---------------------------+-----------+---------- | | Years of | | life at | Reserves| present Mine | (tons) |production ---------------------------+-----------+---------- Utah Copper Co. |200,000,000| 31 Ray Consolidated Copper Co.| 90,000,000| 30 Chino Copper Co. | 80,000,000| 27 Inspiration Consolidated |120,000,000| 20 Nevada Consolidated | 80,000,000| 20 Miami Copper Co. | 50,000,000| 20 +-----------+---------- Total |620,000,000| 26 ---------------------------+-----------+---------- These mines in 1917 produced 31.5 per cent. of the total United States output. The New Cornelia mine is of similar type and has already developed 75,000,000 tons, but as it is new its 1917 output was small. The Arizona Copper Co., Ltd., is also of this type, as are certain new developments in the Phelps-Dodge properties. These “porphyry” deposits occur in or near intrusive igneous rocks of various ages. Fully one-third of the United States production is now and will continue to be obtained from such deposits. On the average, about 1 per cent. copper is recovered from the ore. Distinct from the shallow and horizontal-lying disseminated ores or “porphyry coppers,” are the deep mines. The two oldest and most important deep-mine districts in the United States are Butte, Montana, and the Keweenaw Peninsula, Michigan. The mines of Butte work steeply dipping veins. It cannot be considered that over five years of ore reserves are known, and probably not over 2¹⁄₂ years of reserves are actually blocked out on three sides. However, there are no indications of early exhaustion, as the veins are profitable at more than 3,000 feet, the greatest depth to which mining has yet progressed. The deposits of northern Michigan are in pre-Cambrian rocks. They have been important producers of copper for over 50 years, and several mines have reached a vertical depth of more than 5,000 feet. Certainly not over five years of ore reserves are fully developed, but there are no signs of early exhaustion. These two districts, Butte and Michigan, now produce about 30 per cent. of the total United States output, a smaller proportion than before the development of the “porphyries.” The average copper content of the Michigan deposits ranges from 0.5 per cent. to 2 per cent. and of the Butte deposits 2.5 to 5 per cent.