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Charge distribution 1

The Elura orebody is one example of a subsurface target with a range of electrical resistivities. The cartoons following illustrate the relation between current flow caused by a surveyer's transmitter, charges that build up at material property boundaries, and the voltages measured by the surveyer's DC resistivity instrument.
1.
The Elura ore body. Depth to top of gaussen (in blue) is approximately 100 m.
2. A DC resistivity survey involves injecting current at one location and measuring resulting potentials at another location.
3. Current will flow. Current density increases within conductive regions, and decreases within resistive regions. 
4. Charges build up at interfaces between regions of different electrical conductivity.
5. Variations in charge distribution are detected as variations in distribution of potential, or voltage, at the surface. 
Elura Orebody  
Elura Orebody Electrical resistivities
Rock Type
Ohm-m
Overburden
12
Host rocks
200
Gossan
420
Mineralization (pyritic)
0.6
Mineralization (pyrrhotite)
0.6
 

On the next page, we show that current flow lines are bent because of boundary conditions at the interfaces between regions of differing resistivity.

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