Since 1880 the mines of Butte, Montana, have produced approximately 1,250,000 tons of fine copper. They are now yielding about 200,000,000 pounds per annum, and have attained a maximum depth of 2,200 feet.
Notwithstanding the statements of some writers on ore deposits,* the copper ore of this mining camp is not chalcopyrite, nor is this mineral at all common here. Indeed, it is about as rare as covellite, and a good specimen of either is difficult to procure.
Chalcocite is the principal copper mineral, although bornite and enargite are common; and it is probable that more than 75 per cent of the total output of Butte copper has come from the smelting of the mineral chalcocite or copper glance. It is found in all the mines and on all levels from the highest unoxidized level to the bottom workings. It occurs in small . . .