Geophysical Induced Polarization (IP)
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Induced Polarization (IP) Surveys

Are a type of geophysical survey used to detect subsurface conductive minerals, such as sulfides, that may be associated with mineral deposits. The survey involves injecting a small electrical current into the ground and measuring the resulting polarization of the subsurface materials. The data collected from the survey can be used to create a map of subsurface conductivity, which can be used to identify areas of potential mineralization. IP surveys are commonly used in mineral exploration and can be used in conjunction with other geophysical methods, such as magnetic and resistivity surveys, to create a more comprehensive picture of the subsurface, and can also be used for environmental applications such as mapping contaminated soils and groundwater.

 

The IP method measures the polarization of subsurface materials in response to an applied electrical current, while resistivity method measures the electrical resistance of the subsurface materials to an applied current. Target features: IP method is particularly sensitive to subsurface conductive mineralization, such as sulfides and other conductive minerals, and can be used to locate mineral deposits such as copper, gold, silver, zinc, and lead. On the other hand, resistivity method is sensitive to subsurface resistive materials such as clay, sand, and limestone, and can be used to locate subsurface structures such as faults, fractures, and aquifers.
IP method typically uses surface or borehole electrodes to inject a current and measure polarization, while resistivity method uses surface or borehole electrodes to inject a current and measure the resistance.
IP data is typically interpreted in terms of subsurface conductivity, which can be used to identify areas of potential mineralization, while resistivity data is typically interpreted in terms of subsurface resistivity, which can be used to identify subsurface structures such as faults, fractures, and aquifers.
IP method is limited by the conductivity of the overlying materials and the complexity of the geology, while resistivity method is limited by the size and shape of subsurface structures and the conductivity of subsurface fluids. Overall, IP survey is a relatively non-invasive and inexpensive method for detecting subsurface mineralization and other subsurface features. It uses the natural subsurface charge and does not cause any damage to the environment. It can be conducted on both land and in water and can provide depth of investigation of up to several hundred meters.

Types Of Induced Polarization Geophysical Surveys

There are several types of Induced Polarization (IP) geophysical surveys available, the main ones are:

A 2D surface IP survey is conducted on the surface of the ground using an array of electrodes. The survey typically involves injecting a current into the ground using one set of electrodes and measuring the resulting polarization of the subsurface using another set of electrodes. The data collected from the survey is used to create a 2D map of subsurface conductivity, which can be used to identify areas of potential mineralization.

A 3D surface IP survey is similar to a 2D survey, but it uses a more complex array of electrodes and data collection methods to create a 3D map of subsurface conductivity. This type of survey is more time-consuming and expensive than a 2D survey, but it can provide more detailed information about subsurface conductivity.

A borehole IP survey is conducted by lowering electrodes into a borehole and injecting a current into the ground. The resulting polarization of the subsurface is measured using electrodes at the bottom of the borehole. This type of survey can provide information about subsurface conductivity at greater depths than a surface survey, and it is useful for identifying mineralization in deeper formations.

Induced Polarization Can Used To

  • Define mineral deposits by locating associated Sulfide alteration
  • Identify areas of potential mineralization
  • Delineate Clay alteration
  • Delineate Silicification related to Gold bearing alteration
  • Ideal for locating deep seated Cu-Au
  • Porphyry Deposits

Induced Polarization Method

The Induced Polarization (IP) method is a valuable geophysical technique for detecting subsurface mineralization and other subsurface features,
however, like any method, it has some limitations.

IP method can provide a depth of investigation of up to several hundred meters, however, it is limited by the conductivity of the overlying materials. Low conductive overburden such as clay, can limit the depth of investigation as the signal generated by the IP method decays rapidly with depth.

IP method is sensitive to the conductivity of the subsurface materials, and highly conductive overburden, such as clay or salt, can mask the conductivity of deeper subsurface features, making it difficult to detect mineralization.

 IP method can be affected by complex geology, such as irregular and dipping layers, which can lead to a distorted subsurface conductivity map and make it difficult to interpret the data.

The resolution of the IP method is limited by the spacing between electrodes. The closer the electrodes are, the higher the resolution of the data. However, closer spacing means more electrodes and more time-consuming data collection.

The IP method can produce similar responses from different subsurface features, making it difficult to distinguish between them. For example, a conductive layer may be caused by mineralization or by clay.

Types Of Induced Polarization Instruments

There are several types of IP instruments available, which can be broadly classified into two categories:
surface and borehole instruments.

These instruments are used for conducting 2D and 3D surface IP surveys. They typically consist of an array of electrodes that are used to inject a current into the ground and measure the resulting polarization of the subsurface. Some examples of surface IP instruments include:

This is a common configuration for surface IP surveys, where a current is injected between two electrodes and the resulting polarization is measured using two other electrodes.

  • This configuration is similar to the dipole-dipole array, but the current electrode is replaced by a pole, which is a long electrode driven into the ground.
  • This is another common configuration for surface IP surveys, where the current is injected between two electrodes and the resulting polarization is measured using one other electrode.

These instruments are used for conducting borehole IP surveys. They typically consist of electrodes that are lowered into a borehole and used to inject a current into the ground and measure the resulting polarization of the subsurface. Some examples of borehole IP instruments include:

This is a common type of borehole IP instrument, which uses a combination of electrodes to inject a current and measure the resulting polarization.

This is a specialized borehole IP instrument that measures the frequency-dependent polarization of the subsurface, which can provide more detailed information about subsurface conductivity.

FAQs

The survey can be conducted using surface or borehole techniques. Surface IP surveys typically use an array of electrodes placed on the surface of the ground, while borehole IP surveys use electrodes that are lowered into a borehole.

The survey typically begins with a pre-survey planning and design, including selecting the survey area, survey lines, and electrode configuration. The survey lines are then staked out and the electrodes are placed in the ground at the designated locations. The current is then injected into the ground using the current electrodes, and the resulting polarization is measured using the potential electrodes. The data collected from the survey is then processed and interpreted to create a map of subsurface conductivity.

The data collected from the survey is then used to create a map of subsurface conductivity, which can be used to identify areas of potential mineralization. The conductivity of the subsurface materials is related to their ability to store electrical charge, and certain types of minerals, such as sulfides, will have a higher conductivity than other types of materials.

Induced Polarization (IP) and resistivity methods are both geophysical techniques used to detect subsurface features, such as mineralization and subsurface structures. Both methods rely on the measurement of subsurface electrical properties, but they differ in how they measure these properties and the information they provide.

IP surveys are particularly useful for detecting subsurface conductive mineralization, such as sulfides and other conductive minerals. They are commonly used in mineral exploration, particularly for base and precious metals, and can also be used for environmental applications such as mapping contaminated soils and groundwater. IP surveys are relatively inexpensive and non-invasive, and can be conducted on both land and in water. They are particularly useful when the target is to locate mineral deposits such as copper, gold, silver, zinc, and lead.

On the other hand, resistivity surveys are sensitive to subsurface resistive materials, such as clay, sand, and limestone. They are commonly used to locate subsurface structures such as faults, fractures, and aquifers. Resistivity surveys can also be used for environmental applications such as mapping contaminated soils and groundwater, and monitoring leachate migration. They are particularly useful when the target is to locate subsurface structures such as faults, fractures, and aquifers or to image the subsurface with high resolution.

Overall, IP and resistivity methods are complementary techniques that provide different information about the subsurface, and they can be used in combination to create a more comprehensive picture of the subsurface.