COROCORO COPPER DISTRICT OF BOLIVIA 77 



4. The native copper is associated with waters contain- 

 ing a high percentage of earthy chlorides. 



5. The native copper is characteristically irregular and 

 in the nature of a replacement or infiltration of the 

 country rock. 



6. Not absolutely universal is the occurrence of zeolites. 



It is obvious that these characteristics are more applicable 

 to the North American native copper occurrences than to 

 the Corocoro. Thoroughly applicable to the latter are 

 points i, 2, 4, and 5. Too little is known concerning the 

 Corocoro mine waters to rule out the probability that their 

 chemical character is merely a reflection of the aridity of 

 the climate and the character of the rocks through which 

 they have flowed and that it has no genetic significance 

 with regard to the ore deposition. The other three common 

 characteristics, i, 2, and 5, though probably significant are 

 not of fundamental genetic import. Much of the Lake 

 Superior ore is not in red sandstones, hence they were not 

 essential agents in the precipitation of the native copper and 

 they were not the source of the copper-bearing solutions. 

 The Corocoro copper beds extend through a great thick- 

 ness of strata and the mineralization is so closely related 

 to the Corocoro fault that the ore deposition hardly took 

 place pari passu with the deposition of the sediments. Con- 

 sequently the conditions under which the red beds were 

 formed were not essential to the precipitation of the ores. 

 In other words, one is almost forced to the conclusion that 

 the association with red beds is a fortuitous coincidence 

 rather than a significant genetic factor. The blanching of 

 the sandstones indicates that the mineralizing solutions 

 were capable either of reducing the ferric oxide to which 

 they owe their red color to the ferrous state or of dissolv- 

 ing and removing it. No studies of the chemical 'composi- 

 tion of the bleached and unbleached rock have been carried 

 on to determine which has happened. A priori, one might 

 expect most primary ascending mineralizing waters to be 



