28 



NATURE 



[July 6, 191 1 



of the stamp-mill, the weight of individual stamps has 

 been increased by lengthening the heads, until, with the 

 2000-lb. stamp of the new mill of the City Deep mine, the 

 economic limit of the cam-lifted gravitation stamp appears 

 to have been reached. 



I nderground, efforts have been made to solve the dust 

 problem. With few exceptions, the Witwatersrand mines 

 are dry mines, and the processes of machine-drilling, blast- 

 ing, and shovelling consequently create and distribute 

 through the air great quantities of fine dust. The inhala- 

 tion of the dust-laden air causes a peculiar disease, known 

 as miners' phthisis, a deadly complaint which is responsible 

 for a high mortality among the white miners. By the 

 proper application of water at the point of origin, the 

 formation of dust can, to a large extent, be prevented ; and 

 several ingenious contrivances have been invented for 

 catching the dust from the upward holes, into which water 

 cannot be poured from a can, in the manner usually 

 adopted with downward holes. The chief difficulty, how- 

 ever, appears to be to get the men to use the dust-arresters 

 and to water-down the stopes and other working places 

 after blasting. By better supervision and a stricter enforce- 

 ment of regulations, such difficulties will doubtless be 

 overcome. 



In the early days of the Rand, and, indeed, up to quite 

 recently, it has not been found necessary to employ any 

 artificial system of ventilation, the numerous shafts and 

 outlets to the surface of the outcrop mines having sufficed 

 to maintain an ample supply of fresh air. But with deeper 

 levels, fewer communications with the surface, and an in- 

 creased rock-temperature, artificial ventilation is destined 

 to play an ever more and more important part in the 

 future. It will be impossible to work the deep levels 

 economically without carefully thought-out schemes of 

 ventilation, and for the success of these it will be necessary 

 to have shafts with small frictional resistance and large 

 air space, and to carry the air-current through special 

 ventilating roads. 



The ventilation problem has been seriously attacked 

 on the Rand, and already ventilating fans, varying' 

 in capacity from 50,000 cubic feet per minute at 

 1 inch water gauge to 250,000 cubic feet at 4 inches water 

 gauge have been installed at many of the mines. In 

 splitting the air current, the numerous dykes of igneous 

 rock that traverse the Witwatersrand mines in a north 

 and south direction (i.e. across the strike) can be made 

 to serve as natural brattices, since they cut up the mines 

 into air-tight compartments. The levels which penetrate 

 these dykes must be permanently closed, or, if used for 

 tramming purposes, closed by double swinging-doors. 



Under the changed conditions now prevailing on the 

 Rand, due to the enormouslj increased size "I the proper- 

 ties brought about by recent amalgamations, and the con- 

 sequent possibility of concentrating a large output on 

 fewer main hoisting shafts than heretofore, the evolution 

 of an entirely new system of underground transport is 

 being accomplished. It is becoming 'recognised that the 

 rock, broken in the stnp<^, can only be economically dealt 

 with by handling it on a few main haulage-levels, situated 

 al great intervals apart and driven straight, from point to 

 I 1 " 1 ' 1 , in th footwall of the reef. These main haulage- 

 roads, whirh or,- intended to servi also as the intake 

 of the fresh-air current, can, on account .>f then economic 

 importance, be constructed of large dimensions. They can 

 also be carefully graded and equipped with heavy rai'ls. 



Thi handling ol the In. >]on rock in the stopes is, from 

 an economic point of view, scarcely less important than its 

 haulage on the levels Everything depends on the angle 

 of dip ..I the reef. In many of the outcrop mines of the 

 Central Rand the high dip of the reef permitted the rock, 

 broki n in the stopes, to find its v .1- b] • 1 u itatior to the 

 tramming-level, where it 1 ofl as required from 



the stppe-boxes ; but with the dips oi from 25 to 30 

 obtaining in most of the deep-level mines, the broken rock 



requires to be assisted down the stope-fl bj shovelling. 



