
The present year 2025 marks two remarkable jubilees: 100 years since the foundation of the Bulgarian Geological Society, and 50 years since the resumption of Geologica Balcanica after a 23-years break. In these short notes, some important moments from the history of the journal are shared.
The journal Geologica Balcanica is closely connected with the activities of two remarkable Bulgarian geologists: Prof. Stefan Bončev and his son Academician Prof. Ekim Bončev. Both were bearers of the best traditions of the Bulgarian National Revival of the 19th Century, and made major contributions to the development of all aspects of geosciences in Bulgaria. The journal has been founded in 1934 by Stefan Bončev who published the first three volumes on his own responsibility and means, and obtained the financial aid of the Sofia University for the fourth volume, published in the difficult years of the war. After the war the number of acting geologists diminished, and most journals were suspended or put under strict government control. The situation became favorable again in the next 20 years, and Ekim Bončev succeeded in 1974 to organize the resumption of this important Bulgarian journal. During the fifty years since that time, under a total of six consecutive chief editors, the full collaboration by the Editorial Board and the Geological Institute and financial support by the Bulgarian Academy of Sciences, the journal has been gradually modernized, obtained a good international reputation, and continues to be a good tribune to Balkan geology.
This study investigates groundwater flow reversal and fault-induced aquifer segmentation in the Zazari–Cheimaditida lake system of Northern Greece, a tectonically active basin impacted by extensive lignite mining. Using long-term piezometric data, elevation measurements, and hydrogeological cross-sections, we assess flow regimes, drawdown patterns, and the hydraulic role of fault structures. A major cone of depression (>40 m) has formed around the Amyntaio Lignite Mine, reversing regional groundwater flow toward the excavation void. Fault zones function either as barriers or conduits, as quantified through a newly proposed Tectonic Influence Index (TII). Results reveal a dual aquifer system: a shallow, seasonally artesian phreatic aquifer connected to Lake Zazari, and a deeper, confined aquifer hydraulically decoupled from surface waters. These findings highlight the strong influence of structural segmentation on groundwater dynamics in post-mining environments. The study proposes a conceptual hydrostructural model to guide adaptive groundwater management in fault-controlled basins. The framework supports efforts to maintain aquifer sustainability during the transition from lignite-based energy, especially under evolving climate and land-use conditions. The approach presented here is transferable to other tectonically segmented mining basins undergoing ecological and policy-driven restoration.
A preliminary evaluation on the occurrence of 31 critical elements (CE) in Bulgarian coal fly ashes (FA) and their potential industrial significance was conducted based on our own studies for eleven thermoelectric power plants. The chemical and phase-mineral composition of these FA is variable and depends mostly on the type of combusted coal. The qualitative presence of common minerals and phases in different FA is normally similar; however, their origin and quantitative occurrence is variable. It was found that 17 CE such as Ba, Be, Co, Ga, Mg, Ni, P, Sc, Sr, Tb, Ti, V, and especially As, Cu, Li, Mn, and Sb in definite FA are the most perspective for recovery. Some strong associations in FA were identified such as: Al, K, Si, Ti and Fe with rare earth elements; Fe with Co, Cu, and Ni; Ca with Mn and Sr; P with Ba, Ge, and Li; and Ti with Ni and V; which are important for multi-elements recovery. The modes of CE occurrence in FA are highly variable and complex; however, discrete minerals of Ba, Ce, Cu, La, Mg, Mn, Nb, P, Sb, Sr, Ti, W, and Y were identified, which is important from industrial and ecological points of view. FA are promising sources for extraction of some CE that can yield fractions meeting the cut-off grade for industrial recovery after some preliminary pre-treatment such as magnetic, size and density separations, as well as water leaching; however, much more detailed investigations are required for that purpose.
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