Abstract

Seventy-nine kimberlite intrusions have been identified in the Churchill Province, Nunavut, the result of an aggressive diamond exploration program by Shear Minerals Ltd. and their partners. This is one of Canada’s newest and largest kimberlite districts, situated immediately west of Hudson Bay between the communities of Rankin Inlet and Chesterfield Inlet. This study documents the occurrence of bonafide kimberlite rocks, classified as mainly sparsely macrocrystic, oxide-rich calcite evolved hypabyssal kimberlite and macrocrystic oxide-rich monticellite phlogopite hypabyssal kimberlite. Electron microprobe analyses of olivine, phlogopite, spinel, and perovskite support this petrographical classification. Low 87Sr/86Sr isotopic compositions determined from perovskite indicate a group I affinity. In addition, 27 precise U–Pb perovskite and Rb–Sr phlogopite emplacement ages have been determined for the Churchill kimberlites, indicating that magmatism spans ∼45 million years (225–170 Ma). The Churchill kimberlites belong to the NW–SE-trending corridor of Jurassic–Triassic kimberlite magmatism in eastern North America, which includes the Kirkland Lake, Timiskaming, and Attawapiskat kimberlite fields. Churchill kimberlites extend this corridor ∼800 km northwest, suggesting that the corridor may continue northwest with older kimberlites. This corridor is interpreted as the continental expression of magmatism linked to either a single or multiple mantle-plume hotspot track(s), a pattern geographically coincident with independent estimates for the timing and location of the continental extension of both the Great Meteor and Verde hotspot tracks.

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