Copper minerals are known from at least five stratigraphic levels above and below an angular unconformity recognized within rocks of the Rapitan Group on and near the Nite copper prospect, Mackenzie Mountains. The main showing on the prospect is structurally controlled and occurs in siliceous dolostone near the top of the folded and faulted Coppercap Formation, directly beneath an unconformity separating two local members of the Sayunei Formation (Rapitan Group). The copper was emplaced in tectonically fractured dolostone, precipitated from solutions that may have descended from copper-bearing conglomerates in the Rapitan Group above the unconformity, or ascended from weakly mineralized carbonates below. Mechanical reworking of older strata-bound copper deposits is indicated by significant copper content in clasts eroded from older rocks of the northeastern Mackenzie Mountains. The ultimate source of copper can probably be sought in basaltic dikes and flows emplaced prior to deposition of Redstone River and Coppercap formations during an early phase of crustal extension in the northern part of the Cordilleran miogeosyncline.