452 



EXPLORATION GEOPHYSICS 



The self-potential method is capable of furnishing important data, 

 provided the interpretation is made with due regard to ore occurrence in 

 that particular district. Final utilization of the survey results is accom- 

 pHshed by subsequent drilling or other direct exploration to ascertain the 

 commercial value of the ore. There is no knov^n physical relationship 

 between galvanic currents or surface potentials and the economic value 

 of the mineralization. 



Fig. 270. — Sketch illustrating the displacement of the 

 negative center with respect to the top of the ore body. 

 Equipotential lines, dotted; topographic contours, solid. 



In regions where the water table is considerably below the surface and 

 where the upper near-surface material is highly resistant (as is the case 

 in many desert areas), the magnitude of the galvanic currents which pene- 

 trate the highly resistant overlying materials may be too small to create 

 a measurable potential difference at the surface. Under such conditions, 

 the self-potential method will not give interpretable results. Also, applica- 

 tion of the self-potential method in certain localities will quickly show that 

 many persistent earth potentials are present which are not related to min- 

 eralized areas or ore occurrence. 



