366 Report S.A.A. Advancement of Science. 



Water is used in stamp milling in order to carry the ore from 

 under the stamps. The resulting mixture of slimes and water be- 

 comes of higher specific gravity and is more capable of carrying off 

 fine particles of gold than pure water could do. Subsequent careful 

 settling is necessary in order to collect these particles, and the result 

 of the creation of these undesirable slimes was the evolution of the 

 " slimes treatment," the weak point in the Cyanide process. 



The addition of lime to the water used in Mills has reduced the 

 diflftculty in settling, and also lowered the value of the slimes, but 

 unfortunately without leaving the slimes sufficiently poor to throw 

 away. 



Dr) crushing, chiefly by means of rolls, offers a solution of the 

 problem. The ore can be crushed without water, and the degree of 

 crushing can be controlled to a far greater extent than in stamp mills. 



This system has an additional favourable feature, and that is 

 that in the case of many ores the whole of the gold could be extracted 

 by cyanide in one operation and the cost of the amalgamation process 

 avoided. 



To obtain successful results the ore should be broken down in 

 stages. 



The material as it comes from the Mine often being in large 

 pieces should be first roughly broken in a powerful rock-breaker and 

 then passed on to a smaller sized machine which would still reduce 

 it to a smaller size. From these machines it should be fed to the 

 rolls, each set being adjusted to take the ore from the preceding 

 machine and again reduce it in size. By this means each machine 

 will be kept working on pieces of a size which suits its design and 

 adjustment, and the power available will be economically used. 



The advantages obtained in crushing the ore dr\ preparaton,- to 

 cyaniding may be put down as : — 



1. Economy in expenditure of power partly due to ihe crushing 

 of the ore being carried only to the extent necessary to give a good 

 extraction, and partly to the use of more economical crushers than the 

 gravitation stamps. 



2. The outlay in machinery will be less in proportion to the 

 saving in power. 



3. Economy in water required, as a ton of dry crushed ore can 

 be successfully treated at the expenditure of less than one quarter ot 

 a ton of water, whereas stamp batteries require a ver)' large amount, 

 frequently passing five tons. 



4. The possibility of winning the gold in one operation, namely 

 by exposing the whole of the ore to one cyanide treatment instead 

 of having three operations, i.e. amalgamation, cyanide treatment of 

 coarse sands and collection and treatment of the slimes. 



The objections raised against Dry crushing can be summed up 

 as follows : — 



1. Increased wear of crushing surfaces. 



2. Injurious effects on workmen, machinery, &c.. from the dust 

 produced. 



3. Difficulty of crushing and sifting the ore if it is damp. 



