. Transactions. ls is that the old filled square-setstopes are taken as the center of a circle and the newer stopes proceedfrom the mined area toward the circumference. On the 1300-ft. level,the Mitchell stopes will be used immediately surrounding the old stopedarea while square-set stopes will be used in very heavy ground, or wherethe walls of the orebody are not self-sustaining. On the 1400-ft. level,narrow square-set sections, two sets in width, will principally be used,the weight of the ground being too heavy to permit of the Mitchell system CHARLES A. MITKE 195 being used extensively. How
. Transactions. ls is that the old filled square-setstopes are taken as the center of a circle and the newer stopes proceedfrom the mined area toward the circumference. On the 1300-ft. level,the Mitchell stopes will be used immediately surrounding the old stopedarea while square-set stopes will be used in very heavy ground, or wherethe walls of the orebody are not self-sustaining. On the 1400-ft. level,narrow square-set sections, two sets in width, will principally be used,the weight of the ground being too heavy to permit of the Mitchell system CHARLES A. MITKE 195 being used extensively. However, in exceptional places this system willbe used. In broken ground, where a great weight must be sustained,the underhand square-set system will be used. The stoping on the 1300-ft. level is always to be kept ahead of that onthe 1400-ft. level so that the stopes on the 1300-ft. are finished beforethose on the 1400-ft. are brought up to this level. The sills are to be left BraceFlooring/ ^ ^Stringer1300 Level x. Fig. 1.—Two rows of square sets with pillar of ore between. in on both the 1300-ft. and 1400-ft. levels in order to keep down the repaircost and so that drifts may be kept open for waste filling in the stopesbeneath. A waste raise has already been put through to the surface anda large pit started to supplement the waste filling obtained from ordinarydevelopment work in the mine. The Mitchell stopes consist of parallel leads of square sets, one set inwidth, separated by solid pillars of ore 11 ft. to 16 ft. ( m. to m ) 196 MINING METHODS OF UNITED VERDE EXTENSION MINING CO. (two to three sets) thick. These narrow sections of square sets are car-ried up to the capping and contain chutes every second or third set,through which the ore from the square sets, and later from the pillarsbetween, will be taken out. The pillars of ore are left intact until theleads of square sets on either side have been mined out, and, with the 1300 Level
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
