GRAVITATIONAL METHODS 



425 



Mining Surveys 



Anomalies Over Assumed Bodies. — Theoretical gravity anomalies 

 over hypothetical bodies of rectangular cross section are shown in Figures 

 254, 255, and 256.t In all three cases it is assumed that the body has a 

 density one unit greater than that of the surrounding medium ; that is, denot- 

 ing the density of the medium by a, that of the body is o- + 1. A density 



Fig. 254. — Gravity anomalies over a vertical 

 body. (Hedstrom, A.I.M.E. Geophysical Prospect- 

 ing, Tech. Pub. 953.) 



Fig. 255. — Gravity anomalies 

 over a vertical body of infinite 

 length, located at various depths 

 below the surface. (Hedstrom, 

 A.I.M.E. Geophysical Prespect- 

 ing, Tech. Pub. 953.) 



difference other than one unit would alter the amplitude but not the shape 

 of the curves. In the case of a negative density difference, e.g., minus one 

 unit, the anomalies will be inverted. Figure 254 shows the theoretical 

 gravity anomalies over a vertical body whose length is oo, 200 and 100 

 meters respectively. Figure 255 shows the theoretical gravity anomalies 

 corresponding to a vertical body of "infinite" length, located at various 

 depths below the surface. Figure 256 illustrates the theoretical anomalies 

 corresponding to various dips for ore bodies of "infinite" length. 



t H. Hedstrom, "A New Gravimeter for Ore Prospecting," A.I.M.E. Geophysical Prospecting, 

 Tech. Pub. 953, 1938, 



