The article presents the results of a comprehensive study of diamondiferous lherzolite from the V.Grib kimberlite pipe. The composition of rock-forming minerals (olivine, orthopyroxene, Cr-diopside, Cr-pyrope) in terms of major elements mainly corresponds to minerals from inclusions in diamonds of the lherzolite association and diamondiferous lherzolites of the world. The elevated modal amount of orthopyroxene (18 vol.%) as well as the concentration of FeO (7.5 wt.%) and the value of MgO/SiO2 ratio (0.89) for lherzolite allow assigning it to orthopyroxene-enriched lherzolites. Specific features of the composition of Cr-diopside and Cr-pyrope in respect of rare elements indicate that at the time of capture by kimberlite, lherzolite retained the signs of a slight impact of mantle metasomatism. Modelling results allowed suggesting magnesiocarbonate and silicate high-density fluids (HDF) as the metasomatic agent. No signs of influence of proto-kimberlite melt were found. The degree of nitrogen aggregation in diamond (%B from 6 to 15) indicates a long stay in mantle conditions, which excludes formation shortly before the emplacement of kimberlite. Extremely light values of carbon isotope composition (δ13C = –18.59 ‰) indicate the involvement of organic carbon of subduction origin in diamond formation. Diamond formation could be associated with an ancient metasomatic event occurring with the leading role of low-Mg silicate-carbonate HDF, the source of which were eclogites and/or subducted sedimentary deposits containing organic carbon. The calculated P-T parameters (3.7 GPa, 814 °C) of the last equilibrium of mineral phases of lherzolite point to its capture from a depth of ~118 km, which corresponds to a section of the lithospheric mantle (approximately 95-120 km), within which rocks also demonstrating features of specific transformations under the influence of subduction-related fluids were earlier discovered.