Zlatka Milakovska

This study presents new geochemical data on heavy metals and As in sediments from the Topolnitsa River catchment - a region of both historical and present-day industrial, mining, and agricultural activities. Systematic sampling, analysis, and sediment quality assessment were carried out following the EU Water Framework Directive and SIMONA project methodologies suitable for the predictive survey methods of metal contamination processes in fluvial sediment systems. The sampling of bottom and floodplain sediments, as well as a single suspended sediment sample was performed in three strategic locations along the Topolnitsa River. We explored spatial and temporal patterns in heavy metal (Cu, Pb, Zn, Cd, Hg, Ni, Cr) and As distribution in those sediments. The results showed consistently higher heavy metal loads in river bottom sediments compared with flood sediments for most elements at a given location. The top flood sediments, on the other hand, had systematically lower heavy metal contents compared with bottom flood sediments. The first monitoring point at Staria Kemer had significantly lower heavy metal concentrations for most elements compared with the other two locations (Chavdar and Petrich). On the other hand, As, Hg, Ni, and Pb contents in top flood sediments decreased from Chavdar to Petrich monitorimg points, the latter being the last location studied down the river course. Consistently high Cu concentrations in all analyzed samples indicate an ongoing and/or cycling pollution, suggesting the need for mitigation measures, as well as continued sediment monitoring.

Deep-sea Fe-Mn polymetallic nodules formed nowadays at the deep-sea ocean floor were evaluated as promising critical raw materials (CRMs). Here, we report results of polymetallic nodules from the H22_NE block of the Interoceanmetal (IOM) exploration area in the eastern part of the Clarion–Clipperton Zone (CCZ), NE Pacific Ocean. The polymetallic nodules were studied with X-ray Diffraction, Raman spectroscopy, SEM-EDS, and LA-ICP-MS (bulk nodules and in situ nodule layers). Additionally, we combine geochemical data of polymetallic nodules with the previously reported data of pore waters and sediments from six stations. Our study aims to define the mineral composition and determine the content of CRMs in the polymetallic nodules and to assess the main factors controlling metal deposition and nodule enrichment in some CRMs. Mn content and the Mn/Fe ratio of the nodules classify them mostly as mixed hydrogenetic–diagenetic type. They are also enriched in Ni, Cu, Co, Zn, Mo, W, Li, Tl, and REE. The in situ REE patterns exhibit MREE and HREE enrichment and a variable Ce anomaly that argues for a changing oxic/suboxic environment and periodically changing of diagenetic and hydrogenetic nodule growth. The results of the joint study of the bottom sediments, pore waters, and polymetallic nodules show a complexity of processes that influence the formation of these deposits. The changing oxic and anoxic conditions are well documented in the chemistry of the nodule layers. Probably the most important controlling factors are sedimentation rate, bioturbation, adsorption, desorption, and oxidation. In addition, growth rates, water depth variations, electro-chemical speciation, phosphatization, and the structures of the Fe-Mn adsorbents are also considered. The polymetallic nodule deposits in the IOM contract area are estimated for future mining for Ni, Cu, Co, and Mn resources. They, however, contain additional metals of economic importance, such as REE and other trace elements (referred to as CRMs) that are potential by-products for metal mining. They can significantly increase the economic importance of exploited polymetallic nodules.

The open-pit exploitation of the Maritsa Iztok lignite field (Bulgaria) generated sedimentary waste rocks of low organic matter content that were deposited in internal dumps. Immediately after deposition the re-deposited sediments underwent weathering, including organic matter oxidation leading in some cases to self-heating. The aims of the research were to study the impact of weathering and self-heating on the maceral alterations in the dump site associated with the sediment re-deposition, and organic compounds identification and distribution. The 27 samples collected from Troyanovo-3 Mine internal dump differed in degree of alteration. The first group contained unaltered macerals and showed normal distribution of n-alkanes, phenols were absent and Rock-Eval Tmax ranged from 420 to 430 °C. The second group contained macerals with irregular cracks, paler oxidation rims, higher reflectance, Gaussian distribution of n-alkanes, high concentration of phenols and PAHs, and lowered Tmax values (below 400 °C). The samples contained elevated amount of pyrite which oxidation might contribute to self-hating.

