Chap. 10] 



ELECTRICAL METHODS 



669 



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Aerated Moist 

 __ ~ Surface! on t 



_ / Oxidation - Cattiode-..^ 6os5on< 

 Zone ^Format i on tf r* 



— hydroftnj /■» *\ 



%5Ck 



Neutralized Ity Corbaaates 

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 f*e(Wj *6t1t0-re,0y}ttf0*3HtW^ 



Reduction 

 Zone 



Fig. 10-21. Chemical reaction and electrical activity on pyrite ore body. 



B. Equipment; Electrodes; Surveying Procedure 



The object of a spontaneous polarization survey in mining is the locali- 

 zation of negative centers. This may be done by surveying (a) equipo- 

 tential lines, or (6) potential profiles. In either case nonpolarizable elec- 

 trodes ("porous pots") are employed. The theory of these was discussed 

 in section ii (page 630). Special attention is given to an identity of 

 electrode potentials (that is, maintenance of a saturated solution). Polari- 

 zation (and current density) is kept at a minimum by making the electrode 

 surfaces in contact with the copper sulfate as large as possible. All elec- 

 trode metals are usable that act reversibly, that is, metals in their salt 

 solutions, (Cu in CUSO4 , Zn in ZnS04 , and so on). In practice, Cu in 

 CUSO4 electrodes are most widely employed. The electrodes are satis- 

 factory when the voltage between a pair does not exceed 1.10" volts. 