Only in the extreme East Rand, where the reel lies very 

 flat (dipping at from 8° to ro°) is it po sible to fill the 

 trucks at the stope faces anil to run them thence direct to 

 the tramming-levels. Hand-shovelling is uneconomical, 

 and, moreover, is detrimental to health, on account of the 

 dust it raises. Consequently, several attempts havi 

 NO. 2175, VOL. 87] 



made to substitute for it some conveyer system of handling 

 the broken rock, S tope-conveyers are shaking chutes 

 consisting of iron plates. They are suspended by short 

 chains from the roof next to the working face of the 

 stope, and are kept in motion by ropes attached to the 

 upper ends of the conveyers. Many of these shaking 

 chutes are now in use on the Rand. 



In the past, the use of machine-drills for stoping has 

 not been looked upon with much favour. For this there 

 are several reasons : first, the machine used was the heavy 

 drill employed for development work, and with this type 

 it was impossible to work in narrow stopes without break- 

 ing a large amount of waste ; secondly, the bands of 

 barren quartzite, with which the payable conglomerate is 

 often interstratified, suffered such pulverisation by reason 

 of the large blasting charges used that often it could not 

 afterwards be eliminated by sorting ; and, thirdly, the 

 large blasting charges were found to weaken the roof, so 

 that a greater number of pillars had to be left for its sup- 

 port than was the case with hand-drilling. Only in wide 

 stopes, on a large homogeneous reef with good walls, 

 could these drills be used to economic advantage. The 

 necessity for a good stoping drill for narrow reefs, how- 

 ever, has become more and more pressing with the 

 extension of the mining industry, with which the supply 

 of native labour for hand-drilling has not kept pace. 



By a series of competitive trials carried out under 

 Government supervision, it has been established that 

 machine-drilling in moderately narrow stopes costs no 

 more, and perhaps even less, than hand-drilling by 

 natives. Hundreds of small drills (drilling a hole to take 

 a 5-inch explosive) are already employed for stoping on 

 the Rand, and their average duty is three-quarters ol a 

 fathom per shift. To stope very narrow and low-grade 

 reefs hand-labour has still to be used ; but it is hoped that 

 a drill capable of doing even this class of work will 

 eventually be evolved. 



Another important problem which has recently forced 

 itself on the notice of those responsible for the mining 

 operations on the Rand is the support of the hanging wall. 

 The removal of the gold-bearing conglomerate bed, which, 

 except for its somewhat steeper dip, may be compared to 

 a coal-seam, leaves an open space, which is not allowed 

 to fall in, as in a coal mine worked on the long-wall 

 retreating system, but is supported over enormous areas 

 by pillars of un worked conglomerate in the stopes, by ribs 

 left above and below drives, and by pillars left to ensure 

 the safety of the shafts, supplemented in some cases by 

 the slowing of waste rock. These methods have sufficed 

 in the past to keep open the stopes and drives and to 

 protect the shafts; but owing to the robbing of the stope 

 pillars in the outcrop mines, and more especially to the 

 increased pressure of the superincumbent rock mass in the 

 deep levels, serious movements of the hanging wall have 

 lately been making themselves felt, crushing the pillars in 

 the stopes, destroying the ribs above and below the drives, 

 and in some cases even affecting the shaft pillars. 



To arrest this untoward movement, which at one time 

 threatened the loss of the main thoroughfares of some of 

 the mines, a system of sand-filling has been adopted. By 

 this system the abandoned stopes and other working places 

 in the mines are filled with sand taken from the residue 

 dumps. The sand is mixed with sufficient water to cause it 

 to flow down pipes in the shafts and to be discharged in the 

 stopes prepared for its reception. Underground, the pulp 

 is conducted by wooden launders to the stope to be filled. 

 Barricades are used to keep the sand in place ; but it 

 drains well, and soon packs solid enough to bear the 

 weight of a man. The effluent water is pumped back to 

 the surface. At first it was feared that the cyanide remain- 

 ing in the sand would be dangerous to the mine-workers : 

 but a little research has eliminated this source of danger. 

 The effluent water from the sand-packs underground shows 

 no trace of cyanide, and no hydrocyanic acid his been found 

 in the air of the stopes which are being filled. The filling 

 of the worked-out stopes will also assist ventilation, since 

 it will prevent the dissipation of the fresh-air current. The 

 system is aln 1 many mines, and there is little 



doubt that it will be universally adopted. 



One of the most remarkable economic changes on the 

 Rand is now being brought about by the concentration of 



