Bob Hanmer sent details covering a special operating session on his HO scale Great Northern and Duluth, Missabe & Iron Range layout that serves the mining region. We think you will enjoy this.
Taconite is a hard rock found across the northern parts of Michigan, Wisconsin, and Minnesota. It contains about 30% iron, so for most of the 20th century it was considered waste. That is until the war efforts of World War II and the Korean conflict severely depleted the existing reserves of high quality iron that could be fed directly (or with a little beneficiation) into a blast furnace.