ORIGIN AND SIGNIFICANCE OF HIGH-NICKEL AND CHROMIUM CONCENTRATIONS INPLIOCENE LIGNITE OF THE KOSOVO BASIN, SERBIA

Trace element data from 59 Pliocene lignite cores from the lignite fie ld in the Kosovo Basin, southern Serbia, show localized enrichment of Ni and Cr (33-304 ppm and 8-176 ppm, respectively, whole-coal basis). Concentrations of both elements decrease from the western and southern boundaries of the lignite field. Low-temperature ash and polished coa l pellets of selected bench and whole-coal samples were analyzed by X- ray diffraction and scanning electron microscopy with energy-dispersiv e X-ray analyses, These analyses show that most of the Ni and Cr are i ncorporated in detrital and, to a lesser degree, in authigenic mineral s, The Ni- and Cr-bearing detrital minerals include oxides, chromites, serpentine-group minerals and rare mixed-layer clays. Possible authig enic minerals include Ni-Fe sulfates and sulfides, Analyses of three l ignite samples by a supercritical fluid extraction technique indicate that some (1-11%) of the Ni is organically bound. Ni- and Cr-bearing o xides, mixed-layer clays, chromites and serpentine-group minerals were also identified in weathered and fresh samples of laterite developed on serpentinized Paleozoic peridotite at the nearby Glavica and Cikato vo Ni mines. These mines are located along the western and northwester n rim, respectively, of the Kosovo Basin, where Ni contents are highes t. The detrital Ni- and Cr-bearing minerals identified in lignite samp les from the western part of the Kosovo Basin may have been transporte d into the paleoswamp by rivers that drained the two Paleocene laterit es. Some Ni may have been transported directly into the paleoswamp in solution or, alternatively, Ni may have been leached from detrital min erals by acidic peat water and adsorbed onto organic matter and includ ed into authigenic mineral phases. No minable source of Ni and Cr is k nown in the southern part of the lignite field; however, the mineral a nd chemical data from the lignite and associated rocks suggest that su ch a source area may exist.