Applications:

• detection of disseminated metallic minerals
• discrimination of clay from silt or sand where formation resistives are similar
• measures electrical resistivity
• soil or rock lithology
• soil and groundwater contamination
• saltwater / freshwater interface
• mapping clay layers or sand deposits
• fracture location

Examples:

• mineral exploration
  
• clay zone identification
  
• borehole logging
  
• hydrogeology

The IP Method
The 3D IP Method

The IP Method
The time domain IP technique energizes the ground surface with an alternating square wave pulse via a pair of current electrodes. On most surveys, the IP/Resistivity measurements are made on a regular grid of stations along survey lines.

After the transmitter (Tx) pulse has been transmitted into the ground via the current electrodes, the IP effect is measured as a time diminishing voltage at the receiver electrodes. The IP effect is a measure of the amount of IP polarizable materials in the subsurface rock. Under ideal circumstances, IP chargeability responses are a measure of the amount of disseminated metallic sulfides in the subsurface rocks.

Unfortunately, there are other rock materials that give rise to IP effects, including some graphitic rocks, clays and some metamorphic rocks (serpentinite for example) so that from a geological point of view, IP responses are almost never uniquely interpretable. Because of the non-uniqueness of geophysical measurements it is always prudent to incorporate other data sets to assist in interpretation.

Also, from the IP measurements the apparent (bulk) resistivity of the ground is calculated from the input current and the measured primary voltage.

IP/resistivity measurements are generally considered to be repeatable to within about five percent. However, they will exceed that if field conditions change due to variable water content or variable electrode contact.

IP/resistivity measurements are influenced, to a large degree, by the rock materials nearest the surface (or, more precisely, nearest the measuring electrodes), and the interpretation of the traditional pseudosection presentation of IP data in the past have often been uncertain. This is because stronger responses that are located near surface could mask a weaker one that is located at depth.

The 3D IP Method
Three dimensional IP surveys are designed to take advantage of the interpretational functionality offered by 3-D inversion techniques. Unlike conventional IP, the electrode arrays are no longer restricted to in-line geometry. Typically, current electrodes and receiver electrodes are located on adjacent lines. Under these conditions, multiple current locations can be applied to a single receiver electrode array and data acquisition rates can be significantly improved over conventional surveys.

Technical Papers (PDF)

• 3D Inversionof Resistivity and IP Data: 2 Case Studies from Mineral Exploration

References

• Mining in Manitoba

Click here to learn more about data processing for Induced Polarization Surveys.