency-dependent magnetic susceptibility (χfd%) and firing temperature (Tfire), determined using the magnetic susceptibility method, were combined with data from elemental XRF analyses. Thermomagnetic measurements, employed for identification of magnetic minerals revealed the dominant presence of (titano)magnetite with low Ti-content and/or a fraction of single-domain magnetite and in few cases hematite. Although varying in a wide range, median χ values of ceramic sherds from the Early Iron Age (EIA) periods show similar distribution, while for Late Iron Age (LIA) with the introduction of the wheel-thrown pottery, χ values are higher, presumably due to decreased amount of silica-rich clastics in the clay. Concurrently, χfd% values decrease in ceramics from the LIA, indicating predominant presence of stable single-domain magnetite in the iron oxide composition of the ceramics. Firing temperatures (Tfire) estimations display a systematic pattern of two groups – higher (Tfire between 760 and 800 °C) and lower (Tfire ∼ 400–––600 °C). During the EIA periods both Tfire groups are present, characterized by systematic gradual decrease of the median value of the low Tfire when going from EIA1 towards the EIA2. Wheel-thrown pottery from the LIA show low Tfire ∼ 400 °C only. Based on the differences in thermomagnetic properties of ceramics, their magnetic parameters and Tfire estimates, two possible hypotheses are suggested to explain the observed changes in EIA ceramic characteristics: i) utilization of two differently sourced clay materials (illite-dominated and montmorillonite-dominated) for production of ceramics fired at higher and lower temperatures, respectively; and ii) utilization of one raw clay source, while using two firing regimes – firing at higher temperature for prolonged time, and fast firing to high temperature with successive stage of longer firing at lower temperature. Differences in thermomagnetic properties of wheel-thrown pottery from the LIA period leads to the assumption for utilization of diverse clay source for their production, as compared clay sources for the Early Iron Age periods.

Annual and Seasonal Characteristics of Rainfall Erosivity in the Eastern Rhodopes (Bulgaria)

Rainfall, with its intensity, duration, and seasonal distribution, is among the main factors causing soil erosion, which is a widespread environmental problem in Bulgaria. Rainfall erosivity shows the potential of precipitation to generate erosion processes and is an essential indicator of the climate vulnerability of a region. This paper aims to evaluate rainfall erosivity in a part of the Eastern Rhodopes Mountains, an area that is characterised by high-intensity erosion processes and high erosion risk. Local peculiarities of rainfall erosivity were revealed by the calculation of some precipitation indices based on the monthly precipitation for the period 2000–2021, such as the precipitation concentration index (PCI), Angot precipitation index, Fournier index (FI), and modified Fournier index (MFI). The analysis of the extremely wet and extremely dry months at the annual and seasonal (October–March and April–September) levels was performed to evaluate the susceptibility to erosion. The results from the study show that rainfall erosivity in the studied area varies from low to moderate in the northern part of the study area and from high to very high in the south. According to the MFI, high and very high erosivities have been observed mainly since 2012. The erosivity increases from north to south, to the area with a complex relief, where the combination of orography and atmospheric circulation make favourable conditions for the occurrence of extreme precipitation. The analyses of the calculated indices show that the precipitations in most of the studied area generally have from a low to a moderate erosivity, but this does not exclude the occurrence of cases with high and very high erosivities, which are characteristic of recent years and are related to the increase in annual precipitations and extreme precipitation months. The results of this study can contribute to the development and implementation of measures and preventive activities for the reduction and possible elimination of the negative impacts of extreme precipitation.

Egg parasitoids of Thaumetopoea pityocampa in the region of Gyumyurdzhinski Snezhnik in Eastern Rhodopes, Bulgaria

