DISTRIBUTION OF MN IN CARBONATES FROM THE UPPONY MTS, NE-HUNGARY

Microprobe analyses of metacherts from the Tapolcsany Metachert Member of the Tapolcsany Formation and of limestones from the Lazberc Format ion of the Uppony Mountains were completed to study Mn carbonate miner alization. The carbonate minerals in the metachert samples include cal cite, siderite and ankerite, which contain variable but low amounts of Mn, with a mean Mn content of 0.83 weight percent. In one sample (No. 5), the Mn content is high, 8.15 weight percent, with the host minera l being Mn-rich ankerite. The limestone samples are composed of calcit e and dolomite. Their iron and manganese contents are low, but somewha t higher in dolomite than in calcite. The environment of deposition of the Tapolcsany Metachert was euxine, with a high primary pyrite and o rganic matter content, which favoured a high dissolved manganese conte nt. These conditions however, did not characterize the sedimentary env ironment of the Lazberc Formation, which was more oxic. In chronologic al order the original mineral composition underwent different changes: 1 - primary carbonate minerals included mostly small calcite (and rho dochrosite?) grains; 2 - regional-dynamothermal metamorphism probably changed the primary assemblage; 3 - Fe-Mg metasomatism caused changes due to its chemistry; small quantities of manganese were probably tran sported by the metasomatic fluids; 4 - surface weathering changed the original composition of the rocks; Fr: and Mn was dissolved from the c arbonates and Fe-Mn-oxide concentrations were formed in which the amou nt of Fe and Mn was much higher than in the pre-weathered rocks.