426 



EXPLORATION GEOPHYSICS 



Figure 257 shows the gravity anomalies produced by step blocks located 

 at various depths below the surface. The curves are drawn for the case 

 that the density of the structure is greater than that of the surrounding 

 medium. 



Fig. 256. — Gravity anomalies over bodies of 



different dips. (Hedstrom, A.I.M.E. Geophysical 

 Prospecting, Tech. Pub. 953.) 



Fig. 257. — Relative gravity profiles for an infinite step block of 

 thickness T, located at depths equal to 7/2, T. %T. 4T and 8T below 

 the surface. (Barton, The Science of Petroleum, Vol. I.) 



Gravimeter Surveys over Ore Bodies. — The gravity anomaly over a 

 large ore deposit in the Skellefte district is shown in Figure 258. The sul- 

 fide ore deposit, which had been previously disclosed by geoelectrical pros- 

 pecting, consists of three parallel lenticular veins, dipping steeply to the 

 north. One vein has a thickness of about 10 m. and the other two a thick- 



