82 STUDIES IN GEOLOGY, No. i 



deep, the collar of which is located high up on the south 

 slope of Cerro Corocoro. There are 12 levels extending 

 form a depth of 80 m. to the bottom. The workings are 

 in the vetas Blanca and Azul and in the Dorado. The 

 levels above level 6 are inaccessible and the ores in the 

 deeper levels are exclusively native copper ores. The 

 levels of the Challcoma mine are connected with the 

 corresponding levels of the Guallatiri Grande mine. It is 

 developed by a tunnel 762 m. long from the Guallatiri 

 Grande mill beside the railroad on the level of which two 

 interior shafts have been sunk. Level 8, 240 m. below the 

 tunnel, is the lowest accessible one. The important ore 

 bodies are the Dorado, arid the Umacoya and Azul vetas. 

 The Vizcachani shaft has a depth of 390 m. divided into 

 12 levels. The native copper ores are derived from the 

 Blanco and San Jorge ramos, and the sulphide ores from 

 the upper levels in the vetas. 



The Libertad mine is the only important independent 

 mine in the district and it has been idle for a number of 

 years. It is situated well out in the Ramos and has 

 developed only ramos ore bodies. 



TREATMENT OF ORE 



Until 1912, only the native copper ores were worked and 

 until 1918 only the native copper ores were milled. There 

 were five mills in the district for the concentration of the 

 native copper ores : the Libertad mill at the mine of that 

 name, the San Francisco mill of the Compafiia Corocoro 

 de Bolivia, and the Guaychuni, Guallatiri Grande, and 

 Guallatiri Chico mills of the Corocoro United Copper 

 Mines, Ltd. The Libertad mill has not been operated for 

 some years. 



The treatment of the native copper ores at the San 

 Francisco mill was the following: 



The ore was brought to the mill by serial trams from the 

 mines and dumped on a platform above a Blake crusher. 



