The paper presents new research results on the chemical composition of clinopiroxene (Cpx), orthopyroxene (Opx), plagioclase (Pl) and biotite (Bi) from the gabbro-syenite association occurring in the southwest of the L«-G©m structural zone on East B¾c Bé. The analysis by microprobe has been showing that Cpx corresponds in composition to magnesian diopside-augite, Opx – to iron- and titanium-rich hypersthene, Bi is very titanium-high, alluminium–low and magnesium–low. The crystallization temperature of Cpx and Opx determined by the Lindsey method is about 600-800^oC. The comparison of Cpx, Opx and Bi components from the studied rocks by the content of magnesium, calcium and alluminium with other bedded mafic intrusions in ViÖt Nam shows that they have particular features. Combining with geochemical and isotopic data one can come to the conclusion on the contaminated and hybrid nature of the gabbro-syenite association in the southwest of the L«-G©m structural zone.