ELECTRICAL METHODS 



455 



ground in which the electrolytes have a different composition, an electric current will 

 be generated, and certain zones of the conductor will be oxidized. 



3. Electrolytic corrosion. Stray currents, due to power lines for example, may 

 enter the conductor in certain sections and leave it in others, thus causing oxidation in 

 certain zones. 



t^a Hi/ARrZ OlORltt 



B^ ftRlOOTITE 



tl-"----:j QRANITe QNCIS^ COMPLtX 



_-- FAULT 



^ DIA^^ONO ORILU HOLt 1<1« 



0:j3 tunnel No- 5 WORKm^S 



Fig. 272. — Spontaneous polarization profiles and drill data at 

 Tunnel No. 3, Chelan Nickel Prospect. (Drill data courtesy of 

 U. S. Bureau of Mines.) {A.I.M.E. Tech. Pub. 1953.) 



The effects produced at the surface due to autogalvanic and electrolytic corrosion 

 are entirely analogous to the effects produced by oxidizing ore bodies. Hence, 

 spontaneous polarization methods may be employed to locate the corrosive regions. 



Utilization of Telluric Currents 



In contrast to phenomena of limited areal extent (some man-made, 

 such as streetcar and power Hnes, and others due to local electrochemical 



