EVOLUTION OF LI-F-GRANITES WITH THE FORMA TION OF RARE-METAL MICA SCHLIEREN (BEZYMYANSKY MASSIF, PREBAIKALIA)

Detailed geochemical studies were first carried out in Eastern Prebaik alia for race-metal Li-F-granites of the Bezymyanny Massif, which date from the Jurassic. The main facies rock varieties of the massif are m icrocline-albite and amazonite-albite granites, where the evolution of mica composition proceeds from Fe-biotites to protolithionites and Li -phengites. Unlike typical Li-F-granites of the Mongolo-Transbaikalian Province, associating with rare-metal mineralization, the granites of the Bezymyanny Massif have relatively low contents of Li, F, Rb, Be, Sn, Ta, Nb, with regularities of their distribution being dependent, c hiefly, on the processes of crystallization differentiation of granite magma. The melanocratic mica schlieren found in the Li-F-granites are not foreign inclusions but are autholiths formed with the significant participation of a fluid phase in the process of magmatic evolution o f the Bezymyanny Massif. Geochemical data on rocks, feldspars, and mic a confirm the genetic relationship of amazonite-albite granites and me lanocratic amazonite-mica schlieren. Exemplified by the latter it is s hown that during the fluid-magmatic evolution of the massif of Li-F-gr anites with moderate contents of many lithophile rare elements there c ould be favorable conditions for essential concentration of Li, Rb, Sn , Ta, Nb, Zr, and other elements to form unusual ultrarare-metal mica schlieren. Their further study will be useful in interpretation of way s of Li-F-granite magma evolution.