The Patio and Cazo Process. 51 



lasted not much over two hours, and gave tails which did not con- 

 tain more than $3 to $4 to the ton, but it was only applicable to 

 ores which contain $80 and upward per ton, free from sulphur. 



This process was formerly used in connection with the patio. 

 The ores were first stamped and ground in the arrastra. This is 

 done as a preliminary to a concentration. The grinding is not 

 done so fine that there is danger of any large part of the silver 

 being carried off in the. washings. From the arrastra the pulp is 

 carried to the planilla, where it is concentrated to such an ex- 

 tent that the concentrates do not represent more than two or 

 three per cent, of the original ore. These concentrates are treat- 

 ed in the cazo, while the tails, if rich enough, were formerly 

 treated on the patio. There are two processes known under the 

 name of the cazo, distinguished from each other by the size of 

 the vessel and the mechanical means of doing tho work. The 

 cazo is the smallest vessel. The larger one, constructed on 

 exactly the same principle, is called a fondon. The process 

 itself is very simple and rapid. It consists in boiling the concen- 

 trates, keeping them constantly agitated with salt and sulphate 

 of copper, to which mercury is added, and then treating the 

 amalgam. 



The cazo, as originally invented, was a round vessel made en- 

 tirely of copper, but was afterwards replaced by a vessel, at first 

 made of stone, and then of wood, with a copper bottom turned 

 up at the sides. This vessel was originally quite small. 

 Its dimensions were: diameter above, 1 m; diameter below, 0.60 

 m.; depth 0.45 m. The thickness of the copper bottom was 0.05 m 

 to 0.06 m. This was set over a fireplace without grate, bars or chim- 

 ney, the smoke going out where the fuel was put in. A cazo of such 

 very small dimensions could treat only about 50 kilos, at a time. 

 To treat the ore, water sufficient to make a thin pulp with 

 the charge, was introduced. The fire was lighted, the water 

 brought to a boil, and salt amounting to from 5 to 15 per cent, 

 of the weight of the ore was then added. The workman then 

 rubbed the bottom of the cazo with a piece of wood attached 

 to a long pole, to keep the copper surface perfectly free. If the 

 salt had been added before the ebullition of the pulp, it would 

 have collected on the bottom, from which it would have been 

 difficult to separate it. As soon as all the salt is dissolved, the first 



