COROCORO COPPER DISTRICT OF BOLIVIA 63 



by Strauss that deals principally with mining conditions in 

 the district. The vetas are said to be traceable continuously 

 for over 5 km. but there are no ramos outcrops. Six 

 mineralized layers of each kind have been exploited, the 

 thicknesses of which vary from a few centimeters to 7 

 meters. Sheets and masses of copper, called charque, occur 

 up to 600 pounds in weight, but the copper is found generally 

 in minute grains, pellets, or granular masses of the native 

 metal with which are associated other minerals as malachite, 

 chrysocolla, azurite, domeykite, and chalcocite. Gypsum 

 and salt are the principal gangue minerals. Silver minerals 

 are rare. The vetas are conglomeratic and contain the 

 copper in coarser particles; whereas the ramos are finer- 

 grained and the copper occurs in them in smaller particles 

 and masses. 



F. A. Sundt gives the average grade of the native copper 

 ores of the Compania Corocoro de Bolivia at 4 per cent and 

 of the Capilla mine, the richest in the district, at 7 per cent 

 copper. The native copper veins he says also contain 

 cuprite. Contrasted with these are the "yanabarras" veins, 

 which at the surface have oxides and green sulphates of 

 copper, but at a depth of a few meters consist of "the 

 black sulphides without iron that correspond to chalcocite 

 and are found in an arsenical gangue." Hand-sorted 

 yanabarras ores carry 18 per cent or more copper and some 

 of the veins with a width of 9 m. average 5 per cent copper. 

 He gives no information concerning the relations of .the 

 yanabarras and the native copper ores. 



With respect to their position, Singewald and Miller 

 describe three types of ore bodies the vetas, the ramos, 

 and the dorado. The latter is the name applied to the 

 mineralization in the Corocoro fault plane which is now 

 practically worked out. Louis Gasqual, chief engineer of 

 the Corocoro United Copper Mines Ltd., described the 

 dorado as a shoot of rich ore that lay in the fault plane 

 where it intersected the ramos ore beds. The vetas and 

 ramos are mineralized beds in the shale-sandstone series; 



