COROCORO COPPER DISTRICT OF BOLIVIA 7 



are still coarse grits and fine conglomerates ; and we come upon the 



Veta de Re jo, or Veta Copacabana Still lower in 



the same class of beds, the Veta Remacoia, or main seam of copper 



is encountered Below this metallic bed we find some 



gritty strata and then have a characteristic bed of fine-grained 

 crumbly red sandstones of immense thickness, the upper edge of 

 which is seen on the surface close to the line of fault." 



His description of the Ramos formation from the fault 

 eastward is the following: (p. 43) 



"Crossing now over to the east side of the line of the fault we 

 find an immense development of the same fine-grained sandstones 

 as those composing the last bed met with on the surface to the west- 

 ward of the fault ; and in the lower part of this bed we find 

 developed a series of metalliferous beds A consider- 

 able amount of gypsum is found in the form of strings or veins, also 

 as small crystalline particles disseminated through the beds of red 

 sandstone of this whole series." 



The descriptions are good in recognizing the prominence 

 of coarse sandstones and conglomerates in the Vetas forma- 

 tion and the occurrence of gypsum in the Ramos formation. 



Reck says the rocks in the vicinity of Corocoro are pre- 

 vailingly sandstone beds in which the red color is less pro- 

 nounced than in the same rocks farther north. Intercalated 

 with them are shales of reddish-brown color and gypsum 

 beds and stringers of gypsum and salt intersect the shales. 

 He recognizes a westerly-dipping group of rocks which is 

 dark brownish-red to reddish-gray in color and contains 

 the ore-bearing beds and an easterly-dipping group of rocks 

 which consist of red clay and an impure kaolinic clay which 

 often enclose thin beds of a yellowish-green fine marly 

 sandstone. The sandstones grade over into thin-bedded 

 shaly sandstones. The series is not metalliferous. The 

 rocks about Corocoro, he says, are also coarser than farther 

 north and include conglomerates. 



Mossbach adds little to the description of the stratigraphy 

 of the Corocoro rocks. He says they consist of reddish, 

 regularly stratified, not very hard sandstones with clay 



