HYDROTHERMAL ALTERATION IN VOLCANIC-ROCKS, EASTERN PART OF THE LUKAVICE GROUP, ZELEZNE HORY MOUNTAINS, CZECH-REPUBLIC

Many rocks mapped as felsic metavolcanics in the eastern part of the L ukavice Group are shown to be altered mafic metavolcanics, similar to those in the Noranda and Flin Flon Snow Lake mining districts, Canada. The relatively fresh rocks of the Lukavice Group are rhyolite, dacite -andesite, and andesite-basalt of calcalkaline character. Assuming no substantial volume change during alteration, Ti, P, La, Ce, Yb, Lu, Th (partly), Sc and V contents remained unchanged. Altered rocks are enr iched in (Fe + Mg), K and Si and depleted in Na, Ca and Zr. Some eleme nts show both increased and decreased contents in altered rocks (Mg, B a, Sm, Eu, Tb and Hf). Although hydrothermal alteration in the Lukavic e Group is of large extent, it is of the proximal Kuroko style and not of regional 'Amulet Rhyolite' style. Implications for a large hydroth ermal system within a volcanic pile are discussed in relation to the O rdovician Lukavice Group and its mineral deposits and to some other pa rts of the Bohemian Massif with volcanosedimentary sequences of the sa me age.