Chap. 10] 



ELECTRICAL METHODS 



739 



ered by alluvial beds of high resistivity. The latter thin out where the 

 marls have been forced up by the salt intrusion. Conversely, the salt 

 uplift shown in Fig. 10-69 shows as a resistivity high. It is located at 

 Tschemaja Rieschka and is one of the numerous domes found by geo- 

 physical methods in the Emba district in Russia. 



2. Applications in mining and mining geology. General structure in 

 mining districts can be outlined by means of resistivity mapping, provided 

 that key beds with greatly differing resistivities exist in the section. 

 Faults may be located if the beds on either side differ in resistivity or if 

 mineralized solutions circulate along the fault plane. In this manner, 

 non conductive minerals 

 accumulated on the fault 

 planes may be found in- 

 directly (fluorspar veins 

 in Illinois, see footnote 

 43, page 735). 



Resistivity methods 

 have been used exten- 

 sively in the location of 

 sulfide ore bodies, both 

 at the surface and under- 

 ground. Fig. 10-70 il- 

 lustrates electrical re- 

 sults at the Abana mine. 

 The resistivity curves 

 were obtained by survey- 

 ing with constant elec- 

 trode spacing. The ore 

 body is indicated by a 

 resistivity low. Fig. 10- 

 71 shows resistivity- 

 depth curves for a dip- 

 ping vein taken along three profiles, laid out 15° off strike, at increasing 

 distances from the outcrop. The lows in the curves move out to greater 

 distances (or depths) as the distances of the traverse from the outcrop are 

 increased. In this instance these distances were found to correspond to 

 depth to the dipping vein, although they would be expected to be reckoned 

 perpendicular to the bed. 



Several attempts have been made to apply resistivity methods in lig- 

 nite prospecting. If the lignite beds are soaked with mineralized waters 

 and overburden formations are poor conductors, fairly definite results may 

 be obtained (see Fig. 10-72). However, if conditions are less favorable 



Fig. 10-70. Resistivity curves and self-potential 

 profiles across Abana ore body (after Schlumberger 

 [Eve & Keys]). 



