Bisbee daily review., 1912-10-20

! S0O foot and 800 foot levels.
 Timber Expensive Owing to the scarcity of timber in the neighborhood, and to the high price of imported timber. it has been necessary to adopt mining methods which would eliminate the use Of tim. Der as much as possible. The nature of the rock is such that while it Is not hard to drill or blast, 1t stands without timber in a most remarkable manner in most part of the mine This characteristic of the rock has also prevented the using of the cay 1 ing and topslicing methods, which are used so successfully at Cananea ! in some of the mines. Accordingly, some system of underhand stoping ' had to be devised. and the following 1.-two methods are used:
 t1). The old method. Fig. I. which l is room-and-pillaT with waste filling \ as the work progresses.
 (2D The new method, Fig. ?, which is shrinkage with waste filling after | all the ore has been extracted. Roor-and-PiiIar Mining With the room-and-pillar method | the mine plan is laid on into pillar lines at right agnles 10 the strike of
 the ore and placed 50 feet apart, di- ] yiding it into alternate pillars and stopes. A main working drift is run ! approximately parallel to the strike, i and crosscuts are turned of every I 100 feet in the pillars. From these 1 crosseuts right angle headings are turned of and every 90 feet run to
 the center of the stope and from these the sill floor is cut out to the limits of the ore and to the pillar lines, making the stope 50 feet wide. | The roof, where necessary, is sup ! ported by props or cribs, and a 6-fOot cut is then taken upward with stop 1 ing drills, the blasted ore being
 drawn off immediately, and filling run in from the level above through 1, winzes to within or feet of the roof The short drifts from the cross
 cuts are timbered through the fll- l ing, and cribbed chutes and man. ways are carried up from the ends of these. In a stope 150 feet long
 there would be three of these chutes and manways. i There were no pillars being ex- ] tTacted when l was there. and it was . probably the apparent difficulties of removing these pillars without losing Ia large amount of ore by mining with waste, which led to the adoption Of ] the new method.
 shrinkage Method
 1 With the shrinkage method, de- signed by C. A. Smith, the use Of I timber is almost entirely eliminated, l as not even timber chutes are used. i CrOsscuts are turned of from the l main haUlage drift every 50 feet par allel to the pillar lines and extending | to the limits of the ore.
 The next step is in driving what | are called the "stopes" which are breasts I5 feet wide and the height Of an ordinary drift. These are driven parallel to the crosscuts, and midway between them, and are car i ried to the limit Of the ore. From the crosscuts shoyel-ways are turned or at right angles at intervals of from 20 to 9 feet, and are driven to connect with the stopes. Turn sheets are placed at the mouths of the shOvel-ways. The ground is now ready to commence undeThand stop ing. The stopes are carried mp the same with (15 feet with stoping drills to a height of 20 feet above the floor, and are then widered 10 feet on each side. making them B feet in width, with IS foot pillars in between.
 Machines Set up
 The machines are set up on the broken ore, enough being drawn out through the shoyelways to keep a working entrance. The stope is con tinued up in this manner to the next level This work was started last summer, but 1t is evident that the main drifts will have to be timbered track. and cribbed manways built up where the stops cross them in order to keep the broken ore of of the through the broken ore at these points, but aside from this, with the l exception of an occasional prop, no timber is used at all. There would | be no absolute necessity for man | ways through the broken ore, as the stope can be entered by means | of the winze from the level above.
 Use of ShoVei~sys
 The shovelways, which are merely | rock chutes. have been used in the l mine for a number of years in the | narrower portions of the vein in- l stead of timber chutes. The reasons ] for their adoption are:
 CD No timber required.
 (2) Ease and safety in blasting l large boulders, which can be more | sa sely and easily blasted in the | .shovelways than in the stopes. and | without interfering with the work.
 (3) All work, except timbering. is ] done by contract with the natives. ! and it was found that unless all the ] rock was broken in the stopes sui l ficiently small to pass chute readi- ! ly Ia difficult and expesiye item in 1 ground that breaks big where shrink ! age is employed), it was just as cheap to have it shoveled into the | car as to draw of from a chute that | was continually hanging up, and the | expense of the timber was also eliIni- l mated.
 Cost os Systems
 As regards the comparative costs | of the two systems: stOping in the |