COROCORO COPPER DISTRICT OF BOLIVIA 67 



the exception of the Libertad mine, the shaft of which is 

 l /2 km. east of the fault, all of the mines are located close 

 to the Corocoro fault. 



Two prominent cupriferous horizons in the vetas, called 

 the Yanabarra and the Umacoya, parallel the Corocoro 

 fault and can be easily traced on the surface by their out- 

 crop and lines of old workings to where overlapped by the 

 Desaguadero series. In the mines other workable vetas 

 are encountered. No equally prominent ramos cupriferous 

 beds outcrop, although some of the beds outcropping 

 between the Libertad mine and the fault plane are beds 

 that underground yield workable ore. 



Mineralization has taken place principally in beds of the 

 Ramos series and the Vetas series close to the fault plane, 

 but also to a limited extent in the fault plane itself. The 

 characteristic manner of mineralization has been the impreg- 

 nation of sandy beds by native copper. As until about 

 six years ago no facilities were available for working 

 sulphide ores such ores were disregarded and the extent 

 of the sulphide mineralization not realized. 



No observations are available to indicate clearly the 

 relations between the sulphide ores and the native copper 

 ores, other than the general statement that the sulphides 

 occur in the vetas near the surface and in depth pass over 

 into the native copper ores and that the ramos ores are all 

 native copper ores. In the Gullatiri Grande mine a streak 

 of sulphide ore is encountered on the third level which is 

 about 200 m. below the surface. In the Remedies mine, 

 the sulphide ores extend to 200 m. below the surface and 

 are there replaced by native copper ores. The upper levels 

 of the Vizcachani shaft yield sulphide ores, but the lower 

 levels are in native copper ores. The Umacoya veta in the 

 Vizcachani shaft carries native copper ore to above the fifth 

 level, a depth of about 150 m., whereas the veta adjoining 

 it in the hanging wall still contains the sulphide ores at this 

 depth. The mines in the ridge north of Corocoro, the 

 Estrella, Copacabana, Capilla, Malcocoya, and San Augustin 



