472 NOTES ON SOME OXIDISED COPPEK ORES. 



the waters percolating downwards from the surface. Hence, 

 when once the permanent water-level is reached, or when the 

 lode is so solid as not to admit of air or water circulation, there 

 is no more chance of oxidation. 



Oxidized Ores of the Rocky Mountains, Sfc. — These same effects 

 of oxidation are observed in all mining countries, as for instance 

 in the Eocky Mountains of the United States and the Sierra 

 Madre in Mexico. They have, too, precisely the same limitation 

 in depth by the permanent water-level, or the density and com- 

 pactness of the deposits. But in these countries, where the 

 water-level is very deep owing to the elevation, where there is 

 usually a very small rainfall with comparatively long periods of 

 drought, and where the rocks are frequently very porous and per- 

 meable both to air and water, the oxidized ores are often found 

 at very great depths— the mines being often perfectly dry to a 

 depth of 1000 feet or even much more. As might be expected, 

 the gozzans and oxidized outcrops in Nevada, Utah, Colorado, 

 Arizona, New Mexico, and Old Mexico, are often highly aurifer- 

 ous and argentiferous, and often the precious metals are found 

 in still greater abundance as depth is attained. In some places, 

 too, they are extremely rich in copper, red and black oxides, 

 green and blue carbonates, green chlorides, and variously tinted 

 silicates. So abundant is the copper in many instances that the 

 oxide of iron present is completely masked, and the ordinary 

 gozzany characters disappear. In Arizona numbers of miners 

 have been working on such oxidized ores for years — the ores 

 being raised from the miners and smelted direct in water-jacket 

 furnaces without any admixture of flux. The same kind of ore 

 is worked at Beaver-head in Montana, and at Boleo in Lower 

 California, and similar deposits have lately been found in the 

 San Pedro Mining district in New Mexico, at an elevation of 

 nearly 8000 feet above the sea. At this latter region the ores 

 occur in irregular veins and pockets following the old water- 

 channels, in limestone which is traversed by dykes of felspar 

 porphyry. They consist of carbonates and oxides embedded in 

 highly crystalline calcite associated with garnet, and changing to 

 yellow sulphide in depth. Those raised up to the present and 

 smelted average l;3J per cent, in copper. They are smelted at 

 once into a matte containing about 45 per cent, of copper, and 



