Geology, geochemistry and alteration of the Eagle River Au-deposit near Wawa, Ontario

Abstract

The Eagle River mine is a mesothermal orogenic gold deposit hosted within the Archean Mishibishu Lake greenstone belt, approximately 50 km west of Wawa, Ontario. The underground mine has been in constant production since 1995, mining multiple steeply dipping quartz-bearing, shear-hosted gold horizons that dip to the north. As of the end of 2021 the Eagle River Mine has produced a total of 7.4 Mt of ore averaging 9.86 g/t Au yielding 1.5 M oz of refined Au (SRK, 2022). The majority of the gold mineralization is hosted within an ellipsoidal quartz diorite, with the remainder hosted within the surrounding calc-alkaline to tholeiitic volcanic rocks. The Mishibishu Lake greenstone belt is surrounded by granitic units which include the Bowman Lake batholith to the north-east, the Floating Heart batholith to the south and the Central pluton to the northwest. The objective of the study was to correlate veining in the chaotic unit to mineralization, investigate alteration geochemistry, and to compare Eagle River to other Archean Au deposits. This was undertaken using a combination of geochronology, petrography, and whole rock lithogeochemistry. The thesis focused on four zones within the deposit, the 8, Falcon, Newt Lake, and Peek-a-Boo zones. [...]