Specific Composition and Conditions of Formation of Deep-Seated Minerals in Explosion Pipes of the Onega Peninsula and Kimberlites of Zimnii Coast in the Arkhangelsk Province

Deep-seated minerals (garnet, chrome spinel, clinopyroxene) from kimberlites of the Zolotitsa field are compared with those from explosion pipes of the Onega Peninsula (Nenoksa field). The diamondiferous kimberlites from the Zolotitsa field contain pyropes and chrome spinels, particularly deep-seated indicator minerals paragenetically related to diamond and corresponding in composition to its inclusions. In the Onega-Peninsula pipes, no paragenetic mineral indicators of diamond have been revealed, which is in accordance with the fact that they contain no diamonds. The features of explosion pipes from the Zolotitsa and Nenoksa fields are mirrored in their heavy concentrate haloes. The presence of slightly rounded pyropes in the Zolotitsa field heavy concentrate haloes, which include the pyropes of “diamond” assemblage, gave an impetus in 1976 for selecting this territory as a promising one for diamondiferous kimberlites which soon were discovered there.