THE DEVELOPMENT OF GOLD EXTRACTION 

 METHODS ON THE WITWATERSRAND. 



Bv Henry Arthur White. 



It may be assumed that members of this Association are 

 familiar with the main outhnes of the methods employed in 

 extracting the precious metals from the Witwatersrand banket 

 reefs. 



A reference to the last paper on this subject will make 

 clear to anyone the underlying" principles of the practice then 

 adopted, and these have undergone no considerable change. 

 I refer to the paper read in April, 1903, before this Association 

 by Dr. Caldecott, who, as is well known, has taken a large 

 share in the developments of the last seven vears, with which 

 this paper chiefly deals. It will perhaps be useful to take this 

 statement of the facts of 1903 as a base on which to develop 

 the principal features of present-day practice and to follow 

 the same order of treatment of the various processes to be 

 considered. 



As it is usually necessary in mining to stope out some quan- 

 tity of inter-bedded, but valueless, rock, the first operation to 

 be performed is to remove, as far as practicable, all such 

 " waste " from the valuable ore. The use of sorting tables 

 and belts for this operation is still maintained, and in 1909 

 the average amount of material so discarded was 1445 per 

 cent, of the total mined, against I4'24 per cent, in 1903. This 

 left nearly twenty-one million tons of ore to be further dealt 

 with. Somewhat more than half of this passed over the 

 screening arrangements to be broken down into one and a 

 half inch cubes in the rock breakers. 



There has not been much change in the devices employed for 

 sorting and breaking; and improvement in detail and the use 

 of larger units have been chiefly responsible for the saving 

 effected in cost of operation. In the transport of the crushed 

 ore from the breaking plant to the mill bins, belts have been 

 introduced, where the distance was short, and full-sized rail- 

 way trucks and engines are employed where the mills are 

 further away, and may be seen in operation at the Simmer and 

 Jack or the Simmer Deep. 



It is proposed to use electric haulage on a similar large 

 scale for the new mill being erected at the City Deep, and this 

 is in keeping with the development of electric power utilisa- 

 tion, consequent on the formation of large power companies, 

 whose sole business is the production and distribution of elec- 

 tric energy. 



The considerable saving effected by generating electricity in 

 large quantity, by huge machines centred in suitable localities, 

 will ensure that this means of reducing _ capital ex- 

 penditure and economy in cost of operation will be rapidly 

 extended in the near future. 



Many mills are now driven by electric motors either in large 

 units, driving 100 or more stamps, as at the Angelo, or by 

 means of smaller motors for each lo-stamp battery. 



