The Three Mile showing is located on the east bank of the Illiance River about 5.3 kilometres east of Alice Arm.

The region is underlain by an assemblage of volcanics and sediments comprising the Upper Triassic Stuhini Group, the Lower Jurassic Hazelton Group and the Middle Jurassic to Upper Cretaceous Bowser Lake Group. This assemblage has been folded into a north-northwest trending anticline (Mount McGuire anticline) and regionally metamorphosed to greenschist facies.

The showing consists of various occurrences hosted in Stuhini Group interbedded argillite, sandstone, tuff and agglomerate which strike approximately north and dip 60 degrees east. The main occurrences are two quartzose brecciated zones, 4.6 to 6.1 metres wide, mineralized with pyrite, marcasite and minor galena and sphalerite. A grab sample assayed trace gold, 21 grams per tonne silver, 1.6 per cent lead and 2.8 per cent zinc (Minister of Mines Annual Report 1931, page 39).

At 122 metres elevation, on the east bank of the river, a north striking shear zone is developed in waterlain tuffs. The zone is pyritic, silicified and has been explored by a 61 metre tunnel. On the west bank, a 6 metre tunnel follows a slightly pyritic shear zone hosted in graphitic and calcareous argillite.

The area was explored by stripping and tunnelling during the early 1930s for base and precious metals. In 1930, about 61 metres of crosscut tunnelling was completed towards the mineralized zone. A westerly crosscut from this tunnel is in 42 metres but would have to be extended about 18 metres to cut the zone. On the west bank of the Illiance River about 6 metres of tunnel has been driven into the steep bank.