398 



MAGNETIC METHOD 



[Chap. 8 



For wide inclined dikes or formations of gentle dip, the transverse mag- 

 netic effect is generally not negligible, except under favorable conditions 

 of magnetic latitude and strike. For steeply dipping formations and ore 

 deposits whose width is small compared with their depth extent, the 

 anomalies are,^^ when the transverse magnetization is neglected. 



AH = 2k sin i Zo sin i Joge ^ + cos i(<f2 



nvi 



AZ = — 2k sin i Zo sin i(^ 



•/Jl + ^^3 — ^4) 



r2ri 



(Pi -\- (p3 — fi) — COS i lOge 



TlTi 



(8-61/) 



Above an inclined dike the hori- 

 zontal intensity has a maximum in 

 the south and a minimum in the 

 north. The ratio of their amplitude 

 depends on the dip; for a vertical dike 

 they are approximately equal. The 

 smaller amplitude on the hanging wall 

 side rises to a peak above the dike 

 and then drops rapidly on the foot 

 wall side. On the latter a minimum 

 appears which increases in amplitude 

 as the dip decreases. Fig. 8-53 

 shows the influence of dip for a dike 

 of infinite depth extent and high mag- 

 netic latitudes. The anomalies in- 

 clude transverse horizontal magneti- 

 zation. 



Figs. 8-54a to 8-54c illustrate the 

 influence of strike on magnetic ano- 

 malies for high, intermediate, and 

 low magnetic latitudes. 



" Eve (A.I.M.E. Geophysical Pros- 

 pecting, 204-205 [1932]) gives the follow- 

 ing formulas for an inclined dike: 



AH = 2m log, 





Fig. 8-53. Effect of dip on hori- aZ = 2va.(,<pi — <f>3 — <Pi + <pd- 



zontal and vertical intensities for high 



magnetic latitudes. Strike E-W, I = These expressions obviously hold for a 



63° (after Haalck). Reading down: 90° finite vertical and not for a dipping dike; 



dip, 45° dip, 0° dip. they correspond to equs. 8-61c. 



