14 Geo0rapbfcai wotes on 



one-seventh or one-eighth of the entire American output. From Janu- 

 ary i, 1787, to June n, 1791, the Valenciana yielded 13,896,416 ounces 

 of silver, its ore averaging a little over 100 ounces to the ton. Though 

 flooded, this fine old mine is still far from exhausted. 



Gold occurs chiefly, not on the plateau in association with silver, 

 but on the slopes facing the Pacific, and apparently in greatest abun- 

 dance in Sonora, near the auriferous region of Lower California. The 

 production would have been larger if an improved process of reducing 

 the metals had been used, but during the whole colonial period and up 

 to the present time, we have used the patio system, which consists in 

 grinding the ore, stirring it until it is reduced to a fine dust and mixing 

 it then with salt and copper amalgam ; after the paste dries somewhat, 

 salt is added in proportion to the amount of silver supposed to be in the 

 ore ; the material is then mixed with shovels and trodden by mules, and, 

 after a day or two, another mixture of copper, vitriol, and salt is added ; 

 after that it is mixed and trodden again ; then quicksilver is finally 

 added, and then more mixing and treading. This process is repeated 

 from five to fifteen times until the silver and quicksilver unite to form 

 an amalgam, which is gathered into bags, and that requires about forty 

 days. Most of the quicksilver is squeezed out and the rest is evapo- 

 rated and run off into tubs. This method saves 50 or 60 per cent, of 

 rich ore and, besides being very long, is rather imperfect, as it leaves a 

 great deal of silver in the ore, and only rich ores could be treated by it ; 

 but it was on the whole the easiest and cheapest. 



Some of the old mines were worked until finally they became so deep 

 that, with the methods then used, as buckets were employed instead of 

 pumps, and steam had not been employed as power, it was impossible 

 to drain them. Naturally in a deep mine the water flows in from 

 springs, and the deeper a mine becomes the more water it has. These 

 mines were worked until it was seen that it was impossible to drain 

 them, and then they were abandoned, even though they were rich in 

 metals. During our war of independence almost all the mines were 

 abandoned for the want of guarantee to life and property, and the 

 mining industry, therefore, declined considerably ; but recently the old 

 mines have been worked again and the production of silver has in- 

 creased very considerably. 1 



1 Mr. J. A. R. Waters of the firm of Waters Bros. , Mining Engineers of the City 

 of Mexico, said of his visit to the Jesus Maria District of the State of Chihuahu, where 

 he went to examine the mine worked by the Pinos Altos Co. , as follows : 



' ' The district is very thoroughly mineralized and is pierced by veins more frequently 

 than any district I ever saw. The general formation is very similar to that of Cripple 

 Creek, with the exception that it is not traversed by the great porphyry dikes that occur 

 there and in other parts of Colorado. The country formation is largely braccia. The 

 ore is generally free milling, and is treated with stamps and pan amalgamation, the 

 finer ores being treated with Huntington mills. There is little waste of values." 



