Chap. lOJ 



ELECTRICAL METHODS 



755 



trodes are close together and the spacing of the secondary electrodes is a 

 function of the base length, has been proposed by Koenigsberger.®^ 



In corrosion surveys, the potential ratiometer has been used to deter- 

 mine zones of positive potential (where the greatest destruction is likely 

 to occur), and to record fluctuations in corrosion potential. In the latter, 

 the bridge is set at a fixed ratio, and galvanometer fluctuations with time 

 are recorded. 



D. Results 



P.D.R. methods have been applied in mining, in oil exploration, and in 

 civil engineering. AppUcations in mining fall into two groups: (1) struc- 

 tural and stratigraphic investigations and (2) prospecting for ore bodies. 

 The former include location of faults, shear zones, and quartz veins. 

 Mineralization may accompanj^ such zones or maj^ be related to it in some 

 way. F. Kihlstedt^* has pub- 

 lished a iiumber of examples 

 where the P.D.R. method was 

 supplemented by magnetic 

 tests. Extensive use has been 

 made of the potential-ratio 

 method in search for (gold 

 bearing) quartz veins. Fig. 

 10-83 is reproduced from an 

 article by Hedstrom^* and 

 shows the P.D.R. curve above 

 an andes'ite dike, flanked by 

 volcanic conglomerates on one 

 side and slate on the other, ob- 

 tained near the Lebong Donok 

 mine in Sumatra. Since the 

 andesite is a poor conductor 

 with respect to the conglom- 

 erates and the slate, the observed ratio curve (in terms of BIA) 

 is in accord with the theoretical curve shown in Fig. 10-79c. Edge 

 and Laby have published a number of ratiometer curves, largely for kno^n 

 deposits. In comparison with curves by other investigators it should be 

 noted that measurements were made between two electrodes and that no 



Andfs/ft 



Fig. 10-83. Potential-ratio curve on andesite 

 dike in Sumatra (after Hedstrom). 



62Beitr. angew. Geophys., 1(1) 57 (1930). 



"C. and M. Schlumberger, A.LM.E. Tech. Publ. No. 476 (1932). 



*^ Loc. cit. 



"5 H. Hedstrom, loc. cit. 



