242 Report S.A.A. Advancement of Science. 



the plant constitutes a prominent feature on the surface of all mining 

 properties. 



To illustrate the advances made in methods of gold extraction 

 on the Rand since its early days, the plant and methods employed 

 during 1889, the year immediately preceding the introduction of the 

 cyanide process by John Stewart MacArthur, may be compared with 

 the present state of affairs. The comparison more than justifies his 

 prophecy, made at a meeting of the Society of Chemical Industry 

 on March 31st, 1890, that "cyanide of potassium, hitherto used 

 only to polish amalgamated plates, will take a front rank as chief 

 agent in gold extraction." In 1889 the average mill contained say 

 twenty 750 lb. stamps, and was usually located so near the neighbour- 

 ing creek that the tailings from even the small amount of ore crushed 

 up to that date had from want of fall to be periodically removed 

 from the collecting dams and piled up in heaps. These piles of 

 sands and slimes around the battery were regarded simply as a source 

 of annoyance and expense, and so little was the latent wealth they 

 contained realized that anyone desirous of removing them was wel- 

 come to do so. Owing to the scarcity of water the very turbid over- 

 flow from the tailings dam was used over and over again in the mill. 

 The constant loss of water from soakage and evaporation was of 

 ■course very heavy. The average recovery by amalgamation was 

 50 % to 60 %, and in addition in some few Companies concentration 

 was practised to a limited extent by means of vanners or buddies or 

 blankets, with subsequent treatment of the concentrates in amalama- 

 ting pans or by chlorination. Many Companies were without assay 

 offices, and in fact assaying, owing to defective sampling, was not 

 in much repute, the " pan " being usually taken as a safer guide. At 

 this time also the enormous extent and regularity of the banket reefs 

 and the possibilities of profitable mining to great depths were by 

 no means realized ; many doubts were expressed as to the possibility 

 of successfully treating unweathered pyritic ore as compared with 

 the high-grade oxidized banket then usually milled. This lack of 

 confidence in the future of the fields was doubtless responsible by 

 restricting the investment of capital for many imperfections in the 

 equipment of the mines; and, whilst the working costs were so high 

 and the percentage of gold in the ore actually recovered so low a^ 

 compared with present figures, the average ore now milled could 

 then only have been handled at a loss. 



The first introduction of the cyanide process was made in May, 

 1890, at the Salisbury battery, where trials were made on parcels of 

 tailings and concentrates for the mining Companies and the results 

 published. The plant consisted of small vats of about i| tons capaci- 

 ty fitted with stirring gear, the charge being lowered after a certain 

 period of agitation with 0.5 % to 2 % cyanide solution into leaching 

 filter vats below. The precipitation of the gold was carried out as 

 at present with zinc shavings. The incredulity with which the results 

 claimed were first received and the classification of the MacArthur- 

 Forrest process with other competing but now forgotten methods, were 

 soon changed to a general acceptance of the merits of the new process. 



