This breccia from the now-closed Giant Mine near Yellowknife formed between two faults, and is Pre-Cambrian in origin. Stresses in the rock allowed liquids with dissolved minerals to flow through and cement angular pieces of the rocks together. There are also angular pieces of quartz and arsenopyrite in the rock, and arsenopyrite is a source of arsenic. The gold from Giant Mine was found in the arsenopyrite ore, and the closure of the mine was due to the environmental risk of arsenic tailings seeping into groundwater. Giant Mine was also known for an incident in the 1990s when a miner on strike planted a bomb in the mine, killing 9 “blackleg” workers who were employed while others were on strike.
The Giant Mine Breccia was donated by Robin Wyllie (B.Sc. Honours Earth Science, Class of 1989), Aurora Geosciences Ltd, and Great Late Helicopters Ltd, in memory of R. Gwilym Roberts (1934-2011), Department of Earth Sciences.