Brief Characterisation of Ochre from the Marta Adit (Nižná Slaná, Spiš - Gemer Ore Mts., Eastern Slovakia)

Abstract

The contribution deals with the study on composition of ochre sample from the Marta adit at Nižná Slaná. Three samples were prepared from ochre by hand picking and screening, which were subjected to GA, AAS, XRF and XRD. Salts precipitated on surface at drying contain 17.7 % S (53 % as SO 4 ), 16.5 % MgO, 13.6 % Fe 2 O 3 , 3.54 % CaO and 1 % MnO. As to mineral composition, sulphates such as gypsum, starkeyite and rozenite are dominant. The fraction of grain size under 250 micron contains 30 % Fe 2 O 3 , 28.6 % SiO 2 , 8 % Al 2 O 3 , 6.6 % CaO, 2.9 % MgO and 1.95 % S. Notable is content of arsenic in this fraction, which attain as high as 1.84 %. Quartz and gypsum occur as dominant crystalline phases. As to coarser fraction, i.e. under 150 microns, 44.5 % SiO 2 , 16.8 % Fe 2 O 3 , 11.3 % Al 2 O 3 , 6.9 % CaO, 2.4 % MgO a 2.3 % C were assayed. Dominant quartz is accompanied by mica, plagioclase, ankerite and dolomite. It was shown that arsenic is bonded in finer grain size fraction.