240 CHARLES E. MUNROE 



lem is comparatively simple, also, in the case of siliceous gold 

 bearing deposits free from sulphurets, but the ore must be 

 crushed, and in many instances it is more economical to con- 

 centrate it than to expose the entire mass to the action of 

 the cyanide solution. Moreover, even in the case of neutral 

 and otherwise suitable ores, the fine particles of metallic gold 

 may be so enveloped in an impermeable covering — such as 

 iron or aluminum hydroxide — as to necessitate a preliminary 

 treatment, such as roasting, to rupture the envelope. An 

 example of this kind is found in the ores of the Republic gold 

 mine, Washington, described by T. M. Chatard and Cabell 

 Whitehead. When coarse gold is mingled with the fine, it 

 is usually more economical to separate the coarse gold by 

 amalgamation than to await the slow acting process of solu- 

 tion. With tailings in which the sulphurets are but partly 

 decomposed and which still contain ferrous and ferric salts 

 and sulphuric acid, cyaniding may be preceded by washing 

 and neutralization. 



The treatment of refractory ores is determined, in each 

 case, by the chemical and physical characteristics of the ore 

 under consideration. Hence, we find that cyaniding may 

 be combined not only with crushing, roasting, concentration, 

 and amalgamation, but also with smelting and chlorination. 

 In some instances it is most advantageous to separate the ore 

 into fractions, each of which is subjected to a different treat- 

 ment. In fact, it is essential to success that the ore should 

 be thoroughly examined by a competent metallurgical chem- 

 ist before any investment in a plant for treatment by chemical 

 processes is made, and also that the cyaniding process should 

 be under chemical supervision, in order that, by assays of 

 the ore and tailings and by analyses of the ore and the cyanide 

 solutions as they enter and issue from the zinc boxes, and of 

 the solvent during preparation and regeneration, a complete 

 check may be made upon the operation in each of its stages. 



It is obvious that the cost of the cyanide process will 

 vary at different plants, according to the variations in the 

 chemical composition and physical structure of the ore treated, 

 in the condition of the ore at the time of treatment — that 

 is, whether it be in the form of sand, or slimes — in the char- 



