The Somerset Island kimberlite field is composed of three diatremes Peuyuk, Korvik, and Selatiavak. The largest diatreme, Peuyuk, an enlarged fissure, is a composite intrusion; three petrographically distinct phases (A, B, and C) being recognized on the basis of oxide mineralogy and the presence or absence of immiscible carbonate: (A) spinel and perovskite with no zonations or reaction rims, no immiscible carbonate, (B) epitaxially zoned chrome spinels, magnetite and perovskite with reaction rims, no immiscible carbonate, (C) oxides as in B, but with no magnetite and abundant immiscible carbonate. Selatiavak and Korvik are each composed of two small oval intrusions and are petrographically similar to Peuyuk C. All the kimberlites are characterized by a positive (500–2000γ) magnetic anomaly. Emplacement of the kimberlites has been controlled by structures in the Precambrian basement gneisses, the diatremes being developed from hidden dikes at depth at points of crustal weakness.

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