18 The Patio and Cazo Process. 



ern machinery did not extract more than $15 to «20. In some 

 instances, with the best modern appliances, an ore yielding by 

 assay $700 to $800 did not yield more than $20 to $30 when 

 treated in pans, while fully 75 per cent, of its value was recov- 

 ered by the use of the arrastra. In ores of lower grade, the 

 rapidity of the returns compensated for the loss, but in higher 

 grade ores it did not. It is a matter of great surprise that a 

 machine has not yet been invented to work rapidly on the prin- 

 ciple of the arrastra. 



3. Treatment on the Patio. 



a. Making the Tort a. — The process of amalgamating in the 

 arrastra is used when the ore contains considerable quantities of 

 iodides, bromides, chlorides or native silver or gold. When 

 there are none of these minerals present, it is only ground to be 

 subsequently treated on the patio, as are also the tails from the 

 treatment of the arrastra. The material from the arrastra is 

 carried to the amalgamation court called the patio. This is an 

 enclosure, more or less large, carefully paved and made as imper- 

 vious to mercury as possible. It is inclined so that water will 

 easily flow from it. Little by little, after several years' use, as the 

 tortas are made over the whole surface of the court, the ground 

 will become saturated with mercury. Every two or three years, 

 and oftener if the pavement has to be replaced, and more especi- 

 ally when the hacienda has to be abandoned, it will be worth 

 while to clean up and work the dirt beneath the floor. Very 

 many methods have been tried to make and keep this flooring- 

 tight. It has been made of artificial stone, of cement, and of 

 asphalt, and, in some places, of cut stone, faced on the edges 

 and made tight with cement. In some places, as in Nevada and 

 also in Mexico, timbers tongued and grooved like mill floors, 

 and covered with water when not in use, have been laid down 

 over an area of an acre and a half. Such a floor as this will 

 last several years. All of these devices are excellent and work 

 well ; but as the expense is large, the old method continues 

 in use, and probably will do so till the whole process is aban- 

 doned, as it doubtless will be in the course of a few years, when 

 the railroads now being built are completed, and transportation 

 becomes easy and cheap. 