The region of Gyumyurdzhinski Snezhnik in the Eastern Rhodopes is the closest in Bulgaria to the Aegean Sea. However, the climate is characterized by specific parameters that are determined by its relief. It is poorly protected from the invasion of cold air masses from the north. From the south, the Gyumyurdzhinski Snezhnik hill restrains the Mediterranean influence. The orography of the area favors the retention of cold air masses and a further drop in temperatures. The experimental material for the study includes 5 generations of Thaumetopoea pityocampa (2016, 2017, 2018, 2019, and 2022), collected in 31 locations of four State Forestry Enterprises: Kirkovo, Ardino, Momchilgrad, and Zlatograd. The sample for analysis included 693 egg batches with 148420 eggs in them. Seven primary egg parasitoids were established in this region: Ooencyrtus pityocampae, Baryscapus servadeii, Pediobius bruchicida, Anastatus bifasciatus, Eupelmus vesicularis, E. vladimiri, Trichogramma sp. and one hyperparasitoid (B. transversalis). Dominant parasitoids were B. servadeii and O. pityocampae, and E. vladimiri and P. bruchicida – occasional parasitoids. The hyperparasitoid B. transversalis participated in the complex with a relatively low share. The survival of the egg parasitoids in the laboratory conditions, in which the samples were kept, was low. The total mortality of the parasitoids in larval and adult stages was 47.8%. After collecting the samples, in laboratory conditions, a total of 442 individuals of the hyperparasitoid B. transversalis emerged, of which 56.3% were females and 43.7% were males. The average number of pine processionary moth eggs in a batch was 214.2. 70.8% of all the eggs in the samples hatched successfully. The egg parasitoids are a very serious natural factor, regulating the density of the pine processionary moth, but their impact varied from 2.1% to 30.3%. The natural characteristics of the area, the air temperature during the stages of eggs and young larvae, are favorable for the development of the pine processionary moth. Unhatched larvae without the influence of entomophages were 7.2%.

Picropharmacolite and arsenolite from the Mareshnitsa ore occurrence, Eastern Rhodopes – new minerals for Bulgaria

New for Bulgaria arsenic minerals picropharmacolite and arsenolite from the Mareshnitsa ore occurrence, Eastern Rhodopes are presented. Their formation is due to the oxidation of arsenopyrite, which is abundant in the samples. The composition of the picropharmacolite from Mareshnitsa differs from the picropharmacolite from other deposits around the world. It is characterized by relatively few impurities and excess of Mg, which substitute part of Ca. This is resulting in smaller a parameter of the unit cell. The presence of these two new arsenic minerals sheds additional light on the behaviour of arsenic in the area.

Sulphate mineralization from one locality in Lozen ore field, Eastern Rhodopes

A suite of sulphates from a locality in Lozen ore field in the Eastern Rhodopes has been characterized by chemical analyses and X-ray diffraction. Three mineral species have been identified: epsomite (MgSO4), pickeringite (MgAl2(SO4)4•22H2O) and alunogen (Al2(SO4)3•17H2O). An attempt was made to characterize the phase transformations that occur upon wetting of the studied samples. The results show that at high humidity, pickeringite dissolves, providing constituents for subsequent crystallization of epsomite and alunogen. Further on, upon drying alunogen loses some of its crystallization water and recrystallizes again to pickeringite including magnesium species from the surrounding medium. This study draws light on certain genetic aspects related to the mechanisms and sequence of deposition of sulphate mineralization under similar conditions.

Incorporation of As, Sb and Tl in pyrite from the epithermal Kandilka prospect, Eastern Rhodopes, south Bulgaria

The major and trace-element chemistry of two pyrite generations (Py1 and Py2) from the Kandilka epithermal prospect was studied by EDS-scanning electron microscopy and laser ablation ICP-MS techniques. Both generations of pyrite are distinguished by occurrence and chemical properties. Pyrite from the first generation (Py1) is established as trace-element poor, sub- to euhedral (mainly single) crystals up to 200 µm. The later As-bearing pyrite (Py2) forms fine-grained semi-massive aggregates with increased contents of trace-elements. Except for arsenic, Py2 is enriched in gold and antimony. The As content of Py2 increases in an oscillatory manner from core to rim, reflecting changes in As activity and the chemical evolution of ore-bearing fluids. The oscillatory-zoned pyrite is composed of complex rhythmic overgrowths of alternating As-rich and As-poor bands. Positive correlation between As- and Au-content in Py2 is characteristic. According to the current results, the Kandilka prospect could be concerned as a low-sulphidation deposit.

