Eldorado Bar deposit (Eldorado Strip Mine), Eldorado Bar, East Helena, Lewis and Clark County, Montana, USA
The great quantity of sapphires was recovered from channels in Eldorado Bar, approximately 19 km NE of Helena. Sapphire-bearing pebble-gravel deposits are located on high terraces, 30 to 60 m above the Missouri River. The channel thicknesses locally reach 10 to 12 m. Gold, almandine-pyrope garnet, kyanite, topaz, cassiterite, chalcedony, and pseudomprphs of limonite after pyrite occur with sapphire.Ref: E.Ya. Kievlenko (2003) Geology of gems, p. 70