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Most of investigated kimberlite diatremes of the Siberian platform represent multiphase pipes. Each magmatic phase of intrusion, formed inside diatremes, is composed by kimberlites with specific petrographic and petrochemical type possessing a number of stable, weakly changing with depth typomorphic features. Kimberlites of different intrusion phases in the same diatreme differentiate by both correlation of porphyritic and clastic structural elements and content of indicator minerals. Carried out investigations indicated sufficient distinctions in diamondiferousness of different intrusion phases of kimberlites, which is stipulated by different level of emplacement and duration of functioning of forming them magmatic hotbeds, physical-chemical properties of initial components, as well as by velocity of ascent and character of kimberlite magma advance in the process of different kimberlite-formation stages. Kimberlite breccias of completion stages of pipes formation are most productive in comparison with porphyritic kimberlites of early intrusive penetration phases. Specific features of origin and eruptions of kimberlite melts could sufficiently impact transformation of initial diamond crystals shape, which is cause by their dissolution (sometimes to complete destruction) and corrosion. When assessing productivity of kimberlite pipes it is necessary to consider real correlations of intrusive and explosive processes of kimberlite-formation in diatremes, which usually change in time. Stated materials make it possible to assume that the greater volumes of pipes are composed by porphyritic kimberlites of intrusive penetration phases, the lower is their diamondiferousness, which is confirmed by sampling results of many diatremes on the Siberian platform. The volume of kimberlite breccias increases with depth for all kimberlite pipes of this region that are under development, which emphasizes their commercial valuation. |