Silver-impregnated zeolitized tuffs for environmental degradation of ozone

The natural zeolites were ultrasonically treated and impregnated with silver nanoparticles. The surface stabilized silver nanoparticles dispersion was obtained using an effective electrochemical reduction method. The phase and elemental composition, structure of the Ag-impregnated zeolites (clinoptilolite and mordenite) was studied by various methods such as powder X-ray diffraction, X-ray fluorescence analyses and Fourier-transform infrared spectroscopy. The Ag-impregnated clinoptilolite and mordenite natural zeolite materials with 1.20 wt %, 0.97 wt %, 0.83 wt % and 1.18 wt % silver content were established by XRF analysis. As initial materials were used three types clinoptilolite from Beli Plast, Most, Golobradovo (Kardzhali, Bulgaria) deposits and mordenite from Lyaskovets deposit in Eastern Rhodopes, Bulgaria. The catalytic ability of Ag-mordenite and Ag-clinoptilolites was investigated in the ecologically important reaction of ozone decomposition. The Ag-loaded mordenite demonstrates the higher conversion degree of ozone more than 40% in comparison with Ag-clinoptilolite materials at room temperature.

Trace element geochemistry of altered pyroclastic deposits from the Eastern Rhodopes (SE Bulgaria)

The contents of major and rare elements in 10 samples of altered (mainly zeolitized) pyroclastic rocks from the Eastern Rhodopes are investigated. The samples are selected to represent different secondary mineral associations specific to the area. The obtained results indicate that the diversity in secondary mineral associations has relatively little influence on the trace element geochemistry of zeolitized pyroclastic rocks in the Eastern Rhodopes. Regarding their trace and rare earth element composition, these rocks show the main characteristics seen in the acid lavas in the area.

Efficiency of Modified Natural Clinoptilolite Tuff for As(III) and As(V) Uptake from Model Polluted Water

Granular and powdery clinoptilolite tuff samples from Beli Plast, Eastern Rhodopes, Bulgaria, were coated with metal hydroxides (Fe, Al, Fe-Mg) by two-step alkalization. The prepared sorbents were tested for As(III) and As(V) uptake from a modeled water solution with an arsenic concentration of 44 μg/L. The granular sorbent was used in the sorption columns and showed a high efficiency of arsenic purification from slightly polluted waters. The calculated maximum sorption capacity for the optimal conditions is 32.9 μg/g. The adsorption proceeds according to the Langmuir model. The mechanism of adsorption is most likely inner-sphere complexation. The sorbents’ complete regeneration was achieved by NaOH treatment. The results of the experiments show good possibilities for obtaining water with an arsenic concentration ranging from below the limit of detection to 3.8 µg/L, which is a significantly lower value than the permitted value of 10 μg/L and close to the national environmental quality standard for shallow waters. The high efficiency shows Fe- or Mg,Fe-coated clinoptilolite sorbents. The sorbents are highly efficient in purifying 400 liters of water with an initial concentration of 44 mg/L of either arsenate or arsenite per 1 kilogram of sorbent at a rate of 2.4–2.0 L/h/kg. The powdered sorbents used in a batch system under “static” conditions showed a much higher adsorption capacity than the granular one. Such sorbents are more suitable for small quantities of water with a high concentration of arsenic.

Trace elements in the clinoptilolite tuffs from four Bulgarian deposits, Eastern Rhodopes

In this study, we are focusing on the presence and contents of the rare earth and trace elements in the clinoptilolite-rich tuffs of the four large zeolite deposits Beli Plast, Golobradovo, Most and Beliya Bair (Eastern Rhodopes, Bulgaria). The chemical properties of the tuffs were studied with regard to be used in eco-toxicological experiments as sorbents for detoxification of the experimental animals. The clinoptilolite tuffs are relatively depleted in Sc, V, Cr, Co, Ni, Cu, Zn, Ga, W, Y, Zr, Ba, Hf, and REE. A relative enrichment is found for the elements Be, S, Ag, In, Sn, Sb, Tl, Bi, and Pb. According to the requirements of the European legislation regarding the contents of lead, cadmium, arsenic, clinoptilolite, clay minerals and quartz in the zeolitized rocks, the tuffs from Beli Plast and Most deposits could be used as a sorbent for detoxification purposes.

