ELECTRICAL METHODS 



629 



or a secondary field created by an induced current flowing in an under- 

 ground conductor. 



Much information can be obtained by careful study of the dip and 

 strike curves obtained in properly conducted field work. Because the 

 conditions met with in field practice are varied and complex, care and 

 experience are required in making final interpretations. Due to the greater 

 distortion of the high frequencies, considerable caution must be employed 

 in attempting to draw final conclusions from such work when not sup- 

 ported by supplemental data obtained from the application of other 

 methods. 



-10 

 -20 



^^T f i.j.i^yy^ ^ ^j ^ ^yyy^^-^yy^^'^^: :^^^^^^^^^^ ' 



CONDUCTOR 



CONDUCTOR 



Fig. 395. — Dip and strike relationships over an experimental ore body. 



Figure 395 shows the dip and strike relationships over an experimental 

 ore body which consisted of a conductive sheet (copper-covered wood 

 panel) buried in moist sand. The left-hand portion of the figure shows the 

 symmetrical dip angles obtained when the conductor is vertical. Placing 

 the conductor at an angle of approximately 40° from the vertical gives 

 the unsymmetrical dip curve shown in the right-hand portion of the illus- 

 tration. The strike curve reaches its maximum value in the general vicinity 

 of the point where zero dip is obtained. The relationship between the 

 position for maximum values of strike and minimum or zero dip angles is 

 complicated because it depends on the direction of current flow in the con- 

 ductor, the general distribution of current in the subsurface around the 

 conductor, and the phase relationships between the current flow in the 

 conductor and the primary field. However, because the dip curve passes 

 through zero over the effective electrical axis of the conductor, it serves 

 as a general means for determining the plan location of this axis. The 

 general direction of dip of the conductor may also be predicted from the 

 dip curve, because the smallest angle of dip will usually be obtained on the 

 hanging-wall side. Various empirical methods have been developed for 

 determining the depth of the effective conductive zone, t 



t J. J. Jakosky, "Electrical Prospecting," Proc. Institute of Radio Engineers," Vol. 16, No. 

 10, October 1988, pp. 1305-1355. 



