Kimberlites represent magmas derived from great mantle depths and are the principal source of diamonds. Kimberlites and their xenolith cargo have been extremely useful for determining the chemical composition, melting regime and evolution of the subcontinental mantle. The late-Devonian Udachnaya (means Fortuitous) pipe hosts the largest diamond deposit in Russia (> 60% diamond quantity and value) and one of the largest in the world, supplying gem-quality diamonds (~ 12% of world production). Since its discovery in 1956, the Udachnaya kimberlite pipe has become a “type locality” for geochemists and petrologists studying mantle rocks and mantle physical-chemical conditions. Apart from hosting a diverse suite of extremely well-preserved mantle xenoliths, the host kimberlite (East body) is the only known occurrence of fresh kimberlite, with secondary serpentine almost absent and uniquely high Na2O and Cl (up to 6.2 wt.%) and low H2O (< 1 wt.%) contents. The discovery of such compositional features in the only unaltered kimberlite has profound implications for models of parental kimberlite magma compositions, and the significance of the high Na and Cl abundances in the Udachnaya-East pipe has therefore been subjected to vigorous criticism. The main argument against a primary magmatic origin of high Na-Cl levels involves the possibility of contamination by salt-rich sedimentary rocks known in the subsurface of the Siberian platform, either by assimilation into the parental magma or by post-intrusion reaction with saline groundwaters.