A Diamondiferous Lamprophyre Dike,Gibson Lake Area,Northwest Territories

The Akluilak dike is a narrow lamprophyre intrusion of ultrapotassic composition that has yielded a large content of diamonds; it is the first multidiamond occurrence noted from the central Churchill Province. Xenocrysts of apatite containing monazite have been dated at 1832 ± 28 Ma, thus confirming the correlation with Christopher Island Formation volcanic and intrusive rocks. Only 1 or 2 diamonds per 1000 are greater than 0.5 mm, and the majority are less than 0.075 mm. They occur primarily as octahedra and tetrahexahedroids, but cubes, macles, aggregates, and fragments also are present. Their occurrence points to the presence of a “mantleroot-friendly” lithosphere, and confirms the “highly diamond prospective” nature of the area suggested by previous studies.