Abstract <p>The paper presents results of a petrological study of the Chik alkaline massif in the Sangilen Highland, Tyva: data on the chemical composition of the melteigites, ijolites, urtites, their calcite varieties, carbonatite-like silicate–carbonate rocks composing the massif, the host and contact-reaction rocks, and rock-forming minerals (clinopyroxene, nepheline, and high-Ti garnet). Data are presented on the O, C, S, and Sr isotopic composition of rocks and minerals of the massif. The data indicate a magmatic origin of the urtites, melteigites, calcite melteigite-urtites, and silicate–carbonate and garnet rocks, which have been previously thought to be metasomatic. A petrological model is proposed for the formation of the Chik massif, according to which the massif formed as a result of the assimilation of carbonate material from the host rocks by alkaline magma.</p>