Jovan KOVAČEVIĆ¹, Maja TODOROVIĆ², Marina ĆUK² & Petar PAPIĆ^2*
1Geological Survey of Serbia, Rovinjska 12, 11000 Belgrade, Serbia
²University of Belgrade, Faculty of Mining and Geology, Đušina 7, 11000 Belgrade, Serbia 

∗ Corresponding author: Ćuk M.: marinacuk.rgf@gmail.com

GEOCHEMICAL STUDY OF U, Th AND REE MINERALIZATIONS IN JURASSIC SEDIMENTS AND HYDROCHEMICAL CHARACTERIZATION OF GROUNDWATERS IN EASTERN SERBIA – CASE STUDY: PLAVNA AREA

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This paper research the newly-discovered U, Th-REE mineralization in Jurassic sediments in Eastern Serbia, Carpatho-Balkanides geotectonic unit - Plavna granitoid. During 2009-2013 research was conducted using a range of geological and hydrogeological methods for geochemical and petrographical analyses of rocks. It was found that uranium mineralization occurs in breccia-conglomerates of continental facies, while Th-REE mineralization is located in quartz sandstones without organic matter (marine facies). Mineralized sediment levels are distinguished according to grain sizes and the presence of organic material, which had an important role in the deposition of uranium. The major uranium minerals were uraninite (pitchblende), coffinite, and urano-organic complexes. Electron microprobe analysis (EMPA) showed that monazite crystals vary in shape and typically are lower than 50 μm in size. The ICP ME-MS81 results of 209 geochemical samples revealed a wide range of U, Th and REE concentrations. The median U concentration was found to be 6 ppm, while maximum concentrations were over 1000 ppm. The median Th concentration was 19 ppm, while maximum was over 1000 ppm. Samples showed REE contents in the range of 14.94 ppm to 10125.86 ppm. Their chondrite-normalized REE patterns are steeply right-inclined with similar slopes, with strong LREE/HREE partitioning [(La/Yb)n=1.35－218.2)], and weak to high Eu depletion (δEu=1.26－0.04). Detailed hydrochemical investigations in the area of the Jurassic sediments have shown that the groundwaters are low-mineralized, with neutral pH values, and redox values between 0.075 V and 0.437 V. A high level of uranium was found in a borehole (48.8 μg/L), while Th concentrations were low in all samples (0.00025 - 0.039 μg/L). The sum of REE concentrations in the groundwater ranged from 10.01 to 308.87 ng/L. Hydrochemical research had aim to determine the chemical composition of groundwater in the study area.