14 The ratio and Gazo Process. 



which they run into the settling-vats. Sometimes a spout or 

 plug is put into the sides of the arrastra for the purpose of 

 allowing the pulp to flow into the launders. These troughs are 

 removed as soon as they have been used. When the pulp is 

 dipped out, a cover is put on the floor of the arrastra to pro- 

 tect the amalgam. When no protection is used, care is taken 

 not to go near the bottom. The whole of the slimes are not 

 removed at any one time, except to make a clean-up. In the 

 pits, the slimes are allowed to settle until they are ready to be 

 carried to the patio. It takes about three days to grind a 

 charge. 



At Chihuahua, on native silver ores, the arrastra is generally 

 charged with a ton per day of third-class ore, yielding from 

 $250 to $1,000 per ton, requiring about 25 lbs. of mercury. 

 After three days' run, ore as rich as $2,500 is added, which re- 

 quires more quicksilver. As much of this ore is added as is 

 necessary for the purpose of getting a suitable amount of amal- 

 gam collected in the arrastra, preparatory to the clean-up. 

 Some hours after adding quicksilver, the amalgamator, azugero, 

 takes an assay with the horn spoon, washes it, and judges whether 

 the proper amount of quicksilver is present. These assays are 

 regularly made, and b} r means of them great skill is rapidly ac- 

 quired in learning how to add the mercury. Every morning, 

 after the silver seems to be amalgamated, a large quantity of 

 water is added to the material in the arrastra, and kept in motion 

 from four to six hours. This separates the amalgam from the 

 fine ore, and allows the heavier particles to settle to the bottom. 

 The fine material which has not been amalgamated runs 

 off, carrying with it all the finely ground ore. The coarse 

 grains, not yet sufficiently reduced, remain and are ground 

 in the next charge. The tails which are thus obtained at 

 Chihuahua are poor, so poor that they are not worth more 

 than $3 a ton for the patio process. They contain all the 

 ores other than silver, except a small part of the ruby 

 and sulphide of silver, which have been reduced at the ex- 

 pense of the mercury. The sulphide of silver, being ductile, is 

 not reduced to powder, but settles to the bottom of the arrastra, 

 and is taken out with the amalgam. Any rich tailings which 

 come from the treatment of rich silver ore which has been 



