SOME NOTES ON TREATMENT OF SANDS FOR STOPE FILLING. 205 



the problem of ventilation. This latter is so self-evident as to 

 require no elaboration. From aesthetic and the health point of 

 view, however, the question appeals probably more to the Rand 

 than to any other mining district in the world. Everyone admits 

 that the mine dumps are an eyesore, and they cannot be beautified 

 by any known means, for nothing- will grow on them. Then 

 their presence aggravates the dust nuisance, and may even, as 

 some assert, lead to municipal silicosis. Be that as it may, all 

 resident about Johannesburg look forward with undisguised 

 pleasure to the day when dumps shall be no more ; when they 

 will return whence they came, after having served their undeni- 

 ably useful purpose. From what has just been said it will be 

 surmised that the intention is to sluice these dumps back into 

 the mine again, and this is really what is now being done on a 

 small scale, but the problem is far from being a simple one. 

 True, the Australians have been filling up old worked-out places 

 in their gold mines for years, and although their difficulties are 

 not the same in all respects as those existing on the Witwaters- 

 rand, it is encouraging to know that they have apparently over- 

 come them ; but time alone can tell this. As far as the Rand is 

 concerned, the procedure adopted is comparatively simple, and 

 can be easily described. The tailings (sands, not slimes) are 

 dumped or sluiced into a large chamber, where they are mixed 

 with the proper proportion of water. A further mixing is ensured 

 during their passing through a launder provided with a series of 

 " baffle plates." Ultimately the pulp is lowered into the workings, 

 either through a pipe column, which generally goes down the 

 shaft, or through a borehole specially prepared for the purpose, 

 and by means of suitable branches is distributed to the various 

 stopes which have to be filled in. The sides and bottoms of these 

 are bratticed off at the lowest levels, leaving a semi-firm deposit 

 not unlike the sand left on the beach after the tide has receded. 

 So far as experience goes this has never hardened to any great 

 extent, and is hardly likely to do so, although there is hope of 

 assistance in this direction by addition of one or more of the 

 various bodies suggested, possessing cohesive or setting pro- 

 perties. There is also no experience to show how this mass 

 would behave in the event of a mass of rock coming down on the 

 top of it. The use of a borehole instead of a pipe column, as a 

 channel for introduction of the pulp into the mine, means a large 

 saving on the wear of pipes, which are acted upon mechanically 

 by the sands, and chemically by the acids formed from oxidation 

 of the pyrites. With this latter aspect we shall deal presently. 



The method just outlined is the one most commonly in use 

 on the Rand. Although it demands very little surface plant, it is 

 obvious that much water has to be run into the mine with the 

 sands, and a large portion of this water has to be pumped back 

 to the surface. Another method has been introduced recently 

 which, besides other advantages, is said to have the effect of 

 greatly reducing the quantitv of water to be dealt with. Further 

 reference will be made to it, when dealing with the question of 

 the destruction of cyanide. 



