COROCORO COPPER DISTRICT OF BOLIVIA 47 



Corocoro valley on its west side for a distance of 3-^3 km. 

 It is then covered by wash for over 2 km. to the Pontezuelo 

 River, on the north banks of which it is again plainly dis- 

 cernible. The direction of the fault from Corocoro to the 

 Pontezuelo River is N. 20 W. It continues in the same 

 direction to the Carmen mine, on the Pizakeri River, 5 km. 

 beyond the Pontezuelo River and i mile northwest of 

 Ballivian on the Arica and La Paz Railway, and was traced 

 5 km. farther north to the Grau and Progreso claims. 



That the strike of the Vetas is parallel to that of the fault 

 is shown by the areal mapping of two of the principal ore 

 beds, the Veta Yanabarra and the Veta Umacoya, whose 

 outcrops parallel that of the fault. On the other hand the 

 divergence of the Ramos toward the north and the emergence 

 of successively lower beds in that direction is shown by the 

 mapping of several prominent ledges of the Ramos in the 

 Corocoro valley. Between Corocoro and the Libertad mine, 

 a distance of not quite 3 km., 406 m. of Ramos beds have 

 come to the surface in that way. The Vetas and Ramos 

 show considerable local variations of dip but the average dip 

 of the Vetas is between 55 and 60 and the Ramos between 

 45 and 50 



Three excellent exposures of the fault are at the north 

 and south boundaries of the Vetillas claim, 2 km. north of 

 Corocoro, and in the washout made by a branch of the Coro- 

 coro River near the middle point of the west boundary of 

 the Quillnquilis claim, 3 km. north of Corocoro. At the 

 south boundary of the Vetillas claim the fault plane has a 

 dip of 73 W. The Vetas steepen as they approach it until 

 they are parallel- to it. The Ramos abut against the fault 

 with unchanged dip of 47. In a ravine on the north bound- 

 ary, the fault plane shows a dip of 72 W. and the Vetas 

 steepen to parallelism with it as they approach it. The 

 Ramos have a dip of 47 which is unaffected by proximity 

 to the fault plane. On the Quilinquilis claim the Vetas also 

 steepen to 75 W. at the fault plane but the Ramos retain 

 a dip of 49. Immediately north of Corocoro for a distance 

 of one-half a kilometer the Ramos are steeper, with dips 



