Induced Polarization (IP) Method
Induced Polarization (IP) Method
Induced Polarization (IP) Method
•Membrane/electrolytic Polarization
- result of variations in the mobility of ions in fluids through rock
structures
-may occur in rocks that do not contain metallic minerals
-constitutes background or so-called normal IP effect
or
f F
FE
F
f = apparent resistivity measured at DC or
at very low AC frequency (0.05-0.5Hz)
F = apparent resistivity measured at very high AC frequency
(0.1-10Hz)
Frequency-Domain IP
PFE 100( f F ) / F
f F 5 FE 3 PFE
MF 2 10 5
2 10 2 10
f F f f
•Unit of MF is the same as conductivity [mho/m or or siemen/m ]
Metal factor of earth materials
Field IP Procedures
•IP equipment is similar to that used in resistivity surveys but is
more bulky and elaborate.
•Field procedures for making IP measurements are identical to
those employed for resistivity measurements.
•Theoretically, any standard electrode arrays used in resistivity
surveys can be employed for IP measurements.
•Dipole-dipole array is used the most for IP surveys due to
–Easy to use in the field routine
–The current and potential dipole cables are separated from one another,
spurious signals due to electromagnetic coupling are effectively
reduced.
•Multi-electrode & roll-along system as used for resistivity
surveys is also valid in IP survey to reduce time of operation and
to provide more data coverage.
AB = current electrodes
MN = potential electrodes
•IP is by far the most effective geophysical method that can be used in
the search for such targets.
Homework Exercise
The results in Table below were obtained using frequency-domain IP in
a survey over suspected sulfide mineralization in northern New
Brunswik, Canada. The dipole-dipole array was used with dipole
separations of 100 ft and n=1,2,3. Resistivity values are in the form
ρa/2π Ω−ft. The grid line is roughly N-S with stations every 100 ft. In all
cases the potential dipole was south of the current dipole.
Prepare pseudosection plots for ρa/2π and MF ; draw contours
and interpret the results
Potential dipole n=1 n=2 n=3
ρa/2π MF ρa/2π MF ρa/2π MF
10S-9S - - - - 280 27
9S-8S 180 28 190 24 270 33
8S-7S 210 31 275 36 290 60
7S-6S 270 42 280 35 72 219
6S-5S 315 39 80 172 70 175
5S-4S 480 40 220 17 675 99
4S-3S 330 88 1120 41 1751 61
3S-2S 1091 46 1130 29 1830 31
2S-1S 1200 31 1510 27 1710 28