Drill core samples from a lignite-mudstone succession with variations in organic matter maturity from Troyanovo-3 Mine (Mini Maritsa Iztok EAD) were analyzed for trace element contents. All elements except Hg and Th show one positive spike in their distribution, located at different depths. Molybdenum and Ni peak at the deep level (52.6–3 m); Fe, V, As, Hg, Zn, U, and Th peak at 29.3–29.5 m; Pb and Cu peak at shallow depth – 19.2–20.1 m. All measured concentrations are much higher than the Clarke for low rank coal and sedimentary rocks and comparable with published data for black clays from Troyanovo-3 Mine. The lack of significant correlation between total organic carbon and all analyzed trace elements points to other hosts for the trace elements. The strong positive correlations found for Fe and V, Ni, Cr, As, and Mo suggest incorporation of these elements into Fe sulfide phase(s). The strong positive correlations for Al and Ni, Co, Mo and U, and a weak correlation between Al and V suggest a terrigenous and/or sorbed form of presence. The lack of a strong correlation between mercury and total organic carbon, ash, sulfur and uranium confirms the well-known complex Hg affinity. Our previously outlined hypothesis for OM enhanced maturity as a result of ascended hydrosulfide injection is here further supported by the trace element differentiation at different depths.

Pyrolysis coupled “off-line” with thermal desorption gas chromatography–mass spectrometry (TD-GC/MS) instrument for flue gas analysis is used to specify qualitatively/quantitatively organic functionalities in “Maritsa-Iztok” lignite lithotypes thermal decomposed in the range 250–900 °C. The aim of the study is to specify organic volatiles and to assign identified components to the lignocellulose biomass building blocks of coal forming vegetation. In pyrolysates the total amounts of the analyzed organics, expressed in mg/g TOC, amount up to 58.14 for liptain, 21–37 for humoclarain and xylain, and the lowest values are determined for humovitrain, 12. The samples immaturity reflects in high diversity of phenols, methoxy phenols (only guaiacyl structures), furans, etc. maximizing at xylain lithotype, 68% of the total analyzed amount. Carbohydrate degradation products, i.e. furaldehydes, 2-cyclopenten-1-ones, etc. are identified as well. In lithotypes studied, coal biomarkers as n-alkene/n-alkanes, sesqui-, di-, polar diterpenoids and hopenes/hopanes, are present in different proportions.

The concentrations of Fe, Mn, Co, Cd, Zn, Cu, Mo, and As were registered in broad intervals and are elevated compared to the mean values for the ocean water. Vertical distributions of the element concentrations in the pore waters along four sediment cores show distinct differences, mainly for the elements Fe, Mn, Cu, and Zn. Bioturbation activities developed in the depth interval 7–15 cm could be a probable reason for the variation trends. The distributions for the elements As, Cd, Co and Zn are conservative type and the patterns for the Mo and Ni – scavenged type. The obtained pore water profiles are similar to the distribution trends for areas in the Eastern Equatorial Pacific and show different patterns from the pore waters from the Western Pacific.

A sequence of carbonaceous mudstones interlayering three lignite seams is characterized by geochemical proxies. The core samples studied came from a borehole drilled in Trojanovo-3 Mine of Maritsa Iztok Basin. The n-alkane molecular composition is dominated by the > C29 long-chain homologues, with a strong “odd” over “even” homologue predominance. In addition to, the prevailing smooth signature of n-alkane distribution attests for one major organic matter source – land-derived higher plants. The sesqui- and di-terpenoid assemblage specifies the prevalence of Cupressaceae, Taxodiaceae, and Podocarpaceae species in the coal-forming mire. The lupane-type triterpenoids registered are a sign for Betulaceae family presence. Biomarkers for herb, macrophyte and algal/bacterial contribution are also recognizable.

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.

Geochemical features of the deep-sea sediments from a high polymetallic nodule area in the eastern part of the Clarion-Clipperton Fractures Zone (CCZ), NE Pacific were studied. Box-corer samples from six stations in individual depth layers 0–3, 3–5, 5–10, 10–20 cm were collected from 4300–4500 m depth. The deep-sea sediments were classified as clayey-siliceous oozes according to the mineral and grain-size analyses. The chemical composition of the studied samples is compatible with that of pelagic sediments. Manganese content varies from 0.16% to 0.70% being the highest in the geochemically active layer (top 7–12 cm) and decreases with depth. The Mn/Fe ratio, Ba, Co, Ni and Cu have the highest values in the first (0–3) and second (3–5) layers and decrease with depth. REE range is 195.84–357.79 ppm showing low variation between the layers. PAAS-normalized REE patterns show significant enrichment of MREE and HREE with strong negative Ce anomaly and weak positive Eu and Y anomalies. The geochemical characteristics of the studied sediments infer polygenic origin. The redox sensitive oxides and barite presense, Eh values and negative Ce anomaly, indicate oxidizing environment of sediment formation.