SOME NOTES ON TREATMENT OF SANDS FOR STORE 



FILLING. 



By Thomas Donaldson. 



The past year has witnessed many new developments in 

 connection with the handling and treatment of banket ore, but 

 the so-called " stope filling' " is perhaps the most noteworthy of 

 all. By " stope filling " is meant the filling up of those crevices 

 in the bowels of the earth from which the ore containing gold has 

 been extracted. This is not the place to describe the principle of 

 mining, but it is perfectly evident even to the non-technical person 

 that unless this ore is taken out with great care, i.e., unless 

 strong enough pillars or supports are left for the sunerincumbent 

 rock, there will be a risk of subsidence. That such incidents take 

 place very frequently is part proof at any rate that mining has not 

 been too carefully carried out in the past. Perhaps this is not to 

 be wondered at, for it is most unnatural to leave in position 

 massesof ore which are known to be rich in gold, and which would 

 help to swell dividends. Be this as it may, the Rand has had 

 many warnings during the past few years that something drastic 

 had to be done to prevent bad becoming worse. Only the other 

 day, a little to one side of an important street, a cart and two 

 mules disappeared completely owing to a subsidence, and only 

 by the luckiest chance did the driver escape. On the East Rand 

 a few years ago, a whole dwelling disappeared, and only by the 

 luckiest chance again, was the loss of life not greater. The so- 

 called " earth tremor " which is reported every other day, and the 

 recent air blast of the Cinderella Deep, which was attended by 

 great loss of life, have shown, if that were necessary, that 

 something has to be done quickly. Fortunately our mining 

 engineers are alive to the problem, and a start has been made. 

 Of course, it must be confessed that mining, no matter how 

 carefully it is carried out, will always lead to movement of masses 

 of rock, for anything which disturbs the internal structure of the 

 earth's crust is bound to set up new stresses and strains, and this 

 has been experienced all over the world. Some years ago, in the 

 coal mining districts of Silesia, occurrences not unlike those of 

 the Witwatersrand were taking place, and the authorities in 

 charge then hit on the plan of filling up the disused workings 

 with the waste material which had been taken out, sluicing them 

 down by suitable mechanical and hydraulic arrangements. So 

 far as the information which we have goes, the procedure has 

 proved a success, and a similar plan has recently been adopted 

 for some of the collieries in Scotland. The advantages claimed 

 for the process are, firstly, that it will minimise the chance of 

 rock movement, and, through consolidation of the deposited mass, 

 will allow of the " drawing " of the supporting pillars, thus 

 extending the profitable life of the mine, and secondly — and this 

 is of particular interest to the Witwatersrand — that it will simplify 



