An airborne magnetic survey is the predominant method of remotely collecting geophysical data using a specially modified aircraft outfitted with magnetometers to fly a grid pattern over a targeted area. Airborne magnetic surveys are an effective geological exploration technique to acquire gridded data describing the magnetic anomaly caused by variations in earth materials and structure. Magnetic databases are compiled and interpreted to identify the presence of magnetic anomalies to determine the geological framework of the region and potentially the direct targeting of mineral and hydrocarbon commodities.
Primary types of sensors used in airborne geophysical surveys include:
- Magnetic (Including Total magnetic intensity, horizontal, and vertical gradiometry)
- Radiometric
- Electromagnetic (Either helicopter borne frequency domain electromagnetic, or passive VLF-EM)
- Gravity
The type of aeromagnetic survey specifications, instrumentation and interpretation procedures will largely depend on the objective of the survey. Airborne magnetics are highly effective in identifying the geological framework for; Diamonds, Lode Gold, VMS Deposits , MVT Lead-Zinc Deposits, SEDEX Deposits, Porphyry Copper Deposits, Uranium Deposits, Olympic Dam – Type Deposits, Magmatic Ni-Cu-PGDs Deposits.
Airborne magnetics are highly effective in direct targeting deposits of; Diamonds, VMS Deposits, SEDEX Deposits, Porphyry Copper Deposits, Olympic Dam – Type Deposits
Aeromagnetic surveys are the most commonly employed method of airborne geophysical surveys as magnetics are commonly used in conjunction with each of the other technologies. Typically a magnetometer is housed in either a stinger or in wingtip pods at the end of the aircraft wing providing distance from the aircraft itself or it may be towed behind an aircraft on a long line cable. The magnetometers test the magnetic fields in their current state, as magnetic fields are in constant flux as they are dependent upon spatial variations and solar winds.
There are three main types of temporal magnetic variations:
- Diurnal
- Magnetic Storms
- Micropulsations
Benefits of Airborne Magnetic Surveys
Airborne surveys greatly improve;
- the rate at which magnetic data can be acquired
- the area which can be surveyed
- acquisition of data in challenging and remote terrain
- economical, efficient data acquisition
Important Considerations for Aeromagnetic Survey Planning
- Flight line spacing – determined in conjunction with survey altitude and budget, typically ranging from 50m for detailed surveying to 500m for regional surveys
- Survey Altitude – low as is safely permitted given the MTC, ~70 m using a pre-planned drape surface model
- Line Direction – typically oriented normal to a predominate geological strike direction
- Control Line Spacing – 90 degrees to the flight lines and typically 10x the spacing for correcting the data during the data processing stage
- Sampling Interval - typically 10 times per second, equivalent to a ground spacing of 7 metres per second.
- Noise Envelope – a specified noise envelope sets the target that must be met in eliminating aircraft effects and temporal effects in the execution of a survey
Source; Colin Reeves (Aeromagnetics Surveys – Principles, Practices and Interpretation)
Specialists in Airborne Geophysical 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 surveys, airborne gravity surveys, airborne radiometric surveys, and airborne electromagnetic surveys 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.
Ed. GMH