Adjacent to McGregor Lake in western Nunavut lies the massive Muskox intrusion. It remains as one of the largest and most studied layered intrusions on Earth, as well as one of the most valuable from an economic perspective. The intrusion represents the oldest igneous formation of the Mackenzie magmatic event, having formed between 1,905 and 1,155 million years ago. It maintains a triangular trough-shaped magma chamber that extends below the surface. With a width of and a length of over , the Muskox intrusion is overlain by a sequence of Coppermine flood basalts that remains thick.
