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Show NOTES PROGRESS II LOW-GRADE M!NslG The development of the large low-grade coppers of Utah, Arizona, Nevada and New Mexico has opened up a new field of mining in North and South America, says, the Engineering and Mining Journal. These deposits have offered varying mining min-ing problems, each of which has been successfully suc-cessfully solved according to its nature and conditions. In all cases the ore bodies have been ' thoroughly prospected by drilling prior to underground development, develop-ment, and large capital expenditures have been mado in order ttiat low operating cost might he secured. Loss of ore in pillars and loss of grade by-.dilution have, resDectively, been balanced against the cost of high recovery of ore and a mill feed freed from waste. During the development de-velopment stages, the ore extracted from drifts, crosscuts and raises yields a considerable con-siderable tonnage, and this ore at the newer properties was treated in a pilot mill which performed the double function of sampling the mine and solving the metallurgical problem. At Inspiration, a series of tests was conducted bv the engineering department on a laboratorv scale intended to show the effects of different methods upon the grade of ore and recovery which results from drawing large tonnages of broken ore from under a caving caprocl;. The results of this experimentation, as vel'i-ticd vel'i-ticd by subsequent operations, have, so far as data can be obtained, Justified the expectations. At both Ilav arid Braden. where shrink-itge-stope and pillar-caving methods are used, the pillar problem offered the greatest great-est field for new ideas. In his paper, Mr. Hollistcr describes the solution of the problem at Braden. and his conclusions are the more valuable in that they emanate ema-nate from one who has had long,. Firsthand First-hand experience with mining at both properties. Complete data regarding the- degree of final recovery obtained by the method discussed are as yet unavailable, as the ore bodies ere still far from exhaustion. We shall however, watch with interest the reports from Brnden. which, to Judge from the data given by Mr. ITollistcr. promise o be all that could be expected. |