The article presents a comprehensive analysis of the mineralogical and geochemical features of xenoliths from the V.Grib kimberlite pipe, represented by lower crustal garnet-clinopyroxene granulites and mantle eclogites. A comparative characterization of the two xenolith types is conducted, as clear criteria for their distinction are currently lacking. The study identifies several distinctive features that unequivocally characterize mantle eclogites: elevated Cr contents (in garnets >300 ppm, in clinopyroxenes >1500 ppm), high pyrope content in garnet (>34 mol.%), and evidence of early metasomatism manifested as metasomatic garnet, spongy clinopyroxene replaced by pargasite, and phlogopite rims at garnet-clinopyroxene contacts. Evaluation of the pressure-temperature parameters of the V.Grib pipe xenoliths confirmed the mantle origin of eclogitic xenoliths formed at T = 800-1200 °C and P = 30-50 kbar, and did not refute the initial assumption of a lower crustal origin for granulitic xenoliths characterized by T = 750-800 °C and P = 14-15 kbar. To definitively resolve the issue of identifying lower crustal garnet-clinopyroxene granulites and mantle eclogites, a comprehensive comparison of the isotope-geochemical characteristics of “eclogitic” and “granulitic” zircon is proposed for future research.
As a result of a comprehensive study of the geological structure and diamond presense of the northern part of the East European Platform, generalization of the data accumulated by various organizations in the USSR, the Russian Federation, and other states, three main prospecting models of primary diamond deposits have been identified and characterized: Karelian, Finnish, and Arkhangelsk. Geological, structural, mineralogical, and petrographic criteria of local prediction, as well as the features of the response of kimberlite and lamproite bodies in dispersion haloes and geophysical fields, are considered using known examples, including data on the developed M.V.Lomonosov and V.P.Grib mines. It is shown that the most complicated prospecting environments occur in the covered areas of the Russian Plate, where, in some cases, the primary diamond-bearing rocks are similar in their petrophysical properties to the host formations. The buried dispersion haloes of kimberlite minerals in the continental Carboniferous and Quaternary deposits are traced at a short distance from the sources. Differences in the prospecting features of magnesian (Lomonosov mine) and ferromagnesian (Grib mine) kimberlites are also shown. Conclusions about the diamond potential of the model objects of various types are given in this paper.
On the basis of complex of lithologic-stratigraphic, mineralogical, facial-dynamic, paleogeomorphologic and morphogenetic features of post-kimberlitic terrigenous diamond-bearing rocks and reconstructed synchronous relief three prediction and prospecting types of reflection of buried kimberlite fields are distinguished. It is shown that ranging of diamondiferous territories to various types enables to direct exploration works to discovery of diamond deposits of the certain origin and makes possible to select proper prospecting technique. With the use of suggested criteria of research of promising territories the evaluation of diamond presence in the industrial regions of the Siberian, East-European and African-Arabian platforms is carried out.
