COROCORO COPPER DISTRICT OF BOLIVIA 79 



CONCLUSIONS CONCERNING GENESIS OF COROCORO DEPOSITS 



The Corocoro deposits are unusual or anomolous pri- 

 marily in the occurrence of native copper. But mining 

 developments of recent years have called attention to the 

 large quantities of sulphidic ores and the gradation of the 

 one type of ore into the other, that is, have made less 

 marked the line of separation between the native metal ores 

 and the more common type of copper ores. Experimental 

 chemical work has also demonstrated the ease with which 

 copper may be precipitated from its solutions in the metallic 

 state. Stokes * showed that ferrous sulphate will pre- 

 cipitate copper from a solution of copper sulphate and 

 Fernekes f that ferrous chloride acts in the same way on 

 copper chloride solutions provided the hydrochloric acid 

 is constantly neutralized. These particular reactions hardly 

 apply to the genesis of the Corocoro native copper, because 

 ore deposition seems to have taken place under conditions 

 that produced a concomitant reduction of ferric oxide in 

 the rocks, but they do show the readiness with which 

 native copper can be precipitated. 



Despite many uncertain features and the lack of detailed 

 and exact data, the geologic relations and the mode of 

 occurrence of the Corocoro deposits are now sufficiently 

 w.ell established to rule out all syngenetic theories of their 

 origin. They are due to the impregnation of porous strata 

 along and adjacent to the Corocoro fault by ascending 

 cupriferous solutions. If one could postulate reducing 

 conditions within those strata, the chemistry of the native 

 copper precipitation would be relatively easy to write. It 



* N. H. Stokes : Experiments on the Solution, Transportation 

 and Deposition of Copper, Silver, and Gold. Econ. Geo., Vol. I, 

 1906, pp. 646-647. 



t Gustave Fernekes : Precipitation of Copper from Chloride Solu- 

 tions by Means of Ferrous Chloride. Econ. Geol., Vol. 2, 1907, 

 pp. 580-581. 



