2 STUDIES IN GEOLOGY, No. i 



district, numerous mines were opened, and by 1846 there 

 was an annual production of 35,000 quintals (46Kg) of 

 barilla, or native copper concentrate. In 1850 the pro- 

 duction had been increased to 88,000 quintals, but the 

 average production since that year has been less. The total 

 production "from ,1873 to 1912 was 200,000,000 pounds of 

 copper. Besides leading to a regular and considerable pro- 

 duction, this period is notable for the consolidation of the 

 diversified ownerships of the mines under two strong 

 companies. The Compania Corocoro de Bolivia, a Chilean 

 company, was organized in 1873 ; and the Corocoro United 

 Copper Mines, Ltd., an Anglo-French company, in 1909. 

 All of the producing mines are now under the ownership 

 of these two companies. 



The completion of the Arica-La Paz railroad in 1912 

 marked a new era in the development of the district. From 

 1830 to 1912 the native metal ores were almost the sole 

 object of attention. Owing to extremely adverse trans- 

 portation facilities, only the high grade native copper con- 

 centrate could stand the freight charges ; but, with the open- 

 ing of the new railroad and the construction of the branch 

 into Corocoro itself, the transportation situation was 

 immensely improved, and it became profitable to export 

 sulphide ores which hitherto had been avoided in mining 

 or thrown on the dumps. This led to a sudden augmenta- 

 tion in the production of the district. In the latter part of 

 1914 the Chilean company was shipping at the rate of 1,500 

 tons monthly of hand-picked sulphide and oxidized ore 

 averaging 18 per cent copper, and the European company 

 30 cars per month of the same kind of ore in addition to 

 the usual amounts of native copper concentrates. Shortage 

 of railroad equipment in 1915 and in subsequent years 

 greatly reduced shipments from the district and compelled 

 the lower grade sulphide and oxidized ores to give way to 

 the higher grade metallic copper concentrates. To over- 

 come this difficulty both companies experimented with 

 flotation and in 1918 the Chilean company started in opera- 



