Airborne geophysical surveys and magnetic data acquisition are common practices that benefit the mining industry and a wide range of exploration professionals. Airborne geophysics provides a broad overview of the geology of a particular area, as well as measure the fluctuating magnetic signatures found in the Earth's crust that may be indicative of mineral concentrations.
Airborne surveys are efficient tools in the prospecting step of mineral exploration. They enable large areas of land to be surveyed quickly and cost effectively. The resolution of the acquired data is contingent upon the height and line spacing of the grid-like pattern flown by the aircraft.
There are two specific ways to categorize an airborne geophysics survey: regional and detailed.
A regional survey covers a wider area than a detailed survey, at least 5000 square kilometers and the line spacing is 250 meters or more, meaning that the data resolution is lower.
Regional surveys are applied more by governments for reconnaissance and used as a means of understanding and mapping out the geophysics of a particular terrain. Geologically, regional surveys aid in mapping the structure of hard rocks and sedimentary basins.
Recently, regional surveys have been applied to source out petroleum, coal and other commodities that are non-metallic that are found in sedimentary basins or mineralized in the basement surface.
The nature of detailed surveys is suggested in the name. These surveys offer data that has been acquired at higher resolution with a line spacing of less than 250 meters. It is direct surveying that is closely associated with the prospecting part of the mineral exploration phase as it can render data regarding the concentration levels of minable magnetic ores. Examples of minerals that are found using direct surveys are:
- Magnetic Iron Ores
- Kimberlites
- Asbestos-Bearing Ultramafic Rocks
- Chrome
As airborne surveys are a costly method of exploration, and each survey must be as economically viable as possible, it is extremely important that each be detailed and planned with as much precision as possible. For example, in a situation where a survey may detect information on millions of dollars of minable commodities located in one concentrated area, the cost of an entire exploration program must account for less than the value of the recoverable resources per square foot.
In turn, this has left the onus on geophysical survey companies to utilize state of the art data acquisition systems and cost effective survey techniques. When considering an airborne geophysical survey, consider the type of sensor that is most applicable to the targeted resource.
There are four key types sensors used in airborne geophysical surveys:
- Magnetic Surveys; (Including Total magnetic intensity, horizontal, and vertical gradiometry
- Radiometric
- Electromagnetic (Either helicopter borne frequency domain electromagnetic, or passive VLF-EM)
- Gravity
Each type of survey sensor is unique in the type of information it gathers and also in how each survey must be performed. Magnetic data may be acquired at a higher altitude and aircraft speed than radiometrics which requires a low and slow flying aircraft for superior data. Gravity also requires a typical acquisition rate of 60 meters / second.
Out of the four key sensor types, 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 the more comprehensive an airborne survey is, using as many geophysical exploration tools as possible, the more precise the end outcome of an exploration program. A typical survey will utilize two or even three types of different sensors to gather as much data as feasible for the interpreting geophysicists and geologists to work with.
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