CONTRASTING STYLES OF GOLD AND BASE-METAL MINERALIZATION IN THE NORTH END OF THE YELLOWKNIFE GREENSTONE BELT, NWT, CANADA

Mineralization styles in the north end of the Yellowknife greenstone belt in the Slave Province of Canada’s Northwest Territories differ from those of the area’s major historic mines. Massive sulfides occur in dilatational zones at the intersections of shear zones and display early and late generations of arsenopyrite- and base-metal sulfide-bearing veins. Our research characterizes the relative timing and nature of these mineralization styles in the Archean Kam and Banting Groups, in order to assess the effects of overprinting of multiple hydrothermal systems on the development of economic gold targets.

Within the basal Kam Group, the Greyling Lake prospect shows skarn-type alteration associated with thicker accumulations of massive sulfide, possibly indicating a pre-metamorphic age for its apparent volcanogenic massive sulfide mineralization. The Homer Lake showing contains a band ~40 cm wide, rich in base-metal sulfides, that extends parallel to the metavolcanic stratigraphy (>2743 Ma). This horizon is cut by arsenopyrite-bearing shear zones that contain gold and chalcopyrite. Similar NE-trending shear zones can be traced to Oro Lake, where they have been metamorphosed by the nearby Duckfish Lake pluton (2605 Ma). In contrast, at Arseno Lake, NW-trending shear zones containing arsenopyrite and gold can be traced from the volcanic rocks of the greenstone belt across the contact into the Duckfish granite, indicating that gold mineralization postdates the intrusion.

Ore petrology of showings in metavolcanic and metasedimentary rocks of the younger, overlying Banting Group also reveals a post-arsenopyrite base-metal event, but one that is dominated by major pyrrhotite deposition, which was not observed in the Kam Group. This may indicate that unique ore-depositing hydrothermal systems operated within the Kam and Banting groups.

Ongoing fluid inclusion, cathodoluminescence and stable isotope studies may permit us to identify individual generations of quartz veining associated with specific ore mineralizing events. We hope to develop a petrographic and geochemical methodology to recognize specific styles of mineralization and to document the aerial extent and continuity of their associated hydrothermal systems.