Redox equipotential lines

Fig. 1. Electrical dipole development around a conductor crossing redox equipotential lines. Positive current in the country rock (not shown) travels perpendicular to electrical field lines from the anode to the cathode (modified after Govett 1976 and Hamilton 1998).

Fig. 3-9. The progressive modification of redox equipotential lines in saturated overburden overlying an electronic conductor in bedrock. Negative current flow lines depict the movement of negative charge-carrying species such as Fe, 8203 and Co. Positive charge-carrying ions such as U02 Mo04, so/ and dissolved oxygen radicals have similar flow lines but in the opposite direction. The purpose of the labelled equipotential lines is as in Fig. 3-7 (from Hamilton, 1998).

For every electron passed upward along the conductor, a corresponding amount of reduced species must move away from, or oxidised species move toward, the conductor. This continual migration of redox-active species must be coupled with redox reactions in order to transfer charge. If redox equipotential lines are totally static, the production of reduced species at the conductor must be accompanied by the simultaneous consumption of reduced species somewhere between bedrock and the water table. This would result in the almost instantaneous transfer of electrical current despite the much longer time required for mass transport of reduced species to the ground surface (see discussion on ion mobility, below). 

Fig. 3-7. Interpretation of the equipotential lines and ionic current flow lines around a singlephase sulphide ore body in a uniform redox field, after the model of Sato and Mooney (1960). Equipotential lines are labelled to depict an upward increasing gradient and are not intended to be an actual representation of the Earth field (from Hamilton, 1998).

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