COROCORO COPPER DISTRICT OF BOLIVIA 3 



tion a flotation mill and in 1919 the European company. 

 The grade of the sulphide ores is so much higher than that 

 of the native copper ores, that concentration of the former 

 is now the more profitable operation. The native copper 

 ores are for the time being almost completely neglected 

 and the district is primarily a producer of sulphide ores. 

 In 1919 the production was about 9,000,000 pounds of 

 copper, of which over four-fifths came from the sulphide 

 ores and less than one-fifth from the native copper ores. 



As an important producer of native copper ores for near- 

 ly a century, the Corocoro deposits ranked among the 

 unusual copper deposits of the world. They share with the 

 Lake Superior deposits of the United States, the distinction 

 of being the only commercially important copper districts 

 in which native copper is the principal form of occurrence 

 of the ore. This unique geologic position of the deposits 

 attracted the interest of geologists and mining engineers 

 who have visited Bolivia with the result that the abundant 

 literature listed in the bibliography at the end of this paper 

 is now available, a striking contrast to the very scant litera- 

 ture covering many Bolivian mining districts with a more 

 splendant and meteoric past. Notwithstanding the notable 

 list of contributors to the geology of Corocoro, prior to 1917 

 little progress had been made in getting at the fundamental 

 facts and explanations of the geologic phenomena of the 

 district. Conclusions were hardly more than assumptions 

 and had been based largely on hasty generalizations and 

 unwarranted analogies, so that tb^re was a wide divergence 

 of opinion. The reader of the extensive literature was con- 

 fused more than enlightened with respect to all but the 

 most superficial facts concerning the geology and genesis 

 of the deposits. In 1915, Singewald and Miller collected 

 the first determinable fossils, in the shape of plants, from 

 the Vetas formation on the basis of which Berry was 

 enabled to determine definitely the age of those beds. The 

 results of their work were published in 1917. In 1919, the 

 authors of this paper visited Corocoro in the hope of further 



