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.
First the orebody is shown. The accompanying table lists the resistivity
of each region, keyed by colour.
Click on the button next to each of 5 captions to see corresponding figures.
Data are from I.G. Hone, Geoelectric Properties of the Elura Prospect,
Cobar, NSW", in The Geophysics of the Elura Orebody, Cobar NSW, 1980,
Australian Society of Exploration Geophysicists.
On the next page, we show that current flow lines are bent because of boundary
conditions at the interfaces between regions of differing resistivity.