Archaeometric and experimental study of clays and fragments of wall plaster from the archaeological site Gluhite Kamani, Eastern Rhodopes, Bulgaria

The article presents results of investigation of plasters (mono-layered, inhomogeneous and irregularly pigmented) and clays found during archaeological excavations in the Gluhite Kamani Site in the Eastern Rhodopes, Bulgaria. The applicated methods in this study are: optical, physical and experimental. According to the established natural mineral and rock inclusions, the studied plasters show a similar composition. The samples of clay from the central sector of the archaeological site are with different physical features and similar composition. The conducted experimental firing of these clays and the established composition of the plasters, allows us to assume that the same was used for construction of buildings and for plaster, uncovered in parts of the archeological site.

Comparative characteristics of ancient red pigments used to decorate Thracian sacred sites (4th–3rd centuries BC)

The mineral composition and geochemical features of red pigments from paints and plasters used in the color decoration of the Shushmanets, Dolno Lukovo, Maglizh tombs, the eschars from tumulus 21 and 31 from Sboryanovo National Reserve (Bulgaria) and the Documaci Tomb (Romania) are compared. The results show that red ochre pigment (mainly hematite) was applied in the decoration of all objects, and only in the Maglizh Tomb a red cinnabar pigment was used – separately or in a mixture with red ochre. Regardless of the territorial remoteness of the tombs Dolno Lukovo, Maglizh, Documaci and the eschars, the red ochres used in them contain As, Cu, Zn and inclusion of minerals jarosite, plumbojarosite and native gold. Such mineral and geochemical features are characteristic of the oxidation zones of Au-Pb-Zn deposits. The most likely source of the red ochre is the well-developed oxidation zone of Au-Pb-Zn deposits in the Eastern Rhodopes. A characteristic feature of the red ochre from the Shushmanets Tomb is the lack of heavy metals but the hematite of the ochre contains inclusions of magnetite. A probable source for mining of this pigment was non-economic magnetite-hematite ore deposits hosted in the in the neighborly exposed chlorite-sericite schists.

Detrital zircon age constraint on the low-grade sedimentary succession along the Mareshnitsa River Valley, eastern Circum-Rhodope Belt, Bulgaria

We focused on the eastern Circum-Rhodope belt (CRB) low-grade sequence along the Mareshnitsa River Valley in Bulgaria. U-Pb detrital zircon geochronology revealed latest Late Jurassic maximum depositional age of a metasandstone. A major Jurassic zircon cluster in the metasandstone is consistent with a provenance from the CRB-related Evros arc, whereas the minor cluster of Triassic zircons come from the high-grade basement. The results indicate mostly latest Late Jurasic sedimentation proximal to the Evros arc (CRB) and minor detrital input from the continental margin of Eurasia (Rhodope). The results further support the presence of Mesozoic (Jurassic) oceanic lithosphere mantle remnants within the metamorphic basement of the eastern Rhodope Massif.

Geomorphological and Sedimentological Indicators of Contemporary Erosion Processes: An Example of the Eastern Rhodopes Mountains (Bulgaria)

Erosion processes, triggered by water, occur and propagate on sloping surfaces and have a significant negative impact on the soil quality and vegetation, as well as cause a change of the topographic surface. In the long term, they can lead to an increase in sediment transport, siltation of dams, and higher flood hazard. The development of water erosion reflects on the slope profile and the specific landforms like rills and gullies. In this regard, the geomorphological features of the areas can be considered indicators of the spatial distribution of erosion and accumulation. The sediment properties give information about the conditions of the transport and the intensity of the hydrogeomorphic processes. The current study aims to analyse the short-term changes in erosion and deposition by application of morphometry and grain size analysis. Topographic wetness index (TWI) and cross-section profiles of two small gullies were analysed based on high-resolution digital terrain models (DTMs), generated from unmanned aerial system (UAS) data. Remote sensing was combined with field geomorphological research and sediment sampling. The results of the research show about average 2 cm change in erosion and deposition for the period October 2021 – November 2022. Despite TWI and cross-section profiles depending on the DTMs resolution, they are reliable indicators for erosion and deposition. The grain size analysis supports the morphometric analysis. Coarse to very fine sands are predominant in most cases of sediment sampling. The sorting coefficient shows very poorly to moderately sorted deposits which indicates transport in a more dynamic environment and temporary flow.

