Located 12 miles southwest of Copper Harbor, the Delaware Copper Mine dates from 1847-1887. Eight million pounds of copper were removed from the five shafts that reached a depth of 1,400 feet with ten levels. Known originally as the Northwest Mine, it opened on a fissure deposit in 1847 and produced more than 500,000 lbs of copper over three years, but it cost more to produce the copper than it sold for.

After struggling along for 10 years with an annual deficit, the mine was reorganized as the Pennsylvania. Now working the bedded deposits, rather than the fissure deposits, prospects looked so good that a new stamp mill was erected on Lac LaBelle, 5 miles from the mine. A second company was formed, called the Delaware, and also built a stamp mill on Lac LaBelle. Even with the high price of copper during the Civil War the companies could not turn a profit. In 1876 there was a reorganization and the combined properties renamed the Delaware Copper Mining Company.

The new company had no better luck than the old one and suffered the same financial fate. After five years of losing money a new conglomerate lode was discovered under the greenstone. A new company, called the Conglomerate, was formed. Although the lode was large, it was deficient in copper content and much of the fine copper was lost in the recovery process. The name was changed several times but no further development took place until Calumet and Hecla took over the property under the name of the Manitou Mining Company.