Petrology and geochemistry of the Mel Kimberlite (Rae Craton, Nunavut) and Dharma Kimberlite (Wopmay Orogen, NWT).

Abstract:

Kimberlites are deep-mantle derived ultramafic magmas, which are able to transport a significant load of mantle xenoliths and xenocrysts, including diamond. Kimberlite magmatism in North America occurs over a wide range of time (~45-1100 Ma) and in diverse tectonic settings, including stable cratonic Proterozoic to Archean crust, to Phanerozoic mobile belts.This work presents new mineral chemistry (EPMA) and whole rock geochemical data from kimberlites from two different tectonic settings. The Mel Kimberlites are located on the Melville Peninsula, Nunavut, intruding into Paleoproterozoic gneiss of the Penrhyn Group in the Repulse Bay Block of the Rae Craton. In 2018, North Arrow Minerals Inc. intersected several kimberlite intrusions near Hall Beach, Nunavut (North Arrow Minerals Inc., 2019).The Mel intrusions are classified as archetypal kimberlite based on EPMA data from groundmass spinel and phlogopite, and wholerock geochemistry. Mel kimberlites have a variably altered mineral assemblage of olivine + phlogopite + spinel + calcite + ilmenite + serpentine. Xenocrysts of mantle garnet and ilmenite megacrysts are well preserved. The Dharma kimberlite occurs along the northern shore of Great Bear Lake in the Northwest Territories. The Dharma kimberlite intrudes Proterozoic carbonates of the Hornby Bay Group, Wopmay orogen (Santana Resources Inc, 2008). The Dharma intrusions are also classified as archetypal kimberlite based on EMPA data from groundmass spinel and phlogopite, and wholerock geochemistry. Dharma consists of a olivine + phlogopite + spinel + ilmenite mineral assemblage that is minimally altered kimberlite. Harzburgite and dunite microxenoliths accompany a xenocryst assemblage of garnet, clinopyroxene, orthopyroxene, olivine, and ilmenite.