1054 Subsurface Geologic Methods 



Applications 



Falconhridge Ore Body, Ontario — The vector diagram in figure 551 

 shows that the vectors obtained by combining horizontal and vertical 

 magnetic data cross in a region about 150 to 175 feet below the surface 

 of the ground. Although the intersection is only approximate, it does give 

 an indication of the depth. The top of the ore is actually about 112 feet 

 below the surface. If we allow for the depth of the pole beyond the edge 



J 1 — u 



I mile 



1 \ \ s 



Profile Througn X-Y 



Figure 553. Magnetic effects over Yoast field, Bastrop County, Texas. Magnetic 

 anomaly is due to serpentine intrusion at depth of about 1,500 feet. (Adapted 

 from CoUingwood. Reproduced permission Am. Assoc. Petroleum Geologists.) 



of the ore body, the magnetic results would agree more closely with the 

 actual data. The ore consists in large part of pyrrhotite, a fact which ac- 

 counts for the magnetic eflfects.^^ 



Yoast Field, Bastrop County, Texas — One of the best applications of 

 the magnetometer in prospecting for oil is afforded by the serpentine 

 plugs of south Texas. The plugs offer excellent chances for the wildcatter, 



"Eve and Keys, Studies of Geophysical Methods: Canadian Geological Survey Mem. 170, p. 39, 1930. 



