The main goal of the present study is the characterization of the mineralogical and geochemical features of polymetallic (Mn- and Fe-bearing) nodules, lens- and layer-like bodies from different localities in the central part of the Late Cretaceous Srednogorie metallogenic zone, Bulgaria. The research is based on field studies, sampling and optical microscopy, followed by a combination of analytical techniques: XRD, SEM-EDS, ICP-OES and LA-ICP-MS methods. They define pyrolusite as the main ore mineral of the studied occurrences, while manganite, todorokite, bixbyite, sarkinite, hematite and hauerite are rarer. The most common gangue minerals are quartz, calcite and zeolites. Based on the MnO/SiO2 ratio, the established minerals are divided into two groups: manganese (i) and silica-manganese (ii) phases, respectively. Their trace element composition is dominated by a high content of V, Zn, Mo, W, Co, Ni, Cu, As, Tl and Sr, whereas some of them belong to the group of the critical raw materials for high-tech products. The measured values for Y and rare earth elements of the studied oxides and hydroxides are low compared to their concentrations in modern polymetallic nodules of the Pacific Ocean. Chondrite-normalized patterns indicated weak LREE enrichment with respect to MREEs and HREEs, which are slightly depleted. Common weak to strong negative Ce anomaly, accompanied by various Sm and Eu anomalies, is also observed. The close proximity of the Late Cretaceous volcanic rocks to the Mn- and Fe-bearing ore mineralization and some structural and textural features of the studied minerals suggest hydrothermal origin of the main Mn-Fe ore occurrences in the Panagyurishte area.
The construction of a compacted and stabilized layer with local soil from the excavation, mixed with Portland cement, is a soil improvement technique widely applied in foundation works in collapsible loess ground in Bulgaria. Commonly, the role of that cement-modified layer is to replace a part of the collapsible ground, to increase the bearing capacity of the soil base, and/or to be an engineering barrier against migration of harmful substances in the geoenvironment.
A multi-barrier near-surface short-lived low- and intermediate-level radioactive waste repository is under construction in Bulgaria. A cement-modified soil layer beneath the disposal cells is going to be built by in-situ compacted mixture of local loess and Portland cement. The cement-modified layer (indicated as loess-cement
cushion) is not a continuation of the foundation, but it is a part of the soil base and performs two main functions: to be an engineering barrier against eventual migration of radionuclides in the geoenvironment and to increase the bearing capacity to restrict deferential settlement of the soil base.
The present paper describes a field experiment aiming to verify the strength and deformation characteristics of a selected optimum loess–cement mixture by implementation of in-situ cement-modified loess ground. After 28-day curing at in-situ conditions, the loess-cement did not exhibit any fissuring or other disturbances.
The allowable bearing capacity qa of the cement-modified loess ground exceeded 900 kN/m2, and it possessed the following strength and deformation characteristics: deformation (plate) modulus EPLT = 500 MPa; coefficient of sub-grade reaction ks = 2158 МPa/m, and unconfined compressive strength qu = 2.00 MPa.
Our study is focused on REE and yttrium (REY) geochemistry of pore waters from core-box sediments. The samples were collected from the 0–5 cm, 10–15 cm, 25–30 cm, and 35–40 cm depth intervals of four stations of the eastern part of block H_22 of IOM license area of the Clarion-Clipperton Fracture Zone, NE Pacific. The REE studies in marine pore fluids were limited by analytical challenges. The pore water analysis we applied is based on a modern, improved analytical technique (ICP-MS, Perkin-Elmer SCIEX Elan DRC-e) with a cross-flow nebulizer and a spectrometer optimized (RF, gas flow, lens voltage) using a quadrupole cell in a DRC (Dynamic Reaction Cell) mode that allowed us to define the whole suite of REE. The ƩREY values of the samples vary from 4.05 μg/l to 106.34 μg/l. The REE content is at least one order of magnitude higher than the oceanic water. We followed the natural variations of La, Lu, Ce, and Y in absolute concentrations for station 3607. Cerium and Y are slightly enriched around the water-sediment interface, while La and Lu are enriched in the deeper layers. PAAS normalized REY patterns show a pronounced negative Ce/Ce* ratio together with a little MREE and HREY enrichment. The relatively “flat” REE patterns are typical for the shallow open ocean and characterize REE released from the organic matter degradation. We assume that the decomposition of and adsorption on organic matter and oxidation conditions are the main factors for REE fractionation in the pore water. The reason for some scatter in our REY data might be linked to bioturbation that has affected the sediment profiles.
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