- © 2007 Canadian Institute of Mining, Metallurgy and Petroleum
The Contact Lake Belt forms the NW-trending flank of a collapsed andesite stratovolcano complex adjacent to a subvolcanic intrusion within the northern, 1.87 to 1.85 Ga, Great Bear magmatic zone, Northwest Territories, Canada. It belongs to the Port Radium-Echo Bay historical district that hosts past producers of U, Ag, Cu (± Ra, Ni, Co, Bi) from polymetallic sulfide and arsenide veins. A re-examination of the belt has revealed widespread IOCG-type polymetallic mineralization exposed in numerous veins, stockworks, breccias, and replacement zones within extensive areas of polyphase hydrothermal alteration. The effects are most visible and intense in andesite, but also affect associated synvolcanic intrusions. A weak, pervasive chlorite-epidote-carbonate-sericite alteration is observed in the least-altered volcanic rocks. Subsequent hydrothermal alteration that is progressively superimposed on earlier facies includes: sericitic (sericite, quartz); phyllic (sericite, quartz, pyrite); potassic (K feldspar); earthy and specular hematite; K feldspar-scapolite-albite-magnetite-actinolite-apatite as veins, stockwork, and pegmatitic recrystallization; K feldspar-tourmaline-Fe-oxide-silica-sulfides; and massive albitites locally laced with amphibole. Hydrothermal breccias and diatremes occur locally throughout the belt. The style, size, overprinting relationship, mineralogy, and chemical composition of alteration zones and mineralization support the current IOCG exploration model for polymetallic mineralization in the Contact Lake Belt, as well as for mineralization elsewhere in the Port Radium-Echo Bay district and the Great Bear magmatic zone overall.