Recent Geothermal Measurements in the Michigan Copper District

THE copper mines of the Keweenaw Peninsula in northern Michigan have long been of interest in connection with deep earth-temperature measurements. The extraordinary low geothermal gradient of 1° F. in 223.7 ft. announced by Agassiz1 as a result of measurements dating from 1886, although later" stated as in error, served to focus attention on this region as one offering, because of the great depth of the mines, unusual opportunity along this line. Lane,3 Van Orstrand4 and others have made valuable contributions to this study. Fresh opportunities afforded by the constant deepening of the mines, improvements in the accuracy and reliability of temperature-measuring instruments together with increasing knowledge of the heat conductivities and specific heats of the rocks, led the Michigan College of Mining and Technology in cooperation with some of the mining companies to renew work on this problem. It is planned eventually to complete a survey which will make use of the favorable opportunities for deep rock-tempera-ture measurements presented in these mines. This survey should include the determination of a depth-temperature gradient in both conglomerate and amygdaloid mines, and also the variations in temperature at the same depth in different geological formations. The first problem has a direct bearing on the question of providing equipment for necessary ventilation with increased depth. The second may show that a relation exists between the natural rock temperature and the mineral content of the formation.