Geology of unmineralized and gold-bearing iron formation, Contwoyto Lake – Point Lake region, Northwest Territories, Canada: Reply
Numerous gold occurrences, including the Lupin mine, exist in Archean iron formation within the Contwoyto Lake – Point Lake region of the Slave Province. Early studies suggested that gold was a syngenetic component of the iron formation; however, the present study suggests that the gold and sulphides are epigenetic.At both the Lupin mine and small-scale gold occurrences gold is associated with quartz veins and concentrations of pyrrhotite or pyrite and of arsenides (arsenopyrite ± loellingite) in iron formation. The quartz veins contain 0.03–1.00 ppm Au and comprise sulphide-poor quartz. A zoned sequence of hydrothermal alteration is present in iron formation adjacent to quartz veins. Immediately adjacent to the veins a calc-silicate lithology (0.03–1.00 ppm Au) is sometimes developed that comprises hedenbergite + quartz ± epidote ± scheelite ± grossular. Next is an arsenide-rich zone (5–30 ppm Au) comprising hornblende + quartz ± hedenbergite ± epidote ± actinolite. The next zone is an iron-sulphide zone...