ELECTRICAL METHODS 



555 



this concept may be illustrated by a practical case of a prospect in Sonora, 

 Mexico, t 



In a region characterized by extremely steep topography which is 

 broken in many places by vertical cliffs, a 25-foot, copper-bearing ledge 



2300 



2800 



2400 



2200 



StCTION A-B 



Fig. 341. — Cross section inferred from geophysical survey. 

 L — ledge 



U — undifferentiated sediments 

 SU — silicified undifferentiated sediments 

 5.? — sandstone 

 E — electrical stations 



Electrical stations and topographic contours shown in upper portion 

 of figure. {Canad. Mining Journal.) 



is exposed at the surface for a distance of 500 feet. (See upper part 

 of Figure 341.) To the south, it is cut off by a fault having considerable 

 displacement. To the north, it was traced to station E-\, where it is 

 covered by talus and detritus. 



t J. J. Jakosky, "Geophysical Examination of Prospects," Canad, Mining Journal, Jan. 1934. 



