Abstract
The isotope composition of carbon and oxygen was studied in calcite of dykes and veins of ultramafic lamprophyres, kimberlite, alkaline mica picrites from the Yarma above-intrusion zone, and pyroxene-free picrites intruding the rocks of the Bolshetagninsky carbonatite massif within the Urik-Iya graben hosted by the East Sayan Mountains. The data on δ13C (from −6.6 to −3.9 ‰ relative to VPDB) disclose the ideas on the mantle origin of the carbonate substance of dykes. High values of δ18O (from +13.9 to +11.8 ‰ relative to VSMOW) suggest the impact of deuteric fluids, i.e. magmatic fluids separated from melts, at later stage of formation of the calcite-bearing alkaline ultramafic rocks.
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