Magnetic / Gradiometric
A very large number of airborne geophysical techniques have been developed to assist in mineral and hydrocarbon exploration. Aeromagnetic surveying is one of the most common airborne survey types conducted for both mineral and hydrocarbon exploration.
Airborne methods are usually the most cost effective tools available for both large regional reconnaissance surveys used as aids in geological mapping and for locating target areas for more detailed follow-up using helicopter borne platforms. The type of aeromagnetic survey specifications, instrumentation, and interpretation procedures, will depend on the objective of the survey.
Generally, aeromagnetic surveys are subdivided into two classes: regional and detailed surveys.
These usually have a relatively wide traverse line spacing (500 meters or more), and cover an area of at least 5,000 square kilometers. This class of survey is usually done for one of the following purposes:
- Geological mapping is used to aid in mapping lithology and structure in hard rock environments, and for mapping basement lithology and structure in sedimentary basins or for regional tectonic studies.
- Depth To Basement mapping for applications to petroleum, coal and other non metallic exploration in sedimentary basins or mineralization associated with the basement surface such as strata bound Pb-Zn deposits or U-bearing basal pebble conglomerates.
These have line spacings of less then 500 meters, and are done for a variety of reasons, usually in conjunction with other airborne methods. Reasons for conducting a detailed survey include:
- Direct prospecting for magnetic ores like magnetic iron ores, chromium, asbestos-bearing ultramafic rocks, or kimberlites.
Indirect prospecting, in combination with other methods or alone to:
- Discriminate between metallic and non-metallic conductors.
- Assist in interpreting body geometry and depth.
- Determine the geologic environment of the source.
- Locate specific “basement targets” for investigation using seismic methods in deep hydrocarbon exploration.
- Define the “regional” field for gravity interpretation in sedimentary basins.
- Map weak magnetic lineations related to faulting within the sedimentary section in some hydrocarbon plays.
For a comprehensive discussion on Aeromagnetic surveys and their basic principles, click below: