Geological-petrophysical and mineralogic-petrographic studies of kimberlite rocks

There are three geological-genetic types of primary diamond deposits as magmatic (kimberlite and lamproite), metamorphogenic and impact deposits. The authors carried out a comprehensive study of geological, petrophysical and petrographic features of kimberlite rocks, i.e. the main supplier of diamonds. The upper parts of weakly eroded kimberlite pipes are usually crowned with crater structures, transforming down the section into diatrems, which further turn into dikes. Kimberlite pipes have three-phase sections (crater, diatreme and root part), which differ in textural-structural and mineralogical-petrographic properties. The appearance and composition of different-facies kimberlites (porphyritic varieties, autolithic and kimberlite breccias, tuffs and tuff breccias) are largely determined by the material composition of the diatreme host rocks and the degree of their postmagmatic and hypergenic alterations. Mantle material in kimberlites is represented by xenoliths of ultrabasic, alkaline-ultrabasic and basic rocks and xenograins of minerals from them – diamond, pyrope, picroilmenite, chromospinelide, olivine, clinopyroxene, orthopyroxene, phlogopite, less zircon, apatite, titanoclinogumite and others. Mantle xenoliths in kimberlite pipes usually evidence different levels of the mantle, which are the source of deep matter that underwent diverse alterations during the diatreme formation. The southern part of the Siberian Platform includes high-magnesian garnet peridotites and pyroxenites. For kimberlite diatrems of the northern part of this craton, peridotites predominate in some areas and eclogites in others. Garnet-free peridotites and garnet-pyroxene rocks play a greater role here, which is not typical of kimberlites from the other platforms of the world. The paper underlines the importance of analysing the influence of different mantle rocks on the productivity of kimberlites. The obtained data on the typomorphic features of diamonds and their paragenetic satellites allow to improve both the diamond content criteria of kimberlite rocks and significantly influence the choice of promising territories and sites for forecasting and prospecting diamond deposits.