COROCORO COPPER DISTRICT OF BOLIVIA 65 



ization is described as identical in character with that of 

 the ramos. But toward the surface the ore of the vetas 

 is chiefly chalcocite with which are associated domeykite and 

 other arsenic and sulphur compounds of copper in smaller 

 quantity. Close to the surface these minerals have under- 

 gone oxidation and there is an abundance of green basic 

 copper sulphate, considerable malachite and azurite, and 

 also cuprite. The depth to which the sulphides extend 

 varies in the different vetas, but is in the neighborhood of 

 100 to 150 m. Lower down only the native copper is 

 found. The average grade of the native copper ore is 

 2-*/2 to 4 per cent and of hand-sorted sulphides 10 to 20 

 per cent. 



All published descriptions of the Corocoro district agree 

 in making the Corocoro fault the boundary between the 

 Vetas and the Ramos. A different interpretation of their 

 relations is held by Fernando Dorion, general manager, 

 and Adrian Berton, chief engineer of the Corocoro United 

 Copper Mines, Ltd., as set forth by Singewald and Miller. 

 They believe that the vetas and ramos in the vicinity of 

 Corocoro are the same beds and that both lie west of the 

 Corocoro fault. A southward-pitching zone of disturbance 

 has more or less dislocated the vetas and reversed their dip 

 in depth. Because easterly-dipping beds in the vicinity 

 of the Libertad mine on the east side of the fault were 

 called ramos, the same name was applied to the easterly- 

 dipping parts of the vetas. Subsequently it was erroneously 

 concluded that both sets of easterly-dipping ore bodies are 

 the same. The areal geology is against this view and there 

 is no direct evidence in favor of it, so there is every reason 

 to believe the generally accepted interpretation the correct 

 one. 



Lincoln ascribes a length of n miles to the Corocoro 

 district, including thereby the Carmen and Grau properties 

 on the north side of the railroad near Ballivian station, 

 and a maximum width of about half a mile. Ore has been 

 worked to a depth of 1600 feet. Near Corocoro the vetas 



