Ventilation And Air Conditioning Of The Magma Mine (ca96c0e3-db14-4ebc-b035-91b50da2bd79)

THE Magma mine, of the Magma Copper Co., at Superior, Pinal County, Arizona, is 68 miles east of Phoenix and 21 miles west of Miami, Arizona, on highway U. S. 180. TEMPERATURES AND UNDERGROUND WATERS Surface Temperatures.-The average surface dry-bulb temperature at Superior is 72.4º; wet-bulb, 57.4º; with an indicated relative humidity of 38 per cent. The average yearly rainfall from 1921 to 1936, inclusive, was 18.74 in. The maximum condition of the atmosphere is in June, July and August, and the minimum is in January and February. The surface temperatures, of course, influence the temperatures of the down- cast shafts; however, the variation between winter and summer causes a difference of only 2º to 3º in the stopes and working places that are not close to the intake shafts. Average atmospheric conditions are shown in Fig. 1. Rock Temperatures.-Rock temperatures on the deeper levels of the mine are as follows: [ ] There appears to be no difference in rock temperature for any particular horizon of the various formations or in the vein. Water encountered is always the same temperature as the rock from which it flows, and for this reason it is thought that the water is heated by the rock; not the rock by the water. The country rock apparently has been heated by the various intrusions, perhaps the vein itself, and has not yet had time to cool off. The geothermal gradient (Fig. 2) as indicated by the rock temperatures given above is 1 ½ º per 100 feet. Underground Waters.-The underground water varies from 350 to 565 gal. per min., depending on the rainfall. The limestone and other