COMPARATIVE PETROCHEMICAL CHARACTERISTIC OF POSTMAGMATIC ALTERATION INTENSITY OF KIMBERLITES FROM YAKUTIA AND AFRICA
Study on secondary alteration processes of kimberlites was carried out based on 930 bulk analyses of core samples from holes of the Mir pipe (Yakutia) and pipe «К» (Angola). Mass transfer at secondary alteration of kimberlites can be effectively regarded against a background of parameter Q (normative secondary quartz) variation. The algorithm of calculation Q for each chemical analysis is given. Relatively weakly altered kimberlites of the Mir pipe and essentially altered kimberlites of pipe «К» are characterized by variation in Q up to 25 % in first case and up to 80 % in second one. Slightly altered kimberlites of both the pipes are characterized by close chemical composition. Compositions of all analyzed kimberlites of the Mir pipe and the African pipe differ considerably because of various degrees of secondary alteration. In the Mir pipe occur mainly quartz-bearing kimberlites, and in the African pipe quartzous rocks are present. The main and the earliest process of mass transfer at secondary alteration is the removal of potassium from deep-seated parts and its localization in subsurface parts of the pipes. Petrochemical trends reflecting the formation of quartzous (silicified) kimberlites in the studied pipes do not principally differ. They are the removal of a magnesium and accumulation of Al<sub>2</sub>O<sub>3</sub>. Kimberlites of different extent of secondary alteration occur in both the pipes as in subsurface, as in deep-seated parts of the pipes. The use of values of normative quartz contents at studying of secondary mass transfer was effective both in slightly altered, and in much more altered rocks. Parameter Q was used for testing of genetic hypotheses. According to one of them in the African pipe there are significant volumes of enclosing sedimentary rocks. Variation of Q along the profiles of holes has shown that in all cases it subject to regularities which are peculiar to products of infiltration metasomatism. So, the hypothesis about the presence of sedimentary rocks was rejected.