i873-] Colorado Gold Mines. 27 



concentrated. The gangue is generally soft and light, and 

 easily separable from its mineral contents ; and the mineral 

 is not, as a general rule, distributed in such minute particles 

 through the mass as to necessitate crushing finer than 

 i-6th to i-8th of an inch, in order to obtain a very perfect 

 disengagement of the one from the other. The coarse 

 grains should be concentrated in automatic hutches. It is 

 possible that Messrs. Huet and Geyler's hutches* would 

 separate not only the mineral from the earthy matter, but 

 as the toppings flow from hutch to hutch effect a certain 

 separation of the iron and copper pyrites from the blende 

 and galena. These hutches recommend themselves also 

 by their compactness, and being built entirely of iron. The 

 slime concentration would doubtless be best effected on 

 Rittinger lateral percussion tables, which would certainly 

 not only concentrate, but separate the concentrate into 

 parcels of different specific gravity ; but the machine re- 

 quires for successful working too close attention to so 

 many details to be efficient in the hands of Colorado ore- 

 dressers. Buddies therefore — concave buddies for the coarse, 

 and convex buddies for the fine slimes — would be the most 

 suitable machines. If third class ore, which will not bear 

 expensive carriage, is to be utilised, the concentrating works 

 would need to be at the mines. Water could be delivered 

 to most mines from the Consolidated Ditch. The charges 

 are now high, but it is expected they will be reduced to 

 10 cents per miner's inch per day = 2274 cubic feet of water. 

 Dry concentration is strongly advocated, but where water 

 is accessible it will in most cases be better to adhere to the 

 well-understood system of water dressing. 



If the concentration were as carefully conducted as it is 

 in the best establishments of England and the Continent, 

 the result should be as favourable. In Hungary the allow- 

 ance for loss is 15 per cent. Allow that it would be 20 per 

 cent in Colorado, and that the concentrate would contain 

 four times as much mineral as the crude ore. If, therefore, 

 the mineral contained 1 oz. of gold and 1*5 per cent of 

 copper, the concentrate would contain, after making allow- 

 ance for loss, 4 ozs. of gold and 6 per cent of copper. I 

 leave the silver and lead out of the calculation. If the 

 galena and blende can be separated from the iron and copper 

 pyrites the galena will be an additional source of profit ; 

 if not, the cost of smelting the refractory mixture and the 



* Huet and Geyler, 46, Rue de la Vidtoire, manufacturers of the Ciibles 

 Rapides a Deux et Quatre Compartiments. 



