The Patio and Oazo Process. 41 



is not usual. Water is put into the uoliche, and the sulphurets 

 added and stirred, and then allowed to settle. During the 

 settling it is tapped on the outside with a stick or mallet. The 

 heavy particles containing the sulphurets settle to the bottom, 

 and the sand is on the top. The water is soaked off with rags. 

 The sand is scraped off and thrown away. Below is a brownish 

 layer of poor sulphurets called colas, which are removed to be 

 roasted. Below them are the clean polvillo and a small quantity 

 of amalgam. The polvillo is sent to Europe with the high grade 

 ores for treatment. The roasting of the colas is done in an ordi- 

 nary pile with a central chimney. It is put in layers 0.25 m. thick, 

 and is used damp in order to be able to manage it better. The 

 cover is made of earth. The pile is set on tire, and when the 

 roasting is completed the half burned sticks are removed. Only 

 a part of the material is properly roasted, but it is all ground 

 in an arrastra and added to the torta. In some places where 

 fuel is cheap, the roasting is done in a reverberatory furnace, 

 and is consequently much better done. There is always great 

 uncertainty in roasting in piles. This roasted material was 

 formerly treated in a torta by itself ; but it consumes a great 

 deal of mercury, and does not give very satisfactory results. 

 It is much better to mix it in the piles with the ore. 



In some places, during the washing, a product is obtained 

 which contains gold and silver, and though there is not much 

 of it, it is richer in gold and silver than the original ores, and 

 also contains some little amalgam. As the material is mostly 

 pyrites, it is concentrated, ground and roasted, and used as a 

 magistral. Sometimes 2 per cent, is obtained in this way.* Of 

 late years, in some haciendas, all the tails of the different opera- 

 tions have been treated by the Yon Patera process, f 



4. Treatment or the Amalgam. 



The liquid amalgam is carefully removed from the bottom of 

 the settler. All that caught in the the mercury traps is added 

 to it. This is carried to the mercury house, azogueria, and put 



* Eng. Mining Inst., Vol. 33, p. 104. 



f Trans. Am. Inst. Min. Engs., June Meeting, 1883. 