Geochemistry and tectonic significance of metamorphosed mafic ophiolitic rocks in the upper high-grade basement unit of the eastern Rhodope Massif (Bulgaria–Greece)

Geochemistry and tectonic significance of metamorphosed mafic ophiolitic rocks in the upper high-grade basement unit of the eastern Rhodope Massif (Bulgaria–Greece)

Faunal remains from the Early Iron Age rock-cut complex Gluhite Kamani (Eastern Rhodopes, Bulgaria)

The faunal remains recovered from the Gluhite Kamani site offer the unique opportunity to explore the consumption patterns of the Early Iron Age communities inhabiting the Rhodope Mountains. While a lot high-altitude and rock-cut sanctuaries have been registered within the Rhodope Mountains, this is the only site yielding a larger assemblage (n = 3160) from a stratigraphic sequence dating to the Late Bronze Age - Early Iron Age transition and the Early Iron Age. Domestic animals dominate, with sheep/goat being the main exploited species through all stratigraphic layers. The results show that the percentage of represented domestic animals is relatively continuous, while the number of wild animals seems to vary throughout the different periods., As the site is regarded as a sanctuary during the Iron age, the extent to which we can identify any ritual activity from the osteological assemblage is commented on in the discussion regarding the cull patterns observed, and taphonomy.

Editorial Note: Rhodopes Mountains - a fairy tale in green – Part I (Eastern Rhodopes)

Editorial Note: Rhodopes Mountains - a fairy tale in green – Part I (Eastern Rhodopes)

Antipoisoning activities in Bulgaria to enforce raptors conservation in the country

The first antipoisoning dog unit in Bulgaria was founded in 2016. The dog unit operated more than 4 years (October 2016 – December 2020) in the frame of the Conservation of Black and Griffon Vultures in the cross border Rhodope Mountains (LIFE 14 NAT/NL/901) project. During that time, 153 searches and patrols were conducted. The majority of the patrols were executed in the Eastern Rhodopes (80%), which is the core area of the vulture populations in Bulgaria. The total number of all findings is 310, with 40 of them being illegally poisoned animals, 7 were animal remains, and 10 were poisoned baits. The average number of victims found per poisoning incident is 2.86±3.5. The anti-poisoning dog unit found 11 poisoned animal species. Vultures comprised 17.5% (n=7) of all victims found. In all these cases vultures were unintentional victims as the main cause of poison use were human-predator and human-human conflicts. Wolves and domestic dogs were the most common victims comprising 22.5% and 20% respectively of all poisoned animals found. Carbofuran and Methomyl were identified as the main poison substances used in the investigated cases. Along with the dog unit operation, a development of a National action plan to combat the illegal use of poisons in the wild (hereafter NAP) was initiated with national authorities and NGOs (Ministry of Environment and Waters, Bulgarian Food Safety Agency, Executive Forestry Agency, National Police, Bulgarian Academy of Sciences, other NGOs). In 2021, after intensive communication with the Ministry of Environment and waters, the plan was finally endorsed by the Minister. Local Network of Stakeholders against Wildlife Poisoning in Bulgaria was created in the last two years (2021–2022) in Bulgaria. It includes 55 livestock breeders, farmers, hunters, veterinarians, and mayors of villages.

Изучение биологии гнездования беркута с помощью фотоловушек

Trap camera was installed in an active nest of Golden Eagles (Aquila chrysaetos) in Eastern Rhodopes, Bulgaria. The recordings encompassed 45 days in June and July and the camera took 12 900 photos, from the time when the single nestling was ca. 32 days old until its fledging. 84 food deliveries were recorded, with the prey identified in 76 of them. Land tortoises dominated the diet (65% of the items), followed by Edible Dormouse (Glis glis) (10.5%), snakes (7.9%), and European Hare (Lepus europaeus) (5.2%). The two adults were easily individually identifiable by plumage characteristics, especially on the medium coverts. We recorded unexpectedly high intensity of adding the green material to the nest and cleaning the nest from prey remains, 105 and 35 cases respectively, both done almost exclusively by the female, while the male delivered most of the food – 60 vs 21 of the cases. The female was roosting in the nest with the nestling until when it was 50 days old, after which roosted in the nest only once during a rainy night when nestling was 58 days old. The method provided opportunity for following the lifetime reproductive success of unmarked Golden Eagles.