CONCENTRATION OF RB AND CS IN ANDALUSITE-BEARING AND CORDIERITE-BEARING METASOMATIZED SCHISTS

The replacement of staurolite-biotite-quartz schists by andalusite-cor dierite-biotite-quartz metasomatized schists possibly involved the pro gressive enrichment of ore-forming components during successive evolut ionary stages of the Svecofennian Mobile Belt. The contents of rare al kalis progressively increase in the following sequence from the parent al to metasomatic rocks: sand-clay sediments (sand --> clay) --> staur olite-biotite-quartz schists --> andalusite-cordierite-biotite-quartz metasomatized schists (in ppm). Li (8 --> 28) --> 42 --> 164 (by a fac tor of approximately 6); Rb (77 --> 115) --> 144 --> 182 (by a factor of approximately 1.6); Cs (1.5 --> 5) --> 10 --> 20 (or 27) (by a fact or of approximately 4-5.4). These data suggest that rare alkalis could be gradually accumulated during successive stages of sedimentation, m etamorphism, and accompanying metasomatism of the Svecofennian sequenc e.