135 



The gangue is quartz, but no tetraheclrite was observed. This ga- 

 lena is very poor in silver, containing from 0.1 to 0.2 per cent. only. 

 Thus to the presence of tetrahedrite is apparently due the silver of 

 these ores. 



In this vicinity are several veins of gossan, or oxyd of iron, the 

 cappings of deposits of ore, and themselves containing a moderate 

 per centagCj about one per cent., of silver. 



The wall rock of these veins is a crystalline granular rock, and 

 has a slightly bluish tint on its fresh fracture, while its weathered 

 surface is discolored by oxyd of iron proceeding from the alteration 

 of the httle hornblende contained in the rock. It also has a little 

 mica and disseminated particles of magnetic iron. It thus ap- 

 proaches in composition to a dioritic rock. 



The veins which occur in the metamorphic porphyry have, so far 

 as opened upon, shown a different character from the above. The 

 porphyry itself has a compact gray ground, impregnated with car- 

 bonate of lime, and bearing numerous crystals of opaque, white, 

 triclinic felspar, grains of quartz and dark gray mica in six sided 

 plates. It contains also specks of magnetic iron. 



Veins in this rock are of quartz, often comby, containing a black 

 tetrahedrite, with from four to eight per cent, of silver, and are in 

 places impregnated with galena in small cubes, which contain 0.5 

 per cent, of silver. The gangue is discolored by the blue and 

 green carbonates of copper and black manganese, with films of the 

 sulphuret of silver and of native silver. Experiments made on 

 various quantities, of these ores in the j^citio, with the use of salt 

 and mercury, without roasting or magistral, have given an average 

 yield of fifty per cent, of silver', and comparison with correct assays 

 shows that from eighty to eighty-five per cent, of the silver con- 

 tained can be extracted by the simple action of salt and mercury. 

 This fact would seem to show that the silver of this tetrahedrite is 

 contained as mechanically mixed sulphuret. Some of the veins in 

 this porphyry have been thrown out of position by a large dyke of 

 granite. 



These mines have been but little worked, • although three at- 

 tempts have been made — twice by the Mexicans and recently by 

 the Santa Rita Company, but in each case the Apaches have forced 

 an abandonment. 



The ores reduced by the last Company were divided by hand 

 separation into two classes. The first, containing tetrahedrite in 

 quartz and brownspar, had an average yield of one hundred and 

 seventy-six ounces of silver to the ton. The second class, a quartzy 

 lead ore with little tetrahedrite, averaged eighty-one ounces to the ton. 



Cahuabi Mines. — Westward of the Baboquiveri range, on the 



