Chap. 7] 



GRAVITATIONAL METHODS 



289 



moderate anomaly of 20 to 30 Eotvos amplitude on the well-known 

 Falconbridge ore body in Canada.^^^ In the Tri-State district the torsion 

 balance was tried with the hope of locating lead-zinc ores directly.^®^ 

 However, it was possible only to outline the (Ughter) chert pockets in 

 limestone in which the ore bodies occur. . 



Fig. 7-119 shows torsion balance results obtained by the author at 

 Caribou, Colorado, on a magmatic differentiation type of magnetite de- 

 posit in gabbro. Despite unfavorable terrain conditions indicated in 

 Fig. 7-76, the torsion balance indicates the individual concentrations 





Tertiarif 2.1—1 

 2t 



4a 69 



Triass/c Sonekhne/.K 

 90 mm 



Fig. 7-122. Gradients and curvature values above lignite deposit bounded by sand- 

 stone fault block (after Seblatnigg). 



(accompanied by magnetic anomalies ranging from 20 to 100,000 gammas) 

 rather satisfactorily. Fig. 7-120 gives average curves for the gradients 

 and curvatures across this deposit and also illustrates results of magnetic 

 and electrical investigations. Fig. 7-121 indicates the results of a torsion 

 balance traverse made by McLintock and Phemister^®^ across a dike of 



i"M. Mason, Geophysical Exploration for Ores, A.I.M.E. Geophysical Pros- 

 pecting, 9-36 (1929). 



16" P. W. George, A.I.M.E. Geophysical Prospecting, 661-571 (1929). 

 "^W. F. P. McLintock and J. Phemister. Mining Mag., Dec. 1927. 



