The Patio and Caw Process. -u 



was replaced by the process now used in the vicinity of Copiapo. 

 The ores were reduced to pulp by methods analogous to t hat- 

 in the patio process, from which this one originated. The pulp is 

 carried away by a stream of water to settling-tanks 2 m. in diame- 

 ter and 3 m. deep, made of sheet iron, the number in use de- 

 pending on the size of the works. As fast as one of these set- 

 tling-tanks is full, the stream is turned into another, and so on. 

 The tanks, when full, are left from eight to twelve hours. The 

 clear water above is then run oif, and the mud below carried to 

 the Unas. These are wooden tanks with cast-iron bottoms. 

 They are 1.80 m. in diameter, and 1.20 in. deep. In the centre 

 is an axis which carries a muller, which runs on or close to the 

 bottom of the Una. This machine was undoubtedly sug- 

 gested by the arrastra. The charge for each Una is one 

 and a half tons of pulp. It is introduced into the Una 

 while the muller is still. Mercury is added, to about twenty 

 times the amount of silver contained in the ore, and the muller 

 put into very slow motion, not over four times a minute. At 

 the end of twenty hours the amalgamation was supposed to be 

 completed. A stream of water was then introduced, and the light 

 particles were thus carried oif. When the water ran clear, the 

 particles being too heavy to remain suspended in it, the mercury 

 and amalgam were removed through a hole made in the Una for 

 that purpose, and collected in a cast-iron vessel called a cocha. 

 A complete operation, including the grinding, lasts about 60 

 hours. The cost for ores yielding $80 to the ton is $10 per 

 ton, including the loss in mercury. The tails usually contain 

 from $8 to $10 a ton. They are not allowed to contain more 

 than from $25 to $30. As the ores themselves are very pure, the 

 silver obtained is about .990 tine. So long as the ores were rich 

 and pure, little was done to improve the process, but as they be- 

 came poorer and more impure, the tails grew constantly richer, 

 and it became necessary not only to treat them, but to treat the 

 poor ores, desmontes, which had been thrown aside as not worth 

 treatment. Barrel amalgamation was tried, but failed, as did 

 also the attempt to chlorinize the ores and dissolve out the chlo- 

 ride of silver, as the ammonia cost too much. Eecourse was 

 then had to the abandoned Cazo process, which, with a number 

 of modifications, proved successful. 



