DARK-COLORED MINERALS AS INDICATORS OF RO CK-FORMING AND ORE-FORMING PROCESSES (BY THE EXAMPLE OF THE KALBA GRANITOIDS)

Composition of biotites and garnets in three regions of manifestation of the early granodiorite-leucogranite (GDLGA) and late granite-leucog ranite (GLGA) associations of the Kalba Pluton have been studied. All the biotites belong practically to one class of high-alumina granitoid s and, therefore, are characterized by very close compositions. Nevert heless, the GLGA biotites have higher alumina, magnesium, fluorine, an d, in some cases, Li, Rb, Cs contents, which confirms the correctness of division of granitoids into groups. The differences of biotites of the above associations are most distinct on their comparison by occurr ence areas. The biotite compositions also carry some genetic informati on. By the (Mg+Fe)/Al and Si/Al ratios in biotites, almost all granito ids under study are referred to the groups of low activity of alkalies , which, at high concentrations of the latter in all the rocks, indica tes the formation of granitoids from the terrigenous material of the m ature crust. The character ob source material is impressed by increase d contents of Fe and Ti in the biotites from the GDLGA granitoids. Ana lysis of the contents of indicative trace elements - Cs, Li, Rb, F - i n the biotites suggests the absence of relationship between the biotit e content in granitoids and association of rare-metal deposits with th ese granitoids. By the ratio between Mg, Fe, Ca, and Mn, the garnets a re subdivided into three groups: 1) source material (with the highest contents of Mg and Ca), occurring in the GDLGA varieties; 2) high-temp erature, crystallized from a melt (with intermediate concentrations of Mg and Ca), found in the basic GDLGA granitoids; and 3) crystallized from water-saturated acidic magmas (enriched in Mn and Fe), abundant i n veined leucocratic granitoids.