RB-SR ISOTOPIC STUDIES OF MURUNTAU ORE DE POSIT - ORE-BEARING METASOMATITES

The results of Rb-Sr isotopic studies of 4 metasomatite samples of dif ferent mineral composition and geological position in terms of oreform ation succession are presented: from earliest quartz-felspar-biotite m etasomatite up to chlorite enriched metasomatite of regressive stage. All four isochrones are parallel within the error limit with common de cline corresponding to 272.6+/-3.8 m.y. The initial Sr isotope ratios in metasomatites (0.7138-0.7166) fall within the time interval charact eristic to metasedimentary country rocks (273 m.y.) indicating the abs ence of external source of matter in the metasomatosis. The history of hydrothermal activity at Muruntau could be expressed as a sequence of separate activity impulses; 272.6+/-3.8; 256.2+/-6.4;230.2+/-3.5; 219 .4+/-4.2 m.y.