A General Introduction to Airborne Magnetic Surveys

Airborne magnetic surveys are an important geophysical prospecting tool for many applications. These surveys make it possible to gather detailed information about the presence of various magnetic and non-magnetic materials in the Earth’s crust over large geographical areas. This type of survey is cost-effective, safe and time efficient because of the large areas of land that can be quickly covered.

Magnetometers are installed in fixed-wing aircraft or helicopters, and a grid of pre-planned survey lines are flown over the project area. The magnetic data acquired is a measure of the total intensity of the Earth's magnetic field at each recorded data point in flight.  Each data point is a combination of the regional magnetic field generated in the Earth as well as tiny variations due to constantly changing solar wind, the magnetic effects of the aircraft, and magnetic features on the ground and subsurface.  By subtracting these solar, regional and aircraft effects, the resultant aeromagnetic data shows the relative abundance of magnetic minerals and their spatial distribution in the upper levels of the Earth's crust.  Magnetite is the most common magnetic mineral, and the content of magnetic minerals will vary in different rock types.  Therefore by analyzing the aeromagnetic data, the geological structure of the upper crust can be interpreted, including spatial geometry of rock units and structural features such as contacts, faults and folds.

Regional surveys are flown at higher altitudes and at wider line spacing intervals.  These surveys provide more general magnetic information over larger survey areas, and can provide clues about which areas may require more detailed investigation.  More detailed surveys are flown at lower altitudes with closer line spacing intervals in order to acquire higher resolution data for a more in depth analysis of the project area.  

Applications of Magnetic Surveys

1. Prospecting for magnetic ores or host rocks.

• magnetic iron deposits
• chrome- or PGE-bearing ultramafic rocks
• some massive sulphide bodies (usually nickel)
• diamond-bearing kimberlites
• tin-tungsten or rare-earths associated with granites

2. Geological mapping

• lithologic and structural mapping in weathered or covered areas
• sedimentary basin geometry and structure, mapping intrasedimentary sources
• regional studies for tectonic purposes (e.g. crustal studies)
• exploration for favourable ore environments

3. Depth to basement mapping

• hydrocarbon exploration
• ·non-metallic mineral exploration
• exploration for minerals associated with buried basement surfaces (e.g. gold and unconformity uranium)

4. In conjunction with electromagnetics and induced polarization

• to help discriminate between metallic and non-metallic conduction
• to assist in interpretation of conductive or polarizable body geometry
• to determine geological environment of source

5. Engineering, groundwater, hazard and archaeological studies

• mapping faults and buried valleys
• depth determination to the Curie point isotherm
• mapping geothermal energy potential
• searching for metallic objects

Specialists in Aeromagnetic Surveys

Terraquest was established in 1984 and since then, our dedicated team has flown over 1,500 airborne geophysical surveys using both fixed wing and helicopter platforms.  Our professional crews provide significant experience having carried out airborne magnetic, gravity, gamma ray spectrometry, and electromagnetics on five continents.  Our quality data sets have been utilized in the exploration for base and precious metals, kimberlite, hydrocarbons, uranium, rare earth minerals and water. The company has performed exemplary surveys for both small and large exploration groups as well as many government agencies.  References can be provided upon request.    Visit www.terraquest.ca.